Abstract
BackgroundThe best investigational drug to treat cystic fibrosis (CF) patients with the most common CF-causing mutation (F508del) is VX-809 (lumacaftor) which recently succeeded in Phase III clinical trial in combination with ivacaftor. This corrector rescues F508del-CFTR from its abnormal intracellular localization to the cell surface, a traffic defect shared by all Class II CFTR mutants. Our goal here is to test the efficacy of lumacaftor in other Class II mutants in primary human bronchial epithelial (HBE) cells derived from CF patients. MethodsThe effect of lumacaftor was investigated in primary HBE cells from non-CF and CF patients with F508del/F508del, A561E/A561E, N1303K/G542X, F508del/G542X and F508del/Y1092X genotypes by measurements of Forskolin plus Genistein-inducible equivalent short-circuit current (Ieq-SC-Fsk+Gen) in perfused open-circuit Ussing chambers. Efficacy of corrector C18 was also assessed on A561E/A561E and F508del/F508del cells. ResultsOur data indicate that A561E (when present in both alleles) responds positively to lumacaftor treatment at equivalent efficacy of F508del in primary HBE cells. Similarly, lumacaftor has a positive impact on Y1092X, but not on N1303K. Our data also show that cells with only one copy of F508del-CFTR respond less to VX-809. Moreover, there is great variability in lumacaftor responses among F508del-homozygous cells from different donors. Compound C18 failed to rescue A561E-CFTR but not in F508del-CFTR, thus plausibly it has a different mechanism of action distinct from lumacaftor. ConclusionsCF patients with A561E (and likely also those with Y1029X) can potentially benefit from lumacaftor. Moreover, the methodology used here exemplifies how ex vivo approaches may apply personalized therapies to CF and possibly other respiratory diseases.
Highlights
Cystic fibrosis (CF), the most common life-shortening genetic disease affecting approximately 80,000 people worldwide (Bobadilla et al, 2002; The Molecular Genetic Epidemiology; Farrell, 2008; Rodrigues et al, 2009), is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein
The dominating clinical CF phenotype is the respiratory disease, being hallmarks of this disease the very thick mucus obstructing the airways, chronic inflammation and persistent infections mostly by Pseudomonas aeruginosa, which altogether lead to eventual impairment of Abbreviations: CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance regulator; (ΔIeq-sc), equivalent short-circuit currents; ENaC, epithelial Na+ channel; Fsk, forskolin; Gen, Genistein; HBE, human bronchial epithelial cells; SEM, standard error of the mean; Transepithelial electrical resistance (TEER), transepithelial electrical resistance; Vte, transepithelial voltage; Rte, transepithelial resistance
The equivalent short-circuit current (Ieq-SC) as a measurement of CFTR-mediated Cl− secretion was determined for cAMP-stimulation by both Forskolin (Ieq-SC-Fsk) alone or with Genistein (Ieq-SC-Fsk + Gen). These results show that Fsk + Gen responses of F508del/F508del (2 donors), A561E/A561E F508del/G542X and F508del/Y1092X cells after VX-809/lumacaftor treatment were significantly different from those under DMSO, while that of N1303K/G542X cells was not significantly different (Fig. 3b)
Summary
Cystic fibrosis (CF), the most common life-shortening genetic disease affecting approximately 80,000 people worldwide (Bobadilla et al, 2002; The Molecular Genetic Epidemiology; Farrell, 2008; Rodrigues et al, 2009), is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The best investigational drug to treat cystic fibrosis (CF) patients with the most common CF-causing mutation (F508del) is VX-809 (lumacaftor) which recently succeeded in Phase III clinical trial in combination with ivacaftor. This corrector rescues F508del-CFTR from its abnormal intracellular localization to the cell surface, a traffic defect shared by all Class II CFTR mutants. Results: Our data indicate that A561E (when present in both alleles) responds positively to lumacaftor treatment at equivalent efficacy of F508del in primary HBE cells. The methodology used here exemplifies how ex vivo approaches may apply personalized therapies to CF and possibly other respiratory diseases
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