MELBOURNE – An investigational RNA interference therapeutic that suppresses the production of antithrombin has shown significant reductions in bleeding rates with no major safety events, according to findings presented at the International Society on Thrombosis and Haemostasis congress.
Fitusiran is a once-monthly, fixed-dose subcutaneous therapy that uses RNA interference to silence the gene for the endogenous anticoagulant antithrombin.
Bianca Nogrady/MDedge News
Dr. John Pasi
“The therapeutic hypothesis is based on the fact that hemophilia A and B are essentially thrombin-deficiency disorders, so if we lack factor VIII or factor IX, we can’t generate enough thrombin and we can’t produce a significant and substantial blood clot,” John Pasi, MBChB, PhD, of the Royal London Haemophilia Centre, Barts Health NHS Trust. “If we, however, administer fitusiran, which will suppress antithrombin production, we can rebalance coagulation, generate more thrombin and form a much more substantial clot.”
Dr. Pasi presented results of an interim analysis of safety and efficacy data from an open-label, phase 2 extension study in 34 individuals with hemophilia A or B, with or without inhibitors, who were treated either with 50-mg or 80-mg doses of fitusiran for a median of at least 2 years.
Researchers saw significant declines in annualized bleeding rates in patients with hemophilia A and B, with and without inhibitors. Among those without inhibitors, the median annualized bleeding rate declined from 2.00 in patients already on hemophilia prophylaxis and 12.00 in those using on-demand treatment to 1.08 overall. In patients with inhibitors, the median annualized bleeding rate dropped from 42.00 to 1.04.
The treatment was also associated with substantial reductions in antithrombin production and increases in thrombin generation.
One patient in the phase 1 study experienced a fatal cerebral venous sinus thrombosis, which subsequently led to introduction of a bleed management protocol.
“Following that last case, we revised and reviewed the bleed management guidelines in view of the fact that there might potentially be an interaction between the amount of replacement therapy and thrombin generation,” Dr. Pasi said. Since introduction of that protocol, there have been no related thrombotic events.
The majority of adverse events reported were mild and deemed not related to the study drug, Dr. Pasi said. These included headache, injection site erythema, and arthralgia. A total of 14 subjects – all of whom were positive for hepatitis C at baseline – experienced rises in ALT levels but these were asymptomatic and resolved spontaneously.
One patient with chronic active hepatitis C infection also showed significant ALT/AST elevation which led to discontinuation of treatment.
In an interview, Dr. Pasi said one of the biggest advantages of fitusiran was that it could be used in patients with hemophilia A and B. “You’ve got patients with hemophilia B who’ve got no options at the moment. That would be an obvious specific group that would gain from this.”
Another advantage was fitusiran’s stability and dosing, he said, pointing out that the treatment was fixed dosing and stable at room temperature. Fitusiran is now undergoing phase 3 trials.
The study was funded by Sanofi Genzyme and Alnylam Pharmaceuticals, and six authors were employees of Sanofi Genzyme. Dr. Pasi reported financial relationships with pharmaceutical companies, including Alnylam.
SOURCE: Pasi J et al. 2019 ISTH Congress, Abstract OC 11.3.