Koelreuteria Formosana Extract Induces Growth Inhibition and Cell Death in Human Colon Carcinoma Cells via G2/M Arrest and LC3-II Activation-Dependent Autophagy

Autophagy is a self-destructive process that degrades cytoplasmic constituents. In our previous study, Koelreuteria formosana ethanolic extract (KFEE), which is obtained from natural plants endemic to Taiwan, has inhibited cell metastasis in renal carcinoma cells. However, the anticancer effects of KFEE on colon cancer remain unclear. In this study, KFEE exerted a strong cytotoxic effect on DLD-1 and COLO 205 human colorectal cancer cell lines. KFEE effectively inhibited cancer cell proliferation, induced G2/M-phase arrest associated with downregulaton of cyclin E, cyclin B and cdc25C and upregulation of p21, and induced cell death by activating autophagy but did not cause apoptotic cell death. Exposed KFEE cells showed increased levels of acridine orange, autophagic vacuoles, and LC3-II proteins, which are specific autophagic markers. Bcl-2, p-Akt, and p-mTOR levels, which have been implicated in autophagic downregulation, were decreased after KFEE treatment. Autophagy inhibitor 3-methyladenosine and bafilomycin-A1 and genetic silencing of LC3 attenuated KFEE-induced growth inhibition. These findings suggested that KFEE causes cytostatic effect through autophagy. In xenograft studies, oral administration of KFEE had significantly inhibited the tumor growth in nude mice that had received subcutaneous injection of DLD-1 cells. KFEE is a promising candidate in phytochemical-based, mechanistic, and pathway-targeted cancer prevention strategies.