MBX Biosciences raises $187.5M in stock sale

MBX Biosciences entered into an underwriting agreement for an underwritten public stock offering.

Rhea-AI Filing Summary

MBX Biosciences entered into an underwriting agreement for an underwritten public stock offering. The company sold 11,108,055 shares of common stock at an offering price of $18.00 per share and granted underwriters a 30-day option to purchase up to an additional 1,666,208 shares at the same price, less discounts and commissions. The offering closed on September 26, 2025.

The transaction generated approximately $187.5 million in net proceeds. MBX plans to use this cash, together with its existing cash, cash equivalents and short-term investments, primarily to advance development of its three clinical-stage programs. Remaining funds are earmarked for discovery research and development, additional clinical development, and general corporate purposes including working capital and capital expenditures.

Positive

• MBX Biosciences raised approximately $187.5 million in net proceeds through an underwritten public equity offering, significantly increasing available capital to fund its clinical and research programs.

Negative

• None.

Insights

Biotech capital markets analyst

MBX raises $187.5M in an underwritten stock offering to fund clinical and research programs.

MBX Biosciences completed an underwritten public offering of 11,108,055 common shares at $18.00 per share, with a 30‑day option for underwriters to buy up to 1,666,208 additional shares. Net proceeds are about $187.5 million, indicating a sizable primary capital raise rather than a small administrative transaction.

The company plans to deploy this capital primarily into its three clinical‑stage programs, with the balance for discovery R&D, additional clinical development, and general corporate uses such as working capital and capital expenditures. For a clinical‑stage biotech, this type of financing can extend cash runway and support trial execution, though it also reflects issuance of new equity. Subsequent disclosures in periodic reports can clarify how the new funds affect development timelines and cash needs.

8-K Event Classification

Item 1.01 — Entry into a Material Definitive Agreement

1 item

Item 1.01 Entry into a Material Definitive Agreement Business

The company signed a significant contract such as a merger agreement, credit facility, or major partnership.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did MBX (MBX) announce in this 8-K filing?

MBX Biosciences reported it entered into an underwriting agreement for an underwritten public offering of its common stock and that the offering has closed, providing the company with new capital.

How many MBX Biosciences shares were sold in the offering and at what price?

The company sold 11,108,055 shares of common stock at an offering price of $18.00 per share and granted underwriters a 30-day option to purchase up to an additional 1,666,208 shares at the same price, less underwriting discounts and commissions.

How much money did MBX Biosciences raise from this stock offering?

Net proceeds from the offering were approximately $187.5 million, after deducting underwriting discounts, commissions and other estimated offering expenses payable by the company.

How will MBX Biosciences use the $187.5 million in net proceeds?

MBX intends to use the net proceeds, together with existing cash, cash equivalents and short-term investments, primarily to advance development of its three clinical-stage programs, with the remainder for discovery research and development, additional clinical development, general corporate purposes, working capital and capital expenditures.

Which firms acted as underwriters for the MBX Biosciences offering?

J.P. Morgan Securities LLC and Jefferies LLC acted as representatives of the several underwriters under the underwriting agreement with MBX Biosciences.

Under which registration statements was the MBX Biosciences offering conducted?

The common stock was offered and sold under MBX Biosciences’ registration statements on Form S-1 (File No. 333-290447) and Form S-1MEF (File No. 333-290498), which became effective on September 24, 2025.

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Accepted by SEC EDGAR 09/26/2025 - 04:01 PM Learn about SEC filing dates

0001776111false00017761112025-09-242025-09-24

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): September 24, 2025

MBX Biosciences, Inc.

(Exact name of Registrant as Specified in Its Charter)

Delaware			001-42272	84-1882872
(State or Other Jurisdiction of Incorporation)			(Commission File Number)	(IRS Employer Identification No.)
11711 N. Meridian Street Suite 300
Carmel, Indiana				46032
(Address of Principal Executive Offices)				(Zip Code)

Registrant’s Telephone Number, Including Area Code: (317) 659-0200

(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:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.0001 par value per share		MBX		Nasdaq Global Select Market

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.

Exhibit No.	Description
1.1	Underwriting Agreement, dated September 24, 2025, by and between MBX Biosciences, Inc. and J.P. Morgan Securities LLC and Jefferies LLC.
104	Cover Page Interactive Data File (embedded within the Inline XBRL document)

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.

			MBX BIOSCIENCES, INC.
Date:	September 26, 2025	By:	/s/ P. Kent Hawryluk
			P. Kent Hawryluk, President and Chief Executive Officer