SCHEDULE: Frazier Funds Clarify MBX Biosciences Stake

Frazier Life Sciences funds filed an amended Schedule 13D to clarify beneficial ownership of MBX Biosciences, Inc. common stock, correcting prior attributions.

Summary

• Frazier Life Sciences Public Fund, L.P. (FLSPF) beneficially owns 1,103,920 shares of MBX Biosciences, Inc. Common Stock, representing 3.3% of the class.
• Frazier Life Sciences Public Overage Fund, L.P. (FLSPOF) beneficially owns 325,653 shares, representing 1.0% of the class.
• Frazier Life Sciences X, L.P. (FLS X) beneficially owns 4,552,774 shares, representing 13.6% of the class.
• Frazier Life Sciences XI, L.P. (FLS XI) beneficially owns 3,000 shares, representing 0.0% of the class.
• Patrick J. Heron beneficially owns 4,557,097 shares, representing 13.6% of the class, which includes 4,323 shares from options and shared voting/dispositive power over FLS X shares.
• James N. Topper beneficially owns 4,552,774 shares, representing 13.6% of the class, with shared voting/dispositive power over FLS X shares.
• The total outstanding shares of MBX Biosciences, Inc. Common Stock used for percentage calculations was 33,593,866 as of August 4, 2025.
• The funds for the share purchases originated from the working capital of FLSPF, FLSPOF, FLS X, and FLS XI, with no borrowed funds used.
• Prior to the Issuer's IPO, FLS X purchased Series A and Series B Preferred Stock for approximately $13,000,000 and $25,065,525, respectively.
• FLSPF purchased Series C Preferred Stock for approximately $7,722,000, and FLSPOF purchased Series C Preferred Stock for approximately $2,278,000.
• Upon IPO closing, preferred shares converted to common stock on a 12.0221-to-1 basis.
• During the IPO, FLS X purchased 625,000 common shares, FLSPF purchased 480,312 common shares, FLSPOF purchased 141,688 common shares, and FLS XI purchased 3,000 common shares, all at the IPO price of $16.00 per share.
• The amendment corrects previous attribution and overstatement of beneficial ownership by certain individual members of the investment committees managing the funds.

Sentiment

Score: 5

Explanation: The filing is a factual amendment to clarify beneficial ownership, not indicating any significant positive or negative operational or financial developments for the company.

Positives

• Continued significant institutional investment by Frazier Life Sciences funds in MBX Biosciences, Inc. indicates ongoing confidence in the company.

Future Outlook

No forward-looking statements or guidance are provided in this filing.

Industry Context

This filing is a routine disclosure of beneficial ownership and does not provide specific insights into broader industry trends or competitive landscape beyond the investment activity of a prominent life sciences fund.

Corporate Governance

Related Party Transactions

• The various Frazier Life Sciences funds (Frazier Life Sciences Public Fund, L.P., Frazier Life Sciences Public Overage Fund, L.P., Frazier Life Sciences X, L.P., and Frazier Life Sciences XI, L.P.) are related entities under common management, and their collective investment activities in MBX Biosciences, Inc. are disclosed.

Stakeholder Impact

• Shareholders receive clearer and more accurate information regarding the beneficial ownership structure of significant institutional investors, which can aid in understanding the company's investor base.

Key Dates

Recommendation

The filing is an amendment to a Schedule 13D, primarily clarifying beneficial ownership attribution among the Frazier Life Sciences entities and their managing members. It does not disclose new material financial performance, strategic shifts, or significant changes in the overall investment position that would warrant a change in investment recommendation. The substantial holdings by these institutional investors remain consistent with their prior disclosed positions.

Keywords

MBX Biosciences, SEC filing, Schedule 13D, beneficial ownership, institutional investment, Frazier Life Sciences, common stock, biotechnology, equity holdings