Miyamoto K I, Koga-Takeda K, Koga K, Ohshima T, Nomura M
Faculty of Pharmaceutical Sciences, Hokuriku University, Kanazawa, Japan.
J Pharm Pharmacol. 1996 May;48(5):522-5. doi: 10.1111/j.2042-7158.1996.tb05966.x.
P-glycoprotein acts as an active drug-efflux pump in multidrug-resistant tumour cells. We studied the capacity of P-glycoprotein to extrude drugs from the cells. For nanomolar concentrations of vinblastine P388/ADR cells, which overexpress P-glycoprotein in the plasma membrane, accumulated vinblastine, at 37 degrees C for 30 min, to a much lower extent than the sensitive cells (P388/S), while in the micromolar range the cellular concentration was similar for both types of cells. When cells were incubated with a low (10 nM) or high concentration (1 microM) of vinblastine while energy deprived, the vinblastine concentration increased only in the resistant cells incubated with the low concentration of vinblastine, and this increased level was lowered to the level under the normal conditions by addition of glucose. In contrast, the cellular concentrations in other cases were increased to the normal level by glucose. After cells were loaded with the low concentration of vinblastine, the cellular vinblastine was extruded more rapidly from the resistant cells than from the sensitive cells. The courses of vinblastine efflux from the cells loaded with the high concentration of vinblastine were similar in both types of cells. NA-382, a reported P-glycoprotein inhibitor, effectively increased the intracellular vinblastine and inhibited the drug efflux only from multidrug-resistant cells, P388/ADR and AH66 cells, which were incubated with the low concentration of vinblastine. Cellular uptake of NA-382 was also less in P388/ADR cells than in P388/S cells in culture with 10 nM but not 1 microM of the agent, and this low level was reversed to the level in the sensitive cells by 10 microM vinblastine. These results indicate that P-glycoprotein as a drug-efflux pump works effectively under low extracellular concentrations of substrates, but does not under the high concentrations.
P-糖蛋白在多药耐药肿瘤细胞中作为一种活性药物外排泵发挥作用。我们研究了P-糖蛋白将药物从细胞中排出的能力。对于纳摩尔浓度的长春碱，在质膜中过表达P-糖蛋白的P388/ADR细胞，在37℃孵育30分钟时，长春碱的积累程度比敏感细胞（P388/S）低得多，而在微摩尔范围内，两种细胞类型的细胞内浓度相似。当细胞在能量剥夺的情况下与低浓度（10 nM）或高浓度（1 μM）的长春碱一起孵育时，长春碱浓度仅在与低浓度长春碱孵育的耐药细胞中增加，并且通过添加葡萄糖将这种增加的水平降低到正常条件下的水平。相比之下，在其他情况下，细胞内浓度通过葡萄糖增加到正常水平。在用低浓度长春碱加载细胞后，耐药细胞中细胞内长春碱的排出比敏感细胞更快。两种细胞类型中，从加载高浓度长春碱的细胞中排出长春碱的过程相似。NA-382是一种报道的P-糖蛋白抑制剂，仅在与低浓度长春碱孵育的多药耐药细胞P388/ADR和AH66细胞中，有效增加细胞内长春碱并抑制药物外排。在含有10 nM而非1 μM该试剂的培养物中，P388/ADR细胞对NA-382的细胞摄取也比P388/S细胞少，并且通过10 μM长春碱将这种低水平逆转到敏感细胞中的水平。这些结果表明，作为药物外排泵的P-糖蛋白在底物细胞外低浓度下有效发挥作用，但在高浓度下则不然。
