Cell experiment:

To determine dose-dependent effects of coumestrol, ES2 cells are treated with different concentrations (0, 1, 10, 20, 50 or 100 μM) of coumestrol[1]. Coumestrol is dissolved in DMSO to prepare a 3 mM stock. Breast cancer MCF-7 cells are treated with increasing concentrations of coumestrol for 24, 48 and 72 h. Then, 20 μL of MTT (5 mg/mL) is added each well and re-incubated for additional 3 h. Formazan blue crystals formed are dissolved in 100 μL of DMSO. Absorbance is read at 570 nm using ELISA plate reader[2].

Coumestrol is an antagonist of estrogen receptors with IC50 values of 11 nM and 2 nM for human ERα and human ERβ, respectively. Coumestrol is also a naturally occurring weak antagonist of the human pregnane X receptor with IC50 value of 12 μM [1][2][3].

Estrogen receptors (ERs) are receptors that are activated by the hormone estrogen (17β-estradiol). ERα and ERβ are nuclear estrogen receptors, which are members of the nuclear receptor family of intracellular receptors. Selective estrogen receptor modulators (SERMs) have the potential ability to antagonize the proliferative effects of estrogen on uterine and breast tissue while mimicking estrogen’s effects on the bone and cardiovascular system [1].

Coumestrol is an antagonist of estrogen receptors with IC50 values of 11 nM and 2 nM for human ERα and human ERβ, respectively. Coumestrol increased de novo synthesis of secreted complement C3 [2]. Coumestrol is also a naturally occurring weak antagonist of the human pregnane X receptor (PXR) with IC50 value of 12 μM. In transient transfection assays, coumestrol inhibited the agonist effects of SR12813 on human PXR activity. In primary human hepatocytes, coumestrol inhibited the effects of PXR agonists on the expression of the known PXR target genes, CYP3A4 and CYP2B6. Coumestrol is also a potential inverse agonist of the constitutive androstane receptor with EC50 value of 30 μM [3].

References:
[1].  Chen HY, Dykstra KD, Birzin ET, et al. Estrogen receptor ligands. Part 1: The discovery of flavanoids with subtype selectivity. Bioorg Med Chem Lett. 2004 Mar 22;14(6):1417-21.
[2].  Hopert AC, Beyer A, Frank K, et al. Characterization of estrogenicity of phytoestrogens in an endometrial-derived experimental model. Environ Health Perspect. 1998 Sep;106(9):581-6.
[3].  Wang H, Li H, Moore LB, et al. The phytoestrogen coumestrol is a naturally occurring antagonist of the human pregnane X receptor. Mol Endocrinol. 2008 Apr;22(4):838-57.