Pharmacokinetic Properties of Different rFVIII Products in Rabbits, Rats and FVIII Ko Mice

Introduction: Current state of the art treatment of severe Hemophilia A is prophylactic or on-demand replacement of the deficient factor VIII (FVIII) using plasma derived or recombinant factors [Keeling 2008; Srivastava 2012; Wong 2011]. The compliance to existing therapies is hampered by the short half-life of available FVIII products necessitating multiple intravenous injections per week for adequate prophylaxis [Bjorkman 2009; Sheridan 2011]. Thus, FVIII products with improved pharmacokinetic profiles are currently under development or have recently been made available [Oldenburg 2014]. FVIII's pharmacokinetic (PK) properties are believed to be strongly dictated by its binding to von Willebrand Factor (VWF) [Lenting 2007; Dasgupta 2007; Saenko 2006]. The aim of this study was to compare the binding affinity of different recombinant FVIII (rFVIII) products to plasma derived VWF (pd VWF), and characterize their PK properties in different animal species.

Methods: The PK profiles of rVIII-SingleChain (B-domain-truncated, covalently-linked single chain rFVIII; CSL Behring), Advate® (full-length rFVIII; Baxalta), NovoEight® (B-domain-truncated rFVIII; NovoNordisk), Eloctate® (B-domain-deleted rFVIII fused to Fc portion of IgG; Biogen) and Nuwiq® (B-domain-deleted rFVIII; Octapharma) were compared in FVIII knock out mice (FVIII ko), rats and rabbits following intravenous injection of 150 (mice and rabbits) or 400 or 480 (rats) IU/kg rFVIII. Dose levels were administered based on labelled/nominal chromogenic FVIII activity. Plasma samples were obtained up to 72 h (mice), 48 h (rats) and 96 h (rabbits) post-application. FVIII plasma levels were determined based on antigen (FVIII:Ag) using an ELISA technique (ASSERACHROM®, Stago) and/or based on chromogenic FVIII activity (FVIII:C; COAMATIC® FACTOR VIII, Chromogenix).

Results: The PK of rFVIII products in three different animal species was compared using the area under the plasma concentration time curve (AUC) as an indicator for exposure. In FVIII ko mice, FVIII:Ag based PK of rVIII-SingleChain was comparable to that of Eloctate® and NovoEight®, and superior over Nuwiq® and Advate® based on AUC. In contrast, FVIII:C based PK data did not achieve significant differences, most likely due to the the higher assay variability. In rats, FVIII:Ag PK of rVIII-SingleChain was superior over all tested rFVIII products, i.e. Nuwiq®, NovoEight®, Eloctate® and Advate® based on AUC. In rabbits, rVIII-SingleChain FVIII:Ag PK was comparable to NovoEight® and superior to all other rFVIII products, i.e. Nuwiq®, Eloctate® and Advate®. Thus, across all animal species tested, a favorable PK profile was shown for rVIII-SingleChain.

It was further shown that the binding affinity of rVIII-SingleChain to pd VWF was significantly improved in comparison to the full length molecule Advate® [Zollner 2014]. This higher binding affinity to pd VWF may therefore explain the differences in PK profiles observed.

Conclusion: In general, rVIII-SingleChain showed a favorable PK profile as compared to other rFVIII products such as Advate®, NovoEight®, Eloctate® and Nuwiq® across species, i.e. FVIII ko mice, rats and rabbits. This favorable PK profile of rVIII-SingleChain may be explained by its high binding affinity to VWF.