Low free drug concentration prevents inhibition of F508del CFTR functional expression by the potentiator VX-770 (ivacaftor)

Br J Pharmacol. 2016 Feb;173(3):459-70. doi: 10.1111/bph.13365. Epub 2016 Jan 13.


Background and purpose: The most common cystic fibrosis (CF) mutation F508del inhibits the gating and surface expression of CFTR, a plasma membrane anion channel. Optimal pharmacotherapies will probably require both a 'potentiator' to increase channel open probability and a 'corrector' that improves folding and trafficking of the mutant protein and its stability at the cell surface. Interaction between CF drugs has been reported but remains poorly understood.

Experimental approach: CF bronchial epithelial cells were exposed to the corrector VX-809 (lumacaftor) and potentiator VX-770 (ivacaftor) individually or in combination. Functional expression of CFTR was assayed as the forskolin-stimulated short-circuit current (Isc ) across airway epithelial monolayers expressing F508del CFTR.

Key results: The potentiated Isc response during forskolin stimulation was increased sixfold after pretreatment with VX-809 alone and reached ~11% that measured across non-CF monolayers. VX-770 (100 nM) and genistein (50 μM) caused similar levels of potentiation, which were not additive and were abolished by the CFTR inhibitor CFTRinh -172. The unbound fraction of VX-770 in plasma was 0.13 ± 0.04%, which together with previous measurements in patients given 250 mg p.o. twice daily, suggests a peak free plasma concentration of 1.5-8.5 nM. Chronic exposure to high VX-770 concentrations (>1 μM) inhibited functional correction by VX-809 but not in the presence of physiological protein levels (20-40 mg·mL(-1) ). Chronic exposure to a low concentration of VX-770 (100 nM) together with VX-809 (1 μM) also did not reduce the forskolin-stimulated Isc , relative to cells chronically exposed to VX-809 alone, provided it was assayed acutely using the same, clinically relevant concentration of potentiator.

Conclusions and implications: Chronic exposure to clinically relevant concentrations of VX-770 did not reduce F508del CFTR function. Therapeutic benefit of VX-770 + VX-809 (Orkambi) is probably limited by the efficacy of VX-809 rather than by inhibition by VX-770.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminophenols / pharmacology*
  • Aminopyridines / pharmacology
  • Benzodioxoles / pharmacology
  • Bronchi / cytology
  • Cell Line
  • Cells, Cultured
  • Cystic Fibrosis / genetics
  • Cystic Fibrosis Transmembrane Conductance Regulator / genetics
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism*
  • Drug Interactions
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism
  • Humans
  • Mutation
  • Quinolones / pharmacology*


  • Aminophenols
  • Aminopyridines
  • Benzodioxoles
  • Quinolones
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • ivacaftor
  • lumacaftor