FDA Approval of New Alzheimer’s Drug May Boost Prospects of Other Treatments

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The Food and Drug Administration’s approval of

Biogen Inc.’s

BIIB -0.12%

Aduhelm on Monday may have boosted the prospects of other experimental Alzheimer’s disease drugs that target the disease in a similar way.

In greenlighting Aduhelm, the FDA endorsed a hypothesis about Alzheimer’s that not long ago was thought dead: The disease can be treated by clearing the buildup of a sticky substance in the brain known as amyloid.

Many scientists studying Alzheimer’s aren’t ready to give up on the amyloid hypothesis, but there isn’t a consensus on precisely what role amyloid plays in the disease.

In approving Aduhelm, the FDA said the drug reduced amyloid and thereby likely helps Alzheimer’s patients.

The decision was cheered by many Alzheimer’s patient groups and doctors, who have lacked good options for treatment. The move was criticized, however, by many researchers who said there wasn’t enough evidence to show the drug worked and at a $56,000 yearly list price, it will be costly.

New Treatment for Alzheimer’s

Biogen’s drug Aduhelm may help slow damage to the brain caused by the degenerative disease.

How Alzheimer’s affects the brain

A prominent scientific theory holds that in Alzheimer’s disease, naturally occurring proteins bind together into clumps called amyloid plaques. The clumps build up around brain cells, disrupting their function and contributing to cognitive decline.

Aduhelm is a lab-made antibody, an immune agent that protects the body from harmful substances such as viruses and toxins. Aduhelm is modeled on antibodies taken from older people with very slow or no cognitive decline that scientists discovered are specific to amyloid.

When injected into the body, the Aduhelm antibodies latch onto amyloid clusters in the brain and clear them from the brain, though scientists aren’t sure exactly how.

Aduhelm may clear amyloid from the brain via the blood stream

It may also recruit immune cells to ingest amyloid deposits

A prominent scientific theory holds that in Alzheimer’s disease, naturally occurring proteins bind together into clumps called amyloid plaques. The clumps build up around brain cells, disrupting their function and contributing to cognitive decline.

Aduhelm is a lab-made antibody, an immune agent that protects the body from harmful substances such as viruses and toxins. Aduhelm is modeled on antibodies taken from older people with very slow or no cognitive decline that scientists discovered are specific to amyloid.

When injected into the body, the Aduhelm antibodies latch onto amyloid clusters in the brain and clear them from the brain, though scientists aren’t sure exactly how.

Aduhelm may clear amyloid from the brain via the blood stream

It may also recruit immune cells to ingest amyloid deposits

A prominent scientific theory holds that in Alzheimer’s disease, naturally occurring proteins bind together into clumps called amyloid plaques. The clumps build up around brain cells, disrupting their function and contributing to cognitive decline.

Aduhelm is a lab-made antibody, an immune agent that protects the body from harmful substances such as viruses and toxins. Aduhelm is modeled on antibodies taken from older people with very slow or no cognitive decline that scientists discovered are specific to amyloid.

When injected into the body, the Aduhelm antibodies latch onto amyloid clusters in the brain and clear them from the brain, though scientists aren’t sure exactly how.

Aduhelm may clear amyloid from the brain via the blood stream

It may also recruit immune cells to ingest amyloid deposits

The approval could pave the way for FDA approving other Alzheimer’s drugs that reduce amyloid buildup, including therapies being studied by

Eli Lilly

& Co. and

Roche Holding AG

, analysts say.

Shares in Lilly, which recently released promising results for its drug donanemab in a Phase 2 study, rose 10.2% on Monday. Roche shares gained 2.4% on Monday.

The FDA “made the unproven assertion that removing amyloid from the brain is enough to benefit Alzheimer’s patients, and with that understanding, other drugs that remove the plaque should be able to get approved,” says Ronny Gal, a Bernstein pharmaceuticals analyst.

The FDA cleared Aduhelm under its accelerated approval pathway, which allows for drugs to be brought on the market before definitively showing they result in clinical benefit for patients.

The pathway is most commonly used for cancer drugs, such as

Amgen Inc.’s

lung-cancer treatment Lumakras, which the FDA cleared late last month based on the therapy’s ability to shrink tumors.

The FDA’s acceptance that clearing amyloid is likely to confer benefit to patients could bode well for other treatments aimed at different targets linked to the disease, including the tangled strands of a protein called tau, according to analysts and Alzheimer’s researchers.

“It hearkens good things for the Alzheimer’s field, and not just for amyloid targeted treatments but also tau,” says Maria Carrillo, chief science officer at the Alzheimer’s Association.

Critics of the FDA’s decision say it sends a bad message to drug developers that they can use subpar clinical-trial data to gain regulatory approval.

The agency approved Aduhelm based on clinical trials that Biogen halted early after determining they were unlikely to be successful. The company later analyzed additional data from the studies to seek approval.

“The accelerated approval pathway is not intended for drugs with weaker evidence. You’re still supposed to have high-quality, rigorous trials,” says Aaron Kesselheim, professor of medicine at Harvard Medical School and a member of an FDA advisory committee that rejected endorsing Aduhelm last year. “In this case, the trials were stopped early and not completed,” and Biogen later found signs the drug worked, he said.

The FDA’s advisory committee wasn’t asked to consider whether reducing amyloid is likely to confer clinical benefits to patients, a hypothesis that is still debated because of the large number of amyloid-targeted drugs that have failed in the past, says Dr. Kesselheim.

“There is no good evidence that reducing amyloid leads to meaningful changes in the clinical course of disease,” says Dr. Kesselheim.

Some biotech analysts caution that the FDA’s flexibility toward Aduhelm may not extend to other amyloid-targeted treatments, particularly those that haven’t been proven to be as potent at clearing amyloid from the brain.

“Wall Street is very surprised and, I think, shocked by the approval, but they are not fully convinced just yet that the FDA is open to widely approving lots of Alzheimer’s drugs,” says Michael Yee, a Jefferies biotech analyst. “This is the first step to moving the bar but every company needs to have a large set of data to convince the FDA of clinical efficacy.”

Aduhelm’s approval is likely to spur further investment into Alzheimer’s drugs, says

Alfred Sandrock,

Biogen’s executive vice president for research and development.

“This will be a catalyst for not only other amyloid targeting drugs, but other ways of innovating in Alzheimer’s disease in general,” says Dr. Sandrock. Early multiple-sclerosis drug “beta interferon was approved in 1993 under accelerated approval, and we now have more than 20 drugs approved for MS just in the last 25 years. So it’s happened before, and I think it’ll happen again,” he said.

Aduhelm’s Path to Approval

Write to Joseph Walker at joseph.walker@wsj.com

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