Enhancement of radiation-induced oxidative stress and cytotoxicity in tumor cells by ellagic acid

Background: Failure of treatment of cancer in clinic by radio/chemotherapy is generally attributed to tumor resistance. It is, therefore, important to develop strategies to increase the cytotoxicity of tumor cells by radiation in combination with new tumor selective cytotoxic agents. We describe the role of ellagic acid (EA) and gamma radiation on the oxidative stress and subsequent cytotoxicity of tumor cells in vitro as well as in vivo and their sparing effects on normal cells. Methods: Ehrlich ascites carcinoma (EAC)-transplanted Swiss mice were intraperitoneally injected with EA followed by radiation treatment of 2 Gy for 4 alternate days. Hela cells were used for in vitro studies. Reactive oxygen species (ROS) level was measured by spectrofluorimetric method by using 2, 7-dichlorodihydrofluoresceindiacetate (DCHFDA) fluorescent probe. Cytotoxicity was measured by Trypan blue dye exclusion test and mitochondrial potential was measured using Rhodamine 123 as a probe. Antioxidant enzymes were measured by spectrophotometric methods. Results: EA was found to generate ROS in tumor cells, which increased, by an order of magnitude when cells were treated with EA in combination with gamma radiation. The decrease in mitochondrial potential and the loss of cell viability were remarkably greater in tumor cells from mice treated with EA and radiation than alone treatment with either of them. Moreover, EA was found to protect against radiation-induced oxidative stress in splenic lymphocytes of tumor-transplanted mice. Measurement of antioxidant enzymes such as superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-Px) and glutathione reductase (GR) in tumor cells showed decrease after treatment with EA and radiation in vivo. Treatment of tumor bearing mice with EA and radiation showed significant decrease in animal's body weight suggesting reduced tumor burden.