New and investigational treatments in cystic fibrosis

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1 Therapeutic Advances in Respiratory Disease Review New and investigational treatments in cystic fibrosis Mangala Narasimhan and Rubin Cohen Ther Adv Respir Dis (2011) 5(4) DOI: / ! The Author(s), Reprints and permissions: journalspermissions.nav Abstract: Cystic fibrosis (CF) is an autosomal recessive disorder that affects approximately 1 in 3000 Caucasian births, or 30,000 individuals in the US and 70,000 worldwide. The discovery of the CF gene, isolation of the CFTR protein and understanding of molecular mechanisms behind the clinical expression of CF are being translated into newer treatments. Treatments for CF and its manifestations are discussed in this article including inhaled antibiotics, hydrator therapies, anti-inflammatory agents and protein modifiers. New and experimental treatments that are in development are also discussed. Outcomes for these treatments are forced expiratory volume in one second (FEV 1 ) improvement, CF-related quality of life, use of intravenous antibiotics and frequency of exacerbations and hospitalizations. Keywords: cystic fibrosis, gene therapy, protein modifiers Introduction Cystic fibrosis (CF) is an autosomal recessive disorder that affects approximately 1 in 3000 Caucasian births, or 30,000 individuals in the US and 70,000 worldwide. It is the most common life-shortening genetic disorder in the White population, and less frequently other racial and ethnic groups. Mutations of the cystic fibrosis transmembrane regulator (CTFR) gene account for the clinical manifestations of the disease; about 1500 mutations in CFTR are described, but only 22 occur with significant frequency and the phenotypical distribution varies considerably. The most common mutation, occurring in 70% of patients is the F508del, which results in an abnormal protein that is largely ubiquitinated in the endoplasmic reticulum and degraded in the proteasome. CFTR is found on apical membranes of epithelial cells and functions as a chloride channel. A nonfunctioning CFTR restricts chloride secretion and increases sodium reabsorption, limiting the amount of water that can passively move across the epithelium. This depletes the airway surface liquid, which in turn impairs mucociliary clearance. The result is impaired host defenses and chronic bacterial airway infection. CF is also characterized by a hyperactive airway inflammatory response which cannot be fully accounted for by chronic bacterial infections. CF patients usually present in infancy or childhood with failure to thrive due to pancreatic insufficiency, chronic cough and sputum production, persistent lung and sinus infections, nasal polyps, and digital clubbing [Binder, 2006]. Other presenting manifestations include biliary cirrhosis, rectal prolapse, hypoproteinemia, salt loss syndrome and obstructive azoospermia [Yankaskas et al. 2004]. Respiratory failure accounts for over 90% of deaths [Cystic Fibrosis Foundation, 2002]. Classic CF is the result of two mutations that cause severe disease. Nonclassic disease has at least one mutant CFTR allele that confers partial function and these patients are generally diagnosed later in life. There is great variability in phenotype and survival in CF. This variability exists even in patients homozygous for F508del and is likely due to modifier genes and poorly understood environmental factors [Drumm et al. 2005; Rowe et al. 2005]. The discovery of the CF gene, isolation of the CFTR protein and understanding of molecular mechanisms behind the clinical expression of CF are being translated into newer treatments [Rowe and Clancy, 2006]. These include aggressive treatment with antibiotics and drugs targeted to slow the decline of lung function. Indeed, survival in CF improved markedly over the years, manifested by a growing number of adults with Correspondence to: Mangala Narasimhan, DO The Adult Cystic Fibrosis Center, Division of Pulmonary, Critical Care and Sleep Medicine North Shore University Hospital and Long Island Jewish Medical Center, New Hyde Park, NY 11040, USA mnarasimhan@nshs.edu Rubin Cohen, MD The Adult Cystic Fibrosis Center. Division of Pulmonary, Critical Care and Sleep Medicine North Shore University Hospital and Long Island Jewish Medical Center, New Hyde Park, NY 11040, USA 275

2 Therapeutic Advances in Respiratory Disease 5 (4) this disease. In this article we review the drugs now approved for CF and describe other therapies in development. Inhaled antibiotics In the early stages of disease, Staphylococcus aureus and Haemophilus influenzae are the most common organisms found in the lungs of patients with CF; Pseudomonas aeruginosa (PA) becomes more dominant later in life, and emerges as the most common microbe causing illness in adult patients [Gibson et al. 2003]. Initial infection may be related to increased adherence of PA to the receptors in CF airways [Immundo et al. 1995]. Once PA airway infection is established, eradication becomes extremely difficult. Most patients respond clinically to antibiotics even though sputum cultures remain positive. Infection with the mucoid form of PA is associated with more rapid decline of lung function and poorer survival than infection with nonmucoid strains [Henry et al. 1992]. FDA-approved agents Inhaled aminoglycosides have a high therapeutic index because of the direct delivery of high concentrations of antibiotic to the bronchial lumen with limited systemic toxicity. Aerosolized tobramycin (TOBI Õ ) was FDA-approved in 1997 as the first nebulized antibiotic. The drug is delivered in a special nebulizer that transmits the proper size particles at the correct level to the airway, and not to the central bronchial tree or small airways [Geller et al. 2002]. TOBI had been shown in multicenter trials to decrease the amount of PA in sputum, improve pulmonary function and decrease hospitalization days [Ramsey et al. 1999]. A randomized study evaluated patients with moderate-to-severe pulmonary disease over a 24-week period showed that the group receiving TOBI had a sustained increase in pulmonary function as compared with placebo. Patients with CF and chronic PA infection should be offered this therapy, especially those with active pulmonary disease as shown by increased symptoms or declining pulmonary function. TOBI requires minutes to nebulize, is taken twice daily for cycles of 28 days, followed by 28 days of no treatment. Aerosolized aztreonam lysine (Cayston Õ, Gilead, Seattle, WA) was approved in 2010 for patients with CF and chronic pseudomonas infection [Cystic Fibrosis Foundation, 2011]. Patients treated with 28 days of inhaled aztreonam had a 10.3% increase in forced expiratory volume in one second (FEV 1 ) compared with those who received placebo. There was an associated decrease in PA density in sputum and improvement in the respiratory section of the CF-Quality of Life questionnaire [Retsch-Bogart et al. 2009]. Aztreonam is nebulized using the eflow Õ Nebulizer System (PARI Pharma) over 3 5 minutes at a dose of 75 mg three times a day. Aerosolized antibiotics in development Colistin (Coly-Mycin Õ ) is a polypeptide antibiotic of the polymyxin class. This inhaled antipseudomonal antibiotic is not yet FDAapproved for nebulization, but it has the potential advantage of a lower likelihood of the development of bacterial resistance, and it may lead to a slower rate of FEV 1 decline. However, nebulized colistin often causes bronchospasm, and pulmonary function may not improve [Jensen et al. 1987]. A randomized trial comparing inhaled tobramycin and colistin for 28 days in 109 CF patients showed a 6.7% improvement in FEV 1 in the tobramycin group which was not seen in the colistin group [Hodson et al. 2002]. Another disadvantage to nebulizing colistin is that it is not designed for aerosol delivery; it is available in a powder form manufactured for intravenous administration. The powder can be formulated into a liquid for nebulizing by mixing with sterile saline. Colistin is generally prescribed off-label for patients who cannot tolerate TOBI and in those with active disease (PA infection) in the months that they are off TOBI. A dry powder inhalation form is under development and presents an attractive alternative. Combination fosfomycin/tobramycin inhalation (FTI) therapy (Gilead, Seattle, WA) is intended for CF patients with chronic PA and has completed phase II trials. When administered three times daily using the eflow Õ nebulizer, FTI kills more bacteria than either drug alone in in vitro studies, and the two antibiotics may act synergistically to prevent decline in lung function [MacLeod et al. 2009]. FTI may also be active against MRSA, but this has not yet been established. Phase II trials began on inhaled ciprofloxacin in This drug is administered as a dry powder at a dose of either 50 or 75 mg twice daily (Bayer Pharmaceuticals, New Jersey). The primary endpoints for the ongoing clinical trials are improvement in pulmonary function tests, 276

3 M Narasimhan and R Cohen with secondary endpoints the change in pseudomonas density and resistance, and side effects [Ramsey et al. 1999]. The advantages of a dry powder formulation are ease of administration and stability without refrigeration. Inhaled amikacin (Arikace Õ, Transave) is a liposomal formulation of amikacin that is different than the common intravenous formulation which is occasionally used off label for nebulization. The liposomal encapsulation (nanocapsules measuring 0.3 mm) is postulated to enhance the ability of amikacin to penetrate mucus and biofilm, thereby increasing in vivo activity while minimizing systemic exposure. It is nebulized once daily for 10 minutes. Phase I and II trials in Europe have completed enrollment, and a phase II clinical trial began in the US in Positive results were announced in October 2009 from pooled results of two phase II clinical trials in the treatment of CF patients with PA lung infections. An open-label study showed that a dose of 560 mg nebulized once daily for 28 days for multiple cycles was well tolerated. There was a significant increase in FEV 1 % predicted during the treatment period, and this was sustained during the 2 months off study drug [Minic et al. 2010]. In a similar vein, nebulized liposomal ciprofloxacin is being developed for both CF and non-cf-related bronchiectasis (Aradigm Corporation). A multicenter 14-day treatment phase IIa trial has been completed in Australia and New Zealand. The primary efficacy endpoint was the reduction in the sputum density of PA from baseline in 21 CF subjects. Results demonstrated that PA colony forming units decreased by a mean 1.43 log (p < ), and remained reduced 1 week following discontinuation of the drug. FEV 1 increased by 6.86% (p ¼ 0.04). Nebulized liposomal ciprofloxacin was well tolerated, without reported serious adverse events [Bruinenberg et al. 2010]. MP-376 (Aeroquin) is a new formulation of levofloxacin being developed by Mpex Pharmaceuticals for aerosol administration for the management of chronic pulmonary infections due to PA and other bacteria. A US-based multicenter placebo-controlled phase II trial showed the drug to be well tolerated and caused a reduction of sputum pseudomonas density, improvement in FEV 1, and reduction in need for other inhaled or intravenous antipseudomonal antibiotics in the treatment group compared with the group that received placebo. A new pocket-sized device using a tobramycin inhalation powder (TIP) might offer improved lung function and decreased pseudomonas density, according to results of a phase III study. The primary efficacy measure was the relative change in FEV 1 from day 1 to day 28 in the first cycle. Secondary objectives of the study were to assess antipseudomonal agents, respiratory-related hospitalizations, and changes in sputum PA density and patient safety. The pharmacokinetics and pharmacodynamics of TIP are similar to nebulized tobramycin solution. However, TIP has a more rapid drug delivery system than tobramycin solution, so administration time is much shorter (4 6 minutes versus minutes). Decreased administration time and easier maintenance of the device could improve long-term adherence. In addition to the newer and possibly more effective aerosolized antibiotics, research has also centered on the development of newer delivery systems. The stimulus for these novel systems began with the phase-out of CFC-based inhalers, and continued with the need to target delivery to the airways to improve effectiveness and reduce side effects. Newer devices are far more efficient; they reduce variability of drug delivery, drug waste, and time of administration. Because they are easier to use, more portable, and decrease administration time, they hopefully will also improve adherence [Geller, 2008]. The lightweight, battery operated eflow Õ Nebulizer System enables highly efficient aerosolization of medication, including liposomal formulations, via a vibrating perforated membrane with thousands of laser-drilled holes. This produces aerosols with a very high density of active drug, precisely defined droplet size, and a high proportion of inhalable droplets delivered in a short period. The device also fits in the palm of the patient s hand. Hydrator therapies The secretion of luminal chloride in airway epithelial cells occurs by two distinct pathways. One is the CFTR channel, the other is through an alternative chloride channel. If the alternative chloride channel can be stimulated, this could compensate for reduced CFTR function and may improve clinical status. Denufosol and Molil1901, compounds that promote the 277

4 Therapeutic Advances in Respiratory Disease 5 (4) functioning of alternative chloride channels, are now in clinical trials [Zeitlin, 2007]. Denufosol is a derivative of the P2Y2 receptor agonists of ATP, and has better stability than the natural P2Y2 receptor agonists. Phase I studies have shown it to be safe, and phase II studies demonstrated improved lung function in treated patients. The Transport of Ions to Generate Epithelial Rehydration-1 (TIGER-1) study showed a small (45 ml) but statistically significant improvement in FEV 1 after 24 weeks that was sustained in the follow-up open-label extension phase (112 ml compared with 10 ml for placebo (p ¼ 0.013)) [Moss et al. 2010]. There were no improvements in frequency of exacerbations and quality of life. However, TIGER-1 enrolled only children with very mild disease and normal lung function. The current TIGER-2 study completed enrollment of both adults and children with mild disease (FEV 1 > 75% predicted) and is studying patients for 12 months of treatment. Moli1901 (duramycin) is a peptide that interacts with plasma phospholipids, activating an alternative chloride channel by elevating intracellular calcium levels. A phase II study confirmed safety, tolerability and a sustained benefit on pulmonary function in patients with CF. A multicenter phase III study is being initiated in Europe [Cysticfibrosis.com, 2010]. Agents that inhibit the endothelial sodium channel (ENaC) are also under investigation. ENaC is the rate-limiting step in sodium reabsorption across the airway epithelium. CFTR inhibits ENaC, thereby limiting sodium reabsorption. Defective or absent CFTR activity leads to increased sodium reabsorption contributing to mucus dehydration. ENaC inhibitors are potential targets for CF treatment by reducing sodium reabsorption and increasing mucus hydration through increased water secretion across its diffusion gradient. Aerosolized amiloride was the first ENaC inhibitor tested in CF, but studies showed no significant improvement in FEV 1 ; this was attributed to the very short (30 minute) half-life of amiloride in the lungs. Long-acting amiloride analogs are in development; one such agent, PS552 (Parion Sciences, Durham, NC) was shown to be safe, is detectable up to 4 hours after inhalation, and improves mucociliary clearance in normal subjects. Whether ENaC inhalation will improve important clinical parameters in CF patients is unclear [Donaldson, 2008]. Dornase alpha (DNAse, recombinant human DNase I, rhdnase, Pulmozyme Õ ) and hypertonic saline (HS) are inhaled agents that decrease sputum viscosity and improve mucociliary clearance [Suri et al. 2001; Laube et al. 1996]. Dornase alfa received FDA approval in Dornase alpha is a genetically engineered drug which liquefies bronchial mucus by cleaving extracellular DNA, which is present in very high concentrations in purulent CF airway secretions. A large-scale phase III clinical trial with a 24-week double-blind period and a 24-week open-label extension showed improvement in lung function and reduction in respiratory tract infectious exacerbations requiring intravenous antibiotic therapy. Treatment with dornase alpha was also associated with a reduced rate of hospitalizations, days missed from work or school, and frequency of CF-related symptoms. Adverse events were limited to upper airway irritation (i.e. voice alteration, laryngitis, pharyngitis), rash, chest pain, and conjunctivitis. These were generally mild and transient, and did not limit the use of the drug. This medication is nebulized once daily and requires 6 10 minutes to complete. HS inhalation acts by osmotically drawing water onto the airway surface which helps to restore defective mucociliary transport in patients with CF [King et al. 1997]. Clinical trials show modest improvements in lung function and a reduced rate of pulmonary exacerbations [Aziz and Kastelik, 2006]. HS has may cause bronchospasm, and therefore should be used with an inhaled bronchodilator [Donaldson et al. 2006; Elkins et al. 2006]. It is nebulized twice daily as 4 ml of 7% saline solution, and requires 30 minutes to complete. The long administration time and increased frequency of bronchospasm are obstacles to adherence to treatment. Dry powder mannitol has similar effects to HS on mucociliary transport in patients with CF, with the advantage of taking less time to administer [Wills, 2007]. One study showed that treatment with inhaled mannitol daily for 2 weeks improved the hydration and surface properties of sputum in patients with CF, and that this effect was sustained and correlated with airway function changes [Daviskas et al. 2010]. Another placebo-controlled trial showed that 420 mg of 278

5 M Narasimhan and R Cohen inhaled mannitol was associated with an increase in FEV 1 from baseline with acceptable safety [Bilton et al. 2010]. A similar study showed that mannitol 400 mg twice daily resulted in a 6.5% improvement in FEV 1 compared with baseline. Moreover, in an open-label phase, subjects that went from placebo to mannitol showed a similar improvement in FEV 1 up to 12 months. Administration of a short-acting bronchodilator is necessary prior to mannitol inhalation to protect against drug-induced bronchoconstriction [Jaques et al. 2008]. In all ongoing trials of mannitol, patients are evaluated with spirometry and are excluded from the study if FEV 1 declines by 15% after inhalation of the drug. Anti-inflammatory agents Increased inflammatory cytokine production and neutrophil influx are normal responses to an acute insult, and usually abate as the inciting cause becomes chronic. However, in CF inflammation persists and is increasingly implicated as a significant factor in the decline of respiratory function. Patients with CF have persistence of lung neutrophils, elevated levels of interleukins, TNF and leukotrienes, and reduced levels of anti-inflammatory cytokines [Balfour-Lynn, 2007]. High-dose ibuprofen therapy (20 30 mg/ kg daily) is recommended in patients with CF in patients less than 15 years old. It slows the progression of pulmonary disease in patients with mildly decreased pulmonary function. Regular monitoring for gastrointestinal and renal side effects is appropriate for patients receiving ibuprofen. The drug should be avoided in patients with moderate-to-severe reductions in pulmonary function, as it increases the risk of hemoptysis. Despite studies showing its effectiveness, high-dose ibuprofen therapy has not gained wide acceptance and is used in only 2% of CF patients. Macrolides were first used for chronic treatment of diffuse panbronchiolitis in Japanese adults, and later in patients with CF. Macrolides improve FEV 1, decrease use of oral antibiotics and decrease hospital days in adult patients with chronic pseudomonas infection [Rowe et al. 2005]. It is believed that antimicrobial effects are augmented by biofilm penetration and inhibition of protein synthesis. Macrolides accumulate within neutrophils and affect oxidant production, apoptosis, and cytokine production [Labro, 1998]. A phase III trial of azithromycin 500 mg thrice weekly in CF patients with PA infection showed an increase in FEV 1 and weight, with decreased rate of pulmonary exacerbations compared with placebo [Saiman et al. 2003]. Azithromycin does not improve lung function in CF patients who not chronically infected with PA, although those in the azithromycin group had a 50% reduction in exacerbations (95% CI, 31 79%) and an increase in body weight of 0.58 kg (95% CI, ) compared with the placebo group [Saiman et al. 2010]. This illustrates that while FEV 1 is important and has been the traditional primary outcome in CF studies; there may be other equally important benefits, especially in patients with mild disease. These include CF-related quality of life, use of intravenous antibiotics, and frequency of exacerbations and hospitalizations Protein modifiers The most common mutation in CF is the class II mutation F508del that codes for a misfolded CFTR that is degraded in the endoplasmic reticulum prior to reaching the cell membrane. Improving F508del trafficking (correctors) or improving CFTR functioning (potentiators) are a new therapeutic strategies being actively pursued [Van Goor et al. 2006]. VX-770 (Vertex pharmaceuticals) is a compound that increases cyclic-amp-dependent chloride secretion in cell cultures, and is a potent and selective CFTR potentiator of wild-type, G551D, F508del and R117H forms of CFTR. In a small phase 2 clinical trial, VX-770 administered twice daily in 39 patients with the G551D mutation over a 14-day or 28-day period improved lung function, nasal potential difference measures, and sweat chloride levels [Accurso et al. 2010]. In the phase IIa study, patients who receive the highest dose of VX-770 (150 mg twice daily) had decreases in sweat chloride from a mean 95.5 mmol/l to an astonishing 53.2 mmol/l over the 14-day dosing period (p < ). Six of eight patients in the 150 mg dose group achieved a decrease in sweat chloride to normal levels (<60 mmol/l). Sweat chloride levels did not change in patients who received placebo. Phase III studies of VX-770 are in progress that use the endpoint of sweat chloride measurements to evaluate the effect of VX-770 on improving function of defective CFTR protein [Vertex pharmaceuticals, 2010]

6 Therapeutic Advances in Respiratory Disease 5 (4) VX-809 (Vertex pharmaceuticals) is another orally-administered protein modifier in phase IIa trials. The drug is designed to increase the amount of F508del CFTR protein on the surface of cells lining the airway, and may increase chloride transport across the cell membrane in patients with the F508del CFTR mutation [Donaldson, 2008]. This compound is particularly intriguing as the F508del is the most common mutation in CF. Ataluren (PTC124) is an oral investigational molecule that enables the formation of a functioning protein in nonsense mutations. A nonsense mutation is an alteration in the genetic code that prematurely halts CFTR synthesis resulting in a nonfunctioning protein. Ataluren allows the ribosome to ignore the premature stop signal and to continue translation, but does not cause the ribosome to read through a normal stop signal. Nonsense CF mutations are very common in Ashkenazi Jewish populations, who account for more than 50% of CF patients in Israel and 10% of CF patients worldwide. In a phase II trial of CF adults who had at least one nonsense mutation in the CFTR gene, the study concluded that ataluren suppressed nonsense mutations and reduced the epithelial electrophysiological abnormalities caused by CFTR dysfunction. No patient discontinued the drug because of a drug-related adverse event. Treatment with ataluren was associated with small increases in FEV 1, forced vital capacity (FVC), and body weight in most patients, and a reduction in sputum neutrophil counts. Some patients also reported a decrease in pulmonary symptoms, such as cough. Larger trials are required to confirm such effects, and a phase III trial has begun in the United States [Kerem et al. 2008]. While current CF therapy is improving the quality and duration of life, many infants are now diagnosed via newborn screening; this, combined with the recognition that lung disease occurs in infancy, could lead to much earlier interventions aimed at preserving lung health. Treatments directed at different pathways of disease continue to improve outcomes but at the expense of increasing inconvenience and complexity. Patients may not adhere to burdensome treatments. For patients to make informed decisions about their treatment, the CF practitioner must counsel each patient about the precise nature of their treatment options and the expected benefits. There is few data comparing treatments directly. One small study (38 children) found inhaled mannitol to be at least as effective as rhdnase after 3 months treatment; suggesting that children who do not respond to rhdnase could benefit from a trial of inhaled mannitol. However, the combination of mannitol and rhdnase was not useful in this study [Minasian et al. 2010]. More studies are needed to answer questions about the effectiveness of combinations of agents (including antibiotics), and the relative effectiveness of treatments and their priorities during therapy. We can also expect new treatments in the pipeline. As the life expectancy for patients with CF continues to increase, there will be more clinical trials to answer these questions. Acknowledgement The authors wish to thank Dr. Mark Rosen for his review of this manuscript. Funding This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors. Conflict of interest statement None declared. References Accurso, F.J., Rowe, S.M., Clancy, J.P., Boyle, M.P., Dunitz, J.M., Durie, P.R. et al. (2010) Effect of VX- 770 in persons with cystic fibrosis and the G551D- CFTR mutation. N Engl J Med 363: Aziz, I. and Kastelik, J.A. (2006) Hypertonic saline for cystic fibrosis. N Engl J Med 354: Balfour-Lynn, I.M. (2007) Anti-inflammatory approaches to cystic fibrosis airways disease. Curr Opin Pulm Med 13: Bilton, D., Robinson, P., Cooper, P., Gallagher, C., Kolbe, J. and Charlton, B. (2010) Phase III study of inhaled dry powder mannitol (Bronchitol TM ) in cystic fibrosis results from the 6 month open label phase. Am J Respir Crit Care Med 181: A2338, [abstract]. Binder, H.J. (2006) Causes of chronic diarrhea. N Engl J Med 355: Bruinenberg, P., Serisier, D. and Blanchard, J. (2010) Effects and modulation of release rate of inhaled ciprofloxacin with liposomal formulations in healthy subjects and patients with bronchiectasis. ERS Annual Congress, Oral Presentation of Abstract

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