Discovery of Selective Estrogen Receptor Covalent Antagonists for the Treatment of ERα WT and ERα MUT Breast Cancer

Cancer Discov. 2018 Sep;8(9):1176-1193. doi: 10.1158/2159-8290.CD-17-1229. Epub 2018 Jul 10.


Mutations in estrogen receptor alpha (ERα) that confer resistance to existing classes of endocrine therapies are detected in up to 30% of patients who have relapsed during endocrine treatments. Because a significant proportion of therapy-resistant breast cancer metastases continue to be dependent on ERα signaling, there remains a critical need to develop the next generation of ERα antagonists that can overcome aberrant ERα activity. Through our drug-discovery efforts, we identified H3B-5942, which covalently inactivates both wild-type and mutant ERα by targeting Cys530 and enforcing a unique antagonist conformation. H3B-5942 belongs to a class of ERα antagonists referred to as selective estrogen receptor covalent antagonists (SERCA). In vitro comparisons of H3B-5942 with standard-of-care (SoC) and experimental agents confirmed increased antagonist activity across a panel of ERαWT and ERαMUT cell lines. In vivo, H3B-5942 demonstrated significant single-agent antitumor activity in xenograft models representing ERαWT and ERαY537S breast cancer that was superior to fulvestrant. Lastly, H3B-5942 potency can be further improved in combination with CDK4/6 or mTOR inhibitors in both ERαWT and ERαMUT cell lines and/or tumor models. In summary, H3B-5942 belongs to a class of orally available ERα covalent antagonists with an improved profile over SoCs.Significance: Nearly 30% of endocrine therapy-resistant breast cancer metastases harbor constitutively activating mutations in ERα. SERCA H3B-5942 engages C530 of both ERαWT and ERαMUT, promotes a unique antagonist conformation, and demonstrates improved in vitro and in vivo activity over SoC agents. Importantly, single-agent efficacy can be further enhanced by combining with CDK4/6 or mTOR inhibitors. Cancer Discov; 8(9); 1176-93. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 1047.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Animals
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Cysteine / antagonists & inhibitors
  • Drug Resistance, Neoplasm / drug effects*
  • Drug Screening Assays, Antitumor
  • Drug Synergism
  • Estrogen Receptor Antagonists / administration & dosage*
  • Estrogen Receptor Antagonists / chemistry
  • Estrogen Receptor Antagonists / pharmacology
  • Estrogen Receptor alpha / antagonists & inhibitors*
  • Estrogen Receptor alpha / chemistry
  • Estrogen Receptor alpha / genetics
  • Female
  • Humans
  • Indazoles / administration & dosage*
  • Indazoles / chemistry
  • Indazoles / pharmacology
  • MCF-7 Cells
  • Mice
  • Mutation*
  • Protein Conformation / drug effects
  • Protein Kinase Inhibitors / administration & dosage
  • Protein Kinase Inhibitors / pharmacology
  • Xenograft Model Antitumor Assays


  • ESR1 protein, human
  • Estrogen Receptor Antagonists
  • Estrogen Receptor alpha
  • H3B-5942
  • Indazoles
  • Protein Kinase Inhibitors
  • Cysteine