Structure-based identification of novel PPAR gamma ligands

Tetrazoles and Related Heterocycles as Promising Synthetic Antidiabetic Agents

Tetrazole heterocycle is a promising scaffold in drug design, and it is incorporated into active pharmaceutical ingredients of medications of various actions: hypotensives, diuretics, antihistamines, antibiotics, analgesics, and others. This heterocyclic system is metabolically stable and easily participates in various intermolecular interactions with different biological targets through hydrogen bonding, conjugation, or van der Waals forces. In the present review, a systematic analysis of the activity of tetrazole derivatives against type 2 diabetes mellitus (T2DM) has been performed. As it was shown, the tetrazolyl moiety is a key fragment of many antidiabetic agents with different activities, including the following: peroxisome proliferator-activated receptors (PPARs) agonists, protein tyrosine phosphatase 1B (PTP1B) inhibitors, aldose reductase (AR) inhibitors, dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide 1 (GLP-1) agonists, G protein-coupled receptor (GPCRs) agonists, glycogen phosphorylases (GP) Inhibitors, α-glycosidase (AG) Inhibitors, sodium glucose co-transporter (SGLT) inhibitors, fructose-1,6-bisphosphatase (FBPase) inhibitors, IkB kinase ε (IKKε) and TANK binding kinase 1 (TBK1) inhibitors, and 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). In many cases, the tetrazole-containing leader compounds markedly exceed the activity of medications already known and used in T2DM therapy, and some of them are undergoing clinical trials. In addition, tetrazole derivatives are very often used to act on diabetes-related targets or to treat post-diabetic disorders.

Nano-CuFe2O3-catalyzed green synthesis of novel quinazolinone-tetrazole hybrids as anti-cancer agents

A novel green protocol has been developed for the synthesis of quinazolinone-tetrazole conjugates (7a-g, 8a-g and 9a-g) using recyclable nano-CuFe₂O₃ catalyst in water. Initially, 2-mercapto-3-substituted phenethylquinazolin-4(3H)-one (5a-c) was prepared by using nano-CuFe₂O₃ catalyst in water. Then, compounds (5a-c) were reacted with 1-bromo-3-chloropropane under nano-CuFe₂O₃ catalyst in water solvent to give S-alkylated quinazolinone core intermediate (6a-c), which was subsequently reacted with 1-substituted-1H-tetrazole-5-thiol (2a-g) by employing the similar reaction conditions to afford the final target compounds. The regioselective formation of C-S bond was unambiguously confirmed by single-crystal X-ray diffraction. The anti-cancer activity of the derivatives on various cancer cell lines such as SIHA, MD-AMB-231 and HepG2 was evaluated. Remarkably, compounds, 7f, 8f, 9a, 9d and 9f, showed potent activity in MD-AMB-231 cancer cell line (IC₅₀: 9.13-10.3 µM), while the same derivatives showed significant potent activity in SiHa and HepG2 cancer cell lines (IC₅₀: 17.46-27.0 µM). Most significantly, compound 7o (IC₅₀: 8.15 µM) showed potent activity, compared to the drug etoposide (IC₅₀: 18.11 µM) against MD-AMB-231 cell line. Flow cytometry analysis revealed that compounds 7f, 8f, 9a, 9d and 9f arrested the cell growth in the G1 phase in MD-AMB-231 cell line.

AM-879, a PPARy non-agonist and Ser273 phosphorylation blocker, promotes insulin sensitivity without adverse effects in mice

Obesity is one of the main risk factors for type 2 diabetes, and peroxisome proliferator-activated receptor γ (PPARγ) is considered a promising pathway on insulin sensitivity and adipose tissue metabolism. The search for molecules acting as insulin sensitizers have increased, especially for molecules that block PPARγ-Ser273 phosphorylation, without reaching full agonism. We evaluated the in vivo effects of AM-879, a PPARγ non-agonist, and found that AM-879 exerts different effects in mice depending on the dose. At lower doses, this ligand decreased BAT, increased leptin and Crh expression. However, at a higher dose, it promoted improvement on insulin sensitivity, ameliorates expression of metabolism-related genes, decreased the expression of genes related to liver toxicity, maintaining body weight and adipocyte size. These results present a new lead molecule to ameliorates insulin resistance and confirm AM-879 as a PPARγ non-agonist which blocks Ser273 phosphorylation as a good strategy to modulate insulin sensitivity without developing the adverse effects promoted by PPARγ full agonists.

Cinnamon extract improves abnormalities in glucose tolerance by decreasing Acyl-CoA synthetase long-chain family 1 expression in adipocytes

We previously demonstrated that cinnamon extract (CE) alleviates streptozotocin-induced type 1 diabetes in rats. The present study aimed to elucidate the detailed molecular target of cinnamon in cultured adipocytes and epididymal adipose tissue of type 2 diabetes model mice. Two-dimensional gel electrophoresis was employed to determine the molecular target of cinnamon in adipocytes. The function of Acyl-CoA synthetase long-chain family-1 (ACSL1), a molecular target of cinnamon that was identified in this study, was further investigated in 3T3-L1 adipocytes using specific inhibitors. Type 2 diabetes model mice (KK-Ay/TaJcl) were used to investigate the effect of CE on glucose tolerance, ACSL1 expression, and related signal molecules in vivo. CE decreased ACSL1 mRNA and protein expression in 3T3-L1 adipocytes but increased glucose uptake and AMPK signaling activation; moreover, a similar effect was observed with an ACSL1 inhibitor. CE improved glucose tolerance and downregulated ACSL1 in mice adipose tissue in vivo. ACSL1 was demonstrated as a molecular target of CE in type 2 diabetes both in a cell culture system and diabetic mouse model.

Bisphosphorylation of anhydrides - convenient access to bisphosphonates with a P-O-C-P motif

A novel strategy of bisphosphorylation of anhydrides with P(O)-H reagents via a DMAP-catalyzed and DBU-promoted process has been developed. These one-step transformations proceed efficiently to provide convenient access to a variety of P-O-C-P motif containing organophosphorus compounds. In addition, the gram-scale synthesis and the efficient recovery of the by-product highlight the sustainability and applicability of this method.

Tetrazoles as PPARγ ligands: A structural and computational investigation

Diabetes is an important chronic disease affecting about 10% of the adult population in the US and over 420 million people worldwide, resulting in 1.6 million deaths every year, according to the World Health Organization. The most common type of the disease, type 2 diabetes, can be pharmacologically managed using oral hypoglycemic agents or thiazolidinediones (TZDs), such as pioglitazone, which act by activating the Peroxisome Proliferated-Activated Receptor γ. Despite their beneficial effects in diabetes treatment, TZDs like rosiglitazone and troglitazone were withdrawn due to safety reasons, creating a void in the pharmacological options for the treatment of this important disease. Here, we explored a structure-based approach in the screening for new chemical probes for a deeper investigation of the effects of PPARγ activation. A class of tetrazole compounds was identified and the compounds named T1, T2 and T3 were purchased and evaluated for their ability to interact with the PPARγ ligand binding domain (LBD). The compounds were binders with micromolar range affinity, as determined by their IC₅₀ values. A Monte Carlo simulation of the compound T2 revealed that the tetrazole ring makes favorable interaction with the polar arm of the receptor binding pocket. Finally, the crystal structure of the PPARγ-LBD-T2 complex was solved at 2.3 Å, confirming the binding mode for this compound. The structure also revealed that, when the helix H12 is mispositioned, an alternative binding conformation is observed for the ligand suggesting an H12-dependent binding conformation for the tetrazole compound.

Synthesis and Biological Activity of Piperine Derivatives as Potential PPARγ Agonists

Introduction

Peroxisome proliferator-activated receptor γ (PPARγ) plays a key role in glucose, which is a ligand-mediated transcription factor. The lipid homeostasis often serves as a pharmacological target for new drug discovery and development.

Materials and Methods

In the research, we synthesized a series of piperine derivatives and then used a fluorescence polarization-based PPARγ ligand screening assay to evaluate the agonistic activity of PPARγ. Then, we cultured human normal hepatocytes, which were treated with 100μM compounds 2a, 2t or 3d. Then, the levels of PPARγ gene were determined so as to show whether the compounds could activate or inhibit the expression of PPARγ.

Results

A total of 30 piperine derivatives were synthesized and evaluated. Compound 2a was identified as a potential PPARγ agonist with IC₅₀ at 2.43 μM, which is 2 times more potent than the positive control rosiglitazone with IC₅₀ at 5.61μM. The human hepatocytes cells were cultured and treated with compounds 2a, 2t or 3d as described in the "Materials and Methods" section. We found that compounds 2a, 2t and 3d could activate PPARγ by 11.8, 1.9 and 7.0 times compared with the "blank", with compound 2a activation being the most significant. Molecular docking studies indicated that the piperine derivative 2a stably interacts with the amino acid residues of the PPARγ complex active site, which is consistent with the results of the in vitro PPARγ ligand screening assay.

Rosiglitazone Enhances Browning Adipocytes in Association with MAPK and PI3-K Pathways During the Differentiation of Telomerase-Transformed Mesenchymal Stromal Cells into Adipocytes

Obesity is a major risk for diabetes. Brown adipose tissue (BAT) mediates production of heat while white adipose tissue (WAT) function in the storage of fat. Roles of BAT in the treatment of obesity and related disorders warrants more investigation. Peroxisome proliferator activator receptor gamma (PPAR-γ) is the master regulator of both BAT and WAT adipogenesis and has roles in glucose and fatty acid metabolism. Adipose tissue is the major expression site for PPAR-γ. In this study, the effects of rosiglitazone on the brown adipogenesis and the association of MAPK and PI3K pathways was investigated during the in vitro adipogenic differentiation of telomerase transformed mesenchymal stromal cells (iMSCs). Our data indicate that 2 µM rosiglitazone enhanced adipogenesis by over-expression of PPAR-γ and C/EBP-α. More specifically, brown adipogenesis was enhanced by the upregulation of EBF2 and UCP-1 and evidenced by multilocular fatty droplets morphology of the differentiated adipocytes. We also found that rosiglitazone significantly activated MAPK and PI3K pathways at the maturation stage of differentiation. Overall, the results indicate that rosiglitazone induced overexpression of PPAR-γ that in turn enhanced adipogenesis, particularly browning adipogenesis. This study reports the browning effects of rosiglitazone during the differentiation of iMSCs into adipocytes in association with the activation of MAPK and PI3K signaling pathways.

Synthesis and anticancer cytotoxicity with structural context of an α-hydroxyphosphonate based compound library derived from substituted benzaldehydes

We synthesized substituted benzaldehyde derived α-hydroxyphosphonates (αOHP), α-hydroxyphosphonic acids (αOHPA) and α-phosphinoyloxyphosphonates (αOPP) and characterized their cytotoxicity against a panel of cancer cell lines.

Screening for PPAR Non-Agonist Ligands Followed by Characterization of a Hit, AM-879, with Additional No-Adipogenic and cdk5-Mediated Phosphorylation Inhibition Properties

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of a nuclear receptor superfamily and acts as a ligand-dependent transcription factor, playing key roles in maintenance of adipose tissue and in regulation of glucose and lipid homeostasis. This receptor is the target of thiazolidinediones, a class of antidiabetic drugs, which improve insulin sensitization and regulate glycemia in type 2 diabetes. Despite the beneficial effects of drugs, such as rosiglitazone and pioglitazone, their use is associated with several side effects, including weight gain, heart failure, and liver disease, since these drugs induce full activation of the receptor. By contrast, a promising activation-independent mechanism that involves the inhibition of cyclin-dependent kinase 5 (CDK5)-mediated PPARγ phosphorylation has been related to the insulin-sensitizing effects induced by these drugs. Thus, we aimed to identify novel PPARγ ligands that do not possess agonist properties by conducting a mini-trial with 80 compounds using the sequential steps of thermal shift assay, 8-anilino-1-naphthalenesulfonic acid fluorescence quenching, and a cell-based transactivation assay. We identified two non-agonist PPARγ ligands, AM-879 and P11, and one partial-agonist, R32. Using fluorescence anisotropy, we show that AM-879 does not dissociate the NCOR corepressor in vitro, and it has only a small effect on TRAP coactivator recruitment. In cells, AM-879 could not induce adipocyte differentiation or positively regulate the expression of genes associated with adipogenesis. In addition, AM-879 inhibited CDK5-mediated phosphorylation of PPARγ in vitro. Taken together, these findings supported an interaction between AM-879 and PPARγ; this interaction was identified by the analysis of the crystal structure of the PPARγ:AM-879 complex and evidenced by AM-879's mechanism of action as a putative PPARγ non-agonist with antidiabetic properties. Moreover, we present an optimized assay pipeline capable of detecting ligands that physically bind to PPARγ but do not cause its activation as a new strategy to identify ligands for this nuclear receptor.

Structures of PPARγ complexed with lobeglitazone and pioglitazone reveal key determinants for the recognition of antidiabetic drugs

Peroxisome proliferator-activator receptor (PPAR) γ is a nuclear hormone receptor that regulates glucose homeostasis, lipid metabolism, and adipocyte function. PPARγ is a target for thiazolidinedione (TZD) class of drugs which are widely used for the treatment of type 2 diabetes. Recently, lobeglitazone was developed as a highly effective TZD with reduced side effects by Chong Kun Dang Pharmaceuticals. To identify the structural determinants for the high potency of lobeglitazone as a PPARγ agonist, we determined the crystal structures of the PPARγ ligand binding domain (LBD) in complex with lobeglitazone and pioglitazone at 1.7 and 1.8 Å resolutions, respectively. Comparison of ligand-bound PPARγ structures revealed that the binding modes of TZDs are well conserved. The TZD head group forms hydrogen bonds with the polar residues in the AF-2 pocket and helix 12, stabilizing the active conformation of the LBD. The unique p-methoxyphenoxy group of lobeglitazone makes additional hydrophobic contacts with the Ω-pocket. Docking analysis using the structures of TZD-bound PPARγ suggested that lobeglitazone displays 12 times higher affinity to PPARγ compared to rosiglitazone and pioglitazone. This structural difference correlates with the enhanced affinity and the low effective dose of lobeglitazone compared to the other TZDs.

Synthesis, activity, and docking study of phenylthiazole acids as potential agonists of PPARγ

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-mediated transcription factor playing key roles in glucose and lipid homeostasis, and PPARγ ligands possess therapeutic potential in these as well as other areas. In this study, a series of phenylthiazole acids have been synthesized and evaluated for agonistic activity by a convenient fluorescence polarization-based PPARγ ligand screening assay. Compound 4t, as a potential PPARγ agonist with half maximal effective concentration (EC50) 0.75±0.20 μM, exhibited in vitro potency comparable with a 0.83±0.14 μM of the positive control rosiglitazone. Molecular docking and molecular dynamics simulations indicated that phenylthiazole acid 4t interacted with the amino acid residues of the active site of the PPARγ complex in a stable manner, consistent with the result of the in vitro ligand assay.

Docking Screens for Novel Ligands Conferring New Biology

It is now plausible to dock libraries of 10 million molecules against targets over several days or weeks. When the molecules screened are commercially available, they may be rapidly tested to find new leads. Although docking retains important liabilities (it cannot calculate affinities accurately nor even reliably rank order high-scoring molecules), it can often can distinguish likely from unlikely ligands, often with hit rates above 10%. Here we summarize the improvements in libraries, target quality, and methods that have supported these advances, and the open access resources that make docking accessible. Recent docking screens for new ligands are sketched, as are the binding, crystallographic, and in vivo assays that support them. Like any technique, controls are crucial, and key experimental ones are reviewed. With such controls, docking campaigns can find ligands with new chemotypes, often revealing the new biology that may be docking's greatest impact over the next few years.

Role of Peroxisome Proliferator-Activated Receptor γ in Ocular Diseases

Peroxisome proliferator-activated receptor γ (PPAR γ), a member of the nuclear receptor superfamily, is a ligand-activated transcription factor that plays an important role in the control of a variety of physiological processes. The last decade has witnessed an increasing interest for the role played by the agonists of PPAR γ in antiangiogenesis, antifibrosis, anti-inflammation effects and in controlling oxidative stress response in various organs. As the pathologic mechanisms of major blinding diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), keratitis, and optic neuropathy, often involve neoangiogenesis and inflammation- and oxidative stress-mediated cell death, evidences are accumulating on the potential benefits of PPAR γ to improve or prevent these vision threatening eye diseases. In this paper we describe what is known about the role of PPAR γ in the ocular pathophysiological processes and PPAR γ agonists as novel adjuvants in the treatment of eye diseases.

Pseudolaric acid B inhibits T-cell mediated immune response in vivo via p38MAPK signal cascades and PPARγ activation

AIMS

Pseudolaric acid B (PAB) has been prescribed for its potent immunomodulatory effect. However, the detail of mechanism remains to be demonstrated. The purpose of this study is to further clarify the mechanism of PAB on T-cell mediated immune response in vivo.

MAIN METHODS

Investigations were carried to ascertain the pharmacological effect of PAB in a delayed-type hypersensitivity (DTH) mouse model of T-cell mediated immune response. Histological assessment was examined by hematoxylin and eosin staining. Affymetrix GeneChip® Mouse Genome 430 2.0 arrays were employed to evaluate the expression profile of PAB. Western blot was performed to detect p38MAPK signal cascades, including p38MAPK, ATF-2, MK2, and HSP27. Finally, TNF-α level was analyzed by ELISA, and Jurkat T cells were treated with PAB to determine its role on PPARγ activation using a reporter gene assay.

KEY FINDINGS

The results showed that PAB (5, 10, and 20mg/kg) could lead to a marked improvement for ear swelling and inflammatory infiltrate in DTH mice dose-dependently. According to the associated biological pathways from microarray analysis, PAB resulted in the restoration of abnormal immune-related gene expression linked to MAPK and PPAR signaling pathways. Moreover, PAB inhibited the activation of p38MAPK, ATF-2, MK2, and HSP27 significantly, as well as the production of TNF-α, which was reversed by GW9662, a specific antagonist for PPARγ. In addition, treatment with PAB also increased the transcriptional activity of PPARγ in a dose-dependent manner.

SIGNIFICANCE

These results provide us with novel insights into pharmacological action of PAB as a potential immunomodulator for the treatment of immune-related diseases.

Identification of novel multitargeted PPARα/γ/δ pan agonists by core hopping of rosiglitazone

The thiazolidinedione class peroxisome proliferator-activated receptor gamma (PPARγ) agonists are restricted in clinical use as antidiabetic agents because of side effects such as edema, weight gain, and heart failure. The single and selective agonism of PPARγ is the main cause of these side effects. Multitargeted PPARα/γ/δ pan agonist development is the hot topic in the antidiabetic drug research field. In order to identify PPARα/γ/δ pan agonists, a compound database was established by core hopping of rosiglitazone, which was then docked into a PPARα/γ/δ active site to screen out a number of candidate compounds with a higher docking score and better interaction with the active site. Further, absorption, distribution, metabolism, excretion, and toxicity prediction was done to give eight compounds. Molecular dynamics simulation of the representative Cpd#1 showed more favorable binding conformation for PPARs receptor than the original ligand. Cpd#1 could act as a PPARα/γ/δ pan agonist for novel antidiabetic drug research.