Calenduloside E 6'-methyl ester induces apoptosis in CT-26 mouse colon carcinoma cells and inhibits tumor growth in a CT-26 xenograft animal model.

The aim of the present study was to investigate the cytotoxic effect of calenduloside E 6'-methyl ester (oleanolic acid 3-O-β-D-glucuronopyranoside-6'-methyl ester) isolated from Acanthopanax sessiliflorus fruits was investigated in CT-26 mouse colon carcinoma cells. Calenduloside E 6'-methyl ester dose-dependently inhibited the viability of CT-26 cells. Apoptosis was characterized by the detection of annexin-V and sub-G1 apoptotic cell populations, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and DNA fragmentation experiments. Results showed that the number of immunostained annexin-V-FITC and sub-G1 cells increased after treatment with calenduloside E 6'-methyl ester. Calenduloside E 6'-methyl ester also increased terminal deoxynucleotidyl transferase dUTP nick end labeled-CT-26 cells. It induced DNA fragmentation. and the cleavage of caspase-8, -9, -3 and poly ADP-ribose polymerases. In addition, calenduloside E 6'-methyl ester suppressed the volume and weight of tumors in BALB/c mice subcutaneously implanted with CT-26 cells. These results indicate that calenduloside E 6'-methyl ester induces apoptosis in CT-26 mouse colon carcinoma cells and inhibits tumor growth in a CT-26 carcinoma animal model.