Activities of a non-classical estrogen, Z-bis-dehydrodoisynolic acid, with ERalpha and ERbeta.
(+/-)-Z-bis-Dehydrodoisynolic acid [(+/-)-Z-BDDA] is highly estrogenic in vivo, yet binds to estrogen receptor (ER) poorly. This paradox has raised the possibility of alternative ERs and/or molecular mechanisms. To address the possibility of high activities of Z-BDDA with ERbeta, we determined the activities of (+)-Z-BDDA and (-)-Z-BDDA, in cell culture and in vitro, comparing ERbeta to ERalpha. Transfectional analysis in Hela cells showed (-)-Z-BDDA is an agonist for gene activation with both ERalpha (EC(50) congruent with 0.3nM) and ERbeta (EC(50) congruent with 5nM), while little to no activity was observed with (+)-Z-BDDA. Similarly, in gene repression assays, (-)-Z-BDDA was active (EC(50) congruent with 0.2nM), but again minimal activity was exhibited by (+)-Z-BDDA. Binding to ERalpha and ERbeta in vitro used both competition and a direct binding assay. For ERalpha, the relative affinity of (-)-Z-BDDA was approximately 6% by competition and 1.7% by direct binding versus 17beta-estradiol (E2; 100%), while (+)-Z-BDDA also demonstrated binding, but with relative affinities of only 0.08% by competition and 0.3% by the direct assay. For ERbeta, the affinity of (-)-Z-BDDA was approximately 7% by competition and 1.5% by the direct assay relative to E2 (100%), while (+)-Z-BDDA had lower affinity, approximately 0.2% that of E2 by both assays. The paradox of potent in vivo activity but lower activity in receptor binding and in cell culture reporter gene assays, previously seen with ERalpha is now also associated with ERbeta. The failure of ERbeta to explain the activity-binding paradox indicates the need for additional in vivo metabolic and pharmacokinetic studies and continued consideration of alternative mechanisms.
Meyers
Cal Y
CY
Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale 62901, USA.
Hou
Yuqing
Y
Winters
Todd A
TA
Banz
William J
WJ
Adler
Stuart
S
D000818:Animals; D001667:Binding, Competitive; D004305:Dose-Response Relationship, Drug; D024202:Electrophoretic Mobility Shift Assay; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005786:Gene Expression Regulation; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D010616:Phenanthrenes / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D011960:Receptors, Estrogen / Q000378:metabolism*; D015533:Transcriptional Activation
D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D010616:Phenanthrenes; D011960:Receptors, Estrogen; C118032:bisdehydrodoisynolic acid