γ-Glutamylcysteine Synthetase Gene Overexpression Results in Increased Activity of the ATP-Dependent Glutathione S-Conjugate Export Pump and Cisplatin Resistance

First Department of Internal Medicine, Akita University, Akita, Akita, Japan
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 12/1995; 216(1):258-64. DOI: 10.1006/bbrc.1995.2618
Source: PubMed


The ATP-dependent glutathione S-conjugate export pump (GS-X pump) has been suggested to play a role in the mechanism of cisplatin resistance. The purpose of this study was to determine the relationship between intracellular glutathione (GSH) levels and GS-X pump activity and whether GS-X pump overexpression results in cisplatin resistance. We transfected the human gamma-glutamylcysteine synthetase (gamma-GCS) gene into a human small-cell lung cancer cell line, SBC-3, producing SBC-3/GCS. The intracellular GSH content of SBC-3/GCS was twice that of the parental line, its GS-X pump activity was significantly enhanced and cellular cisplatin accumulation decreased. SBC-3/GCS showed higher resistance (relative resistance value of 7.4) to cisplatin than the parental line SBC-3. These data indicate that gamma-GCS gene overexpression induces cellular cisplatin resistance associated with increases in both the GSH content and GS-X pump activity, resulting in reduced cisplatin accumulation. In conclusion, GS-X pump expression is related to cellular GSH metabolism and involved in cisplatin resistance.

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    • "Comparison of the GST staining indices of our eight HNSCC lines with the IC50 values of these lines revealed no correlation (see Table 2), which is in agreement with the results of Yellin and colleagues (1994) for a panel of 14 HNSCC lines. It cannot be excluded that the other factors in the GSH-associated detoxification system play a role in cisplatin sensitivity ; this includes the enzymes glutathione peroxidase, glutathione synthetase, glutathione reductase and dipeptide gamma-glutamylcysteine (Kramer et al, 1988; Kurokawa et al, 1995). "
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    ABSTRACT: Resistance to chemotherapy is a major problem in the treatment of patients with head and neck squamous cell carcinoma (HNSCC). Important factors involved are drug detoxification by glutathione (GSH) and reduced drug accumulation due to active transport out of the cell by so-called 'multidrug resistance-related proteins'. We have studied a panel of eight HNSCC cell lines showing differences in sensitivity to the anti-cancer drug cisplatin. Our previous studies indicated that the IC50 values were inversely correlated with the intracellular accumulation of platinum (Pt). In the present study, cellular GSH levels were found not to be related to the IC50 values. The expression levels of the enzymes glutathione S-transferase (GST) alpha, mu, and pi, the multidrug resistance-related proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP) and the lung resistance protein (LRP) were determined semiquantitatively by means of immunocytochemistry. The levels of the GSTs, P-gp and LRP were not found to be correlated with the IC50 values of the HNSCC cell lines. Surprisingly, however, an inverse correlation was found between MRP levels and IC50 values. The MRP expression levels were in agreement with the results of the MRP functional assay, based on the transport of calcein across the cell membrane as performed for two of the cell lines. Further studies should prove whether other pump mechanisms or DNA repair are involved in the cisplatin accumulation and the subsequent HNSCC cell growth inhibition.
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