Fitusiran is a small interfering RNA molecule that blocks antithrombin production in liver cells. Instead of taking the traditional approach in hemophilia treatment of boosting the coagulation cascade by replacing what’s missing, the idea of fitusiran is to short circuit the body’s anticoagulation system by targeting antithrombin.
Patients in two trials presented at the meeting, ATLAS-A/B and ATLAS-INH, had about a 90% reduction in their annualized bleeding rates when treated with prophylactic fitusiran, with half or more having no bleeds that required treatment during the 9-month trials. The median annualized bleeding rate fell to 0, trial investigators reported at the meeting.
These findings held in both hemophilia A and B with and without inhibitors, which are antibodies formed against exogenous clotting factors, and on subanalysis of spontaneous and joint bleeding rates. Reduced bleeding was associated with substantial improvements in health-care related quality of life, particularly in the physical health domain.
A question about study design
An audience member at ASH noted that the trials didn’t compare fitusiran against prophylactic treatment, which is standard of care for hemophilia, but rather against episodic treatment – concentrated factors or bypassing agents in subjects with inhibitors – once subjects in the control groups started to bleed.
Still, the numbers reported in the studies “have never been achieved with standard prophylaxis in the past.” Furthermore, standard prophylaxis requires lifelong intravenous infusions, sometimes several a week, said lead ATLAS-A/B investigator Alok Srivastava, MD, a hematologist at the Christian Medical College in Vellore, India.
Fitusiran was dosed in the studies as a once-a-month 80 mg subcutaneous injection, so is much less bothersome. Also, it seems likely that some patients will only need dosing every other month. Maker Sanofi Genzyme is exploring lower and less frequent dosing to reduce thrombotic event risks that emerged in earlier studies, said Steven Pipe, MD, a pediatric hematologist at the University of Michigan, Ann Arbor, and the senior investigator on ATLAS-A/B, which assessed fitusiran in patients without inhibitors.
Serious thrombotic events occurred in two fitusiran patients in the trials, one of which led to discontinuation.
No pricing information
Overall, “I think [fitusiran] is a tremendous leap forward” with “the opportunity to transform the day-to-day lives of patients,” particularly those with hemophilia B, who have limited treatment options, Dr. Pipe said.
If approved for the U.S. market, fitusiran will go up against the monoclonal antibody emicizumab (Hemlibra), a subcutaneous injection dosed weekly to monthly that mimics the function of factor VIII, so it’s approved only for hemophilia A with or without inhibitors.
Several audience members at ASH noted that a major consideration for fitusiran, if approved, will be its cost. There’s no pricing information yet, but annual list price for emicizumab is reported to be in the $500,000 range.
For hemophilia A, “it will come to what proves to be the most efficacious and safe, with also consideration given to pricing,” Nigel Key, MD, a hematologist at the University of North Carolina at Chapel Hill, said in a comment.