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

• Published in: Journal of thrombosis and haemostasis Vol. 13; no. 9; pp. 1694 - 1698
• Main Authors: George, L. A., Thalji, N. K., Raffini, L. J., Gimotty, P. A., Camire, R. M.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Limited 01.09.2015
• Subjects: coagulation time, whole blood; deficiency, factor VIII; factor X, activated; hemophilia A, congenital; hemophilia B; inhibitor, blood coagulation factor
• ISSN: 1538-7933; 1538-7836; 1538-7836
• DOI: 10.1111/jth.13059

Summary 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.