SR-Exenatide (PT320) to Eveluate Efficacy and Safety in Patients With Early Parkinson's Disease

Inclusion Criteria: 1. Patient who is male or female aged 40-75 and is diagnosed with Parkinson's Disease (using Queen Square Brain Bank criteria) 2. Patient who is diagnosed of Parkinson's Disease less than 24 months prior to the screening 3. Patient who has a modified Hoehn and Yahr stage ≤ 2. 5 4. Patient who has been taking L-dopa stable-dose less than 600 mg/day or who has not previously taken any medication for the treatment of Parkinson's Disease from 4 weeks prior to the screening. 5. Patient who is able to inject an Investigational Product by himself/herself or a his/her guardian. 6. Patient or legally acceptable representative who signs the informed consent form voluntarily and is able to comply with all study procedures Exclusion Criteria: 1. Patient who is diagnosed or suspected to have Parkinson-plus syndromes (e.g., Multiple System Atrophy, Progressive Supranuclear Palsy, Corticobasal Degeneration, Diffuse Lewy Body Disease, and etc.) 2. Patient who has a BMI \< 18.5 at the screening 3. Patient who has known abnormalities on CT or MRI brain imaging that may have an impact on the protocol compliance and/or PET scan 4. Patient who has dementia with MoCA-K ≤ 22 5. Patient who has a history of severe heart failure (NYHA class III to IV), stroke, cerebral ischemic attack, or seizure within 1 year prior to screening; or a history myocardial infarction or unstable angina within 6 months prior to screening. 6. Patient who has severe liver disease or has AST or ALT level 3 times more than ULN at the screening 7. Patient who has clinically significant depression \[\> 18 of Korean Beck Depression Inventory II score (K-BDI-II)\] 8. Patient who has a history of brain surgery for any treatment of Parkinson's disease 9. Patient who has participated in any clinical trials for the treatment of Parkinson's Disease within 3 months prior to screening 10. Patient who took exenatide within 90 days prior to randomization 11. Patient who has a history of gastroduodenal ulcer or gastroparesis within 3 months prior to administration of investigational product or is currently on medication for acute or chronic gastritis 12. Patient who has severe kidney function injury (creatinine clearance \< 30 ml/min) 13. Patient who has a history of pancreatitis 14. Patient who has type 1 or type 2 diabetes or HbA1c ≥ 6.5% at screening 15. Patient who has a history or suspected to thyroid cancer or multiple endocrine adenomatosis 16. Patient who has known or suspected intolerance in PET scan or fluoropropyl-CIT (18F) 17. Woman childbearing potential who doesn't agree to use the medically acceptable methods of contraception\* during this study and up to 24 weeks after the last injection of investigational product \*Medically acceptable methods of contraception: oral contraceptives, intrauterine contraceptive devices, vasectomy for male partner, barrier method \[condom, spermicidal foam/gel/film/cream/suppository with sealed cap (diaphragm or cervix/bolt cap)\]. 18. Woman who is pregnant or breastfeeding 19. Patient who has a history of hypersensitivity reactions to any ingredients of investigational product 20. Patient who is not eligible for the study at the discretion of the investigator