• Actimab-A combinations enhanced in vivo AML cell killing across multiple preclinical models, independent of mutation status, when combined with standard-of-care targeted and non-targeted therapies including revumenib (menin-KMT2A inhibitor), gilteritinib (FLT3 inhibitor), and azacitidine (hypomethylating agent) - three pillars of modern AML treatment - supporting its potential role as a universal combination backbone
     
  • Transcriptional reprogramming identified as a central mechanism showing that Actimab-A combinations don't just add cytotoxicity, they reprogram AML cells from proliferation toward differentiation and apoptosis, providing the mechanistic basis for deeper, more durable MRD-negative responses and reinforcing Actimab-A's role as a universal combination backbone across AML
     
  • Robust cytotoxicity observed in primary AML patient samples across key mutations (FLT3, KMT2A, NPM1, IDH1, IDH2, or TP53), reinforcing Actimab-A's potential as a mutation-agnostic backbone therapy, complementing the manageable safety profile of Actimab-A observed across prior clinical trials in over 150 AML patients

NEW YORK, April 22, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a pioneer in the development of targeted radiotherapies, today highlighted data presented at the American Association for Cancer Research (AACR) Annual Meeting supporting transcriptional reprogramming as a central mechanism driving the mutation-agnostic anti-leukemic activity of Actimab-A (lintuzumab-Ac225) in acute myeloid leukemia (AML).

Preclinical translational data demonstrated that lintuzumab-Ac225 delivers potent cytotoxic activity across AML models harboring common mutations, including FLT3, NPM1, KMT2A, and TP53, as well as in primary patient samples. Importantly, combining Actimab-A with standard-of-care therapies - the menin inhibitor revumenib, the FLT3 inhibitor gilteritinib, and the hypomethylating agent azacitidine - resulted in enhanced leukemic cell killing in vivo across all tested models, independent of mutation status. These results support a combination-driven clinical strategy aimed at improving depth and durability of response. The findings provide the mechanistic foundation for Actimab-A's observed clinical activity and, together with the manageable safety profile demonstrated across prior Actimab-A trials in more than 150 AML patients, reinforce its suitability as a combination backbone across multiple treatment settings.

Actimab-A is Actinium's lead clinical radiotherapy delivering Actinium-225, a potent alpha-emitter radioisotope payload that produces lethal double-strand DNA breaks to kill CD33-expressing AML cells. CD33 is expressed ubiquitously in AML and other myeloid malignancies. Actimab-A has been evaluated in more than 150 AML patients across multiple treatment settings, including as monotherapy and in combination with the chemotherapy regimen CLAG-M and with the BCL-2 inhibitor venetoclax, where it has demonstrated compelling clinical activity and a manageable safety profile. Under our Cooperative Research and Development Agreement (CRADA) with the National Cancer Institute (NCI), Actimab-A is being advanced through the NCI's National Clinical Trials Network, including an ongoing frontline triplet trial combining Actimab-A with venetoclax and the hypomethylating agent ASTX-727 in newly diagnosed AML patients. The data presented at AACR 2026 further support Actimab-A's mutation-agnostic mechanism of action and its synergistic activity with targeted therapies approved for patients with the most commonly expressed AML mutations.