Alzheimer's drug succeeds in slowing cognitive decline, say Eisai and Biogen

An experimental Alzheimer's drug developed by Eisai Co Ltd and Biogen Inc significantly slowed cognitive and functional decline in a large trial, which involved patients in the early stages of the disease, the companies said on Tuesday.

The injected drug, lecanemab, slowed progress of the brain-wasting disease by 27 per cent compared to a placebo — meeting the study's main goal, and offering an apparent win for the companies, and potentially for patients and their families desperate for an effective treatment.

Eisai said the results from the 1,800-patient trial prove the long-standing theory that removal of sticky deposits of a protein called amyloid beta from the brains of people with early Alzheimer's can delay advance of the debilitating disease.

Analysts, such as Salim Syed at Mizuho Securities, have said that the results would be considered a "win" if lecanemab slowed the rate of decline by around 25 per cent, and that shares of both companies could jump on the news.

Lecanemab, like the companies' previous drug Aduhelm, is an antibody designed to remove those amyloid deposits. Unlike Aduhelm, lecanemab targets forms of amyloid that have not yet clumped together.

The so-called amyloid hypothesis has been challenged by some scientists, particularly after the US Food and Drug Administration's (FDA) controversial approval of Aduhelm in 2021 based on its plaque-clearing ability rather than proof that it helped slow cognitive decline. The decision came after the FDA's own panel of outside experts had advised against approval.

Aduhelm was the first new Alzheimer's drug approved in 20 years, after a long list of high-profile failures for the industry.

Eisai, leader of the 50-50 partnership's lecanemab program, is seeking FDA approval under the same accelerated pathway as Aduhelm, with a decision expected in early January. On Tuesday, the Japanese drugmaker said it would use the new efficacy results to submit lecanemab for traditional FDA review.

The company said it would also seek authorisation in Japan and Europe during its current fiscal year, ending March 31.

The Phase III trial evaluated the drug's ability to reduce cognitive and functional decline based on the Clinical Dementia Rating-Sum of Boxes (CDR-SB) — a numerical scale used to quantify the severity of dementia in patients in areas such as memory, orientation, judgement and problem solving and personal care.

Brain swelling

The rate of ARIA-E, a brain swelling side effect associated with anti-amyloid treatments, was 12.5 per cent in the lecanemab group, versus 1.7 per cent in the placebo group.

While the side effect showed up on imaging, many of these cases were not symptomatic, the companies said. Symptomatic brain swelling was seen in 2.8 per cent of those in the lecanemab group and none of the placebo group, they said.

The trial also tracked the rate of micro-haemorrhages in the brain, which occurred at a rate of 17 per cent in the lecanemab group, and 8.7 per cent in the placebo group.

Other plaque-targeting antibodies in late-stage development for Alzheimer's patients include Roche Holding AG's gantenerumab, and Eli Lilly and Co's donanemab.