Where are we with transformational therapies for patients with cystic fibrosis?

Theratyping of the Rare CFTR Genotype A559T in Rectal Organoids and Nasal Cells Reveals a Relevant Response to Elexacaftor (VX-445) and Tezacaftor (VX-661) Combination

Despite the promising results of new CFTR targeting drugs designed for the recovery of F508del- and class III variants activity, none of them have been approved for individuals with selected rare mutations, because uncharacterized CFTR variants lack information associated with the ability of these compounds in recovering their molecular defects. Here we used both rectal organoids (colonoids) and primary nasal brushed cells (hNEC) derived from a CF patient homozygous for A559T (c.1675G>A) variant to evaluate the responsiveness of this pathogenic variant to available CFTR targeted drugs that include VX-770, VX-809, VX-661 and VX-661 combined with VX-445. A559T is a rare mutation, found in African-Americans people with CF (PwCF) with only 85 patients registered in the CFTR2 database. At present, there is no treatment approved by FDA (U.S. Food and Drug Administration) for this genotype. Short-circuit current (Isc) measurements indicate that A559T-CFTR presents a minimal function. The acute addition of VX-770 following CFTR activation by forskolin had no significant increment of baseline level of anion transport in both colonoids and nasal cells. However, the combined treatment, VX-661-VX-445, significantly increases the chloride secretion in A559T-colonoids monolayers and hNEC, reaching approximately 10% of WT-CFTR function. These results were confirmed by forskolin-induced swelling assay and by western blotting in rectal organoids. Overall, our data show a relevant response to VX-661-VX-445 in rectal organoids and hNEC with CFTR genotype A559T/A559T. This could provide a strong rationale for treating patients carrying this variant with VX-661-VX-445-VX-770 combination.

Pathophysiology of Lung Disease and Wound Repair in Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal recessive, life-threatening condition affecting many organs and tissues, the lung disease being the chief cause of morbidity and mortality. Mutations affecting the CF Transmembrane Conductance Regulator (CFTR) gene determine the expression of a dysfunctional protein that, in turn, triggers a pathophysiological cascade, leading to airway epithelium injury and remodeling. In vitro and in vivo studies point to a dysregulated regeneration and wound repair in CF airways, to be traced back to epithelial CFTR lack/dysfunction. Subsequent altered ion/fluid fluxes and/or signaling result in reduced cell migration and proliferation. Furthermore, the epithelial-mesenchymal transition appears to be partially triggered in CF, contributing to wound closure alteration. Finally, we pose our attention to diverse approaches to tackle this defect, discussing the therapeutic role of protease inhibitors, CFTR modulators and mesenchymal stem cells. Although the pathophysiology of wound repair in CF has been disclosed in some mechanisms, further studies are warranted to understand the cellular and molecular events in more details and to better address therapeutic interventions.

Evaluation of Fused Pyrrolothiazole Systems as Correctors of Mutant CFTR Protein

Cystic fibrosis (CF) is a genetic disease caused by mutations that impair the function of the CFTR chloride channel. The most frequent mutation, F508del, causes misfolding and premature degradation of CFTR protein. This defect can be overcome with pharmacological agents named “correctors”. So far, at least three different classes of correctors have been identified based on the additive/synergistic effects that are obtained when compounds of different classes are combined together. The development of class 2 correctors has lagged behind that of compounds belonging to the other classes. It was shown that the efficacy of the prototypical class 2 corrector, the bithiazole corr-4a, could be improved by generating conformationally-locked bithiazoles. In the present study, we investigated the effect of tricyclic pyrrolothiazoles as analogues of constrained bithiazoles. Thirty-five compounds were tested using the functional assay based on the halide-sensitive yellow fluorescent protein (HS-YFP) that measured CFTR activity. One compound, having a six atom carbocyle central ring in the tricyclic pyrrolothiazole system and bearing a pivalamide group at the thiazole moiety and a 5-chloro-2-methoxyphenyl carboxamide at the pyrrole ring, significantly increased F508del-CFTR activity. This compound could lead to the synthesis of a novel class of CFTR correctors.

Small Molecule Anion Carriers Correct Abnormal Airway Surface Liquid Properties in Cystic Fibrosis Airway Epithelia

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.

Discovery of a picomolar potency pharmacological corrector of the mutant CFTR chloride channel

F508del, the most frequent mutation causing cystic fibrosis (CF), results in mistrafficking and premature degradation of the CFTR chloride channel. Small molecules named correctors may rescue F508del-CFTR and therefore represent promising drugs to target the basic defect in CF. We screened a carefully designed chemical library to find F508del-CFTR correctors. The initial active compound resulting from the primary screening underwent extensive chemical optimization. The final compound, ARN23765, showed an extremely high potency in bronchial epithelial cells from F508del homozygous patients, with an EC₅₀ of 38 picomolar, which is more than 5000-fold lower compared to presently available corrector drugs. ARN23765 also showed high efficacy, synergy with other types of correctors, and compatibility with chronic VX-770 potentiator. Besides being a promising drug, particularly suited for drug combinations, ARN23765 represents a high-affinity probe for CFTR structure-function studies.

An Up-to-Date Overview of the Complexity of Genotype-Phenotype Relationships in Myotonic Channelopathies

Myotonic disorders are inherited neuromuscular diseases divided into dystrophic myotonias and non-dystrophic myotonias (NDM). The latter is a group of dominant or recessive diseases caused by mutations in genes encoding ion channels that participate in the generation and control of the skeletal muscle action potential. Their altered function causes hyperexcitability of the muscle membrane, thereby triggering myotonia, the main sign in NDM. Mutations in the genes encoding voltage-gated Cl⁻ and Na⁺ channels (respectively, CLCN1 and SCN4A) produce a wide spectrum of phenotypes, which differ in age of onset, affected muscles, severity of myotonia, degree of hypertrophy, and muscle weakness, disease progression, among others. More than 200 CLCN1 and 65 SCN4A mutations have been identified and described, but just about half of them have been functionally characterized, an approach that is likely extremely helpful to contribute to improving the so-far rather poor clinical correlations present in NDM. The observed poor correlations may be due to: (1) the wide spectrum of symptoms and overlapping phenotypes present in both groups (Cl⁻ and Na⁺ myotonic channelopathies) and (2) both genes present high genotypic variability. On the one hand, several mutations cause a unique and reproducible phenotype in most patients. On the other hand, some mutations can have different inheritance pattern and clinical phenotypes in different families. Conversely, different mutations can be translated into very similar phenotypes. For these reasons, the genotype-phenotype relationships in myotonic channelopathies are considered complex. Although the molecular bases for the clinical variability present in myotonic channelopathies remain obscure, several hypotheses have been put forward to explain the variability, which include: (a) differential allelic expression; (b) trans-acting genetic modifiers; (c) epigenetic, hormonal, or environmental factors; and (d) dominance with low penetrance. Improvements in clinical tests, the recognition of the different phenotypes that result from particular mutations and the understanding of how a mutation affects the structure and function of the ion channel, together with genetic screening, is expected to improve clinical correlation in NDMs.

Exercise Physiology Across the Lifespan in Cystic Fibrosis

Cystic fibrosis (CF), a severe life-limiting disease, is associated with multi-organ pathologies that contribute to a reduced exercise capacity. At present, the impact of, and interaction between, disease progression and other age-related physiological changes in CF on exercise capacity from child- to adult-hood is poorly understood. Indeed, the influences of disease progression and aging are inherently linked, leading to increasingly complex interactions. Thus, when interpreting age-related differences in exercise tolerance and devising exercise-based therapies for those with CF, it is critical to consider age-specific factors. Specifically, changes in lung function, chronic airway colonization by increasingly pathogenic and drug-resistant bacteria, the frequency and severity of pulmonary exacerbations, endocrine comorbidities, nutrition-related factors, and CFTR (cystic fibrosis transmembrane conductance regulator protein) modulator therapy, duration, and age of onset are important to consider. Accounting for how these factors ultimately influence the ability to exercise is central to understanding exercise impairments in individuals with CF, especially as the expected lifespan with CF continues to increase with advancements in therapies. Further studies are required that account for these factors and the changing landscape of CF in order to better understand how the evolution of CF disease impacts exercise (in)tolerance across the lifespan and thereby identify appropriate intervention targets and strategies.

Beyond cystic fibrosis transmembrane conductance regulator therapy: a perspective on gene therapy and small molecule treatment for cystic fibrosis

Cystic fibrosis (CF) is a life-limiting disease caused by defective or deficient cystic fibrosis transmembrane conductance regulator (CFTR) activity. The recent advent of the FDA-approved CFTR modulator drug ivacaftor, alone or in combination with lumacaftor or tezacaftor, has enabled treatment of the majority of patients suffering from CF. Even before the identification of the CFTR gene, gene therapy was put forward as a viable treatment option for this genetic condition. However, initial enthusiasm has been hampered as CFTR gene delivery to the lungs has proven to be more challenging than expected. This review covers the contemporary clinical and scientific knowledge base for small molecule CFTR modulator drug therapy, gene delivery vectors and CRISPR/Cas9 gene editing and highlights the prospect of these technologies for future treatment options.

Small molecule-facilitated anion transporters in cells for a novel therapeutic approach to cystic fibrosis

BACKGROUND AND PURPOSE

Cystic fibrosis (CF) is a lethal autosomal recessive genetic disease that originates from the defective function of the CF transmembrane conductance regulator (CFTR) protein, a cAMP-dependent anion channel involved in fluid transport across epithelium. Because small synthetic transmembrane anion transporters (anionophores) can replace the biological anion transport mechanisms, independent of genetic mutations in the CFTR, such anionophores are candidates as new potential treatments for CF.

EXPERIMENTAL APPROACH

In order to assess their effects on cell physiology, we have analysed the transport properties of five anionophore compounds, three prodigiosines and two tambjamines. Chloride efflux was measured in large uni-lamellar vesicles and in HEK293 cells with chloride-sensitive electrodes. Iodide influx was evaluated in FRT cells transfected with iodide-sensitive YFP. Transport of bicarbonate was assessed by changes of pH after a NH₄ ⁺ pre-pulse using the BCECF fluorescent probe. Assays were also carried out in FRT cells permanently transfected with wild type and mutant human CFTR.

KEY RESULTS

All studied compounds are capable of transporting halides and bicarbonate across the cell membrane, with a higher transport capacity at acidic pH. Interestingly, the presence of these anionophores did not interfere with the activation of CFTR and did not modify the action of lumacaftor (a CFTR corrector) or ivacaftor (a CFTR potentiator).

CONCLUSION AND IMPLICATIONS

These anionophores, at low concentrations, transported chloride and bicarbonate across cell membranes, without affecting CFTR function. They therefore provide promising starting points for the development of novel treatments for CF.

Two CFTR mutations within codon 970 differently impact on the chloride channel functionality

Pharmacological rescue of mutant cystic fibrosis transmembrane conductance regulator (CFTR) in cystic fibrosis (CF) depends on the specific defect caused by different mutation classes. We asked whether a patient with the rare p.Gly970Asp (c.2909G>A) mutation could benefit from CFTR pharmacotherapy since a similar missense mutant p.Gly970Arg (c.2908G>C) was previously found to be sensitive to potentiators in vitro but not in vivo. By complementary DNA transfection, we found that both mutations are associated with defective CFTR function amenable to pharmacological treatment. However, analysis of messenger RNA (mRNA) from patient's cells revealed that c.2908G>C impairs RNA splicing whereas c.2909G>A does not perturb splicing and leads to the expected p.Gly970Asp mutation. In agreement with these results, nasal epithelial cells from the p.Gly970Asp patient showed significant improvement of CFTR function upon pharmacological treatment. Our results underline the importance of controlling the effect of CF mutation at the mRNA level to determine if the pharmacotherapy of CFTR basic defect is appropriate.

Lumacaftor-rescued F508del-CFTR has a modified bicarbonate permeability

Deletion of phenylalanine at position 508, F508del, the most frequent mutation among Cystic fibrosis (CF) patients, destabilizes the protein, thus causing both a folding and a trafficking defect, resulting in a dramatic reduction in expression of CFTR. In vitro treatment with lumacaftor produces an enhancement of anion transport in cells. We studied the permeability properties of the CFTR mutant F508del treated with the corrector lumacaftor, showing that the rescued protein has selectivity properties different than the wild type CFTR, showing an augmented bicarbonate permeability. This difference would indicate a diverse conformation of the rescued F508del-CFTR, that is plausibly reflected on an improper regulation of the airway surface liquid, lessening the efficacy of the corrector. Our findings rather support the idea that a combination of correctors would be required to address the CFTR-dependent bicarbonate permeability.

Extent of rescue of F508del-CFTR function by VX-809 and VX-770 in human nasal epithelial cells correlates with SNP rs7512462 in SLC26A9 gene in F508del/F508del Cystic Fibrosis patients

BACKGROUND

We analyzed the CFTR response to VX-809/VX-770 drugs in conditionally reprogrammed cells (CRC) of human nasal epithelium (HNE) from F508del/F508del patients based on SNP rs7512462 in the Solute Carrier Family 26, Member 9 (SLC26A9; MIM: 608481) gene.

METHODS

The I_sc-eq measurements of primary nasal epithelial cells from F508del/F508del patients (n = 12) for CFTR function were performed in micro Ussing chambers and compared with non-CF controls (n = 2). Data were analyzed according to the rs7512462 genotype which were determined by real-time PCR.

RESULTS

The CRC-HNE cells from F508del/F508del patients evidenced high variability in the basal levels of CFTR function. Also, the rs7512462*C allele showed an increased basal CFTR function and higher responses to VX-809 + VX-770. The rs7512462*CC + CT genotypes together evidenced CFTR function levels of 14.89% relatively to wt/wt (rs7512462*CT alone-15.29%) i.e., almost double of rs7512462*TT (7.13%). Furthermore, sweat [Cl^-] and body mass index of patients also evidenced an association with the rs7512462 genotype.

CONCLUSION

The CFTR function can be performed in F508del/F508del patient-derived CRC-HNEs and its function and responses to VX-809 + VX-770 combination as well as clinical data, are all associated with the rs7512462 variant, which partially sheds light on the generally inter-individual phenotypic variability and in personalized responses to CFTR modulator drugs.

Anion-Transport Mechanism of a Triazole-Bearing Derivative of Prodigiosine: A Candidate for Cystic Fibrosis Therapy

Cystic fibrosis (CF) is a genetic lethal disease, originated from the defective function of the CFTR protein, a chloride and bicarbonate permeable transmembrane channel. CF mutations affect CFTR protein through a variety of molecular mechanisms which result in different functional defects. Current therapeutic approaches are targeted to specific groups of patients that share a common functional defect. We seek to develop an innovative therapeutic approach for the treatment of CF using anionophores, small molecules that facilitate the transmembrane transport of anions. We have characterized the anion transport mechanism of a synthetic molecule based on the structure of prodigiosine, a red pigment produced by bacteria. Anionophore-driven chloride efflux from large unilamellar vesicles is consistent with activity of an uniporter carrier that facilitates the transport of anions through lipid membranes down the electrochemical gradient. There are no evidences of transport coupling with protons. The selectivity sequence of the prodigiosin inspired EH160 ionophore is formate > acetate > nitrate > chloride > bicarbonate. Sulfate, phosphate, aspartate, isothionate, and gluconate are not significantly transported by these anionophores. Protonation at acidic pH is important for the transport capacity of the anionophore. This prodigiosin derived ionophore induces anion transport in living cells. Its low toxicity and capacity to transport chloride and bicarbonate, when applied at low concentration, constitute a promising starting point for the development of drug candidates for CF therapy.

CFTR rescue with VX-809 and VX-770 favors the repair of primary airway epithelial cell cultures from patients with class II mutations in the presence of Pseudomonas aeruginosa exoproducts

BACKGROUND

Progressive airway damage due to bacterial infections, especially with Pseudomonas aeruginosa remains the first cause of morbidity and mortality in CF patients. Our previous work revealed a repair delay in CF airway epithelia compared to non-CF. This delay was partially prevented after CFTR correction (with VRT-325) in the absence of infection. Our goals were now to evaluate the effect of the Orkambi combination (CFTR VX-809 corrector + VX-770 potentiator) on the repair of CF primary airway epithelia, in infectious conditions.

METHODS

Primary airway epithelial cell cultures from patients with class II mutations were mechanically injured and wound healing rates and transepithelial resistances were monitored after CFTR rescue, in the absence and presence of P. aeruginosa exoproducts.

RESULTS

Our data revealed that combined treatment with VX-809 and VX-770 elicited a greater beneficial impact on airway epithelial repair than VX-809 alone, in the absence of infection. The treatment with Orkambi was effective not only in airway epithelial cell cultures from patients homozygous for the F508del mutation but also from heterozygous patients carrying F508del and another class II mutation (N1303 K, I507del). The stimulatory effect of the Orkambi treatment was prevented by CFTR inhibition with GlyH101. Finally, Orkambi combination elicited a slight but significant improvement in airway epithelial repair and transepithelial resistance, despite the presence of P. aeruginosa exoproducts.

CONCLUSIONS

Our findings indicate that Orkambi may favor airway epithelial integrity in CF patients with class II mutations. Complementary approaches would however be needed to further improve CFTR rescue and airway epithelial repair.

Bronchiectasis: new therapies and new perspectives

European Respiratory Society guidelines for the management of adult bronchiectasis highlight the paucity of treatment options available for patients with this disorder. No treatments have been licensed by regulatory agencies worldwide, and most therapies used in clinical practice are based on very little evidence. Development of new treatments is needed urgently. We did a systematic review of scientific literature and clinical trial registries to identify agents in early-to-late clinical development for bronchiectasis in adults. In this Review, we discuss the mechanisms and potential roles of emerging therapies, including drugs that target airway and systemic inflammation, mucociliary clearance, and epithelial dysfunction. To ensure these treatments achieve success in randomised clinical trials-and therefore reach patients-we propose a reassessment of the current approach to bronchiectasis. Although understanding of the pathophysiology of bronchiectasis is at an early stage, we argue that bronchiectasis is a heterogeneous disease with many different biological mechanisms that drive disease progression (endotypes), and therefore the so-called treatable traits approach used in asthma and chronic obstructive pulmonary disease could be applied to bronchiectasis, with future trials targeted at the specific disease subgroups most likely to benefit.