Genistein sensitizes inhibitory effect of tamoxifen on the growth of estrogen receptor-positive and HER2-overexpressing human breast cancer cells

Mol Carcinog. 2007 Jul;46(7):534-42. doi: 10.1002/mc.20300.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • Apoptosis / drug effects
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Caspases / metabolism
  • Cell Line, Tumor / drug effects
  • Cell Proliferation
  • Drug Synergism
  • Genistein / administration & dosage
  • Humans
  • Neoplasms, Hormone-Dependent / drug therapy*
  • Neoplasms, Hormone-Dependent / metabolism
  • Neoplasms, Hormone-Dependent / pathology
  • Receptor, ErbB-2 / metabolism*
  • Receptors, Estrogen / metabolism*
  • Tamoxifen / administration & dosage


  • Receptors, Estrogen
  • Tamoxifen
  • Genistein
  • Receptor, ErbB-2
  • Caspases