['cystic fibrosis']
['pti-428', 'placebo']

        Inclusion Criteria:

          -  Confirmed diagnosis of CF.

          -  Forced expiratory volume in 1 second (FEV1) 40-90% predicted.

          -  Non-smoker and non-tobacco user for a minimum of 30 days prior to screening and for
             the duration of the study.

        Exclusion Criteria:

          -  Participation in another clinical trial or treatment with an investigational agent
             within 30 days or 5 half-lives, whichever is longer, prior to Study Day 1.

          -  History of cancer within the past five years (excluding cervical CIS with curative
             therapy for at least one year prior to screening and non-melanoma skin cancer).

          -  History of organ transplantation.

          -  Any sinopulmonary infection or CF exacerbation requiring a change or addition of
             medication (including antibiotics) within 1 month of Study Day 1 or any other
             clinically significant infection as determined by the investigator within 1 month of
             Day 1.

          -  History of alcohol or drug abuse or dependence within 12 months of screening as
             determined by the Investigator.

          -  Male and female of child-bearing potential, unless they are using highly effective
             methods of contraception during participation in the clinical study and for 4 weeks
             after termination from study.

          -  Pregnant or nursing women.
      