SCHEDULE: Frazier Life Sciences Boosts MBX Biosciences Stake

Frazier Life Sciences and affiliated entities have increased their beneficial ownership in MBX Biosciences, Inc., with a recent purchase of 666,666 shares at $18.00 per share.

Summary

• Frazier Life Sciences Public Fund, L.P. (FLSPF), Frazier Life Sciences Public Overage Fund, L.P. (FLSPOF), Frazier Life Sciences X, L.P. (FLS X), and Frazier Life Sciences XI, L.P. (FLS XI), along with their general partners and managing members, are reporting persons.
• As of September 26, 2025, FLSPF beneficially owns 1,103,920 shares (2.5% of class), FLSPOF owns 325,653 shares (0.7% of class), FLS X owns 5,219,440 shares (11.7% of class), and FLS XI owns 3,000 shares (0.0% of class).
• James N. Topper and Patrick J. Heron, as members of FHMLS X, L.L.C., share voting and investment power over FLS X's 5,219,440 shares, representing 11.7% of the class.
• Patrick J. Heron also directly holds 4,655 shares issuable upon option exercise, bringing his total beneficial ownership to 5,224,095 shares (11.7% of class).
• The percentage of class is calculated based on 33,593,866 shares outstanding as of August 4, 2025, and an additional 11,108,055 shares sold on September 26, 2025.
• Prior to the IPO, FLS X purchased Series A and 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, these preferred shares converted into common stock, resulting in FLS X holding 3,927,774 shares, FLSPF holding 623,608 shares, and FLSPOF holding 183,965 shares of common stock.
• At the time of the IPO, FLS X purchased 625,000 shares, FLSPF purchased 480,312 shares, FLSPOF purchased 141,688 shares, and FLS XI purchased 3,000 shares, all at an IPO price of $16.00 per share.
• On September 26, 2025, FLS X purchased an additional 666,666 shares of Common Stock at a price of $18.00 per share.
• The funds for these purchases came from the working capital of the respective Frazier Life Sciences funds, with no borrowed funds used.

Sentiment

Score: 7

Explanation: The increased stake by Frazier Life Sciences, particularly the recent purchase at a higher price than the IPO, indicates continued confidence from a significant institutional investor in MBX Biosciences. This is a positive signal, though the filing itself is a disclosure of ownership rather than a performance report.

Positives

• Increased beneficial ownership by Frazier Life Sciences, a prominent institutional investor, signals continued confidence in MBX Biosciences.
• The recent purchase of 666,666 shares by FLS X on September 26, 2025, was executed at $18.00 per share, which is higher than the IPO price of $16.00 per share, indicating a positive valuation outlook from the investor.

Future Outlook

The filing does not contain any explicit forward-looking statements or guidance from MBX Biosciences or the reporting persons regarding the company's future performance or strategic direction.

Industry Context

This filing reflects a routine disclosure of increased institutional ownership in a publicly traded company, common in the life sciences sector where venture capital and private equity funds often take significant stakes and continue to invest post-IPO. The continued investment by Frazier Life Sciences, a specialized life sciences investor, suggests ongoing belief in MBX Biosciences' potential within the industry.

Comparison to Industry Standards

• The filing does not provide sufficient specific financial or operational data for a detailed comparison of MBX Biosciences' performance against global industry benchmarks or specific comparable companies/projects.

Related Party Transactions

• The initial private transactions and IPO purchases of preferred and common stock by Frazier Life Sciences funds from MBX Biosciences represent dealings between the issuer and significant shareholders.
• The purchase of 666,666 shares by FLS X on September 26, 2025, at $18.00 per share, involves a significant shareholder and is considered a related party transaction.

Stakeholder Impact

• Shareholders may view the increased institutional ownership as a positive indicator of long-term value and stability, potentially boosting investor confidence.
• The continued investment by a specialized life sciences fund could signal a stronger financial backing for MBX Biosciences' strategic initiatives.

Key Dates

Recommendation

The filing indicates continued and increased confidence from a major institutional investor, Frazier Life Sciences, in MBX Biosciences. The recent purchase of additional shares at a higher price suggests a positive outlook from a sophisticated investor. However, without further fundamental company performance data, a 'hold' recommendation is prudent, acknowledging the positive signal while awaiting more comprehensive financial and operational updates.

Keywords

MBX Biosciences, Frazier Life Sciences, Schedule 13D, beneficial ownership, institutional investment, common stock, equity stake, biotech, life sciences