Chen G, Waxman D J
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
Biochem Pharmacol. 1994 Mar 15;47(6):1079-87. doi: 10.1016/0006-2952(94)90420-0.
Glutathione (GSH) and glutathione S-transferases (GSTs) play an important role in the protection of cells against toxic effects of many electrophilic drugs and chemicals. Modulation of cellular GSH and/or GST activity levels provides a potentially useful approach to sensitizing tumor cells to electrophilic anti-cancer drugs. In this study, we describe the interactions of four representative alkylating agents (AAs), melphalan, 4-hydroperoxy-cyclophosphamide (4HC), an an activated form of cyclophosphamide, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), and cisplatin, with GSH and GST in the human breast cancer cell line MCF-7. Depletion of cellular GSH pools by approximately 80% by treatment of the cells with the GSH synthesis inhibitor buthionine sulfoximine (BSO) sensitized the tumor cells to each AA to a different extent, with dose-modifying factors of 2.39, 2.21, 1.64, and 1.27 observed for melphalan, 4HC, cisplatin, and BCNU, respectively. Treatment of the cells with the GST inhibitor ethacrynic acid (EA) failed to show any significant effects on the cytotoxicity of these AAs. However, EA did potentiate the cytotoxicity of melphalan when given in combination with BSO, an effect that may be due to a more complete depletion of cellular GSH levels by the combined modulator treatment. Following a 1-hr exposure to cytotoxic-equivalent concentrations of these AAs, GSH levels decreased substantially in the case of 4HC and BCNU, but increased by 30-50% in the case of cisplatin and melphalan. BSO pretreatment largely blocked this effect of cisplatin and melphalan on cellular GSH, while it further enhanced the GSH-depleting activity of both 4HC and BCNU. On the basis of these results, it is concluded that (a) GSH affects the cytotoxicity of different AAs to different extents, (b) basal GST expression in MCF-7 cells does not play a major role in AA metabolism, (c) EA can potentiate the enhancing effect of BSO on melphalan cytotoxicity in MCF-7 cells, and (d) depletion of cellular GSH by pretreatment with BCNU or cyclophosphamide may correspond to a useful strategy for enhancing the anti-tumor activity of other AAs given in a sequential combination.
谷胱甘肽（GSH）和谷胱甘肽S-转移酶（GSTs）在保护细胞免受许多亲电药物和化学物质的毒性作用方面发挥着重要作用。调节细胞内GSH和/或GST活性水平为使肿瘤细胞对亲电抗癌药物敏感提供了一种潜在有用的方法。在本研究中，我们描述了四种代表性烷化剂（AAs），美法仑、4-氢过氧环磷酰胺（4HC，环磷酰胺的一种活化形式）、1,3-双（2-氯乙基）-1-亚硝基脲（BCNU）和顺铂，与人乳腺癌细胞系MCF-7中GSH和GST的相互作用。用GSH合成抑制剂丁硫氨酸亚砜胺（BSO）处理细胞，使细胞内GSH池消耗约80%，使肿瘤细胞对每种AA的敏感性在不同程度上增加，美法仑、4HC、顺铂和BCNU的剂量修正因子分别为2.39、2.21、1.64和1.27。用GST抑制剂依他尼酸（EA）处理细胞，未显示对这些AA的细胞毒性有任何显著影响。然而，当EA与BSO联合使用时，确实增强了美法仑的细胞毒性，这种效应可能是由于联合调节剂处理使细胞内GSH水平更完全地耗尽。在接触细胞毒性等效浓度的这些AA 1小时后，4HC和BCNU情况下GSH水平大幅下降，但顺铂和美法仑情况下GSH水平增加30 - 50%。BSO预处理在很大程度上阻断了顺铂和美法仑对细胞内GSH的这种作用，而它进一步增强了4HC和BCNU的GSH消耗活性。基于这些结果，得出以下结论：（a）GSH对不同AA的细胞毒性有不同程度的影响；（b）MCF-7细胞中的基础GST表达在AA代谢中不发挥主要作用；（c）EA可增强BSO对MCF-7细胞中美法仑细胞毒性的增强作用；（d）用BCNU或环磷酰胺预处理使细胞内GSH耗尽可能是增强序贯联合使用的其他AA抗肿瘤活性的一种有用策略。
