title: Transfection of a human topoisomerase II alpha gene into etoposide-resistant human breast tumor cells sensitizes the cells to etoposide.
abstract: The etoposide-resistant human breast cancer cell line MDA-VP was derived from MDA-parent cells by sequential selection in increasing concentrations of etoposide. MDA-VP cells express a lower amount of topoisomerase II alpha mRNA than the MDA-parent does, have mutations in topoisomerase II alpha (topo II) cDNA, and show cross-resistance to doxorubicin and amsacrine. We investigated whether transfer of a normal human topoisomerase II alpha (H-topo II) gene into MDA-VP cells could overcome their resistance to etoposide. H-topo II in a mammalian expression vector containing a glucocorticoid-inducible mouse mammary tumor virus (MMTV) promoter (pMAMneo) was transfected into MDA-VP cells (MDA-VP-hTOP2MAM). These H-topo II-transfected cells showed increased H-topo II mRNA expression and protein levels compared with MDA-VP parental cells or with MDA-VP cells transfected with the control pMAM vector (MDA-VP-MAM). Following cell exposure to dexamethasone, DNA-protein cleavable complex formation and cytotoxicity induced by etoposide, doxorubicin, and amsacrine were increased in the MDA-VP-hTOP2MAM cells compared with MDA-VP-MAM cells. However, these changes were short-lived, and by 24 h, cytotoxicity, cleavable DNA-protein complex formation, and H-topo II protein levels returned to baseline values. These results indicate that sensitivity of MDA-VP cells correlated with changes in cellular H-topo II. The gene transfer of a normal H-topo II gene can sensitize MDA-VP cells to the actions of multiple antineoplastic agents that target topo II.
authors.affiliation: Department of Cell Biology, University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: T
authors.initials: T
authors.lastname: Asano
authors.forename: T
authors.initials: T
authors.lastname: An
authors.forename: L A
authors.initials: LA
authors.lastname: Zwelling
authors.forename: H
authors.initials: H
authors.lastname: Takano
authors.forename: A T
authors.initials: AT
authors.lastname: Fojo
authors.forename: E S
authors.initials: ES
authors.lastname: Kleinerman
mesh_terms: D000677:Amsacrine / Q000008:administration & dosage; D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy*; D002453:Cell Cycle / Q000235:genetics; D016923:Cell Death / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004268:DNA-Binding Proteins; D004317:Doxorubicin / Q000008:administration & dosage; D018432:Drug Resistance, Multiple / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005047:Etoposide / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000235:genetics*; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000951:Antigens, Neoplasm; D000972:Antineoplastic Agents, Phytogenic; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D012333:RNA, Messenger; D000677:Amsacrine; D005047:Etoposide; D004317:Doxorubicin; D004250:DNA Topoisomerases, Type II