Objective:
The binding behavior of rVIII-SingleChain to plasma-derived von Willebrand Factor (pdVWF) was assessed in surface plasmon resonance (SPR) studies.
Methods:
The purification of VWF from human plasma–yielded pdVWF free of factor VIII (FVIII). Subsequently, isolated pdVWF was immobilized on a SPR gold chip using monoclonal antibodies (MAbs). Thereafter, the binding behavior of rVIII-SingleChain and full-length rFVIII molecules were studied and binding kinetics were calculated. Regeneration of pd-VWF was performed with calcium chloride, while regeneration of the covalently coupled anti-VWF MAbs was achieved in the presence of an acidic pH.
Summary:
The affinity of CSL Behring’s rVIII-SingleChain to pdVWF was significantly higher than those of commercially available rFVIII full-length molecules. The higher affinity was derived from a higher association rate constant, while the dissociation rate constants were comparable. Intriguingly, the higher affinity had no influence on other functional characteristics of rVIII-SingleChain (eg, the binding to phospholipids, thrombin generation capacity, and FVIII enzymatic activity were comparable to full-length rFVIII). The results obtained from the SPR studies in vitro appear consistent with the observation of improved pharmacokinetic characteristics for rVIII-SingleChain in comparison to full-length rFVIII. After treatment of hemophilia A mice with single doses of rVIII-SingleChain or full-length rFVIII, the systemic availability and mean residence time were found to be increased for rVIII- SingleChain compared to full-length rFVIII. In addition, a decreased clearance rate and an enhanced terminal half-life were observed for rVIII-SingleChain, while in vivo recovery and volume of distribution of rVIII-SingleChain were comparable to full-length rFVIII.
Conclusion:
Overall, it seems conceivable that the higher affinity of CSLB’s rVIII-SingleChain to pdVWF may have a positive effect on its systemic availability by a delayed elimination from plasma.