Aim: To discover novel ligands of estrogen receptor (ER) β using pharmacophore mapping and structure-based screening.
Methods: A computer-aided strategy combining pharmacophore mapping and structure-based screening was used to screen the Maybridge and Enamine databases. Yeast two-hybrid (Y2H) assay was used to detect the activity and selectivity of the chosen compounds. The transcriptional activities of the chosen compounds were demonstrated with luciferase reporter assays. The anti-proliferative effects of ER antagonists against MCF-7 and MDA-MB-231 breast cancer cells were examined using MTT assay, and the mechanisms of action were analyzed with flow cytometry analysis and Western blotting.
Results: Through in silico screen, 95 compounds were chosen for testing in Y2H assay, which led to 20 potent ligands, including 10 agonists, 8 antagonists and 2 partial agonists with EC50 or IC50 values at μmol/L. Furthermore, 6 agonists exhibited absolute selectivity for ERβ, and 3 agonists showed higher selectivity for ERβ. The agonists 1g and 1h (10, 25, and 50 μmol/L) dose-dependently increased ER transcriptional activities, whereas the antagonists 2a and 2d (10, 25, and 50 μmol/L) caused dose-dependent inhibition on the activities. The antagonists and partial agonists at 100 μmol/L suppressed the proliferation of ERα positive MCF-7 cells and ERβ positive MDA-MB-231 cells, but were more effective against MDA-MB-231 cells. Treatment of MDA-MB-231 cells with antagonists 2a and 2d (25 and 50 μmol/L) dose-dependently increased the population of cells in the S phase. Both 2a and 2d treatment dose-dependently decreased the expression levels of cyclin A and CDK2. Meanwhile, the downregulation of cyclin E was only caused by 2d, while 2a treatment did not cause significant changes in the protein levels of cyclin E.
Conclusion: The selective ligands discovered in this study are promising drug candidates to be used as molecular probes to explore the differences between ERα and ERβ.