of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Other Events On July 6, 2026, Prime Medicine, Inc. (the "Company") received a final award (the "Final Award") from the arbitration tribunal (the "Tribunal") in the Company's binding arbitration proceedings with Beam Therapeutics, Inc. ("Beam") regarding the parties' 2019 Collaboration and License Agreement (the "Agreement"). In the Final Award, the Tribunal declared that PM647, the Company's development candidate for the treatment of Alpha-1 Antitrypsin Deficiency ("AATD"), is within the Comp…

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Chief Financial Officer and Principal Financial Officer — Svetlana Makhni: Prime Medicine appointed Svetlana Makhni as the Chief Financial Officer and Principal Financial Officer.

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the “Securities Act”) or the Exchange Act, except as expressly set forth by specific reference in such a fil…

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

The filing describes a special meeting of stockholders, not a management change.

Entry into a Material Definitive Agreement. On July 30, 2025, Prime Medicine, Inc. (the “Company”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with TD Securities (USA) LLC and BMO Capital Markets Corp., as representatives of the several underwriters listed on Schedule 1 thereto (collectively, the “Underwriters”), related to an underwritten public offering (the “Offering”) of 38,000,000 shares (the “Underwritten Shares”) of the Company’s common stock, par value $0.000…

Other Events Effective July 30, 2025, the Company terminated the sales agreement prospectus (the “ATM Prospectus”) filed with the Company’s registration statement on Form S-3 (File No. 333-275321) and related to the shares of the Company’s common stock, par value $0.00001 per share (“Common Stock”), issuable pursuant to the Open Market Sale Agreement SM , dated November 3, 2023, by and between the Company and Jefferies LLC (the “Sales Agreement”). As a result, the Company will not make any sa…

Results of Operations and Financial Condition On July 30, 2025, Prime Medicine, Inc. (the “Company”) announced that the preliminary unaudited estimates of its cash, cash equivalents, short-term investments, and related party short-term investments were approximately $101.8 million as of June 30, 2025, excluding its restricted cash of approximately $13.7 million. The Company has not yet completed its quarter-end financial close process for the quarter ended June 30, 2025. The foregoing informa…

Chief Scientific Officer — Jeremy Duffield, M.D. Ph.D., FRCP: Dr. Jeremy Duffield is stepping down from his role as Chief Scientific Officer.

Other Events. Appointment of Executive Chair On May 16, 2025, the Board appointed Jeffrey Marrazzo, a member of the Board, as Executive Chair of the Board, in addition to his service as a director, effective as of May 19, 2025. Pipeline Prioritization On May 19, 2025, the Company announced a strategic restructuring, including the deprioritization of its Chronic Granulomatous Disease (“CGD”) programs, as well as a cost and workforce reduction to focus on its liver franchise and programs funded…

Regulation FD Disclosure. On May 19, 2025, the Company issued press releases titled “Prime Medicine Announces Breakthrough Clinical Data Showing Rapid Restoration of DHR Positivity After Single Infusion of PM359, an Investigational Prime Editor for Chronic Granulomatous Disease” and “Prime Medicine Announces Strategic Restructuring to Focus on Opportunities in Large Genetic Liver Diseases, Cystic Fibrosis, and Partnered Programs Alongside CEO Leadership Transition.” A copy of each press relea…

President, Chief Executive Officer and Principal Executive Officer — Keith Gottesdiener, M.D.: Dr. Keith Gottesdiener resigned from all his roles including CEO and Board member.

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Other Events. On March 18, 2025, the Company unveiled a preclinical program for the treatment of alpha-1 antitrypsin deficiency (“AATD”), the next program within its liver franchise. The AATD program leverages the Company’s universal liver lipid nanoparticle (“LNP”) to edit the E342K (“Pi*Z”) mutation in the SERPINA1 gene, the prevalent disease-causing mutation in AATD, restoring the mutated protein sequence back to wild-type M protein, with the potential to treat both lung- and liver-associa…

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Regulation FD Disclosure. On September 30, 2024, the Company issued press releases entitled “Prime Medicine Announces Strategic Research Collaboration and License Agreement with Bristol Myers Squibb to Develop and Commercialize Multiple Prime Edited Ex Vivo T-Cell Therapies” and “Prime Medicine Unveils Strategically Focused Pipeline.” A copy of each press release is furnished as Exhibit 99.1 and Exhibit 99.2, respectively, to this Current Report on Form 8-K, which is incorporated herein by re…

Unregistered Sales of Equity Securities. The information set forth above in

Entry into a Material Definitive Agreement. On September 28, 2024 (the “Effective Date”), Prime Medicine, Inc. (the “Company”) entered into a Research Collaboration and License Agreement (the “Collaboration Agreement”) with Juno Therapeutics, Inc., a wholly-owned subsidiary of the Bristol-Myers Squibb Company (“BMS”). Under the terms of the Collaboration Agreement, the Company granted to BMS an exclusive worldwide license to certain Prime Editing technology for developing, manufacturing and c…

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.