Patrick J. Heron - Sep 26, 2025 Form 4 Insider Report for MBX Biosciences, Inc. (MBX)

Role
Director, 10%+ Owner
Signature
/s/ Steve R. Bailey, Attorney-in-Fact For Patrick J. Heron
Stock symbol
MBX
Transactions as of
Sep 26, 2025
Transactions value $
$11,999,988
Form type
4
Date filed
9/30/2025, 04:59 PM
Previous filing
Jun 25, 2025
SEC
View on sec.gov

Reporting Owners (5)

Name Relationship Address Signature Signature date CIK
Heron Patrick J Director, 10%+ Owner 1001 PAGE MILL RD, BUILDING 4, SUITE B, PALO ALTO /s/ Steve R. Bailey, Attorney-in-Fact For Patrick J. Heron 2025-09-30 0001365617
FHMLS X, L.P. 10%+ Owner FRAZIER LIFE SCIENCES MANAGEMENT, L.P., 1001 PAGE MILL RD, BUILDING 4, SUITE B, PALO ALTO By Steve R. Bailey, CFO of FHMLS X, L.L.C., GP of FHMLS X, L.P., GP of Frazier Life Sciences X, L.P. 2025-09-30 0001790880
FHMLS X, L.L.C. 10%+ Owner FRAZIER LIFE SCIENCES MANAGEMENT, L.P., 1001 PAGE MILL RD, BUILDING 4, SUITE B, PALO ALTO By Steve R. Bailey, CFO of FHMLS X, L.L.C., GP of FHMLS X, L.P. 2025-09-30 0001790811
Topper James N 10%+ Owner FRAZIER LIFE SCIENCES MANAGEMENT, L.P., 1001 PAGE MILL RD, BUILDING 4, SUITE B, PALO ALTO By Steve R. Bailey, CFO of FHMLS X, L.L.C. 2025-09-30 0001341382
Frazier Life Sciences X, L.P. 10%+ Owner FRAZIER LIFE SCIENCES MANAGEMENT, L.P., 1001 PAGE MILL RD, BUILDING 4, SUITE B, PALO ALTO /s/ Steve R. Bailey, Attorney-in-Fact For James N. Topper 2025-09-30 0001790879

Transactions Table

Type Sym Class Transaction Value $ Shares Change % * Price $ Shares After Date Ownership Footnotes
transaction MBX Common Stock Purchase $12M +667K +14.64% $18.00 5.22M Sep 26, 2025 By Frazier Life Sciences X, L.P. F1
* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id Content
F1 The shares reported herein are held of record by Frazier Life Sciences X, L.P. FHMLS X, L.P. is the general partner of Frazier Life Sciences X, L.P. and FHMLS X, L.L.C. is the general partner of FHMLS X, L.P. James N. Topper and Patrick J. Heron are the sole managing members of FHMLS X, L.L.C. and share voting and investment power over the shares held by Frazier Life Sciences X, L.P. Dr. Topper and Mr. Heron disclaim beneficial ownership of such securities except to the extent of their pecuniary interest therein.