Jeffrey Shaw

Blockade of PI3Kgamma suppresses joint inflammation and damage in mouse models of rheumatoid arthritis

Phosphoinositide 3-kinases (PI3K) have long been considered promising drug targets for the treatment of inflammatory and autoimmune disorders as well as cancer and cardiovascular diseases. But the lack of specificity, isoform selectivity and poor biopharmaceutical profile of PI3K inhibitors have so far hampered rigorous disease-relevant target validation. Here we describe the identification and development of specific, selective and orally active small-molecule inhibitors of PI3Kγ (encoded by Pik3cg). We show that Pik3cg−/− mice are largely protected in mouse models of rheumatoid arthritis; this protection correlates with defective neutrophil migration, further validating PI3Kγ as a therapeutic target. We also describe that oral treatment with a PI3Kγ inhibitor suppresses the progression of joint inflammation and damage in two distinct mouse models of rheumatoid arthritis, reproducing the protective effects shown by Pik3cg−/− mice. Our results identify selective PI3Kγ inhibitors as potential therapeutic molecules for the treatment of chronic inflammatory disorders such as rheumatoid arthritis.

Substrate Recognition Domains within Extracellular Signal-regulated Kinase Mediate Binding and Catalytic Activation of Mitogen-activated Protein Kinase Phosphatase-3

Mitogen-activated protein (MAP) kinase phosphatase-3 (MKP-3) is a dual specificity phosphatase that inactivates extracellular signal-regulated kinase (ERK) MAP kinases. This reflects tight and specific binding between ERK and the MKP-3 amino terminus with consequent phosphatase activation and dephosphorylation of the bound MAP kinase. We have used a series of p38/ERK chimeric molecules to identify domains within ERK necessary for binding and catalytic activation of MKP-3. These studies demonstrate that ERK kinase subdomains V-XI are necessary and sufficient for binding and catalytic activation of MKP-3. These domains constitute the major COOH-terminal structural lobe of ERK. p38/ERK chimeras possessing these regions display increased sensitivity to inactivation by MKP-3. These data also reveal an overlap between ERK domains interacting with MKP-3 and those known to confer substrate specificity on the ERK MAP kinase. Consistent with this, we show that peptides representing docking sites within the target substrates Elk-1 and p90 rsk inhibit ERK-dependent activation of MKP-3. In addition, abolition of ERK-dependent phosphatase activation following mutation of a putative kinase interactionmotif (KIM) within the MKP-3 NH2 terminus suggests that key sites of contact for the ERK COOH-terminal structural lobe include residues localized between the Cdc25 homology domains (CH2) found conserved between members of the DSP gene family.

Identification and Characterization of Novel Small Molecules as Potent Inhibitors of the Plasmodial Calcium-Dependent Protein Kinase 1

Malaria remains a major killer in many parts of the world. Recently, there has been an increase in the role of public-private partnerships inciting academic and industrial scientists to merge their expertise in drug-target validation and in the early stage of drug discovery to identify potential new medicines. There is a need to identify and characterize new molecules showing high efficacy, low toxicity with low propensity to induce resistance in the parasite. In this context, we have studied the structural requirements of the inhibition of PfCDPK1. This is a calcium-dependent protein kinase expressed in Plasmodium falciparum, which has been genetically confirmed as essential for survival. A primary screening assay has been developed. A total of 54000 compounds were tested, yielding two distinct chemical series of nanomolar small molecule inhibitors. The most potent members of each series were further characterized through enzymatic and biophysical analyses. Dissociation rates of the inhibitor-kinase complexes were shown to be key parameters to differentiate both series. Finally, a homology-based model of the kinase core domain has been built which allows rational design of the next generation of inhibitors.

Glycosaminoglycan analogs as a novel anti-inflammatory strategy

Heparin, a glycosaminoglycan (GAG), has both anti-inflammatory and anti-coagulant properties. The clinical use of heparin against inflammation, however, has been limited by concerns about increased bleeding. While the anti-coagulant activity of heparin is well understood, its anti-inflammatory properties are less so. Heparin is known to bind to certain cytokines, including chemokines, small proteins which mediate inflammation through their control of leukocyte migration and activation. Molecules which can interrupt the chemokine-GAG interaction without inhibiting coagulation could therefore, represent a new class of anti-inflammatory agents. In the present study, two approaches were undertaken, both focusing on the heparin-chemokine relationship. In the first, a structure based strategy was used: after an initial screening of potential small molecule binders using protein NMR on a target chemokine, binding molecules were optimized through structure-based design. In the second approach, commercially available short oligosaccharides were polysulfated. In vitro, these molecules prevented chemokine-GAG binding and chemokine receptor activation without disrupting coagulation. However, in vivo, these compounds caused variable results in a murine peritoneal recruitment assay, with a general increase of cell recruitment. In more disease specific models, such as antigen-induced arthritis and delayed-type hypersensitivity, an overall decrease in inflammation was noted, suggesting that the primary anti-inflammatory effect may also involve factors beyond the chemokine system.

Chapter 2.2 – Chemokines

Publisher Summary This chapter concentrates on aspects related to the structure of chemokines and chemokine analogues and how these aspects relate to their biology. The monomer structures of all chemokines are superimposable. The important structural differences that can be observed within a class lie at the generally floppy N- and C-termini. These are probably the result of the technique and conditions used to determine the structure. The structure of the N-termini of many of these chemokines has been shown to play a very important role in their biological activity. A few native chemokines and several modified and truncated analogues have been observed as monomers, but the majority has been observed to adopt tetramer structures. The biological relevance of oligomerization of chemokines into larger molecular oligomer states under the influence of glycosaminoglycans remains to be investigated. Modifications of CC chemokines have been shown to produce antagonists. N-terminally truncated RANTES, MCP-1, and MCP-3 proteins have been shown to antagonize the effect of their parent ligands in vitro. The extension of the amino terminal of certain chemokines can have a profound effect on the biological properties. With the availability of receptor antagonists and the development of small molecule chemokine receptor antagonists, intervention with this system appears more promising as a therapeutic approach.