Allosteric folding correction of F508del and rare CFTR mutants by elexacaftor-tezacaftor-ivacaftor (Trikafta) combination

The relationship between cancer risk and cystic fibrosis: the role of CFTR in cell growth and cancer development

Cystic fibrosis (CF) is a life-limiting genetic disease that affects multiple organ systems. It is caused by a mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which results in the absence or damage of a relevant protein. If left untreated, it causes death in early childhood. The advent of more efficacious treatments has resulted in a notable increase in the life expectancy of CF patients. This has, in turn, led to an elevated risk of developing specific types of cancer. This review commences with an examination of CF from the standpoint of its etiology and therapeutic modalities. Subsequently, it presents a list of epidemiological studies that suggest an altered predisposition to certain cancers. A heightened risk is well documented, particularly in relation to the gastrointestinal tract. The following section addresses the role of CFTR in view of its potential involvement in the progression of various types of cancer. Several studies have indicated that the levels of the CFTR protein are reduced in many tumors and that this reduction is associated with the progression of the tumors. These decreased expressions are known to occur in the gastrointestinal tract, lungs, bladder, and/or prostate cancer. Conversely, ovarian, stomach, and cervical cancer are connected with its higher expression. The final section of the review focuses on the molecular mechanism of action of the CFTR protein in signaling pathways that affect cell proliferation and the process of carcinogenesis. This section attempts to explain the increased predisposition to cancer observed in patients with CF.

The potentiator ivacaftor is essential for pharmacological restoration of F508del-CFTR function and mucociliary clearance in cystic fibrosis

Pharmacological rescue of F508del-CFTR by the triple combination CFTR modulator therapy elexacaftor/tezacaftor/ivacaftor (ETI) leads to unprecedented clinical benefits in patients with cystic fibrosis (CF). However, previous studies in CF primary human airway epithelial cultures demonstrated that chronic treatment with the potentiator ivacaftor can render the F508del protein unstable, thus limiting restoration of CFTR chloride channel function. Even so, quantitative studies of this unwanted effect of ivacaftor on F508del channel function with dependency on cell culture conditions remain limited, and the impact of chronic ivacaftor exposure on restoration of mucociliary clearance that is impaired in patients with CF has not been studied. In patient-derived primary nasal epithelial cultures, we found that different culture conditions (UNC-ALI medium vs. PneumaCult medium) have profound effects on ETI-mediated restoration of F508del-CFTR function. Chronic treatment with ivacaftor as part of ETI triple therapy limited the rescue of F508del-CFTR chloride channel function when CF nasal epithelial cultures were grown in UNC-ALI medium but not in PneumaCult medium. In PneumaCult medium, both chronic and acute addition of ivacaftor as part of ETI treatment led to constitutive CFTR-mediated chloride secretion in the absence of exogenous cAMP-dependent stimulation. This constitutive CFTR-mediated chloride secretion was essential to improve viscoelastic properties of the mucus layer and to restore mucociliary transport on CF nasal epithelial cultures. Furthermore, nasal potential difference measurements in patients with CF showed that ETI restored constitutive F508del-CFTR activity in vivo. These results demonstrate that ivacaftor as a component of ETI therapy is essential to restore mucociliary clearance and suggest that this effect is facilitated by its constitutive activation of F508del channels following their folding correction in patients with CF.

Progress of personalized medicine of cystic fibrosis in the times of efficient CFTR modulators

BACKGROUND

Cystic fibrosis (CF) is a systemic disorder of exocrine glands that is caused by mutations in the CFTR gene.

MAIN BODY

The basic defect in people with CF (pwCF) leads to impaired epithelial transport of chloride and bicarbonate that can be assessed by CFTR biomarkers, i.e. the β-adrenergic sweat rate and sweat chloride concentration (SCC), chloride conductance of the nasal respiratory epithelium (NPD), urine secretion of bicarbonate, intestinal current measurements (ICM) of chloride secretory responses in rectal biopsies and in bioassays of chloride transport in organoids or cell cultures. CFTR modulators are a novel class of drugs that improve defective posttranslational processing, trafficking and function of mutant CFTR. By April 2025, triple combination therapy with the CFTR potentiator ivacaftor (IVA) and the CFTR correctors elexacaftor (ELX) and tezacaftor (TEZ) has been approved in Europe for the treatment of all pwCF who do not carry two minimal function CFTR mutations. Previous phase 3 and post-approval phase 4 studies in pwCF who harbour one or two alleles of the major mutation F508del consistently reported significant improvements of lung function and anthropometry upon initiation of ELX/TEZ/IVA compared to baseline. Normalization of SCC, NPD and ICM correlated with clinical outcomes on the population level, but the restoration of CFTR function was diverse and not predictive for clinical outcome in the individual patient. Theratyping of non-F508del CF genotypes in patient-derived organoids and cell cultures revealed for most cases clinically meaningful increases of CFTR activity upon exposure to ELX/TEZ/IVA. Likewise, every second CF patient with non-F508del genotypes improved in SCC and clinical outcome upon exposure to ELX/TEZ/IVA indicating that triple CFTR modulator therapy is potentially beneficial for all pwCF who do not carry two minimal function CFTR mutations. This group who is not eligible for CFTR modulators may opt for gene addition therapy in the future, as the first-in-human trial with a recombinant lentiviral vector is underway.

FUTURE DIRECTIONS

The upcoming generation of pwCF will probably experience a rather normal life in childhood and adolescence. To classify the upcoming personal signatures of CF disease in the times of efficient modulators, we need more sensitive CFTR biomarkers that address the long-term course of airway and gut microbiome, host defense, epithelial homeostasis and multiorgan metabolism.

Ivacaftor-tezacaftor-elexacaftor, tezacaftor-ivacaftor and lumacaftor-ivacaftor for treating cystic fibrosis: a systematic review and economic evaluation

Background

Cystic fibrosis is a life-limiting genetic condition that affects over 9000 people in England. Cystic fibrosis is usually diagnosed through newborn screening and causes symptoms throughout the body, including the lungs and digestive system. Around 90% of individuals with cystic fibrosis have at least one copy of the F508del mutation on the cystic fibrosis transmembrane conductance regulator gene.

Objectives

To appraise the clinical effectiveness and cost-effectiveness of elexacaftor-tezacaftor-ivacaftor, tezacaftor-ivacaftor and lumacaftor-ivacaftor within their expected marketing authorisations for treating people with cystic fibrosis and at least one F508del mutation, compared with each other and with established clinical management before these treatments.

Methods

A de novo systematic literature review (search date February 2023) was conducted searching electronic databases (MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials), bibliographies of relevant systematic literature reviews, clinical trial registers, recent conferences and evidence provided by Vertex Pharmaceuticals (Boston, MA, USA). Data on the following outcomes were summarised: acute change in per cent predicted forced expiratory volume in 1 second (change in weight-for-age z-score; and change in pulmonary exacerbation frequency requiring intravenous antibiotics. Network meta-analyses were conducted where head-to-head data were not available. Data from clinical trials and real-world evidence were examined to assess long-term effectiveness. A patient-level simulation model was developed to assess the cost-effectiveness of the three modulator treatments. The model employed a lifetime horizon and was developed from the perspective of the National Health Service.

Results

Data from 19 primary studies and 7 open-label extension studies were prioritised in the systematic literature review. Elexacaftor/tezacaftor/ivacaftor was associated with a statistically significant increase in predicted forced expiratory volume in 1 second and weight-for-age z-score and a reduction in pulmonary exacerbations compared with established clinical management, lumacaftor/ivacaftor and tezacaftor/ivacaftor, and also led to a reduction in the rate of predicted forced expiratory volume in 1 second decline relative to established clinical management, although the magnitude of this decrease was uncertain. Lumacaftor/ivacaftor and tezacaftor/ivacaftor were also associated with a statistically significant increase in predicted forced expiratory volume in 1 second and reduction in pulmonary exacerbations relative to established clinical management, but with a smaller effect size than elexacaftor/tezacaftor/ivacaftor. There was some evidence that tezacaftor/ivacaftor reduced the rate of predicted forced expiratory volume in 1 second decline relative to established clinical management, but little evidence that lumacaftor/ivacaftor reduced the rate of predicted forced expiratory volume in 1 second decline relative to established clinical management. The incremental cost-effectiveness ratios from the economic analysis were confidential. However, for all genotypes studied the incremental cost-effectiveness ratios were above what would be considered cost-effective based on the National Institute for Health and Care Excellence threshold of £20,000-30,000 per quality-adjusted life-year gained.

Conclusions

Despite the improved clinical benefits observed, none of the cystic fibrosis transmembrane conductance regulator gene modulators assessed would be considered cost-effective based on the National Institute for Health and Care Excellence threshold of £20,000-30,000 per quality-adjusted life-year gained. This is largely driven by the high acquisition costs of cystic fibrosis transmembrane conductance regulator gene modulator treatments.

Study registration

This study is registered as PROSPERO CRD42023399583.

Funding

This award was funded by the National Institute for Health and Care Research (NIHR) Evidence Synthesis programme (NIHR award ref: NIHR135829) and is published in full in Health Technology Assessment; Vol. 29, No. 19. See the NIHR Funding and Awards website for further award information.

Recent developments in cystic fibrosis drug discovery: where are we today?

INTRODUCTION

The advent of variant-specific disease-modifying drugs into clinical practice has provided remarkable benefits for people with cystic fibrosis (PwCF), a multi-organ life-limiting inherited disease. However, further efforts are needed to maximize therapeutic benefits as well as to increase the number of PwCF taking CFTR modulators.

AREA COVERED

The authors discuss some of the key limitations of the currently available CFTR modulator therapies (e.g. adverse reactions) and strategies in development to increase the number of available therapeutics for CF. These include novel methods to accelerate theratyping and identification of novel small molecules and cellular targets representing alternative or complementary therapies for CF.

EXPERT OPINION

While the CF therapy development pipeline continues to grow, there is a critical need to optimize strategies that will accelerate testing and approval of effective therapies for (ultra)rare CFTR variants as traditional assays and trials are not suitable to address such issues. Another major barrier that needs to be solved is the restricted access to currently available modulator therapies, which remains a significant burden for PwCF who are from racial and ethnic minorities and/or living in underprivileged regions.

Proteostasis landscapes of cystic fibrosis variants reveal drug response vulnerability

Cystic fibrosis (CF) is a lethal genetic disorder caused by variants in CF transmembrane conductance regulator (CFTR). Many variants are treatable with correctors, which enhance the folding and trafficking of CFTR. However, approximately 3% of persons with CF harbor poorly responsive variants. Here, we used affinity purification mass spectrometry proteomics to profile the protein homeostasis (proteostasis) changes of CFTR variants during correction to assess modulated interactions with protein folding and maturation pathways. Responsive variant interactions converged on similar proteostasis pathways during correction. In contrast, poorly responsive variants subtly diverged, revealing a partial restoration of protein quality control surveillance and partial correction. Computational structural modeling showed that corrector VX-445 failed to confer enough NBD1 stability to poor responders. NBD1 secondary stabilizing mutations rescued poorly responsive variants, revealing structural vulnerabilities in NBD1 required for treating poor responders. Our study provides a framework for discerning the underlying protein quality control and structural defects of CFTR variants not reached with existing drugs to expand therapeutics to all susceptible CFTR variants.

Trikafta rescues F508del-CFTR by tightening specific phosphorylation-dependent interdomain interactions

Trikafta is well-known for correcting thermal and gating defects caused by the most common cystic fibrosis mutation F508del in the human cystic fibrosis transmembrane conductance regulator even at a physiological temperature. However, the exact correction pathway is still unclear. Here, noncovalent interactions among two transmembrane domains (TMD1 and TMD2), the regulatory (R) domain and two nucleotide binding domains (NBD1 and NBD2) were analyzed. The thermal stability of NBD1 was also evaluated through its tertiary constrained noncovalent interaction networks or thermoring structures. The results demonstrated that Trikafta binding to flexible TMD1 and TMD2 rearranged their interactions with the R domain upon phosphorylation, coupling tightened cytoplasmic TMD1-TMD2 interactions to tightened Mg/ATP-dependent NBD1-NBD2 dimerization, which stabilized NBD1 above human body temperature. Overall, although the deletion of F508 induces the primary thermal defect in NBD1 and then the gating defect at the TMD1-TMD2 interface, Trikafta rescued them in a reverse manner allosterically. These mechanistic insights into the precise correction pathway of this misfolded channel facilitate optimizing cystic fibrosis treatment.

Mutant protein chemical rescue: From mechanisms to therapeutics

Chemical rescue is a technique for restoring the activity and/or structure of an engineered or naturally occurring (e.g., disease-associated) mutant protein by the introduction of a "molecular crutch" that abrogates the mutation's effect. This method was developed about 4 decades ago to facilitate mechanistic analysis of enzymes. Since then, a variety of purified proteins inactivated by site-directed mutagenesis have been successfully rescued by substrate moieties or exogenous small molecules, an approach that has continued to serve as an important tool for mechanistic enzymologists. More recently, chemical rescue has been applied to activate engineered proteins in intact biological systems for phenotypic and pathway-level analyses. There is growing interest in therapeutic applications of chemical rescue to correct protein mutations that give rise to human diseases. In this review, we first contextualize chemical rescue and discuss its utility in protein mechanistic analysis. Second, we review the advantages and caveats associated with using this approach to study protein function within biological settings. Third, we provide an overview of efforts to develop folding correctors that restore the proper function of disease-associated protein mutants. To conclude, future directions and challenges for the chemical rescue field are discussed.

Functional variants in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are associated with increased risk of colorectal cancer

BACKGROUND

Individuals with cystic fibrosis (CF; a recessive disorder) have an increased risk of colorectal cancer (CRC). Evidence suggests individuals with a single CFTR variant may also have increased CRC risk.

METHODS

Using population-based studies (GECCO, CORECT, CCFR, and ARIC; 53 785 CRC cases and 58 010 controls), we tested for an association between the most common CFTR variant (Phe508del) and CRC risk. For replication, we used whole exome sequencing data from UK Biobank (UKB; 5126 cases and 20 504 controls matched 4:1 based on genetic distance, age, and sex), and extended our analyses to all other heterozygous CFTR variants annotated as CF-causing.

RESULTS

In our meta-analysis of GECCO-CORECT-CCFR-ARIC, the odds ratio (OR) for CRC risk associated with Phe508del was 1.11 (P = 0.010). In our UKB replication, the OR for CRC risk associated with Phe508del was 1.28 (P = 0.002). The sequencing data from UKB also revealed an association between the presence of any other single CF-causing variant (excluding Phe508del) and CRC risk (OR = 1.33; P = 0.030). When stratifying CFTR variants by functional class, class I variants (no protein produced) had a stronger association (OR = 1.77; p = 0.002), while class II variants (misfolding and retention of the protein in the endoplasmic reticulum) other than Phe508del (OR = 1.75; p = 0.107) had similar effect size as Phe508del, and variants in classes III-VI had non-significant ORs less than 1.0 and/or were not present in cases.

CONCLUSIONS

CF-causing heterozygous variants, especially class I variants, are associated with a modest but statistically significant increased CRC risk. More research is needed to explain the biology underlying these associations.

Esc peptides and derivatives potentiate the activity of CFTR with gating defects and display antipseudomonal activity in cystic fibrosis-like lung disease

Cystic fibrosis (CF) is a rare disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), a chloride channel with an important role in the airways. Despite the clinical efficacy of present modulators in restoring the activity of defective CFTR, there are patients who show persistent pulmonary infections, mainly due to Pseudomonas aeruginosa. Recently, we reported an unprecedented property of antimicrobial peptides i.e. Esc peptides, which consists in their ability to act as potentiators of CFTR carrying the most common mutation (the loss of phenylalanine 508) affecting protein folding, trafficking and gating. In this work, by electrophysiology experiments and computational studies, the capability of these peptides and de-novo designed analogs was demonstrated to recover the function of other mutated forms of CFTR which severely affect the channel gating (G551D and G1349D). This is presumably due to direct interaction of the peptides with the nucleotide binding domains (NBDs) of CFTR, followed by a novel local phenomenon consisting in distancing residues located at the cytosolic side of the NBDs interface, thus stabilizing the open conformation of the pore at its cytosolic end. The most promising peptides for the dual antimicrobial and CFTR potentiator activities were also shown to display antipseudomonal activity in conditions mimicking the CF pulmonary ion transport and mucus obstruction, with a higher efficacy than the clinically used colistin. These studies should assist in development of novel drugs for lung pathology in CF, with dual CFTR potentiator and large spectrum antibiotic activities.

Target Identification with Live-Cell Photoaffinity Labeling and Mechanism of Action Elucidation of ARN23765, a Highly Potent CFTR Corrector

Molecular-targeted therapies for the treatment of cystic fibrosis (CF) rely on small-molecule modulators that rescue the activity of the defective CF transmembrane conductance regulator (CFTR) anion channel. ARN23765 is a small molecule with subnanomolar potency in rescuing the function of mutant CFTR in bronchial epithelial cells from CF patients carrying the F508del-CFTR mutation. Considering the multifaceted interactions of CFTR with the plasma membrane and the complexity of the protein network within the cellular compartments, here we report the investigation of ARN23765's molecular mechanism in live cells. We used the photoaffinity labeling (PAL) approach to demonstrate the interaction of ARN23765-derived probes with CFTR in cells. We showed that ARN23765 contributes to F508del-CFTR rescue by stabilizing the membrane-spanning domain-1 and interacting with CFTR at the same site as other type I CFTR correctors. Our study characterizes ARN23765's mode of action and highlights the potential of studying the interactions between CFTR and its correctors in live cells.

Integrative analysis of KCNQ1 variants reveals molecular mechanisms of type 1 long QT syndrome pathogenesis

Loss-of-function (LOF) pathogenic variants in KCNQ1 encoding a cardiac potassium channel predispose to sudden cardiac death in type 1 congenital long QT syndrome (LQT1). To determine the spectrum of molecular mechanisms responsible for this life-threatening condition, we used an integrative approach to determine the biophysical, functional, and trafficking properties of 61 KCNQ1 variants distributed throughout all domains of the channel. Impaired trafficking to the plasma membrane was the most common cause of LOF across all channel domains, often but not always coinciding with protein instability. However, many LOF variants, particularly in transmembrane domains, trafficked normally, but when coexpressed with KCNE1 exhibited impaired conductance, altered voltage dependence, or abnormal gating kinetics, highlighting diverse pathogenic mechanisms. This indicates a need for personalized treatment approaches for LQT1. Use of our data to benchmark variant pathogenicity prediction methods demonstrated that prediction accuracy depends on the exact mechanism of pathogenicity associated with a given variant.

Discovery and Development of CFTR Modulators for the Treatment of Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which regulates ion and fluid transport across epithelial cells. Mutations lead to complications, with life-limiting lung disease being the most severe manifestation. Traditional treatments focused on managing symptoms, but advances in understanding CF's molecular basis led to small-molecule CFTR modulators. Ivacaftor, which is a potentiator, was approved for gating mutations. Dual combinations like ivacaftor/lumacaftor and ivacaftor/tezacaftor brought together a potentiator and a class 1 corrector for F508del homozygous patients. Triple-combination CFTR modulators, including ivacaftor/tezacaftor/elexacaftor with an additional class 2 corrector, are now the standard of care for most CF patients, transforming the outlook for this disease. These drugs stabilize and potentiate the CFTR protein, improving lung function, sweat chloride levels, quality of life, and survival. This Perspective discusses CFTR structure and mutations, biological assays, medicinal chemistry research in identifying CFTR modulators, and clinical data of these agents.

Effect of CFTR modulators Elexacaftor/Tezacaftor/Ivacaftor on lipid metabolism in human bronchial epithelial cells

Cystic Fibrosis (CF) is a life-threatening hereditary disease resulting from mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene that encodes a chloride channel essential for ion transport in epithelial cells. Mutations in CFTR, notably the prevalent F508del mutation, impair chloride transport, severely affecting the respiratory system and leading to recurrent infections. Recent therapeutic advancements include CFTR modulators such as ETI, a combination of two correctors (Elexacaftor and Tezacaftor) and a potentiator (Ivacaftor), that can improve CFTR function in patients with the F508del mutation. This study investigated ETI's impact on the maturation of the mutated CFTR, the expression levels of its scaffolding proteins, and lipid composition of cells using bronchial epithelial cell lines expressing both wild-type and F508del CFTR. Our findings revealed that ETI treatment enhances CFTR and its scaffolding proteins expression and aids in rescuing mature F508del CFTR, causing also significant alterations in the lipid profile including reduced levels of lactosylceramide and increased content of gangliosides GM1 and GD1a. These changes were linked to ETI's influence on enzymes involved in the sphingolipid metabolism, in particular GM3 synthase and sialidase. Through this work, we aim to deepen understanding CFTR interactions with lipids, and to elucidate the mechanisms of action of CFTR modulators. Our findings may support the development of potential therapeutic strategies contributing to the ongoing efforts to design effective correctors and potentiators for CF treatment.

Proteostasis Landscapes of Cystic Fibrosis Variants Reveals Drug Response Vulnerability

Cystic Fibrosis (CF) is a lethal genetic disorder caused by variants in CF transmembrane conductance regulator (CFTR). Many variants are treatable with correctors, which enhance the folding and trafficking of CFTR. However, approximately 3% of persons with CF harbor poorly responsive variants. Here, we used affinity purification mass spectrometry proteomics to profile the protein homeostasis (proteostasis) changes of CFTR variants during correction to assess modulated interactions with protein folding and maturation pathways. Responsive variant interactions converged on similar proteostasis pathways during correction. In contrast, poorly responsive variants subtly diverged, revealing a partial restoration of protein quality control surveillance and partial correction. Computational structural modeling showed that corrector VX-445 failed to confer enough NBD1 stability to poor responders. NBD1 secondary stabilizing mutations rescued poorly responsive variants, revealing structural vulnerabilities in NBD1 required for treating poor responders. Our study provides a framework for discerning the underlying protein quality control and structural defects of CFTR variants not reached with existing drugs to expand therapeutics to all susceptible CFTR variants.

SIGNIFICANCE STATEMENT

Cystic Fibrosis (CF) is a lethal genetic disease with variants leading to misfolding of an anion channel protein. Enhancing productive channel folding using a novel class of small molecules called correctors has emerged as the current CF treatment paradigm. However, correctors fail to reach all patient variants. Using high throughput interactomics, Rosetta simulations, and biochemical trafficking assays, this study demonstrates poorly responsive CF variants experience diverse misfolding pathways caused by structural defects in the core of a nucleotide-binding domain. Stabilizing secondary mutations in this domain rescues poorly responsive variants, paving the way for mechanistic-based therapeutic development for untreatable CF variants and future protein misfolding corrector drugs.

BioID-Based Proximity Mapping of Transmembrane Proteins in Human Airway Cell Models

The cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel residing primarily at the apical membrane of epithelial cells, plays a major role in fluid secretion and the maintenance of epithelial surface hydration. Mutations in the CFTR gene lead to the fatal disease known as cystic fibrosis (CF). Drugs that improve mutant CFTR protein folding and channel function have dramatically improved CF patient outcomes. However, the current regimen only restores the function of the most common mutant, ΔF508, to ~62% of wildtype (WT). Notably, ~10% of patients harboring hundreds of less common CFTR mutations are not eligible or do not respond at all to treatment with current CFTR modulators. Better characterizing the WT and mutant CFTR protein interactomes could provide critical insight into how to treat patients with rarer mutations and thereby improve the druggability of this devastating disease. Here we describe how BioID (proximity-dependent biotin identification) can be used to map the CFTR interactome in a human airway model-bronchial epithelial cells grown at the air-liquid interface. Approximately 26% (>5500) of all human protein-coding genes are predicted to code for membrane proteins, which together account for ~30% of the druggable proteome. The methods described here could thus also be applied to improve our understanding of many additional respiratory, autoimmune, and metabolic diseases.

Cystic fibrosis: new challenges and perspectives beyond elexacaftor/tezacaftor/ivacaftor

Over the past decade, major clinical advances have been made in the healthcare and therapeutic development for cystic fibrosis (CF), a lethal genetic disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR) protein. CFTR modulators represent innovative treatments that directly target the primary defects in the mutated CFTR protein and have demonstrated significant clinical benefits for many people with CF (pwCF) who are eligible for these treatments. In particular, the triple combination therapy composed of elexacaftor, tezacaftor, and ivacaftor (ETI) has changed the CF therapeutic landscape by significantly improving lung function, quality of life, and predicted survival rates. Here, we provided a comprehensive summary of the impact of ETI on clinical outcomes and the need for further research on long-term efficacy, side effects, pregnancy, possible drug-drug interactions, and extra-pulmonary manifestations. Moreover, a significant number of pwCF are unresponsive to these drugs or cannot afford their high costs. We, therefore, discussed health inequity issues and alternative therapeutic strategies under development aiming to obtain effective therapies for all pwCF.

Rescue of Mutant CFTR Channel Activity by Investigational Co-Potentiator Therapy

Background: The potentiator VX-770 (ivacaftor) has been approved as a monotherapy for over 95 cystic fibrosis (CF)-causing variants associated with gating/conductance defects of the CF transmembrane conductance regulator (CFTR) channel. However, despite its therapeutic success, VX-770 only partially restores CFTR activity for many of these variants, indicating they may benefit from the combination of potentiators exhibiting distinct mechanisms of action (i.e., co-potentiators). We previously identified LSO-24, a hydroxy-1,2,3-triazole-based compound, as a modest potentiator of p.Arg334Trp-CFTR, a variant with a conductance defect for which no modulator therapy is currently approved. Objective/Methods: We synthesized a new set of LSO-24 structure-based compounds, screened their effects on p.Arg334Trp-CFTR activity, and assessed the additivity of hit compounds to VX-770, ABBV-974, ABBV-3067, and apigenin. After validation by electrophysiological assays, the most promising hits were also assessed in cells expressing other variants with defective gating/conductance, namely p.Pro205Ser, p.Ser549Arg, p.Gly551Asp, p.Ser945Leu, and p.Gly1349Asp. Results: We found that five compounds were able to increase p.Arg334Trp-CFTR activity with similar efficacy, but slightly greater potency promoted by LSO-150 and LSO-153 (EC50: 1.01 and 1.26 μM, respectively). These two compounds also displayed a higher rescue of p.Arg334Trp-CFTR activity in combination with VX-770, ABBV-974, and ABBV-3067, but not with apigenin. When tested in cells expressing other CFTR variants, LSO-24 and its derivative LSO-150 increased CFTR activity for the variants p.Ser549Arg, p.Gly551Asp, and p.Ser945Leu with a further effect in combination with VX-770 or ABBV-3067. No potentiator was able to rescue CFTR activity in p.Pro205Ser-expressing cells, while p.Gly1349Asp-CFTR responded to VX-770 and ABBV-3067 but not to LSO-24 or LSO-150. Conclusions: Our data suggest that these new potentiators might share a common mechanism with apigenin, which is conceivably distinct from that of VX-770 and ABBV-3067. The additive rescue of p.Arg334Trp-, p.Ser549Arg-, p.Gly551Asp-, and p.Ser945Leu-CFTR also indicates that these variants could benefit from the development of a co-potentiator therapy.

BOS-318 treatment enhances elexacaftor-tezacaftor-ivacaftor-mediated improvements in airway hydration and mucociliary transport

Background

Cystic fibrosis transmembrane conductance regulator (CFTR) triple modulator therapy, elexacaftor-tezacaftor-ivacaftor (ETI) has transformed care for people with cystic fibrosis (CF) who have eligible mutations. It is, however, not curative. Response to treatment also varies and lung disease, although slowed, remains progressive. We have previously demonstrated inhibition of the epithelial sodium channel (ENaC) by selective furin inhibition to be an alternative, mutation-agnostic approach that can enhance airways hydration and restore mucociliary transport (MCT) in CF. Inhibition of furin therefore, offers a potential therapeutic strategy for those ineligible, intolerant or nonresponsive to ETI and may provide a further opportunity for clinical benefit for those currently treated with ETI. The aim of this study was to determine the impact of furin inhibition on ETI responses to assess its utility as an adjunct therapy.

Methods

Differentiated primary CF human bronchial epithelial cells (HBECs) were treated with the highly selective furin inhibitor BOS-318 and with ETI. Ion channel function was measured using a 24-channel Transepithelial Current Clamp (TECC-24) system and airways surface hydration was investigated by measuring airway surface liquid (ASL) height and MCT rate.

Results

The presence of BOS-318 had no effect on the ability of ETI to stimulate CFTR-mediated Cl- secretion but contributed a reduced Na+ transport via robust inhibition of ENaC. This altered ion transport profile effected an improved ASL height and MCT rate, which were significantly greater than improvements observed with ETI alone, demonstrating the benefits of the dual approach.

Conclusions

Selective furin inhibition has the potential to further improve clinical outcomes for all people with CF and offers opportunity as an adjunct to improve responses to currently available CFTR modulator therapies.

Successful Therapy over 12 Months of People with Cystic Fibrosis with Rare Non-phe508del Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Mutations with Elexacaftor/Tezacaftor/Ivacaftor (ETI)

Background: Elexacaftor/Tezacaftor/Ivacaftor (ETI) is a CFTR modulator therapy approved for people with cystic fibrosis (pwCF) who have at least one phe508del mutation. However, its approval in the European Union (EU) for pwCF with non-phe508del mutations is lacking, because data on treatment response in this subgroup are scarce. Methods: This retrospective observational study evaluated six pwCF (ages 6 to 66) with responsive CFTR mutations (M1101K, R347P, 2789+5G>A, G551D) undergoing off-label ETI therapy. Evaluations were conducted at 0, 3, 6, 9, and 12 months, assessing lung function (FEV1), sweat chloride levels, body mass index (BMI), quality of life, medication satisfaction, ear, nose and throat (ENT) symptoms, and physical activity. A control group of four pwCF with classic symptoms and no ETI treatment was included. Results: FEV1 improved significantly after 3 and 6 months (p < 0.05) and stabilized by 12 months. Sweat chloride levels decreased significantly, with four pwCF achieving levels <60 mmol/L. Improvements in the upper and lower airway symptoms, medication satisfaction, and increased BMI were noted. Conclusions: ETI demonstrates high efficacy in this small group of pwCF with rare CFTR mutations, offering a treatment option that warrants further monitoring and evaluation.

The F508del-CFTR trafficking correctors elexacaftor and tezacaftor are CFTR-independent Ca2+-mobilizing agonists normalizing abnormal Ca2+ levels in human airway epithelial cells

BACKGROUND

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) channel. For people with CF (pwCF) affected by the most common pathogenic variant F508del, a tritherapy, named Trikafta/Kaftrio (ETI: elexacaftor (VX-445) /tezacaftor (VX-661) / ivacaftor (VX-770)) was successfully developed. However, in CF airway epithelial cells the calcium homeostasis is also disturbed; it is observed an increased calcium mobilization in CF cells compared to non-CF cells. Here, we studied the effects of ETI on intracellular calcium levels in F508del-CFTR airway epithelial cells to determine whether these compounds, individually or collectively, could normalize intracellular calcium levels.

METHODS

We measured intracellular calcium variations using human airway epithelial cells (hAEC) from pwCF, human bronchial epithelial CFBE41o- F508del-CFTR cells and Chinese Hamster Ovary (CHO) cells using the fluorescent probe Fluo4-AM, in the presence or absence of extracellular calcium. The rescue to the plasma membrane of F508del-CFTR protein by ETI was determined by western blot. The SarcoEndoplasmic Reticulum Calcium ATPase (SERCA), was also analysed by western blotting and by interference assay.

RESULTS

We show that ETI normalizes calcium homeostasis in our cellular models. However, we also found that (1) each ETI-corrector compound is capable of mobilizing calcium acutely in the absence of CFTR, and (2) tezacaftor mobilizes calcium from the endoplasmic reticulum (ER) probably via inhibition of the SERCA pump.

CONCLUSIONS

We show that ETI not only corrects the abnormal trafficking and function of F508del-CFTR but also normalizes calcium homeostasis in our cellular models. Finally, we identified SERCA as a potential intracellular target for tezacaftor.

Elexacaftor/tezacaftor/ivacaftor in people with cystic fibrosis and rare mutations

INTRODUCTION

The triple combination of elexacaftor/tezacaftor/ivacaftor (ETI) has dramatically improved the outcome of people with Cystic Fibrosis (pwCF) with at least one F508del mutation. However, carriers of rare cystic fibrosis transmembrane conductance regulator (CFTR) variants are not candidates for this innovative treatment.

METHODS

In this observational study, we report the results of the compassionate use of ETI in 10 pwCF carriers of rare mutations after 2 months of treatment. Rectal organoids and short-term cultures of nasal epithelium obtained from rectal suction biopsies and nasal brushing were obtained from four subjects.

RESULTS

After 2 months of ETI, all patients (4 males, mean age 30.1 ± 13.3 years) showed a significant increase of FEV1% predicted values [+8.0 (3.5-12.7) %, p < 0.010], body mass index [+0.85 (0-1.22) kg/m2, p < 0.020] and cystic fibrosis questionnaire-revised [+19.5 (6.3-29.2) points, p < 0.009]. A significant decrease of sweat chloride concentration [-11.2 (-1.7 to -34.0) mmol/L, p < 0.020] and exacerbations [-1.5 (-2 to -1), p < 0.008] was also recorded. Overall, 7 out of 10 participants were considered full responders. All patients reported cough disappearance (n = 3) or reduction (n = 7). Long-term oxygen was discontinued in two out of three patients and one also stopped noninvasive ventilation and was removed from the lung transplantation waiting list.

CONCLUSIONS

Despite the limited number of cases, our results support the use of CFTR modulators in patients with rare CFTR variants that are not currently approved for ETI in Europe.

ATP-Binding Cassette and Solute Carrier Transporters: Understanding Their Mechanisms and Drug Modulation Through Structural and Modeling Approaches

The ATP-binding cassette (ABC) and solute carrier (SLC) transporters play pivotal roles in cellular transport mechanisms, influencing a wide range of physiological processes and impacting various medical conditions. Recent advancements in structural biology and computational modeling have provided significant insights into their function and regulation. This review provides an overview of the current knowledge of human ABC and SLC transporters, emphasizing their structural and functional relationships, transport mechanisms, and the contribution of computational approaches to their understanding. Current challenges and promising future research and methodological directions are also discussed.

Investigation of CFTR Function in Human Nasal Epithelial Cells Informs Personalized Medicine

We broaden the clinical versatility of human nasal epithelial (HNE) cells. HNEs were isolated from 10 participants harboring cystic fibrosis transmembrane conductance regulator (CFTR) variants: 9 with rare variants (Q359R [n = 2], G480S, R334W [n = 5], and R560T) and 1 harboring R117H;7T;TG10/5T;TG12. Cultures were differentiated at the air-liquid interface. CFTR function was measured in Ussing chambers at three conditions: baseline, ivacaftor, and elexacaftor + tezacaftor + ivacaftor (ETI). Four participants initiated modulators. Q359R HNEs had 5.4% (% wild-type) baseline CFTR function and 25.5% with ivacaftor. With therapy, sweat [Cl-] decreased and symptoms resolved. G480S HNEs had 4.1% baseline and 32.1% CFTR function with ETI. Clinically, forced expiratory volume in 1 second increased and sweat [Cl-] decreased (119 to 46 mmol/L) with ETI. In vitro cultures derived from 5 participants harboring R334W showed a moderate increase in CFTR function with exposure to modulators. For one of these participants, ETI was begun in vivo; symptoms and forced expiratory volume in 1 second improved. The c.1679G>C (R560T) HNEs had less than 4% baseline CFTR function and no modulator response. RNA analysis confirmed that c.1679G>C completely missplices. A symptomatic patient harboring R117H;7T;TG10/5T;TG12 exhibited reduced CFTR function (17.5%) in HNEs, facilitating a diagnosis of mild CF. HNEs responded to modulators (ivacaftor: 32.8%, ETI: 55.5%), and, since beginning therapy, lung function improved. We reaffirm HNE use for guiding therapeutic approaches, inform predictions on modulator response (e.g., R334W), and closely assess variants that affect splicing (e.g., c.1679G>C). Notably, functional studies in HNEs harboring R117H;7T;TG10/5T;TG12 facilitated a diagnosis of mild CF, suggesting the use for HNE functional studies as a clinical diagnostic test.

Lentiviral vector gene therapy and CFTR modulators show comparable effectiveness in cystic fibrosis rat airway models

Mutation-agnostic treatments such as airway gene therapy have the potential to treat any individual with cystic fibrosis (CF), irrespective of their CF transmembrane conductance regulator (CFTR) gene variants. The aim of this study was to employ two CF rat models, Phe508del and CFTR knockout (KO), to assess the comparative effectiveness of CFTR modulators and lentiviral (LV) vector-mediated gene therapy. Cells were isolated from the tracheas of rats and used to establish air-liquid interface (ALI) cultures. Phe508del rat ALIs were treated with the modulator combination, elexacaftor-tezacaftor-ivacaftor (ETI), and separate groups of Phe508del and KO tracheal epithelial cells were treated with LV-CFTR followed by differentiation at ALI. Ussing chamber measurements were performed to assess CFTR function. ETI-treated Phe508del ALI cultures demonstrated CFTR function that was 59% of wild-type level, while gene-addition therapy restored Phe508del to 68% and KO to 47% of wild-type level, respectively. Our findings show that rat Phe508del-CFTR protein can be successfully rescued with ETI treatment, and that CFTR gene-addition therapy provides significant CFTR correction in Phe508del and KO ALI cultures to levels that were comparable to ETI. These findings highlight the potential of an LV vector-based gene therapy for the treatment of CF lung disease.

ABC transporters involved in respiratory and cholestatic diseases: From rare to very rare monogenic diseases

ATP-binding cassette (ABC) transporters constitute a 49-member superfamily in humans. These proteins, most of them being transmembrane, allow the active transport of an important variety of substrates across biological membranes, using ATP hydrolysis as an energy source. For an important proportion of these ABC transporters, genetic variations of the loci encoding them have been correlated with rare genetic diseases, including cystic fibrosis and interstitial lung disease (variations in CFTR/ABCC7 and ABCA3) as well as cholestatic liver diseases (variations in ABCB4 and ABCB11). In this review, we first describe these ABC transporters and how their molecular dysfunction may lead to human diseases. Then, we propose a classification of the genetic variants according to their molecular defect (expression, traffic, function and/or stability), which may be considered as a general guideline for all ABC transporters' variants. Finally, we discuss recent progress in the field of targeted pharmacotherapy, which aim to correct specific molecular defects using small molecules. In conclusion, we are opening the path to treatment repurposing for diseases involving similar deficiencies in other ABC transporters.

Ribosomal frameshifting selectively modulates the assembly, function, and pharmacological rescue of a misfolded CFTR variant

The cotranslational misfolding of the cystic fibrosis transmembrane conductance regulator chloride channel (CFTR) plays a central role in the molecular basis of CF. The misfolding of the most common CF variant (ΔF508) remodels both the translational regulation and quality control of CFTR. Nevertheless, it is unclear how the misassembly of the nascent polypeptide may directly influence the activity of the translation machinery. In this work, we identify a structural motif within the CFTR transcript that stimulates efficient -1 ribosomal frameshifting and triggers the premature termination of translation. Though this motif does not appear to impact the interactome of wild-type CFTR, silent mutations that disrupt this RNA structure alter the association of nascent ΔF508 CFTR with numerous translation and quality control proteins. Moreover, disrupting this RNA structure enhances the functional gating of the ΔF508 CFTR channel at the plasma membrane and its pharmacological rescue by the CFTR modulators contained in the CF drug Trikafta. The effects of the RNA structure on ΔF508 CFTR appear to be attenuated in the absence of the ER membrane protein complex, which was previously found to modulate ribosome collisions during "preemptive quality control" of a misfolded CFTR homolog. Together, our results reveal that ribosomal frameshifting selectively modulates the assembly, function, and pharmacological rescue of a misfolded CFTR variant. These findings suggest that interactions between the nascent chain, quality control machinery, and ribosome may dynamically modulate ribosomal frameshifting in order to tune the processivity of translation in response to cotranslational misfolding.

A nonnatural peptide targeting the A-kinase anchoring function of PI3Kγ for therapeutic cAMP modulation in pulmonary cells

A-kinase anchoring proteins (AKAPs) are key orchestrators of cAMP signaling that act by recruiting protein kinase A (PKA) in proximity of its substrates and regulators to specific subcellular compartments. Modulation of AKAPs function offers the opportunity to achieve compartment-restricted modulation of the cAMP/PKA axis, paving the way to new targeted treatments. For instance, blocking the AKAP activity of phosphoinositide 3-kinase γ (PI3Kγ) improves lung function by inducing cAMP-mediated bronchorelaxation, ion transport, and antiinflammatory responses. Here, we report the generation of a nonnatural peptide, D-retroinverso (DRI)-Pep #20, optimized to disrupt the AKAP function of PI3Kγ. DRI-Pep #20 mimicked the native interaction between the N-terminal domain of PI3Kγ and PKA, demonstrating nanomolar affinity for PKA, high resistance to protease degradation and high permeability to the pulmonary mucus barrier. DRI-Pep #20 triggered cAMP elevation both in vivo in the airway tract of mice upon intratracheal administration, and in vitro in bronchial epithelial cells of cystic fibrosis (CF) patients. In CF cells, DRI-Pep #20 rescued the defective function of the cAMP-operated channel cystic fibrosis transmembrane conductance regulator, by boosting the efficacy of approved cystic fibrosis transmembrane conductance regulator modulators. Overall, this study unveils DRI-Pep #20 as a potent PI3Kγ/PKA disruptor for achieving therapeutic cAMP elevation in chronic respiratory disorders.

TMEM16 proteins: Ca2+‑activated chloride channels and phospholipid scramblases as potential drug targets (Review)

TMEM16 proteins, which function as Ca2+‑activated Cl‑ channels are involved in regulating a wide variety of cellular pathways and functions. The modulators of Cl‑ channels can be used for the molecule‑based treatment of respiratory diseases, cystic fibrosis, tumors, cancer, osteoporosis and coronavirus disease 2019. The TMEM16 proteins link Ca2+ signaling, cellular electrical activity and lipid transport. Thus, deciphering these complex regulatory mechanisms may enable a more comprehensive understanding of the physiological functions of the TMEM16 proteins and assist in ascertaining the applicability of these proteins as potential pharmacological targets for the treatment of a range of diseases. The present review examined the structures, functions and characteristics of the different types of TMEM16 proteins, their association with the pathogenesis of various diseases and the applicability of TMEM16 modulator‑based treatment methods.

Successful Desensitization With ELX/TEZ/IVA

Elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) was given US Food and Drug Administration approval based on its therapeutic benefits to treat patients with cystic fibrosis (CF) who had at least 1 allele of the CF transmembrane conductance regulator (CFTR) with phenylalanine deleted at position 508 (F508del). The increase in genotyping studies has increased the frequency of use of CFTR modulators; however, severe allergic reactions to CFTR modulators have also been described. It is critical to avoid the offending medication and select alternative treatments while dealing with drug allergies. Drug desensitization may be taken into consideration in situations where there is no other option. This article describes home desensitization treatment for a patient with CF who developed a maculopapular rash following CFTR modulator medication. There are currently no alternative drugs for CFTR modulators, which are crucial for patients with CF, and limited experience is available with allergic reactions to these drugs. It is important to establish desensitization protocols in order to control drug reactions to CFTR modulators, which are vital for individuals with CF.

Systematic deletion of symmetrical CFTR exons reveals new therapeutic targets for exon skipping antisense oligonucleotides

There is a major need for therapeutics that treat disease caused by premature termination codons (PTCs). Splice-switching antisense oligonucleotides (ASOs) can be directed to block splicing and cause exon skipping, a process that can be used to effectively remove PTCs from an mRNA. This ASO-induced exon skipping can restore protein coding potential when the exons on either side of the skipped exon are in the same reading frame, or symmetrical. We demonstrate the potential of this approach as a therapeutic using the cystic fibrosis (CF) transmembrane regulator (CFTR) gene, which has CF-associated, PTC-causing variants in all 27 of its exons. We functionally screened all CFTR isoforms that can be generated by deletion of symmetrical exons and identify four that are functionally responsive to CFTR modulators. We identified ASOs that induce skipping of these exons and show that they recover CFTR function in airway cells derived from individuals with CFTR PTC variants. This study demonstrates that systematic functional analysis of in-frame exon-deleted protein isoforms can successfully identify targets for ASO-based splice-switching therapies, a therapeutic concept that can be broadly applied to any multi-exon protein-coding gene disrupted by PTCs.

Effect of CFTR Modulators on Oxidative Stress and Autophagy in Non-CFTR-Expressing Cells

The triple combination therapy for cystic fibrosis (CF), including elexacaftor, tezacaftor and ivacaftor (ETI or Trikafta), has been shown to improve lung function and reduce pulmonary exacerbations, thereby enhancing the quality of life for most CF patients. Recent findings suggest that both the individual components and ETI may have potential off-target effects, highlighting the need to understand how these modulators impact cellular physiology, particularly in cells that do not express CF transmembrane conductance regulator (CFTR). We used HEK293 cells, as a cell model not expressing the CFTR protein, to evaluate the effect of ETI and each of its components on autophagic machinery and on the Rab5/7 components of the Rab pathway. We firstly demonstrate that the single modulators Teza and Iva, and the combinations ET and ETI, increased ROS production in the absence of their target while decreasing it in cells expressing the CFTR ∆F508del. This increase in cellular stress was followed by an increase in the total level of polyubiquitinated proteins as well as the p62 level and LC3II/LC3I ratio. Furthermore, we found that ETI had the opposite effect on Rabs by increasing Rab5 levels while decreasing Rab7. Interestingly, these changes were abolished by the expression of mutated CFTR. Overall, our data suggest that in the absence of their target, both the individual modulators and ETI increased ROS production and halted both autophagic flux and plasma membrane protein recycling.

CFTR modulators response of S737F and T465N CFTR variants on patient-derived rectal organoids

BACKGROUND

Predictions based on patient-derived materials of CFTR modulators efficacy have been performed lately in patient-derived cells, extending FDA-approved drugs for CF patients harboring rare variants. Here we developed intestinal organoids from subjects carrying S737F- and T465N-CFTR in trans with null alleles to evaluate their functional impact on CFTR protein function and their restoration upon CFTR modulator treatment. The characterization of S737F-CFTR was performed in two subjects recently assessed in nasal epithelial cells but not in colonoids.

RESULTS

Our functional analysis (Ussing chamber) confirmed that S737F-CFTR is a mild variant with residual function as investigated in colonoids of patients with S737F/Dele22-24 and S737F/W1282X genotypes. An increase of current upon Elexacaftor/Tezacaftor/Ivacaftor (ETI) treatment was recorded for the former genotype. T465N is a poorly characterized missense variant that strongly impacts CFTR function, as almost no CFTR-mediated anion secretion was registered for T465N/Q39X colonoids. ETI treatment substantially improved CFTR-mediated anion secretion and increased the rescue of mature CFTR expression compared to either untreated colonoids or to dual CFTR modulator therapies.

CONCLUSIONS

Our study confirms the presence of a residual function of the S737F variant and its limited response to CFTR modulators while predicting for the first time the potential clinical benefit of Trikafta® for patients carrying the rare T465N variant.

Synthesis and Biological Evaluation of Pyrazole-Pyrimidones as a New Class of Correctors of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)

Cystic fibrosis (CF) is caused by the functional expression defect of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Despite the recent success in CFTR modulator development, the available correctors only partially restore the F508del-CFTR channel function, and several rare CF mutations show resistance to available drugs. We previously identified compound 4172 that synergistically rescued the F508del-CFTR folding defect in combination with the existing corrector drugs VX-809 and VX-661. Here, novel CFTR correctors were designed by applying a classical medicinal chemistry approach on the 4172 scaffold. Molecular docking and three-dimensional quantitative structure-activity relationship (3D-QSAR) studies were conducted to propose a plausible binding site and design more potent and effective analogs. We identified three optimized compounds, which, in combination with VX-809 and the investigational corrector 3151, increased the plasma membrane density and function of F508del-CFTR and other rare CFTR mutants resistant to the currently approved therapies.

Allosteric inhibition of CFTR gating by CFTRinh-172 binding in the pore

Loss-of-function mutations of the CFTR gene cause the life-shortening genetic disease cystic fibrosis (CF), whereas overactivity of CFTR may lead to secretory diarrhea and polycystic kidney disease. While effective drugs targeting the CFTR protein have been developed for the treatment of CF, little progress has been made for diseases caused by hyper-activated CFTR. Here, we solve the cryo-EM structure of CFTR in complex with CFTRinh-172 (Inh-172), a CFTR gating inhibitor with promising potency and efficacy. We find that Inh-172 binds inside the pore of CFTR, interacting with amino acid residues from transmembrane segments (TMs) 1, 6, 8, 9, and 12 through mostly hydrophobic interactions and a salt bridge. Substitution of these residues lowers the apparent affinity of Inh-172. The inhibitor-bound structure reveals re-orientations of the extracellular segment of TMs 1, 8, and 12, supporting an allosteric modulation mechanism involving post-binding conformational changes. This allosteric inhibitory mechanism readily explains our observations that pig CFTR, which preserves all the amino acid residues involved in Inh-172 binding, exhibits a much-reduced sensitivity to Inh-172 and that the apparent affinity of Inh-172 is altered by the CF drug ivacaftor (i.e., VX-770) which enhances CFTR's activity through binding to a site also comprising TM8.

Ribosomal Frameshifting Selectively Modulates the Assembly, Function, and Pharmacological Rescue of a Misfolded CFTR Variant

The cotranslational misfolding of the cystic fibrosis transmembrane conductance regulator chloride channel (CFTR) plays a central role in the molecular basis of cystic fibrosis (CF). The misfolding of the most common CF variant (ΔF508) remodels both the translational regulation and quality control of CFTR. Nevertheless, it is unclear how the misassembly of the nascent polypeptide may directly influence the activity of the translation machinery. In this work, we identify a structural motif within the CFTR transcript that stimulates efficient -1 ribosomal frameshifting and triggers the premature termination of translation. Though this motif does not appear to impact the interactome of wild-type CFTR, silent mutations that disrupt this RNA structure alter the association of nascent ΔF508 CFTR with numerous translation and quality control proteins. Moreover, disrupting this RNA structure enhances the functional gating of the ΔF508 CFTR channel at the plasma membrane and its pharmacological rescue by the CFTR modulators contained in the CF drug Trikafta. The effects of the RNA structure on ΔF508 CFTR appear to be attenuated in the absence of the ER membrane protein complex (EMC), which was previously found to modulate ribosome collisions during "preemptive quality control" of a misfolded CFTR homolog. Together, our results reveal that ribosomal frameshifting selectively modulates the assembly, function, and pharmacological rescue of a misfolded CFTR variant. These findings suggest interactions between the nascent chain, quality control machinery, and ribosome may dynamically modulate ribosomal frameshifting in order to tune the processivity of translation in response to cotranslational misfolding.

Potentiation of BKCa channels by cystic fibrosis transmembrane conductance regulator correctors VX-445 and VX-121

Cystic fibrosis results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, ultimately leading to diminished transepithelial anion secretion and mucociliary clearance. CFTR correctors are therapeutics that restore the folding/trafficking of mutated CFTR to the plasma membrane. The large-conductance calcium-activated potassium channel (BKCa, KCa1.1) is also critical for maintaining lung airway surface liquid (ASL) volume. Here, we show that the class 2 (C2) CFTR corrector VX-445 (elexacaftor) induces K+ secretion across WT and F508del CFTR primary human bronchial epithelial cells (HBEs), which was entirely inhibited by the BKCa antagonist paxilline. Similar results were observed with VX-121, a corrector under clinical evaluation. Whole-cell patch-clamp recordings verified that CFTR correctors potentiated BKCa activity from both primary HBEs and HEK cells stably expressing the α subunit (HEK-BK cells). Furthermore, excised patch-clamp recordings from HEK-BK cells verified direct action on the channel and demonstrated a significant increase in open probability. In mouse mesenteric artery, VX-445 induced a paxilline-sensitive vasorelaxation of preconstricted arteries. VX-445 also reduced firing frequency in primary rat hippocampal and cortical neurons. We raise the possibilities that C2 CFTR correctors gain additional clinical benefit by activation of BKCa in the lung yet may lead to adverse events through BKCa activation elsewhere.

Diverse role, structural trends, and applications of fluorinated sulphonamide compounds in agrochemical and pharmaceutical fields

Our knowledge of fluorine's unique and complex properties has significantly increased over the past 20 years. Consequently, more sophisticated and innovative techniques have emerged to incorporate this feature into the design of potential drug candidates. In recent years, researchers have become interested in synthesizing fluoro-sulphonamide compounds to discover new chemical entities with distinct and unexpected physical, chemical, and biological characteristics. The fluorinated sulphonamide molecules have shown significant biomedical importance. Their potential is not limited to biomedical applications but also includes crop protection. The discovery of novel fluorine and Sulfur compounds has highlighted their importance in the chemical sector, particularly in the agrochemical and medicinal fields. Recently, several fluorinated sulphonamide derivatives have been developed and frequently used by agriculturalists to produce food for the growing global population. These molecules have also exhibited their potential in health by inhibiting various human diseases. In today's world, it is crucial to have a steady supply of innovative pharmaceutical and agrochemical molecules that are highly effective, less harmful to the environment, and affordable. This review summarizes the available information on the activity of Fluorine and Sulphonamide compounds, which have proven active in pharmaceuticals and agrochemicals with excellent environmental and human health approaches. Moreover, it focuses on the current literature on the chemical structures, the application of fluorinated sulphonamide compounds against various pathological conditions, and their effectiveness in crop protection.

Ligand-based virtual-screening identified a novel CFTR ligand which improves the defective cell surface expression of misfolded ABC transporters

Cystic fibrosis (CF) is a monogenetic disease caused by the mutation of CFTR, a cAMP-regulated Cl- channel expressing at the apical plasma membrane (PM) of epithelia. ∆F508-CFTR, the most common mutant in CF, fails to reach the PM due to its misfolding and premature degradation at the endoplasmic reticulum (ER). Recently, CFTR modulators have been developed to correct CFTR abnormalities, with some being used as therapeutic agents for CF treatment. One notable example is Trikafta, a triple combination of CFTR modulators (TEZ/ELX/IVA), which significantly enhances the functionality of ΔF508-CFTR on the PM. However, there's room for improvement in its therapeutic effectiveness since TEZ/ELX/IVA doesn't fully stabilize ΔF508-CFTR on the PM. To discover new CFTR modulators, we conducted a virtual screening of approximately 4.3 million compounds based on the chemical structures of existing CFTR modulators. This effort led us to identify a novel CFTR ligand named FR3. Unlike clinically available CFTR modulators, FR3 appears to operate through a distinct mechanism of action. FR3 enhances the functional expression of ΔF508-CFTR on the apical PM in airway epithelial cell lines by stabilizing NBD1. Notably, FR3 counteracted the degradation of mature ΔF508-CFTR, which still occurs despite the presence of TEZ/ELX/IVA. Furthermore, FR3 corrected the defective PM expression of a misfolded ABCB1 mutant. Therefore, FR3 may be a potential lead compound for addressing diseases resulting from the misfolding of ABC transporters.

Functional Consequences of CFTR Interactions in Cystic Fibrosis

Cystic fibrosis (CF) is a fatal autosomal recessive disorder caused by the loss of function mutations within a single gene for the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). CFTR is a chloride channel that regulates ion and fluid transport across various epithelia. The discovery of CFTR as the CF gene and its cloning in 1989, coupled with extensive research that went into the understanding of the underlying biological mechanisms of CF, have led to the development of revolutionary therapies in CF that we see today. The highly effective modulator therapies have increased the survival rates of CF patients and shifted the epidemiological landscape and disease prognosis. However, the differential effect of modulators among CF patients and the presence of non-responders and ineligible patients underscore the need to develop specialized and customized therapies for a significant number of patients. Recent advances in the understanding of the CFTR structure, its expression, and defined cellular compositions will aid in developing more precise therapies. As the lifespan of CF patients continues to increase, it is becoming critical to clinically address the extra-pulmonary manifestations of CF disease to improve the quality of life of the patients. In-depth analysis of the molecular signature of different CF organs at the transcriptional and post-transcriptional levels is rapidly advancing and will help address the etiological causes and variability of CF among patients and develop precision medicine in CF. In this review, we will provide an overview of CF disease, leading to the discovery and characterization of CFTR and the development of CFTR modulators. The later sections of the review will delve into the key findings derived from single-molecule and single-cell-level analyses of CFTR, followed by an exploration of disease-relevant protein complexes of CFTR that may ultimately define the etiological course of CF disease.

Response to Elexacaftor/Tezacaftor/Ivacaftor in people with cystic fibrosis with the N1303K mutation: Case report and review of the literature

Cystic fibrosis (CF) is caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Thousands of CFTR mutations have been identified, but only a fraction are known to cause CF, with the most common being the prototypical class II CFTR mutation F508del. Elexacaftor-Tezacaftor-Ivacaftor (ETI) is a CFTR modulator that significantly increases ppFEV1 and reduces exacerbation frequencies. It is indicated for people with CF (pwCF) 2 years or older with at least one copy of F508del or one copy of the other 177 CFTR mutations that are responsive to ETI based on clinical or in vitro data. N1303K is the second most common class II mutation in the U.S. but is not yet FDA-approved for CFTR modulator therapy. However, N1303K is very similar to the F508del mutation and reveals variable in vitro responses to ETI. Theratyping provides an opportunity to consider ETI therapy for pwCF with mutations currently not approved by the FDA. We describe the case of an adult CF patient with W1282X and N1303K CFTR mutations and advanced CF lung disease (ACFLD) and declining lung function in which ETI was started after theratyping of nasal cells showed a meaningful response to ETI (current enhanced to over 10% of WT CFTR). The patient experienced clinical improvement with a 5% improvement in ppFEV1 and 10% increase in weight. However, there was no change in sweat chloride and the increase in ppFEV1 was less than what has been described for ACFLD patients with more typical ETI-amenable mutations. However, the response was in line with a few other cases described in the literature. This suggests a partial functional CFTR rescue like first-generation modulators for F508del. Thus, pwCF with N1303K CFTR variant could be considered for ETI eligibility.

PTI-801 (posenacaftor) shares a common mechanism with VX-445 (elexacaftor) to rescue p.Phe508del-CFTR

The deletion of a phenylalanine at position 508 (p.Phe508del) in the CFTR anion channel is the most prevalent variant in people with Cystic Fibrosis (CF). This variant impairs folding and stability of the CF transmembrane conductance regulator (CFTR) protein, resulting in its defective trafficking and premature degradation. Over the last years, therapeutic accomplishments have been attained in developing small molecules that partially correct p.Phe508del-CFTR defects; however, the mechanism of action (MoA) of these compounds has only started to be uncovered. In this study, we employed biochemical, fluorescence microscopy, and functional assays to examine the efficacy and properties of PTI-801, a newly developed p.Phe508del-CFTR corrector. To exploit its MoA, we assessed PTI-801 effects in combination with low temperature, genetic revertants of p.Phe508del-CFTR (the in cis p.Val510Asp, p.Gly550Glu, p.Arg1070Trp, and 4RK) and other correctors. Our results demonstrated that PTI-801 rescues p.Phe508del-CFTR processing, PM trafficking, and channel function (upon agonist stimulation) with greater correction effects in combination with ABBV-2222, FDL-169, VX-661, or VX-809, but not with VX-445. Although PTI-801 exhibited no potentiator activity on low temperature- and corrector-rescued p.Phe508del-CFTR, this compound displayed similar behavior to that of VX-445 on genetic revertants. Such evidence associated with the lack of additivity when PTI-801 and VX-445 were combined indicates that they share a common binding site to correct p.Phe508del-CFTR defects. Despite the high efficacy of PTI-801 in combination with ABBV-2222, FDL-169, VX-661, or VX-809, these dual corrector combinations only partially restored p.Phe508del-CFTR conformational stability, as shown by the lower half-life of the mutant protein compared to that of WT-CFTR. In summary, PTI-801 likely shares a common MoA with VX-445 in rescuing p.Phe508del-CFTR, thus being a feasible alternative for the development of novel corrector combinations with greater capacity to rescue mutant CFTR folding and stability.

A uniquely efficacious type of CFTR corrector with complementary mode of action

Three distinct pharmacological corrector types (I, II, III) with different binding sites and additive behavior only partially rescue the F508del-cystic fibrosis transmembrane conductance regulator (CFTR) folding and trafficking defect observed in cystic fibrosis. We describe uniquely effective, macrocyclic CFTR correctors that were additive to the known corrector types, exerting a complementary "type IV" corrector mechanism. Macrocycles achieved wild-type-like folding efficiency of F508del-CFTR at the endoplasmic reticulum and normalized CFTR currents in reconstituted patient-derived bronchial epithelium. Using photo-activatable macrocycles, docking studies and site-directed mutagenesis a highly probable binding site and pose for type IV correctors was identified in a cavity between lasso helix-1 (Lh1) and transmembrane helix-1 of membrane spanning domain (MSD)-1, distinct from the known corrector binding sites. Since only F508del-CFTR fragments spanning from Lh1 until MSD2 responded to type IV correctors, these likely promote cotranslational assembly of Lh1, MSD1, and MSD2. Previously corrector-resistant CFTR folding mutants were also robustly rescued, suggesting substantial therapeutic potential for type IV correctors.

Organic Synthesis and Current Understanding of the Mechanisms of CFTR Modulator Drugs Ivacaftor, Tezacaftor, and Elexacaftor

The monogenic rare disease Cystic Fibrosis (CF) is caused by mutations in the gene encoding the CF transmembrane conductance (CFTR) protein, an anion channel expressed at the apical plasma membrane of epithelial cells. The discovery and subsequent development of CFTR modulators-small molecules acting on the basic molecular defect in CF-have revolutionized the standard of care for people with CF (PwCF), thus drastically improving their clinical features, prognosis, and quality of life. Currently, four of these drugs are approved for clinical use: potentiator ivacaftor (VX-770) alone or in combination with correctors lumacaftor, (VX-809), tezacaftor (VX-661), and elexacaftor (VX-445). Noteworthily, the triple combinatorial therapy composed of ivacaftor, tezacaftor, and elexacaftor constitutes the most effective modulator therapy nowadays for the majority of PwCF. In this review, we exploit the organic synthesis of ivacaftor, tezacaftor, and elexacaftor by providing a retrosynthetic drug analysis for these CFTR modulators. Furthermore, we describe the current understanding of the mechanisms of action (MoA's) of these compounds by discussing several studies that report the key findings on the molecular mechanisms underlying their action on the CFTR protein.

Small molecule modulators of cystic fibrosis transmembrane conductance regulator (CFTR): Structure, classification, and mechanisms

The advent of small molecule modulators targeting the cystic fibrosis transmembrane conductance regulator (CFTR) has revolutionized the treatment of persons with cystic fibrosis (CF) (pwCF). Presently, these small molecule CFTR modulators have gained approval for usage in approximately 90 % of adult pwCF. Ongoing drug development endeavors are focused on optimizing the therapeutic benefits while mitigating potential adverse effects associated with this treatment approach. Based on their mode of interaction with CFTR, these drugs can be classified into two distinct categories: specific CFTR modulators and non-specific CFTR modulators. Specific CFTR modulators encompass potentiators and correctors, whereas non-specific CFTR modulators encompass activators, proteostasis modulators, stabilizers, reader-through agents, and amplifiers. Currently, four small molecule modulators, all classified as potentiators and correctors, have obtained marketing approval. Furthermore, numerous novel small molecule modulators, exhibiting diverse mechanisms of action, are currently undergoing development. This review aims to explore the classification, mechanisms of action, molecular structures, developmental processes, and interrelationships among small molecule CFTR modulators.

Small-molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states

Over 80% of people with cystic fibrosis (CF) carry the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel at the apical plasma membrane (PM) of epithelial cells. F508del impairs CFTR folding causing it to be destroyed by endoplasmic reticulum associated degradation (ERAD). Small-molecule correctors, which act as pharmacological chaperones to divert CFTR-F508del from ERAD, are the primary strategy for treating CF, yet corrector development continues with only a rudimentary understanding of how ERAD targets CFTR-F508del. We conducted genome-wide CRISPR/Cas9 knockout screens to systematically identify the molecular machinery that underlies CFTR-F508del ERAD. Although the ER-resident ubiquitin ligase, RNF5 was the top E3 hit, knocking out RNF5 only modestly reduced CFTR-F508del degradation. Sublibrary screens in an RNF5 knockout background identified RNF185 as a redundant ligase and demonstrated that CFTR-F508del ERAD is robust. Gene-drug interaction experiments illustrated that correctors tezacaftor (VX-661) and elexacaftor (VX-445) stabilize sequential, RNF5-resistant folding states. We propose that binding of correctors to nascent CFTR-F508del alters its folding landscape by stabilizing folding states that are not substrates for RNF5-mediated ubiquitylation.

Use of elexacaftor/tezacaftor/ivacaftor combination in pregnancy

INTRODUCTION

Management of cystic fibrosis has recently stepped forward with the introduction of cystic fibrosis transmembrane conductance regulator (CFTR) modulators, although data on potential adverse effects are lacking for many categories of patients, such as pregnant women.

METHODS

We report one of the first reports on the outcome of pregnancy in a woman treated with Elexacaftor/Tezacaftor/Ivacaftor during the second and third trimester of pregnancy, showing a significant improvement of respiratory status, compared with the first trimester when the medication was discontinued due to unknown and, therefore, potential teratogenic effects. Also, we performed the review of the existing literature on the topic.

RESULTS

The course of pregnancy was uneventful, with reference to major obstetric complications, and the patient delivered a healthy neonate. These results were similar to those coming from other short series of pregnant women affected by cystic fibrosis and treated with CFTR modulators during pregnancy.

CONCLUSIONS

Thus, despite the lack of evidence on the topic, the use of Elexacaftor/Tezacaftor/Ivacaftor in pregnancy seems to be apparently not associated with major adverse events, thus opening optimistic scenarios in terms of management of these patients.

CFTR Modulators: From Mechanism to Targeted Therapeutics

People with cystic fibrosis (CF) suffer from a multi-organ disorder caused by loss-of-function variants in the gene encoding the epithelial anion channel cystic fibrosis transmembrane conductance regulator (CFTR). Tremendous progress has been made in both basic and clinical sciences over the past three decades since the identification of the CFTR gene. Over 90% of people with CF now have access to therapies targeting dysfunctional CFTR. This success was made possible by numerous studies in the field that incrementally paved the way for the development of small molecules known as CFTR modulators. The advent of CFTR modulators transformed this life-threatening illness into a treatable disease by directly binding to the CFTR protein and correcting defects induced by pathogenic variants. In this chapter, we trace the trajectory of structural and functional studies that brought CF therapies from bench to bedside, with an emphasis on mechanistic understanding of CFTR modulators.