Functional evidence of CFTR gene transfer in nasal epithelium of cystic fibrosis mice in vivo following luminal application of DNA complexes targeted to the serpin-enzyme complex receptor

A Systematic Review of the Effect of Cystic Fibrosis Treatments on the Nasal Potential Difference Test in Animals and Humans

To address unmet treatment needs in cystic fibrosis (CF), preclinical and clinical studies are warranted. Because it directly reflects the function of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR), the nasal potential difference test (nPD) can not only be used as a reliable diagnostic test for CF but also to assess efficacy of experimental treatments. We performed a full comprehensive systematic review of the effect of CF treatments on the nPD compared to control conditions tested in separate groups of animal and human subjects. Our review followed a preregistered protocol. We included 34 references: 20 describing mouse studies, 12 describing human studies, and 2 describing both. We provide a comprehensive list of these studies, which assessed the effects of antibiotics, bone marrow transplant, CFTR protein, CFTR RNA, directly and indirectly CFTR-targeting drugs, non-viral and viral gene transfer, and other treatments. Our results support the nPD representing a reliable method for testing treatment effects in both animal models and human patients, as well as for diagnosing CF. However, we also observed the need for improved reporting to ensure reproducibility of the experiments and quantitative comparability of the results within and between species (e.g., with meta-analyses). Currently, data gaps warrant further primary studies.

Genetic Modification of the Lung Directed Toward Treatment of Human Disease

Genetic modification therapy is a promising therapeutic strategy for many diseases of the lung intractable to other treatments. Lung gene therapy has been the subject of numerous preclinical animal experiments and human clinical trials, for targets including genetic diseases such as cystic fibrosis and α1-antitrypsin deficiency, complex disorders such as asthma, allergy, and lung cancer, infections such as respiratory syncytial virus (RSV) and Pseudomonas, as well as pulmonary arterial hypertension, transplant rejection, and lung injury. A variety of viral and non-viral vectors have been employed to overcome the many physical barriers to gene transfer imposed by lung anatomy and natural defenses. Beyond the treatment of lung diseases, the lung has the potential to be used as a metabolic factory for generating proteins for delivery to the circulation for treatment of systemic diseases. Although much has been learned through a myriad of experiments about the development of genetic modification of the lung, more work is still needed to improve the delivery vehicles and to overcome challenges such as entry barriers, persistent expression, specific cell targeting, and circumventing host anti-vector responses.

DNA Nanotechnology for Precise Control over Drug Delivery and Gene Therapy

Nanomedicine has been growing exponentially due to its enhanced drug targeting and reduced drug toxicity. It uses the interactions where nanotechnological components and biological systems communicate with each other to facilitate the delivery performance. At this scale, the physiochemical properties of delivery systems strongly affect their capacities. Among current delivery systems, DNA nanotechnology shows many advantages because of its unprecedented engineering abilities. Through molecular recognition, DNA nanotechnology can be used to construct a variety of nanostructures with precisely controllable size, shape, and surface chemistry, which can be appreciated in the delivery process. In this review, different approaches that are currently used for the construction of DNA nanostructures are reported. Further, the utilization of these DNA nanostructures with the well-defined parameters for the precise control in drug delivery and gene therapy is discussed.

Nanocomplexes for gene therapy of respiratory diseases: Targeting and overcoming the mucus barrier

Gene therapy, i.e. the delivery and expression of therapeutic genes, holds great promise for congenital and acquired respiratory diseases. Non-viral vectors are less toxic and immunogenic than viral vectors, although they are characterized by lower efficiency. However, they have to overcome many barriers, including inflammatory and immune mediators and cells. The respiratory and airway epithelial cells, the main target of these vectors, are coated with a layer of mucus, which hampers the effective reaching of gene therapy vectors carrying either plasmid DNA or small interfering RNA. This barrier is thicker in many lung diseases, such as cystic fibrosis. This review summarizes the most important advancements in the field of non-viral vectors that have been achieved with the use of nanoparticulate (NP) systems, composed either of polymers or lipids, in the lung gene delivery. In particular, different strategies of targeting of respiratory and airway lung cells will be described. Then, we will focus on the two approaches that attempt to overcome the mucus barrier: coating of the nanoparticulate system with poly(ethylene glycol) and treatment with mucolytics. Our conclusions are: 1) Ligand and physical targeting can direct therapeutic gene expression in specific cell types in the respiratory tract; 2) Mucopenetrating NPs are endowed with promising features to be useful in treating respiratory diseases and should be now advanced in pre-clinical trials. Finally, we discuss the development of such polymer- and lipid-based NPs in the context of in vitro and in vivo disease models, such as lung cancer, as well as in clinical trials.

The effect and role of carbon atoms in poly(β-amino ester)s for DNA binding and gene delivery

Polymeric vectors for gene delivery are a promising alternative for clinical applications, as they are generally safer than viral counterparts. Our objective was to further our mechanistic understanding of polymer structure-function relationships to allow the rational design of new biomaterials. Utilizing poly(β-amino ester)s (PBAEs), we investigated polymer-DNA binding by systematically varying the polymer molecular weight, adding single carbons to the backbone and side chain of the monomers that constitute the polymers, and varying the type of polymer end group. We then sought to correlate how PBAE binding affects the polyplex diameter and ζ potential, the transfection efficacy, and its associated cytotoxicity in human breast and brain cancer cells in vitro. Among other trends, we observed in both cell lines that the PBAE-DNA binding constant is biphasic with the transfection efficacy and that the optimal values of the binding constant with respect to the transfection efficacy are in the range (1-6) × 10(4) M(-1). A binding constant in this range is necessary but not sufficient for effective transfection.

Current Status of Gene Therapy for Cystic Fibrosis Pulmonary Disease

Cystic fibrosis (CF) is a common lethal genetic disorder that affects all ethnic populations; however, it is most prevalent in Caucasians. Intensive basic research over the last 20 years has resulted in a wealth of information regarding the CF gene, its protein product and the mutational basis of disease. This increased understanding has lead to the development of gene therapy for the treatment of CF pulmonary disease. Delivery of the CF gene to the airway requires direct in vivo transfer using vectors encoding for normal CF transmembrane regulator (CFTR) protein. Several vectors are currently available for CF gene transfer and include both viral (adenoviruses, adeno-associated viruses) and non-viral (liposomal) systems. Initial clinical trials with each of these vectors have demonstrated that gene transfer to the CF airway is possible. The efficiency of transfer and duration of expression, however, have been limited. The effects of gene transfer on correction of the basic ion transport defects have also been highly variable and inconsistent, irrespective of the vector. Currently, the risk of severe immunological reactions is the primary factor limiting the clinical advancement of gene therapy. Both the adenoviral and liposomal vectors are associated with significant acute inflammatory reactions. The adenoviruses and adeno-associated viruses also elicit humoral immune responses that significantly reduce the efficiency of transgene expression and increase the risk of readministration. Several strategies are under investigation to improve the efficiency of gene transfer to the CF airway. These include overcoming local barriers in the lung, circumventing the immune response and improving vector internalization and/or uptake. Application of gene transfer in the child and possibly the fetus are also potential future clinical applications of gene therapy. However, despite considerable research with gene therapy, there is little evidence to suggest that a well tolerated and effective gene transfer method is imminent and aggressive use of conventional pharmacological therapies currently offer the greatest promise in the treatment of patients with CF.

Pulmonary gene delivery using polymeric nonviral vectors

Pulmonary delivery provides an easy and well tolerated means of access for the administration of biomacromolecules to the pulmonary epithelium and could therefore be an attractive approach for local and systemic therapies. A growing number of reports, which are summarized in this review, mirror the viability of pulmonary gene delivery. Special attention has been paid to the biological barriers in the lung that must be overcome for successful delivery, and which can be divided into anatomic, physical, immunologic, and metabolic barriers. In light of these barriers, successful nonviral polymer-based formulations of therapeutic genes are presented depending on the chemical nature of the polymer. In addition to polyethyleneimine-based nonviral vectors, which have been most intensively studied for pulmonary gene delivery in the past, other polymeric, dendritic, and targeted materials are also described here, including novel and biodegradable polymers. As new materials need in vitro or ex vivo testing before in vivo application, sophisticated models for all three approaches have been illustrated. Although pulmonary siRNA delivery enjoys popularity in clinical trials, pulmonary gene delivery has so far not been translated into clinical applications. With this review, potential hurdles are demonstrated, but novel approaches that may lead to optimized systems are described as well.

Nanoparticles for retinal gene therapy

Ocular gene therapy is becoming a well-established field. Viral gene therapies for the treatment of Leber's congentinal amaurosis (LCA) are in clinical trials, and many other gene therapy approaches are being rapidly developed for application to diverse ophthalmic pathologies. Of late, development of non-viral gene therapies has been an area of intense focus and one technology, polymer-compacted DNA nanoparticles, is especially promising. However, development of pharmaceutically and clinically viable therapeutics depends not only on having an effective and safe vector but also on a practical treatment strategy. Inherited retinal pathologies are caused by mutations in over 220 genes, some of which contain over 200 individual disease-causing mutations, which are individually very rare. This review will focus on both the progress and future of nanoparticles and also on what will be required to make them relevant ocular pharmaceutics.

Detection of CFTR transgene mRNA expression in respiratory epithelium isolated from the murine nasal cavity

BACKGROUND

When assessing the efficacy of gene transfer agents (GTAs) for cystic fibrosis (CF) gene therapy, we routinely evaluate gene transfer in the mouse nose and measure transfection efficiency by assessing transgene-specific mRNA using the real-time (TaqMan) quantitative reverse transcriptase-polymerase chain reaction. TaqMan is traditionally used to quantify expression in whole tissue homogenates, which in the nose would contain many cells types, including respiratory and olfactory epithelium. Only the respiratory epithelium is a satisfactory model for human airway epithelium and therefore CFTR gene transfer should be specifically assessed in respiratory epithelial cells (RECs).

METHODS

We have compared laser microdissection, pronase digestion and nasal brushing for: (i) the ability to enrich RECs from the wild-type mouse nose and (ii) the length of time to perform the procedure. Using TaqMan, we subsequently assessed gene transfer in enriched RECs after nasal perfusion of GL67A/pCF1-CFTR complexes in a CF mouse model.

RESULTS

Laser microdissection successfully isolated RECs; however, time-consuming sample preparation made this technique unsuitable for high-throughput studies. Pronase digestion was sufficiently rapid but only yielded 19% (range = 13%) RECs (n = 6). The nasal brushing method was superior, yielding 92% (range = 15%) RECs (n = 8) and was equally effective in CF knockout mice (91%, range = 14%, n = 10). Importantly, gene transfer was detectable in brushed RECs from 70% of perfused mice and the number of vector-specific transcripts was comparable to 3.5% of endogenous wild-type Cftr levels.

CONCLUSIONS

Isolation of RECs by brushing allows accurate assessment of GTA transfection efficiency in an experimental system that is relevant for CF gene therapy.

Cystic fibrosis: exploiting its genetic basis in the hunt for new therapies

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel expressed in epithelial cells throughout the body. In the lungs, absence or dysfunction of CFTR results in altered epithelial salt and water transport eventuating in impaired mucociliary clearance, chronic infection and inflammation, and tissue damage. CF lung disease is the major cause of morbidity and mortality in CF despite the many therapies aimed at reducing it. However, recent technological advances combined with two decades of research driven by the discovery of the CFTR gene have resulted in the development and clinical testing of novel therapies aimed at the principal underlying defect in CF, thereby ushering in a new age of therapy for CF.

Gene transfer to the lung: lessons learned from more than 2 decades of CF gene therapy

Gene therapy is currently being developed for a wide range of acute and chronic lung diseases. The target cells, and to a degree the extra and intra-cellular barriers, are disease-specific and over the past decade the gene therapy community has recognized that no one vector is good for all applications, but that the gene transfer agent (GTA) has to be carefully matched to the specific disease target. Gene therapy is particularly attractive for diseases that currently do not have satisfactory treatment options and probably easier for monogenic disorders than for complex diseases. Cystic fibrosis (CF) fulfils these criteria and is, therefore, a good candidate for gene therapy-based treatment. This review will focus on CF as an example for lung gene therapy, but lessons learned may be applicable to other target diseases.

Polyethylenimine-mediated gene delivery to the lung and therapeutic applications

Nonviral gene delivery is now considered a promising alternative to viral vectors. Among nonviral gene delivery agents, polyethylenimine (PEI) has emerged as a potent candidate for gene delivery to the lung. PEI has some advantages over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. However, intracellular (mainly the nuclear membrane) and extracellular obstacles still hamper its efficiency in vitro and in vivo, depending on the route of administration and the type of PEI. Nuclear delivery has been increased by adding nuclear localization signals. To overcome nonspecific interactions with biological fluids, extracellular matrix components and nontarget cells, strategies have been developed to protect polyplexes from these interactions and to increase target specificity and gene expression. When gene delivery into airway epithelial cells of the conducting airways is necessary, aerosolization of complexes seems to be better suited to guarantee higher transgene expression in the airway epithelial cells with lower toxicity than observed with either intratracheal or intravenous administration. Aerosolization, indeed, is useful to target the alveolar epithelium and pulmonary endothelium. Proof-of-principle that PEI-mediated gene delivery has therapeutic application to some genetic and acquired lung disease is presented, using as genetic material either plasmidic DNA or small-interfering RNA, although optimization of formulation and delivery protocols and limitation of toxicity need further studies.

Gene therapy for cystic fibrosis

Cystic Fibrosis (CF) is an autosomal recessive disorder due to mutations in the CF transmembrane conductance regulator (CFTR) gene that lead to defective ion transport in the conducting pulmonary airways and exocrine glands. Through a process that is not fully understood, CFTR defects predispose affected patients to chronic endobronchial infections with organisms such as Pseudomonas aeruginosa and Staphylococcus aureus. Following the discovery of the CFTR gene in 1989, CF became one of the primary targets for gene therapy research. Early enthusiasm surrounded the new field of gene therapy during most of the 1990s and it led academics and clinicians on a big effort to apply gene therapy for cystic fibrosis. Clinical studies have been pursued using recombinant adenovirus, recombinant adeno-associated virus, cationic liposomes, and cationic polymer vectors. Although to this date no dramatic therapeutic benefits have been observed, a lot of information has been gained from the pre-clinical and clinical studies that were performed. This learning curve has led to the optimization of vector technology and an appreciation of immune and mechanical barriers that have to be overcome for successful delivery.

Real-time imaging of gene delivery and expression with DNA nanoparticle technologies

The construction of safe, efficient, and modifiable synthetic DNA nanoparticles is an emerging technology that has achieved important milestones of success in the past 5 years. Advances in chemical conjugation, purification, and controlled synthesis have allowed researchers to produce uniform and stable particles, whose physical characteristics can be well characterized and monitored. As a result of these improvements, DNA nanoparticles have now been cleared for clinical testing, and show good potential for human gene therapy. A very important recent development in the study of DNA nanoparticles is the use of small-animal imaging. Real-time imaging has become a valuable technique for tracking particle biodistribution and gene transfer efficacy. In this chapter, we discuss how bioluminescent, positron emission tomography, and magnetic resonance imaging can be used separately or in concert to study particle delivery, localization, and magnitude of gene expression in vivo.

Comparison of the effects of serpin A1, a recombinant serpin A1-IGF chimera and serpin A1 C-terminal peptide on wound healing

Serpin A1 (alpha1-antitrypsin, alpha1-proteinase inhibitor), a potent neutrophil elastase inhibitor, has therapeutic potential as a wound-healing agent. We compared the in vitro wound-healing action of serpin A1-IGF, a recombinant fusion protein of serpin A1(M351E-M358L) and insulin-like growth factor I with that observed in the presence of natural serpin A1 or A1-C26, the synthetic C-terminal 26 residue peptide of serpin A1, previously shown to have mitogenic and antiviral activities. All agents reduced wound sizes in monolayers of the kidney epithelial cell line LLC-PK1 and in primary cultures of human skin fibroblasts. Wound reduction in primary human keratinocytes was only observed with the serpin A1-IGF chimera. None of the factors stimulated cell proliferation using a colorimetric assay, with the exception of the serpin A1-IGF chimera, which caused a significant increase of cell proliferation and thymidine incorporation in human skin fibroblasts. However, wound healing by the A1-IGF chimera was reduced in keratinocytes in the presence of mitomycin C, suggesting a role of cell proliferation in wound reduction. The hydrophobic A1-C26 peptide significantly increased the production of collagen I in skin fibroblasts, an appealing asset for skin care applications.

Expression of CFTR from a ciliated cell-specific promoter is ineffective at correcting nasal potential difference in CF mice

Successful gene therapy will require that the therapeutic gene be expressed at a sufficient level in the correct cell type(s). To improve the specificity of gene transfer for cystic fibrosis (CF) and other airway diseases, we have begun to develop cell-type specific promoters to target the expression of transgenes to specific airway cell types. Using a FOXJ1 promoter construct previously shown to direct transgene expression specifically to ciliated cells, we have generated transgenic mice expressing human cystic fibrosis transmembrane conductance regulator (CFTR) in the murine tracheal and nasal epithelia. RNA analysis demonstrated levels of CFTR expression is greater than or equal to the level of endogenous mouse CFTR. Immunoprecipitation and western blotting demonstrated the production of human CFTR protein, and immunochemistry confirmed that CFTR was expressed in the apical region of ciliated cells. The transgenic animals were bred to CFTR null mice (Cftr(tm1Unc)) to determine if expression of CFTR from the FOXJ1 promoter is capable of correcting the airway defects in Cl(-) secretion and Na(+) absorption that accompany CF. Isolated trachea from neonatal CF mice expressing the FOXJ1/CFTR transgene demonstrated a correction of forskolin-stimulated Cl(-) secretion. However, expression of human CFTR in ciliated cells of the nasal epithelia failed to significantly change the nasal bioelectrics of the CF mice.

Sendai virus-mediated CFTR gene transfer to the airway epithelium

The potential for gene therapy to be an effective treatment for cystic fibrosis has been hampered by the limited gene transfer efficiency of current vectors. We have shown that recombinant Sendai virus (SeV) is highly efficient in mediating gene transfer to differentiated airway epithelial cells, because of its capacity to overcome the intra- and extracellular barriers known to limit gene delivery. Here, we have identified a novel method to allow the cystic fibrosis transmembrane conductance regulator (CFTR) cDNA sequence to be inserted within SeV (SeV-CFTR). Following in vitro transduction with SeV-CFTR, a chloride-selective current was observed using whole-cell and single-channel patch-clamp techniques. SeV-CFTR administration to the nasal epithelium of cystic fibrosis (CF) mice (Cftr(G551D) and Cftr(tm1Unc)TgN(FABPCFTR)#Jaw mice) led to partial correction of the CF chloride transport defect. In addition, when compared to a SeV control vector, a higher degree of inflammation and epithelial damage was found in the nasal epithelium of mice treated with SeV-CFTR. Second-generation transmission-incompetent F-deleted SeV-CFTR led to similar correction of the CF chloride transport defect in vivo as first-generation transmission-competent vectors. Further modifications to the vector or the host may make it easier to translate these studies into clinical trials of cystic fibrosis.

Use of ultrasound to enhance nonviral lung gene transfer in vivo

We have assessed if high-frequency ultrasound (US) can enhance nonviral gene transfer to the mouse lung. Cationic lipid GL67/pDNA, polyethylenimine (PEI)/pDNA and naked plasmid DNA (pDNA) were delivered via intranasal instillation, mixed with Optison microbubbles, and the animals were then exposed to 1 MHz US. Addition of Optison alone significantly reduced the transfection efficiency of all three gene transfer agents. US exposure did not increase GL67/pDNA or PEI/pDNA gene transfer compared to Optison-treated animals. However, it increased naked pDNA transfection efficiency by approximately 15-fold compared to Optison-treated animals, suggesting that despite ultrasound being attenuated by air in the lung, sufficient energy penetrates the tissue to increase gene transfer. US-induced lung haemorrhage, assessed histologically, increased with prolonged US exposure. The left lung was more affected than the right and this was mirrored by a lesser increase in naked pDNA gene transfer, in the left lung. The positive effect of US was dependent on Optison, as in its absence US did not increase naked pDNA transfection efficiency. We have thus established proof of principle that US can increase nonviral gene transfer, in the air-filled murine lung.

Serpin A1 and CD91 as host instruments against HIV-1 infection: are extracellular antiviral peptides acting as intracellular messengers?

Serpin A1 (alpha1-antitrypsin, alpha1-proteinase inhibitor) has been shown to be a non-cytolytic antiviral factor present in blood and effective against HIV infection. The best known physiological role of serpin A1 is to inhibit neutrophil elastase, a proteinase which is secreted by neutrophils at sites of infection and inflammation. Decreased HIV-infectivity is associated with decreased density of membrane-associated elastase. The enzyme may facilitate binding of the HIV membrane protein gp120 to host cells, and it specifically cleaves SDF-1, the physiological ligand of the HIV-1 co-receptor CXCR4. It has been suggested that one of the actions of serpin A1 as antiviral agent is to reduce HIV infectivity, and this property could be due to elastase inhibition. However, the most dramatic effect of serpin A1 is inhibition of HIV production. In vitro experiments indicate that the C-terminal peptide of serpin A1, produced during the formation of the complex of serpin with serine proteinases, may be responsible for the inhibition of HIV-1 expression in infected cells. This peptide, an integral part of the serpin-enzyme complex, is internalized by several scavenger receptors. Peptides corresponding to the C-terminal section of serpin A1 inhibit HIV-1 long-terminal-repeat-driven transcription and interact with nuclear proteins, such as alpha1-fetoprotein transcription factor. LDL-receptor-related protein 1 (LRP1/CD91), the best known receptor for serpin-enzyme complexes, is up-regulated in monocytes of HIV-1-infected true non-progressors. CD91 could be one of the major players in host resistance against HIV-1. It has the capacity of internalizing antiviral peptides such as serpin C-terminal fragments and alpha-defensins, and is at the same time the receptor for heat-shock proteins in antigen-presenting cells, in which chaperoned viral peptides could lead to the induction of cytotoxic T-cell responses.

Using magnetic forces to enhance non-viral gene transfer to airway epithelium in vivo

We have assessed whether magnetic forces (magnetofection) can enhance non-viral gene transfer to the airways. TransMAG(PEI), a superparamagnetic particle was coupled to Lipofectamine 2000 or cationic lipid 67 (GL67)/plasmid DNA (pDNA) liposome complexes. In vitro transfection with these formulations resulted in approximately 300- and 30-fold increase in reporter gene expression, respectively, after exposure to a magnetic field, but only at suboptimal pDNA concentrations. Because GL67 has been formulated for in vivo use, we next assessed TransMAG(PEI) in the murine nasal epithelium in vivo, and compared this to naked pDNA. At the concentrations required for in vivo experiments, precipitation of magnetic complexes was seen. After extensive optimization, addition of non-precipitated magnetic particles resulted in approximately seven- and 90-fold decrease in gene expression for naked pDNA and GL67/pDNA liposome complexes, respectively, compared to non-magnetic particles. Thus, whereas exposure to a magnetic field improved in vitro transfection efficiency, translation to the in vivo setting remains difficult.

Mechanism of efficient transfection of the nasal airway epithelium by hypotonic shock

The main barrier to gene transfer in the airway epithelium is the low rate of apical endocytosis limiting naked DNA uptake. Deionized water is known to stimulate the exocytosis of numerous intracellular vesicles during hypotonic cell swelling, in order to expand plasma membrane and prevent cell lysis. This is followed by the phase of regulatory volume decrease (RVD), during which the excess plasma membrane is retrieved by intensive endocytosis. Here we show that the more hypotonic the DNA solution, the higher the transfection of the nasal tissue. P2 receptors are known to be involved in RVD and we demonstrate that some P2 agonists and a P2 antagonist impair transfection in a time-dependent manner. Our study strongly suggests that the nasal airway epithelial cells take up plasmid DNA in deionized water during RVD, within approximately half an hour. Our simple gene delivery system may constitute a promising method for respiratory tract gene therapy.

Gene Therapy for Lung Diseases

Gene therapy is under development for a variety of lung disease, both those caused by single gene defects, such as cystic fibrosis and α₁-antitrypsin deficiency, and multifactorial diseases such as cancer, asthma, lung fibrosis, and ARDS. Both viral and nonviral approaches have been explored, the major limitation to the former being the inability to repeatedly administer, which renders this approach perhaps more applicable to conditions requiring single administration, such as cancer. Progress in development and clinical trials in each of these diseases is reviewed, together with some potential newer approaches for the future.

Pre-clinical and clinical endpoint assays for cystic fibrosis gene therapy

The credibility and hence value of pre-clinical and clinical cystic fibrosis gene therapy studies depend on the assays used to evaluate gene transfer. Awareness of assay suitability, sensitivity and variability is therefore crucial to the design of experimental programmes. Here, we review the assays that are in use to assess the efficacy of gene transfer in pre-clinical and clinical CF gene therapy research, highlight their weaknesses and suggest possible new strategies that may help to overcome current limitations.

Mechanism of uptake of C105Y, a novel cell-penetrating peptide

C105Y, a synthetic peptide (CSIPPEVKFNKPFVYLI) based on the amino acid sequence corresponding to residues 359-374 of alpha1-antitrypsin, enhances gene expression from DNA nanoparticles. To investigate how this enhancement occurs, C105Y was fluorescently labeled to study its uptake and intracellular trafficking. When human hepatoma cells (HuH7) were incubated with fluorescently labeled C105Y for as little as 3 min, C105Y displayed nuclear and cytoplasmic staining with enrichment of fluorescent signal in the nucleus and nucleolus. Uptake and nucleolar localization were observed with the short sequence PFVYLI, but not with SIPPEVKFNK, and the D-isomer was readily taken up into cells but not into the nucleus. We found that the C105Y peptide is routed to the nucleolus very rapidly in an energy-dependent fashion, whereas membrane translocation and nuclear localization are energy-independent. When we tested the involvement of known endocytosis pathways in uptake and trafficking of this peptide, we demonstrated that C105Y peptide is internalized by a clathrin- and caveolin-independent pathway, although lipid raft-mediated endocytosis may play a role in peptide intracellular trafficking. Efficient energy-independent cell entry with rapid nuclear localization probably accounts for enhancement of gene expression from inclusion of C105Y into DNA nanoparticles.

Airway gene therapy

Given both the accessibility and the genetic basis of several pulmonary diseases, the lungs and airways initially seemed ideal candidates for gene therapy. Several routes of access are available, many of which have been refined and optimized for nongene drug delivery. Two respiratory diseases, cystic fibrosis (CF) and alpha1-antitrypsin (alpha1-AT) deficiency, are relatively common; the single gene responsible has been identified and current treatment strategies are not curative. This type of inherited disease was the obvious initial target for gene therapy, but it has become clear that nongenetic and acquired diseases, including cancer, may also be amenable to this approach. The majority of preclinical and clinical studies in the airway have involved viral vectors, although for diseases such as CF, likely to require repeated application, non-viral delivery systems have clear advantages. However, with both approaches a range of barriers to gene expression have been identified that are limiting success in the airway and alveolar region. This chapter reviews these issues, strategies aimed at overcoming them, and progress into clinical trials with non-viral vectors in a variety of pulmonary diseases.

Copolymers of poly-L-lysine with serine and tryptophan form stable DNA vectors: implications for receptor-mediated gene transfer

Inefficient gene transfer and poor stability in physiological medium are important shortcomings for receptor-mediated gene transfer vectors. Here, we evaluate vectors formulated with random copolymers of L-lysine/L-serine (3:1) and L-lysine/L-tryptophan (4:1), focusing on both their biophysical and functional characterization. By means of dynamic light scattering (DLS) and transmission electron microscopy (TEM), we demonstrate that poly-L-lysine (pK), poly-L-lysine-L-tryptophan (pKW) and poly-L-lysine-L-serine (pKS) are able to form compacted, small particles when mixed with plasmid DNA in the absence of salt. Upon dilution in physiological medium, copolymers of both lys/ser and lys/trp do not aggregate, in contrast with poly-L-lysine DNA complexes as determined by scattering, DLS and TEM measurements. Tight packing, as demonstrated by resistance to heparin, SDS and trypsin treatments, is also featured in tryptophan-containing complexes. Successful receptor-mediated endocytosis gene transfer using galactosylated copolymers into cells expressing the asiagloglycoprotein receptor correlated with lack of aggregation. Particles obtained using galactosylated poly-L-lysine-L-tryptophan (Gal-pKW) copolymer demonstrated specific receptor-mediated gene transfer since reporter gene activity dropped in the presence of an excess ligand in the culture medium during transfection. Although copolymers of galactosylated poly-L-lysine-L-serine (Gal-pKS) do not aggregate in the presence of salt, they are not able to internalize in a specific receptor-mediated endocytosis fashion. The introduction of bulky aromatic/hydrophobic (tryptophan) or hydrophillic (serine) moieties into the positively charged vectors allows the compacted particles to disperse into salt-containing medium avoiding salt-induced aggregation. Moreover, tryptophan-containing particles are able to mediate specific gene transfer via receptor-mediated endocytosis.

Progress towards gene therapy for cystic fibrosis

A decade ago it was widely anticipated that cystic fibrosis would be one of the first diseases to be treated by gene therapy. The difficult hurdle of cloning the responsible gene had been accomplished, its function was established and the lung appeared readily accessible for gene replacement. Since the first clinical trials for cystic fibrosis lung disease in the early 1990s it has become increasingly apparent that successful lung-directed gene therapy is significantly more complex than was first envisioned. Numerous obstacles including vector toxicity, inefficient transgene expression and limited vector production have delayed progress. An increased understanding of vector biology and host interaction has led to the development of novel strategies to enhance the efficiency and selectivity of gene delivery to the lung. Although significant challenges remain, there is now a realistic prospect of a clinically effective treatment in the next 10 years.

Compacted DNA nanoparticles administered to the nasal mucosa of cystic fibrosis subjects are safe and demonstrate partial to complete cystic fibrosis transmembrane regulator reconstitution

A double-blind, dose escalation gene transfer trial was conducted in subjects with cystic fibrosis (CF), among whom placebo (saline) or compacted DNA was superfused onto the inferior turbinate of the right or left nostril. The vector consisted of single molecules of plasmid DNA carrying the cystic fibrosis transmembrane regulator- encoding gene compacted into DNA nanoparticles, using polyethylene glycol-substituted 30-mer lysine peptides. Entry criteria included age greater than 18 years, FEV1 exceeding 50% predicted, and basal nasal potential difference (NPD) isoproterenol responses (> or = -5 mV) that are typical for subjects with classic CF. Twelve subjects were enrolled: 2 in dose level I (DLI) (0.8 mg DNA), 4 in DLII (2.67 mg), and 6 in DLIII (8.0 mg). The primary trial end points were safety and tolerability, and secondary gene transfer end points were assessed. In addition to routine clinical assessments and laboratory tests, subjects were serially evaluated for serum IL-6, complement, and C-reactive protein; nasal washings were taken for cell counts, protein, IL-6, and IL-8; and pulmonary function and hearing tests were performed. No serious adverse events occurred, and no events were attributed to compacted DNA. There was no association of serum or nasal washing inflammatory mediators with administration of compacted DNA. Day 14 vector polymerase chain reaction analysis showed a mean value in DLIII nasal scraping samples of 0.58 copy per cell. Partial to complete NPD isoproterenol responses were observed in eight subjects: one of two in DLI, three of four in DLII, and four of six in DLIII. Corrections persisted for as long as 6 days (1 subject to day 28) after gene transfer. In conclusion, compacted DNA nanoparticles can be safely administered to the nares of CF subjects, with evidence of vector gene transfer and partial NPD correction.

Emerging drug treatments for cystic fibrosis

Cystic fibrosis (CF) is one of the most common life-shortening inherited disorders. Mutations in the cystic fibrosis transmembrane regulator (CFTR) gene disrupt the localisation and function of the cAMP-mediated chloride channel. Most of the morbidity and mortality arise from the lung disease which is characterised by excessive inflammation and chronic infection. Research into the mechanisms of wild-type and mutant CFTR biogenesis suggest that multiple drug targets can be identified. This review explores the current understanding of the nature of the different mutant CFTR forms and the potential for repair of the chloride channel defect. High-throughput screening, pharmacogenomics and proteomics bring recent technological advances to the field.

Targeted gene delivery to human airway epithelial cells with synthetic vectors incorporating novel targeting peptides selected by phage display

Human airway epithelial cell targeting peptides were identified by biopanning on 1HAEo-cells, a well characterised epithelial cell line. Bound phage were recovered after three rounds of binding, high stringency washing and elution, leading to the production of an enriched phage peptide population. DNA sequencing of 56 clones revealed 14 unique sequences. Subsequent binding analysis revealed that 13 of these peptides bound 1HAEo-cells with high affinity. Three peptides, SERSMNF, YGLPHKF and PSGAARA were represented at high frequency. Three clearly defined families of peptide were identified on the basis of sequence motifs including (R/K)SM, L(P/Q)HK and PSG(A/T)ARA. Two peptides, LPHKSMP and LQHKSMP contained two motifs. Further detailed sequence analysis by comparison of peptide sequences with the SWISSPROT protein database revealed that some of the peptides closely resembled the cell binding proteins of viral and bacterial pathogens including Herpes Simplex Virus, rotavirus, Mycoplasma pneumoniae and rhinovirus, the latter two being respiratory pathogens, as well as peptide YGLPHKF having similarity to a protein of unknown function from the respiratory pathogen Legionella pneumophila. Peptides were incorporated into gene delivery formulations with the cationic lipid Lipofectin and plasmid DNA and shown to confer a high degree of transfection efficiency and specificity in 1HAEo-cells. Improved transfection efficiency and specificity was also observed in human endothelial cells, fibroblasts and keratinocytes. Therefore, on the basis of clone frequency after biopanning, cell binding affinity, peptide sequence conservation and pathogenic similarity, we have identified 3 novel peptide families and 5 specific peptides that have the potential for gene transfer to respiratory epithelium in vivo as well as providing useful in vitro transfection reagents for primary human cell types of scientific and commercial interest.

Defining strategies to extend duration of gene expression from targeted compacted DNA vectors

Gene transfer complexes containing poly-L-lysine (poly-K) and DNA with ligands directed at the serpin enzyme complex receptor (sec-R) deliver reporter genes to receptor-bearing cells in vivo. Expression lasts for about 30 days, when complexes containing long-chain poly-K are used. Extending the duration of expression would be desirable if correction of genetic defects is the goal. To test whether the mechanism by which expression is extinguished was due to an immune response to the transgene, or the loss of the transgene, we conducted two experiments. In the first, we injected sec-R-targeted lacZ complexes intravenously (i.v.) into mice genetically engineered to express this gene briefly during development. These mice, who should recognize the protein as 'self', also extinguished lacZ expression after 30 days. In a second experiment, we injected immunodeficient animals with sec-R-targeted human factor IX complexes. A similar temporal pattern of expression was observed in Rag-1 -/- mice, in whom expression also extinguished by 40 days. Moreover, factor IX plasmid DNA was detected in the lung and spleen 50 days after injection of complexes, suggesting that not all cells which had taken up the transgene had been destroyed. Thus, the host's immune response to the transgene may not account for the loss of reporter gene expression from these molecular conjugates. We further tested whether repeat administration of sec-R-targeted complexes will be limited by host immune responses. Mice were pre-dosed twice with sec-R-targeted complexes containing lacZ over a 40-day period. We then injected the animals i.v. with sec-R-targeted human factor IX complexes and measured gene expression and antibody production. Although 14 of 36 animals displayed low-titer antibodies to the ligand in targeted complex, expression levels were unaffected compared with virgin dosing. When the complexes were administered three times intranasally (n=10), no antibodies against the complex were detected in blood. Plasma from mice dosed with saline, nontargeted complex or naked DNA did not react with the ligand, ligand-poly K conjugate or targeted complex. All animals exhibiting human factor IX expression developed antibodies to that transgene by 21 days. Thus, at least three repeat administrations of sec-R-directed molecular conjugates are possible, provided that immune responses to the transgene itself are not limiting.

Gene therapy for cystic fibrosis: an example for lung gene therapy

Gene therapy is currently being evaluated for a wide range of acute and chronic lung diseases. The requirement of gene transfer into the individual cell types of the complex lung structure will very much depend on the target disease. Over the last decade, the gene therapy community has recognized that there is not even one vector that is good for all applications, but that the gene transfer agent has to be carefully chosen. Gene therapy is particularly attractive for diseases that currently do not have satisfactory treatment options and probably easier for monogenic disorders than for complex diseases. Cystic fibrosis (CF) fulfills these criteria and is therefore a good candidate for gene therapy-based treatment. This review will focus on CF as an example for lung gene therapy and discuss the progress made in this field over the last couple of years.

Non-viral vectors in cystic fibrosis gene therapy: progress and challenges

Although the viability of cystic fibrosis (CF) gene transfer to airway epithelium has been demonstrated in vitro and in animal models, so far none of the clinical investigations using adenovirus, adeno-associated virus, lentivirus, cationic lipids or polymers has shown a persistent correction of the ion transport defects that occur in CF. Despite disappointing results, these studies have shown that non-viral vectors could represent a viable alternative for gene therapy in CF airway epithelium. The transfer efficiency of non-viral vectors is currently low, however, and thus these systems are not clinically relevant as yet. Before clinical application, several limitations encountered by non-viral delivery systems must be addressed. Recent progress has been made towards overcoming these limitations and towards making non-viral gene therapy a more realistic option for CF.

Transfection of airway epithelium by stable PEGylated poly-L-lysine DNA nanoparticles in vivo

DNA can be compacted using polyethylene glycol-substituted poly-L-lysine into discrete unimolecular (with respect to DNA) nanoparticles with minor diameter < 20 nm that are stable in normal saline for at least 23 months at 4 degrees C. We compared the activity of firefly luciferase in lungs of C57BL/6 mice that received 100 microg compacted plasmid in 25 microl saline (shown to be the optimal dose) via intratracheal or intranasal instillation with levels in animals given 100 microg naked plasmid or in untreated mice. Mice dosed with compacted DNA nanoparticles had peak activity of luciferase in lung at 2 days postinstillation, which declined in log-linear fashion with a half-life of 1.4 days. Luciferase activity in animals dosed with naked DNA was 200-fold less. Addition of polyethylene glycol to the complex was necessary for efficient gene transfer and animals that received DNA compacted with unmodified poly-L-lysine did not exhibit luciferase activity above background. Immunohistochemical staining for bacterial beta-galactosidase 2 days after administration of a compacted lacZ expression plasmid (n = 8) revealed expression predominantly in the dependent portions of the right lungs of mice, in alveolar and airway epithelial cells, though macrophages and sometimes endothelial cells also were transfected. No staining for beta-galactosidase was observed in uninjected animals (n = 4) or those dosed with naked lacZ plasmid (n = 7). Tissue survey for transgene expression shows expression only in lung and trachea following intranasal administration. Stable compacted DNA nanoparticles transfer exogenous genes to airway epithelium and show promise for lung gene therapy.

CFTR involvement in nasal potential differences in mice and pigs studied using a thiazolidinone CFTR inhibitor

Nasal potential difference (PD) measurements have been used to demonstrate defective CFTR function in cystic fibrosis (CF) and to evaluate potential CF therapies. We used the selective thiazolidinone CFTR inhibitor CFTR(inh)-172 to define the involvement of CFTR in nasal PD changes in mice and pigs. In normal mice infused intranasally with a physiological saline solution containing amiloride, nasal PD was -4.7 +/- 0.7 mV, hyperpolarizing by 15 +/- 1 mV after a low-Cl- solution, and a further 3.9 +/- 0.5 mV after forskolin. CFTR(inh)-172 produced 1.1 +/- 0.9- and 4.3 +/- 0.7-mV depolarizations when added after low Cl- and forskolin, respectively. Systemically administered CFTR(inh)-172 reduced the forskolin-induced hyperpolarization from 4.7 +/- 0.4 to 0.9 +/- 0.1 mV but did not reduce the low Cl(-)-induced hyperpolarization. Nasal PD was -12 +/- 1 mV in CF mice after amiloride, changing by <0.5 mV after low Cl- or forskolin. In pigs, nasal PD was -14 +/- 3 mV after amiloride, hyperpolarizing by 13 +/- 2 mV after low Cl- and a further 9 +/- 1 mV after forskolin. CFTR(inh)-172 and glibenclamide did not affect nasal PD in pigs. Our results suggest that cAMP-dependent nasal PDs in mice primarily involve CFTR-mediated Cl- conductance, whereas cAMP-independent PDs are produced by a different, but CFTR-dependent, Cl- channel. In pigs, CFTR may not be responsible for Cl- channel-dependent nasal PDs. These results have important implications for interpreting nasal PDs in terms of CFTR function in animal models of CFTR activation and inhibition.

Molecular imaging for pediatric lung diseases

Molecular imaging is a rapidly developing multidisciplinary field that combines advances in contrast agent development, instrumentation, and molecular/cell biology to follow cellular and sub-cellular events in intact organisms. Platforms for molecular imaging include radionuclide-based methods, optical methods, and magnetic resonance. To date, molecular imaging studies of the lungs have been used to monitor the effectiveness of gene transfer, neutrophilic inflammation, and cell trafficking. Eventually, the goal will be to translate these new techniques to clinical settings such as cystic fibrosis.

Nanoparticles of compacted DNA transfect postmitotic cells

Charge-neutral DNA nanoparticles have been developed in which single molecules of DNA are compacted to their minimal possible size. We speculated that the small size of these DNA nanoparticles may facilitate gene transfer in postmitotic cells, permitting nuclear uptake across the 25-nm nuclear membrane pore. To determine whether DNA nanoparticles can transfect nondividing cells, growth-arrested neuroblastoma and hepatoma cells were transfected with DNA/liposome mixtures encoding luciferase. In both models, growth-arrested cells were robustly transfected by compacted DNA (6,900-360-fold more than naked DNA). To evaluate mechanisms responsible for enhanced transfection, HuH-7 cells were microinjected with naked or compacted plasmids encoding enhanced green fluorescent protein. Cytoplasmic microinjection of DNA nanoparticles generated a approximately 10-fold improvement in transgene expression as compared with naked DNA; this enhancement was reversed by the nuclear pore inhibitor, wheat germ agglutinin. To determine the upper size limit for gene transfer, DNA nanoparticles of various sizes were microinjected into the cytoplasm. A marked decrease in transgene expression was observed as the minor ellipsoidal diameter approached 25 nm. In summary, suitably sized DNA nanoparticles productively transfect growth arrested cells by traversing the nuclear membrane pore.

Non-viral gene transfer therapy for cystic fibrosis

Non-viral methods of gene transfer are being investigated to treat cystic fibrosis (CF) and include naked DNA, lipid-DNA complexes and complexes of DNA with polycations such as poly-L-lysine (poly K) or polyethylenimine (PEI), all of which can carry the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most recent promising strategy is the use of polycation-DNA complexes, particularly those prepared with poly-K and substituted with polyethylene glycol. These complexes produced partial correction of the CF defect in a mouse model with minimal toxicity, and have advanced to clinical trial. Improvements in this and other non-viral methods are in process and include i). targeting the complexes to the desired cells using receptor ligands, ii). lessening toxicity by changing the mix of lipids or adding protective molecules to polycations, iii). modifying the plasmid DNA to reduce inflammatory CpG sequences and enhance intensity, duration and tissue specificity of expression, and iv). modification of the complexes to improve nuclear access.

Gene therapy progress and prospects: cystic fibrosis

Since the cloning of the cystic fibrosis gene (CFTR) in 1989, 18 clinical trials have been carried out, including five in the 2 years reviewed here. Most trials demonstrated proof-of-principle for gene transfer to the airway. However, gene transfer efficiency with each of the three gene transfer agents (adenovirus (Ad), adeno-associated virus 2 (AAV2) and cationic liposomes) was low, and most likely insufficient to achieve clinical benefit. Here, we will review the clinical and pre-clinical progress for the last 2 years (2000-2001) and briefly speculate on future prospects for the next 2 in CF gene therapy.