Preparation and Evaluation of Radiolabeled Antibody Recruiting Small Molecules that Target Prostate Specific Membrane Antigen (PSMA) for Combined Radiotherapy and Immunotherapy.

The feasibility of developing a single agent that can deliver radioactive iodine and also direct cellular immune function by engaging endogenous antibodies, as an antibody recruiting small molecule (ARM), was determined.

A library of new prostate-specific membrane antigen (PSMA)-binding ligands that contained antibody recruiting, 2,4-dinitrophenyl (DNP) groups and iodine, were synthesized and screened in vitro and in vivo. A lead compound (9b) showed high affinity for PSMA and the ability to bind anti-DNP antibodies. Biodistribution studies of the iodine-125 analogue showed 3% ID/g in LNCaP xenograft tumors at 1 h post-injection, with tumor-to-blood and tumor-to-muscle ratios of 10:1 and 44:1. The radiolabeled analogue was bound and internalized by LNCaP cells, with both functions blocked using a known PSMA inhibitor. A second candidate showed high tumor uptake (>10% ID/g), but had minimal binding to anti-DNP antibodies. The compounds reported represent the first examples of small molecules developed specifically for combination immunotherapy and radiotherapy for prostate cancer.

Journal of medicinal chemistry. 2016 Feb 19 [Epub ahead of print]

Afaf R Genady, Nancy Janzen, Laura Banevicius, Mahmoud El-Gamal, Mohamed E El-Zaria, John F Valliant