A Study to Evaluate Safety, PK and PD of FDL169 in Cystic Fibrosis Subjects

Inclusion Criteria: * Male or female subjects with a confirmed diagnosis of CF defined as a sweat chloride value ≥60 mmol/L by quantitative pilocarpine iontophoresis or two CF-causing mutations,documented in the subject's medical record or confirmed at screening. * Age 18 and above on the date of informed consent. * Weight ≥40 kg. * Homozygous for the F508del-CFTR mutation. Genotyping to be confirmed at screening. * Ability to perform a valid, reproducible spirometry test with demonstration of a forced expiratory volume in 1 sec (FEV1) \>40% of predicted normal for age, sex and height. * Screening laboratory tests with no clinically significant abnormalities that would interfere with the study assessments (as judged by the Investigator). * Subjects who are sexually active must agree to follow the study's contraception requirements. Exclusion Criteria: * An acute upper or lower respiratory tract infection, pulmonary exacerbation, or changes in therapy for pulmonary disease within 4 weeks prior to Day 1. * Major complications of lung disease (including massive hemoptysis, pneumothorax, or pleural effusion) within 8 weeks prior to screening. * Impaired renal function or known portal hypertension. * History of prolonged QT and/or QTcF (Fridericia's correction) interval (\>450 msec) or QTcF \>450 msec at Screening. * History of solid organ or hematological transplantation. * History of alcohol abuse or drug addiction (including cannabis, cocaine and opiates) during the past year, (as judged by the Investigator). * Use of ivacaftor or lumacaftor, within 4 weeks of Day 1 * Any change (initiation, change in type of drug, dose modification, schedule modification, interruption, discontinuation, or re-initiation) in a chronic treatment/prophylaxis regimen for CF or for CF-related conditions within 4 weeks prior to Day 1. * Ongoing immunosuppressive therapy (including systemic corticosteroids). * Hemoglobin \<10 g/dL. * Abnormal liver function, at screening. * Abnormal renal function at screening. * Ongoing participation in another clinical study or prior participation without appropriate washout (minimum of 10 half- lives or 30 days, whichever is longer) prior to Screening visit.