A Pharmacologic Evaluation of BAY 79-4980 (Liposome-Formulated Kogenate® FS) in the Hemophilia A Mouse.

Background: BAY 79-4980 refers to recombinant FVIII (rFVIII; Kogenate^®-FS, KGFS) reconstituted with a PEGylated Liposome diluent. rFVIII binds non-covalently but with high affinity on the external surface of the PEGylated Liposome and retains procoagulant activity and normal vWF binding in vitro. In initial in vivo experiments in hemophilia A mice (FVIII −/−) subject to multiple tail clippings, hemostatic activity with BAY 79-4980 was augmented compared to FVIII alone. In the current studies, a more extensive pharmacologic analysis of BAY 79-4980 was performed in Hemophilia A mice using an acute FVIII dependent bleeding model (Landskroner et al).

Objectives: To more thoroughly evaluate the pharmacologic properties of BAY 79-4980 using an acute FVIII dependent bleed model in the hemophilic A mouse. We examined BAY-4980 under three conditions: (1) Prophylaxis treatment, where drug is administered via the jugular vein and 5 minutes later the tail is transected; (2) On demand treatment, where drug is administered 3–5 minutes after the tail is severed and bleeding is extant; (3) PK/PD, where drug is administered via tail vein and 4 or 24 hrs is allowed to elapse before the tail is severed.

Methods: Hemophilia A mice were anesthetized with isoflurane, the tail is then warmed and the right jugular vein is exposed. At t = 0 the tail is cut by a scalpel and the transected tail is placed back into a new tube of warmed saline (37–40°C). Blood is collected over 40 minutes into the plastic tubes and blood loss is measured gravimetrically. In all studies, BAY 79-4980 is compared with a similar dose of KGFS measured in chromogenic units/mouse. The data is analyzed in two ways; (1) the quantity (μl) of blood lost over 40 minutes and the frequency (% of mice) in the respective treatment group bleeding >150 μl. The 150 μl value is used as a cut-off value to determine a real bleeding event. This value was derived from the mean + 2.5 SD of bleeding in control (C57BL) mice administered 5% albumin.

Results: With Prophylaxis treatment at 2.5 U/mouse, blood loss was 205 ± 59 μl with KGFS and 62 ± 16 μl with BAY 79-4980 (P = 0.12). Percentage of animals protected was not significantly different (73% versus 93%, respectively). With on demand treatment at 1 and 2.5 U/mouse, the results were 660 ± 69 μl with KGFS and 447 ± 69 μl with BAY 79-4980 (P = 0.02) at 1 U/mouse and 466 ± 107 μl with KGFS and 211 ± 52 μl with BAY 79-4980 at 2.5 U/mouse. The percent protected was 10% versus 36% at 1 U/mouse and 47% versus 60% at 2.5 U/mouse, respectively. When drug was administered at 2.5 U and 4 hours was allowed to elapse the results were 432 ± 102 μl with KGFS and 187 ± 70 μl with BAY 79-4980 (P = 0.04), and the percentage of mice protected was 47% and 73%, respectively. When drug was administered at a dose of 8 U/mouse and the tail was cut at 24 hours, the results were 822 ± 97 μl with KGFS and 395 ± 112 μl with BAY 79-4980 (P = 0.02), and the percentage of mice protected was 13% versus 53%, respectively (P = 0.05).

Conclusions: These results demonstrate that BAY 79-4980 has good hemostatic activity when administered acutely compared to KGFS. It appeared that under certain conditions, BAY 79-4980 exhibited enhanced hemostatic benefit, even when administered acutely. When BAY 79-4980 was administered prophylactically and 4 or 24 hours was allowed to elapse, enhanced hemostatic activity was demonstrated compared to KGFS alone.