Plasma kallikrein plays an important role in the pathogenesis of inflammation and thrombosis. Kallikrein cleaves high molecular weight kininogen (HK) to liberate the potent pro-inflammatory peptide bradykinin (BK). BK upon activation of its constitutive B2 receptors on endothelial cells leads to an increase in intracellular Ca2+ level and subsequent production of nitric oxide (NO) and prostacyclin (PGI2), ultimately leading to vasodilation, hypotension, increased vascular permeability and vascular leakage. Further, kallikrein activates the complement system and stimulates neutrophil chemotaxis, aggregation and elastase release. Furthermore, kallikrein mediates the conversion of factor XII (FXII) to activated factor XII (FXIIa) thereby potentiating the intrinsic pathway of coagulation. Thus, plasma kallikrein represents an important target for the development of novel anti-inflammatory and anti-thrombotic agents. The primary objective of this study was to develop and characterize a novel small molecule inhibitor of plasma kallikrein and to evaluate its potential usefulness in the treatment of kallikrein-mediated inflammatory and thrombotic disorders. Using in vitro biochemical assays, PF-04886847 was identified as a potent and selective inhibitor of plasma kallikrein. PF-04886847 inhibited kallikrein-mediated BK production and subsequent BK-dependent B2 receptor signaling pathway in cultured endothelial cells. PF-04886847 abolished BK-induced increase in endothelial monolayer permeability as well as relaxation of lipopolysaccharide (LPS)-treated isolated rat aortic rings. In a rat model of LPS-induced sepsis and acute lung injury, PF-04886847 attenuated LPS-induced increase in granulocyte count in the systemic circulation and total leukocyte count in the bronchoalveolar lavage fluid. Lastly, in a balloon-induced femoral artery injury model of thrombosis in hypercholesterolemic rabbits, PF-04886847 reduced thrombus mass and prolonged both prothrombin time (PT) and activated partial thromboplastin time (aPTT). Overall, our results indicate that PF-04886847 is a novel, potent small molecule inhibitor of plasma kallikrein that would be useful for the treatment of kallikrein-mediated inflammatory and/or thrombotic disorders
