Spica Prunellae extract promotes mitochondrion-dependent apoptosis in human colon carcinoma cell line

Spica Prunellae (Prunella vulgaris fruiting spikes) has long been used as an important component in formulated prescriptions of Chinese traditional medicine to treat various kinds of cancer. However, the precise mechanism of the anti-cancer activity of Spica Prunellae remains to be elucidated. In this report, we investigated the cellular effects of the ethanol extract of Spica Prunellae (EESP) in the HT-29 human colon carcinoma cell line. We found that EESP inhibited the growth of HT-29 cells as evidenced by EESP-induced cell morphological changes and reduced cell viability in dose-and time-dependent manners. Furthermore, we demonstrated that the HT-29 cell growth inhibitory activity of EESP was due to apoptosis, as EESP treatment resulted in the loss of plasma membrane asymmetry (externalization of phosphatidylserine), collapse of mitochondrial membrane potential, activation of caspase-9 and caspase-3, and increase in the ratio of pro-apoptotic Bax to anti-apoptotic Bcl-2. Taken together, these results suggest that Spica Prunellae inhibits the growth of HT-29 colon cancer cells through mitochondrion-mediated apoptosis, which may, in part, explain its anti-cancer activity.