Different mechanisms for γ-glutamyltransferase-dependent resistance to carboplatin and cisplatin

• Published in: Biochemical pharmacology 2003-08, Vol.66 (4), p.595-604
• Main Authors: Daubeuf, Sandrine, Balin, Diane, Leroy, Pierre, Visvikis, Athanase
• Format: Article
• Language: English
• Subjects: Adducts; Antineoplastic Agents - pharmacology; Biochemistry; Biochemistry, Molecular Biology; Biological and medical sciences; Cancer; Carboplatin; Carboplatin - metabolism; Carboplatin - pharmacology; Cisplatin; Cisplatin - metabolism; Cisplatin - pharmacology; Drug Resistance, Neoplasm; gamma-Glutamyltransferase - physiology; Glutamate-Cysteine Ligase - metabolism; Glutathione - analysis; GSH; HeLa Cells; Humans; Life Sciences; Medical sciences; Pharmacology. Drug treatments; Resistance; γ-Glutamyltransferase
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(03)00343-5

In this work, we investigated the effect of γ-glutamyltransferase (GGT) overexpression on cell viability after carboplatin treatment and compared with cisplatin. Carboplatin challenge of HeLa cells induced GGT and glutamate-cystine ligase (GCL) activities by 2- and 1.4-fold, respectively and concomitantly increased the intracellular reduced glutathione (GSH) level (1.5-fold). To study the role of GGT, HeLa-GGT cells, a stably transfected cell line overexpressing GGT (120–150mU/mg protein) and the parental HeLa cells (10–15mU/mg protein) were used. Both cell lines exhibited comparable viability (ic50~150μM) after carboplatin treatment when cultured in standard (250μM cystine) medium. Culture in low (50μM) cystine medium resulted in a dramatic decrease (~90%) of the intracellular GSH level and to a 2.5-fold increase of carboplatin cytotoxicity (ic50~60μM). When GSH (50μM) was included in the culture medium, only HeLa-GGT cells exhibited increased resistance to carboplatin. Using partially purified GGT from HeLa-GGT cells, we show that cisplatin forms adducts with cysteinylglycine, depending only on GGT activity whereas carboplatin did not efficiently react with cysteinylglycine. Thus, in this model system, GGT activity can affect platinum drugs cytotoxocity by two different ways: cisplatin can be detoxified extracellularly after reaction with the -SH group of cysteinylglycine; in the case of carboplatin, the supply of GSH precursors, initiated by GGT, increases the intracellular level of the tripeptide and provides enhanced defensive mechanisms to the cell.