Study Assessing PTI-428 Safety, Tolerability, and Pharmacokinetics in Subjects With Cystic Fibrosis

PART A The SAD treatment group is comprised of 3 cohorts where subjects will be randomized to either PTI-428 or placebo. Following the conclusion of at least 3 SAD treatment groups, a set of adult subjects diagnosed with CF will participate in an assigned MAD treatment group. The MAD treatment group is comprised of 3 cohorts. MAD Cohort 1 will enroll adult subjects with CF currently on stable ORKAMBI® background therapy for a minimum of 3 months at the time of randomization. MAD Cohorts 2 and 3 will enroll adult subjects with CF who are not currently on any background therapies. Subjects in all MAD cohorts will be randomized to either PTI-428 or placebo. Each dose will be administered once daily (QD) for a total of 7 Days. PART B Following the conclusion of MAD Cohort 1, a set of adult subjects diagnosed with CF currently on stable ORKAMBI® background therapy for a minimum of 3 months will participate in Part B. The Part B Phase II treatment group is comprised of 2 cohorts where subjects will be randomized to either PTI-428 or placebo. Each dose will be administered QD for a total of 28 days. PART C Following the conclusion of Part B Phase II, a set of adult subjects diagnosed with CF will participate in Part C. The Part C Phase II treatment group is comprised of 3 cohorts. Part C Cohort 1 will enroll adult subjects with CF who are eligible to take, but not currently taking, ORKAMBI® in accordance with the approved label. Part C Cohort 2 will enroll adult subjects with CF currently on stable KALYDECO® background therapy for a minimum of 3 months at the time of randomization. Part C Cohort 3 will enroll adult subjects with CF who are not currently on any background therapies and are pancreatic sufficient. Each PTI-428 or placebo dose will be administered QD for a total of 28 days.