Vaccines, Blood & Biologics
Studies of Clearance from the Circulation of the Blood Clotting Factor VIII, Aimed at Improving the Safety and Efficacy of FVIII Products
Principal Investigator: Andrey Sarafanov, PhD
Office / Division / Lab: OBRR / DH / LH
Hemophilia A is a bleeding disorder caused by a deficiency of a protein called factor VIII (FVIII) in the blood. The condition occurs in about one in 10,000 males but is very rare in women.
The treatment for hemophilia A is replacement of FVIII, which compensates for the deficiency of this protein in the blood. Therapeutic FVIII is either obtained from human blood or artificially manufactured using recombinant DNA technology. FVIII obtained from human blood carries the risk of blood-borne infections that can be transmitted to the patient. Therefore, most physicians prefer to use FVIII that is made through recombinant DNA technology.
Another problem with hemophilia A treatment is that it is expensive, costing more than $100,000 per year. In addition, it is complicated, since the treatment includes as many as three to four infusions of FVIII each week. Thus, the treatment would be simpler and less expensive using an improved recombinant FVIII that lasts longer in the circulation and does not have to be infused as often.
The Division of Hematology is responsible for the review of FVIII products used for the treatment of hemophilia A patients. In order to better characterize these products, we are studying how the structure of FVIII affects the speed with which the liver removes it from the circulation. Our laboratory is currently studying the mechanisms by which the liver removes FVIII from the circulation by means of hepatic receptors--proteins on liver cells to which FVIII binds.
The results of this study could further improve our understanding of the mechanisms of FVIII removal from blood, and facilitate the FDA review and approval process for FVIII products, especially of those that are designed to have a long lifetime in the circulation.
Deficiency in factor VIII (FVIII) results in the blood coagulation disorder Hemophilia A, which is treated with infusions of either plasma-derived or recombinant FVIII. The hemophilia community has been hoping for improvements in FVIII products, in particular for products with a prolonged lifetime in the circulation. This would eliminate the need for frequent FVIII infusions and thus reduce both the complexity and cost of the treatment.
Several manufacturers modify the structure of the natural FVIII molecule in order to create a recombinant version that lasts longer in the circulation. Therefore, it is important for FDA regulatory scientists to understand the structure and catabolism of FVIII in order to effectively assess the efficacy and safety of licensed and emerging anti-hemophilic products being developed to improve the management of hemophilia A.
The half-life of FVIII in the circulation depends on a number of factors, among which is its interaction with hepatic clearance receptors, such as low-density lipoprotein receptor (LDLR) and low-density lipoprotein receptor-related protein (LRP). These proteins act in concert to catabolize FVIII, a process mediated by cell-surface heparin sulfate proteoglycans. We plan to map the liver receptor binding sites on FVIII using site-directed mutagenesis to express FVIII variants in a heterologous system and test their interactions with the receptors. We will further characterize these FVIII variant(s) for their activity, activation rate, ability to bind von Willebrand factor, and whether their half-life is increased compared to wild-type FVIII. Another part of the project aims to compare the immunogenicity of existing and new FVIII variants in animal models to evaluate the differential epitope specificity of induced FVIII inhibitors.
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