Timothy I. Richardson

Modulation of Retinoic Acid Receptor-related Orphan Receptor α and γ Activity by 7-Oxygenated Sterol Ligands

The retinoic acid receptor-related orphan receptors α and γ (RORα (NR1F1) and RORγ (NR1F3)) are orphan nuclear receptors and perform critical roles in regulation of development, metabolism, and immune function. Cholesterol and cholesterol sulfate have been suggested to be RORα ligands, but the physiological significance is unclear. To date, no endogenous RORγ ligands have been described. Here, we demonstrate that 7-oxygenated sterols function as high affinity ligands for both RORα and RORγ by directly binding to their ligand-binding domains (Ki ∼20 nm), modulating coactivator binding, and suppressing the transcriptional activity of the receptors. One of the 7-oxygenated sterols, 7α-hydroxycholesterol (7α-OHC), serves as a key intermediate in bile acid metabolism, and we show that 7α-OHC modulates the expression of ROR target genes, including Glc-6-Pase and phosphoenolpyruvate carboxykinase, in an ROR-dependent manner. Furthermore, glucose output from hepatocytes is suppressed by 7α-OHC functioning as an RORα/γ ligand. Thus, RORα and RORγ are ligand-regulated members of the NR superfamily and may serve as sensors for 7-oxygenated sterols.

Benzopyrans are selective estrogen receptor Beta agonists with novel activity in models of benign prostatic hyperplasia.

Benzopyran selective estrogen receptor beta agonist-1 (SERBA-1) shows potent, selective binding and agonist function in estrogen receptor beta (ERbeta) in vitro assays. X-ray crystal structures of SERBA-1 in ERalpha and beta help explain observed beta-selectivity of this ligand. SERBA-1 in vivo demonstrates involution of the ventral prostate in CD-1 mice (ERbeta effect), while having no effect on gonadal hormone levels (ERalpha effect) at 10x the efficacious dose, consistent with in vitro properties of this molecule.

Reduction of dendritic spines and elevation of GABAergic signaling in the brains of mice treated with an estrogen receptor β ligand

An estrogen receptor (ER) β ligand (LY3201) with a preference for ERβ over ERα was administered in s.c. pellets releasing 0.04 mg/d. The brains of these mice were examined 3 d after treatment had begun. Although estradiol-17β is known to increase spine density and glutaminergic signaling, as measured by Golgi staining, a clear reduction in spines was evident on the dendritic branches in LY3201-treated mice but no morphological alteration and no difference in the number of dendritic spines on dendritic stems were observed. In the LY3201-treatment group, there was higher expression of glutamic acid decarboxylase (GAD) in layer V of cortex and in the CA1 of hippocampus, more GAD+ terminals surrounding the pyramidal neurons and less glutamate receptor (NMDAR) on the neurons in layer V. There were no alterations in expression of Iba1 or in Olig2 or CNPase. However, GFAP+ astrocytes were increased in the LY3201-treatment group. There were also more projections characteristic of activated astrocytes and increased expression of glutamine synthetase (GS). No expression of ERβ was detectable in the nuclei of astrocytes. Clearly, LY3201 caused a shift in the balance between excitatory and inhibitory neurotransmission in favor of inhibition. This shift was due in part to increased synthesis of GABA and increased removal of glutamate from the synaptic cleft by astrocytes. The data reveal that treatment with a selective ERβ agonist results in changes opposite to those reported in estradiol-17β–treated mice and suggests that ERα and ERβ play opposing roles in the brain.

Estrogen Receptor Modulators: Relationships of Ligand Structure, Receptor Affinity and Functional Activity

The estrogen receptor is a regulator of a wide range of physiological functions, including the female reproductive system, in addition to bone, cardiovascular and CNS function. ER ligands have been approved for the treatment of menopausal symptoms, breast cancer and osteoporosis, however the search continues for new modulators of ER function with improved properties. Progress in medicinal chemistry programs has resulted in the identification of structurally diverse molecules with unique biological properties. Recent advances in the design and synthesis of these non-steroidal and steroidal estrogen receptor ligands is reviewed. The relationship between the structural features of the ligand and receptor function is also discussed.

Novel 3-aryl indoles as progesterone receptor antagonists for uterine fibroids.

We report the synthesis and characterization of novel 3-aryl indoles as potent and efficacious progesterone receptor (PR) antagonists with potential for the treatment of uterine fibroids. These compounds demonstrated excellent selectivity over other steroid nuclear hormone receptors such as the mineralocorticoid receptor (MR). They were prepared from 2-bromo-6-nitro indole in four to six steps using a Suzuki cross-coupling as the key step. Compound 8f was orally active in the complement 3 model of progesterone antagonism in the rat uterus and demonstrated partial antagonism in the McPhail model of progesterone activity.

Chapter 10 Novel Selective Estrogen Receptor Modulators (SERMs)

Publisher Summary Selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene have demonstrated the ability to mimic estrogen (E2) in some tissues, such as bone, while suppressing its effects in other tissues, such as the breast and uterus. This unique tissue selectivity has proven beneficial for the prevention and treatment of diseases such as breast cancer and osteoporosis. This chapter reviews the progress made in development of structurally novel SERMs that have demonstrated tissue-selective pharmacology in pre-clinical models. The chapter also discusses SERMs for hot flushes, ovarian selective SERMS, and estrogen receptor alpha (ERα) selective SERMs. Because SERMs are largely ineffective at treating hot flushes, significant pre-clinical efforts have been directed towards the identification of ligands that could potentially alleviate this prevalent symptom in post-menopausal women. The chromene-derived SERM has been reported to exhibit traditional SERM estrogen agonist properties on bone and lipid parameters in ovariectomized (ovx) rats while having estrogen antagonist properties on breast and uterine tissues. Despite the discovery of ERα selective SERMs and their subsequent use as chemical tools to evaluate the pharmacological significance of this receptor subtype, the respective roles that ERα and ERβ play in regulating tissue selectivity is not yet clear. As a result, the identification of non-receptor subtype selective SERMs remains of considerable interest.

Identification of potent and selective retinoic acid receptor gamma (RARγ) antagonists for the treatment of osteoarthritis pain using structure based drug design.

A series of triaryl pyrazoles were identified as potent pan antagonists for the retinoic acid receptors (RARs) α, β and γ. X-ray crystallography and structure-based drug design were used to improve selectivity for RARγ by targeting residue differences in the ligand binding pockets of these receptors. This resulted in the discovery of novel antagonists which maintained RARγ potency but were greater than 500-fold selective versus RARα and RARβ. The potent and selective RARγ antagonist LY2955303 demonstrated good pharmacokinetic properties and was efficacious in the MIA model of osteoarthritis-like joint pain. This compound demonstrated an improved margin to RARα-mediated adverse effects.

Development of an HTS-Compatible Assay for Discovery of RORα Modulators Using AlphaScreen® Technology

The retinoid acid receptor–related orphan receptors (RORs) represent important targets for the treatment of metabolic and immune disorders. Here the authors describe the application of AlphaScreen® technology to develop a high-throughput screening (HTS)–compatible assay to facilitate the discovery of RORα modulators. Using the ligand binding domain (LBD) of RORα and a peptide derived from the NR1 box of the nuclear receptor coactivator PGC-1α, a 384-well format assay was developed exhibiting high sensitivity, requiring only low nanomolar concentration of reagents. Recently, it was shown that oxysterols such as 7α-hydroxycholesterol (7α-OHC) function as modulators of the RORs. In this assay, 7α-OHC produced a concentration-response curve with an EC50 of 162 nM, a Z′ factor of 0.6, and a signal-to-background (S/B) ratio of 4.2, demonstrating that the assay is HTS compatible. Validation of the assay was afforded by screening against the Sigma LOPAC1280™ library in a 384-well format. In summary, the results presented here demonstrate that this assay can be used to screen large chemical libraries to discover novel modulators of RORα.