Identification of spirooxindole and dibenzoxazepine motifs as potent mineralocorticoid receptor antagonists.

Mineralocorticoid receptor (MR) antagonists continue to be a prevalent area of research in the pharmaceutical industry. Herein we report the discovery of various spirooxindole and dibenzoxazepine constructs as potent MR antagonists. SAR analysis of our spirooxindole hit led to highly potent compounds containing polar solubilizing groups, which interact with the helix-11 region of the MR ligand binding domain (LBD). Various dibenzoxazepine moieties were also prepared in an effort to replace a known dibenzoxepane system which interacts with the hydrophobic region of the MR LBD. In addition, an X-ray crystal structure was obtained from a highly potent compound which was shown to exhibit both partial agonist and antagonist modes of action against MR.

Regulation of sphingomyelin phosphodiesterase acid-like 3A gene (SMPDL3A) by liver X receptors.

Liver X receptor (LXR) α and LXRß function as physiological sensors of cholesterol metabolites (oxysterols), regulating key genes involved in cholesterol and lipid metabolism. LXRs have been extensively studied in both human and rodent cell systems, revealing their potential therapeutic value in the contexts of atherosclerosis and inflammatory diseases. The LXR genome landscape has been investigated in murine macrophages but not in human THP-1 cells, which represent one of the frequently used monocyte/macrophage cell systems to study immune responses. We used a whole-genome screen to detect direct LXR target genes in THP-1 cells treated with two widely used LXR ligands [N-(2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)-ethyl]phenyl]-benzenesulfonamide (T0901317) and 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy] phenylacetic acid hydrochloride (GW3965)]. This screen identified the sphingomyelin phosphodiesterase acid-like 3A (SMPDL3A) gene as a novel LXR-regulated gene, with an LXR response element within its promoter. We investigated the regulation of SMPDL3A gene expression by LXRs across several human and mouse cell types. These studies indicate that the induction of SMPDL3A is LXR-dependent and is restricted to human blood cells with no induction observed in mouse cellular systems.

Discovery of a series of 2-(1H-pyrazol-1-yl)pyridines as ALK5 inhibitors with potential utility in the prevention of dermal scarring.

A series of 2-(1H-pyrazol-1-yl)pyridines are described as inhibitors of ALK5 (TGFß receptor I kinase). Modeling compounds in the ALK5 kinase domain enabled some optimization of potency via substitutions on the pyrazole core. One of these compounds PF-03671148 gave a dose dependent reduction in TGFß induced fibrotic gene expression in human fibroblasts. A similar reduction in fibrotic gene expression was observed when PF-03671148 was applied topically in a rat wound repair model. Thus these compounds have potential utility for the prevention of dermal scarring.

The ligand-dependent interaction of mineralocorticoid receptor with coactivator and corepressor peptides suggests multiple activation mechanisms.

We investigated the coregulator (coactivator and corepressor) interactions with the mineralocorticoid receptor (MR) that lead to activation and inhibition of the receptor in the presence of agonist and/or antagonist. Our results indicate that MR ligand binding domain (LBD) interacts strongly with only a few specific coactivator peptides in the presence of the agonist aldosterone and that these interactions are blocked by the antagonist eplerenone. We also discovered that cortisol, the preferred physiological ligand for the glucocorticoid receptor in humans, is a partial MR agonist/antagonist, providing a possible molecular explanation of the tissue-selective effects of glucocorticoids on MR. However, when we examined the coactivator and corepressor peptide interactions in the presence of cortisol, we found that MR bound with cortisol or aldosterone interacted with the same set of peptides. Thus, the partial agonism shown by cortisol is unlikely to be the result of differential interaction with known coactivators and corepressors. On the other hand, we have identified coactivator binding groove mutations that are critical for cortisol activation but not for aldosterone activation, suggesting that the two steroids induce different MR LBD conformations. In addition, we also show that cortisol becomes full agonist when S810L mutation is introduced in the LBD of MR. Interestingly, MR antagonists, such as eplerenone and progesterone, become partial agonist/antagonist of S810L but are still able to recruit LXXLL peptides to the mutant receptor. Together, these findings suggest a model to explain the MR activation by various ligands.

Influence of sub-chronic selective 11ß-hydroxysteroid dehydrogenase 1 inhibition on the hypothalamic-pituitary-adrenal axis in female cynomolgus monkeys.

Inhibition of local cortisol regeneration from circulating cortisone by blocking 11ß-hydroxysteroid dehydrogenase 1 (11ß-HSD1) has been shown to ameliorate the risk factors associated with the metabolic syndrome. Chronic modulation of glucocorticoid homeostasis may result in hypothalamic-pituitary-adrenal (HPA) axis stimulation. HPA axis over-activation leading androgen excess would be undesirable in a therapeutic intervention designed to treat a chronic condition such as the metabolic syndrome. To address whether 11ß-HSD1 inhibition would lead to excess androgens, we treated female cynomolgus monkeys with a selective inhibitor, BI 135558, for 4 weeks. Continual action of the compound over the dosing period was confirmed by constant plasma exposure, and a maintained change in urinary glucocorticoid metabolites consistent with 11ß-HSD1 inhibition. No significant changes in adrenal function, as evidenced by an adrenocorticotropic hormone (ATCH) challenge, were observed. An examination of androgenic hormones revealed a slight increase in dehydroepiandrosterone sulfate (DHEA-S), while other hormones such as testosterone remained within reference values. Overall, treatment with BI 135558 in monkeys did not result in obvious over-activation of the HPA axis.

The liver X receptors.

The liver X receptors (LXRs), members of the nuclear receptor superfamily, are potential targets for a variety of diseases. While there are many opportunities for the development of LXR-based therapeutics, there are some major hurdles, such as the ability of LXRs to cause hypertriglyceridemia, as well as some species-dependent aspects of LXR-mediated gene regulation. In addition to classical pharmacological approaches using relevant cellular and animal models, systematic molecular-based strategies will be important in overcoming these obstacles.

Molecular mechanisms of mineralocorticoid receptor antagonism by eplerenone.

Mineralocorticoid receptor (MR) antagonism has proven to effectively attenuate the pathophysiological effects of aldosterone in clinical and experimental settings of hypertension and heart failure. MR activates transcription of target genes upon aldosterone binding, and eplerenone selectively binds to MR and blocks aldosterone- mediated activation. In this review, we summarize the preclinical and clinical evidence supporting the beneficial effects of eplerenone (INSPRA), a selective aldosterone blocker, in the treatment of hypertension and heart failure. We also review the current status in understanding the molecular mechanisms of action of the MR and its ligand. In addition, we compare the effects of eplerenone and spironolactone, a nonselective aldosterone blocker, on the transcriptional activity of MR and provide a molecular explanation for the improved side-effect profile of eplerenone compared with spironolactone.

Repression of p65 transcriptional activation by the glucocorticoid receptor in the absence of receptor-coactivator interactions.

Glucocorticoids are among the most potent antiinflammatory agents, acting through the glucocorticoid receptor (GR) to suppress gene expression of a variety of cytokines. This appears to be via transcriptional interference (or transrepression) of key regulatory factors such as nuclear factor-kappaB and activator protein 1. Ligand-bound GR can also activate gene transcription (transactivation) via direct binding to glucocorticoid response elements. Transactivation by GR is potentiated by accessory coactivators such as steroid receptor coactivator 1 and peroxisome proliferator-activated receptor gamma coactivator 1, whereas the role of these proteins in transrepression is unclear.Here, we show that GR can recruit several coactivator receptor interacting domains in a ligand-dependent manner. All interactions require the charge clamp defined by K579/E755, while a subset also requires a second charge clamp defined by R585/D590, within the GR ligand-binding domain. A point mutation, E755A, abolished all GR-receptor interacting domain interactions and led to a decrease in GR-mediated transactivation, but did not significantly affect GR-mediated transrepression of Gal4-p65 activity. Overexpression of a GR-interacting coactivator peptide blocked transactivation but did not affect transrepression of p65 or TNFalpha-induced IL-6 promoter activity. Finally, the GR antagonist RU486 did not recruit coactivators to GR but maintained the ability to transrepress p65 activity. Our data suggest that different coactivators utilize distinct contact points to interact with GR. Although GR interactions with specific coactivators are critical for transactivation, they appear to be dispensable for at least certain aspects of GR-mediated transrepression of nuclear factor-kappaB. This is consistent with the notion that all GR- mediated repression is not intrinsically linked to activation and can be separated mechanistically.

Liver X receptors interact with corepressors to regulate gene expression.

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that regulate gene expression in response to oxysterols and play a critical role in cholesterol homeostasis by regulating genes that are involved in cholesterol transport, catabolism, and triglyceride synthesis. Oxysterols and synthetic agonists bind LXRs and activate transcription by recruiting coactivator proteins. The role of LXRs in regulating target gene expression in the absence of ligand is unknown. Here we show that LXRs interact with corepressors, N-CoR (nuclear receptor corepressor) and SMRT (silent mediator of retinoic acid receptor and thyroid receptor), which are released upon binding agonists. The LXR-corepressor interaction is isoform selective, wherein LXRalpha has a very strong interaction with corepressors and LXRbeta only shows weak interaction. LXRs also exhibit a preference for interacting with N-CoR vs. SMRT. Similar to other nuclear receptors, mutations in the LXR helix 3 and 4 region abolish corepressor interaction. Using a transient transfection assay, we demonstrate that LXR represses transcription that can be further increased by cotransfecting N-CoR into cells. Chromatin immunoprecipitation experiments further indicated that N-CoR is recruited onto endogenous LXR target genes, and addition of LXR agonists releases N-CoR from their promoters. Collectively, these results suggest that corepressors play an important role in regulating LXR target gene expression.

The hypolipidemic natural product guggulsterone acts as an antagonist of the bile acid receptor.

Ayurveda, the ancient Indian system of health care and medicine, has a well-organized materia medica in which plants form a dominant part. A key illustration of the exploitation of this knowledge toward the development of a modern drug is the isolation and characterization of two antihyperlipidemic compounds, Z-, and E-guggulsterone from the tree Commiphora mukul, the exudate of which has been traditionally used for mitigating lipid disorders. Here, we demonstrate that Z-guggulsterone and an analog, 80-574 currently in clinical trials, act as antagonists of the bile acid receptor (BAR), a member of the intracellular receptor superfamily. These compounds antagonize the activity of BAR in vitro, and in cell culture systems on promoters and endogenous target genes. In biochemical assays, they are able to displace coactivator peptides from the receptor in a dose-dependent manner. The mechanism by which they act as BAR antagonists is likely through their inability to recruit coactivator proteins, failure to release corepressor proteins from unliganded receptor, and ability to compete with BAR agonists to block coactivator recruitment. Our data suggest these compounds may mediate at least some of their effects via the BAR.

Induction of human liver X receptor alpha gene expression via an autoregulatory loop mechanism.

The liver X receptors (LXRs), members of the nuclear receptor superfamily, play an important role in controlling lipid homeostasis by activating several genes involved in reverse cholesterol transport. These include members of the ATP binding cassette (ABC) superfamily of transporter proteins ABCA1 and ABCG1, surface constituents of plasma lipoproteins like apolipoprotein E, and cholesterol ester transport protein. They also play an important role in fatty acid metabolism by activating the sterol regulatory element-binding protein 1c gene. Here, we identify human LXRalpha (hLXRalpha) as an autoinducible gene. Induction in response to LXR ligands is observed in multiple human cell types including macrophages and occurs within 2--4 h. Analysis of the hLXRalpha promoter revealed three LXR response elements (LXREs); one exhibits strong affinity for both LXRalpha:RXR and LXRbeta:RXR (a type I LXRE), and deletion and mutational studies indicate it plays a critical role in LXR-mediated induction. The other two LXREs are identical to each other, exist within highly conserved Alu repeats, and exhibit selective binding to LXRalpha:RXR (type II LXREs). In transfections, the type I LXRE acts as a strong mediator of both LXRalpha and LXRbeta activity, whereas the type II LXRE acts as a weaker and selective mediator of LXRalpha activity. Our data suggest a model in which LXR ligands trigger an autoregulatory loop leading to selective induction of hLXRalpha gene expression. This would lead to increased hLXRalpha levels and transcription of its downstream target genes such as ABCA1, providing a simple yet exquisite mechanism for cells to respond to LXR ligands and cholesterol loading.

Pharmacological characterization of the selective 11ß-hydroxysteroid dehydrogenase 1 inhibitor, BI 135585, a clinical candidate for the treatment of type 2 diabetes.

To combat the increased morbidity and mortality associated with the developing diabetes epidemic new therapeutic interventions are desirable. Inhibition of intracellular cortisol generation from cortisone by blocking 11ß-hydroxysteroid dehydrogenase 1 (11ß-HSD1) has been shown to ameliorate the risk factors associated with the metabolic syndrome. A challenge in developing 11ß-HSD1 inhibitors has been the species selectivity of small molecules, as many compounds are primate specific. Here we describe our strategy to identify potent selective 11ß-HSD1 inhibitors while ensuring target engagement in key metabolic tissues, liver and fat. This strategy enabled the identification of the clinical candidate, BI 135585.

Multiplexing nuclear receptors for agonist identification in a cell-based reporter gene high-throughput screen.

High-throughput screening (HTS) has become an essential part of the drug discovery process. Due to the rising requirements for both data quality and quantity, along with increased screening cost and the demand to shorten the time for lead identification, increasing throughput and cost-effectiveness has become a necessity in the hit identification process. The authors present a multiplexed HTS for 2 nuclear receptors, the farnesoid X-activated receptor and the peroxisome proliferator-activated receptor delta in a viable cell-based reporter gene assay. The 2 nuclear receptors were individually transfected into human hepatoma cells, and the transient transfected cell lines were pooled for the multiplexed screen. Hits identified by the multiplexed screen are similar to those identified by the individual receptor screens. Furthermore, the multiplexed screen provides selectivity information if ligands selective for one and not the other receptor are one of the hit criteria. The data demonstrate that multiplexing nuclear receptors can be a simple, efficient, cost-effective, and reliable alternative to traditional HTS of individual targets without compromising data quality.

Liver X receptors and atherosclerosis.

Cardiovascular disease, the primary cause of death and illness in the industrialized world, is typically due to complications of atherosclerosis, a multifactorial disease of the arterial intima. The liver X receptors (LXRs), LXRalpha and LXRbeta, are intracellular receptors that appear to play an important role in protection against atherosclerosis; however, LXR activation also leads to a dramatic increase in liver and serum triglycerides. This presents a challenge to developing drugs via these targets. This article discusses the role of LXRs in atherosclerosis and lipid regulation and the possibility of designing LXR ligands that may be anti-atherogenic without side effects.

The medicinal chemistry of liver X receptor (LXR) modulators.

LXRs have been of interest as targets for the treatment of atherosclerosis for over a decade. In recent years, LXR modulators have also garnered interest for potential use in the treatment of inflammation, Alzheimer's disease (AD), dermatological conditions, hepatic steatosis, and oncology. To date, no LXR modulator has successfully progressed beyond phase I clinical trials. In this Perspective, we summarize published medicinal chemistry efforts in the context of the available crystallographic data, druglikeness, and isoform selectivity. In addition, we discuss the challenges that need to be overcome before an LXR modulator can reach clinical use.

An activin receptor-like kinase 5 inhibitor reduces collagen deposition in a rat dermal incision wound healing model.

BACKGROUND: Excessive dermal scarring is characterized by an overabundant deposition of extracellular matrix caused by fibrosis. The purpose of this study was to modify a rodent model of cutaneous healing for use in the development of compounds to minimize scarring, and to test the model with a small molecule inhibitor of transforming growth factor-ß type I receptor, activin receptor-like kinase 5, because this class of inhibitors has been demonstrated to be effective in minimizing fibrosis in other organs. METHODS: The rodent model of cutaneous healing consists of uniform full-thickness incisional dermal wounds in rats. Wounds were allowed to heal by secondary intention, generally over a 14-day period. The usefulness of the model was tested by the application of an activin receptor-like kinase 5 inhibitor, CP-639180. Activin receptor-like kinase 5 inhibition antagonizes the transforming growth factor-ß pathway, and was used to determine whether there was an effect on collagen deposition in wounds. The compound was applied once per day for 7 days starting at postwounding day 0 or 7 (early or late treatment regimens). Wounds were analyzed histologically for collagen deposition and biochemically for quantification of collagen changes. RESULTS: Early and late treatment regimens with the activin receptor-like kinase 5 inhibitor significantly reduced collagen deposition without impairing wound healing. CONCLUSIONS: Application of a small molecular inhibitor of activin receptor-like kinase 5 appears to significantly reduce collagen deposition in rat dermal wounds as reported here for the first time. Activin receptor-like kinase 5 inhibition may offer a novel approach to reducing proliferative scars in humans because collagen accumulation is a core event in scarring.

Steroidogenic factor 1: an essential mediator of endocrine development.

The orphan nuclear receptor steroidogenic factor 1 (SF-1, also called Ad4BP and officially designated NR5A1) has emerged as an essential regulator of endocrine development and function. Initially identified as a tissue-specific transcriptional regulator of the cytochrome P450 steroid hydroxylases, SF-1 has considerably broader roles, as evidenced from studies in knockout mice lacking SF-1. The SF-1-knockout mice lacked adrenal glands and gonads and therefore died from adrenal insufficiency within the first week after birth. In addition, SF-1 knockout mice exhibited male-to-female sex reversal of their internal and external genitalia, impaired expression of multiple markers of pituitary gonadotropes, and agenesis of the ventromedial hypothalamic nucleus (VMH). These studies delineated essential roles of SF-I in regulating endocrine differentiation and function at multiple levels, particularly with respect to reproduction. This chapter will review the experiments that established SF-1 as a pivotal, global determinant of endocrine differentiation and function. We next discuss recent insights into the mechanisms controlling the expression and function of SF-1 as well as the current status of research aimed at delineating its roles in specific tissues. Finally, we highlight areas where additional studies are needed to expand our understanding of SF-1 action.