Design and synthesis of subtype- and species-selective peroxisome proliferator-activated receptor (PPAR) alpha ligands

The molecular pharmacological discovery of the nuclear receptor peroxisome proliferator-activated receptor alpha (PPAR alpha) as the master regulator of lipid and lipoprotein homeostasis, and the rapid development of a parallel screening approach to evaluate activity towards other PPAR subtypes (PPAR delta, and PPAR gamma) have provided an opportunity to develop novel PPAR alpha-selective, PPAR alpha/gamma dual, and PPAR pan agonists. This review focuses on the molecular pharmacology of PPAR alpha, and summarizes our current design, synthesis, and evaluation of subtype-selective PPAR alpha agonists. The species selectivity of several classes of PPAR alpha selective agonists in response to in vitro PPAR alpha transactivation activity is also reported. These studies should help us to understand the structure-activity relationships and the mode of interaction between ligands and PPAR alpha, and also help to create novel therapeutic choices for the treatment of metabolic disorders.     

Integrated virtual screening for the identification of novel and selective peroxisome proliferator-activated receptor (PPAR) scaffolds

We describe a fully customizable and integrated target-specific "tiered" virtual screening approach tailored to identifying and characterizing novel peroxisome proliferator activated receptor γ (PPARγ) scaffolds. Built on structure- and ligand-based computational techniques, a consensus protocol was developed for use in the virtual screening of chemical databases, focused toward retrieval of novel bioactive chemical scaffolds for PPARγ. Consequent from application, three novel PPAR scaffolds displaying distinct chemotypes have been identified, namely, 5-(4-(benzyloxy)-3-chlorobenzylidene)dihydro-2-thioxopyrimidine-4,6(1H,5H)-dione (MDG 548), 3-((4-bromophenoxy)methyl)-N-(4-nitro-1H-pyrazol-1-yl)benzamide (MDG 559), and ethyl 2-[3-hydroxy-5-(5-methyl-2-furyl)-2-oxo-4-(2-thienylcarbonyl)-2,5-dihydro-1H-pyrrol-1-yl]-4-methyl-1,3-thiazole-5-carboxylate (MDG 582). Fluorescence polarization(FP) and time resolved fluorescence resonance energy transfer (TR-FRET) show that these compounds display high affinity competitive binding to the PPARγ-LBD (EC(50) of 215 nM to 5.45 μM). Consequent characterization by a TR-FRET activation reporter assay demonstrated agonism of PPARγ by all three compounds (EC(50) of 467-594 nM). Additionally, differential PPAR isotype specificity was demonstrated through assay against PPARα and PPARδ subtypes. This work showcases the ability of target specific "tiered screen" protocols to successfully identify novel scaffolds of individual receptor subtypes with greater efficacy than isolated screening methods.     

Biochemical and morphological effects of K-111, a peroxisome proliferator-activated receptor (PPAR)alpha activator, in non-human primates

K-111 has been characterized as a potent peroxisome proliferator-activated receptor (PPAR)alpha activator. Antidiabetic potency and amelioration of disturbed lipid metabolism were demonstrated in rodents, which were accompanied by elevations of peroxisomal enzymes and liver weight. To examine the possible therapeutic application of K-111 we have now assessed its efficacy in non-human primates with high transferability to humans. For this purpose obese, hypertriglyceridaemic, hyperinsulinaemic prediabetic rhesus monkeys were dosed sequentially with 0, 1, 3 and 10mg/kg per day orally over a period of 4 weeks each. In addition, the effect of K-111 on the peroxisome compartment was analyzed in cynomolgus monkeys using liver samples obtained following a 13-week oral toxicity study. In prediabetic monkeys, the reduction of hyperinsulinaemia and improvement of insulin-stimulated glucose uptake rate indicated amelioration of insulin resistance. These effects were nearly maximal at a dose of 3mg/kg per day, while triglycerides and body weight were lowered significantly in a dose-dependent manner. This reduction of body weight contrasts sharply with the adipogenic response observed with thiazolidinediones, another family of insulin-sensitizing agents. In young cynomolgus monkeys at a dosage of 5mg/kg per day and more, K-111 induced an up to three-fold increase in lipid beta-oxidation enzymes with an 1.5- to 2-fold increase in peroxisome volume density. This moderate increase in peroxisomal activity by K-111 in monkeys is consistent with its role as an PPARalpha activator and corresponds to the observations with fibrates in other low responder mammalian species. The increase in beta-oxidation may explain, at least in part, the lipid modulating effect as well as the antidiabetic potency of K-111. This pharmacological profile makes K-111 a highly promising drug candidate for clinical applications in the treatment of type 2 diabetes, dyslipidaemia, obesity and the metabolic syndrome.     

Evidence for peroxisome proliferator-activated receptor (PPAR)alpha-independent peroxisome proliferation: effects of PPARgamma/delta-specific agonists in PPARalpha-null mice

Peroxisome proliferators are a diverse group of compounds that cause hepatic hypertrophy and hyperplasia, increase peroxisome number, and on chronic high-dose administration, lead to rodent liver tumorigenesis. Various lines of evidence have led to the conclusion that these agents induce their pleiotropic effects exclusively via agonism of peroxisome proliferator-activated receptor (PPAR)alpha, a member of the steroid receptor superfamily involved in the regulation of fatty acid metabolism. Recently, agonists of two other members of this receptor family have been identified. PPARgamma is predominantly expressed in adipocytes where it mediates differentiation; PPARdelta is a widely expressed orphan receptor with yet unresolved physiologic functions. In the course of characterizing newer PPAR ligands, we noted that highly selective PPARgamma agonists or dual PPARgamma/PPARdelta agonists, lacking apparent murine PPARalpha agonist activity, cause peroxisome proliferation in CD-1 mice. We therefore made use of PPARalpha knockout mice to investigate whether these effects resulted from agonism of PPARalpha by these agents at very high dose levels or whether PPARgamma (or PPARdelta) agonism alone can result in peroxisome proliferation. We report here that several parameters linked to the hepatic peroxisome proliferation response in mice that were seen with these agents resulted from PPARalpha-independent effects.     

Structural basis for the structure-activity relationships of peroxisome proliferator-activated receptor agonists

Type 2 diabetes has rapidly reached an epidemic proportion becoming a major threat to global public health. PPAR agonists have emerged as a leading class of oral antidiabetic drugs. We report a structure biology analysis of novel indole-based PPAR agonists to explain the structure-activity relationships and present a critical analysis of reasons for change in selectivity with change in the orientation of the same scaffolds. The results would be helpful in designing novel PPAR agonists.     

Modulation of peroxisome proliferator-activated receptors (PPARs) by PPAR(alpha)- and PPAR(gamma)-specific ligands and by 17beta-estradiol in isolated zebrafish hepatocytes.

Peroxisome proliferation is a phenomenon occurring when responsive animals are exposed to certain compounds so-called peroxisome proliferators and is regulated through a nuclear receptor named peroxisome proliferator-activated receptor (PPAR). PPAR family members exhibit a strong binding affinity for both saturated and unsaturated fatty acids. Activators of PPAR(alpha) include a variety of endogenously present fatty acids, leukotrienes and hydroxyeicosatetraenoic acids (HETEs) and clinically used drugs, such as fibrates. PPAR(beta) activators include fatty acids, prostaglandin A2 (PGA2) and prostacyclin (PGI2). PPAR(gamma) is the most selective receptor and, among others, 15-deoxy-Delta(12,14) prostaglandin J2 (PGJ2) has been described to be a PPAR(gamma)-specific ligand. The aim of the present study was to determine if known PPAR(alpha) and PPAR(gamma) ligands were able to alter the expression of these subtypes in an in vitro model of zebrafish primary hepatocyte culture. With this purpose, a PPAR(alpha) specific ligand (8S-HETE), a PPARgamma specific ligand (PGJ) and a peroxisome proliferator of the fibrate class (clofibrate) were selected. In addition, the female hormone 17beta-estradiol was also used as it is known to interact with PPARs. After cell exposure for 24 h, cells were immunohistochemically stained for both PPARs and immunolabeling was quantified as percentage of positive nuclei and cells. Levels of expression of PPARs were also measured by image analysis as grey level per cell. Expression was induced for both PPAR(alpha) and PPAR(gamma) by clofibrate (at 0.5 mM for PPAR(alpha) and at 1 and 2 mM for PPAR(gamma)), by HETE (1 microM), and by PGJ2 (0.3 and 1 microM for PPAR(alpha) and 0.3 microM for PPAR(gamma)). Expression of PPARgamma was also induced at 10 microM by 17beta-estradiol. The percentage of PPAR(alpha) positive nuclei increased significantly at 1 microM HETE and the percentage of PPAR(gamma) positive cells decreased at 10 microM 17beta-estradiol. As a conclusion, clofibrate, HETE and PGJ2 are able to induce expression of both PPAR(alpha) and PPAR(gamma) in zebrafish primary hepatocyte cultures. Further studies are needed to identify how the expression of different PPAR subtypes is regulated and to elucidate the implication of PPAR subtypes in zebrafish cell functions.     

以PPAR为靶标的抗2型糖尿病药物研发策略

近年来发现2型糖尿病与过氧化物酶增殖体活化受(peroxisome proliferator-activated receptor，PPAR)存在着密切的联系，该受体也因此成为设计抗2型糖尿病药物的主要靶标。目前，有很多针对PPAR所设计的化合物处于临床研究阶段，现介绍这方面的进展，并阐述开发抗2型糖尿病药物所面临的困难及相应的策略。     

Recent progress in research on peroxisome proliferator-activated receptor alpha-selective ligands

The understanding of the functions of the nuclear receptor peroxisome proliferator-activated receptor a (PPARalpha) as a regulator of lipid and lipoprotein homeostasis, and the rapid development of parallel high-throughput screening assays to evaluate the activity toward other PPAR subtypes (PPARdelta and PPARgamma), have provided an opportunity to develop novel PPARalpha-selective, PPARalpha/gamma dual and PPAR pan agonists for the treatment of various metabolic diseases. This review focuses on the molecular pharmacology of PPARalpha, and summarizes recent literature and patent applications disclosing medicinal chemistry strategies to identify new PPARalpha-selective agonists. The species selectivity of some classes of PPARalpha-selective agonists in response to in vitro PPARalpha transactivation activity is also reported.     

Relationship between peroxisome proliferator-activated receptors (PPAR alpha and PPAR gamma) and endothelium-dependent relaxation in streptozotocin-induced diabetic rats

(1) The aim of the present study was to investigate the causal relationship between peroxisome proliferator-activated receptor (PPAR) and endothelium-dependent relaxation in streptozotocin (STZ)-induced diabetic rats. (2) Acetylcholine (ACh)-induced endothelium-dependent relaxation was significantly weaker in diabetic rats than in age-matched controls. The decreased relaxation in diabetes was improved by the chronic administration of bezafibrate (30 mg kg-1, p.o., 4 weeks). (3) The expressions of the mRNAs for PPARalpha and PPARgamma were significantly decreased in STZ-induced diabetic rats (compared with the controls) and this decrease was restored partially, but not completely, by the chronic administration of bezafibrate. (4) Superoxide dismutase activity in the aorta was not significantly different between diabetic rats and bezafibrate-treated diabetic rats. (5) The expression of the mRNA for the p22phox subunit of NAD(P)H oxidase was significantly higher in diabetics than in controls, but it was lower in bezafibrate-treated diabetic rats than in nontreated diabetic rats. Although the expression of the mRNA for prepro ET-1 (ppET-1) was markedly increased in diabetic rats (compared with controls), this increase was prevented to a significant extent by the chronic administration of bezafibrate. (6) These results suggest that downregulations of PPARalpha and PPARgamma may lead to an increased expression of ppET-1 mRNA in diabetic states and this increment may trigger endothelial dysfunction.     

Design and synthesis of a potent and selective triazolone-based peroxisome proliferator-activated receptor alpha agonist

A new series of hPPARalpha agonists containing a 2,4-dihydro-3H-1,2,4-triazol-3-one (triazolone) core is described leading to the discovery of 5 (LY518674), a highly potent and selective PPARalpha agonist.     

The potential of peroxisome proliferator-activated receptor gamma (PPARgamma) ligands in the treatment of hematological malignancies

PPARgamma has emerged as a key regulator of cell growth and survival, whose activity is modulated by a number of synthetic and natural ligands. Here we shall review the activities of PPARgamma ligands in the control of immune cell proliferation, differentiation and apoptosis and their potential therapeutic applications to hematological malignancies.     

非甾体类孕酮受体配体构效关系的研究进展

孕酮受体配体(PRLs)通过孕酮受体介导发挥作用,有广泛的妇科疾病治疗前景.目前临床用药多为甾体类,不良反应多,临床应用极为有限.非甾体类PRLs具有高度的受体和组织选择性,有望降低不良反应,扩大其在临床上的应用.文中分类综述近年来非甾体类PRLs的研发进展,其中包括吲唑类、哒嗪类、苯并吡喃并喹啉类、苯并嗯嗪类、吲哚类、苯并咪唑和苯并噻唑类、氢化喹啉、吡唑类、二氮革类、苯并吲哚及萘并呋喃类化合物.