Modulation of Oxidative Stress Responsive Genes and Enzymes in Radiosensitization by Metabolic Modifiers

Abstract

Cancer cells invariably exhibit altered glucose metabolism that occurs as result of newlinemetabolic shift during their course of evolution. This metabolic shift has been suggested as newlinea differential approach to enhance the radiation damage selectively in malignant cells. In newlinethe present as well as in our earlier studies, we have shown that the simultaneous inhibition newlineof glycolysis (using 2-deoxy-D-glucose; 2-DG) and pentose phosphate pathway (using 6- newlineaminonicotinamide: 6-AN) leads to the selective radiosensitization in a variety of newlinemalignant cells. The present study was carried out to investigate the effects of combination newlineof 2-DG (5 mM) and 6-AN (5 and#956;M) on intricately regulated antioxidant defense and global newlinegene expression besides level and localization of various regulatory proteins involved in newlinethe selective radiosensitization by this combination. Two human malignant; (i) Head and newlineNeck squamous carcinoma (KB) and (ii) Cerebral glioma (BMG-1) and one non-malignant newlinehuman embryonic kidney (HEK) cells were used in this study. Presence of 2-DG and 6-AN newline(added just before irradiation) for 4 h following irradiation, significantly decreased the newlineclonogenicity and metabolic viability of KB and BMG-1 cell lines, while no significant newlineloss of clonogenicity and metabolic viability was noted in HEK cells. Accumulation of newlineROS was observed in malignant cells only that compromised the redox status by enhancing newlinethe NADP+/NADPH and GSSG/GSH ratio with concomitant decrease in glutathione newlinereductase expression (mRNA and protein) and activity at 24 h post treatment. The levels newlineand activities of Cu, Zn-SOD and Mn-SOD increased with ROS accompanied by a newlinedecrease in GPx. However, the protein level and activity of catalase remain unaltered in all newlinethe cell lines under these conditions. These results suggest that non-coordinated expression newlineof antioxidant defense, besides compromised redox status, against the ROS led to enhanced newlineradiosensitization observed selectively in the malignantly transformed cells.