Recombinant VWF Fragments Improve Bioavailability of Subcutaneous Factor VIII in Hemophilia A Mice.

Conventional treatment of hemophilia A (HA) requires repetitive intravenous (IV) injection of coagulation factor VIII (FVIII). Subcutaneous (SC) administration of FVIII is inefficient because of binding to the extravascular matrix, in particular to phospholipids (PL), and subsequent proteolysis. To overcome this, recombinant dimeric fragments of von Willebrand factor (VWF) containing the FVIII stabilizing D3 domain were engineered. Two fragments, called VWF-12 and VWF-13, demonstrated high binding affinity to recombinant human FVIII (rhFVIII) and suppressed PL-binding in a dose-dependent manner. High concentrations of VWF fragments did not interfere with the functional properties of full-length VWF in vitro. The HA mouse model was used to study the effects of VWF-12 or VWF-13 on the in vivo pharmacokinetics of rhFVIII, demonstrating (i) no significant impact on rhFVIII recovery or half-life after a single IV administration; (ii) enhanced bioavailability (up to 18.5 %) of rhFVIII after SC administration; (iii) slow absorption (cmax 6h) and prolonged half-life (up to 2.5-fold) of rhFVIII after SC administration. Formation of anti-FVIII antibodies was not increased after administration of rhFVIII/VWF-12 SC compared to rhFVIII IV. A single SC dose of rhFVIII/VWF-12 provided protection in the HA tail bleeding model for up to 24h. In conclusion, recombinant VWF fragments support FVIII delivery through the SC space into vascular circulation without interfering with VWF or FVIII function. Slow resorption and excretion of FVIII after SC administration highlight the potential application of VWF fragments for SC FVIII prophylaxis in HA.