Glucocorticoid receptor modulators informed by crystallography lead to a new rationale for receptor selectivity, function, and implications for structure-based design.

The structural basis of the pharmacology enabling the use of glucocorticoids as reliable treatments for inflammation and autoimmune diseases has been augmented with a new group of glucocorticoid receptor (GR) ligands. Compound 10, the archetype of a new family of dibenzoxepane and dibenzosuberane sulfonamides, is a potent anti-inflammatory agent with selectivity for the GR versus other steroid receptors and a differentiated gene expression profile versus clinical glucocorticoids (lower GR transactivation with comparable transrepression). A stereospecific synthesis of this chiral molecule provides the unique topology needed for biological activity and structural biology. In vivo activity of 10 in acute and chronic models of inflammation is equivalent to prednisolone. The crystal structure of compound 10 within the GR ligand binding domain (LBD) unveils a novel binding conformation distinct from the classic model adopted by cognate ligands. The overall conformation of the GR LBD/10 complex provides a new basis for binding, selectivity, and anti-inflammatory activity and a path for further insights into structure-based ligand design.

Identification of a novel selective peroxisome proliferator-activated receptor alpha agonist, 2-methyl-2-(4-{3-[1-(4-methylbenzyl)-5-oxo-4,5-dihydro-1H-1,2,4-triazol-3-yl]propyl}phenoxy)propanoic acid (LY518674), that produces marked changes in serum lipids and apolipoprotein A-1 expression.

Low high-density lipoprotein-cholesterol (HDL-c) is an important risk factor of coronary artery disease (CAD). Optimum therapy for raising HDL-c is still not available. Identification of novel HDL-raising agents would produce a major impact on CAD. In this study, we have identified a potent (IC50 approximately 24 nM) and selective peroxisome proliferator-activated receptor alpha (PPARalpha) agonist, 2-methyl-2-(4-{3-[1-(4-methylbenzyl)-5-oxo-4,5-dihydro-1H-1,2,4-triazol-3-yl]propyl}phenoxy)propanoic acid (LY518674). In human apolipoprotein A-1 (apoA-1) transgenic mice, LY518674 produced a dose-dependent increase in serum HDL-c, resulting in 208 +/- 15% elevation at optimum dose. A new synthesis of apoA-1 contributed to the increase in HDL-c. LY518674 increased apoA-1 mRNA levels in liver. Moreover, liver slices from animals treated with LY518674 secreted 3- to 6-fold more apoA-1 than control liver slices. In cultured hepatocytes, LY518674 produced 50% higher apoA-1 secretion, which was associated with increase in radiolabeled methionine incorporation in apoA-1. Thus, LY518674 is a potent and selective PPARalpha agonist that produced a much greater increase in serum HDL-c than the known fibrate drugs. The increase in HDL-c was associated with de novo synthesis of apoA-1.

A peroxisome proliferator-activated receptor alpha/gamma dual agonist with a unique in vitro profile and potent glucose and lipid effects in rodent models of type 2 diabetes and dyslipidemia.

LSN862 is a novel peroxisome proliferator-activated receptor (PPAR)alpha/gamma dual agonist with a unique in vitro profile that shows improvements on glucose and lipid levels in rodent models of type 2 diabetes and dyslipidemia. Data from in vitro binding, cotransfection, and cofactor recruitment assays characterize LSN862 as a high-affinity PPARgamma partial agonist with relatively less but significant PPARalpha agonist activity. Using these same assays, rosiglitazone was characterized as a high-affinity PPARgamma full agonist with no PPARalpha activity. When administered to Zucker diabetic fatty rats, LSN862 displayed significant glucose and triglyceride lowering and a significantly greater increase in adiponectin levels compared with rosiglitazone. Expression of genes involved in metabolic pathways in the liver and in two fat depots from compound-treated Zucker diabetic fatty rats was evaluated. Only LSN862 significantly elevated mRNA levels of pyruvate dehydrogenase kinase isozyme 4 and bifunctional enzyme in the liver and lipoprotein lipase in both fat depots. In contrast, both LSN862 and rosiglitazone decreased phosphoenol pyruvate carboxykinase in the liver and increased malic enzyme mRNA levels in the fat. In addition, LSN862 was examined in a second rodent model of type 2 diabetes, db/db mice. In this study, LSN862 demonstrated statistically better antidiabetic efficacy compared with rosiglitazone with an equivalent side effect profile. LSN862, rosiglitazone, and fenofibrate were each evaluated in the humanized apoA1 transgenic mouse. At the highest dose administered, LSN862 and fenofibrate reduced very low-density lipoprotein cholesterol, whereas, rosiglitazone increased very low-density lipoprotein cholesterol. LSN862, fenofibrate, and rosiglitazone produced maximal increases in high-density lipoprotein cholesterol of 65, 54, and 30%, respectively. These findings show that PPARgamma full agonist activity is not necessary to achieve potent and efficacious insulin-sensitizing benefits and demonstrate the therapeutic advantages of a PPARalpha/gamma dual agonist.

The hypolipidemic natural product guggulsterone is a promiscuous steroid receptor ligand.

Guggulsterone (GS) is the active substance in guggulipid, an extract of the guggul tree, Commiphora mukul, used to treat a variety of disorders in humans, including dyslipidemia, obesity, and inflammation. The activity of GS has been suggested to be mediated by antagonism of the receptor for bile acids, the farnesoid X receptor (FXR). Here, we demonstrate that both stereoisomers of the plant sterol, (E)- and (Z)-GS, bind to the steroid receptors at a much higher affinity than to FXR. Both stereoisomers bind to the mineralocorticoid receptor (MR) with a Ki value of approximately 35 nM, which is greater than 100 times more potent than their affinity for FXR. Both (E)- and (Z)-GS also displayed high affinity for other steroid receptors, including the androgen (AR), glucocorticoid (GR), and progesterone receptors (PR) with Ki values ranging from 224 to 315 nM. In cell-based functional cotransfection assays, GSs behaved as antagonists of AR, GR, and MR, but as agonists of PR. Agonist activity was also demonstrated with estrogen receptor (ER) alpha; however, the potency was very low (EC50 > 5000 nM). In addition, GS displayed activity in functional assays in cell lines expressing endogenous AR, GR, ER, and PR. These data suggest that the variety of pharmacological effects exhibited by GS may be mediated by targeting several steroid receptors.

A natural product ligand of the oxysterol receptor, liver X receptor.

Natural products have been identified as ligands for a number of members of the nuclear hormone receptor (NHR) superfamily. Often these natural products are used as dietary supplements to treat myriad ailments ranging from perimenopausal hot flashes to hypercholesterolemia and reduced cognitive function. Examples of some natural product ligands for NHRs include genestein (estrogen receptors NR3A1 and NR3A2), guggulsterone (farnesoid X receptor NR1H4), and St. John's wort (pregnane X receptor, NR1I2). In this study, we identified the first nonoxysterol natural product that functions as a ligand for the liver X receptor (LXRalpha and LXRbeta; NR1H3, NR1H2), a NHR that acts as the receptor for oxysterols and plays a key role in regulation of cholesterol metabolism and transport as well as glucose metabolism. We show that paxilline, a fungal metabolite, is an efficacious agonist of both LXRalpha and LXRbeta in biochemical and in vitro cell-based assays. Paxilline binds directly to both receptors and is an activator of LXR-dependent transcription in cell-based reporter assays. We also demonstrate that paxilline binding to the receptors results in efficient activation of transcription of two physiological LXR target genes, ABCA1 and SREBP. The discovery of paxilline, the first reported nonoxysterol natural product ligand of the LXRs, may provide insight into the mechanism of ligand recognition by these receptors and reaffirms the utility of examining natural product libraries for identifying novel NHR ligands.

A chemical switch regulates fibrate specificity for peroxisome proliferator-activated receptor alpha (PPARalpha ) versus liver X receptor.

Fenofibrate is clinically successful in treating hypertriglyceridemia and mixed hyperlipidemia presumably through peroxisome proliferator-activated receptor alpha (PPARalpha)-dependent induction of genes that control fatty acid beta-oxidation. Lipid homeostasis and cholesterol metabolism also are regulated by the nuclear oxysterol receptors, liver X receptors alpha and beta (LXRalpha and LXRbeta). Here we show that fenofibrate ester, but not fenofibric acid, functions as an LXR antagonist by directly binding to LXRs. Likewise, ester forms, but not carboxylic acid forms, of other members of the fibrate class of molecules antagonize the LXRs. The fibrate esters display greater affinity for LXRs than the corresponding fibric acids have for PPARalpha. Thus, these two nuclear receptors display a degree of conservation in their recognition of ligands; yet, the acid/ester moiety acts as a chemical switch that determines PPARalpha versus LXR specificity. Consistent with its LXR antagonistic activity, fenofibrate potently represses LXR agonist-induced transcription of hepatic lipogenic genes. Surprisingly, fenofibrate does not repress LXR-induced transcription of various ATP-binding cassette transporters either in liver or in macrophages, suggesting that fenofibrate manifests variable biocharacter in the context of differing gene promoters. These findings provide not only an unexpected mechanism by which fenofibrate inhibits lipogenesis but also the basis for examination of the pharmacology of an LXR ligand in humans.

A tailored therapy for the metabolic syndrome: the dual peroxisome proliferator-activated receptor-alpha/gamma agonist LY465608 ameliorates insulin resistance and diabetic hyperglycemia while improving cardiovascular risk factors in preclinical models.

A novel nonthiazolidinedione dual peroxisome proliferator- activated receptor (PPAR)-alpha/gamma agonist, LY465608, was designed to address the major metabolic disturbances of type 2 diabetes. LY465608 altered PPAR-responsive genes in liver and fat of db/db mice and dose-dependently lowered plasma glucose in hyperglycemic male Zucker diabetic fatty (ZDF) rats, with an ED(50) for glucose normalization of 3.8 mg small middle dot kg(-1) small middle dot day(-1). Metabolic improvements were associated with enhanced insulin sensitivity, as demonstrated in female obese Zucker (fa/fa) rats using both oral glucose tolerance tests and hyperinsulinemic-euglycemic clamps. Further characterization of LY465608 revealed metabolic changes distinct from a selective PPAR-gamma agonist, which were presumably due to the concomitant PPAR-alpha agonism, lower respiratory quotient, and less fat accumulation, despite a similar impact on glycemia in male ZDF rats. In addition to these alterations in diabetic and insulin-resistant animals, LY465608 dose-dependently elevated HDL cholesterol and lowered plasma triglycerides in human apolipoprotein A-I transgenic mice, demonstrating that this compound significantly improves primary cardiovascular risk factors. Overall, these studies demonstrate that LY465608 beneficially impacts multiple facets of type 2 diabetes and associated cardiovascular risk, including those facets involved in the development of micro- and macrovascular complications, which are the major sources for morbidity and mortality in these patients.