MBX Biosciences, Inc. Common Stock (MBX) Form 3 MBX Biosciences / James N Topper ownership change

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

Frazier Life Sciences X, L.P.

(Last) (First) (Middle)

601 UNION STREET, SUITE 3200

(Street)

SEATTLE WA 98101

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
09/12/2024

3. Issuer Name and Ticker or Trading Symbol
MBX Biosciences, Inc. [ MBX ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

Director	X	10% Owner
Officer (give title below)		Other (specify below)

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series A Convertible Preferred Stock	(1)	(1)	Common Stock	1,574,005	(1)	D(2)
Series B Convertible Preferred Stock	(1)	(1)	Common Stock	2,353,769	(1)	D(2)

1. Name and Address of Reporting Person^*

Frazier Life Sciences X, L.P.

(Last) (First) (Middle)

601 UNION STREET, SUITE 3200

(Street)

SEATTLE WA 98101

(City) (State) (Zip)

1. Name and Address of Reporting Person^*

FHMLS X, L.P.

(Last) (First) (Middle)

601 UNION STREET, SUITE 3200

(Street)

SEATTLE WA 98101

(City) (State) (Zip)

1. Name and Address of Reporting Person^*

FHMLS X, L.L.C.

(Last) (First) (Middle)

601 UNION STREET, SUITE 3200

(Street)

SEATTLE WA 98101

(City) (State) (Zip)

1. Name and Address of Reporting Person^*

Topper James N

(Last) (First) (Middle)

601 UNION STREET, SUITE 3200

(Street)

SEATTLE WA 98101

(City) (State) (Zip)

Explanation of Responses:

1. Each share of Series A Convertible Preferred Stock, Series B Convertible Preferred Stock and Series C Convertible Preferred Stock (collectively, the "Preferred Stock") is convertible into Common Stock on a one-for-12.0221 basis at any time at the option of the holder, and will automatically convert into the number of shares shown in Column 3 immediately prior to the closing of the Issuer's initial public offering. The Preferred Stock has no expiration date.

2. These securities are held of record by Frazier Life Sciences X, L.P. ("FLS X"). FHMLS X, L.P. is the general partner of FLS X, and FHMLS X, L.L.C. is the general partner of FHMLS X, L.P. Patrick Heron and James Topper, M.D., Ph.D., are the sole managing members of FHMLS X, L.L.C. and share voting and investment power of the securities held by FLS X, and as a result, may be deemed to have beneficial ownership over such securities. Mr. Heron and Dr. Topper disclaim beneficial ownership of such securities except to the extent of their pecuniary interest therein.

Remarks:

Exhibit 24 - Power of Attorney

	Frazier Life Sciences X, L.P., By: FHMLS X, L.P., its general partner, By: FHMLS X, L.L.C., its general partner, By: /s/ Steve R. Bailey, Chief Financial Officer	09/12/2024
	FHMLS X, L.P., By: FHMLS X, L.L.C., its general partner, By: /s/ Steve R. Bailey, Chief Financial Officer	09/12/2024
	FHMLS X, L.L.C., By: /s/ Steve R. Bailey, Chief Financial Officer	09/12/2024
	/s/ Steve R. Bailey, Attorney-in-Fact for James N. Topper	09/12/2024
	** Signature of Reporting Person	Date
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