Identification of mammalian DNA topoisomerase I as an intracellular target of the anticancer drug camptothecin.
Camptothecin, a plant alkaloid with antitumor activity, has been shown to be a potent inhibitor of nucleic acid synthesis and a strong inducer of DNA strand breaks in mammalian cells. Previous studies have shown that camptothecin inhibits purified mammalian DNA topoisomerase I by trapping a reversible enzyme-DNA "cleavable complex" (Hsiang et al., J. Biol. Chem., 260: 14873-14878, 1985). Our present studies, using L1210 cells and SV40-infected monkey cells, have shown that camptothecin-induced strand breaks are protein linked. The linked protein is most likely DNA topoisomerase I as revealed by immunoblot analysis, using antibodies against purified mammalian DNA topoisomerase I. Brief heating of camptothecin-treated cells to 65 degrees C resulted in a rapid reduction of the number of protein-linked DNA breaks. Reversal of the camptothecin-induced topoisomerase I-DNA complex by heat was also observed in an in vitro system by using purified mammalian DNA topoisomerase I. Our results suggest that camptothecin interferes with DNA topoisomerase I both in cultured mammalian cells and in the purified system by trapping a reversible enzyme-DNA cleavable complex.
Hsiang
Y H
YH
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Liu
L F
LF
D000818:Animals; D002166:Camptothecin / Q000494:pharmacology*; D002460:Cell Line; D003432:Cross-Linking Reagents; D004249:DNA Damage; D004279:DNA, Viral / Q000187:drug effects; D007939:Leukemia L1210; D051379:Mice; D013539:Simian virus 40 / Q000235:genetics; D059004:Topoisomerase I Inhibitors
D003432:Cross-Linking Reagents; D004279:DNA, Viral; D059004:Topoisomerase I Inhibitors; D002166:Camptothecin