Early Signs of Efficacy Study With Riociguat in Adult Homozygous Delta F508 Cystic Fibrosis Patients

Inclusion Criteria: * Signed informed consent available before any study specific tests or procedures are performed * Patients must be at least 18 years of age at time of inclusion (i.e. upon signature of informed consent) * Patient diagnosed with Cystic Fibrosis according to standard criteria (i.e. either elevated sweat chloride content above 60 mmol/ L and/ or genetic testing) * Patient is homozygous for the deltaF508 mutation * Patient has a mild-to-moderate stage of lung disease as determined by FEV1 (FEV1 between 40 and 100% predicted) * Patient has a stable condition of lung disease (no ongoing or recent pulmonary exacerbation and no change in current treatment) within the last 4 weeks prior to screening * Ability and willingness to understand and follow study procedures for the entire study * Patients do not smoke. Patients with a history of smoking can be included, if they have refrained from smoking for the last 3 months. If a patients starts smoking during the study participation, he/ she needs to be excluded and considered to be a drop out * Body mass index (BMI): ≥ 16 kg/ m² (calculated by dividing the patient's weight by the square of his/ her height \[kg/ m2\]) Inclusion criterion valid for study part 1 only: \- Women of childbearing potential must agree to use adequate contraception when sexually active. 'Adequate contraception' is defined as one highly effective form of contraception (intrauterine devices \[IUD\], contraceptive implants or tubal sterilization) or a combination of methods (hormone method with a barrier method ). If a partner's vasectomy is the chosen method of contraception or if a partner has documented azoospermia, a hormone or barrier method must be used in combination. Adequate contraception is required from the signing of the informed consent form up until 4 weeks after the last study drug administration Inclusion criteria valid for study part 2 only: * Women of childbearing potential must agree to use adequate contraception when sexually active. 'Adequate contraception' is defined as one highly effective form of contraception (intrauterine devices \[IUD\], contraceptive implants or tubal sterilization) or a combination of methods (hormone method with a barrier method). For patients on Orkambi hormonal methods (including hormonal oral contraceptives) cannot be accepted in this study. They need to choose non-hormonal methods. If a partner's vasectomy is the chosen method of contraception or if a partner has documented azoospermia, a hormone or barrier method must be used in combination. Adequate contraception is required from the signing of the informed consent form up until 4 weeks after the last study drug administration * Patients receiving Orkambi (Lumcaftor + Ivacaftor) as part of their standard care need to be on stable Orkambi treatment for at least 3 months prior to screening (patients on Lumacaftor and/or Ivacaftor are excluded in part 1) Exclusion Criteria: * Patients with Cystic Fibrosis with any background other than homozygous deltaF508 mutation * Exclusion criterion only valid for study part 1: Patients receiving treatment with Lumacaftor and/ or Ivacaftor * Active state of hemoptysis or pulmonary hemorrhage, including those events managed by bronchial artery embolization. Also any history of moderate hemoptysis within the 3 months prior to inclusion * Any history of pneumothorax, bronchial artery embolization or massive hemoptysis. Massive hemoptysis being defined as acute bleeding \>240 mL in a 24-hour period or recurrent bleeding \>100 mL/ d over several days * A positive sputum culture for Burkholderia cenocepacia, Burkholderia dolosa, and/ or Mycobacterium abscessus either currently or within the previous year * Active allergic broncho-pulmonary aspergillosis * Current pulmonary exacerbation * Known history of solid organ transplantation * Known history of any form of pulmonary hypertension * Clinically relevant deviations of the screened laboratory parameters from reference ranges outside of expected changes for Cystic Fibrosis patients, especially a hemoglobin value below 110 g/L or a creatinine clearance based on the Cockcroft-Gault formula \< 15 ml/ min