title: Differential effects of P-glycoprotein inhibitors on NIH3T3 cells transfected with wild-type (G185) or mutant (V185) multidrug transporters.
abstract: Multidrug resistance (MDR) may be associated with the expression of the MDR1 gene which encodes the 170-kDa cell surface P-glycoprotein (PGP) acting as an energy-dependent multidrug efflux pump. This pump can be inhibited by a variety of drugs including cyclosporin A, quinidine, and verapamil. Substrate specificity of the MDR1 gene product can be altered by a point mutation at amino acid residue 185 in which valine is substituted for glycine, but the effect of this mutation on inhibition of PGP is unknown. Multidrug-resistant NIH3T3 cells transfected with the MDR1 retroviral vector pHaMDR-1/A (G185) or pHaMDR1/A (V185) expressing comparable levels of PGP were compared for patterns of drug resistance and inhibition of drug resistance by MDR reversing agents. The NIH-MDR-G185 transfectants were somewhat preferentially resistant to daunorubicin, taxol, and vinblastine. The mutant (V185) conferred increased resistance to colchicine. This MDR phenotype in both NIH-MDR-G185- and NIH-MDR-V185-transfected NIH3T3 cells was overcome by the addition of cyclosporin A, quinidine, or verapamil. Verapamil was the most potent of the three agents affecting wild-type PGP. However, specific inhibitors showed different potency with wild-type or mutant transporters, depending on the cytotoxic drug whose resistance was being reversed. For example, cyclosporin A at a concentration of 1 microgram/ml, was a powerful reverser of taxol and colchicine resistance for the mutant drug transporter, but was much less effective for the wild-type transporter. In contrast, verapamil reversed resistance to vinblastine more efficiently for the wild-type transporter than for the mutant transporter. These results suggest that the sensitivity of a multidrug transporter to a reversing agent will depend on the reversing agent, the cytotoxic drug, and the presence or absence of mutations which alter substrate specificity.
authors.affiliation: Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255.
authors.forename: C O
authors.initials: CO
authors.lastname: Cardarelli
authors.forename: I
authors.initials: I
authors.lastname: Aksentijevich
authors.forename: I
authors.initials: I
authors.lastname: Pastan
authors.forename: M M
authors.initials: MM
authors.lastname: Gottesman
mesh_terms: D016475:3T3 Cells / Q000187:drug effects* / Q000502:physiology*; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000235:genetics*; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000235:genetics* / Q000493:pharmacokinetics*; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003078:Colchicine / Q000633:toxicity; D016572:Cyclosporine / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000235:genetics*; D004354:Drug Screening Assays, Antitumor; D008562:Membrane Glycoproteins / Q000032:analysis; D051379:Mice; D010641:Phenotype; D017354:Point Mutation; D011802:Quinidine / Q000494:pharmacology; D014162:Transfection; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D016572:Cyclosporine; D014700:Verapamil; D011802:Quinidine; D003078:Colchicine