title: Genistein sensitizes inhibitory effect of tamoxifen on the growth of estrogen receptor-positive and HER2-overexpressing human breast cancer cells.
abstract: Although tamoxifen (TAM) is used for the front-line treatment and prevention of estrogen receptor-positive (ER+) breast tumors, nearly 40% of estrogen-dependent breast tumors do not respond to TAM treatment. Moreover, the positive response is usually of short duration, and most tumors eventually develop TAM-resistance. Overexpression of HER2 gene is associated with TAM-resistance of breast tumor, and suppression of HER2 expression enhances the TAM activity. Soy isoflavone genistein has been shown to have anti-cancer activities and suppress expression of HER2 and ERalpha. The objective of this study was to test the hypothesis that genistein may sensitize the response of ER+ and HER2-overexpressing breast cancer cells to TAM treatment. The combination treatment of TAM and genistein inhibited the growth of ER+/HER2-overexpressing BT-474 human breast cancer cells in a synergistic manner in vitro. Determination of cellular markers indicated that this synergistic inhibitory effect might be contributed in part from combined effects on cell-cycle arrest at G(1) phase and on induction of apoptosis. Further determination of the molecular markers showed that TAM and genistein combination synergistically induced BT-474 cell apoptosis in part by synergistic downregulation of the expression of survivin, one of the apoptotic effectors, and downregulation of EGFR, HER2, and ERalpha expression. Our research may provide a novel approach for the prevention and/or treatment of TAM insensitive/resistant human breast cancer, and warrants further in vivo studies to verify the efficacy of genistein and TAM combination on the growth of ER+/HER2-overexpressing breast tumors and to elucidate the in vivo mechanisms of synergistic actions.
authors.affiliation: Nutrition/Metabolism Laboratory, Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Mai
authors.forename: George L
authors.initials: GL
authors.lastname: Blackburn
authors.forename: Jin-Rong
authors.initials: JR
authors.lastname: Zhou
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor / Q000187:drug effects; D049109:Cell Proliferation; D004357:Drug Synergism; D019833:Genistein / Q000008:administration & dosage; D006801:Humans; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*; D013629:Tamoxifen / Q000008:administration & dosage
chemical_list: D020169:Caspases; D019833:Genistein; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D013629:Tamoxifen