5-fluorouracil (5-FU) has been used in the treatment of colorectal cancer for >50 years. However, drug resistance remains an obstacle in the application of 5-FU-based chemotherapy. Bufalin, a type of steroid with anti-tumor activity, may be purified from the skin and parotid venom glands of toads. In order to improve the anti-tumor effect of 5-FU, the present study examined the combined effects of bufalin with 5-FU on human colorectal cancer HCT116 cells. Following treatment, cell proliferation was quantified using MTT assay and apoptotic cell percentage was assessed by flow cytometry. The apoptosis-associated protein expression was evaluated by western blotting. It was observed that bufalin enhanced the cytotoxicity of 5-FU in HCT116 cells via the induction of the mitochondrial apoptotic pathway. Additionally, bufalin combined with 5-FU reduced the expression levels of anti-apoptotic proteins, such as Mcl-1, XIAP and Bcl-2 and upregulated the levels of the pro-apoptotic proteins, Bax and Bad. To verify the role of Bax, RNA interference was used to knock-down Bax. It was determined that the synergistic effect between 5-FU and bufalin was diminished following the silencing of Bax. In summary, bufalin in combination with 5-FU may induce a higher level of apoptosis compared with monotherapy, and the combination mat be a potential therapeutic strategy for the treatment of colorectal cancer.
Keywords: 5-fluorouracil; B-cell lymphoma-2-associated X protein; apoptosis; bufalin; colorectal cancer.