On June 17, 2024 Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a leader in the development of Antibody Radiation Conjugates (ARCs) and other targeted radiotherapies, reported that an abstract detailing the first ever preclinical data from the combination of menin inhibitors with Actinium’s ARC Actimab-A in acute myeloid leukemia (AML) models was presented at the 2024 European Hematology Association (EHA) (Free EHA Whitepaper) Congress held June 13 – 16, 2024, in Madrid, Spain (Press release, Actinium Pharmaceuticals, JUN 17, 2024, View Source [SID1234644403]). Actinium studied Actimab-A in combination with the leading menin inhibitors, revumenib (Syndax Pharmaceuticals, Inc.) and ziftomenib (Kura Oncology, Inc.), which are being developed for patients with KMT2A rearrangements and NMP1 mutations, which are present in approximately 10% and 30% of AML patients, respectively.

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Actimab-A + Menin inhibitor combination results include:

Actimab-A as a single agent showed potent in vitro AML cell killing activity in both MV-4-11 and MOLM-13 KMT2A mutant cell lines, compared to the non-radio conjugated CD33 antibody lintuzumab (p<0.0001)

Actimab-A enhanced AML cell death when combined with both revumenib and ziftomenib at all dose levels in difficult to treat KMT2A mutant AML

The combination of Actimab-A with leading menin inhibitors triggered an acute increase in AML necrosis and cell death in vivo relative to single agent therapy within 72 hours of dosing

Anti-tumor effect was significantly potentiated and prolonged when combining Actimab-A with a leading menin inhibitor compared to monotherapies in xenograft leukemia models in vivo (p<0.0024 Actimab-A + menin) as shown in the exhibit below
The Actimab-A + Menin Inhibitor combination presentation can be accessed on the investor relations page of Actinium’s website here.

Actimab-A targets CD33, a marker expressed ubiquitously in patients with AML, and is conjugated with the alpha-partible payload Actinium-225. The broad expression of CD33 and the differentiated mutation agnostic cell-killing mechanism of targeted radiotherapy make Actimab-A broadly applicable for combinations with chemotherapy, targeted agents including venetoclax, FLT3 and menin inhibitors, immunotherapies and cellular therapies supporting its potential backbone therapy profile across the AML patient treatment journey.

Sandesh Seth, Actinium’s Chairman and CEO, said, "Combining with menin inhibitors is an exciting expansion of the already broad potential of Actimab-A in AML. Across single agent and combination studies, Actimab-A has produced high rates of response, MRD negativity and improved survival in high-risk, relapsed and refractory patients including those with a TP53 mutation and venetoclax failures. The broad expression of CD33 in AML coupled with the potency of Actinium-225 make Actimab-A an ideal agent for treating radiation sensitive AML. We are encouraged by this highly promising initial data and the synergistic potential of Actimab-A with menin inhibitors, which has broad potential across the AML treatment continuum including frontline, maintenance and relapsed/refractory settings. We are eager to continue to study this combination and generate additional data that could support advancing into clinical studies of Actimab-A with menin inhibitors."

Menin inhibitors are a class of drug candidates being developed for patients with AML that have a rearrangement of the KMT2A gene, previously known as the mixed-lineage leukemia (MLL) or mutation of the NPM1 gene. There are multiple menin inhibitors in development for these patients with revumenib (Syndax Pharmaceuticals, Inc.) being most advanced having a PDUFA data of September 2024 and ziftomenib (Kura Oncology, Inc.) enrolling patients in a registration Phase 2 trial. Multiple menin inhibitors are being studied in Phase 1 clinical trials by companies including Johnson & Johnson, Sumitomo Pharma Co., Ltd., Hutchmed, Biomea Fusion, Inc. and BioNova Pharmaceuticals Pvt Ltd.