Phase 1 Dose-escalating Study to Evaluate the Safety, Pharmacokinetics, and Pharmacodynamics of a Recombinant Factor Xa Variant (FXa )

Summary: Background FXa (PF-05230907) is a zymogen-like variant of activated factor X (FXa). It shows enhanced resistance to inactivation by endogenous inhibitors as compared with wild-type FXa, and restores hemostatic activity in non-clinical models of various bleeding conditions. Objectives To evaluate the safety, pharmacokinetics and pharmacodynamics of FXa by performing a phase 1, first-in-human, dose-escalation clinical trial in healthy adult volunteers. Methods Participants were assigned to one of six ascending single-dose cohorts (0.1, 0.3, 1, 2, 3 or 5 μg kg ), each planned to comprise six volunteers treated with FXa and two treated with placebo. Assessments included safety monitoring, pharmacokinetic and pharmacodynamic (PD) analyses, and immunogenicity testing. Results The trial enrolled 49 male volunteers. Administration of a single intravenous bolus dose of FXa was safe and tolerated at all dose levels tested, with no dose-limiting toxicity or serious adverse events. FXa plasma levels appeared to increase dose-proportionally, with a half-life of ~ 4 min. Treatment-related PD changes were observed for activated partial thromboplastin time, thrombin generation assay, thrombin-antithrombin complexes, prothrombin fragment 1 + 2, and D-dimer. One volunteer had a weak and transient non-neutralizing antidrug antibody response, which did not cross-react with native FX or native FXa. Conclusions FXa was safe and tolerated, and showed a pharmacologic effect in healthy adults when administered at doses up to 5 μg kg . The safety profile, pharmacokinetics and pharmacodynamics observed in this clinical trial support the further development of FXa for hemostatic treatment in individuals with acute hemorrhagic conditions.