Induction of apoptosis by lupeol in human epidermoid carcinoma A431 cells through regulation of mitochondrial, Akt/PKB and NFkappaB signaling pathways

Abstract

The rising incidence of skin cancer in humans makes it equivalent to malignancies of organs. Therefore, it is necessary to intensify our efforts for better understanding and development of novel treatment and preventive approaches for skin cancer. Fruits and other plant derived products have gained considerable attention as they can reduce the risk of several cancer types. Lupeol, a triterpene, present in many fruits and medicinal plants, has been shown to possess many pharmacological properties including anti-cancer effect in both in vitro and in vivo assay systems. In the present study, apoptosis inducing effects of lupeol were studied in human epidermoid carcinoma A431 cells. Cell cycle analysis showed that lupeol treatment induces apoptosis (14-37%) in a dose-dependent manner as evident by an increased sub G(1) cell population. The RT-PCR and Western blot analysis showed that lupeol-induced apoptosis was associated with caspase dependent mitochondrial cell death pathway through activation of Bax, caspases, Apaf1, decrease in Bcl-2 expression and subsequent cleavage of PARP. Lupeol treatment also inhibited Akt/PKB signaling pathway by inhibition of Bad (Ser136) phosphorylation and 14-3-3 expression. In addition, lupeol treatment inhibited cell survival by inactivation of NFkappaB through upregulation of its inhibitor Ikappabetaalpha. The Caspase mediated apoptosis was noticed by decrease in lupeol induced apoptosis by Caspase inhibitors as well as increase in reactive oxygen species generation and loss of mitochondrial membrane potential. These results suggest that lupeol could be an effective anti-cancer agent and merits further investigation.