Abstract
KRAS‑mutant colorectal cancer (CRC) is a highly malignant cancer with a poor prognosis, however specific therapies targeting KRAS mutations do not yet exist. Anti‑epidermal growth factor receptor (EGFR) agents, including cetuximab and panitumumab, are effective for the treatment of certain patients with CRC. However, these anti‑EGFR treatments have no effect on KRAS‑mutant CRC. Therefore, new therapeutic strategies targeting KRAS‑mutant CRC are urgently needed. To clarify the direct effect of KRAS gene mutations, the present study transduced mutant forms of the KRAS gene (G12D, G12V and G13D) into CACO‑2 cells. A drug‑screening system (Mix Culture assay) was then applied, revealing that the cells were most sensitive to the MEK inhibitor trametinib among tested drugs, Cetuximab, Panitumumab, Regorafenib, Vemurafenib, BEZ‑235 and Palbociclib. Trametinib suppressed phosphorylated ERK (p‑ERK) expression and inhibited the proliferation of KRAS‑mutant CACO‑2 cells. However, low‑dose treatment with trametinib also increased the expression of the anti‑apoptotic protein Bcl‑xL in a dose‑dependent manner, leading to drug resistance. To overcome the resistance of KRAS‑mutant CRC to apoptosis, the combination of trametinib and the Bcl‑xL antagonist ABT263 was assessed by in vitro and in vivo experiments. Compared with the effects of low‑dose trametinib monotherapy, combination treatment with ABT263 had a synergistic effect on apoptosis in mutant KRAS transductants in vitro. Furthermore, in vivo combination therapy using low‑dose trametinib and ABT263 against a KRAS‑mutant (G12V) xenograft synergistically suppressed growth, with an increase in apoptosis compared with the effects of trametinib monotherapy. These data suggest that a low dose of trametinib (10 nM), rather than the usual dose of 100 nM, in combination with ABT263 can overcome the resistance to apoptosis induced by Bcl‑xL expression, which occurs concurrently with p‑ERK suppression in KRAS‑mutant cells. This strategy may represent a promising new approach for treating KRAS‑mutant CRC.