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

Primary Objective: * Assess the efficacy of N91115 at 12 weeks when added to preexisting treatment with lumacaftor/ivacaftor in adult patients with CF who are homozygous for the F508del-CFTR mutation Secondary Objectives: * Assess the effect of N91115 added to lumacaftor/ivacaftor on safety * Assess the effect of lumacaftor/ivacaftor added to N91115 on the pharmacokinetics of N91115, lumacaftor, and ivacaftor