Inclusion Criteria:
1. Participants must have a written informed consent obtained prior to any study-related procedures.
2. Participants must be able to understand and comply with the requirements of the study, as judged by the Investigator or delegate.
3. Male and female participants aged between 18-55 years inclusive, at the time of informed consent.
4. Female participants must either be:
1. of non-childbearing potential,
2. of childbearing potential who are not pregnant, breast feeding or lactating and use an approved method of highly effective birth control method from either the time of informed consent (non-hormonal contraception) or at least 2 weeks prior to informed consent (hormonal contraception) and for 30 days following the last administered dose of IMP.
5. Male participants who are sexually active with a partner of childbearing potential must use, with their partner, a male condom plus an approved method of highly effective contraception from the time of informed consent and for 30 days following their last administered dose of IMP.
6. Participants must agree not to donate semen or ova/oocytes from the time of informed consent and for 30 days after the last dose of IMP.
7. Participants must have a body weight of ≥50kg and body mass index (BMI) ≥ 18 kg/m2 and ≤ 29.9 kg/m2 at screening.
8. Participants must be in good health as determined by medical history, concomitant medication use, physical examination, vital signs, 12-lead ECG and clinical laboratory assessments at the time of screening and pre-dose Day 1 (as applicable) as judged by the Investigator or delegate.
Exclusion Criteria:
1. History or presence of any clinically relevant acute or chronic medical or psychiatric condition that could interfere with the participant's safety during the clinical study, expose the participant to undue risk or could interfere with the objectives of the study as judged by the Investigator or delegate.
2. Significant history of seasonal allergies or chronic rhinosinusitis as judged by the Investigator or delegate.
3. Any significant abnormality or piercing altering the anatomy of the nose or nasopharynx in a substantial way, including evidence of nasal inflammation, nasal polyps or known difficulties previously tolerating intranasal dosing that may prevent intranasal dosing on this study as judged by the Investigator or delegate.
4. Significant history of epistaxis (large nosebleeds) or recurrent epistaxis prior to screening as judged by the Investigator or delegate and/or history of being hospitalised due to epistaxis on any previous occasion.
5. Any nasal or sinus surgery within 3 months prior to screening.
6. Any signs of respiratory tract infection within 4 weeks of screening or prior to dosing on Day 1 that is deemed clinically significant in the opinion of the Investigator or delegate.
7. Malignancy within the past 5 years of screening with the exception of in situ removal of basal cell carcinoma or resected benign colonic polyps.
8. Any planned major surgery within the duration of the study or in the 30 days following study completion.
9. Any other clinically significant illness, medical/surgical procedure or trauma within 6 weeks of screening or prior to the first administration of IMP (Day 1) as judged by the Investigator or delegate.
10. Female participants with a positive urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of human chorionic gonadotropin \[HCG\]) at screening or prior to dosing on Day 1.
11. Positive serum hepatitis B surface antigen (HBsAg), hepatitis C virus antibodies (HCVAb) or human immunodeficiency virus (HIV) 1 and/or 2 antibodies at screening.
12. History of any drug and/or alcohol abuse in the past 2 years prior to screening.
13. The use of tobacco products, oral nicotine products, or e-cigarettes within 6 months prior to screening, or a cumulative smoking history equivalent of \>5 pack-years. Nicotine replacement therapy (e.g., nicotine patches or gum) used for smoking cessation is permitted.
14. Receiving any of the prohibited concomitant medications specified in Section 5.5.3 or any other concomitant medication that could interfere with the participant's safety during the clinical study, expose the participant to undue risk or could interfere with the objectives of the study as judged by the Investigator or delegate.
15. Any changes to prescribed, chronic concomitant medications or commenced any new medications within 6 weeks of screening or prior to the first administration of IMP (Day 1).
16. Plasma donation within one month of screening or blood donation (or corresponding blood loss) ≥400ml during the three months prior to screening.
17. Participants who do not have suitable veins for multiple venepunctures as assessed by the Investigator or delegate at screen.
18. Participant has dietary restrictions incompatible with the diet that can be provided by the study location, in the opinion of the Investigator or delegate, or is unwilling to refrain from consuming restricted foods and beverages during the study.
19. Known history of intolerance or hypersensitivity to HEX17 or to any other component of the formulation.
20. Known history of intolerance to placebo or excipients.
21. Clinically significant serious adverse reaction, allergy or serious hypersensitivity, including to any drug or food, as judged by the Investigator or delegate.
22. Involvement in the planning and conduct of the study.
23. Participation in another clinical study with an experimental drug within 3 months (non-biologics), 6 months (biologics) or 5 half-lives, whichever is longer, before the administration of IMP.
24. Considered unsuitable for entry into the study in any other way at the discretion of the Investigator or delegate, e.g. Investigator or delegate considers the participant unlikely to comply with study procedures, restrictions and requirements.
