George M. Solomon

An International Randomized Multicenter Comparison of Nasal Potential Difference Techniques

BACKGROUND The transepithelial nasal potential difference (NPD) is used to assess cystic fibrosis transmembrane conductance regulator (CFTR) activity. Unreliability, excessive artifacts, and lack of standardization of current testing systems can compromise its use as a diagnostic test and outcome measure for clinical trials. METHODS To determine whether a nonperfusing (agar gel) nasal catheter for NPD measurement is more reliable and less susceptible to artifacts than a continuously perfusing nasal catheter, we performed a multicenter, randomized, crossover trial comparing a standardized NPD protocol using an agar nasal catheter with the same protocol using a continuously perfusing catheter. The data capture technique was identical in both protocols. A total of 26 normal adult subjects underwent NPD testing at six different centers. RESULTS Artifact frequency was reduced by 75% (P < .001), and duration was less pronounced using the agar catheter. The measurement of sodium conductance was similar between the two catheter methods, but the agar catheter demonstrated significantly greater CFTR-dependent hyperpolarization, because Δ zero Cl- + isoproterenol measurements were significantly more hyperpolarized with the agar catheter (224.2 ± 12.9 mV with agar vs 18.2 ± 9.1 mV with perfusion, P < .05). CONCLUSIONS The agar nasal catheter approach demonstrates superior reliability compared with the perfusion nasal catheter method for measurement of NPD. This nonperfusion catheter method should be considered for adoption as a standardized protocol to monitor CFTR activity in clinical trials.

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. Pediatr Pulmonol. 2015; 50:S3–S13.

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.

In vivo imaging of airway cilia and mucus clearance with micro-optical coherence tomography

We have designed and fabricated a 4 mm diameter rigid endoscopic probe to obtain high resolution micro-optical coherence tomography (µOCT) images from the tracheal epithelium of living swine. Our common-path fiber-optic probe used gradient-index focusing optics, a selectively coated prism reflector to implement a circular-obscuration apodization for depth-of-focus enhancement, and a common-path reference arm and an ultra-broadbrand supercontinuum laser to achieve high axial resolution. Benchtop characterization demonstrated lateral and axial resolutions of 3.4 μm and 1.7 μm, respectively (in tissue). Mechanical standoff rails flanking the imaging window allowed the epithelial surface to be maintained in focus without disrupting mucus flow. During in vivo imaging, relative motion was mitigated by inflating an airway balloon to hold the standoff rails on the epithelium. Software implemented image stabilization was also implemented during post-processing. The resulting image sequences yielded co-registered quantitative outputs of airway surface liquid and periciliary liquid layer thicknesses, ciliary beat frequency, and mucociliary transport rate, metrics that directly indicate airway epithelial function that have dominated in vitro research in diseases such as cystic fibrosis, but have not been available in vivo.

Standardized Treatment of Pulmonary exacerbations (STOP) study: Physician treatment practices and outcomes for individuals with cystic fibrosis with pulmonary exacerbations

BACKGROUND Pulmonary Exacerbations (PEx) are associated with increased morbidity and mortality in individuals with CF. PEx management practices vary widely, and optimization through interventional trials could potentially improve outcomes. The object of this analysis was to evaluate current physician treatment practices and patient outcomes for PEx. METHODS The Standardized Treatment of Pulmonary Exacerbations (STOP) observational study enrolled 220 participants ≥12years old admitted to the hospital for PEx at 11 U.S. CF centers. Spirometry and daily symptom scores were collected during the study. Physicians were surveyed on treatment goals and their management practices were observed. Treatment outcomes were compared to stated goals. RESULTS The mean (SD) duration of IV antibiotic treatment was 15.9 (6.0) days. Those individuals with more severe lung disease (<50% FEV1) were treated nearly two days longer than those with >50% FEV1. Physician-reported FEV1 improvement goals were 10% (95% CI: 5%, 14%) lower for patients with 6-month baseline FEV1 ≤50% predicted compared with those with 6-month baseline FEV1 >50% predicted. There were clinically and statistically significant improvements in symptoms from the start of IV antibiotic treatment to the end of IV antibiotic treatment and 28days after the start of treatment. The mean absolute increase in FEV1 from admission was 9% predicted at end of IV antibiotic treatment, and 7% predicted at day 28. Only 39% fully recovered lost lung function, and only 65% recovered at least 90% of lost lung function. Treatment was deemed successful by 84% of clinicians, although 6-month baseline FEV1 was only recovered in 39% of PEx. CONCLUSIONS In this prospective observational study of PEx, treatment regimens and durations showed substantial variation. A significant proportion of patients did not reach physicians treatment goals, yet treatment was deemed successful.

Standardized Treatment of Pulmonary Exacerbations (STOP) study: Observations at the initiation of intravenous antibiotics for cystic fibrosis pulmonary exacerbations

BACKGROUND The Standardized Treatment of Pulmonary Exacerbations (STOP) program has the intent of defining best practices in the treatment of pulmonary exacerbations (PEx) in patients with cystic fibrosis (CF). The objective of this analysis was to describe the clinical presentations of patients admitted for intravenous (IV) antibiotics and enrolled in a prospective observational PEx study as well as to understand physician treatment goals at the start of the intervention. METHODS We enrolled adolescents and adults admitted to the hospital for a PEx treated with IV antibiotics. We recorded patient and PEx characteristics at the time of enrollment. We surveyed treating physicians on treatment goals as well as their willingness to enroll patients in various study designs. Additional demographic and clinical data were obtained from the CF Foundation Patient Registry. RESULTS Of 220 patients enrolled, 56% were female, 19% were adolescents, and 71% were infected with P. aeruginosa. The mean (SD) FEV1 at enrollment was 51.1 (21.6)% predicted. Most patients (85%) experienced symptoms for ≥7days before admission, 43% had received IV antibiotics within the previous 6months, and 48% received oral and/or inhaled antibiotics prior to IV antibiotic initiation. Forty percent had ≥10% FEV1 decrease from their best value recorded in the previous 6months, but for 20% of patients, their enrollment FEV1 was their best FEV1 recorded within the previous 6months. Physicians reported that their primary treatment objectives were lung function recovery (53%) and improvement of symptoms (47%) of PEx. Most physicians stated they would enroll patients in studies involving 10-day (72%) or 14-day (87%), but not 7-day (29%), treatment regimens. CONCLUSIONS Based on the results of this study, prospective studies are feasible and physician willingness for interventional studies of PEx exists. Results of this observational study will help design future PEx trials.

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.

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.

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.

MicroRNA-145 Antagonism Reverses TGF-β Inhibition of F508del CFTR Correction in Airway Epithelia

Rationale: MicroRNAs (miRNAs) destabilize mRNA transcripts and inhibit protein translation. miR‐145 is of particular interest in cystic fibrosis (CF) as it has a direct binding site in the 3′‐untranslated region of CFTR (cystic fibrosis transmembrane conductance regulator) and is upregulated by the CF genetic modifier TGF (transforming growth factor)‐&bgr;. Objectives: To demonstrate that miR‐145 mediates TGF‐&bgr; inhibition of CFTR synthesis and function in airway epithelia. Methods: Primary human CF (F508del homozygous) and non‐CF airway epithelial cells were grown to terminal differentiation at the air‐liquid interface on permeable supports. TGF‐&bgr; (5 ng/ml), a miR‐145 mimic (20 nM), and a miR‐145 antagonist (20 nM) were used to manipulate CFTR function. In CF cells, lumacaftor (3 &mgr;M) and ivacaftor (10 &mgr;M) corrected mutant F508del CFTR. Quantification of CFTR mRNA, protein, and function was done by standard techniques. Measurements and Main Results: miR‐145 is increased fourfold in CF BAL fluid compared with non‐CF (P < 0.01) and increased 10‐fold in CF primary airway epithelial cells (P < 0.01). Exogenous TGF‐&bgr; doubles miR‐145 expression (P < 0.05), halves wild‐type CFTR mRNA and protein levels (P < 0.01), and nullifies lumacaftor/ivacaftor F508del CFTR correction. miR‐145 overexpression similarly decreases wild‐type CFTR protein synthesis (P < 0.01) and function (P < 0.05), and eliminates F508del corrector benefit. miR‐145 antagonism blocks TGF‐&bgr; suppression of CFTR and enhances lumacaftor correction of F508del CFTR. Conclusions: miR‐145 mediates TGF‐&bgr; inhibition of CFTR synthesis and function in airway epithelia. Specific antagonists to miR‐145 interrupt TGF‐&bgr; signaling to restore F508del CFTR modulation. miR‐145 antagonism may offer a novel therapeutic opportunity to enhance therapeutic benefit of F508del CFTR correction in CF epithelia.