Targeting autophagy promote the 5-fluorouracil induced apoptosis in human colon cancer cells

Colon cancer is a leading cause of cancer-related death in developed countries. Although 5-fluorouracil (5FU) has traditionally been studied for its potential to induce apoptosis, its clinical use had been greatly limited as a result of the development of drug resistance in patients. Besides the medicines that could induce apoptosis in cancer cells, several other alternative treatments, which had different mechanisms of action (such as autophagy), had gained more and more attention recently. As for colon cancer, autophagy appeared to have certain protective effects in tumor cells by antagonizing the inhibition caused by chemotherapy and radiotherapy. Therefore, autophagy inhibition seemed to be an effective mean for cancer treatment. In this study, HT29 and SW480 cells were treated with autophagy inhibitors together with/without 5-FU, the proliferation rate, apoptosis and autophagy induction effects were then evaluated. The proliferation rate of cancer cells was analyzed by MTT assay. Apoptosis was quantified by flow-cytometry after the cells were double-stained with Annexin V/PI. Autophagy and apoptosis were both further confirmed by western blot analysis. Finally, to confirm the effects of combinational use of 5-FU with 3-methyladenine (3-MA) and Chloroquine (CQ), the colony formation assay was also performed. Our results demonstrated that 5-FU could induce apoptosis and autophagy in colon cancer cells. Both 3-MA and CQ could enhance the apoptosis induced by 5-FU in colon cancer cells, while CQ had better inhibitory effect against the proliferation of colon cancer cells. Meanwhile, CQ could induce a caspase-dependent apoptosis in colon cancer cells. Cathepins might function in the synergistic interaction between 5-FU and CQ. Based on the above results, we proposed the combinational use of 5-FU and CQ might be a novel therapeutic method for the treatment of colon cancer.