Glutathione metabolism and glutathione S‐conjugate export ATPase (MRP1/GS‐X pump) activity in cancer

Abstract

Mg2+‐dependent vanadate‐sensitive glutathione S‐conjugate ATPase (GS‐X pump) activity is a common feature of some ATP‐binding cassette (ABC) transporters, such as the multidrug resistance‐associated protein (MRP1) gene product, that exports biologically active electrophiles after their conjugation with intracellular glutathione (GSH) from normal and cancer cells. Antitumor electrophiles (e.g. naturally occurring cyclopentenone prostaglandins and anticancer chemicals) can be intracellularly conjugated with GSH via a glutathione S‐transferase catalyzed reaction and be eliminated through GS‐X pumps thus threatening cancer chemotherapeutics. Since different sensitivities to antitumor electrophiles are shown by different cell types, the ability of several human cancer cell lines to produce and export S‐(2,4‐dinitrophenyl)‐glutathione (DNP‐SG) conjugate through the GS‐X pump, using whole cells and inside‐out membrane vesicle preparations, is investigated. Different cancer cell lines exhibited characteristically different GS‐X pump activity. In particular, HEp‐2 larynx carcinoma cells possess an elevated DNP‐SG export rate through the GS‐X pump compared with HeLa, K562, U937 or HL‐60 cells, which exhibit the lowest activity. The differences in DNP‐SG export rates are not due to decreased glutathione S‐transferase activity or impaired de novo synthesis of GSH. The findings suggest that the GS‐X pump may be involved in the modulation of the biological activity of both naturally occurring electrophiles and anticancer drugs. The differential expression of GS‐X pumps may lead to an improved understanding of multidrug resistance and may be exploited in the development of new therapeutic strategies for the treatment of cancer patients.

The Role of Oxidative Stress in the Development of Cisplatin Resistance in Epithelial Ovarian Cancer

“…[20][21][22] However, it was shown that once cancer is established, high levels of GSH could be deleterious by preventing the cytotoxic effect of various chemotherapeutic agents through detoxification and increased activity of efflux pump. [23][24][25] Conversely, it has also been reported that low levels of GSH are linked to impaired immune response and tumor progression. [26][27][28] The latter is more aligned with our findings, because low expression of GSR is indicative of low GSH and increased oxidative stress, since GSH will not be adequately regenerated from its oxidized form (GSSG).…”

Low expression ofMRP1/GS-X pump ATPase in lymphocytes of Walker 256 tumour-bearing rats is associated with cyclopentenone prostaglandin accumulation and cancer immunodeficiency

“…37 Spectrophotometric assay of glutathione S-conjugates exported from cells MRP1/GS-X pump-mediated GS-conjugate export by whole cell preparations was assessed by treating cells with the electrophile 1-Cl-2,4-dinitrobenzene (CDNB, Sigma) as described. 13 CDNB reacts promptly with GSH to produce the stable conjugate S-(2,4-dinitrophenyl)-glutathione (DNP-SG) with a UV spectrum ( max ¼ 340 nm) different from that of CDNB ( max ¼ 252 nm). CDNB was kept as a 1 mM ethanolic stock solution and control preparations received an equal amount of ethanol (0.05% v/v, final concentration).…”

“…Spectrophotometric-based analyses of cell supernatant fractions were compared to HPLC patterns of the same samples and were found to be identical to those of enzymically prepared DNP-SG standard. 13 The rates of DNP-SG production in pmol/min per 10 6 cells or nmol/min per mg of cell protein were calculated on the basis of the absorption coefficient for DNP-SG (" 340 ¼ 9.6 mM À1 .cm À1 ).…”

Janus-Faced Tumor Microenvironment and Redox

“…The synthesis of cysteinyl-glycine is catalyzed by plasma membrane-bound c-glutamyltransferase (GGT) from extracellular GSH. The activity of GGT (12,21,27,29,30) as well as expression of GSH complex export transporters, GS-X pumps (1,14,45), are often significantly elevated in cancer cells, including human malignancies, supporting the potential importance of GGT/GSH-dependent mechanism in TME extracellular superoxide production (17).…”