Edinburgh, Edinburgh Royal Infirmary, Edinburgh EH3 9 YW; and 3Department of Clinical Oncology, Newcastle General Hospital, Newcastle-upon-Tyne, UK.Summary An increasing body of evidence indicates that glutathione S-transferases play a role in the intrinsic and acquired resistance of tumours to anticancer drugs. In view of the wide use of tumour cell lines to understand the factors which confer either sensitivity or resistance to chemotherapeutic agents we have determined glutathione S-transferase (GST) activity and isozyme composition in nine human cell lines. These data have been compared with the values obtained in solid tumours. In most cases overall GST activity was higher in the tumours than in the cell lines. This was most pronounced for the breast tumour samples relative to MCF7 cell line. The pi class GST subunit was present at similar concentration in the cell lines and the tumours, and in most cases was the most abundant subunit present. The alpha and mu class GST were expressed in most of the cell lines but at much lower concentration than the pi class subunit. Also considerable variability particularly in the expression of the mu subunits was observed. This was also the case for the expression of these subunits in the solid tumour samples. The levels of these GSTs (when expressed) in the solid tumours was invariably higher than that observed in the cell lines. There are therefore several similarities but also some significant differences in GST expression in solid tumours and cell lines. Whether the differences are because expression is lost during the generation of the cell lines or whether it reflects the individuality of human tumours remains to be clearly established.The glutathione S-transferases (GST) are a multigene family of dimeric proteins which play a central role in the detoxification of electrophilic xenobiotics (Chasseaud, 1979). In man, cytosolic GSTs have been divided into three major classes termed alpha (basic), mu (neutral) and pi (acidic) (Mannervik, 1985;Stockman et al., 1987). Proteins within these groups have marked differences in their substrate specificity. There is a growing body of evidence which indicates that GST play an important role in both carcinogenesis and drug resistance. For example, certain compounds which inhibit chemical carcinogenesis are often inducers of the GST in the target tissue (Benson et al., 1978;Benson & Barretto, 1985). These proteins are also overexpressed in preneoplastic lesions (Kitahara et al., 1984;Pickett et al., 1984; Buchmann et al., 1985) and, in addition, have been demonstrated to be increased in both normal and tumour cells exposed to cytotoxic drugs (Adams et al., 1985;Wang & Tew, 1985;Carmichael et al., 1986;Batist et al., 1986;Evans et al., 1987;Robson et al., 1987;Wolf et al., 1987a;.It is likely that glutathione S-transferase levels and isoenzyme composition will play a role in both the intrinsic and acquired resistance to cancer chemotherapy (McGowan & Fox, 1986;Wolf et al., 1987b;Buller et al., 1987;Lewis et al., 1988a). Surpris...

Summary Drug resistance in haemopoietic cells may be partly related to the expression of the glutathione-stransferase (GST) pi and mdr-l genes. We have used RNA slot blotting techniques to investigate the expression of GST pi in peripheral blood and bone marrow of eleven normal subjects, nine patients with myelodysplastic syndrome (MDS), eighteen patients with acute myeloblastic leukaemia (AML), and thirty-two patients with chronic lymphocyte leukaemia (CLL). We found increased expression of GST pi in 8 of 9 MDS, (7 peripheral blood, I bone marrow) 12

Glutathione S-transferase (GST) enzymes are often over-expressed in tumor cells made resistant to cytotoxic drugs but it is unclear whether GST over-expression is directly linked to the resistance mechanism. We have made a human lung tumor cell line resistant to 1 -chloro-2,4-dinitrobenzene (CDNB) in order to establish whether selection for resistance with a model GST substrate results in selection of a cell line with higher GST levels. The resistant line (CDNB'), although only twofold more resistant to this compound, exhibited a marked (15-fold) increase in GST activity compared to the wild-type cell line (28 -+ 10 versus 357 -+ 30 nmol CDNB conjugated . min-' . mg-' protein, respectively). Resistance to CDNB was associated with a marked increase in the level of both alphaclass and pi-class GST. Resolution of the GST by reverse-phase HPLC demonstrated that the increase in the expression of the alpha-class enzymes was due to elevated levels of both the B, and B, subunits. The increased levels of alpha-class and pi-class GST in the CDNB' cells was not due to either gene amplification or increased mRNA levels and appears to involve either altered mRNA utilization or protein stabilization. In addition to being resistant to CDNB, the CDNB' cell line also showed a 2.5-fold resistance to cumene hydroperoxide but was not cross-resistant to the anticancer drug chlorambucil. To demonstrate that the increased GST level was part of the resistance mechanism the alpha-class GST B, cDNA under control of the p-actin promoter was stably expressed in the breast tumor cell line MCF-7. The cell lines generated were twofold more resistant to CDNB relative to the parental line.Many cancer patients who initially respond to treatment with anti-tumour drugs subsequently become resistant to chemotherapy. To help increase the clinical effectiveness of chemotherapy considerable effort has been made to identify the biochemical and genetic changes responsible for the drugresistant phenotype. Such work has demonstrated the existence of numerous resistance mechanisms [l], including alterations in drug transport, decreased activation of pro-drugs, increased drug detoxification, increased drug sequestration and mutation in drug target site(s). Although tumor cells can develop tolerance to chemotherapeutic agents by diverse processes, most resistance mechanisms are drug specific. For example, increased levels of P-glycoprotein, a transmembrane efflux pump of broad specificity, can confer resistance against anthracyclines, vinca alkaloids and podophylotoxin derivatives but not alkylating agents nor cis-platinum [I].The glutathione S-transferases (GST), a supergene family of detoxication enzymes, have been shown to become increased in many models of drug resistance (reviewed in [2-41). The GST are represented by several gene families, DDI 9SYAbbreviations. CDNB, 1 -chloro-2,4-dinitrobenzene; Me,SO, dimethyl sulphoxide; GST, glutathione S-transferase; MTT, 3-(4,sdimethylthiazol-2-yl)-2,S-diphenyl tetrazolium bromide; SV40, simian sarcoma virus 40;...