- Alnylam Pharmaceuticals Inc. and its partner Sanofi SA can continue human testing of fitusiran now that the Food and Drug Administration has lifted a clinical hold on the investigational RNA interference therapy.
- In September, Alnylam suspended dosing in all ongoing studies of fitusiran after a patient in a Phase 2 open-label extension trial suffered a fatal thrombotic event. The trial was evaluating the drug in patients with moderate or severe hemophilia A or B.
- The FDA's decision comes about a month after it met with Alnylam and Sanofi to discuss safety measures and a risk mitigation strategy for further study of fitusiran. With their new clinical protocols approved, the companies plan on re-commencing the extension trial as well as the Phase 3 ATLAS program, which is testing the drug in patients with hemophilia A and B with or without inhibitors.
Despite the positive regulatory outcome, Sanofi and Alnylam aren't exactly out of the woods. The blood disorder market, particularly with regard to hemophilia, has gotten significantly more crowded in recent years. Roche AG's Hemlibra (emicizumab), for instance, gained approval just last month, and will likely be a market disruptor with its weekly dosing regimen and strong efficacy profile.
What's more, Alnylam has hinted there may be some issues ramping back up fitusiran development.
"[W]e may experience difficulty enrolling our clinical trials, including, but not limited to, our clinical trials for fitusiran, due to the availability of existing approved treatments, as well as other investigational treatments in development," the company said in its most recent quarterly filing. "Moreover, given the recent temporary suspension of dosing in our fitusiran studies due to a fatal thrombotic [serious adverse event], people with hemophilia may be more reluctant to enroll in our ATLAS Phase 3 program when it is resumed."
Jefferies analyst Maury Raycroft still has optimism for Alnylam and its drug's ability to compete, though, issuing a Buy rating in a Dec. 15 investor note.
"Though behind Hemlibra in respect to development timeline, we continue to believe fitusiran's appeal as a non-peptide/antibody-based therapy [with] broad potential in heme A/B will have competitive advantages," Raycroft wrote.
Fitusiran is an RNA interference therapy that works by regulating antithrombin in plasma. While not as far along as patisiran — a treatment for hereditary ATTR Amyloidosis that was submitted to the FDA earlier this month — fitusiran is an integral piece of Alynlam's pipeline.
So when the company reported on Sept. 7 that a patient taking the drug died from a blood clot, the news understandably shook investors. By market's close, Alnylam stock had fallen more than 11%.
Alnylam claimed the death wasn't related to fitusiran treatment, but suspended dosing across all clinical trials. Interim meetings with the FDA have apparently been fruitful, as the agency has given the all-clear for studies to restart with a revised safety protocol.
"With the additional risk mitigation measures in place, we look forward to the continued late-stage development of fitusiran and expect to resume dosing around year-end," Akin Akinc, Alnylam's vice president and general manager of fitusiran, said in a Dec. 15 statement.
Alnylam shares were up 5.3% to $130.16 apiece by Friday's market open. Sanofi's shares were up less than 1% to $43.24 apiece in mid-morning trading.