Available drugs are unable to effectively rescue the folding defects in vitro and ameliorate the clinical-phenotype of cystic fibrosis (CF), caused by deletion of F508 (ΔF508 or F508del) and some point mutations in the CF transmembrane conductance regulator (CFTR), a plasma membrane (PM) anion channel. To overcome the corrector efficacy ceiling, here we show that compounds targeting distinct structural defects of CFTR can synergistically rescue mutants expression and function at the PM. High throughput cell-based screens and mechanistic analysis identified three small-molecule series that target defects at the nucleotide binding domain (NBD1), NBD2 and their membrane spanning domains (MSDs) interfaces. While individually these compounds marginally improve ΔF508-CFTR folding efficiency, function, and stability, their combinations lead to ~50–100% of wild type-level correction in immortalized and primary human airway epithelia, and in mouse nasal epithelia. Likewise, corrector combinations were effective for rare missense mutations in various CFTR domains, probably acting via structural allostery, suggesting a mechanistic framework for their broad application.

Cystic fibrosis (CF) is caused by defective Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein. Morbidity is mainly due to early airway infection. We hypothesized that S. aureus clearance during the first hours of infection was impaired in CF human Airway Surface Liquid (ASL) because of a lowered pH. The ASL pH of human bronchial epithelial cell lines and primary respiratory cells from healthy controls (WT) and patients with CF was measured with a pH microelectrode. The antimicrobial capacity of airway cells was studied after S. aureus apical infection by counting surviving bacteria. ASL was significantly more acidic in CF than in WT respiratory cells. This was consistent with a defect in bicarbonate secretion involving CFTR and SLC26A4 (pendrin) and a persistent proton secretion by ATP12A. ASL demonstrated a defect in S. aureus clearance which was improved by pH normalization. Pendrin inhibition in WT airways recapitulated the CF airway defect and increased S. aureus proliferation. ATP12A inhibition by ouabain decreased bacterial proliferation. Antimicrobial peptides LL-37 and hBD1 demonstrated a pH-dependent activity. Normalizing ASL pH might improve innate airway defense in newborns with CF during onset of S. aureus infection. Pendrin activation and ATP12A inhibition could represent novel therapeutic strategies to normalize pH in CF airways.