title: Nuclear topoisomerase II levels correlate with the sensitivity of mammalian cells to intercalating agents and epipodophyllotoxins.
abstract: We have investigated the biochemical basis for the hypersensitivity to intercalating agents and epipodophyllotoxins of a Chinese hamster cell mutant, ADR-1. More topoisomerase II-induced DNA strand breaks are accumulated by ADR-1 than by parental CHO-K1 cells following exposure to the intercalating agent amsacrine. Levels of induced DNA strand breaks correlate with cell killing. Topoisomerase II activity is elevated in ADR-1 cells as a consequence of an increased cellular level of topoisomerase II protein. We have studied the phenotype of cell hybrids generated by fusing parental and mutant cells. The hybrid ADR-1/CHO-K1 exhibits normal levels of resistance to amsacrine and expresses the lower, parental level of topoisomerase II. These results provide additional evidence that topoisomerase II mediates the cytotoxic action of intercalating agents and epipodophyllotoxins and suggest that the intracellular level of topoisomerase II is an important determinant of cellular sensitivity to these drugs. This has implications for antitumor therapy. ADR-1 cells provide a model system for studying the effects of topoisomerase II overproduction on cell proliferation and chromosome organization.
authors.affiliation: Department of Clinical Oncology, University of Newcastle upon Tyne, Royal Victoria Infirmary, United Kingdom.
authors.forename: S M
authors.initials: SM
authors.lastname: Davies
authors.forename: C N
authors.initials: CN
authors.lastname: Robson
authors.forename: S L
authors.initials: SL
authors.lastname: Davies
authors.forename: I D
authors.initials: ID
authors.lastname: Hickson
mesh_terms: D000677:Amsacrine / Q000494:pharmacology*; D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology*; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology*; D007364:Intercalating Agents / Q000494:pharmacology*; D009154:Mutation
chemical_list: D004277:DNA, Single-Stranded; D007364:Intercalating Agents; D000677:Amsacrine; D004317:Doxorubicin; D004250:DNA Topoisomerases, Type II