Actinium Pharmaceuticals Inc. (NYSE American: ATNM) presented preclinical data for its ATNM-400 targeted radiotherapy at the American Association for Cancer Research Annual Meeting in San Diego. The experimental treatment showed activity across prostate, lung, and breast cancer models in laboratory studies.

ATNM-400 uses the Actinium-225 radioisotope and targets a membrane antigen that the company states is overexpressed in treatment-resistant solid tumors. In prostate cancer models, the therapy demonstrated efficacy in both high and low PSMA-expressing cancers, as well as PSMA-negative models.

The treatment showed greater tumor growth inhibition than osimertinib plus chemotherapy in EGFR-mutant non-small cell lung cancer models. The company also reported that ATNM-400 outperformed several approved and experimental therapies, including Dato-DXd, amivantamab, and izalontamab brengitecan in these models.

In breast cancer studies, ATNM-400 achieved efficacy comparable to trastuzumab deruxtecan in trastuzumab-resistant models. The company reported that tumor control continued after treatment discontinuation, suggesting potential for less frequent dosing compared to antibody-drug conjugates.

The preclinical studies showed no significant toxicity at therapeutic doses. ATNM-400 targets what Actinium describes as a non-PSMA membrane antigen that becomes upregulated following standard treatments.

"The data we presented at AACR are an important new piece of a much larger picture for ATNM-400," said Sandesh Seth, Actinium's Chairman and CEO. He noted the therapy's activity in treatment-resistant settings and combination potential.

Actinium develops targeted radiotherapies for cancer treatment. The company's pipeline includes treatments for solid tumors and blood cancers, with ATNM-400 representing its pan-tumor approach using radioconjugate technology.