Surfactant inhibits cationic liposome-mediated gene transfer

Inhalable Gene Therapy and the Lung Surfactant Problem

Lung-targeting RNA-carrying lipid nanoparticles (LNPs) are often intravenously administered and accumulate in the pulmonary endothelium. However, most respiratory diseases are localized in the airway or the alveolar epithelium. Inhalation has been explored as a more direct delivery method, but it presents its own challenges. We believe that one reason LNPs have failed to transfect RNA into alveolar epithelial cells is their interaction with the lung surfactant (LS). We propose that inhalable LNP design should take inspiration from biological agents and other nanoparticles to overcome this barrier. Screening should first focus on LS penetration and then be optimized for cell uptake and endosomal release. This will enable more efficient applications of RNA-LNPs in lung diseases.

New Directions in Pulmonary Gene Therapy

The lung has long been a target for gene therapy, yet efficient delivery and phenotypic disease correction has remained challenging. Although there have been significant advancements in gene therapies of other organs, including the development of several ex vivo therapies, in vivo therapeutics of the lung have been slower to transition to the clinic. Within the past few years, the field has witnessed an explosion in the development of new gene addition and gene editing strategies for the treatment of monogenic disorders. In this review, we will summarize current developments in gene therapy for cystic fibrosis, alpha-1 antitrypsin deficiency, and surfactant protein deficiencies. We will explore the different gene addition and gene editing strategies under investigation and review the challenges of delivery to the lung.

Lipid-Based DNA Therapeutics: Hallmarks of Non-Viral Gene Delivery

Gene therapy is a promising strategy for the treatment of monogenic disorders. Non-viral gene delivery systems including lipid-based DNA therapeutics offer the opportunity to deliver an encoding gene sequence specifically to the target tissue and thus enable the expression of therapeutic proteins in diseased cells. Currently, available gene delivery approaches based on DNA are inefficient and require improvements to achieve clinical utility. In this Review, we discuss state-of-the-art lipid-based DNA delivery systems that have been investigated in a preclinical setting. We emphasize factors influencing the delivery and subsequent gene expression in vitro, ex vivo, and in vivo. In addition, we cover aspects of nanoparticle engineering and optimization for DNA therapeutics. Finally, we highlight achievements of lipid-based DNA therapies in clinical trials.

Inhaled gene delivery: a formulation and delivery approach

INTRODUCTION

Gene therapy is a potential alternative to treat a number of diseases. Different hurdles are associated with aerosol gene delivery due to the susceptibility of plasmid DNA (pDNA) structure to be degraded during the aerosolization process. Different strategies have been investigated in order to protect and efficiently deliver pDNA to the lungs using non-viral vectors. To date, no successful therapy involving non-viral vectors has been marketed, highlighting the need for further investigation in this field. Areas covered: This review is focused on the formulation and delivery of DNA to the lungs, using non-viral vectors. Aerosol gene formulations are divided according to the current delivery systems for the lung: nebulizers, dry powder inhalers and pressurized metered dose inhalers; highlighting its benefits, challenges and potential application. Expert opinion: Successful aerosol delivery is achieved when the supercoiled DNA structure is protected during aerosolization. A formulation strategy or compounds that can protect, stabilize and efficiently transfect DNA into the cells is desired in order to produce an effective, low-cost and safe formulation. Nebulizers and dry powder inhalers are the most promising approaches to be used for aerosol delivery, due to the lower shear forces involved. In this context it is also important to highlight the importance of considering the 'pDNA-formulation-device system' as an integral part of the formulation development for a successful nucleic acid delivery.

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.

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.

In vitro reporter gene transfection via plasmid DNA delivered by metered dose inhaler

Aerosolised DNA administration could potentially advance the treatment of inheritable lung diseases, lung malignancies and provide genetic immunisation against infection. Jet nebulisation, the current standard for introducing DNA formulations into the lung, is inherently inefficient. Pressurised metered dose inhalers (pMDIs) offer a potentially more efficacious and convenient alternative, especially for repeat administration. We aim to modify a novel low-energy nanotechnology process to prepare surfactant-coated pDNA nanoparticles for pulmonary gene delivery via a pMDI. Water-in-oil microemulsions containing green fluorescent protein reporter plasmid were snap-frozen and lyophilised. Lyophilised pDNA, in some cases following a surfactant wash, was incorporated into pMDIs with hydrofluoroalkane 134a (HFA134a) propellant and ethanol as cosolvent. To assess biological functionality, A549 human lung epithelial cells were exposed to aerosolised pDNA particles in the presence of dioleoyl-trimethylammonium propane (DOTAP). Transfection studies demonstrated that pDNA biological functionality was maintained following aerosolisation. In vitro toxicity assays (MTT) showed no significant cell viability loss following aerosolised pDNA treatment. We have demonstrated that pDNA particles can be incorporated into an HFA134a formulation and aerosolised using a standard valve and actuator. Particles prepared by this novel process have potential for stable and efficient delivery of pDNA to the lower respiratory tract via standard pMDI technology.

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.

Efficient targeting to alveolar macrophages by intratracheal administration of mannosylated liposomes in rats

The success of targeting systems to alveolar macrophages critically depends on internalization into these cells for pharmacological intervention. Direct respiratory delivery via inhalation of mannose modified liposomal carriers to alveolar macrophages is of great interest. To evaluate the targeting efficiency to alveolar macrophages by intratracheal administration of mannosylated liposomes (Man-liposomes), Man-liposomes with various ratio of mannosylated cholesterol derivatives, cholesten-5-yloxy-N-(4-((1-imino-2-D-thiomannosylethyl)amino)alkyl)formamide (Man-C4-Chol) as mannose receptor ligand were investigated with regard to their in vitro uptake in primary cultured alveolar macrophages and in vivo intratracheal administration in rats. The in vitro uptake of Man-liposomes took place in a concentration-dependent manner. The internalization of Man-liposomes with 7.5% (Man-7.5-liposomes) and 5.0% (Man-5.0-liposomes) Man-C4-Chol was considerably higher than that of Man-liposomes with 2.5% of Man-C4-Chol (Man-2.5-liposomes) and Bare-liposomes and significantly inhibited by an excess of mannan, suggesting mannose receptor-mediated endocytosis. After intratracheal administration of Man-7.5 and Man-5.0-liposomes in rats, a significantly high internalization and selective targeting to alveolar macrophages was observed. The enhanced cellular uptake in alveolar macrophages related to the mannose density of Man-liposomes was also confirmed both in vitro and in vivo confocal microscopy studies. These results demonstrate the efficient targeting to alveolar macrophages by the intratracheally administered Man-liposomes via mannose receptor-mediated endocytosis.

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

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

Polyethyleneimine-based gene therapy by inhalation

The delivery of genes by inhalation holds promise for the treatment of a wide range of pulmonary and non-pulmonary disorders and offers numerous advantages over more invasive modes of delivery. Subsequent to the cloning of the cystic fibrosis gene, there was great interest in the delivery of genes directly to the lung surfaces by aerosol, and most early efforts focused on the use of non-viral vectors, particularly cationic lipids. Unfortunately, nebulisation shear forces, inefficient penetration of mucous barriers and inhibitory effects of surfactant and other lung-specific features have generally resulted in a lack of therapeutic effect, and much of this work has diminished in recent years as a consequence. Polyethyleneimine (PEI)-based formulations have proven stable during nebulisation and result in nearly 100% efficient transfection throughout the airways, as well as significant, although lower, levels of transfection throughout the lung parenchyma. Most importantly, therapeutic responses have been obtained in several animal lung tumour models when PEI-based complexes of p53 and IL-12 genes were delivered by aerosol. This approach may also prove useful as a means of localised genetic immunisation. In addition, this mode of delivery seems to be associated with surprisingly low toxicity, and results in little or no CpG immunostimulatory response, which has presented a challenge to repeated gene therapy via other modes of delivery.

Mobility and stability of gene complexes in biogels

The tenacious secretions lining the conductive airways of cystic fibrosis (CF) patients may pose a significant barrier to successful gene therapy to the lung. In this work, we evaluated the diffusion of nanospheres and cationic DOTAP lipoplexes through CF sputum and the influence of CF mucus components on the physicochemical properties and gene expression of cationic DOTAP lipoplexes and neutral, pegylated GL67 lipoplexes. The number of particles transported through the sputum was extremely low (<0.5%) and strongly depending on the size of the particles, with almost no transport for the largest nanospheres (560 nm). For small particles (<150 nm), the low transport was primarily due to the long distance they have to travel through the sputum, while for larger particles also sterical obstruction was responsible for the low transport. Upon exposure of the cationic DOTAP lipoplexes to albumin, linear DNA or mucin (at concentration ratios expected to occur in vivo) a significant decrease in gene transfection activity was observed. This was primarily due to aggregation of the lipoplexes. However, exposure of pegylated GL67 lipoplexes to the same components did not affect their gene transfection activity. Indeed, it was determined that CF mucus components did not interact significantly with these neutral, pegylated GL67 lipoplexes.

Pulmonary gene delivery by chitosan-pDNA complex powder prepared by a supercritical carbon dioxide process

Chitosan-plasmid DNA (pDNA) complex powders as a pulmonary gene delivery system were prepared with a supercritical carbon dioxide (CO(2)) process and their in vivo activity was evaluated. The powders with mannitol as a carrier were prepared by dispersing aqueous solutions of a luciferase expression plasmid driven by the cytomegalovirus promoter (pCMV-Luc) with or without chitosan as a cationic vector in a supercritical CO(2)/ethanol admixture. The supercritical CO(2) process with a V-shaped nozzle successfully produced chitosan-pDNA powders. The addition of chitosan suppressed the degradation of pCMV-Luc during the supercritical CO(2) process and increased the yield of powders. The luciferase activity in mouse lung was evaluated after pulmonary administration of the powders or pCMV-Luc solutions. The chitosan-pDNA powders increased the luciferase activity in mouse lung compared with pCMV-Luc powders without chitosan or pCMV-Luc solutions with or without chitosan. The chitosan-pDNA powder with an N/P ratio = 5 increased the luciferase activity to 2700% of that of the pCMV-Luc solution. These results suggest that gene powder with chitosan is a useful pulmonary gene delivery system.

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

BACKGROUND

Plasmid DNA complexed with cationic lipids (lipoplexes) or cationic polymers (polyplexes) has been used for gene transfer into the lung. Topical gene administration of lipoplexes or polyplexes into the lung after intratracheal instillation or aerosolisation could cause interaction of the complexes with extracellular substances of the airway surface liquid (ASL). These extracellular interactions might be causal for the observed inefficient transfection rate in vivo after topical administration. Therefore, we studied the impact of bronchoalveolar lavage fluid (BALF) on reporter gene expression mediated by non-viral gene vectors. BALF was considered as a model system to mimic possible interactions of the gene vectors with the ASL.

METHODS

BALF was taken from 15 patients who underwent diagnostic bronchoscopy. Lipoplexes and polyplexes were incubated with increasing concentrations of BALF and major components of the BALF such as albumin, mucin and alpha(1)-glycoprotein, as a representative of glycosylated proteins. As cationic polymers, we tested dendrimers (fractured PAMAM) and polyethylenimine 25 kDa (PEI) and, as cationic liposomes, we used Lipofect-AMINE. The effect of BALF on polyplexes and lipoplexes was analysed by transfection experiments, fluorescence-quenching assay, 2-D-gel electrophoresis, SDS-PAGE, DNAse protection assay, size and zeta-potential measurements.

RESULTS

BALF inhibited polyplex- and lipoplex-mediated gene transfer. Analysing components of BALF, we found that dendrimer-mediated gene transfer was not inhibited by any specific component. PEI-mediated gene transfer was dose-dependently inhibited by alpha(1)-glycoprotein, slightly inhibited by mucin, but not inhibited in the presence of albumin. Lipoplex-mediated gene transfer was inhibited by mucin at higher concentrations and by albumin, but not by alpha(1)-glycoprotein. 2-D-gel electrophoresis revealed that proteins of the BALF were adsorbed more intensively to lipoplexes than to polyplexes. In addition, mucin and alpha(1)-glycoprotein also adsorbed more intensively to lipoplexes than to polyplexes. Adsorption of BALF components led to a decrease in the positive zeta-potential of lipoplexes and led to a negative zeta-potential of polyplexes. Complement cleavage fragment C3 beta, and in the case of lipoplexes also the C3 alpha fragment, were found among the proteins opsonised on gene vectors.

CONCLUSIONS

Our study shows that BALF contains inhibitory components for non-viral gene transfer. We could not detect a specific inhibitory component, but inhibition was most likely due to the change in the surface charge of the gene vectors. Interestingly, there is evidence for complement activation when the route of pulmonary gene vector administration is chosen. Consequently, shielding of gene vectors to circumvent interaction with the ASL environment should be a focus for pulmonary administration in the future.

Pegylated GL67 lipoplexes retain their gene transfection activity after exposure to components of CF mucus

The highly viscous secretions lining the upper airways and bronchi of cystic fibrosis (CF) patients may pose a significant barrier to successful gene therapy of the lung. In this report we examined the influence of CF mucus components (albumin, DNA, mucin and phospholipids) on the gene transfection activity of cationic DOTAP-based lipoplexes and pegylated GL67-based lipoplexes which previously have been used in CF clinical studies. Upon exposure of the cationic DOTAP:DOPE lipoplexes to either albumin, linear DNA or mucin (at concentration ratios expected to occur in vivo) a significant decrease in gene transfection activity was observed. This was primarily due to aggregation of the lipoplexes. However, exposure of pegylated GL67 lipoplexes to the same components did not affect their gene transfection activity. Indeed, it was determined that CF mucus components did not interact significantly with these pegylated GL67 lipoplexes. These results suggest that charge shielding of cationic gene carriers with pEG may favor their physicochemical stability in CF mucus and thereby aid in preserving their transfection activity.

Lectin-functionalized liposomes for pulmonary drug delivery: effect of nebulization on stability and bioadhesion

The generation of respirable aerosols of a functionalized colloidal carrier has been investigated in this study. Lectin-functionalized liposomes, which proved to show improved cell association (using A549 cell line and primary human alveolar cells) even in the presence of a commercial lung surfactant preparation, have been developed. The stability of non-functionalized liposomes during nebulization using a jet nebulizer (Pari II provocation nebulizer, operated using an air flow of 30 l/min) was firstly investigated, and the experimental and formulation conditions were optimized and applied for the preparation of lectin-functionalized liposomes. The incorporation of cholesterol enhanced the stability of the liposomes during nebulization (from 15-20% leakage of a hydrophilic marker to 8% upon cholesterol incorporation) and upon incubation with lung surfactant preparation. Nebulization of the functionalized liposomes did not significantly influence their physical stability. Their enhanced cell binding capability (compared to non-functionalized liposomes) was also maintained. A drop in cell association compared to fresh functionalized liposomes was detected after nebulization, nevertheless, the binding was still significantly higher than that of the non-functionalized liposomes. The deposition of the liposomal preparation in lung periphery, proved by the deposition of the liposomal preparation on the lower stages of an ASTRA type cascade impinger and a mean median aerodynamic diameter (MMAD) of 2.85 microm, makes it a potential candidate as a macromolecule-drug carrier for local and/or systemic administration.

Improved in vitro gene transfer mediated by fluorinated lipoplexes in the presence of a bile salt surfactant

BACKGROUND

Progress in the field of gene transfer with non-viral vectors requires systems that allow efficient gene expression in the presence of biological fluids such as pulmonary surfactants, for gene transfer to the respiratory epithelium for cystic fibrosis gene therapy, or bile salts (which contain powerful anionic detergents), for gene transfer to the biliary epithelium for gene therapy of the hepatobiliary disease associated with cystic fibrosis (CF). We have performed a comparative analysis of the disintegration and DNA accessibility of fluorinated and conventional lipoplexes, and their in vitro transfection potential in the presence of a powerful biliary surfactant.

METHODS

The disintegration and DNA accessibility of conventional and fluorinated cationic lipoplexes and their in vitro transfection efficiency of human lung carcinoma epithelial A549 cells were studied in the presence of various concentrations of sodium taurocholate (STC), an anionic bile salt detergent. The conventional and fluorinated lipoplexes were formulated from Transfectam" (or DOGS) and from fluorinated lipospermines, analogs of DOGS, respectively, and a luciferase reporter plasmid. The fluorinated lipids used in the present study were selected for their different degrees of fluorination in order to investigate the impact on stability and transfection. The effects of the detergent on lipoplex integrity were examined by evaluating the ability of the lipospermines to prevent, in the presence of the surfactant, ethidium bromide (BET) intercalation into the plasmid (fluorescence monitoring).

RESULTS

Fluorinated cationic lipoplexes exhibited greater stability than DOGS lipoplexes with respect to STC lytic activity. Indeed, while the DOGS lipoplexes were fully disintegrated at a [STC]/[lipid] molar ratio of 1,320, all the DNA intercalation sites of the most fluorinated lipoplexes investigated became accessible to BET for a two-fold higher [STC]/[lipid] molar ratio. A higher transfection potential in the presence of the detergent was also shown for the fluorinated lipoplexes as compared with the DOGS preparation. At a 10 mM concentration of STC and at a [STC]/[lipid] molar ratio of 264, lipofection when mediated by DOGS was fully inhibited while the detergent had no inhibitory effects on the lipofection mediated by the fluorinated DF4C11-GS [spermine-5-carboxyglycine N,N-di-11-(F-butyl)-undecylamide] or DF6E11-GS [spermine-5-carboxyglycine N,N-di-[11-(F-hexyl)-undec-10-enyl]amide] lipospermines. A higher detergent concentration (up to 17.5 mM) and a higher [STC]/[lipid] ratio (up to 462) were necessary to inhibit lipofection by the fluorinated formulations. Overall, the lipoplex stability and transfection potential in the presence of the detergent was found to improve with increasing degrees of fluorination of the lipospermines.

CONCLUSIONS

The present work shows improved stability of, and higher lipofection levels with, fluorinated lipoplexes in the presence of surfactants. The results confirm the very promising potential of fluorinated lipoplexes as gene transfer vectors. These compounds constitute a very attractive alternative to their more conventional homologs. The correlation found between the degree of fluorination of the lipoplexes, their stability and their lipofection levels suggests that enhanced lipophobic and hydrophobic properties protect them against disintegration and, consequently, prevents DNA from being degraded and from interacting with lipophilic and hydrophilic biocompounds responsible for lipofection inhibition.

Efficient naked plasmid cotransfection of lung grafts by extended lung/plasmid exposure time

BACKGROUND

Multiple gene cotransfection may be an effective strategy to modulate concurrent pathologic events after lung transplantation. We investigated in vivo naked plasmid lung cotransfection during cold preservation and the role of lung parenchyma/naked plasmid exposure time.

METHODS

F344 rats underwent left main bronchus instillation of pCF1-CAT (chloramphenicol acetyl transferase) (130 microg) +/- pCF1-beta-Gal (beta-galactosidase) (130 microg) in saline. Part Ia: 4 degrees C preservation versus cotransfection. Lung isografts (4 groups, n = 8) were stored after transfection for 1 (2 groups: one received only pCF1-CAT), 6, and 18 hours. Recipient sacrifice was after 48 hours. Part Ib: 4 degrees C preservation versus transgene expression. Rats were sacrificed 48 hours after transfection in a nontransplant setting (2 groups, n = 8; one received only pCF1-CAT). In a third group (n = 8) lungs were harvested 24 hours after transfection, stored for 18 hours, and recipients were sacrificed after 24 hours. The CAT and beta-Gal enzymatic-linked immunosorbent assays were performed. Part II: Lung/plasmid exposure time. In three groups (n = 6) after pCF1-CAT transfection the left main bronchus was not clamped, clamped for 10 minutes, or clamped for 1 hour. Sacrifice was after 48 hours.

RESULTS

Part Ia: Lung CAT protein was (in picograms per 100 microg of total protein): median, 42 (range, 25 to 95) after 1 hour (only CAT); 67 (19 to 296) after 1 hour, 32 (6 to 157) after 6 hours; and 9 (5 to 243) after 18 hours. Lung beta-Gal protein was (in picograms per 100 microg of total protein): median, 20 (range, 5 to 353) after 1 hour; 17 (6 to 157) after 6 hours; 4 (1 to 74) after 18 hours (1 hour versus 18 hours, p = 0.04 for both proteins). CAT and beta-Gal production were significantly correlated (p = 0.0001, r = 0.924). Part Ib: Lung CAT protein was (in picograms per 100 microg of total protein): median, 2 (range, 0.6 to 10) no transplant, only CAT; 7 (0.3 to 13) no transplant; 3 (0.9 to 14) transplant. Part II: Left lung CAT protein was (in picograms per 100 microg of total protein): median, 31 (range, 6 to 83) no clamp; 74 (25 to 430) 10 minutes of clamp; 111 (30 to 263) 1 hour of clamp. Right lung CAT protein was (in picograms per 100 microg of total protein): median, 0.06 (range, 0 to 0.9) no clamp; 1 (0 to 6) 10 minutes of clamp; 1 (0 to 18) 1 hour of clamp.

CONCLUSIONS

Efficient lung isograft endobronchial cotransfection results from using naked plasmid. Cold preservation affects transfection efficiency but not transgene expression. Lung parenchyma/naked plasmid exposure time determines transfection efficiency.

Key issues in non-viral gene delivery

The future of non-viral gene therapy depends on a detailed understanding of the barriers to delivery of polynucleotides. These include physicomechanical barriers, which limit the design of delivery devices, physicochemical barriers that influence self-assembly of colloidal particulate formulations, and biological barriers that compromise delivery of the DNA to its target site. It is important that realistic delivery strategies are adopted for early clinical trials in non-viral gene therapy. In the longer term, it should be possible to improve the efficiency of gene delivery by learning from the attributes which viruses have evolved; attributes that enable translocation of viral components across biological membranes. Assembly of stable, organized virus-like particles will require a higher level of control than current practice. Here, we summarize present knowledge of the biodistribution and cellular interactions of gene delivery systems and consider how improvements in gene delivery will be accomplished in the future.

Intranasal immunization with mumps virus DNA vaccine delivered by influenza virosomes elicits mucosal and systemic immunity

To improve the efficiency of liposome-mediated DNA transfer as a tool for gene therapy or vaccinology, we have further developed a new delivery system based on the modified immunopotentiating reconstituted influenza virus (IRIV). In this study, we engineered a plasmid DNA vector expressing the mumps virus hemagglutinin or the fusion protein. The administration of this DNA vaccine delivered by influenza virosomes, in combination with the mucosal adjuvant Escheriagen via the intranasal route, was efficient for inducing an immune response, both mucosally and systemically, in mice. The production of IgG2a mumps virus-specific antibodies and the secretion of interleukin 10 (IL-10) by antigen-specific T cells indicated that not only Th1 but also Th2 responses were induced by this DNA vaccine formulation. These results suggest that cationic virosomes in combination with Escheriagen may have great potential as an efficient delivery system for intranasal DNA immunization and provide an immune barrier at the mucosal sites.

Biodistribution and transgene expression with nonviral cationic vector/DNA complexes in the lungs

Biodistribution of nonviral cationic vector/DNA complexes was studied after systemic or intratracheal administration to the lungs and correlated with transgene expression. Intravenous injection in C57Bl/6 mice gave maximal and significant luciferase expression in the lungs with the cationic polymer PEI 22K/DNA complexes at the highest ratios of positive/negative charges versus DNA alone. While DOTAP/DNA complexes with high charge ratio determined lower but still significant luciferase activity versus uncomplexed DNA, GL-67A and PEI 25K mediated negligible luciferase expression. Labelled PEI 22K and DOTAP complexes were evenly distributed in the alveolar region, where GFP expression was revealed, while PEI 25K and GL-67A complexes were not detected, suggesting a different interaction of these complexes with the plasma membrane of endothelial cells. Following an intratracheal injection, the highest and significant levels of transfection were obtained with slightly positive PEI complexes as compared with DNA alone, whereas cationic lipid-based vectors, DOTAP and GL-67A, gave not significant luciferase activity. Both types of polyplexes gave similar levels of lung luciferase expression by targeting different airway cell populations. PEI 25K complexes determined high levels of GFP in the bronchial cells, confirming confocal data on fluorescent complexes internalization. PEI 22K complexes gave mainly high GFP signal in the distal tract of the bronchial tree, where tagged complexes were recovered. Fluorescent lipid complexes were found in aggregates in the lumen of bronchi totally (DOTAP) or partially (GL-67A) co-localizing with surfactant protein A. Results indicated that cationic polymers could overcome the surfactant barrier which inhibited airway cell transfection mediated by cationic lipids.

Differential induction of tumor necrosis factor alpha and manganese superoxide dismutase by endotoxin in human monocytes: role of protein tyrosine kinase, mitogen-activated protein kinase, and nuclear factor kappaB

A mutant Escherichia coli lipopolysaccharide (LPS) lacking myristoyl fatty acid markedly stimulates the activity of manganese superoxide dismutase (MnSOD) without inducing tumor necrosis factor alpha (TNFalpha) production by human monocytes (Tian et al., 1998, Am J Physiol 275:C740.), suggesting that induction of MnSOD and TNFalpha by LPS are regulated through different signal transduction pathways. The protein tyrosine kinase (PTK)/mitogen-activated protein kinase (MAPK) pathway plays an important role in the LPS-induced TNFalpha production. In the current study, we determined the effects of PTK inhibitors, genistein and herbimycin A, on the induction of MnSOD and TNFalpha in human monocytes. Genistein (10 microg/ml) and herbimycin A (1 microg/ml) markedly inhibited LPS-induced protein tyrosine phosphorylation, phosphorylation and nuclear translocation of MAPK (p42 ERK, extracellular signal-regulated kinase), and increases in the steady state level of TNFalpha mRNA as well as TNFalpha production. In contrast, at similar concentrations, genistein and herbimycin A had no effect on the LPS-induced activation of nuclear factor kappaB (NFkappaB) and induction of MnSOD (mRNA and enzyme activity) in human monocytes. In addition, inhibition of NFkappaB activation by gliotoxin and pyrrodiline dithiocarbamate, inhibited LPS induction of TNFalpha and MnSOD mRNAs. These results suggest that (1) while PTK and MAPK are essential for the production of TNFalpha, they are not necessary for the induction of MnSOD by LPS, and (2) while activation of NFkappaB alone is insufficient for the induction of TNFalpha mRNA by LPS, it is necessary for the induction of TNFalpha as well as MnSOD mRNAs.

Aerosol delivery of robust polyethyleneimine-DNA complexes for gene therapy and genetic immunization

Aerosol delivery of plasmid DNA to the lungs offers the possibility of direct application of gene preparations to pulmonary surfaces as a means of treating a variety of genetic pulmonary disorders. However, the process of jet nebulization rapidly degrades naked DNA, viral vectors, and many lipid-based formulations. While complexing DNA with cationic lipids has been shown to significantly stabilize plasmid DNA, losses of biological activity often occur during nebulization, severely limiting the efficiency of aerosol delivery of many such complexes. In conjunction with the design of aerosol delivery systems appropriate for DNA delivery, we have developed formulations using polyethyleneimine (PEI, a polycationic polymer) and DNA that result in a high level of pulmonary transfection (10- to 100-fold greater than many cationic lipids) and are stable during nebulization. In addition, these PEI-based formulations exhibit a high degree of specificity for the lungs. The properties of PEI-based formulations that make them resistant to nebulization and efficient as DNA delivery vectors for pulmonary sites have been investigated. Potential applications of this technology, including the use of aerosolized PEI-DNA for genetic immunization, are discussed.

Solvoplex: a new type of synthetic vector for intrapulmonary gene delivery

A novel type of synthetic vector, termed solvoplex, is described that can greatly enhance gene expression in lung after intrapulmonary delivery. Solvoplexes consist of plasmid DNA and organic solvents. Several organic solvents were analyzed, and luciferase reporter gene expression was observed after intrapulmonary delivery of solvoplexes containing DPSO (di-n-propylsulfoxide), TMU (tetramethylurea), or BMSO (butylmethylsulfoxide). Expression levels correlated with the amount of solvent used at constant DNA amounts. Highest expression was obtained in the lung after intratracheal injection with 15% DPSO resulting in an increase up to 440-fold compared with DNA alone. DPSO-solvoplexes (15%) gave higher reporter gene expression than polyplexes (ExGen 500) or lipoplexes (DOTAP-cholesterol or DOTAP-DOPE). Solvoplex-mediated gene expression did not depend on the delivery mode, and was observed in both mice and rats. Readministration of DPSO-solvoplexes was possible. A second injection after 4 weeks resulted in expression levels similar to the first administration. Histological analyses using lacZ and GFP reporter genes demonstrated gene expression in the lung airway epithelium after intratracheal and microspray delivery. When luciferase expression levels in lung homogenates were compared with adenovirus vectors, DPSO-solvoplexes were 4- or 100-fold less efficient, depending on the promoter used in the viral vector. A quantitative histological comparison between solvoplexes and adenovirus vectors in the best expressing regions revealed that solvoplexes yielded about 2% LacZ-positive cells in the lung airway epithelium, and adenovirus vectors about 20%. Using the microsprayer system, we demonstrated that DNA remained intact in solvoplexes on spraying and that reporter gene expression was observed in mice after intrapulmonary delivery of a solvoplex spray. DNA in DPSO-solvoplexes remained stable and functional after prolonged storage at room temperature.

Enhancement of dendrimer-mediated transfection using synthetic lung surfactant exosurf neonatal in vitro

Pulmonary surfactants enhance adenovirus-mediated gene transfer but inhibit cationic liposome-mediated transfection in lung epithelial cells in vitro. This study examines the effect of the synthetic lung surfactant Exosurf on dendrimer-mediated transfection in eukaryotic cells. Exosurf significantly enhanced dendrimer-luciferase plasmid transfection in a number of cell lines and was very effective in primary cells. Luciferase expression increased up to 40-fold in primary normal human bronchial/tracheal epithelial cells (NHBE). FACScan analysis demonstrated that the transfection rate of the human T cell leukemia Jurkat cell line has significantly improved from 10 to 90% of cells at 24 h after transfection. Analysis of the components of Exosurf revealed that the nonionic surfactant tyloxapol was responsible for the enhancement of dendrimer-mediated gene transfer. The tyloxapol effect was due to increased cell membrane porosity and DNA uptake. Our results demonstrate that Exosurf and its component, tyloxapol, constitute a powerful enhancer for dendrimer-mediated gene transfer in vitro.

Interaction of liposomal and polycationic transfection complexes with pulmonary surfactant

BACKGROUND

The delivery of genes to the airways holds promise for the treatment of lung diseases such as cystic fibrosis and asthma. Current non-viral gene delivery systems lack sufficient transfection efficiency. Pulmonary surfactant has been reported to be a barrier to gene transfer into the airways. Here we analyze the interaction of liposomal and polycationic transfection complexes with pulmonary surfactant.

METHODS

The efficiency of non-viral transfection of cultured human airway epithelial cells (16HBE14o-), COS7 cells and porcine primary airway epithelial cells was studied in the presence of various surfactant preparations in order to model the conditions prevailing in the airways during transfection.

RESULTS

The natural pulmonary surfactant, Alveofact, an extract from bovine lung lavage, was found to inhibit lipofection with lipofectAMINE for all cell lines investigated. Dendrimer meditated polyfection was unaffected for pulmonary cell lines and was weakly affected for COS7 cells. PEI-mediated polyfection was unaffected for all cell lines tested. The synthetic surfactant preparation Exosurf containing L-alpha-phosphatidylcholine-dipalmitoyl (DPPC) as the sole lipid ingredient had no statistically significant effect on polymer- and lipid-mediated transfection. The transfection efficiencies are related to structural changes in the DNA complexes as demonstrated by DNase-accessibility tests and fluorescence spectroscopy. In the presence of the phospholipid POPG, which is a constituent of Alveofact, DNA condensed in lipofectAMINE lipoplexes became accessible to DNaseI, while DNA condensed with PAMAM dendrimer or PEI was less accessible to DNase I as compared to lipoplexes. Consistently, the fluorescence of a DNA-intercalating dye increased after addition of Alveofact only in the case of lipoplexes.

CONCLUSIONS

In contrast to lipofection, gene transfer with cationic polymers to airway epithelial cells is not inhibited by pulmonary surfactant in vitro. Depending on the surfactant concentration even an increase in polymermediated transfection can be seen. In conclusion, cationic polymers appear to be the more stable gene delivery systems for topical application into the airways.

Endobronchial transfection of naked TGF-beta1 cDNA attenuates acute lung rejection

BACKGROUND

We investigated endobronchial transfection of CAT and TGF-beta1 cDNA selectively delivered to the lung graft with or without liposomes.

METHODS

Phase I: F344 rats received 130 microg of naked plasmid pCF1-CAT or complexed to liposome GL67 via left main bronchus instillation. Rats were awakened (pCF1-CAT, n = 4; GL67:pCF1-CAT, n = 4) or served as donors in an isogenic transplant (pCF1-CAT, n = 5; GL67:pCF1-CAT, n = 5). ELISA was performed on lungs, hearts, and livers on POD 2. Phase II: BN lungs received TGF-beta1 sense (n = 6); antisense (n = 5); GL67:TGF-beta1 sense (n = 10); or saline solution (n = 10). F344 recipients were sacrificed on POD 5. The arterial pO2 and rejection were assessed. RT-PCR for murine TGF-beta1 was performed.

RESULTS

Phase I: CAT expression was 519+/-287 pg and 63+/-68 with pCF1-CAT and 104+/-67 and 37+/-45 with GL67:pCF1-CAT, respectively, in the non-transplant and in the transplant setting. No protein was detected in the hearts, livers, and in the native lung of the recipients. Phase II: RT-PCR confirmed murine TGF-beta1 transfection. pO2 was 362.7+/-110.2 (mean mm Hg +/- SD) for sense TGF-beta1; 146.88+/-85.5 for antisense; 241.5+/-181.5 for GL67-TGF-beta1 sense; and 88.4+/-38.7 for saline. TGF-beta1 sense versus all other groups, p<0.05, GL67-TGF-beta1 sense versus saline, p = 0.01. Rejection was significantly lower for TGF-beta1 sense versus saline, p = 0.04.

CONCLUSIONS

Endobronchial administration of naked plasmid achieves selective transfection of lung grafts. Using this strategy, TGF-beta1 reduces early lung allograft rejection.

Antisense oligonucleotides directed against the viral RNA polymerase gene enhance survival of mice infected with influenza A

We have investigated the ability of antisense phosphorothioate oligonucleotides to enhance the survival of mice infected with influenza A virus. The oligonucleotides were complementary to sequences surrounding the translation initiation codons of the viral PB2 or PA genes (PB2-as or PA-as, respectively) of the influenza A virus RNA polymerases. Intravenous administration of PB2-as in a complex with a cationic liposome, Tfx-10, significantly prolonged the mean survival time in days and increased overall survival rates of mice infected with the influenza A virus. Liposomally encapsulated PB2-as inhibited viral growth in lung tissues and reduced pulmonary consolidations. Liposomally encapsulated PB2-as could be an effective therapeutic agent against influenza A virus.

Key issues in non-viral gene delivery

The future of non-viral gene therapy depends on a detailed understanding of the barriers to delivery of polynucleotides. These include physicomechanical barriers, which limit the design of delivery devices, physicochemical barriers that influence self-assembly of colloidal particulate formulations, and biological barriers that compromise delivery of the DNA to its target site. It is important that realistic delivery strategies are adopted for early clinical trials in non-viral gene therapy. In the longer term, it should be possible to improve the efficiency of gene delivery by learning from the attributes which viruses have evolved; attributes that enable translocation of viral components across biological membranes. Assembly of stable, organized virus-like particles will require a higher level of control than current practice. Here, we summarize present knowledge of the biodistribution and cellular interactions of gene delivery systems and consider how improvements in gene delivery will be accomplished in the future.

Direct gene transfer to the respiratory tract of mice with pure plasmid and lipid-formulated DNA

Direct gene transfer into the respiratory system could be carried out for either therapeutic or immunization purposes. Here we demonstrate that cells in the lung can take up and express plasmid DNA encoding a luciferase reporter gene whether it is administered in naked form or formulated with cationic liposomes. Depending on the lipid used, the transfection efficiency with liposome-formulated DNA may be higher, the same as, or less than that with pure plasmid DNA. Tetramethyltetraalkylspermine analogs with alkyl groups of 16 or 18 carbons and DMRIE/cholesterol formulations proved particularly effective. Similar results for reporter gene expression in the lung were obtained whether the DNA (naked or lipid formulated) was administered by indirect, noninvasive intranasal delivery (inhaled or instilled) or by invasive, direct intratracheal delivery (injected or via a cannula). Reporter gene expression peaks around 4 days, then falls off dramatically by 9 days. The dose-response is linear, at least up to 100 microg plasmid DNA, suggesting better transfection efficiencies might be realized if there was not a volume limitation. For a given dose of DNA, the best results are obtained when the DNA is mixed with the minimum amount of lipid that can complex it completely. These results are discussed in the context of direct gene transfer for either gene therapy or delivery of a mucosal DNA vaccine.