Cyclopia extracts act as ERα antagonists and ERβ agonists, in vitro and in vivo

PLoS One. 2013 Nov 4;8(11):e79223. doi: 10.1371/journal.pone.0079223. eCollection 2013.

Abstract

Hormone replacement therapy associated risks, and the concomitant reluctance of usage, has instigated the search for new generations of estrogen analogues that would maintain estrogen benefits without associated risks. Furthermore, if these analogues display chemo-preventative properties in breast and endometrial tissues it would be of great value. Both the selective estrogen receptor modulators as well as the selective estrogen receptor subtype modulators have been proposed as estrogen analogues with improved risk profiles. Phytoestrogen containing extracts of Cyclopia, an indigenous South African fynbos plant used to prepare Honeybush tea may serve as a source of new estrogen analogues. In this study three extracts, P104, SM6Met, and cup-of-tea, from two species of Cyclopia, C. genistoides and C. subternata, were evaluated for ER subtype specific agonism and antagonism both in transactivation and transrepression. For transactivation, the Cyclopia extracts displayed ERα antagonism and ERβ agonism when ER subtypes were expressed separately, however, when co-expressed only agonism was uniformly observed. In contrast, for transrepression, this uniform behavior was lost, with some extracts (P104) displaying uniform agonism, while others (SM6Met) displayed antagonism when subtypes were expressed separately and agonism when co-expressed. In addition, breast cancer cell proliferation assays indicate that extracts antagonize cell proliferation in the presence of estrogen at lower concentrations than that required for proliferation. Furthermore, lack of uterine growth and delayed vaginal opening in an immature rat uterotrophic model validates the ERα antagonism of extracts observed in vitro and supports the potential of the Cyclopia extracts as a source of estrogen analogues with a reduced risk profile.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • COS Cells
  • Cell Proliferation / drug effects
  • Chlorocebus aethiops
  • Estradiol / analogs & derivatives
  • Estradiol / pharmacology
  • Estrogen Receptor alpha / antagonists & inhibitors*
  • Estrogen Receptor alpha / genetics
  • Estrogen Receptor alpha / metabolism
  • Estrogen Receptor beta / agonists*
  • Estrogen Receptor beta / genetics
  • Estrogen Receptor beta / metabolism
  • Fabaceae / chemistry*
  • Fabaceae / classification
  • Female
  • Fulvestrant
  • Genistein / pharmacology
  • Humans
  • Luciferases / genetics
  • Luciferases / metabolism
  • MCF-7 Cells
  • NF-kappa B / genetics
  • NF-kappa B / metabolism
  • Phytoestrogens / pharmacology
  • Plant Extracts / pharmacology*
  • Promoter Regions, Genetic / genetics
  • Rats
  • Rats, Wistar
  • Species Specificity
  • Uterus / drug effects
  • Uterus / growth & development
  • Vagina / drug effects
  • Vagina / physiology

Substances

  • Estrogen Receptor alpha
  • Estrogen Receptor beta
  • NF-kappa B
  • Phytoestrogens
  • Plant Extracts
  • Fulvestrant
  • Estradiol
  • Genistein
  • Luciferases

Grants and funding

The authors would like to thank the Medical Research Council (MRC) and the Cancer Association of South Africa (CANSA) for financial support to A. L. (grant for projects entitled “Cyclopia Phytoestrogens”and “Cyclopia and breast cancer”) and for financial support to K. V. and M. M. the National Research Foundation (NRF) and the Harry Crossley foundation is acknowledged. Any opinion, findings and conclusions or recommendations expressed in this material are those of the author(s) and therefore the funders do not accept any liability in regard thereto. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.