Study to Determine the Single and Repeat Dose Pharmacokinetics, Food Effect, Proton Pump Inhibitor (PPI) Drug Interaction, Safety and Tolerability of Oral Prototype Formulations of BOS172767 in Healthy Subjects

Part 1 is comprised of a single-dose, part-randomized, open-label, 6-way crossover in 12 healthy participants. Participants will be dosed on 6 separate occasions (in 6 treatment periods), and will receive a single prototype of BOS172767 in each treatment period.

Part 2 is comprised of a single ascending dose, fixed-sequence, open-label, 3-way crossover with an optional fourth dosing period in 10 healthy participants. Participants will be dosed on 4 separate occasions (in 4 treatment periods), and will receive a single prototype of BOS172767 in each treatment period.

Part 3 is a double-blind (sponsor-open), placebo-controlled, randomized MAD part in 36 healthy participants (12 per study cohort). Participants will be dosed on 3 separate occasions (in 3 treatment periods), and will receive a single prototype of BOS172767 in each treatment period.

Parts 2 and 3 are contingent upon successful completion of Part 1.

Inclusion criteria

• Healthy males or healthy females of non-child bearing potential
• Age 18 to 50 years of age at time of signing informed consent
• Body mass index of 18.0 to 32.0 kilograms per meters squared (kg/m^2) at Screening, or, if outside the range, considered not clinically significant by the investigator
• Must be willing and able to communicate and participate in the whole study
• Must have a negative Quantiferon tuberculosis test at Screening
• Must provide written informed consent
• Must agree to use an adequate method of contraception

Exclusion criteria

• Participants who have received any investigational medicinal product (IMP) in a clinical research study within the previous 3 months prior to dosing
• Participants who are study site employees, or immediate family members of a study site or sponsor employee
• Participants who have previously been enrolled (dosed) in this study
• History of any drug or alcohol abuse in the past 2 years prior to Screening
• Regular alcohol consumption in males >21 units per week and females >14 units per week (1 unit = ½ pint beer, 25 milliliters [mL] of 40% spirit or a 125 mL glass of wine)
• Current smokers and those who have smoked within the last 12 months prior to Screening. A breath carbon monoxide reading of greater than 20 parts per million at Screening or admission
• Current users of e-cigarettes and nicotine replacement products and those who have used these products within the last 12 months prior to Screening
• Females of childbearing potential
• Participants who do not have suitable veins for multiple venepunctures/cannulation as assessed by the investigator at Screening
• Clinically significant abnormal biochemistry, haematology or urinalysis as judged by the investigator
• Confirmed positive drugs of abuse test result
• Positive hepatitis B surface antigen, hepatitis C virus antibody or human immunodeficiency virus results
• Evidence of renal impairment at Screening, as indicated by an estimated creatinine clearance of <70 mL/minute using the Cockcroft-Gault equation
• History of clinically significant cardiovascular, renal, hepatic, chronic respiratory or gastrointestinal disease (including gall stones and/or cholecystectomy), neurological or psychiatric disorder, as judged by the investigator
• Serious adverse reaction or serious hypersensitivity to any drug or the IMP formulation excipients
• Adverse reaction to rabeprazole, its excipients or any proton pump inhibitors (Part 2 only)
• Presence or history of clinically significant allergy requiring treatment, as judged by the investigator. Hay fever is allowed unless it is active.
• Donation or loss of greater than 400 mL of blood within the previous 3 months
• Participants who are taking, or have taken, any prescribed or over-the-counter drug (other than 4 grams per day paracetamol or hormone replacement therapy) or herbal remedies in the 14 days before IMP administration. Exceptions may apply on a case by case basis, if considered not to interfere with the objectives of the study, as agreed by the Principal Investigator and sponsor's medical monitor.
• Participants who have any ongoing fungal infections (stable toe nail onychomycosis is allowed)
• Failure to satisfy the investigator of fitness to participate for any other reason