Pomegranate extract inhibits the proliferation and viability of MMTV-Wnt-1 mouse mammary cancer stem cells in vitro

Pomegranate (Punica granatum L.) is known to possess anticancer activities. The effects of a standardized extract of pomegranate (PE) on a mouse mammary cancer cell line (designated WA4) derived from mouse MMTV-Wnt-1 mammary tumors were examined in this study. The WA4 cell line has been previously characterized as containing a majority of cells possessing stem cell characteristics. PE inhibited the proliferation of WA4 cells in a time- and concentration-dependent manner. This was due to an arrest of cell cycle progression in the G0/G1 phase. PE was also cytotoxic to quiescent WA4 cells in a concentration-dependent manner at concentrations >10 µg/ml. PE treatment of WA4 cells resulted in an increase in caspase-3 enzyme activity in a time- and concentration-dependent manner, indicating that the cytotoxic effect of PE was due to the induction of apoptosis. We tested the effect of several individual phytochemicals derived from PE on WA4 cells. Ellagic acid, ursolic acid and luteolin caused a time- and concentration-dependent reduction of cell proliferation and viability, suggesting that they contribute to the inhibitory effect of PE, while caffeic acid had no effect. Cancer stem cells, which are highly resistant to conventional chemotherapeutic agents, are thought to be the origin of both primary and secondary breast tumors, and thus are a critical target in both breast cancer therapy and prevention. These data suggest that PE, which is a proven and safe dietary supplement, has promise as an treatment against breast cancer by preventing proliferation of cancer stem cells.