title: Topoisomerase I alteration in a camptothecin-resistant cell line derived from Chinese hamster DC3F cells in culture.
abstract: Camptothecin-resistant DC3F Chinese hamster lung fibroblast cell lines were obtained after mutagenic treatment with ethylmethanesulfonate and subsequent exposure to 1 microM camptothecin (CPT). The most resistant cell line, which was obtained after exposure to CPT for 10 days, was designated DC3F/C-10. Comparison of 50% inhibitory concentration values after 8-h CPT treatments showed that DC3F/C-10 cells were 134-fold resistant to CPT. Resistance was associated with marked reduction of CPT-induced DNA single-strand breaks and DNA-protein cross-links. This reduction was not due to reduced amounts of immunoreactive DNA topoisomerase I protein, although nuclear extracts from DC3F/C-10 cells had less enzyme catalytic activity than those from DC3F cells. Also, fast protein liquid chromatography-purified DNA topoisomerase I from DC3F/C-10 had lower specific catalytic activity than that from DC3F cells. DNA topoisomerase I from DC3F/C-10 was resistant to inhibition of catalytic activity and induction of DNA cleavage by CPT. These results suggest that CPT resistance in DC3F/C-10 cells is due to qualitative alteration of DNA topoisomerase I.
authors.affiliation: Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: A
authors.initials: A
authors.lastname: Tanizawa
authors.forename: Y
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000494:pharmacology*; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification / Q000378:metabolism*; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007700:Kinetics; D008168:Lung; D008970:Molecular Weight
chemical_list: D000970:Antineoplastic Agents; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin