title: Altered stability of etoposide-induced topoisomerase II-DNA complexes in resistant human leukaemia K562 cells.
abstract: K562 leukaemia cells were selected for resistance using 0.5 microM etoposide (VP-16). Cloned K/VP.5 cells were 30-fold resistant to growth inhibition by VP-16 and 5- to 13-fold resistant to m-AMSA, adriamycin and mitoxantrone. K/VP.5 cells did not overexpress P-glycoprotein; VP-16 accumulation was similar to that in K562 cells. VP-16-induced DNA damage was reduced in cells and nuclei from K/VP.5 cells compared with K562 cells. Topoisomerase II protein was reduced 3- to 7-fold and topoisomerase II alpha and topoisomerase II beta mRNAs were each reduced 3-fold in resistant cells. After drug removal, VP-16-induced DNA damage disappeared 1.7 times more rapidly and VP-16-induced DNA-topoisomerase II adducts dissociated 1.5 times more rapidly in K/VP.5 cells than in K562 cells. ATP (1 mM) was more effective in enhancing VP-16-induced DNA damage in nuclei isolated from sensitive cells than in nuclei from resistant cells. In addition, ATP (0.3-5 mM) stimulated VP-16-induced DNA-topoisomerase II adducts to a greater extent in K562 nuclei than in K/VP.5 nuclei. Taken together, these results indicate that resistance to VP-16 in a K562 subline is associated with a quantitative reduction in topoisomerase II protein and, in addition, a distinct qualitative alteration in topoisomerase II affecting the stability of drug-induced DNA-topoisomerase II complexes.
authors.affiliation: Department of Pharmacology, University of Pittsburgh School of Medicine, Pennsylvania 15261.
authors.forename: M K
authors.initials: MK
authors.lastname: Ritke
authors.forename: D
authors.initials: D
authors.lastname: Roberts
authors.forename: W P
authors.initials: WP
authors.lastname: Allan
authors.forename: J
authors.initials: J
authors.lastname: Raymond
authors.forename: V V
authors.initials: VV
authors.lastname: Bergoltz
authors.forename: J C
authors.initials: JC
authors.lastname: Yalowich
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000187:drug effects / Q000378:metabolism*; D004351:Drug Resistance / Q000235:genetics / Q000502:physiology*; D005047:Etoposide / Q000494:pharmacology*; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics; D012334:RNA, Neoplasm / Q000032:analysis; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology
chemical_list: D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D012334:RNA, Neoplasm; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D004250:DNA Topoisomerases, Type II