Lumacaftor/ivacaftor in people with cystic fibrosis with an A455E–CFTR mutation

Background Previous in vitro organoid data showed A455E–CFTR, a rare CFTR mutation with 4.1% prevalence in the Netherlands, responds to lumacaftor/ivacaftor (LUM/IVA). We explored LUM/IVA's clinical efficacy in people with CF and ≥1 A455E–CFTR mutation. Methods Participants aged ≥12 years were randomized to 1 of 2 treatment sequences (LUM/IVA→placebo or placebo→LUM/IVA) with an 8–week washout period between. Primary endpoint was absolute change in ppFEV1 from study baseline through 8 weeks. Additional endpoints were change in sweat chloride concentration (SwCl) and CFQ–R respiratory domain score. Correlations between organoid–based measurements and clinical endpoints were investigated. Results Twenty participants were randomized at 2 sites in the Netherlands. Mean absolute change in ppFEV1 from study baseline through Week 8 showed a treatment difference of 0.1 percentage points (95% CI, –2.5 to 2.7; P = 0.928) between LUM/IVA (within–group mean change, 2.7) and placebo (within–group mean change, 2.6). The mean absolute change in SwCl concentration from study baseline through Week 8 showed a treatment difference of –7.8 mmol/L between LUM/IVA and placebo (P = 0.004), while the absolute change in CFQ–R respiratory domain score showed a treatment difference of 3.5 between LUM/IVA and placebo (P = 0.469). The in vitro organoid–based assay demonstrated a concentration–dependent swelling increase with LUM/IVA. Exploratory correlation analyses between organoid swelling and ppFEV1 and SwCl outcomes showed correlation coefficients of 0.49 and –0.11, respectively. Conclusions In this exploratory study, LUM/IVA elicited an in vitro response in organoid swelling and in vivo response in SwCl in participants with CF and ≥1 A455E–CFTR mutation. The primary endpoint (ppFEV1) did not show a statistically significant difference between LUM/IVA and placebo; correlations between in vitro and in vivo responses were not established (NCT03061331).