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

Discovery of Clinically Approved Agents That Promote Suppression of Cystic Fibrosis Transmembrane Conductance Regulator Nonsense Mutations

RATIONALE

Premature termination codons (PTCs) in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF). Several agents are known to suppress PTCs but are poorly efficacious or toxic.

OBJECTIVES

To determine whether there are clinically available agents that elicit translational readthrough and improve CFTR function sufficient to confer therapeutic benefit to patients with CF with PTCs.

METHODS

Two independent screens, firefly luciferase and CFTR-mediated transepithelial chloride conductance assay, were performed on a library of 1,600 clinically approved compounds using fisher rat thyroid cells stably transfected with stop codons. Select agents were further evaluated using secondary screening assays including short circuit current analysis on primary cells from patients with CF. In addition, the effect of CFTR modulators (ivacaftor) was tested in combination with the most efficacious agents.

MEASUREMENTS AND MAIN RESULTS

From the primary screen, 48 agents were selected as potentially active. Following confirmatory tests in the transepithelial chloride conductance assay and prioritizing agents based on favorable pharmacologic properties, eight agents were advanced for secondary screening. Ivacaftor significantly increased short circuit current following forskolin stimulation in cells treated with pyranoradine tetraphosphate, potassium p-aminobenzoate, and escin as compared with vehicle control. Escin, an herbal agent, consistently induced readthrough activity as demonstrated by enhanced CFTR expression and function in vitro.

CONCLUSIONS

Clinically approved drugs identified as potential readthrough agents, in combination with ivacaftor, may induce nonsense suppression to restore therapeutic levels of CFTR function. One or more agents may be suitable to advance to human testing.

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.

Traitement de l'inflammation bronchique dans la mucoviscidose

Cystic fibrosis airway inflammation is characterized by neutrophilic efflux and high levels of proinflammatory cytokines such as IL-8 and IL-6. Inhaled corticosteroids are widely used despite lack of evidence of efficacity. Despite evidence of efficacity of ibuprofen, many clinicians have chosen not to use this therapy because of concerns regarding potential side effects. Azithromycin has antiinflammatory properties and is effective in cystic fibrosis (CF) patients. Deoxyribonuclease (rhDNase) has been shown to improve lung function in patients with cystic fibrosis and may also have a positive effect on inflammation. Other antiinflammatory drugs are in the process of validation.

Colchicine today

Colchicine is used chiefly in the treatment of gout but is also valuable in other inflammatory diseases such as familial Mediterranean fever (FMF). Three proteins play pivotal roles in colchicine pharmacokinetics: the colchicine receptor, tubulin, which governs the plasma elimination half-life of the drug; intestinal and hepatic CYP3A4, which is key to the biotransformation of colchicine; and P-glycoprotein, a cell efflux pump that regulates the tissue distribution of colchicine, as well as its excretion via the biliary tract and kidneys. Pharmacokinetic studies have been performed using a radioimmunology assay to measure blood colchicine levels. Absorption after oral ingestion varies widely (from 24% to 88% of the dose), the volume of distribution is extremely large (7 l/kg), and binding to albumin is moderate. Colchicine is excreted chiefly through the liver and has an elimination half-life of 20-40 hours. With repeated doses of about 1mg/day, the steady-state is achieved within 8 days and concentrations range from 0.3 to 2.5 ng/ml. Studies of associations between pharmacokinetic parameters and pharmacodynamics show that effects are correlated, not to plasma levels, but to levels in leukocytes. Adverse events are not uncommon, most notably when colchicine is used in combination with drugs that interact with CYP3A4 and/or P-glycoprotein, thereby decreasing the renal and/or hepatic elimination of colchicine. Careful monitoring in this situation is effective in preventing the development of toxicity.

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.

Antiinflammatory Therapies for Cystic Fibrosis: Past, Present, and Future

Inflammation is a major component of the vicious cycle characterizing cystic fibrosis pulmonary disease. If untreated, this inflammatory process irreversibly damages the airways, leading to bronchiectasis and ultimately respiratory failure. Antiinflammatory drugs for cystic fibrosis lung disease appear to have beneficial effects on disease parameters. These agents include oral corticosteroids and ibuprofen, as well as azithromycin, which, in addition to its antimicrobial effects, also possesses antiinflammatory properties. Inhaled corticosteroids, colchicine, methotrexate, montelukast, pentoxifylline, nutritional supplements, and protease replacement have not had a significant impact on the disease. Therapy with oral corticosteroids, ibuprofen, and fish oil is limited by adverse effects. Azithromycin appears to be safe and effective, and is thus the most promising antiinflammatory therapy available for patients with cystic fibrosis. Pharmacologic therapy with antiinflammatory agents should be started early in the disease course, before extensive irreversible lung damage has occurred.

Effects of CFTR, interleukin-10, and Pseudomonas aeruginosa on gene expression profiles in a CF bronchial epithelial cell Line

Mutations in CFTR lead to a complex phenotype that includes increased susceptibility to Pseudomonas infections, a functional deficiency of IL-10, and an exaggerated proinflammatory cytokine response. We examined the effects of CFTR gene correction on the gene expression profile of a CF bronchial epithelial cell line (IB3-1) and determined which CF-related gene expression changes could be reversed by IL-10 expression. We performed microarray experiments to monitor the gene expression profile of three cell lines over a time course of exposure to Pseudomonas. At baseline, we identified 843 genes with statistically different levels of expression in CFTR-corrected (S9) cells compared to the IB3-1 line or the IL-10-expressing line. K-means clustering and functional group analysis revealed a primary up-regulation of ubiquitination enzymes and TNF pathway components and a primary down-regulation of protease inhibitors and protein glycosylation enzymes in CF. Key gene expression changes were confirmed by real-time RT-PCR. Massive reprogramming of gene expression occurred 3 h after Pseudomonas exposure. Changes specific to CF included exaggerated activation of cytokines, blunted activation of anti-proteases, and repression of protein glycosylation enzymes. In conclusion, the CFTR genotype changes the expression of multiple genes at baseline and in response to bacterial challenge, and only a subset of these changes is secondary to IL-10 deficiency.

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.

Low-dose methotrexate for advanced pulmonary disease in patients with cystic fibrosis

Inflammation is a hallmark in the pathogenesis of pulmonary destruction in cystic fibrosis (CF). There is no proven effective systemic anti-inflammatory treatment for CF patients with advanced pulmonary disease. Methotrexate (MTX) is known as an effective anti-inflammatory treatment in asthma and in juvenile rheumatoid arthritis. The question was: Is an improvement in pulmonary function achievable with low-dose MTX in patients with cystic fibrosis and advanced pulmonary disease.?

METHODS

We treated five CF patients with advanced pulmonary disease, who deteriorated in spite of intensive conventional therapy on an individual basis with low-dose MTX. FEV1% and immunoglobulin G (IgG) serum levels were followed from the year before to the year after starting with MTX.

RESULTS

In the year before starting with MTX, FEV1% decreased (median: 10% FEV1; range 9-15% FEV1; P<0.005) after starting with MTX, FEV1% increased (median: 9% FEV1; range: 2-15% FEV1; P<0.05). IgG changed (median: -2 g/l; range: 0.2 to -7.3 g/l) in the first year with MTX.

CONCLUSION

These preliminary data suggest a beneficial effect of MTX even in advanced pulmonary disease in CF patients and supports the need for a controlled prospective study.

Rethinking cystic fibrosis pathology: the critical role of abnormal reduced glutathione (GSH) transport caused by CFTR mutation

Though the cause of cystic fibrosis (CF) pathology is understood to be the mutation of the CFTR protein, it has been difficult to trace the exact mechanisms by which the pathology arises and progresses from the mutation. Recent research findings have noted that the CFTR channel is not only permeant to chloride anions, but other, larger organic anions, including reduced glutathione (GSH). This explains the longstanding finding of extracellular GSH deficit and dramatically reduced extracellular GSH:GSSG (glutathione disulfide) ratio found to be chronic and progressive in CF patients. Given the vital role of GSH as an antioxidant, a mucolytic, and a regulator of inflammation, immune response, and cell viability via its redox status in the human body, it is reasonable to hypothesize that this condition plays some role in the pathogenesis of CF. This hypothesis is advanced by comparing the literature on pathological phenomena associated with GSH deficiency to the literature documenting CF pathology, with striking similarities noted. Several puzzling hallmarks of CF pathology, including reduced exhaled NO, exaggerated inflammation with decreased immunocompetence, increased mucus viscoelasticity, and lack of appropriate apoptosis by infected epithelial cells, are better understood when abnormal GSH transport from epithelia (those without anion channels redundant to the CFTR at the apical surface) is added as an additional explanatory factor. Such epithelia should have normal levels of total glutathione (though perhaps with diminished GSH:GSSG ratio in the cytosol), but impaired GSH transport due to CFTR mutation should lead to progressive extracellular deficit of both total glutathione and GSH, and, hypothetically, GSH:GSSG ratio alteration or even total glutathione deficit in cells with redundant anion channels, such as leukocytes, lymphocytes, erythrocytes, and hepatocytes. Therapeutic implications, including alternative methods of GSH augmentation, are discussed.

Pharmacological treatment of the ion transport defect in cystic fibrosis

Cystic fibrosis (CF) is a lethal monogenetic disease characterised by impaired water and ion transport over epithelia. The lung pathology is fatal and causes death in 95% of CF patients. The genetic basis of the disease is a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-regulated chloride channel. The most common mutation, DeltaF508, results in a protein that cannot properly be folded in the endoplasmic reticulum, is destroyed and hence does not reach the apical cell membrane. This paper will discuss those pharmacological approaches that are directed at correcting the defect in ion transport. At present, no clinically effective drug is available, although research has defined areas in which progress might be made. These are the following: (1) the drug 4-phenylbutyrate (4PBA) increases the expression of DeltaF508-CFTR in the cell membrane, probably by breaking the association between DeltaF508-CFTR and a chaperone; (2) a number of xanthines, in particular 8-cyclopentyl-1, 3-dipropylxanthine (CPX), are effective in activating CFTR, presumably by direct binding and also possibly by correcting the trafficking defect; (3) the isoflavone genistein can activate both wild-type and mutant CFTR, probably through direct binding to the channel; (4) purinergic agonists (ATP and UTP) can stimulate chloride secretion via a Ca(2+)-dependent chloride channel and in this way compensate for the defect in CFTR, but stable analogues will be required before this type of treatment has clinical significance; (5) treatment with inhaled amiloride may correct the excessive absorption of Na(+) ions and water by airway epithelial cells that appears connected to the defect in CFTR; although clinical tests have not been very successful so far, amiloride analogues with a longer half-life may give better results. The role of CFTR in bicarbonate secretion has not yet been established with certainty, but correction of the defect in bicarbonate secretion may be important in clinical treatment of the disease. Currently, major efforts are directed at developing a pharmacological treatment of the ion transport defect in CF, but much basic research remains to be done, in particular, with regard to the mechanism by which defective CFTR is removed in the endoplasmic reticulum by the ubiquitin-proteasome pathway, which is a central pathway in protein production and of significance for several other diseases apart from CF.

Clinical and pharmacological experience with LJP-394

LJP-394 is a synthetic biological with immunomodulatory functions. Composed of four double-stranded oligodeoxynucleotides attached to a central branched platform, the drug acts as an anti-"anti-ds-DNA" B-cell toleragen by rendering specific B-lymphocytes unresponsive to immunogen so they do not produce autoantibodies. Extensive animal studies and Phase II clinical trials suggested that the effects of LJP-394 are effective and safe when used as a weekly dose of 100 mg intravenously. Analysis of a multicentre, international Phase II/III clinical trial showed that patients with lupus nephritis and high affinity IgG antibodies to LJP-394 have clinical benefits. This includes increased time to renal flares, reduced number of renal flares, time to institution of high-dose corticosteroids and/or cyclophosphamide and lower anti-ds-DNA levels. A definitive trial is in progress. LJP-394 appears to be free of serious adverse reactions. Though promising, the role of LJP-394 in patients with active, organ-threatening lupus is still not known.

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).