This trial will consist of three arms: Part A, Part B, and Part C. Part A has two groups. The first group will enroll adult subjects with cystic fibrosis (CF) into a single ascending dose (SAD) treatment group. The second group will enroll adult subjects with CF, including those on background treatment with ORKAMBI® and those not on a cystic fibrosis transmembrane conductance regulator (CFTR) modulator, into a multiple ascending dose (MAD) treatment group. Part B will enroll adult subjects with CF currently on stable ORKAMBI® background therapy for a minimum of 3 months into a Phase II treatment group consisting of two cohorts. Part C will enroll adult subjects with CF, including those on background treatment with KALYDECO® and those not on a CFTR modulator, into a Phase II treatment group consisting of three cohorts. Approximately 136 subjects will be enrolled.