The nutritional herb inhibits the growth in a model for the Luminal A molecular subtype of breast cancer.

The Luminal A subtype of breast cancer expresses the estrogen receptor (ER)-α and progesterone receptor (PR), but not the human epidermal growth factor receptor (HER)-2 oncogene. This subtype of breast cancer responds to endocrine therapy involving the use of selective estrogen receptor modulators and/or inhibitors of estrogen biosynthesis. However, these therapeutic agents are frequently associated with long-term systemic toxicity and acquired tumor resistance, emphasizing the need to identify non-toxic alternative treatments for chemo-endocrine therapy responsive breast cancer. The present study utilized the human mammary carcinoma-derived, ER/PR/HER-2 MCF-7 cell line as a model of the Luminal A subtype of breast cancer to examine the growth inhibitory effect of the Chinese nutritional herb (EG) and determine the mechanisms underlying this effect. MCF-7 cells maintained in a serum-depleted culture medium retained their ability to grow in response to 17β-estradiol (E). Treatment of the MCF-7 cells with EG resulted in dose-dependent inhibition of E-promoted growth. Mechanistically, EG inhibited E-promoted cell cycle progression through G stage arrest and modulated the cellular metabolism of E, increasing the formation of the anti-proliferative metabolites 2-hydroxyestrone and estriol. Long-term treatment of MCF-7 cells with EG inhibited E-promoted anchorage independent growth, a surrogate biomarker of tumorigenesis. In conclusion, the results of the present study demonstrate the growth inhibitory effects of EG on MCF-7 cells and identified clinically relevant mechanistic leads for its anti-tumorigenic efficacy.