Evaluation of the toxicology, pharmacokinetics, and local tolerance of recombinant factor IX Fc fusion protein in animals

- Recombinant factor IX Fc fusion protein (rFIXFc) is a longer-acting factor.
- Repeat-dose rat and monkey toxicology studies showed no adverse effects of rFIXFc.
- rFIXFc had no adverse local tolerance or thrombogenicity findings in rabbits.
- Animal rFIXFc pharmacokinetics can predict those of humans by allometric scaling.

IntroductionRecombinant factor IX Fc fusion protein (rFIXFc) is a recombinant coagulation factor composed of a single molecule of recombinant factor IX (rFIX) covalently fused to the Fc domain of human immunoglobulin G1 (IgG1) with no intervening sequence. An extensive nonclinical program was performed to support the clinical development of rFIXFc for treatment of people with hemophilia B.Materials and MethodsRepeat-dose toxicology studies of rFIXFc were performed in 2 relevant species: Sprague Dawley rats (4-week study) and cynomolgus monkeys (5- and 27-week studies). Assessments included in-life observations, electrocardiograms (monkeys only), laboratory evaluations (including hematology and blood chemistry), postmortem analyses, local tolerance, and pharmacokinetics (PK). Allometric scaling was performed with PK data from multiple species, including humans. Local tolerance (single-dose study) and thrombogenic potential (Wessler stasis model) of rFIXFc were tested in New Zealand White rabbits.ResultsThere were no significant local or systemic toxicity findings in the repeat-dose studies. Allometric scaling data suggested that animal rFIXFc PK results are predictive of human PK parameters. There were no findings from the local tolerance study in rabbits; thrombogenic activity was less than that elicited by rFIX and a prothrombin complex concentrate, and similar to vehicle control.ConclusionsrFIXFc was well tolerated in toxicology studies and demonstrated a low thrombogenic potential. These results are consistent with phase 1/2a and phase 3 clinical studies of rFIXFc in people with hemophilia B.