UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): August 11, 2026

MEREO BIOPHARMA GROUP PLC

(Exact name of registrant as specified in its charter)

4th Floor, One Cavendish Place,

London, W1G 0QF

United Kingdom

(Address of principal executive offices, including zip code)

+44-333-023-7300

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

*Not for trading, but only in connection with the listing of the American Depositary Shares on The Nasdaq Stock Market LLC.

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

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. ☐

Item 1.01 Entry into a Material Definitive Agreement

On August 11, 2026, Mereo BioPharma Group plc (the “Company” or "Mereo") entered into an Option and License Agreement (the “Agreement”) with Sentynl Therapeutics, Inc. (“Sentynl”), a U.S.-based biopharmaceutical company, for the U.S. commercial and global manufacturing rights to alvelestat for alpha-1 antitrypsin deficiency-associated lung disease (“AATD-LD”). Under the Agreement, Mereo will receive a non-refundable option fee and, on option exercise, is eligible to receive $40 million in upfront and R&D payments, up to $435 million in potential milestones, and double-digit tiered royalties on U.S. sales of alvelestat. Mereo will lead the global Phase 3 study and regulatory interactions until the study is completed. During the option period, the Company and Sentynl will collaborate to advance manufacturing and refine the Phase 3 study design.

The Agreement contains various representations, warranties, covenants, dispute resolution mechanisms, indemnities and other provisions customary for transactions of this nature.

The foregoing description of the Agreement does not purport to be complete and is qualified in its entirety by the terms of the Agreement. A copy of the Agreement is expected to be filed as an exhibit to the Company’s Quarterly Report on Form 10-Q for the fiscal quarter ending September 30, 2026.

Item 7.01 Regulation FD Disclosure.

On August 11, 2026, the Company issued a press release relating to the Agreement discussed in Item 1.01. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The information contained in this Item 7.01, including Exhibit 99.1 shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liability of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the “Securities Act”) or the Exchange Act, except as shall be expressly set forth by reference in such a filing.

Forward Looking Statements

This Current Report on Form 8-K contains “forward-looking statements.” All statements other than statements of historical fact contained herein are forward-looking statements within the meaning of Section 27A of the Securities Act, and Section 21E of the Exchange Act. Forward-looking statements usually relate to future events and anticipated revenues, earnings, cash flows or other aspects of the Company’s operations or operating results. Forward-looking statements are often identified by the words “believe,” “expect,” “anticipate,” “plan,” “intend,” “foresee,” “should,” “would,” “could,” “may,” “estimate,” “outlook,” “will,” “continue” and similar expressions, including the negative thereof. The absence of these words, however, does not mean that the statements are not forward-looking. These forward-looking statements are based on Mereo’s current expectations, beliefs and assumptions concerning future developments and business conditions and their potential effect on Mereo. While management believes that these forward-looking statements are reasonable as and when made, there can be no assurance that future developments affecting Mereo will be those that it anticipates. All of Mereo’s forward-looking statements involve known and unknown risks and uncertainties some of which are significant or beyond its control and assumptions that could cause actual results to differ materially from Mereo’s historical experience and its present expectations or projections. Such risks and uncertainties include, among others, the uncertainties inherent in the clinical development process; Mereo’s reliance on third parties to conduct 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; Mereo’s dependence on enrollment of patients in its clinical trials; potentially smaller than anticipated market opportunities for Mereo’s product candidates; Mereo’s dependence on its key executives; the Company’s dependence on its strategic partners; and the Company’s ability to maintain compliance with Nasdaq continued listing requirements. You should carefully consider the foregoing factors and the other risks and uncertainties that affect Mereo’s business, including those described in the “Risk Factors” section of its latest Annual Report on Form 10-K, as well as discussions of potential risks, uncertainties, and other important factors in Mereo’s subsequent filings with the Securities and Exchange Commission. Mereo wishes to caution you not to place undue reliance on any forward-looking statements, which speak only as of the date hereof. Mereo undertakes no obligation to publicly update or revise any of our forward-looking statements after the date they are made, whether as a result of new information, future events or otherwise, except to the extent required by law.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized.