The Research Of Molecular Mechanisms Of Icaritin's Growth Inhibition In Triple-negative Breast Cancer

Triple-negative breast cancer is one subtype of breast cancer that lacks expression of estrogen receptor(ER)and progesterone receptor(PR)and human epidermal growth factor receptor 2(HER2),and that identifies approximately 15%of breast cancers with a feature of higher relapse rates and shorter overall survival compared to other subtypes of breast cancer.Since lack of necessary targets,TNBC is refractory to HER2-targeted therapies such as trastuzumab as well as hormonal therapies such as tamoxifen and aromatase inhibitors.Considering the severe cell toxicity,side effects and poor responding of conventional chemotherapies,a more effective and less toxic therapeutic agent is urgently needed.Recently,it has been reported that an isoform of estrogen receptor-alpha ER-a36 is expressed and plays a critical role in development of TNBC.ER-?36 forms a positive regulatory loop with epidermal growth factor receptor(EGFR),which promotes malignant growth of TNBC cells.Thus,ER-a36 has been proposed as an important target for development of novel drugs for TNBC.In this study,we evaluated the effects of icaritin,a prenylflavonoid derivant purified from Epimedium Genus,on growth of TNBC cells and examined the possible underlying mechanisms.Flow cytometry,MTT,and colony formation assay were used to evaluate cell proliferation,cell distribution and cell apoptosis.The mRNA and protein levels were analyzed by quantitative RT-PCR and Western blot assay.ChIP assays were used to detect the activity of activator protein-1(AP-1)in triple-negative breast cancer cells.Our study demonstrated that icartin decreased both ER-a36 and EGFR protein expression,and induced apoptosis in TNBC MDA-MB-231 and MDA-MB-453 cells in a dose-and time-dependent manner.We also found that icaritin inhibited E2-induced MAPK/ERK signaling through ER-a36,declined E2-induced cyclin D1 expression in the nuclear region.Moreover,icaritin mediated nuclear translocation and activation of AP-1,which appeared to be required for E2-induced cyclin D1 expression and subsequently cell proliferation.Descending triple-negative breast cancer stem/progenitor cells are detected after icaritin treatment.Our results thus indicated that icaritin has a potential to be developed into a novel therapeutic agent for human TNBC.