ERR is present early in the
ERRβ is present early in the developing placenta in a subset of β(1,3)-d-glucan synthase in extra-embryonic ectoderm destined to make up the chorion.19, 20 ERRβ is likely essential for reproduction. ERRβ expression is essential for the maintenance of pluripotency and self-renewal potential in mouse embryonic stem cells and is among the core transcription factors that can reprogram fibroblasts into pluripotent stem cells.22, 23 Biochemical evidence also suggests that ERRβ may be a potential therapeutic target involved in cancers and metabolic disorders. However, studies have been hampered by the embryonic lethality of ERRβ-/- mouse model and the lack of small molecule modulators to study ERRβ function. Selective ERRβ ligands would provide an invaluable research tool to examine the biological function of ERRβ. ERRγ regulates gluconeogenesis in liver and is a potential candidate drug target to reverse hyperglycemia and hepatic fat accumulation in the context of insulin resistance.25, 26 ERRγ/PGC-1β promotes oxidative metabolism in cancer cells, and unlike ERRα, ERRγ expression is a favorable biomarkers in human breast cancer. Thus, targeting the ERRγ pathway may be a powerful therapeutic strategy to treat metabolic disorders and cancer. A critical step to advance the understanding of ERR biology is to design or identify selective modulators (agonists and inverse agonists) that can be used to target isoform specific processes in cells and in vivo. Notably, no endogenous ligand for any of the ERRs has been identified to date. The synthetic selective ligands developed to target ERRα are described as inverse agonists (antagonists of constitutive ERR activity) and agonists,29, 30 and have been utilized in cell culture and in vivo studies to investigate the physiologic activity of ERRα. However, little is known about the molecular mechanisms or biological activities downstream of ERRβ and ERRγ receptor activation because of the lack of selective ERRβ/γ ligands. Recently, a small molecule agonist of the ERRγ and ERRβ was identified that mimics the protein ligand PGC-1α in activating human ERRβ and ERRγ,31, 32 and compounds including and DES (Fig. 1), have been shown to act as nonselective ERRγ inverse agonists.33, 34, 35 Structure-based approach was used to design the ERRγ selective inverse agonist GSK5182 and its analog (Fig. 1).36, 37 Likewise, 4-methylenesterols isolated from the marine sponge steroids, have been reported to act as ERRβ antagonists. However, these new antagonists exhibit lower potency than DES in transactivation experiments. Despite these advances, the development of ERRβ and ERRγ inverse agonists with better potency and selectivity remains a formidable challenge. As a part of our ongoing program to explore novel classes of ERR modulators with the goal of increasing the potency and selectivity for ERRβ and ERRγ subtypes which might prove to be of therapeutic value in treating a variety of ERRβ and ERRγ-linked pathologies, we applied a strategy of altering the structure of triarylethylene core which is a template of Z-4-OHT. The compound Z-4-OHT has a very poor inverse agonist profile for ERRγ and ERRβ but binds to the LBD of these receptors; therefore it was used as a scaffold to generate higher potency antagonists. The design was based on SAR of Z-4-OHT analogs combined with analysis of the X-ray crystal structures of bound to the ligand binding domains of ERRγ and ERα. Analogs bearing extension or branched alkyl groups at the C2 position of the triarylethylene core with the basic side chain exhibited improved binding affinity and selectivity profiles for ERRγ compared to . The existing X-ray crystal structure of bound to ERRγ and ERα LBD provided a model for the molecular basis of activity and selectivity. In the current study, we describe the chemical synthesis and SAR (structure-activity relationship) for several triarylethylene derivatives as well as molecular modeling of receptor binding and in vitro activity profiles of the compounds.