The interaction of factor VIIa with rehydrated, lyophilized platelets

The experiments presented here were undertaken to determine if factor VIIa (rFVIIa, the Novo Nordisk product NovoSeven) will directly bind to rehydrated, lyophilized (RL) platelets for the formation of a catalytic surface with an enhanced ability to generate thrombin. The interaction between rFVIIa and the RL platelet surface was examined by measuring equilibrium and non-equilibrium binding of the coagulation factor to the cells and by following the effects of the surface modification on the kinetics of thrombin generation. The association of rFVIIa with RL platelets was rapid with saturation occurring within minutes. Disassociation was slow, with over half of the coagulation factor remaining bound after two hours. Densities of over one million molecules of rFVIIa per RL platelet were obtained when high concentrations of rFVIIa were incubated with RL platelets. Thrombin generation measurements showed that RL platelet-bound rFVIIa was catalytically active. Thus we can expect that RL platelets, which have been shown to effectively bind to sites of vascular injury, will localize rFVIIa to wounds for an increase in therapeutic index. These studies indicate that rFVIIa-RL platelets are worthy of preclinical and clinical development as an infusion agent for severe bleeding.