Coordinated global trials show prasinezumab slows motor progression in rapidly advancing Parkinson's

The quest to slow down the progression of Parkinson's has taken a significant step forward with the latest findings from two major clinical trials, PASADENA and PADOVA. For years, therapies have focused primarily on managing symptoms rather than altering the course of the condition itself. However, the development of prasinezumab, an antibody designed to target and bind to clumping proteins in the brain called alpha-synuclein, represents a fresh approach to tackling the root biology of the condition. This clinical journey represents a major, coordinated international effort led by the Swiss pharmaceutical company Roche in collaboration with the biotechnology firm Prothena. Together, they have moved the antibody through multiple rigorous testing phases across global research sites to see if it can alter the future of living with the condition. The initial Phase 2a PASADENA trial began enrolling participants in 2017, focusing on 316 people with very early-stage Parkinson's who were not yet taking standard dopamine-replacing medications. The study set out to evaluate how well monthly intravenous infusions of either a 1,500 mg dose of prasinezumab or a placebo could slow progression over the first year. While the study did not meet its main overall target across all participants initially, researchers noticed a fascinating trend. A closer look at the data revealed that prasinezumab successfully slowed down the worsening of movement-related symptoms in a specific subset of people, particularly those whose symptoms were progressing more rapidly or those already taking standard maintenance therapies. Building directly on these insights, researchers launched the larger Phase 2b PADOVA study in May 2021. This second trial expanded the scope to 586 participants across multiple international sites, zeroing in specifically on individuals with early-stage Parkinson's who were already on a stable, single symptomatic medication, such as levodopa or MAO-B inhibitors. By focusing on this group, the trial provided a much clearer picture of the antibody's potential. The methodology for these studies paired traditional clinical observations with modern digital monitoring tools over an 18-to-24-month period. To measure physical effects, investigators tracked changes through the standard Movement Disorder Society-Sponsored Unified Parkinson's Disease Rating Scale Part III, which rates physical movement. Crucially, the trials also used smartphones and wearable sensors to continuously track passive data, like walking speed and hand tremors, during daily life. Both the active physical assessments and the passive digital tracking confirmed that prasinezumab successfully slowed motor symptom progression. Long-term data presented at the AD/PD 2026 International Conference in Copenhagen, Denmark, provided an even clearer picture of the therapy's potential. Five-year data from the open-label extension of the PASADENA trial, where all remaining participants received the active drug, showed a sustained slowing of motor decline. By using mathematical models to compare these individuals against an external cohort from the Parkinson's Progression Markers Initiative, researchers calculated that long-term treatment resulted in an average of two years of progression avoided. Additionally, advanced MRI imaging from the PADOVA study offered the first biological evidence of the antibody's activity, showing a visible slowing in the loss of neuromelanin within the substantia nigra, the brain region most affected by the condition. What have we ultimately learned from PASADENA and PADOVA? Designing trials to prove a therapy can modify a condition like Parkinson's is incredibly complex because symptoms and progression rates vary naturally from person to person. While prasinezumab is not a cure, these trials demonstrate that targeting alpha-synuclein can meaningfully delay the worsening of physical movement. The success in the PADOVA study underscores the importance of precision in clinical design, proving that identifying the right window of time and the right group of people is the key to unlocking therapies that can slow down progression. To firmly establish these findings, a definitive Phase III trial named PARAISO has now been initiated. This study uses a refined goal, focusing explicitly on the length of time a person can avoid reaching a confirmed stage of motor progression, and is scheduled to run through June 2029.