The purpose of this study is to assess the safety, tolerability and pharmacokinetics of NNZ-2591 when administered to healthy volunteers.

This study is in two stages:

Stage 1: A First-in-Human (FIH), single dose escalation study of oral NNZ-2591 in healthy volunteers to establish safety, tolerability and pharmacokinetic parameters.

Stage 2: A First-in-Human (FIH), randomised, double-blind, placebo-controlled, Multiple Ascending Dose study (MAD) in healthy volunteers to establish safety, tolerability and pharmacokinetic parameters.

Inclusion Criteria:

1. Male or female subjects aged 18 to 55 years, inclusive;

2. Weight at screening and admission between 45 kg and 100 kg;

3. Body mass index (BMI) between 18.0 and 32.0 kg/m2 inclusive;

4. Healthy as determined by the Investigator based on pre-study medical history, physical examination, vital signs, complete neurological examination and 12-lead electrocardiogram (ECG);

5. Negative tests for Hepatitis B surface antigen (HBsAg), hepatitis C virus antibody (anti-HCV) and human immunodeficiency virus (HIV)-1 and HIV-2 antibody at screening;

6. Clinical laboratory test results up to >1.5 x Lower Limit of Normal (LLN) or <1.5 x Upper Limit of Normal (ULN) at screening and admission and deemed not clinically significant by the Investigator;

7. Negative screen for alcohol and drugs of abuse at screening and admission;

8. Non-smokers or ex-smokers (must have ceased smoking >3 months prior to screening visit);

   If female:

9. Woman with no childbearing potential by reason of surgery or at least 1year post- menopause (i.e., 12 months post last menstrual period), and menopause confirmed by follicle-stimulating hormone (FSH) testing;

10. If of childbearing potential, using an effective nonhormonal method of contraception (intrauterine device; condom or occlusive cap [diaphragm or cervical or vault caps]; true abstinence; or vasectomized male partner (provided that he is the sole partner of that subject and had a vasectomy ≥30 days prior to screening) for the duration of the study and up to one month after the last investigational medicinal product (IMP) administration;

11. Negative serum pregnancy test at screening and negative urine pregnancy test on admission (women of childbearing potential only);

    If male:

12. Using an effective method of contraception (condom) if sexually active with a female partner of child-bearing potential; true abstinence; or vasectomy ≥30 days prior to screening) throughout the study and for one month after the last IMP administration.

Exclusion Criteria:

1. Subjects who have a clinically relevant history as determined by the Investigator, or presence of respiratory, gastrointestinal, renal, hepatic, haematological, lymphatic, neurological, cardiovascular, psychiatric, musculoskeletal, genitourinary, immunological, dermatological, endocrine, connective tissue diseases or disorders;

2. Fridericia's correction factor for QT (QTcF) > 450 ms for male participants and >470ms for female participants or history of QT interval prolongation.

3. Have a clinically relevant surgical history, as determined by the Investigator;

4. Have a history of relevant atopy or drug hypersensitivity;

5. Have a history of alcoholism or drug abuse;

6. Consume more than 21 standard drinks a week for males and more than 14 standard drink if female [1 standard drink is any drink containing 10g of alcohol, regardless of container size or alcohol type].

7. Have a significant infection or known inflammatory process on screening or admission;

8. Have acute gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea, heartburn) at the time of screening or admission;

9. Have used any prescription or non-prescription medicines within 2 weeks of admission, unless in the investigator's opinion will not affect determination of safety or other study assessments. Occasional paracetamol use (up to 2g/day is permitted);

10. Have received any investigational drug within 30 days prior to screening;

11. Have used tobacco or nicotine products within 3 months of screening

12. Have donated or received any blood or blood products within the 3 months prior to screening;

13. Cannot communicate reliably with the investigator;

14. Are unlikely to co-operate with the requirements of the study;

15. Are unwilling or unable to give written informed consent.

    If female:

16. Pregnancy or breast-feeding;

17. Woman of childbearing potential not willing to use an accepted effective contraceptive method or using hormonal contraceptives;

    If male:

18. Not willing to use an accepted effective method of contraception.

Stage 1: None Stage 2: Double-blind