Efficacy of Baxter’s Longer Acting rFVIII (BAX 855) in Mouse Models of Hemophilia A

Abstract 4350

Factor VIII (FVIII) is a critical component of the intrinsic coagulation pathway. FVIII concentrates are used in patients with hemophilia A to provide a hemostatic FVIII level sufficient to treat and prevent bleeding episodes. Multiple prophylactic administrations per week are necessary to maintain a FVIII level of at least 1% of normal to effectively prevent or reduce spontaneous bleeding episodes. A longer acting FVIII concentrate would reduce the frequency of infusions. Baxter and Nektar have developed a longer-acting PEGylated variant (BAX 855) of Baxter’s recombinant FVIII (ADVATE process). The aim of the presented studies was to evaluate the efficacy of BAX 855 in two primary pharmacodynamics in hemophilia A mice: a tail-tip bleeding model (TTBM) and a carotid occlusion model (COM).

BAX 855 was tested at a dose of 200 IU/kg rFVIII. ADVATE™ served as the active reference item, and formulation buffer as the negative control item. Mice received intravenous treatment with either BAX 855 or ADVATE™ 12–40h prior to the experiment. Buffer was administered 5–15min prior to the experiment.

Animals were anesthetized using ketamine and xylazine. In the TTBM (n=16) the tip of the tail was cut off and total blood loss [mg] was assessed over 60 minutes. In the COM study (n=10) the left carotid artery was exposed and the endothelium was denuded by topical application of FeCl₃. Time to occlusion [min] was assessed.

Buffer-treated animals had a median blood loss of 951 mg in the TTBM and did not show vessel occlusion within 30 min in the COM. In the TTBM, a prophylactic effect of ADVATE™ could be observed for up to 18 h, leading to a reduction in blood loss to 121 mg after this treatment interval. Prophylactic efficacy after treatment with BAX 855 could be observed for up to 40 h with a median blood loss of 73 mg after 30 h and 436 mg after 40 h. In the COM, treatment with ADVATE™ 12 h before the experiment shortened the time to occlusion to 3.8 min. With BAX 855, a similar efficacy could be observed for up to 24 h after administration (5.2 min).

In summary, the results of our studies show that BAX 855 is efficacious in these two mouse models of hemophilia A and that the efficacy of BAX 855 is prolonged compared with an unmodified rFVIII. Furthermore, the intravenous injection of BAX 855 was well tolerated in all animals across all treatment groups without any signs of acute toxicity.