In February 2019, the results of the phase 2 Bristol study investigating the use of a neurotrophic factor called GDNF (Glial cell-derived neurotrophic factor) in people with Parkinson’s were published in the research journals ‘Brain’ and the ‘Journal of Parkinson’s Disease‘. 

This ground-breaking trial involved the mechanical delivery of this experimental treatment directly into the brains of people with Parkinson’s in an attempt to rescue and restore damaged neurons.

While this clinical trial of GDNF did not meet its primary endpoint (this is a pre-determined measure of efficacy), there were some very interesting findings. The brain imaging data, for example, suggested that GDNF was having a biological effect in the brain. But importantly the clinical findings of the study did not mirror the participant’s experience in terms of benefit. Examples of this were demonstrated in the award winning BBC2 documentary: The Parkinson’s Drug Trial: A Miracle Cure?.

As a result, the interpretation of all the results of this trial has been challenging. 

Cure Parkinson’s has been involved in and has championed the GDNF story since 2003 through the commitment and determination of the charity’s late co-founder and president Tom Isaacs. Cure Parkinson’s has been working with research partners and the Parkinson’s community to address some of the uncertainties and issues raised in the GDNF trial and to explore the appropriate pathway forward.

What progress has been made since the Bristol trial?

Research community consensus

Cure Parkinson’s asked Professor Roger Barker of the University of Cambridge to chair a ‘closed’ meeting of international key opinion leaders with direct knowledge and practical experience in the field of GDNF and associated neurotrophic factors. The goal of the meeting was to bring together the wide range of views to identify and agree on what is known pre-clinically and clinically about GDNF, and what still needs further investigation in the field. It is from consensus and a strong scientific foundation that we will be able to find a pathway forward.

In the light of the GDNF trial results, it was important to bring together all the teams internationally that have worked with GDNF over the last 25 years to better understand how to take this therapy and related compounds forward for the benefit of people with Parkinson’s. 

Helen Matthews, Deputy CEO – Cure Parkinson’s

The meeting took place in 2019 kindly hosted by Van Andel Institute, and Cure Parkinson’s was joined by other key Parkinson’s funding agencies: Michael J Fox Foundation, Parkinson’s UK and the NIH. The meeting also included GDNF trial participant Eros Bresolin and Lyndsey Isaacs, who supported her late husband and trial participant Tom Isaacs. Tom championed GDNF, leading to the recent Bristol trial. A summary of the discussions at that meeting were published in the Journal of Parkinson’s. 

Clinical outcomes

The clinical outcomes, that are used to evaluate the progression of Parkinson’s, remain an important focus. Many of the participants in the Phase II Bristol trial of GDNF felt their clinical scores did not reflect some of their experiences. Cure Parkinson’s and researchers involved in the GDNF study conducted more in-depth analysis of the entire study dataset to determine whether there might be combinations of clinical measures that could be brought together to offer a more insightful way to demonstrate any therapeutic effect. The result of this effort is a new composite measurement scale, called PDCORE.

I am delighted to work with the outstanding team of co-authors of the PDCORE paper who, using a most original approach, successfully re-analysed a complex collection of patient data to produce a completely new way evaluating the clinical progress of patients with Parkinson’s.

Dr Richard Wyse, Director of Research and Development – Cure Parkinson’s

The researchers stress that this type of ‘post-hoc’ analysis is NOT intended to provide evidence that GDNF demonstrated efficacy in the Bristol study. Rather they have very carefully analysed the available data with the goal of identifying a superior way to evaluate Parkinson’s patients which is likely to be useful in evaluating therapies, like GDNF, in future trials. This study paper was published in the medical journal Brain.

In addition to these advances , further efforts are being made to progress neurotrophic factor-based clinical research for Parkinson’s. COVID-19 has delayed activities but a new clinical trial testing a GDNF-based gene therapy approach in individuals with Parkinson’s is getting underway. In addition, the biotech company Herantis Global engineering technologies company Renishaw has announced that its drug delivery device, neuroinfuse™, has continued to safely and effectively deliver infusions as part of an extension to a first-in-human clinical trial of cerebral dopamine neurotrophic factor (CDNF). This device was the same used in the recent, Cure Parkinson’s-supported Phase II GDNF trial in Bristol. This phase 1-2 clinical study of CDNF, carried out jointly with Herantis Pharma plc, investigated the safety and performance/tolerability of CDNF and neuroinfuse, as a treatment for Parkinson’s disease.

Cure Parkinson’s continues to explore every opportunity for neurotrophic factors in Parkinson’s and will persevere within this field of research until this condition is cured!