Molecular analysis of the selective pro-apoptotic effect of the herbal extract BN108 on breast cancer cells.
Authors: F King, S Fong, J Cadaoas, M Shoemaker, M Tagliaferri, I Cohen, E Shtivelman
Journal: Cancer Research (2009)

Abstract Abstract #3018 We present preclinical data on the potential mechanisms of the cytotoxic effect of the herbal extract BN108 towards cancer cells. Botanical medicine is one of the most popular complementary medical approaches, and herbal therapies are frequently sought and used by breast cancer patients. However, the molecular mechanisms through which certain herbal extracts exert growth inhibitory activity on breast cancer cells remain largely unknown.&amp;#x2028; Treatment of a panel of breast cancer cell lines and normal mammary cells with BN108 induced cell death selectively in breast cancer lines. Normal mammary epithelial cells and fibroblasts were resistant to the cytotoxic effects of BN108. Breast cancer cells sensitive to BN108 underwent apoptotic death confirmed by Annexin V staining, caspase activation, cleavage of PARP and DNA fragmentation. In particular, caspases 4 and 9, whose activation is observed during apoptosis induced by endoplasmic reticulum stress, were proteolytically activated. Inhibition of caspase 4 partially protected breast cancer cells from cell death induced by BN108.&amp;#x2028; Expression array analysis of cells treated with BN108 showed induction of expression of several known pro-apoptotic and anti-proliferative genes such as REDD1, p21CIP, cyclin G2, stratifin and more. BN108 induced rapid inactivation of AKT and mTOR kinases in breast cancer but not in non-transformed cells. Moreover, the well-defined targets of mTORC1, S6kinase and 4eBP1 were inactivated in BN108 treated cells.&amp;#x2028; The expression array analysis also showed the induction by BN108 of numerous genes whose products code for enzymes within the cholesterol synthesis pathway. Interestingly, a transient increase in cholesterol synthesis was seen in breast cancer cells but not in normal cells following BN108 treatment. In general, cholesterol levels are higher in breast cancer cells compared to normal cells. Steroidal saponins are major components of BN108 extract, and they are known to deplete cell membrane cholesterol. Similar to BN108 extract, treatment with purified timosaponin AIII (a component of BN108 extract) also induced apoptosis and changes in cholesterol production in breast cancer cells but not in normal cells. It is possible that steroidal saponins induce a very transient depletion of cholesterol, followed by inactivation of AKT and mTOR, and negative feedback inhibition of the cholesterol synthesis pathway that is, in the end, is futile. None of these events are observed in normal cells.&amp;#x2028; In conclusion, BN108 extract contains cytotoxic activity selective for transformed versus normal cells. These selective cytotoxic properties of BN108 could be related to its differential effects on cholesterol synthesis in breast cancer cells versus normal cells, as well as inhibition of major oncogenic pathways. Future studies will be aimed at understanding the molecular relationship between the BN1008 effect on cholesterol synthesis and induction of apoptosis, which may give rise to a unique pathway for targeting tumor cells. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3018.