Study of Cavosonstat (N91115) in Patients With CF Homozygous for the F508del-CFTR Mutation

Inclusion Criteria: * Patients must have been treated with lumacaftor/ivacaftor for at least 8 weeks prior to Day 1 (start of dosing) * A history of Sweat Chloride (SC) ≥ 60 mEq/L by quantitative pilocarpine iontophoresis test (QPIT) (either before or after starting lumacaftor/ivacaftor treatment) * Body weight ≥ 40 kg * ppFEV1 40 - 85 % predicted (inclusive) at screening * Oxygen saturation ≥ 90% breathing ambient air at screening Exclusion Criteria: * Any acute infection that requires treatment or hospitalization within 2 weeks of Study Day 1 * Colonization with organisms associated with more rapid decline in pulmonary status, such as Burkholderia cenocepacia, Burkholderia dolosa, and Mycobacterium abscessus * Any change in the regimen for chronic therapies for CF lung disease (e.g., Pulmozyme®, hypertonic saline, Azithromycin, TOBI®, Cayston®) within 4 weeks of Study Day 1 * Are pregnant, planning a pregnancy, or breast-feeding at screening * Blood hemoglobin \< 10 g/dL at screening * Serum albumin \< 2.5 g/dL at screening * Abnormal liver function defined as ≥ 3 x upper limit of normal (ULN) * History of abnormal renal function within 3 months of screening * History of ventricular tachycardia or other clinically significant ventricular arrhythmias * History, including the screening assessment, of prolonged QT and/or QTcF (Fridericia's correction) interval * History of solid organ or hematological transplantation * History of alcohol abuse or drug abuse * Ongoing participation in another therapeutic clinical trial * Use of continuous (24 hr/day) or nocturnal supplemental oxygen