Efficacy, PK and Safety Results of a Phase I/II Clinical Trial of Recombinant Fusion Protein Linking Coagulation Factor IX with Albumin (rIX-FP) in Previously Treated Patients with Haemophilia B (PROLONG - 9FP)

Abstract 1121

Factor IX (FIX) replacement therapy is the standard of care for patients with haemophilia B. FIX products currently available have a relatively short half-life, requiring 2–3 times a week intravenous prophylactic treatment to achieve a significant bleeding reduction. A recombinant FIX albumin fusion protein (rIX-FP) was generated by genetic fusion of human recombinant albumin to rFIX to extend the half life of FIX. A Phase I/II open-label, multicenter, clinical study of rIX-FP has been completed in previously treated patients with severe hemophilia B (FIX ≤ 2%) as part of the PROLONG - 9FP clinical developmental program. The objectives of the study were to evaluate the prevention of bleeding episodes during once weekly prophylaxis and to assess the hemostatic efficacy of rIX-FP for the treatment of bleeding, in addition to safety and pharmacokinetic (PK) assessments.

The study consisted of a 10 to 14 day PK evaluation period, and a 3 to 12 month safety and efficacy evaluation period, during which subjects received either on-demand or prophylaxis treatment. Subjects receiving weekly prophylactic treatment were initially treated with a dose based upon the subject's PK profile, bleeding phenotype, and physical activity level. The dose could be adjusted based on clinical outcome, while maintaining a 7 day treatment interval. Subjects receiving on-demand treatment were treated with a dose based upon the subject's PK profile and WFH recommendations for treatment of bleeding episodes.

Seventeen study subjects from hemophilia treatment centers in Israel and Bulgaria participated in the study, 13 of whom received weekly prophylaxis treatment and 4 of whom received on-demand treatment. Following a single infusion of 25 IU/kg rIX-FP (n=13), the PK parameters (t_1/2 = 94 hrs, AUC_0-inf= 3414 hr*IU/dL) were comparable to those previously reported from the Phase I study (Blood prepublished Aug 2, 2012). In addition, rIX-FP maintained a baseline-corrected mean trough level of 3.8% and 2.7% at Day 7 and Day 14, respectively, after 25 IU/kg rIX-FP administration. There were no AEs considered as possibly related to rIX-FP. There were no allergic reactions, inhibitors to FIX or antibodies to rIX-FP reported. All 10 prophylaxis subjects who were previously receiving routine prophylaxis with FIX were maintained successfully on weekly treatment with rIX-FP for the entire study. Furthermore, three prophylaxis subjects who were previously treated on-demand were maintained successfully on weekly prophylaxis treatment with rIX-FP with at least 85% reduction in the annualized spontaneous and total bleeding rate compared to the annualized bleeding rate prior to study entry. All of the bleeding events were treated successfully, including approximately 90% of the events with a single infusion of rIX-FP. The mean weekly product consumption of rIX-FP (IUs) was reduced compared to the consumption of the previous FIX product (IUs). No subject was withdrawn from the study due to safety concerns or lack of hemostatic efficacy. This Phase I/II study has demonstrated the clinical efficacy of rIX-FP for once weekly routine prophylaxis to prevent spontaneous bleeding episodes and treatment of bleeding episodes, in addition to the excellent safety characteristics and improved PK profile. A detailed analysis of the efficacy of weekly routine prophylaxis and treatment of bleeding episodes, improved PK and safety properties of rIX-FP will be presented.