The mechanisms responsible for the radiosensitizing effects of sorafenib on colon cancer cells.

Colorectal cancer is one of the most common malignancies in the world, and is generally treated more effectively by chemoradiotherapy rather than radiotherapy or chemotherapy alone. Targeted radiosensitizers are often used in order to enhance the radiosensitivity of tumor cells. The aim of the present study was to identify the mechanism of radiosensitization by sorafenib in colorectal cancer. Three human colorectal adenocarcinoma cell lines (HCT116, HT29 and SW480) were treated with sorafenib alone or radiation followed by sorafenib. In vitro tests were performed using colony forming assays, FACS analysis, immunohistochemistry, tumor cell motility assays, invasion assays and endothelial tube formation assays. Sorafenib enhanced the anti-proliferative effects of radiation, reducing colony formation, increasing G2/M arrest and enhancing radiation-induced apoptosis by reactive oxygen species. Sorafenib also inhibited the repair of radiation-induced DNA damage by blocking the activation of DNA-dependent protein kinase. Combination treatment significantly inhibited tumor cell migration, tumor cell invasion and vascular endothelial growth factor-mediated angiogenesis in vitro. Taken together, our results provide a scientific rationale for the use of sorafenib with radiotherapy in colon cancer and suggest a clinical utility for this approach.