Characterization of protein unable to bind von Willebrand factor in recombinant factor VIII products.

Background: Therapeutic products with coagulation factor VIII (FVIII) have a wide range of specific activities, implying presence of protein with altered structure. Previous studies showed that recombinant FVIII products (rFVIII) contain a fraction (FVIII ) unable to bind von Willebrand factor (VWF) and reported to lack activity. Because of loss of function(s), FVIII can be defined as a product-related impurity, whose properties and levels in rFVIII products should be investigated.

Objective: To isolate and characterize the FVIII fraction in rFVIII products.

Methods: Protein fractions unable (FVIII ) and able (FVIII ) to bind VWF were isolated from rFVIII products using immobilized VWF affinity chromatography (IVAC) and characterized by gel electrophoresis, immunoblotting, FVIII activity test, surface plasmon resonance, mass spectrometry, and for plasma clearance in mice.

Results And Conclusions: A robust IVAC methodology was developed and applied for analysis of 10 rFVIII products marketed in the United States. FVIII was found at various contents (0.4%-21.5%) in all products. Compared with FVIII , FVIII had similar patterns of polypeptide bands by gel electrophoresis, but lower functional activity. In several representative products, FVIII was found to have reduced sulfation at Tyr1680, important for VWF binding, decreased interaction with a low-density lipoprotein receptor-related protein 1 fragment, and faster plasma clearance in mice. These findings provide basic characterization of FVIII and demonstrate a potential for IVAC to control this impurity in rFVIII products to improve their efficacy in therapy of hemophilia A.