Fitusiran reduces bleeding in factor X-deficient mice.

Area of Science:

• Hematology
• Pharmacology

Background:

• Factor X (FX) deficiency is a rare bleeding disorder characterized by impaired thrombin generation and increased bleeding risk.
• Current treatments often involve FX replacement therapy, which can be limited by supply and administration challenges.

Purpose of the Study:

• To investigate the therapeutic potential of fitusiran, a small interfering RNA targeting antithrombin, for managing Factor X deficiency.
• To evaluate the efficacy of reducing antithrombin levels in enhancing hemostasis in a preclinical model of FX deficiency.

Main Methods:

• Development of a novel inducible mouse model of severe Factor X deficiency (f10low mice) with <1% FX activity.
• Assessment of hemostatic function using in vitro clotting assays (PT, aPTT), thrombin generation assays, and in vivo bleeding models (tail-clip, saphenous vein puncture).
• Evaluation of fitusiran treatment in f10low mice, measuring antithrombin activity, thrombin generation, and bleeding parameters.

Main Results:

• f10low mice exhibited significantly prolonged clotting times, severely reduced thrombin generation, and an increased bleeding tendency compared to control mice.
• Fitusiran treatment in f10low mice led to reduced antithrombin activity, increased thrombin generation, and improved hemostasis in a saphenous vein puncture bleeding model.
• Bleeding in f10low mice was corrected by infusion of purified FX, validating the model and FX's role.

Conclusions:

• The study demonstrates that reducing antithrombin levels via fitusiran can enhance thrombin generation and improve hemostatic potential in the context of Factor X deficiency.
• This preclinical data supports the potential of targeting antithrombin as a novel therapeutic strategy for Factor X deficiency and potentially other bleeding disorders.
• The developed inducible FX deficiency model serves as a valuable tool for future research in hemostasis and thrombosis.