Could existing drugs provide new treatments for Parkinson’s?
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At Parkinson’s UK, we receive a lot of enquiries from people who have heard about the possibility of drugs for other conditions being beneficial for people with Parkinson’s. We’re asked if these drugs could help and why they are not being offered by doctors or specialists. So, what needs to happen before a repurposed drug becomes available for people with Parkinson’s?
Developing new treatments is a slow and expensive process. First, basic research must reveal the biological causes of a condition, identifying what is going wrong and how it may be corrected. Chemical specialists then painstakingly develop molecules to target the specific parts of a cell that are affected, and then turn these molecules into drugs. And finally, any potential drugs must go through three phases of clinical trials before they are licensed.
Drug repurposing involves testing a drug that is already approved for one condition for its potential to treat another. For example, Aspirin is one of our oldest drugs for treating fever and pain, but has been shown to have other powerful effects — such as reducing the risk of heart attacks and stroke.
And more recently, we’ve shared news about a diabetes drug, called exenatide, that may also have potential for Parkinson’s.
As these drugs have already been developed and tested in people, this may mean they become available more quickly, easily and cheaply. But while repurposing drugs can make the research process a lot quicker, it cannot be skipped altogether.
Why do approved drugs need to go through clinical trials?
When recruiting people to participate in clinical trials, researchers have specific criteria for who can take part. Researchers will be looking for people with a certain condition, of a certain age and who may have specific symptoms. So, while an approved drug will have been shown to be safe in clinical trials, the drug will have only been tested in a small proportion of people and may not be safe for everyone.
For example, most drugs approved for the treatment of hallucinations are dopamine blockers — they have been tested and found to be safe in clinical trials. But, as there is not enough dopamine in the brains of people with Parkinson’s, this treatment could make Parkinson’s symptoms worse.
Another consideration is how long someone will need to take the drug for. Some drugs may be safe to take short term but have side-effects, or become less effective when taken for longer periods, which would likely be needed to treat Parkinson’s. Drugs may also interact with each other — reducing the effectiveness of other medications or causing unwanted side-effects.
So even approved drugs need to go through clinical trials to make sure they are safe for people with Parkinson’s. However, for repurposed drugs, this can be a much quicker process. We already know much about these drugs so they may move into the later phases of trials more swiftly.
How do you find drugs that may be repurposed for Parkinson’s?
There are a number of ways repurposed treatments have been identified. And researchers continue to use these techniques to identify other promising drugs so they can be moved rapidly into clinical trials.
- Observational studies
Many people will take drugs for more than one condition. This can lead to some people noticing the effects of other drugs on their symptoms. Health care professionals have also noticed patterns in people with Parkinson’s who are taking other treatments.
One doctor noticed that a group of Parkinson’s patients were progressing more slowly than others. Intrigued, the doctor investigated and found that this group were all being treated for cancer, and were taking a drug to boost their immune system following chemotherapy. This lead to interest in the drug, sargramostim, and it’s potential for treating Parkinson’s.
A Phase 1 clinical trial in people with Parkinson’s has been conducted, where the drug was shown to be well tolerated and have modest benefits for movement. The drug now needs to be investigated further in larger studies.
- Population studies
Promising drugs for Parkinson’s have emerged from trends in other research areas. For example, one study found that people who were taking a drug for high blood pressure were less likely to go on to develop Parkinson’s.
The drug blocks calcium from entering cells in the brain, and excess calcium is thought to contribute to the loss of nerve cells in Parkinson’s. A phase 2 clinical trial showed the drug to be safe for people with early stage Parkinson’s. And now a phase 3 trial is underway, in which researchers are testing whether the drug could be used as a treatment to slow down the progression of Parkinson’s.
- Basic science
Scientists are studying the underlying biological mechanisms that are altered in Parkinson’s. If changes associated with the condition are identified, it may be possible to find existing drugs that can target what is going wrong. However, the blood-brain barrier blocks many compounds from entering the brain, including many drugs that are effective for other conditions. So, an additional challenge is to find drugs than can reach the brain cells that are being lost in Parkinson’s.
An example of this came from the discovery that people with Parkinson’s have more iron in their brains. Excess iron can cause damage to cells, so this finding lead to an interest in iron chelators, molecules that bind to iron to stop the iron damaging cells, as potential drugs for Parkinson’s.
However, iron has important roles in parts of our cells and bodies, and iron chelators can cause side effects. A Parkinson’s UK funded project is currently exploring if it is possible to remove iron from specific sites within cells where it is causing problems.
- New computational biology techniques
A number of new technologies are helping in the search for potential drugs to repurpose. From robots that automate and speed up research to test thousands of licenced drugs for their potential in Parkinson’s, to databases that connect our knowledge about Parkinson’s to the drugs that are already out there.
Earlier this year, a research team at the Oxford Parkinson’s Disease Centre developed a new way to identify drugs that could be repurposed for Parkinson’s. The team used a stem cell technique to create dopamine-producing brain cells, identical to those lost in Parkinson’s, from the skin cells of people with Parkinson’s. They compared the gene activity of these cells to brain cells grown from people without the condition, and noticed some key differences. The researchers were then able to search a database for drugs that may alter the gene activity in Parkinson’s cells to make it more like the unaffected cells, i.e. drugs that may be suitable for repurposing for Parkinson’s.
Repurposing to deliver better treatments quicker
Current Parkinson’s medications do not slow-down the loss of, or repair, the brain cells affected in the condition. And we know that people with Parkinson’s need better treatments faster.
That’s why we’re funding a number of repurposing projects. One is looking at whether chemical messengers other than dopamine, such as GABA, may be depleted in people with Parkinson’s. If this is the case, drugs that mimic the effects of GABA, such as those currently used to treat insomnia, may be beneficial for people with Parkinson’s.
Another project is investigating whether drugs that help memory and thinking in Parkinson’s might also be useful for preventing falls, which is the number one priority area for research for improving the quality of life of people with Parkinson’s.
There is also a global effort to find these potential treatments, and progress towards testing repurposed drugs is being made. As well as exenatide, there are a number of other repurposing projects to keep an eye on: two dementia drugs, Trazodone and rivastigmine, and a cancer drug, nilotinib, are currently being tested in people with Parkinson’s.
As always, we’ll be keeping a close eye on developments in this area and reporting on any advances. You can stay connected with the latest developments with the Research Support Network.
