Molecular analysis of the selective pro-apoptotic effect of BN107 on estrogen receptor negative breast cancer cells.
Authors: R Chu, M Shoemaker, M Tagliaferi, I Cohen, E Shtivelman, S Fong
Journal: Cancer Research (2009)

Abstract Abstract #3128 While advances in early detection and adjuvant therapy for breast cancer have had a favorable impact on survival, patients who develop metastatic breast cancer generally succumb to death. Hormonal, targeted or chemotherapeutic strategies largely depend on the expression of their cognate receptors and are often accompanied by toxicities and intolerable side effects. Effective and less toxic therapies against the more aggressive and hormonal therapy-resistant estrogen receptor negative (ER-) breast cancer are urgently needed.&amp;#x2028; Botanical medicine is one of the most popular complementary and alternative medical approaches, and Chinese herbal therapies are frequently sought and used by breast cancer patients. However, the molecular mechanisms through which certain herbal extracts exert anti-breast cancer activities remain largely unknown. Bionovo Inc. has a pipeline of anti-breast cancer products (BN#) based on herbal medicine in development. Here, we present preclinical data on the potential mechanisms of the pro-apoptotic effect of BN107 on breast cancer cells.&amp;#x2028; A panel of breast cancer cell lines was examined and the most significant cytotoxic effect was observed in the less-differentiated, more aggressive, ER- breast cancer lines. Apoptosis appeared to be the major cellular pathway mediating the cytotoxicity of BN107 as evident from Annexin V binding, dissipation of mitochondrial potential, activation of caspases, and DNA fragmentation. Transcriptomic analysis comparing sensitive (ER+) versus resistant (ER-) cell lines revealed distinct patterns of gene expression in response to BN107. ER- breast cancer cells responded to BN107 by upregulating genes involved in apoptotic responses and cholesterol synthesis pathways; while ER+ breast cancer cells did so by regulating genes involved in cell growth and IGF-1 receptor signaling pathways. Further molecular analysis showed that BN107 induced death preferentially in ER- cells via rapid inactivation of AKT/ mTOR pathways. In addition, the sensitivity to BN107 was greatly reduced when ER expression was introduced in MDA-MB-231, an ER- cell line highly sensitive to BN107.&amp;#x2028; BN107, an extract rich in triterpenoids, caused rapid alterations in cholesterol metabolism, presumably by interfering with cell membrane permeability/integrity. Co-administration of BN107 and cholesterol abolished the pro-apoptotic effect of BN107. We found that ER- breast cancer cells rich in caveolae/lipid rafts were highly sensitive to BN107. We showed that BN107 treatment in these cells resulted in subcellular redistribution of proteins that are associated with these specialized membrane/cellular structures.&amp;#x2028; In conclusion, BN107 exerts pro-apoptotic activity preferentially on the more aggressive, ER- breast cancer cells. The cytotoxic activity of BN107 may be attributed to its ability to modify membrane permeability/integrity. Activity-guided isolation and further mechanistic studies are underway to identify potential chemical constituents responsible for the selective cytotoxic activities against ER- breast cancer cells. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3128.