LAUSR

Background and Purpose Following inflammatory stimuli neutrophils are recruited to sites of inflammation and exert effector functions that often have deleterious effects on tissue integrity, which can lead to organ failure. Btk is expressed in neutrophils, and constitutes a promising pharmacological target for neutrophil mediated tissue damage. Here we evaluate a selective reversible inhibitor of the Bruton's tyrosine kinase (PRN473) for its ability to dampen neutrophil influx via inhibition of adhesion receptor signaling pathways. Experimental Approach In vitro assays were used to assess Fpr1-mediated binding of ligands to the adhesion receptors macrophage antigen-1 and lymphocyte function antigen-1. Intravital microscopy of the murine cremaster was used to evaluate post-adhesion strengthening and endoluminal crawling. Finally, neutrophil influx was visualized in a clinically relevant model of sterile liver injury in vivo. Btk knock out animals were used as points of reference for Btk functions. Key Results Pharmacological inhibition of Btk by PRN473 reduced fMLP-induced phosphorylation of Btk and Mac-1 activation. Biochemistry experiments demonstrate the specificity of the inhibitor. PRN473 (20 mg/kg) significantly reduced intravascular crawling and neutrophil recruitment into inflamed tissue in a model of sterile liver injury to levels seen in Btk deficient animals. A higher dose did not provide additional reduction of intravascular crawling and neutrophil recruitment. Conclusions and Implications PRN473, a highly selective inhibitor of Btk, potently attenuates sterile liver injury by inhibiting the activation of the β2-integrin Mac-1 and subsequently neutrophil recruitment into inflamed tissue.