Histamine mediates its physiological function through binding to four known histamine receptors. Here, we describe the first selective antagonist of the histamine H 4 receptor, the newest member of the histamine receptor family, and provide evidence that such antagonists have anti-inflammatory activity in vivo.

Histamine is an important inflammatory mediator that is released in airways during an asthmatic response. However, current antihistamine drugs are not effective in controlling the disease. The discovery of the histamine H4 receptor (H4R) prompted us to reinvestigate the role of histamine in pulmonary allergic responses. H4R-deficient mice and mice treated with H4R antagonists exhibited decreased allergic lung inflammation, with decreases in infiltrating lung eosinophils and lymphocytes and decreases in Th2 responses. Ex vivo restimulation of T cells showed decreases in IL-4, IL-5, IL-13, IL-6, and IL-17 levels, suggesting that T cell functions were disrupted. In vitro studies indicated that blockade of the H4R on dendritic cells leads to decreases in cytokine and chemokine production and limits their ability to induce Th2 responses in T cells. This work suggests that the H4R can modulate allergic responses via its influence on T cell activation. The study expands the known influences of histamine on the immune system and highlights the therapeutic potential of H4R antagonists in allergic conditions.

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Leukotriene A 4 hydrolase (LTA 4 H) catalyzes production of the proinflammatory lipid mediator, leukotriene (LT) B 4 , which is implicated in a number of inflammatory diseases. We have identified a potent and selective inhibitor of both the epoxide hydrolase and aminopeptidase activities of recombinant human LTA 4 H (IC 50 , approximately 10 nM). In a murine model of arachidonic acid-induced ear inflammation, the LTA 4 H inhibitor, JNJ-26993135 (1-[4-(benzothiazol-2-yloxy)-benzyl]-piperidine-4-carboxylic acid), dose-dependently inhibited ex vivo LTB 4 production in blood, in parallel with dose-dependent inhibition of neutrophil influx (ED 50 , 1-3 mg/kg) and ear edema. In murine whole blood and in zymosan-induced peritonitis, JNJ-26993135 selectively inhibited LTB 4 production, without affecting cysteinyl leukotriene production, while maintaining or increasing production of the anti-inflammatory mediator, lipoxin (LX) A 4 . The 5-lipoxygenase (5-LO) inhibitor zileuton showed inhibition of LTB 4 , LTC 4 , and LXA 4 production. Although zileuton inhibited LTB 4 production in the peritonitis model more effectively than the LTA 4 H inhibitor, the influx of neutrophils into the peritoneum after 1 and 2 h was significantly higher in zileuton-versus JNJ-26993135-treated animals. This difference may have been mediated by the increased LXA 4 levels in the presence of the LTA 4 H inhibitor. The selective inhibition of LTB 4 production by JNJ-26993135, while increasing levels of the anti-inflammatory mediator, LXA 4 , may translate to superior therapeutic efficacy versus 5-LO or 5-LO-activating protein inhibitors in LTB 4 -mediated inflammatory diseases.

LTA 4H is a ubiquitously distributed 69 kDa zinc-containing cytosolic enzyme with both hydrolase and aminopeptidase activity. As a hydrolase, LTA 4H stereospecifically catalyzes the transformation of the unstable epoxide LTA 4 to the diol LTB 4, a potent chemoattractant and activator of neutrophils and a chemoattractant of eosinophils, macrophages, mast cells, and T cells. Inhibiting the formation of LTB 4 is expected to be beneficial in the treatment of inflammatory diseases such as inflammatory bowel disease (IBD), asthma, and atherosclerosis. We developed a pharmacophore model using a known inhibitor manually docked into the active site of LTA 4H to identify a subset of compounds for screening. From this work we identified a series of benzoxazole, benzthiazole, and benzimidazole inhibitors. SAR studies resulted in the identification of several potent inhibitors with an appropriate cross-reactivity profile and excellent PK/PD properties. Our efforts focused on further profiling JNJ 27265732, which showed encouraging efficacy in a disease model relevant to IBD.

Cathepsin S is considered crucial for normal presentation of major histocompatibility complex (MHC) class II-restricted antigens by antigen presenting cells to CD4 ϩ T cells. It is a key enzyme for the degradation of the class II-associated invariant chain, a process that is required for effective antigen loading of class II molecules. Here, we report a selective, orally available, high-affinity cathepsin S inhibitor, 1-, that represents a novel class of immunosuppressive compounds. JNJ 10329670 is a highly potent (K i of ϳ30 nM), nonpeptidic, noncovalent inhibitor of human cathepsin S, but it is much less active against the mouse, dog, monkey, and bovine enzymes. The compound is inactive against other proteases, including the closely related cathepsins L, F, and K. This selectivity makes JNJ 10329670 an excellent tool for exploring the role of cathepsin S in human systems. Treatment of human B cell lines and primary human dendritic cells with JNJ 10329670 resulted in the accumulation of the p10 fragment of the invariant chain (IC 50 of ϳ1 M). In contrast, inhibition of invariant chain proteolysis was much less effective in a human monocytic cell line, suggesting that other enzymes may degrade the invariant chain in this cell type. JNJ 10329670 was shown to block the proteolysis of the invariant chain in vivo by using immunocompromised mice injected with human peripheral blood mononuclear cells (PBMCs). Furthermore, this inhibitor blocks the presentation of tetanus toxoid and giant ragweed by human PBMCs. The properties of JNJ 10329670 make it a candidate for immunosuppressive therapy of allergies and autoimmune diseases. The presentation of antigens by MHC class II (MHC II) molecules is the crucial initiating step in a CD4ϩ T cellmediated immune response. Antigen presenting cells, mainly dendritic cells, B cells, and macrophages, take up and present antigens from the extracellular environment. The internalized protein antigens are processed by endosomal or lysosomal proteases to generate peptides that become associated with MHC II molecules. Peptide-loaded MHC II molecules are subsequently transported to the cell surface for display to CD4 ϩ T cells. Recognition of the MHC II/peptide complexes triggers the activation of antigen-specific CD4 ϩ T cells, which in turn activate other components of the immune system such as B cells, macrophages, and CD8 ϩ T cells. These cellular responses are crucial for the body's response to pathogens, but they are also responsible for the development and symptoms of allergy and autoimmune disease.Cathepsin S is a cysteine protease found in the lysosome of hematopoietic cells. It is a member of the papain superfamily and has 57% identity to cathepsins L and K. Unlike most other lysosomal proteases that are only active under acidic conditions, the activity of cathepsin S exhibits a broad pH optimum that extends to alkaline pH. In contrast to the housekeeping enzymes cathepsins B, D, and L, which are expressed ubiquitously, cathepsin S is expressed mainly in dendritic cells,...

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