T-SN38 B

**T-SN38 B** is an investigational antibody-drug conjugate (ADC) composed of the monoclonal antibody trastuzumab covalently linked to the cytotoxic payload SN-38 (the active metabolite of irinotecan) using a carbonate linker. It is engineered to specifically target HER2-positive cancer cells (primarily ovarian and potentially breast cancer) by harnessing trastuzumab’s specificity for the HER2 receptor, thereby delivering SN-38 directly to tumor cells. Preclinical studies demonstrated that T-SN38 B exhibits potent antitumor activity in HER2-positive ovarian cancer models, outperforming both free SN-38 and trastuzumab alone. The conjugate is reported to have a drug-to-antibody ratio (DAR) of ~3.2. SN-38 acts by inhibiting DNA topoisomerase I, resulting in DNA damage and apoptosis of targeted cancer cells. The carbonate bond linker in T-SN38 B provides a balance of stability in circulation and efficient release of SN-38 in the tumor microenvironment.