A Phase 2 Study to Assess the Effects of SUL-238 on High Energy Phosphates With ³¹P-MRS in Patients With Early, Untreated Parkinson's Disease

The main goal of the study is to investigate how well the new drug SUL-238 works in Parkinson's Disease (PD). This is done by means of an MRS scan. An MRS scan is similar to a regular MRI scan. It will also learn about the safety of new drug SUL-238. The main questions it aims to answer are: * Does new drug SUL-238 improve the mitochondrial function in patients with Parkinson's Disease (PD)? * What medical problems do participants have when taking new drug SUL-238? Researchers will compare new drug SUL-238 to a placebo (a look-alike substance that contains no drug) to see if SUL-238 works to improve mitochondrial function in patients with PD. Participants will: * Take new drug SUL-238 or a placebo every day for 28 days * Visit the clinic once every 2 weeks for checkups and tests during the treatment period and finally 28 days after the last dose of SUL-238 * Keep a diary of their symptoms and the number of times they use oral new drug SUL-238

Two different oral doses of SUL-238 (1500 mg t.i.d. or 500 mg t.i.d) or placebo will be administered to patients with early, untreated Parkinson's Disease (PD), aged ≥40 years. Patients will be randomly assigned to one of the 3 groups using 1:1:1 randomization, each group will consist of 15 patients. Patients will be stratified based on their sex in to ensure similar distribution of both sexes in each group. Drop-outs will be replaced with new patients to reach 15 patients in each group. Study drugs will be administered after fasting from all food and drink except water for a minimum of 1 hour prior to dosing. Patients will be allowed to eat 1 hour after receiving their dose. Only morning dose will be given on day 28, there will be no dosing between day 29 and 56. There will be three study periods per treatment group: * A maximum of four-week screening period (Screening Period) * A four-week treatment period (Treatment Period) * A four-week follow-up period (End-of-Study Assessment) Patients will be visiting the study center in the morning, in total five times for study assessments and collections of blood samples until day 56. Blood samples will be collected on days 1, 14, 28, and 56 (On day 1 \[pre-dose baseline, post-dose at 1 hr\], and days 14 \[pre-dose\], 28 \[post-morning dose at 1 hr and 4 hr\]). Patients who agreed to provide CSF in each group will give one CSF sample on day 28 at 4 hours post-morning dose. Voxel Metabolite Measurements: MRI/MRS scans will be conducted on a Siemens 3 MAGNETOM Cima.X scanner located at the at the UMCG. Patients will undergo 31P-MRS scans to measure concentrations of the following mitochondria-related brain metabolites: ATP, phosphocreatine and inorganic phosphate, as well as membrane related phospholipids PME and PDE. Preparation: A 31P/1H T/R head coil will be used. The head of the patient will be positioned at the center of the coil. Prior to 31P-MRS, T1 and T2 weighted structural images are acquired for reference purposes during voxel placement. 31P-MRS scans: 31P spectra will be acquired from voxels placed in the precentral gyrus, substantia nigra and putamen regions (each contralateral to the most affected side of the body). Spectra for the precentral gyrus and putamen will be recorded at rest, during fist clenching on the contralateral side and during recovery. For substantia nigra, spectra will only be acquired during rest. For each ROI the total acquisition will be at most 15 minutes.