Rhee M S, Wang Y, Nair M G, Galivan J
Wadsworth Center for Laboratories and Research, New York State Dept. of Health, Albany 12201-0509.
Cancer Res. 1993 May 15;53(10 Suppl):2227-30.
A subline of H35 hepatoma cells has been developed which exhibits 80-fold resistance to 5,10-dideazatetrahydrofolate, an antifolate which inhibits glycinamideribonucleotide transformylase. The cells are cross-resistant to methotrexate, an inhibitor of dihydrofolate reductase and 10-propargyl-5,8-dideazafolate and its 2-desamino-2-methyl derivative, both inhibitors of thymidylate synthase. The resistant cells are characterized by an impaired activity of the reduced folate transport system which affects cellular import of methotrexate, 5,10-dideazatetrahydrofolate, and 2-desamino-2-methyl-10-propargyl-5,8-dideazafolate but not 10-propargyl-5,8-dideazafolate. In addition, the resistant cells exhibit a severalfold increased activity of gamma-glutamyl hydrolase, the enzyme which cleaves the intracellular polyglutamate derivatives of the antifolates. Evidence for the involvement of gamma-glutamyl hydrolase in resistance is derived from the observation that polyglutamate derivatives of 10-propargyl-5,8-dideazafolate in resistant cells are maintained at one-third the amount of that in parental cells in the presence of the same extracellular concentration. This is the first observation that an increase in gamma-glutamyl hydrolase contributes to acquired resistance to antifolates.
已培育出一种H35肝癌细胞亚系，该亚系对5,10-二去氮四氢叶酸表现出80倍的抗性，5,10-二去氮四氢叶酸是一种抑制甘氨酰胺核糖核苷酸转甲酰酶的抗叶酸剂。这些细胞对甲氨蝶呤（一种二氢叶酸还原酶抑制剂）、10-炔丙基-5,8-二去氮叶酸及其2-脱氨基-2-甲基衍生物（两者均为胸苷酸合成酶抑制剂）具有交叉抗性。抗性细胞的特征是还原型叶酸转运系统活性受损，这影响了甲氨蝶呤、5,10-二去氮四氢叶酸和2-脱氨基-2-甲基-10-炔丙基-5,8-二去氮叶酸的细胞摄取，但不影响10-炔丙基-5,8-二去氮叶酸的摄取。此外，抗性细胞的γ-谷氨酰水解酶活性增加了几倍，γ-谷氨酰水解酶是一种裂解抗叶酸剂细胞内多聚谷氨酸衍生物的酶。γ-谷氨酰水解酶参与抗性的证据来自以下观察结果：在相同的细胞外浓度下，抗性细胞中10-炔丙基-5,8-二去氮叶酸的多聚谷氨酸衍生物的含量维持在亲本细胞的三分之一。这是首次观察到γ-谷氨酰水解酶的增加有助于获得性抗叶酸抗性。
