DC1Sme, a DC1 derivative, exhibits IC50 values of 22 pM, 10 pM, 32 pM and 250 pM for Ramos, Namalwa, HL60/s and COLO 205 cancer cells, respectively. DC1, an analogue of the minor groove-binding DNA alkylator CC-1065, is a ADC Cytotoxin. DC1 can be used in synthesis of antibody-drug conjugates for the targeted treatment of cancer.