Chronic and acute modulator treatment restore wild-type-like activity and stability to the primary cystic...

Elexacaftor-tezacaftor-ivacaftor has transformed the treatment of people with cystic fibrosis (CF) and the predominant cystic fibrosis transmembrane conductance regulator (CFTR) variant F508del by delivering the faulty channel to the plasma membrane and potentiating its activity. However, the action of elexacaftor-tezacaftor-ivacaftor on the molecular behavior of F508del-CFTR is unknown. Here, we investigated the impact of elexacaftor-tezacaftor-ivacaftor on individual human F508del-CFTR Cl^- channels using the patch-clamp technique and cells heterologously expressing F508del-CFTR. Chronic treatment of F508del-CFTR-expressing cells with elexacaftor-tezacaftor-ivacaftor, but not pairs of CFTR modulators, stabilized F508del-CFTR, preventing channel deactivation in cell-free membrane patches and conferring upon it the current amplitude of wild-type CFTR with channel activity sustained at a level one-third that of wild-type CFTR. By incubating cells with different drug concentrations, we demonstrated that elexacaftor stabilizes the open-channel conformation of elexacaftor-tezacaftor-ivacaftor-rescued F508del-CFTR, while acute treatment of wild-type CFTR with elexacaftor increased current flow through the channel and potentiated channel gating. Of note, acute treatment of elexacaftor-tezacaftor-ivacaftor-rescued F508del-CFTR Cl^- channels with elexacaftor and ivacaftor restored wild-type levels of channel activity to the CFTR variant, albeit its gating pattern was distinct from that of wild-type CFTR and characterized by infrequent prolonged bursts of channel openings. In conclusion, chronic treatment with elexacaftor-tezacaftor-ivacaftor plus acute treatment with elexacaftor and ivacaftor robustly corrects the processing, stability, and gating defects of F508del-CFTR. Our results reveal that elexacaftor is a triple-acting CFTR modulator with corrector, potentiator, and conduction activities, making it a valuable therapeutic to rescue CFTR variants with distinct molecular mechanisms of CFTR dysfunction.