BSI-737

BSI-737 is a bispecific antibody-drug conjugate (ADC) targeting B7-H3 (CD276) and PD-L1 (CD274), currently in preclinical development by Biosion. The molecule consists of a humanized bispecific antibody conjugated to the topoisomerase I inhibitor exatecan via a cleavable linker using a proprietary glycol-site-specific conjugation technology, achieving a drug-to-antibody ratio (DAR) of 4. BSI-737 is designed with a dual mechanism of action: it selectively delivers a potent cytotoxic payload to tumor cells co-expressing B7-H3 and PD-L1, while simultaneously blocking the PD-1/PD-L1 signaling pathway to alleviate immune suppression and exacerbate anti-tumor immune responses. Preclinical data presented at AACR 2026 demonstrated high affinity binding, efficient internalization, and significant anti-tumor activity, including complete tumor regression in xenograft models with varying levels of target expression.