Estrogenic and anti-proliferative properties of novel prenylflavone from Epimedium brevicornum

Abstract

Estrogens maintain female sexual health, but also drive estrogen receptor (ER) positive breast tumor growth. Epidemiological evidence suggests that phytoestrogens may confer health benefits without increasing the risk of hormone-dependent cancers. We have screened herbs from the Traditional Chinese Pharmacopoeia and encountered one, Epimedium brevicornum (EB) which exhibited strong and specific estrogenic transactivation properties in estrogen-driven reporter gene bioassays. EB raw materials were sourced from various places and systematically characterized with informative DNA markers and by chemical profiling. Ethanolic extracts of EB prepared using these authenticated raw materials were extensively characterized with respect to their estrogenic properties. EB extracts increased estrogen-responsive breast cancer (MCF-7) cell proliferation at low doses, but paradoxically inhibited growth profoundly at higher doses, accompanied by down-regulation of mRNA and protein levels of estrogen-driven genes. Laborious bioassay-guided fractionation led to the isolation and characterization of novel estrogenic prenylflavones 3'-prenylapigenin and breviflavone B (BB) from EB. The previously unknown prenylflavone, BB exerted biphasic stimulatory and inhibitory effects on breast cancer cell (MCF-7) proliferation. High doses of BB almost eliminated ERalpha protein, potentially mediated through increased proteasome degradation. Using a rat model, we showed that ER-driven reporter gene and MCF-7 cell proliferation bioassay systems could readily track the global estrogenic activities of compounds, known and unknown, in rat sera. These animal modeling studies provide a new basis for the modeling of summated estrogenic activities following administration of complex mixtures that constitute herbal extracts. Our studies provide the scientific basis for the potential development of EB extracts and/or novel estrogenic compounds contained therein for estrogen replacement therapy with favorable effects on breast health.