A Phase Ia/Ib, Multiple-site Study to Assess the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of KL1333 After a Single and Multiple Ascending Oral Doses in Healthy Subjects and Patients With Primary Mitochondrial Disease

Part A: Eight healthy subjects will be studied in a single cohort (Group A1). Potential subjects will be screened to assess their eligibility to enter the study within 28 days prior to the first dose administration. Subjects will participate in 2 treatment periods, fasting or after consuming a standard high-fat breakfast. For each treatment period, subjects will reside at the Phase I clinical site from Days 1 to 3 (48 hours postdose). Subjects will return to the clinical site for outpatient visits on Days 4 and 5. There will be at least a 10 day washout between doses Additional single-dose cohorts may be enrolled based on data obtained from either Parts A or B.

Part B: Sixteen healthy subjects will be studied in 2 cohorts (Groups B1 and B2), with each cohort consisting of 8 subjects. Following review of safety, tolerability, and PK data, up to 3 additional dose cohorts of healthy subjects may be added to further explore the PK, safety, and tolerability of KL1333. Potential subjects will be screened to assess their eligibility to enter the study within 28 days prior to the first dose administration. All subjects will participate in 1 treatment period and will reside at the Phase I clinical site from Days -1 to 12 (48 hours post final dose). Subjects will return to the clinical site for outpatient visits on Days 13 and 14. On Day 1, 6 subjects will be randomised to receive KL1333 and 2 subjects will be randomised to receive placebo. Subjects will return for a Follow-up visit on Day 15, 5 days after their final dose.

Part C: A total of 8 patients diagnosed with any mitochondrial disease will be enrolled in this part of the study. Part C may start after the dose selection conference has been completed for the final cohort of Part B, at a daily dose no higher than the highest well-tolerated dose in Part B. Potential study patients will be screened to assess their eligibility to enter the study within 35 days prior to the first dose administration. Patients will reside at the clinical site from Days -1 to 2 and Days 10 to 11 and return to the clinical site for outpatient visits on Days 4 and 8. It is planned for patients to receive study drug once daily on Days 1 to 10. Patients will return for a Follow-up visit on Day 15, 5 days after their final dose.