Barriers to the Pharmacologic Rescue of W1282X CFTR

W1282X CFTR is the most prevalent CF-causing variant among cystic fibrosis patients of Ashkenazi descent and a mutational defect for which targeted drug therapy is not available. We show that administration of the potentiator VX-770 can augment levels of truncated W1282X CFTR in the plasma membrane, demonstrating that an established gating activator (i.e., "potentiator") also rescues W1282X protein expression and surface localization (i.e., "corrector" function). Additionally, acute in vitro treatments with approved modulators VX-809 or VX-661 result in immediate potentiation of W1282X-dependent ion transport, showing that F508del CFTR correctors also augment W1282X CFTR channel activity. To investigate the mechanism, we tested a CFTR variant (G551D) exhibiting higher levels of CFTR-dependent potentiation following corrector treatment. Clinically approved CFTR correctors VX-445, VX-121, and VX-809 elicited potentiation of G551D CFTR. Forskolin dose dependence and molecular dynamic simulations indicated that corrector molecules promote acute CFTR gating by modifying protein conformation and enhancing heterodimerization of nucleotide binding domains, leading to potentiator-like effects. Although W1282X is poorly responsive to "readthrough" agents such as G418, the drug unexpectedly increases W1282X mRNA, augments surface-localized (truncated) protein, and promotes CFTR function, even in the absence of detectable stop codon suppression. Moreover, unlike other CFTR mutations such as F508del, proteasome blockade using ALLN partially rescues W1282X at the plasma membrane. These results highlight ways in which detailed mechanistic analysis and modulator profiling are needed to characterize CFTR mutations such as W1282X and that modulator function in rare variants can be quite distinct from classical findings based strictly upon F508del CFTR.