Differential Effect of Duocarmycin A and Its Novel Derivative DU‐86 on DNA Strand Breaks in HeLa S(3) Cells

Duocarmycin A (DUMA) and DU‐86, a semisynthetic derivative of duocarmycins (DUMs) and a possible active form of KW‐2189, both showed potent cell growth‐inhibitory and cell‐killing activities against human uterine cervix carcinoma HeLa (83) cells. Both drugs showed similar profiles of inhibition of macromolecular synthesis and influence on cell‐cycle distribution. Namely, they inhibited [(3)H]thymidine uptake at lower concentrations than [(3)H]uridine or [(3)H]Ieucine uptake, suggesting that the inhibition of DNA synthesis is the primary site of their actions. Furthermore, they induced the accumulation of cells in early S phase. However, a significant difference was observed between these drugs in terms of DNA‐fragmentation activity against HeLa S(3) cells by using two independent methods, pulse‐field gel electrophoresis and alkaline elution. DNA fragmentation was insignificant in the cells treated with DU‐86, in contrast to the cells treated with DUMA. The analysis of DNA adducts in the cells revealed that DU‐86 alkylated adenine quite selectively, while DUMA alkylated both adenine and guanine. These results suggest that the pyrrolidone ring of DUMA is responsible for its adduct formation with guanine and the subsequent DNA‐fragmentation and inhibition of DNA synthesis, while DU‐86 alkylated adenine and inhibited DNA synthesis through mechanisms other than DNA‐fragmentation.