ATNM News & Events

Actinium Pharmaceuticals on June 2 presented new preclinical data on ATNM-400 in non-small cell lung cancer, or NSCLC, at the Society of Nuclear Medicine and Molecular Imaging 2026 Annual Meeting in Los Angeles, California. The new KRAS-mutant data, together with a growing body of EGFR-mutant data, demonstrate ATNM-400's activity across the two major mutation driver classes in NSCLC and support a distinct strategic opportunity. ATNM-400 can be developed as a potential mutation-agnostic backbone for the broader NSCLC market, alone or in combination with standard-of-care therapies, rather than as another mutation-specific drug for a narrow subset. NSCLC accounts for roughly 85% of the more than two million lung cancer cases diagnosed globally each year, a market more than twice the size of prostate cancer. It is also highly heterogeneous: no single mutation dominates, so treatments are fragmented across mutation-specific therapies such as EGFR, KRAS, BRAF, ALK and others, each marketed by different companies, each addressing only a molecular subset, and each ultimately limited by acquired resistance. ATNM-400, Actinium-225 antibody radioconjugate, is designed to break out of that single-mutation paradigm. Rather than blocking a specific mutant protein, it delivers a high-linear-energy-transfer alpha-particle payload that induces dense, irreversible double-strand DNA breaks and tumor-cell death independent of a tumor's driver mutation or signaling pathway, the mechanistic basis of its mutation-agnostic activity. In new KRAS-mutant studies presented at SNMMI, sotorasib and adagrasib increased ATNM-400's target up to 3.5- and 3.8-fold, respectively, and adding ATNM-400 deepened tumor-cell killing beyond either inhibitor alone. These results demonstrate the same target-expression increasing, synergy-enabling biology shown previously with the EGFR inhibitor osimertinib, which produced tumor growth inhibition of 107% when combined with ATNM-400. These combination benefits also broaden ATNM-400's commercial opportunity. The franchises it could enhance are substantial; the KRAS inhibitor class in NSCLC is projected to exceed $5B in peak sales, and the EGFR-mutant segment has peak sales estimates over $15B, led by osimertinib which generated $7.3B in 2025. This positions ATNM-400 to participate in these established markets by enhancing the standard of care, while also reaching the broader NSCLC population beyond any single mutation.

Actinium Pharmaceuticals announced the appointment of Steffen Heeger, MD, MSc, as Chief Medical Officer. Dr. Heeger brings a rare combination of radiotherapy expertise, global oncology drug development leadership, and public-company experience. Over his career, he has translated multiple programs from IND submission through global clinical approval in the US, EU, and Japan including the blockbuster Erbitux and led as CMO an oncology company acquired for $1.4B. Most recently Dr. Heeger served as CMO of a clinical-stage radiotherapy company where he advanced into global development, a PSMA program directly relevant to Actinium's ATNM-400 asset. His appointment comes at a pivotal moment as Actinium prepares to advance Actimab-A, ATNM-400, and Iomab-ACT toward key data readouts and expanded clinical trials in the second half of 2026.

Actinium Pharmaceuticals, on May 31, presented new radiochemistry data at the Society of Nuclear Medicine and Molecular Imaging 2026 Annual Meeting taking place in Los Angeles, California. Highlights: Antibody-DOTA conjugates spanning CAR 0.7-9 were prepared. CAR greater than or equal to1.7 enabled robust 225Ac labeling, while CAR 0.7 was insufficient. This establishes the minimum loading needed to carry an effective radioactive dose. Antigen binding stayed high at low CAR (91-98% at CAR 0.7-3.2) but fell at high CAR (79-85% at CAR 7-9), and low-CAR conjugates internalized more, keeping more of the antibody functional. Median Fluorescence Intensity (MFI) is a proxy for binding or antigen affinity retention. Findings suggest overloading the antibody degrades its ability to find and enter cancer cells. In vivo, both conjugates showed comparable tumor uptake and sustained retention through 192 h, but the low-CAR (2.5) conjugate significantly reduced liver and spleen uptake, providing a basis for a wider therapeutic index. Both conjugates remained stable over 7 days (radiochemical purity above 97%), showing that CAR can be optimized for performance without compromising manufacturability or clinical supply. Safety and targeting gains can come with no manufacturing trade-off. A wider therapeutic index could allow more dose to reach the tumor at a given level of safety, a proprietary radiochemistry framework Actinium is applying to de-risk its broader pipeline resulting in lower technical risk across the portfolio.