Estrogen Receptor-β Potency-Selective Ligands:  Structure−Activity Relationship Studies of Diarylpropionitriles and Their Acetylene and Polar Analogues

Abstract

Through an effort to develop novel ligands that have subtype selectivity for the estrogen receptors alpha (ERalpha) and beta (ERbeta), we have found that 2,3-bis(4-hydroxyphenyl)propionitrile (DPN) acts as an agonist on both ER subtypes, but has a 70-fold higher relative binding affinity and 170-fold higher relative potency in transcription assays with ERbeta than with ERalpha. To investigate the ERbeta affinity- and potency-selective character of this DPN further, we prepared a series of DPN analogues in which both the ligand core and the aromatic rings were modified by the repositioning of phenolic hydroxy groups and by the addition of alkyl substituents and nitrile groups. We also prepared other series of DPN analogues in which the nitrile functionality was replaced with acetylene groups or polar functions, to mimic the linear geometry or polarity of the nitrile, respectively. To varying degrees, all of the analogues show preferential binding affinity for ERbeta (i.e., they are ERbeta affinity-selective), and many, but not all of them, are also more potent in activating transcription through ERbeta than through ERalpha (i.e., they are ERbeta potency-selective). meso-2,3-Bis(4-hydroxyphenyl)succinonitrile and dl-2,3-bis(4-hydroxyphenyl)succinonitrile are among the highest ERbeta affinity-selective ligands, and they have an ERbeta potency selectivity that is equivalent to that of DPN. The acetylene analogues have higher binding affinities but somewhat lower selectivities than their nitrile counterparts. The polar analogues have lower affinities, and only the fluorinated polar analogues have substantial affinity selectivities. This study suggests that, in this series of ligands, the nitrile functionality is critical to ERbeta selectivity because it provides the optimal combination of linear geometry and polarity. Furthermore, the addition of a second nitrile group beta to the nitrile in DPN or the addition of a methyl substitutent at an ortho position on the beta-aromatic ring increases the affinity and selectivity of these compounds for ERbeta. These ERbeta-selective compounds may prove to be valuable tools in understanding the differences in structure and biological function of ERalpha and ERbeta.

Effect of ligand-activated estrogen receptor β on lymphoma growth in vitro and in vivo

“…DPN has previously been shown to have a 70-fold selectivity for ERb over ERa. 24 The selectivity of KB9520 was determined by transfecting ER-negative HEK293 cells with an ER-responsive luciferase reporter gene alone or together with ERa-or ERb-expressing vectors, whereafter cells were treated with E 2 (which activates both ERa and ERb), the ERa-selective agonist PPT or the ERb agonist KB9520. In the absence of co-transfected ERs, no stimulation of reporter gene expression was seen with any of the ER ligands (data not shown).…”

“…23 The experimentally most commonly used selective ERb agonist, diarylpropionitrile (DPN), displays a 70-fold binding preference for ERb over ERa. 24 In this report, we have used DPN and a newly developed highly selective ERb agonist, KB9520, which displays a 700-fold selectivity for ERb over ERa. Using DPN and this highly selective ERb agonist, we showed that targeting ERb in a murine T-cell lymphoma in culture and in vivo, as well as in human Burkitt's lymphoma-derived cell lines, results in an antiproliferative effect.…”

Estrogen anti-inflammatory activity in brain: A therapeutic opportunity for menopause and neurodegenerative diseases

“…Since their original description ( [163,216]) ERa and ERb selective modulators (SERMs) have been employed to dissect the relative contribution of each ER subtype and to obtain more potent responses devoid of toxic effects. The ERa selective ligand propyl pyrazole triol (PPT) provides neuroprotection and anti-inflammatory activities in brain in experimental models of neurodegenerative diseases, including ischemia [165], MPTP-induced neurotoxicity [52] and EAE ( [69,170]).…”

Tools to evaluate estrogenic potency of dietary phytoestrogens:A consensus paper from the EU Thematic Network “Phytohealth” (QLKI-2002-2453)

“…for menopausal health, are made based solely on in vitro data on binding of plant compounds to ERβ over ERα. (Meyers et al, 2001, Harringron et al, 2003. Among phytoestrogens, genistein is one of the compounds binding preferentially to ERβ (Kuiper et al, 1996), but the exact degree of dissociation has never been calculated for genistein or any other dietary compound.…”