Acquired defects in CFTR-dependent β-adrenergic sweat secretion in chronic obstructive pulmonary disease

Inflammation in the COVID-19 airway is due to inhibition of CFTR signaling by the SARS-CoV-2 spike protein

SARS-CoV-2-contributes to sickness and death in COVID-19 patients partly by inducing a hyper-proinflammatory immune response in the host airway. This hyper-proinflammatory state involves activation of signaling by NFκB, and unexpectedly, ENaC, the epithelial sodium channel. Post-infection inflammation may also contribute to "Long COVID"/PASC. Enhanced signaling by NFκB and ENaC also marks the airway of patients suffering from cystic fibrosis, a life-limiting proinflammatory genetic disease due to inactivating mutations in the CFTR gene. We therefore hypothesized that inflammation in the COVID-19 airway might similarly be due to inhibition of CFTR signaling by SARS-CoV-2 spike protein, and therefore activation of both NFκB and ENaC signaling. We used western blot and electrophysiological techniques, and an organoid model of normal airway epithelia, differentiated on an air-liquid-interface (ALI). We found that CFTR protein expression and CFTR cAMP-activated chloride channel activity were lost when the model epithelium was exposed to SARS-CoV-2 spike proteins. As hypothesized, the absence of CFTR led to activation of both TNFα/NFκB signaling and α and γ ENaC. We had previously shown that the cardiac glycoside drugs digoxin, digitoxin and ouabain blocked interaction of spike protein and ACE2. Consistently, addition of 30 nM concentrations of the cardiac glycoside drugs, prevented loss of both CFTR protein and CFTR channel activity. ACE2 and CFTR were found to co-immunoprecipitate in both basal cells and differentiated epithelia. Thus spike-dependent CFTR loss might involve ACE2 as a bridge between Spike and CFTR. In addition, spike exposure to the epithelia resulted in failure of endosomal recycling to return CFTR to the plasma membrane. Thus, failure of CFTR recovery from endosomal recycling might be a mechanism for spike-dependent loss of CFTR. Finally, we found that authentic SARS-CoV-2 virus infection induced loss of CFTR protein, which was rescued by the cardiac glycoside drugs digitoxin and ouabain. Based on experiments with this organoid model of small airway epithelia, and comparisons with 16HBE14o- and other cell types expressing normal CFTR, we predict that inflammation in the COVID-19 airway may be mediated by inhibition of CFTR signaling by the SARS-CoV-2 spike protein, thus inducing a cystic fibrosis-like clinical phenotype. To our knowledge this is the first time COVID-19 airway inflammation has been experimentally traced in normal subjects to a contribution from SARS-CoV-2 spike-dependent inhibition of CFTR signaling.

Association between biomarkers of tobacco smoke exposure and clinical efficacy of ivacaftor in the G551D observational trial (GOAL)

BACKGROUND

Acrolein, an aldehyde in smoke from tobacco products, inhibits CFTR function in vitro. Ivacaftor is an FDA-approved potentiator that improves mutant CFTR function. This human clinical study investigated the relationship between two urinary markers of tobacco smoke exposure - the acrolein metabolite 3-HPMA and the nicotine metabolite NNAL - and sweat chloride response to ivacaftor in the G551D Observational Trial (GOAL).

METHODS

3-HPMA (low: <50th centile; moderate: 50-75th centile; high: >75th centile) and NNAL (detectable/undetectable) in GOAL samples was quantified with LC-MS/MS. Self-report of tobacco smoke exposure (Y/N) served as a subjective measure. Change in sweat chloride from pre- to 6 months post-ivacaftor treatment (ΔSC) was the primary CFTR-dependent readout.

RESULTS

The sample included 151 individuals, mean age 20.7 (SD 11.4) years, range 6-59 years. Smoke exposure prevalence was 15 % per self-reports but 27 % based on detectable NNAL. 3-HPMA was increased in those reporting tobacco smoke exposure (607 vs 354 ng/ml, p = 0.008), with a higher proportion of smoke-exposed in the high- vs low-acrolein group (31 % vs 9 %, p=0.040). Compared to low-acrolein counterparts, high-acrolein participants experienced less decrease in sweat chloride (-35.2 vs -48.2 mmol/L; p = 0.020) and had higher sweat chloride values (50.6 vs 37.6 mmol/L; p = 0.020) 6 months post-ivacaftor. The odds of ivacaftor-mediated potentiation to near normative CFTR function (defined as SC6mo <40 mmol/L) was more than twice as high in the low-acrolein cohort (OR: 2.51, p = 0.026).

CONCLUSIONS

Increased urinary 3-HPMA, an acrolein metabolite of tobacco smoke, is associated with a diminished sweat chloride response to ivacaftor potentiation of CFTR function.

Evaluation of a novel CFTR potentiator in COPD ferrets with acquired CFTR dysfunction

RATIONALE

The majority of chronic obstructive pulmonary disease (COPD) patients have chronic bronchitis, for which specific therapies are unavailable. Acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction is observed in chronic bronchitis, but has not been proven in a controlled animal model with airway disease. Furthermore, the potential of CFTR as a therapeutic target has not been tested in vivo, given limitations to rodent models of COPD. Ferrets exhibit cystic fibrosis-related lung pathology when CFTR is absent and COPD with bronchitis following cigarette smoke exposure.

OBJECTIVES

To evaluate CFTR dysfunction induced by smoking and test its pharmacological reversal by a novel CFTR potentiator, GLPG2196, in a ferret model of COPD with chronic bronchitis.

METHODS

Ferrets were exposed for 6 months to cigarette smoke to induce COPD and chronic bronchitis and then treated with enteral GLPG2196 once daily for 1 month. Electrophysiological measurements of ion transport and CFTR function, assessment of mucociliary function by one-micron optical coherence tomography imaging and particle-tracking microrheology, microcomputed tomography imaging, histopathological analysis and quantification of CFTR protein and mRNA expression were used to evaluate mechanistic and pathophysiological changes.

MEASUREMENTS AND MAIN RESULTS

Following cigarette smoke exposure, ferrets exhibited CFTR dysfunction, increased mucus viscosity, delayed mucociliary clearance, airway wall thickening and airway epithelial hypertrophy. In COPD ferrets, GLPG2196 treatment reversed CFTR dysfunction, increased mucus transport by decreasing mucus viscosity, and reduced bronchial wall thickening and airway epithelial hypertrophy.

CONCLUSIONS

The pharmacologic reversal of acquired CFTR dysfunction is beneficial against pathological features of chronic bronchitis in a COPD ferret model.

An Adverse Outcome Pathway for Decreased Lung Function Focusing on Mechanisms of Impaired Mucociliary Clearance Following Inhalation Exposure

Adverse outcome pathways (AOPs) help to organize available mechanistic information related to an adverse outcome into key events (KEs) spanning all organizational levels of a biological system(s). AOPs, therefore, aid in the biological understanding of a particular pathogenesis and also help with linking exposures to eventual toxic effects. In the regulatory context, knowledge of disease mechanisms can help design testing strategies using in vitro methods that can measure or predict KEs relevant to the biological effect of interest. The AOP described here evaluates the major processes known to be involved in regulating efficient mucociliary clearance (MCC) following exposures causing oxidative stress. MCC is a key aspect of the innate immune defense against airborne pathogens and inhaled chemicals and is governed by the concerted action of its functional components, the cilia and airway surface liquid (ASL). The AOP network described here consists of sequences of KEs that culminate in the modulation of ciliary beat frequency and ASL height as well as mucus viscosity and hence, impairment of MCC, which in turn leads to decreased lung function.

Dysfunction in the Cystic Fibrosis Transmembrane Regulator in Chronic Obstructive Pulmonary Disease as a Potential Target for Personalised Medicine

In recent years, numerous pathways were explored in the pathogenesis of COPD in the quest for new potential therapeutic targets for more personalised medical care. In this context, the study of the cystic fibrosis transmembrane conductance regulator (CFTR) began to gain importance, especially since the advent of the new CFTR modulators which had the potential to correct this protein's dysfunction in COPD. The CFTR is an ion transporter that regulates the hydration and viscosity of mucous secretions in the airway. Therefore, its abnormal function favours the accumulation of thicker and more viscous secretions, reduces the periciliary layer and mucociliary clearance, and produces inflammation in the airway, as a consequence of a bronchial infection by both bacteria and viruses. Identifying CFTR dysfunction in the context of COPD pathogenesis is key to fully understanding its role in the complex pathophysiology of COPD and the potential of the different therapeutic approaches proposed to overcome this dysfunction. In particular, the potential of the rehydration of mucus and the role of antioxidants and phosphodiesterase inhibitors should be discussed. Additionally, the modulatory drugs which enhance or restore decreased levels of the protein CFTR were recently described. In particular, two CFTR potentiators, ivacaftor and icenticaftor, were explored in COPD. The present review updated the pathophysiology of the complex role of CFTR in COPD and the therapeutic options which could be explored.

Discovery of Icenticaftor (QBW251), a Cystic Fibrosis Transmembrane Conductance Regulator Potentiator with Clinical Efficacy in Cystic Fibrosis and Chronic Obstructive Pulmonary Disease

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel are established as the primary causative factor in the devastating lung disease cystic fibrosis (CF). More recently, cigarette smoke exposure has been shown to be associated with dysfunctional airway epithelial ion transport, suggesting a role for CFTR in the pathogenesis of chronic obstructive pulmonary disease (COPD). Here, the identification and characterization of a high throughput screening hit 6 as a potentiator of mutant human F508del and wild-type CFTR channels is reported. The design, synthesis, and biological evaluation of compounds 7-33 to establish structure-activity relationships of the scaffold are described, leading to the identification of clinical development compound icenticaftor (QBW251) 33, which has subsequently progressed to deliver two positive clinical proofs of concept in patients with CF and COPD and is now being further developed as a novel therapeutic approach for COPD patients.

Efficacy and Safety of the CFTR Potentiator Icenticaftor (QBW251) in COPD: Results from a Phase 2 Randomized Trial

Rationale

Excess mucus plays a key role in COPD pathogenesis. Cigarette smoke-induced cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction may contribute to disease pathogenesis by depleting airway surface liquid and reducing mucociliary transport; these defects can be corrected in vitro by potentiating CFTR.

Objective

To assess the efficacy of the CFTR potentiator icenticaftor in improving airflow obstruction in COPD patients with symptoms of chronic bronchitis.

Methods

In this double-blind, placebo-controlled study, COPD patients were randomized (2:1) to either icenticaftor 300 mg or placebo b.i.d. This non-confirmatory proof of concept study was powered for lung clearance index (LCI) and pre-bronchodilator FEV₁, with an estimated sample size of 90 patients. The primary endpoint was change from baseline in LCI for icenticaftor versus placebo at Day 29; key secondary endpoints included change from baseline in pre- and post-bronchodilator FEV₁ on Day 29. Key exploratory endpoints included change from baseline in sweat chloride, plasma fibrinogen levels, and sputum colonization.

Results

Ninety-two patients were randomized (icenticaftor, n=64; placebo, n=28). At Day 29, icenticaftor showed no improvement in change in LCI (treatment difference: 0.28 [19% probability of being better than placebo]), an improvement in pre-bronchodilator FEV₁ (mean: 50 mL [84% probability]) and an improvement in post-bronchodilator FEV₁ (mean: 63 mL [91% probability]) over placebo. Improvements in sweat chloride, fibrinogen and sputum bacterial colonization were also observed. Icenticaftor was safe and well tolerated.

Conclusion

The CFTR potentiator icenticaftor increased FEV₁ versus placebo after 28 days and was associated with improvements in systemic inflammation and sputum bacterial colonization in COPD patients; no improvements in LCI with icenticaftor were observed.

Tobacco smoke exposure limits the therapeutic benefit of tezacaftor/ivacaftor in pediatric patients with cystic fibrosis

OBJECTIVES

Tobacco smoke exposure reduces CFTR functional expression in vitro and contributes to acquired CFTR dysfunction. We investigated whether it also inhibits the clinical benefit of CFTR modulators, focusing on tezacaftor/ivacaftor, approved in February 2018 for individuals with CF age ≥12 years.

METHODS

A retrospective longitudinal analysis of encounter-based data from the CF Foundation Patient Registry (2016-2018) compared the slope of change in lung function (GLI FEV₁% predicted) before and after tezacaftor/ivacaftor initiation in smoke-exposed vs unexposed age-eligible pediatric patients. Tobacco smoke exposure (Ever/Never) was determined from caregiver self-report. Statistical analyses used hierarchical linear mixed modeling and fixed effects regression modeling.

RESULTS

The sample included 6,653 individuals with a total of 105,539 person-period observations. Tezacaftor/ivacaftor was prescribed to 19% (1,251) of individuals, mean age 17 years, mean baseline ppFEV₁ 83%, 28% smoke-exposed. Tezacaftor/ivacaftor users who were smoke-exposed had a lower baseline ppFEV₁ and experienced a greater lung function decline. Over two years, the difference in ppFEV₁ by smoke exposure among tezacaftor/ivacaftor users increased by 1.2% (7.6% to 8.8%, p<0.001). In both mixed effects and fixed effects regression models, tezacaftor/ivacaftor use was associated with improved ppFEV₁ among unexposed individuals (1.2% and 1.7%, respectively; p<0.001 for both) but provided no benefit among smoke-exposed counterparts (0.3%, p = 0.5 and 0.6%, p = 0.07, respectively).

CONCLUSION

Tobacco smoke exposure nullifies the therapeutic benefit of tezacaftor/ivacaftor among individuals with CF aged 12-20 years old. To maximize the therapeutic opportunity of CFTR modulators, every effort must be taken to eliminate smoke exposure in CF.

CFTR targeted therapies: recent advances in cystic fibrosis and possibilities in other diseases of the airways

Cystic fibrosis transmembrane conductance regulator (CFTR) is an ion transporter that regulates mucus hydration, viscosity and acidity of the airway epithelial surface. Genetic defects in CFTR impair regulation of mucus homeostasis, causing severe defects of mucociliary clearance as seen in cystic fibrosis. Recent work has established that CFTR dysfunction can be acquired in chronic obstructive pulmonary disease (COPD) and may also contribute to other diseases that share clinical features of cystic fibrosis, such as asthma, allergic bronchopulmonary aspergillosis and bronchiectasis. Protean causes of CFTR dysfunction have been identified including cigarette smoke exposure, toxic metals and downstream effects of neutrophil activation pathways. Recently, CFTR modulators, small molecule agents that potentiate CFTR or restore diminished protein levels at the cell surface, have been successfully developed for various CFTR gene defects, prompting interest in their use to treat diseases of acquired dysfunction. The spectrum of CFTR dysfunction, strategies for CFTR modulation, and candidate diseases for CFTR modulation beyond cystic fibrosis will be reviewed in this manuscript.

CFTR dysfunction may be part of the pathophysiology of many diseases of the airways. Exploration of mechanisms of dysfunction and options for CFTR-directed therapies are examined in this article. http://bit.ly/33o6nDu

Vaporized E-Cigarette Liquids Induce Ion Transport Dysfunction in Airway Epithelia

Cigarette smoking is associated with chronic obstructive pulmonary disease and chronic bronchitis. Acquired ion transport abnormalities, including cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction, caused by cigarette smoking have been proposed as potential mechanisms for mucus obstruction in chronic bronchitis. Although e-cigarette use is popular and perceived to be safe, whether it harms the airways via mechanisms altering ion transport remains unclear. In the present study, we sought to determine if e-cigarette vapor, like cigarette smoke, has the potential to induce acquired CFTR dysfunction, and to what degree. Electrophysiological methods demonstrated reduced chloride transport caused by vaporized e-cigarette liquid or vegetable glycerin at various exposures (30 min, 57.2% and 14.4% respectively, vs. control; P < 0.0001), but not by unvaporized liquid (60 min, 17.6% vs. untreated), indicating that thermal degradation of these products is required to induce the observed defects. We also observed reduced ATP-dependent responses (-10.8 ± 3.0 vs. -18.8 ± 5.1 μA/cm² control) and epithelial sodium channel activity (95.8% reduction) in primary human bronchial epithelial cells after 5 minutes, suggesting that exposures dramatically inhibit epithelial ion transport beyond CFTR, even without diminished transepithelial resistance or cytotoxicity. Vaporizing e-cigarette liquid produced reactive aldehydes, including acrolein (shown to induce acquired CFTR dysfunction), as quantified by mass spectrometry, demonstrating that respiratory toxicants in cigarette smoke can also be found in e-cigarette vapor (30 min air, 224.5 ± 15.99; unvaporized liquid, 284.8 ± 35.03; vapor, 54,468 ± 3,908 ng/ml; P < 0.0001). E-cigarettes can induce ion channel dysfunction in airway epithelial cells, partly through acrolein production. These findings indicate a heretofore unknown toxicity of e-cigarette use known to be associated with chronic bronchitis onset and progression, as well as with chronic obstructive pulmonary disease severity.

Combined Antioxidant, Anti-inflammaging and Mesenchymal Stem Cell Treatment: A Possible Therapeutic Direction in Elderly Patients with Chronic Obstructive Pulmonary Disease

Chronic Obstructive Pulmonary Disease (COPD) is a worldwide health problem associated with high morbidity and mortality, especially in elderly patients. Aging functions include mitochondrial dysfunction, cell-to-cell information exchange, protein homeostasis and extracellular matrix dysregulation, which are closely related to chronic inflammatory response and oxidation-antioxidant imbalance in the pathogenesis of COPD. COPD displays distinct inflammaging features, including increased cellular senescence and oxidative stress, stem cell exhaustion, alterations in the extracellular matrix, reduced levels of endogenous anti-inflammaging molecules, and reduced autophagy. Given that COPD and inflammaging share similar general features, it is very important to identify the specific mechanisms of inflammaging, which involve oxidative stress, inflammation and lung mesenchymal stem cell function in the development of COPD, especially in elderly COPD patients. In this review, we highlight the studies relevant to COPD progression, and focus on mechanisms associated with inflammaging.

Excess mucus viscosity and airway dehydration impact COPD airway clearance

The mechanisms by which cigarette smoking impairs airway mucus clearance are not well understood. We recently established a ferret model of cigarette smoke-induced chronic obstructive pulmonary disease (COPD) exhibiting chronic bronchitis. We investigated the effects of cigarette smoke on mucociliary transport (MCT).Adult ferrets were exposed to cigarette smoke for 6 months, with in vivo mucociliary clearance measured by technetium-labelled DTPA retention. Excised tracheae were imaged with micro-optical coherence tomography. Mucus changes in primary human airway epithelial cells and ex vivo ferret airways were assessed by histology and particle tracking microrheology. Linear mixed models for repeated measures identified key determinants of MCT.Compared to air controls, cigarette smoke-exposed ferrets exhibited mucus hypersecretion, delayed mucociliary clearance (-89.0%, p<0.01) and impaired tracheal MCT (-29.4%, p<0.05). Cholinergic stimulus augmented airway surface liquid (ASL) depth (5.8±0.3 to 7.3±0.6 µm, p<0.0001) and restored MCT (6.8±0.8 to 12.9±1.2 mm·min-1, p<0.0001). Mixed model analysis controlling for covariates indicated smoking exposure, mucus hydration (ASL) and ciliary beat frequency were important predictors of MCT. Ferret mucus was hyperviscous following smoke exposure in vivo or in vitro, and contributed to diminished MCT. Primary cells from smokers with and without COPD recapitulated these findings, which persisted despite the absence of continued smoke exposure.Cigarette smoke impairs MCT by inducing airway dehydration and increased mucus viscosity, and can be partially abrogated by cholinergic secretion of fluid secretion. These data elucidate the detrimental effects of cigarette smoke exposure on mucus clearance and suggest additional avenues for therapeutic intervention.

Sweat rate analysis of ivacaftor potentiation of CFTR in non-CF adults

To determine if ivacaftor (Kalydeco) influences non-CF human CFTR function in vivo, we measured CFTR-dependent (C-sweat) and CFTR-independent (M-sweat) rates from multiple identified sweat glands in 8 non-CF adults. The two types of sweating were stimulated sequentially with intradermal injections of appropriate reagents; each gland served as its own control via alternating off-on drug tests on both arms, given at weekly intervals with 3 off and 3 on tests per subject. We compared drug effects on C-sweating stimulated by either high or low concentrations of β-adrenergic cocktail, and on methacholine-stimulated M-sweating. For each subject we measured ~700 sweat volumes from ~75 glands per arm (maximum 12 readings per gland), and sweat volumes were log-transformed for statistical analysis. T-tests derived from linear mixed models (LMMs) were more conservative than the familiar paired sample t-tests, and show that ivacaftor significantly increased C-sweating stimulated by both levels of agonist, with a larger effect in the low cocktail condition; ivacaftor did not increase M-sweat. Concurrent sweat chloride tests detected no effect of ivacaftor. We conclude that ivacaftor in vivo increases the open channel probability (P_O) of WT CFTR, provided it is not already maximally stimulated.

Precision medicine in united airways disease: A "treatable traits" approach

United airways disease (UAD) is the concept that the upper and lower airways, which are anatomically and immunologically related, form a single organ. According to this concept, upper and lower airway diseases are frequently comorbid because they reflect manifestations of a single underlying disease at different sites of the respiratory tract. Allergic asthma-allergic rhinitis is the archetypal UAD, but emerging data indicate that UAD is a heterogeneous condition and consists of multiple phenotypes (observable clinical characteristics) and endotypes (pathobiologic mechanisms). The UAD paradigm also extends to myriad sinonasal diseases (eg, chronic rhinosinusitis with or without nasal polyps) and lower airway diseases (eg, bronchiectasis, chronic obstructive pulmonary disease). Here, we review currently known phenoendotypes of UAD and propose a "treatable traits" approach for the classification and management of UAD, wherein pathophysiological mechanisms and factors contributing to disease are identified and targeted for treatment. Treatable traits in UAD can be analyzed according to a framework comprising airway inflammation (eosinophilic, neutrophilic), impaired airway mucosal defense (impaired mucociliary clearance, antibody deficiency), and exogenous cofactors (allergic sensitizers, tobacco smoke, microbes). Appreciation of treatable traits is necessary in advancing the effort to deliver precise treatments and achieve better outcomes in patients with UAD.

Cigarette Smoke-Induced Acquired Dysfunction of Cystic Fibrosis Transmembrane Conductance Regulator in the Pathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a disease state characterized by airflow limitation that is not fully reversible. Cigarette smoke and oxidative stress are main etiological risks in COPD. Interestingly, recent studies suggest a considerable overlap between chronic bronchitis (CB) phenotypic COPD and cystic fibrosis (CF), a common fatal hereditary lung disease caused by genetic mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Phenotypically, CF and COPD are associated with an impaired mucociliary clearance and mucus hypersecretion, although they are two distinct entities of unrelated origin. Mechanistically, the cigarette smoke-increased oxidative stress-induced CFTR dysfunction is implicated in COPD. This underscores CFTR in understanding and improving therapies for COPD by altering CFTR function with antioxidant agents and CFTR modulators as a great promising strategy for COPD treatments. Indeed, treatments that restore CFTR function, including mucolytic therapy, antioxidant ROS scavenger, CFTR stimulator (roflumilast), and CFTR potentiator (ivacaftor), have been tested in COPD. This review article is aimed at summarizing the molecular, cellular, and clinical evidence of oxidative stress, particularly the cigarette smoke-increased oxidative stress-impaired CFTR function, as well as signaling pathways of CFTR involved in the pathogenesis of COPD, with a highlight on the therapeutic potential of targeting CFTR for COPD treatment.

Hydrator Therapies for Chronic Bronchitis. Lessons from Cystic Fibrosis

Patients with the chronic bronchitis form of chronic obstructive pulmonary disease and cystic fibrosis share similar clinical features, including mucus obstruction of airways and the development of chronic/recurrent airways infections that often manifest as disease exacerbations. There is growing evidence that these diseases may have parallels in disease pathogenesis as well, including cystic fibrosis transmembrane conductance regulator dysfunction, mucus dehydration, and defective mucociliary clearance. As progress is made in the development of therapies that target the basic defects that lead to cystic fibrosis lung disease, it is possible that similar approaches could also benefit patients with chronic bronchitis. A deeper understanding of how tobacco smoke and other triggers of chronic bronchitis actually lead to disease, and exploration of the concept that therapies that restore cystic fibrosis transmembrane conductance regulator function, mucus hydration, and/or mucociliary clearance may benefit patients with chronic bronchitis, hold the prospect of significant progress in treating this prevalent disease.

Therapeutic Approaches to Acquired Cystic Fibrosis Transmembrane Conductance Regulator Dysfunction in Chronic Bronchitis

Chronic obstructive pulmonary disease is a common cause of morbidity and a rising cause of mortality worldwide. Its rising impact indicates the ongoing unmet need for novel and effective therapies. Previous work has established a pathophysiological link between the chronic bronchitis phenotype of chronic obstructive pulmonary disease and cystic fibrosis as well as phenotypic similarities between these two airways diseases. An extensive body of evidence has established that cigarette smoke and its constituents contribute to acquired dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein in the airways, pointing to a mechanistic link with smoking-related and chronic bronchitis. Recent interest surrounding new drugs that target both mutant and wild-type CFTR channels has paved the way for a new treatment opportunity addressing the mucus defect in chronic bronchitis. We review the clinical and pathologic evidence for modulating CFTR to address acquired CFTR dysfunction and pragmatic issues surrounding clinical trials as well as a discussion of other ion channels that may represent alternative therapeutic targets.

Tezacaftor-Ivacaftor in Residual-Function Heterozygotes with Cystic Fibrosis

BACKGROUND

Cystic fibrosis is an autosomal recessive disease caused by mutations in the CFTR gene that lead to progressive respiratory decline. Some mutant CFTR proteins show residual function and respond to the CFTR potentiator ivacaftor in vitro, whereas ivacaftor alone does not restore activity to Phe508del mutant CFTR.

METHODS

We conducted a randomized, double-blind, placebo-controlled, phase 3, crossover trial to evaluate the efficacy and safety of ivacaftor alone or in combination with tezacaftor, a CFTR corrector, in 248 patients 12 years of age or older who had cystic fibrosis and were heterozygous for the Phe508del mutation and a CFTR mutation associated with residual CFTR function. Patients were randomly assigned to one of six sequences, each involving two 8-week intervention periods separated by an 8-week washout period. They received tezacaftor-ivacaftor, ivacaftor monotherapy, or placebo. The primary end point was the absolute change in the percentage of predicted forced expiratory volume in 1 second (FEV1) from the baseline value to the average of the week 4 and week 8 measurements in each intervention period.

RESULTS

The number of analyzed intervention periods was 162 for tezacaftor-ivacaftor, 157 for ivacaftor alone, and 162 for placebo. The least-squares mean difference versus placebo with respect to the absolute change in the percentage of predicted FEV1 was 6.8 percentage points for tezacaftor-ivacaftor and 4.7 percentage points for ivacaftor alone (P<0.001 for both comparisons). Scores on the respiratory domain of the Cystic Fibrosis Questionnaire-Revised, a quality-of-life measure, also significantly favored the active-treatment groups. The incidence of adverse events was similar across intervention groups; most events were mild or moderate in severity, with no discontinuations of the trial regimen due to adverse events for tezacaftor-ivacaftor and few for ivacaftor alone (1% of patients) and placebo (<1%).

CONCLUSIONS

CFTR modulator therapy with tezacaftor-ivacaftor or ivacaftor alone was efficacious in patients with cystic fibrosis who were heterozygous for the Phe508del deletion and a CFTR residual-function mutation. (Funded by Vertex Pharmaceuticals and others; EXPAND ClinicalTrials.gov number, NCT02392234 .).

The therapeutic potential of CFTR modulators for COPD and other airway diseases

Airways diseases, especially chronic obstructive pulmonary disease (COPD) and asthma, are common causes of morbidity and mortality worldwide. There is an ongoing unmet need for novel and effective therapies. There is an established pathophysiological link and phenotypic similarity between the chronic bronchitis phenotype of COPD and cystic fibrosis (CF). New evidence suggests that CFTR dysfunction may play a role in other common airways diseases such as COPD, non-atopic asthma and non-CF bronchiectasis. Newly approved and investigational drugs that target both mutant and wild-type CFTR channels have provided a new treatment opportunity addressing the mucus defect in pulmonary diseases that share the same pathophysiology with CF.

Roflumilast reverses CFTR-mediated ion transport dysfunction in cigarette smoke-exposed mice

BACKGROUND

Dysfunction in cystic fibrosis transmembrane conductance regulator (CFTR) can be elicited by cigarette smoke and is observed in patients with chronic bronchitis. We have previously demonstrated in human airway epithelial cell monolayers that roflumilast, a clinically approved phosphodiesterase 4 inhibitor that reduces the risk of exacerbations in chronic obstructive pulmonary disease patients with chronic bronchitis and a history of exacerbations, activates CFTR-dependent chloride secretion via a cAMP-mediated pathway, partially restores the detrimental effects of cigarette smoke on CFTR-mediated ion transport, and increases CFTR-dependent gastrointestinal fluid secretion in isolated murine intestine segments. Based on these findings, we hypothesized that roflumilast could improve CFTR-mediated chloride transport and induce secretory diarrhea in mice exhibiting cigarette smoke-induced CFTR dysfunction.

METHODS

A/J mice expressing wild type CFTR (+/+) were exposed to cigarette smoke or air with or without roflumilast and the effect of treatment on CFTR-dependent chloride transport was quantified using nasal potential difference (NPD) measurements in vivo and short-circuit current (Isc) analysis of trachea ex vivo. Stool specimen were collected and the wet/dry ratio measured to assess the effect of roflumilast on secretory diarrhea.

RESULTS

Acute roflumilast treatment increased CFTR-dependent chloride transport in both smoke- and air-exposed mice (smoke, -2.0 ± 0.4 mV, 131.3 ± 29.3 μA/cm², P < 0.01 and air, 3.9 ± 0.8 mV, 147.7 ± 38.0 μA/cm², P < 0.01 vs. vehicle -0.3 ± 0.7 mV, 10.4 ± 7.0 μA/cm²). Oral administration of roflumilast over five weeks completely reversed the deleterious effects of cigarette smoke on CFTR function in smoke-exposed animals, in which CFTR-dependent chloride transport was 64% that of air controls (roflumilast, -15.22 ± 2.7 mV vs. air, -14.45 ± 1.4 mV, P < 0.05). Smoke exposure increased the wet/dry ratio of stool specimen to a level beyond which roflumilast had little additional effect.

CONCLUSIONS

Roflumilast effectively rescues CFTR-mediated chloride transport in vivo, further implicating CFTR activation as a mechanism through which roflumilast benefits patients with bronchitis.

Dendrimer-based selective autophagy-induction rescues ΔF508-CFTR and inhibits Pseudomonas aeruginosa infection in cystic fibrosis

Background

Cystic Fibrosis (CF) is a genetic disorder caused by mutation(s) in the CF-transmembrane conductance regulator (Cftr) gene. The most common mutation, ΔF508, leads to accumulation of defective-CFTR protein in aggresome-bodies. Additionally, Pseudomonas aeruginosa (Pa), a common CF pathogen, exacerbates obstructive CF lung pathology. In the present study, we aimed to develop and test a novel strategy to improve the bioavailability and potentially achieve targeted drug delivery of cysteamine, a potent autophagy-inducing drug with anti-bacterial properties, by developing a dendrimer (PAMAM-DEN)-based cysteamine analogue.

Results

We first evaluated the effect of dendrimer-based cysteamine analogue (PAMAM-DEN^CYS) on the intrinsic autophagy response in IB3-1 cells and observed a significant reduction in Ub-RFP and LC3-GFP co-localization (aggresome-bodies) by PAMAM-DEN^CYS treatment as compared to plain dendrimer (PAMAM-DEN) control. Next, we observed that PAMAM-DEN^CYS treatment shows a modest rescue of ΔF508-CFTR as the C-form. Moreover, immunofluorescence microscopy of HEK-293 cells transfected with ΔF508-CFTR-GFP showed that PAMAM-DEN^CYS is able to rescue the misfolded-ΔF508-CFTR from aggresome-bodies by inducing its trafficking to the plasma membrane. We further verified these results by flow cytometry and observed significant (p<0.05; PAMAM-DEN vs. PAMAM-DEN^CYS) rescue of membrane-ΔF508-CFTR with PAMAM-DEN^CYS treatment using non-permeabilized IB3-1 cells immunostained for CFTR. Finally, we assessed the autophagy-mediated bacterial clearance potential of PAMAM-DEN^CYS by treating IB3-1 cells infected with PA01-GFP, and observed a significant (p<0.01; PAMAM-DEN vs. PAMAM-DEN^CYS) decrease in intracellular bacterial counts by immunofluorescence microscopy and flow cytometry. Also, PAMAM-DEN^CYS treatment significantly inhibits the growth of PA01-GFP bacteria and demonstrates potent mucolytic properties.

Conclusions

We demonstrate here the efficacy of dendrimer-based autophagy-induction in preventing sequestration of ΔF508-CFTR to aggresome-bodies while promoting its trafficking to the plasma membrane. Moreover, PAMAM-DEN^CYS decreases Pa infection and growth, while showing mucolytic properties, suggesting its potential in rescuing Pa-induced ΔF508-CF lung disease that warrants further investigation in CF murine model.

The Cystic Fibrosis Transmembrane Conductance Regulator Potentiator Ivacaftor Augments Mucociliary Clearance Abrogating Cystic Fibrosis Transmembrane Conductance Regulator Inhibition by Cigarette Smoke

Acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction may contribute to chronic obstructive pulmonary disease pathogenesis and is a potential therapeutic target. We sought to determine the acute effects of cigarette smoke on ion transport and the mucociliary transport apparatus, their mechanistic basis, and whether deleterious effects could be reversed with the CFTR potentiator ivacaftor (VX-770). Primary human bronchial epithelial (HBE) cells and human bronchi were exposed to cigarette smoke extract (CSE) and/or ivacaftor. CFTR function and expression were measured in Ussing chambers and by surface biotinylation. CSE-derived acrolein modifications on CFTR were determined by mass spectroscopic analysis of purified protein, and the functional microanatomy of the airway epithelia was measured by 1-μm resolution optical coherence tomography. CSE reduced CFTR-dependent current in HBE cells (P < 0.05) and human bronchi (P < 0.05) within minutes of exposure. The mechanism involved CSE-induced reduction of CFTR gating, decreasing CFTR open-channel probability by approximately 75% immediately after exposure (P < 0.05), whereas surface CFTR expression was partially reduced with chronic exposure, but was stable acutely. CSE treatment of purified CFTR resulted in acrolein modifications on lysine and cysteine residues that likely disrupt CFTR gating. In primary HBE cells, CSE reduced airway surface liquid depth (P < 0.05) and ciliary beat frequency (P < 0.05) within 60 minutes that was restored by coadministration with ivacaftor (P < 0.005). Cigarette smoking transmits acute reductions in CFTR activity, adversely affecting the airway surface. These effects are reversible by a CFTR potentiator in vitro, representing a potential therapeutic strategy in patients with chronic obstructive pulmonary disease with chronic bronchitis.

Cystic fibrosis

Cystic fibrosis is a common life-limiting autosomal recessive genetic disorder, with highest prevalence in Europe, North America, and Australia. The disease is caused by mutation of a gene that encodes a chloride-conducting transmembrane channel called the cystic fibrosis transmembrane conductance regulator (CFTR), which regulates anion transport and mucociliary clearance in the airways. Functional failure of CFTR results in mucus retention and chronic infection and subsequently in local airway inflammation that is harmful to the lungs. CFTR dysfunction mainly affects epithelial cells, although there is evidence of a role in immune cells. Cystic fibrosis affects several body systems, and morbidity and mortality is mostly caused by bronchiectasis, small airways obstruction, and progressive respiratory impairment. Important comorbidities caused by epithelial cell dysfunction occur in the pancreas (malabsorption), liver (biliary cirrhosis), sweat glands (heat shock), and vas deferens (infertility). The development and delivery of drugs that improve the clearance of mucus from the lungs and treat the consequent infection, in combination with correction of pancreatic insufficiency and undernutrition by multidisciplinary teams, have resulted in remarkable improvements in quality of life and clinical outcomes in patients with cystic fibrosis, with median life expectancy now older than 40 years. Innovative and transformational therapies that target the basic defect in cystic fibrosis have recently been developed and are effective in improving lung function and reducing pulmonary exacerbations. Further small molecule and gene-based therapies are being developed to restore CFTR function; these therapies promise to be disease modifying and to improve the lives of people with cystic fibrosis.

Nano-based rescue of dysfunctional autophagy in chronic obstructive lung diseases

INTRODUCTION

ΔF508-CFTR (cystic fibrosis transmembrane conductance regulator) is a common CF-mutation that is known to induce oxidative-inflammatory stress through activation of reactive oxygen species (ROS), which induces autophagy-impairment resulting in accumulation of CFTR in aggresome-bodies. Cysteamine, the reduced form of cystamine, is a FDA-approved drug that has anti-oxidant, anti-bacterial, and mucolytic properties. This drug has been shown in a recent clinical trial to decrease lung inflammation and improve lung function in CF patients by potentially restoring autophagy and allowing CFTR to be trafficked to the cell membrane. Areas covered: The delivery of cysteamine to airway epithelia of chronic subjects prerequisite the need for a delivery system to allow rescue of dysfunctional autophagy. Expert opinion: We anticipate based on our ongoing studies that PLGA-PEG- or Dendrimer-mediated cysteamine delivery could allow sustained airway delivery over standard cysteamine tablets or delay release capsules that are currently used for systemic treatment. In addition, proposed nano-based autophagy induction strategy can also allow rescue of cigarette smoke (CS) induced acquired-CFTR dysfunction seen in chronic obstructive pulmonary disease (COPD)-emphysema subjects. The CS induced acquired-CFTR dysfunction involves CFTR-accumulation in aggresome-bodies that can be rescued by an autophagy-inducing antioxidant drug, cysteamine. Moreover, chronic CS-exposure generates ROS that induces overall protein-misfolding and aggregation of ubiquitinated-proteins as aggresome-bodies via autophagy-impairment that can be also be resolved by treatment with autophagy-inducing antioxidant drug, cysteamine.

Acquired Cystic Fibrosis Transmembrane Conductance Regulator Dysfunction in Chronic Bronchitis and Other Diseases of Mucus Clearance

Chronic obstructive pulmonary disease (COPD) is a major public health problem. No therapies alter the natural history of the disease. Chronic bronchitis is perhaps the most clinically troublesome phenotype. Emerging data strongly suggest that cigarette smoke and its components can lead to acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. Findings in vitro, in animal models, and in smokers with and without COPD also show acquired CFTR dysfunction, which is associated with chronic bronchitis. This abnormality is also present in extrapulmonary organs, suggesting that CFTR dysfunction may contribute to smoking-related systemic diseases.

Immunohistochemical Detection of Markers for Translational Studies of Lung Disease in Pigs and Humans

Genetically engineered pigs are increasingly recognized as valuable models for the study of human disease. Immunohistochemical study of cellular markers of disease is an important tool for the investigation of these novel models so as to evaluate genotype and treatment differences. Even so, there remains a lack of validated markers for pig tissues that can serve as a translational link to human disease in organs such as the lung. Herein, we evaluate markers of cellular inflammation (cluster of differentiation [CD]3, CD79a, B cell lymphoma [BCL] 6, ionized calcium-binding adapter molecule [IBA]1, and myeloperoxidase) and those that may be involved with tissue remodeling (alpha-smooth muscle actin, beta-tubulin-III, lactoferrin, mucin [MUC]5AC, MUC5B, and cystic fibrosis transmembrane conductance regulator [CFTR]) for study of lung tissues. We compare the utility of these markers between pig and human lungs to validate translational relevance of each marker. Our results suggest these markers can be a useful addition in the pathological evaluation of porcine models of human disease.

Heme oxygenase-1-mediated autophagy protects against pulmonary endothelial cell death and development of emphysema in cadmium-treated mice

Pulmonary exposure to cadmium, a major component of cigarette smoke, has a dramatic impact on lung function and the development of emphysema. Cigarette smoke exposure induces heme oxygenase-1 (HO-1), a cytoprotective enzyme. In this study, we employed a truncated mouse model of emphysema by intratracheal instillation of cadmium (CdCl2) solution (0.025% per 1 mg/kg body wt) in HO-1(+/+), HO-1(-/-), and overexpressing humanized HO-1 bacterial artificial chromosome (hHO-1BAC) mice. We evaluated the role of HO-1 in cadmium-induced emphysema in mice by analyzing histopathology, micro-computed tomography scans, and lung function tests. CdCl2-exposed HO-1(-/-) mice exhibited more severe emphysema compared with HO-1(+/+) or hHO-1BAC mice. Loss of pulmonary endothelial cells (PECs) from the alveolar capillary membrane is recognized to be a target in emphysema. PECs from HO-1(+/+), HO-1(-/-), and hHO-1BAC were employed to define the underlying molecular mechanism for the protection from emphysema by HO-1. Electron microscopy, expression of autophagic markers (microtubule-associated protein 1B-light chain 3 II, autophagy protein 5, and Beclin1) and apoptotic marker (cleaved caspase 3) suggested induction of autophagy and apoptosis in PECs after CdCl2 treatment. CdCl2-treated HO-1(-/-) PECs exhibited downregulation of autophagic markers and significantly increased cleaved caspase 3 expression and activity (∼4-fold higher). Moreover, hHO-1BAC PECs demonstrated upregulated autophagy and absence of cleaved caspase 3 expression or activity. Pretreatment of HO-1(+/+) PECs with rapamycin induced autophagy and resulted in reduced cell death upon cadmium treatment. Induction of autophagy following CdCl2 treatment was found to be protective from apoptotic cell death. HO-1 induced protective autophagy in PECs and mitigated cadmium-induced emphysema.

Novel personalized therapies for cystic fibrosis: treating the basic defect in all patients

Cystic fibrosis (CF) is the most common genetic life-shortening condition in Caucasians. Despite being a multi-organ disease, CF is classically diagnosed by symptoms of acute/chronic respiratory disease, with persistent pulmonary infections and mucus plugging of the airways and failure to thrive. These multiple symptoms originate from dysfunction of the CF transmembrane conductance regulator (CFTR) protein, a channel that mediates anion transport across epithelia. Indeed, establishment of a definite CF diagnosis requires proof of CFTR dysfunction, commonly through the so-called sweat Cl(-) test. Many drug therapies, including mucolytics and antibiotics, aim to alleviate the symptoms of CF lung disease. However, new therapies to modulate defective CFTR, the basic defect underlying CF, have started to reach the clinic, and several others are in development or in clinical trials. The novelty of these therapies is that, besides targeting the basic defect underlying CF, they are mutation specific. Indeed, even this monogenic disease is influenced by a large number of different genes and biological pathways as well as by environmental factors that are difficult to assess. Accordingly, every person with CF is unique and so functional assessment of patients' tissues ex vivo is key for diagnosing and predicting the severity of this disease. Of note, such assessment will also be crucial to assess drug responses, in order to effectively treat all CF patients. It is not because it is a monogenic disorder that personalized treatment for CF is much easier than for complex disorders.