A new drug form of blood coagulation factor IX: red blood cell-entrapped factor IX

Deficiency of factor IX causes hemophilia B, and primary treatment for hemophilia B is based on recurrent infusions of deficient factor IX. Frequent infusions of foreign protein diminish patients' quality of life, and increase the risk of development of immune reaction. We entrapped factor IX into erythrocytes-carriers (pharmacocytes) to prolong the drug's circulation life time, and to prevent immune response to the drug.

Factor IX was biotynilated by standard method and then loaded aseptically into volunteers' erythrocytes with our gentle procedure of stepwise dialysis. The comparison of pharmacokinetics for free and autologous erythrocytes-entrapped biotinylated factor IX (FIXbiot) was done. Concentrations of factor IXbiot in plasma and lysates of erythrocytes were quantitatively assessed with a sandwich ELISA.

Stepwise dialysis method allowed stable loading of factor IXbiot into erythrocytes. Elimination of the loaded erythrocytes followed the first-order kinetics. The mean half-time of elimination for free FIXbiot was 8.8±5.6 hours, and for RBC-entrapped factor IXbiot 73.9±16.0 hours. Elimination of FIXbiot from plasma did not follow the first order kinetics because this factor concentration depended not only on the rate of its elimination, but also on the rate of factor appearance in plasma as a result of pharmackocytes' degradation. A rough estimate of the feasibility of the approach was done.

The life time of the erythrocyte-based form of FIXbiot in the circulation is significantly (5-10 times) prolonged compared with its free form, suggesting that this form has potential clinical applications.