2022-07-12| Trials & Approvals

Sanofi’s siRNA Therapy Reduces Bleeds in Hemophilia, Meets Primary Endpoint

by Joy Lin
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Preventive treatment with fitusiran, a small interference RNA (siRNA) therapeutic, reduced bleeds by 61% in patients with hemophilia A or B, with or without inhibitor, who have previously received factor or bypassing agent (BPA) prophylaxis, said Sanofi. The results of the Phase 3 ATLAS-PPX study evaluating fitusiran met the primary endpoint. 

The data was presented at the International Society of Thrombosis and Haemostasis (ISTH) 2022 Congress. 


Reducing Bleeds by 61.1%


Key findings from the Phase 3 study showed that fitusiran prophylaxis resulted in an overall median annualized bleeding rate (ABR) of 0.0, compared to a median ABR of 4.4 with prior prophylaxis. This siRNA therapeutic significantly reduced estimated annual bleeding by 61.1% compared to factor or BPA prophylaxis. During the trial, 63.1% of patients treated with fitusiran experienced zero treated bleeds compared to. 16.9% with prior factor or BPA prophylaxis. 

The most common side effects of fitusiran treatment included increased alanine aminotransferase, nasopharyngitis, and upper respiratory tract infection. Thromboembolic events were reported in 2 patients (3.0%), which were consistent with previously identified risk of fitusiran.

Related article: Sanofi Launches Nonprofit Brand To Distribute Medicines to Low-Income Countries


Treating Hemophilia Comes With Challenges


Hemophilia is an inherited bleeding disorder caused by a deficiency in blood clotting factors, which leads to spontaneous and excessive bleeding. 

The disease is typically treated with replacement of the clotting factors, but the body’s immune system may generate inhibitors to the replacement therapy, creating complications. For people who have developed a high level of inhibitors, BPA prophylaxis is used to circumvent the need for the missing clotting factors and generate thrombin. In recent years, several therapeutic approaches show promise as complementary or alternative treatments for hemophilia. 

One of these approaches, siRNA, silences genes by binding to target mRNA, inducing its cleavage which results in degradation. Fitusiran targets the anti-clotting protein antithrombin. By lowering levels of antithrombin, the drug promotes thrombin generation to restore hemostasis (the body’s response to bleeding) and prevent bleeding. 

Fitusiran uses Alnylam’s ESC-GaINAc conjugate technology which enables subcutaneous dosing with increased potency and durability. It may have the potential to provide prophylactic treatment for people with hemophilia A or B, with or without inhibitors, with as few as six injections per year. 

However, the investigational drug has its share of challenges. Fitusiran ran into its first FDA clinical hold in 2017 after a patient died due to a blood clot during a Phase 2 study. The hold was resolved within the year, but a second hold followed in 2020 as Sanofi investigated new clotting complications resulting from fitusiran treatment. Sanofi has since switched to a lower dosing regimen for fitusiran, but has said regulatory filings may be delayed until 2024.


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