Quinoline-3-carboxamide containing sulfones as liver X receptor (LXR) agonists with binding selectivity for LXRbeta and low blood-brain penetration

A structural perspective of liver X receptors

Liver X receptors α and β are members of the nuclear receptor family, which comprise a flexible N-terminal domain, a DNA binding domain, a hinge linker, and a ligand binding domain. Liver X receptors are important regulators of cholesterol and lipid homeostasis by controlling the transcription of numerous genes. Key to their transcriptional role is synergetic interaction among the domains. DNA binding domain binds on DNA; ligand binding domain is a crucial switch to control the transcription activity through conformational change caused by ligand binding. The Liver X receptors form heterodimers with retinoid X receptor and then the liganded heterodimer may recruit other necessary transcription components to form an active transcription complex.

Discovery of new LXRβ agonists as glioblastoma inhibitors

Discovery and optimization of selective liver X receptor β (LXRβ) agonists are challenging due to the high homology of LXRα and LXRβ in the ligand-binding domain. There is only one different residue (Val versus Ile) at the ligand-binding pocket of LXRs. With machine learning methods, we identified pan LXR agonists with a novel scaffold (spiro[pyrrolidine-3,3'-oxindole]). Then, we figured out the mechanism of LXR isoform selectivity from co-crystal structures. Based on the mechanism and the new scaffold, LXRβ selective agonists were designed and synthesized. This led to the discovery of LXRβ agonists 4-7rr, 4-13 and 4-13rr with IC₅₀ values ranging from 1.78 to 6.36 μM against glioblastoma in vitro. Treatment with 50 mg/kg/day of 4-13 for 15 days significantly reduced tumor growth using an in vivo xenograft glioblastoma model.

Structural analysis identifies an escape route from the adverse lipogenic effects of liver X receptor ligands

Liver X receptors (LXRs) are attractive drug targets for cardiovascular disease treatment due to their role in regulating cholesterol homeostasis and immunity. The anti-atherogenic properties of LXRs have prompted development of synthetic ligands, but these cause major adverse effects-such as increased lipogenesis-which are challenging to dissect from their beneficial activities. Here we show that LXR compounds displaying diverse functional responses in animal models induce distinct receptor conformations. Combination of hydrogen/deuterium exchange mass spectrometry and multivariate analysis allowed identification of LXR regions differentially correlating with anti-atherogenic and lipogenic activities of ligands. We show that lipogenic compounds stabilize active states of LXRα and LXRβ while the anti-atherogenic expression of the cholesterol transporter ABCA1 is associated with the ligand-induced stabilization of LXRα helix 3. Our data indicates that avoiding ligand interaction with the activation helix 12 while engaging helix 3 may provide directions for development of ligands with improved therapeutic profiles.

The challenges and promise of targeting the Liver X Receptors for treatment of inflammatory disease

The Liver X Receptors (LXRs) are oxysterol-activated transcription factors that upregulate a suite of genes that together promote coordinated mobilization of excess cholesterol from cells and from the body. The LXRs, like other nuclear receptors, are anti-inflammatory, inhibiting signal-dependent induction of pro-inflammatory genes by nuclear factor-κB, activating protein-1, and other transcription factors. Synthetic LXR agonists have been shown to ameliorate atherosclerosis and a wide range of inflammatory disorders in preclinical animal models. Although this has suggested potential for application to human disease, systemic LXR activation is complicated by hepatic steatosis and hypertriglyceridemia, consequences of lipogenic gene induction in the liver by LXRα. The past several years have seen the development of multiple advanced LXR therapeutics aiming to avoid hepatic lipogenesis, including LXRβ-selective agonists, tissue-selective agonists, and transrepression-selective agonists. Although several synthetic LXR agonists have made it to phase I clinical trials, none have progressed due to unforeseen adverse reactions or undisclosed reasons. Nonetheless, several sophisticated pharmacologic strategies, including structure-guided drug design, cell-specific drug targeting, as well as non-systemic drug routes have been initiated and remain to be comprehensively explored. In addition, recent studies have identified potential utility for targeting the LXRs during therapy with other agents, such as glucocorticoids and rexinoids. Despite the pitfalls encountered to date in translation of LXR agonists to human disease, it appears likely that this accelerating field will ultimately yield effective and safe applications for LXR targeting in humans.

Liver X receptors link lipid metabolism and inflammation

The response of immune cells to pathogens is often associated with changes in the flux through basic metabolic pathways. Indeed, in many cases changes in metabolism appear to be necessary for a robust immune response. The Liver X receptors (LXRs) are members of the nuclear hormone receptor superfamily that regulate gene networks controlling cholesterol and lipid metabolism. In immune cells, particularly in macrophages, LXRs also inhibit proinflammatory gene expression. This Review will highlight recent studies that connect LXR-dependent control of lipid metabolism to regulation of the immune response.

Site-selective Suzuki-Miyaura coupling of heteroaryl halides - understanding the trends for pharmaceutically important classes

Suzuki-Miyaura cross-coupling reactions of heteroaryl polyhalides with aryl boronates are surveyed. Drawing on data from literature sources as well as bespoke searches of Pfizer's global chemistry RKB and CAS Scifinder® databases, the factors that determine the site-selectivity of these reactions are discussed with a view to rationalising the trends found.

Orphan nuclear receptors as drug targets for the treatment of prostate and breast cancers

Nuclear receptors (NRs), a family of 48 transcriptional factors, have been studied intensively for their roles in cancer development and progression. The presence of distinctive ligand binding sites capable of interacting with small molecules has made NRs attractive targets for developing cancer therapeutics. In particular, a number of drugs have been developed over the years to target human androgen- and estrogen receptors for the treatment of prostate cancer and breast cancer. In contrast, orphan nuclear receptors (ONRs), which in many cases lack known biological functions or ligands, are still largely under investigated. This review is a summary on ONRs that have been implicated in prostate and breast cancers, specifically retinoic acid-receptor-related orphan receptors (RORs), liver X receptors (LXRs), chicken ovalbumin upstream promoter transcription factors (COUP-TFs), estrogen related receptors (ERRs), nerve growth factor 1B-like receptors, and ‘‘dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1’’ (DAX1). Discovery and development of small molecules that can bind at various functional sites on these ONRs will help determine their biological functions. In addition, these molecules have the potential to act as prototypes for future drug development. Ultimately, the therapeutic value of targeting the ONRs may go well beyond prostate and breast cancers.

Predicting selective liver X receptor β agonists using multiple machine learning methods

The classification models for predicting selective LXRβ agonists were firstly established using multiple machine learning methods. The top models can predict selective LXRβ agonists with chemical structure diversity.

Liver X receptor modulators: a review of recently patented compounds (2009 - 2012)

INTRODUCTION

The development of small molecule agonists of the liver X receptors (LXRs) has been an area of interest for over a decade, given the critical role of those receptors in cholesterol metabolism, glucose homeostasis, inflammation, innate immunity and lipogenesis. Many potential indications have been characterized over time including atherosclerosis, diabetes, inflammation, Alzheimer's disease and cancer. However, concerns about the lipogenic effects of full LXRα/β agonists have required extensive efforts aimed at identifying LXRβ agonist with limited activity on the LXRα receptor to increase the safety margins.

AREAS COVERED

This review includes a summary of the LXR agonists that have reached the clinic and summarizes the patent applications for LXR modulators from September 2009 to December 2012 with emphasis on chemical matters, biological data associated with selected analogs and therapeutic indications.

EXPERT OPINION

As LXR agonists have the potential to be useful for many indications, the scientific community, despite setbacks due to on-target side effects, has maintained interest and devised strategies to overcome safety hurdles. While a clinical proof of concept still remains elusive, the recent advancement of compounds into the clinic highlights that acceptable safety margins in preclinical species have been achieved.

The effect of diet on the response of low-density lipoprotein receptor knockout mice to the liver X receptor agonist T1317

It has been previously observed that low-density lipoprotein receptor knockout (LDLR--/--) mice fed a Western-type diet without cholate and given the liver X receptor agonist T1317 develop a persistent and enhanced hypertriglyceridemia. In contrast, LDLR--/-- mice fed a Paigen diet with cholate exhibit only a transient increase in plasma triglycerides when given T1317. Cholate as an activator of farnesoid X receptor may attenuate T1317-induced triglyceridemia. To determine if cholate was responsible for this transient nature of the hypertriglyceridemia, we orally administered T1317 to LDLR--/-- mice fed a modified Paigen diet without cholate. T1317 transiently elevated plasma triglycerides by increasing plasma very-low-density lipoprotein. Cholesterol and triglyceride levels in plasma very-low-density lipoprotein in T1317-treated mice decreased from peak levels to levels found in vehicle-treated mice after 8 weeks of treatment. A gradual decline of hepatic cholesterol and a transient increase in hepatic triglycerides were also observed in T1317-treated mice. T1317 only transiently activated the expression of genes related to liver de novo lipogenesis, whereas genes related to lipid metabolism were induced in T1317-treated mice, including a gradual increase in plasma lipoprotein lipase activity. Atheroprotective effects of T1317 were observed in the innominate artery and aortic arch but not in the aortic sinus. This work indicates that some component(s) in the Paigen diet other than cholate affect the T1317-induced gene expression profile and ameliorate its effects on lipid synthesis, which lead to hypertriglyceridemia and fatty liver. These findings are important for liver X receptor-related pharmaceutical development for the treatment of cardiovascular disease.

What has polar surface area ever done for drug discovery?

Over the last decade, polar surface area (PSA) has become a ubiquitous term in medicinal and computational chemistry circles. This article charts the development of the increasingly efficient methods for the calculation of PSA before illustrating its usefulness through selected examples drawn from the medicinal chemistry literature. Consideration of PSA is shown to assist in the improvement of cellular potency, intestinal absorption and blood-brain barrier permeation or restriction to the peripheral circulation.

Liver X receptor modulators: a review of recently patented compounds (2007 - 2009)

IMPORTANCE OF THE FIELD

Liver X receptors (LXRs) are ligand activated transcription factors involved in cholesterol metabolism, glucose homeostasis, inflammation and lipogenesis. With the important physiological role of LXRs in reverse cholesterol transport (RCT), atherosclerosis is the best investigated therapeutic indication. While atherosclerosis is not yet clinically validated, Wyeth's LXRalpha/beta agonist LXR-623 indicated the key LXR target genes involved in RCT (ABCA1 and ABCG1) are upregulated in peripheral blood cells in a dose-dependent manner. While discontinued for CNS safety concerns, investigation of LXR-623 supports atherosclerosis as a clinical indication, and the possibility of identifying LXR agonists with profiles that avoid the strong lipogenic effects of full LXRalpha/beta agonists.

AREAS COVERED IN THIS REVIEW

Patents for LXR agonists from late 2006 up to August 2009 with emphasis on chemical matters and relationship to earlier disclosures, the biological data associated with selected analogues and therapeutic indications.

WHAT THE READER WILL GAIN

An overview of the majority of LXR scaffolds with representative structure activity relationships as well as the companies that are the chief players in the field.

TAKE HOME MESSAGE

The future application of LXR agonists depends upon the discovery of LXR agents without lipogenic effects. Limiting activation of LXRalpha is a popular strategy.