A bispecific nanobody for the treatment of von Willebrand disease type 1.

Von Willebrand disease (VWD)-type 1 is a bleeding disorder characterized by a quantitative deficiency of functional von Willebrand factor (VWF). We designed a novel bispecific nanobody, named KB-V13A12, that aims to increase endogenous VWF levels by bridging it to albumin. KB-V13A12 comprises two single-domain antibodies, one targeting VWF and one targeting albumin. VWF bound efficiently to the albumin/KB-V13A12 complex (2.0±0.4 nM) in immunosorbent assays and binding was stable at pH 5.6 and 7.4. VWF ristocetin activity and factor VIII binding remained unaffected in the presence of a 100 to 200-fold molar excess of KB-V13A12/albumin. Humanized VWD-type 1 mice were used for in vivo analysis. A single subcutaneous dose of KB-V13A12 (5 mg/kg) was associated with a nanobody half-life of 3.0±0.7 days and dose-dependently increased VWF in VWD-type 1 mice 1.4 to 2.1-fold for up to 14 days. FVIII activity was also increased during this period. The VWF-propeptide/VWF-antigen ratio (a marker for VWF clearance) was significantly reduced in the presence of KB-V13A12, suggesting that delayed clearance contributes to increased VWF levels. Clearance experiments in wild-type mice using recombinant VWF pre-incubated with KB-V13A12 indeed confirmed a prolonged survival, while this prolongation was absent in FcRn-deficient-mice. Finally, treatment with KB-V13A12 resulted in a significantly improved bleeding tendency in VWD-type 1 mice when using the saphenous vein puncture-model. In conclusion, KB-V13A12 is a bispecific nanobody that efficiently increases functional levels of endogenous VWF, and could be a therapeutic option to treat VWD-type 1.