New Alzheimer's drug from Biogen and Eisai is just the beginning

A successful late-stage trial of lecanemab gives researchers promising new avenues for tackling this hard-to-beat disease.

A drug developed by Biogen Inc. and Eisai Co. has achieved a first in Alzheimer’s research: In a large, late-stage trial, lecanemab slowed down the cognitive decline in people with early disease.

The therapy’s effect was modest. But given the litany of failures in Alzheimer’s drug development, it’s a stunning turn for the field. And while skepticism about the true meaning of these results — for patients, for the fate of similar drugs, for our understanding of the disease — is warranted, the result is meaningful enough to let the Alzheimer’s community celebrate a possible win.

Biogen and Eisai’s drug slowed cognitive decline by 27% over 18 months compared to a placebo in a large trial with nearly 1,800 people with early Alzheimer’s. Those data make it the first to show a clinical benefit in a late-stage study, but it won’t be the first amyloid-targeting drug to reach the market.

That milestone last year went to Aduhelm, also developed by Biogen and Eisai. But that controversial regulatory nod was based on Aduhelm’s ability to get rid of amyloid plaques, which some scientists think are a major cause of Alzheimer’s, not on its ability to slow down the cognitive decline in the disease. As a consequence, Medicare decided not to pay for the drug unless it was being given in the context of a trial that could confirm its benefits.  Without a commercial market, Biogen essentially stopped trying to sell it.

The companies have already asked the Food and Drug Administration to grant lecanemab so-called “accelerated approval” based on its ability to clear amyloid — that should come by early 2023. This new data should support a full approval, one that would convince insurers to cover it, by the second half of 2023. The clear win for a drug that enters a multi-billion-dollar market lifted Biogen’s stock as much as 44% this morning.

But the results come with many caveats. The companies provided the data in a press release, not a paper. The full details will be presented at a conference in late November, and neurologists will pore over them to ensure the drug’s already modest benefits haven’t been oversold.

Lecanemab, like other amyloid-targeting antibodies, also has safety issue — swelling and bleeding of the brain. Although for most people in the study, these side effects were mild, the frequency with which they occurred could have made it easy for doctors to know which patients in the trial were getting the drug versus placebo, a situation that may have biased the results.

The biggest asterisk is that lecanemab is not a cure — unfortunately, it’s not even close to one. We don’t know how much a modest slowdown in the disease will have on the lives of people with Alzheimer’s and their families. And any impact the drug might have would be blunted if the price puts it out of reach.

Another thing the results don’t do is, as Eisai’s chief executive officer Haruo Naito claimed in a press release, “prove the amyloid hypothesis,” the theory that Alzheimer’s is driven by the protein that clumps together to form plaques on the brains of people with the disease.

But the results also aren’t the death knell for the theory that many, myself included, expected.

In the last two decades, companies have spent hundreds of millions of dollars on drug after drug intended to reduce those plaques. All of those efforts failed, causing skeptics to ask whether amyloid buildup was a consequence rather than a driver of the disease.

With each fresh failure, proponents of the amyloid hypothesis broke out a few standard explanations: The trial didn’t enroll the right patients; it was tested too late in the disease to make a difference; the drug didn’t quite work in the right way.

And it’s true that older studies sometimes were deeply flawed. But it was hard not to see these as excuses to keep the focus on amyloid. Many critics (again, myself included) felt it was long past time for the pharma industry to move on — or at the very least to devote a much larger portion of research dollars to other ideas.

The truth now seems somewhere between these extremes. Amyloid isn’t the only driver of the disease, but Biogen and Eisai’s data confirm that targeting it is worthwhile.

What’s more exciting is the idea that this first success could accelerate other efforts — efforts that could have a more profound impact on patients’ lives. Alzheimer’s experts have long acknowledged that altering the course of the disease will take more than one drug. Perhaps an amyloid therapy should be paired with, for example, one targeting tau tangles or adding in a treatment that can keep neurons from dying.

But getting to drug combinations has been challenging to impossible without first having at least one treatment with a proven clinical benefit. Results from studies of two experimental drugs would be too hard to parse. If a trial failed or succeeded, it would be hard to tell if the benefit was because of one drug, the other, or the combination. If a safety issue emerged, which drug would be to blame?

Academic researchers recently launched the first such trial, which studies the effect of combining lecanemab with a tau-targeted drug (also made by Eisai). It took years to get off the ground, and because of its meticulous design, it’ll take years to run.

Now, these types of studies should be easier to get up and running, particularly if lecanemab or one of the other amyloid-targeting drugs in the last stages of development become a routine part of Alzheimer’s care.

The good news on lecanemab shouldn’t further entrench the Alzheimer’s field in amyloid research, but instead should inspire a range of creative trials that could help bring more substantive change to the lives of people with the disease.

Experts will and should go over the new data with a fine-toothed comb to understand the true value of the new treatment. The field should also embrace the idea that successes are possible — and start pushing hard on ways to improve upon this one.