ERB-26

ERB-26 is a synthetic estrogen and a selective agonist of the ERβ.[1][2] It is the active enantiomer of the racemic mixture ERB-79.[1] Whereas ERB-79 shows 484-fold selectivity for the ERβ over the ERα,[3] ERB-26 differs slightly in that it is even more selective, showing greater than 1,000-fold selectivity for transactivation of the ERβ relative to the ERα.[1] Its EC₅₀ value for the ERβ is 0.21 nM (4-fold weaker than estradiol) and for the ERα is 260 nM (10,000-fold weaker than estradiol).[1] It has no antagonistic activity at either receptor.[1] ERB-26 is active in prevention of prostate cancer development in preclinical models.[1] In contrast to ERB-26, the selective ERα agonist ERA-45 induced prostate cancer development in preclinical models when it was given in combination with testosterone, whereas testosterone alone did not do so.[1] These findings suggest opposing roles of the ERα and ERβ in the prostate gland.[1] The chemical structure of ERB-26 does not appear to have been disclosed.