Flexible-Dose Trial in Early Parkinson's Disease (PD)

Key Inclusion Criteria

• Male and female participants aged 40 to 80 years, inclusive, at the time of signing the informed consent form (ICF).
• Sexually active men or women of childbearing potential must agree to use acceptable (at minimum) or highly effective birth control, or remain abstinent during the trial and for 4 weeks after the last dose of trial treatment.
• Participants who are capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in the protocol.
• Participants with a diagnosis of PD that is consistent with the UK Parkinson's Disease Society Brain Bank diagnostic criteria.
• Participants with modified Hoehn and Yahr stage 1, 1.5, or 2.
• Participants with disease duration (from time of diagnosis) of less than ( =2 and Part III score >=10 at the Screening Visit and at the Baseline Visit.
• Participants with early PD who, in the opinion of the investigator, require pharmacologic intervention for disease management.
• Participants who are treatment naive or have a history of prior incidental treatment with dopaminergic agents (including L-Dopa and dopamine receptor agonist medications) for 90 days before the Baseline Visit and the dosage will remain stable for the duration of the trial (ie, no change in the MAO-B inhibitor dose is permitted during the trial).
• Participants who are willing and able to refrain from any PD medications that are not permitted by the protocol (including dopaminergic agents) throughout participation in the trial.

Key Exclusion Criteria

• Participants with a history or clinical features consistent with essential tremor, atypical or secondary parkinsonian syndrome (including, but not limited to, progressive supra nuclear palsy, multiple system atrophy, cortico-basal degeneration, or drug-induced or post stroke parkinsonism).
• Participants with a history of nonresponse or insufficient response to L-Dopa at therapeutic dosages.
• Participants with a history or current diagnosis of a clinically significant impulse control disorder (Disruptive, Impulse Control, and Conduct Disorder per DSM-5).
• Participants with the presence of or history of brain tumor, hospitalization for severe head trauma, epilepsy (as defined by the International League Against Epilepsy), or seizures.
• Participants with a history of psychosis or hallucinations within the previous 12 months.
• Participants who answer "yes" on the C-SSRS Suicidal Ideation Item 4 or Item 5 (Active Suicidal Ideation with Some Intent to Act, Without Specific Plan, or Active Suicidal Ideation with Specific Plan and Intent) and whose most recent episode meeting the criteria for C-SSRS Item 4 or Item 5 occurred within the last 6 months, OR Participants who answer "yes" on any of the 5 C-SSRS Suicidal Behavior Items (actual attempt, interrupted attempt, aborted attempt, preparatory acts, or behavior) and whose most recent episode meeting the criteria for any of these 5 C-SSRS Suicidal Behavior Items occurred within the last 2 years, OR Participants who, in the opinion of the investigator, present a serious risk of suicide.
• Participants with substance abuse or dependence disorder, including alcohol, benzodiazepines, and opioids, but excluding nicotine, within the past 6 months (180 days).
• Participants with dementia or cognitive impairment that, in the judgement of the investigator, would exclude the participant from understanding the ICF or participating in the trial.
• Participants with any condition that could possibly affect drug absorption, including bowel resections, bariatric weight loss surgery, or gastrectomy (this does not include gastric banding).
• Participants who have a positive result for human immunodeficiency virus (HIV) antibodies, hepatitis B surface antigen (HbsAg), or hepatitis C virus (HCV) antibodies at screening.
• Participants with a history of myocardial infarction with residual atrial, nodal, or ventricular arrhythmias that are not control