Biochemical and functional characterization of a recombinant monomeric factor VIII-Fc fusion protein

. Background: HemophiliaA results from a deficiency in factorVIII activity. Current treatment regimens require frequent dosing, owing to the short half-life of FVIII. A recombinant FVIIIFc fusion protein (rFVIIIFc) was molecularly engineered to increase the half-life of FVIII, by 1.52-fold, in several preclinical animal models and humans. Objective: To perform a biochemical and functional invitro characterization of rFVIIIFc, with existing FVIII products as comparators.Methods: rFVIIIFc was examined by utilizing a series of structural and analytic assays, including mass spectrometry following lysyl endopeptidase or thrombin digestion. rFVIIIFc activity was determined in both one-stage clotting (activated partial thromboplastin time) and chromogenic activity assays, in the context of the FXase complex with purified components, and in both invitro and exvivo rotational thromboelastometry (ROTEM) assays performed in whole blood. Results: rFVIIIFc contained the predicted primary structure and post-translational modifications, with an FVIII moiety that was similar to other recombinant FVIII products. The von Willebrand factor-binding and specific activity of rFVIIIFc were also found to be similar to those of other recombinant FVIII molecules. Both chromogenic and one-stage assays of rFVIIIFc gave similar results. Exvivo ROTEM studies demonstrated that circulating rFVIIIFc activity was prolonged in mice with hemophiliaA in comparison with B-domain-deleted or full-length FVIII. Clot parameters at early time points were similar to those for FVIII, whereas rFVIIIFc showed prolonged improvement of clot formation. Conclusions: rFVIIIFc maintains normal FVIII interactions with other proteins necessary for its activity, with prolonged invivo activity, owing to fusion with the Fc region of IgG1.