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 S3 cells. Both drugs showed similar profiles of inhibition of macromolecular synthesis and influence on cell-cycle distribution. Namely, they inhibited [3H]
thymidine uptake at lower concentrations than [3H]
uridine or [3H]
leucine 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 S3 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.