UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

MBX Biosciences, Inc.

(Exact name of Registrant as Specified in Its Charter)

(Former Name or Former Address, if Changed Since Last Report)

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:

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 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

Effective as of April 7, 2025, the board of directors (the “Board”) of MBX Biosciences, Inc. (the “Company”), upon the recommendation of the Nominating and Corporate Governance Committee of the Board (the “NCG Committee”), appointed Steven L. Hoerter as a director of the Company. The Board determined that Mr. Hoerter is independent under the applicable listing standards of The Nasdaq Stock Market (“Nasdaq”). In connection with the appointment, the Board approved an increase in the size of the Board from eight to nine members.

Mr. Hoerter has been designated as a Class III director, to serve until the Company’s 2027 Annual Meeting of Stockholders, in accordance with the Company’s amended and restated by-laws and to serve thereafter until his successor has been duly elected and qualified or until his earlier death, removal or resignation.

In connection with his appointment as a non-employee director, Mr. Hoerter will receive the same compensation paid to other non-employee directors, which is described under the caption "Non-employee director compensation policy" in the Company's prospectus dated September 12, 2024 filed on September 13, 2024. In addition, in connection with his election, the Company is entering into an indemnification agreement with Mr. Hoerter in the same form as used with the Company’s other directors.

There are no arrangements or understandings between Mr. Hoerter and any other persons pursuant to which he was selected as a director of the Company, and there are no transactions in which Mr. Hoerter has an interest requiring disclosure under Item 404(a) of Regulation S-K.

The compositions of the Compensation Committee, Nominating and Corporate Governance Committee, Audit Committee and Science and Medicine Committee remain unchanged.

Item 7.01 Regulation FD Disclosure.

On April 7, 2025, the Company issued a press release announcing Mr. Hoerter’s appointment to the Board. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K.

The information in Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1, is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that Section, nor shall it be deemed subject to the requirements of amended Item 10 of Regulation S-K, nor shall it be deemed incorporated by reference into any filing of the Company under the Securities Act of 1933, as amended, or the Exchange Act, whether made before or after the date hereof, regardless of any general incorporation language in such filing. The furnishing of this information hereby shall not be deemed an admission as to the materiality of any such information.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

SIGNATURES

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

EX-99.1

MBX Biosciences Appoints Veteran Pharmaceutical Executive Steve Hoerter to Board of Directors

Hoerter brings decades of pharmaceutical commercialization, leadership, and board experience to help guide MBX’s next phase of growth

CARMEL, Ind., April 7, 2025 (GLOBE NEWSWIRE) -- MBX Biosciences, Inc. (Nasdaq: MBX), a clinical-stage biopharmaceutical company focused on the discovery and development of novel precision peptide therapies for the treatment of endocrine and metabolic disorders, today announced the appointment of Steve Hoerter as an independent director to the Company’s Board of Directors. Mr. Hoerter brings over three decades of pharmaceutical commercialization and executive leadership experience as well as a proven track record of building and growing life science companies.

“I am thrilled to welcome Steve Hoerter to the Company’s Board as an independent director,” said Kent Hawryluk, President and Chief Executive Officer of MBX Biosciences. “As a seasoned leader within the biopharmaceutical industry, Steve has scaled multiple biotech companies into revenue-generating commercial enterprises. We look forward to benefiting from his contributions as we advance MBX Biosciences’ growing pipeline of programs in endocrine and metabolic disorders, including hypoparathyroidism, post-bariatric hypoglycemia, and obesity.”

Steve Hoerter said, “It is an exciting time to join the MBX Biosciences’ Board as an independent director and I look forward to joining such an esteemed group of industry leaders. The Company’s portfolio of innovative Precision Endocrine Peptides™ and its experienced management team represent clear competitive advantages for the Company, and I am excited to collaborate with this group as we endeavor to deliver differentiated endocrine and metabolic compounds to underserved patients.”

Mr. Hoerter previously served as President, Chief Executive Officer and Director of Deciphera Pharmaceuticals until its $2.4 billion acquisition by Ono Pharmaceutical in 2024. Prior to leading Deciphera, Mr. Hoerter served in senior commercial leadership roles at Agios Pharmaceuticals, Clovis Oncology, Roche and Genentech. Mr. Hoerter currently serves as a Board member at ORIC Pharmaceuticals and as a member of its Audit and Compensation committees, and as a board member at C4 Therapeutics. Mr. Hoerter’s previous board experience includes Constellation Pharmaceuticals, which was acquired by Morphosys in 2021 for $1.7 billion, and Ignyta, which was acquired by Roche in 2017 for $1.7 billion. He holds a B.A. in Russian and Political Science from Bucknell University, PA; an M.B.A. from TIAS Business School, Tilburg University, The Netherlands; and a M.Sc. in Management from Krannert School of Management, Purdue University, IN.

About MBX Biosciences

MBX Biosciences is a biopharmaceutical company focused on the discovery and development of novel precision peptide therapies based on its proprietary PEP™ platform, for the treatment

of endocrine and metabolic disorders. The Company is advancing a pipeline of novel candidates for endocrine and metabolic disorders with clinically validated targets, established endpoints for regulatory approval, significant unmet medical needs and large potential market opportunities. The Company’s pipeline includes its lead product candidate canvuparatide (MBX 2109), in Phase 2 development for the treatment of chronic hypoparathyroidism (HP); MBX 1416, in Phase 1 development for the treatment of post-bariatric hypoglycemia (PBH); and an obesity portfolio that includes MBX 4291, with an IND filing anticipated in Q2 2025, as well as multiple discovery and pre-clinical candidates in development for the treatment of obesity. The Company is based in Carmel, Indiana. To learn more, please visit the Company website at www.mbxbio.com and follow it on LinkedIn.

Forward-Looking Statements

This press release contains “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, each as amended. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “target,” “would” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. These forward-looking statements include, but are not limited to, express or implied statements regarding: MBX Biosciences’ expectations regarding the further advancement of its pipeline of programs in endocrine and metabolic disorders; statements regarding MBX Biosciences' delivery of differentiated endocrine and metabolic compounds to underserved patients; and the contributions of its board of directors.

Forward-looking statements are based on management’s current expectations and are subject to risks and uncertainties that could negatively affect MBX Biosciences’ business, operating results, financial condition and stock value. Factors that could cause actual results to differ materially from those currently anticipated include: risks relating to the Company’s research and development activities; MBX Biosciences’ ability to execute on its strategy including obtaining the requisite regulatory approvals on the expected timeline, if at all; uncertainties relating to preclinical and clinical development activities; the Company’s dependence on third parties to conduct clinical trials, manufacture its product candidates and develop and commercialize its product candidates, if approved; MBX Biosciences’ ability to attract, integrate and retain key personnel; risks related to the Company’s financial condition and need for substantial additional funds in order to complete development activities and commercialize a product candidate, if approved; risks related to regulatory developments and approval processes of the U.S. Food and Drug Administration and comparable foreign regulatory authorities; risks related to establishing and maintaining MBX Biosciences’ intellectual property protections; and risks related to the competitive landscape for MBX Biosciences’ product candidates; as well as other risks described in “Risk Factors,” in MBX Biosciences’ Annual Report on Form 10-K for the year ended December 31, 2024 filed with the Securities and Exchange Commission (SEC), as well as subsequent filings with the SEC. MBX Biosciences expressly disclaims any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in its expectations or any changes in events, conditions or circumstances on which any such statement is based, except as required by law, and claims the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995.

MBX uses and intends to continue to use its Investor Relations website as a means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor the Company's Investor Relations

website, in addition to following the Company's press releases, SEC filings, public conference calls, presentations, and webcasts.

Media Contact: Katie Beach Oltsik Inizio Evoke Comms katie.beach@inizioevoke.com (937) 232-4889

Investor Contact:

Jim DeNike

MBX Biosciences

jdenike@mbxbio.com