A Phase 1 Study Evaluating Safety and Tolerability of RCT2100 in Healthy Participants and in Participants With CF

Part 1 Major Inclusion Criteria:

• Healthy, adult, male or female, 18-55 years of age, inclusive, at screening.

• Body weight greater than or equal to 50 kg and body mass index (BMI) between 16-32kg/m2, inclusive

• The participant has a forced expiratory volume in one second (FEV1) of at least 80%predicted

• The participant is considered by the investigator to be in good general health asdetermined by medical history, clinical laboratory test results, vital signmeasurements, 12-lead ECG results, and physical examination findings at screening.

• Understands the study procedures in the informed consent form (ICF), and is willingand able to comply with the protocol.

Part 1 Major Exclusion Criteria:

• History or presence of clinically significant medical, surgical, clinicallaboratory, or psychiatric condition or disease.

• The participant has supine blood pressure (BP) >150 mm Hg (systolic) or >90 mm Hg (diastolic), following at least 5 minutes of supine rest.

• The participant has abnormal clinical laboratory tests at screening, as assessed bythe study-specific laboratory.

• The participant is a smoker or has used nicotine or nicotine-containing products 6weeks before the first dose of study drug. Former smokers with greater than 10 packyears of smoking history are excluded.

Part 2 Major Inclusion Criteria:

• Confirmed diagnosis of CF

• Forced expiratory volume in 1 second ≥40% and ≤100% of predicted mean value for age,sex, and height

• a) Not eligible for CFTR modulators based on having mutations of CFTR gene on bothalleles that are not responsive to CFTR modulator therapy OR

• b) Eligible for CFTR modulators (based on local prescribing information) but notusing CFTR modulators due to intolerance or contraindications

Part 2 Major Exclusion Criteria:

• Hepatic cirrhosis with portal hypertension, moderate hepatic impairment (Child PughScore 7 to 9), or severe hepatic impairment (Child Pugh Score 10 to 15)

• An acute upper or lower respiratory infection, pulmonary exacerbation, or changes intherapy (including antibiotics) for sinopulmonary disease within 4 weeks before thefirst dose of study drug

• Lung infection with organisms associated with a more rapid decline in pulmonarystatus

• Arterial oxygen saturation on room air less than 94% at screening

• Values of AST, ALT, alkaline phosphatase, or gamma-glutamyl transferase (GGT) ≥3×ULN

• Treatment with a CFTR modulator (Kalydeco, Trikafta, Symdeko, or Orkambi) within 12weeks of Screening

Other protocol defined Inclusion/Exclusion criteria may apply.