Two-tier Selectivity in PROTAC-Prodrugs Targeting Prostate Cancer

PROteolysis TArgeting Chimeras (PROTACs) is a highly promising class of therapeutic agents that degrade target proteins through a catalytic, event-driven mechanism. However, their broad activity and lack of tissue selectivity can lead to on-target toxicities off-site in healthy tissues, limiting their clinical potential. To address this, we developed a novel two-tier selective PROTAC prodrug 1, that specifically targets prostate cancer (PCa), based on the well-established BRD4 degrader MZ1. Compound 1 combines a PSMA-617-derived ligand for selective uptake into prostate-specific membrane antigen (PSMA)-positive PCa cells with a glutathione (GSH)-responsive disulfide linker to release the active PROTAC MZ1 inside cancerous cells, which have elevated levels of GSH. The probe efficiently released MZ1 in a GSH-dependent manner ex cellulo, however, remained stable in cell culture media alone. In cellular studies, 1 degraded BRD4 and showed potent antiproliferative activity in PSMA-positive LNCaP cells, while considerably reducing toxicity in healthy tissue-derived MRC5 and HEK293T cells. These results highlight the potential of our PROTAC prodrug strategy for targeted therapy of PCa and provide a foundation for further mechanistic studies using ex and in cellulo models.