10-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K

For the fiscal year ended December 31, 2025

For the transition period from to

Commission File Number 001-38452

MEREO BIOPHARMA GROUP PLC

(Exact name of Registrant as specified in its charter)

England and Wales Not Applicable

One Cavendish Place, 4th Floor

London, W1G 0QF

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

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

* Not for trading, but only in connection with the registration of American Depositary Shares representing such Ordinary Shares pursuant to the requirements of the U.S. Securities and Exchange Commission.

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 No

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 No

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 No

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 and post such files). Yes No

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.

Emerging growth company 

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. 

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. ☐

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. ☐

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). ☐

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

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the registrant as of June 30, 2025, the last business day of the registrant’s most recently completed second fiscal quarter, was approximately $368,470,120.

As of March 18, 2026 the number of outstanding ordinary shares, par value £0.003 per share, of the registrant was 798,078,829

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive Proxy Statement relating to its 2026 Annual Meeting of Stockholders (“Proxy Statement”) are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Proxy Statement will be filed with the United States Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.

Table of Contents

Page

PART I

Item 1. Business 6

Item 1A. Risk Factors 36

Item 1B. Unresolved Staff Comments 86

Item 1C. Cybersecurity 86

Item 2. Properties 88

Item 3. Legal Proceedings 88

Item 4. Mine Safety Disclosures 88

PART II

Item 6. [Reserved] 89

Item 7A. Quantitative and Qualitative Disclosures About Market Risk 100

Item 8. Financial Statements and Supplementary Data 100

Item 9A. Controls and Procedures 101

Item 9B. Other Information 101

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections 101

PART III

Item 10. Directors, Executive Officers and Corporate Governance 102

Item 11. Executive Compensation 102

Item 14. Principal Accountant Fees and Services 102

PART IV

Item 15. Exhibit and Financial Statement Schedules 103

Signatures

CERTAIN DEFINITIONS

Unless otherwise indicated and except where the context otherwise requires, references in this Annual Report on Form 10-K (defined below) to:

•

“AATD” are to alpha-1 antitrypsin deficiency, a lack of alpha 1 anti-trypsin protein, a protein made by the liver that’s released into the bloodstream to protect the body from neutrophil serine proteases damaging the lungs;

•

“Acumapimod” are to an oral p38 MAP kinase inhibitor for potential treatment of AECOPD;

•

“Alvelestat” are to an oral neutrophil elastase inhibitor for potential treatment of AATD;

•

"ADO2" are to Autosomal Dominant Osteopetrosis Type 2, an inherited metabolic bone disorder characterized by impaired osteoclast function.

•

“ADSs” are to our American Depositary Shares, each of which represents five ordinary shares of Mereo BioPharma Group plc;

•

“ADRs” are to the American Depositary Receipts that evidence our ADSs;

•

“AECOPD” are to acute exacerbation of chronic obstructive pulmonary disease;

•

"ASBMR 2025" are to the American Society for Bone and Mineral Research Annual Meeting held in September 2025;

•

"Āshibio" are to āshibio, Inc.;

•

“BLA” are to Biologics License Application;

•

“CMO” are to contract manufacturing organization;

•

“COPD” are to chronic obstructive pulmonary disease, the name for a group of lung conditions that cause breathing difficulties;

•

“CRO” are to contract research organization;

•

“EMA” are to European Medicines Agency;

•

“Etigilimab” are to an anti-TIGIT designed to activate the immune system through multiple mechanisms and enable anti-tumor activity;

•

“Exchange Act” are to the United States Securities and Exchange Act of 1934;

•

“Feng Biosciences” are to Feng Biosciences, Inc. In 2023, OncXerna Therapeutics, Inc. (“OncXerna”) was renamed as Feng Biosciences, Inc.;

•

“FDA” are to the United States Food and Drug Administration;

•

“HH” are to hypogonadotropic hypogonadism, a condition in which the male testes or the female ovaries produce little or no sex hormones;

•

"IND" are to Investigational New Drug Application;

•

“Leflutrozole” are to an oral aromatase inhibitor for potential treatment of male infertility associated with HH;

•

“MAA” are to Marketing Authorization Applications;

•

“Mereo,” the “Company,” the “Group,” “we,” “our,” “ours,” “us” or similar terms are to Mereo BioPharma Group plc, together with its subsidiaries;

•

the “Merger” are to the merger of Mereo MergerCo One Inc. and OncoMed Pharmaceuticals, Inc. (“OncoMed”), with OncoMed surviving as a wholly-owned subsidiary of Mereo US Holdings Inc., and as an indirect wholly-owned subsidiary of Mereo BioPharma Group plc, and in 2020 OncoMed was renamed as Mereo BioPharma 5, Inc. (“Mereo BioPharma 5”);

•

"MHRA" are to the United Kingdom Medicines and Healthcare products Regulatory Agency;

•

“Navicixizumab” are to an anti-DLL4/VEGF bispecific antibody for the potential treatment of post platinum ovarian cancer;

•

“NDA” are to New Drug Application;

•

“NE” neutrophil elastase, a serine protease and a major constituent of lung elastoytic activity;

•

“OI” are to osteogenesis imperfecta a rare genetic bone disorder characterized by fragile bones that break easily, also known as brittle bone disease;

•

“ordinary shares” are to our ordinary shares, each of £0.003 nominal value;

•

“SEC” are to the United States Securities and Exchange Commission;

•

“Setrusumab” are to a fully human monoclonal antibody for potential treatment of OI;

•

“$,” “USD,” “US$” and “U.S. dollar” are to the United States dollar;

•

“TIGIT” are to T-cell immunoreceptor with Ig and ITIM domains;

•

“Ultragenyx” are to Ultragenyx Pharmaceutical, Inc.;

•

“U.S. GAAP” are to accounting principles generally accepted in the United States of America;

•

"Vantictumab" are to an anti-FZD monoclonal antibody for potential treatment of Autosomal Dominant Osteopetrosis Type 2;

•

“£,” “GBP,” “pound sterling,” “pence” and “p” are to the British pound sterling (or units thereof).

GENERAL INFORMATION

In this Annual Report on Form 10‐K (“Annual Report”), “Mereo,” the “Group,” the “Company,” “we,” “us” and “our” refer to Mereo BioPharma Group plc and its consolidated subsidiaries, except where the context otherwise requires. “Mereo,” the Mereo logo and other trademarks, trade names or service marks of Mereo appearing in this Annual Report are the property of Mereo.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report contains forward-looking statements that involve substantial risks and uncertainties, as well as assumptions that, if they never materialize or prove incorrect, could cause our results to differ materially from those expressed or implied by such forward-looking statements. We make such forward-looking statements pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995 and other federal securities laws. All statements other than statements of historical facts contained in this Annual Report are forward-looking statements within the meaning of Section 27A of the United States Securities Act of 1933, as amended, and Section 21E of the United States Securities Exchange Act of 1934, as amended. In some cases, you can identify forward-looking statements by words such as “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect”, “plan,” “foresee,” “should,” “would,” “could,” “outlook,” and similar expressions, including the negative thereof. The absence of these words, however, does not mean that the statements are not forward-looking.

Any forward-looking statements in this Annual Report reflect our current expectations, beliefs and assumptions concerningfuture events or to our future financial performance and involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by these forward-looking statements. Factors that may cause actual results to differ materially from current expectations include, among other things, the uncertainties inherent in the clinical development process; the Company’s reliance on third parties to conduct its clinical trials and provide funding for its clinical trials; the sufficiency of existing cash to fund operations and/or the inability to raise additional funding on favorable terms or at all; the uncertainty inherent in regulatory review processes, including varying interpretations and analyses of data from clinical trials; the Company’s dependence on enrollment of patients in its clinical trials; potentially smaller than anticipated market opportunities for the Company's product candidates; the Company’s dependence on its key executives; the Company’s ability to maintain compliance with Nasdaq continued listing requirements; and additional factorslisted under Part I, Item 1A. Risk Factors and elsewhere in this Annual Report. Given these uncertainties, you should not place undue reliance on these forward-looking statements. Except as required by law, we assume no obligation to update or revise these forward-looking statements for any reason, even if new information becomes available in the future.

This Annual Report also contains estimates, projections and other information concerning our industry, our business, and the markets for certain diseases, including data regarding the estimated size of those markets, and the incidence and prevalence of certain medical conditions. Information that is based on estimates, forecasts, projections, market research or similar methodologies is inherently subject to uncertainties and actual events or circumstances may differ materially from events and circumstances reflected in this information. Unless otherwise expressly stated, we obtained this industry, business, market and other data from reports, research surveys, studies and similar data prepared by third parties, industry, medical and general publications, government data and similar sources.

SUMMARY RISK FACTORS

You should carefully consider the risks and uncertainties described below, together with the other information contained in this Annual Report, before making any investment decision. Any of the following risks and uncertainties could have a material adverse effect on our business, prospects, results of operations and financial condition. The market price of our ADSs could decline due to any of these risks and uncertainties, and you could lose all or part of your investment. The risks described below are those that we currently believe may materially affect us. We may face additional risks and uncertainties not currently known to us or that we currently deem to be immaterial.

•

We have a limited operating history and have never generated any revenue from product sales.

•

We will need additional funding to complete the development of our current product candidates; to license, acquire, and develop future product candidates; and to commercialize our product candidates, if approved. If we are unable to raise capital when needed, we could be forced to delay, reduce, or eliminate research and development programs, any future commercialization efforts or acquisitions of potential product candidates.

•

We depend heavily on the success of setrusumab and alvelestat. We cannot give any assurance that any of these product candidates will receive regulatory approval, which is necessary before they can be commercialized. If we are unable to

commercialize setrusumab and alvelestat, whether on our own or through agreements with third parties, or experience significant delays in doing so, our ability to generate revenue and our financial condition will be adversely affected.

•

Our future growth and ability to compete depends on retaining our key personnel and recruiting additional qualified personnel.

•

We depend on enrollment of patients in our clinical trials for our product candidates. If we are unable to enroll patients in our clinical trials, or enrollment is slower than anticipated, in particular for our product candidates with rare disease indications, our research and development efforts could be adversely affected.

•

We may become exposed to costly and damaging liability claims, either when testing our product candidates in the clinic or at the commercial stage, and our product liability insurance may not cover all damages from such claims.

•

The regulatory approval processes of the FDA and comparable foreign authorities, such as the EMA and MHRA, are lengthy, time consuming and inherently unpredictable, and if we are ultimately unable to obtain regulatory approval for our product candidates, our business will be harmed substantially.

•

Enacted and future healthcare legislation may increase the difficulty and cost for us to obtain marketing approval of and commercialize our product candidates and may affect the prices we may set.

•

We operate in a highly competitive and rapidly changing industry, which may result in others acquiring, developing, or commercializing competing product candidates before or more successfully than we do.

•

We intend to directly commercialize or co-commercialize our product candidates for rare diseases and to out-license or sell our other product candidates for further development and/or commercialization. If we are unable to develop our own sales, marketing, and distribution capabilities or enter into business arrangements, we may not be successful in commercializing our product candidates.

•

The successful commercialization of our product candidates will depend in part on the extent to which governmental authorities and health insurers establish adequate coverage, reimbursement levels, and pricing policies. Failure to obtain or maintain coverage and adequate reimbursement for our product candidates, if approved, could limit our ability to market those product candidates and decrease our ability to generate revenue.

•

Our existing and future product candidates may not gain market acceptance, in which case our ability to generate revenues from product sales will be compromised.

•

We rely, and expect to continue to rely, on our partners to develop and commercialize our licensed or partnered product candidates. If our partners do not secure adequate funding or satisfy their obligations under our agreements with them, or if they terminate our licenses, partnerships or collaborations with them, we may not be able to develop or commercialize our licensed or partnered product candidates as planned.

•

We rely, and expect to continue to rely, on third parties, including independent investigators and CROs, to conduct our clinical trials. If these CROs do not successfully carry out their contractual duties or meet expected deadlines, we may not be able to obtain regulatory approval for or commercialize our product candidates, or such approval or commercialization may be delayed, and our business could be substantially harmed.

•

We currently rely on third-party CMOs for the production of clinical supply of our product candidates and intend to rely on CMOs for the production of commercial supply of our product candidates, if approved. Our dependence on CMOs may impair the development of our product candidates and may impair the commercialization of our product candidates, which would adversely impact our business and financial position.

•

We rely on patents and other intellectual property rights to protect our product candidates, the obtainment, enforcement, defense and maintenance of which may be challenging and costly. Failure to enforce or protect these rights adequately could harm our ability to compete and impair our business.

•

We may become subject to third parties’ claims alleging infringement of third-party patents and proprietary rights, or we may be involved in lawsuits to protect or enforce our patents and other proprietary rights, which could be costly and time consuming, delay or prevent the development and commercialization of our product candidates, or put our patents and other proprietary rights at risk.

•

Our business and operations may suffer, and proprietary information may be lost, in the event of information technology system failures, cyberattacks or deficiencies in our cybersecurity.

•

Commencing January 1, 2024 we were required to comply with the domestic reporting regime under the Exchange Act and will continue to incur significant legal, accounting and other expenses, and our management must devote substantial time to public company compliance initiatives and corporate governance matters.

•

We may not satisfy Nasdaq’s requirements for continued listing. If we cannot satisfy these requirements, Nasdaq could delist our ADSs which could have an adverse impact on the liquidity and market price of our ADSs.

•

Failure to establish and maintain effective internal controls could have a material adverse effect on our business and stock price.

Item 1. Business

Overview

We are a biopharmaceutical company focused on the development of innovative therapeutics for rare diseases. We have developed a portfolio of late-stage clinical product candidates. Our late-stage rare disease product candidates are setrusumab for the treatment of osteogenesis imperfecta (“OI”) and alvelestat for the treatment of severe alpha-1 antitrypsin deficiency-associated lung disease (“AATD-LD”). Setrusumab has received orphan designation for OI from the European Commission (“EC”) and the FDA, PRIME designation from the EMA and has Breakthrough Therapy designation and rare pediatric disease designation from the FDA. Alvelestat has received orphan designation for AATD from the EC and the FDA, and Fast Track designation for the treatment of AATD-LD from the FDA. We also have an early-stage rare disease program, vantictumab, for the treatment of a second bone disease, autosomal dominant osteopetrosis Type 2 (“ADO2”). The global development of vantictumab is being funded and led by our partner, āshibio, and we retain the European commercial rights.

Our strategy is to selectively acquire and develop product candidates for rare diseases that have already received significant investment from large pharmaceutical and biotechnology companies and that have substantial pre-clinical, clinical and manufacturing data packages. Since our formation in March 2015, we have successfully executed on this strategy by acquiring all of our clinical-stage product candidates of which three were in rare diseases. We have successfully completed large, randomized Phase 2 clinical trials for four of our product candidates and the Phase 1b portion of a Phase 1b/2 for a fifth product candidate, and we and our partner Ultragenyx recently announced the results from two Phase 3 studies for our lead program setrusumab in OI.

Rare diseases represent an attractive development and, in some cases, commercialization opportunity for us since they typically have high unmet medical need and can utilize regulatory pathways that facilitate acceleration to approval and to the potential market. Development of products for rare diseases involves close collaboration with key opinion leaders and investigators, and close coordination with patient organizations. Rare disease patients are typically treated at a limited number of specialized sites which helps identification of the patient population and enables a small, targeted sales infrastructure to commercialize the products in key markets.

Our Strategy

We intend to become a leading biopharmaceutical company developing innovative therapeutics that aim to improve outcomes for patients with rare diseases. The key elements of our strategy to achieve this goal include:

•

Rapidly develop and potentially commercialize our rare disease product candidates. Our late-stage rare disease product candidates setrusumab and alvelestat have been acquired or in-licensed from pharmaceutical companies following strategic de-prioritization. Prior to this they have received significant investment in preclinical, toxicology, clinical studies and CMC. We have built expertise in the areas of patient identification, clinical study design and regulatory strategy. This combination of prior investment and our expertise has allowed us to rapidly develop our two late-stage rare disease product candidates. For example, setrusumab has completed a Phase 2 in adult OI patients and we and our partner Ultragenyx recently reported data from two Phase 3 studies in pediatric and young adult OI patients, and alvelestat has completed two Phase 2 studies and is ready to progress into Phase 3. We may seek to partner our rare disease product candidates for further development where it makes strategic sense to do so, including potentially seeking partnerships on a regional basis. However, as commercialization of rare disease products can be achieved using a highly specialized and focused infrastructure, we may seek to commercialize our rare disease product candidates, once approved, in select markets. For example, as part of our partnership with Ultragenyx, we have the retained the commercial rights to setrusumab in Europe and the U.K., and we have out-licensed our early-stage rare disease product candidate vantictumab to āshibio, while retaining rights to commercialize in Europe and the U.K.

•

Continue to be a partner of choice for pharmaceutical and biotechnology companies. We believe that we are a preferred partner for pharmaceutical and biotechnology companies as they seek to unlock the potential in their development pipelines and deliver therapeutics to patients in areas of high unmet medical need. We have strong relationships with these companies, as evidenced by our agreements with Novartis AG ("Novartis") and AstraZeneca AB ("AstraZeneca"), as well as our partnership with Ultragenyx, and a track record of structuring transactions that enable us to leverage our core capabilities while creating value for all stakeholders. We intend to continue to enter into strategic relationships that align our interests with those of pharmaceutical and biotechnology companies and that we believe to be mutually beneficial.

•

Leverage our expertise in business development. Our senior management team has extensive relationships with large pharmaceutical and biotechnology companies. These relationships are important to us as we seek to form strategic partnerships on our product candidates, such as our partnership with Ultragenyx, and to grow our pipeline of product candidates in rare diseases.

•

Explore out-licensing or sale opportunities with third parties for further clinical development and/or commercialization of our non-core and non-rare disease programs. In March 2018, we reported top-line Phase 2b data for leflutrozole for the treatment of HH and in December 2018, we reported positive results from the safety extension study for leflutrozole. In December 2023, leflutrozole was partnered on a global basis with ReproNovo SA ("ReproNovo") and ReproNovo has commenced a Phase 2 clinical trial for leflutrozole for the treatment of infertility in men with low serum testosterone. Navicixizumab, for the treatment of late line ovarian cancer has completed a Phase 1 study and was partnered on a global basis with Feng Biosciences in January 2020. Etigilimab and acumapimod remain available for partnering.

Our Pipeline

The following table summarizes our pipeline for our core product candidates. We have global commercial rights to alvelestat, commercial rights to setrusumab in Europe and the U.K., and commercial rights to vantictumab in Europe and the U.K. We granted exclusive licenses to Ultragenyx to develop and commercialize setrusumab and to āshibio to develop and commercialize vantictumab outside our territories in the U.S. and rest of the world. In addition, we have licensed global rights for leflutrozole to ReproNovo and for navicixizumab to Feng Biosciences. We have global rights to etigilimab and acumapimod, which both remain available for partnering.

Core Rare Disease Product Candidates

Setrusumab (BPS-804/UX143) for the Treatment of Osteogenesis Imperfecta

Overview

In collaboration with Ultragenyx, we are developing setrusumab for the treatment of OI, a rare genetic disease, which is caused by variants in the COL1A1 or COL1A2 genes, which results in bones that can break easily and is commonly known as brittle bone disease. Setrusumab is a novel, intravenously administered antibody that is designed to inhibit sclerostin, a protein that inhibits the activity of bone-forming cells, known as osteoblasts. We believe that by blocking sclerostin, setrusumab has the potential to induce or increase osteoblast function and maturation of these cells, and to inhibit bone-resorption through osteoclasts, increasing overall bone mass and thereby reducing fractures in OI patients.

Background of Osteogenesis Imperfecta

OI is a genetic disorder characterized by fragile bones and reduced bone mass, resulting in bones that break easily, loose joints and weakened teeth. In severe cases, patients may experience hundreds of fractures in a lifetime. In addition, people with OI often suffer from muscle weakness, early hearing loss, fatigue, curved bones, scoliosis (curved spine), brittle teeth, respiratory

problems and short stature. The disease can be extremely debilitating and even fatal in newborn infants with a severe form of the disease. OI is a rare condition that affects an estimated 60,000 people in the U.S. and Europe, according to estimates by Orphanet.

There are many different recognized forms of OI, but the Type I, II, III and IV are estimated to represent approximately 80% to 90% of the total population. Type I is cited to be the least severe, although patients can still have many fractures and other physical manifestations of the disease, while Type II is the most severe and frequently causes death at or shortly after birth. Type I is the most prevalent and estimated to occur in approximately 50% to 60% of OI patients. Type III and Type IV patients may be wheelchair bound and typically have many fractures through their lifetime. Type III and Type IV patients may also have short stature, scoliosis and hearing loss by the time they are young adults. OI is typically diagnosed at birth with most patients being born with a blue or gray tint to the sclera, the part of the eye that is usually white.

Current Treatment Landscape for Osteogenesis Imperfecta

There are no therapies approved by the FDA, EMA or MHRA for the treatment of OI, except for neridronate which is approved for the treatment of OI in Italy. The only treatments available to OI patients are the acute management of fractures as they occur and drugs such as bisphosphonates which are typically used to treat osteoporosis and are not approved for OI but are commonly used off-label in both children and adults. Bisphosphonates reduce the rate of bone resorption by inhibiting osteoclastic activity. These anti-resorptives include Aredia (pamidronate), Fosamax (alendronate), Reclast (zoledronic acid) and neridronate (which is approved for the treatment of OI in Italy). Bisphosphonates have not consistently been shown to reduce fractures in pediatric or adult OI patients and the effect of long-term therapy with these drugs remains unclear in both children and adults.

Current treatment of OI is directed towards management of fractures with casting or surgical fixation. Following either of these, physical therapy will often be required. Preventative surgeries, such as intramedullary, or in-bone, rodding fixation are also undertaken. Supportive care for the disease involves surgery to correct deformities, internal splinting of bones with metal rods, bracing to support weak limbs and decrease pain, physical therapy and muscle strengthening and aerobic conditioning to improve bone mass and strength.

Our Approach

Setrusumab, our product candidate for the treatment of OI, is specifically designed to inhibit sclerostin. Sclerostin is produced in osteocytes, which are mature bone cells that are thought to be the mechanoreceptor cells that regulate the activity of bone-building osteoblasts and bone-resorbing osteoclasts. Sclerostin inhibits the activity of osteoblasts. We believe that by blocking sclerostin, setrusumab has the potential to induce or increase osteoblast activity and maturation of these cells, increasing overall bone mass, and thereby reducing fractures in OI patients.

In 2016, we obtained orphan drug designation in OI for setrusumab in the U.S. and the EU and, in November 2017, the program was accepted into the PRIority MEdicinePriority Medicines scheme (“PRIME”) of the EMA. In September 2020 we received rare pediatric disease designation for setrusumab in OI from the FDA. In October 2024 our partner, Ultragenyx, received Breakthrough Therapy designation from the FDA. See “—Government Regulation—Foreign Government Regulation.”

Clinical Development of Setrusumab

Prior to our acquisition of setrusumab, Novartis conducted four clinical trials in 106 patients and healthy volunteers. In 2019 we completed a Phase 2b dose-finding study (ASTEROID) study of setrusumab in 112 adult patients with Type I, III and IV OI. Following the 12-month dosing part of the trial, patients were followed for a further twelve months to examine the off-effects of setrusumab. The results of this Phase 2b trial supported the progression of setrusumab into a pivotal study in OI. Setrusumab was safe and well-tolerated in the study. There were no cardiac-related safety concerns observed in the study.

Top-line Data from Setrusumab Phase 2 Portion of Phase 2/3 Orbit Study

In June 2023, we along with our partner, Ultragenyx, announced successful completion of the Phase 2 portion of the pivotal Phase 2/3 Orbit study in 24 pediatric and young adult patients (5 to <26 years old) for setrusumab in OI, which compared two different doses of setrusumab, 20 and 40 mg/kg, to determine the optimal dose for the Phase 3. The primary endpoint of the Phase 2 study was circulating levels of P1NP, a biomarker reflective of bone formation. The study also evaluated numerous other endpoints, including bone mineral density (“BMD”) and annualized fracture rates, PK and safety. Across all patients evaluated at both doses, these data showed statistically significant increases in levels of serum P1NP, a sensitive marker of bone formation, and substantial and significant improvement in BMD by three months. An increase in lumbar spine BMD from baseline of 9.4% at 20 mg/kg (n=10) was observed, with a substantial mean change in the Z-score of +0.65 from -2.12 (n=11) at baseline. There was no significant difference between the two doses tested, accordingly, the 20 mg/kg was selected as the Phase 3 dose. The changes observed in BMD in these younger patients at three months are equivalent to the changes following 12 months treatment with setrusumab in adult patients reported from the Phase 2b ASTEROID study. The 24 patients from the Phase 2 portion of the Orbit study are continuing to receive setrusumab treatment in an open-label extension study.

Additional data from the Phase 2 portion of the Phase 2/3 Orbit study were reported at the annual ASBMR meeting in October 2023 and demonstrated that treatment with setrusumab significantly reduced incidence of fractures in patients with OI with at least six months of follow-up and continued to demonstrate ongoing and meaningful improvements in lumbar spine BMD. As of the cut-off date and following at least six months of treatment with setrusumab, the annualized fracture rate across all 24 patients in the Phase 2 portion of the study was reduced by 67%. The median annualized fracture rate of 0.72 in the two years prior to treatment was reduced to 0.00 (n=24, p=0.042) during the mean treatment duration period of nine months. These fractures excluded fractures of the fingers, toes, skull and face consistent with the Phase 3 study design. Following initiation of treatment with setrusumab, 20 patients experienced no radiographic-confirmed fractures, and four patients experienced seven radiographic-confirmed fractures in five separate events. Two of these fractures occurred within the first two months of treatment, a time in which setrusumab-induced increases in BMD may have been suboptimal in reducing fractures.

At the six-month timepoint, treatment with setrusumab resulted in a mean increase in lumbar spine BMD from baseline of 13% at 20 mg/kg (n=11) and 16% at 40 mg/kg (n=8), which represented the same substantial mean improvement in Z-score of +0.85 for both dose groups at six months compared to a combined mean baseline Z-score of –1.68. The small apparent difference in BMD change from baseline is likely related to differences in patients assigned to the two treated groups. There was no statistically significant difference in BMD percent change or Z-score change from baseline between the 20 and 40 mg/kg dosing cohorts. As of the data cut-off for our October 2023 announcement, there were no treatment-related serious adverse events observed in the study.

In data reported in June 2024, the large reduction in annualized radiologically confirmed fracture rate previously reported in patients treated for a minimum of six months was sustained in patients treated for at least 14 months with a high degree of statistical significance. The median annualized rate of radiologically confirmed fractures across all 24 patients in the two years prior to treatment was 0.72. Following a mean treatment duration period of 16 months, the median annualized fracture rate was reduced to 0.00 (p=0.0014; n=24), reflecting a 67% reduction relative to the pre-treatment period. Patients enrolled in the Phase 2 portion of the Orbit study are continuing to receive setrusumab treatment at 20 mg/kg in an open label extension study.

Phase 3 Orbit and Cosmic Studies

The Phase 3 portion of the Orbit study completed enrollment in April 2024 of 158 patients (aged 5 - <26 years old) at 45 sites across 11 countries. Patients were randomized 2:1 to receive setrusumab (20 mg/kg) or placebo, respectively, with a primary efficacy endpoint of a reduction in annualized clinical fracture rate, excluding fingers, toes, skull and face.

A second study, Cosmic, a Phase 3 open-label study in younger children (aged 2 - < 7 years old) completed enrollment in April 2024 of 66 patients at 21 sites across seven countries. The Cosmic study is an active-controlled study evaluating the effect of setrusumab compared to intravenous bisphosphonates (IV-BP) therapy (randomized 1:1) on annualized total fracture rate.

Top-line Data from Setrusumab Phase 3 Orbit and Cosmic Studies

On December 29, 2025, we announced the results from the Phase 3 Orbit and Cosmic studies evaluating setrusumab in pediatric and young adult patients with OI. Neither study achieved statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively. Both studies achieved their secondary endpoints of improvements in BMD against comparators (placebo and bisphosphonates) with strong statistical significance. There was no change in the safety profile observed.

In the Orbit study, participants experienced statistically significant and substantial improvements in BMD compared to placebo, at levels consistent with the treatment effect observed in Phase 2 studies. These BMD changes were not accompanied by a corresponding reduction in annualized fracture rates and there was a low fracture rate in the placebo group.

In the pediatric Cosmic study, patients had a substantially higher baseline fracture rate compared to the patients enrolled in Orbit. In this younger patient population, meaningful improvements in BMD were associated with a reduction in annualized fracture rate for setrusumab treated patients over bisphosphonates treated patients, though the reduction did not meet statistical significance.

Following the top-line data release, additional analyses from both studies indicate that in pediatrics and teens, setrusumab results in a reduction in vertebral fractures, and has a positive impact on pain and mobility/sports activity. The data continue to be analyzed and once completed, we expect to determine the next steps, including potential regulatory interactions.

Alvelestat (MPH-966) for the Treatment of Severe Alpha-1 Antitrypsin Deficiency-Associated Lung Disease (AATD-LD)

Overview

We are developing alvelestat for the treatment of severe AATD-LD. AATD-LD is a potentially life-threatening rare, genetic condition that results in severe debilitating diseases, including early-onset pulmonary emphysema. Alvelestat is a novel, oral small molecule designed to inhibit NE. Scientific data indicate that the increased risk of lung tissue injury in patients with AATD-LD may

be due to inadequately controlled NE caused by insufficient alpha-1 antitrypsin (AAT). We believe that by inhibiting NE, alvelestat has the potential to reduce the destruction of lung tissue and stabilize clinical deterioration in patients with severe AATD-LD patients.

Background of Alpha-1-Antitrypsin Deficiency

AATD is a genetic disease. There are estimated to be 50,000 people in North America and 60,000 in Europe with severe AATD, which we define as AATD in patients with serum AAT levels <11mM, (most commonly either a PiZZ genotype or Null/Null genotype) although there are approximately only 10,000 people diagnosed in North America. The major function of AAT in the lungs is to protect the connective tissue from NE released from triggered neutrophils. The lungs are normally defended from NE attack by AAT, which is a highly effective inhibitor of NE. People with severe AATD produce ineffective or no AAT and are, therefore, unable to defend against NE attack. As a result, individuals with severe AATD commonly experience degeneration of lung function, such as early-onset pulmonary emphysema, which significantly affects quality of life and life expectancy. They may require oxygen therapy in order to continue their daily lives and the most severe patients may require lung transplantation.

AATD is the result of a mutation of the SERPINA1 gene. Most people with severe AATD inherit two copies of the defective PiZ allele, or gene variant, of the SERPINA1 gene, resulting in a PiZZ genotype. Patients with a PiZZ genotype have approximately 15% of normal AAT levels. Individuals who inherit two copies of the Null allele, resulting in a Null/Null genotype, do not produce any AAT. These two groups are at very high risk of developing lung disease. Patients with the PiZZ genotype experience loss of lung tissue as measured by lung density on computed tomographic (CT) scanning, a decline in FEV1, a standard measure of exhalation, acute exacerbations of respiratory disease and poor quality of life. Respiratory disease can progress to need for chronic oxygen therapy, lung transplant and death. The annual mortality rate in this genotype is estimated to be 4%. Given that individuals with the Null/Null genotype do not produce any AAT, we believe that they are likely to experience an even greater annual decline in lung function.

Current Treatment Landscape for Alpha-1 Antitrypsin Deficiency-Associated Lung Disease

AATD-LD patients are monitored by pulmonary functions tests, including spirometry. Treatment involves bronchodilators and inhaled corticosteroid medications and pulmonary rehabilitation, with increased intensity of therapy guided by disease severity. Surgical options include lung volume reduction surgery and lung transplantation. Both are highly invasive, and transplantation is only an option for a portion of patients with end-stage disease despite optimal therapy.

Augmentation therapy is available for AATD-LD, using a partially purified plasma preparation highly enriched for AAT that is administered weekly by intravenous infusion. This therapy was first approved by the FDA in the 1980s based on its biochemical efficacy, meaning its ability to raise blood levels of AAT, but not based on clinical outcome data. Several observational studies have suggested that AAT augmentation therapy may slow the rate of decline in lung function in a subgroup of AATD-LD patients with moderate-to-severe airflow obstruction, but not for those with earlier stages of lung disease. In a randomized, controlled trial of augmentation therapy, patients had some reduction in the progression of emphysema, as assessed by measuring lung density using computed tomography. The study did not show a slowing in the decline in FEV1.

We believe that current therapies for AATD-LD are inadequate. Surgical options are limited to a few patients, are highly invasive, have variable results, and do not address the underlying pathology of AATD-LD. AAT augmentation therapy, while FDA approved, was not approved on the basis of clinical outcome data. Benefit has not been demonstrated in patients with earlier stages of lung disease where there is an unmet need to reduce progression of irreversible lung tissue loss. In Europe, regulatory approval was on efficacy based on slowing of CT density decline, without effects on other measures such as FEV1 or patient-reported outcomes. Further, AAT augmentation therapy is not universally reimbursed and thus is not currently available to patients in several jurisdictions, including some key European markets. In addition, AAT augmentation therapy requires potentially inconvenient weekly intravenous infusions.

Our Approach

Our product candidate for treating severe AATD-LD is alvelestat, a potent, specific oral small molecule that is designed to inhibit NE. We believe that by inhibiting NE, alvelestat has the potential to reduce the enzymatic destruction of lung tissue. Furthermore, we believe that convenient oral dosing of alvelestat could provide a significant advantage compared to the current treatments for AATD of weekly intravenous AAT augmentation therapy. Alvelestat is not being investigated for treatment of the hepatic disease which is due to the damaging effect of accumulated abnormal ZZ protein in the liver, rather than the protein deficiency. Severe liver disease occurs in approximately 10% cases of severe AATD, predominantly in children.

Alvelestat has received orphan designation for AATD from the EC and the FDA, and Fast Track designation for the treatment of AATD-LD from the FDA.

Clinical Development of Alvelestat

Prior to our license of alvelestat, AstraZeneca conducted 12 clinical trials involving 1,776 subjects, including trials in COPD, bronchiectasis and cystic fibrosis. Although these trials were conducted in diseases other than AATD-LD, we believe the data demonstrated potential clinical benefit and biomarker evidence of treatment effect for AATD-LD patients. These trials created a safety database of 1,149 subjects treated with alvelestat.

Phase 2 Clinical Trials in AATD-LD

In May 2022, we successfully completed a Phase 2, placebo-controlled, 12-week, dose-ranging, proof-of-concept clinical trial (ASTRAEUS) in 99 patients with AATD-LD in the U.S. and the EU which demonstrated statistically significant changes in NE activity and biomarkers of disease severity at different time points up to 12 weeks. We enrolled only adult patients with PiZZ or Null/Null genotypes or rare genotypes with severe deficiency of alpha-1 antitrypsin (<11 microMolar) with confirmed emphysema, who had not received AAT augmentation therapy or had undergone a wash-out period following AAT augmentation therapy. The study examined two doses of alvelestat (120 mg and 240 mg) compared to placebo with three primary endpoints along the pathogenic pathway of lung disease in AATD-LD patients. These primary endpoints were plasma desmosine (a biomarker of protease-driven elastin breakdown), Aα-Val360, a specific biomarker of NE proteolytic activity, and NE activity in blood. Secondary endpoints were safety, exacerbation frequency, and pharmacokinetics. Exploratory endpoints were St. Georges Respiratory Questionnaire (SGRQ) which is a patient-reported outcome of Respiratory Health Status and lung function tests, including FEV1.

We subsequently announced additional Phase 2 data from this study in October 2022 demonstrating the association of biomarker responders in alvelestat-treated patients to improvement in the Activity domain of the St George’s Respiratory Questionnaire, but not in patients treated with placebo.

No new safety signals were detected in patients with AATD-LD compared to the previous studies conducted by AstraZeneca. The most frequent adverse event was headache which was more frequently observed at the higher doses of alvelestat (120 mg and 240 mg) used in AATD-LD than at the lower doses used in previous studies in COPD, bronchiectasis and cystic fibrosis. There was evidence of tolerance to headache being induced, and we intend to use a dose-escalation regime for initiation of treatment in future trials. Monitoring for Adverse Events of Special Interest (AESIs) documented a single treatment-emergent adverse event (TEAE) of liver function abnormality (raised hepatic transaminases, without meeting Hy’s Law) and one AESI of prolonged QTc, in which study-drug stopping criteria being met were reported in the ASTRAEUS trial. Both events fully resolved on study drug cessation.

In October 2023, the University of Alabama at Birmingham (UAB) and Mereo reported on the ATALANTa study, a multi-center, double-blind, placebo-controlled, proof-of-concept investigator-led study run by Professor Mark Dransfield, Director of the Division of Pulmonary, Allergy and Critical Care, UAB, in collaboration with Mereo. ATALANTa investigated the safety and efficacy of alvelestat 120 mg, or matched placebo, twice daily, for 12 weeks in a broad range of individuals with AATD-LD, including those with less severe phenotypes (Pi*SZ) and earlier stage patients than were enrolled in the Company-sponsored ASTRAEUS Phase 2 study, and those receiving augmentation therapy. The study randomized 63 patients, 32 in the 120 mg alvelestat arm (44% on augmentation therapy) and 31 in the placebo arm (48% on augmentation therapy). The results demonstrated with the 120 mg dose of alvelestat (the lower dose used in the Phase 2 ASTRAEUS study) are consistent with those observed in ASTRAEUS on blood NE activity and changes in the disease-activity biomarkers, desmosine and Aα-val360. The data demonstrate that the 120 mg dose of alvelestat appears generally safe on top of augmentation. The greater biomarker efficacy supports Mereo’s selection of the 240 mg dose to be studied in the planned Phase 3 pivotal trial. Exploratory endpoints in ATALANTa demonstrated statistically significant improvement in SGRQ Activity score (p=0.0106 versus placebo) and a trend to improvement in SGRQ Total score at 12 weeks in patients not receiving augmentation therapy and having earlier stage lung disease (based on their FEV1). The ATALANTa and ASTRAEUS data support the use of the SGRQ Total score in the planned Phase 3 pivotal trial and inclusion of patients with earlier stages of lung disease. Safety in ATALANTa was consistent with the known alvelestat profile and there were no liver or QTc AESIs documented.

Planned Phase 3 Clinical Trial in AATD-LD

In March 2023, we announced the outcome of the end-of-Phase 2 discussions with the FDA and the EMA (Scientific Advice) and the guidance on the Phase 3 endpoints received from both Regulatory Agencies. In the EU, the Company received guidance that lung density by computed tomography (CT) scan with a relaxed p value (p<0.1) may be sufficient for full regulatory approval. In the U.S., following additional FDA interactions in the second half of 2023, the Company has aligned on St George’s Respiratory questionnaire (SGRQ) total score as the primary endpoint, with a functional assessment as a key secondary endpoint, which, if successful, is expected to support submissions for full regulatory approval in the U.S. Inclusion of patients with earlier and later stage lung disease progression in the planned registrational study could increase the addressable patient population for alvelestat. Based on the guidance from the FDA and the EMA, the Company has designed a single, global, Phase 3 study evaluating the 240 mg dose of alvelestat versus placebo in approximately 220 patients with AATD-LD with two independent primary endpoints to support applications for full marketing approvals in both the U.S. and EU. Qualitative research to test that the SGRQ is fit for purpose in the

AATD-LD population, as required by FDA, was completed in 2024. A Pediatric Investigation Plan ("PIP") full waiver was agreed by the EMA in 2024, meaning that no pediatric studies are required.

The Company continues to evaluate non-dilutive financing options for the development and potential commercialization of alvelestat in AATD-LD while continuing to progress the program towards the initiation of the planned Phase 3.

Phase 1b/2 Clinical Trial in Bronchiolitis Obliterans Syndrome (“BOS”)

BOS is a rare progressive, fibrosing disease of the lungs affecting approximately 6% of the estimated 12,000 stem cell transplants a year in the U.S., often as part of graft versus host disease. BOS is characterized by neutrophil infiltration in the lung, excess NE and inflammation.

An investigator-sponsored open-label Phase 1b/2 study in BOS following allogeneic stem cell transplant is being conducted. In January 2025, the Clinical Trial Agreement between Mereo and The Center for Cancer Research, National Cancer Institute was amended to expire on the earlier of completion of the research or May 31, 2026 and no subject was enrolled in the trial after May 31, 2025.

Vantictumab (OMP-18R5) for the Treatment of Autosomal Dominant Osteopetrosis Type 2

Vantictumab is an anti-FZD monoclonal antibody that we acquired in the Merger, which is being investigated for treatment in ADO2. In August 2025, we announced a license agreement with āshibio under which āshibio will fund and lead global clinical development of vantictumab and we retain rights to commercialize vantictumab in Europe and the U.K. with āshibio having exclusive rights in the U.S. and rest of world.

ADO2 (also known as Albers-Schönberg disease) is a rare inherited metabolic bone disorder for which there is currently no approved therapy. ADO2 is caused by reduced function of osteoclasts. Impaired osteoclast function results in dense, brittle bone and leads to complications such as multiple fractures, poor bone healing, low blood counts (due to encroachment of the bone marrow), and nerve compression that can cause pain, deafness, and/or blindness. ADO2 results from a mutation in the chloride channel 7 (CLCN7) gene, with the most common mutation being G215R.

The Wnt pathway plays a key role in bone homeostasis. Vantictumab is a novel antibody that binds to certain Frizzled receptors and inhibits the Wnt signaling pathway. This enhances bone resorption by promoting osteoclast activity resulting in re-established bone homeostasis. Between 2011 and 2017 vantictumab was investigated in approximately 100 patients in four Phase 1a/1b studies in oncology indications. Biomarker data demonstrated an impact on osteoclast function and high bone turnover leading to fragility fractures in some patients.

Āshibio reported promising pre-clinical data at ASBMR 2025 with vantictumab significantly decreasing areal BMD in the ADO2 mouse model (whole body, femur and spine), improving measures of bone structure and quality and rescuing the bone phenotype in ADO2 mice. These results support the clinical development of vantictumab and āshibio expect to file an IND in the second half of 2026.

Our Non-Core Partnered Programs

Following completion of successful Phase 1b or Phase 2 studies the products below are programs which we have successfully partnered.

Leflutrozole (BGS-649) for the Treatment of Hypogonadotropic Hypogonadism

Leflutrozole is an oral inhibitor of aromatase. Excess aromatase in fat tissue reduces testosterone, luteinizing hormone ("LH") and follicle-stimulating hormone ("FSH"), leading to HH. In Phase 2 trials, leflutrozole normalized testosterone, increased LH and FSH, improved total sperm count, and was reported to be well-tolerated.

In December 2023, we entered into an exclusive global license agreement with ReproNovo for the development and commercialization of leflutrozole, a non-steroidal aromatase inhibitor. See “—Other Licensing Agreements—Licensing Agreement for Leflutrozole.” Under the terms of the license agreement, ReproNovo, a reproductive medicine company, is responsible for all future development and commercialization of leflutrozole.

Mereo previously received an upfront payment of $1.0 million in 2023 and received an additional $0.5 million milestone payment in the year ended December 31, 2025 following the announcement that the first participant had been included in a Phase 2

trial of leflutrozole. Mereo will be eligible to receive up to $63.8 million for additional development, regulatory and commercial milestones as well as tiered mid-single digit royalties on global annual net sales of leflutrozole.

Navicixizumab (OMP-305B83) for the Treatment of Ovarian Cancer

Navicixizumab is a bispecific antibody that inhibits delta-like ligand 4 (DLL4) and vascular endothelial growth factor (VEGF).

We acquired navicixizumab in the Merger. In January 2020, we out-licensed navicixizumab to Feng Biosciences. See “— Other Licensing Agreements—Licensing Agreement for Navicixizumab.”

Our Non-Core Programs Available for Partnering

Following completion of successful Phase 1b or Phase 2 studies, the following programs are available for partnering.

Etigilimab (MPH-313) for the Treatment of Advanced Solid Tumors

Etigilimab is an antibody against TIGIT. TIGIT is a next generation checkpoint receptor shown to block T-cell activation and the body’s natural anti-cancer immune response. Etigilimab is an IgG1 monoclonal antibody which binds to the human TIGIT receptor on immune cells with a goal of improving the activation and effectiveness of T-cell and NK cell anti-tumor activity. Etigilimab has completed a Phase 1a dose escalation clinical trial in 23 patients with advanced solid tumors and has been evaluated in a Phase 1b study in combination with nivolumab in select tumor types.

Acumapimod (BCT-197) for the Treatment of AECOPD

Acumapimod is a p38 MAP kinase inhibitor therapy for treatment during severe acute exacerbations of COPD (AECOPD). In a Phase 2 trial, acumapimod given over five days in patients hospitalized with AECOPD demonstrated a statistically significant reduction in re-hospitalization for treatment failure and recurrent exacerbations. Acumapimod was reported to be safe and well tolerated. Following meetings with FDA and EMA a global Phase 3 registrational program has been designed.

We intend to out-license or sell etigilimab and acumapimod to third parties for the further development, recognizing the need for greater resources to take these product candidates to market.

Material Agreements

Agreements with Ultragenyx for Setrusumab

On December 17, 2020, we announced that we entered into a license and collaboration agreement with Ultragenyx, for setrusumab for OI. Under the terms of the agreement, Ultragenyx will lead future global development of setrusumab in both pediatric and adult patients. We granted Ultragenyx an exclusive license to develop and commercialize setrusumab in the U.S. and rest of the world, excluding Europe and the U.K., where we retain commercial rights. Each party will be responsible for post-marketing commitments in their respective territories. Under the terms of the agreement, Ultragenyx made an upfront payment of $50 million to Mereo and a $9.0 million payment during the year ended December 31, 2023 upon achievement of a clinical milestone. Ultragenyx will pay up to $245 million in additional development, regulatory and commercial milestones and tiered double digit percentage royalties to us on net sales outside of Europe and the U.K. and we will pay a fixed double digit percentage royalty to Ultragenyx on net sales in Europe and the U.K. If Ultragenyx receives and resells an FDA priority review voucher (“PRV”) in connection with a new drug application approval, Mereo is entitled to receive a portion of the proceeds from the sale of the PRV or a cash payment from Ultragenyx, in the event they choose to retain the PRV. Under the terms of our 2015 agreement with Novartis, we will pay Novartis a percentage of proceeds, subject to certain deductions, and we will receive a substantial majority of the payments from Ultragenyx.

In December 2024, we entered into a manufacturing and supply agreement with Ultragenyx (the “Ultragenyx Manufacturing and Supply Agreement”) under which Ultragenyx is responsible for the manufacture and supply of setrusumab to Mereo in our territories. We are also required to reimburse Ultragenyx for a portion of the manufacturing process development costs, future commercial supply costs as well as a portion of costs in the event of cancellation of certain manufacturing slots.

Licensing Agreement with AstraZeneca

In October 2017, we entered into an exclusive license and option agreement (“the AstraZeneca License Agreement”) and subscription deed (the “AstraZeneca Subscription Deed”), together (the “Original Agreements”) with AstraZeneca AB. Each of these

were amended on November 8, 2024, when we entered into an amendment and restatement agreement related to the AstraZeneca License Agreement (the “Amended AstraZeneca License Agreement”) and a Deed of Amendment and Restatement related to the AstraZeneca Subscription Deed (the “Amended AstraZeneca Subscription Deed”) together (the “Amended AstraZeneca Agreements”).

Under the terms of the Original Agreements, we obtained from AstraZeneca an exclusive worldwide, sub-licensable license under AstraZeneca’s intellectual property rights relating to alvelestat, with an option to acquire such intellectual property rights following commencement of a pivotal trial and payment of related milestone payments, together with the acquisition of certain related assets. Upon entering into the Original Agreements, we made a payment of $3.0 million and issued 490,798 ordinary shares (equivalent to 98,159 ADSs) to AstraZeneca, for an aggregate upfront payment equal to $5.0 million. Upon execution of the Amended AstraZeneca License Agreement, we issued 2,044,390 ordinary shares and paid $0.5 million to AstraZeneca in respect of an agreed milestone.

Under the terms of the Amended AstraZeneca Agreements, we have agreed, in connection with certain further development and regulatory milestones, to make potential future payments both in cash and through the issue of a variable number of additional ADSs to AstraZeneca of up to $114.3 million in the aggregate for products included in the Amended AstraZeneca License Agreement. The number of ADSs to be issued to satisfy equity milestones is determined by dividing a monetary amount by a defined subscription price (the “Subscription Price”). In addition, we have agreed to make payments to AstraZeneca based on specified commercial milestones of the product. We have also agreed to pay a specified percentage of sub-licensing revenue to AstraZeneca and to make royalty payments to AstraZeneca equal to ascending specified percentages of tiered annual worldwide net sales by us of licensed products (subject to certain reductions), ranging from the high single digits to low double digits. Royalties will be payable on a licensed-product-by-licensed-product and country-by-country basis until the later of ten years after the first commercial sale of such licensed product in such country and expiration of the last patent covering such licensed product in such country that would be sufficient to prevent generic entry. We have agreed to use commercially reasonable efforts to develop and commercialize at least one licensed product.

The Amended AstraZeneca License Agreement will expire on the expiration of the last-to-expire royalty term with respect to all licensed products. Upon the expiration of the royalty term for a licensed product in a particular country, the licenses to us for such product in such country will become fully paid and irrevocable. Prior to exercise of the Option, if at all, we may terminate the Amended AstraZeneca License Agreement upon prior written notice. Either party may terminate the agreement upon prior written notice for the other party’s material breach that remains uncured for a specified period of time or insolvency.

Novartis Agreements

In July 2015, three of our wholly-owned subsidiaries, Mereo BioPharma 3 Limited, Mereo BioPharma 2 Limited, and Mereo BioPharma 1 Limited (the “Subsidiaries”), entered into asset purchase agreements (the “Purchase Agreements”), to acquire from Novartis rights to setrusumab, acumapimod, and leflutrozole (the “Compounds”), respectively, and certain related assets (together with the Compounds, the “Novartis Assets”).

Under the Purchase Agreements, we have agreed to make tiered royalty payments to Novartis based on annual worldwide net sales of product candidates that include the Compounds (the “Acquired Novartis Product Candidates”), at percentages ranging from the high single digits to low double digits. In the event that the parties agree or it is otherwise determined in accordance with the Purchase Agreements that we require third-party intellectual property rights to exploit the Acquired Novartis Product Candidates, we are entitled to offset a specified percentage of amounts paid to such third parties in consideration for such intellectual property rights against the royalties due to Novartis. The royalty payments are payable for a period of ten years after the first commercial sale of an Acquired Novartis Product. We further agreed that in the event of a change in control that involves the transfer, license, assignment or lease of all or substantially all of a Subsidiary’s assets, including a Compound and related assets, we will pay Novartis a percentage of the proceeds of such transaction, with the majority of the proceeds being retained by us. No payment, however, is required with respect to any transaction of Mereo BioPharma Group plc involving its equity interests, a merger or consolidation of it, or a sale of any of its assets.

We also entered into a sublicense agreement with Novartis (the “Sublicense Agreement”), pursuant to which Novartis granted us an exclusive, worldwide, royalty-bearing sublicense for certain therapeutic antibody product candidates directed against sclerostin (the “Antibody Product Candidates”), including setrusumab. Under the Sublicense Agreement, we have agreed to pay Novartis royalties in the low single digits on worldwide net sales of Antibody Product Candidates. Royalties will be payable on a country-by-country basis until the later of expiration of the last valid claim of the licensed patents covering the Antibody Product Candidates in a country and ten years after the first commercial sale of the Antibody Product Candidates in such country, with a maximum royalty term of 12 years after the first commercial sale of the Antibody Product Candidates in such country. We have also agreed to pay Novartis up to $3.25 million in development and regulatory milestones, of which $0.8 million was paid in 2023, and to use

commercially reasonable efforts to develop and commercialize an Antibody Product. The Sublicense Agreement will expire on the earlier of the termination of the agreement under which Novartis is granting us a sublicense (the “Original License Agreement”) and, on a product-by-product and country-by-country basis, the expiration of the royalty term with respect to such Antibody Product Candidate in such country. The Original License Agreement has a perpetual term and may be terminated for breach or upon a change in control of the licensing party. We may terminate the Sublicense Agreement upon written notice to Novartis and either party may terminate the Sublicense Agreement for the other party’s uncured material breach or bankruptcy.

In addition, as of December 31, 2025, Novartis has warrants outstanding to purchase a total of 2,000,000 ordinary shares at an exercise price of £0.150 per ordinary share, exercisable until February 10, 2028. These warrants were issued on February 10, 2023, in connection with the amendment of a £3.8 million convertible loan note instrument (the "Novartis Loan Note") that we originally entered into on February 10, 2020, and which was fully converted in February 2025.

Other Licensing Agreements

Licensing Agreement for Vantictumab

In August 2025, we announced a license agreement with āshibio for the development and commercialization of vantictumab, an anti-FZD monoclonal antibody that we acquired in the Merger, which is being investigated for treatment in ADO2. Under the terms of the license agreement, āshibio will fund and lead global clinical development of vantictumab and we retain rights to commercialize vantictumab in Europe in the U.K., with āshibio having exclusive rights in the U.S. and rest of world. We received an upfront payment of $0.3 million and will be eligible to receive up to €13 million of additional development and regulatory milestones as well as tiered mid-single digit royalties on annual net sales of vantictumab outside of Europe and the U.K from āshibio. Mereo is obligated to pay āshibio up to $190 million in future milestone payments, contingent upon the achievement of certain regulatory and commercial milestones, as well as tiered mid-single and low-double digit royalties on annual net sales of vantictumab in Europe and the U.K.

Licensing Agreement for Leflutrozole

In December 2023, we entered into an exclusive global license agreement with ReproNovo for the development and commercialization of leflutrozole, a non-steroidal aromatase inhibitor. Under the terms of the license agreement, ReproNovo, a reproductive medicine company, is responsible for all future development and commercialization of leflutrozole. Mereo previously received an upfront payment of $1.0 million in 2023 and received an additional $0.5 million milestone payment in the year ended December 31, 2025 following the announcement that the first participant had been included in a Phase 2 trial of leflutrozole. Mereo will be eligible to receive up to $63.8 million additional development, regulatory and commercial milestones as well as tiered mid-single digit royalties on global annual net sales of leflutrozole.

Licensing Agreement for Navicixizumab

In January 2020, we entered into a global license agreement with Feng Biosciences for the development and commercialization of navicixizumab, an anti-DLL4/VEGF bispecific antibody, which, at the time, was being evaluated in a Phase 1b study in combination with paclitaxel in patients with advanced heavily pretreated ovarian cancer. Navicixizumab previously completed a Phase 1a monotherapy study in patients with various types of refractory solid tumors and is one of two product candidates we acquired through the Merger.

Under the terms of the license agreement, Feng Biosciences received an exclusive worldwide license to develop and commercialize navicixizumab. We received an upfront payment of $4.0 million and in February 2022 we received an additional payment of $2.0 million, following satisfaction of a milestone. Feng Biosciences will be responsible for all future research, development and commercialization of navicixizumab. Additionally, we will be eligible to receive up to $300 million in future clinical, regulatory and commercial milestones, tiered royalties ranging from the mid-single-digit to sub-teen percentages on global annual net sales of navicixizumab, as well as a negotiated percentage of sublicensing revenues from any sublicensees. We will only be eligible to receive a negotiated percentage of sublicensing revenues in the event Feng Biosciences elects only to sublicense and not commercialize navicixizumab, or a negotiated percentage of the total consideration paid by a purchaser in the event of change of control of Feng Biosciences.

In February 2022, we received a milestone payment of $2.0 million (£1.5 million) under the Navicixizumab License Agreement with Feng Biosciences. An associated payment was made to the former shareholders of Mereo BioPharma 5, (formerly OncoMed) under the CVR Agreement of a total of $0.9 million (£0.7 million), after deductions of costs, charges and expenditures.

In the fourth quarter of 2023, Feng Biosciences completed a restructuring, recapitalization and closed on a refinancing. Feng Biosciences is a clinical stage therapeutics company advancing precision medicine for people with cancer. Feng Biosciences will continue to utilize its XernaTM platform to progress navicixizumab.

Manufacturing

We do not own or operate manufacturing facilities for the production of our product candidates, nor do we have plans to develop our own manufacturing operations in the foreseeable future. We have entered into manufacturing agreements with a number of drug substance, drug product, and other manufacturers and suppliers for setrusumab and alvelestat, and we intend to enter into additional manufacturing agreements as necessary. Following our license of alvelestat, we acquired certain clinical trial materials and we subsequently outsourced production of further clinical supplies to our own manufacturing suppliers. We also outsource certain product formulation trials. We expect that drug product pre-validation and validation batches will be manufactured to satisfy regulatory requirements where we progress product candidates to late-stage trials.

In December 2024, we entered into the Ultragenyx Manufacturing and Supply Agreement under which Ultragenyx is responsible for the manufacture and supply of setrusumab to Mereo in our territories. We intend to enter into contractual relationships for the packaging and labeling of commercial supplies for setrusumab and for the manufacture, packaging and labeling of commercial supplies for alvelestat, if approved. Any batches of product candidates for commercialization will need to be manufactured in facilities, and by processes, that comply with the requirements of the FDA, the EMA, and the regulatory agencies of other jurisdictions in which we are seeking approval. We employ internal resources to manage our manufacturing contractors and ensure they are compliant with current good manufacturing practices.

Commercialization, Sales and Marketing

We do not have our own marketing, sales, or distribution capabilities. In order to commercialize our product candidates, if approved for commercial sale, we must either develop a sales and marketing infrastructure or collaborate with third parties that have sales and marketing experience. In December 2020, we entered into a license and collaboration agreement with Ultragenyx for setrusumab and in August 2025 we announced a license agreement with āshibio for vantictumab, under which we retain rights to commercialize both product candidates in Europe and the U.K. For our other partnered programs, leflutrozole and navicixizumab, global commercialization rights are held by our partners. For our other current and future product candidates, we intend to take strategic decisions on whether to further develop them, potentially through to approval, directly commercializing globally or in certain territories, or to seek a partner for further development, co-development and/or commercialization. For product candidates we intend to commercialize or co-commercialize, we must either establish a sales and marketing organization with technical expertise and supporting distribution capabilities in major markets or potentially outsource aspects of these functions to third parties or partners.

Competition

We compete directly with other biopharmaceutical and pharmaceutical companies that focus on the treatment of OI, AATD and ADO2, as well as face competition in treatments for solid tumors and AECOPD potentially impacting our ability to partner our non-core programs. We may also face competition from academic research institutions, governmental agencies and other various public and private research institutions. We expect to face increasingly intense competition as new technologies become available. Any product candidates, including setrusumab, alvelestat, vantictumab, etigilimab and acumapimod that we or our partners successfully develop and commercialize will compete with existing therapies and new therapies that may become available in the future.

We consider setrusumab’s current closest potential competitors in development for the treatment of OI to be Amgen and UCB’s anti-sclerostin antibody, romosozumab (Evenity), which was approved for osteoporosis in the U.S. in April 2019 and in December 2019 in Europe. Amgen Inc. (“Amgen”) and UCB Pharma SA ("UCB") are studying romosozumab in an open-label Phase 3 study in children and adolescents with OI in line with their pediatric investigation plan. In addition, Transcenta Holding has licensed the Chinese rights to the anti-sclerostin antibody blosozumab from Eli Lilly and Company (“Lilly”) and plans to develop it for osteoporosis. Amgen has also terminated a Phase 3 study and an open label extension study of denosumab (Prolia) an anti-resorptive agent in pediatric patients with OI. BOOST Pharma has conducted a Phase 1/2 trial of its fetal-derived mesenchymal stem cell therapy in prenatal & postnatal patients with severe OI and is now planning a Phase 3 trial. Furthermore, Angitia Biopharmaceuticals has completed a Phase 1 trial of its Sclerostin & Dickkopf-1 bispecific antibody and is now planning a Phase 2 Clinical Trial in adults with OI.

We consider alvelestat’s current closest potential competitors for the treatment of severe AATD to be alpha-1 proteinase inhibitors that are administered intravenously in AAT augmentation therapy. Currently, there are four inhibitors on the market in the U.S. and the EU: Prolastin-C from Grifols, S.A. (“Grifols”), Aralast from Shire plc, now a subsidiary of Takeda Pharmaceutical Company Ltd (“Shire”), Zemaira from CSL Limited (“CSL”), and Glassia from Kamada Ltd. (“Kamada”). Kamada also has a recombinant alpha-1 antitrypsin in early development. Sanofi S.A. (“Sanofi”) has completed a Phase 2 potentially registrational trial of SAR-447537, a recombinant human alpha-1 antitrypsin Fc fusion protein (rhAAT-Fc) for replacement therapy and are now seeking regulatory guidance. Wave Life Sciences Ltd. (“Wave”) has initiated a Phase 1/2 study of RNA base-editing oligonucleotide

(WVE-0006) to restore wild-type protein in lung and liver disease. Beam Therapeutics Inc. (“Beam”) commenced a Phase 1/2 study of BEAM-302, a genome editing therapy to correct mutant Z-AAT. Krystal Biotech, Inc. (“Krystal”) commenced a Phase 1 study of KB-408, an inhaled gene therapy. Korro Bio, Inc. (“Korro”) were in preliminary stages of clinical development of an RNA Base editing oligonucleotide therapy and now are expected to nominate a new development candidate in 2026. We expect Yoltech Therapeutics, Cornell University, AIRNA, Prime Medicine, CRISPR Therapeutics, and Tessera Therapeutics (a program that is partnered with Regeneron) each to begin early-stage clinical trials in AATD over the next 12-18 months.

There are no therapies with regulatory approval for ADO2. We consider vantictumab's closest competitor to be the pre-clinical CLCN7-targeting siRNA developed by SiSaf Ltd.

We consider etigilimab’s current closest potential competitors to include other anti-TIGIT agents being developed by companies including Roche, Merck, iTeos and GSK, BeOne Medicines, Arcus/Gilead, and Compugen amongst others. In addition, there are other combinations of existing cancer therapies available commercially for example, Yervoy and Opdivo and Opdivo or Keytruda in combination with chemotherapeutic targeted agents. There are a number of bispecific antibodies with an anti-TIGIT arm in development including a Phase 3 program in NSCLC being developed by AstraZeneca. There are also a number of other agents in development to other immuno-oncology targets that could compete with an anti-TIGIT approach, for example anti-LAG3.

For acumapimod, although we are not aware of any approved therapies for the treatment of AECOPD, there are a wide range of established therapies available for the treatment of COPD as well as a number of product candidates in development. We consider acumapimod’s current closest potential competitor for the treatment of AECOPD to be Merck & Co’s nebulized and inhaled ensifentrine (Ohtuvayre), a PDE3 / PDE4 dual inhibitor that recently received regulatory approval as a bronchodilator and anti-inflammatory agent for COPD, Asthma and Cystic Fibrosis patients. Pulmatrix, Inc. (“Pulmatrix”) has PUR1800, a narrow-spectrum kinase inhibitor (NSKI) that completed a Phase 1b trial in COPD. In addition to Pulmatrix, there are several compounds, which directly or indirectly target the p38 MAP Kinase pathway in clinical development by Poolbeg Pharma Plc (“Poolbeg), Fulcrum Therapeutics Inc (“Fulcrum”), GEn1E Lifesciences Inc (“GEn1E Lifesciences”), CervoMed Inc (“CervoMed”), Kinarus AG (“Kinarus”), Neurokine Therapeutics (“Neurokine”), and Inovio Pharmaceuticals Inc (“Inovio”), among others, for therapeutic indications outside the COPD setting. In addition, ReAlta Life Sciences commenced a Phase 2 clinical trial evaluating its complement 1 sub-component inhibitor for the treatment of AECOPD.

We may face increasing competition for additional new product acquisitions from pharmaceutical companies as new companies emerge with a similar business model and other more established companies focus on acquiring product candidates to develop their pipelines. Many of our competitors have significantly greater name recognition, financial, manufacturing, marketing, drug development, technical and human resources than we do. Mergers and acquisitions in the biopharmaceutical and pharmaceutical industries may result in even more resources being concentrated among a smaller number of our competitors. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies. These competitors also compete with us in recruiting and retaining top qualified scientific and management personnel, establishing clinical trial sites and patient registration for clinical trials and in acquiring technologies complementary to, or necessary for, our programs.

The key competitive factors affecting the success of setrusumab, alvelestat, vantictumab, etigilimab and acumapimod, if approved, are likely to be their efficacy, safety, dosing convenience, price, the effectiveness of companion diagnostics in guiding the use of related therapeutics, the level of generic competition and the availability of reimbursement from government and other third-party payors.

Our commercial opportunity could be reduced or eliminated if our competitors develop and commercialize product candidates that are safer, more effective, less expensive, convenient or easier to administer or have fewer or less severe side effects than any product candidates that we may develop. Our competitors may also obtain FDA, EMA, MHRA or other regulatory approval for their product candidates more rapidly than we may obtain approval for our own product candidates, which could result in our competitors establishing a strong market position before we are able to enter the market. Even if setrusumab, alvelestat, vantictumab, etigilimab, or acumapimod achieve marketing approval, they may be priced at a significant premium over competing product candidates if any have been approved by then, potentially reducing our market opportunity. For more information, see “Item 1A. Risk Factors—Risks Related to Commercialization—We operate in a highly competitive and rapidly changing industry, which may result in others acquiring, developing, or commercializing competing product candidates before or more successfully than we or our partners do.”

Intellectual Property

We have acquired or exclusively licensed our intellectual property portfolio from Novartis, AstraZeneca and Mereo BioPharma 5 (formerly OncoMed). We strive to protect and enhance the proprietary technologies, inventions and improvements that

we believe are important to our business, including seeking, maintaining and defending patent rights, whether developed internally or acquired or licensed from third parties. Our policy is to seek to protect our proprietary position by, among other methods, pursuing and obtaining patent protection in the U.S. and in jurisdictions outside of the U.S. related to our proprietary technology, inventions, improvements, platforms and our product candidates that are important to the development and implementation of our business.

Our intellectual property is held by our wholly owned subsidiaries. As of December 31, 2025, our patent portfolio comprises approximately 559 issued patents and approximately 57 pending patent applications on a global basis.

Individual patents extend for varying periods depending on the date of filing of the patent application or the date of patent issuance and the legal term of patents in the countries in which they are obtained. Generally, patents issued for regularly filed applications in the U.S. are granted a term of 20 years from the earliest effective non-provisional filing date. In addition, in certain instances, a patent term can be extended to recapture a portion of the USPTO delay in issuing the patent as well as a portion of the term effectively lost as a result of the FDA regulatory review period. However, as to the FDA component, the restoration period cannot be longer than five years and the total patent term including the restoration period must not exceed 14 years following FDA approval. The duration of foreign patents varies in accordance with provisions of applicable local law, but typically the duration of foreign issued patents is also 20 years from the earliest effective filing date.

However, the actual protection afforded by a given patent varies on a product-by-product basis and from country to country, dependent on many factors, including the type of patent, the scope of its coverage, the availability of regulatory-related extensions, the availability of legal remedies in a particular country and the validity and enforceability of the patent.

In addition to patent protection, we also rely upon trademarks, trade secrets and know-how, and continuing technological innovation, to develop and maintain our competitive position. We seek to protect our proprietary information, in part, using confidentiality agreements with our collaborators, employees and consultants and invention assignment agreements with our employees. We also have confidentiality agreements or invention assignment agreements with our collaborators and selected consultants. These agreements are designed to protect our proprietary information and, in the case of the invention assignment agreements, to grant us ownership of technologies that are developed through a relationship with a third party. These agreements may be breached, and we may not have adequate remedies for any breach. In addition, our trade secrets may otherwise become known or be independently discovered by competitors. To the extent that our collaborators, employees and consultants use intellectual property owned by others in their work for us, disputes may arise as to the rights in related or resulting know-how and inventions.

Our commercial success will also depend in part on not infringing upon the proprietary rights of third parties. It is uncertain whether the issuance of any third-party patent would require us to alter our development or commercial strategies, or our product candidates or processes, obtain licenses or cease certain activities. Our breach of any license agreements or failure to obtain a license to proprietary rights that we may require to develop or commercialize our product candidates may have an adverse impact on us. If third parties have prepared and filed patent applications prior to March 16, 2013, in the U.S., that also claim technology to which we have rights, we may have to participate in interference proceedings in the USPTO, to determine priority of invention. For more information, please see “Item 1A. Risk Factors—Risks Related to Intellectual Property.”

Setrusumab (BPS-804/UX143)

As of December 31, 2025, we have 132 patents globally (including 5 issued U.S. patents) and 20 patent applications globally (including 2 pending U.S. patent applications) relating to setrusumab and its use for the treatment of OI. A first patent family includes 3 issued U.S. patents and 88 corresponding issued foreign patents that relate to the setrusumab antibody, nucleic acids encoding setrusumab, processes for producing setrusumab, and setrusumab’s use as a medicament. Patents emanating from this first patent family expire in 2028 (not accounting for any available patent term extension). We also have two additional patent families, including 2 issued U.S. patents and 39 issued foreign patents that relate to methods of using anti-sclerostin antibodies, including setrusumab, for the treatment of OI. Patents emanating from these additional patent families expire in 2037 (not accounting for any available patent term extension). Beyond these patents and patent applications, we jointly own with Ultragenyx one additional patent family relating to dosing regimens for the use of anti-sclerostin antibodies, including setrusumab, in the treatment of OI; we expect any patents emanating from this patent family to expire in 2042 (not accounting for any available patent term extension). In December 2020, we entered into a license and collaboration agreement with Ultragenyx for setrusumab for OI, under which Ultragenyx have exclusive rights under all setrusumab patent families outside of Europe. See “—Licensing Agreements with Ultragenyx for Setrusumab.”

On February 3, 2023, Ultragenyx, Mereo BioPharma 3 Limited, UCB and Amgen entered into a non-exclusive worldwide, royalty-free license to research, develop, and commercialize setrusumab in OI under certain UCB/Amgen-owned patent rights related to anti-sclerostin compounds and their uses.

Alvelestat (MPH-966)

As of December 31, 2025, our patent portfolio relating to our product candidate alvelestat consisted of 2 issued U.S. patents, no pending U.S. patent applications, 17 issued or allowed foreign patents and 1 pending foreign patent application, licensed under our agreement with AstraZeneca. See “—Material Agreements—Licensing Agreement with AstraZeneca.” These issued patents and patent applications, if issued, include claims directed to 2-pyridone derivatives as NE inhibitors and their uses as well as claims to a specific polymorph of a tosylate salt of alvelestat, with expected expiry dates between 2027 and 2030.

Our patent portfolio relating to our product candidate alvelestat also includes 4 pending international patent applications filed under the PCT, 4 pending U.S. patent applications, 35 granted foreign patents and 17 pending foreign patent applications which have been filed subsequent to the license agreement with AstraZeneca. These patent applications, if issued, include claims directed to dosing regimens of alvelestat, methods of treatment using alvelestat, and dosage forms of alvelestat with expected expiry dates between 2040 and 2045.

Vantictumab (OMP-18R5)

As of December 31, 2025, our patent portfolio relating to vantictumab and related compounds consisted of 3 U.S. patents. These patents were licensed to āshibio pursuant to the terms of a global licensing agreement announced in August 2025.

Etigilimab (MPH-313)

As of December 31, 2025, our patent portfolio relating to our product candidate etigilimab consisted of 4 granted U.S. patents as well as corresponding patents and patent applications in major foreign jurisdictions.

The patent portfolio relating to our product candidate etigilimab contains one core patent family that covers the product per se as well as medical uses thereof. This patent family currently consists of 2 granted U.S. patents, 32 granted or allowed foreign patents and 2 pending foreign patent applications. Patents that issue from this core family are generally expected to expire in 2036.

The portfolio also includes a second patent family that relates to specific methods of treatment using etigilimab. This patent family currently consists of 2 granted U.S. patents and 7 granted or allowed foreign patents. Any patents that issue from this family are generally expected to expire in 2037.

Navicixizumab (OMP-305B83)

As of December 31, 2025, our patent portfolio relating to navicixizumab consisted of 21 issued or allowed U.S. patents and 3 pending U.S. patent applications, as well as corresponding patents or patent applications in major foreign jurisdictions.

The patent portfolio relating to navicixizumab contains two core patent families, both of which cover the product per se as well as medical uses thereof. Patents and patent applications, if issued, in these core families are expected to expire between 2030 and 2032.

The portfolio also includes several other patent families including issued U.S. and foreign patents and pending applications that relate to specific methods of treatment using navicixizumab. Patents and patent applications, if issued, in these families are expected to expire between 2030 and 2039. Navicixizumab was licensed to Feng Biosciences in January 2020 pursuant to the terms of a global licensing agreement. See “—Other Licensing Agreements—Licensing Agreement for Navicixizumab.”

Acumapimod (BCT-197)

As of December 31, 2025, our patent portfolio relating to our product acumapimod consisted of 10 issued or allowed U.S. patents, no pending U.S. patent applications, 202 issued or allowed foreign patents and 6 pending foreign applications. These issued patents and patent applications, if issued, include claims directed to 5-membered heterocycle-based p38 kinase inhibitors, the use of acumapimod in the treatment of AECOPD, dosage regimens of acumapimod, the use of acumapimod in the treatment of specific patient subpopulations, specific polymorphs of acumapimod, methods of producing specific polymorphs of acumapimod and synthetic methods of production of acumapimod with expected expiry dates between 2025 and 2039.

Leflutrozole (BGS-649)

As of December 31, 2025, our patent portfolio relating to our product leflutrozole consisted of 4 issued U.S. patents and 90 issued foreign patents. These issued patents include claims directed to leflutrozole formulations and the use of leflutrozole in treating hypogonadism according to a specific dosing regimen, with expected expiry dates in 2032 and 2037. Leflutrozole was licensed to

ReproNovo in December 2023 pursuant to the terms of global licensing agreement. See "—Other Licensing Agreements—Licensing Agreement for Leflutrozole".

Government Regulation

Among others, the FDA, U.S. Department of Health and Human Services Office of Inspector General, Centers for Medicare & Medicaid Services ("CMS") and comparable regulatory authorities in state, local and foreign jurisdictions and in other countries impose substantial and burdensome 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 regulate, among other things, the research and development, testing, manufacture, quality control, safety, effectiveness, labeling, storage, record keeping, approval, advertising and promotion, distribution, post-approval monitoring and reporting, sampling and export and import of our product candidates.

U.S. Government Regulation

In the U.S., the FDA regulates drugs under the Federal Food, Drug, and Cosmetic Act ("FDCA") and its implementing regulations, and biological product candidates (“biologics”), under both the FDCA and the Public Health Service Act ("PHSA") and its implementing regulations.

The process of obtaining regulatory approvals and the 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 U.S. requirements at any time during the product development process, approval process or after approval, may subject an applicant to a variety of administrative or judicial sanctions, such as the FDA’s refusal to approve pending applications, withdrawal of an approval, imposition of a clinical hold, issuance of warning 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 penalties.

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

•

completion of pre-clinical laboratory tests, animal studies and formulation studies, certain of which must be conducted in compliance with the FDA’s Good Laboratory Practice (“GLP”) regulations and other applicable regulations;

•

submission to the FDA of an investigational new drug application (an “IND”), which must become effective before human clinical trials may begin;

•

approval by an independent Institutional Review Board (“IRB”) or ethics committee at each clinical site before each trial may be initiated;

•

Good Clinical Practice (“GCP”) requirements to evaluate the safety, purity, potency and/or efficacy of the product candidate for its intended use;

•

submission to the FDA of an NDA or BLA after completion of all pivotal trials;

•

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

•

satisfactory completion of an FDA inspection of the manufacturing facility or facilities at which the product is produced to assess compliance with current Good Manufacturing Practice (“GMP”) 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 potential FDA audits of clinical trials sites and the sponsor’s clinical trial records to assure compliance with GCPs and the integrity of the clinical data; and

•

payment of user fees, if applicable, and FDA review and approval of the NDA or BLA.

Pre-clinical Studies

Once a product candidate is identified for development, it enters the pre-clinical testing stage. Pre-clinical studies include laboratory evaluation of product chemistry, toxicity and formulation, as well as animal studies to assess potential safety and efficacy. An IND sponsor must submit the results of the pre-clinical tests, together with manufacturing information, analytical data and any

available clinical data or literature, among other things, to the FDA as part of an IND. An IND is a request for authorization from the FDA to administer an investigational drug product to humans. An IND will also include a protocol detailing, among other things, the objectives of the clinical trial, the parameters to be used in monitoring safety, and the effectiveness criteria to be evaluated, if the trial includes an efficacy evaluation. Some pre-clinical testing 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. In such a case, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical trial can begin. As a result, submission of an IND may not result in the FDA allowing clinical trials to commence. Clinical holds also may be imposed by the FDA at any time before or during clinical trials due to safety concerns about on-going or proposed clinical trials or non-compliance with specific FDA requirements, and the trials may not begin or continue until the FDA notifies the sponsor that the hold has been lifted.

Clinical Trials

Clinical trials involve the administration of the investigational new drug or biologic to human subjects under the supervision of qualified investigators in accordance with GCP requirements, which among other things, include the requirement that all research subjects provide their informed consent in writing for their participation in any clinical trial. Clinical trials are conducted under protocols detailing, among other things, the objectives or endpoints of the trial, the parameters to be used in monitoring safety, and the effectiveness criteria to be evaluated. A protocol for each clinical trial and any subsequent protocol amendments must be submitted to the FDA as part of the IND. While the IND is active, progress reports summarizing the results of the clinical trials and nonclinical studies performed since the last progress report, among other information, must be submitted at least annually to the FDA, and written IND safety reports must be submitted to the FDA and investigators for serious and unexpected suspected adverse events, findings from other studies suggesting a significant risk to humans exposed to the same or similar drugs, findings from animal or in vitro testing suggesting a significant risk to humans, and any clinically important increased incidence of a serious suspected adverse reaction compared to that listed in the protocol or investigator brochure.

In addition, an IRB must review and approve the plan for a clinical trial. This can be a central or local IRB. In the case of a central IRB a single IRB will be the source of record for all sites in a trial; otherwise, a local IRB at each institution participating in the clinical trial must review and approve the plan for any clinical trial before it commences at that institution. The FDA or the sponsor may suspend a clinical trial at any time on various grounds, including a finding that the research subjects or patients are being exposed to an unacceptable health risk. Similarly, an IRB can suspend or terminate approval of a clinical trial at its institution if the clinical trial is not being conducted in accordance with the IRB’s requirements or if the drug has been associated with unexpected serious harm to patients. In addition, some clinical trials are overseen by an independent group of qualified experts organized by the sponsor, known as a data safety monitoring board or committee. Depending on its charter, this group may determine whether a trial may move forward at designated check points based on access to certain data from the trial. Information about certain clinical trials must also be submitted within specific timeframes to the National Institutes of Health for public dissemination on their website, www.clinicaltrials.gov.

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

•

Phase 1: The product candidate is initially introduced into healthy human subjects or patients with the target disease or condition and tested for safety, dosage tolerance, absorption, metabolism, distribution, excretion and, if possible, to gain an early indication of its effectiveness.

•

Phase 2: The product candidate is administered to a limited patient population 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.

•

Phase 3: The product candidate 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 the labeling of the product.

Post-approval trials, sometimes referred to as Phase 4 studies, 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. In certain instances, the FDA may mandate the performance of Phase 4 clinical trials as a condition of approval of a BLA or NDA.

Concurrent with clinical trials, companies usually complete additional animal studies and must also develop additional information about the chemistry and physical characteristics of the drug and finalize a process for manufacturing the product in commercial quantities in accordance with cGMPs or similar foreign requirements. The manufacturing process must be capable of

consistently producing quality batches of the product candidate and, among other things, the manufacturer must develop methods for testing the identity, strength, quality and purity of the final product. In addition, 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.

Rare Pediatric Disease Priority Review Voucher Program

In 2012, Congress authorized the FDA to award priority review vouchers to sponsors of certain rare pediatric disease product applications. This program is designed to encourage development of new drug and biological products for prevention and treatment of certain rare pediatric diseases. Specifically, under this program, a sponsor who receives an approval for a drug or biologic for a “rare pediatric disease” may qualify for a voucher that can be redeemed to receive a priority review of a subsequent marketing application for a different product.

The sponsor of a rare pediatric disease drug product receiving a priority review voucher may transfer (including by sale) the voucher to another sponsor. The voucher may be further transferred any number of times before the voucher is used, as long as the sponsor making the transfer has not yet submitted the application. The FDA may also revoke any priority review voucher if the rare pediatric disease drug for which the voucher was awarded is not marketed in the U.S. within one year following the date of approval.

For purposes of this program, a “rare pediatric disease” is a (a) serious or life-threatening disease in which the serious or life-threatening manifestations primarily affect individuals aged from birth to 18 years, including age groups often called neonates, infants, children, and adolescents; and (b) rare diseases or conditions within the meaning of the Orphan Drug Act. Congress has only authorized the Rare Pediatric Disease Priority Review Voucher program until September 30, 2029. Consequently, unless Congress reauthorizes the program, the sponsor of the marketing application for a drug that receives Rare Pediatric Disease Designation will only be eligible to receive a voucher if the FDA grants the designation on or before September 30, 2029.

Orphan Product Designation and Exclusivity

Under the Orphan Drug Act, the FDA may grant orphan designation to a drug or biologic product if it is intended to treat a rare disease or condition (generally meaning that it affects fewer than 200,000 individuals in the U.S., or more in cases in which there is no reasonable expectation that the cost of developing and making a drug product available in the U.S. for treatment of the disease or condition will be recovered from sales of the product). A company must request orphan product designation before submitting an NDA or BLA. If the request is granted, the FDA will publicly disclose the identity of the therapeutic agent and its potential use. Orphan product 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 a use or indication within the rare disease or condition for which it has such designation, the product is entitled to orphan-product exclusivity. Orphan-product exclusivity means that the FDA may not approve any other applications for the same drug, as defined by the FDA, for the same approved use or indication within the applicable rare disease or condition for seven years, except in certain limited circumstances. If a product designated as an orphan product ultimately receives marketing approval for disease or condition broader than what was designated in its orphan-product application, it may not be entitled to exclusivity. Orphan exclusivity will not bar approval of another product under certain circumstances, including if a subsequent product with the same active ingredient is shown to be clinically superior to the approved product with respect to the same approved use or indication 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 use or indication within the same rare disease or condition as long as the product candidates contain different active ingredients. Moreover, competitors may receive approval of different product candidates for the same use or indication within the rare disease or condition for which the orphan product has exclusivity or obtain approval for the same product but for a different use or indication.

Marketing Approval

Assuming successful completion of the required clinical testing, the results of the pre-clinical studies and clinical trials, 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 or BLA requesting approval to market the product for one or more indications. In most cases, the submission of an NDA or BLA is subject to a substantial application user fee.

In addition, under the Pediatric Research Equity Act of 2003, as amended and reauthorized (“PREA”), certain NDAs, BLAs or supplements to an NDA or BLA must contain data that are adequate to assess the safety and effectiveness of the product 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, unless the sponsor has received a deferral or waiver. The required assessments must

evaluate the safety and effectiveness of the product for the claimed indications in all relevant pediatric subpopulations and support dosing and administration for each pediatric subpopulation for which the product is safe and effective. The sponsor or FDA may request a deferral of pediatric clinical trials for some or all of the pediatric subpopulations for several reasons, including a finding that the drug is ready for approval for use in adults before pediatric clinical trials are complete or that additional safety or effectiveness data needs to be collected before the pediatric clinical trials begin. The FDA must send a non-compliance letter to any sponsor that fails to submit the required assessment, keep a deferral current or fails to submit a request for approval of a pediatric formulation.

The FDA conducts a preliminary review of all NDAs and BLAs within the first 60 days after submission, 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 application 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 application to determine, among other things, whether the drug is safe and effective (for biologics, the standard is referred to as safe, pure and potent) 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. Under the goals and policies agreed to by the FDA under the Prescription Drug User Fee Act (“PDUFA”) for new molecular entity NDAs and original BLAs, the FDA has 10 months from the filing date in which to complete its initial review of a standard application and respond to the applicant, and six months from the filing date for an application with priority review. This review typically takes 12 months from the date the NDA or BLA is submitted to the FDA, because the FDA has approximately two months to make a “filing” decision.

The FDA may refer an application for a novel drug or biologic candidate 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.

Before approving an application, the FDA typically will inspect the facility or facilities where the product is manufactured. The FDA will not approve an application 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. Additionally, before approving an application, the FDA may inspect the sponsor and one or more clinical trial sites to assure compliance with GCP requirements and the integrity of the clinical data submitted in an NDA.

After evaluating the application 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 that the application will not be approved in its present form. A complete response letter generally details specific conditions that must be met in order to secure approval of the application and may require additional clinical or pre-clinical testing in order for FDA to reconsider the application. 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 product with specific prescribing information for specific indications.

Even if the FDA approves a product, it may limit the approved indications for use of the product, require additional contraindications, warnings or precautions to be included in the product labeling, require that post-approval studies, including Phase 4 clinical trials, be conducted to further assess a product’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. 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 an approved REMS, if required. A REMS could include medication guides, physician communication plans or elements to assure safe use, such as restricted distribution methods, patient registries and other risk minimization tools. Any of these limitations on approval or marketing could restrict the commercial promotion, distribution, prescription or dispensing of products. 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.

Post-Approval Requirements

Drugs and biologics manufactured or distributed pursuant to FDA approvals are subject to pervasive and continuing regulation by the FDA, including, among other things, requirements relating to recordkeeping, periodic reporting, product sampling and distribution, advertising and promotion and reporting of adverse experiences with the product. After approval, most changes to the

approved product, such as adding new indications or other labeling claims are subject to prior FDA review and approval. There also are continuing, annual user fee requirements for any marketed product candidates and the establishments at which such product candidates are manufactured, as well as new application fees for supplemental applications with clinical data.

The FDA may impose a number of post-approval requirements as a condition of approval of an NDA or BLA. For example, the FDA may require post-marketing testing, including Phase 4 clinical trials, and surveillance to further assess and monitor the product’s safety and effectiveness after commercialization.

In addition, manufacturers and other entities involved in the manufacture and distribution of approved product candidates are required to register their establishments with the FDA and state agencies and are subject to periodic unannounced inspections by the FDA and these state agencies for compliance with cGMP requirements. Changes to the manufacturing process are strictly regulated and often require prior FDA approval before being implemented. FDA regulations also require investigation and correction of any deviations from cGMP requirements and impose reporting and documentation requirements upon the sponsor and any third-party manufacturers that the sponsor may decide to use. Accordingly, manufacturers must continue to expend time, money and effort in the area of production and quality control to maintain cGMP compliance.

Once an approval is granted, the FDA may withdraw the approval if compliance with regulatory requirements and standards is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems with a product, including adverse events of unanticipated severity or frequency, or with manufacturing processes, or failure to comply with regulatory requirements, may result in mandatory revisions to the approved labeling to add new safety information; imposition of post-market studies or clinical trials to assess new safety risks; or imposition of distribution or other restrictions under a REMS program. Other potential consequences include, among other things:

•

restrictions on the marketing or manufacturing of the product, complete withdrawal of the product from the market or product recalls;

•

fines, warning letters or holds on post-approval clinical trials;

•

refusal of the FDA to approve pending applications or supplements to approved applications or suspension or revocation of product approvals;

•

product seizure or detention or refusal to permit the import or export of product candidates;

•

injunctions or the imposition of civil or criminal penalties;

•

consent decrees, corporate integrity agreements, debarment or exclusion from federal healthcare programs;

•

mandated modification of promotional materials and labeling and the issuance of corrective information; or

•

the FDA or other regulatory authorities may issue safety alerts, “Dear Healthcare Provider” letters, press releases or other communications containing warnings or other safety information about the product.

The FDA strictly regulates marketing, labeling, advertising and promotion of product candidates that are placed on the market. Product candidates may be promoted only for the approved indications and in accordance with the provisions of the approved label. Physicians may prescribe legally available products for uses that are not described in the product’s labeling and that differ from those approved by the FDA. Such off-label uses are common across medical specialties. Physicians may believe that such off-label uses are the best treatment for many patients in varied circumstances. The FDA does not regulate the behavior of physicians in their choice of treatments. The FDA does, however, restrict manufacturer’s communications on the subject of off-label use of their products. The FDA and other agencies actively enforce the laws and regulations prohibiting the promotion of off-label uses, and a company that is found to have improperly promoted off-label uses may be subject to significant liability.

Special FDA Expedited Review and Approval

The FDA has various programs, such as Fast Track designation, Breakthrough Therapy designation, accelerated approval, and priority review, which are intended to expedite or simplify the process for the development and FDA review of drugs and biologics that are intended for the treatment of serious or life-threatening diseases or conditions and demonstrate the potential to address unmet medical needs.

To be eligible for a Fast Track designation, the FDA must determine, based on the request of a sponsor, that a product candidate is intended to treat a serious or life-threatening disease or condition and demonstrates the potential to address an unmet medical need for such disease or condition. Fast Track designation provides opportunities for frequent interactions with the FDA review team to expedite development and review of the product. The FDA may also review sections of the NDA or BLA for a Fast Track-designated product on a rolling basis before the complete application is submitted, if the sponsor and FDA agree on a schedule for the submission of the application sections, and the sponsor pays any required user fees upon submission of the first section of the NDA or BLA.

In addition, a sponsor can request designation of a product as a “Breakthrough Therapy.” A Breakthrough Therapy is defined as a drug or biologic that is intended, alone or in combination with one or more other drugs or biologics, to treat a serious or life-threatening disease or condition, and preliminary clinical evidence indicates that the drug or biologic may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. The designation includes all of the Fast Track program features, as well as more intensive FDA interaction and guidance beginning as early as Phase 1 and an organizational commitment to expedite the development and review of the product candidate, including involvement of senior managers.

Depending on the design of the relevant clinical studies, product candidates studied for their safety and effectiveness in treating serious or life-threatening illnesses and that have the potential to provide meaningful therapeutic benefit over existing treatments may be eligible for accelerated approval upon a determination the product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality (“IMM”) that is reasonably likely to predict an effect on IMM or other clinical benefit, taking into account the severity, rarity or prevalence of the condition and the availability or lack of alternative treatments. As a condition of approval, the FDA generally require a sponsor of a product receiving accelerated approval to perform adequate and well-controlled confirmatory trials to verify and describe the predicted clinical benefit, and may require that such confirmatory trails be underway prior to granting any accelerated approval. Products receiving accelerated approval may be subject to expedited withdrawal procedures if the sponsor fails to conduct the required confirmatory trials in a timely manner or if such trials fail to verify the predicted clinical benefit. Sponsors of such products are also required to send updates to the FDA every 180 days regarding the progress of any required confirmatory studies. In addition, the FDA requires pre-approval of promotional materials a condition of accelerated approval, which could adversely impact the timing of the commercial launch of the product.

Once an NDA or BLA is submitted for a product intended to treat a serious condition, the FDA may assign a priority review designation to the application if the FDA determines that the product candidate, if approved, would provide a significant improvement in safety or effectiveness. The FDA will attempt to direct additional resources to the evaluation of an NDA or BLA designated for priority review in an effort to facilitate the review. The FDA endeavors to review NDAs for new molecular entities and original BLAs with priority review designations within six months of the filing date as compared to ten months under its current review goals.

Fast Track designation, Breakthrough Therapy designation, priority review, and accelerated approval do not change the standards for approval but may ultimately expedite the development or approval process. Even if a product qualifies for one or more of these programs, the FDA may later decide that the product no longer meets the conditions for qualification or decide that the time period for FDA review or approval will not be shortened.

Drug and Biological Product Exclusivities

Market exclusivity provisions authorized under the FDCA can delay the submission or the approval of some marketing applications. For example, the FDCA provides a five-year period of non-patent data exclusivity within the U.S. to the first applicant to obtain approval of an NDA for a new chemical entity. A drug is a new chemical entity if the FDA has not previously approved any other new drug containing the same active moiety, which is the molecule or ion, excluding those appended portions of the molecule that cause the drug to be an ester, salt, including a salt with hydrogen or coordination bonds, or other noncovalent derivative, such as a complex, chelate, or clathrate, responsible for the action of the drug substance. During the exclusivity period, the FDA may not approve or even accept for review an abbreviated new drug application (“ANDA”) or an NDA submitted under Section 505(b)(2) (“505(b)(2) NDA”), submitted by another company for another drug based on the same active moiety, regardless of whether the drug is intended for the same indication as the original innovative drug or for another indication, where the applicant does not own or have a legal right of reference to all the data required for approval. However, an application may be submitted after four years if it contains a certification of patent invalidity or non-infringement to one of the patents listed with the FDA by the innovator NDA holder.

The FDCA alternatively provides three years of non-patent exclusivity for an NDA, or supplement to an existing NDA if new clinical investigations, other than bioavailability studies, that were conducted or sponsored by the applicant are deemed by the FDA to be essential to the approval of the application, for example, for new indications, dosages or strengths of an existing drug. This three-year exclusivity covers only the conditions of approval for which the drug received approval on the basis of the new clinical

investigations and does not prohibit the FDA from approving ANDAs or 505(b) (2) NDAs for drugs containing the active agent for the original indication or condition of use. Five-year and three-year exclusivity will not delay the submission or approval of a full NDA. However, an applicant submitting a full NDA would be required to conduct or obtain a right of reference to any pre-clinical studies and adequate and well-controlled clinical trials necessary to demonstrate safety and effectiveness.

In addition, the Biologics Price Competition and Innovation Act of 2009 ("BPCIA"), created an abbreviated approval pathway for biological products that are highly similar, or “biosimilar,” to or interchangeable with an FDA-approved reference biological product. The FDA has issued several guidance documents outlining an approach to review and approval of biosimilars. Biosimilarity, which requires that there be no clinically meaningful differences between the biological product and the reference product in terms of safety, purity, and potency, is generally shown through analytical studies, animal studies, and a clinical study or studies. Interchangeability requires that a product is biosimilar to the reference product and the product must demonstrate that it can be expected to produce the same clinical results as the reference product in any given patient and, for products that are administered multiple times to an individual, the biologic and the reference biologic may be alternated or switched after one has been previously administered without increasing safety risks or risks of diminished efficacy relative to exclusive use of the reference biologic. A product shown to be biosimilar or interchangeable with an FDA-approved reference biological product may rely in part on the FDA’s previous determination of safety and effectiveness for the reference product for approval, which can potentially reduce the cost and time required to obtain approval to market the product.

Under the BPCIA, an application for a biosimilar product may not be submitted to the FDA until four years following the date that the reference product was first licensed by the FDA. In addition, the approval of a biosimilar product may not be made effective by the FDA until 12 years from the date on which the reference product was first licensed. During this 12-year period of exclusivity, another company may still market a competing version of the reference product if the FDA approves a full BLA for the competing product containing that applicant’s own pre-clinical data and data from adequate and well-controlled clinical trials to demonstrate the safety, purity and potency of its product.

Pediatric exclusivity is another type of regulatory exclusivity available in the U.S. Pediatric exclusivity provides for an additional six months of exclusivity attached to another existing patent term or period of regulatory exclusivity if a sponsor conducts clinical trials in children in response to a “written request” from the FDA. The issuance of a written request does not require the sponsor to undertake the described clinical trials.

Foreign Government Regulation

Our product candidates are subject to similar laws and regulations imposed by jurisdictions outside of the U.S., and, in particular, the European Union (“EU”), governing, among other things, clinical trials, marketing authorization (“MA”), commercial sales and distribution of our products. The foreign regulatory approval process includes all of the risks associated with FDA approval set forth above, as well as additional country-specific regulation. Because biologically sourced, raw materials are subject to unique contamination risks and their use may be restricted in some countries.

Whether or not we obtain FDA approval for a product, we must obtain approval of a product by the comparable regulatory authorities of foreign countries before we can commence clinical trials or marketing of the product in those countries. Approval by one regulatory authority does not ensure approval by regulatory authorities in other jurisdictions. The approval process varies from country to country, can involve additional testing beyond that required by FDA, and may be longer or shorter than that required for FDA approval. The requirements governing the conduct of clinical trials, product licensing, pricing, promotion, and reimbursement vary greatly from country to country.

Non-clinical Studies and Clinical Trials

Similarly to the U.S., the various phases of non-clinical and clinical research in the EU, are subject to significant regulatory controls.

Non-clinical studies are performed to demonstrate the health or environmental safety of new chemical or biological substances. Non-clinical (pharmaco-toxicological) studies must be conducted in compliance with the principles of GLP, as set forth in EU Directive 2004/10/EC (unless otherwise justified for certain particular medicinal products - e.g., radio-pharmaceutical precursors for radio-labeling purposes). In particular, non-clinical studies, both in vitro and in vivo, must be planned, performed, monitored, recorded, reported and archived in accordance with the GLP principles, which define a set of rules and criteria for a quality system for the organizational process and the conditions for non-clinical studies. These GLP standards reflect the Organization for Economic Co-operation and Development requirements.

Clinical trials of medicinal products in the EU must be conducted in accordance with EU and national regulations and the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (“ICH”) guidelines on Good Clinical Practices (“GCP”) as well as the applicable regulatory requirements and the ethical principles that have their origin in the Declaration of Helsinki. If the sponsor of the clinical trial is not established within the EU, it must appoint an EU entity to act as its legal representative. The sponsor must take out a clinical trial insurance policy, and in most EU member states, the sponsor is liable to provide ‘no fault’ compensation to any study subject injured in the clinical trial.

The regulatory landscape related to clinical trials in the EU has been subject to recent changes. The EU Clinical Trials Regulation (“CTR”) which was adopted in April 2014 and repeals the EU Clinical Trials Directive, became applicable on January 31, 2022. Unlike directives, the CTR is directly applicable in all EU member states without the need for member states to further implement it into national law. The CTR notably harmonizes the assessment and supervision processes for clinical trials throughout the EU via a Clinical Trials Information System, which contains a centralized EU portal and database.

While the EU Clinical Trials Directive required a separate clinical trial application (“CTA”) to be submitted in each member state in which the clinical trial takes place, to both the competent national health authority and an independent ethics committee, much like the FDA and IRB respectively, the CTR introduces a centralized process and only requires the submission of a single application for multi-center trials. The CTR allows sponsors to make a single submission to both the competent authority and an ethics committee in each member state, leading to a single decision per member state. The CTA must include, among other things, a copy of the trial protocol and an investigational medicinal product dossier containing information about the manufacture and quality of the medicinal product under investigation. The assessment procedure of the CTA has been harmonized as well, including a joint assessment by all member states concerned, and a separate assessment by each member state with respect to specific requirements related to its own territory, including ethics rules. Each member state’s decision is communicated to the sponsor via the centralized EU portal. Once the CTA is approved, clinical study development may proceed.

The CTR transition period ended on January 31, 2025, and all clinical trials (and related applications) are now fully subject to the provisions of the CTR.

Medicines used in clinical trials must be manufactured in accordance with GMP. Other national and EU-wide regulatory requirements may also apply.

Marketing Authorization

In order to market our product candidates in the EU, and many other foreign jurisdictions, we must obtain separate regulatory approvals. More concretely, in the EU, medicinal product candidates can only be commercialized after obtaining a MA. To obtain regulatory approval of a product candidate under EU regulatory systems, we must submit a MA application (“MAA”). The process for doing this depends, among other things, on the nature of the medicinal product. There are two types of MAs:

•

“Centralized MAs” are issued by the EC through the centralized procedure, based on the opinion of the Committee for Medicinal Products for Human Use (“CHMP”) of the European Medicines Agency (“EMA”) and are valid throughout the EU. The centralized procedure is mandatory for certain types of medicinal products, such as (i) medicinal products derived from biotechnological processes, (ii) designated orphan medicinal products, (iii) advanced therapy medicinal products (“ATMPs”) (such as gene therapy, somatic cell therapy and tissue engineered products) and (iv) medicinal products containing a new active substance indicated for the treatment of certain diseases, such as HIV/AIDS, cancer, neurodegenerative diseases, diabetes, autoimmune diseases and other immune dysfunctions, and viral diseases. The centralized procedure is optional for products containing a new active substance not yet authorized in the EU, or for products that constitute a significant therapeutic, scientific or technical innovation or which are in the interest of public health in the EU; and

•

“National MAs” are issued by the competent authorities of the EU member states, only cover their respective territory, and are available for product candidates not falling within the mandatory scope of the centralized procedure. Where a product has already been authorized for marketing in an EU member state, this national MA can be recognized in another member state through the mutual recognition procedure. If the product has not received a national MA in any member state at the time of application, it can be approved simultaneously in various member states through the decentralized procedure. Under the decentralized procedure an identical dossier is submitted to the competent authorities of each of the member states in which the MA is sought, one of which is selected by the applicant as the reference member state.

Under the centralized procedure the maximum timeframe for the evaluation of an MAA by the EMA is 210 days, excluding clock stops. In exceptional cases, the CHMP might perform an accelerated review of a MAA in no more than 150 days (not including clock stops). Innovative products that target an unmet medical need and are expected to be of major public health interest may be eligible for a number of expedited development and review programs, such as the PRIME scheme, which provides incentives similar

to the Breakthrough Therapy designation in the U.S. In March 2016, the EMA launched the PRIME scheme. PRIME is a voluntary scheme aimed at enhancing the EMA’s support for the development of medicines that target unmet medical needs. It is based on increased interaction and early dialogue with companies developing promising medicines, to optimize their product development plans and speed up their evaluation to help them reach patients earlier. Product developers that benefit from PRIME designation can expect to be eligible for accelerated assessment, but this is not guaranteed. An initial meeting initiates these relationships and includes a team of multidisciplinary experts at the EMA to provide guidance on the overall development and regulatory strategies. The benefits of a PRIME designation includes, but not limited to, the appointment of a dedicated contact and rapporteur from the CHMP before submission of an MAA, early and proactive dialogue and scientific advice at key development milestones, and the ability to request for accelerated review earlier in the application process, however this is at the discretion of the CHMP. Setrusumab was granted PRIME designation in November 2017.

Moreover, in the EU, a “conditional” MA may be granted in cases where all the required safety and efficacy data are not yet available. The conditional MA is subject to conditions to be fulfilled for generating the missing data or ensuring increased safety measures. It is valid for one year and has to be renewed annually until fulfillment of all the conditions. Once the pending studies are provided, it can become a “standard” MA. However, if the conditions are not fulfilled within the timeframe (timelines may be re-negotiated with CHMP approval if appropriate) set by the EMA, the MA ceases to be renewed. The EMA may also grant a MA in absence of comprehensive data under “exceptional circumstances”. Unlike a conditional MA, where MA is granted in the likelihood that the sponsor will provide such data within an agreed timeframe, the EMA can grant authorization under exceptional circumstances when comprehensive data cannot be obtained even after authorization.

Under the above described procedures, before granting the MA, the CHMP or the competent authorities of the EU member states make an assessment of the risk-benefit balance of the product on the basis of scientific criteria concerning its quality, safety and efficacy. MAs have an initial duration of five years. After these five years, the authorization may be renewed on the basis of a reevaluation of the risk-benefit balance.

Adaptive pathways

The EMA has an adaptive pathways program which allows for early and progressive patient access to a medicine. The adaptive pathways concept is an approach to medicines approval that aims to improve patients’ access to medicines in cases of high unmet medical need. To achieve this goal, several approaches are envisaged: identifying small populations with severe disease where a medicine’s benefit-risk balance could be favorable; making more use of real-world data where appropriate to support clinical trial data; and involving health technology assessment (“HTA”) bodies early in development to increase the chance that medicines will be recommended for payment and ultimately covered by national healthcare systems. The adaptive pathways concept applies primarily to treatments in areas of high medical need where it is difficult to collect data via traditional routes and where large clinical trials would unnecessarily expose patients who are unlikely to benefit from the medicine. The approach builds on regulatory processes already in place within the existing EU legal framework. These include: scientific advice; compassionate use; the conditional approval mechanism (for medicines addressing life-threatening conditions); patient registries and other pharmacovigilance tools that allow collection of real-life data and development of a risk-management plan for each medicine.

The adaptive pathways program does not change the standards for the evaluation of benefits and risks or the requirement to demonstrate a positive benefit-risk balance to obtain MA. In February 2017, setrusumab was accepted into the adaptive pathways program.

Data and marketing exclusivity

In the EU, new product candidates authorized for marketing, or reference product candidates, generally receive eight years of data exclusivity and an additional two years of market exclusivity upon MA. If granted the data exclusivity period prevents generic or biosimilar applicants from relying on the preclinical and clinical trial data contained in the dossier of the reference product when applying for a generic or biosimilar MA in the EU during a period of eight years from the date on which the reference product was first authorized in the EU. The market exclusivity period prevents a successful generic or biosimilar applicant from commercializing its product in the EU until ten-years have elapsed from the initial MA of the reference product in the EU. The overall 10-year market exclusivity period can be extended to a maximum of eleven years if, during the first eight years of those ten years, the MA holder obtains an authorization for one or more new therapeutic indications which, during the scientific evaluation prior to their authorization, are held to bring a significant clinical benefit in comparison with existing therapies. However, there is no guarantee that a product will be considered by the EU’s regulatory authorities to be a new chemical or biological entity, and products may not qualify for data exclusivity.

There is a special regime for biosimilars, or biological medicinal products that are similar to a reference medicinal product but that do not meet the definition of a generic medicinal product, for example, because of differences in raw materials or manufacturing processes. For such products, the results of appropriate pre-clinical or clinical trials must be provided, and guidelines

from the EMA detail the type of quantity of supplementary data to be provided for different types of biological product. There are no such guidelines for complex biological products, such as gene or cell therapy medicinal products, and so it is unlikely that biosimilars of those products will currently be approved in the EU. However, guidance from the EMA states that they will be considered in the future in light of the scientific knowledge and regulatory experience gained at the time.

Orphan Medicinal Products

The criteria for designating an “orphan medicinal product” in the EU are similar in principle to those in the U.S. A medicinal product can be designated as an orphan if its sponsor can establish that: (1) the product is intended for the diagnosis, prevention or treatment of a life threatening or chronically debilitating condition, (2) either (a) affecting not more than five in 10,000 persons in the EU when the application is made, or (b) that the product without the benefits derived from the orphan status, would not generate sufficient return in the EU to justify the necessary investment; and (3) there exists no satisfactory method of diagnosis, prevention or treatment of the condition in question that has been authorized for marketing in the EU or, if such method exists, the product will be of significant benefit to those affected by that condition.

Orphan designation must be requested before submitting an MAA. Orphan designation entitles a party to incentives such as reduction of fees or fee waivers, protocol assistance, and access to the centralized procedure. Upon grant of a MA for an orphan medicinal product, applicants are entitled to a ten-year period of market exclusivity for the approved indication. During this market exclusivity period, the competent authorities cannot accept another application for a MA, or grant a MA, or accept an application to extend a MA for a similar medicinal product for the same indication. The period of market exclusivity is extended by two years for orphan medicinal products that have also complied with an agreed PIP. No extension to any supplementary protection certificate can be granted on the basis of pediatric studies for orphan indications. Orphan designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process. This period of orphan market exclusivity may, however, be reduced to six years if, at the end of the fifth year, it is established that the product no longer meets the criteria for which it received orphan destination, i.e. the prevalence of the condition has increased above the threshold or it is judged that the product is sufficiently profitable not to justify maintenance of market exclusivity. Additionally, MA may be granted for another similar product for the same indication at any time if (i) the applicant can establish that its product, although similar, is safer, more effective or otherwise clinically superior; (ii) the applicant consents to a second orphan medicinal product application; or (iii) the applicant cannot supply enough orphan medicinal product.

Pediatric Development

In the EU MAA for new medicinal product candidates have to include the results of studies conducted in the pediatric population, in compliance with a PIP, agreed with the EMA’s Pediatric Committee (“PDCO”). The PIP sets out the timing and measures proposed to generate data to support a pediatric indication of the product candidate for which MA is being sought. The PDCO can grant a deferral of the obligation to implement some or all of the measures of the PIP until there are sufficient data to demonstrate the efficacy and safety of the product in adults. Further, the obligation to provide pediatric clinical trial data can be waived by the PDCO when these data are not needed or appropriate because the product is likely to be ineffective or unsafe in children, the disease or condition for which the product is intended occurs only in adult populations, or when the product does not represent a significant therapeutic benefit over existing treatments for pediatric patients. Once the MA is obtained in all member states of the EU and study results are included in the product information, even when negative, the product is eligible for a six-month supplementary protection certificate extension (if any is in effect at the time of approval) or, in the case of orphan medicinal products, a two-year extension of orphan market exclusivity.

Post-Approval Requirements

Similar to the U.S., both MA holders and manufacturers of medicinal products are subject to comprehensive regulatory oversight by the EMA, the EC and/or the competent regulatory authorities of the member states. The holder of a MA must establish and maintain a pharmacovigilance system and appoint an individual qualified person for pharmacovigilance (“QPPV”) who is responsible for the establishment and maintenance of that system, and oversees the safety profiles of medicinal products and any emerging safety concerns. Key obligations include expedited reporting of suspected serious adverse reactions and submission of periodic safety update reports, or PSURs.

All new MAA must include a risk management plan (“RMP”) describing the risk management system that the company will put in place and documenting measures to prevent or minimize the risks associated with the product. The RMP must be updated any time new information on the medicinal product becomes available which has a significant impact on the content of the RMP. The regulatory authorities may also impose specific obligations as a condition of the MA. Such risk-minimization measures or post-authorization obligations may include additional safety monitoring, more frequent submission of PSURs, or the conduct of additional clinical trials or post-authorization safety studies.

MREO US Equity

MREO · 10-K · period ended 2025-12-31

Item 1. Business

MREO US Equity☆

MREO · 10-K · period ended 2025-12-31

Item 1. Business

MREO US Equity