Anti-tumor efficacy of RAF/MEK inhibitor VS6766 in KRAS-mutated colorectal cancer cells.

PURPOSE: Colorectal cancer (CRC) ranks third among most prevalent cancers worldwide. KRAS is the most frequently (30-40%) mutated oncogene in CRC, which has been defined as an "undruggable" therapeutic target over the past four decades. METHODS: In this study, we applied four HT-29 cell lines, namely HT-29-wild-type (HT-29-WT), point-mutated HT-29-KRAS(G12V), HT-29-KRAS(G12C) and HT-29-KRAS(G12D), in order to detect the efficiency of RAF-MEK inhibitor VS6766, the BRAF(V600E) inhibitor PLX4720 was selected as the control. The analyses of in vitro cytotoxicity, cell cycle and apoptosis of HT-29 cell lines after VS6766 alone or combined with 5-Fluorouracil (5-FU)/MK2206 treatment were carried out by Cell Counting Kit-8 (CCK-8), colony formation, and flow cytometry assay, respectively. The expression changes of proteins were confirmed by western blot. RESULTS: Treatment with VS6766 inhibited the proliferation of all four HT29 cells, while PLX4720 had a modest inhibitory effect. VS6766 induced G1-phase arrest as well as cell apoptosis, accompanied by the downregulation of p-ERK and p-MEK. Moreover, VS6766 and 5-FU synergistically suppressed HT-29 cells' growth. Meanwhile, p-AKT was upregulated after VS6766 treatment. The AKT inhibitor MK2206 and VS6766 showed synergistic effect in all four cell lines. CONCLUSION: Taken together, this study provides the first experimental evidence to demonstrate that all G12 mutation cell lines are sensitive to VS6766 applied either alone or combined with 5-FU or AKT inhibitor.