Mereo BioPharma Group plc

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K

For the fiscal year ended December 31,2024

OR

For the transition period from to

Commission File Number 001-38452

(Exact name of Registrant as specified in its charter)

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

• 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.

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, 2024, the last business day of the registrant’s most recently completed second fiscal quarter, was approximately $ 471,388,208.

As of March 25, 2025 the number of outstanding ordinary shares, par value £0.003 per share, of the registrant was 795,001,444

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive Proxy Statement relating to its 2025 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

CERTAIN DEFINITIONS

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

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“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;

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

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

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

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

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

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“BLA” are to Biologics License Application;

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“CMO” are to contract manufacturing organization;

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

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“CRO” are to contract research organization;

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“EMA” are to European Medicines Agency;

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

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

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

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

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

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

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“MAA” are to Marketing Authorization Application;

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

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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”);

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

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“NDA” are to New Drug Application;

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

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

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

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

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

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

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

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“Ultragenyx” are to Ultragenyx Pharmaceutical, Inc.;

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

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“£,” “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 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. In some cases, you can identify forward-looking statements by words such as “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect” or the negative of these words or other comparable terminology.

Any forward-looking statements in this Annual Report reflect our current views with respect to future 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, those listed 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.

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

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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.

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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.

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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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