The D₁/D₅Dopamine Partial Agonist PF-06412562 in Advanced-Stage Parkinson's Disease: A Feasibility Study

Background: Current drug treatments have little efficacy in advanced-to-end-stage Parkinson's disease (advPD), yet there are no reports of interventional trials in advPD. D1 dopamine agonists have the potential to provide benefit. Objective: To determine the feasibility and safety of the selective D1/D5 dopamine partial agonist PF 06412562 in advPD. Methods: A two-week, randomized, double blind, crossover phase Ib study in advPD patients compared standard-of-care (SoC) carbidopa/levodopa with PF 06412562. Each week, there was a Day 1 baseline evaluation with overnight levodopa washout, then treatment on Days 2 and 3 with either SoC or PF-06412562 (split dose 25+20mg), followed by discharge on Day 4. Primary endpoints were safety and tolerability. Secondary endpoints were global clinical impression of change (GCI-C) rated by clinicians and caregivers. Results: Eight advPD patients and their caregivers consented to participate and six were randomized (average disease duration: 22y). None withdrew voluntarily. One participant with baseline Day 1 dehydration, pre-renal kidney injury, and autonomic dysfunction experienced symptomatic and serious hypotension after receiving PF-06412562 in Week 1 and was discontinued from the study. All other adverse events were rated mild (PF-06412562: n=1, SoC: n=0), moderate (PF-06412562: n=1, SoC: n=1), or severe but non-serious (PF-06412562: n=3, SoC: n=2). No clinically meaningful laboratory changes were observed. Among the five participants who completed the study, GCI-C favored PF-06412562 in two per clinicians' and four participants per caregivers' rating. Conclusion: PF-06412562 was tolerated in advPD patients. This study provides the feasibility for future safety and efficacy studies in this population with unmet needs.