Gene therapy progress and prospects: cystic fibrosis

CFTR gene transfer to human cystic fibrosis pancreatic duct cells using a Sendai virus vector

Cystic fibrosis (CF) is a fatal inherited disease caused by the absence or dysfunction of the CF transmembrane conductance regulator (CFTR) Cl- channel. About 70% of CF patients are exocrine pancreatic insufficient due to failure of the pancreatic ducts to secrete a HCO3- -rich fluid. Our aim in this study was to investigate the potential of a recombinant Sendai virus (SeV) vector to introduce normal CFTR into human CF pancreatic duct (CFPAC-1) cells, and to assess the effect of CFTR gene transfer on the key transporters involved in HCO3- transport. Using polarized cultures of homozygous F508del CFPAC-1 cells as a model for the human CF pancreatic ductal epithelium we showed that SeV was an efficient gene transfer agent when applied to the apical membrane. The presence of functional CFTR was confirmed using iodide efflux assay. CFTR expression had no effect on cell growth, monolayer integrity, and mRNA levels for key transporters in the duct cell (pNBC, AE2, NHE2, NHE3, DRA, and PAT-1), but did upregulate the activity of apical Cl-/HCO3- and Na+/H+ exchangers (NHEs). In CFTR-corrected cells, apical Cl-/HCO3- exchange activity was further enhanced by cAMP, a key feature exhibited by normal pancreatic duct cells. The cAMP stimulated Cl-/HCO3- exchange was inhibited by dihydro-4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (H2-DIDS), but not by a specific CFTR inhibitor, CFTR(inh)-172. Our data show that SeV vector is a potential CFTR gene transfer agent for human pancreatic duct cells and that expression of CFTR in CF cells is associated with a restoration of Cl- and HCO3- transport at the apical membrane.

What have we learned from mouse models for cystic fibrosis?

Genetically modified mouse strains are important research tools for the study of numerous human diseases. These models provide us with differentiated tissues, which are not often available from human sources. Furthermore, they allow for testing the effects of genetic manipulation and experimental therapeutics on physiology and pathology. Their importance relies on the assumption that biological processes in the mouse very closely resemble those in humans. Cystic fibrosis (CF) is the most common lethal genetic disease in the Caucasian population. CF is a monogenic disease whose phenotype variability is also attributed to genetic variation in other genes, the so-called modifier genes. Modulation of such modifier genes could be a therapeutic strategy to treat CF. CF mice models have been essential not only for understanding the disease better, but also for the discovery of modifier genes and testing of chemical compounds developed to repair the main protein dysfunction in CF, the CF transmembrane conductance regulator. Mice were also indispensable in gene therapy trials and for the study of CF and non-CF lung response to bacterial infections and inflammation challenges, although no spontaneous lung disease is developed in these mice. In this review, mouse models and their most important contribution to the understanding and management of CF will be presented and discussed.

New pulmonary therapies for cystic fibrosis

PURPOSE OF REVIEW

Improved knowledge of the molecular mechanisms underlying cystic fibrosis has led to a wide spectrum of new treatment approaches. This review addresses recent therapeutic strategies that either target the underlying defect or early steps in cystic fibrosis pathophysiology.

RECENT FINDINGS

While gene therapy does not appear to be a therapeutic option in the near future, cystic fibrosis transmembrane regulator pharmacotherapy is currently being developed as an alternative to reduce cystic fibrosis transmembrane regulator degradation or improve its function. Two drugs that increase chloride secretion via an alternative chloride channel, Moli1901 and denufosol, have been shown to be safe in clinical studies that also suggested clinical efficacy. Osmotic therapy may be an alternative approach to increase airway surface liquid and is being studied as an early intervention strategy.

SUMMARY

The spectrum of treatments for cystic fibrosis lung disease is rapidly increasing. While clinical efficacy for most of the compounds still has to be proven in large clinical trials, there is considerable hope that cystic fibrosis therapy will move from addressing the downstream sequelae of the cystic fibrosis transmembrane regulator defect to a more causal approach in the near future.

A receptor-binding-based bioassay to determine the potency of a plasmid biopharmaceutical encoding VEGF-C

Over the last decade biological assays (bioassays) have gained much importance for quality control in biopharmaceutical development and manufacturing. Here we describe the development and validation of a bioassay to determine the biological activity (potency) of the plasmid biopharmaceutical pVGI.1 which encodes the VEGF-C (VEGF-2) protein. This assay was developed to test drug substance and drug product for release and stability testing for phase I and II clinical trials. The main focus was on fast assay development and easy handling of the assay, combined with valid results representing the specific therapeutic mechanism. The method includes the expression of the VEGF-C protein in mammalian cells and its binding to the cell surface receptor VEGFR-3. The binding activity of VEGF-C to its immobilized receptor is quantified in a colorimetric assay. IC50 values of VEGF-C expressed after transfection with sample plasmid and an in-house standard plasmid are determined. The ratio of the IC50 value of the test article to that of the reference standard reflects the potency of the sample. The potency assay meets the criteria generally requested by authorities for precision, linearity, accuracy, and range. Therefore the assay can be used in pharmaceutical quality control and is a suitable basis for development of related bioassays.

Lentivirus vector-mediated gene transfer to the developing bronchiolar airway epithelium in the fetal lamb

BACKGROUND

Development of effective and durable gene therapy for treatment of the respiratory manifestations of cystic fibrosis remains a formidable challenge. Obstacles include difficulty in achieving efficient gene transfer to mature airway epithelium and the need to stably transduce self-renewing epithelial progenitor cells in order to avoid loss of transgene expression through epithelial turnover. Targeting the developing airway epithelium during fetal life offers the prospect of circumventing these challenges.

METHODS

In the current study we investigated vesicular stomatitis virus glycoprotein (VSVg)-pseudotyped HIV-1-derived lentivirus vector-mediated gene transfer to the airway epithelium of mid-gestation fetal lambs, both in vitro and in vivo. In the in vitro studies epithelial sheet explants and lung organ culture were used to examine transduction of the proximal and more distal airway epithelium, respectively. For the in vivo studies, vector was delivered directly into the proximal airway.

RESULTS

We found that even during the early pseudoglandular and canalicular phases of lung development, occurring through mid-gestation, the proximal bronchial airway epithelium was relatively mature and highly resistant to lentivirus-mediated transduction. In contrast, the more distal bronchiolar airway epithelium was relatively permissive for transduction although the absolute levels achieved remained low.

CONCLUSION

This result is promising as the bronchiolar airway epithelium is a major site of pathology in the cystic fibrosis airway, and much higher levels of transduction are likely to be achieved by developing strategies that increase the amount of vector reaching the more distal airway after intratracheal delivery.

Update on the treatment of primary immunodeficiencies

A general review of advances in the treatment of Primary Immunodeficiencies (PID) has been performed. Treatment with immunoglobulins is indicated in cases of humoral immunodeficiencies and in selected cases of combined immunodeficiencies. The use of intramuscular immunoglobulins in the treatment of PID was abandoned after obtaining the intravenous immunoglobulins, since these are much more effective and have fewer adverse effects. Now subcutaneous immunoglobulins are also available. Immunoglobulins help to keep the patients free of symptoms and infections as these substances are able to neutralise infectious agents, modulate and promote the immune response and favour phagocytosis. Adverse effects have been reported in 5-15 % of patients receiving IVIg, and patients with deficiencies of subclasses of IgG with IgA deficiency and/or anti-IgA antibodies are at risk of severe reactions. No severe adverse effects of subcutaneous immuneglobulins have been reported and the medication can be self-administered. The efficacy and safety of IVIg and SCIg are similar and SCIg administered at home is associated with better quality of life. Stem Cell Transplantation (SCT) in Primary Immunodeficiencies is aimed at restoring the number and/or function of lymphocytes or phagocytes. Matched, related or unrelated donors, or related haploidentical donors are selected. HLA class II mismatched unrelated donors are avoided owing to the risk of severe graft versus host disease (GVHD). Stem cells are obtained from bone marrow, cord blood or peripheral blood. Prophylactic immunossupression (as well as donor T lymphocyte depletion in haploidentical and unrelated donors) is performed to avoid or minimize GVHD. Less toxic "reduced intensity" protocols now exist for pre-transplantation conditioning, indicated to avoid graft rejection if there is residual T-lymphocyte immunity in the host. In the majority of Severe Combined Immunodeficiencies (SCID), SCT results in T lymphocytes graft and the antibody immunodeficiency persists in many cases. The results are better the earlier it is performed, with the absence of previous infections, and with the degree of matching. The patient must be maintained in a laminar flow room with broad anti-infectious prophylaxis and with the intravenous administration of gammaglobulin for a variable period. Many other complications can be expected. Gene therapy. Patients with PID are ideal candidates, as they are monogenic, the haematopoietic cells are easily obtained and virus replication is easy within them. Vectors (viruses) "infect" the stem cells of the patient's bone marrow, producing the transfection of the wild (healthy) gene in these cells. Encouraging results have been achieved in X-linked SCID as there are a number of patients who are considered "cured", although neoplastic processes have occurred due to the activation of proto-oncogenes close to the point of insertion of the external gene, using retroviruses as vectors; there are now trials with adenovirus, physical methods (direct injection...) and chemical methods (viral modification, artificial viruses...). Gene therapy has also been performed in patients with Chronic Granulomatous Disease and trials will improve in the future with changes in protocols used in oncology and infectious diseases.

Repeated Aerosolized AAV-CFTR for Treatment of Cystic Fibrosis: A Randomized Placebo-Controlled Phase 2B Trial

Previous studies have demonstrated that delivery of a recombinant adeno-associated virus (AAV) vector encoding the complete human cystic fibrosis transmembrane regulator (CFTR) cDNA (tgAAVCF) to the nose, sinus, and lungs of subjects with cystic fibrosis (CF) was safe and well tolerated. In a small randomized, double-blind study of three doses of aerosolized tgAAVCF or placebo at 30-day intervals, encouraging but non-significant trends in pulmonary function and induced sputum interleukin 8 (IL-8) levels were seen at early time points. This larger study was conducted to verify these trends. One hundred and two subjects aged 12 years and older with mild-to-moderate cystic fibrosis (forced expiratory flow in 1 sec [FEV1]:60% predicted) were randomized to two aerosolized doses of 1x10(13)DNase-resistant particles of tgAAVCF (n=51) or matching placebo (n=51) administered 30 days apart. Although tgAAVCF was well tolerated, the study did not meet its primary efficacy end point of statistically significant improvement in FEV1 30 days after initial administration of tgAAVCF compared with placebo. There were no significant differences in spirometric lung function over time, induced sputum biologic markers, or days of antibiotic use in either treatment group. Thus repeated doses of aerosolized tgAAVCF were safe and well tolerated, but did not result in significant improvement in lung function over time. Because gene transfer is the simplest, most basic way to correct the underlying genetic defect that leads to disease in CF, further research is warranted to develop an effective gene transfer agent for the treatment of CF.

Cystic fibrosis transmembrane regulator protein mutations: 'class' opportunity for novel drug innovation

Cystic fibrosis (CF) is the most common autosomal, recessive, life-span shortening disease in Caucasians. Since discovery of the gene for CF (cystic fibrosis transmembrane conductance regulator [CFTR]) in 1989, knowledge of the molecular function of this gene and its interactions has offered new therapeutic targets. New therapeutics aimed at improving mutant CFTR protein function, also known as 'protein repair therapy,' have been proposed but are yet to be successful in clinical trials. Some of the most exciting efforts involve a new field known as small molecule discovery, which entails the identification, evaluation, and optimization of small organic compounds that can alter the function of a selected gene target or cell phenotype. More than 1300 CFTR mutations have been identified. Many of the more common mutations have been organized into five broad classes based on the fate of the mutant CFTR protein. In each of these mutation classes, interventions have been able to restore some level of CFTR function in vitro. While these 'repairs' have yet to be demonstrated clinically, some early clinical trials are underway. Questions regarding the amount of CFTR correction needed, delivery methods, and optimal therapeutic combinations, however, remain outstanding.

A novel environment-sensitive biodegradable polydisulfide with protonatable pendants for nucleic acid delivery

Clinical application of nucleic acid-based therapies is limited by the lack of safe and efficient delivery systems. The purpose of this study is to design and evaluate novel biodegradable polymeric carriers sensitive to environmental changes for efficient delivery of nucleic acids, including plasmid DNA and siRNA. A novel polydisulfide with protonatable pendants was synthesized by the oxidative polymerization of a dithiol monomer, which was readily prepared by solid phase chemistry. The polydisulfide exhibited good buffering capacity and low cytotoxicity. It formed stable complexes with both plasmid DNA and siRNA. The particle sizes of the complexes decreased with the increase of the N/P ratios in the range of 100 to 750 nm. The complexes were stable in the presence of salt and heparin under normal physiological conditions, but dissociated to release nucleic acids in a reductive environment similar to cytoplasm. The polydisulfide demonstrated N/P ratio dependent transfection efficiency for plasmid DNA and gene silencing efficiency for siRNA. The presence of an endosomal disrupting agent, chloroquine, did not affect the DNA transfection efficiency of the polydisulfide. The transfection or gene silencing efficiency of the polydisulfide/DNA or siRNA complexes was comparable to or slightly lower than that of corresponding PEI complexes. Moreover, the polydisulfide showed better serum-friendly feature than PEI when delivering either DNA or siRNA in the presence of 10% FBS. This novel polydisulfide is a promising lead for further design and development of safe and efficient delivery systems for nucleic acids.

Pseudomonas aeruginosaInfection Destroys the Barrier Function of Lung Epithelium and Enhances Polyplex-Mediated Transfection

Challenged by the lack of success of experimental gene therapy of cystic fibrosis, we set out to investigate one of the potential causes of this failure, the barrier function of the airway epithelium and the way this is affected by bacterial infection. In an in vitro model of the airway epithelium we determined the effect of Pseudomonas aeruginosa or Escherichia coli on the transfection efficiency of polyethylenimine (PEI)-plasmid DNA complexes, carrying a luciferase gene, as well as on the barrier function of the epithelial cell layer, using transepithelial resistance (TER), cytotoxicity, bacterial transmigration, and morphological appearance as parameters. The level of luciferase expression was more than one order of magnitude higher in the cells which, before transfection, were incubated with P. aeruginosa. TER was strongly reduced by P. aeruginosa, whereas E. coli had no effect. Pseudomonas aeruginosa also effectively destroyed the structure of the tight junctions, as visualized by immunostaining of the zonula occludens. By the same token, small but significant numbers of P. aeruginosa cells were found to migrate through the epithelial layer, whereas no E. coli cells were observed at the transcompartment of the wells. Release of lactate dehydrogenase from the epithelial cells, a parameter of cell damage, occurred in a dose-dependent manner on incubation with P. aeruginosa, but not with E. coli. To evaluate the relevance of these results for the in vivo situation, we infected C57BL/6 mice with P. aeruginosa or E. coli 48 hr before transfecting them intratracheally with PEI-DNA polyplexes. Infection with P. aeruginosa caused a 5-fold increase in luciferase expression whereas infection with E. coli had no effect. Fluorescence microscopy of lung sections, after administration of fluorescein isothiocyanate-labeled polyplexes, showed that prior treatment with P. aeruginosa effectuated penetration of the complexes deeper into the epithelium than in untreated animals. In P. aeruginosa-treated animals fluorescence was detected not only in the airway epithelium itself but also in the parenchyma. We conclude that infection with P. aeruginosa causes disruption of the tight junctions between the cells and thus of the barrier function of the epithelium. As a consequence, PEI-DNA complexes injected intratracheally into infected animals gain access to the basolateral side of the cells and to spaces across the epithelial lining, giving rise to substantially increased transfection efficiency.

Molecular targeting of CFTR as a therapeutic approach to cystic fibrosis

One of the major challenges facing the pharmaceutical field is the identification of novel, 'druggable' targets common to distinct diseases that, despite their clinical diversity, share the same basic molecular defect(s) - thus, being termed 'horizontal diseases'. Membrane proteins constitute one of the largest families in the human genome and, given their major roles in cells and organisms, they are relevant to common human disorders such as cardiovascular disease and cancer, but also to rare genetic conditions such as cystic fibrosis (CF). Here, we review therapeutic approaches to correcting the basic defect in CF, which is caused mainly by the intracellular retention of a misfolded protein, and focus on various recent drug-discovery strategies for this important and paradigmatic disease. These strategies have possible applications in many membrane protein disorders, including other channelopathies. The mechanisms of action of potent and specific compounds, representing promising drug leads for CF pharmacotherapy, are explained and discussed.

Novel Therapies for the Treatment of Cystic Fibrosis: New Developments in Gene and Stem Cell Therapy

Cystic fibrosis (CF) was one of the first target diseases for lung gene therapy. Studies of lung gene transfer for CF have provided many insights into the necessary components of successful gene therapy for lung diseases. Many advancements have been achieved with promising results in vitro and in small animal models. However, studies in primate models and patients have been discouraging despite a large number of clinical trials. This reflects a number of obstacles to successful, sustained, and repeatable gene transfer in the lung. Cell-based therapy with embryonic stem cells and adult stem cells (bone marrow or cord blood), have been investigated recently and may provide a viable therapeutic approach in the future. In this article, the authors review CF pathophysiology with a focus on specific targets in the lung epithelium for gene transfer and summarize the current status and future directions of gene- and cell-based therapies.

Impact of deletion of envelope-related genes of recombinant Sendai viruses on immune responses following pulmonary gene transfer of neonatal mice

We demonstrated previously that the additive-type recombinant Sendai virus (rSeV) is highly efficient for use in pulmonary gene transfer; however, rSeV exhibits inflammatory responses. To overcome this problem, we tested newly developed non-transmissible constructs, namely, temperature-sensitive F-deleted vector, rSeV/dF (ts-rSeV/dF) and a rSeV with all the envelope-related genes deleted (rSeV/dFdMdHN), for pulmonary gene transfer in neonatal mice, by assessing their toxicity and immune responses. The gene expression in the lungs of neonatal ICR mice peaked on day 2, then gradually decreased until almost disappearing at 14 days after infection in all constructs. Loss of body weight and mortality rate, however, were dramatically improved in mice treated with SeV/dFdMdHN (mortality=0%, n=41) and ts-rSeV/dF (24.2%, n=33) compared with additive rSeV (70.7%, n=58). Although the deletion of envelope-related genes of SeV had a small impact on the production of antibody and cytotoxic T-lymphocyte activity in both adults and neonates, a dramatic reduction was found in the events related to innate responses, including the production of proinflammatory cytokines, particularly in the case of neonates. These results indicate that pulmonary gene transfer using SeV/dFdMdHN warrants further investigation for its possible use in developing safer therapeutics for neonatal lung diseases, including cystic fibrosis.