Dissecting Physiological Roles of Estrogen Receptor α and β with Potent Selective Ligands from Structure-Based Design

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2004-07, Vol.18 (7), p.1599-1609
• Main Authors: Hillisch, Alexander, Peters, Olaf, Kosemund, Dirk, Müller, Gerd, Walter, Alexander, Schneider, Birgitt, Reddersen, Gudrun, Elger, Walter, Fritzemeier, Karl-Heinrich
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Angiotensin I - blood; Angiotensin I - drug effects; Animals; Binding Sites; Biochemistry - methods; Bone and Bones - drug effects; Bone and Bones - metabolism; Estradiol - pharmacology; Estrogen Receptor alpha - agonists; Estrogen Receptor alpha - chemistry; Estrogen Receptor alpha - physiology; Estrogen Receptor beta - agonists; Estrogen Receptor beta - chemistry; Estrogen Receptor beta - physiology; Female; Follicle Stimulating Hormone - blood; Ligands; Liver - drug effects; Liver - metabolism; Luteinizing Hormone - blood; Male; Molecular Sequence Data; Pituitary Gland - drug effects; Pituitary Gland - metabolism; Rats; Rats, Wistar; Structure-Activity Relationship; Uterus - drug effects; Uterus - growth & development; Uterus - metabolism
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2004-0050

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 comparison to 17β-estradiol. The ERα agonist induced uterine growth, caused bone-protective effects, reduced LH and FSH plasma levels, and increased angiotensin I, whereas the ERβ agonist did not at all or only at high doses lead to such effects, despite high plasma levels. It can thus be concluded that estrogen effects on the uterus, pituitary, bone, and liver are primarily mediated via ERα. Simultaneous administration of the ERα and ERβ ligand did not lead to an attenuation of ERα-mediated effects on the uterus, pituitary, and liver parameters.