On November 6, 2023 Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a leader in the development of targeted radiotherapies, reported data was presented at Society of Immunotherapy of Cancer (SITC) (Free SITC Whitepaper) 38th Annual Meeting on Saturday, November 4, 2023, further supporting Actimab-A, the Company’s clinical stage targeted radiotherapeutic comprised of the CD33 targeting antibody lintuzumab and the Actinium-225 (Ac-225) alpha-particle emitting payload (Press release, Actinium Pharmaceuticals, NOV 6, 2023, View Source [SID1234637008]).
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The poster highlighted Actimab-A’s ability to target and deplete myeloid-derived suppressor cells (MDSCs), which uniformly express CD33. MDSCs are a cell population of interest as they remodel the tumor environment and promote immune evasion. Actinium believes Actimab-A has the potential to be used in combination with immunotherapy, including immune checkpoint inhibitors, to enhance antitumor immunity via targeted MDSC depletion. Supportive data from the SITC (Free SITC Whitepaper) presentation includes:
Actimab-A reduced cancer patient-derived MDSCs in a dose-dependent manner ex vivo and decreased MDSC viability approximately two-fold greater than a non-radiolabeled CD33 antibody
MDSC suppression of activated T cell proliferation and cytokine effector function ex vivo was restored following treatment with Actimab-A
Actimab-A significantly depleted MDSCs in peripheral blood of tumor-bearing humanized mice compared to non-radiolabeled CD33 antibody in vivo
SPECT/CT imaging confirmed uptake of lintuzumab in humanized mice at the sites of non-small cell lung cancer tumor indicating enrichment of CD33+ MDSCs in the tumor microenvironment
Sandesh Seth, Actinium’s Chairman and CEO, commented, "These data further increase our enthusiasm for Actimab-A’s potential in solid tumor indications. Immunotherapy has had a profound impact on patient outcomes across multiple solid tumor indications, however, there are still several indications with high unmet needs and significant room to further improve patient outcomes. By depleting MDSCs in a targeted manner, we are excited by the prospect of Actimab-A synergizing with immunotherapy to enhance antitumor immunity. We look forward to continuing to advance this initiative in continuing our goal to address high unmet patient needs with our targeted radiotherapeutics."