Biogen gets much-needed pipeline lift with speedy ALS drug review

Beleaguered Biogen has been handed some encouraging news from the FDA, after the regulator agreed to complete its review of amyotrophic lateral sclerosis (ALS) therapy tofersen within six months.

The priority review of the Ionis-partnered SOD-1-targeted antisense drug marks the latest stage in the resurrection of the programme, which was all-but written off last October when it failed a phase 3 trial.

A few months later, Biogen brought tofersen back to life with a fresh analysis of data from that trial plus an open-label extension – in an echo of the approach it took with ill-fated Alzheimer's therapy Aduhelm (aducanumab) – and it has now filed for approval on 12-month data in patients with ALS associated with a mutation in the SOD-1 gene.

If approved, tofersen would be the first treatment to target a genetic cause of ALS, albeit one that is vanishingly rare with only around 330 patients in the US.

The FDA's priority review means that it will make a decision on the marketing application by 25 January, and Biogen will also have to make the case for its drug at an advisory committee meeting. So far, no date for that has been scheduled.

Biogen is seeking approval for tofersen based on its effects on a neurofilament biomarker that it says is "reasonably likely to predict clinical benefit," along with 12-month results from the phase 3 VALOR study that according to the company showed that early treatment trended towards slower decline in measures of clinical and lung function, muscle strength and quality of life.

That position will almost certainly be keenly debated extensively at the advisory committee meeting, and Biogen will be hoping for a better outcome than at the Aduhelm meeting.

The FDA's advisors voted against approval based on amyloid beta as a surrogate marker for efficacy – only to be overruled when the agency approved it a few weeks later – although Aduhelm bombed commercially despite reaching the market.

Over a third of patients treated with the drug in VALOR also experienced serious adverse events, and 17% discontinued therapy as a result, which will also no doubt exercise the FDA's expert advisors.

In tofersen's favour is that SOD1-ALS has a devastating impact on patients, with an average life expectancy of just three to five years after the onset of symptoms.

As it did with Aduhelm, Biogen is seeking accelerated approval on the strength of the current dataset while it waits for confirmation results from the ongoing ATLAS phase 3 trial in SOD1-ALS.

The rarity of SOD1-ALS means however that tofersen is unlikely to make big sales, even if it has a high price. With Biogen squeezed between competitive pressures to its current multiple sclerosis and spinal muscular atrophy products and almost zero sales of Aduhelm, a lot is riding on its Alzheimer's follow-up lecanemab, which has been filed in the US.