Scientists are cautiously optimistic about the promise of an experimental drug shown to modestly slow the progression of Alzheimer's disease in some patients.
Alzheimer's disease is the most common form of dementia and is a physical brain condition that causes impaired memory, thinking and behaviour.
It has no cure and, so far, treatments have focused more on managing symptoms — with limited success — as opposed to a new drug, lecanemab, which is designed to slow the progression of Alzheimer's.
A stage-three clinical trial was conducted, involving administering the drug to people in the early stages of the disease.
Full results — published in the New England Journal of Medicine [NEJM] — showed lecanemab modestly slowed the progression of Alzheimer's over an 18-month trial period.
On an 18-point scale, patients who took the drug were 0.45 points better off than those on the placebo.
However, there were also notable side effects and scientific opinion remains divided about the significance of the findings.
Scientia Professor Henry Brodaty is co-director of the Centre for Healthy Brain Ageing at the University of New South Wales (UNSW).
"The current drugs we have … they're [addressing symptoms]. They don't actually slow the disease process," he said.
Not a 'magic bullet'
In patients with Alzheimer's disease, there is a build-up in the brain of an abnormal but somewhat common protein called amyloid and that's what this drug targets.
"There have been a number of trials looking at antibodies to remove this protein," Professor Brodaty said.
"This is the first trial to reach its primary outcome as stipulated, in reducing the rate of cognitive decline. So, it's quite exciting.
"But let me emphasise it's not a magic bullet."
Professor Brodaty said trial participants declined by about half a point less than the people not on the drug.
"So they were able to able to stay about five months ahead of the person on placebo in an 18-month trial," he said.
There are also concerns about some side effects experienced by patients in the trial.
"Some people get swelling of the brain and some people get micro haemorrhages," Professor Brodaty said.
"Some people on placebo get micro haemorrhages, too, but [on the drug] it's about double the rate."
The NEJM research paper concludes that "longer trials are warranted to determine the efficacy and safety of Iecanemab in early Alzheimer's disease".
Two patients who took part in the trial also died during the study.
Investigators have not linked the deaths to the treatment itself, however, it has led to questions about the wider use of the drug, especially in people who may be taking multiple medications.
Professor Peter Schofield is the chief executive of Neuroscience Research Australia and thinks it's an exciting finding for the advancement of medical research.
"I'm an optimist," he said. "This is the first of the new generation of Alzheimer's drugs that has actually shown improvements in cognition, a slowing of decline — not a huge impact — but the first drug to actually show that.
"Some will say, 'Well, it's not a big effect, therefore, how big a breakthrough is this?' And I understand exactly where those people come from. But you've got to start somewhere."
FDA approval pending
Professor Brodaty anticipates the findings will lead to further fine-tuning of drugs targeting the amyloid protein.
"I think we're still going to need a lot more innovation to get past that threshold and lead to more significant effect, reduced frequency of dosing, less side effects," he said.
"You've got to sort of have the conceptual pathway open and then, all of a sudden, more people will join that pathway, looking to see what they could bring forward as innovation."
The United States Food and Drug Regulator (FDA) is weighing up whether or not to grant approval for the use of lecanemab.
Professor Brodaty suspects that will happen.
"But antibody drugs are expensive biologicals," he said, "and, so, it's one thing to have approval. It's another thing to be in broad common use and very affordable."
