Dissecting physiological roles of estrogen receptor α and β with potent selective ligands from structure-based design

The distinct roles of the two estrogen receptor (ER) isotypes, ERα and ERβ, in mediating the physiological responses to estrogens are not completely understood. Although knockout animal experiments have been aiding to gain insight into estrogen signaling, additional information on the function of ERα and ERβ will be provided by the application of isotype-selective ER agonists. Based on the crystal structure of the ERα ligand binding domain and a homology model of the ERβ-ligand binding domain, we have designed steroidal ligands that exploit the differences in size and flexibility of the two ligand binding cavities. Compounds predicted to bind preferentially to either ERα or ERβ were synthesized and tested in vitro using radio-ligand competition and transactivation assays. This approach directly led to highly ER isotype-selective (∼200-fold) and potent ligands. To unravel physiological roles of the two receptors, in vivo experiments with rats were conducted using the ERα- and ERβ-selective agonists in comp...