Characterization of recombinant factor IX fusion proteins enabling subcutaneous administration
Kathrin Schön 1),2), Sabine Pestel 1), Julia Riedesel 1); Waltraud Seyfert-Brandt 3), Philipp Claar 3), Eva Herzog 4), Alireza Rezvani-Sharif 5), Padmapriya Ponnuswamy 1), Marc W. Nolte 1)
1) Pharmacology & Toxicology, Research, CSL Innovation GmbH, Marburg, Hesse, Germany
2) Institute of Pharmacology, Biochemical-Pharmacological Center, University of Marburg, Marburg, Hesse, Germany
3) Recombinant Protein Expression, Research, CSL Innovation GmbH, Marburg, Hesse, Germany
4) Pharmacology & Toxicology, Research, CSL Behring LLC, King of Prussia, Pennsylvania, USA
5) Pharmacology & Toxicology, Research, CSL Limited, Melbourne, Victoria, Australia
Abstract
Background
The X-linked bleeding disorder hemophilia B, caused by mutation(s) in the coagulation factor (F)IX gene, leads to partial or total loss of its function, requiring lifelong FIX replacement therapy. Although new recombinant FIX (rIX) therapeutics like albumin fusion proteins (rIX-FP) enable longer plasma half-life and thus less frequent administration, the complexity of intravenous (i.v.) injection remains.
Objectives
The study aimed to characterize rIX-FP variants with anticipated enhanced specific activity, which would leverage rIX-FP’s superior pharmacokinetic profile with beneficial characteristics for subcutaneous (s.c.) administration.
Methods
Two rIX-FP variants, R338L (“Padua variant”) and R338L/E410K, were characterized in vitro. Pharmacokinetic profiles of FIX antigen and activity levels were evaluated in FIX-deficient mice after i.v. and s.c. administration of these variants (dosing based on antigen levels). The efficacy of the most promising variant was tested after i.v. and s.c. administration (dosing based on activity) in a tail clip bleeding model. A marketed wild-type (WT) rIX-FP product served as the comparator.
Results
Both rIX-FP variants showed a 4- to 5-fold increase in specific activity in vitro compared with rIX(WT)-FP, while FXIa-mediated activation was the fastest for rIX(WT)-FP and rIX(R338L)-FP. Compared with rIX(WT)-FP and rIX(R338L/E410K)-FP, rIX(R338L)-FP exhibited higher FIX activity exposure after i.v. and s.c. administration and demonstrated comparable efficacy with rIX(WT)-FP in reducing bleeding time and blood loss in FIX-deficient mice requiring ∼4 times lower protein amount.
Conclusion
rIX(R338L)-FP was shown to be a promising candidate for s.c. administration, exhibiting increased specific activity combined with higher activity-based exposure and indicating efficacy at a lower protein dose.