Inhibition of spleen tyrosine kinase attenuates allergen-mediated airway constriction.

Spleen tyrosine kinase (SYK) is a key activator of signaling pathways downstream of multiple surface receptors implicated in asthma. SYK function has been extensively studied in mast cells downstream of the high-affinity IgE receptor, FcεR1. Preclinical studies have demonstrated a role for SYK in models of allergic inflammation, but a role in airway constriction has not been demonstrated. Here, we have used a potent and selective pharmacological inhibitor of SYK to determine the role of SYK in allergen-mediated inflammation and airway constriction in preclinical models. Attenuation of allergic airway responses was evaluated in a rat passive anaphylaxis model and rat and sheep inhaled allergen challenge models, as well as an ex vivo model of allergen-mediated airway constriction in rats and cynomolgus monkeys. Pharmacological inhibition of SYK dose-dependently blocked IgE-mediated tracheal plasma extravasation in rats. In a rat ovalbumin-sensitized airway challenge model, oral dosing with an SYK inhibitor led to a dose-dependent reduction in lung inflammatory cells. Ex vivo analysis of allergen-induced airway constriction in ovalbumin-sensitized brown Norway rats showed a complete attenuation with treatment of a SYK inhibitor, as well as a complete block of allergen-induced serotonin release. Similarly, allergen-mediated airway constriction was attenuated in ex vivo studies from nonhuman primate lungs. Intravenous administration of an SYK inhibitor attenuated both early- and late-phase allergen-induced increases in airway resistance in an Ascaris-sensitive sheep allergen challenge model. These data support a key role for SYK signaling in mediating allergic airway responses.

A human tissue-based functional assay platform to evaluate the immune function impact of small molecule inhibitors that target the immune system.

While the immune system is essential for the maintenance of the homeostasis, health and survival of humans, aberrant immune responses can lead to chronic inflammatory and autoimmune disorders. Pharmacological modulation of drug targets in the immune system to ameliorate disease also carry a risk of immunosuppression that could lead to adverse outcomes. Therefore, it is important to understand the 'immune fingerprint' of novel therapeutics as they relate to current and, clinically used immunological therapies to better understand their potential therapeutic benefit as well as immunosuppressive ability that might lead to adverse events such as infection risks and cancer. Since the mechanistic investigation of pharmacological modulators in a drug discovery setting is largely compound- and mechanism-centric but not comprehensive in terms of immune system impact, we developed a human tissue based functional assay platform to evaluate the impact of pharmacological modulators on a range of innate and adaptive immune functions. Here, we demonstrate that it is possible to generate a qualitative and quantitative immune system impact of pharmacological modulators, which might help better understand and predict the benefit-risk profiles of these compounds in the treatment of immune disorders.

TLR4, TLR7/8 agonist-induced miR-146a promotes macrophage tolerance to MyD88-dependent TLR agonists.

TLRs facilitate the recognition of pathogens by immune cells and the initiation of the immune response, leading to the production of proinflammatory cytokines and chemokines. Production of proinflammatory mediators by innate immune cells, such as macrophages, is tightly regulated to facilitate pathogen clearance while limiting an adverse impact on host tissue. Exposure of innate immune cells to TLR ligands induces a state of temporary refractoriness to a subsequent exposure of a TLR ligand, a phenomenon referred to as "tolerance." This study sought to evaluate the mechanistic regulation of TLR4 and TLR7/8 ligand-induced tolerance to other TLRs by microRNA-146a. With the use of THP-1 macrophages, as well as human classic and alternative macrophages, we demonstrate that priming with a TLR4 agonist (LPS) or a TLR7/8 agonist (R848) induces homologous and heterologous tolerance to various TLR ligands in macrophages, leading to the impaired production of cytokines and chemokines. We also demonstrate that overexpression of microRNA-146a is sufficient to mimic LPS or R848-induced hyporesponsiveness. Conversely, inhibition of microRNA-146a activity leads to LPS- or R848-induced TLR hyper-responsiveness in TLR signaling tolerance. Furthermore, we demonstrate that microRNA-146a dampens cytokine production following a primary stimulus with MyD88-dependent but not MyD88-independent TLR pathways. Collectively, these data provide comprehensive evidence of the central role of microRNA-146a in TLR signaling tolerance to plasma membrane, as well as endosomal TLR ligands in human macrophages.