Experts hope these changes will be matched by improvements in memory and functioning, with an 18-month trial of 1600 patients now under way.
Separate research will examine whether the drug could be given to people without any signs of dementia, in the same way that statins are used to ward off heart disease.
Today, experts said the findings were “very promising”, suggesting that the drug was much more powerful than existing medications, with far fewer side effects.
Around one million people in the United Kingdom suffer from dementia, with Alzheimer’s disease the most common form.
Powerful precise effects at low doses
Trontinemab is one of a class of new medicines aimed at clearing amyloid plaques. The new findings from phase two trials suggest that, in less than seven months, it has outperformed the ability of existing drugs to clear plaques in 18 months.
Experts hope that if given early enough, the drug could save some patients from developing symptoms at all.
It has been engineered to more easily cross the blood-brain barrier, meaning it can ensure powerful precise effects at low doses.
The lack of side effects means it could be offered to large populations.
This also means it could be offered at a far lower price than current medications, which require intense monitoring, including regular scans.
Experts believe it could become the first Alzheimer’s drug to be funded by Britain’s health service.
Last year, medicines regulators in the UK gave the green light to the first two treatments found to slow progression of Alzheimer’s disease.
Both lecanemab and donanemab use monoclonal antibodies to clear amyloid plaques in Alzheimer’s disease.
In trials they have been found to slow decline by 27% and 35% respectively, over 18 months. However, the risk of brain swelling and brain bleeds means they need intense monitoring.
The new drug appears to have a far better safety profile. The phase two trial of 149 patients found less than 5% of cases suffering amyloid-related imaging abnormalities, and all cases quickly resolved.
It also requires less frequent infusions, with mass trials to examine the impact of giving the drug to patients once a month for six months, then every three months.
Scientists have been intrigued by the promise of trontinemab because of the way it has been designed to be transported across the blood brain-barrier, which normally prevents chemicals in the bloodstream from entering the brain.
‘Game-changing’
Professor Sir John Hardy, the chairman of molecular biology of neurological disease at University College London’s Institute of Neurology said the advance could be “game-changing”.
He told the Telegraph: “This is absolutely great news. It sucks the plaque out of the brain really quickly, much faster than we have seen with lecanemab or donanemab.”
The scientist, who was the first to identify the role of amyloid in the disease, said the drug’s safety profile was a “massive improvement” on the current drugs on the market, raising hopes it could be used both to prevent disease and stop it in its tracks.
He said: “There is no doubt this could be game-changing. We hope that if we can use these drugs to people early, we can halt the progression of disease, even before people have symptoms. Now we need to see the size of the clinical effect.”
Neither of the current drugs have been funded by the UK health service as a result of their high costs, much of which stems from the need for intense monitoring, including regular scans.
Hardy said: “These results show it is much faster and safer than previous drugs, which means less monitoring”.
“That brings down the cost significantly, it means fewer MRI scans, so that would surely mean it would get Nice [National Institute of Health and Care Excellence] approval.”
‘Very promising evidence’
Professor Jonathan Schott, the chief medical officer at Alzheimer’s Research UK said: “We urgently need a range of treatments for Alzheimer’s that are effective and safe for the people affected by this devastating disease”.
“Evidence presented at the Alzheimer’s Association conference in Toronto on trontinemab is very promising, showing that the drug can effectively and rapidly clear amyloid from the brain, seemingly with very few side effects.
“We now need to see whether these early stage results carry through to later stage clinical trials, which are planned to start later this year, including in the UK. These trials will show whether the drug is not only safe, but impacts on memory, thinking and quality of life.”
He said it was “exciting” that the drug would now be tested in some people without symptoms under the phase three trials.
Levi Garraway, Roche’s chief medical officer said: “Combining new treatment avenues with advanced diagnostics may enable earlier and potentially more effective intervention”.
“With plans for phase three trials in both early symptomatic and preclinical Alzheimer’s disease, we are advancing science with the goal of delaying – and ultimately preventing – progression of this devastating condition.”
