Cass C E, Janowska-Wieczorek A, Lynch M A, Sheinin H, Hindenburg A A, Beck W T
McEachern Laboratory, Department of Biochemistry, University of Alberta, Edmonton, Canada.
Cancer Res. 1989 Nov 1;49(21):5798-804.
Verapamil sensitizes multidrug-resistant cell lines to various heterocyclic anticancer drugs by inhibition of energy-dependent release of drug, presumably by interaction with membrane glycoproteins involved in drug efflux. This work assessed verapamil sensitization of human multidrug-resistant lymphocytic and myeloid leukemic cell lines (CEM/VLB100, HL-60/AR) to vincristine during exposures of short duration (4 h). When cells were transferred to drug-free medium immediately after simultaneous 4-h exposures to vincristine and verapamil, the antiproliferative activity of vincristine was not altered in CEM/VLB100 cells and was only moderately increased in HL-60/AR cells. In contrast, when cells were transferred to verapamil-containing medium, vincristine activity was greatly increased against both CEM/VLB100 and HL-60/AR cells. Verapamil enhanced accumulation and inhibited release of [3H]vincristine by CEM/VLB100 and HL-60/AR cells, indicating that the sensitization was due to an increase in cell-associated vincristine after transfer of cells to vincristine-free medium. Slot blot analysis of cellular RNA with the pMDR1 probe revealed high levels of expression of the mdr1 gene in CEM/VLB100 cells but no detectable expression in HL-60/AR cells. Consistent with this finding, polypeptides (Mr 170,000 to 180,000) that were recognized by a monoclonal antibody (C219) against P-glycoprotein were greatly overexpressed in CEM/VLB100 cells, but were expressed at low levels, if at all, in HL-60/AR cells. These results demonstrate the importance of duration of exposure to verapamil in reversing multidrug resistance, not only in cells that overexpress P-glycoprotein but also in cells, such as HL-60/AR, that express little, if any, P-glycoprotein.
维拉帕米通过抑制能量依赖性药物释放，可能是通过与参与药物外排的膜糖蛋白相互作用，使多药耐药细胞系对各种杂环抗癌药物敏感。这项研究评估了在短时间（4小时）暴露期间，维拉帕米对人多药耐药淋巴细胞和髓细胞白血病细胞系（CEM/VLB100、HL-60/AR）对长春新碱的增敏作用。当细胞在同时暴露于长春新碱和维拉帕米4小时后立即转移到无药培养基中时，长春新碱在CEM/VLB100细胞中的抗增殖活性未改变，在HL-60/AR细胞中仅适度增加。相反，当细胞转移到含维拉帕米的培养基中时，长春新碱对CEM/VLB100和HL-60/AR细胞的活性都大大增加。维拉帕米增强了CEM/VLB100和HL-60/AR细胞对[3H]长春新碱的摄取并抑制其释放，表明增敏作用是由于细胞转移到无长春新碱培养基后细胞相关长春新碱增加所致。用pMDR1探针进行的细胞RNA斑点杂交分析显示，mdr1基因在CEM/VLB100细胞中高水平表达，但在HL-60/AR细胞中未检测到表达。与这一发现一致，被抗P-糖蛋白单克隆抗体（C219）识别的多肽（分子量170,000至180,000）在CEM/VLB100细胞中大量过表达，但在HL-60/AR细胞中即使有表达也水平很低。这些结果证明了维拉帕米暴露时间在逆转多药耐药中的重要性，不仅在过度表达P-糖蛋白的细胞中如此，在如HL-60/AR等几乎不表达或不表达P-糖蛋白的细胞中也是如此。
