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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2007;27:683.)
© 2007 American Heart Association, Inc.

Thrombosis

A Variant of Recombinant Factor VIIa With Enhanced Procoagulant and Antifibrinolytic Activities in an In Vitro Model of Hemophilia

Geoffrey A. Allen; Egon Persson; Robert A. Campbell; Mirella Ezban; Ulla Hedner; Alisa S. Wolberg

From the Department of Pediatrics (G.A.A.), University of North Carolina, Chapel Hill; Novo Nordisk A/S (E.P., M.E., U.H.), Novo Nordisk Park, Maaloev, Denmark; and the Department of Pathology and Laboratory Medicine (R.A.C., A.S.W.), University of North Carolina, Chapel Hill. Current address for G.A.A.: Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, Ill.

Correspondence to Alisa Wolberg, PhD, Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, 816A Brinkhous Bullitt Building, CB #7525, Chapel Hill, NC 27599-7525. E-mail alisa_wolberg{at}med.unc.edu

Objective— Recombinant factor VIIa (rFVIIa, NovoSeven) has proven efficacy in treating bleeding in hemophilia patients with inhibitors. A rFVIIa analog with mutations V158D/E296V/M298Q (NN1731) exhibits increased procoagulant activity in in vitro and in vivo models. The aim of this work was to define the effects of NN1731 toward factor X activation, platelet activation, thrombin generation, and fibrin clot formation and stability.

Methods and Results— In a cell-based in vitro model of hemophilia, rFVIIa and NN1731 similarly increased factor X activation on tissue factor–bearing cells; however, NN1731 exhibited 30-fold higher factor Xa generation on platelets than similar rFVIIa concentrations. NN1731-mediated thrombin generation depended on platelet activation, but NN1731 did not directly activate platelets. NN1731 produced 4- to 10-fold higher maximal thrombin generation rates than equal rFVIIa concentrations. Both rFVIIa and NN1731 shortened clotting times in the absence of factors IX and VIII; however, NN1731 did so at 50-fold lower concentrations than were required of rFVIIa. In fibrinolytic conditions, both rFVIIa and NN1731 increased fibrin formation and stability; however, NN1731 was effective at 50-fold lower concentrations than were required of rFVIIa.

Conclusions— By increasing factor Xa generation, NN1731 promotes the formation of thrombin and a stable clot to a greater degree than rFVIIa.

We compared the effects of recombinant factor VIIa (rFVIIa) and analog NN1731 on procoagulant activity in hemophilia. This analog did not activate platelets, but exhibited higher platelet factor Xa and thrombin generation, and shortened the clotting time and increased fibrin formation and stability more than rFVIIa.

Key Words: factor VIIa • hemophilia • fibrinolysis • fibrinogen

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