MBX Biosciences Inc. filed SEC Form 8-K: Entry into a Material Definitive Agreement, Financial Statements and Exhibits

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

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:

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 1.01 Entry into a Material Definitive Agreement.

On September 24, 2025, MBX Biosciences, Inc. (the “Company”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with J.P. Morgan Securities LLC and Jefferies LLC, as representatives of the several underwriters (collectively, the “Underwriters”), related to an underwritten public offering (the “Offering”) of 11,108,055 shares of the Company’s common stock, par value $0.0001 per share (“Common Stock”), at a purchase price per share of $18.00 (the "Offering Price"). Pursuant to the Underwriting Agreement, the Company granted the Underwriters a 30-day option to purchase up to an additional 1,666,208 shares of Common Stock at the Offering Price, less any underwriting discounts and commissions. The Offering closed on September 26, 2025.

The Common Stock was offered and sold to the public pursuant to the Company’s registration statement on Form S-1 (File No. 333-290447) and Form S-1MEF (File No. 333-290498), filed by the Company with the Securities and Exchange Commission (the “SEC”) under the Securities Act of 1933, as amended (the “Securities Act”), on September 22, 2025 and September 24, 2025, respectively, which became effective on September 24, 2025.

Net proceeds from the Offering were approximately $187.5 million, after deducting the underwriting discounts and commissions and other estimated offering expenses payable by the Company. The Company intends to use the net proceeds from the Offering, together with its existing cash, cash equivalents and short-term investments, primarily to advance development of its three clinical-stage programs and the remainder to fund its discovery research and development activities and additional clinical development, and for general corporate purposes, working capital and capital expenditures.

The Underwriting Agreement contains customary representations, warranties and covenants by the Company. It also provides for customary indemnification by each of the Company and the underwriters for losses or damages arising out of or in connection with the Offering, including for liabilities under the Securities Act, other obligations of the parties and termination provisions. The provisions of the Underwriting Agreement, including the representations and warranties contained therein, are not for the benefit of any party other than the parties to such agreement and are not intended as a document for investors or the public to obtain factual information about the current state of affairs of the Company.

The foregoing summary of the terms of the Underwriting Agreement is subject to, and qualified in its entirety by, the full text of the Underwriting Agreement, which is filed as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated by reference herein.

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.