Exclusion Criteria

A severe asthma exacerbation within 8 weeks of screening visit 1.
A positive test result of an approved antigen test (confirmed by a positive RT-PCR test) or a positive RT-PCR test for SARS-CoV-2, the virus responsible for COVID-19, at screening Visit 1 or at Visit 2 for the PK Lead-in cohort. For Part 1 and Part 2 the testing will be done at Visit 3. Results from the mandatory tests at Visit 2 (PK Lead-in cohort) and Visit 3 (Part 1, Part 2) must not be older than 48 hours and must be available before randomisation.
Participants with a significant COVID-19 illness within 6 months of enrolment.
Clinically important pulmonary disease other than asthma.
Any disorder, including, but not limited to, cardiovascular, gastrointestinal, hepatic, renal, neurological, musculoskeletal, infectious, endocrine, metabolic, haematological, psychiatric, or major physical impairment that is not stable.
Any clinically significant cardiac disease.
History of severe renal disease or history of creatinine clearance < 30 mL/min × m2 calculated using Cockcroft-Gault equation.
Severe hepatic impairment (Child-Pugh class C).
Previous hepatotoxicity related to zileuton or leukotriene receptor antagonist (LTRAs) (eg montelukast).
Participants with a recent history of, or who have a positive test for, infective hepatitis or unexplained jaundice, or participants who have been treated for hepatitis B, hepatitis C, or human immunodeficiency virus (HIV).
Evidence of active or untreated latent tuberculosis (TB).
Current or history of alcohol or drug abuse (including marijuana).
Current diagnosis of cancer, not including in-situ or non-melanoma skin cancer or other previous malignancies where curative therapy was completed at least 5 years prior to screening Visit 1.
Clinically important ongoing or previous psychiatric disease, especially suicidal behaviour, that in the opinion of the investigator might compromise the safety of the participant in the study.
Treatment with any serum creatinine-altering drugs within 1 month prior to screening Visit 1 including but not limited to amphotericin, cimetidine, clofibrate, dronedarone, ketoconazole, probenecid, ranolazine, trimethoprim, aminoglycosides, or cephalosporins.
Treatment with systemic corticosteroid use within 8 weeks (oral) or 12 weeks (intramuscular) before screening Visit 1.
Treatment with marketed biologics including benralizumab, mepolizumab, reslizumab, omalizumab, and dupilumab within 6 months of screening Visit 1 or 5 half-lives whichever is longer.
Treatment with 5-lipoxygenase inhibitors (eg zileuton or other 5-LO inhibiting supplements) within 6 weeks prior to Visit 0 and within 8 weeks prior to Visit 1).Treatment with LTRAs (eg, montelukast) within 2 weeks prior to Visit 0 and within 4 weeks prior to screening Visit 1.
Inhaled corticosteroid + fast-acting β2 agonist as a reliever (eg Symbicort or Fostair Maintenance and Reliever Treatment) is not allowed 15 days prior to screening Visit 1, during screening (Visit 1)/run-in and the treatment period and preferably 1 week after the last dose of study intervention.
Live or attenuated vaccines within 4 weeks of screening Visit 1.
Immunoglobulin or blood products within 4 weeks of screening Visit 1.
Treatment with Gemfibrozil within 4 weeks of screening Visit 1.
Any immunotherapy within 6 months of screening Visit 1, except for stable maintenance dose allergen-specific immunotherapy started at least 4 weeks prior to screening Visit 1 and expected to continue through to the end of the follow-up period.
Potent inducers/inhibitors of cytochrome P450 3A4 within 4 weeks of screening Visit 1.
Treatment with simvastatin, lovastatin, and atorvastatin at doses > 40 mg per day within 1 month prior to screening Visit 1. Treatment with sensitive cytochrome 3A substrates with narrow therapeutic window should be avoided from randomization to study drug.
For female participants on ethinyl oestradiol containing combined oral contraceptives.
Concurrent enrolment in another clinical study.
Previous participation in the current clinical study.
Participant treated with any investigational drug within 4 months prior to screening Visit 1.
Known history of allergy or reaction to any component of the study intervention formulation.
For female participants only: Currently pregnant or breast-feeding.
Smokers with smoking history of < 10 pack-years or users of vaping or e-cigarettes, must have stopped at least 6 months prior to screening Visit 1.
Involvement in the planning and/or conduct of the study.
Donation of blood (≥ 450 mL) within 3 months or donation of plasma within 14 days before screening Visit 1.
Major surgery within 8 weeks prior to screening Visit 1, or planned inpatient surgery, major dental procedure or hospitalisation during the screening (Visit 1), treatment or follow-up periods.