Enhancement of radiation induced oxidative stress in tumour cells by EGCG

In view of the fact that radiotherapy fails in the later stages of cancer due to the radioresistant tumor cells, it is most important in radiobiology to enhance the oxidative damage of the tumor cells by using a tumor selective cytotoxic agent. The increase in radiosensitivity is important both for optimizing radiation dose for tumors and for designing strategies to improve the therapeutic ratio. Amount and time of treatment of radiation (IR), epigallocatechin gallate (EGCG) and epicatechin (EC) were determined using MTT assay. Biochemical assay, Flow cytometry and immune blots were employed to elucidate the enhanced sensitization of EC and EGCG along with IR in hepatocellular carcinoma cells (HepG2). The effects were more effective in killing the HepG2 cells compared to only irradiation. It was observed that the ROS generation was significantly increased in combination group (IR+EGCG/EC) over the IR group. Lower reduced glutathione content, higher TBARS and decreased catalase activity in combination group provided additive support. Combination treatment caused cell cycle arrest at G2/M phase. Mitochondrial membrane potential was greatly reduced and the percentage of apoptotic population increased in combination group compared to IR alone. Moreover, the higher expression of p53 and activation of caspase 3 in combination group over the IR alone indicated EC and EGCG along with ionizing radiation increase the oxidative stressed condition in HepG2 cell that leads the apoptosis of the cells. The novel use of this combination of radiation and tea polyphenol will remain an effective radiotherapeutic strategy. (author)