Induction by antitumoral drugs of proteins that functionally complement CFTR: a novel therapy for cystic fibrosis?

Biophysical Reviews' "Meet the Editors Series": a profile of Christina Sizun

This edition of the continuing "Biophysical Reviews Meet the Editors Series" introduces Dr. Christina Sizun, physical chemist, member of the Biophysical Reviews editorial board and current Treasurer of the International Union for Pure and Applied Biophysics (IUPAB).

Increasing incidence rate of breast cancer in cystic fibrosis - relationship between pathogenesis, oncogenesis and prediction of the treatment effect in the context of worse clinical outcome and prognosis of cystic fibrosis due to estrogens

Cystic fibrosis (CF) is the most common genetic disease in the Caucasion population. Thanks to the CFTR modulators therapy, life expectancy will significantly improve. New therapeutic challenges can be expected, including diseases associated with ageing and higher incidence of cancer, as evidenced by recent epidemiological studies. The increasing incidence of tumors includes also breast cancer. The risk of breast cancer is higher in CF patients compared to the general population. Sex hormones, especially estrogens, also affect on the pathophysiology and immunology of the CF. Previous research, has demonstrated unequivocal survival rates for female CF patients compared to their male counterparts. Is demonstrated, that chemotherapy used for breast cancer affects the CFTR channel and CFTR modulator therapy has frequent side effects on breast tissue. In this review, we focus on the effects of female sex hormones on CF disease, pathophysiological relationships between CF and breast cancer, and the impact of antitumor treatment on both, malignant disease and CF. The potential for further investigation is also discussed.

Osteogenic Sarcoma in an Adolescent With Cystic Fibrosis: Successful Treatment Despite Significant Obstacles

Introduction: We describe the case of a 16-year old male with cystic fiborosis (CF) who presented with an osteosarcoma of his right distal tibia. Case Report: Treatment consisted of neoadjuvant chemotherapy of cisplatin, doxorubicin and high dose methotrexate followed by distal tibial resection and free fibula flap reconstruction and consolidation chemotherapy. Treatment was complicated by a pulmonary exacerbation, where Pseudomonas aeruginosa (PsA) and Staphylococcus aureus were grown on sputum culture which was treated with a 2-week course of intravenous piptazobactam and tobramycin. Mycobacterium intracellulare and Mycobacterium abscessus were also cultured following commencement of chemotherapy and successfully treated with a 6-month course of oral azithromycin, ethambutol, and moxifloxacin along with a 1-month course of inhaled amikacin. Pulmonary function improved during his treatment from baseline FEV1 of 3.8 l (93.9%) to 4.15 l (102.3% predicted) whilst nutritional status remained stable. Discussion: The combination of CF and osteosarcoma is rare with only one previous case reported (1). Our case is instructive as the patient faced the challenge of chronic PsA and the first reported culturing and successful treatment of non-tuberculous mycobacterium (NTM) during chemotherapy. Fatal outcomes have been reported previously for CF patients during immunosuppression (2). In concordance with our findings, a recent report noted an improvement in respiratory function in a child treated for leukemia (3). The anti-inflammatory nature of some chemotherapy agents could be responsible for the observed clinical improvement in CF with low dose methotrexate having been shown to increase FEV1 in adolescents with advanced CF (4). Whilst doxorubicin could improve pulmonary outcomes through increased total cellular CFTR protein expression and CFTR associated chloride secretion (5). It is hypothesized that the improved pulmonary function in patients with CF who require chemotherapy could be due to increased production of Multi-Drug Resistance Proteins (MDR) and Multi-Drug Resistant Associated Proteins (MRP) that may complement the depleted CFTR protein (6). Concluding Remarks: We report the well-tolerated management of osteosarcoma in a patient with CF including the first reported identification and eradication of NTM during chemotherapy. The observed positive pulmonary outcome following chemotherapy highlights several potential cellular mechanisms that deserve to be explored.

Increased Expression of Plasma-Induced ABCC1 mRNA in Cystic Fibrosis

The ABCC1 gene is structurally and functionally related to the cystic fibrosis transmembrane conductance regulator gene (CFTR). Upregulation of ABCC1 is thought to improve lung function in patients with cystic fibrosis (CF); the mechanism underlying this effect is unknown. We analyzed the ABCC1 promoter single nucleotide polymorphism (SNP rs504348), plasma-induced ABCC1 mRNA expression levels, and ABCC1 methylation status and their correlation with clinical variables among CF subjects with differing CFTR mutations. We assigned 93 CF subjects into disease severity groups and genotyped SNP rs504348. For 23 CF subjects and 7 healthy controls, donor peripheral blood mononuclear cells (PBMCs) stimulated with plasma underwent gene expression analysis via qRT-PCR. ABCC1 promoter methylation was analyzed in the same 23 CF subjects. No significant correlation was observed between rs504348 genotypes and CF disease severity, but pancreatic insufficient CF subjects showed increased colonization with any form of Pseudomonas aeruginosa (OR = 3.125, 95% CI: 1.192-8.190) and mucoid P. aeruginosa (OR = 5.075, 95% CI: 1.307-28.620) compared to the pancreatic sufficient group. A significantly higher expression of ABCC1 mRNA was induced by CF plasma compared to healthy control plasma (p < 0.001). CF subjects with rs504348 (CC/CG) also had higher mRNA expression compared to those with the ancestral GG genotype (p < 0.005). ABCC1 promoter was completely unmethylated; therefore, we did not detect any association between methylation and CF disease severity. In silico predictions suggested that histone modifications are crucial for regulating ABCC1 expression in PBMCs. Our results suggest that ABCC1 expression has a role in CFTR activity thereby increasing our understanding of the molecular underpinnings of the clinical heterogeneity in CF.

Deciphering miRNA transcription factor feed-forward loops to identify drug repurposing candidates for cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) is a fatal genetic disorder caused by mutations in the CF transmembrane conductance regulator (CFTR) gene that primarily affects the lungs and the digestive system, and the current drug treatment is mainly able to alleviate symptoms. To improve disease management for CF, we considered the repurposing of approved drugs and hypothesized that specific microRNA (miRNA) transcription factors (TF) gene networks can be used to generate feed-forward loops (FFLs), thus providing treatment opportunities on the basis of disease specific FFLs.

METHODS

Comprehensive database searches revealed significantly enriched TFs and miRNAs in CF and CFTR gene networks. The target genes were validated using ChIPBase and by employing a consensus approach of diverse algorithms to predict miRNA gene targets. STRING analysis confirmed protein-protein interactions (PPIs) among network partners and motif searches defined composite FFLs. Using information extracted from SM2miR and Pharmaco-miR, an in silico drug repurposing pipeline was established based on the regulation of miRNA/TFs in CF/CFTR networks.

RESULTS

In human airway epithelium, a total of 15 composite FFLs were constructed based on CFTR specific miRNA/TF gene networks. Importantly, nine of them were confirmed in patient samples and CF epithelial cells lines, and STRING PPI analysis provided evidence that the targets interacted with each other. Functional analysis revealed that ubiquitin-mediated proteolysis and protein processing in the endoplasmic reticulum dominate the composite FFLs, whose major functions are folding, sorting, and degradation. Given that the mutated CFTR gene disrupts the function of the chloride channel, the constructed FFLs address mechanistic aspects of the disease and, among 48 repurposing drug candidates, 26 were confirmed with literature reports and/or existing clinical trials relevant to the treatment of CF patients.

CONCLUSION

The construction of FFLs identified promising drug repurposing candidates for CF and the developed strategy may be applied to other diseases as well.

Pharmacological Approaches to Correcting the Ion Transport Defect in Cystic Fibrosis

Cystic fibrosis (CF) is a lethal genetic disease caused by a mutation in a membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), which mainly (but not exclusively) functions as a chloride channel. The main clinical symptoms are chronic obstructive lung disease, which is responsible for most of the morbidity and mortality associated with CF, and pancreatic insufficiency. About 1000 mutations of the gene coding for CFTR are currently known; the most common of these, present in the great majority of the patients (Delta508) results in the deletion of a phenylalanine at position 508. In this mutation, the aberrant CFTR is not transported to the membrane but degraded in the ubiquitin-proteasome pathway. The aim of this review is to give an overview of the pharmacologic strategies currently used in attempts to overcome the ion transport defect in CF. One strategy to develop pharmacologic treatment for CF is to inhibit the breakdown of DeltaF508-CFTR by interfering with the chaperones involved in the folding of CFTR. At least in in vitro systems, this can be accomplished by sodium phenylbutyrate, or S-nitrosoglutathione (GSNO), and also by genistein or benzo[c]quinolizinium compounds. It is also possible to stimulate CFTR or its mutated forms, when present in the plasma membrane, using xanthines, genistein, and various other compounds, such as benzamidizoles and benzoxazoles, benzo[c]quinolizinium compounds or phenantrolines. Experimental results are not always unambiguous, and adverse effects have been incompletely tested. Some clinical tests have been done on sodium phenyl butyrate, GSNO and genistein, mostly in respect to other diseases, and the results demonstrate that these drugs are reasonably well tolerated. Their efficiency in the treatment of CF has not yet been demonstrated, however. An alternative strategy is to compensate for the defective chloride transport by CFTR by stimulation of other chloride channels. This can be done via purinergic receptors. A phase I study using a stable uridine triphosphate analog has recently been completed. A second alternative strategy is to attempt to maintain hydration of the airway mucus by inhibiting Na(+) uptake by the epithelial Na(+) channel using amiloride or stable analogs of amiloride. Clinical tests so far have been inconclusive. A number of other suggestions are currently being explored. The minority of patients with CF who have a stop mutation may benefit from treatment with gentamicin. The difficulties in finding a pharmacologic treatment for CF may be due to the fact that CFTR has additional functions besides chloride transport, and interfering with CFTR biosynthesis or activation implies interference with central cellular processes, which may have undesirable adverse effects.

Inhaled chemotherapy in lung cancer: future concept of nanomedicine

Regional chemotherapy was first used for lung cancer 30 years ago. Since then, new methods of drug delivery and pharmaceuticals have been investigated in vitro, and in animals and humans. An extensive review of drug delivery systems, pharmaceuticals, patient monitoring, methods of enhancing inhaled drug deposition, safety and efficacy, and also additional applications of inhaled chemotherapy and its advantages and disadvantages are presented. Regional chemotherapy to the lung parenchyma for lung cancer is feasible and efficient. Safety depends on the chemotherapy agent delivered to the lungs and is dose-dependent and time-dependent. Further evaluation is needed to provide data regarding early lung cancer stages, and whether regional chemotherapy can be used as neoadjuvant or adjuvant treatment. Finally, inhaled chemotherapy could one day be administered at home with fewer systemic adverse effects.

Impact of polymorphism of Multidrug Resistance-associated Protein 1 (ABCC1) gene on the severity of cystic fibrosis

A 5'FR/G-260C (NCBI reference: 010393.16:g.15983174C>G) functional polymorphism of Multidrug Resistance-associated Protein 1 (ABCC1) promoter has been reported which influences ABCC1 expression including inflammatory related events. We aimed at investigating the impact of this polymorphism on the severity of CF disease. In this multicentric study, key clinical features of 203 CF patients homozygous for the F508del mutation were recorded. Kaplan-Meier analysis showed that patients with the rare CC genotype were chronically colonized by PA around 6 years earlier (mean ± SD: 11.2 year ± 7.8, 95% CI for the mean: 5.7-16.8) than those with the GG or the CG alleles (p<=0.01) and a FEV1 <60% predicted was first observed earlier in this group (p<0.05). Concordant trends to better nutritional status and FEV1 were observed in the slightly older GG subgroup. The potential role of ABCC1 promoter as a modifier gene deserves further study.

Mechanisms of action and clinical application of macrolides as immunomodulatory medications

Macrolides have diverse biological activities and an ability to modulate inflammation and immunity in eukaryotes without affecting homeostatic immunity. These properties have led to their long-term use in treating neutrophil-dominated inflammation in diffuse panbronchiolitis, bronchiectasis, rhinosinusitis, and cystic fibrosis. These immunomodulatory activities appear to be polymodal, but evidence suggests that many of these effects are due to inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and nuclear factor kappa B (NF-kappaB) activation. Macrolides accumulate within cells, suggesting that they may associate with receptors or carriers responsible for the regulation of cell cycle and immunity. A concern is that long-term use of macrolides increases the emergence of antimicrobial resistance. Nonantimicrobial macrolides are now in development as potential immunomodulatory therapies.

Drug transporters in the lung--do they play a role in the biopharmaceutics of inhaled drugs?

The role of transporters in drug absorption, distribution and elimination processes as well as in drug-drug interactions is increasingly being recognised. Although the lungs express high levels of both efflux and uptake drug transporters, little is known of the implications for the biopharmaceutics of inhaled drugs. The current knowledge of the expression, localisation and functionality of drug transporters in the pulmonary tissue and the few studies that have looked at their impact on pulmonary drug absorption is extensively reviewed. The emphasis is on transporters most likely to affect the disposition of inhaled drugs: (1) the ATP-binding cassette (ABC) superfamily which includes the efflux pumps P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs), breast cancer resistance protein (BCRP) and (2) the solute-linked carrier (SLC and SLCO) superfamily to which belong the organic cation transporter (OCT) family, the peptide transporter (PEPT) family, the organic anion transporter (OAT) family and the organic anion transporting polypeptide (OATP) family. Whenever available, expression and localisation in the intact human tissue are compared with those in animal lungs and respiratory epithelial cell models in vitro. The influence of lung diseases or exogenous agents on transporter expression is also mentioned.

[Usefulness of macrolides as anti-inflammatories in respiratory diseases]

The macrolides are antibiotics that, besides their anti-bacterial action, have an anti-inflammatory effect, by decreasing the activity of the immune cells and bacteria cell changes. An increase the survival of patients suffering from diffuse panbronchiolitis was already seen in the 1980s, after being treated with erythromycin. Currently, the use of macrolides in various chronic inflammatory diseases has increased significantly. Clinical improvements associated to the administration of macrolides have been observed in diseases such as, cystic fibrosis, asthma, and bronchiectasis. However, despite the apparent clinical benefit they seem to provide, the published results up until now are controversial and conclusive results are unable to be obtained. This means that further clinical trials are necessary to confirm or refute the long-term use of these drugs, which are not free of adverse effects, mainly the appearance of resistant bacteria.

Azithromycin increases chloride efflux from cystic fibrosis airway epithelial cells

It was investigated whether azithromycin (AZM) stimulates chloride (Cl-) efflux from cystic fibrosis (CF) and non-CF airway epithelial cells, possibly secondary to up-regulation of the multidrug resistance protein (MDR). CF and non-CF human airway epithelial cell lines (CFBE and 16HBE) were treated with 0.4, 4, and 40 microg/mL AZM for 4 days. Cl- efflux was explored in the presence or absence of specific inhibitors of CFTR and alternative Cl- channels. Six CF patients received AZM (500 mg daily) for 6 months. The percentage of predicted forced vital capacity (FVC%), forced expiratory volume (FEV1%), and the number of acute exacerbations were compared before and after treatment. Nasal biopsies were taken before and after treatment, and mRNA expression of MDR and CFTR was determined by in situ hybridization. A significant dose-dependent increase of Cl- efflux from CFBE cells (but not from 16HBE cells) was observed after AZM treatment. A CFTR inhibitor significantly reduced AZM-stimulated Cl- efflux from CFBE cells. A significant improvement in FEV1%, and fewer exacerbations were observed. AZM treatment did not affect mRNA expression of MDR and CFTR. The stimulation of Cl- efflux could be part of the explanation for the clinical improvement seen among the patients.

Effects of azithromycin on the expression of ATP binding cassette transporters in epithelial cells from the airways of cystic fibrosis patients

Induction of ATP Binding Cassette (ABC) proteins involved in chloride transport has been proposed as a possible mechanism of the beneficial effects of azithromycin (AZM) in cystic fibrosis (CF) patients. This study focused on the effects of AZM on mRNA and protein expression of Multidrug Resistance-associated Protein 1 (MRP1) and Multidrug Resistance Protein 1 (MDR1) by real-time quantitative PCR, flow cytometry and gene reporter assays in two CF and two isogenic non-CF airway epithelial cell lines. We detected higher levels of MRP1 and lower levels of MDR1 mRNA in CF versus non-CF cells while both proteins were not differentially expressed. After AZM treatment we found modest differences in MRP1 and MDR1 mRNA expression while protein levels were unaffected. The ability of AZM to regulate MRP1 promoter transcriptional activity was excluded by gene reporter assays. Our data do not support the hypothesis of induction of ABC transporters by AZM.

Immunomodulatory effects of macrolide antibiotics in respiratory disease: therapeutic implications for asthma and cystic fibrosis

The macrolide antibiotics are a family of related 14- or 15-membered lactone ring antibiotics. There has been recent interest in the beneficial effects of these drugs as immune modulators in respiratory conditions in children. Cystic fibrosis (CF) and asthma, both of which occur in childhood, have an underlying inflammatory component and are associated with significant morbidity. The pathogenesis of both conditions is poorly understood but several molecular mechanisms have been suggested. In CF, these mechanisms broadly involve altered chloride transport and alteration of the airway surface liquid with disordered neutrophilic inflammation. There is much evidence for a proinflammatory propensity in CF immune effector and epithelial cells and many studies indicate that macrolides modulate these inflammatory processes. Recent studies have confirmed a clinical improvement in CF following treatment with macrolides, but the exact mechanisms by which they work are unknown. Asthma is likely to represent several different phenotypes but in all of these, airway obstruction, bronchial hyperresponsiveness, and inflammation are central processes. Results from trials using macrolides have suggested an improvement in clinical outcome. The putative mechanisms of macrolide immunomodulatory action include improvement of the primary defense mechanisms, inhibition of the bacteria-epithelial cell interaction, modulation of the signaling pathway and chemokine release, and direct neutrophil effects. Putative mechanisms of phenotypic modulation have also been proposed involving interactions with nitric oxide, endothelin-1, and bronchoconstriction, endothelial growth factors and airway remodeling, and bioactive phospholipids in both CF and asthma. Further characterization of these effects and development of targeted designer drugs will further expand our therapeutic repertoire and lead to improved quality and quantity of life for patients with CF and asthma.

A new model of cystic fibrosis pathology: Lack of transport of glutathione and its thiocyanate conjugates

Many of the symptoms of cystic fibrosis are not explained by the current disease mechanisms. Therefore, the authors conducted an extensive literature review and present a new model of cystic fibrosis pathology, which is the culmination of this research. Understanding that the cystic fibrosis transmembrane conductance regulator (CFTR) is responsible for glutathione (GSH) transport, the authors hypothesize that mutations of the CFTR, which create abnormal GSH transport, will lead to aberrations of GSH levels in both the intracellular as well as the extracellular milieu. These alterations in normal cellular GSH levels affect the redox state of the cell, thereby affecting the intracellular stress protein, metallothionein. The authors describe how this disruption of the redox state caused by excess cellular GSH, will naturally prevent the delivery of zinc as a cofactor for various enzymatic processes, and how these disruptions in normal redox may cause alterations in both humoral and cell-mediated immunity. Moreover, the symptom of thick sticky mucus in these patients might be explained through the understanding that oversulfation of mucus is a direct result of elevated cellular GSH and cysteine. The issues of hyperinflammation, altered pH and the imbalance of fatty acids that are typical in cystic fibrosis are addressed-all of which may also be linked to disruptions in GSH homeostasis. Additionally, this new model of cystic fibrosis pathology, clarifies the relationship between the CFTR and the multi-drug resistance proteins, and the lack of cell-mediated immunity by predicting that the substrate of these proteins is a glutathione adduct of thiocyanate. Finally, a new therapeutic strategy by using isothiocyanates to rectify the GSH imbalance and restore the immune system is suggested for the treatment of cystic fibrosis patients.

Exploring the mechanisms of macrolides in cystic fibrosis

Several studies have reported clinical improvements in cystic fibrosis (CF) patients on macrolide antibiotics although the mechanism of action remains unclear. We conducted an open-label study of azithromycin (500 mg daily for 2 weeks) in 9 adult CF patients to explore 3 possible mechanisms: up-regulation of the multi-drug resistance (MDR) or cystic fibrosis transmembrane regulator (CFTR) proteins, correction of epithelial ion transport and reduced bacterial adherence. End-points included nasal potential difference (PD) measurements, nasal epithelial MDR and CFTR mRNA levels and Pseudomonas aeruginosa adherence to nasal epithelium. Forced expiratory volume in the 1st second (FEV(1)) increased significantly after 2 weeks of azithromycin (pre- 41.1 [5.0]%; post- 44.6 [5.8]%; P<0.05), although improvements in forced vital capacity (FVC) did not reach significance (pre- 61.3 [4.0]%; post- 67.1 [5.4]%, NS). Before treatment all subjects had nasal PD measurements characteristic of CF. Treatment led to no significant group differences in any measures of either sodium absorption or chloride secretion. Neither CFTR nor MDR mRNA levels had altered significantly and the adherence of P. aeruginosa did not decrease. We conclude that these are unlikely to be significant contributing mechanisms accounting for the consistent beneficial results observed in clinical trials of macrolides in CF.

The GCC repeat length in the 5'UTR of MRP1 gene is polymorphic: a functional characterization of its relevance for cystic fibrosis

Background

Among the members of the ATP binding cassette transporter superfamily, MRPs share the closest homology with the CFTR protein, which is defective in CF disease. MRP1 has been proposed as a potential modifier gene and/or as novel target for pharmacotherapy of CF to explain the clinical benefits observed in some CF patients treated with the macrolide AZM. The 5'UTR of the MRP1 gene contains a GCC triplet repeat that could represent a polymorphic site and affect the activity of the promoter.

Methods

The MRP1 5' flanking region was amplified by PCR from 36 CF patients and 100 non-CF subjects and the number of GCC triplets of each allele was determined by sequence and electrophoretic analysis. We performed gene reporter studies in CF airway epithelial cells 16HBE14o-AS3, in basal conditions and in the presence of AZM.

Results

We found that the GCC repeat is polymorphic, ranging from 7 to 14 triplets either in CF or in non-CF subjects. Our data are preliminary and have to be confirmed on a larger population of CF subjects. The transcriptional activity of the proximal MRP1 5' regulatory region revealed no statistically significant correlations between the number of repeats and treatment with AZM.

Conclusion

We identified a novel polymorphism in the 5'UTR of MRP1 gene that provides multiple alleles in a gene relevant for multidrug resistance as well as for CF, determining that this region is transcriptionally active and that this activity does not appear to be influenced by AZM treatment.

P-glycoprotein expression increases ATP release in respiratory cystic fibrosis cells

P-glycoprotein (Pgp) is a well-defined ATP-binding cassette (ABC) protein and a close relative of cystic fibrosis transmembrane conductance regulator (CFTR), whose dysfunction causes cystic fibrosis (CF). It is postulated that Pgp can complement deficient CFTR functions because of structural and functional homologies. One of the most relevant functions appears to be the regulation of ATP release, which influences mucociliary clearance in respiratory epithelia by nucleotide receptor stimulation. However, mechanisms involved in ATP secretion remain a controversial issue. In the present study, CF epithelial cells (sigmaCFTE29ó) were transduced with the retroviral vector MP1m encoding Pgp, and thus, a stable Pgp-overexpressing CF cell line (sigmaCFTE29óPgp) was established and used for studies of hypothesized CFTR complementation. In addition, overexpression of native Pgp in sigmaCFTE29ó could also be achieved by long-term treatment with colchicine, a drug, which may be of great interest in CF therapy. We confirmed that overexpression of Pgp causes a significant increase in cellular ATP release, which could even be enhanced by stimulation with hypoosmolar medium. A potential clinical benefit is discussed.

Arsenite Regulates Cystic Fibrosis Transmem­brane Conductance Regulator and P-glycoprotein: Evidence of Pathway Independence

In the past, people have argued for and against the theory of reciprocal regulation of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) and P-glycoprotein (Pgp). Data have indicated that this may occur in vitro during drug-induced selection of cells, and in vivo during development. Much of this debate has been caused by a severe lack of mechanistic details involved in such regulation. Our past data indicate that certain Pgp modulators can affect CFTR expression and function. The goal of this study was to investigate the effects of trivalent arsenic (arsenite), a known transcriptional activator of Pgp, on CFTR expression. In vitro analyses in T-84 cells that express basal levels of Pgp and CFTR were conducted using a variety of molecular techniques. Expressions of both genes were altered following treatment with arsenite in a dose- and time-dependent fashion. CFTR expression was suppressed almost three-fold by arsenite, along with a concomitant increase in P-glycoprotein expression. We also report that a member of the MAPK-family, the ERK-mediated signaling cascade is implicated in suppression of CFTR expression following treatment with arsenite. However, this particular pathway is not involved in regulation of P-glycoprotein expression in T-84 cells following treatment with arsenite. Thus, the regulatory pathways that control functional expression of CFTR and P-glycoprotein following arsenite treatment in T-84 cells are distinct and independent.

Long-term azithromycin in cystic fibrosis: another possible mechanism of action?

Azithromycin is used for the treatment of cystic fibrosis lung disease, although its mechanisms of action are not completely understood. Besides its antiinflammatory and antimicrobial activities, one possibility could be the overexpression induction of the multidrug resistance-associated protein (MRP), which could affect chloride transport, thus overcoming the ion transport defect of cystic fibrosis. Seven patients were evaluated before and after 4 weeks of azithromycin treatment (500 mg once daily). Ion transport was studied in vivo by measuring nasal potential difference (NPD). MRP mRNA expression was studied in nasal cells by an internal standard-based semiquantitative RT-PCR assay. NPD was consistent with cystic fibrosis before treatment. After azithromycin treatment, sodium transport was still impaired, whereas a significant increase in chloride conductance was observed (p = 0.03). A significant direct correlation was found between MRP mRNA expression levels and NPD chloride response after azithromycin treatment (p = 0.04, r = 0.78). In conclusion, azithromycin may induce MRP overexpression and restore chloride conductance in the airways of cystic fibrosis patients. These findings suggest a new potential role of azithromycin in the treatment of cystic fibrosis pulmonary disease, i.e. the possibility to upregulate proteins whose function may, at least in part, compensate for the basic defect of cystic fibrosis.

Ionic currents in multidrug resistant K562 human leukemic cells

In this study, the expression and functional characterization of currents through the CFTR (cystic fibrosis transmembrane regulator) and ORCC (outwardly rectifying chloride channels) were determined in wild-type K562 chronic human leukemia cells (K562-WT) and in its resistant counterpart, the vincristine resistant cell line (K562-Vinc). Expression of the CFTR and MDR1 (multidrug resistant) gene products was determined by a semi-quantitative RT-PCR protocol. The amplified products in K562-WT and K562-Vinc showed two bands corresponding to CFTR and MDR1. MDR1 mRNA increased by 20-fold in K562-Vinc whereas no change in CFTR mRNA levels was observed. CFTR and ORCC channel activity were measured with a whole cell configuration of the patch clamp technique. Forskolin (40 microM n activator of adenylate cyclase, added to the extracellular side increased the current in both cell lines. A fraction of the activated whole cell currents was inhibited by 500 microM 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS) and subsequent addition of 500 microM diphenylamine-2-carboxylate (DPC plus DIDS) further inhibited the remaining currents. The levels of forskolin-activated currents and subsequent blockade were similar in both cell lines. The effect of forskolin was prevented in cells previously exposed to 500 microM DPC. The effects of DIDS and DPC on the forskolin-activated whole cell currents support the idea that both CFTR and ORCC are generating a significant fraction of these currents with DIDS inhibiting ORCC currents and DPC inhibiting CFTR currents when the blockers are added one after another to the extracellular side. Finally, we show that exposure of K562 cells to vincristine which results in the over expression of MDR1 is not accompanied by a significant down regulation of CFTR as in other cells.

Increased chloride efflux in colchicine-resistant airway epithelial cell lines

Colchicine has been proposed as a treatment to alleviate chronic lung inflammation in cystic fibrosis patients and clinical trials are ongoing. Our aim was to investigate whether chronic exposure of cystic fibrosis cells to colchicine can affect their ability to transport chloride in response to cAMP. Colchicine-resistant cells were selected by growing in medium containing nanomolar concentrations of the drug. While microtubuli were affected by acute exposure to colchicine, they appeared normal in colchicine-resistant cells. Colchicine-resistant clones had higher expression of multidrug resistance proteins compared to untreated cells. Cystic fibrosis transmembrane conductance regulator (CFTR) labelling by immunocytochemistry showed no significant changes. The intracellular chloride concentration and basal chloride efflux of the cystic fibrosis treated cells increased significantly compared with untreated cells, while for the cAMP-stimulated Cl-efflux there was no significant change. The results suggest that colchicine promotes chloride efflux via alternative chloride channels. Since this is an accepted strategy for pharmacological treatment of cystic fibrosis, the results strengthen the notion that colchicine would be beneficial to these patients.

Evaluation of MRP1-5 gene expression in cystic fibrosis patients homozygous for the delta F508 mutation

Cystic fibrosis (CF), due to mutations of the cystic fibrosis transmembrane conductance regulator (CFTR), exhibits a wide range of disease severity, even among deltaF508 homozygous patients, and the mechanisms of this variability have yet to be elucidated. In view of the close structural homology and possible functional overlap between CFTR and Multidrug Resistance-associated Proteins (MRPs), MRPs were investigated as potentially relevant factors in CF pathophysiology. MRP1-5 gene expression was analyzed in nasal respiratory epithelial cells from deltaF508 homozygous patients (n = 19) and control subjects (n = 20) using semiquantitative RT-PCR. Significantly lower MRP1 and MRP5 transcript levels were found in CF patients than in control subjects. MRP1 and MRP5 transcript levels were strongly correlated (r = 0.71). In CF patients, low MRP1 transcript levels were associated with more severe disease as assessed by the Shwachman score. A relation was also observed between MRP1 levels and presence of a cAMP-independent chloride conductive pathway, as determined by a halide-sensitive fluorescent assay. These results suggest that MRPs, especially MRP1, might play a role in CF phenotype and might therefore constitute a target for a novel pharmacotherapy of CF.

Potential role of macrolide antibiotics in the management of cystic fibrosis lung disease

Current management of cystic fibrosis (CF) lung disease includes the use of antibiotics, nutritional support, and airway clearance therapies. However, despite recent advances in pharmacologic therapies including DNase and aerosolized tobramycin, deterioration in lung function persists. Recent investigations have shed new light on the pathogenic mechanisms by which establishes itself within the airways of patients with CF and contributes to the progressive decline in lung function. In particular, the presence of biofilms and other virulence mechanisms allow evasion of local host defenses and establishment of a chronic localized inflammatory response resulting in lung damage. Macrolide antibiotics appear to have a promising role in the management of CF lung disease even though they do not exhibit intrinsic antipseudomonal activity. Recent evidence demonstrates that they can disrupt quorum sensing, a cell-to-cell signaling process linked to the formation of biofilms. In addition, they inhibit NF-kappab and AP-1, nuclear factors that control the expression of proinflammatory cytokines. Their ability to decrease sputum viscosity and increase sputum clearance may complement existing airway clearance therapies. Preliminary clinical trials have shown modest improvement in pulmonary function.

Therapy with macrolides in patients with cystic fibrosis

Cystic fibrosis affects 1/2500 individuals and is the most common lethal autosomal recessive disease in people of northern European descent. It is characterized by chronic infections with mucoid Pseudomonas aeruginosa and progressive deterioration of respiratory function. Much research has focused on the inflammatory component of the disease. Macrolide antibiotics are postulated to suppress inflammatory mediators and interfere with biofilm formation produced by P. aeruginosa. In vitro studies show promising results, and a limited number of human studies reported improvements in respiratory function with the drugs. Macrolide antibiotics are generally safe and well tolerated and may prove to be effective in patients with cystic fibrosis.

Increased functional cell surface expression of CFTR and DeltaF508-CFTR by the anthracycline doxorubicin

Cystic fibrosis (CF) is a disease that is caused by mutations within the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most common mutation, DeltaF508, accounts for 70% of all CF alleles and results in a protein that is defective in folding and trafficking to the cell surface. However, DeltaF508-CFTR is functional when properly localized. We report that a single, noncytotoxic dose of the anthracycline doxorubicin (Dox, 0.25 microM) significantly increased total cellular CFTR protein expression, cell surface CFTR protein expression, and CFTR-associated chloride secretion in cultured T84 epithelial cells. Dox treatment also increased DeltaF508-CFTR cell surface expression and DeltaF508-CFTR-associated chloride secretion in stably transfected Madin-Darby canine kidney cells. These results suggest that anthracycline analogs may be useful for the clinical treatment of CF.

CFTR, MDR1, and MRP1 immunolocalization in normal human nasal respiratory mucosa

CFTR (cystic fibrosis transmembrane conductance regulator), MDR1 (multidrug resistance), and MRP1 (multidrug resistance-associated protein), members of the ABC transporter superfamily, possess multiple functions, particularly Cl(-), anion, and glutathione conjugate transport and cell detoxification. They are also hypothesized to have a number of complementary functions. It is generally accepted that data obtained from nasal mucosa can be extrapolated to lower airway cell physiology. The aim of the present study was to investigate by immunohistochemistry the differential localization of CFTR, MDR1, and MRP1 in the normal mucosa of 10 human nasal turbinates. In ciliated epithelial cells, CFTR was inconstantly expressed at the apical cell surface, intense membranous labeling was observed for MDR1, and intense cytoplasmic labeling was observed for MRP1. In the glands, a higher level of expression was observed on serous cells, at the apical surface (for CFTR), on lateral membranes (for MDR1), and with an intracytoplasmic distribution (for MRP1). In conclusion, CFTR, MDR1 and MRP1 are expressed in the epithelium and glands of the nasal respiratory mucosa, but with different patterns of expression. These results suggest major roles for CFTR, MDR1, and MRP1 in serous glandular cells and a protective function for MDR1 and MRP1 in respiratory ciliated cells. (J Histochem Cytochem 48:1215-1222, 2000)

Nucleotide-binding domain 1 of cystic fibrosis transmembrane conductance regulator production of a suitable protein for structural studies

Cystic fibrosis is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). This protein belongs to the large ATP-binding cassette (ABC) family of transporters. Most patients with cystic fibrosis bear a mutation in the nucleotide-binding domain 1 (NBD1) of CFTR, which plays a key role in the activation of the channel function of CFTR. Determination of the three dimensional structure of NBD1 is essential to better understand its structure-function relationship, and relate it to the biological features of CFTR. In this paper, we report the first preparation of recombinant His-tagged NBD1, as a soluble, stable and isolated domain. The method avoids the use of renaturing processes or fusion constructs. ATPase activity assays show that the recombinant domain is functional. Using tryptophan intrinsic fluorescence, we point out that the local conformation, in the region of the most frequent mutation DeltaF508, could differ from that of the nucleotide-binding subunit of histidine permease, the only available ABC structure. We have undertaken three dimensional structure determination of NBD1, and the first two dimensional 15N-1H NMR spectra demonstrate that the domain is folded. The method should be applicable to the structural studies of NBD2 or of other NBDs from different ABC proteins of major biological interest, such as multidrug resistance protein 1 or multidrug resistance associated protein 1.

Improvement of cystic fibrosis using antitumoral drugs: a hypothesis

The improvement of cystic fibrosis using antitumoral drugs has been reported. The hypothesis of a somatic reduction to heterozygosity of the CFTR gene mutations by homologous recombination in lung epithelium is proposed.

ABC-ATPases, adaptable energy generators fuelling transmembrane movement of a variety of molecules in organisms from bacteria to humans

The approximately 27 kDa ABC-ATPase, an extraordinarily conserved, unique type of ATPase, acts as a machine to fuel the movement across membranes of almost any type of molecule, from large polypeptides to small ions, via many different membrane-spanning proteins. A particular ABC-ATPase must therefore be tailor-made to function in a complex with its cognate membrane protein, forming a transport pathway appropriate for a specific type of molecule, or in the case of some ABC-transporters, several types of molecule. Molecules to be transported recognise their own transporter, bind and switch on the ATPase, which in turn activates or opens the transport pathway. ABC-dependent transport can be inwards across the membrane, or outwards to the cell exterior, and the ABC-ATPase can fuel transport through pathways which may involve a classical channel (CFTR), a "gateway" mechanism through a proteinacious chamber spanning the bilayer, or conceivably via a pathway at the protein-lipid interface of the outside of the membrane domain. This may be the case for drugs transported by Pgp, a multidrug resistance transporter. In this review, we try to identify the common fundamental principles which unite all ABC-transporters, including the basis of specificity for different transported compounds (allocrites), the interactions between the ATPase and membrane domains, activation of the ATPase and the coupling of consequent conformational changes, to the final movement of an allocrite through a given transport pathway. We discuss the so far limited structural information for the intact ABC-transporter complex and the exciting information from the first crystal structure of an ABC-ATPase. Finally, the action of specific transporters, CFTR (Cl- transport), Pgp, MRP and LmrA, all transporting many different drug molecules and HlyB transporting a large protein toxin are discussed.

Substrates of multidrug resistance-associated proteins block the cystic fibrosis transmembrane conductance regulator chloride channel

1. The effects of physiological substrates of multidrug resistance-associated proteins (MRPs) on cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel currents were examined using patch clamp recording from CFTR-transfected mammalian cell lines. 2. Two MRP substrates, taurolithocholate-3-sulphate (TLCS) and beta-estradiol 17-(beta-D-glucuronide) (E217betaG) caused a voltage-dependent block of macroscopic CFTR Cl- currents when applied to the intracellular face of excised membrane patches, with mean apparent dissociation constants (KDs) of 96+/-10 and 563+/-103 microM (at 0 mV) respectively. The unconjugated bile salts taurocholate and cholate were also effective CFTR channel blockers under these conditions, with KDs of 453+/-44 and 3760+/-710 microM (at 0 mV) respectively. 3. Reducing the extracellular Cl- concentration from 154 to 20 mM decreased the KD for block intracellular TLCS to 54+/-1 microM, and also significantly reduced the voltage dependence of block, by suggesting that TLCS blocks Cl- permeation through CFTR by binding within the channel pore. 4. Intracellular TLCS reduced the apparent amplitude of CFTR single channel currents, suggesting that the duration of block is very fast compared to the gating of the channel. 5. The apparent affinity of block by TLCs is comparable to that of other well-known CFTR channel blockers, suggesting that MRP substrates may comprise a novel class of probes of the CFTR channel pore. 6. These results also suggest that the related proteins CFTR and MRP may share a structurally similar anion binding site at the cytoplasmic face of the membrane.

Inflammation and CFTR: might neutrophils be the key in cystic fibrosis?

The aim of this hypothesis is to provide new insights into the still unclear mechanisms governing airway inflammation in cystic fibrosis. Although the genetic basis of cystic fibrosis as well as the molecular structure of cystic fibrosis transmembrane regulator (CFTR), the mutated protein which causes the disease, have been well defined, a clear relationship between the genetic defect and the pulmonary pathophysiology, especially chronic infections and neutrophil-dominated airway inflammation has not been established. Cystic fibrosis is thus a unique pathological situation in that neutrophils can be depicted as both an antiinfectious and a proinflammatory cell. In cystic fibrosis there is an emerging picture of an imbalance between these two roles with both a reduction in the antiinfectious efficacy and an augmentation of the proinflammatory functions. Better knowledge of fundamental defects in neutrophil function in cystic fibrosis as well as a novel cellular function of CFTR, which will be reviewed, will allow identification of potentially new clinical targets and aid selective therapeutic action aimed at counteracting the lethal neutrophil-induced airway inflammation. The rationale for colchicine therapy is a significant example of a drug which might act both at the molecular levels on CFTR expression in epithelial cells and on neutrophils to mediate antiinflammatory effects. Preliminary results are presented in this issue (Med Inflamm 1999; 8: 13-15).

Interest of colchicine for the treatment of cystic fibrosis patients. Preliminary report

Cystic fibrosis (CF) lung disease is characterized by persistent inflammation. Antiinflammatory drugs, such as corticosteroids and ibuprofen, have proved to slow the decline of pulmonary function although their use is limited because of frequent adverse events. We hypothesized that colchicine could be an alternative treatment because of its antiinflammatory properties and upregulatory effect on cystic fibrosis transmembrane regulator (CFTR) closely related proteins. We herein present results obtained in an open study of eight CF children treated with colchicine for at least 6 months. Clinical status was better in all patients and respiratory function tests significantly improved in five. Median duration of antibiotherapy decreased significantly. These preliminary results support our hypothesis of a beneficial effect of colchicine in CF patients and stress the need for a controlled therapeutic trial.

[Mucoviscidosis: therapeutic strategies are multiplying]

Since the cloning of the defective gene in cystic fibrosis, much has been learned on the function of CFTR and on the mechanisms regulating its expression. Based on the current understanding of the processes involved in lung disease progression, a number of approaches have been developed using gene therapy and pharmacological agents. Several of these agents have been reported to restitute a function to CFTR with specific mutations. Other molecules act on channels other than CFTR, and may be effective by bypassing CFTR itself. In the present review the various therapeutical strategies currently investigated are discussed.

Therapies directed at the basic defect in cystic fibrosis

There are over 600 unique mutations in the cystic fibrosis (CF) gene that can be classified in five general categories with respect to specific defect. Through basic research into the genetic and physiologic consequences of these mutations, it has become possible to design genotype-specific therapeutic strategies. New pharmaceutical agents are under development for the rescue of defective cystic fibrosis transmembrane conductance regulator mRNA or protein. Some of these compounds are undergoing study in CF patients in Phase I clinical trials. This article evaluates the current research directed at translating a basic molecular understanding of the disease into innovative new treatments.

Glutathione permeability of CFTR

The cystic fibrosis transmembrane conductance regulator (CFTR) forms an ion channel that is permeable both to Cl- and to larger organic anions. Here we show, using macroscopic current recording from excised membrane patches, that the anionic antioxidant tripeptide glutathione is permeant in the CFTR channel. This permeability may account for the high concentrations of glutathione that have been measured in the surface fluid that coats airway epithelial cells. Furthermore, loss of this pathway for glutathione transport may contribute to the reduced levels of glutathione observed in airway surface fluid of cystic fibrosis patients, which has been suggested to contribute to the oxidative stress observed in the lung in cystic fibrosis. We suggest that release of glutathione into airway surface fluid may be a novel function of CFTR.

Adenosine triphosphate-dependent asymmetry of anion permeation in the cystic fibrosis transmembrane conductance regulator chloride channel

The cystic fibrosis transmembrane conductance regulator (CFTR) forms a tightly regulated channel that mediates the passive diffusion of Cl- ions. Here we show, using macroscopic current recording from excised membrane patches, that CFTR also shows significant, but highly asymmetrical, permeability to a broad range of large organic anions. Thus, all large organic anions tested were permeant when present in the intracellular solution under biionic conditions (PX/PCl = 0.048-0.25), whereas most were not measurably permeant when present in the extracellular solution. This asymmetry was not observed for smaller anions. ATPase inhibitors that "lock" CFTR channels in the open state (pyrophosphate, 5'-adenylylimidodiphosphate) disrupted the asymmetry of large anion permeation by allowing their influx from the extracellular solution, which suggests that ATP hydrolysis is required to maintain asymmetric permeability. The ability of CFTR to allow efflux of large organic anions represents a novel function of CFTR. Loss of this function may contribute to the pleiotropic symptoms seen in cystic fibrosis.