Other Events. On November 2, 2026, the Company announced that it will present new nonclinical data supporting its lead investigational therapy ATR 1072 for the potential treatment of Protein Kinase AMP-activated non-catalytic subunit Gamma 2 (“PRKAG2”) syndrome during HCMS at the American Heart Association Scientific Sessions 2026, taking place on November 6, 2026, in Chicago, Illinois. The nonclinical results being presented at HCMS were generated in a new mouse model of PRKAG2 syndrome deve…

Other Events. As previously disclosed in the Original Form 8-K, on October 7, 2026, the Company entered into a securities purchase agreement with selected investors that qualify as “accredited investors” (collectively, the “PIPE Investors”), as defined in Rule 501(a) of Regulation D promulgated under the United States Securities Act of 1933, as amended, to sell to the PIPE Investors an aggregate of (i) 5,170,384 shares of the Company’s common stock, par value $0.001 per share (the “Common Sto…

Other Events. On October 8, 2026, the Company issued a press release announcing the Offering. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference. The aggregate gross proceeds to the Company from the Offering are expected to be approximately $50 million before deducting placement agent fees and other offering expenses. The Company intends to use the net proceeds from the Offering, together with its existing cash, cash equivalents and marketab…

Entry into a Material Definitive Agreement. Securities Purchase Agreement On October 7, 2026, Atrium Therapeutics, Inc. (the “Company”) entered into a securities purchase agreement (the “Securities Purchase Agreement”) with selected investors that qualify as “accredited investors” (collectively, the “PIPE Investors”), as defined in Rule 501(a) of Regulation D promulgated under the United States Securities Act of 1933, as amended (the “Securities Act”), to sell to the PIPE Investors an aggrega…

The Shares, the Pre-Funded Warrants and the Warrant Shares, are being sold and/or issued without registration under the Securities Act in reliance on the exemption provided by Section 4(a)(2) of the Securities Act as a transaction not involving a public offering, as well as available exemptions under applicable state securities laws.

of this Form 8-K, including Exhibit 99.1 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (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, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

of this Form 8-K, including Exhibit 99.1 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (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, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Changes in Control of Registrant. Immediately prior to the Separation and Distribution, Avidity was the sole stockholder of the Company. Following completion of the Separation and Distribution, the Company became an independent, publicly traded company, and Avidity retains no ownership interest in the Company. The description of the Separation and Distribution included under

Entry into a Material Definitive Agreement On February 26, 2026, Avidity Biosciences, Inc. (“Avidity”) completed the previously announced separation of all of its assets and liabilities exclusively related to its early stage precision cardiology programs, including ATR 1086 and ATR 1072, and certain collaboration agreements, consisting of those with Bristol-Myers Squibb Company and Eli Lilly and Company, into a separate, independent publicly traded company (the “Separation”), Atrium Therapeut…

Director: Election of new directors as part of a routine board reorganization.

of this Current Report on Form 8-K, including Exhibit 99.1 is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. Forward-Looking Statements This Current Report on Form 8-K contains forward-lo…