Cystic fibrosis (CF) is a genetic disease characterized by the lack of cystic fibrosis transmembrane conductance regulator (CFTR) protein expressed in epithelial cells. The resulting defective chloride and bicarbonate secretion and imbalance of the transepithelial homeostasis lead to abnormal airway surface liquid (ASL) composition and properties. The reduced ASL volume impairs ciliary beating with the consequent accumulation of sticky mucus. This situation prevents the normal mucociliary clearance, favouring the survival and proliferation of bacteria and contributing to the genesis of CF lung disease. Here, we have explored the potential of small molecules capable of facilitating the transmembrane transport of chloride and bicarbonate in order to replace the defective transport activity elicited by CFTR in CF airway epithelia. Primary human bronchial epithelial cells obtained from CF and non-CF patients were differentiated into a mucociliated epithelia in order to assess the effects of our compounds on some key properties of ASL. The treatment of these functional models with non-toxic doses of the synthetic anionophores improved the periciliary fluid composition, reducing the fluid re-absorption, correcting the ASL pH and reducing the viscosity of the mucus, thus representing promising drug candidates for CF therapy.

Cystic fibrosis (CF) is a genetic disease associated with the defective function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein that causes obstructive disease and chronic bacterial infections in airway epithelia. The most prevalent CF-causing mutation, the deletion of phenylalanine at position 508 (F508del), leads to CFTR misfolding, trafficking defects and premature degradation. A number of correctors that are able to partially rescue F508del-CFTR processing defects have been identified. Clinical trials have demonstrated that, unfortunately, mono-therapy with the best correctors identified to date does not ameliorate lung function or sweat chloride concentration in homozygous F508del patients. Understanding the mechanisms exerted by currently available correctors to increase mutant F508del-CFTR expression is essential for the development of new CF-therapeutics. We investigated the activity of correctors on the mutant F508del and wild type (WT) CFTR to identify the protein domains whose expression is mostly affected by the action of correctors, and we investigated their mechanisms of action. We found that the four correctors under study, lumacaftor (VX809), the quinazoline derivative VX325, the bithiazole compound corr4a, and the new molecule tezacaftor (VX661), do not influence either the total expression or the maturation of the WT-CFTR transiently expressed in human embryonic kidney 293 (HEK293) cells. Contrarily, they significantly enhance the expression and the maturation of the full length F508del molecule. Three out of four correctors, VX809, VX661 and VX325, seem to specifically improve the expression and the maturation of the mutant CFTR N-half (M1N1, residues 1–633). By contrast, the CFTR C-half (M2N2, residues 837–1480) appears to be the region mainly affected by corr4a. VX809 was shown to stabilize both the WT- and F508del-CFTR N-half isoforms, while VX661 and VX325 demonstrated the ability to enhance the stability only of the mutant F508del polypeptide.

Cystic fibrosis (CF) is a recessive genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein, a chloride and bicarbonate channel localized on the plasma membrane of epithelial cells. Over the last three decades, high-throughput screening assays have been extensively employed in identifying drugs that target specific defects arising from CFTR mutations. The two main categories of such compounds are potentiators, which enhance CFTR gating by increasing the channel’s open probability, and correctors, which improve CFTR protein folding and trafficking to the plasma membrane. In addition to these, other investigational molecules include amplifiers and stabilizers, which enhance the levels and the stability of CFTR on the cell surface, and read-through agents that promote the insertion of correct amino acids at premature termination codons. Currently, four CFTR modulators are clinically approved: the potentiator ivacaftor (VX-770), either as monotherapy or in combination with the correctors lumacaftor (VX-809), tezacaftor (VX-661), and elexacaftor (VX-445). Among these, the triple combination VX-445/VX-661/VX-770 (marketed as Trikafta^® in the US and Kaftrio^® in Europe) has emerged as the most effective CFTR modulator therapy to date, demonstrating significant clinical benefits in phase III trials for patients with at least one F508del CFTR allele. Despite these advancements, the mechanisms of action and binding sites of these modulators on CFTR have only recently begun to be elucidated. A deeper understanding of these mechanisms could provide essential insights for developing more potent and effective modulators, particularly in combination therapies. This narrative review delves into the mechanism of action, binding sites, and combinatorial effects of approved and investigational CFTR modulators, highlighting ongoing efforts to broaden therapeutic options for individuals with CF.