RXDX Prometheus Biosciences Inc

As filed with the Securities and Exchange Commission on June 16, 2023

Registration No. 333-264091

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1

TO

FORM S-3

REGISTRATION STATEMENT (REG. NO. 333-264091)

UNDER

THE SECURITIES ACT OF 1933

Kelly E.W. Grez

Secretary

Prometheus Biosciences, Inc.

3050 Science Park Road

San Diego, California 92121

(858) 422-4300

(Address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Scott A. Barshay

Laura C. Turano

Paul, Weiss, Rifkind, Wharton & Garrison LLP

1285 Avenue of the Americas

New York, NY 10019

(212) 373-3000

Approximate date of commencement of proposed sale to the public: Not applicable. Removal from registration of securities that were not sold pursuant to the above referenced registration statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.  ☐

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, other than securities offered only in connection with dividend or interest reinvestment plans, 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.  ☐

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 registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective on filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.  ☒

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.  ☐

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.

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 Securities Act.  ☐

DEREGISTRATION OF SECURITIES

This Post-Effective Amendment No. 1 (the “Post-Effective Amendment”) relates to the following Registration Statement on Form S-3 (the “Registration Statement”), filed with the Securities and Exchange Commission (the “SEC”) by Prometheus Biosciences, Inc., a Delaware corporation (the “Registrant”):

On June 16, 2023, pursuant to the terms of an Agreement and Plan of Merger (the “Merger Agreement”), dated as of April 15, 2023, among Merck & Co., Inc., a New Jersey corporation (“Parent”), Splash Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Parent (“Merger Sub”) and the Registrant, Merger Sub merged with and into the Registrant, with the Registrant surviving the merger as a wholly owned subsidiary of Parent (the “Merger”).

As a result of the Merger and the other transactions contemplated by the Merger Agreement, the Registrant has terminated any and all offerings of its securities pursuant to the Registration Statement. In accordance with an undertaking made by the Registrant in the Registration Statement to remove from registration, by means of a post-effective amendment, any of the securities registered under the Registration Statement that remain unissued at the termination of the offerings, by filing this Post-Effective Amendment, the Registrant hereby removes from registration all securities registered but unsold under the Registration Statement, if any, as of the date hereof, and the Registration Statement is hereby amended, as appropriate, to reflect the deregistration of such securities.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment to the Registration Statement on Form S-3 to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Diego, State of California, on June 16, 2023.

No other person is required to sign this Post-Effective Amendment to the Registration Statement on Form S-3 in reliance on Rule 478 of the Securities Act of 1933, as amended.