Targeting of Antithrombin in Hemophilia A or B with RNAi Therapy

Targeting of Antithrombin in Hemophilia A or B with RNAi Therapy
Fitusiran is an RNA interference molecule that targets antithrombin RNA (and thereby decreases the amount of circulating antithrombin). This approach is theorized to decrease the number of bleeds in patients with hemophilia of any type and to potentially lower the requirement for prophylactic factor.
This phase I study addressed the safety, pharmacodynamics, and pharmacokinetics of fitusiran. 4 healthy controls and 30 adults with hemophilia were enrolled. The primary outcome was plasma antithrombin levels.
Antithrombin levels decreased and thrombin levels concurrently increased both with weekly and monthly dosing. In an exploratory analysis, there were fewer bleeds/month after treatment than before. The safety profile was tolerable.
This is a phase I study and so clinical utility is still limited.
A new avenue for treatment of hemophilia and one of the few examples of clinical use of RNA interference therapy. The safety profile is encouraging - it will likely have phase III results reported shortly.