Ecallantide

The kallikrein-kinin system is a complex proteolytic cascade that promotes inflammatory and coagulation pathways. Human plasma kallikrein acts as a protease to mediate the conversion of High Molecular Weight (HMW) kininogen to bradykinin, which is a vasoactive mediator that increases vascular permeability and induces localized swelling, inflammation, and pain. The actions of kallikrein is regulated by the major endogenous inhibitor, C1-esterase-inhibitor (C1-INH). C1-INH also functions to regulate the activation of the complement and intrinsic coagulation (contact system pathway), which also initiates the production of bradykinin. Upon audoactivation via exposure to negatively charged surfaces, factor XII promotes the generation of factor XIIa and kallikrein. C1-INH inhibits both factor XIIa and kallikrein. Kallikrein may in turn reciprocally activate more FXII. Hereditary angioedema is associated with a deficiency of the C1 inhibitor is caused by a mutation in the C1 INH gene. Resulting effect is excessive production of the vasodilator, bradykinin. The actions of bradykinin produce typical edematous signs and symptoms of hereditary angioedema by enhancing vascular and endothelial permeability, leading to increased outflow of plasma into the interstitium to produce local edema.

Ecallantide is a potent, specific and reversible plasma kallikrein inhibitor with an Inhibitory Constant (Ki) of 25 pM. Upon binding to kallikrein and blocking its active site, ecallantide prevents the conversion of HMW kininogen to bradykinin and attenuates the production of bradykinin. By blocking the actions of kallikrein, ecallantide also reduces further activation of fXIIa, halting the positive feedback mechanism leading to more kallikrein production.