Actinium Pharmaceuticals Presents New Radiochemistry Data at Annual Meeting

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.