A Novel FVIIa Variant with Increased Potency and Duration of Effect Compared to Wildtype FVIIa. A Study in a Dog Model of Hemophilia A

Abstract

Abstract 2252Hemophilia patients are treated by replacement therapy, receiving the plasma-derived or recombinant clotting factor in which they are deficient. A significant number of hemophilia patients, however, develop inhibitory antibodies against the factor they receive, becoming refractory to replacement therapy. In these inhibitor patients, hemostasis can be achieved using bypass agents, activated plasma-derived prothombin complex concentrates (aPCC) or recombinant activated Factor VIIa (FVIIa). However, these treatments do not match the efficacy seen in traditional replacement therapy. To overcome this limitation, 813, a modified recombinant human Factor VIIa with enhanced biological properties was developed using a rational protein design approach. 813 was selected from a series of FVIIa variants and is characterized by increased catalytic activity and prolonged duration of effect in vivo. Compared to recombinant wild-type FVIIa, 813 has 7-fold increased catalytic activity, measured by the rate of Factor Xa generation in vitro, both in the presence and absence of tissue factor (TF).813 was studied in Factor VIII (FVIII)-deficient dogs with NovoSeven RT (wt-FVIIa) as comparator. The FVIII-deficient dogs exhibit a severe hemophilia A phenotype, with less than 1% normal coagulant activity. Dogs were dosed intravenously with 813 or wt-FVIIa and blood and plasma were collected at various time points post dosing. Plasma FVIIa levels were measured using a FVIIa-specific clotting assay. Starting from initial peak plasma levels, a time-dependent decrease in FVIIa plasma concentration was observed for wt-FVIIa and variant. Compared to wt-FVIIa, 813 exhibited a smaller volume of distribution (35–48 mL/kg vs. 108–134 ml/kg), a lower rate of clearance (10–18 mL/hr/kg vs. 45 mL/kg/hr) and consequently an increased dose adjusted exposure. Hemophilia A dogs have a prolonged activated partial thromboplastin time (aPTT); treatment with wt-FVIIa or 813 led to a dose-dependent decrease in aPTT. At equivalent doses the peak effect of 813 on decreasing aPTT was approximately two-fold compared to wt-FVIIa. Similar dose-dependent effects were observed when studying whole blood clotting profiles by thromboelastography (TEG). Treatment effects were seen for all TEG parameters monitored (time to clotting onset, rate and strength of clot formation). However, compared to wt-FVIIa, 813 given at equivalent doses caused significantly stronger effects on all TEG parameters; acute peak effects on TEG parameters measured for 813 at 10 ug/kg, were similar to those seen with 50 ug/kg wt-FVIIa. This difference became even more pronounced when monitoring treatment effect over time. All dogs used in this study were monitored throughout the study for possible treatment-related changes; both 813 and wt-FVIIa were well tolerated. No overt adverse events, no significant changes in plasma clinical chemistry or cellular blood counts were observed.In conclusion, 813 is a novel FVIIa protein with increased potency, prolonged duration of effect and a preclinical safety profile comparable to wt-FVIIa. 813 is currently in early clinical development for acute and prophylactic treatment of hemophilia patients with inhibitors. Disclosures:Pittman:Pfizer: Employment. Weston:Pfizer: Employment. Shields:Pfizer: Employment. Parng:Pfizer: Employment. Arkin:Pfizer: Employment. Madison:Catalyst Biosciences: Employment. Nichols:Pfizer: Research Funding. Fruebis:Pfizer: Employment.