title: Expression of topoisomerase II, bcl-2, and p53 in three human brain tumor cell lines and their possible relationship to intrinsic resistance to etoposide.
abstract: We characterized three human brain tumor cell lines (D54, HBT-20, and HBT-28) with respect to resistance to etoposide (VP-16), a topoisomerase II-reactive drug. All three cell lines were inherently resistant to VP-16 when compared to other human cell lines, with D54 showing the greatest resistance using colony formation assays. Resistance to VP-16 has been attributed to decreased drug uptake and changes in topoisomerase II; however, drug uptake and topoisomerase II protein levels (immunoblot) were no lower in D54 than in HBT-20 and HBT-28, cell lines relatively more sensitive to VP-16. More to the point, measurement of topoisomerase II-mediated DNA cleavage of cellular DNA after treatment with VP-16 showed that the topoisomerase II in these cells was active. These data indicate mechanisms other than those attributable to decreased drug uptake or altered topoisomerase II exist for clinical resistance to VP-16. VP-16-induced DNA cleavage has been associated with apoptosis in some cell lines; however, neither DNA laddering nor morphological changes characteristic of apoptosis were detected in these cell lines after treatment with VP-16. Bcl-2 and mutant p53 were present in these cells. Either of these conditions can prevent apoptosis and could explain a dissociation between the proximal mediator of VP-16-induced cytotoxicity (topoisomerase II-DNA complex formation) and cellular death.
authors.affiliation: Departments of Clinical Pediatrics, Cell Biology, and Clinical Investigation, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: C E
authors.initials: CE
authors.lastname: Herzog
authors.forename: L A
authors.initials: LA
authors.lastname: Zwelling
authors.forename: A
authors.initials: A
authors.lastname: McWatters
authors.forename: E S
authors.initials: ES
authors.lastname: Kleinerman
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics / Q000494:pharmacology*; D017209:Apoptosis; D001932:Brain Neoplasms / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000187:drug effects / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D009363:Neoplasm Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014410:Tumor Stem Cell Assay; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D005047:Etoposide; D004250:DNA Topoisomerases, Type II