Protein‐Structure‐Based Prediction of Animal Model Suitability for Pharmacodynamic Studies of Subtype‐Selective Estrogens

Subtype‐selective estrogens are of increasing importance as tools used to unravel physiological roles of the estrogen receptors, ERα and ERβ, in various species. Although human ERα and ERβ differ by only two amino acids within the binding pockets, we and others recently succeeded in generating subtype‐selective agonists. We have proposed that the selectivity of the steroidal compounds 16α‐lactone‐estradiol (16α‐LE 2 , hERα selective) and 8β‐vinyl‐estradiol (8β‐VE 2 , hERβ selective) is based on the interaction of certain substituents of these compounds with essentially one amino acid in the respective ER binding pockets. For in vitro and ex vivo pharmacological experiments with these compounds we intended to use bovine tissues available from slaughterhouses in larger quantities. Using homology modeling techniques we determined that the amino acid conferring high hERβ‐selectivity to 8β‐VE 2 is not exchanged between human and bovine ERα and bovine ERβ. Thus, we predicted our steroidal hERβ‐selective compound to exhibit only weak agonistic activity at bERβ and that bovine tissue is therefore not suited for investigation of ERβ functions. The situation is presumably identical for pig, sheep, and the common marmoset, whereas rats, mice, and rhesus macaques are appropriate animal models to study pharmacological effects of 8β‐VE 2 in vivo. This prediction was confirmed in transactivation studies assessing estradiol (E 2 ) and the two subtype‐selective ligands on bovine ERβ and on a series of hERα and hERβ with mutations in their respective ligand‐binding pockets. We have shown that the detailed understanding of the interactions of a compound with its target protein enables the identification of relevant species for pharmacological studies.