Combination of AURKA inhibitor and MEK inhibitor strongly enhances G1 arrest and induces synergistic antitumor effect on KRAS or BRAF mutant colon cancer cells

Abstract Background In colorectal cancer, RAS and BRAF are major mutation points in the RAS-MAPK signaling pathway. These gene mutations are known to be important causes of resistance to anti-EGFR antibody therapies. MEK inhibitors have been hoped to be an effective therapy for RAS or BRAF mutation tumors; however, their suppression effect for the RAS-MAPK signaling pathway is not sufficient when used as a single agent. Aurora kinase A (AURKA), one of the mitotic kinases, is expected to be a novel therapeutic target in cancers. Recently, it has been reported that AURKA interacts with the EGFR-RAS-MAPK signaling pathway. In this study, we examined whether the combination of MK-5108 (AURKA inhibitor) and trametinib (MEK inhibitor) enhanced the antitumor effect for colon cancer cell lines. Methods We used four cell lines, HCT116, LoVo (TP53 wild, KRAS mutant), DLD1 (TP53 mutant, KRAS mutant), and HT29 (TP53 mutant, BRAF mutant). To determine the antitumor effects, a WST-8 assay was performed. Combination index was used to evaluate the efficacy of the combination of MK-5108 and trametinib. EdU assay and PI staining were performed to estimate cell cycle arrest and cell apoptosis. To identify the molecular mechanisms of the antitumor effects of the combination therapy, protein expressions were evaluated by immunoblot analysis. Results The combination of MK-5108 and trametinib showed synergistic enhancements of antitumor effect in all cell lines. MK-5108 and trametinib induced G2/M arrest and G1 arrest, respectively, and the two-drug combination further enhanced G1 arrest. The addition of MK-5108 to trametinib enhanced the suppression of p-ERK and other G1/S progression-related proteins expression. In HCT116 cells, harboring wild-type TP53, the combination therapy induced more potent cell proliferation suppression and apoptosis induction than in TP53 knockout cells. These were related to enhancement of p53 expression and caspase activation. Conclusion The combination of MK-5108 and trametinib showed synergistic enhancement of antitumor effect with either KRAS or BRAF mutation. Furthermore, the combination therapy could be more effective in wild-type TP53 cells.