Clinical mechanism of the cystic fibrosis transmembrane conductance regulator potentiator ivacaftor in G551D-mediated cystic fibrosis

Morphological and Functional Assessment of Oesophageal Mucosa Integrity in Children With Cystic Fibrosis

OBJECTIVES

The aim of the study was to investigate morphological and functional characteristics of oesophageal epithelial barrier in children with cystic fibrosis (CF) with or without gastro-oesophageal reflux disease (GORD) in comparison to healthy controls.

METHODS

Oesophagogastroduodenoscopy with oesophageal biopsies and combined oesophageal multichannel intraluminal impedance-pH monitoring was performed in 17 children with CF (CFtot) with (CFgord) or without GORD (CFnorm). Histological combined severity score was calculated and widths of spaces between epithelial cells were measured. Basal impedance value was used to assess functional integrity of epithelial barrier. Results of each investigation were compared with a group of children without oesophageal disease.

RESULTS

CFtot, but also CFnorm, had more severe pathohistological changes included in the compound severity score than controls (0.75 ± 0.32 and 0.75 ± 0.20 vs 0.27 ± 0.25; P < 0.001 and P = 0.001, respectively). They also had more dilated intercellular spaces (2.6 μm ± 0.6 and 2.7 μm ± 0.5 vs 1.9 μm ± 0.2; P = 0.001 and P < 0.001, respectively). Baseline impedance values between proximal and distal pairs of electrodes were significantly lower in CFtot (2876 Ω ± 484, 2590 Ω ± 1013) and also in CFnorm (2922 Ω ± 363, 2844 Ω ± 457) than in controls (3703 Ω ± 859, 3753 Ω ± 1070) (P = 0.012 and P = 0.002; and P = 0.027 and P = 0.005, respectively). The treatment of CFgord with proton pump inhibitor increased, but did not normalise the baseline impedance values (2860 Ω ± 560 to 3355 Ω ± 750 and 2178 Ω ± 1564 to 3057 Ω ± 594).

CONCLUSIONS

Children with CF had morphological and functional changes of oesophageal mucosal integrity even in the absence of GORD.

Forecasting US ivacaftor outcomes and cost in cystic fibrosis patients with the G551D mutation

Ivacaftor, a breakthrough treatment for cystic fibrosis (CF) patients with the G551D genetic mutation, lacks long-term clinical and cost projections. This study forecasted outcomes and cost by comparing ivacaftor plus usual care versus usual care alone.

A lifetime Markov model was conducted from a US payer perspective. The model consisted of five health states: 1) forced expiratory volume in 1 s (FEV1) % pred ≥70%, 2) 40%≤ FEV1 % pred <70%, 3) FEV1 % pred <40%, 4) lung transplantation and 5) death. All inputs were extracted from published literature. Budget impact was also estimated. We estimated ivacaftor's improvement in outcomes compared with a non-CF referent population.

Ivacaftor was associated with 18.25 (95% credible interval (CrI) 13.71–22.20) additional life-years and 15.03 (95% CrI 11.13–18.73) additional quality-adjusted life-years (QALYs). Ivacaftor was associated with improvements in survival and QALYs equivalent to 68% and 56%, respectively, for the survival and QALY gaps between CF usual care and their non-CF peers. The incremental lifetime cost was $3 374 584. The budget impact was $0.087 per member per month.

Ivacaftor increased life-years and QALYs in CF patients with the G551D mutation, and moved morbidity and mortality closer to that of their non-CF peers. Ivacaftor costs much more than usual care, but comes at a relatively limited budget impact.

Acute administration of ivacaftor to people with cystic fibrosis and a G551D-CFTR mutation reveals smooth muscle abnormalities

BACKGROUND

Airflow obstruction is common in cystic fibrosis (CF), yet the underlying pathogenesis remains incompletely understood. People with CF often exhibit airway hyperresponsiveness, CF transmembrane conductance regulator (CFTR) is present in airway smooth muscle (ASM), and ASM from newborn CF pigs has increased contractile tone, suggesting that loss of CFTR causes a primary defect in ASM function. We hypothesized that restoring CFTR activity would decrease smooth muscle tone in people with CF.

METHODS

To increase or potentiate CFTR function, we administered ivacaftor to 12 adults with CF with the G551D-CFTR mutation; ivacaftor stimulates G551D-CFTR function. We studied people before and immediately after initiation of ivacaftor (48 hours) to minimize secondary consequences of CFTR restoration. We tested smooth muscle function by investigating spirometry, airway distensibility, and vascular tone.

RESULTS

Ivacaftor rapidly restored CFTR function, indicated by reduced sweat chloride concentration. Airflow obstruction and air trapping also improved. Airway distensibility increased in airways less than 4.5 mm but not in larger-sized airways. To assess smooth muscle function in a tissue outside the lung, we measured vascular pulse wave velocity (PWV) and augmentation index, which both decreased following CFTR potentiation. Finally, change in distensibility of <4.5-mm airways correlated with changes in PWV.

CONCLUSIONS

Acute CFTR potentiation provided a unique opportunity to investigate CFTR-dependent mechanisms of CF pathogenesis. The rapid effects of ivacaftor on airway distensibility and vascular tone suggest that CFTR dysfunction may directly cause increased smooth muscle tone in people with CF and that ivacaftor may relax smooth muscle.

FUNDING

This work was funded in part from an unrestricted grant from the Vertex Investigator-Initiated Studies Program.

New and emerging targeted therapies for cystic fibrosis

Cystic fibrosis (CF) is a monogenic autosomal recessive disorder that affects about 70,000 people worldwide. The clinical manifestations of the disease are caused by defects in the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The discovery of the CFTR gene in 1989 has led to a sophisticated understanding of how thousands of mutations in the CFTR gene affect the structure and function of the CFTR protein. Much progress has been made over the past decade with the development of orally bioavailable small molecule drugs that target defective CFTR proteins caused by specific mutations. Furthermore, there is considerable optimism about the prospect of gene replacement or editing therapies to correct all mutations in cystic fibrosis. The recent approvals of ivacaftor and lumacaftor represent the genesis of a new era of precision medicine in the treatment of this condition. These drugs are having a positive impact on the lives of people with cystic fibrosis and are potentially disease modifying. This review provides an update on advances in our understanding of the structure and function of the CFTR, with a focus on state of the art targeted drugs that are in development.

Pseudomonas infection and mucociliary and absorptive clearance in the cystic fibrosis lung

Airway surface liquid hyperabsorption and mucus accumulation are key elements of cystic fibrosis lung disease that can be assessed in vivo using functional imaging methods. In this study we evaluated experimental factors affecting measurements of mucociliary clearance (MCC) and small-molecule absorption (ABS) and patient factors associated with abnormal absorption and mucus clearance.Our imaging technique utilises two radiopharmaceutical probes delivered by inhalation. Measurement repeatability was assessed in 10 adult cystic fibrosis subjects. Experimental factors were assessed in 29 adult and paediatric cystic fibrosis subjects (51 scans). Patient factors were assessed in a subgroup with optimal aerosol deposition (37 scans; 24 subjects). Paediatric subjects (n=9) underwent initial and 2-year follow-up scans. Control subjects from a previously reported study are included for comparison.High rates of central aerosol deposition influenced measurements of ABS and, to a lesser extent, MCC. Depressed MCC in cystic fibrosis was only detectable in subjects with previous Pseudomonas aeruginosa infection. Cystic fibrosis subjects without P. aeruginosa had similar MCC to control subjects. Cystic fibrosis subjects had consistently higher ABS rates.We conclude that the primary experimental factor affecting MCC/ABS measurements is central deposition percentage. Depressed MCC in cystic fibrosis is associated with P. aeruginosa infection. ABS is consistently increased in cystic fibrosis.

Combination therapy with cystic fibrosis transmembrane conductance regulator modulators augment the airway functional microanatomy

Recently approved therapies that modulate CFTR function have shown significant clinical benefit, but recent investigations regarding their molecular mechanism when used in combination have not been consistent with clinical results. We employed micro-optical coherence tomography as a novel means to assess the mechanism of action of CFTR modulators, focusing on the effects on mucociliary clearance. Primary human airway monolayers from patients with a G551D mutation responded to ivacaftor treatment with increased ion transport, airway surface liquid depth, ciliary beat frequency, and mucociliary transport rate, in addition to decreased effective viscosity of the mucus layer, a unique mechanism established by our findings. These endpoints are consistent with the benefit observed in G551D patients treated with ivacaftor, and identify a novel mechanism involving mucus viscosity. In monolayers derived from F508del patients, the situation is more complicated, compounded by disparate effects on CFTR expression and function. However, by combining ion transport measurements with functional imaging, we establish a crucial link between in vitro data and clinical benefit, a finding not explained by ion transport studies alone. We establish that F508del cells exhibit increased mucociliary transport and decreased mucus effective viscosity, but only when ivacaftor is added to the regimen. We further show that improvement in the functional microanatomy in vitro corresponds with lung function benefit observed in the clinical trials, whereas ion transport in vitro corresponds to changes in sweat chloride. Functional imaging reveals insights into clinical efficacy and CFTR biology that significantly impact our understanding of novel therapies.

Current and Emerging Therapies for the Treatment of Cystic Fibrosis or Mitigation of Its Symptoms

Clinical presentation of the chronic, heritable condition cystic fibrosis (CF) is complex, with a diverse range of symptoms often affecting multiple organs with varying severity. The primary source of morbidity and mortality is due to progressive destruction of the airways attributable to chronic inflammation arising from microbial colonisation. Antimicrobial therapy combined with practises to remove obstructive mucopurulent deposits form the cornerstone of current therapy. However, new treatment options are emerging which offer, for the first time, the opportunity to effect remission from the underlying cause of CF. Here, we discuss these therapies, their mechanisms of action, and their successes and failures in order to illustrate the shift in the nature of how CF will likely be managed into the future.

Innate and Adaptive Immunity in Cystic Fibrosis

Cystic fibrosis (CF) lung disease is characterized by persistent and unresolved inflammation, with elevated proinflammatory and decreased anti-inflammatory cytokines, and greater numbers of immune cells. Hyperinflammation is recognized as a leading cause of lung tissue destruction in CF. Hyper-inflammation is not solely observed in the lungs of CF patients, since it may contribute to destruction of exocrine pancreas and, likely, to defects in gastrointestinal tract tissue integrity. Paradoxically, despite the robust inflammatory response, and elevated number of immune cells (such as neutrophils and macrophages), CF lungs fail to clear bacteria and are more susceptible to infections. Here, we have summarized the current understanding of immune dysregulation in CF, which may drive hyperinflammation and impaired host defense.

Cystic fibrosis from the gastroenterologist's perspective

Cystic fibrosis is a life-limiting, recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Increased survival outcomes and the multisystem nature of the disease, including the involvement of hepatobiliary and gastrointestinal tracts, now require the need for more extensive knowledge and expertise in cystic fibrosis among gastroenterologists. Manifestations are either a direct consequence of the primary defect in cystic fibrosis or a secondary complication of the disease or therapy. Adult patients with cystic fibrosis also have an increased risk of malignancy in the gastrointestinal and pancreatico-biliary tracts compared with the general population. Novel treatments that target the basic defects in the CFTR protein have emerged, but to date not much is known about their effects on the gastrointestinal and hepatobiliary systems. The introduction of such therapies has provided new opportunities for the application of intestinal endpoints in clinical trials and the understanding of underlying disease mechanisms that affect the gut in cystic fibrosis.

Bowel ultrasound imaging in patients with cystic fibrosis: Relationship with clinical symptoms and CFTR genotype

BACKGROUND

Ultrasound imaging is used to assess bowel abnormalities in gastrointestinal diseases. We aimed to assess the rate of predefined bowel ultrasound signs and their relationship with gastrointestinal symptoms and the cystic fibrosis transmembrane conductance regulator (CFTR) genotype in cystic fibrosis patients in regular follow-up.

METHODS

Prospective study of 70 consecutive patients with cystic fibrosis and 45 controls who underwent abdominal ultrasound; pertinent findings were related to gastrointestinal symptoms and, in cystic fibrosis patients, to pancreatic status, malabsorption degree, lipase intake, CFTR genotype (classified as severe or mild against functional class of CFTR mutations).

RESULTS

96% patients showed at least one abnormal bowel ultrasound sign. Most frequent signs were lymph node enlargement (64%), bowel loop dilatation (55%), thick corpuscular intraluminal content (49%), bowel wall hypervascularization (26%), thickened bowel wall (22%) and intussusception (17%). Patients with recurrent abdominal pain showed more bowel wall hypervascularization than patients without recurrent pain (47% vs. 19%, respectively; p = 0.02) and intussusception (58% vs. 17%, respectively; p < 0.01). Genotype was not associated to specific bowel ultrasound signs. Patients with bowel loop intussusception showed greater lipase intake than those without intussusception (8.118 ± 2.083 vs. 5.994 ± 4.187, respectively; p < 0.01).

CONCLUSION

Cystic fibrosis patients present a higher rate of bowel ultrasound abnormalities than controls. Bowel ultrasound abnormalities are associated with abdominal symptoms.

Advancing clinical development pathways for new CFTR modulators in cystic fibrosis

Cystic fibrosis (CF) is a life-shortening genetic disease affecting approximately 70,000 individuals worldwide. Until recently, drug development efforts have emphasised therapies treating downstream signs and symptoms resulting from the underlying CF biological defect: reduced function of the CF transmembrane conductance regulator (CFTR) protein. The current CF drug development landscape has expanded to include therapies that enhance CFTR function by either restoring wild-type CFTR protein expression or increasing (modulating) the function of mutant CFTR proteins in cells. To date, two systemic small-molecule CFTR modulators have been evaluated in pivotal clinical trials in individuals with CF and specific mutant CFTR genotypes that have led to regulatory review and/or approval. Advances in the discovery of CFTR modulators as a promising new class of therapies have been impressive, yet work remains to develop highly effective, disease-modifying modulators for individuals of all CF genotypes. The objectives of this review are to outline the challenges and opportunities in drug development created by systemic genotype-specific CFTR modulators, highlight the advantages of sweat chloride as an established biomarker of CFTR activity to streamline early-phase development and summarise options for later phase clinical trial designs that respond to the adoption of approved genotype-specific modulators into standard of care. An optimal development framework will be needed to move the most promising therapies efficiently through the drug development pipeline and ultimately deliver efficacious and safe therapies to all individuals with CF.

Country to country variation: what can be learnt from national cystic fibrosis registries

PURPOSE OF REVIEW

This review will address the evolving science involving international comparisons of populations of persons living with cystic fibrosis. Understanding the current clinical outcomes in cystic fibrosis is critical prior to assessing such comparisons. Countries that differ in clinical approaches provide natural experiments to assess those approaches.

RECENT FINDINGS

Recent studies have highlighted that the population of persons with cystic fibrosis is changing; estimates predict a continued growth of cystic fibrosis populations with substantial increases in persons with cystic fibrosis who are adults. Additional work highlighted differences in subpopulations (i.e. children); US cystic fibrosis children appear to have better lung function, but similar nutritional status, compared to UK cystic fibrosis children. These differences were associated with differences in intensity of care, with a higher proportion of US children receiving more cystic fibrosis-specific therapies. Additional research raises important questions regarding potential sampling bias in different patient registries and differing rates of unconfirmed cases of cystic fibrosis. These and other limitations are highlighted.

SUMMARY

Differences in both demographics and clinical outcomes in cystic fibrosis between nations can be informative, but, like many types of observational research, are at risk of unrecognized bias. Despite this limitation, these comparisons can lead to substantive improvements in care in cystic fibrosis.

[New therapies for cystic fibrosis targeting the CFTR gene or the CFTR protein]

BACKGROUND

The treatment of cystic fibrosis has been symptom-based for a number of years. New therapies that aim to improve CFTR protein function are now emerging.

CURRENT SCIENTIFIC KNOWLEDGE

The results of gene therapy has been modest but a recent clinical trial shows a positive effect on FEV1. Recent research has focused primarily on CFTR protein function. Significant respiratory improvement (an average 10% FEV1 increase and a decrease in the frequency of exacerbations) has been achieved with ivacaftor, a CFTR potentiator, in patients with gating mutations, resulting in its marketing authorization (in 2012 for the G551D mutation and in 2015 for rarer mutations). In phe508del homozygous patients, the combination of ivacaftor with a CFTR corrector (lumacaftor) has also led to respiratory improvement, albeit less impressive. The effectiveness of ataluren in patients with nonsense mutations is being evaluated.

OUTLOOK

New CFTR correctors and potentiators are being developed. CFTR protein therapy could change the course of the disease but cost/effectiveness issues should not be overlooked.

CONCLUSION

Ivacaftor can be prescribed in CF patients with a class 3 mutation from the age of 6 years. The Orkambi^® will soon be available for homozygous phe508del patients from the age of 12 years.

Nutritional Status Improved in Cystic Fibrosis Patients with the G551D Mutation After Treatment with Ivacaftor

BACKGROUND

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gating mutation G551D prevents sufficient ion transport due to reduced channel-open probability. Ivacaftor, an oral CFTR potentiator, increases the channel-open probability.

AIM

To further analyze improvements in weight and body mass index (BMI) in two studies of ivacaftor in patients aged ≥6 years with CF and the G551D mutation.

METHODS

Patients were randomized 1:1 to ivacaftor 150 mg or placebo every 12 h for 48 weeks. Primary end point (lung function) was reported previously. Other outcomes included weight and height measurements and CF Questionnaire-Revised (CFQ-R).

RESULTS

Studies included 213 patients (aged ≤ 20 years, n = 105; aged > 20 years, n = 108). In patients ≤20 years, adjusted mean change from baseline to week 48 in body weight was 4.9 versus 2.2 kg (ivacaftor vs. placebo, p = 0.0008). At week 48, change from baseline in mean weight-for-age z-score was 0.29 versus -0.06 (p < 0.0001); change in mean BMI-for-age z-score was 0.26 versus -0.13 (p < 0.0001). In patients >20 years, adjusted mean change from baseline to week 48 in body weight was 2.7 versus -0.2 kg (p = 0.0003). Mean BMI change at week 48 was 0.9 versus -0.1 kg/m(2) (p = 0.0003). There was no linear correlation evident between changes in body weight and improvements in lung function or sweat chloride. Significant CFQ-R improvements were seen in perception of eating, body image, and sense of ability to gain weight.

CONCLUSIONS

Nutritional status improved following treatment with ivacaftor for 48 weeks.

Searching for a cure for cystic fibrosis. A 25-year quest in a nutshell

After 25 years of intensive search, there is not yet a cure for cystic fibrosis (CF). However, the quest has led to major breakthroughs in understanding the basic disease defect and defining strategies to correct it. The first cystic fibrosis transmembrane conductance regulator (CFTR) modulators have been introduced in clinic. Some show an impressive clinical benefit, like the potentiator ivacaftor for the 4% of patients with a class III defect. Others offer at present only a limited benefit, like the combination corrector lumacaftor plus potentiator ivacaftor for subjects homozygous for F508del. These findings prove that the basic defect in CF can be modified and hold the promise that one day CF will no longer be a life-shortening disease.

CONCLUSION

This review updates the clinician on recent achievements as well as on the CF research pipeline.

WHAT IS KNOWN

Cystic fibrosis (CF) is a common and life-shortening disease that currently cannot be cured. However, for each of the six CF mutation classes, disease-modifying drugs are under way.

WHAT IS NEW

This review is a concise update for the clinician on new drugs that reached the CF clinical pipeline. The research strategies in CF have become a paradigm for clinical trials in other inherited diseases.

CFTR Modulator Therapies for Cystic Fibrosis

The cloning of cystic fibrosis transmembrane conductance regulator (CFTR) set into motion a cascade of discoveries that have helped to reveal the underlying pathophysiologic basis of cystic fibrosis (CF). This discovery and the knowledge that followed have also provided the opportunity to target this basic defect, with the hope of reversing or preventing the serious clinical consequences that result from absent CFTR function. With the recent approval of 2 therapies that directly modulate CFTR function in more than half of the CF population, we are now at the beginning of a pathway to providing increasingly effective therapies that have the potential to provide a fundamental change in the outcome of most patients with CF.

2014 year in review: Cystic fibrosis

In this article, we highlight cystic fibrosis (CF) research published in Pediatric Pulmonology during 2014, as well as related articles published in other journals.

AIT (allergen immunotherapy): a model for the "precision medicine"

The interpretation of medical approaches, especially therapy, evolved rapidly in the last century. Starting from the simple description of symptoms, we moved to the pathophysiological descriptions, to the evidence-based medicine, until the so-called "precision medicine". This latter can be defined as a structural model aimed at customizing healthcare, with medical decisions/products tailored on an individual patient at a highly detailed level. In this sense, allergen immunotherapy represents an optimal model of "precision medicine", since we know and describe symptoms, function, aetiological agents at molecular level, and we have the possibility to intervene on the natural history of the disease. If considered under the point of view of pharmaco-economy, that is prescribing the optimal treatment to the right patient, allergen immunotherapy represents an almost-ideal model of precision medicine.

Inflammation and its genesis in cystic fibrosis

The host inflammatory response in cystic fibrosis (CF) lung disease has long been recognized as a central pathological feature and an important therapeutic target. Indeed, many believe that bronchiectasis results largely from the oxidative and proteolytic damage comprised within an exuberant airway inflammatory response that is dominated by neutrophils. In this review, we address the longstanding argument of whether or not the inflammatory response is directly attributable to impairment of the cystic fibrosis transmembrane conductance regulator or only secondary to airway obstruction and chronic bacterial infection and challenge the importance of this distinction in the context of therapy. We also review the centrality of neutrophils in CF lung pathophysiology and highlight more recent data that suggest the importance of other cell types and signaling beyond NF-κB activation. We discuss how protease and redox imbalance are critical factors in CF airway inflammation and end by reviewing some of the more promising therapeutic approaches now under development.

Cystic Fibrosis Papers of the Year, 2013-2014

Studies published in the last year in the field of cystic fibrosis have provided more data on the safety and efficacy of a number of therapies, including mutation-specific drugs. There have also been a number of publications on monitoring of early lung disease including the use of lung clearance index and magnetic resonance scanning. Evidence suggests early lung changes may remain relatively static over the first year of life. There are important outcome differences across national patient registries and there is also the increasing recognition of psychological illnesses and possible drug interactions as treatment becomes more complicated and survival improves.

CFTR, bicarbonate, and the pathophysiology of cystic fibrosis

The gene that encodes for the cystic fibrosis transmembrane regulator protein (CFTR) was identified in 1989, yet major pathophysiologic questions remain unanswered. There is emerging evidence that CFTR is a bicarbonate channel, a driver of chloride-bicarbonate exchange and through its action on local pH, a regulator of other ion channels and of proteins that function optimally in a neutral environment. In both the respiratory and gastrointestinal (GI) tracts, bicarbonate drives ionic content and fluid on epithelial surfaces, allows mucins to unfold and become slippery, and contributes to innate immunity. In the GI tract bicarbonate neutralizes gastric acid to support digestion and absorption. When CFTR is dysfunctional, lack of bicarbonate secretion disrupts these normal processes and thus leads directly to the clinical symptoms and signs of CF. This article synthesizes evidence from cell, animal, and human investigations that support these concepts. Bicarbonate secretion does not seem to be the same in all tissues and varies with physiologic demand. Thus, tissue type and whether conditions are baseline or stimulated needs to be taken into account when evaluating the evidence concerning the role of bicarbonate in the pathophysiology of CF as a regulator of local pH. Basic and applied research that focuses on the role of CFTR-mediated bicarbonate secretion helps explain many of the diverse clinical manifestations that are CF.

Highlights of the 28(th) North American Cystic Fibrosis Conference 2014

This is a selection of papers presented at the 28(th) North American Cystic Fibrosis Conference held in Atlanta in October 2014. The papers discussed are thought to be of particular interest to CF caregivers in the UK. Topics discussed include recent progress in the modification of the cystic fibrosis transmembrane regulator (CFTR), the potential of OligoG, a novel inhaled alginate mucolytic, and the changing approach to cystic fibrosis-related diabetes screening.

Breakthrough therapies: Cystic fibrosis (CF) potentiators and correctors

Cystic Fibrosis is caused by mutations in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene resulting in abnormal protein function. Recent advances of targeted molecular therapies and high throughput screening have resulted in multiple drug therapies that target many important mutations in the CFTR protein. In this review, we provide the latest results and current progress of CFTR modulators for the treatment of cystic fibrosis, focusing on potentiators of CFTR channel gating and Phe508del processing correctors for the Phe508del CFTR mutation. Special emphasis is placed on the molecular basis underlying these new therapies and emerging results from the latest clinical trials. The future directions for augmenting the rescue of Phe508del with CFTR modulators are also emphasized.

Lumacaftor and ivacaftor in the management of patients with cystic fibrosis: current evidence and future prospects

Cystic fibrosis (CF) is a genetic disorder that causes multiorgan morbidity and premature death, most commonly from pulmonary dysfunction. Mutations in the CF transmembrane conductance regulator (CFTR) gene, of which almost 2000 have been described, result in a dysfunctional CFTR protein. This protein is an adenosine triphosphate binding anion channel, present primarily at the surface of epithelial cells. Loss of function mutations in this anion channel result in decreased or absent chloride/bicarbonate transport. The subsequent abnormal salt and water transport at epithelial cell surfaces leads to thickened secretions, and infection or inflammation in affected organs. In the last 20 years, therapeutics have been developed to treat the signs and symptoms of CF. However, in 2012, the small molecule drug, ivacaftor, became the first approved therapy that addresses the basic defect in CF. Ivacaftor is a potentiator of CFTR channels defective in their chloride/bicarbonate gating/conductance, but present at the epithelial cell surface. It is only approved for 10 mutations carried by approximately 7% of the population of patients with CF. F508del is the most common CFTR mutation, present in homozygosity in approximately 50% of patients with CF. The F508del mutation results in multiple CFTR channel defects that require both correction (stabilization of misfolded CFTR and trafficking to the epithelial cell membrane) and potentiation. This article reviews the in vitro and clinical trial data for the potential use of the potentiator, ivacaftor, and the corrector, lumacaftor, in patients with CF.

Targeted therapies to improve CFTR function in cystic fibrosis

Cystic fibrosis is the most common genetically determined, life-limiting disorder in populations of European ancestry. The genetic basis of cystic fibrosis is well established to be mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that codes for an apical membrane chloride channel principally expressed by epithelial cells. Conventional approaches to cystic fibrosis care involve a heavy daily burden of supportive treatments to combat lung infection, help clear airway secretions and maintain nutritional status. In 2012, a new era of precision medicine in cystic fibrosis therapeutics began with the licensing of a small molecule, ivacaftor, which successfully targets the underlying defect and improves CFTR function in a subgroup of patients in a genotype-specific manner. Here, we review the three main targeted approaches that have been adopted to improve CFTR function: potentiators, which recover the function of CFTR at the apical surface of epithelial cells that is disrupted in class III and IV genetic mutations; correctors, which improve intracellular processing of CFTR, increasing surface expression, in class II mutations; and production correctors or read-through agents, which promote transcription of CFTR in class I mutations. The further development of such approaches offers great promise for future therapeutic strategies in cystic fibrosis.

Lumacaftor-Ivacaftor in Patients with Cystic Fibrosis Homozygous for Phe508del CFTR

BACKGROUND

Cystic fibrosis is a life-limiting disease that is caused by defective or deficient cystic fibrosis transmembrane conductance regulator (CFTR) protein activity. Phe508del is the most common CFTR mutation.

METHODS

We conducted two phase 3, randomized, double-blind, placebo-controlled studies that were designed to assess the effects of lumacaftor (VX-809), a CFTR corrector, in combination with ivacaftor (VX-770), a CFTR potentiator, in patients 12 years of age or older who had cystic fibrosis and were homozygous for the Phe508del CFTR mutation. In both studies, patients were randomly assigned to receive either lumacaftor (600 mg once daily or 400 mg every 12 hours) in combination with ivacaftor (250 mg every 12 hours) or matched placebo for 24 weeks. The primary end point was the absolute change from baseline in the percentage of predicted forced expiratory volume in 1 second (FEV1) at week 24.

RESULTS

A total of 1108 patients underwent randomization and received study drug. The mean baseline FEV1 was 61% of the predicted value. In both studies, there were significant improvements in the primary end point in both lumacaftor-ivacaftor dose groups; the difference between active treatment and placebo with respect to the mean absolute improvement in the percentage of predicted FEV1 ranged from 2.6 to 4.0 percentage points (P<0.001), which corresponded to a mean relative treatment difference of 4.3 to 6.7% (P<0.001). Pooled analyses showed that the rate of pulmonary exacerbations was 30 to 39% lower in the lumacaftor-ivacaftor groups than in the placebo group; the rate of events leading to hospitalization or the use of intravenous antibiotics was lower in the lumacaftor-ivacaftor groups as well. The incidence of adverse events was generally similar in the lumacaftor-ivacaftor and placebo groups. The rate of discontinuation due to an adverse event was 4.2% among patients who received lumacaftor-ivacaftor versus 1.6% among those who received placebo.

CONCLUSIONS

These data show that lumacaftor in combination with ivacaftor provided a benefit for patients with cystic fibrosis homozygous for the Phe508del CFTR mutation. (Funded by Vertex Pharmaceuticals and others; TRAFFIC and TRANSPORT ClinicalTrials.gov numbers, NCT01807923 and NCT01807949.).

Effect of ivacaftor treatment in patients with cystic fibrosis and the G551D-CFTR mutation: patient-reported outcomes in the STRIVE randomized, controlled trial

BACKGROUND

Cystic fibrosis (CF) is an inherited, rare autosomal recessive disease that results in chronically debilitating morbidities and high premature mortality. We evaluated how ivacaftor treatment affected CF symptoms, functioning, and well-being, as measured by the Cystic Fibrosis Questionnaire-Revised (CFQ-R), a widely-used patient-reported outcome (PRO) measure.

METHODS

STRIVE, a double-blind, placebo-controlled randomized trial, evaluated ivacaftor (150 mg) in CF patients aged 12+ with the G551D-CFTR mutation for 48 weeks. Treatment effect analysis used a mixed-effects repeated measures model. Treatment benefit analyses applied the cumulative distribution function and a categorical analysis of change scores ("improvement," "no change," or "decline"). Content-based interpretation examined treatment effect on specific item responses.

RESULTS

Data from 152 patients with a baseline CFQ-R assessment were analyzed. The treatment effect analysis favored treatment with ivacaftor over placebo on the Body Image, Eating, Health Perceptions, Physical Functioning, Respiratory, Social Functioning, Treatment Burden, and Vitality scales. Findings were supported by the analysis of categorical change. On all CFQ-R scales, the percentage of patients who improved was greater for ivacaftor. In the content-based analysis, the treatment benefit was characterized by better scores across a broad range of domains.

CONCLUSIONS

Results illustrate broad benefits of ivacaftor treatment across many domains: respiratory symptoms, physical and social functioning, health perceptions, and vitality, as measured by the CFQ-R. The breadth of improvements reflects the systemic mechanism of action of ivacaftor compared to other therapies. Findings support the patient-reported value of ivacaftor treatment in this patient population.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00909532.

Targeting ion channels in cystic fibrosis

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause a characteristic defect in epithelial ion transport that plays a central role in the pathogenesis of cystic fibrosis (CF). Hence, pharmacological correction of this ion transport defect by targeting of mutant CFTR, or alternative ion channels that may compensate for CFTR dysfunction, has long been considered as an attractive approach to a causal therapy of this life-limiting disease. The recent introduction of the CFTR potentiator ivacaftor into the therapy of a subgroup of patients with specific CFTR mutations was a major milestone and enormous stimulus for seeking effective ion transport modulators for all patients with CF. In this review, we discuss recent breakthroughs and setbacks with CFTR modulators designed to rescue mutant CFTR including the common mutation F508del. Further, we examine the alternative chloride channels TMEM16A and SLC26A9, as well as the epithelial sodium channel ENaC as alternative targets in CF lung disease, which remains the major cause of morbidity and mortality in patients with CF. Finally, we will focus on the hurdles that still need to be overcome to make effective ion transport modulation therapies available for all patients with CF irrespective of their CFTR genotype.

Electronic monitoring reveals highly variable adherence patterns in patients prescribed ivacaftor

BACKGROUND

Previous studies of CF treatments have shown suboptimal adherence, though little has been reported regarding adherence patterns to ivacaftor. Electronic monitoring (EM) of adherence is considered a gold standard of measurement.

METHODS

Adherence rates by EM were prospectively obtained and patterns over time were analyzed. EM-derived adherence rates were compared to pharmacy refill history and self-report.

RESULTS

12 subjects (age 6-48 years; CFTR-G551D mutation) previously prescribed ivacaftor were monitored for a mean of 118 days. Overall adherence by EM was 61% (SD=28%) and decreased over time. Median duration between doses was 16.9 hours (IQR 13.9-24.1 hours) and increased over time. There was no correlation between EM-derived adherence and either refill history (84%, r=0.26, p=0.42) or self-report (100%, r=0.40, p=0.22).

CONCLUSIONS

Despite the promising nature of ivacaftor, our data suggest adherence rates are suboptimal and comparable to other prescribed CF therapies, and more commonly used assessments of adherence may be unreliable.

Recent advances in cystic fibrosis

PURPOSE OF REVIEW

The field of cystic fibrosis (CF) continues to evolve at a fast pace thanks to novel observations that have enabled deeper understanding of the disease pathophysiology. Parallel groundbreaking developments in innovative therapies permit, for the first time, distinct disease modification.

RECENT FINDINGS

This review highlights important discoveries in fluid homeostasis and mucus secretion in CF that further informs the pathophysiology of the airway disease that characterizes CF. In addition, current concepts and novel paradigms, such as 'theratypes' and 'CF transmembrane conductance regulator chaperome', which will be important for the continued development of disease modifying therapies, are reviewed.

SUMMARY

The rate of progress in the field continues to accelerate with new knowledge informing the development of innovative therapies. This has already led to tangible substantial and unprecedented clinical benefit for selected subsets of the CF patient population. In the years ahead, further knowledge acquisition may motivate the extension of these benefits to the larger population of people with CF.

Cystic fibrosis

Cystic fibrosis is an autosomal recessive, monogenetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The gene defect was first described 25 years ago and much progress has been made since then in our understanding of how CFTR mutations cause disease and how this can be addressed therapeutically. CFTR is a transmembrane protein that transports ions across the surface of epithelial cells. CFTR dysfunction affects many organs; however, lung disease is responsible for the vast majority of morbidity and mortality in patients with cystic fibrosis. Prenatal diagnostics, newborn screening and new treatment algorithms are changing the incidence and the prevalence of the disease. Until recently, the standard of care in cystic fibrosis treatment focused on preventing and treating complications of the disease; now, novel treatment strategies directly targeting the ion channel abnormality are becoming available and it will be important to evaluate how these treatments affect disease progression and the quality of life of patients. In this Primer, we summarize the current knowledge, and provide an outlook on how cystic fibrosis clinical care and research will be affected by new knowledge and therapeutic options in the near future. For an illustrated summary of this Primer, visit: http://go.nature.com/4VrefN.

Improved clinical and radiographic outcomes after treatment with ivacaftor in a young adult with cystic fibrosis with the P67L CFTR mutation

The underlying cause of cystic fibrosis (CF) is the loss of epithelial chloride and bicarbonate transport due to mutations in the CF transmembrane conductance regulator (CFTR) gene encoding the CFTR protein. Ivacaftor is a gene-specific CFTR potentiator that augments in vivo chloride transport in CFTR mutations affecting channel gating. Originally approved for the G511D CFTR mutation, ivacaftor is now approved for eight additional alleles exhibiting gating defects and has also been tested in R117H, a CFTR mutation with residual function that exhibits abnormal gating. P67L is a class 4 conductance (nongating) mutation exhibiting residual CFTR function. We report marked clinical improvement, normalization of spirometry, and dramatic reduction in radiographic structural airway changes after > 1 year of treatment with ivacaftor in a young adult with the compound heterozygous genotype P67L/F508del CFTR. The case suggests that ivacaftor may have a potential benefit for patients with CF with nongating mutations.

Paediatrics: messages from Munich

The aim of this article is to describe paediatric highlights from the 2014 European Respiratory Society (ERS) International Congress in Munich, Germany. Abstracts from the seven groups of the ERS Paediatric Assembly (Respiratory Physiology and Sleep, Asthma and Allergy, Cystic Fibrosis, Respiratory Infection and Immunology, Neonatology and Paediatric Intensive Care, Respiratory Epidemiology, and Bronchology) are presented in the context of the current literature.

Efficacy response in CF patients treated with ivacaftor: post-hoc analysis

Clinical studies in patients with cystic fibrosis and G551D-CFTR showed that the group treated with ivacaftor had improved clinical outcomes. To better understand the effect of ivacaftor therapy across the distribution of individual FEV(1) responses, data from Phase 3 studies (STRIVE/ENVISION) were re-examined. In this post-hoc analysis of patients (n = 209) who received 48 weeks of ivacaftor or placebo, patients were assigned to tertiles according to FEV(1) response. These groups were then used to evaluate response (FEV(1), sweat chloride, weight, CFQ-R, and pulmonary exacerbation). The number needed to treat (NNT) was calculated for specific thresholds for each outcome. Across all tertiles, numerical improvements in FEV(1), sweat chloride, CFQ-R and the frequency of pulmonary exacerbations were observed in ivacaftor-treated patients: the treatment difference versus placebo was statistically significant for all outcomes in the upper tertile and for some outcomes in the lower and middle tertiles. The NNT for a ≥ 5% improvement in %predicted FEV(1) was 1.90, for a ≥ 5% body weight increase was 5.74, and to prevent a pulmonary exacerbation was 3.85. This analysis suggests that the majority of patients with clinical characteristics similar to STRIVE/ENVISION patients have the potential to benefit from ivacaftor therapy.

Impact of the CFTR-potentiator ivacaftor on airway microbiota in cystic fibrosis patients carrying a G551D mutation

Background

Airway microbiota composition has been clearly correlated with many pulmonary diseases, and notably with cystic fibrosis (CF), an autosomal genetic disorder caused by mutation in the CF transmembrane conductance regulator (CFTR). Recently, a new molecule, ivacaftor, has been shown to re-establish the functionality of the G551D-mutated CFTR, allowing significant improvement in lung function.

Objective and Methods

The purpose of this study was to follow the evolution of the airway microbiota in CF patients treated with ivacaftor, using quantitative PCR and pyrosequencing of 16S rRNA amplicons, in order to identify quantitative and qualitative changes in bacterial communities. Three G551D children were followed up longitudinally over a mean period of more than one year covering several months before and after initiation of ivacaftor treatment.

Results

129 operational taxonomy units (OTUs), representing 64 genera, were identified. There was no significant difference in total bacterial load before and after treatment. Comparison of global community composition found no significant changes in microbiota. Two OTUs, however, showed contrasting dynamics: after initiation of ivacaftor, the relative abundance of the anaerobe Porphyromonas 1 increased (p<0.01) and that of Streptococcus 1 (S. mitis group) decreased (p<0.05), possibly in relation to the anti-Gram-positive properties of ivacaftor. The anaerobe Prevotella 2 correlated positively with the pulmonary function test FEV-1 (r=0.73, p<0.05). The study confirmed the presumed positive role of anaerobes in lung function.

Conclusion

Several airway microbiota components, notably anaerobes (obligate or facultative anaerobes), could be valuable biomarkers of lung function improvement under ivacaftor, and could shed light on the pathophysiology of lung disease in CF patients.

Intestinal inflammation and impact on growth in children with cystic fibrosis

OBJECTIVE

The aim of the study was to evaluate and compare faecal markers of intestinal inflammation in children with cystic fibrosis (CF), and determine whether intestinal inflammation adversely affects the nutritional phenotype.

METHODS

Faecal samples for markers of intestinal inflammation, calprotectin, S100A12, and osteoprotegerin, were collected from children with CF, healthy controls (HCs), and Crohn disease (CD). Associations between inflammatory markers and clinical and nutritional indices were determined in subjects with CF.

RESULTS

Twenty-eight children with CF (mean [standard deviation (SD)] 8.4 [3.3] years old, 22 pancreatic insufficient [PI]), 47 HC, and 30 CD were recruited. Mean (SD) faecal calprotectin in CF (94.3 [100.6] mg/kg) was greater than HC (26.7 [15.4] mg/kg, P < 0.0001), but lower than CD (2133 [2781] mg/kg, P = 0.0003). Abnormal faecal calprotectin was found in subjects only with PI (17/22 (77%), P = 0.001). There was no difference in faecal mean (SD) S100A12 (0.8 [0.9] vs 1.5 [2.2] mg/kg, P = 0.14) and osteoprotegerin concentrations (72.7 [52.2] vs 62.5 [0.0] pg/mL, P = 0.2) between CF and HC. Patients with CD had significantly elevated S100A12 and osteoprotegerin compared with CF and HC. Faecal calprotectin inversely correlated with both weight (r = -0.5, P = 0.003) and height z scores (r = -0.6, P = 0.002) in CF.

CONCLUSIONS

The pattern of intestinal inflammation in CF is unique and distinct from inflammatory bowel disease, with elevated faecal calprotectin but normal faecal S100A12 and osteoprotegerin concentrations. The severity of intestinal inflammation, based on faecal calprotectin, significantly correlates with poor growth.

Early pulmonary inflammation and lung damage in children with cystic fibrosis

Individuals with cystic fibrosis (CF) suffer progressive airway inflammation, infection and lung damage. Airway inflammation and infection are present from early in life, often before children are symptomatic. CF gene mutations cause changes in the CF transmembrane regulator protein that result in an aberrant airway microenvironment including airway surface liquid (ASL) dehydration, reduced ASL acidity, altered airway mucin and a dysregulated inflammatory response. This review discusses how an altered microenvironment drives CF lung disease before overt airway infection, the response of the CF airway to early infection, and methods to prevent inflammation and early lung disease.