title: Enhanced sensitivity to camptothecin in ataxia-telangiectasia cells and its relationship with the expression of DNA topoisomerase I.
abstract: The antitumour drug camptothecin (CPT) can trap covalently bound topoisomerase I-DNA intermediates as complexes which conceal single-strand scissions. In an attempt to evaluate the cytotoxic potential of these lesions in human cells we have measured: (1) cell cycle delay and cell killing by CPT in primary and transformed fibroblasts, and in lymphoblastoid lines derived from normal, X-ray sensitive ataxia-telangiectasia (A-T) and xeroderma pigmentosum (XP) donors; (2) the properties of sublines obtained by high-dose selection in CPT: (3) levels of drug-induced DNA strand scission in intact cells; (4) the cellular availability of extractable topoisomerase I. The drug induced a marked cell cycle block in G2 phase, the magnitude of the block being closely related to cell kill. XP group A cells showed normal sensitivity to CPT, whereas A-T derived cells were consistently hypersensitive (3-5 fold) in a manner which could not be related to a primary deficiency in topoisomerase I activity, abnormal capacity for complex formation or anomalies in the intracellular generation of DNA strand breaks. A CPT-resistant A-T subline had reduced topoisomerase I activity but retained the characteristic of hypersensitivity to X-radiation. The subline lost resistance upon in vitro passage with evidence that resistance was initially an unstable feature of a subpopulation of cells. The findings have implications for the role of topoisomerase I in the in vitro phenotype of A-T cells, and the contribution made by topoisomerase I-dependent damage to the cytotoxic action of CPT.
authors.affiliation: Medical Research Council Clinical Oncology and Radiotherapeutics Unit, Cambridge, U.K.
authors.forename: P J
authors.initials: PJ
authors.lastname: Smith
authors.forename: T A
authors.initials: TA
authors.lastname: Makinson
authors.forename: J V
authors.initials: JV
authors.lastname: Watson
mesh_terms: D001260:Ataxia Telangiectasia / Q000201:enzymology* / Q000473:pathology; D002166:Camptothecin / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004354:Drug Screening Assays, Antitumor; D005347:Fibroblasts / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D014983:Xeroderma Pigmentosum / Q000201:enzymology / Q000473:pathology
chemical_list: D004264:DNA Topoisomerases, Type I; D002166:Camptothecin