Chen G, Waxman D J
Department of Biology, Boston University, MA 02215, USA.
Biochem Pharmacol. 1995 May 26;49(11):1691-701. doi: 10.1016/0006-2952(95)00079-f.
Aldehyde dehydrogenase (ALDH) is well known for its involvement in the resistance of tumor cells to cyclophosphamide (CPA) and its activated derivatives, such as 4-hydroperoxy-CPA (4HC). The role of other drug-metabolizing enzymes such as glutathione S-transferase (GST) in CPA resistance is, however, less certain. In the present study of a human breast cancer cell line (MCF-7) exhibiting about 6-fold resistance to 4HC (MCF/HC), cellular levels of glutathione (GSH) were increased 1.4-fold, while cytosolic GST and ALDH activities were increased 2.7- and 7.2-fold, respectively, relative to the MCF-7 parental line. No significant changes in glutathione peroxidase and NADPH cytochrome P450 reductase activity, and no increase in microsomal GST and GST pi mRNAs were found in the resistant cells. Treatment with the ALDH substrate octanal sensitized the cells to the cytotoxic effects of 4HC to a modest extent in both MCF-7 and MCF/HC cells [dose modification factor (DMF) of 1.4 and 1.6, respectively]. Depletion of GSH by treatment with the GSH synthesis inhibitor buthionine sulfoximine (BSO) enhanced the cytotoxic effect of 4HC to a similar extent in both cell lines. By contrast, ethacrynic acid, which inhibited GST activity by > 85% in MCF-7 and MCF/HC cell extracts without depletion of GSH, sensitized the resistant but not the parental cells to 4HC cytotoxicity, indicating the importance of GST as a determinant of 4HC resistance in these cells. This conclusion is supported by the observation that in MCF/HC cells, ethacrynic acid in combination with BSO increased the DMF 3-fold higher than did BSO or EA alone, while in the parental MCF-7 cells ethacrynic acid with BSO had no significant chemosensitization effect over BSO alone. These studies establish that in addition to ALDH, GST overexpression can contribute to acquired resistance of tumor cells to 4HC and, furthermore, suggest that modulators that target the GSH/GST system could be useful in overcoming CPA resistance in the clinic.
醛脱氢酶（ALDH）因参与肿瘤细胞对环磷酰胺（CPA）及其活化衍生物（如4-氢过氧环磷酰胺（4HC））的耐药性而广为人知。然而，其他药物代谢酶（如谷胱甘肽S-转移酶（GST））在CPA耐药性中的作用尚不太明确。在本研究中，一种对4HC表现出约6倍耐药性的人乳腺癌细胞系（MCF-7）（MCF/HC），其细胞内谷胱甘肽（GSH）水平增加了1.4倍，而胞质GST和ALDH活性相对于MCF-7亲代细胞系分别增加了2.7倍和7.2倍。在耐药细胞中，未发现谷胱甘肽过氧化物酶和NADPH细胞色素P450还原酶活性有显著变化，微粒体GST和GST π mRNA也未增加。用ALDH底物辛醛处理，在MCF-7和MCF/HC细胞中均使细胞对4HC的细胞毒性有一定程度的敏感化（剂量修正因子（DMF）分别为1.4和1.6）。用谷胱甘肽合成抑制剂丁硫氨酸亚砜胺（BSO）处理耗尽GSH，在两种细胞系中均使4HC的细胞毒性增强程度相似。相比之下，依他尼酸在不耗尽GSH的情况下，在MCF-7和MCF/HC细胞提取物中抑制GST活性超过85%，使耐药细胞而非亲代细胞对4HC细胞毒性敏感，表明GST作为这些细胞中4HC耐药性的决定因素的重要性。这一结论得到以下观察结果的支持：在MCF/HC细胞中，依他尼酸与BSO联合使用使DMF比单独使用BSO或依他尼酸高出3倍，而在亲代MCF-7细胞中，依他尼酸与BSO联合使用相对于单独使用BSO没有显著的化学增敏作用。这些研究表明，除了ALDH外，GST过表达也可导致肿瘤细胞对4HC产生获得性耐药，此外，还表明靶向GSH/GST系统的调节剂可能有助于在临床上克服CPA耐药性。
