A new drug which could halt the progression of Alzheimer's has been hailed the “beginning of the end” in the search for treatment after it reduced memory decline among patients with early stages of the disease.
Lecanemab, which is designed to target and clear amyloid — a protein that builds up in the brains of people with Alzheimer's — was found to slow the decline in patients' memory and thinking.
The phase-three clinical trial results have been reported by Eisai, a pharmaceutical company in Tokyo that has teamed up with US biotech firm Biogen to develop lecanemab.
Eisai reported initial results in September from a trial involving 1,795 patients with early Alzheimer's disease, showing the drug delayed deterioration by about five months over the course of the study.
But concerns have been raised about side effects after two deaths in the trial.
Scientists found that after 18 months the drug slowed disease progression by 27 per cent compared with patients taking a placebo.
Full results have been published in The New England Journal of Medicine, with experts hailing it as long-awaited proof that Alzheimer's can be treated.
Prof John Hardy, group leader at the UK Dementia Research Institute at University College London, who was at the Clinical Trials on Alzheimer’s Disease conference in San Francisco on Tuesday where the news was announced, said there was a "real sense of celebration" among scientists.
"I was a young guy when we made the findings with our colleagues that led us to think this was how the disease came about," Prof Hardy told Radio 4's Today show. "So yes, I am relieved and of course really pleased. There was really an air of celebration among everybody at the meeting last night.
"I think everyone in the whole field is really delighted."
While not involved in the development of the drug, Prof Hardy's team helped prove the build-up of amyloid was implicated in the development of Alzheimer's by spotting a mutation in the amyloid gene among a group of family members affected by the disease.
"What the drug does is it kind of pumps up the immune system so your immune system removes the amyloid from the brain," he said.
"It’s really only the first or the second drug to remove amyloid from the brain and that, after a while, starts to slow the disease process down."
He said the trial was an important first step that represents "the beginning of the end" of the fight against the disease.
“The first step is the hardest and we now know exactly what we need to do to develop effective drugs," he said. "It's exciting to think that future work will build on this and we will soon have life-changing treatments to tackle this disease.”
He said data suggested it was possible the drug works better the longer you take it.
"We don’t know that yet but that’s how the data looks," he said.
US regulators could approve the drug as soon as January. Prof Hardy said he expected lecanemab to be available to the British public within two years, if it is deemed effective by authorities.
However, experts stressed that more work was needed to investigate the drug's side effects.
Results showed 17.3 per cent of patients for whom the drug had been administered experienced brain bleeding, compared with 9 per cent of those receiving a placebo.
And 12.6 per cent of those taking the drug experienced brain swelling, compared with only 1.7 per cent in the placebo group.
Shares in the Japanese drug maker fell more than 6 per cent on Tuesday after reports that a woman in the Alzheimer's trial had died from a brain haemorrhage.
The haemorrhage occurred after the woman suffered a stroke and was given a medicine known as tissue plasminogen activator (tPA) to clear blood clots, the journal Science.org reported on Sunday.
Some analysts said it was not clear if use of the lecanemab was raising the risk of bleeding, and cautioned against the use of blood thinners with the drug.
"We think the interpretation that lecanemab is the causative factor is aggressive," said Brian Skorney, research analyst with Baird. "This patient clearly went into crisis following tPA administration."
It was the second media report of a death among patients who were enrolled in the lecanemab trial after a man in his 80s who was receiving a blood thinner died in June.
Prof Hardy said side effects should be monitored "but it’s not something that caused people running the trial to take people out".
"I don’t think it’s something that’s going to stop the drug from being useful."
Hope that sufferers could have more time with loved ones
Bart De Strooper, director of the UK Dementia Research Institute, said lecanemab was the first drug that provided "a real treatment option for people with Alzheimer's".
And Stephen Salloway, a study investigator and neurology professor at Warren Alpert Medical School of Brown University, said: “It takes it out of the untreatable category."
Dr Richard Oakley, associate director of research at UK charity Alzheimer's Society, said the results had the potential to be “game-changing”.
“They give us hope that in the future people with early Alzheimer's disease could have more time with their loved ones,” he said.
There are two ways to tell whether there is amyloid on the brain — a brain scan or biomarker test which is currently done through lumbar puncture.
While a blood test is on the horizon, dementia services must rely on current tests, which are expensive and can have long waiting lists in places such as the UK.
Private patients and those living near to big dementia services can access these diagnostic tests, but the vast majority of the public cannot, experts said.
They warned that unless there are major changes in diagnostic services, people could become ineligible for lecanemab treatment while on the waiting list for diagnosis because it can only be given to patients with mild forms of the disease.
If their disease progresses to a moderate stage while on the waiting list, they will no longer be eligible for treatment.
Prof De Strooper said: “The participants of this trial were all people with very early-stage Alzheimer's disease, which raises the question of how we ensure that people can access these drugs at the right stage in their disease course.
“In parallel, we must focus on making early diagnosis easier and more accessible, so that treatments can be administered when they are most likely to have a positive impact, before amyloid levels are too high and start to cause damage to the brain.”