Correction of human hemophilia A whole blood abnormalities with a novel bypass agent: Zymogen-like FXaI16L

Abstract

Background: Approximately 30% of hemophilia A (HA) and 5% of hemophilia B patients develop inhibitors to protein replacement therapy, and this is the major cause of disease-related morbidity in the developed world. We previously developed zymogen-like factor Xa (FXa) molecules with impaired active site maturation, enabling a greater half-life than wild-type FXa while maintaining full procoagulant function in the prothrombinase complex. Here we evaluated the ability of zymogen-like FXaI16L to correct whole blood thromboelastometry abnormalities of severe HA subjects with and without inhibitors. Methods: Fourteen severe HA subjects without and five with inhibitors were enrolled at baseline (FVIII:C < 1%) > 5 half-lives from factor or bypass therapy. The subjects' whole blood was evaluated by thromboelastography (ROTEM®) using INTEM analysis with two concentrations of FXaI16L or recombinant factor VIIa (rFVIIa). Results: With 0.1 nm FXaI16L, clot time (CT, in minutes [min]) among HA subjects without and with inhibitors (mean = 2.87 min, 95% CI = 2.58-3.15 min, and mean = 2.9 min, 95% CI = 2.07-3.73 min, respectively) did not significantly differ from control CT (mean = 2.73 min, 95% CI = 2.62-2.85 min). Addition of 20 nm rFVIIa, simulating a 90-μg/kg dose, resulted in significantly prolonged CTs for HA subjects without and with inhibitors (mean = 5.43 min, 95% CI = 4.53-6.35 min, and mean = 4.25 min, 95% CI = 3.32-5.17 min, respectively) relative to controls. Conclusions: FXaI16L restored thromboelastometry CT to control values in severe HA subjects with and without inhibitors. The findings corroborate previous animal data and demonstrate the first evidence of zymogen-like FXaI16L correcting human HA subjects' whole-blood abnormalities and support the use of FXaI16L as a novel hemostatic agent.