10-K

a2025_sionnatherapeuticsin.htm

10-K

Document

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

___________________________

FORM 10-K

__________________________

(Mark One)

For the fiscal year ended December 31, 2024

Commission file number 001-42504

_________________________________________________

SIONNA THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

_________________________________________________

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code : (617) 819-2020

Securities registered pursuant to Section 12(b) of the Act:

Title of each class Trading Symbol(s) Name of each exchange on which registered

Common Stock, $0.001 par value per share SION The Nasdaq Global Market

Securities registered pursuant to section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes o No x

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes o No x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes o No x

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes x No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,”and "emerging growth company" in Rule 12b-2 of the Exchange Act.

Large accelerated filer o Accelerated filer o

Non-accelerated filer x Smaller reporting company x

Emerging growth company x

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. o

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. o

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). o

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Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes o No x

As of June 30, 2024, the last business day of the registrant’s most recently completed second quarter, there was no established public trading market for the registrant’s equity securities as the registrant was not a public company and therefore cannot calculate the aggregate market value of its voting and non-voting equity held by non-affiliates as of such date. The registrant’s common stock began trading on the Nasdaq Global Market on February 7, 2025.

The number of shares of registrant’s common stock outstanding as of March 1, 2025 was 44,124,394

DOCUMENTS INCORPORATED BY REFERENCE

The registrant intends to file a definitive proxy statement pursuant to Regulation 14A relating to the 2025 Annual Meeting of Stockholders within 120 days of the end of the registrant’s fiscal year ended December 31, 2024. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K (the “Annual Report”) contains forward-looking statements about us and our industry that involve substantial risks and uncertainties, and which are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”) and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). All statements other than statements of historical facts contained in this Annual Report, including statements regarding our future results of operations and financial position, business strategy, product candidates, preclinical studies and clinical trials, results of preclinical studies and clinical trials, research and development costs, regulatory approvals, commercial strategy, timing and likelihood of success, as well as plans and objectives of management for future operations, are forward-looking statements. Although we believe that the expectations reflected in these forward-looking statements are reasonable, these statements involve known and unknown risks, uncertainties and other important factors that are in some cases beyond our control and may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements.

In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “would,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions. Forward-looking statements contained in this Annual Report include, but are not limited to, statements about:

•the initiation, timing, progress and results of our research and development programs, preclinical studies and clinical trials;

•the ability of clinical trials to demonstrate safety and efficacy of our product candidates, and other positive results, and the ability of our preclinical studies to predict later clinical trial results;

•the timing, scope and likelihood of regulatory filings and approvals of our product candidates;

•the implementation of our business model, and strategic plans for our business, programs, and current and future product candidates;

•our ability to obtain additional cash and the sufficiency of our existing cash, cash equivalents and investments in marketable securities to fund our future operating expenses and capital expenditure requirements;

•the accuracy of our estimates regarding expenses, future revenue, capital requirements and needs for additional financing;

•the size and growth potential of the markets for our product candidates, and our ability to serve those markets; our potential and ability to successfully manufacture and supply our current and future product candidates for clinical trials and for commercial use, if approved; the scope of protection we are able to establish and maintain for intellectual property rights covering our product candidates;

•developments relating to our competitors and our industry, including competing product candidates and therapies;

•existing regulations and regulatory developments in the U.S. and other jurisdictions, including changes in U.S. federal policy, such as trade policies or tariffs;

•expectations regarding future events under collaboration and licensing agreements, including potential future payments, as well as our plans and strategies for entering into further collaboration and licensing agreements;

•general economic, industry and market conditions, including elevated interest rates and inflation;

•our ability to attract and retain the continued service of our key personnel and to identify, hire and then retain additional qualified personnel;

•our expectations regarding the period during which we will qualify as an emerging growth company under the JOBS Act; and

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•our anticipated use of our existing cash, cash equivalents and investments in marketable securities.

We have based these forward-looking statements largely on our current expectations and projections about our business, the industry in which we operate and financial trends that we believe may affect our business, financial condition, results of operations and prospects, and these forward-looking statements are not guarantees of future performance or development. These forward-looking statements speak only as of the date of this Annual Report and are subject to a number of risks, uncertainties and assumptions described in the section entitled “Risk Factors” and elsewhere in this Annual Report. Because forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified, you should not rely on these forward-looking statements as predictions of future events. The events and circumstances reflected in our forward-looking statements may not be achieved or occur and actual results could differ materially from those projected in the forward-looking statements. Except as required by applicable law, we do not plan to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events or otherwise.

In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this Annual Report, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain, and you are cautioned not to unduly rely upon these statements.

You should read this Annual Report and the documents that we reference herein or incorporated by reference as exhibits hereto with the understanding that our actual future results, levels of activity, performance and events and circumstances may be materially different from what we expect.

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NOTE REGARDING TRADEMARKS

Sionna Therapeutics, Inc. is the owner of the SIONNA trademark, as well as certain other trademarks, including design versions of some of these trademarks. The symbols TM and ® are not used in connection with the presentation of these trademarks in this report and their absence does not indicate a lack of trademark rights. Certain other trademarks used in this report are the property of third-party trademark owners and may be presented with or without trademark references.

All brand names or trademarks appearing in this report are the property of their respective owners. Unless the context requires otherwise, references in this report to “Sionna,” the “Company,” “we,” “us” and “our” refer to Sionna Therapeutics, Inc. and its subsidiary.

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SUMMARY OF MATERIAL RISKS ASSOCIATED WITH OUR BUSINESS

We are subject to numerous risks and uncertainties, including those further described below in the section entitled “Risk Factors” in this Annual Report, as well as in other documents that we file with the U.S. Securities and Exchange Commission (“SEC”). The following considerations, among others, may offset our competitive strengths or have a negative effect on our business strategy, which could materially adversely affect our business, financial conditions, results of operations and future growth prospects:

•We are a clinical-stage biopharmaceutical company and have incurred significant operating losses since inception and anticipate that we will continue to incur significant operating losses for the foreseeable future. Our net losses were $61.7 million and $47.3 million for the years ended December 31, 2024 and 2023, respectively. We had an accumulated deficit of $181.1 million and $119.4 million as of December 31, 2024 and 2023, respectively. We may never achieve or maintain profitability.

•We will need substantial additional funding to develop and commercialize our product candidates and identify and invest in new product candidates. We may be unable to raise capital on acceptable terms, if at all, and, as a result, we may be required to delay, reduce or eliminate our product development programs or commercialization efforts.

•We are substantially dependent on the success of at least one of our NBD1 stabilizers. If we are unable to advance an NBD1 stabilizer product candidate into later-stage clinical development or unable to obtain regulatory approval and commercialize an NBD1 stabilizer-anchored therapy for the treatment of cystic fibrosis, or experience significant delays in doing so, our business will be materially harmed.

•We intend to develop an NBD1 stabilizer product candidate to be administered in combination with one of our complementary modulators or as an add-on to the standard of care. Developing combination treatments increases complexity and risk, including risks of drug-drug interactions, unforeseen side effects or failures in our clinical trials that could delay or prevent their regulatory approval or limit the commercial profile of an approved label.

•The regulatory approval processes of the FDA and comparable foreign authorities are lengthy, time-consuming and inherently unpredictable. If we are not able to obtain the required regulatory approval for any product candidate, our business will be substantially harmed.

•We have not yet completed all testing of any product candidate in clinical trials. Preclinical, interim, topline and preliminary results from our preclinical studies or clinical trials are not necessarily predictive of the results or analyses of such results of later clinical trials. If we cannot replicate the positive results from any preclinical studies or clinical trials of our current or potential future product candidates that have positive results, or if we suffer any other significant setbacks in our later clinical trials, we may be unable to successfully develop, obtain regulatory approval for and commercialize our current or potential future product candidates.

•Targeting the NBD1 domain of the CFTR protein is novel, and we do not know whether we will be able to successfully develop any products.

•Our preclinical studies and clinical trials may fail to demonstrate the safety and efficacy of our product candidates, or serious or unacceptable adverse side effects or unexpected toxicology findings may be identified during the development of our product candidates, which could prevent or delay further clinical development, regulatory approvals and commercialization, impact the product’s labeling, if approved, increase our costs or necessitate the abandonment or limitation of the development of some of our product candidates.

•We may expend our limited resources to pursue a particular product candidate or indication and fail to capitalize on product candidates or indications that may be more profitable or for which there is a greater likelihood of success.

•We are dependent on licensed intellectual property. If we were to lose our rights to licensed intellectual property, we may not be able to continue developing or commercializing our product candidates, if approved. If we breach any of the agreements under which we license the use, development and commercialization

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rights to our product candidates from third parties or, in certain cases, we fail to meet certain development deadlines, we could lose license rights that are important to our business.

•We contract with third parties for the manufacture of our product candidates for clinical drug supply and expect to continue to do so for commercialization, if our product candidates are approved. This reliance on third parties increases the risk that we will not have sufficient quantities of our product candidates or such quantities at an acceptable cost or quality, which could delay, prevent or impair our development or commercialization efforts.

•If we or our licensors are unable to obtain, maintain and enforce intellectual property rights relating to any of our product candidates, or if the scope of the protection obtained is not sufficiently broad, our competitors or other third parties could develop and commercialize products similar or identical to ours, our ability to successfully commercialize our product candidates may be adversely affected and we may not be able to compete effectively in our markets.

•We face substantial competition. Our main competitor in the CF market holds substantial market share and has substantially greater resources than we do. We may not be able to compete successfully in this environment and, in particular, against a much larger competitor.

•The trading price of the shares of our common stock may be volatile, and investors could lose all or part of their investment.

The summary risk factors described above should be read together with the text of the full risk factors in the section titled “Risk Factors” and the other information set forth in this Annual Report, including our audited consolidated financial statements and the related notes, as well as in other documents that we file with the SEC. The risks summarized above or described in full elsewhere in this Annual Report are not the only risks that we face. Additional risks and uncertainties not presently known to us, or that we currently deem to be immaterial may also materially adversely affect our business, financial condition, results of operations and future growth prospects.

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TABLE OF CONTENTS

Page No.

PART I

Item 1. Business 10

Item 1A. Risk Factors 59

Item 1B. Unresolved Staff Comments 115

Item 1C. Cybersecurity 115

Item 2. Properties 115

Item 3. Legal Proceedings 116

Item 4. Mine Safety Disclosures 116

PART II

Item 6. [Reserved] 118

Item 7A. Quantitative and Qualitative Disclosures About Market Risk 131

Item 8. Financial Statements and Supplementary Data F-1

Item 9A. Controls and Procedures 120

Item 9B. Other Information 121

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections 121

PART III

Item 10. Directors, Executive Officers and Corporate Governance 122

Item 11. Executive Compensation 122

Item 14. Principal Accountant Fees and Services 122

PART IV

Item 15. Exhibits and Financial Statement Schedules 123

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PART I

ITEM 1. BUSINESS

Overview

We are a clinical-stage biopharmaceutical company on a mission to revolutionize the current treatment paradigm for cystic fibrosis (“CF”) patients by developing novel medicines that normalize the function of the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein to deliver clinically meaningful benefit to CF patients. CF is a progressive and life-threatening genetic disease caused by inherited mutations in the CFTR gene, which lead to insufficient CFTR function. While advances in the discovery and development of CFTR modulators have significantly improved the lives of people living with CF, at least two-thirds of patients on the current standard of care do not have normal CFTR function, defined as sweat chloride levels below 30 mmol/L. Patients with reduced CFTR function can experience debilitating multi-system complications that lead to significantly reduced quality of life and shorter life expectancy. Our goal is to deliver differentiated medicines for people living with CF that can restore their CFTR function to as close to normal as possible by directly stabilizing CFTR’s nucleotide-binding domain 1 (“NBD1”). Despite having long been identified as a critical component for proper CFTR function, NBD1 has been considered “undruggable,” and none of the currently approved CF therapies directly stabilizes NBD1. Worldwide revenue for approved CFTR modulators was approximately $11 billion in 2024 and is expected to grow to $15 billion by 2029. Leveraging more than a decade of our co-founders’ research on NBD1, we are advancing a pipeline of small molecules engineered to correct the defects caused by the F508del genetic mutation, which resides in the NBD1 domain. Approximately 90% of people with CF carry at least one copy of the F508del genetic mutation.

We believe stabilizing NBD1 is central to unlocking dramatic improvements in clinical outcomes and quality of life for CF patients. The NBD1 domain of the CFTR protein, as illustrated in Figure 1, plays a key role in the folding, stability and trafficking of CFTR to a cell’s surface, where it normally functions to conduct chloride and other ions and regulate the flow of water. Within the NBD1 domain, F508del severely destabilizes CFTR, preventing normal folding and trafficking of CFTR to a cell’s surface and impairing chloride channel function. We have employed biophysical, cell-based and virtual screening campaigns and extensive use of structural biology to guide the optimization of novel small molecule NBD1 stabilizers.

Figure 1. CFTR Structure

In February 2025, we disclosed interim data from two ongoing randomized, double-blinded, placebo-controlled Phase 1 clinical trials of our highly potent NBD1 stabilizers—SION-719 and SION-451—evaluating the safety, tolerability and PK of single ascending doses ("SAD") and multiple ascending doses ("MAD") of each product candidate in healthy subjects. As of the interim data cutoff date of January 14, 2025, five SAD cohorts

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and three MAD cohorts of SION-719 had been completed, with over 60 healthy subjects dosed, and six SAD cohorts and three MAD cohorts of SION-451 had been completed, with over 70 subjects dosed. Both SION-719 and SION-451 were generally well tolerated based on interim Phase 1 clinical data as of the interim data cutoff date. In these trials, at both single and multiple doses, SION-719 and SION-451 exposures were achieved that have the potential, based on our preclinical CFHBE model, to provide clinically meaningful benefit if SION-719 or SION-451 were administered as part of a dual combination or as an add-on to the standard of care (“SOC”). Since reporting interim data, we have completed dosing in the MAD part of the Phase 1 trial of SION-451, and the final MAD cohort of the SION-719 trial, evaluating 120 mg of SION-719, is planned. The additional completed cohorts evaluated 225 mg and 25 mg (fed) of SION-451 and 160 mg of SION-719, dosed twice daily ("BID") over 10 days. All MAD data, including from the recently completed cohorts, remain blinded to individual subject treatment assignment. Both compounds were generally well tolerated in these additional cohorts. The Part C of each trial, in which we are evaluating the effect of food on the PK of each product candidate and the bioequivalence of a table formulation, is ongoing. Topline data from the Phase 1 trials are expected in the first half of 2025.

We are also developing a portfolio of complementary CFTR modulators designed to work synergistically with our NBD1 stabilizers to improve CFTR function, as seen in preclinical models. In July 2024, we in-licensed three clinical-stage compounds from AbbVie Global Enterprises Ltd. (“AbbVie”) to expand our portfolio of combination product opportunities, including galicaftor (SION-2222), which targets CFTR’s transmembrane domain 1 (“TMD1”), and has completed Phase 2 clinical trials. In December 2024, we completed a Phase 1 clinical trial evaluating SION-109, which targets CFTR’s intracellular loop 4 (“ICL4”) region.

Our vision is to build a CF franchise anchored by our NBD1 stabilizers to deliver clinically meaningful benefit to CF patients. We believe our robust pipeline of NBD1 stabilizers and complementary modulators provide multiple potential pathways to achieving that vision, either in combination with each other to produce a proprietary combination CF therapy, or in combination with the current standard of care. We plan to evaluate multiple NBD1 stabilizer candidates and complementary modulator candidates and select the most promising candidates to advance into later-stage development. Initially, we intend to evaluate an NBD1 stabilizer candidate in combination with the current standard of care in a Phase 2a proof-of-concept trial, expected to begin in the second half of 2025. In parallel, we will determine the proprietary dual combination that we believe is optimal to advance into a later-stage clinical trial in CF patients, as illustrated in Figure 2.

Figure 2. Our NBD1 Stabilizers Have Multiple Potential Pathways to Deliver Clinically Meaningful Benefit to CF Patients

Central to our development strategy is our use of the industry standard, clinically predictive preclinical cystic fibrosis human bronchial epithelial (“CFHBE”) model to measure CFTR function. The CFHBE model uses lung cells from CF patients and has been highly predictive of clinical outcomes for approved CFTR modulators. Vertex Pharmaceuticals, Inc. (“Vertex”), the manufacturer of the five approved CFTR modulators, has demonstrated that increased chloride transport in the CFHBE model is strongly correlated with improved CFTR function in CF patients. In head-to-head preclinical studies using the CFHBE model, we evaluated several of our proprietary dual combinations (combining each of SION-719 and SION-451 with each of SION-2222 and SION-109) in direct comparison to elexacaftor/tezacaftor/ivacaftor (“ETI”) (which we synthesized using methods described in publicly available sources), with all compounds at their respective highest effective dose (“Emax”). In other head-to-head preclinical studies using the CFHBE model, we evaluated “add-on” combinations (SION-719 and ETI, and 451 and ETI), in direct comparison to ETI alone, with all compounds at Emax. In all of these studies, whether evaluating a proprietary dual combination or an “add-on” combination of an NBD1 stabilizer and ETI, we observed a marked improvement in CFTR protein activity of more than 1.5-fold relative to ETI alone. The CFHBE model has helped us identify active compounds and predict the potential clinical exposures needed to achieve a target level of clinical activity in humans. We intend to continue to leverage insights from the CFHBE model as we make critical pipeline prioritization and development decisions.

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Our Pipeline

Our proprietary portfolio includes NBD1 stabilizers and complementary modulators. There are two types of complementary modulators: correctors, which partially improve CFTR protein folding to aid its trafficking to the cell surface, and potentiators, which increase CFTR channel function by enabling chloride flow through the cell membrane. We believe the synergistic approach of combining NBD1 stabilizers with complementary modulators provides the highest probability of normalizing CFTR function for CF patients. Our portfolio includes:

•SION-719 and SION-451, our highly potent NBD1 stabilizers, are both in Phase 1 trials in Australia to evaluate their pharmacokinetic (“PK”) profile, safety and tolerability in healthy subjects. We have completed dosing in the SAD parts of both trials and the MAD part of the SION-451 trial; the final MAD cohort of the SION-719 trial is planned. Both NBD1 stabilizers have been generally well tolerated in these ongoing trials based on interim data to date. Topline results from our SION-719 and SION-451 Phase 1 clinical trials are expected in the first half of 2025.

•Galicaftor (SION-2222) and SION-2851 are TMD1-directed CFTR correctors. Galicaftor was generally well-tolerated in Phase 1 and Phase 2 trials. Improvement in sweat chloride as a monotherapy and improvements in sweat chloride and lung function as a combination therapy with navocaftor were observed. SION-2851 has completed a Phase 1 single ascending dose (“SAD”) trial in healthy volunteers.

•SION-109, an ICL4-directed CFTR corrector, has been evaluated in a recently completed Phase 1 clinical trial in healthy volunteers. SION-109 was generally well tolerated at all dose levels administered in all parts of this Phase 1 trial. The target exposure for SION-109 as part of a dual combination with SION-451 or SION-719 was achieved with single and multiple doses.

•Navocaftor (SION-3067), a potentiator, has been evaluated in Phase 2 trials, where it demonstrated potential as a combination therapy.

Figure 3 below captures the targeted binding locations within the CFTR structure for our pipeline of NBD1 stabilizers and complementary modulators.

Figure 3. Our Multi-Prong Approach to Potentially Improving CFTR Function

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Our current portfolio of programs is summarized in Figure 4 below:

Figure 4. Our Proprietary Pipeline of Product Candidates for the Treatment of CF

Clinical trials for galicaftor, SION-2851, and navocaftor were conducted by AbbVie or Galapagos NV.

Our Strategy

Our mission is to revolutionize the current treatment paradigm for CF patients by developing novel medicines that normalize the function of the CFTR protein to deliver clinically meaningful benefit to CF patients. The key pillars of our strategy are:

•Advance our novel NBD1 stabilizers. Topline data from our Phase 1 clinical trials of SION-719 and SION-451 are expected in the first half of 2025. After completion of a drug-drug interaction trial, we plan to initiate a Phase 2a proof-of-concept trial in the second half of 2025 to evaluate an NBD1 stabilizer in combination with the current standard of care in CF patients, as well as combination MAD trial(s) evaluating dual combinations of an NBD1 stabilizer with galifactor (SION-2222) and/or SION-109 in healthy subjects. In preclinical studies using the CFHBE model, the combination of SION-719 or SION-451 with one of our complementary modulators or ETI showed increased chloride transport, which indicates improvement in in vitro CFTR activity. Given the clinically predictive nature of the CFHBE model, we believe these data indicate the potential for an NBD1-anchored dual combination to improve CFTR activity, which we believe will deliver clinically meaningful benefit to CF patients.

•Develop and advance our pipeline of complementary modulators for proprietary combination product development. We are developing a proprietary pipeline of complementary CFTR modulators designed to work synergistically with our NBD1 stabilizers to improve CFTR function, as seen in our CFHBE model. We have several CFTR modulators in development, including galicaftor (SION-2222), a TMD1-directed corrector which has completed Phase 2 clinical trials, and SION-109, an ICL4-directed corrector which completed a Phase 1 clinical trial in December 2024.

•Build upon our NBD1-centric CF franchise through a data-driven dual combination path. Our goal is to develop proprietary combination therapies that provide clinically meaningful benefit to CF patients. Based on the results of the combination MAD trial(s) we plan to initiate in the second half of 2025, evaluating dual combinations of an NBD1 stabilizer with galicaftor and/or SION-109 in healthy subjects, we plan to select the most promising proprietary dual combination to advance into Phase 2b dose-ranging trials in patients with CF.

•Fortify our CF franchise through continued research efforts and utilization of the translational CFHBE model. We aim to build a CF franchise anchored by our NBD1 stabilizers while executing on our mission to deliver medicines that provide clinically meaningful benefit to CF patients. The CFHBE model has been highly predictive of clinical outcomes for approved CFTR modulators, and our application of the model provides a key translational roadmap for us to prioritize compounds for further evaluation. We believe the model allows us to determine the target exposure needed to achieve a

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desired level of clinical activity, such as the level of improvement in a patient’s forced expiratory volume in one second (“FEV1”), a measure of lung function, and sweat chloride level, the clinical biomarker of CFTR function. We intend to invest in research activities and leverage insights from the model in our pursuit of delivering additional differentiated product candidates that meaningfully impact the lives of CF patients and facilitate our company’s long-term growth. We also intend to opportunistically consider strategic in-licensing opportunities to maximize the value of our pipeline.

Our Company’s History and Our Team

Sionna was founded in 2019 to continue to explore novel approaches to treating CF by targeting NBD1. Our co-founders, Greg Hurlbut, Ph.D., and Mark Munson, Ph.D., spent over a decade extensively researching the NBD1 target as research leaders at Sanofi SA (f/k/a Sanofi Genzyme) (“Sanofi”). Shortly after our inception, we entered into an exclusive license agreement with Sanofi to acquire exclusive worldwide rights to research, develop and commercialize certain compounds designed to stabilize NBD1, as well as an ICL4 corrector.

In addition, we have assembled a leadership team with deep expertise in drug discovery and developing CF and other rare disease therapies, launching and commercializing therapeutics globally, and building successful public pharmaceutical companies. Mike Cloonan, our President and Chief Executive Officer, has more than 20 years of leadership experience at global organizations, most recently as Chief Operating Officer at Sage Therapeutics, Inc. and prior to that as Senior Vice President of U.S. Commercial at Biogen, Inc. Charlotte McKee, M.D., our Chief Medical Officer, is a pulmonologist with more than 20 years of drug development experience who, while serving as Vice President of CF and Alpha-1 Antitrypsin Deficiency Clinical Development at Vertex, was instrumental in the development and regulatory approvals of three of Vertex’s five approved CFTR modulators, including Trikafta. Elena Ridloff, C.F.A., our Chief Financial Officer and Head of Corporate Development, has more than 20 years of experience in finance in the life sciences industry, most recently as Chief Financial Officer at ACADIA Pharmaceuticals Inc.

Our leadership team is supported by a dedicated team of employees with deep industry-leading expertise, our board of directors, scientific and clinical advisory boards and a group of premier life sciences investors. We also received founding support from the Cystic Fibrosis Foundation (“CFF”), which has been a committed investor and supporter of our research and development work. Prior to our inception, the CFF spent more than a decade funding early-stage F508del corrector discovery work at Sanofi that contributed to our pipeline.

Overview of Cystic Fibrosis, CFTR Function and the F508del Mutation

An estimated 106,000 people have been diagnosed with CF across 94 countries, including approximately 33,000 adults and children living with CF in the U.S., according to the CFF. While life expectancy for CF patients has improved significantly over the years since the first CFTR modulator was approved, the median predicted survival age for individuals with CF born in the U.S. between 2019 and 2023 is still just 61 years, according to the 2023 CFF patient registry. The majority of people who have been diagnosed with CF live in the U.S., the United Kingdom and Europe. CF is the most common fatal inherited disease in the U.S., and it can affect people of every racial and ethnic group. CF is caused by mutations to the CFTR gene that result in reduced or no function of the CFTR protein. The disease is autosomal recessive, meaning that two copies of a CFTR mutation are required to cause the disease, either two copies of the same mutation (“homozygous”) or two different mutations (“heterozygous”). Approximately 90% of people with CF carry at least one copy of the F508del mutation, and approximately 44% of people with CF are homozygous for F508del. The F508del mutation (a deletion of the amino acid phenylalanine at position 508, in NBD1) is considered a severe CF mutation, and individuals with this mutation tend to fall at the worst end of the CF severity spectrum because they have little or no CFTR function in epithelial cells.

In people with CF, mutations in the CFTR gene cause the CFTR protein to become dysfunctional. The CFTR protein is found on the apical membrane, or surface, of epithelial cells throughout the body, including in the lungs, pancreas, sweat glands, biliary tract and intestines. The CFTR protein is critical for proper salt and water balance in the cell, which drives production of freely flowing mucus for tissue hydration in the airways, digestive system and other organs. When the CFTR protein is not working properly, chloride—a component of salt—gets trapped in cells, as illustrated in Figure 5. Without chloride to attract water to the cell surface, thick mucus accumulates in vital organs such as the lungs, pancreas and gastrointestinal tract and causes

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multisystem complications, including respiratory infections, chronic lung inflammation, poor nutrient absorption and often progressive respiratory failure, which is the primary cause of death in people with CF.

Figure 5. CFTR Regulates Chloride Transport in Epithelial Cells

Source: Favia, 2019

As illustrated in Figure 6, the CFTR protein includes two nucleotide binding domains (NBD1 and NBD2) and two transmembrane domains (TMD1 and TMD2). The transmembrane domains form the ion channel across an epithelial cell’s membrane. The nucleotide binding domains facilitate the ion channel’s opening and closing by binding and hydrolyzing adenosine triphosphate. There are also four intracellular loops that link the nucleotide binding domains to the transmembrane domains and are important to regulating ion channel gating.

Figure 6. The CFTR Protein and the F508del Mutation

The F508del mutation resides in the NBD1 domain near an interface with the fourth intracellular loop, ICL4, which is particularly critical to the folding of CFTR. When the ICL4 interface is disrupted, as it is by the F508del mutation, CFTR can neither fold nor function properly. The F508del mutation severely destabilizes CFTR’s NBD1 domain, preventing normal folding and trafficking of CFTR to a cell’s surface and impairing chloride channel function. Support for NBD1 as a key target is based in part on in vitro studies that introduced mutations at other sites on NBD1 that suppressed the effect of the F508del mutation.

Current Unmet Need and Market Opportunity

While advances in the treatment of patients with CF have improved the lives of patients and resulted in a large commercial market, we believe significant opportunity remains to provide clinically meaningful benefit to CF patients through the development of NBD1-anchored treatments. NBD1 has long been considered an important target to normalize CFTR function because it is the site where the F508del mutation—the most common mutation that causes CF—resides. However, attempts by others to stabilize NBD1 have fallen short,

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leading to the view that NBD1 is “undruggable.” The current standard of care, Trikafta, as well as the recently approved Alyftrek, are made up of three components that target certain domains of CFTR, but not NBD1. At least two-thirds of patients on Trikafta do not have normal CFTR function, defined as sweat chloride levels below 30 mmol/L. Even treated CF patients can continue to experience the ongoing effects of reduced CFTR function over time, including respiratory infections, pulmonary exacerbations, or “lung attacks,” and continued lung function decline. More than 6,000 patients have discontinued use of approved CFTR modulators, none of which target NBD1. Additionally, some patients on Trikafta reduce dosages due to tolerability issues, including elevated liver function tests and mental health effects such as mood disturbances, depression, and mental fogginess. In December 2024, the Trikafta label was updated to include a boxed warning for the risks of drug-induced liver injury and liver failure, and the Alyftrek label includes the same boxed warning. Seven to eight percent of patients on Trikafta have experienced significant mental health effects, and depression, including suicidal ideation and attempt, is listed in the warnings and precautions section of the summary of product characteristics for Kaftrio, the brand name for Trikafta in Europe. Patients who discontinue use of Trikafta or experience tolerability challenges have limited or no alternative treatments available to improve their clinical outcomes or quality of life. Currently, the alternatives for these patients are limited to less efficacious combination products that include one or more components of Trikafta, or Alyftrek, which demonstrated non-inferiority to Trikafta in the primary endpoint of two Phase 3 clinical trials, providing patients with similar FEV1 as Trikafta and sweat chloride level improvements of 3 to 8 mmol/L. Approximately 69% of Alyftrek patients in two Phase 3 clinical trials did not achieve normal CFTR function, defined as sweat chloride levels below 30 mmol/L. Our research with key opinion leaders has indicated the desire for more treatment options for CF patients, support for a new mechanism of action that could provide clinically meaningful benefit for people living with CF, and need for an alternative for those patients who experience tolerability issues on Trikafta. We aim to expand the current treatment paradigm through a proprietary dual combination or as an add-on to the standard of care.

Worldwide revenue for approved CFTR modulators was approximately $11 billion in 2024, and it is expected to grow to $15 billion by 2029. Vertex, which markets all five of the currently approved CFTR modulators, reported revenues in 2024 from global sales of its then-approved CFTR modulators of approximately $11.0 billion, more than $10.2 billion of which the company attributed to Trikafta. Vertex's approved CFTR modulators target approximately 92,000 CF patients in North America, Europe and Australia, and more than 20% of eligible patients are currently not on CFTR modulators. CF screening of newborn infants has served to identify CF patients as early as possible in their lives. For example, newborn screening for CF has been required in the U.S. since 2010, and in 2021, 64.4% of newly diagnosed people with CF in the U.S. were identified by newborn screening, based on CFF registry data. The availability of CFTR modulators has also increased the use of genetic testing to determine eligibility for treatment.

Current Standard of Care and its Limitations

The approved CFTR modulators are oral small molecule therapies that improve CFTR function either by potentiating channel gating or by improving cellular processing and trafficking of the CFTR protein. The current standard of care for people with the F508del mutation is a triple combination product marketed by Vertex as Trikafta (elexacaftor, tezacaftor, ivacaftor and ivacaftor). In addition, in December 2024, Vertex received approval from the FDA for a second-generation, triple modulator combination, Alyftrek, for the treatment of CF in patients aged six years and older who have at least one F508del mutation or another responsive mutation in the CFTR gene. Vertex also markets three other approved CFTR modulators. None of the approved modulators directly stabilize NBD1. The drugs and their approved indications in the U.S. are summarized in Figure 7.

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Figure 7. FDA-Approved CFTR Modulators and Summary Indications

Despite the clinical benefits Trikafta provides CF patients, including improved lung function and quality of life, at least two-thirds of people with CF being treated on Trikafta or another approved CFTR modulator do not have normal CFTR function. CF progression is most commonly assessed through a patient’s mean lung function, as measured by FEV1 improvement. In addition, sweat chloride level, the clinical biomarker of CFTR function, has been used for decades as a diagnostic test for CF and has served as a highly useful tool in the development of approved CFTR modulators. A sweat chloride level greater than or equal to 60mmol/L indicates that CF is likely, while a sweat chloride level under 30 mmol/L is normal and indicates that CF is unlikely. Sweat chloride levels between 30 mmol/L and 59 mmol/L are considered abnormal, indicating partial CFTR dysfunction or “residual function” in diagnostic settings. An observational study of 3,131 individuals with CF from the CFF Registry found that, while treatment with Trikafta resulted in improvements in sweat chloride level to below 60 mmol/L in most patients, two-thirds of patients still had sweat chloride levels above normal levels (i.e., above 30 mmol/L) (Figure 8).

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Figure 8. Approximately Two-Thirds of Patients on Approved Therapies Do Not Have Normal CFTR Function as Measured by Sweat Chloride Levels

(Sweat chloride levels less than or equal to 29 mmol/L indicate that CF is unlikely; levels of 30 - 59 mmol/L indicate that CF is possible and additional testing is needed; and levels greater than or equal to 60 mmol/L indicate that CF is likely.)

Two-year interim data from a five-year post-marketing real-world observational trial of patients taking Trikafta showed that mean rates of pulmonary exacerbations and the presence of bacterial pathogens improved but were not normalized after initiating treatment on Trikafta. The three-year interim data, presented at the European CF Society meeting in Glasgow in 2024, showed numerical increases in mean rates of pulmonary exacerbations and decreases in mean lung function compared to the two-year interim data, supporting the opportunity for clinical improvements over the current standard of care. In addition to continued pulmonary complications, patients also experienced negative mental health side effects, including numerical increases in rates of depression, anxiety disorder and hypertension after initiating treatment on Trikafta. Another side effect associated with ivacaftor is cataracts, which can complicate use and requires monitoring, especially in children. In addition, in December 2024, the Trikafta label was updated to include a boxed warning for the risks of drug-induced liver injury and liver failure. The Alyftrek label includes the same boxed warning.

Alyftrek demonstrated non-inferiority to Trikafta in the primary endpoint of two Phase 3 clinical trials, providing patients with similar FEV1 as Trikafta and sweat chloride level improvements of 3 to 8 mmol/L. Approximately 69% of Alyftrek patients in two Phase 3 clinical trials did not achieve normal CFTR function. These results support our beliefs that NBD1 stabilization is required to meaningfully improve upon the current standard of care and that a high unmet need remains for an alternative therapy that can provide clinically meaningful benefit to CF patients.

Research Findings Support NBD1 as a Key Target for Stabilizing F508del-CFTR

Multiple studies by third parties have concluded that NBD1 is a key drug target for correcting the F508del mutation, including in vitro studies that introduced mutations at other sites on NBD1 that suppressed the effect of the F508del mutation. For example, researchers at Utrecht University and University of Texas Southwestern Medical Center identified a second site NBD1 mutation (“I539T”) that rescued the misfolding and

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instability of F508del-CFTR. They concluded the “co-translational rescue of F508del NBD1 misfolding in CFTR by I539T advocates this domain as the most important drug target for cystic fibrosis.”

At University of Texas Southwestern Medical Center, University of Alabama Birmingham, and McGill University, a second group of researchers identified additional mutations that suppressed the effect of F508del and which, in in vitro studies, stabilized NBD1 and the NBD1-ICL4 interface and fully restored F508del-CFTR maturation and function to wild-type levels, as shown in the western blot in Figure 9. A western blot is an assay that uses gel electrophoresis to separate a mixture of proteins, which are then transferred to a solid membrane, and then an antibody is used to detect a specific protein in the sample. The mature apical CFTR band is seen with wild-type CFTR. Partial restoration is observed with NBD1 stabilization and ICL4 interface restoration individually; full restoration of CFTR function occurred in the presence of both NBD1 and ICL4 suppressor mutations. Without a suppressor mutation, no F508del-CFTR is produced (Ø).

Figure 9. NBD1 Stabilization Synergizes with Improved Domain-Domain Assembly to Fully Correct F508del-CFTR

Source: Thibodeau, 2010

Research Findings Link Further Improvements in CFTR Function to Improved Clinical Outcomes

Clinical evidence obtained by third parties has illustrated that further reductions in sweat chloride, the clinical biomarker of CFTR function, towards wild-type levels, are associated with improved clinical outcomes, even for patients who have already experienced some benefits from an approved modulator therapy. According to a trial published in the New England Journal of Medicine, when CF patients heterozygous for F508del and a “gating” mutation were switched from Kalydeco, which does not target F508del, to Trikafta, which targets F508del, they experienced significant improvements in CFTR function, as measured by improvements in the mean sweat chloride levels, and in mean lung function, as measured by FEV1. Patients with a gating mutation represent approximately 6% of the CF patient population. Their mean sweat chloride level at baseline was 50.9 mmol/L. After eight weeks of treatment with Trikafta, the patients’ mean sweat chloride level was 32.7 mmol/L, representing an improvement of approximately 20 mmol/L, and their mean lung function level, as measured by FEV1, improved by 5.8 percentage points.

Our Approach and Leveraging the CFHBE Model

Our programs leverage an industry standard, clinically predictive CFHBE model to measure CFTR protein function in vitro. Activity in this model has been shown to be correlated to chloride transport activity, which in turn, has been shown to be correlated to improved lung function in clinical trials designed to evaluate product candidates in CF patients. We have used, and plan to continue to use, insights from the CFHBE model to inform critical pipeline prioritization and development decisions. For example, we selected SION-719 and SION-451 to advance based on their preclinical profiles, including potency in the CFHBE model. We assessed SION-719 and SION-451 in our CFHBE model in direct, head-to-head comparison to ETI, the components of Trikafta. When evaluated in our CFHBE model at Emax concentrations, both SION-719 and SION-451, in dual combination with one of our complementary modulators, improved in vitro CFTR protein activity to wild-type, or normal, levels. This was a more than 1.5-fold improvement in CFTR protein activity compared to the improvement in such activity observed with ETI at Emax in the same experiment. We believe that we can leverage the reproducible correlation between chloride transport at different drug exposure levels in the CFHBE model and clinical outcomes to predict the target level of exposure to achieve clinically meaningful benefit in CF patients.

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The CFHBE model uses electrophysiology to evaluate CFTR function by measuring CFTR protein activity in an Ussing Chamber, which is commonly used in CF drug discovery efforts. In this model, human bronchial cells derived from the lungs of CF patients are cultured in a manner to resemble the lung epithelium and to increase their numbers. These cultured cells are then placed in the Ussing Chamber, which uses electrodes to measure ion movement across the membranes of the cultured epithelial cells grown into a monolayer with tight junctions. Cultured CFHBE cells exhibit many of the structural and functional attributes believed to be associated with CF airway disease.

Vertex has successfully applied a variation of the CFHBE model with 20% human serum for multiple CFTR modulators advanced to clinical trials, including their five approved modulators. Importantly, the CFHBE model provided key preclinical data on CFTR function to support the clinical evaluation of elexacaftor as part of Trikafta. Based on publications detailing Vertex’s use of the CFHBE model, we believe we conducted our CFHBE model using similar methods and under similar experimental conditions to those Vertex employed. Similar to Vertex, in our model, cell culture media is supplemented with human serum to 20% by volume to estimate the amount of free drug available to engage CFTR in CFHBE cells. This adjustment is designed to simulate the in vivo environment, where much of a drug is bound to serum proteins and not available to enter epithelial cells.

We conduct detailed dose-response studies in our CFHBE model to estimate the level of clinical improvement we believe we can achieve with our modulators at specific levels of drug exposure in clinical trials. The addition of human serum helps correct for the high levels of protein binding that are characteristic of our modulators, similar to approved modulators, which we believe enables our model to more accurately predict the clinical exposure required for efficacy. Our CFHBE model accurately predicted the required total plasma concentration of lumacaftor (a component of Orkambi) at its efficacious clinical exposures, as shown in Figure 10 below. We compared lumacaftor’s CFTR-dependent chloride transport activity in two CFHBE model variants—with 20% human serum (like our model) and without 20% human serum—and benchmarked these against published Phase 2 clinical results regarding sweat chloride levels for lumacaftor. Figure 10 shows that the predicted lumacaftor dose response, as depicted by the red line, closely matched lumacaftor’s clinical dose response, as depicted by the black line. The CFHBE model without 20% human serum, depicted by the blue line, failed to accurately predict the clinical exposure of lumacaftor required for efficacy, even if adjusted for lumacaftor’s measured free fraction in human plasma, depicted by the dotted green line.

Figure 10. Our CFHBE Model is Designed to More Accurately Predict the Required Clinical Exposure than Standard CFHBE Model

Using published data from the clinical trials of Vertex’s approved CFTR modulators, we have validated internally our CFHBE model by assessing the relationship between in vitro CFTR protein function, as measured by chloride transport in our CFHBE model, and the mean sweat chloride levels seen in Vertex’s clinical trials of these approved modulators.

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As shown in Figure 11 below, improvements in CFTR function we observed in our CFHBE model for approved and investigational CFTR modulators have been highly correlated with improvements in sweat chloride measurements from clinical trials for these therapies. Notably, we have used the CFHBE model to predict negative clinical trial outcomes, too. For example, we modeled other third-party modulators previously in development and independently determined that these compounds had insufficient activity to demonstrate target clinical efficacy, which was supported by published clinical trial data.

Figure 11. CFHBE Model Has Been Predictive of Sweat Chloride Improvement

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Mean improvements in sweat chloride levels in clinical trials have been shown to be correlated with mean improvements in lung function as measured by FEV1, as shown in Figure 12 below.

Figure 12. Sweat Chloride Has Been Correlated With Lung Function Benefit

We consider our CFHBE model a translational roadmap because of its ability to correlate with sweat chloride improvement in clinical trials, as seen in Figure 11 above, which in turn has been shown to correlate to improved lung function in clinical trials, as shown in Figure 12 above. We have observed this correlation with our CFHBE data and clinical lung function data for approved and investigational CFTR modulators that demonstrated activity in clinical trials, including galicaftor and navocaftor, as shown in Figure 13 below.

Figure 13. CFHBE Model Correlates to Improved Lung Function

We believe our CFHBE model allows us to predict the target exposure needed for our product candidates to achieve a desired level of clinical activity, such as the level of improvement in patients’ lung function, as measured by FEV1 improvement, and sweat chloride levels. We have tested our product candidates in the CFHBE model at Emax and generated a prediction of sweat chloride and FEV1 changes, based on the documented correlation, observed in clinical trials of approved and investigational modulators, between improvements in sweat chloride levels and improvements in lung function. We believe that the CFTR function

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improvement observed in our CFHBE model of our product candidates has the potential to translate clinically to deliver clinically meaningful benefit to CF patients.

Our CF Programs

We have a portfolio of NBD1 stabilizers and complementary modulators that target other regions of the CFTR protein, with the goal of advancing a combination therapy that has the potential to deliver clinically meaningful benefit to CF patients. We plan to advance an NBD1 stabilizer candidate and NBD1 dual combination into Phase 2 clinical trials in CF patients based on initial human data on safety, tolerability and PK in healthy volunteers.

NBD1 Stabilizer Program

NBD1 is recognized as a key target in treating CF patients with the F508del mutation, as the mutation drives NBD1 instability and defects in its interface assembly. However, NBD1 has presented significant challenges as a drug target due to the attributes of the region’s binding sites. Our NBD1 program builds on more than a decade of our cofounders’ research, which has combined biophysical, cell-based and virtual screening campaigns, along with extensive use of structural biology. We believe the technical challenge associated with NBD1-targeted drug discovery, along with our intellectual property rights, represent a substantial competitive barrier.

We selected SION-719 and SION-451 for clinical evaluation based on their potency, PK profiles and safety as observed in preclinical studies. We assessed SION-719 and SION-451 in our CFHBE model in direct, head-to-head comparison to ETI, the components of Trikafta. When evaluated in our CFHBE model at their respective Emax concentrations, both SION-719 and SION-451, in dual combination with one of our complementary modulators, improved in vitro CFTR protein activity of F508del-CFTR to wild-type, or normal, levels. This was a more than 1.5-fold improvement in CFTR protein activity compared to the improvement in such activity observed with ETI at Emax in the same experiment. Based on predicted exposure levels in the CFHBE model, we believe co-administering SION-719 or SION-451 with a complementary modulator has the potential to achieve clinically meaningful benefit in CF patients.

In addition, we have nominated two NBD1 stabilizers with differentiated profiles as development candidates.

SION-719 and SION-451

Phase 1 Clinical Development

We initiated Phase 1 SAD and MAD clinical trials of SION-719 and SION-451 in healthy subjects in July 2024 and August 2024, respectively. These trials are randomized, double-blinded, placebo-controlled trials designed to evaluate safety, tolerability and PK of each product candidate. Both trials are being conducted in Australia, and we intend to enroll up to 120 healthy subjects in each trial.

In February 2025, we disclosed interim data from both trials, which is summarized below. Since disclosing interim data, we have completed dosing in the MAD part of the SION-451 trial, and the final MAD cohort of the SION-719 trial, to evaluate 120 mg SION-719, is planned. The additional completed cohorts evaluated 225 mg and 25 mg (fed) of SION-451 and 160 mg of SION-719, each dosed BID over 10 days. All MAD data, including from the recently completed cohorts, remain blinded to individual subject treatment assignment. Both compounds were generally well tolerated in these additional MAD cohorts. There were no serious adverse events (“SAEs”), and most treatment-emergent adverse events (“TEAEs”) were mild to moderate. There were no TEAEs related to liver function tests and no TEAEs that led to discontinuation of trial drug. The Part C of each trial, in which we are evaluating the effect of food on the PK of each product candidate and the bioequivalence of a tablet formulation, is ongoing. We expect topline data for both trials in the first half of 2025.

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Interim Phase 1 Trial Data for SION-719

As of January 14, 2025, the interim data cutoff date, over 60 healthy subjects had been dosed in the Phase 1 clinical trial of SION-719. The trial was designed to enroll eight subjects, randomized 3:1 active:placebo, in each dosing cohort. As of the data cutoff date, five SAD cohorts had been completed, evaluating single doses of 20 mg, 40 mg, 80 mg, 160 mg and 20 mg taken with food to provide a preliminary assessment of the effect of food on PK, and three MAD cohorts had been completed, evaluating 20 mg, 40 mg, and 80 mg of SION-719 BID over 10 dosing days. As of the data cutoff date, all data remained blinded to individual subject treatment assignment, with the exception of selected individual subjects unblinded for administrative and study planning purposes according to the clinical trial protocol.

SION-719 was generally well tolerated at all dose levels administered based on interim Phase 1 clinical data as of the data cutoff date of January 14, 2025. There were no SAEs. Most TEAEs were mild to moderate (Grade 1 or Grade 2), and no TEAEs led to the discontinuation of trial drug. The most common TEAEs, occurring in >1 subject, were headache, hypoglycemia and diarrhea. All TEAEs occurring in >1 subject were Grade 1 or Grade 2, except a single Grade 4 hypoglycemia TEAE in a placebo subject in a SAD cohort. There were no TEAEs related to liver function tests. No dose-limiting TEAEs or safety trends of concern have been observed, including in the additional MAD cohort completed after the interim data cutoff date.

Increasing exposure was observed with increasing single and multiple doses as of the interim data cutoff date. The concentration targets for SION-719 as an add-on to SOC and as part of a dual combination with SION-2222 or SION-109 were achieved with single and multiple doses. A PK summary of SION-719 data as of the cutoff date of January 14, 2025 is shown in Figures 14 and 15 below. The observed PK was consistent with BID dosing.

Figure 14. Preliminary Phase 1 PK Summary for SION-719 in the SAD Portion of the Trial

(Each solid line shows mean concentration data from a dosing cohort. Dotted lines represent average PK concentration exposure targets that have the potential, based on our preclinical CFHBE model, to provide clinically meaningful benefit, if SION-719 is administered in a proprietary dual combination with either SION-2222 or SION-109, or as an add-on to SOC.)

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Figure 15. Preliminary Phase 1 PK Summary for SION-719 in the MAD Portion of the Trial

(Each solid line shows mean concentration data from a dosing cohort on Day 10. Dotted lines represent average PK concentration exposure targets that have the potential, based on our preclinical CFHBE model, to provide clinically meaningful benefit, if SION-719 is administered in a proprietary dual combination with either SION-2222 or SION-109, or as an add-on to SOC.)

Interim Phase 1 Trial Data for SION-451

As of January 14, 2025, over 70 healthy subjects had been dosed in the Phase 1 clinical trial of SION-451. The trial was designed to enroll eight subjects, randomized 3:1 active:placebo, in each dosing cohort. Six SAD cohorts had been completed, evaluating single doses of 75 mg, 150 mg, 300 mg and 450 mg, as well as single doses of 75 mg and 25 mg with food to provide a preliminary assessment of the effect of food on PK. Three MAD cohorts had been completed as of the data cutoff date, evaluating 75 mg, 150 mg, and 300 mg of SION-451 BID over 10 dosing days. As of the data cutoff date, all data remained blinded to individual subject treatment assignment.

SION-451 was generally well tolerated at all dose levels administered based on interim Phase 1 clinical data as of the data cutoff date of January 14, 2025. There were no SAEs, and most TEAEs were mild to moderate (Grade 1 or Grade 2). No TEAEs led to the discontinuation of trial drug. The most common TEAEs, occurring in more than one subject, were headache, abdominal pain, contact dermatitis, influenza, presyncope, fatigue and upper respiratory tract infection. All TEAEs occurring in >1 subject were Grade 1 or Grade 2, and many were in an isolated dose cohort that was impacted by an outbreak of respiratory infection in the Phase 1 unit. One Grade 1 TEAE of increased transaminases had been observed, in a subject with influenza A infection. No dose limiting TEAEs or safety trends of concern have been observed, including in the additional MAD cohorts completed after the interim data cutoff date.

Increasing exposure was observed with increasing single and multiple doses as of the interim data cutoff date. The concentration targets for SION-451 as both an add-on to SOC and as part of a dual combination with SION-2222 or SION-109 were achieved with single and multiple doses. A PK summary of SION-451 as of the cutoff date of January 14, 2025 is shown in Figures 16 and 17 below. The observed PK was consistent with BID dosing.

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Figure 16. Preliminary Phase 1 PK Summary for SION-451 in the SAD Portion of the Trial

(Each solid line shows mean concentration data from a dosing cohort. Dotted lines represent average PK concentration exposure targets that have the potential, based on our preclinical CFHBE model, to provide clinically meaningful benefit, if SION-451 is administered in a proprietary dual combination with either SION-2222 or SION-109, or as an add-on to SOC.)

Figure 17. Preliminary Phase 1 PK Summary for SION-451 in the MAD Portion of the Trial

(Each solid line shows mean concentration data from a dosing cohort on Day 10. Dotted lines represent average PK concentration exposure targets that have the potential, based on our preclinical CFHBE model, to provide clinically meaningful benefit, if SION-451 is administered in a proprietary dual combination with either SION-2222 or SION-109, or as an add-on to SOC.)

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Phase 2 Clinical Development Plans

Our current expectations for our clinical development strategy are depicted in Figure 18 below.

Figure 18. Our Strategic Development Plan to Advance Our Pipeline of NBD1 Stabilizers and Complementary Modulators

Phase 2a Proof-of-Concept Clinical Trial—NBD1 stabilizer + Trikafta

We plan to initiate a Phase 2a proof-of-concept trial in CF patients in the second half of 2025, following completion of our Phase 1 clinical trials of SION-719 and SION-451 and a drug-drug interaction trial. We expect the Phase 2a trial to be a two-way crossover trial in which we enroll up to 20 trial subjects with CF who are stable on physician-prescribed Trikafta. All trial subjects will be randomly allocated to one of two trial arms and continue taking Trikafta throughout the trial. Trial subjects in “Arm A” will first receive Trikafta in combination with an NBD1 stabilizer for 14 days, and, after a 28-day washout period, will receive Trikafta in combination with placebo for 14 days. Trial subjects in “Arm B” will receive the same treatments in reverse order. All subjects will have a 28-day safety follow-up period. We expect to select safety as the primary endpoint, and PK and improvements to sweat chloride levels as the secondary endpoints.

Combination MAD Clinical Trial(s)—NBD1 stabilizer + galicaftor and/or SION-109

We intend to initiate combination MAD trial(s) in the second half of 2025, assessing the safety, tolerability and PK of dual combination(s) of an NBD1 stabilizer with galicaftor and/or SION-109 in healthy volunteers, following completion of combination toxicology studies. Following the completion of such trial(s), we intend to select a dual combination to advance into a Phase 2b dose-ranging trial in CF patients.

Preclinical Studies

We have used numerous complementary methods to validate and characterize the activity of our compounds. In addition to the CFHBE model, we have utilized differential static light scattering (“DSLS”) experiments to measure the thermal stability of the NBD1 protein, surface plasmon resonance (“SPR”) studies to evaluate the interaction of SION-719 and SION-451 with the NBD1 domain, and CFTR western blot analysis to assess the impact of NBD1 stabilizers on the folding, maturation and stability of F508del-CFTR. Given the results of these preclinical studies, we believe that we have identified highly potent NBD1 stabilizers with robust preclinical activity.

SION-719 and SION-451 Increased NBD1 Thermal Stability

In preclinical studies, SION-719 and SION-451 increased the stability of the NBD1 domain as measured using DSLS experiments. Light scattering provides a measure of the temperature at which a protein unfolds. As the temperature rises, the CFTR protein unfolds and creates aggregates that interfere with the passage of light.

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These preclinical studies evaluated the change in temperature that the protein aggregated as the ratio of the compound to CFTR protein increased, which is an indicator of stability. We also evaluated ETI in these preclinical studies, and we found that they had no effect on NBD1 thermal stability, as measured by light scattering techniques. Restoration of NBD1 thermal stability has been highlighted as being both necessary and sufficient to correct F508del CFTR folding and assembly. Both SION-719 (Figure 19, left) and SION-451 (Figure 19, right) increased F508del-NBD1 stability by approximately 16°C. These preclinical models show the ability of SION-719 and SION-451 to improve the stability of NBD1 as compared to ETI, as measured by light scattering techniques.

Figure 19. SION-719 and SION-451 Increased Stability of the NBD1 Domain

SION-719 and SION-451 Bound to NBD1 with High Affinity

To evaluate the binding ability of our stabilizer candidates, we employed SPR studies to evaluate the interaction of SION-719 and SION-451 with the NBD1 domain. SPR studies measure changes in the mass of biomolecules immobilized on a metal film. When a small molecule ligand binds to the immobilized target protein, the refractive index of the metal film changes, resulting in a changed reflection angle of light. In these studies, we found that the strength of the binding interaction was high; the binding affinity of SION-719 to F508del-NBD1 was approximately 4.3 nM and the binding affinity of SION-451 to F508del-NBD1 was approximately 2.4 nM, each expressed as a KD value.

SION-719 and SION-451 Restored F508del Folding and Maturation

In preclinical studies, we evaluated SION-719 and SION-451 in various combinations, including with ETI, galicaftor, and SION-109 to assess these combinations’ ability to improve CFTR folding, maturation and stability and thereby correct F508del-CFTR. Preclinical studies with both SION-719 and SION-451-based combinations resulted in F508del-CFTR maturation to levels that are similar to wild-type CFTR. We believe these results demonstrated potential synergy between an NBD1 stabilizer and these complementary modulators.

The results of studies of CFTR maturation in human CF submucosal gland epithelial (“CFSMEo”) cells by western blot with SION-719 are shown in Figure 20 (top), and the results with SION-451 combinations are shown in Figure 20 (bottom). Together, the western blots illustrate F508del-CFTR protein in a submucosal-gland epithelial cell line that expresses CFTR, treated with various combinations of CFTR modulators. The high molecular weight bands, labeled C-band, indicate the presence of the active, mature apical glycoform of CFTR (dark bands), which is responsible for CFTR channel function. The compounds were evaluated at their Emax.

In Figure 20, the far-left column in the C-band is F508del in dimethylsulfoxide (“DMSO”) alone, showing no mature protein, and the far-right column is wild-type CFTR in DMSO with a dark bank indicating the presence of mature CFTR protein. As seen in Figure 20 (top), dual combinations of SION-719 with galicaftor or SION-109, or the addition of SION-719 to ETI, resulted in wild-type levels of corrected F508del-CFTR protein. Treatment with SION-719 as a single agent demonstrated a greater effect on F508del maturation than ETI at

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Emax. On the other hand, there was little improvement in the maturation of F508del-CFTR protein with galicaftor alone, SION-109 alone or ETI at their respective Emax concentrations, as indicated by the light gray bands. The results with SION-451 presented in Figure 20 (bottom) are similar. The western blots below demonstrate the importance of NBD1 stabilization to the correction of F508del maturation.

Figure 20. F508del-CFTR Maturation in CFSMEo-Cells Was Fully Restored with Our SION-719 and SION-451 Corrector Combinations

SION-719 and SION-451 Normalized CFTR Function in CFHBE Model at Emax

In our CFHBE model, SION-719 and SION-451 as single agents at Emax improved F508del-CFTR activity to levels observed near those with triple combination ETI at Emax. The results of the SION-719 and SION-451 studies are shown in Figure 21. In Figure 21, CFTR activity is expressed as a ratio relative to ETI at Emax. The vertical bars represent the mean CFTR channel activity (+/- standard error of eight replicates) from a representative study in homozygous F508del CFHBE cells in response to the treatments indicated. The dashed line represents the average response to ETI in each study.

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Figure 21. SION-719 and SION-451 Were Highly Active in the CFHBE Model at Emax

In our CFHBE model, both SION-719 and SION-451, in dual combinations with galicaftor or SION-109, improved in vitro F508del-CFTR activity to wild-type levels, when administered at Emax. This was a more than 1.5-fold improvement in CFTR protein activity compared to the improvement in such activity observed with ETI at Emax in the same experiment. As noted above, improvements in CFTR function we observed in our CFHBE model have been highly correlated with mean improvements in sweat chloride levels and mean improvements in lung function.

Figure 22. SION-719 and SION-451 Combinations with Galicaftor or SION-109 Were Highly Active in the CFHBE Model at Emax

Based on our findings in these preclinical studies and the strong correlation between chloride conductance and improved clinical activity, we believe that both SION-719 and SION-451, in combination with a complementary CFTR modulator, have the potential to achieve significant improvement in CFTR function, as measured by sweat chloride levels and lung function, and thereby have the potential to lead to clinically meaningful benefit for CF patients. However, the results observed from our preclinical studies may not necessarily be predictive of clinical outcomes, and actual outcomes may differ. We will need to complete additional clinical studies to determine the safety and efficacy of SION-719 and SION-451.

Setting Initial Clinical Exposure Targets Based on CFHBE Model

To set total plasma concentration targets in our Phase 1 clinical trials with SION-719 and SION-451 in healthy volunteers, we conducted multiple dose response studies of both compounds in our CFHBE model that assessed F508del-CFTR activity as a function of each compound’s concentration in cell culture media supplemented with human serum to 20% by volume. We selected a target exposure for our Phase 1 trials based on an average of these preclinical dose response studies along with studies to define an adequate safety

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margin. Figure 23 below presents illustrative dose responses of SION-719, as a single agent and in combination with ETI, SION-109 or galicaftor (SION-2222), as a function of the fold efficacy (CFTR activity) of ETI at increasing dose concentrations, in CFHBE cells from single donors. The black dotted horizontal line indicates ETI’s improvement in F508del-CFTR activity at Emax, the teal horizontal line indicates our minimum target for clinically meaningful improvement in F508del-CFTR activity based on our CFHBE assay, and the green horizontal line represents the lower bound of the CFTR activity range observed across a panel of eight CFTR wild-type CFHBE donors. The X-axis shows increasing drug concentrations on a logarithmic scale. A roughly two-fold increase over ETI, as seen with SION-719 treatment at its Emax in each of the three combinations, is in the range of wild-type channel activity.

Figure 23. Representative ΔF508/ΔF508 CFHBE Dose-Response of SION-719 as Single Agent and in Combination with ETI, SION-109 or SION-2222

(ETI = 3 μM Elexacaftor + 45 μM Tezacaftor + 0.3 μM Ivacaftor. SION-109 and SION-2222 were used at 3 μM.)

Figure 24 below presents illustrative dose responses of SION-451, as a single agent and in combination with ETI, SION-109 or galicaftor (SION-2222), as a function of the fold efficacy (CFTR activity) of ETI at increasing dose concentrations, in CFHBE cells from single donors. A roughly two-fold increase over ETI, as seen with SION-451 treatment at its Emax in each of the three combinations, is in the range of wild-type channel activity.

Figure 24. Representative ΔF508/ΔF508 CFHBE Dose-Response of SION-451 as Single Agent and in Combination with ETI, SION-109 or SION-2222

(ETI = 3 μM Elexacaftor + 45 μM Tezacaftor + 0.3 μM Ivacaftor. SION-109 and SION-2222 were used at 3 μM.)

These dose response curves illustrate that our NBD1 stabilizers work synergistically with complementary modulators, and with the standard of care, to significantly improve CFTR function in preclinical models. Given the correlation seen in our preclinical studies between CFTR function and clinical activity, we believe that achieving target exposure levels for our product candidates in our ongoing and future clinical trials has the potential to translate to significant improvements in sweat chloride and lung function, as measured by FEV1, in CF patients.

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Preclinical Safety/Pharmacology and Toxicology to Support Clinical Trials

For both SION-719 and SION-451, we conducted standard in vitro and in vivo toxicology and safety pharmacology studies necessary to support first in human studies. The preclinical study results supported early clinical testing above exposure levels that we have predicted can be effective.

Additional NBD1 Stabilizer Candidates

Our portfolio includes additional NBD1 stabilizer candidates with differentiated profiles from SION-719 and SION-451.

We have nominated two additional NBD1 stabilizers as development candidates.

Complementary Programs

We have established a pipeline of proprietary complementary modulators, representing three different mechanisms of action, TMD1-directed correctors, an ICL4-directed corrector, and a potentiator, that can potentially be combined with our NBD1 stabilizers. Our two prioritized clinical-stage complementary modulators are galicaftor (SION-2222) and SION-109. Following completion of our NBD1 stabilizer Phase 1 clinical trials, we plan to evaluate galicaftor and/or SION-109 in dual combination with an NBD1 stabilizer in Phase 1 MAD trials in healthy volunteers.

Our portfolio includes additional complementary compounds that we may advance for future combination development with an NBD1 stabilizer, including navocaftor, which has been evaluated in Phase 1 and Phase 2 clinical trials, including in combination with galicaftor, provides our pipeline with a third mechanism of action complementary to NBD1 stabilizers and future opportunities to develop additional combination products to potentially expand our CF franchise.

Clinical Data — Complementary Modulators

TMD1 Programs—Galicaftor (SION-2222) and SION-2851

In a Phase 2 clinical trial conducted by AbbVie prior to our in-licensing transaction, galicaftor demonstrated clinical activity in improving sweat chloride and lung function as part of a combination trial with navocaftor. Galicaftor has been evaluated in Phase 1, Phase 1b and Phase 2 clinical trials involving healthy subjects and CF patients. Galicaftor was generally well-tolerated at all doses administered. The majority of adverse events were mild to moderate in severity. No serious adverse events were reported in healthy volunteers, and among CF patients, serious adverse events were reported infrequently and consisted of common manifestations of the underlying CF disease. Based on galicaftor’s preclinical profile, we do not expect significant PK or drug/drug interactions with our NBD1 stabilizers or other complementary modulators. The PK profile of galicaftor in CF patients was similar to that observed in healthy volunteers. The activity of galicaftor in patients with CF has been evaluated in three randomized, double-blind, placebo-controlled Phase 2 trials, as summarized below.

Trials GLPG-2222-CL-201 and GLPG-2222-CL-202 had at least 80% power to detect selected changes in sweat chloride. In clinical trials, least squares means, or “LS means,” represent the average predicted values of the outcome variable in a statistical model and estimate the effect of a treatment while controlling for other covariates that may influence the outcome. These means provide a clearer comparison between treatment groups by minimizing potential biases from imbalanced covariates. A confidence interval (“CI”) is a range of values, derived from the sample data, that is believed to contain the treatment effect with a specified level of confidence, usually 95%. In clinical trials, the p-value quantifies the probability of observing the trial results (or more extreme results) assuming there is no effect or no difference between treatment groups. A p-value of < 0.05 is generally considered statistically significant, meaning that the probability of the results occurring by chance alone is less than five percent.

•Trial M19-530 was a Phase 2 dose-ranging trial conducted by AbbVie in Europe and the U.S. to evaluate the safety, tolerability and efficacy of navocaftor alone and in combination with galicaftor in 76 CF patients that were homozygous for F508del mutation. The primary efficacy endpoint of this trial was

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absolute change in lung function (ppFEV1) from baseline (day 1) through day 29. The trial was completed in June 2022.

•This trial included eight total arms: a single placebo arm, two arms with different doses of navocaftor in combination with placebo for galicaftor, and five treatment arms across a range of doses of galicaftor (doses 10 mg, 30 mg, 100 mg, 200 mg, 300 mg once daily (“QD”)) in combination with navocaftor 150 mg for 28 days.

•The mean absolute change from baseline in ppFEV1 from baseline through Day 29 ranged from -0.1 to 3.5 percentage points for the five dual combination dose groups (navocaftor 150 mg and galicaftor across a range of doses). The least squares means (“LS means”) change from baseline in ppFEV1 was statistically significant in the 200 mg and 300 mg galicaftor combination groups, 3.5 ppFEV1 (p<0.05) and 3.1 ppFEV1 (p<0.05), respectively. These data are from the analysis in which all spirometry values were used, regardless of usage status of bronchodilator or airway clearance regimen before spirometry collection. LS means with standard errors (“SE”) and p-values are from mixed-effect model repeat measures analysis.

•AbbVie also assessed sweat chloride improvement as a secondary efficacy endpoint. Mean SwCl improvement occurred in all groups with galicaftor 30 mg or higher, with improvement of 18.6 mmol/L in the 200 mg group (p<0.001) and 19.9 mmol/L in the 300 mg group (p<0.001).

•Galicaftor was generally well-tolerated in combination with navocaftor in this trial. Most reported AEs were mild to moderate in severity. Two serious adverse events (“SAEs”) occurred in two subjects receiving galicaftor in combination with navocaftor (ileus and cholecystitis acute); both were considered unrelated to the trial drugs by the investigator.

•Trial GLPG-2222-CL-202 was a Phase 2 dose-ranging trial conducted by Galapagos in Europe and the U.S. to evaluate the safety and tolerability and the effect on CFTR function (as assessed by sweat chloride), pulmonary function and the Cystic Fibrosis Questionnaire— Revised (“CFQ-R”), which measures health-related quality of life, of galicaftor in 59 CF patients that were homozygous for F508del mutation. The trial was completed in October 2017.

•Four doses of galicaftor were tested in this trial (50 mg, 100 mg, 200 mg, 400 mg QD) over 29 days.

•Galicaftor was generally well-tolerated in this trial. The majority of reported treatment-emergent AEs were mild or moderate in severity. A total of four SAEs were reported (two after galicaftor, two after placebo) in two subjects in the pooled placebo and one subject in the galicaftor 100 mg QD treatment group, respectively. The three subjects experienced one or two events of infective pulmonary exacerbation of CF, all of which were considered not related to trial drug.

•Sweat chloride levels, lung function (ppFEV1) and CFQ-R were also assessed as secondary endpoints. Mean sweat chloride concentrations decreased dose-dependently with increasing doses of galicaftor, with a maximum decrease observed in the 200 mg QD treatment group on days 15 and 29, with statistically significant LS means differences compared to placebo of -11.2 (95% CI, -19.1; -3.3; p=0.0062) and -15.8 (95% CI, -23.2; -8.3; p<0.0001) mmol/L, respectively. After termination of the trial drug, mean sweat chloride concentrations returned to baseline values in all treatment groups. Percent predicted FEV1 and CFQ-R did not significantly improve in any group.

•Trial GLPG-2222-CL-201 was a Phase 2 trial conducted by Galapagos in Europe and Australia that evaluated the safety and tolerability and the effect on CFTR function (sweat chloride), lung function (ppFEV1) and CFQ-R of galicaftor in 37 CF patients that were heterozygous for F508del and a gating mutation, receiving ivacaftor. The trial was completed in August 2017.

•Two doses of galicaftor were tested in this trial (150 mg or 300 mg QD) over 29 days.

•Galicaftor was well-tolerated in this trial. Most treatment-emergent AEs were mild in severity, and there were no SAEs.

•Changes from baseline in sweat chloride, ppFEV1 and CFQ-R at day 29 were also assessed as secondary endpoints. The galicaftor 300 mg QD treatment group had a statistically significant LS means with CI difference compared to placebo of -11.7 (95% CI, -21.1; -2.2) mmol/L (p=0.0170). There were no statistically significant changes in sweat chloride in the 150 mg and 300 mg treatment groups. Lung function and CFQ-R did not significantly improve in any group. All results are described for the modified intent to treat population, which excluded one subject who received an incorrect trial kit.

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These Phase 2 results demonstrated that galicaftor as a single agent increased CFTR activity in patients with the F508del mutation. The activity of galicaftor in combination with navocaftor in Trial M19-530 was similar to the activity of approved dual combination modulators, as seen via indirect, cross-trial comparisons and as predicted based on our CFHBE model (Figure 25). These data supported the selection of a 200 mg dose QD of galicaftor for subsequent trials in combination with navocaftor.

Figure 25. Galicaftor + Navocaftor Combination Showed Similar Activity to Symdeko in Phase 2 Cross-Trial Comparison

In addition to galicaftor, we licensed SION-2851 from AbbVie in July 2024. SION-2851 is a potent TMD1-directed corrector that has completed a Phase 1 SAD trial in 16 healthy volunteers. The trial was conducted by AbbVie and Galapagos in Belgium in 2018. The primary endpoint was safety and tolerability, assessed by the number of subjects with adverse events. Based on its mechanism of action and preclinical studies, we believe it may be potentially synergistic with NBD1 stabilizers.

ICL4 Program—SION-109

We are also advancing SION-109, which targets the ICL4 interface, for development in combination with an NBD1 stabilizer.

In December 2024, we completed a randomized, double blind, placebo-controlled Phase 1 clinical trial of SION-109 in healthy subjects, following clearance of its Investigational New Drug application ("IND") by the U.S. Food and Drug Administration (the "FDA") in June 2023. The trial was conducted in the U.S. and was designed to evaluate the safety, tolerability and PK profile of single and multiple ascending doses of SION-109, administered as an oral suspension. In a Part C of the Phase 1 trial, we evaluated the effect of food on PK and the bioequivalence of a tablet formation compared to the oral suspension used in the Phase 1 SAD and MAD trials.

102 healthy adult subjects were dosed in this Phase 1 trial. The trial was designed to enroll 8 subjects, randomized 3:1 active:placebo, to each dosing cohort. Six SAD cohorts evaluated single doses from 50 mg to 400 mg. Five MAD cohorts evaluated from 50 mg to 150 mg BID over 10 dosing days. 15 subjects enrolled in the open-label food effect and tablet bioequivalence part evaluating 100 mg single doses each of suspension fasted, tablet fasted, and tablet fed.

SION-109 was generally well tolerated at all dose levels administered in all parts of this Phase 1 trial. A summary table of reported TEAEs is shown in Figure 26 below. There were no SAEs, and most TEAEs were mild to moderate (Grade 1 or Grade 2). No TEAEs led to the discontinuation of trial drug, and no dose-limiting TEAEs were observed. Sporadic increases in potassium were observed that were determined to be related to sample collection and/or processing. A 150 mg MAD cohort was repeated with revised sampling guidance, and no increased potassium values were observed. Isolated and transient increases in transaminases were observed associated with four AEs in three subjects in the MAD and Part C (one Grade 1 AE, two Grade 2 AEs and one Grade 3 AE) whose values returned to the normal range in follow-up. Other liver function tests, including bilirubin, were unremarkable. There were no clinically meaningful, treatment-emergent trends in other safety parameters, vital signs or electrocardiograms.

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Figure 26. Phase 1 TEAEs for SION-109 in the MAD Portion of the Trial

(Safety observations in the SAD and Part C portions of the trial were generally consistent with the MAD findings shown.)

Increasing exposure was observed with increasing single and multiple doses. The target exposure for SION-109 as part of a dual combination with SION-451 or SION-719 was achieved with multiple doses of 75 mg BID and higher doses.

A PK summary of SION-109 is shown in Figure 27 below. The PK observed was consistent with BID dosing.

Figure 27. Phase 1 PK Summary for SION-109 in the MAD Portion of the Trial

(Each solid line shows mean concentration data for a dosing cohort over 10 days of dosing. Data points for Day 2 through Day 9 are trough (pre-dose) concentrations. The dotted line represents the Cminimum (trough) PK exposure target for SION-109, with the aim to achieve targeted exposure to deliver clinically meaningful benefit when administered in a proprietary dual combination with SION-451 or SION-719, based on CFHBE assay

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data. PK observations in the SAD and Part C portions of the trial were generally consistent with the MAD findings shown.)

Potentiator Program—Navocaftor (SION-3067)

Navocaftor is a clinical-stage potentiator of CFTR gating activity that we have licensed from AbbVie. Navocaftor provides our pipeline with a third mechanism of action complementary to NBD1 stabilizers and future opportunities to develop additional combination products to potentially expand our CF franchise. Navocaftor has completed Phase 1, Phase 1b and Phase 2 trials in over 300 subjects and was generally well-tolerated in CF subjects and healthy volunteers, with improvements observed in sweat chloride levels in combination with galicaftor.

In Phase 1 trials evaluating safety and tolerability in healthy subjects, navocaftor was generally well-tolerated in combination with galicaftor, in each case at doses up to 500 mg BID for 14 days. These trials were conducted in Europe and the U.S. In addition, navocaftor has been generally well-tolerated in both CF subjects and healthy volunteers. When navocaftor was given as a monotherapy or in combination with galicaftor, all AEs were mild to moderate. The PK profile in CF patients was similar in healthy volunteers.

The activity of navocaftor in patients with CF was evaluated in a randomized, double-blind, placebo-controlled Phase 2 trial in combination with a galicaftor dose range from 10 mg to 300 mg QD, as summarized above. Combination treatment of navocaftor 150 mg QD with galicaftor resulted in improvements in FEV1 and sweat chloride levels in the homozygous F508del population. As expected, treatment with 50 mg QD or 150 mg QD navocaftor monotherapy for 28 days did not result in improvements in FEV1 or sweat chloride levels.

Manufacturing

We have leveraged multiple third-party manufacturers to support the manufacturing of our product candidates for clinical trials and, if we receive regulatory approval, we intend to rely on third parties for commercial manufacture. We do not own or operate, and currently have no plans to establish, any manufacturing facilities. We expect this strategy will enable us to maintain a more efficient infrastructure, outsourcing instead of building manufacturing and supply chain capabilities, while simultaneously enabling us to focus our expertise on the clinical development of our product candidates. We expect to enter into commercial supply agreements with such manufacturers prior to any potential approval of our product candidates.

Commercialization

We have exclusive worldwide commercial rights to our product candidates. Given our stage of development, we have not yet established a commercial organization or distribution capabilities. The CF patient populations are well-characterized and clearly identified in the U.S., Canada, Europe and several other regions around the world, with highly active and informed CF patient advocacy groups. Most CF patients are treated at a limited number of centralized CF patient care centers by a team of healthcare professionals who are experts in and dedicated to treating CF.

We plan to independently commercialize our products, if approved, in the U.S. and other regions where we determine it makes commercial sense to do so. Given the established CF patient care centers and identified teams of healthcare professionals, we believe we could commercialize our product(s) for CF with a relatively small specialty sales force that calls on a limited and focused group of prescribing healthcare professionals. At the appropriate time, we will recruit a sales force and a medical affairs team and take other steps to establish the necessary commercial infrastructure. As product candidates advance through our pipeline, our plans may change.

Competition

The biotechnology and pharmaceutical industries are characterized by rapidly advancing technologies, intense competition and a strong emphasis on proprietary products. While we believe we have competitive advantages, we face substantial competition from many different sources, including major pharmaceutical, specialty pharmaceutical and biotechnology companies, academic research institutions and governmental

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agencies, and public and private research institutions. This may include other small-molecule drug discovery companies using similar approaches or other types of therapies, such as small molecule, gene therapy, gene editing and/or mRNA therapies.

In particular, we expect to compete with Vertex, which has multiple approved products, as well as additional product candidates in development, for the treatment of CF that would compete with our product candidates, if approved. Vertex is the manufacturer of the five approved CFTR modulators, including the standard of care, Trikafta, a triple combination therapy approved for patients with at least one F508del mutation or responsive mutations based on in vitro data. Vertex's marketed products generated approximately $11 billion in sales in 2024. In addition, in December 2024, Vertex received approval from the FDA for a second-generation, triple modulator combination, Alyftrek, for treatment of CF in patients aged six years and older who have at least one F508del mutation or another responsive mutation in the CFTR gene. Alyftrek demonstrated non-inferiority to Trikafta in the primary endpoint of two Phase 3 clinical trials, providing patients with similar FEV1 as Trikafta and sweat chloride improvements of 3 to 8 mmol/L. Any product candidates that we successfully develop and commercialize will compete with these existing therapies, as well as any new therapies that may become available in the future that are approved to treat the same diseases for which we may obtain approval for our product candidates.

We may also face competition from other companies attempting to develop therapeutics targeting CF. For example, in January 2025, Fair Therapeutics, Inc. announced completion of enrollment in their phase IIb trial evaluating their CFTR modulators. Multiple companies are developing CF-utilizing nucleic acid therapies, which are compounds that allow expression of a functional CFTR protein and are relevant for the more than 5,000 people with CF who cannot make full-length CFTR protein and are not eligible for CFTR modulators. In addition, multiple companies are developing candidates for gene therapy approaches to treat CF.

Some of our competitors have significantly greater financial resources than we do and an established presence in the market. Our competitors may have greater expertise in research and development, manufacturing, obtaining regulatory approvals and marketing approved products and may obtain regulatory approvals for their products more rapidly than we can, if at all. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies. We also compete with these companies in recruiting, hiring and retaining qualified scientific and management talent, establishing clinical trial sites and patient registration for clinical trials and obtaining manufacturing slots at contract manufacturing organizations.

If our product candidates do not offer advantages over available products, we may not be able to successfully compete against current and future competitors. The key factors affecting the success of our products, if approved, are likely to be their potential efficacy, safety, convenience and availability of reimbursement.

Intellectual Property

We strive to protect and enhance the intellectual property and proprietary technology that we consider important to our business, including by pursuing patent applications that cover our product candidates and methods of using the same, as well as any other relevant inventions and improvements that we believe to be commercially important to the development of our business. We also rely on trade secrets relating to our proprietary know-how, continuing innovation and in-licensing opportunities to develop, strengthen and maintain our proprietary and intellectual property position. We additionally may rely on regulatory protection afforded through data exclusivity, market exclusivity and patent term extensions, where available.

Our commercial success may depend in part on our ability to: obtain, maintain, enforce and protect our intellectual property and other proprietary rights for commercially important technology, inventions and know-how related to our business; defend and enforce any patents we may own or in-license in the future; prevent others from infringing any patents we may own or in-license in the future; preserve the confidentiality of our trade secrets; and operate without infringing the valid enforceable patents and proprietary rights of third parties. Our ability to limit third parties from making, using, selling, offering to sell or importing our products may depend on the extent to which we have rights under valid and enforceable licenses, patents or trade secrets that cover these activities. In some cases, enforcement of these rights may depend on third party licensors. With respect to both licensed and company-owned intellectual property, we cannot be sure that patents will be granted with respect to any of our pending patent applications or with respect to any patent applications filed by us in the

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future, nor can we be sure that any of our existing patents or any patents that may be granted to us in the future will be commercially useful in protecting our commercial products and methods of manufacturing the same.

Patent expiration dates noted in the following paragraphs refer to statutory expiration dates and do not take into account any potential patent term adjustment or extension that may be available.

NBD1 Stabilizers

We co-own with Sanofi a patent family that discloses and covers each of SION-719 and SION-451 and methods of using SION-719 and SION-451 for the treatment of CF. The patent family is in the Patent Cooperation Treaty (“PCT”) stage and is also pending in Argentina and Taiwan. The statutory expiration for this family is September 2043. We own a non-provisional patent application that discloses and claims the use of our NBD1 stabilizer product candidates in combination with other agents for the treatment of CF, which has a statutory expiration of March 2045.

Complementary Modulators

We exclusively license from Sanofi one patent family that discloses and covers SION-109 and methods of using SION-109 for the treatment of CF. The patent family has entered national phase and is pending in the U.S., the European Patent Office, African Regional Industrial Property Organization, African Intellectual Property Organization, Algeria, Australia, Bahrain, Brazil, Canada, Chile, China, Colombia, Eurasian Patent Office, Ecuador, Egypt, Guatemala, Hong Kong, Honduras, Indonesia, Israel, India, Jordan, Japan, Kuwait, Mexico, Malaysia, New Zealand, Nigeria, Oman, Panama, Peru, Philippines, Saudi Arabia, Singapore, South Africa, South Korea, Sri Lanka, Thailand, the United Arab Emirates and Vietnam. The statutory expiration for this family is November 2040.

We exclusively license from AbbVie one patent family that discloses and covers galicaftor and methods of using galicaftor for the treatment of CF. The patent family includes granted patents in the U.S., Albania, Argentina, Austria, Australia, Belgium, Bulgaria, Brazil, Canada, Chile, China, Colombia, Costa Rica, Croatia, Czech Republic, Cyprus, Denmark, Dominican Republic, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, Iceland, India, Indonesia, Ireland, Israel, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Malaysia, Mexico, Monaco, Netherlands, Norway, Panama, Peru, Poland, Portugal, Republic of North Macedonia, Romania, Russia, San Marino, Serbia, Singapore, Slovakia, Slovenia, Spain, South Africa, South Korea, Sweden, Switzerland, Turkey, Taiwan, Ukraine, the United Kingdom and Uruguay, and has a statutory expiration date of October 2035. We exclusively license from AbbVie one patent family that discloses and covers SION-2851 and methods of using SION-2851 for the treatment of CF. The patent family includes granted patents in the U.S., Australia, Brazil, Canada, Chile, China, Colombia, Costa Rica, Dominican Republic, France, Germany, India, Indonesia, Israel, Italy, Japan, Malaysia, Mexico, Panama, Peru, Pakistan, Russia, Singapore, Spain, South Africa, Taiwan, Ukraine, the United Kingdom, Uruguay and Vietnam, and has a statutory expiration date of July 2036.

We exclusively license from AbbVie one patent family that discloses and covers SION-3067 and methods of using SION-3067 for the treatment of CF. The patent family includes granted patents in the U.S., Albania, Austria, Australia, Belgium, Bulgaria, Chile, China, Colombia, Costa Rica, Croatia, Czech Republic, Cyprus, Denmark, Dominican Republic, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, Iceland, India, Ireland, Israel, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Macao, Malta, Malaysia, Mexico, Monaco, Netherlands, Norway, Panama, Peru, Philippines, Portugal, Poland, Republic of North Macedonia, Romania, Russia, San Marino, Serbia, Singapore, Slovakia, Slovenia, Spain, South Africa, South Korea, Sweden, Switzerland, Turkey and the United Kingdom, a pending application in Canada, and has a statutory expiration date of May 2037. Additionally, the patent family includes granted patents in Argentina and Taiwan, each of which has a statutory expiration date of June 2037.

We own two patent applications that each disclose and contain claims that recite the use of our NBD1 stabilizer product candidates in combination with SION-109, galicaftor, SION-3067, Trikafta and/or other modulators for the treatment of CF. The first is a PCT international application and has a statutory expiration of October 2043, and the second is a non-provisional patent application, which has a statutory expiration of March 2045.

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Licensing and Collaboration Agreements

Sanofi License Agreement

On December 20, 2019, we entered into a license agreement, as amended by Amendment No. 1 dated May 14, 2020, Amendment No. 2 on June 8, 2020, Amendment No. 3 on December 14, 2021, Amendment No. 4 on January 28, 2022, Amendment No. 5 on February 21, 2023 and Amendment No. 6 on October 28, 2024 (as amended, the “Sanofi License Agreement”), with Sanofi, pursuant to which we have been granted an exclusive, worldwide license to develop, commercialize, manufacture, use, hold, keep, register or dispose of certain compounds, patents and proprietary information and inventions, in each case for therapeutic, prophylactic, prognostic and diagnostic purposes in or for humans, subject to retained rights. The licensed and derived rights are directed, among other things, to CFTR modulator therapies which are being utilized in SION-719, SION-109 and SION-451.

Pursuant to the terms of the Sanofi License Agreement, we must use commercially reasonable efforts to develop, pursue regulatory approval for and commercialize a licensed product. Sanofi and its affiliates retain the right to practice under the licensed patents and use the licensed know-how solely to conduct non-clinical research for all therapeutic, prophylactic, prognostic and diagnostic uses in or for humans, other than for CF; provided, however, that Sanofi will not exercise these retained rights until after December 20, 2024, and will not file any patents that claim a licensed compound.

As initial consideration for the license, we paid a non-refundable, upfront payment of $1.5 million, as well as a reimbursement of $0.3 million for Sanofi’s research and development expenses. In addition, we are required to pay Sanofi a total of up to $40 million upon achievement of certain late-stage developmental and commercial milestones. None of such milestones have been achieved to date. We are also required to pay royalties to Sanofi in the low single-digit percentage range based on net sales of licensed products, subject to customary reductions and offsets. Such royalty payments shall be reduced for products covered by derived patents. The royalty term will terminate on a product-by-product and country-by-country basis upon the later of (i) the expiration of the last-to-expire valid claim within the relevant licensed patent rights, (ii) the expiration of regulatory exclusivity in such country for such licensed product and (iii) the tenth anniversary of the first commercial sale of a licensed product in such country.

We are entitled to sublicense the rights granted to us under the Sanofi License Agreement under certain circumstances, provided that any such sublicense must be consistent with the terms of the Sanofi License Agreement. If we receive sublicense income from any such sublicense, we are required to pay Sanofi a low double digit percentage of such sublicense income.

We have also granted Sanofi an exclusive option to purchase, at a defined price, any priority review voucher (“PRV”) granted to us as a result of the development of the licensed compounds or products. In the event that Sanofi does not exercise its option with respect to any PRV, we may (x) use the PRV, in which case we must pay Sanofi a high seven-digit amount or (y) sell the PRV to a third party, in which case we must share a sub-teen double-digit percentage of the sale consideration with Sanofi.

We have the right, but not the obligation, to prepare, file, prosecute and maintain the licensed patents and product trademarks at our own cost. We have the first right to enforce and defend any licensed patents, with Sanofi having back-up enforcement and defense rights. We also have the sole right to enforce and defend any product trademarks at our sole cost and expense.

We have the right to terminate the Sanofi License Agreement for convenience, subject to a 90-day notice period. Sanofi has customary termination rights under the Sanofi License Agreement, including for our material breach, payment default, bankruptcy or challenge of the validity of any patent right, subject to specified notice and cure periods. Unless earlier terminated, the Sanofi License Agreement will expire in each country upon the expiration of the last-to-expire royalty term in such country and, with respect to the Sanofi License Agreement in its entirety, upon the expiration of the royalty term for the last licensed product for which there has been a first commercial sale. Upon expiration of the Sanofi License Agreement, the license granted to us will become non-exclusive, royalty-free, fully paid-up and perpetual.

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CFF Payment Agreement

On December 20, 2019, we entered into a payment agreement (the “CFF Payment Agreement”) with CFF, pursuant to which we agreed to provide CFF with compensation in exchange for the grant of, or forbearance from exercising, certain of CFF’s rights existing under the Research, Development and Commercialization Agreement, dated October 1, 2011, by and between CFF (through an assignment by Cystic Fibrosis Foundation Therapeutics, Inc.) and Genzyme Corporation, an affiliate of Sanofi (the “CFFT-Genzyme Agreement”). As described above, we have been granted a license to certain compounds, patents and know-how pursuant to the Sanofi License Agreement, some of which were generated as a result of a research plan under the CFFT-Genzyme Agreement. Under the CFF Payment Agreement, we are obligated to compensate CFF in connection with our development and commercialization of licensed products under the Sanofi License Agreement. Concurrent with the execution of the CFF Payment Agreement, Sanofi and CFF terminated the CFFT-Genzyme Agreement.

As initial consideration for CFF’s grant of, and forbearance from exercising, its rights under the CFFT-Genzyme Agreement, we issued CFF 300,300 shares of our Series Seed preferred stock. In addition, we agreed to pay CFF a sub-teen double-digit percentage of any amounts paid by us to Sanofi under the Sanofi License Agreement, other than milestone, royalty or reimbursement payments. As of December 31, 2024, we have paid CFF a total of approximately $0.2 million in accordance with the terms of the CFF Payment Agreement. In addition, we are required to pay CFF a total of up to $40 million upon achievement of certain late-stage developmental and commercial milestones. None of such milestones have been achieved to date. We are also required to pay revenue-shares of royalty payments to CFF in the low single-digit percentage range based on net sales of licensed products, subject to customary reductions and offsets. Such milestone and royalty payments shall be reduced for products covered by derived patents. The royalty term will terminate on a product-by-product and country-by-country basis upon the later of (i) the expiration of the last-to-expire valid claim within the relevant patent rights that claims such product or its exploitation in such country, (ii) the tenth anniversary of the first commercial sale of a product in such country and (iii) expiration of regulatory exclusivity of a product in such country. Further, a side letter was executed between us and Sanofi, which clarifies the relationship between us, Sanofi and CFF, under which we are obligated to pay Sanofi 20% of the milestones it would have been obligated to pay CFF, net of the milestone amounts it is obligated to pay under the Sanofi License Agreement.

If at any time prior to the first commercial sale of a product developed as a result of the CFF Payment Agreement, we cease to use commercially reasonably efforts to develop, and obtain and maintain regulatory approvals for, at least one of our products for therapeutic, prophylactic, prognostic or diagnostic uses in or for humans in specified major markets for a continuous period of 365 days, CFF has the option to exercise rights to an exclusive, irrevocable, worldwide interruption license under our patents, the licensed patents and the licensed know-how, to develop, manufacture, use, sell, offer to sell and import any of our products containing a licensed compound or any compound covered by a licensed patent or incorporating licensed know-how.

Either party may terminate the CFF Payment Agreement for a material breach by the other party, subject to a specified notice and cure period. Unless earlier terminated, the CFF Payment Agreement will expire (a) with respect to each product in each country, upon the expiration of the last-to-expire royalty term in such country, and (b) with respect to the CFF Payment Agreement in its entirety, upon the later of (i) the expiration of the royalty term for the last licensed product for which there has been a first commercial sale or (ii) the expiration or termination of our obligation to pay consideration to Sanofi under the Sanofi License Agreement.

AbbVie License Agreement

On July 11, 2024, we entered into a license agreement (the “AbbVie License Agreement”) with AbbVie, pursuant to which we have been granted an exclusive worldwide, royalty-bearing, sublicensable license to certain patent and other intellectual property rights to research, develop, commercialize, make, manufacture, use, import and sell products for prophylactic or therapeutic use in humans for all indications, subject to certain limitations and retained rights. The licensed rights are directed, among other things, to three clinical-stage CFTR modulator therapies: galicaftor (ABBV-2222, now referred to as SION-2222), a TMD1-directed CFTR corrector, navocaftor (ABBV-3067, now referred to as SION-3067), a CFTR potentiator, and ABBV-2851 (now referred to as SION-2851), a TMD1-directed corrector. Under the AbbVie License Agreement, we have assumed all global development and commercialization responsibilities for such therapies. Pursuant to the terms of the AbbVie License Agreement, we must use commercially reasonable efforts to develop, pursue

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regulatory approval for and commercialize a licensed product. We are also required to achieve certain development milestones within specified time periods for products incorporating intellectual property covered by the AbbVie License Agreement.

The license granted to us under the AbbVie License Agreement is subject to certain preexisting rights held by AbbVie and Galapagos NV (“Galapagos”). In particular, certain of the licensed patents and other intellectual property rights were developed by or on behalf of Galapagos and are sublicensed to us subject to the terms of the second amended and restated collaboration agreement between Galapagos and AbbVie dated as of October 24, 2018 (the “Galapagos License Agreement”), as amended by a side letter between Galapagos and AbbVie dated as of July 11, 2024. We are also entitled to sublicense the rights granted to us under the AbbVie License Agreement under certain circumstances, provided that any such sublicense must be consistent with the terms of the AbbVie License Agreement and the Galapagos License Agreement.

As initial consideration for the license, we paid a non-refundable, upfront payment of $5 million and issued 1,414,445 shares of our common stock to AbbVie. In addition, we are required to pay AbbVie a total of up to $360 million upon achievement of certain development and commercial milestones, consisting of up to $70.0 million in late-stage development milestones and up to $290.0 million in commercial milestones. None of such milestones have been achieved to date. We are also required to pay royalties to AbbVie in the low to mid single-digit percentage range based on net sales of licensed products, subject to customary reductions and offsets, with the percentage range depending in part on the compounds used. The royalty term will terminate on a product-by-product and country-by-country basis upon the later of (i) the expiration of the last-to-expire valid claim within the relevant patent rights that covers the manufacture, use, sale or other exploitation of a product in such country, (ii) the tenth anniversary of the first commercial sale of a product in such country and (iii) expiration of regulatory exclusivity of a product in such country. In addition, we are required to pay AbbVie up to $130 million in commercial and sales-based milestone payments, mid to high single-digit royalties on the licensed products or other payments due to Galapagos pursuant to the Galapagos License Agreement, to the extent such payments are triggered by our use of the licensed rights under the AbbVie License Agreement. To date, no payments have been triggered.

We have also granted AbbVie a right of first negotiation (the “ROFN”) if we decide to pursue a license or sublicense to commercialize a licensed product (a “Commercial License Transaction”) prior to initiating Phase 3 clinical trials. If AbbVie timely exercises the ROFN, then it will have an exclusive period to negotiate in good faith the terms of a Commercial License Transaction. In the event (x) AbbVie does not timely exercise the ROFN or notifies us that it does not intend to pursue a Commercial License Transaction (including after timely exercising the ROFN) or (y) the parties fail to reach agreement or enter into a definitive agreement for the Commercial License Transaction within the exclusive negotiation period, then the ROFN regarding all licensed products will terminate.

We are responsible for the prosecution and maintenance of the licensed patents at our own cost. We have the first right to enforce and defend any licensed patent at our own cost, with AbbVie having back-up enforcement and defense rights.

We have the right to terminate the AbbVie License Agreement for convenience, subject to a prescribed notice period. AbbVie has customary termination rights under the AbbVie License Agreement, including for our material breach, payment default, bankruptcy, challenge of the validity of any patent right or shelving of a product for a specified time period, subject to specified notice and cure periods. Unless earlier terminated, the AbbVie License Agreement will expire upon the expiration of the last-to-expire royalty term. Upon expiration of the AbbVie License Agreement, the license granted to us will become non-exclusive, royalty-free, fully paid-up and perpetual.

In the event the AbbVie License Agreement is terminated, we and AbbVie shall agree upon a transition plan to revert the licensed compounds or licensed products containing such licensed compounds to AbbVie. Within a prescribed time period of such termination, we are obligated to (i) assign and transfer all of our rights and interests in the documentation and data related to the reverting compounds or products to AbbVie, (ii) grant to AbbVie a non-exclusive, royalty-free license right of reference for AbbVie to develop or commercialize any of the reverting compounds or products, (iii) grant to AbbVie an exclusive, royalty-bearing worldwide license to exploit any of the reverting compounds or products and (iv) transfer to AbbVie control of all clinical studies being conducted for any of the reverting compounds or products.

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Government Regulation

The FDA and comparable regulatory authorities in federal, state and local jurisdictions and in other foreign countries impose extensive requirements upon companies involved in the clinical development, manufacture, marketing and distribution of drugs, such as those we are developing. These agencies and other federal, state and local entities extensively regulate, among other things, the research and development, testing, manufacture, quality control, safety, effectiveness, labeling, packaging, storage, record keeping, approval, advertising and promotion, distribution, post-approval monitoring and reporting, sampling and export and import of drugs. The process of obtaining regulatory approvals in the U.S. and in foreign countries and jurisdictions, along with subsequent compliance with applicable federal, state, local and foreign statutes and regulations, requires the expenditure of substantial time and financial resources. Failure to comply with the applicable requirements at any time during the product development process, approval process or after approval, may subject an applicant and/or sponsor to a variety of sanctions. For example, failure to comply with the applicable U.S. requirements may result in administrative or judicial sanctions including refusal by FDA to approve pending applications, withdrawal of an approval, imposition of a clinical hold, issuance of warning letters and untitled letters, product recalls, product seizures, total or partial suspension of production or distribution, injunctions, fines, refusals of government contracts, restitution, disgorgement or civil or criminal investigations and penalties brought by the FDA and the Department of Justice or other governmental entities.

Review and Approval of Drugs in the United States

In the U.S., the FDA regulates drugs under the Federal Food, Drug, and Cosmetic Act (“FDCA”), and its implementing regulations. Drugs are also subject to other federal, state and local statutes and regulations.

The process required by the FDA before a drug may be marketed in the U.S. generally involves the following:

•completion of extensive nonclinical, or preclinical, laboratory tests, animal studies and formulation studies in compliance with the FDA’s Good Laboratory Practice (“GLP”) regulations;

•submission to the FDA of an IND, which must become effective before human clinical trials may begin and must be updated annually and when certain changes are made;

•approval by an institutional review board (“IRB”) or independent ethics committee (“IEC”) at each clinical site before each trial may be initiated at that site;

•performance of adequate and well-controlled human clinical trials in accordance with Good Clinical Practices (“GCP”) requirements and other clinical trial-related regulations to establish the safety and efficacy of the investigational drug product for each proposed indication;

•preparation and submission to the FDA of an NDA after completion of all pivotal trials, together with the payment of application user fees, as applicable;

• a determination by the FDA within 60 days of its receipt of an NDA to accept the marketing application for review;

•satisfactory completion of an FDA advisory committee review, if applicable;

•satisfactory completion of one or more FDA inspections of the manufacturing facility or facilities at which the product is produced to assess compliance with cGMP requirements and to assure that the facilities, methods and controls are adequate to preserve the product’s identity, strength, quality and purity;

•satisfactory completion of FDA audits of clinical trial sites to assure compliance with GCPs and the integrity of the clinical data; and

•FDA review and approval of the NDA.

Preclinical Studies

Before testing any drug product candidate, including our product candidates, in humans, the product candidate must undergo rigorous preclinical testing. Preclinical studies include laboratory evaluations of the product’s chemistry, purity, toxicity, formulation, and stability as well as in vitro and animal studies to assess potential safety and efficacy and in some cases to establish the rationale for therapeutic use. The conduct of

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preclinical studies is subject to federal regulations and requirements, including GLP regulations for safety and toxicology studies.

The IND and IRB Process

Prior to beginning the first clinical trial with a product candidate in the U.S., we must submit an IND to the FDA. An IND sponsor must submit a protocol for each clinical trial, the results of the preclinical tests, manufacturing information, analytical data and any available clinical data or literature and plans for clinical studies, among other things, to the FDA as part of an IND. An IND is a request for authorization from the FDA to grant an exemption that allows an unapproved drug to be shipped in interstate commerce for use and administration in an investigational clinical trial for humans. The IND must become effective before human clinical trials may begin in the U.S. Some preclinical testing, such as animal tests of reproductive adverse events and carcinogenicity, may continue even after the IND is submitted. An IND automatically becomes effective 30 days after receipt by the FDA, unless before that time the FDA raises concerns or questions related to one or more proposed clinical trials and places the clinical trial on a clinical hold. A clinical hold is an order issued by the FDA to the sponsor to delay a proposed clinical investigation or to suspend an ongoing clinical trial. Clinical holds may be imposed by the FDA when there is concern for patient safety, and may be a result of new data, findings or developments in clinical, nonclinical, and/or chemistry, manufacturing and controls or where there is non-compliance with regulatory requirements. A partial clinical hold is a delay or suspension of only part of the clinical work requested under the IND. Following issuance of a clinical hold or partial clinical hold, an investigation (or full investigation in the case of a partial clinical hold) may only resume after the FDA has notified the sponsor that the investigation may proceed. As a result, submission of an IND may not result in the FDA allowing clinical trials to initiate.

A separate submission to an existing IND must also be made for each successive clinical trial to be conducted, and the FDA must grant permission, either explicitly or implicitly by not objecting, before each clinical trial can begin.

A sponsor may choose, but is not required, to conduct a foreign clinical trial under an IND. When a foreign clinical trial is conducted under an IND, all FDA IND requirements must be met unless waived. When the foreign clinical trial is not conducted under an IND, such as our ongoing Phase 1 clinical trials of SION-719 and SION-451 being conducted in Australia, the sponsor must ensure that the study is conducted in accordance with GCP, including review and approval by an IEC and informed consent from subjects. FDA must be able to validate the data from the study through an on-site inspection if necessary.

In addition to the foregoing IND requirements, an IRB representing each institution participating in the clinical trial must review and approve the plan for any clinical trial before it commences at that institution, and the IRB must conduct continuing review of the study. The IRB is charged with protecting the welfare and rights of trial participants and considers whether the risks to individuals participating in the clinical trials are minimized and are reasonable in relation to anticipated benefits. The IRB must review and approve, among other things, the study protocol and informed consent information to be provided to study subjects and must monitor the clinical trial until completion. An IRB can suspend or terminate approval of a clinical trial at its institution, or an institution it represents, if the clinical trial is not being conducted in accordance with the IRB’s requirements or if the product candidate has been associated with unexpected serious harm to patients.

Clinical Trials in Support of an NDA

Clinical trials involve the administration of the investigational new drug to human subjects under the supervision of qualified investigator in accordance with GCP requirements, which include the requirement that all research subjects, or their legal representative, provide their informed consent in writing for their participation in any clinical trial. Clinical trials are conducted under written study protocols detailing, among other things, the exclusion and inclusion criteria, the objectives of the trial, dosing procedures, subject selection, the parameters to be used in monitoring safety and the effectiveness criteria to be evaluated. As part of an IND, a protocol for each clinical trial and any subsequent protocol amendments must be submitted to the FDA.

Regulatory authorities, the IRB or the sponsor may suspend a clinical trial at any time on various grounds, including a finding that the subjects are being exposed to an unacceptable health risk or that the trial is unlikely to meet its stated objectives. Some studies also include oversight by an independent group of qualified

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experts organized by the clinical study sponsor, known as a data and safety monitoring board (“DSMB”), which provides authorization for whether or not a study may move forward at designated check points based on access to certain data from the study and may halt the clinical trial if it determines that there is an unacceptable safety or health risk for subjects or other grounds, such as no demonstration of efficacy.

Information about certain clinical trials must be submitted within specific timeframes to the National Institutes of Health (“NIH”) for public dissemination on their www.clinicaltrials.gov website. Information related to the investigational product, patient population, phase of investigation, study sites and investigators and other aspects of the clinical trial is made public as part of the registration of the clinical trial. Although sponsors are obligated to disclose the results of their clinical trials after completion, disclosure of the results can be delayed in some cases for some time. Failure to timely register a covered clinical study or to submit study results as provided for in the law can give rise to civil monetary penalties and also prevent the non-compliant party from receiving future grant funds from the federal government.

Human clinical trials are typically conducted in three sequential phases, which may overlap or be combined:

•Phase 1: The investigational drug is initially introduced into a limited population of healthy human subjects or, in certain indications such as cancer, patients with the target disease or condition and tested for safety, dosage tolerance, absorption, metabolism, distribution, excretion, side effects, and, if possible, to gain an early indication of its effectiveness or determine optimal dosage.

• Phase 2: The investigational drug is administered to a limited patient population with a specified disease or condition to identify possible adverse effects and safety risks, to preliminarily evaluate the efficacy of the product for specific targeted diseases and to determine dosage tolerance and optimal dosage. Multiple Phase 2 clinical trials may be conducted to obtain information prior to beginning Phase 3 clinical trials.

•Phase 3: The investigational drug is administered to an expanded patient population, generally at geographically dispersed clinical trial sites, in well-controlled clinical trials to generate enough data to statistically evaluate the efficacy and safety of the product for approval, to establish the overall risk/benefit profile of the product, and to provide adequate information for product approval and labeling of the product. Generally, two adequate and well-controlled Phase 3 clinical trials are required by the FDA for approval of an NDA.

Post-approval trials, sometimes referred to as Phase 4 clinical trials, may be conducted after initial marketing approval. These trials are used to gain additional experience from the treatment of patients in the intended therapeutic indication and are commonly intended to generate additional safety data regarding use of the product in a clinical setting. In certain instances, the FDA may mandate the performance of Phase 4 clinical trials as a condition of approval on an NDA.

Progress reports detailing the results of the clinical trials must be submitted at least annually to the FDA and more frequently if serious adverse events occur. In addition, within 15 calendar days after the sponsor determines that the information qualifies for reporting, written IND safety reports must be submitted to the FDA and investigators for serious and unexpected suspected adverse events, findings from other studies or animal or in vitro testing that suggest a significant risk for human subjects and any clinically important increase in the rate of a serious suspected adverse reaction over that listed in the protocol or investigator brochure. The sponsor also must notify the FDA of any unexpected fatal or life-threatening suspected adverse reaction within seven calendar days after the sponsor’s initial receipt of the information. The FDA will typically inspect one or more clinical sites to assure compliance with GCP and the integrity of the clinical data submitted.

During the development of a new drug, sponsors are given opportunities to meet with the FDA at certain points. These points may be prior to submission of an IND, at the end of Phase 2, and before an NDA is submitted. Meetings at other times may be requested. These meetings can provide an opportunity for the sponsor to share information about the data gathered to date and for the FDA to provide advice.

Concurrent with clinical trials, companies usually complete additional animal studies and must also develop additional information about the chemistry and physical characteristics of the product candidate and finalize a process for manufacturing the drug product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of consistently producing quality batches of the

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product candidate and manufacturers must develop, among other things, methods for testing the identity, strength, quality and purity of the final drug product. Additionally, appropriate packaging must be selected and tested, and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

FDA Review of an NDA Submission and FDA Approval

Assuming successful completion of the required clinical testing, the results of the preclinical and clinical studies, together with detailed information relating to the product’s chemistry, manufacture, controls and proposed labeling, among other things, are submitted to the FDA as part of an NDA requesting approval to market the product for one or more indications. An NDA is a request for approval to market a new drug for one or more specified indications and must contain proof of the drug’s safety and efficacy for the requested indications. FDA must approve an NDA before a drug may be marketed in the U.S. For companies, the marketing application is required to include both negative and ambiguous results of preclinical studies and clinical trials, as well as positive findings. Data may come from company-sponsored clinical trials intended to test the safety and effectiveness of a use of a product, or from a number of alternative sources, including studies initiated by investigators. To support marketing approval, the data submitted must be sufficient in quality and quantity to establish the safety and effectiveness of the investigational drug product for the proposed indication to the satisfaction of the FDA. In most cases, the submission of an NDA is subject to a significant application user fee. Fee exceptions or fee waivers may be obtained under certain limited circumstances.

The FDA conducts a preliminary review of all NDAs within the first 60 days of its receipt, before accepting them for filing, to determine whether they are sufficiently complete to permit substantive review. The FDA may request additional information rather than accept an NDA for filing. In this event, the application must be resubmitted with the additional information. The resubmitted application is also subject to review before the FDA accepts it for filing. Once the submission is accepted for filing, the FDA begins an in-depth substantive review. The FDA reviews an NDA to determine, among other things, whether the drug is safe and effective and whether the facility in which it is manufactured, processed, packaged or held meets standards designed to assure the product’s continued safety, quality and purity.

During its review of an NDA, the FDA typically will inspect the facility or facilities where the product is or will be manufactured. These pre-approval inspections may cover all facilities associated with an NDA, including drug component manufacturing (such as APIs), finished drug product manufacturing and control testing laboratories. The FDA will not approve an NDA unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product within required specifications.

In addition, as a condition of approval, or post-approval if it becomes aware of a serious risk associated with the use of the product, the FDA may require the submission of a Risk Evaluation and Mitigation Strategy (“REMS”), if it determines that a REMS is necessary to ensure that the benefits of the drug outweigh its risks and to assure the safe use of the drug. If the FDA concludes a REMS is needed, the sponsor of the NDA must submit a proposed REMS. The FDA will not approve the NDA without a REMS, if required. A REMS may include one or more elements, including medication guides, physician communication plans, patient package insert and/or elements to assure safe use, such as special training or certification for prescribing or dispensing, restricted distribution methods, special monitoring, patient registries or other risk minimization tools.

Under the Prescription Drug User Fee Act (“PDUFA”) guidelines that are currently in effect, the FDA has a goal of ten months from the date of “filing” of a standard NDA, for a new molecular entity, to review and act on the submission, and six months from the filing date of a new molecular entity NDA with priority review. Accordingly, this review process typically takes 12 months and eight months, respectively, from the date the NDA is submitted to the FDA. The FDA does not always meet its PDUFA goal dates for standard or priority NDAs, and the review process is often extended by FDA requests for additional information or clarification.

In addition, under the Pediatric Research Equity Act of 2003, as amended (“PREA”), certain NDAs or supplements to an NDA must contain data that are adequate to assess the safety and effectiveness of the drug for the claimed indications in all relevant pediatric subpopulations and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective. The FDA may, on its own initiative or at the request of the applicant, grant deferrals for submission of some or all pediatric data until after approval of

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the product for use in adults, or full or partial waivers from the pediatric data requirements. A sponsor who is planning to submit a marketing application for a drug that includes a new active ingredient, new indication, new dosage form, new dosing regimen or new route of administration must submit an initial Pediatric Study Plan (“PSP”), within 60 days of an end-of-Phase 2 meeting or, if there is no such meeting, as early as practicable before initiation of the Phase 3 or Phase 2/3 study. The initial PSP must include an outline of the pediatric study or studies that the sponsor plans to conduct, including study objectives and design, age groups, relevant endpoints and statistical approach, or a justification for not including such detailed information, and any request for a deferral of pediatric assessments or a full or partial waiver of the requirement to provide data from pediatric studies along with supporting information. The FDA and the sponsor must reach an agreement on the PSP. A sponsor can submit amendments to an agreed-upon initial PSP at any time if changes to the pediatric plan need to be considered based on data collected from preclinical studies, early phase clinical trials and/or other clinical development programs.

The FDA may refer an application for a novel drug or a drug that presents difficult questions of safety or efficacy to an advisory committee. An advisory committee is a panel of independent experts, including clinicians and other scientific experts, that reviews, evaluates and provides a recommendation as to whether the application should be approved and under what conditions. The FDA is not bound by the recommendations of an advisory committee, but it considers such recommendations carefully when making decisions.

After evaluating the NDA and all related information, including the advisory committee recommendation, if any, and inspection reports regarding the manufacturing facilities and clinical trial sites, the FDA may issue an approval letter, or, in some cases, a Complete Response Letter. A Complete Response Letter indicates that the review cycle of the application is complete, and the application will not be approved in its present form. A Complete Response Letter generally outlines the deficiencies in the submission and contains a statement of specific conditions that must be met in order to secure final approval of the NDA and it may require additional clinical or preclinical testing in order for FDA to reconsider the application. If a Complete Response Letter is issued, the applicant may resubmit the NDA, addressing all of the deficiencies identified in the letter, withdraw the application, or request a hearing. Even with submission of this additional information, the FDA ultimately may decide that the application does not satisfy the regulatory criteria for approval. If and when those conditions have been met to the FDA’s satisfaction, the FDA will typically issue an approval letter. An approval letter authorizes commercial marketing of the drug with specific prescribing information for specific indications.

Even if the FDA approves a product, depending on the specific risk(s) to be addressed, it may limit the approved indications for use of the product, require that contraindications, warnings or precautions be included in the product labeling, require that post-approval studies, including Phase 4 clinical trials, be conducted to further assess a drug’s safety after approval, require testing and surveillance programs to monitor the product after commercialization or impose other conditions, including distribution and use restrictions or other risk management mechanisms under a REMS, which can materially affect the potential market and profitability of the product. The FDA may prevent or limit further marketing of a product based on the results of post-marketing studies or surveillance programs. After approval, some types of changes to the approved product, such as adding new indications, manufacturing changes and additional labeling claims, are subject to further testing requirements and FDA review and approval.

Orphan Drug Designation and Exclusivity

Under the Orphan Drug Act, the FDA may grant orphan designation to a drug product intended to treat a rare disease or condition, which is generally a disease or condition that affects either (i) fewer than 200,000 individuals in the U.S. or (ii) more than 200,000 individuals in the U.S. and for which there is no reasonable expectation that the cost of developing and making the product available in the U.S. for this type of disease or condition will be recovered from sales of the product. A company must request orphan drug designation before submitting an NDA. If the request is granted, the FDA will disclose the identity of the therapeutic agent and its potential use. Orphan drug designation does not convey any advantage in or shorten the duration of the regulatory review and approval process.

If a product with orphan status receives the first FDA approval for the disease or condition for which it has such designation or for a select indication or use within the rare disease or condition for which it was designated, the product is entitled to orphan product exclusivity. Orphan product exclusivity means that the FDA may not approve any other applications to market the same product for the same indication for seven years,

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except in certain limited circumstances, including if a subsequent product with the same active ingredient for the same indication is shown to be clinically superior to the approved product on the basis of greater efficacy or safety, or providing a major contribution to patient care, or if the company with orphan drug exclusivity is not able to meet market demand. Further, the FDA may approve more than one product for the same orphan indication or disease as long as the products contain different active ingredients. Moreover, competitors may receive approval of different products for the indication for which the orphan product has exclusivity or obtain approval for the same product but for a different indication for which the orphan drug has exclusivity. Orphan drug designation entitles a party to financial incentives such as opportunities for grant funding towards clinical trial costs, tax advantages, and user-fee waivers.

A designated orphan drug may not receive orphan drug exclusivity if it is approved for a use that is broader than the indication for which it received orphan designation. In addition, orphan drug exclusive marketing rights in the U.S. may be lost if the FDA later determines that the request for designation was materially defective or, as noted above, if a second applicant demonstrates that its product is clinically superior to the approved product with orphan exclusivity or the manufacturer of the approved product is unable to assure sufficient quantities of the product to meet the needs of patients with the rare disease or condition.

The FDA has historically taken the position that the scope of orphan exclusivity aligns with the approved indication or use of a product, rather than the disease or condition for which the product received orphan designation. However, in Catalyst Pharms., Inc. v. Becerra, 14 F.4th 1299 (11th Cir. 2021), the court disagreed with this position, holding that orphan-drug exclusivity blocked the FDA’s approval of the same drug for all uses or indications within the same orphan-designated disease. On January 24, 2023, the FDA published a notice in the Federal Register to clarify that the FDA intends to continue to apply its longstanding interpretation of the regulations to all matters outside of the scope of the Catalyst order and will continue tying the scope of orphan drug exclusivity to the uses or indications for which a drug is approved. It is unclear how future litigation, legislation, agency decisions and administrative actions will impact the scope of orphan drug exclusivity.

Expedited Development and Review Programs for Drugs

The FDA maintains several programs intended to facilitate and expedite development and review of new drugs that were intended to address unmet medical needs in the treatment of serious or life-threatening diseases or conditions. Some of these programs are referred to as Fast Track designation, Breakthrough Therapy designation, Priority Review and Accelerated Approval, and the purpose of these programs is to either expedite the development or review of important new drugs to get them to patients earlier than under standard FDA development and review procedures.

SION US Equity

SION · 10-K · period ended 2024-12-31

ITEM 1. BUSINESS

SION US Equity☆

SION · 10-K · period ended 2024-12-31

ITEM 1. BUSINESS

SION US Equity