Sanofi Genzyme Places Trials for Fitusiran on Hold

Due to the identification of new adverse events, Sanofi Genzyme has placed a dosing hold on its full clinical development program for fitusiran, an investigational treatment for hemophilia.

The decision was announced in a joint statement from the World Federation of Hemophilia, the European Haemophilia Consortium and the National Hemophilia Foundation. The statement did not specify the events that led to this stoppage.

“We are maintaining close communication with all relevant stakeholders and will share additional information as soon as available,” the organizations wrote.

Fitusiran, also known as ALN-AT3, is an experimental RNA interference (RNAi) agent being developed by Sanofi Genzyme and Alnylam Pharmaceuticals as a treatment for hemophilia A and B. The therapy is intended for people with or without inhibitors (neutralizing antibodies that limit the effectiveness of replacement therapies).

The investigational medication works by blocking the activity of a protein called antithrombin, which normally helps to prevent clotting. By blocking this protein’s activity, fitusiran is intended to promote clotting — and thereby prevent bleeding — in people with hemophilia. The therapy is administered via subcutaneous (under-the-skin) injection once per month.

Results from a Phase 1 trial (NCT02035605) completed in 2017 indicated the medication reduced the levels of antithrombin and restored the balance of clotting proteins in adults with hemophilia A or B. Participants who completed that Phase 1 trial were permitted to enroll in an extension study (NCT02554773).

Yet, clinical trials evaluating fitusiran were suspended in 2017, after a participant in the extension study died due to a blood clot that caused bleeding in the brain.

After that, amendments to the trial’s protocol were made, including the implementation of new measures to minimize risk to participants. Clinical testing resumed at the end of 2017, with approval from the U.S. Food and Drug Administration.

Data from the extension study, announced earlier this year, showed that the investigational medication decreased antithrombin levels and reduced the frequency of bleeding episodes in patients with moderate-to-severe hemophilia A or B. The findings also indicated the therapy was generally safe and well-tolerated. Two serious adverse events were reported, including a case of excessive liver enzymes levels. The most common adverse events included increases in liver enzymes, headache, irritation at the injection site, common cold, upper respiratory tract infection, and diarrhea.

In addition to the extension study, six clinical trials testing fitusiran in people with hemophilia are ongoing: ATLAS-INH (NCT03417102), ATLAS-A/B (NCT03417245), ATLAS-PPX (NCT03549871), ATLAS-PEDS (NCT03974113), and ATLAS-OLE (NCT03754790).

Participants are currently being recruited for ATLAS-PPX (enrolling males 12 and older) and ATLAS-PEDS — enrolling boys ages 1 to 11. ATLAS-OLE is recruiting males with severe hemophilia A or B who have completed a Phase 3 clinical trial of fitusiran.