Prospects for Inhibitors of Protein Tyrosine Phosphatase 1B as Antidiabetic Drugs

Dual Targeting of PTP1B and Aldose Reductase with Marine Drug Phosphoeleganin: A Promising Strategy for Treatment of Type 2 Diabetes

An in-depth study on the inhibitory mechanism on protein tyrosine phosphatase 1B (PTP1B) and aldose reductase (AR) enzymes, including analysis of the insulin signalling pathway, of phosphoeleganin, a marine-derived phosphorylated polyketide, was achieved. Phosphoeleganin was demonstrated to inhibit both enzymes, acting respectively as a pure non-competitive inhibitor of PTP1B and a mixed-type inhibitor of AR. In addition, in silico docking analyses to evaluate the interaction mode of phosphoeleganin with both enzymes were performed. Interestingly, this study showed that phosphoeleganin is the first example of a dual inhibitor polyketide extracted from a marine invertebrate, and it could be used as a versatile scaffold structure for the synthesis of new designed multiple ligands.

Pyrazoles as novel protein tyrosine phosphatase 1B (PTP1B) inhibitors: An in vitro and in silico study

Type 2 diabetes mellitus (DM) is a complex chronic disorder and a major global health problem. Insulin resistance is the primary detectable abnormality and the main characteristic feature in individuals with type 2 DM. Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of the insulin signaling pathway, which dephosphorylates insulin receptor and insulin receptor substrates, suppressing the insulin signaling cascade. Therefore, the inhibition of PTP1B has become a potential strategy in the management of type 2 DM. In this study, a library of 22 pyrazoles was evaluated here for the first time against human PTP1B activity, using a microanalysis screening system. The results showed that 5-(2-hydroxyphenyl)-3-{2-[3-(4-nitrophenyl)-1,2,3,4-tetrahydronaphthyl]}-1-phenylpyrazole 20 and 3-(2-hydroxyphenyl)-5-{2-[3-(4-methoxyphenyl)]naphthyl}pyrazole 22 excelled as the most potent inhibitors of PTP1B, through noncompetitive inhibition mechanism. These findings suggest that the presence of additional benzene rings as functional groups in the pyrazole moiety increases the ability of pyrazoles to inhibit PTP1B. The most active compounds showed selectivity over the homologous T-cell protein tyrosine phosphatase (TCPTP). Molecular docking analyses were performed and revealed a particular contact signature involving residues like TYR46, ASP48, PHE182, TYR46, ALA217 and ILE219. This study represents a significant beginning for the design of novel PTP1B inhibitors.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

One bis-indole alkaloid-voacamine from Voacanga africana Stapf: biological activity evaluation of PTP1B in vitro utilizing enzymology method based on SPRi expriment

One known bis-indole alkaloid-voacamine was isolated from Voacanga africana Stapf and Surface Plasmon Resonance imaging (SPRi) exprement showed that this alkaloid could be combine with Protein Tyrosine Phosphatase1B (PTP1B). Then the PTP1B activity inhibition experiment display that the compound showed an outstanding promoting activity to PTP1B.

PTP1B Inhibitors from the Entomogenous Fungi Isaria fumosorosea

Protein tyrosine phosphatase 1B (PTP1B) is implicated as a negative regulator of insulin receptor (IR) signaling and a potential drug target for the treatment of type II diabetes and other associated metabolic syndromes. Thus, small molecule inhibitors of PTP1B can be considered as an attractive approach for the design of new therapeutic agents of type II diabetes and cancer diseases. In a continuing search for new PTP1B inhibitors, a new tetramic acid possessing a rare pyrrolidinedione skeleton named fumosorinone A (1), together with five known ones 2-6 were isolated from the entomogenous fungus Isaria fumosorosea. The structures of 2-6 were elucidated by extensive spectroscopic analysis. Fumosorinone A (1) and beauvericin (6) showed significant PTP1B inhibitory activity with IC₅₀ value of 3.24 μM and 0.59 μM.

PAIN-less identification and evaluation of small molecule inhibitors against protein tyrosine phosphatase 1B

A highly miniaturized biochemical assay was set up to test a focused set of natural products against the enzymatic activity of protein tyrosine phosphatase 1B (PTP1B). The screen resulted in the identification of the natural product alkaloids, berberine and palmatine as well as α-tocopheryl succinate (α-TOS) as potential inhibitors of PTP1B. In a second step, several read-out and counter assays were applied to confirm the observed inhibitory activity of the identified hits and to remove false positives which target the enzymatic activity of PTP1B by a non-specific mechanism, also known as PAINS (pan-assay interference compounds). Both, berberine and palmatine were identified as false positives which interfered with the assay read-out. Using NMR spectroscopy, self-association via stacking interactions was detected for berberine in aqueous media, which may also contribute to the non-specific inhibition of PTP1B. α-TOS was confirmed as a novel reversible and competitive inhibitor of PTP1B. A concise structure-activity relationship study identified the carboxyl group and the saturated phytyl-side chain as being critical for PTP1B inhibition.

A Microfluidics-Based Mobility Shift Assay to Discover New Tyrosine Phosphatase Inhibitors

Protein tyrosine phosphatases (PTPs) play key roles in regulating tyrosine phosphorylation levels in cells. Since the discovery of PTP1B as a major drug target for diabetes and obesity, PTPs have emerged as a new and promising class of signaling targets for drug development in a variety of therapeutic areas. The routine use of generic substrate 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP) in our hands led to the discovery of very similar and often not very selective molecules. Therefore, to increase the chances to discover novel chemical scaffolds, a side-by-side comparison between the DiFMUP assay and a chip-based mobility shift assay with a specific phosphopeptide was performed, on 1 PTP, using a focused set of compounds. Assay robustness and sensitivity were comparable for both the DiFMUP and mobility shift assays. The off-chip mobility shift assay required a longer development time because of identification, synthesis, and characterization of a specific peptide, and its cost per point was higher. However, although most potent scaffolds found with the DiFMUP assay were confirmed in the mobility shift format, the off-chip mobility shift assay led to the identification of previously unidentified chemical scaffolds with improved druglike properties.

Sulfone-stabilized carbanions for the reversible covalent capture of a posttranslationally-generated cysteine oxoform found in protein tyrosine phosphatase 1B (PTP1B)

Redox regulation of protein tyrosine phosphatase 1B (PTP1B) involves oxidative conversion of the active site cysteine thiolate into an electrophilic sulfenyl amide residue. Reduction of the sulfenyl amide by biological thiols regenerates the native cysteine residue. Here we explored fundamental chemical reactions that may enable covalent capture of the sulfenyl amide residue in oxidized PTP1B. Various sulfone-containing carbon acids were found to react readily with a model peptide sulfenyl amide via attack of the sulfonyl carbanion on the electrophilic sulfur center in the sulfenyl amide. Both the products and the rates of these reactions were characterized. The results suggest that capture of a peptide sulfenyl amide residue by sulfone-stabilized carbanions can slow, but not completely prevent, thiol-mediated generation of the corresponding cysteine-containing peptide. Sulfone-containing carbon acids may be useful components in the construction of agents that knock down PTP1B activity in cells via transient covalent capture of the sulfenyl amide oxoform generated during insulin signaling processes.

Highly enantioselective hydrogenation of α-oxy functionalized α,β-unsaturated acids catalyzed by a ChenPhos–Rh complex in CF3CH2OH

A Chenphos–Rh complex is demonstrated to be a highly efficient catalyst for asymmetric hydrogenation of α-oxy functionalized α,β-unsaturated carboxylic acidsviaan ionic interaction between the ligand and the substrate.

Design and synthesis of novel 1,2-dithiolan-4-yl benzoate derivatives as PTP1B inhibitors

A series of novel 1,2-dithiolan-4-yl benzoate compounds were synthesized and evaluated for in vitro PTP1B inhibitory activity. Some derivatives exhibited improved PTP1B inhibitory activity and selectivity compared to hit 6a, a compound from in-house library screening inspired by marine cyclic disulfide. The preliminary SAR analysis with assistance of molecular modeling approach revealed 6j (IC50=0.59μM) as the most potent PTP1B inhibitor among all derivatives.

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

A review of the synthesis of natural products and bioactive compounds adopting phosphonamide anion technology is presented highlighting the utility of phosphonamide reagents in stereocontrolled bond-forming reactions. Methodologies utilizing phosphonamide anions in asymmetric alkylations, Michael additions, olefinations, and cyclopropanations will be summarized, as well as an overview of the synthesis of the employed phosphonamide reagents.

Penostatin derivatives, a novel kind of protein phosphatase 1b inhibitors isolated from solid cultures of the entomogenous fungus Isaria tenuipes

Protein tyrosine phosphatase 1B (PTP1B) is implicated as a negative regulator of insulin receptor (IR) signaling and a potential drug target for the treatment of type II diabetes and other associated metabolic syndromes. Therefore, small molecular inhibitors of PTP1B can be considered as an attractive approach for the design of new therapeutic agents of type II diabetes diseases. In a continuing search for new protein phosphatase inhibitors from fungi, we have isolated a new compound, named penostatin J (1), together with three known ones, penostatin C (2), penostatin A (3), and penostatin B (4), from cultures of the entomogenous fungus Isaria tenuipes. The structure of penostatin J (1) was elucidated by extensive spectroscopic analysis. We also demonstrate for the first time that penostatin derivatives exhibit the best PTP1B inhibitory action. These findings suggest that penostatin derivatives are a potential novel kind of PTP1B inhibitors.

SAR and Computer-Aided Drug Design Approaches in the Discovery of Peroxisome Proliferator-Activated Receptor γ Activators: A Perspective

Activators of PPARγ, Troglitazone (TGZ), Rosiglitazone (RGZ), and Pioglitazone (PGZ) were introduced for treatment of Type 2 diabetes, but TGZ and RGZ have been withdrawn from the market along with other promising leads due cardiovascular side effects and hepatotoxicity. However, the continuously improving understanding of the structure/function of PPARγ and its interactions with potential ligands maintain the importance of PPARγ as an antidiabetic target. Extensive structure activity relationship (SAR) studies have thus been performed on a variety of structural scaffolds by various research groups. Computer-aided drug discovery (CADD) approaches have also played a vital role in the search and optimization of potential lead compounds. This paper focuses on these approaches adopted for the discovery of PPARγ ligands for the treatment of Type 2 diabetes. Key concepts employed during the discovery phase, classification based on agonistic character, applications of various QSAR, pharmacophore mapping, virtual screening, molecular docking, and molecular dynamics studies are highlighted. Molecular level analysis of the dynamic nature of ligand-receptor interaction is presented for the future design of ligands with better potency and safety profiles. Recently identified mechanism of inhibition of phosphorylation of PPARγ at SER273 by ligands is reviewed as a new strategy to identify novel drug candidates.

HPN, a synthetic analogue of bromophenol from red alga Rhodomela confervoides: synthesis and anti-diabetic effects in C57BL/KsJ-db/db mice

3,4-dibromo-5-(2-bromo-3,4-dihydroxy-6-(isopropoxymethyl)benzyl)benzene-1,2-diol (HPN) is a synthetic analogue of 3,4-dibromo-5-(2-bromo-3,4-dihydroxy-6-(ethoxymethyl)benzyl)benzene-1,2-diol (BPN), which is isolated from marine red alga Rhodomela confervoides with potent protein tyrosine phosphatase 1B (PTP1B) inhibition (IC₅₀ = 0.84 μmol/L). The in vitro assay showed that HPN exhibited enhanced inhibitory activity against PTP1B with IC₅₀ 0.63 μmol/L and high selectivity against other PTPs (T cell protein tyrosine phosphatase (TCPTP), leucocyte antigen-related tyrosine phosphatase (LAR), Src homology 2-containing protein tyrosine phosphatase-1 (SHP-1) and SHP-2). The results of antihyperglycemic activity using db/db mouse model demonstrated that HPN significantly decreased plasma glucose (P < 0.01) after eight weeks treatment period. HPN lowered serum triglycerides and total cholesterol concentration in a dose-dependent manner. Besides, both of the high and medium dose groups of HPN remarkably decreased HbA1c levels (P < 0.05). HPN in the high dose group markedly lowered the insulin level compared to the model group (P < 0.05), whereas the effects were less potent than the positive drug rosiglitazone. Western blotting results showed that HPN decreased PTP1B levels in pancreatic tissue. Last but not least, the results of an intraperitoneal glucose tolerance test in Sprague–Dawley rats indicate that HPN have a similar antihyperglycemic activity as rosiglitazone. HPN therefore have potential for development as treatments for Type 2 diabetes.

Inhibitory effects of decavanadate on several enzymes and Leishmania tarentolae in vitro

Multiple studies report apparent effects of vanadium on various systems in vivo and in vitro. Vanadium species may be possible deterrents for the growth of the Leishmania parasite, which causes the sometimes deadly diseases known as leishmaniasis. The current studies focus specifically on decavanadate V(10)O(28)(6-) (V10), which has a potential to be a potent effector for disease treatment. The X-ray structure of a new solvate salt of V10, namely (NH(4))(6)V(10)O(28)·5H(2)O, is also reported. Other vanadium complexes with imidazole carboxylate, anthranilate, or picolinate were also evaluated. The yellow-orange oxoanion, used as the (NH(4))(6)V(10)O(28)·6H(2)O salt, was tested (at 1-100 μM) directly with two strains of Leishmania tarentolae promastigotes in culture to evaluate the effect on cell viability. Vanadium coordination complexes are known effective inhibitors of phosphatases. Using the artificial phosphatase substrate para-nitrophenylphosphate in the presence of a bovine calf intestine alkaline phosphatase enzyme, V10 (from 5 to 100 μM) was shown to be a mixed inhibitor for this enzyme and decreased the activity of the other two phosphatases tested. The effect of V10 and the other vanadium complexes on the activity of phosphoglycerate mutase B (PGAM), an important enzyme in glycolysis and gluconeogenesis, was also evaluated. At 10 μM, V10 was the most potent inhibitor of PGAM, with an apparent reduction of about 50%. Taken together, we speculate that V10 could have a role in treating Leishmania diseases.

Mechanism of attenuation of diabetes mellitus and hypercholesterolemia induced vascular endothelial dysfunction by protein tyrosine phosphatase inhibition

The study has been designed to investigate downstream mechanisms in the PTPase inhibition mediated attenuation of diabetes mellitus and hypercholesterolemia-induced vascular endothelial dysfunction. Diabetes mellitus was induced in rats using streptozotocin (55 mg/kg, i.v. once), while hypercholesterolemia was produced by feeding high cholesterol diet. After 4 weeks of streptozotocin and Cholesterol rich diet administration, vascular endothelium dysfunction was assessed, in terms of attenuation of acetylcholine-induced, endothelium-dependent relaxation (Isolated Aortic Ring Preparation), a decrease in serum nitrate/nitrite level, as well as mRNA expression of eNOS (rtPCR) and disruption of integrity of vascular endothelium (Electron microscopy). After 14 days of daily administration, sodium orthovanadate (8 mg/kg, p.o., 16 mg/kg, p.o and 24 mg/kg, p.o) and atorvastatin (30 mg/kg, p.o) (positive control) significantly improved acetylcholine-induced endothelium-dependent relaxation, serum nitrate/nitrite level, mRNA expression of eNOS and maintained integrity of vascular endothelium. However, this ameliorative effect of SOV was significantly blocked by UCN-01, (PDK inhibitor) and L-NAME (Inhibitor of eNOS). Therefore, it may be concluded that sodium orthovanadate, a specific inhibitor of PTPase, may stimulate PDK and eNOS and consequently improve vascular endothelium dysfunction. Thus, inhibition of PTPase might be a useful approach in the therapeutics of vascular endothelium dysfunction.

Prodrug delivery of novel PTP1B inhibitors to enhance insulin signalling

A growing percentage of the population is resistant to two key hormones - insulin and leptin - as a result of increased obesity, often leading to significant health consequences such as type 2 diabetes. Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of signalling by both of these hormones, so that inhibitors of this enzyme may provide promise for correcting endocrine abnormalities in both diabetes and obesity. As with other tyrosine phosphatases, identification of viable drug candidates targeting PTP1B has been elusive because of the nature of its active site. Beginning with novel phosphotyrosine mimetics, we have designed some of the most potent PTP1B inhibitors. However, their highly acidic structures limit intrinsic permeability and pharmacokinetics. Ester prodrugs of these inhibitors improve their drug-like properties with the goal of delivering these nanomolar inhibitors to the cytoplasm of cells within target tissues. In addition to identifying prodrugs that is able to deliver active drugs into cells to inhibit PTP1B and increase insulin signalling, these compounds were further modified to gain a variety of cleavage properties for targeting activity in vivo. One such prodrug candidate improved insulin sensitivity in ob/ob mice, with lowered fasting blood glucose levels seen in the context of lowered fasting insulin levels following 4 days of intraperitoneal dosing. The results presented in this study highlight the potential for design of orally active drug candidates targeting PTP1B, while also delineating the considerable challenges remaining.

Docking simulations and in vitro assay unveil potent inhibitory action of papaverine against protein tyrosine phosphatase 1B

The structural similarity between papaverine and berberine, a known inhibitor of human protein tyrosine phosphatase 1B (h-PTP 1B), prompted us to investigate the potential of papaverine as h-PTP 1B inhibitor. The investigation included simulated docking experiments to fit papaverine into the binding pocket of h-PTP 1B. Papaverine was found to readily dock within the binding pocket of h-PTP 1B in a low energy orientation via an optimal set of attractive interactions. Experimentally, papaverine illustrated potent in vitro inhibitory effect against recombinant h-PTP 1B (IC(50)=1.20 microM). In vivo, papaverine significantly decreased fasting blood glucose level of Balb/c mice. Our findings should encourage screening of other natural alkaloids for possible anti-h-PTP 1B activities.

GLEPP1/protein-tyrosine phosphatase phi inhibitors block chemotaxis in vitro and in vivo and improve murine ulcerative colitis

We describe novel, cell-permeable, and bioavailable salicylic acid derivatives that are potent and selective inhibitors of GLEPP1/protein-tyrosine phosphatase . Two previously described GLEPP1 substrates, paxillin and Syk, are both required for cytoskeletal rearrangement and cellular motility of leukocytes in chemotaxis. We show here that GLEPP1 inhibitors prevent dephosphorylation of Syk1 and paxillin in resting cells and block primary human monocyte and mouse bone marrow-derived macrophage chemotaxis in a gradient of monocyte chemotactic protein-1. In mice, the GLEPP1 inhibitors also reduce thioglycolate-induced peritoneal chemotaxis of neutrophils, lymphocytes, and macrophages. In murine disease models, the GLEPP1 inhibitors significantly reduce severity of contact hypersensitivity, a model for allergic dermatitis, and dextran sulfate sodium-induced ulcerative colitis, a model for inflammatory bowel disease. Taken together, our data provide confirmation that GLEPP1 plays an important role in controlling chemotaxis of multiple types of leukocytes and that pharmacological inhibition of this phosphatase may have therapeutic use.

Berberine potently inhibits protein tyrosine phosphatase 1B: Investigation by docking simulation and experimental validation

Berberine was investigated as an inhibitor of human protein tyrosine phosphatase 1B (h-PTP 1B) in an attempt to explain its anti-hyperglycemic activitiy. The investigation included simulated docking experiments to fit berberine within the binding pocket of h-PTP 1B. Berberine was found to readily fit within the binding pocket of h-PTP 1B in a low energy orientation characterized with optimal electrostatic attractive interactions bridging the isoquinolinium positively charged nitrogen atom of berberine and the negatively charged acidic residue of ASP 48 of h-PTP 1B. Experimentally, berberine was found to potently competitively inhibit recombinant h-PTP 1B in vitro (Ki value = 91.3 nM). Our findings strongly suggest that h-PTP 1B inhibition is at least one of the reasons for the reported anti-hyperglycemic activities of berberine.

Molecular dynamics simulation study of PTP1B with allosteric inhibitor and its application in receptor based pharmacophore modeling

Allosteric inhibition of protein tyrosine phosphatase 1B (PTP1B), has paved a new path to design specific inhibitors for PTP1B, which is an important drug target for the treatment of type II diabetes and obesity. The PTP1B1-282-allosteric inhibitor complex crystal structure lacks alpha7 (287-298) and moreover there is no available 3D structure of PTP1B1-298 in open form. As the interaction between alpha7 and alpha6-alpha3 helices plays a crucial role in allosteric inhibition, alpha7 was modeled to the PTP1B1-282 in open form complexed with an allosteric inhibitor (compound-2) and a 5 ns MD simulation was performed to investigate the relative orientation of the alpha7-alpha6-alpha3 helices. The simulation conformational space was statistically sampled by clustering analyses. This approach was helpful to reveal certain clues on PTP1B allosteric inhibition. The simulation was also utilized in the generation of receptor based pharmacophore models to include the conformational flexibility of the protein-inhibitor complex. Three cluster representative structures of the highly populated clusters were selected for pharmacophore model generation. The three pharmacophore models were subsequently utilized for screening databases to retrieve molecules containing the features that complement the allosteric site. The retrieved hits were filtered based on certain drug-like properties and molecular docking simulations were performed in two different conformations of protein. Thus, performing MD simulation with alpha7 to investigate the changes at the allosteric site, then developing receptor based pharmacophore models and finally docking the retrieved hits into two distinct conformations will be a reliable methodology in identifying PTP1B allosteric inhibitors.

Oxidative inactivation of protein tyrosine phosphatase 1B by organic hydroperoxides

Protein tyrosine phosphatases (PTPs) are cysteine-dependent enzymes that play a central role in cell signaling. Organic hydroperoxides cause thiol-reversible, oxidative inactivation of PTP1B in a manner that mirrors the endogenous signaling agent hydrogen peroxide.

Recent development of small molecular specific inhibitor of protein tyrosine phosphatase 1B

Protein tyrosine phosphatases (PTPs), a large family of signaling enzymes, play essential roles in intracellular signal transduction by regulating the cellular level of tyrosine phosphorylation to control cell growth and differentiation, metabolism, cell migration, gene transcription, ion-channel activity, immune response, cell apoptosis, and bone development. Among all PTPs, protein tyrosine phosphatase 1B (PTP1B) plays a seminal role in cellular signaling and in many human diseases, including cancer, diabetes, and obesity. Therefore, small molecular inhibitors of PTP1B can be promising drug candidates. Because of the structural homologies in many families of PTPs, it is a challenging task to find inhibitors specific to each PTP. Recent studies suggested that secondary binding pockets or peripheral binding sites around the conserved active site should be exploited to design novel potent and selective PTP1B inhibitors. In this review, we discuss the structural and biological features of small molecular PTP1B-specific inhibitors, with particular emphasis on small molecular inhibitors targeting PTP1B over the other PTPs that have been synthesized in the past 4 years.

Pharmacophore modeling for protein tyrosine phosphatase 1B inhibitors

A three dimensional chemical feature based pharmacophore model was developed for the inhibitors of protein tyrosine phosphatase 1B (PTP1B) using the CATALYST software, which would provide useful knowledge for performing virtual screening to identify new inhibitors targeted toward type II diabetes and obesity. A dataset of 27 inhibitors, with diverse structural properties, and activities ranging from 0.026 to 600 microM, was selected as a training set. Hypol, the most reliable quantitative four featured pharmacophore hypothesis, was generated from a training set composed of compounds with two H-bond acceptors, one hydrophobic aromatic and one ring aromatic features. It has a correlation coefficient, RMSD and cost difference (null cost-total cost) of 0.946, 0.840 and 65.731, respectively. The best hypothesis (Hypol) was validated using four different methods. Firstly, a cross validation was performed by randomizing the data using the Cat-Scramble technique. The results confirmed that the pharmacophore models generated from the training set were valid. Secondly, a test set of 281 molecules was scored, with a correlation of 0.882 obtained between the experimental and predicted activities. Hypol performed well in correctly discriminating the active and inactive molecules. Thirdly, the model was investigated by mapping on two PTP1B inhibitors identified by different pharmaceutical companies. The Hypol model correctly predicted these compounds as being highly active. Finally, docking simulations were performed on few compounds to substantiate the role of the pharmacophore features at the binding site of the protein by analyzing their binding conformations. These multiple validation approaches provided confidence in the utility of this pharmacophore model as a 3D query for virtual screening to retrieve new chemical entities showing potential as potent PTP1B inhibitors.

Redox regulation of protein tyrosine phosphatase 1B (PTP1B): a biomimetic study on the unexpected formation of a sulfenyl amide intermediate

The effect of steric and electronic environments around the sulfur and nitrogen atoms and the role of nonbonded S...O/N interactions on the cyclization reactions of amide substituted benzene sulfenic acids are described. The reaction profiles and the role of different substituents on the cyclization are investigated in detail by theoretical calculations. It is shown that the synthetic thiols having ortho-amide substituents may serve as good models for the enforced proximity of the amide and cysteine thiol groups at the active site of protein tyrosine phosphatase 1B (PTP1B). However, some of the sulfenic acids derived from such models do not effectively mimic the cyclization of protein sulfenic acids. This is mainly due to the requirement of very high energy for breaking the S-O bond to form a planar five-membered ring of isothiazolidinone. It is shown that the sulfenic acid having two substituents-an amide moiety and a heterocyclic group-in the ortho-positions undergoes a rapid cyclization reaction to produce the corresponding sulfenyl amide species. These studies reveal that the introduction of a substituent at the 6-position of the benzene ring enhances the cyclization process not only by facilitating a closer approach of the -OH group and the backbone -NH moiety but also by increasing the electrophilicity of the sulfur atom in the sulfenic acid.

An enzyme-linked immunosorbent assay to measure insulin receptor dephosphorylation by PTP1B

Considerable effort exists within drug discovery to develop novel compounds to improve the underlying metabolic defects in type 2 diabetes. One approach is focused on inhibition of the tyrosine phosphatase, PTP1B, an important negative regulator of both insulin and leptin signaling. Historically, tyrosine phosphatase assays have used either small organic phosphates or, alternatively, phosphorylated peptides from the target proteins themselves. In characterizing inhibitors of PTP1B, measuring turnover of small organic phosphates is limited to evaluation of compounds that bind the active site itself. Peptide substrates allow identification of additional subsets of inhibitors (e.g., those that bind the second aryl-phosphate site), but assays of peptide turnover often involve detection steps that then limit full kinetic evaluation of inhibitors. Here we use a polyclonal antibody specific for the phosphorylated insulin receptor to allow much more sensitive detection of peptide phosphorylation. This kinetically robust enzyme-linked immunosorbent assay (ELISA) gives k(cat) and K(m) values for a phosphorylated insulin receptor peptide consistent with values determined by a continuous fluorescence-based assay. Furthermore, IC50 values determined for well-behaved active site inhibitors agree well with values determined for p-nitrophenyl phosphate cleavage. This assay permits full characterization of a larger subset of inhibitors as drug candidates for this promising target.

Improvement of peripheral endothelial dysfunction by protein tyrosine phosphatase inhibitors in heart failure

BACKGROUND

Chronic heart failure (CHF) induces endothelial dysfunction characterized by a decrease in nitric oxide (NO) production in response to flow (flow-mediated dilatation [FMD]). Because activation of endothelial NO synthase (eNOS) by flow requires tyrosine phosphorylation, we tested whether endothelial dysfunction could be corrected by increasing phosphotyrosine levels using protein tyrosine phosphatase (PTP) inhibitors and especially inhibitors of PTP1B.

METHODS AND RESULTS

CHF was induced by coronary ligation in mice, and FMD was assessed in isolated and cannulated mesenteric artery segments (2 mm in length and <300 microm in diameter). CHF almost abolished FMD but only moderately affected the response to acetylcholine. In mice with CHF, the PTP1B inhibitors AS279, AS098, and AS713 restored FMD to levels similar to those of normal mice. This restoration was reduced by inhibitors of eNOS and phosphatidylinositol-3 kinase. Polymerase chain reaction and Western blot showed that arteries express PTP1B, and this expression was not affected by CHF. Immunolocalization revealed the presence of PTP1B in the endothelium and the adventitia. Flow induced a transient eNOS phosphorylation that was absent in CHF. PTP1B inhibition stimulated early eNOS phosphorylation and increased phosphorylation of Akt.

CONCLUSIONS

Our results demonstrate for the first time that PTP1B inhibitors may be potent treatments for endothelial dysfunction.

Natural compounds as a source of protein tyrosine phosphatase inhibitors: application to the rational design of small-molecule derivatives

Reversible phosphorylation of tyrosine residues is a key regulatory mechanism for numerous cellular events. Protein tyrosine kinases and protein tyrosine phosphatases (PTPs) have a pivotal role in regulating both normal cell physiology and pathophysiology. Accordingly, deregulated activity of both protein tyrosine kinases and PTPs is involved in the development of numerous congenitically inherited and acquired human diseases, prompting obvious pharmaceutical and academic research interest. The development of compound libraries with higher selective PTP inhibitory activity has been bolstered by the realization that many natural products have such activity and thus are interesting biologically lead compounds, which properties are widely exploited. In addition, more rational approaches have focused on the incorporation of phosphotyrosine mimetics into specific peptide templates (peptidomimetic backbones). Additional factors furthering discovery as well as therapeutic application of new bioactive molecules are the integration of functional genomics, cell biology, structural biology, drug design, molecular screening and chemical diversity. Together, all these factors will lead to new avenues to treat clinical disease based on PTP inhibition.

Isothiazolidinone heterocycles as inhibitors of protein tyrosine phosphatases: Synthesis and structure–activity relationships of a peptide scaffold

The structure-based design and discovery of the isothiazolidinone (IZD) heterocycle as a mimic of phosphotyrosine (pTyr) has led to the identification of novel IZD-containing inhibitors of protein tyrosine phosphatase 1B (PTP1B). The structure-activity relationships (SARs) of peptidic IZD-containing inhibitors of PTP1B are described along with a novel synthesis of the aryl-IZD fragments via a Suzuki coupling. The SAR revealed the saturated IZD heterocycle (42) is the most potent heterocyclic pTyr mimetic compared to the unsaturated IZD (25), the thiadiazolidinone (TDZ) (38), and the regioisomeric unsaturated IZD (31). The X-ray crystal structures of 11c and 25 complexed with PTP1B were solved and revealed nearly identical binding interactions in the active site. Ab initio calculations effectively explain the strong binding of the (S)-IZD due to the preorganized binding of the IZD in its low energy conformation.

Monocyclic thiophenes as protein tyrosine phosphatase 1B inhibitors: Capturing interactions with Asp48

A series of monocyclic thiophenes was designed and synthesized as PTP1B inhibitors. Guided by X-ray co-crystal structural information and computational modeling, rational design led to key interactions with Asp48 and improved inhibitory potency against PTP1B.

PTP-1B inhibitors: Cyclopenta[d][1,2]-oxazine derivatives

A series of novel cyclopenta[d][1,2]-oxazine derivatives was prepared and evaluated for their inhibitory activity toward protein tyrosine phosphatase 1B (PTP-1B). Compound 6s was found to be an inhibitor of PTP-1B with nanomolar IC(50) value and high level of selectivity over other recombinant phosphatases.