Tyson Haller, carrying a family history of Alzheimer's, participates in the AHEAD 3-45 study to evaluate lecanemab's potential in preventing the onset of the disease. This trial marks a significant step forward after decades of setbacks in Alzheimer's drug development. The study is based on the hypothesis that intervening early, before significant cognitive decline, may yield better outcomes.
Lecanemab's Mechanism and Clinical Data
Lecanemab, marketed as Leqembi, is a monoclonal antibody targeting beta amyloid plaques, a hallmark of Alzheimer's disease. These plaques are believed to trigger a cascade of events leading to brain cell death. The drug has already received approval in the United States, Japan, and China for patients with mild cognitive impairment or mild dementia due to Alzheimer's. Regulatory decisions are pending in Canada, the UK, and Europe.
The phase 3 CLARITY-AD study demonstrated that lecanemab slowed cognitive and functional decline by 27% compared to placebo over 18 months (p<0.05). Patients on lecanemab experienced 0.45 points less decline on an 18-point clinical dementia rating scale. Secondary endpoints also showed significant disease-slowing, with functional decline reduced by 37%. According to Sharon Cohen, medical director of the Toronto Memory Program, the data strongly supports the premise that tackling amyloid early can slow clinical disease.
Prevention Trials and the Future of Alzheimer's Treatment
Alongside lecanemab, donanemab, another anti-amyloid medication from Eli Lilly, is also being tested for prevention in the TRAILBLAZER-ALZ-3 trial. These prevention trials, slated to run until 2027 and 2029 respectively, represent a critical juncture in Alzheimer's research. Howard Chertkow, chair in cognitive neurology and innovation at Baycrest Health Sciences in Toronto, notes that while anti-amyloid drugs represent progress, the extent of that progress remains a question.
The emergence of simple blood tests for Alzheimer's diagnosis further accelerates the possibility of early detection and intervention. Suzanne Schindler, a neurologist at Washington University School of Medicine in St. Louis, anticipates that blood tests will soon replace cerebrospinal fluid tests and amyloid PET scans for determining amyloid status.
Ethical and Practical Considerations
Despite the optimism, challenges remain. The new anti-amyloid drugs do not halt the progression of Alzheimer's but only slow it down. They are also expensive, with lecanemab costing US$26,500 per year in the US, and carry risks of brain microbleeds and swelling requiring frequent MRI monitoring. Jennifer Watt, a geriatrician-scientist at St. Michael's Hospital in Toronto, raises concerns about the cost-effectiveness of these drugs compared to other essential services for dementia patients, such as home care.
Furthermore, the U.S. Alzheimer's Association's draft framework proposing that asymptomatic individuals with amyloid buildup be designated as "stage 1" Alzheimer's patients has sparked controversy. Critics, including the American Geriatrics Society, warn of potential discrimination and question the influence of pharmaceutical companies on diagnostic criteria. Clifford Jack, an Alzheimer's researcher at the Mayo Clinic and chair of the working group, defends the framework as a necessary step in defining the biological criteria for Alzheimer's disease and separating it from other causes of dementia.
Ultimately, the success of the TRAILBLAZER and AHEAD studies will determine the future direction of Alzheimer's diagnosis and treatment. As Jason Karlawish, co-director of the Penn Memory Center at the University of Pennsylvania, puts it, the field is getting close to a place where cognitively well people with elevated amyloid levels should be diagnosed with Alzheimer's disease, but whether we are "there yet" remains to be seen.
