FDA Extends Review Time for Biogen’s ALS Therapy


If approved, tofersen will be the first treatment that targets a genetic cause of ALS. The updated PDUFA date is April 25, 2023.

The FDA has extended the review of tofersen to treat patients with amyotrophic lateral sclerosis (ALS). Tofersen is being evaluated specifically to treat patients with superoxide dismutase 1 (SOD1) ALS. Developed by Ionis Pharmaceuticals and licensed to Biogen, toferson is an antisense drug that binds to SODI mRNA, which leads to its degradation.

In July, the FDA had accepted the a new drug Application (NDA), granting the application priority review and given a Prescription Drug User Fee Act action date of Jan. 25, 2023. At the time, the FDA indicated that it is planning to hold an advisory committee meeting for this application.

Biogen submitted responses to information requests by the FDA, which the agency considers a major amendment that will require additional time for review. The updated PDUFA date is April 25, 2023.

The average life expectancy for people with ALS is three to five years from time of symptom onset. There is currently no treatment targeted for SOD1-ALS. Mutations in the SOD1 gene are responsible for about 2% of the estimated 168,000 people who have ALS globally. Life expectancy in SOD1-ALS varies widely with some patients surviving less than a year.

Biogen is seeking approval based on the use of a neurofilament as a surrogate biomarker. Neurofilaments are normal proteins found in healthy neurons; they are increased in blood and cerebrospinal fluid when damage has been done to neurons or their axons and are a marker of neurodegeneration. In ALS, higher levels of neurofilaments have been found to predict more rapid decline in clinical function and shortened survival.

The application is based the phase 3 VALOR trial and an open-label extension study, as well as integrated 12-month results from both of these studies.

The six-month VALOR study did not meet the primary endpoint of change from baseline to week 28 in the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale. But trends of reduced disease progression across multiple secondary and exploratory endpoints were observed. The 12-month integrated data showed that earlier initiation of tofersen led to sustained reductions in neurofilament and slowed decline across multiple efficacy endpoints.

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