# EDGAR Filing Document

**Accession Number:** 0001776111
**File Stem:** 0001193125-25-216138
**Filing Date:** 2025-9
**Character Count:** 13959
**Document Hash:** 05fedf80a642b321836189d4beb668fe
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-216138.hdr.sgml**: 20250924

**ACCESSION NUMBER**: 0001193125-25-216138

**CONFORMED SUBMISSION TYPE**: S-1MEF

**PUBLIC DOCUMENT COUNT**: 15

**FILED AS OF DATE**: 20250924

**DATE AS OF CHANGE**: 20250924

**EFFECTIVENESS DATE**: 20250924

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** MBX Biosciences, Inc.
- **CENTRAL INDEX KEY:** 0001776111
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** S-1MEF
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-290498
- **FILM NUMBER:** 251340027

**BUSINESS ADDRESS:**
- **STREET 1:** 11711 N. MERIDIAN STREET
- **STREET 2:** SUITE 300
- **CITY:** CARMEL
- **STATE:** IN
- **ZIP:** 46032
- **BUSINESS PHONE:** 3179893100

**MAIL ADDRESS:**
- **STREET 1:** 11711 N. MERIDIAN STREET
- **STREET 2:** SUITE 300
- **CITY:** CARMEL
- **STATE:** IN
- **ZIP:** 46032

**As filed with the Securities and Exchange Commission on September 24, 2025.**

**Registration No. 333–**

**UNITED STATES**

**SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

**FORM S-1**

**REGISTRATION STATEMENT**

***UNDER***

***THE SECURITIES ACT OF 1933***

**MBX Biosciences, Inc.** 

**(Exact name of registrant as specified in its charter)**

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| | | |
|:---|:---|:---|
| **Delaware** | **2834** | **84-1882872** |
| **(State or other jurisdiction of** <br>**incorporation or organization)** | **(Primary Standard Industrial<br>Classification Code Number)** | **(I.R.S. Employer<br>Identification No.)** |

---

**MBX Biosciences, Inc.** 

**11711 N. Meridian Street, Suite 300** 

**Carmel, Indiana 46032** 

**(317) 659-0200 <br>(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)**

**P. Kent Hawryluk** 

**President and Chief Executive Officer** 

**MBX Biosciences, Inc.** 

**11711 N. Meridian Street, Suite 300** 

**Carmel, Indiana 46032** 

**(317) 659-0200**

**(Name, address, including zip code, and telephone number, including area code, of agent for service)**

***Copies to:***

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| | |
|:---|:---|
| **Mitchell S. Bloom**<br>**Edwin O'Connor**<br>**Goodwin Procter LLP<br> 100 Northern Avenue<br>Boston, Massachusetts 02210<br>(617) 570-1000** | **Richard D. Truesdell, Jr.<br>Yasin Keshvargar**<br>**Arisa A. Sin<br>Davis Polk & Wardwell LLP<br>450 Lexington Avenue**<br>**New York, New York 10017**<br>**(212) 450-4000** |

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**Approximate date of commencement of proposed sale to the public**: As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box: ◻

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ⌧ (333-290447)

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If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ◻

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ◻

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company" and "emerging growth company" in Rule 12b-2 of the Exchange Act.

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| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ◻ | Accelerated filer | ◻ |
| Non-accelerated filer | ⌧ | Smaller reporting company | ⌧ |
|  |  | Emerging growth company | ⌧ |

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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 7(a)(2)(B) of the Securities Act. ◻

**The Registration Statement shall become effective upon filing in accordance with Rule 462(b) promulgated under the Securities Act of 1933, as amended.**

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**EXPLANATORY NOTE AND INCORPORATION BY REFERENCE**

This Registration Statement is being filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the "Securities Act"), for the sole purpose of increasing the aggregate number of shares of common stock offered by MBX Biosciences, Inc. (the "Registrant") by 1,274,263 shares, 166,208 of which are subject to purchase upon exercise of the underwriters' option to purchase additional shares of the Registrant's common stock. The contents of the Registration Statement on Form S-1, as amended (File No. 333-290447), filed by the Registrant with the Securities and Exchange Commission (the "Commission") pursuant to the Securities Act, including all amendments and exhibits thereto (the "Prior Registration Statement"), which was declared effective by the Commission on September 24, 2025, are incorporated by reference into this Registration Statement.

The additional shares of common stock that are being registered for issuance and sale are in an amount and at a price that together represent no more than 20% of the maximum aggregate offering price set forth in Exhibit 107 of the Prior Registration Statement.

The required opinion and consents are listed on an Exhibit Index attached hereto and filed herewith or incorporated by reference herein.

**EXHIBIT INDEX**

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| | |
|:---|:---|
| **Exhibit<br>No.** | **Exhibit Index** |
| 5.1 | [<u>Opinion of Goodwin Procter LLP</u>](mbx-ex5_1.htm) |
| 23.1 | [<u>Consent of Ernst & Young LLP, Independent Registered Public Accounting Firm</u>](mbx-ex23_1.htm) |
| 23.2 | [<u>Consent of Goodwin Procter LLP (included in Exhibit 5.1)</u>](mbx-ex5_1.htm) |
| 24.1\* | [<u>Power of Attorney</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312525211320/mbx-20250922.htm#poa) |
| 107 | [<u>Filing Fee Table</u>](mbx_exfilingfees.htm) |

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\* Previously included on the signature page to the Prior Registration Statement, originally filed with the Securities and Exchange Commission on September 22, 2025 and incorporated by reference herein.

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**SIGNATURES**

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Carmel, Indiana, on the 24<sup>th</sup> day of September, 2025.

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| | |
|:---|:---|
| **MBX Biosciences, Inc.** | **MBX Biosciences, Inc.** |
| By: | /s/ P. Kent Hawryluk |
|  | P. Kent Hawryluk |
|  | President and Chief Executive Officer |

---

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons in their capacities and on the date indicated.

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| | |
|:---|:---|
| **Signature** | **Title** |
| /s/ P. Kent Hawryluk<br>P. Kent Hawryluk | President, Chief Executive Officer and Director<br>(Principal Executive Officer) |
| /s/ Richard Bartram<br>Richard Bartram | Chief Financial Officer<br>(Principal Financial Officer and Principal Accounting Officer) |
| \*<br>Tiba Aynechi | Director |
| \*<br>James M. Cornelius | Director |
| \*<br>Steven L. Hoerter | Director |
| \*<br>Patrick Heron | Director |
| \*<br>Edward T. Mathers | Director |
| \*<br>Ora Pescovitz | Director |
| \*<br>Steven Ryder | Director |

---

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| | |
|:---|:---|
| \*By: | /s/ P. Kent Hawryluk |
|  | P. Kent Hawryluk |
|  | Attorney-in-Fact |

---

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## Exhibit 5.1

**Exhibit 5.1**

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| | |
|:---|:---|
| &nbsp;&nbsp;![img84162877_0.jpg](img84162877_0.jpg) | &nbsp;&nbsp;Goodwin Procter LLP<br>100 Northern Avenue<br>Boston, MA 02210<br>goodwinlaw.com<br>+1 617 570 1000 |

---

September 24, 2025

MBX Biosciences, Inc.

11711 N. Meridian Street, Suite 300

Carmel, IN 46032

Re: <u>Securities Registered under Registration Statement on Form S-1</u>

We have acted as counsel to you in connection with your filing of (i) a Registration Statement on Form S-1 (File No. 333-290447) (as amended or supplemented, the "Initial Registration Statement") pursuant to the Securities Act of 1933, as amended (the "Securities Act"), and (ii) a second Registration Statement on Form S-1 filed pursuant to Rule 462(b) promulgated under the Securities Act (the "462(b) Registration Statement," and together with the Initial Registration Statement, the "Registration Statement"). This opinion letter is being furnished to you in connection with your filing of the 462(b) Registration Statement relating to the registration of the offering by MBX Biosciences, Inc., a Delaware corporation (the "Company"), of up to 1,274,263 shares (the "Shares") of the Company's Common Stock, $0.0001 par value per share, including Shares purchasable by the underwriters upon their exercise of an over-allotment option granted to the underwriters by the Company. The Shares are being sold to the several underwriters named in, and pursuant to, an underwriting agreement among the Company and such underwriters (the "Underwriting Agreement").

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinions set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinions set forth below, on certificates of officers of the Company.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, when delivered and paid for in accordance with the terms of the Underwriting Agreement, will be validly issued, fully paid and non-assessable.

This opinion letter and the opinion it contains shall be interpreted in accordance with the Core Opinion Principles as published in 74 *Business Lawyer* 815 (Summer 2019).

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement and to the references to our firm under the caption "Legal Matters" in the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

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Very truly yours,

/s/ Goodwin Procter LLP

GOODWIN PROCTER LLP

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## Exhibit 23.1

**Exhibit 23.1**

**Consent of Independent Registered Public Accounting Firm**

We consent to the reference to our firm under the caption "Experts" in the Registration Statement (Form S-1) and related Prospectus of MBX Biosciences, Inc. for the registration of shares of its common stock and to the incorporation by reference therein of our report dated March 17, 2025, with respect to the financial statements of MBX Biosciences, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2024, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Indianapolis, Indiana

September 24, 2025

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## Ex-Filing

?xml version='1.0' encoding='ASCII'? EX-FILING FEES

**Exhibit 107**

**Calculation of Filing Fee Table**

<u>Form</u> S-1

(Form Type)

MBX Biosciences, Inc.

(Exact name of registrant as specified in its charter)

<u>Table 1: Newly Registered Securities</u>

---

| | | | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|:---|:---|
|  |  | Security Type | Security<br>Class<br>Title  | Fee<br>Calculation<br>Rule | Amount to be<br>Registered | Proposed<br>Maximum<br>Offering<br>Price Per<br>Share | Maximum<br>Aggregate<br>Offering<br>Price | Fee<br>Rate  | Amount of<br>Registration<br>Fee |
| Fees to be paid | (1) | Equity | Common Stock, par value $0.0001 per share | 457(a) | 1274263 | $18.00 | $22936734 | 0.00015310 | $3511.62 |
|  |  | Total Offering Amounts | Total Offering Amounts | Total Offering Amounts | Total Offering Amounts |  | $22936734 |  | $3511.62 |
|  |  | Total Fees Previously Paid | Total Fees Previously Paid | Total Fees Previously Paid | Total Fees Previously Paid |  |  |  |  |
|  |  | Total Fee Offsets | Total Fee Offsets | Total Fee Offsets | Total Fee Offsets |  |  |  |  |
|  |  | Net Fee Due | Net Fee Due | Net Fee Due | Net Fee Due |  |  |  | $3511.62 |

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(1)Represents only the additional number of shares being registered and includes 166,208 shares of common stock that the underwriters have the option to purchase. Does not include the securities that the Registrant previously registered on the Registration Statement on Form S-1 (File No. 333-290447), as amended (the "Prior Registration Statement").

Estimated solely for the purpose of computing the registration fee in accordance with Rule 457(a) under the Securities Act of 1933, as amended (the "Securities Act").

The registrant previously registered securities at an aggregate offering price not to exceed $114,683,750, which was declared effective by the Securities and Exchange Commission on September 24, 2025. In accordance with Rule 462(b) under the Securities Act, an additional amount of securities having a proposed maximum aggregate offering price of $18.00 per share is hereby registered, which includes shares issuable upon the exercise of the underwriters' option to purchase additional shares.

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