China's drug regulator has cleared InnoCare Pharma (HKSE: 9969) to begin clinical testing of ICP-B381, a bispecific antibody-drug conjugate (ADC) designed to simultaneously engage two prostate cancer-associated antigens, prostate-specific membrane antigen (PSMA) and six-transmembrane epithelial antigen of the prostate 1 (STEAP1). The Center for Drug Evaluation (CDE) of China's National Medical Products Administration (NMPA) approved the investigational new drug application for the treatment of solid tumors, with prostate cancer as a primary focus.
The dual-targeting approach addresses a limitation common to single-antigen ADCs: tumor antigen heterogeneity, where subpopulations of cells with low or absent target expression can survive and drive resistance. By engaging both PSMA and STEAP1 simultaneously, ICP-B381 is designed to address antigen heterogeneity and potentially reduce tumor escape associated with low or lost expression. Both targets are significantly overexpressed in prostate cancer cells with limited expression in normal tissue, according to InnoCare.
ICP-B381 is built on InnoCare's proprietary ADC platform and comprises a humanized anti-PSMA/STEAP1 bispecific antibody conjugated to a proprietary cytotoxic payload via what the company described as a next-generation irreversible linker. The specific payload class has not been disclosed. This is InnoCare's first bispecific ADC to enter clinical development and its third ADC overall to reach this stage.
PSMA is already clinically validated as a prostate cancer target through radioligand therapies such as Novartis’s Pluvicto, although ICP-B381 uses a distinct ADC modality. ICP-B381 is not the first PSMA/STEAP1 bispecific ADC to reach the clinic. AbbVie is already evaluating ABBV-969 in Phase I in metastatic castration-resistant prostate cancer, where the candidate produced a 45% confirmed objective response rate among RECIST-evaluable patients and a 67% PSA50 response rate at active doses in data presented at ASCO 2026. No PSMA/STEAP1 bispecific ADC has been approved.