Interaction of bronchoalveolar lavage fluid with polyplexes and lipoplexes: analysing the role of proteins and glycoproteins

Mucus-producing epithelial models for investigating the activity of gene delivery systems in the lung

Inhaled transfection particles have to penetrate the mucus layer lining the airways to successfully deliver their therapeutic nucleic acid payload to target cells in the underlying epithelium. However, the in vitro models used for evaluating gene carrier efficiency often disregard this viscous defensive barrier. In this study, the two mucus-secreting cell lines NCI-H292 and Calu-3 were selected to develop a series of epithelial models displaying gradual mucus production. In NCI-H292 models, a gradual increase in the MUC5AC mucin was obtained after cell exposure to inducers. In Calu-3 models, MUC5AC production increased as a function of culture duration (3, 7, 14 days) at the air-liquid interface (ALI). Six DOPC-derived cationic lipids were designed and their pDNA delivery activity was evaluated to validate these cellular models. The strongest impairment of the lipid delivery activity was observed in the Calu-3 14-d ALI model. The MUC5AC production in this model was the greatest and the mucus layer was 20 µm thick. The mucus exhibited a solid viscoelastic behaviour, and represented a major hindrance to lipoplex diffusion. The Calu-3 14-d ALI model will be highly useful for accurate evaluation of gene carriers intended for airway administration and characterization of their interactions with the mucus.

Bridging micro/nano-platform and airway allergy intervention

Allergic airway diseases, with incidence augmenting visibly as industrial development and environmental degradation, are characterized by sneezing, itching, wheezing, chest tightness, airway obstruction, and hyperresponsiveness. Current medical modalities attempt to combat these symptoms mostly by small molecule chemotherapeutants, such as corticosteroids, antihistamines, etc., via intranasal approach which is one of the most noninvasive, rapid-absorbed, and patient-friendly routes. Nevertheless, inherent defects for irritation to respiratory mucosa, drug inactivation and degradation, and rapid drug dispersal to off-target sites are inevitable. Lately, intratracheal micro/nano therapeutic systems are emerging as innovative alternatives for airway allergy interventions. This overview introduces several potential application directions of mic/nano-platform in the treatment of airway allergic diseases, including carriers, therapeutic agents, and immunomodulators. The improvement of the existing drug therapy of respiratory allergy management by micro/nano-platform is described in detail. The challenges of the micro/nano-platform nasal approach in the treatment of airway allergy are summarized and the development of micro/nano-platform is also prospected. Although still a burgeoning area, micro/nano therapeutic systems are gradually turning to be realistic orientations as crucial future alternative therapeutic options in allergic airway inflammation interventions.

Pulmonary siRNA delivery for lung disease: Review of recent progress and challenges

Lung diseases are a leading cause of mortality worldwide and there exists urgent need for new therapies. Approval of the first siRNA treatments in humans has opened the door for further exploration of this therapeutic strategy for other disease states. Pulmonary delivery of siRNA-based biopharmaceuticals offers the potential to address multiple unmet medical needs in lung-related diseases because of the specific physiology of the lung and characteristic properties of siRNA. Inhalation-based siRNA delivery designed for efficient, targeted delivery to specific cells within the lung holds great promise. Efficient delivery of siRNA directly to the lung, however, is relatively complex. This review focuses on the barriers that impact pulmonary siRNA delivery and successful recent approaches to advance this field forward. We focus on the pulmonary barriers that affect siRNA delivery, the disease-dependent pathological changes and their role in pulmonary disease and impact on siRNA delivery, as well as the recent development on the pulmonary siRNA delivery systems.

The Anti-Pseudomonal Peptide D-BMAP18 Is Active in Cystic Fibrosis Sputum and Displays Anti-Inflammatory In Vitro Activity

Most Cystic Fibrosis (CF) patients succumb to airway inflammation and pulmonary infections due to Pseudomonas aeruginosa. D-BMAP18, a membrane-permeabilizing antimicrobial peptide composed of D-amino acids, was evaluated as a possible antibacterial aimed to address this issue. The antipseudomonal activity of D-BMAP18 was tested in a pathophysiological context. The peptide displayed activity against CF isolates of Pseudomonas aeruginosa in the presence of CF sputum when combined with sodium chloride and DNase I. In combination with DNase I, D-BMAP18 discouraged the deposition of new biofilm and eradicated preformed biofilms of some P. aeruginosa strains. In addition, D-BMAP18 down regulated the production of TNF-α, IL1-β, and TGF-β in LPS-stimulated or IFN-γ macrophages derived from THP-1 cells indicating an anti-inflammatory activity. The biocompatibility of D-BMAP18 was assessed using four different cell lines, showing that residual cell-specific cytotoxicity at bactericidal concentrations could be abolished by the presence of CF sputum. Overall, this study suggests that D-BMAP18 may be an interesting molecule as a starting point to develop a novel therapeutic agent to simultaneously contrast lung infections and inflammation in CF patients.

The role of cells and their products in respiratory drug delivery: the past, present, and future

INTRODUCTION

Cell-based delivery systems offer considerable promise as novel and innovative therapeutics to target the respiratory system. These systems consist of cells and/or their extracellular vesicles that deliver their contents, such as anti-microbial peptides, micro RNAs, and even mitochondria to the lung, exerting direct therapeutic effects.

AREAS COVERED

The purpose of this article is to critically review the status of cell-based therapies in the delivery of therapeutics to the lung, evaluate current progress, and elucidate key challenges to the further development of these novel approaches. An overview as to how these cells and/or their products may be modified to enhance efficacy is given. More complex delivery cell-based systems, including cells or vesicles that are genetically modified to (over)express specific therapeutic products, such as proteins and therapeutic nucleic acids are also discussed. Focus is given to the use of the aerosol route to deliver these products directly into the lung.

EXPERT OPINION

The use of biological carriers to deliver chemical or biological agents demonstrates great potential in modern medicine. The next generation of drug delivery systems may comprise 'cell-inspired' drug carriers that are entirely synthetic, developed using insights from cell-based therapeutics to overcome limitations of current generation synthetic carriers.

Nanocarriers in effective pulmonary delivery of siRNA: current approaches and challenges

Research on siRNA is increasing due to its wide applicability as a therapeutic agent in irreversible medical conditions. siRNA inhibits expression of the specific gene after its delivery from formulation to cytosol region of a cell. RNAi (RNA interference) is a mechanism by which siRNA is silencing gene expression for a particular disease. Numerous studies revealed that naked siRNA delivery is not preferred due to instability and poor pharmacokinetic performance. Nanocarriers based delivery of siRNA has the advantage to overcome physiological barriers and protect the integrity of siRNA from degradation by RNAase. Various diseases like lung cancer, cystic fibrosis, asthma, etc can be treated effectively by local lung delivery. The selective targeted therapeutic action in diseased organ and least off targeted cytotoxicity are the key benefits of pulmonary delivery. The current review highlights recent developments in pulmonary delivery of siRNA with novel nanosized formulation approach with the proven in vitro/in vivo applications.

Barriers to inhaled gene therapy of obstructive lung diseases: A review

Knowledge of genetic origins of obstructive lung diseases has made inhaled gene therapy an attractive alternative to the current standards of care that are limited to managing disease symptoms. Initial lung gene therapy clinical trials occurred in the early 1990s following the discovery of the genetic defect responsible for cystic fibrosis (CF), a monogenic disorder. However, despite over two decades of intensive effort, gene therapy has yet to help patients with CF or any other obstructive lung disease. The slow progress is due in part to poor understanding of the biological barriers to inhaled gene therapy. Encouragingly, clinical trials have shown that inhaled gene therapy with various viral vectors and non-viral gene vectors is well tolerated by patients, and continued research has provided valuable lessons and resources that may lead to future success of this therapeutic strategy. In this review, we first introduce representative obstructive lung diseases and examine limitations of currently available therapeutic options. We then review key components for successful execution of inhaled gene therapy, including gene delivery systems, primary physiological barriers and strategies to overcome them, and advances in preclinical disease models with which the most promising systems may be identified for human clinical trials.

Inter-molecular β-sheet structure facilitates lung-targeting siRNA delivery

Size-dependent passive targeting based on the characteristics of tissues is a basic mechanism of drug delivery. While the nanometer-sized particles are efficiently captured by the liver and spleen, the micron-sized particles are most likely entrapped within the lung owing to its unique capillary structure and physiological features. To exploit this property in lung-targeting siRNA delivery, we designed and studied a multi-domain peptide named K-β, which was able to form inter-molecular β-sheet structures. Results showed that K-β peptides and siRNAs formed stable complex particles of 60 nm when mixed together. A critical property of such particles was that, after being intravenously injected into mice, they further associated into loose and micron-sized aggregates, and thus effectively entrapped within the capillaries of the lung, leading to a passive accumulation and gene-silencing. The large size aggregates can dissociate or break down by the shear stress generated by blood flow, alleviating the pulmonary embolism. Besides the lung, siRNA enrichment and targeted gene silencing were also observed in the liver. This drug delivery strategy, together with the low toxicity, biodegradability, and programmability of peptide carriers, show great potentials in vivo applications.

Bio-inspired materials in drug delivery: Exploring the role of pulmonary surfactant in siRNA inhalation therapy

Many pathologies of the respiratory tract are inadequately treated with existing small molecule-based therapies. The emergence of RNA interference (RNAi) enables the post-transcriptional silencing of key molecular disease factors that cannot readily be targeted with conventional small molecule drugs. Pulmonary administration of RNAi effectors, such as small interfering RNA (siRNA), allows direct delivery into the lung tissue, hence reducing systemic exposure. Unfortunately, the clinical translation of RNAi is severely hampered by inefficient delivery of siRNA therapeutics towards the cytoplasm of the target cells. In order to have a better control of the siRNA delivery process, both extra- and intracellular, siRNAs are typically formulated in nanosized delivery vehicles (nanoparticles, NPs). In the lower airways, which are the targeted sites of action for multiple pulmonary disorders, these siRNA-loaded NPs will encounter the pulmonary surfactant (PS) layer, covering the entire alveolar surface. The interaction between the instilled siRNA-loaded NPs and the PS at this nano-bio interface results in the adsorption of PS components onto the surface of the NPs. The formation of this so-called biomolecular corona conceals the original NP surface and will therefore profoundly determine the biological efficacy of the NP. Though this interplay has initially been regarded as a barrier towards efficient siRNA delivery to the respiratory target cell, recent reports have illustrated that the interaction with PS might also be beneficial for local pulmonary siRNA delivery.

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.

Inhalable dry powder formulations of siRNA and pH-responsive peptides with antiviral activity against H1N1 influenza virus

Pulmonary delivery of siRNA has considerable therapeutic potential for treating viral respiratory infectious diseases including influenza. By introducing siRNA that targets the conserved region of viral genes encoding nucleocapsid protein (NP), viral mRNAs can be degraded and viral replication can be inhibited in mammalian cells. To enable siRNA to be used as an antiviral agent, the nucleic acid delivery barrier must be overcome. Effective local delivery of siRNA to lung tissues is required to reduce the therapeutic dose and minimize systemic adverse effects. To develop a formulation suited for clinical application, complexes of pH-responsive peptides, containing either histidine or 2,3-diaminopropionic acid (Dap), and siRNA were prepared into dry powders by spray drying with mannitol, which was used as a bulking agent. The spray-dried (SD) powders were characterized and found to be suitable for inhalation with good stability, preserving the integrity of the siRNA as well as the biological and antiviral activities. The formulations mediated highly effective in vitro delivery of antiviral siRNA into mammalian lung epithelial cells, leading to significant inhibition of viral replication when the transfected cells were subsequently challenged with H1N1 influenza virus. SD siRNA powders containing pH-responsive peptides are a promising inhalable formulation to deliver antiviral siRNA against influenza and are readily adapted for the treatment of other respiratory diseases.

siRNA delivery to the lung: what's new?

RNA interference (RNAi) has been thought of as the general answer to many unmet medical needs. After the first success stories, it soon became obvious that short interfering RNA (siRNA) is not suitable for systemic administration due to its poor pharmacokinetics. Therefore local administration routes have been adopted for more successful in vivo RNAi. This paper reviews nucleic acid modifications, nanocarrier chemistry, animal models used in successful pulmonary siRNA delivery, as well as clinical translation approaches. We summarize what has been published recently and conclude with the potential problems that may still hamper the efficient clinical application of RNAi in the lung.

Formulation of pH responsive peptides as inhalable dry powders for pulmonary delivery of nucleic acids

Nucleic acids have the potential to be used as therapies or vaccines for many different types of disease, but delivery remains the most significant challenge to their clinical adoption. pH responsive peptides containing either histidine or derivatives of 2,3-diaminopropionic acid (Dap) can mediate effective DNA transfection in lung epithelial cells with the latter remaining effective even in the presence of lung surfactant containing bronchoalveolar lavage fluid (BALF), making this class of peptides attractive candidates for delivering nucleic acids to lung tissues. To further assess the suitability of pH responsive peptides for pulmonary delivery by inhalation, dry powder formulations of pH responsive peptides and plasmid DNA, with mannitol as carrier, were produced by either spray drying (SD) or spray freeze drying (SFD). The properties of the two types of powders were characterised and compared using scanning electron microscopy (SEM), next generation impactor (NGI), gel retardation and in vitro transfection via a twin stage impinger (TSI) following aerosolisation by a dry powder inhaler (Osmohaler™). Although the aerodynamic performance and transfection efficacy of both powders were good, the overall performance revealed SD powders to have a number of advantages over SFD powders and are the more effective formulation with potential for efficient nucleic acid delivery through inhalation.

Delivery systems and local administration routes for therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.

Flow cytometry-based cell type-specific assessment of target regulation by pulmonary siRNA delivery

Pulmonary siRNA delivery has attracted strong interest and has been reported to successfully mediate target gene knockdown in a number of disease models. However, the nature of the epithelial cells that eventually take up siRNA and the question if other lung cell types may also be transfected have so far been neglected. Therefore, we describe here a flow cytometry-based method using transgenic enhanced green fluorescence protein-expressing mice (EGFP mice) for the differentiation of transfected lung cell populations based on their antigen expression.

Pulmonary delivery of therapeutic siRNA

Small interfering RNA (siRNA) has a huge potential for the treatment or prevention of various lung diseases. Once the RNA molecules have successfully entered the target cells, they could inhibit the expression of specific gene sequence through RNA interference (RNAi) mechanism and generate therapeutic effects. The biggest obstacle to translating siRNA therapy from the laboratories into the clinics is delivery. An ideal delivery agent should protect the siRNA from enzymatic degradation, facilitate cellular uptake and promote endosomal escape inside the cells, with negligible toxicity. Lung targeting could be achieved by systemic delivery or pulmonary delivery. The latter route of administration could potentially enhance siRNA retention in the lungs and reduce systemic toxic effects. However the presence of mucus, the mucociliary clearance actions and the high degree branching of the airways present major barriers to targeted pulmonary delivery. The delivery systems need to be designed carefully in order to maximize the siRNA deposition to the diseased area of the airways. In most of the pulmonary siRNA therapy studies in vivo, siRNA was delivered either intratracheally or intranasally. Very limited work was done on the formulation of siRNA for inhalation which is believed to be the direction for future development. This review focuses on the latest development of pulmonary delivery of siRNA for the treatment of various lung diseases.

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.

Efficient topical delivery of plasmid DNA to lung in vivo mediated by putative triggered, PEGylated pDNA nanoparticles

Non-viral vectors are considered safer than viral vectors and show clinical potential, but remain less efficient in terms of DNA delivery. Here we report how cationic liposomes, prepared from new cationic lipid, N',N',-dioctadecyl-N-4,8-diaza-10-aminodecanoylglycine amide (DODAG) and neutral lipid dioleoyl-L-α-phos-phatidylethanolamine (DOPE), can be formulated with plasmid DNA (pDNA) in the presence of stabilizer cholesteryl-oxycarbonylpolyethlylene glycol(4600) (PEG(4600)-Chol) giving PEGylated pDNA nanoparticles (pDNA-ABC nanoparticles) that are proposed to be half-life triggered nanoparticles. In particular, the PEGylated pDNA nanoparticle formulation DODAG/DOPE/PEG(4600)-Chol (43:43:14, m/m/m)-pDNA (total lipid/pDNA ratio 4:1 w/w) (pTRANSplus nanoparticles) is shown to mediate efficient transfection of murine lung tissue in vivo. Levels of transfection compare well with the results of polyethylenimine (PEI) mediated pDNA transfection in vivo and even of adenovirus mediated transduction. Cryo-EM imaging indicates that pTRANSplus formulations are somewhat heterogeneous but do consist primarily of bilammellar lipoplex nanoparticles with a few multilammellar nanoparticle aggregates. Lung histology confirms that pTRANSplus mediated transfection in vivo targets substantially the epithelial cells of bronchii and bronchioli airway passages. The pTRANSplus nanoparticle system is a useful new starting point for nucleic acid therapeutic strategies to counter lung disorders such as viral infection and possibly cystic fibrosis.

Improvement of adenoviral vector-mediated gene transfer to airway epithelia by folate-modified anionic liposomes

Despite remarkable progress in the development of both viral and nonviral gene delivery vectors for airway disease treatment, poor gene transfer efficiency to the airway epithelium is a major obstacle in clinical application. To take advantage of the unique features of viral and nonviral vectors, we have developed complexes of adenovirus vector and anionic liposomes (AL-Ad5) by the calcium-induced phase change method. In the current study, based on the fact that there are overexpressed folate receptors on the surface of airway epithelia, we further modified the AL-Ad5 complexes with folate (F-AL-Ad5) to improve the transduction ability of Ad5 in airway epithelia. The transduction efficiencies of the obtained F-AL-Ad5 and AL-Ad5 complexes were assessed in primary-cultured airway epithelia in vitro. Our results indicated that compared with naked adenovirus vector, both AL-Ad5 and F-AL-Ad5 could significantly enhance the gene transduction efficiency of adenovirus vector in primary-cultured airway epithelial cells. Moreover, the enhancement mediated by F-AL-Ad5 was more dramatic than that by AL-Ad5. These results suggested that F-AL-Ad5 may be a useful strategy to deliver therapeutic genes to the airway epithelia and is promising in clinical application.

Anionic liposomes enhance and prolong adenovirus-mediated gene expression in airway epithelia in vitro and in vivo

Adenoviral vector mediated gene therapy has received extensive attention in airway disease treatment. However, the lack of the requisite coxsackie-adenovirus receptor (CAR) on the apical surface of airway epithelium and the host immune response to adenoviruses limit their in vivo application. In our study, we developed for the first time a novel formulation composed of anionic liposomes and adenoviruses (AL-Ad5) using a calcium-induced phase change method. The obtained formulation was employed to enhance the transduction efficiency of airway gene delivery. Our results indicated that primary cultured airway epithelial cells infected by AL-Ad5 displayed higher LacZ gene expression compared to naked adenovirus. Importantly, AL-Ad5 significantly improved and prolonged LacZ gene expression in murine airway tissues when delivered in vivo by intratracheal instillation. Additionally, it was found that anionic liposomes provided immunoprotection to the adenovirus from neutralizing antibody, thus slowing down the elimination of Ad5 particles meanwhile reducing the inflammatory reaction caused by the Ad5 vector. These results suggested that the combination of anionic liposomes with adenovirus may be a useful strategy to deliver therapeutic genes into the airway epithelia and is promising in clinical application.

Stem cell therapy for cystic fibrosis: current status and future prospects

Although cystic fibrosis (CF), an autosomal recessive disease caused by mutations in the gene encoding for the CF transmembrane conductance regulator (CFTR), seems a good candidate for gene therapy, 15 years of intense investigation and a number of clinical trials have not yet produced a viable clinical gene-therapy strategy. In addition, the duration of gene expression has been shown to be limited, only lasting 1-4 weeks. Therefore, alternative approaches involve the search for, and use of, stem cell populations. Bone marrow contains different stem cell types, including hematopoietic stem cells and multipotent mesenchymal stromal cells. Numerous studies have now demonstrated the ability of hematopoietic stem cells and mesenchymal stromal cells to home to the lung and differentiate into epithelial cells of both the conducting airways and the alveolar region. However, engraftment of bone marrow-derived stem cells into the airways is a very inefficient process. Detailed knowledge of the cellular and molecular determinants governing homing to the lung and transformation of marrow cells into lung epithelial cells would benefit this process. Despite a very low level of engraftment of donor cells into the nose and gut, significant CFTR mRNA expression and a measurable level of correction of the electrophysiological defect were observed after transplantation of wild-type marrow cells into CF mice. It is uncertain whether this effect is due to the presence of CFTR-expressing epithelial cells derived from donor cells or to the immunomodulatory role of transplanted cells. Finally, initial studies on the usefulness of umbilical cord blood and embryonic stem cells in the generation of airway epithelial cells will be discussed in this review.

The effect of CpG motifs on gene expression and clearance kinetics of aerosol administered polyethylenimine (PEI)-plasmid DNA complexes in the lung

Presence of CpG motifs within pDNA is widely reported to influence transgene expression as well as inflammatory response to nonviral gene vector complexes. Here, we analyzed gene expression kinetics and lung clearance after aerosol delivery of polyethylenimine (PEI) complexes with two different plasmid vectors: a first generation plasmid, pCMVLuc, and a plasmid with depleted CpG motifs, pCpG-free-Luc. After aerosol delivery, equal nanogram amounts of PEI-pDNA complexes were deposited in murine lungs. Luciferase expression observed at day one post administration of PEI-pCpG-free-Luc complexes was 60-fold higher than for PEI-pCMVLuc complexes and decreased 16-fold at day 7 post application. In contrast, luciferase expression from PEI-pCMVLuc particles remained at levels comparable to day 1 post application. In agreement with these observations, PEI-pCpG-free-Luc complexes were cleared from the lungs at rates 6-fold faster than those observed for PEI-pCMVLuc particles. A more detailed analysis of pDNA distribution within bronchoalveolar lavage fluid (BALF), BALF cells and lung tissue showed 660-fold higher amounts of pCpG-free-Luc in BALF cells compared to pCMVLuc, whereas the amount of pCpG-free-Luc in lung tissue was 15-fold lower compared to pCMVLuc 1h after administration. Our results demonstrate that complexes of PEI with CpG-motif-free DNA are taken up more extensively by BALF cells, while the clearance of pCMVLuc from the lung tissue is significantly slower than for the CpG-free plasmid. Administration of PEI-pCpG-free-Luc caused transient decrease in number of resident lung cells, while their activation was more pronounced with PEI-pCMVLuc particles. Our results demonstrate that the level of transgene expression is increased with CpG-motif-free pDNA but the longevity of expression correlates with pDNA clearance pattern depending on the presence of CpG motifs within the plasmid.

Vectors for pulmonary gene therapy

The success of gene transfer in preclinical animal models and proof of principle clinical studies has made gene therapy an attractive concept for disease treatment. A variety of diseases affecting the lung are candidates for gene therapy. Delivery of genes to the lungs seems to be straightforward, because of the easy accessibility of epithelial cells via the airways. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of the diseased state have proven elusive. This review presents a brief summary about current status and future prospects in the development of viral and non-viral strategies for pulmonary gene therapy.

How to study dendriplexes II: Transfection and cytotoxicity

This paper reviews different techniques for analyzing the transfection efficiencies and cytotoxicities of dendriplexes-complexes of nucleic acids with dendrimers. Analysis shows that three plasmids are mainly used in transfection experiments: plasmid DNA encoding luciferase from the firefly Photinus pyralis, beta-galactosidase, or green fluorescent protein. The effective charge ratio of transfection does not directly correlate with the charge ratio obtained from gel electrophoresis, zeta-potential or ethidium bromide intercalation data. The most popular cells for transfection studies are human embryonic kidney cells (HEK293), mouse embryonic cells (NIH/3T3), SV40 transformed monkey kidney fibroblasts (COS-7) and human epithelioid cervical carcinoma cells (HeLa). Cellular uptake is estimated using fluorescently-labeled dendrimers or nucleic acids. Transfection efficiency is measured by the luciferase reporter assay for luciferase, X-Gal staining or beta-galactosidase assay for beta-galactosidase, and confocal microscopy for green fluorescent protein. Cytotoxicity is determined by the MTT test and lactate dehydrogenase assays. On the basis of the papers reviewed, a standard essential set of techniques for characterizing dendriplexes was constructed: (1) analysis of size and shape of dendriplexes in dried/frozen state by electron or atomic force microscopy; (2) analysis of charge/molar ratio of complexes by gel electrophoresis or ethidium bromide intercalation assay or zeta-potential measurement; (3) analysis of hydrodynamic diameter of dendriplexes in solution by dynamic light scattering. For the evaluation of transfection efficiency the essential techniques are (4) luciferase reporter assay, beta-galactosidase assay or green fluorescent protein microscopy, and (5) cytotoxicity by the MTT test. All these tests allow the transfection efficiencies and cytotoxicities of different kinds of dendrimers to be compared.

Extracellular barriers in respiratory gene therapy

Respiratory gene therapy has been considered for the treatment of a broad range of pulmonary disorders. However, respiratory secretions form an important barrier towards the pulmonary delivery of therapeutic nucleic acids. In this review we will start with a brief description of the biophysical properties of respiratory mucus and alveolar fluid. This must allow the reader to gain insights into the mechanisms by which respiratory secretions may impede the gene transfer efficiency of nucleic acid containing nanoparticles (NANs). Subsequently, we will summarize the efforts that have been done to understand the barrier properties of respiratory mucus and alveolar fluid towards the respiratory delivery of therapeutic nucleic acids. Finally, new and current strategies that can overcome the inhibitory effects of respiratory secretions are discussed.

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.

The role of macromolecular architecture in passively targeted polymeric carriers for drug and gene delivery

The use of polymeric carriers for drug delivery has become increasingly popular because of the ability to easily tune the physical and biological properties of macromolecules. With the growing commercial accessibility of branched and dendritic polymers, their incorporation into polymeric carriers is being explored with increased frequency. However, while a handful of systematic studies have explored the use of branched macromolecules for drug delivery, the role of polymer architecture in optimizing the polymeric carriers is not yet fully understood. Herein, the authors summarize the effect that architecture has on the basic physical properties of polymers, and review our preliminary understanding of the architectural effects on polymer-assisted drug delivery.

Effects of size and topology of DNA molecules on intracellular delivery with non-viral gene carriers

Background

Efforts to improve the efficiency of non-viral gene delivery require a better understanding of delivery kinetics of DNA molecules into clinically relevant cells. Towards this goal, three DNA molecules were employed to investigate the effects of DNA properties on cellular delivery: a circular plasmid DNA (c-DNA), a linearized plasmid DNA (l-DNA) formulated by single-site digestion of c-DNA, and smaller linear gene cassette generated by PCR (pcr-DNA). Four non-viral gene carriers were investigated for DNA delivery: polyethyleneimine (PEI), poly-L-Lysine (PLL), palmitic acid-grafted PLL (PLL-PA), and Lipofectamine-2000™. Particle formation, binding and dissociation characteristics, and DNA uptake by rat bone marrow stromal cells were investigated.

Results

For individual carriers, there was no discernible difference in the morphology of particles formed as a result of carrier complexation with different DNA molecules. With PEI and PLL carriers, no difference was observed in the binding interaction, dissociation characteristics, and DNA uptake among the three DNA molecules. The presence of serum in cell culture media did not significantly affect the DNA delivery by the polymeric carriers, unlike other lipophilic carriers. Using PEI as the carrier, c-DNA was more effective for transgene expression as compared to its linear equivalent (l-DNA) by using the reporter gene for Enhanced Green Fluorescent Protein. pcr-DNA was the least effective despite being delivered into the cells to the same extent.

Conclusion

We conclude that the nature of gene carriers was the primary determinant of cellular delivery of DNA molecules, and circular form of the DNA was more effectively processed for transgene expression.

Hydroxyethylated cationic cholesterol derivatives in liposome vectors promote gene expression in the lung

Three cationic cholesterol derivatives (CCDs), which differ in their types of amine and bear a hydroxyethyl group at the amine group, were synthesized and formulated into liposomes and nanoparticles as gene delivery vectors. In vitro transfection into A549 cells proved that liposomes formulated with CCDs and dioleoylphosphatidylethanolamine (DOPE) of 1/2 molar ratio were more effective than the corresponding nanoparticles with CCDs and Tween 80 at charge ratios (+/-) of 1/2, 3/1 and 5/1. Among the liposomal formulations, non-hydroxyethylated CCDs were more effective than hydroxyethylated ones in vitro. However, gene transfection in the lung through intratracheal injection showed opposite results to those in vitro, with liposomes containing hydroxyethylated CCDs being more potent than those containing non-hydroxyethylated CCDs. Transfection by liposomes with N,N-methyl hydroxyethyl aminopropane carbamoyl cholesterol iodide (MHAPC) showed the highest luciferase activity, resulting in 2- and 60-fold higher gene expression than jet-PEI and naked DNA, respectively. The distribution of MHAPC lipoplex after intratracheal injection was heterogeneous, and luciferase was expressed in epithelial cells lining the bronchi and bronchioles. All the lipoplexes led to higher TNF-alpha levels in the lung compared to the nanoplex and jet-PEI, but our findings suggested that modification of the cationic cholesterol with a hydroxyethyl group at the tertiary amine terminal, MHAPC, promoted gene expression in the lung without increasing the toxicity compared with other CCDs. This work firstly proved that liposomes containing hydroxyethylated CCDs could promote gene expression in the lung through intratracheal injection.

Optimizing aerosol gene delivery and expression in the ovine lung

We have developed the sheep as a large animal model for optimizing cystic fibrosis gene therapy protocols. We administered aerosolized gene transfer agents (GTAs) to the ovine lung in order to test the delivery, efficacy, and safety of GTAs using a clinically relevant nebulizer. A preliminary study demonstrated GTA distribution and reporter gene expression throughout the lung after aerosol administration of plasmid DNA (pDNA):GL67 and pDNA:PEI complexes. A more comprehensive study examined the dose-response relationship for pDNA:PEI and assessed the influence of adjunct therapeutic agents. We found that the sheep model can differentiate between doses of GTA and that the anticholinergic, glycopyrrolate, enhanced transgene expression. Dose-related toxicity of GTA was reduced by aerosol administration compared to direct instillation. This large animal model will allow us to move toward clinical studies with greater confidence.

Water-soluble carbosilane dendrimers protect phosphorothioate oligonucleotides from binding to serum proteins

Treatment of dendriplexes formed between water-soluble carbosilane dendrimers and phosphorothioate oligodeoxynucleotides (ODN) with the anionic detergent sodium dodecyl sulfate disrupted the complexes indicating that the nature of the union in such dendriplexes is merely electrostatic. However, dendriplexes were not dissociated by serum proteins like bovine or human serum albumins, as assessed by gel electrophoresis and fluorescence experiments. This would imply a dendrimer-mediated protective effect able to prevent ODN interactions with serum proteins and additionally could translate into a reduction of the ODN doses needed to achieve the biological effects. The employment of carbosilane dendrimers as carriers may solve the problem of ODN kidnapping by plasmatic proteins as a key drawback for therapeutics involving ODNs. As examples, transfection processes on normal primary peripheral blood cells and diagnosis of HIV infection in the presence of serum have been assayed.

Non-viral siRNA delivery to the lung

SiRNAs exert their biological effect by guiding the degradation of their cognate mRNA sequence, thereby shutting down the corresponding protein production (gene silencing by RNA interference or RNAi). Due to this property, siRNAs are emerging as promising therapeutic agents for the treatment of inherited and acquired diseases, as well as research tools for the elucidation of gene function in both health and disease. Because of their lethality and prevalence, lung diseases have attracted particular attention as targets of siRNA-mediated cures. In addition, lung is accessible to therapeutic agents via multiple routes, e.g., through the nose and the mouth, thus obviating the need for targeting and making it an appealing target for RNAi-based therapeutic strategies. The clinical success of siRNA-mediated interventions critically depends upon the safety and efficacy of the delivery methods and agents. Delivery of siRNAs relevant to lung diseases has been attempted through multiple routes and using various carriers in animal models. This review focuses on the recent progress in non-viral delivery of siRNAs for the treatment of lung diseases, particularly infectious diseases. The rapid progress will put siRNA-based therapeutics on fast track to the clinic.

Nonviral gene delivery: what we know and what is next

Gene delivery using nonviral approaches has been extensively studied as a basic tool for intracellular gene transfer and gene therapy. In the past, the primary focus has been on application of physical, chemical, and biological principles to development of a safe and efficient method that delivers a transgene into target cells for appropriate expression. This review summarizes the current status of the most commonly used nonviral methods, with an emphasis on their mechanism of action for gene delivery, and their advantages and limitations for gene therapy applications. The technical aspects of each delivery system are also reviewed, with a focus on how to achieve optimal delivery efficiency. A brief discussion of future development and further improvement of the current systems is intended to stimulate new ideas and encourage rapid advancement in this new and promising field.

Polycation-mediated delivery of siRNAs for prophylaxis and treatment of influenza virus infection

Influenza A virus causes one of the most prevalent infections in humans. In a typical year, 10-20% of the population of the US is infected by influenza virus, resulting in up to 40,000 deaths and 200,000 hospitalisations. Vaccination is the most effective preventative measure that can protect 70-90% of healthy adults aged < 65; however, the protection rate is much lower in those most susceptible to infection, namely infants, the elderly and individuals with weakened immune systems. Although four drugs have been approved by the FDA for use as prophylaxis and/or treatment of influenza, concerns about their side effects and the emergence of drug-resistant viruses persist. RNA interference (RNAi), an emerging method of post transcriptional gene silencing, appears ideal for the prevention and treatment of influenza. RNAi in mammals can be mediated by short interfering RNAs (siRNAs) of approximately 21-27 nucleotides in length. The authors have previously shown that siRNAs specific for conserved regions of the influenza virus genome are potent inhibitors of influenza virus replication in both cell lines and chicken embryos. This review discusses the recent progress in the in vivo inhibition of influenza virus by the delivery of siRNAs mediated by non-viral vectors, and the prospects of this strategy for prophylaxis and treatment of influenza infection in humans.

Nano-carriers for DNA delivery to the lung based upon a TAT-derived peptide covalently coupled to PEG-PEI

Gene therapy aimed at the respiratory epithelium holds therapeutic potential for diseases such as cystic fibrosis and lung cancer. Polyethylenimine (PEI) has been utilized for gene delivery to the airways. In this study, we describe a new modification of PEI, in which an oligopeptide related to the protein transduction domain of HIV-1 TAT was covalently coupled to 25 kDa PEI (PEI) through a heterobifunctional polyethylenglycol (PEG) spacer resulting in a TAT-PEG-PEI conjugate. Improved DNA reporter gene complexation and protection was observed for small (approximately 90 nm) polyplexes as well as significantly improved stability against polyanions, Alveofact, bronchial alveolar lining fluid and DNase. To determine polyplex toxicity in vitro, MTT assays were performed and, for in vivo testing, the mice bronchial alveolar lavage was investigated for total cell counts, quantity of neutrophils, total protein and TNF-alpha concentration. All parameters suggest significantly lower toxicity for TAT-PEG-PEI. Transfection efficiencies of both PEI and TAT-PEG-PEI polyplexes with DNA were studied under in vitro conditions (A549) and in mice after intratracheal instillation. While luciferase expression in A549 cells was much lower for TAT-PEG-PEI (0.2 ng/mg protein) than for PEI (2 ng/mg), significantly higher transfection efficiencies for TAT-PEG-PEI were detected in mice. Reporter gene expression was distributed through bronchial and alveolar tissue. Thus, TAT-PEG-PEI represents a new approach to non-viral gene carriers for lung therapy, comprising protection for plasmid DNA, low toxicity and significantly enhanced transfection efficiency under in vivo conditions.

Serum albumin enhances polyethylenimine-mediated gene delivery to human respiratory epithelial cells

BACKGROUND

The interaction of polyethylenimine (PEI) polyplexes with proteins in cystic fibrosis (CF) airway secretions poses a significant hurdle to this nonviral delivery system. The aim of this study was to evaluate whether albumin may increase the efficiency of PEI complexes in mediating gene transfer into respiratory epithelial cells in the presence of CF mucus.

METHODS

PEI (25 kDa) was complexed to DNA in the presence of human serum albumin (HSA) and used to transfect confluent A549 and 9HTEo- cells. Alternatively, albumin was added to preformed PEI-DNA complexes. The cytotoxicity of complexes was analysed by the LDH (lactate dehydrogenase) assay. CF CFT1-C2 cells were allowed to polarise and were transfected either with luciferase- or CFTR-expressing plasmids. To evaluate the effect of CF respiratory secretions on transfection efficiency, confluent cells were transfected in the presence of sputum obtained from two CF patients.

RESULTS

The ternary PEI-HSA complexes increased luciferase expression in confluent cultures in a dose-dependent fashion up to 100 times as compared to PEI-DNA. The number of GFP-expressing cells, as evaluated by epifluorescence, was augmented several-fold. When HSA was added to preformed PEI-DNA complexes, a further 5-10-fold increase in gene expression was observed. No significant cytotoxicity was observed with either PEI or PEI-HSA polyplexes. The ternary complexes determined detectable CFTR gene transfer and expression at the apical membrane in polarised CFT1-C2 cells, as evaluated by confocal microscopy. CF sputum inhibited PEI-mediated gene transfer by 7-186-fold. Although luciferase expression mediated by PEI-HSA was still inhibited by CF sputum, these levels were 18-83.8-fold higher than with PEI.

CONCLUSIONS

Our results demonstrate that albumin increases PEI gene transfer efficiency in confluent and polarised respiratory epithelial cells and can allow CFTR gene expression in the appropriate cellular compartment. PEI-HSA complexes display a higher efficiency than PEI also in the presence of CF sputum, indicating that albumin-containing polyplexes may help overcome barriers imposed by CF airway secretions.

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.