When triple therapy is not working: A reverse iceberg perspective

Cystic fibrosis is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, and nearly 90% of patients have at least one copy of the Phe508del CFTR mutation. In a phase 2 trial involving patients who were heterozygous for the Phe508del CFTR mutation and a minimal-function mutation (Phe508del-minimal function genotype), the next-generation CFTR corrector elexacaftor, in combination with tezacaftor and ivacaftor, improved Phe508del CFTR function and clinical outcomes.

Cystic fibrosis transmembrane conductance regulator (CFTR) modulators correct the basic defect caused by CFTR mutations. Improvements in health outcomes have been achieved using the combination of a CFTR corrector and potentiator in people with CF (pwCF) homozygous for F508del . The addition of elexacaftor (ELX; VX-445), a next-generation CFTR corrector, to tezacaftor/ivacaftor (TEZ/IVA) further improved F508del-CFTR function and clinical outcomes in a phase 2 study in pwCF homozygous for F508del . A phase 3, multi-centre, randomised, double-blind, active-controlled trial of ELX in triple combination with TEZ/IVA (ELX/TEZ/IVA) in pwCF homozygous for F508del was conducted. Eligible participants were aged ≥12 years with stable disease and percent predicted forced expiratory volume in 1 second (ppFEV 1 ) of 40 to 90, inclusive. After a four-week TEZ/IVA run-in, participants were randomised 1:1 to four weeks of ELX/TEZ/IVA versus TEZ/IVA alone. The primary endpoint was absolute change from baseline (measured at the end of the TEZ/IVA run-in) in ppFEV 1 at week 4. Key secondary endpoints were absolute change in sweat chloride and CF Questionnaire–Revised respiratory domain (CFQ-R RD) score. ClinicalTrials.gov , number NCT03525548 . Between August and December 2018, 113 participants were enrolled. Following the run-in, 107 participants were randomised and completed the 4-week treatment period. The ELX/TEZ/IVA group had improvements in ppFEV 1 (10·0 percentage points, 95% CI 7·4 to 12·6, p<0·0001), sweat chloride concentration (−45·1 mmol/L, 95% CI −50·1 to −40·1, p<0·0001), and CFQ-R RD score (17·4 points, 95% CI 11·8 to 23·0, p<0·0001) compared with the TEZ/IVA group. ELX/TEZ/IVA was well tolerated, with no discontinuations. Most adverse events were mild or moderate; serious adverse events occurred in 4% (n=2) of participants receiving ELX/TEZ/IVA and 2% (n=1) receiving TEZ/IVA. ELX/TEZ/IVA provided clinically robust benefit vs TEZ/IVA alone with a favourable safety profile and demonstrates the potential to lead to transformative improvements in the lives of pwCF homozygous for F508del .

The Cystic Fibrosis Questionnaire-Revised (CFQ-R) is a validated patient-reported outcome (PRO) containing both generic scales and scales specific to cystic fibrosis (CF). The minimal clinically important difference (MCID) score for a PRO corresponds to the smallest clinically relevant change a patient can detect. MCID scores for the CFQ-R respiratory symptom (CFQ-R-Respiratory) scale were determined using data from two 28 day, open-label, tobramycin inhalation solution (TIS) studies in patients with CF and chronic Pseudomonas aeruginosa airway infection. At study enrollment, patients in the study 1-exacerbation had symptoms indicative of pulmonary exacerbation (n = 84; or = 14 years of age, 53 patients); patients in study 2-stable had stable respiratory symptoms (n = 140; or = 14 years, 126 patients). The anchor-based method utilized a global rating-of-change questionnaire (GRCQ) that assessed patients' perceptions of change in their respiratory symptoms after TIS treatment. The mean change from baseline CFQ-R-Respiratory scores were mapped onto the GRCQ to estimate the MCID. The two distribution-based methods were as follows: (1) 0.5 SD of mean change in CFQ-R-Respiratory scores (baseline to end of TIS treatment); and (2) 1 SEM for baseline CFQ-R-Respiratory scores. Triangulation of these three estimates defined the MCIDs. MCID scores were larger for patients in study 1-exacerbation (8.5 points) than for those in study 2-stable (4.0 points), likely reflecting differences in patient disease status (exacerbation/stable) between these studies. Patient benefit from new and current CF therapies can be evaluated using changes in CFQ-R-Respiratory scores. Using the MCID provides a systematic way to interpret these changes, and facilitates the identification of CF treatments that improve both symptoms and physiologic variables, potentially leading to better treatment adherence and clinical outcomes. Trial registration (study 1-exacerbation): Australian-New Zealand Clinical Trials Registry Identifier: ACTRN 12605000602628 Trial registration (study 2-stable): ClinicalTrials.gov Identifier: NCT00104520.