Critical role of kallikrein in hereditary angioedema pathogenesis: A clinical trial of ecallantide, a novel kallikrein inhibitor

Background: Hereditary angioedema (HAE) is a rare, autosomal-dominant disorder caused by C1 inhibitor gene mutation. Patients with HAE experience intermittent attacks of edema affecting the oropharynx, abdomen, gastrointestinal tract, and limbs. C1 inhibitor is the primary endogenous inhibitor of the kallikrein-kinin (contact) cascade. Unregulated kallikrein activation generates bradykinin, the likely mediator of the swelling and pain characterizing HAE attacks. Ecallantide, a novel, recombinant protein, potently inhibits kallikrein. This is the first placebo-controlled assessment in human beings of a therapeutic intervention to) improve symptoms of HAE attacks under the hypothesis that the contact cascade is the putative pathway responsible for HAE pathology. Objective: To determine the safety and efficacy of ecallantide in patients with HAE. Methods: This double-blind, placebo-controlled, ascending-dose study assessed efficacy and tolerability of ecallantide (5, 10, 20, or 40 mg/m(2) intravenously) in individuals experiencing acute HAE attacks (N = 49). Twelve patients were assigned to each dose level: 10 to ecallantide and 2 to placebo, per cohort. Results: Ecallantide treatment ameliorated the symptoms of HAE attacks: 72.5 % (29/40) of patients treated with ecallantide versus 25.0% (2/8) of placebo patients reported significant improvement in symptoms within 4 hours (P =.0169). Ecallantide was well tolerated at all doses. Conclusion: Ecallantide, a potent, specific inhibitor of plasma kallikrein, significantly improved HAE symptoms over placebo. The trial provides strong support for the role of the kallikrein-kinin cascade and its end product, bradykinin, in the pathophysiology of HAE. Further clinical trials are underway. Clinical implications: Ecallantide is a promising new therapy for HAE attacks.