Parkinson’s disease (PD) is a chronic progressive disorder with a high unmet need for disease-modifying therapies (DMTs). However, there are significant challenges in the development of these therapies, as discussed in several sessions at the AD/PD 2022 International Conference on Alzheimer’s disease (AD) and PD.

A key challenge in the development of DMTs for PD is the lack of meaningful endpoints that are able to measure early changes in disease progression. Potential DMTs are likely to have the greatest impact on disease progression the earlier they can be administered. However, although PD is a progressive disorder, the rate of change is slow during the early stages of the disorder – when administering a DMT would be most beneficial, making it hard to measure the effects of such a treatment. Further, the well-established endpoints used in PD trials such as the Movement Disorder Society’s revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS), are focused on the later stages of the disease and so are not suitable for measuring changes early in disease progression. Therefore, there is a significant unmet need for the development of novel endpoints to better assess progression in early-stage patients and to aid in the development of DMTs for PD.

Despite this unmet need, one solution to assessing potential DMTs in early-stage patients is to use the current endpoints in new ways that are more sensitive to changes in early PD. For example, instead of looking at changes from baseline in MDS-UPDRS Part III, evaluating the time to a greater than a five-point increase in MDS-UPDRS Part III score provides a more meaningful measure of worsening motor function in early PD. Another challenge for PD drug development is that symptomatic therapies can mask the effects of the investigational DMT, and it has recently been demonstrated that the time-to-event approach can help to mitigate this effect.

One important aspect of PD pathophysiology is the fluctuating symptoms experienced by patients. This presents a further challenge for investigators trying to capture the effect of an investigational drug through traditional methods of assessment during infrequent clinic visits. To overcome this, developers are looking to digital technologies that will allow for the continuous remote monitoring of patients, potentially enabling a more accurate analysis of treatment effects. For example, Roche has developed a smartwatch to passively measure aspects of motor function such as mobility and gait, as well as a mobile application that actively measures motor function through targeted tests including those for dexterity and tremor severity.

Lastly, a key aspect in the clinical trials for DMTs in AD is the measurement of biomarkers to help demonstrate clinical benefit. Biogen’s Aduhelm (aducanumab) was actually approved by the FDA based on the surrogate endpoint of amyloid-beta clearance rather than meeting a clinical endpoint. However, in PD, the development of biomarkers is still at a very early stage with no biomarkers being routinely used in clinical trials. Therefore, there is a key unmet need for biomarkers for PD that can be used as markers of disease progression that will aid developers to demonstrate meaningful effects of DMTs.