Inclusion Criteria:

   - Confirmed diagnosis of CF defined as: with 2 CF-causing mutations, chronic
   sinopulmonary disease or gastrointestinal/nutritional abnormalities

   - Subjects who weigh ≥15 kg without shoes at Screening Visit

   - Subjects who are homozygous for the F508del-CFTR mutation

   - Subjects with percent predicted forced expiratory volume in 1 second (FEV1) of 70% to
   105% (inclusive) (Part A) or ≥40% (Part B) at Screening Visit where the predicted
   values are adjusted for age, sex, and height using the Wang equation

   - Subjects with stable CF disease and who are willing to remain on stable CF medication
   regimen

   - Able to swallow tablets

Exclusion Criteria:

   - History of any illness or condition that might confound the results of the study or
   pose an additional risk in administering study drug to the subject

   - Acute respiratory infection, pulmonary exacerbation, or changes in therapy for
   pulmonary disease within 28 days before Day 1 of the study

   - Abnormal liver function as defined in the protocol at Screening Visit

   - Abnormal renal function as defined in the protocol at Screening Visit

   - History of solid organ or hematological transplantation

   - Ongoing participation in an investigational drug study or prior participation in an
   investigational drug study within 30 days prior of Screening Visit

   - History or evidence of lens opacity or cataract at Screening Visit

   - Colonization with organisms associated with a more rapid decline in pulmonary status
   at Screening Visit (Part A only)

   - A standard 12-lead ECG demonstrating QTcF >450 msec at Screening Visit