Effect of Cobalt and Chromium Content on Microstructure and Properties of WC-Co-Cr Coatings Prepared by High-Velocity Oxy-Fuel Spraying.

To explore the Co/Cr ratio impact on the high-velocity oxygen fuel (HVOF)-sprayed WC-Co-Cr coatings microstructure and performances, three kinds of WC-Co-Cr coatings, namely WC-4Co-10Cr, WC-7Co-7Cr, and WC-10Co-4Cr, were prepared by using a high-velocity oxygen fuel (HVOF) spraying process. The three coatings' phase composition, microstructure, basic mechanical properties, abrasive wear, and corrosion resistance were investigated. The results show that all three WC-Co-Cr coatings comprise the main phase WC, minor W2C, and amorphous W-Co-Cr phase, besides the WC-4Co-10Cr coating containing a small amount of CrxCy phase. In addition, WC-7Co-7Cr coating exhibited the highest hardness and abrasive wear resistance, followed by WC-10Co-4Cr and WC-4Co-10Cr coatings. The corrosion resistance as a hierarchy was found to be WC-10Co-4Cr > WC-7Co-7Cr > WC-4Co-10Cr.

Development of a scintillation proximity binding assay for high-throughput screening of hematopoietic prostaglandin D2 synthase.

Prostaglandin D2 synthase (PGDS) catalyzes the isomerization of prostaglandin H2 (PGH2) to prostaglandin D2 (PGD2). PGD2 produced by hematopoietic prostaglandin D2 synthase (H-PGDS) in mast cells and Th2 cells is proposed to be a mediator of allergic and inflammatory responses. Consequently, inhibitors of H-PGDS represent potential therapeutic agents for the treatment of inflammatory diseases such as asthma. Due to the instability of the PGDS substrate PGH2, an in-vitro enzymatic assay is not feasible for large-scale screening of H-PGDS inhibitors. Herein, we report the development of a competition binding assay amenable to high-throughput screening (HTS) in a scintillation proximity assay (SPA) format. This assay was used to screen an in-house compound library of approximately 280,000 compounds for novel H-PGDS inhibitors. The hit rate of the H-PGDS primary screen was found to be 4%. This high hit rate suggests that the active site of H-PGDS can accommodate a large diversity of chemical scaffolds. For hit prioritization, these initial hits were rescreened at a lower concentration in SPA and tested in the LAD2 cell assay. 116 compounds were active in both assays with IC50s ranging from 6 to 807 nM in SPA and 82 nM to 10 µM in the LAD2 cell assay.

Photo-crosslinking of proteins in intact cells reveals a dimeric structure of cyclooxygenase-2 and an inhibitor-sensitive oligomeric structure of microsomal prostaglandin E2 synthase-1.

We have characterized the structures of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E(2) synthase-1 (mPGES-1) in intact cells using bifunctional and photo-activatable crosslinking agents. A dimeric complex was detected for COX-2 by both crosslinking approaches, consistent with the crystal structure of the enzyme. For mPGES-1, treatment of A549 cells with disuccinimidyl suberate yielded immunoreactive protein bands corresponding to a dimer (33 kDa) and a trimer (45 kDa), as observed for the isolated enzyme. Photo-crosslinking with photoactivatable methionine in intact cells generated complexes with molecular weights corresponding to the dimer (33 kDa) and two putative trimer forms (50 and 55 kDa). Treatment with the selective mPGES-1 inhibitor MF63 prevented the formation of the 50 and 55 kDa crosslinked complexes, while an inactive structural analogue had no effect. Our data indicate that COX-2 forms a dimer in intact cells and that mPGES-1 has an oligomeric structure that can be disrupted by a selective inhibitor.

Adenovirus IL-13-induced airway disease in mice: a corticosteroid-resistant model of severe asthma.

Interleukin 13 (IL-13) is considered to be a key driver of the development of airway allergic inflammation and remodeling leading to airway hyperresponsiveness (AHR). How precisely IL-13 leads to the development of airway inflammation, AHR, and mucus production is not fully understood. In order to identify key mediators downstream of IL-13, we administered adenovirus IL-13 to specifically induce IL-13-dependent inflammation in the lungs of mice. This approach was shown to induce cardinal features of lung disease, specifically airway inflammation, elevated cytokines, AHR, and mucus secretion. Notably, the model is resistant to corticosteroid treatment and is characterized by marked neutrophilia, two hallmarks of more severe forms of asthma. To identify IL-13-dependent mediators, we performed a limited-scale two-dimensional SDS-PAGE proteomic analysis and identified proteins significantly modulated in this model. Intriguingly, several identified proteins were unique to this model, whereas others correlated with those modulated in a mouse ovalbumin-induced pulmonary inflammation model. We corroborated this approach by illustrating that proteomic analysis can identify known pathways/mediators downstream of IL-13. Thus, we have characterized a murine adenovirus IL-13 lung model that recapitulates specific disease traits observed in human asthma, and have exploited this model to identify effectors downstream of IL-13. Collectively, these findings will enable a broader appreciation of IL-13 and its impact on disease pathways in the lung.

Catalytic inactivation of protein tyrosine phosphatase CD45 and protein tyrosine phosphatase 1B by polyaromatic quinones.

Polyaromatic quinones, such as the environmental pollutants 9,10-phenanthrenediones, elicit a wide range of responses including growth inhibition, immune suppression, and glucose normalization in diabetic models. Yet the molecular mechanisms behind these effects remain controversial. Here we report that many of them are oxygen-dependent and catalytic inactivators of protein tyrosine phosphatases (PTP). Under aerobic conditions, the PTP inactivation by 2-nitro-9,10-phenanthrenedione followed a pseudo-first-order process, with the rate of inactivation increasing nearly linearly with increasing inhibitor concentration, yielding apparent inactivation rate constants of 4300, 387, and 5200 M(-1) s(-1) at pH 7.2 against CD45, PTP1B, and LAR, respectively. The rate of CD45 inactivation increased approximately 25-fold from pH 6.0 to 7.5, with complete inactivation achieved using a catalytic amount (0.05 molar equiv) of the inhibitor. The quinone-catalyzed CD45 inactivation was prevented by catalase or superoxide dismutase. Inactivated CD45 after (125)I-9,10-phenanthrenedione treatment carried no radioactivity, indicating the absence of a stable inhibitor/enzyme complex. The activity of inactivated CD45 was partially restored ( approximately 10%) by hydroxylamine or dithiothreitol, supporting the presence of a small population of sulfenic acid or sulfenyl-amide species. Treatment of PTP1B with 2-nitro-9,10-phenanthrenedione resulted in the specific and sequential oxidation of the catalytic cysteine to the sulfinic and sulfonic acid. These results suggest that reactive oxygen species and the semiquinone radical, continuously generated during quinone-catalyzed redox cycling, mediate the specific catalytic cysteine oxidation. Naturally occurring quinones may act as efficient regulators of protein tyrosine phosphorylation in biological systems. Aberrant phosphotyrosine homeostasis resulting from continued polyaromatic hydrocarbon quinone exposure may play a significant role in their disease etiology.

Synthesis of a novel peptidic photoaffinity probe for the PTP-1B enzyme.

The synthesis of a novel radioactive peptidic photoaffinity probe for the PTP-1B enzyme as well as some SAR leading to the choice of this compound as a photoaffinity probe are presented.

The development of potent non-peptidic PTP-1B inhibitors.

The SAR from our peptide libraries was exploited to design a series of potent deoxybenzoin PTP-1B inhibitors. The introduction of an ortho bromo substituent next to the difluoromethylphosphonate warhead gave up to 20-fold increase in potency compared to the desbromo analogues. In addition, these compounds were orally bioavailable and active in the animal models of non-insulin dependent diabetes mellitus (NIDDM).

Structure based design of a series of potent and selective non peptidic PTP-1B inhibitors.

A series of benzotriazole phenyldifluoromethylphosphonic acids were found to be potent PTP-1B inhibitors. Molecular modeling on the X-ray crystal structure of the lead structure led to the design of potent PTP-1B inhibitors that show moderate selectivity against TC-PTP, a very closely related protein tyrosine phosphatase.

The structural basis for the selectivity of benzotriazole inhibitors of PTP1B.

Protein tyrosine phosphatase 1B (PTP1B) has been implicated in the regulation of the insulin signaling pathway and represents an attractive target for the design of inhibitors in the treatment of type 2 diabetes and obesity. Inspection of the structure of PTP1B indicates that potent PTP1B inhibitors may be obtained by targeting a secondary aryl phosphate-binding site as well as the catalytic site. We report here the crystal structures of PTP1B in complex with first and second generation aryldifluoromethyl-phosphonic acid inhibitors. While all compounds bind in a previously unexploited binding pocket near the primary binding site, the second generation compounds also reach into the secondary binding site, and exhibit moderate selectivity for PTP1B over the closely related T-cell phosphatase. The molecular basis for the selectivity has been confirmed by single point mutation at position 52, where the two phosphatases differ by a phenylalanine-to-tyrosine switch. These compounds present a novel platform for the development of potent and selective PTP1B inhibitors.

Protein tyrosine phosphatase 1B: a novel target for type 2 diabetes and obesity.

The identification of autophosphorylation of the insulin receptor as a pivotal component in the signal transduction induced by insulin, initiated the hunt to identify the tyrosine phosphatase(s) that were responsible for regulating dephosphorylation, and thus inactivation of the receptor. Compelling evidence for the existence of an insulin receptor specific PTP has come from the remarkable phenotype of the PTP1B deficient mouse. PTP1B deficient mice display an insulin sensitive phenotype and are able to maintain glucose homeostasis with about half the level of circulating insulin. In response to insulin administration PTP1B deficient mice have a significant increase in insulin receptor phosphorylation in liver and muscle compared to wild type controls. Unexpectedly these animals were also resistant to diet induced obesity. These observations strongly support PTP1B as a negative regulator of insulin action, thereby making it an ideal therapeutic target for intervention in type 2 diabetes and obesity.

Novel caged fluorescein diphosphates as photoactivatable substrates for protein tyrosine phosphatases.

We have characterized some novel caged fluorescein diphosphates as photoactivatable, cell-permeable substrates for protein tyrosine phosphatases and explored their usefulness in identifying inhibitors of tyrosine phosphatases. 1-(2-Nitrophenyl)ethyl protected fluorescein diphosphate (NPE-FDP) undergoes rapid photolysis to release FDP upon irradiation with a 450-W UV immersion lamp and its by-product does not inactivate protein tyrosine phosphatase 1B (PTP1B) or alters the viability of cells. The generated FDP from photolysis of NPE-FDP was shown to have exactly the same properties as FDP, which can be used as a PTP substrate in pure enzyme assays. We have also demonstrated that the PTP activity can be measured using NPE-FDP in small droplets. Its advantage as an inert substrate before photolysis allows the possibility of applying nanospray technology in screening and optimizing PTP inhibitors through a large chemical library. Like other caged bioeffectors such as nucleotide and inositol trisphosphate, NPE-FDP is cell-permeable. The NPE-FDP can be photolyzed to generate FDP inside cells, and then can be hydrolyzed by phosphatases to produce fluorescein monophosphate and subsequently to fluorescein. Although Jurkat cells contain high concentrations of CD45, it has not been possible to use FDP as a substrate to measure CD45 activity in the intact cell. This is due to the hydrolysis of FDP by several other cellular phosphatases. However, NPE-FDP can be useful as a cell-permeable substrate for overexpressed phosphatases such as alkaline phosphatase.

Development of a time-resolved fluorescent assay for measuring tyrosine-phosphorylated proteins in cells.

We have developed a time-resolved fluorescent assay using Wallac's DELFIA system (DELFIA assay) to monitor changes in the phosphorylation level of insulin receptor from rat hepatoma (KRC-7) cells in response to ligand and the nonspecific, protein-tyrosine phosphatase inhibitor pervanadate. In this system, a biotinylated antiinsulin receptor antibody was used to capture the insulin receptor and an europium-labeled antiphosphotyrosine antibody was used to assess tyrosine phosphorylation. This assay provides a highly sensitive, nonradioactive readout of receptor phosphorylation. We have validated the DELFIA assay by directly comparing receptor phosphorylation using the well-established technique of immunoblotting. The utility of the DELFIA assay in measuring the phosphorylation status of other receptors has also been demonstrated using epidermal growth factor receptor from A431 cells.

The structure of PTP-1B in complex with a peptide inhibitor reveals an alternative binding mode for bisphosphonates.

Inhibitors of PTP-1B could be therapeutically beneficial in the treatment of type 2 diabetes. Owing to the large number of phosphatases in the cell, inhibitors against PTP-1B must not only be potent but selective as well. N-Benzoyl-L-glutamyl-[4-phosphono(difluoromethyl)]-L-phenylalanine-[4-phosphono(difluoro-methyl)]-L-phenylalanineamide (BzN-EJJ-amide) is a low nanomolar inhibitor of PTP-1B that shows selectivity over several protein tyrosine phosphatases. To gain an insight into the basis of its potency and selectivity, we evaluated several analogues of the inhibitor and introduced amino acid substitutions into PTP-1B by site-directed mutagenesis. We also determined the crystal structure of PTP-1B in complex with BzN-EJJ-amide at 2.5 A resolution. Our results indicate that the high inhibitory potency is due to interactions of several of its chemical groups with specific protein residues. An interaction between BzN-EJJ-amide and Asp48 is of particular significance, as substitution of Asp48 to alanine resulted in a 100-fold loss in potency. The crystal structure also revealed an unexpected binding orientation for a bisphosphonate inhibitor on PTP-1B, where the second difluorophosphonomethyl phenylalanine (F(2)PMP) moiety is bound close to Arg47 rather than in the previously identified second aryl phosphate site demarked by Arg24 and Arg254. Our results suggest that potent and selective PTP-1B inhibitors may be designed by targeting the region containing Arg47 and Asp48.