Prasinezumab is a potential therapeutic drug currently working its way through the clinical trial pipeline. It is also one of the few disease-modifying therapy candidates for Parkinson’s that has made it to Phase III trials. This marks an exciting time in Parkinson’s research, with several promising treatments now in the final stage of clinical trials, including prasinezumab, bemdaneprocel, and the repurposed drug ambroxol. 

Overview 

Q: What is prasinezumab?  

A: It’s a monoclonal antibody drug developed by Roche that targets toxic alpha-synuclein proteins in the brain. These are proteins that are believed to play a key role in the development and progression of Parkinson’s.  

Q: Why is prasinezumab significant?  

A: If successful in this clinical trial, it could become one of the first disease-modifying treatments for Parkinson’s. That means it could potentially slow down, stop, or even prevent the biological changes that cause Parkinson’s, rather than just treating the symptoms 

Read more about disease-modifying therapies in this blog post. 

Clinical trials: Where are we now? 

Q: What stage of clinical testing is prasinezumab in?  

A: As of June 17, 2025, prasinezumab has entered Phase III clinical trials. This is the largest and most comprehensive stage before potential regulatory approval of a drug.  

Q: How does Phase III differ from earlier phases?  

A: Phase III involves large-scale testing in large numbers of volunteers, focusing on safety, side effects, and definitive evidence of effectiveness that is necessary for regulatory approval. 

Q: What did earlier trials show?  

A: The Phase II trials, known as PASADENA and PADOVA, showed promising signs, with participants treated with prasinezumab progressing more slowly in motor symptoms. The effects were strongest in individuals early in their Parkinson’s progression. 

Q: How many other potential disease-modifying therapies are in Phase III trials? 

A: Currently, there are four disease-modifying therapy candidates in Phase III trials for Parkinson’s. Studies of ambroxol and lactobacillus acidophilus are unique in that they are investigating existing therapeutics that are already used for other conditions. Prasinezumab and bemdaneprocel are the only drugs originally developed to address Parkinson’s that are in Phase III trials. 

How it works 

Q: How does prasinezumab work?  

A: Prasinezumab binds to misfolded alpha-synuclein proteins, preventing them from aggregating (i.e., clumping together) and spreading in the brain. This may protect the neurons that produce dopamine (cells that are gradually lost in Parkinson’s). 

Q: Why target alpha-synuclein?  

A: Accumulation of alpha-synuclein into harmful clumps is a hallmark of Parkinson’s.  This approach is similar to recent strategies used in Alzheimer’s research, where targeting protein build-up (like beta-amyloid) has led to the first approved disease-modifying treatments. 

Future outlook 

Q: When will we know if it works? 

A: Phase III trials are typically lengthy; no exact timeline or enrollment details are available yet, so it will likely be at least several years before results are known.  

Q: What if the trial isn’t successful?  

A: Even if prasinezumab fails to show disease-modifying benefits, it will still provide valuable data. It may help researchers better understand the role of alpha-synuclein in Parkinson’s and inform the design of future therapies. 

More to know 

Q: What’s the difference between disease-modifying and symptomatic treatments? 

A: Disease-modifying therapies target and alter the underlying biological process contributing to Parkinson’s (e.g., protein aggregation), whereas symptomatic treatments manage symptoms without changing the progression of Parkinson’s.  

Q: Are there other drugs targeting alpha-synuclein?  

A: Yes; multiple organizations and researchers are investigating alpha-synuclein antibodies, vaccines, and small molecules, including researchers supported by Parkinson Canada. 

As the Parkinson’s community watches the progress of prasinezumab and other potential therapies, one thing is clear: we’ve entered a new and hopeful chapter in the search for treatments that not only manage symptoms, but fundamentally change the course of the condition.