Drug repurposing: Turning existing drugs into new dementia treatments

Currently, there is no cure for dementia, despite it being the UK’s biggest killer. We urgently need new treatments for this devastating condition, but developing them from scratch can take many years, cost billions of pounds and can end in failure when treatments don’t prove safe or effective. 

That’s why researchers are exploring a faster, more cost-effective route to new dementia treatments. This approach tests whether existing, safe medicines could be adapted and used to treat dementia. 

What is drug repurposing?

Drug repurposing means taking medicines that already exist and are approved for treatments of other conditions and testing them to see if they could also work as dementia treatments. 

Because these medicines have already passed safety tests and are often routinely prescribed, so doctors are familiar with how they work and what side effects they may cause. This makes them an good option for dementia research. 

By building on what we already know about the existing drugs, and adapting them to treat dementia, researchers can save time and resources compared to developing brand-new medicines from scratch. This offers a faster, more cost-effective way to finding potential new dementia treatments.

Why try it for dementia?

Dementia the UK’s biggest killer and right now there is no cure. Dementia is caused by a mix of complex changes in the brain, which including inflammation, problems with how brain cells communicate and damage to blood vessels that supply the brain with oxygen and nutrients. But many of these same processes also play a role in other diseases, for example, inflammation we see in arthritis or the blood vessel damage found in heart disease.

This overlap in disease processes means that some existing medicines, which were originally developed for other conditions, may already target the same biological processes that go wrong in dementia. If these drugs can also help protect brain cells or slow down the damage, they could be adapted as effective dementia treatments.

By testing these existing, already-approved medicines, researcher can take a faster and more effective route toward finding new dementia treatments. 

How repurposing studies work 

Drug repurposing usually follows a series of careful steps, from identifying potential targets in the brain to testing promising drugs in people. Here’s how this process works:

1. Spot the target

Researchers start by studying what happens in the brains of people with dementia, such as damaged brain cells or problems with how cells communicate. They will then look at any existing medicines already used for other conditions to see whether they could target the same problems and help protect the brain or slow down dementia. 

2. Check real-world evidence

Next, scientists look at health records or previous studies to see if people already taking these drugs for other conditions seem to have lower risk of dementia, or better memory and thinking over time. This real-world evidence offers valuable early clues about which drugs might be worth testing further. 

3. Test in the lab

Promising drugs are tested and studied in the lab, using brain cells grown in dishes or animal models that mimic dementia. This helps researchers to understand whether these drugs can protect brain cells or prevent damage and confirm that they are safety to use in this new way.

Recently, we commissioned and funded research by Professors Anne Corbett and Clive Ballard at the University of Exeter to identify existing drugs from that could be repurposed for dementia. After a careful review, three drugs were selected for their relevance to Alzheimer’s disease processes, and showed promising results in lab and animal studies:

• Shingles vaccine – may help the immune system protect against changes seen in Alzheimer’s.
• Sildenafil (Viagra) – shown to protect brain cells and reduce harmful protein build-up in the brain.
• Riluzole – currently used for motor neurone disease, it could improve memory and thinking skills while reducing harmful protein build-up in the brain.

Findings from this study will guide researchers in designing future clinical trials to determine whether these drugs could help treat or prevent Alzheimer’s disease.

4. Run small clinical trials

If the lab results look promising, researchers move on to small clinical trials. During this stage, researchers carefully test the drug in a small group of people with dementia to see if it improves memory and thinking skills or slows the progression of the disease.

For example, we’re funding research led by Professor Philip Bath, who is investigating whether two drugs already used for other conditions can improve blood flow to the brain in people with small vessel disease – a key factor in vascular dementia.

This early trial will help the researchers gather evidence on whether these drugs are effective and safe in this context. If it’s successful, the results could be used to run larger trials and, eventually, bring these medicines into clinical use to help prevent vascular dementia.

5. Scale up the clinical trials

Finally, if the early results look good, then larger and longer clinical trials are carried out to confirm who benefits most, the right dose to use, and the best time to start treatment. Only after the drug passes these rigorous tests, it can be repurposed and submitted to regulators for approval as a new dementia treatment. 

An example of a drug in this stage is semaglutide, which has the brand names Ozempic and Wegovy. Originally used to manage type 2 diabetes and aid weight loss, semaglutide may also have positive effects in the brain, such as reducing inflammation and protein build up. Semaglutide is currently being tested in clinical trials as a potential treatment for Alzheimer’s disease.

Professor Fiona Carragher, Chief Policy and Research Officer at Alzheimer’s Society, said: 

"Dementia devastates lives, but we believe research will beat it. 

Years ago, we saw aspirin being repurposed from being a painkiller to helping people reduce their risk of heart attack or stroke. This is what we want to see in the field of dementia. 

We believe drug repurposing is one of the most exciting frontiers in dementia research.