Inhibition of histone deacetylase enhances the anti-proliferative action of antiestrogens on breast cancer cells and blocks tamoxifen-induced proliferation of uterine cells

Breast Cancer Res Treat. 2007 Nov;105(3):297-309. doi: 10.1007/s10549-006-9459-6. Epub 2006 Dec 21.


Here we report a novel potential therapeutic strategy using histone deacetylase (HDAC) inhibitors to enhance the action of hormonal therapy agents in estrogen receptor alpha (ER alpha)-positive breast cancer. HDAC inhibitors [trichostatin A (TSA), suberoylanilide hydroxamic acid (SAHA) and valproic acid (VPA)], inhibited proliferation of MCF-7 breast cancer cells and, in combination with tamoxifen inhibited proliferation better than with either agent alone. VPA, an anti-convulsant drug with HDAC inhibitory activity, enhanced tamoxifen action at doses within the concentration range used for anti-convulsive therapy. VPA cooperated with tamoxifen in a variety of ER alpha-positive cell lines and was also effective when combined with other antiestrogens, and with aromatase inhibition. VPA enhanced antiestrogen action by promoting cell death via apoptosis without affecting cell cycling. Some of this action may be due to VPA's ability to induce the pro-apoptotic gene Bik, which is also induced by antiestrogens. Remarkably, VPA blocked the undesirable pro-proliferative action of tamoxifen on uterine endometrial cells. Our in vitro results suggest that VPA and other HDAC inhibitors have the potential to enhance hormonal therapy for ER alpha-positive breast cancer and simultaneously reverse the adverse effects of antiestrogens in the uterus.

Publication types

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

MeSH terms

  • Aromatase / metabolism
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology*
  • Cell Line
  • Cell Proliferation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Estrogen Antagonists / pharmacology*
  • Estrogen Receptor alpha / genetics
  • Estrogen Receptor alpha / metabolism
  • Estrogens / metabolism
  • Female
  • Gene Expression Regulation, Neoplastic
  • Histone Deacetylase Inhibitors*
  • Histone Deacetylases / metabolism
  • Humans
  • Receptor, ErbB-2 / metabolism
  • Sensitivity and Specificity
  • Tamoxifen / antagonists & inhibitors
  • Tamoxifen / pharmacology*
  • Uterus / cytology*
  • Uterus / drug effects*
  • Valproic Acid / pharmacology


  • Enzyme Inhibitors
  • Estrogen Antagonists
  • Estrogen Receptor alpha
  • Estrogens
  • Histone Deacetylase Inhibitors
  • Tamoxifen
  • Valproic Acid
  • Aromatase
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • Histone Deacetylases