Correction of the coagulation defect in hemophilia using a factor Xa variant with novel engineered protease function

Effective therapies are needed to control excessive bleeding in a range of clinical conditions. We describe a surprisingly useful approach to improve hemostasis in vivo using a variant of coagulation factor Xa (FXa(I16L)). This conformationally pliant derivative is partially inactive due to a defect in transitioning from zymogen to protease (1,2). Using mouse models of hemophilia, we show that FXa(I16L) has a prolonged half-life, relative to wild-type FXa and does not cause excessive activation of coagulation. Once clotting mechanisms are activated to produce its cofactor FVa, FXa(I16L) is driven to the protease state and restores hemostasis in hemophilic animals upon vascular injury. Moreover, using human or murine analogs, we show that FXa(I16L) is more efficacious than FVIIa which is used to treat bleeding in hemophilia inhibitor patients(3). Because of its underlying mechanism of action, FXa(I16L) may provide an effective strategy to enhance blood clot formation and act as a rapid pan-hemostatic agent for the treatment of bleeding conditions.