Ascorbic Acid And Its Therapeutic Potential Against Colorectal Adenocarcinoma

ABSTRACT Introduction Colorectal cancer (CRC) is a major health problem, with more than 800,000 new cases diagnosed worldwide every year. A better understanding of the processes involved in the transformation of normal cells into cancer cells has led to the development of new therapies which target cancer through different mechanisms. The use of vitamin C in the treatment of cancer has been the source of many controversies over the last 25 years. Vitamin C is available in its reduced form (ascorbic acid - AA) and in its oxidized form (dehydroascorbic acid). Although AA is most commonly known for its antioxidant properties, it is also known to function as a pro-oxidant at pharmacological concentrations, promoting the formation of reactive oxygen species (ROS). The increased production of hydrogen peroxide, coupled with the breakdown of the activity of antioxidant enzymes and the presence of transition metals in cancer cells, may result in the selective cytotoxicity of vitamin C and the subsequent revelation of its therapeutic potential. The aim of this study is to evaluate the therapeutic potential of AA in human colorectal adenocarcinoma cell lines in vitro and in vivo. Methods Two human colorectal adenocarcinoma cell lines, the cells WiDr and C2BBe1, were cultured in DMEM supplemented with 10% FBS. Cells were incubated in absence and with different concentrations of AA during different periods of time. The half maximal inhibitory concentration (IC50) was calculated after 24, 48, 72 and 96 hours by the sulforodamine B (SRB) assay. In order to evaluate cell survival, clonogenic assays were performed. At tenth day, the number of colonies was counted, being the plate efficiency and the survival factor determined. In order to verify in vivo the evolution of tumor growth after the daily injection of AA, WiDr cells were inoculated on the back of Balb/c nu/nu mice and, during several days, the body weight and tumor size of mice were monitored. AA was not administered to control animals. Results Our results obtained with SRB show that AA induces a decrease in cell proliferation in both cell lines, in a dose-dependent way. It was also verified that the IC50 of AA decreases in both cell lines in a time-dependent way. The clonogenic assays revealed that, as the concentration of AA increases, the survival factor decreases. This behaviour was observed in both cell lines, being more evident in WiDr cells (the reduction factor is 44.88% in cells treated with 0.5mM and above 80% when cells are treated with 2, 3 and 5mM). The in vivo studies suggest that AA administered daily at 150 mg/kg inhibits tumor growth since there are significant differences between the two murine groups (control vs treated mice). Conclusion Our study suggests that AA induces an anti-proliferative effect and a decrease in WiDr and C2BBe1 cells survival. Our results also indicate that AA stabilizes tumor growth in a mice model of CRC. The data obtained in the two different human cell lines of colorectal adenocarcinoma could contribute to the insights of the role of antioxidants as anti-cancer therapies.