title: Genetic characterization of the multidrug-resistant phenotype of VM-26-resistant human leukemic cells.
abstract: Our human T-cell leukemia line, CEM/VM-1, selected for resistance to VM-26 (teniposide), is cross-resistant to several drugs that interact with topoisomerase II, including VP-16 (etoposide), 4'-(9-acridinylamino)methanesulphon-m-anisidide, daunorubicin, and mitoxantrone. However, in contrast to cell lines exhibiting multidrug resistance (MDR) associated with overexpression of P-glycoprotein, this line is not cross-resistant to the Vinca alkaloids, is not impaired in drug accumulation, and does not overexpress the mdrl gene (Cancer Res., 47: 1297, 5455, 1987). More recently we found that nuclear extracts of these cells exhibit decreased topoisomerase II catalytic and cleavage activity, compared to the drug-sensitive line (Biochemistry, 1988). These results suggest that an alteration in topoisomerase II or a modulator of this enzyme may be responsible for this altered topoisomerase II-form of multidrug resistance (at-MDR). In the present work, we studied the somatic cell genetics of at-MDR. We produced hybrid cell lines by polyethylene glycol-mediated fusion of the CEM/VM-1 line with a hypoxanthine-guanine phosphoribosyl transferase-deficient, ouabain-resistant CEM line (CEM.AG1.OU1.5) that exhibits VM-26 sensitivity. Ten of the hybrid lines that grew in selective medium were randomly chosen for expansion and four were analyzed for both DNA content by flow cytometry and VM-26 sensitivity in a 72-h growth inhibition assay. The hybrid lines all contained approximately 2x DNA compared to unfused controls, indicating that the fusions were successful. The IC50 for VM-26 in 3 of the 4 lines was the same as that of the sensitive controls, ranging from 4.7 to 7.4 x 10(-8) M, and another was 76 x 10(-8) M. These data indicate that drug sensitivity was reconstituted by the hybridization procedure. By comparison, the VM-26 IC50 values in the CEM/VM-1 cells and CEM/VM-1 x CEM/VM-1 control "fusions" were 360 and 750 x 10(-8) M, respectively. To determine whether a topoisomerase II-mediated function was reconstituted in the hybrids, we measured drug-stimulated DNA cleavage ("cleavable complex formation"). Using 32P-labeled pBR322 DNA as substrate with nuclear extracts from drug sensitive cells, 100 microM VM-26 maximally stimulated DNA cleavage by approximately 11-fold compared to no-drug controls.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Biochemical and Clinical Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101.
authors.forename: J S
authors.initials: JS
authors.lastname: Wolverton
authors.forename: M K
authors.initials: MK
authors.lastname: Danks
authors.forename: C A
authors.initials: CA
authors.lastname: Schmidt
authors.forename: W T
authors.initials: WT
authors.lastname: Beck
mesh_terms: D003470:Culture Media; D004250:DNA Topoisomerases, Type II / Q000032:analysis; D004273:DNA, Neoplasm / Q000032:analysis / Q000378:metabolism; D004351:Drug Resistance / Q000235:genetics*; D006801:Humans; D006822:Hybrid Cells; D015458:Leukemia, T-Cell / Q000235:genetics*; D010641:Phenotype; D011034:Podophyllotoxin / Q000031:analogs & derivatives*; D013713:Teniposide / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D003470:Culture Media; D004273:DNA, Neoplasm; D013713:Teniposide; D004250:DNA Topoisomerases, Type II; D011034:Podophyllotoxin