Sakamoto H, Hara H, Hirano K, Adachi T
Laboratory of Clinical Pharmaceutics, Gifu Pharmaceutical University, Japan.
Cancer Lett. 1999 Jan 8;135(1):113-9. doi: 10.1016/s0304-3835(98)00285-7.
Multidrug resistance-associated protein (MRP) has been shown to transport glutathione (GSH) S-conjugates such as leukotriene C4 (LTC4) and S-(2,4-dinitrophenyl)-glutathione (DNP-SG). On the other hand, it has while it has been reported that MRP-overexpressing cells exhibit decreased sensitivity to drugs which do not form GSH S-conjugates. In this study, we found that GSH affects the transport of glucuronosyl etoposide as a major metabolite of etoposide in MRP-overexpressing KB/VP-4 cells. The relative resistance level of KB/VP-4 cells to etoposide was 70-fold that of wild-type KB cells. Membrane vesicles prepared from KB/VP-4 cells exhibited markedly enhanced ATP-dependent transport of glucuronosyl etoposide as well as LTC4. Transport of glucuronosyl etoposide was augmented in the presence of GSH. Treatment of KB/VP-4 cells with buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, resulted in about 75% depletion of cellular GSH levels, a four-fold increase of the sensitivity to etoposide and depression of glucuronosyl etoposide efflux. These results suggest that GSH plays a role in the enhancement of MRP-mediated glucuronosyl etoposide transport.
多药耐药相关蛋白（MRP）已被证明可转运谷胱甘肽（GSH）S-共轭物，如白三烯C4（LTC4）和S-（2,4-二硝基苯基）-谷胱甘肽（DNP-SG）。另一方面，虽然有报道称过表达MRP的细胞对不形成GSH S-共轭物的药物敏感性降低。在本研究中，我们发现GSH影响MRP过表达的KB/VP-4细胞中作为依托泊苷主要代谢产物的葡萄糖醛酸基依托泊苷的转运。KB/VP-4细胞对依托泊苷的相对耐药水平是野生型KB细胞的70倍。从KB/VP-4细胞制备的膜囊泡显示出葡萄糖醛酸基依托泊苷以及LTC4的ATP依赖性转运显著增强。在GSH存在下，葡萄糖醛酸基依托泊苷的转运增加。用谷胱甘肽合成抑制剂丁硫氨酸亚砜胺（BSO）处理KB/VP-4细胞，导致细胞内GSH水平降低约75%，对依托泊苷的敏感性增加四倍，葡萄糖醛酸基依托泊苷外排减少。这些结果表明，GSH在增强MRP介导的葡萄糖醛酸基依托泊苷转运中起作用。
