Key Findings
ICP-B381, an innovative bispecific antibody-drug conjugate (ADC) targeting prostate-specific membrane antigen (PSMA) and six-transmembrane epithelial antigen of prostate 1 (STEAP1), has received approval from Chinese regulatory authorities to proceed with Phase 1 clinical trials for prostate cancer. This dual-targeting approach aims to circumvent resistance mechanisms often observed with single-target therapies, thereby broadening the exposure of the ADC to heterogeneous tumor cell populations.
Technical / Clinical Details
The distinctive feature of ICP-B381 lies in its engineering as a bispecific antibody, capable of recognizing and binding to both PSMA and STEAP1, two antigens highly expressed in prostate cancer cells. This design strategy is intended to overcome the potential for tumor cells to evade treatment by downregulating a single antigen. In preclinical animal models, ICP-B381 demonstrated superior tumor suppressive effects compared to its monospecific ADC counterparts, particularly in 22Rv1 prostate cancer xenograft models characterized by low PSMA and very low STEAP1 expression. This suggests that the bispecific design offers an advantage in targeting tumors with heterogeneous or low antigen expression. The ADC incorporates a potent cytotoxic payload linked via a specific linker, enabling targeted drug delivery to cancer cells while minimizing systemic toxicity.
Background & Context
Metastatic castration-resistant prostate cancer (mCRPC) remains a challenging disease with significant unmet medical needs. While PSMA-targeted therapies have shown promise, their efficacy can be limited by heterogeneous PSMA expression or loss in some patients. STEAP1 is another emerging target in prostate cancer, with various therapeutic strategies under investigation. The bispecific approach of ICP-B381 aims to synergistically leverage both targets, potentially improving response rates and extending the therapeutic window beyond what single-target ADCs can achieve. This innovative design addresses a critical limitation in current ADC therapies, which can be susceptible to tumor escape mechanisms via antigen downregulation.
Strategic Significance & Outlook
Following the initiation of clinical trials in China, an Investigational New Drug (IND) application in the United States is planned for September 2026, highlighting a rapid global development strategy for ICP-B381. The Phase 1 trial will primarily evaluate the safety, tolerability, pharmacokinetics, and preliminary anti-tumor activity in human subjects. If successful, ICP-B381 could represent a significant advancement in the treatment of prostate cancer, offering a novel, more robust therapeutic option for patients with this difficult-to-treat malignancy. The progress of this bispecific ADC will be closely watched by the oncology community.
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