title: Camptothecin hyper-resistant P388 cells: drug-dependent reduction in topoisomerase I content.
abstract: A subline of P388 leukemia made 10-fold resistant to camptothecin (CPT) by serial passage in drug-treated mice was adapted to growth in tissue culture and made hyper-resistant to CPT by passage in the presence of increasing concentrations of the drug. Cells were obtained that were 1,000-fold resistant to CPT, compared to wild-type P388 cells. Neither topoisomerase I mRNA nor 100 kDa topoisomerase I enzyme was detectable in these cells, and topoisomerase I activity extracted from nuclei was less than 4% of that extracted from nuclei of wild-type cells. An immunoreactive 130 kDa protein that could be an altered, inactive form of topoisomerase I was evident in the hyper-resistant cells. In addition, the cells deficient in topoisomerase I contained enhanced topoisomerase II activity. Maintenance of the hyper-resistant phenotype required continued exposure to CPT; growth in its absence led to loss of hyper-resistance, increased topoisomerase I content and activity, and decreased topoisomerase II activity. The sensitivity of the cells to killing by a number of inhibitors of topoisomerases I and II was consistent with these observations. Thus, P388 cells have the potential to become highly resistant to CPT by severely curtailing topoisomerase I expression; in these circumstances, topoisomerase I and II activities are regulated coordinately.
authors.affiliation: Research & Development, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406.
authors.forename: R D
authors.initials: RD
authors.lastname: Woessner
authors.forename: W K
authors.initials: WK
authors.lastname: Eng
authors.forename: G A
authors.initials: GA
authors.lastname: Hofmann
authors.forename: D J
authors.initials: DJ
authors.lastname: Rieman
authors.forename: F L
authors.initials: FL
authors.lastname: McCabe
authors.forename: R P
authors.initials: RP
authors.lastname: Hertzberg
authors.forename: M R
authors.initials: MR
authors.lastname: Mattern
authors.forename: K B
authors.initials: KB
authors.lastname: Tan
authors.forename: R K
authors.initials: RK
authors.lastname: Johnson
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology*; D002467:Cell Nucleus / Q000201:enzymology; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004351:Drug Resistance; D015870:Gene Expression; D005796:Genes; D066298:In Vitro Techniques; D008264:Macrophages / Q000201:enzymology*; D008745:Methylation; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics; D014407:Tumor Cells, Cultured
chemical_list: D012333:RNA, Messenger; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin