5-FU preferably induces apoptosis in BRAF V600E colorectal cancer cells via downregulation of Bcl-xL.

Fluorouracil (5-FU) which has been widely used in postoperative adjuvant therapy in patients with colon cancer, remains the main backbone of combination treatment of patients with colon cancer. However, the efficacy of 5-FU alone in colorectal cancer patients with BRAFV600E is not clear. In this study, we demonstrated that BRAFV600E confers sensitivity to 5-FU in vitro and in vivo xenograft model, using the paired isogenic colorectal cancer cell lines RKO with either BRAF Wild Type (WT)(+/-) or mutant (Mut) (600E/-). Our results revealed 5-FU preferably induces marked apoptosis in BRAF-mutant colorectal cancer cells, through attenuating expression of Bcl-xL and activation caspase-3/9 pathway, eventually conferring the anti-tumor efficacy of 5-FU in vitro and in vivo. Meanwhile, expression of Bcl-xL remained unchanged in BRAF WT group after treatment of 5-FU, although low extent of anti-tumor activity of 5-FU still being observed. In conclusion, these results provided a better understanding of clinical outcome of 5-FU between BRAF WT and mutant colorectal cancer patients, and suggested the inhibition of Bcl-xL might present an alternative strategy to enhance the therapeutic efficacy of 5-FU in colorectal cancer patients with BRAF mutation.