Lipophilicity of the Cystic Fibrosis Drug, Ivacaftor (VX-770), and Its Destabilizing Effect on the Major CF-causing Mutation: F508del

Abstract

The major Cystic Fibrosis (CF) causing mutation, the deletion of phenylalanine at position 508 (F508del) at the cystic fibrosis transmembrane conductance regulator (CFTR), occurs in approximately 90% of the CF population. Recently, a combination therapy, comprising a corrector (VX-809) that rescues the processing defects of F508del-CFTR and a potentiator (VX-770) that rescues mutant channel activity, was approved for CF patients homozygous for this mutation. However, clinical studies revealed that the efficacy of this drug on lung function was modest and variable amongst patients. It has been proposed that this modest effect may partially relate to a destabilizing effect of VX-770 on mutant protein. In the current studies, we observed a similar concentration-dependent destabilizing effect of VX-770 on F508del-CFTR and on other ion transporters. We found that the relative destabilizing effect of a panel of VX-770 derivatives correlated with their predicted lipophilicity. Given the importance of CFTR association with lipid rafts, we were prompted to determine if VX-770 directly disrupted lipid rafts. Polarized total internal reflection fluorescence microscopy on a supported lipid bilayer model shows that VX-770, and not its less lipophilic derivative, increased the fluidity of and reorganized the membrane. In summary, our findings support the claim that VX-770 modulates CFTR stability via interaction with membrane lipids.