A Phase I Study in Healthy Volunteers and Parkinson's Disease (PD) Patients.

Inclusion Criteria:

Part 1, 2 ,4

1. Healthy male and female (Part 1-2 only) participant, aged ≥ 18 to ≤ 55 years.
2. Female participant of childbearing potential (Part 1-2 only)
3. Female participant of non-childbearing potential (Part 1-2 only).
4. Female participant (Part 1-2 only) with a negative pregnancy test at Screening visit.
5. Female participant of menopausal status (Part 1-2 only) confirmed by demonstrating at Screening that the serum level of the follicle stimulating hormone (FSH) falls within the respective pathology reference range.
6. Male participant (and partner of childbearing potential) willing to use a highly effective method of contraception
7. Participant with a body weight of at least 50.0 kg and body mass index (BMI) of 1832 kg/m2. BMI = body weight (kg) / [height (m)]2.
8. No clinically significant history of previous allergy / sensitivity to MTX325 or any of the excipients contained within the IMP.
9. No clinically significant abnormal test results for serum biochemistry, haematology, coagulation
10. Participant with a negative urinary drugs of abuse (DOA) screen (including alcohol) test results, determined within 35 days (45 days Part 4 only) before first dose of IMP.
11. Participant with negative human immunodeficiency virus (HIV), hepatitis B surface antigen [HbsAg]) and hepatitis C virus antibody (HCV Ab) test results at Screening.
12. No clinically significant abnormalities in 12-lead electrocardiogram (ECG)
13. No clinically significant abnormalities in vital signs
14. Participant must be available to complete the study (including all follow-up visits).
15. Participant must satisfy an Investigator about his/her fitness to participate in the study.
16. Participant must provide written informed consent to participate in the study.
17. Participants with a negative COVID-19 test on admission (if required).
18. Part 4 only: Participant with normal MRI performed within 3 months of dosing, as judged by the investigator.

Part 4 Only

1. Participants who have had previous exposure to ionizing radiation from research studies
2. Participant has any contraindication to arterial line insertion
3. Inability to lie supine for up to 120 mins for PET procedures.
4. Participant has any contra-indication to MRI as determined by screening procedures and MRI safety questionnaire
5. Participant suffers from claustrophobia or needle phobia.
6. Any history of allergy/atopy including drug-induced allergy or any history of severe cutaneous adverse reaction or other type 4/delayed-type hypersensitivity.
7. Current or previous history of eosinophilia with either unknown cause, or where known, the inciting factor is not removed or avoided.
8. Previous history of Erythema Multiforme and/or identified current risk factor(s) for Erythema Part 3 Only

1. Healthy male and female participant, ≥ 65 years of age. 2. Female participant of non-childbearing potential. 3. Female participant of menopausal status confirmed by demonstrating at Screening that the serum level of the follicle stimulating hormone (FSH) falls within the respective pathology reference range.

4. Male participant (and partner of childbearing potential) willing to use a highly effective method of contraception 5. Participant with a body weight of at least 50.0 kg and BMI of 18-32 kg/m2. 6. No clinically significant history of previous allergy / sensitivity to MTX325 or any of the excipients contained within the IMP.

7. No clinically significant abnormal test results for serum biochemistry, haematology and/or urine analyses determined within 35 days before first dose of IMP.

8. Participant with an estimated glomerular filtration rate (eGFR) calculated by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation >60 mL/min/1.73 m2.

9. Participant with a negative urinary drugs of abuse (DOA) 10. Participant with negative human immunodeficiency virus (HIV), hepatitis B surface antigen [HbsAg]) and hepatitis C virus antibody (HCV Ab) test results at Screening.

11. No clinically significant abnormalities in 12-lead electrocardiogram (ECG) 12. No clinically significant abnormalities in vital signs 13. Participant must be available to complete the study (including all follow-up visits).

14. Participant must satisfy an Investigator about his/her fitness to participate in the study.

15. Participant must provide written informed consent to participate in the study.

16. Participants with a negative COVID-19 test on admission. Part 5 Only

1. Male and female participants aged ≥ 40 to ≤ 75 years.
2. Male or female participants. Female participants of childbearing potential must be willing to use highly effective forms of contraception (refer to Section 9.7.1 for details on highly effective methods of contraception and definitions of women of childbearing potential and of fertile men):
3. Body mass index (BMI) between 18 and 34.0 kg/m2, inclusive.
4. If being treated with selective serotonin reuptake inhibitors (SSRIs) for anxiety/ depression, must be on a stable dose for 60 days prior to Day -1 and must remain on that dose for the remainder of the study.
5. Must have had other causes of Parkinsonism excluded
6. No clinically significant history of previous allergy/ sensitivity to MTX325 or any of the excipients contained within the IMP.
7. Participant with a negative urinary drugs of abuse (DOA) screen (excluding alcohol).
8. Participant with negative human immunodeficiency virus (HIV), hepatitis B surface antigen [HbsAg]) and hepatitis C virus antibody (HCV Ab) test results at Screening.
9. No history of torsade de pointes or long QT syndrome and no heart failure, hypokalaemia, or any other additional cardiac risk factors if judged clinically significant in the opinion of the Investigator.
10. No clinically significant abnormalities in vital signs during the screening period.
11. Able to perform all protocol assessments and comply with the study visit schedule. 12. Able and willing to provide informed consent.

13. Clinically established PD as per MDS Criteria[ 14. Absence of dementia as shown by a baseline Montreal Cognitive Assessment (MoCA®) Exclusion Criteria (Part 1, 2, 4)

1. A clinically significant history of gastrointestinal disorder likely to influence IMP absorption.
2. Use of prescription or non-prescription drugs, excluding allowable drugs and contraception
3. Reports having experienced suicidal ideation (Type 4 on 5 on the Columbia-Suicide Severity Rating Scale [C-SSRS©] him/herself or others - Part 2 only.
4. Evidence of renal, hepatic, central nervous system, respiratory, cardiovascular or metabolic dysfunction.
5. A clinically significant history of drug or alcohol abuse (defined as the consumption of more than 14 units
6. Inability to communicate well with the Investigators
7. Participation (dosed) in a New Chemical Entity (NCE) clinical study within the previous 3 months or five half-lives
8. Donation of 450 mL or more blood within the 3 months before the first dose of IMP.
9. Vegans, vegetarians or other dietary restrictions (Part 1 food effect evaluation, only).
10. Users of nicotine products
11. Participants with an excessive habitual daily intake of caffeine
12. Female participants who are pregnant, breastfeeding or lactating (Part 1-2 only).
13. Participants with veins unsuitable for venepuncture and cannulation.
14. Participants with recent COVID-19 infection without resolution of symptoms
15. Participants who have received a COVID-19 vaccine injection

Part 1 Treatment Period 2a (CSF sampling) Cohort(s) only:

1. Participants who have criteria that would preclude a lumbar puncture (LP)
2. Participant who has a history of clinically significant hypersensitivity to local anaesthesia
3. Participant who has a history of clinically significant or major back pathology (lumbar) surgery

Part 4 only:

1. Participants who have had previous exposure to ionizing radiation from research studies, such that, in combination with the exposure from this study, their exposure will be >10 mSv for the previous 12 months.
2. Participant has any contraindication to arterial line insertion
3. Inability to lie supine for up to 120 mins for PET procedures.
4. Participant has any contra-indication to MRI
5. Participant suffers from claustrophobia or needle phobia.
6. Any history of allergy/atopy
7. Current or previous history of eosinophilia with either unknown cause, or where known, the inciting factor is not removed or avoided.
8. Previous history of Erythema Multiforme and/or identified current risk factor(s) for Erythema Multiforme Part 3 Only

1. A clinically significant history of gastrointestinal disorder likely to influence IMP absorption.

2. Evidence of febrile illness within 1 week of first dose of IMP. 3. Use of prescription or non-prescription drugs, including vitamins, herbal and dietary supplements or any medication known to prolong the QT/QTc interval within 35 days or 5 half-lives 4. Evidence of clinically significant renal, hepatic, central nervous system, respiratory, cardiovascular or metabolic dysfunction.

5. History of torsade de pointes, heart failure, hypokalaemia, long QT syndrome or any other additional cardiac risk factors.

6. A clinically significant history of drug or alcohol abuse 7. Participants with an excess habitual daily intake of caffeine 8. Inability to communicate well with the Investigators 9. Participation in a NCE clinical study within the previous 3 months or five half-lives 10. Donation of 450 mL or more blood within the 3 months before the first dose of IMP.

11. Participants who have received a COVID-19 vaccine injection within 35 days prior to first dose of IMP.

12. Users of nicotine products 13. Participants with veins unsuitable for venepuncture and cannulation. 14. Participants with recent COVID-19 infection with resolution of symptoms Part 5

1. A clinically significant history of gastrointestinal disorders or any significant medical conditions that would be likely to influence IMP absorption, or evidence of clinically significant central nervous system, respiratory, cardiovascular or metabolic dysfunction or other significant medical conditions with potential to impact participant safety or hinder interpretation of study results.
2. Clinically significant neurologic disorder other than PD, including history of stroke within 12 months of Screening, seizure within 5 years of Screening, or head trauma with loss of consciousness within 6 months of Screening.
3. Those with known PD risk genes (per medical history).
4. Reside in a nursing home or assisted care facility.
5. No more than 2 PD related freezing episodes or falls in the past 6 months.
6. Any condition that may predispose participant to complications or technical difficulty with lumbar puncture, in the opinion of the Investigator.
7. Participant who has a history of clinically significant hypersensitivity to local anaesthesia, or its derivatives used during CSF collection or to any medication used to prepare the area of LP.
8. Reports having experienced suicidal ideation (Type 4 on 5 on the Columbia-Suicide Severity Rating Scale [C-SSRS©]
9. Participants should not be in receipt of any known MATE2k substrates
10. Plan to receive or administration of rotigotine, catechol-o-methyltransferase (COMT) inhibitors (e.g., entacapone, tolcapone or opicapone), neuroleptics, venlafaxine, NMN, nicotinamide riboside or non-selective Monoamine oxidase [MAO] inhibitors within 7 days or 5 half-lives (whichever is longer) prior to first dose and during the study conduct.
11. Clinically significant abnormal test results for serum biochemistry, haematology, coagulation and/or urine analyses as determined within 45 days before first dose of IMP.
12. A clinically significant history of gastrointestinal disorder likely to influence IMP absorption.
13. Participant has any condition that, in the opinion of the investigator, is clinically significant and may put the participant at greater safety risk, influence response to study product, or interfere with study assessment.
14. Inability to communicate well with the Investigators.
15. Participation (dosed) in a NCE clinical study within the previous 3 months or five half lives
16. Donation of 450 mL or more blood within the 3 months before the first dose of IMP.
17. Female participants who are pregnant, breastfeeding or lactating.
18. Clinically significant abnormalities in 12-lead electrocardiogram (ECG)
19. Participants with recent COVID-19 infection without resolution of symptoms
20. Participants who have received a COVID-19 vaccine injection from the Screening visit up to first dose of IMP
21. A clinically significant history of drug or alcohol abuse within the past 2 years. Currently prescribed treatment for Parkinson's Disease symptoms.
22. Any history of allergy/atopy including drug-induced allergy history of severe cutaneous adverse reaction or other type 4/delayed-type hypersensitivity.
23. Current or previous history of eosinophilia with either unknown cause, or where known, the inciting factor is not removed or avoided.
24. Previous history of Erythema Multiforme and/or identified current risk factor(s) for Erythema Multiforme
25. Participant has any contra-indication to PET or MRI as determined by screening procedures and PET and MRI safety questionnaires as conducted by the site.
26. Clinically significant history of previous allergy/ sensitivity to [18F] FDG.
27. Participants who have had previous exposure to ionizing radiation
28. Chronic kidney disease defined as glomerular filtration rate (GFR) 1.5 × the upper limit of normal (ULN) or ALT or AST >3 × ULN or if participant has Child-Pugh Class C cirrhosis or equivalent severe hepatic impairment.
29. Hepatic disease or altered liver function as defined by total bilirubin >1.5 × the upper limit of normal (ULN) or ALT or AST >3 × ULN or if participant has Child-Pugh Class C cirrhosis or equivalent severe hepatic impairment.
30. Patients with uncontrolled type I or type II diabetes (insulin or non-insulin dependent).
31. Current symptomatic Hay fever or any history of hay fever involving more than nose and eyes.