Correction of chloride transport and mislocalization of CFTR protein by vardenafil in the gastrointestinal tract of cystic fibrosis mice

Localization and function of humanized F508del-CFTR in mouse intestine following activation of serum glucocorticoid kinase 1 and Trikafta

The CFTR modulator Trikafta has markedly improved lung disease for Cystic Fibrosis (CF) patients carrying the common delta F508 (F508del-CFTR) CFTR mutation. F508del-CFTR results in an apical trafficking defect and loss of function in CFTR-expressing epithelial cells. However, Trikafta has not resulted in improved gastrointestinal function in CF patients. A humanized mouse model of F508del-CFTR was recently generated to evaluate CFTR modulators and other compounds to treat human F508del-CFTR CF intestinal disease. Short-term (4 h) treatment of rats with Dexamethasone (Dex) potently activates serum glucocorticoid kinase 1 (SGK1) and increases CFTR apical traffic and ion transport in the native intestine. This study examined CFTR localization and ion transport in intestinal segments from humanized F508del-CFTR mice following treatment with Dex in the presence/absence of Trikafta. Dex treatment improved apical CFTR localization and function but was inconsistent along intestinal segments. Combined treatment with Dex and Trikafta was superior to Dex alone but inconsistently improved CFTR localization and function. These data suggest further optimization of humanized CF mouse models will be necessary to test the efficacy of compounds to treat human CF intestinal disease.

Advancements in Phosphodiesterase 5 Inhibitors: Unveiling Present and Future Perspectives

Phosphodiesterase 5 (PDE5) inhibitors presented themselves as important players in the nitric oxide/cGMP pathway, thus exerting a profound impact on various physiological and pathological processes. Beyond their well-known efficacy in treating male erectile dysfunction (ED) and pulmonary arterial hypertension (PAH), a plethora of studies have unveiled their significance in the treatment of a myriad of other diseases, including cognitive functions, heart failure, multiple drug resistance in cancer therapy, immune diseases, systemic sclerosis and others. This comprehensive review aims to provide an updated assessment of the crucial role played by PDE5 inhibitors (PDE5-Is) as disease-modifying agents taking their limiting side effects into consideration. From a medicinal chemistry and drug discovery perspective, the published PDE5-Is over the last 10 years and their binding characteristics are systemically discussed, and advancement in properties is exposed. A persistent challenge encountered with these agents lies in their limited isozyme selectivity; considering this obstacle, this review also highlights the breakthrough development of the recently reported PDE5 allosteric inhibitors, which exhibit an unparalleled level of selectivity that was rarely achievable by competitive inhibitors. The implications and potential impact of these novel allosteric inhibitors are meticulously explored. Additionally, the concept of multi-targeted ligands is critically evaluated in relation to PDE5-Is by inspecting the broader spectrum of their molecular interactions and effects. The objective of this review is to provide insight into the design of potent, selective PDE5-Is and an overview of their biological function, limitations, challenges, therapeutic potentials, undergoing clinical trials, future prospects and emerging uses, thus guiding upcoming endeavors in both academia and industry within this domain.

Pathological Significance of Macrophages in Erectile Dysfunction Including Peyronie's Disease

Erectile function is regulated by complex mechanisms centered on vascular- and nerve-related systems. Hence, dysregulation of these systems leads to erectile dysfunction (ED), which causes mental distress and decreases the quality of life of patients and their partners. At the molecular level, many factors, such as fibrosis, lipid metabolism abnormalities, the immune system, and stem cells, play crucial roles in the etiology and development of ED. Although phosphodiesterase type 5 (PDE5) inhibitors are currently the standard treatment agents for patients with ED, they are effective only in a subgroup of patients. Therefore, further insight into the pathological mechanism underlying ED is needed to discuss ED treatment strategies. In this review, we focused on the biological and pathological significance of macrophages in ED because the interaction of macrophages with ED-related mechanisms have not been well explored, despite their important roles in vasculogenic and neurogenic diseases. Furthermore, we examined the pathological significance of macrophages in Peyronie’s disease (PD), a cause of ED characterized by penile deformation (visible curvature) during erection and pain. Although microinjury and the subsequent abnormal healing process of the tunica albuginea are known to be important processes in this disease, the detailed etiology and pathophysiology of PD are not fully understood. This is the first review on the pathological role of macrophages in PD.

Riociguat for the treatment of Phe508del homozygous adults with cystic fibrosis

BACKGROUND

Riociguat is a first-in-class soluble guanylate cyclase stimulator for which preclinical data suggested improvements in cystic fibrosis transmembrane conductance regulator (CFTR) function.

METHODS

This international, multicenter, two-part, Phase II study of riociguat enrolled adults with cystic fibrosis (CF) homozygous for Phe508del CFTR. Part 1 was a 28-day, randomized, double-blind, placebo-controlled study in participants not receiving CFTR modulator therapy. Twenty-one participants were randomized 1:2 to placebo or oral riociguat (0.5 mg three times daily [tid] for 14 days, increased to 1.0 mg tid for the subsequent 14 days). The primary and secondary efficacy endpoints were change in sweat chloride concentration and percent predicted forced expiratory volume in 1 second (ppFEV₁), respectively, from baseline to Day 14 and Day 28 with riociguat compared with placebo.

RESULTS

Riociguat did not alter CFTR activity (change in sweat chloride) or lung function (change in ppFEV₁) at doses up to 1.0 mg tid after 28 days. The most common drug-related adverse event (AE) was headache occurring in three participants (21%); serious AEs occurred in one participant receiving riociguat (7%) and one participant receiving placebo (14%). This safety profile was consistent with the underlying disease and the known safety of riociguat for its approved indications.

CONCLUSIONS

The Rio-CF study was terminated due to lack of efficacy and the changing landscape of CF therapeutic development. The current study⁠, within its limits of a small sample size, did not provide evidence that riociguat could be a valid treatment option for CF.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02170025.

Riociguat: Clinical research and evolving role in therapy

Riociguat is a first-in-class soluble guanylate cyclase stimulator, approved for the treatment of adults with pulmonary arterial hypertension (PAH), inoperable chronic thromboembolic pulmonary hypertension (CTEPH), or persistent or recurrent CTEPH after pulmonary endarterectomy. Approval was based on the results of the phase III PATENT-1 (PAH) and CHEST-1 (CTEPH) studies, with significant improvements in the primary endpoint of 6-minute walk distance vs placebo of +36 m and +46 m, respectively, as well as improvements in secondary endpoints such as pulmonary vascular resistance and World Health Organization functional class. Riociguat acts as a stimulator of cyclic guanosine monophosphate synthesis rather than as an inhibitor of cGMP metabolism. As with other approved therapies for PAH, riociguat has antifibrotic, antiproliferative and anti-inflammatory effects, in addition to vasodilatory properties. This has led to further clinical studies in patients who do not achieve a satisfactory clinical response with phosphodiesterase type-5 inhibitors. Riociguat has also been evaluated in patients with World Health Organization group 2 and 3 pulmonary hypertension, and other conditions including diffuse cutaneous systemic sclerosis, Raynaud's phenomenon and cystic fibrosis. This review evaluates the results of the original clinical trials of riociguat for the treatment of PAH and CTEPH, and summarises the body of work that has examined the safety and efficacy of riociguat for the treatment of other types of pulmonary hypertension.

Cyclic nucleotide phosphodiesterase inhibitors as therapeutic interventions for cystic fibrosis

Cystic Fibrosis (CF) lung disease results from mutations in the CFTR anion channel that reduce anion and fluid secretion by airway epithelia. Impaired secretion compromises airway innate defence mechanisms and leads to bacterial colonization, excessive inflammation and tissue damage; thus, restoration of CFTR function is the goal of many CF therapies. CFTR channels are activated by cyclic nucleotide-dependent protein kinases. The second messengers 3'5'-cAMP and 3'5'-cGMP are hydrolysed by a large family of cyclic nucleotide phosphodiesterases that provide subcellular spatial and temporal control of cyclic nucleotide-dependent signalling. Selective inhibition of these enzymes elevates cyclic nucleotide levels, leading to activation of CFTR and other downstream effectors. Here we examine members of the PDE family that are likely to regulate CFTR-dependent ion and fluid secretion in the airways and discuss other actions of PDE inhibitors that can influence cyclic nucleotide-regulated mucociliary transport, inflammation and bronchodilation. Finally, we review PDE inhibitors and the potential benefits they could provide as CF therapeutics.

Vardenafil increases intracellular accumulation of the most prevalent mutant cystic fibrosis transmembrane conductance regulator (CTFR) in human bronchial epithelial cells

Cystic fibrosis (CF) is a genetic disease characterized by progressive lung and chronic digestive manifestations. We have shown that therapeutic doses of vardenafil, a phosphodiesterase type 5 (PDE5) inhibitor, corrects CF Transmembrane conductance Regulator (CFTR)-dependent chloride transport in respiratory and intestinal tissues of F508del homozygous mice. Here, we studied the effect of vardenafil on CFTR in 16HBE14o- and CFBE41o- cell lines. First, the expression levels of PDE5 mRNA in these cell lines were monitored. The two cell lines were exposed to different drugs (dimethyl sulfoxide, 8-Br-cGMP, forskolin or vardenafil). The cAMP and cGMP intracellular concentrations were measured. Finally, we localised the CFTR by immunolabelling. PDE5 was similarly expressed in both wild-type and in CF cells. A fast and transient rise in cGMP intracellular contents followed treatment with vardenafil, confirming its PDE5 inhibitory effect. We showed that vardenafil promoted both the early steps of the cellular processing and the trafficking of F508del without fully addressing the protein to the plasma membrane. The effect was not reproduced by the brominated cGMP analogue and it was not prevented by the combination of a protein kinase G (PKG) inhibitor and vardenafil. These findings support the view that vardenafil partially rescues F508del through cGMP/PKG-independent mechanisms.

Optical Nanosensors for in vivo Physiological Chloride Detection for Monitoring Cystic Fibrosis Treatment

Personalized approaches for continuous monitoring of chloride levels are potentially valuable for evaluating the efficacy of new treatments of genetic disorders such as cystic fibrosis. In this report, we validated optode-based nanosensors for real-time chloride monitoring in the interstitial fluid of living animals. These nanosensors take advantage of a ratiometric sensing scheme which demonstrates reversible and selective chloride detection in the physiological range. We further investigate how skin pigmentation affects the sensor performance during in vivo fluorescence imaging. We successfully monitored endogenous chloride changes using nanosensors during pharmacological treatment in a cystic fibrosis mouse model. We believe this platform is a valuable tool for chloride detection which could assess the efficacy of new treatments for cystic fibrosis.

Efficacy and safety of oral sildenafil in cystic fibrosis children with mild to moderate lung disease

BACKGROUND

Airway inflammation due to chronic infection is the leading cause of respiratory failure and death in most of patients with cystic fibrosis (CF). There is some evidence about anti-inflammatory activity of phosphodiesterase inhibitors in adult patients with CF. This study was designed to evaluate the efficacy, safety, and tolerability of sildenafil (a phosphodiesterase inhibitor drug) in children with CF.

METHOD

This uncontrolled before-after study was conducted on 20 children with CF (mean age 14 ± 2.8 years, 50% male) with mild to moderate lung disease who were referred to CF clinic of Imam Hossein hospital in Isfahan, Iran. The patients received oral sildenafil (1 mg/kg p.o tid for 3 months). Changes in spirometric values, maximal exercise capacity, and patient-reported health by using the cystic fibrosis questionnaire-revised (CFQ-R) were evaluated before and after treatment.

RESULT

CFQ-R (69.54 ± 4.6 vs 76.90 ± 5.4; P < .001) and exercise duration (401 ± 45.6 vs 497 ± 60.1 second; P < .01) increased following sildenafil therapy. In contrast, the forced expiratory value (FEV_1; 84.60 ± 13.67 vs 78.40 ± 12.95; P < .001) and FEF25-75 (77.80 ± 27.33 vs 69.20 ± 21.91; P = .004) showed significant decreases. However, the mean of FEV₁ /forced vital capacity did not change significantly during the study (P = .682).

CONCLUSIONS

Although sildenafil can improve the quality of life and exercise capacities in CF children, it significantly decreases lung function. So, administration of this drug for CF children should be reconsidered.

Cystic fibrosis transmembrane conductance regulator modulates enteric cholinergic activities and is abnormally expressed in the enteric ganglia of patients with slow transit constipation

BACKGROUND

Cystic fibrosis transmembrane conductance regulator (CFTR) was recently found in the enteric nervous system, where its role is unclear. We aimed to identify which enteric neuronal structures express CFTR, whether CFTR modulates enteric neurotransmission and if altered CFTR expression is associated with slow transit constipation (STC).

METHODS

Immunofluorescence double labeling was performed to localize CFTR with various neuronal and glial cell markers in the human colon. The immunoreactivity (IR) of CFTR and choline acetyltransferase (ChAT) on myenteric plexus of control and STC colon was quantitatively analyzed. In control colonic muscle strips, electrical field stimulation (EFS) evoked contractile responses and the release of acetylcholine (ACh) was measured in the presence of the CFTR channel inhibitor, CFTR(inh)-172.

RESULTS

CFTR-IR was densely localized to myenteric ganglia, where it was co-localized with neuronal markers HuC/D and β-tubulin, and glial marker S-100 but little with glial fibrillary acidic protein. Vesicular ACh transport was almost exclusively co-localized with CFTR, but neurons expressing nitric oxide synthase were CFTR negative. Significant reductions of CFTR-IR (P < 0.01) and ChAT-IR (P < 0.05) were observed on myenteric ganglia of STC compared to control. Pre-treatment of colonic muscle strips with CFTR(inh)-172 (10 µM) significantly inhibited EFS-evoked contractile responses (P < 0.01) and ACh release (P < 0.05).

CONCLUSIONS

Co-localization of CFTR-IR with cholinergic markers, inhibition of EFS-induced colonic muscle contractility and ACh release by CFTR(inh)-172 suggest that CFTR modulates enteric cholinergic neurotransmission. The downregulation of CFTR and ChAT in myenteric ganglia of STC correlated with the impaired contractile responses to EFS.

Evaluation of eluforsen, a novel RNA oligonucleotide for restoration of CFTR function in in vitro and murine models of p.Phe508del cystic fibrosis

Cystic fibrosis (CF) is caused by mutations in the gene encoding the epithelial chloride channel CF transmembrane conductance regulator (CFTR) protein. The most common mutation is a deletion of three nucleotides leading to the loss of phenylalanine at position 508 (p.Phe508del) in the protein. This study evaluates eluforsen, a novel, single-stranded, 33-nucleotide antisense oligonucleotide designed to restore CFTR function, in in vitro and in vivo models of p.Phe508del CF. The aims of the study were to demonstrate cellular uptake of eluforsen, and its efficacy in functional restoration of p.Phe508del-CFTR both in vitro and in vivo. In vitro, the effect of eluforsen was investigated in human CF pancreatic adenocarcinoma cells and human bronchial epithelial cells. Two mouse models were used to evaluate eluforsen in vivo. In vitro, eluforsen improved chloride efflux in CF pancreatic adenocarcinoma cell cultures and increased short-circuit current in primary human bronchial epithelial cells, both indicating restoration of CFTR function. In vivo, eluforsen was taken up by airway epithelium following oro-tracheal administration in mice, resulting in systemic exposure of eluforsen. In female F508del-CFTR mice, eluforsen significantly increased CFTR-mediated saliva secretion (used as a measure of CFTR function, equivalent to the sweat test in humans). Similarly, intranasal administration of eluforsen significantly improved nasal potential difference (NPD), and therefore CFTR conductance, in two CF mouse models. These findings indicate that eluforsen improved CFTR function in cell and animal models of p.Phe508del-CFTR-mediated CF and supported further development of eluforsen in human clinical trials, where eluforsen has also been shown to improve CFTR activity as measured by NPD.

The Phosphodiesterase-5 Inhibitors and Prostate Cancer – What We Rely Know About It?

Phosphodiesterase-5 inhibitors (PDE5Is) represent a group of drugs that are registered for the treatment of erectile dysfunctions predominantly, but recently also for treatment of pulmonary hypertension and benign prostatic hypertrophy. However, more and more research deals with possible antitumor potential of PDE5Is in different types of cancers, including prostate cancer. Prostate cancer represents the one of the most common carcinoma in the male population, whose incidence is continuously increasing. Early detection combined with radical prostatectomy increases the survival rate, but also it is necessary to keep in mind the quality of life of patients undergoing prostatectomy in light of bladder control and erectile function. Authors of various clinical studies presented the results that often lead to totally opposing conclusions. For example, Chavez and colleagues have shown that use of PDE5Is in men with erectile dysfunction decreases the risk of developing prostate cancer, while, on the other hand, Michl and colleagues pointed out the adversely effect of PDE5Is on biochemical recurrence after bilateral nerve sparing radical prostatectomy. In that sense, the aim of this review was to present as many as possible of existing results dealing with of action of PDE5Is in the field of prostatic carcinoma. Taking into account all presented data, it can be concluded that eff ect of PDE5Is on formation, development and outcome of treatment in patients with prostate carcinoma is very intriguing question, whose response requires additional both experimental and clinical research.

Vardenafil reduces macrophage pro-inflammatory overresponses in cystic fibrosis through PDE5- and CFTR-dependent mechanisms

Chronic inflammation that progressively disrupts the lung tissue is a hallmark of cystic fibrosis (CF). In mice, vardenafil, an inhibitor of phosphodiesterase type 5 (PDE5), restores transepithelial ion transport and corrects mislocalization of the most common CF mutation, F508del-CFTR. It also reduces lung pro-inflammatory responses in mice and in patients with CF. To test the hypothesis that macrophages are target effector cells of the immunomo-dulatory effect of vardenafil, we isolated lung macrophages from mice homozygous for the F508del mutation or invalidated for the cftr gene and from their corresponding wild-type (WT) littermates. We then evaluated the effect of vardenafil on the classical M1 polarization, mirroring release of pro-inflammatory cytokines. We confirmed that macrophages from different body compartments express CF transmembrane conductance regulator (CFTR) and showed that vardenafil targets the cells through PDE5- and CFTR-dependent mechanisms. In the presence of the F508del mutation, vardenafil down-regulated overresponses of the M1 markers, tumour necrosis factor (TNF)-α and inducible nitric oxide synthase (NOS)-2. Our study identifies lung macrophages as target cells of the anti-inflammatory effect of vardenafil in CF and supports the view that the drug is potentially beneficial for treating CF as it combines rescue of CFTR protein and anti-inflammatory properties.

Cystic fibrosis transmembrane conductance regulator modulators in cystic fibrosis: current perspectives

Mutations of the CFTR gene cause cystic fibrosis (CF), the most common recessive monogenic disease worldwide. These mutations alter the synthesis, processing, function, or half-life of CFTR, the main chloride channel expressed in the apical membrane of epithelial cells in the airway, intestine, pancreas, and reproductive tract. Lung disease is the most critical manifestation of CF. It is characterized by airway obstruction, infection, and inflammation that lead to fatal tissue destruction. In spite of great advances in early and multidisciplinary medical care, and in our understanding of the pathophysiology, CF is still considerably reducing the life expectancy of patients. This review highlights the current development in pharmacological modulators of CFTR, which aim at rescuing the expression and/or function of mutated CFTR. While only Kalydeco® and Orkambi® are currently available to patients, many other families of CFTR modulators are undergoing preclinical and clinical investigations. Drug repositioning and personalized medicine are particularly detailed in this review as they represent the most promising strategies for restoring CFTR function in CF.

Strategies in early clinical development for the treatment of basic defects of cystic fibrosis

INTRODUCTION

Twenty-six years after the identification of the gene responsible for cystic fibrosis (CF), controversies still surround the pathogenesis of the disease that continues to burden and shorten lives. Therefore, finding effective therapeutic strategies that target the basic defect of CF is crucially needed.

AREAS COVERED

This review offers a comprehensive survey of fundamental therapies in early stages of development for the treatment of CF. The first part describes recent strategies targeting the basic defect either at the gene or at the transcript level. The second part summarizes a panel of novel strategies targeting protein repair. The third part reports strategies targeting non-CFTR channels.

EXPERT OPINION

Recent major breakthroughs in CF therapy have been made, raising hope to find a cure for CF. Apart from Vertex corrector and potentiator molecules (lumacaftor, ivacaftor, VX-661) and from ataluren, used to correct nonsense mutations, most compounds being currently tested are in very early (I-II) phases of development and definitive clinical results are keenly expected. Among the broad list of molecules and strategies being tested, the QR-010 compound and inhibitors of phosphodiesterase type 5 (sildenafil, vardenafil) could reveal a strong potentiality as therapeutic candidates to cure CF.

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.

Therapeutic options for hydrating airway mucus in cystic fibrosis

BACKGROUND

In cystic fibrosis (CF), genetic mutations in the CF transmembrane conductance regulator (CFTR) gene cause reduced chloride efflux from ciliated airway epithelial cells. This results in a reduction in periciliary liquid (PCL) depth of the airway surface liquid due to associated reduced water efflux. PCL layer dehydration reduces mucociliary clearance (MCC), leading to airway obstruction (reduced airflow and inflammation due to pathogen invasion) with mucus plug formation.

SUMMARY

Rehydrating mucus increases MCC. Mucus hydration can be achieved by direct hydration (administering osmotic agents to set up an osmotic gradient), using CFTR modulators to correct dysfunctional CFTR, or it can be achieved pharmacologically (targeting other ion channels on airway epithelial cells). Key Messages: The molecular mechanisms of several therapies are discussed in the context of pre-clinical and clinical trial studies. Currently, only the osmotic agent 7% hypertonic saline and the CFTR 'potentiator' VX-770 (ivacaftor) are used clinically to hydrate mucus. Emerging therapies include the osmotic agent mannitol (Bronchitol), the intracellular Ca(2+)-raising agent Moli1901/lancovutide, the CFTR potentiator sildenafil [phosphodiesterase type 5 (PDE5) inhibitor] and the CFTR 'corrector' VX-809 (lumacaftor). Other CFTR correctors (e.g. 'chemical chaperones') are also showing pre-clinical promise.

Cystic fibrosis mouse model-dependent intestinal structure and gut microbiome

Mice with a null mutation in the cystic fibrosis transmembrane conductance regulator (Cftr) gene show intestinal structure alterations and bacterial overgrowth. To determine whether these changes are model-dependent and whether the intestinal microbiome is altered in cystic fibrosis (CF) mouse models, we characterized the ileal tissue and intestinal microbiome of mice with the clinically common ΔF508 Cftr mutation (FVB/N Cftr(tm1Eur)) and with Cftr null mutations (BALB/c Cftr(tm1UNC) and C57BL/6 Cftr(tm1UNC)). Intestinal disease in 12-week-old CF mice, relative to wild-type strain controls, was measured histologically. The microbiome was characterized by pyrosequencing of the V4-V6 region of the 16S rRNA gene and intestinal load was measured by RT-PCR of the 16S rRNA gene. The CF-associated increases in ileal crypt to villus axis distention, goblet cell hyperplasia, and muscularis externa thickness were more severe in the BALB/c and C57BL/6 Cftr(tm1UNC) mice than in the FVB/N Cftr(tm1Eur) mice. Intestinal bacterial load was significantly increased in all CF models, compared to levels in controls, and positively correlated with circular muscle thickness in CF, but not wild-type, mice. Microbiome profiling identified Bifidobacterium and groups of Lactobacillus to be of altered abundance in the CF mice but overall bacterial frequencies were not common to the three CF strains and were not correlative of major histological changes. In conclusion, intestinal structure alterations, bacterial overgrowth, and dysbiosis were each more severe in BALB/c and C57BL/6 Cftr(tm1UNC) mice than in the FVB/N Cftr(tm1Eur) mice. The intestinal microbiome differed among the three CF mouse models.

Pharmacokinetics and tolerability of oral sildenafil in adults with cystic fibrosis lung disease

RATIONALE

Airway inflammation is central to cystic fibrosis (CF) pathophysiology. Pre-clinical models have shown that phosphodiesterase inhibitors (PDEi) like sildenafil have anti-inflammatory activity. PDEi have not been studied in CF subjects.

OBJECTIVES

We evaluated the pharmacokinetics, tolerability, and safety of sildenafil in subjects with CF. Sputum biomarkers were used to explore efficacy.

METHODS

An open-label pilot study of oral sildenafil administration was conducted in adults with mild to moderate CF lung disease. Subjects received oral sildenafil 20 or 40 mg p.o. t.i.d. for 6 weeks.

MEASUREMENTS AND MAIN RESULTS

Twenty subjects completed the study. Estimated elimination rate constants were statistically different in subjects with CF compared to previously published non-CF subjects. Side effects were generally mild. There were no drug-related serious adverse events. Sputum neutrophil elastase activity decreased.

CONCLUSIONS

Subjects with CF may eliminate sildenafil at a faster rate than non-CF subjects. Sildenafil administration was safe in subjects with CF and decreased sputum elastase activity. Sildenafil warrants further study as an anti-inflammatory in CF.

Cystic fibrosis: toward personalized therapies

Cystic fibrosis (CF), the most common, life-threatening monogenetic disease in Caucasians, is caused by mutations in the CFTR gene, encoding a cAMP- and cGMP-regulated epithelial chloride channel. Symptomatic therapies treating end-organ manifestations have increased the life expectancy of CF patients toward a mean of 40 years. The recent development of CFTR-targeted drugs that emerged from high-throughput screening and are capable of correcting the basic defect promises to transform the therapeutic landscape from a trial-and-error prescription to personalized medicine. This stratified approach is tailored to a specific functional class of mutations in CFTR, but can be refined further to an individual level by exploiting recent advances in ex vivo drug testing methods. These tests range from CFTR functional measurements in rectal biopsies donated by a CF patient to the use of patient-derived intestinal or pulmonary organoids. Such organoids may serve as an inexhaustible source of epithelial cells that can be stored in biobanks and allow medium- to high-throughput screening of CFTR activators, correctors and potentiators on the basis of a simple microscopic assay monitoring organoid swelling. Thus the recent breakthrough in stem cell biology allowing the culturing of mini-organs from individual patients is not only relevant for future stem cell therapy, but may also allow the preclinical testing of new drugs or combinations that are optimally suited for an individual patient.