A Two-Part Study to Assess the Effects of Ritonavir on PRN1008 Pharmacokinetics, and the Effect of PRN1008 on QTc Interval Compared to Placebo and Moxifloxacin in Healthy Participants

This will be a single center, two-part (Parts A & B) study in healthy adult participants. Participants will be screened for participation within 28 days before dosing. Participants may be enrolled in Part A or Part B of the study; participants may not be enrolled in both Parts. Part A is randomized, open-label, three-period, complete crossover study with a 7-day washout between treatment periods. All participants will complete 3 treatment periods in Part A of the study, and will be randomized to receive one of the following treatments in each period: • Treatment 1: single dose of 100 mg PRN1008 tablet under fasting conditions • Treatment 2: single dose of 100 mg PRN1008 plus 100 mg oral ritonavir oral tablet under fasting conditions, with a second dose of 100mg ritonavir tablet only 12 hours after the first dose • Treatment 3: single dose of 1200 mg (4 x 300 mg tablet) PRN1008 tablet under fasting conditions There are 6 possible sequences in which the listed treatments for Part A will be administered. Part A participants will be admitted to the study unit one day (Day -1) before dosing in each Period. On Day 1 Periods, 1, 2, and 3, following an overnight fast, participants will be randomized to receive Treatment 1, 2, or 3. Following dosing, blood samples for pharmacokinetic (PK) analysis of PRN1008 will be collected over a period of 24 hours. In each period, participants will be admitted to the study unit on Day -1 and remain in the study unit to Day 2. Participants will be discharged on Day 2, then return to the study unit on Day 6 (Day -1, Period 2) for follow-up safety assessments and check-in for the next dosing period. Following discharge of Period 3, participants will complete a follow-up visit approximately 7 days (± 1 day) after the last dose of study drug. Part B is a randomized, single-dose, placebo-controlled, 4 period, complete crossover study with a 7-day washout between treatment periods. All participants will complete 4 treatment periods in Part B of the study, and will be randomized to receive one of the following single-dose treatments in each period: • Treatment 1 (Therapeutic dose): 400 mg (1 x 100 mg tablet and 1 x 300 mg tablet) PRN1008 under fasting conditions • Treatment 2 (Supratherapeutic dose): Either 1200 mg (4 x 300 mg tablet) PRN1008 or (TBD) mg PRN1008 with 100 mg ritonavir oral tablet. The supratherapeutic regimen will be determined following review of Part A data. If dosed with ritonavir, a second dose of 100mg ritonavir tablet will be administered 12 hours after the morning dose. Based on emerging data from Part A, the second dose of 100mg ritonavir in Treatment 2 may be omitted as needed. • Treatment 3: PRN1008 Placebo under fasting conditions • Treatment 4: Moxifloxacin 400 mg tablet (positive control) under fasting conditions There are 12 possible sequences in which the listed treatments will be administered. Participants in Part B will be screened for participation in the study within 28 days before dosing. Participants will be admitted to the study unit two days (Day -2) before dosing in Period 1. Following confirmation of study eligibility on Day -1, participants will be randomized to treatment order and baseline pre-treatment ECGs will be collected via Holter monitor for 24 hours. On Day 1 of each period, following an overnight fast, participants will receive Treatment 1, 2, 3, or 4, and blood samples for PK analysis of PRN1008 will be collected over a period of 24 hours. In each subsequent period, participants will be admitted to the study unit on Day -1 and remain in the study unit to Day 2. Participants will be discharged on Day 2, then return to the study unit on Day 6 (Day -1, Period 2) for follow-up safety assessments and check-in for the next dosing period. Following discharge of Period 4, participants will complete a follow-up visit approximately 7 days (± 1 day) after the last dose of study drug.