CFTR correctors potentiate gating mutants causing cystic fibrosis

The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) modulator VX-445 (Elexacaftor) used to treat cystic fibrosis presents both corrector and potentiator activities. This drug binds to a pocket within the CFTR membrane-spanning domain (MSD) assembly, in contact with the lasso motif. We have previously shown that the corrector activity of VX-445 is modulated by mutations within MSD1 and the nucleotide binding domain NBD1. Here, we evaluate if mutations affecting VX-445's corrector activity also affect its potentiator activity. Responses to increasing concentrations of VX-445 were measured using the halide sensitive fluorescent assay after transfection of CFTR mutants in HEK293 cells. Results show that VX-445 potentiated gating mutants causing cystic fibrosis located in the NBDs (NBD1 G551D and NBD2 G1349D) and in the IntraCellular Loops (ICL1 G178R and ICL3 G970R). Mutations within the VX-445 binding site inhibited potentiation of G551D, contrary to some mutations located outside this site that affected its corrector activity, two of which (M212A and F224A) were found to induce CFTR gain-of-function. Potentiation of G551D was also observed with correctors VX-809 and VX-121. In conclusion, CFTR modulator VX-445 can promote channel activity of gating mutants, an effect which is dependent on the integrity of its binding site. Potentiation could also be observed with correctors VX-809 and VX-121, indicating that more generally, CFTR correctors can promote channel activity.