title: Differential expression of DNA topoisomerase II alpha and -beta in P-gp and MRP-negative VM26, mAMSA and mitoxantrone-resistant sublines of the human SCLC cell line GLC4.
abstract: Sublines of the human small-cell lung carcinoma (SCLC) cell line GLC4 with acquired resistance to teniposide, amsacrine and mitoxantrone (GLC4/VM20x, GLC4/AM3x and GLC4/MIT60x, respectively) were derived to study the contribution of DNA topoisomerase II alpha and -beta (TopoII alpha and -beta) to resistance for TopoII-targeting drugs. The cell lines did not overexpress P-glycoprotein or the multidrug resistance-associated protein but were cross-resistant to other TopoII drugs. GLC4/VM20x showed a major decrease in TopoII alpha protein (54%; for all assays presented in this paper the GLC4 level was defined to be 100%) without reduction in TopoII beta protein; GLC4/AM3x showed only a major decrease in TopoII beta protein (to 18%) and not in TopoII alpha. In GLC4/MIT60x, the TopoII alpha and -beta protein levels were both decreased (TopoII alpha to 31%; TopoII beta protein was undetectable). The decrease in TopoII alpha protein in GLC4/VM20x and GLC4/MIT60x, was mediated by decreased TopoII alpha mRNA levels. Loss of TopoII alpha gene copies contributed to the mRNA decrease in these cell lines. Only in the GLC4/MIT60x cell line was an accumulation defect observed for the drug against which the cell line was made resistant. In conclusion, TopoII alpha and -beta levels were decreased differentially in the resistant cell lines, suggesting that resistance to these drugs may be mediated by a decrease in a specific isozyme.
authors.affiliation: Department of Internal Medicine, University Hospital Groningen, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Withoff
authors.forename: E G
authors.initials: EG
authors.lastname: de Vries
authors.forename: W N
authors.initials: WN
authors.lastname: Keith
authors.forename: E F
authors.initials: EF
authors.lastname: Nienhuis
authors.forename: W T
authors.initials: WT
authors.lastname: van der Graaf
authors.forename: D R
authors.initials: DR
authors.lastname: Uges
authors.forename: N H
authors.initials: NH
authors.lastname: Mulder
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis / Q000096:biosynthesis*; D018528:ATP-Binding Cassette Transporters / Q000032:analysis*; D000677:Amsacrine / Q000494:pharmacology; D000951:Antigens, Neoplasm / Q000096:biosynthesis*; D018288:Carcinoma, Small Cell / Q000235:genetics / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000096:biosynthesis*; D004268:DNA-Binding Proteins; D018432:Drug Resistance, Multiple; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D007527:Isoenzymes / Q000096:biosynthesis* / Q000378:metabolism; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D008942:Mitoxantrone / Q000494:pharmacology; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D013713:Teniposide / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000677:Amsacrine; D000951:Antigens, Neoplasm; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D008942:Mitoxantrone; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D013713:Teniposide