Cardarelli C O, Aksentijevich I, Pastan I, Gottesman M M
Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255.
Cancer Res. 1995 Mar 1;55(5):1086-91.
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.
多药耐药性（MDR）可能与MDR1基因的表达有关，该基因编码170 kDa的细胞表面P-糖蛋白（PGP），它作为一种能量依赖性多药外排泵发挥作用。这种泵可被包括环孢素A、奎尼丁和维拉帕米在内的多种药物抑制。MDR1基因产物的底物特异性可因氨基酸残基185处的点突变而改变，其中缬氨酸取代了甘氨酸，但这种突变对PGP抑制作用的影响尚不清楚。比较了用表达相当水平PGP的MDR1逆转录病毒载体pHaMDR-1/A（G185）或pHaMDR1/A（V185）转染的多药耐药NIH3T3细胞的耐药模式以及MDR逆转剂对耐药性的抑制作用。NIH-MDR-G185转染子对柔红霉素、紫杉醇和长春碱有一定程度的优先耐药性。突变体（V185）赋予对秋水仙碱的耐药性增加。添加环孢素A、奎尼丁或维拉帕米可克服NIH-MDR-G185和NIH-MDR-V185转染的NIH3T3细胞中的这种MDR表型。维拉帕米是影响野生型PGP的三种药物中最有效的。然而，根据所逆转耐药性的细胞毒性药物不同，特异性抑制剂对野生型或突变型转运蛋白显示出不同的效力。例如，浓度为1微克/毫升的环孢素A是突变型药物转运蛋白对紫杉醇和秋水仙碱耐药性的强力逆转剂，但对野生型转运蛋白的效果要差得多。相反，维拉帕米对野生型转运蛋白逆转长春碱耐药性的效率比对突变型转运蛋白更高。这些结果表明，多药转运蛋白对逆转剂的敏感性将取决于逆转剂、细胞毒性药物以及改变底物特异性的突变的存在与否。
