A Study to Evaluate Safety and Efficacy of KM-819 in Healthy Adults and Participants With Parkinson's Disease

The goal of this study is to test KM-819 in halting or slowing the progression of Parkinson's disease.The study evaluates the safety and tolerability of multiple ascending doses of KM-819 in healthy older adults and participants with Parkinson's disease.

Inclusion Criteria:Participant is a healthy volunteer or has a clinical diagnosis of idiopathic Parkinson's disease.Participant is on a stable dose of medications to treat Parkinson's disease at least 8 weeks prior to randomizationPresence of idiopathic Parkinson's disease Hoehn and Yahr Stage ≤ 4History or current use of dopamine/dopaminergic drugs, levodopa with decarboxylase inhibitor or dopaminergic agonists, with a stable dosage for at least 30 days prior to ScreeningBody mass index (BMI) within the range 18.5 to 35 kg/m2 (inclusive)A male participant must not have a pregnant or breastfeeding partner and must agree to use a highly effective contraception method starting from Screening and refrain from donating sperm during this periodA female participant is eligible to participate if she is not pregnant, not breastfeedingExclusion Criteria:Diagnosis of neurodegenerative disorder other than idiopathic Parkinson's disease resulting in dementia or atypical parkinsonismLife-time history of a suicide attempt as determined by the Columbia-Suicide Severity Rating Scale (C-SSRS) for the ScreeningEvidence of cognitive decline defined by the Montreal Cognitive Assessment (MoCA) score ≤25 for healthy normal population (Part 1a) and ≤21 for the patient population (Part 1b and Part 2)History of levodopa-induced motor fluctuations or dyskinesiaPrior surgical treatment for Parkinson's diseaseClinically significant brain abnormalities on or contraindication to a structural magnetic resonance imaging (MRI)Significant respiratory, hepatic, renal, gastrointestinal, endocrinological, hematological, pancreatic, musculoskeletal, genitourinary, immunological or dermatological disorders.