New pharmacological approaches for cystic fibrosis: promises, progress, pitfalls

With the discovery of the CFTR gene in 1989, the search for therapies to improve the basic defects of cystic fibrosis (CF) commenced. Pharmacological manipulation provides the opportunity to enhance CF transmembrane conductance regulator (CFTR) protein synthesis and/or function. CFTR modulators include potentiators to improve channel gating (class III mutations), correctors to improve abnormal CFTR protein folding and trafficking (class II mutations) and stop codon mutation read-through drugs relevant for patients with premature stop codons (most class I mutations). After several successful clinical trials the potentiator, ivacaftor, is now licenced for use in adults and children (>six years), with CF bearing the class III G551D mutation and FDA licence was recently expanded to include 8 additional class III mutations. Alternative approaches for class I and class II mutations are currently being studied. Combination drug treatment with correctors and potentiators appears to be required to restore CFTR function of F508del, the most common CFTR mutation. Alternative therapies such as gene therapy and pharmacological modulation of other ion channels may be advantageous because they are mutation-class independent, however progress is less well advanced. Clinical trials for CFTR modulators have been enthusiastically embraced by patients with CF and health care providers. Whilst novel trial end-points are being evaluated allowing CFTR modulators to be efficiently tested, many challenges related to the complexity of CFTR and the biology of the epithelium still need to be overcome.