Actinium’s ATNM-400 Shows Promising Efficacy in Multiple Cancer Models
Actinium Pharmaceuticals, Inc. has reported encouraging preclinical data from its novel radiotherapy, ATNM-400, across various cancer models. Presented at the American Association for Cancer Research (AACR) Annual Meeting in San Diego, the findings highlight ATNM-400’s potential efficacy in prostate, lung, and breast cancers.
ATNM-400 targets a non-PSMA membrane antigen highly expressed in advanced solid tumors, including prostate cancer, non-small cell lung cancer (NSCLC), and breast cancer. This targeted radiotherapy employs Actinium-225 (Ac-225), an alpha-emitting isotope that delivers potent radiation with precision, potentially minimizing off-target effects and enhancing therapeutic outcomes.
Prostate Cancer Findings
ATNM-400 demonstrated efficacy in prostate cancer models with varying levels of PSMA expression, including PSMA-negative models. It outperformed vehicle control and other therapies like 177Lu–PSMA-617, showing potential to benefit metastatic castration-resistant prostate cancer (mCRPC) patients, particularly those not responding to existing PSMA-targeted radioligands.
Lung Cancer Studies
In NSCLC, particularly in EGFR-mutant models resistant to osimertinib, ATNM-400, alone or in combination with osimertinib, surpassed the current standard osimertinib with chemotherapy. This radiotherapy showed greater tumor inhibition compared to treatments like Dato-DXd and amivantamab (RYBREVANT®).
Breast Cancer Data
In trastuzumab-resistant HER2+ breast cancer models, ATNM-400 efficacy was comparable to trastuzumab deruxtecan (ENHERTU®), providing durable tumor control even after treatment discontinuation. This suggests potential for less frequent dosing, benefiting patients who experience toxicities from current treatments.
Overall, ATNM-400 exhibited no significant in vivo toxicities, suggesting a favorable therapeutic index. Actinium’s CEO, Sandesh Seth, emphasized that the data supports ATNM-400's utility as both a standalone and combination therapy across resistant cancer settings, with additional clinical data expected later in 2026.