I’ve seen enough false dawns to take a jaded view of new breakthroughs in Parkinson’s – and with good reason. People with Parkinson’s have lived with the same tired handful of medications for too long; our best drug therapy, levodopa, is 50 years old. Apart from a handful of other drugs (dopamine agonists or inhibitors of dopamine metabolism), that’s your lot. These are drugs to treat the symptoms but nothing that will slow down the progression of the underlying illness. Such a thing would be perceived as the holy grail of Parkinson’s therapy.
Treating the symptoms is all well and good but eventually the drugs can no longer mask the underlying neurodegeneration. At that point your treatment options begin to dry up.
Until now that is. Friday’s publication in The Lancet from Prof Tom Foltynie’s group at University College London  examined the effect of once weekly Exenatide, a drug derived from the saliva of the Gila monster (I’m not making this up) on motor symptoms in Parkinson’s patients. They found a substantial and significant difference that outlasted the period of treatment by three months.
This finding is remarkable for two reasons. Firstly, it reports the first data indicating that the speed of progression of Parkinson’s can be slowed. The significance of which cannot be overstated. Nothing up to this point (and we can debate the Rasagiline data until the end of time) has shown evidence for disease modification. The paper’s authors are cautious of making such a claim; the data is nonetheless exciting.
Of course, we are used to media hype, but this is something quite different. This is a placebo-controlled clinical trial of a drug in humans. This is data with direct relevance to the wider patient community. We do not need to extrapolate. We do not need to hype the hope. The results are clear-cut. I am as jaded a scientist as you get. I’ve seen it all before. But I’m persuaded by this new dataset. I believe this is probably the first evidence of disease modification.
The second reason why this was a remarkable study is, in many respects, just as exciting. This is not the trial of a code number drug XYZ 123 at the early stage of the development cycle that may last ten to 15 years. Exenatide is a medicine that is already marketed. It is a drug for diabetes that has been repurposed for Parkinson’s.
Why is this important? It is important because we already know the medication is, in broad terms, safe. (I should at this point probably insert a long caveat about the meaning of ‘safe’ because, ultimately, nothing is absolutely safe.) Much is known about the toxicity or lack of toxicity of the drug. In essence, we can lop years off the development cycle of a new medication by using an existing one. The drug is available clinically, albeit for a different purpose, and, in theory at least, you or I could take the drug tomorrow.
So what is there to stop us? Why should we not visit our local neurologist and persuade him to prescribe it for us? Patients are understandably impatient when it comes to new medications. Many may well try to take this foreshortened path to improve their own health. In some ways it’s hard to counsel against this. With any degenerative condition, time is not on our side but we should nonetheless be cautious. We cannot be certain that the drug will behave the same way in people with PD as it does in people with diabetes.
So let’s be a little cautious… at the same time let’s rejoice in these findings. This is genuine cause for excitement – and it’s long overdue.
 Dilan Athauda, MRCP, Kate Maclagan, PhD, Simon S Skene, PhD, et al (2017) Exenatide once weekly versus placebo in Parkinson’s disease: a randomised, double-blind, placebo-controlled trial. The Lancet DOI: http://dx.doi.org/10.1016/S0140-6736(17)31585-4. Published 03 August 2017.
Dr Jon Stamford is a retired neuroscientist with Parkinson’s. For more than a decade he directed a research lab looking at the actions of drugs in Parkinson’s before being diagnosed with the condition himself in 2006. Dr Stamford was among the first group of ambassadors for the World Parkinson Congress in Montréal in 2010 and was, until retirement, Scientific and Advocate Communication Coordinator for the Cure Parkinson’s Trust and Director of Parkinson’s Movement. He is co-founder of the Parkinson’s Inside-Out group and Research Consultant for Spotlight YOPD.