Biogen's ALS drug candidate shows mixed results; FDA panel weighs in

An FDA advisory panel voted for and against the clinical benefit of tofersen — Biogen's investigational drug for amyotrophic lateral sclerosis, which failed to pass its primary endpoint in a late-stage trial — on March 22. 

During a daylong meeting, all nine panelists agreed that the drug's reduction in plasma NfL concentration could predict a benefit. But, when asked on its relevant biomarkers, three said the data provided convincing evidence of efficacy, five said no and one member abstained. 

The mean life expectancy rate of ALS is about two to five years after diagnosis, according to the ALS Association. If approved, tofersen would be the first drug for a rare form of ALS, CNBC reported.

In a phase 3 study, Biogen tested 108 ALS patients with superoxide dismutase 1, which is "an antioxidant enzyme protecting the cell from reactive oxygen species toxicity," according to the National Institutes of Health. This "ultra-rare genetic form" of ALS affects about 330 people in the U.S., Biogen said Jan. 23. 

The agency denied the experimental ALS drug in April 2020 after a phase 1 trial "did not demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints," according to an FDA document preceding the panel's meeting. 

Biogen submitted a new drug application in 2022 along with phase 3 data with the request for accelerated approval and priority review. Accelerated drug approvals can be granted for investigational drugs that are intended to treat serious conditions, "fill an unmet need" and have a surrogate endpoint — including "laboratory measurement, radiographic image, physical sign or other measure" — that points to, but cannot ensure, a clinical benefit, according to the FDA.

The agency gave tofersen priority review to determine whether to hand the drug candidate accelerated approval. 

The FDA is expected to make its decision by April 25.

Phase 3 results "failed to show a statistically significant difference between the tofersen and placebo groups for the primary or secondary endpoints," the FDA said in a committee briefing document. Biogen said in its application there are a few reasons why this trial did not pass its main endpoints. Read more here.

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