Figure 1. Structures of irinotecan, SN-38, and CL2A-SN-38.

A. Irinotecan schematic indicates the molecule's 7, 10, & 20 positions. B. IMMU-132 ADC shows SN-38 positioning, site of SN-38 cleavage, PEG moiety to enhance solubility, and site coupled to the antibody. C. In vitro serum stability of IMMU-132 in monkey or human serum.