Caspase Dependent Apoptosis is Only Inhibited on Γ Irradiation of Cells Conditioned by Repetitive Oxidative Stress

V79C cells were derived from V79 cell line by through chronic oxidative stress that was found to be radio-resistant. These cells had demonstrated transformation?like stable changes and could be used as model system to study oxidant induced carcinogenesis. Our objective was to understand mechanism of radiation-resistance in these cells. Apoptotic cell death was inhibited in these cells as visualized microscopically by Hoechst staining and nucleosomal ladder formation in agarose gel. Release of cytochrome c in cytoplasm and Apoptosis Inducing Factor in the mitochondrial and nuclear fraction of cells were determined by Western blotting. The caspase 9 and caspase 3 activities in these cells were estimated from fluorimetric assays. These results revealed that the radiation resistance was due to inhibition of caspase-dependent apoptotic death pathways although Apoptosis Inducing Factor mediated pathway remained unaffected. These findings may aid in understanding the mechanism of radiation resistance in tumors arising from oxidative stress.