Biogen Inc. announced that the U.S. Food and Drug Administration (FDA) has extended the review period of the new drug application (NDA) for tofersen by three months. Tofersen is an investigational treatment for superoxide dismutase 1 (SOD1) amyotrophic lateral sclerosis (ALS). The updated Prescription Drug User Fee Act (PDUFA) goal date is April 25, 2023.

As part of the ongoing review, Biogen submitted responses to information requests by the FDA which the FDA considered a Major Amendment to the application that will require additional time for review. The FDA accepted the tofersen NDA in July 2022 under the accelerated pathway and granted priority review. Tofersen is an antisense drug being evaluated for the potential treatment of SOD1-ALS.

Tofersen binds to SOD1 mRNA, allowing for its degradation by RNase-H in an effort to reduce synthesis of SOD1 protein production. In addition to the ongoing open label extension of VALOR, tofersen is being studied in the Phase 3 ATLAS study designed to evaluate whether tofersen can delay clinical onset when initiated in presymptomatic individuals with a SOD1 genetic mutation and biomarker evidence of disease activity. Biogen licensed tofersen from Ionis Pharmaceuticals Inc. under a collaborative development and license agreement.

Amyotrophic lateral sclerosis (ALS) is a rare, progressive and fatal neurodegenerative disease that results in the loss of motor neurons in the brain and the spinal cord that are responsible for controlling voluntary muscle movement. People with ALS experience muscle weakness and atrophy, causing them to lose independence as they steadily lose the ability to move, speak, eat, and eventually breathe. Average life expectancy for people with ALS is three to five years from time of symptom onset.

Multiple genes have been implicated in ALS. Genetic testing helps determine if a person's ALS is associated with a genetic mutation, even in individuals without a family history of the disease. Currently, there are no genetically targeted treatment options for ALS.

Mutations in the SOD1 gene are responsible for approximately 2% of the estimated 168,000 people who have ALS globally (SOD1-ALS). Life expectancy in SOD1-ALS varies widely with some patients surviving less than a year. For over a decade, Biogen has been committed to advancing ALS research to provide a deeper understanding of all forms of the disease. The company has continued to invest in and pioneer research despite making the difficult decision to discontinue a late-stage ALS asset in 2013.

Biogen has applied important learnings to its portfolio of assets for genetic and other forms of ALS, with the goal of increasing the probability of bringing a potential therapy to patients in need. These applied learnings include evaluating genetically validated targets in defined patient populations, pursuing the most appropriate modality for each target and employing sensitive clinical endpoints. The company has a pipeline of investigational drugs being evaluated in ALS, including tofersen and BIIB105.