Induction of apoptosis in HeLa cells by 3beta-hydroxyurs-12-en-27-oic acid

3Beta-hydroxyurs-12-en-27-oic acid (1), a pentacyclic triterpenoid isolated from the rhizomes of Astilbe chinensis, was structurally very similar to ursolic acid, with the only difference being the interchange of the COOH and Me group at C(14) and C(17). Ursane-type triterpene with a COOH group at C(14) is present in a limited number of natural resources. Compound 1 was found to exhibit more distinctive cytotoxicity toward human cervical squamous carcinoma (HeLa) cells than ursolic acid, suggesting that the position of the COOH group significantly affects the cytotoxicity of ursane-type pentacyclic triterpenes with a COOH group. To elucidate the underlying biological mechanism responsible for the cytotoxicity of 1, we investigated its growth-inhibitory and apoptosis-inducing effect on HeLa cells. Compound 1 induced a marked concentration- and time-dependent inhibition of cell proliferation with an IC50 value of 6.80+/-0.88 microg/ml following 48 h incubation. The drug-treated HeLa cells displayed typical morphological apoptotic characteristics and formation of DNA ladders in agarose-gel electrophoresis. Flow cytometric analysis showed that the cell cycle was arrested in G0/G1 phase by 1, and the apoptotic rate of HeLa cells treated for 48 h with 20 microg/ml of 1 was 21.08+/-2.14%. Also, 1 increased and decreased the expression of Bax and Bcl-2 proteins, respectively, and lowered the mitochondrial transmembrane potential (delta psi(m)). The peptidic caspase-3 inhibitor DEVD-CHO (NH2-Asp-Glu-Val-Asp-CHO, at 2 microM) could increase the viability of HeLa cells previously treated with 1. These results indicate that 1 induces efficient cell apoptosis through down-regulating Bcl-2 expression, up-regulating Bax expression, lowering delta psi(m), and by activating the caspase-3 pathway.