Two existing cancer medications have caught researchers’ attention after experiments suggested they could help reverse some of the brain changes associated with Alzheimer’s disease. When scientists combined the drugs in mice, they observed reduced harmful protein buildup and improvements in learning and memory, offering a new direction in the search for treatments.
The medications are letrozole, commonly used to treat certain types of breast cancer, and irinotecan, which is used for colorectal cancer and some other cancers. Both are already approved by US regulators for cancer treatment, potentially making further investigation easier. However, the findings remain at the experimental stage, and human trials will be needed to determine whether the combination is safe and effective for people living with Alzheimer’s.
How Researchers Found Two Existing Cancer Drugs
Alzheimer’s disease causes progressive changes in the brain that can interfere with memory, learning and everyday activities. Developing effective treatments has proved challenging because the disease involves multiple genes, proteins and types of brain cells rather than one isolated biological problem. Researchers from the University of California, San Francisco, and Gladstone Institutes investigated whether existing medications could reverse some of these disease-related changes instead of starting drug development from scratch.
The team began by studying changes in gene expression associated with Alzheimer’s disease. Gene expression describes how cells use genetic instructions to produce molecules that influence their behaviour and function. The researchers then searched a medical database called the Connectivity Map to identify drugs that could reverse patterns associated with the disease. By comparing those findings with clinical records from people who had received cancer treatments, they identified letrozole and irinotecan as candidates worthy of further investigation.
Computational biologist Marina Sirota of UCSF explained the challenge behind the research: “Alzheimer’s disease comes with complex changes to the brain, which has made it tough to study and treat, but our computational tools opened up the possibility of tackling the complexity directly.” The approach gave the researchers a way to examine a complicated disease through several sources of biological and clinical information. However, the patient records showed an association with Alzheimer’s risk, not proof that the medications prevented the disease.
What Happened When Scientists Tested the Drugs in Mice
After identifying the two candidates, researchers tested them in mouse models of Alzheimer’s disease. The experiments examined whether the medications could influence the biological changes associated with the condition and whether those effects were accompanied by improvements in learning and memory. The results suggested that combining the drugs could produce benefits across several measures of disease-related brain damage.
The researchers observed several encouraging effects in the treated mice:
- Reduced tau protein buildup: The combination lowered the accumulation of abnormal tau proteins associated with Alzheimer’s disease.
- Improved learning and memory: Treated mice performed better on certain behavioural tasks designed to assess cognitive abilities.
- Changes in disease-related brain damage: The researchers reported improvements in measures of Alzheimer’s-associated pathology.
- Effects across different brain cells: The drugs appeared to influence separate cellular processes involved in the disease.
The combined treatment generally produced stronger results on important measures than either medication alone. The researchers also observed differences in some behavioural outcomes between male and female mice, suggesting that the effects were not identical across all animals. These findings offer a reason to continue investigating the combination, although mouse experiments cannot establish whether people with Alzheimer’s would experience the same benefits.
Why the Combination May Be More Effective
One of the most interesting findings involved the different ways the medications appeared to affect brain cells. The brain contains neurons, which transmit information, and glial cells, which help maintain the environment needed for healthy brain function. Alzheimer’s disease can disrupt both groups, contributing to the changes that affect cognition as the condition progresses.
Letrozole appeared to counter some Alzheimer’s-related changes in neurons, while irinotecan influenced disease-associated processes in glial cells. By targeting different cellular pathways, the combination may have addressed a broader range of changes than either medication could influence on its own. This approach reflects a growing research interest in understanding how several biological processes contribute to a single disease.
Neuroscientist Yadong Huang of UCSF and Gladstone Institutes explained the difficulty researchers face when developing treatments for Alzheimer’s: “Alzheimer’s is likely the result of numerous alterations in many genes and proteins that, together, disrupt brain health.” The researchers believe that examining multiple pathways together could help identify treatment strategies that better match the complexity of the disease. Further experiments will be needed to establish precisely how the two drugs interact and which effects are most important.
The Safety Questions That Still Need Answers
Although both medications are already approved for certain cancers, that does not automatically make them suitable for Alzheimer’s treatment. Their known risks and side effects must be considered in the context of a different disease, a different patient population and potentially longer treatment periods. Researchers would need to establish whether the benefits of the combination could outweigh its risks for people living with Alzheimer’s.
Several questions need to be answered before the treatment could be considered for routine care:
- Appropriate dosing: Researchers must determine safe and effective doses for people rather than relying on amounts used in mice.
- Long-term safety: Studies must examine whether taking the medications over extended periods causes unacceptable side effects.
- Meaningful cognitive benefits: Human trials must establish whether any biological improvements translate into better memory or everyday functioning.
- Individual differences: Researchers need to determine whether the combination works differently depending on a person’s biology, medical history or stage of disease.
The patient-record analysis also has limitations. The number of people who received both medications was too small to establish a conclusive statistical relationship between the combination and Alzheimer’s risk. The animal experiments provide additional evidence for investigating the drugs, but they do not eliminate the need for carefully controlled clinical studies.
People should not take letrozole or irinotecan to prevent or treat Alzheimer’s outside appropriate medical research. Both medications can cause significant side effects and require medical supervision. Their approval for cancer treatment does not establish their safety or effectiveness for a neurological condition.
Could Existing Medications Lead to New Alzheimer’s Treatments?
The next major step is to determine whether the findings can be translated into human clinical trials. Researchers would need to investigate appropriate dosing, possible interactions between the medications, side effects and whether the combination improves outcomes that matter to patients. They would also need to establish whether any benefits persist over time and whether particular groups of patients are more likely to respond.
The computational approach used in the study could also help scientists identify other existing medications worth investigating. By comparing changes in gene expression with information about how drugs affect biological processes, researchers may be able to narrow down potential treatments more efficiently. However, identifying a promising candidate is only an early step, and each proposed treatment must still pass safety and effectiveness testing.
Alzheimer’s affects millions of people worldwide, making the search for treatments that preserve memory and independence a major health priority. The findings provide researchers with a new combination to investigate and suggest that targeting several biological pathways may be useful. For now, the crucial question is whether the improvements observed in mice can be reproduced safely in people. Until human studies provide that evidence, letrozole and irinotecan remain experimental candidates for Alzheimer’s research rather than established treatments.
