Estimation of glutathione S-transferase and its Pi isoenzyme in tumor tissues and sera of patients with ovarian cancer

Abstract

OBJECTIVES: The Pi class GST is the most ubiquitous of the human GST family, being expressed in different tissues. However, its role in ovarian cancer is still poorly defined. To establish normal and tumor related changes, the levels of total GST as well as its isoenzyme GST Pi, were therefore measured in ovarian tissue samples and the corresponding serum specimens obtained from patients undergoing primary surgical treatment for their disease (n = 68). The total GST activity was spectrophotometrically determined utilizing 1-Chloro- 2,4-dinitrobenzene (CDNB) as the substrate. The GST Pi isoenzyme was measured by ELISA and immunohistochemical methods. RESULTS: The total GST activity, the level of GST Pi isoenzyme, the DNA content and S phase fraction were significantly higher in the malignant than in non-malignant ovarian tissues. In the malignant group the values of both cytosolic total GST and GST Pi were significantly correlated (r = 0.56, P = < 0.01). In spite of the absence of a significant correlation with a number of important prognostic features including the patient age, FlGO stage, DNA content and S-phase fraction, both total GST and GST Pi were significantly higher in the grade I than in grades II and III malignant tumors. Additionally, the total GST was significantly lower in the serous than non-serous malignant tumors. CONCLUSION: In the malignant group, although the elevation of blood content of GST and its Pi isoenzyme was not as significant as that of the tissue content, the fact that higher serum values of patients with some cancers often reverted to the normal range after treatment of the cancer suggested the direct derivation of these enzymes from tumor tissues. Thus, follow up of elevated serum GST and GST Pi levels may be useful for monitoring ovarian cancer patients during the course of treatment