Methodological optimization of polyethylenimine (PEI)-based gene delivery to the lungs of mice via aerosol application

RNA Nanomedicine: Delivery Strategies and Applications

Delivery of RNA using nanomaterials has emerged as a new modality to expand therapeutic applications in biomedical research. However, the delivery of RNA presents unique challenges due to its susceptibility to degradation and the requirement for efficient intracellular delivery. The integration of nanotechnologies with RNA delivery has addressed many of these challenges. In this review, we discuss different strategies employed in the design and development of nanomaterials for RNA delivery. We also highlight recent advances in the pharmaceutical applications of RNA delivered via nanomaterials. Various nanomaterials, such as lipids, polymers, peptides, nucleic acids, and inorganic nanomaterials, have been utilized for delivering functional RNAs, including messenger RNA (mRNA), small interfering RNA, single guide RNA, and microRNA. Furthermore, the utilization of nanomaterials has expanded the applications of functional RNA as active pharmaceutical ingredients. For instance, the delivery of antigen-encoding mRNA using nanomaterials enables the transient expression of vaccine antigens, leading to immunogenicity and prevention against infectious diseases. Additionally, nanomaterial-mediated RNA delivery has been investigated for engineering cells to express exogenous functional proteins. Nanomaterials have also been employed for co-delivering single guide RNA and mRNA to facilitate gene editing of genetic diseases. Apart from the progress made in RNA medicine, we discuss the current challenges and future directions in this field.

Polyethylenimine (PEI) in gene therapy: Current status and clinical applications

Polyethlyenimine (PEI) was introduced 1995 as a cationic polymer for nucleic acid delivery. PEI and its derivatives are extensively used in basic research and as reference formulations in the field of polymer-based gene delivery. Despite its widespread use, the number of clinical applications to date is limited. Thus, this review aims to consolidate the past applications of PEI in DNA delivery, elucidate the obstacles that hinder its transition to clinical use, and highlight potential prospects for novel iterations of PEI derivatives. The present review article is divided into three sections. The first section examines the mechanism of action employed by PEI, examining fundamental aspects of cellular delivery including uptake mechanisms, release from endosomes, and transport into the cell nucleus, along with potential strategies for enhancing these delivery phases. Moreover, an in-depth analysis is conducted concerning the mechanism underlying cellular toxicity, accompanied with approaches to overcome this major challenge. The second part is devoted to the in vivo performance of PEI and its application in various therapeutic indications. While systemic administration has proven to be challenging, alternative localized delivery routes hold promise, such as treatment of solid tumors, application as a vaccine, or serving as a therapeutic agent for pulmonary delivery. In the last section, the outcome of completed and ongoing clinical trials is summarized. Finally, an expert opinion is provided on the potential of PEI and its future applications. PEI-based formulations for nucleic acid delivery have a promising potential, it will be an important task for the years to come to introduce innovations that address PEI-associated shortcomings by introducing well-designed PEI formulations in combination with an appropriate route of administration.

Polyplex designs for improving the stability and safety of RNA therapeutics

Nanoparticle-based delivery systems have contributed to the recent clinical success of RNA therapeutics, including siRNA and mRNA. RNA delivery using polymers has several distinct properties, such as enabling RNA delivery into extra-hepatic organs, modulation of immune responses to RNA, and regulation of intracellular RNA release. However, delivery systems should overcome safety and stability issues to achieve widespread therapeutic applications. Safety concerns include direct damage to cellular components, innate and adaptive immune responses, complement activation, and interaction with surrounding molecules and cells in the blood circulation. The stability of the delivery systems should balance extracellular RNA protection and controlled intracellular RNA release, which requires optimization for each RNA species. Further, polymer designs for improving safety and stability often conflict with each other. This review covers advances in polymer-based approaches to address these issues over several years, focusing on biological understanding and design concepts for delivery systems rather than material chemistry.

Hermansky-Pudlak syndrome: Gene therapy for pulmonary fibrosis

Pulmonary fibrosis is a progressive and often fatal lung disease that manifests in most patients with Hermansky-Pudlak syndrome (HPS) type 1. Although the pathobiology of HPS pulmonary fibrosis is unknown, several studies highlight the pathogenic roles of different cell types, including type 2 alveolar epithelial cells, alveolar macrophages, fibroblasts, myofibroblasts, and immune cells. Despite the identification of the HPS1 gene and progress in understanding the pathobiology of HPS pulmonary fibrosis, specific treatment for HPS pulmonary fibrosis is not available, emphasizing the need to identify cellular and molecular targets and to develop therapeutic strategies for this devastating disease. This commentary summarizes recent advances and aims to provide insights into gene therapy for HPS pulmonary fibrosis.

Chemical priming of natural killer cells with branched polyethylenimine for cancer immunotherapy

Background

Due to their powerful immune surveillance activity and ability to kill and clear cancer cells, natural killer (NK) cells are an emerging anticancer immunotherapeutic agent. Therefore, there is much interest in developing efficient technologies that further enhance the therapeutic antitumor efficacy of NK cells.

Methods

To produce chemically primed NK cells, we screened polymers with various electric charges and examined their ability to enhance the cytotoxicity of NK cells. The effect of primary amine and electric charges of 25 kDa branched polyethylenimine (25KbPEI) was investigated by fluorination of the chemical. The role of 25KbPEI in determining the major priming mechanism was investigated in terms of calcium influx into NK cells. In vivo therapeutic efficacy of chemically primed NK cells was evaluated against solid tumor mouse model of triple negative breast and ovarian cancers.

Results

Chem_NK that was produced by the priming activity of 25KbPEI showed potent antitumor activity to various cancer cells. Chem_NK showed an activated phenotype, which manifests as increased expression of activating/adhesion/chemokine receptors and perforin accumulation, leading to enhanced migration ability and antitumor activity. Chem_NK display potent therapeutic efficacy against in vivo mouse model of triple negative breast and ovarian cancers. Fluorination of the primary amine group reduces the activity of 25KbPEI to prime NK cells, indicating that the cationic charge on the chemical plays a critical role in NK cell activation. A major priming mechanism was 25KbPEI-mediated calcium influx into NK cells, which occurred mainly via the Ca2⁺-permeable non-selective cation channel transient receptor potential melastatin 2.

Conclusions

NK cells can be chemically primed with 25KbPEI to express potent antitumor activity as well as enhanced migration ability. Because PEI is a biocompatible and Food and Drug Administration-approved chemical for biomedical use, these results suggest a cost-effective and simple method of producing therapeutic NK cells.

Optimization of lipid nanoparticles for the delivery of nebulized therapeutic mRNA to the lungs

Lipid nanoparticles (LNPs) for the efficient delivery of drugs need to be designed for the particular administration route and type of drug. Here we report the design of LNPs for the efficient delivery of therapeutic RNAs to the lung via nebulization. We optimized the composition, molar ratios and structure of LNPs made of lipids, neutral or cationic helper lipids and poly(ethylene glycol) (PEG) by evaluating the performance of LNPs belonging to six clusters occupying extremes in chemical space, and then pooling the lead clusters and expanding their diversity. We found that a low (high) molar ratio of PEG improves the performance of LNPs with neutral (cationic) helper lipids, an identified and optimal LNP for low-dose messenger RNA delivery. Nebulized delivery of an mRNA encoding a broadly neutralizing antibody targeting haemagglutinin via the optimized LNP protected mice from a lethal challenge of the H1N1 subtype of influenza A virus, and delivered mRNA more efficiently than LNPs previously optimized for systemic delivery. A cluster approach to LNP design may facilitate the optimization of LNPs for other administration routes and therapeutics.

In Vitro Investigations on Optimizing and Nebulization of IVT-mRNA Formulations for Potential Pulmonary-Based Alpha-1-Antitrypsin Deficiency Treatment

In vitro-transcribed (IVT) mRNA has come into focus in recent years as a potential therapeutic approach for the treatment of genetic diseases. The nebulized formulations of IVT-mRNA-encoding alpha-1-antitrypsin (A1AT-mRNA) would be a highly acceptable and tolerable remedy for the protein replacement therapy for alpha-1-antitrypsin deficiency in the future. Here we show that lipoplexes containing A1AT-mRNA prepared in optimum conditions could successfully transfect human bronchial epithelial cells without significant toxicity. A reduction in transfection efficiency was observed for aerosolized lipoplexes that can be partially overcome by increasing the initial number of components. A1AT produced from cells transfected by nebulized A1AT-mRNA lipoplexes is functional and could successfully inhibit the enzyme activity of trypsin as well as elastase. Our data indicate that aerosolization of A1AT-mRNA therapy constitutes a potentially powerful means to transfect airway epithelial cells with the purpose of producing functional A1AT, while bringing along the unique advantages of IVT-mRNA.

Inhaled Nanoformulated mRNA Polyplexes for Protein Production in Lung Epithelium

Noninvasive aerosol inhalation is an established method of drug delivery to the lung, and remains a desirable route for nucleic-acid-based therapeutics. In vitro transcribed (IVT) mRNA has broad therapeutic applicability as it permits temporal and dose-dependent control of encoded protein expression. Inhaled delivery of IVT-mRNA has not yet been demonstrated and requires development of safe and effective materials. To meet this need, hyperbranched poly(beta amino esters) (hPBAEs) are synthesized to enable nanoformulation of stable and concentrated polyplexes suitable for inhalation. This strategy achieves uniform distribution of luciferase mRNA throughout all five lobes of the lung and produces 101.2 ng g^-1 of luciferase protein 24 h after inhalation of hPBAE polyplexes. Importantly, delivery is localized to the lung, and no luminescence is observed in other tissues. Furthermore, using an Ai14 reporter mouse model it is identified that 24.6% of the total lung epithelial cell population is transfected after a single dose. Repeat dosing of inhaled hPBAE-mRNA generates consistent protein production in the lung, without local or systemic toxicity. The results indicate that nebulized delivery of IVT-mRNA facilitated by hPBAE vectors may provide a clinically relevant delivery system to lung epithelium.

Chitosan in Non-Viral Gene Delivery: Role of Structure, Characterization Methods, and Insights in Cancer and Rare Diseases Therapies

Non-viral gene delivery vectors have lagged far behind viral ones in the current pipeline of clinical trials of gene therapy nanomedicines. Even when non-viral nanovectors pose less safety risks than do viruses, their efficacy is much lower. Since the early studies to deliver pDNA, chitosan has been regarded as a highly attractive biopolymer to deliver nucleic acids intracellularly and induce a transgenic response resulting in either upregulation of protein expression (for pDNA, mRNA) or its downregulation (for siRNA or microRNA). This is explained as the consequence of a multi-step process involving condensation of nucleic acids, protection against degradation, stabilization in physiological conditions, cellular internalization, release from the endolysosome ("proton sponge" effect), unpacking and enabling the trafficking of pDNA to the nucleus or the siRNA to the RNA interference silencing complex (RISC). Given the multiple steps and complexity involved in the gene transfection process, there is a dearth of understanding of the role of chitosan's structural features (Mw and degree of acetylation, DA%) on each step that dictates the net transfection efficiency and its kinetics. The use of fully characterized chitosan samples along with the utilization of complementary biophysical and biological techniques is key to bridging this gap of knowledge and identifying the optimal chitosans for delivering a specific gene. Other aspects such as cell type and administration route are also at play. At the same time, the role of chitosan structural features on the morphology, size and surface composition of synthetic virus-like particles has barely been addressed. The ongoing revolution brought about by the recent discovery of CRISPR-Cas9 technology will undoubtedly be a game changer in this field in the short term. In the field of rare diseases, gene therapy is perhaps where the greatest potential lies and we anticipate that chitosans will be key players in the translation of research to the clinic.

In vivo fate tracking of degradable nanoparticles for lung gene transfer using PET and Ĉerenkov imaging

Nanoparticles (NPs) play expanding roles in biomedical applications including imaging and therapy, however, their long-term fate and clearance profiles have yet to be fully characterized in vivo. NP delivery via the airway is particularly challenging, as the clearance may be inefficient and lung immune responses complex. Thus, specific material design is required for cargo delivery and quantitative, noninvasive methods are needed to characterize NP pharmacokinetics. Here, biocompatible poly(acrylamidoethylamine)-b-poly(dl-lactide) block copolymer-based degradable, cationic, shell-cross-linked knedel-like NPs (Dg-cSCKs) were employed to transfect plasmid DNA. Radioactive and optical beacons were attached to monitor biodistribution and imaging. The preferential release of cargo in acidic conditions provided enhanced transfection efficiency compared to non-degradable counterparts. In vivo gene transfer to the lung was correlated with NP pharmacokinetics by radiolabeling Dg-cSCKs and performing quantitative biodistribution with parallel positron emission tomography and Čerenkov imaging. Quantitation of imaging over 14 days corresponded with the pharmacokinetics of NP movement from the lung to gastrointestinal and renal routes, consistent with predicted degradation and excretion. This ability to noninvasively and accurately track NP fate highlights the advantage of incorporating multifunctionality into particle design.

Cellular delivery of shRNA using aptamer-conjugated PLL-alkyl-PEI nanoparticles

Introduction of an efficient gene delivery vector is still the main challenge of gene therapy. Both polyethylenimine (PEI) and poly(l-lysine) (PLL) comprise disadvantages which limited their application. To explore whether their deficiencies could be compensated by preparing copolymers consisting of both PLL and PEI, we generated several combinations of PLL-alkyl-PEI copolymers conjugated to aptamer and evaluated their both gene delivery efficiency and down-regulation of Bcl-XL, an anti-apoptotic gene, in lung cancer cell line. PLL was conjugated to either 10% or 50% of PEI by grafting different percentages of PEI to alkylated-PLL as core. The properties of modified polymers including size, surface charge density, DNA condensation ability, buffering capacity and cytotoxicity were evaluated. According to transfection results, aptamer conjugated PLL-alkyl-10%-PEI (PLPE8%) was selected for further gene silencing study by plasmid shRNA. Decrease in Bcl-XL gene expression was estimated by both RT-PCR and western-blot experiments. The obtained results revealed that the new copolymers had appropriate nano-scale size (117-128 nm) even after aptamer conjugation (168-183 nm). Moreover, they exhibited increased transfection efficiencies by up to 1.8-5 folds and acceptable cytotoxicity. The apoptosis was induced in transfected cells by shRNA-aptamer-copolymer due to the down-regulation of mRNA and protein levels. This study suggested a new vector for targeted non-viral gene delivery with high transfection efficiency in lung cancer or pulmonary systems.

Nebulisation of IVT mRNA Complexes for Intrapulmonary Administration

During the last years the potential role of in vitro transcribed (IVT) mRNA as a vehicle to deliver genetic information has come into focus. IVT mRNA could be used for anti-cancer therapies, vaccination purposes, generation of pluripotent stem cells and also for genome engineering or protein replacement. However, the administration of IVT mRNA into the target organ is still challenging. The lung with its large surface area is not only of interest for delivery of genetic information for treatment of e.g. for cystic fibrosis or alpha-1-antitrypsin deficiency, but also for vaccination purposes. Administration of IVT mRNA to the lung can be performed by direct intratracheal instillation or by aerosol inhalation/nebulisation. The latter approach shows a non-invasive tool, although it is not known, if IVT mRNA is resistant during the process of nebulisation. Therefore, we investigated the transfection efficiency of non-nebulised and nebulised IVT mRNA polyplexes and lipoplexes in human bronchial epithelial cells (16HBE). A slight reduction in transfection efficiency was observed for lipoplexes (Lipofectamine 2000) in the nebulised part compared to the non-nebulised which can be overcome by increasing the amount of Lipofectamine. However, Lipofectamine was more than three times more efficient in transfecting 16HBE than DMRIE and linear PEI performed almost 10 times better than its branched derivative. By contrast, the nebulisation process did not affect the cationic polymer complexes. Furthermore, aerosolisation of IVT mRNA complexes did neither affect the protein duration nor the toxicity of the cationic complexes. Taken together, these data show that aerosolisation of cationic IVT mRNA complexes constitute a potentially powerful means to transfect cells in the lung with the purpose of protein replacement for genetic diseases such as cystic fibrosis or alpha-1-antitrypsin deficiency or for infectious disease vaccines, while bringing along the advantages of IVT mRNA as compared to pDNA as transfection agent.

A novel reduction-sensitive modified polyethylenimine oligonucleotide vector

A reduction-sensitive cross-linked polyethylenimine derivative PEI-SS-OA was synthesized and evaluated for oligonucleotide delivery. PEI-SS-OA was shown to condense LOR-2501, an oligonucleotide targeting ribonucleotide reductase R1 subunit (RRM1), into positively charged complexes. The reductive degradation of the PEI-SS-OA induced by dithiothreitol was confirmed by a gel retardation assay. In vitro experiments revealed that the reduction-sensitive PEI-SS-OA was less cytotoxic and more effective in oligonucleotide delivery than the control 25kDa PEI. This study demonstrates that a reducibly degradable cationic polymer PEI-SS-OA possesses both higher oligonucleotide delivery efficiency and lower cytotoxicity than PEI (25 kDa), therefore is an attractive candidate for further in vivo evaluation.

Cystic fibrosis transmembrane conductance regulator-mRNA delivery: a novel alternative for cystic fibrosis gene therapy

BACKGROUND

Cystic fibrosis (CF) is the most frequent lethal genetic disease in the Caucasian population. CF is caused by a defective gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP- and ATP-dependent Cl(-) channel and central regulatory protein in epithelia. CFTR influences the fluid composition of the mucus in the respiratory tract. The most common mutation inducing CF, ΔF508, impairs CFTR processing within the cell and thus prevents functional CFTR expression in the apical membrane. The present study aimed to investigate the functional restoration of CFTR in human CF airway epithelia after transfection with optimized wild-type (wt)CFTR-mRNA.

METHODS

We used primary cultured human nasal epithelial (HNE) cells and the human bronchial epithelial cell line CFBE41o(-) that stably expresses ΔF508-CFTR and carried out transepithelial Ussing chamber measurements after transfection with optimized wtCFTR-mRNA. We confirmed the data obtained using immunofluorescence and protein biochemical approaches.

RESULTS

Transfection of the CFBE41o(-) cells with wtCFTR-mRNA restored cAMP-induced CFTR currents similar to the values seen in control cells (16HBE14o(-)). Using immunofluorescence approaches, we demonstrated that a considerable amount of CFTR is located at the apical surface in the CF cells after transfection. Western blot analyses of wtCFTR-mRNA transfected CFBE41o(-) cells confirmed these findings. Furthermore, we demonstrated physiological relevance by using primary cultured HNE cells and showed an almost two-fold increase in the cAMP-stimulated CFTR current after transfection.

CONCLUSIONS

From these data, we conclude that CFTR-mRNA transfection could comprise a novel alternative for gene therapy to restore impaired CFTR function.

Effective pulmonary delivery of an aerosolized plasmid DNA vaccine via surface acoustic wave nebulization

BACKGROUND

Pulmonary-delivered gene therapy promises to mitigate vaccine safety issues and reduce the need for needles and skilled personnel to use them. While plasmid DNA (pDNA) offers a rapid route to vaccine production without side effects or reliance on cold chain storage, its delivery to the lung has proved challenging. Conventional methods, including jet and ultrasonic nebulizers, fail to deliver large biomolecules like pDNA intact due to the shear and cavitational stresses present during nebulization.

METHODS

In vitro structural analysis followed by in vivo protein expression studies served in assessing the integrity of the pDNA subjected to surface acoustic wave (SAW) nebulisation. In vivo immunization trials were then carried out in rats using SAW nebulized pDNA (influenza A, human hemagglutinin H1N1) condensate delivered via intratracheal instillation. Finally, in vivo pulmonary vaccinations using pDNA for influenza was nebulized and delivered via a respirator to sheep.

RESULTS

The SAW nebulizer was effective at generating pDNA aerosols with sizes optimal for deep lung delivery. Successful gene expression was observed in mouse lung epithelial cells, when SAW-nebulized pDNA was delivered to male Swiss mice via intratracheal instillation. Effective systemic and mucosal antibody responses were found in rats via post-nebulized, condensed fluid instillation. Significantly, we demonstrated the suitability of the SAW nebulizer to administer unprotected pDNA encoding an influenza A virus surface glycoprotein to respirated sheep via aerosolized inhalation.

CONCLUSION

Given the difficulty of inducing functional antibody responses for DNA vaccination in large animals, we report here the first instance of successful aerosolized inhalation delivery of a pDNA vaccine in a large animal model relevant to human lung development, structure, physiology, and disease, using a novel, low-power (<1 W) surface acoustic wave (SAW) hand-held nebulizer to produce droplets of pDNA with a size range suitable for delivery to the lower respiratory airways.

Polyethyleneimine is a potent mucosal adjuvant for viral glycoprotein antigens

Protection against mucosally transmitted infections probably requires immunity at the site of pathogen entry, yet there are no mucosal adjuvant formulations licensed for human use. Polyethyleneimine (PEI) represents a family of organic polycations used as nucleic acid transfection reagents in vitro and DNA vaccine delivery vehicles in vivo. Here we show that diverse PEI forms have potent mucosal adjuvant activity for viral subunit glycoprotein antigens. A single intranasal administration of influenza hemagglutinin or herpes simplex virus type-2 (HSV-2) glycoprotein D with PEI elicited robust antibody-mediated protection from an otherwise lethal infection, and was superior to existing experimental mucosal adjuvants. PEI formed nanoscale complexes with antigen, which were taken up by antigen-presenting cells in vitro and in vivo, promoted dendritic cell trafficking to draining lymph nodes and induced non-proinflammatory cytokine responses. PEI adjuvanticity required release of host double-stranded DNA that triggered Irf3-dependent signaling. PEI therefore merits further investigation as a mucosal adjuvant for human use.

Vectors for inhaled gene therapy in lung cancer. Application for nano oncology and safety of bio nanotechnology

Novel aerosol therapeutic modalities have been investigated for lung cancer. Inhaled gene therapy has presented safety and effectiveness previously in cystic fibrosis. However, safety concerns have been raised regarding the safety of non-viral vectors for inhaled gene therapy in lung cancer, and therefore small steps have been made towards this multifunctional treatment modality. During the last decade, numerous new nanocomplexes have been created and investigated as a safe gene delivery nano-vehicle. These formulations are multifunctional; they can be used as either local therapy or carrier for an effective inhaled gene therapy for lung cancer. Herein, we present current and future perspectives of nanocomplexes for inhaled gene therapy treatment in lung cancer.

In vivo transfection study of chitosan-DNA-FAP-B nanoparticles as a new non viral vector for gene delivery to the lung

Gene therapy targeted at the respiratory epithelium holds therapeutic potential for diseases such as cystic fibrosis and lung cancer. We recently reported that Chitosan-DNA-FAP-B nanoparticles are good candidates for targeted gene delivery to fibronectin molecules (FAP-B receptors) of lung epithelial cell membrane. In this study Chitosan-DNA-FAP-B nanoparticles were nebulized to mice using air jet nebulizer. The effect of nebulization on size, zeta potential and DNA binding ability of nanoparticles were studied. The level of gene expression in the mice lungs was evaluated. Nebulization did not affect the physicochemical properties of nanoparticles. Aerosol delivery of Chitosan-DNA-FAP-B nanoparticles resulted in 16-fold increase of gene expression in the mice lungs compared with Chitosan-DNA nanoparticles. This study suggested that Chitosan-FAP-B nanoparticle can be a promising carrier for targeted gene delivery to the lung.

Ultrasound- and liposome microbubble-mediated targeted gene transfer to cardiomyocytes in vivo accompanied by polyethylenimine

OBJECTIVES

Gene transfer to cardiomyocytes in vivo has received much research attention in the last decade but remains a substantial hurdle. Gene transfer using ultrasound-targeted microbubble destruction is a promising tool for gene therapy. Little data have shown the feasibility and optimization of this method for primary myocardial disease. In this study, we sought to determine the feasibility and efficiency of in vivo gene transfer to the myocardium mediated by ultrasound-targeted microbubble destruction accompanied by polyethylenimine.

METHODS

Three plasmids (luciferase reporter, red fluorescent protein reporter, and enhanced green fluorescent protein reporter) were used in this study. The ultrasound parameters were also optimized. A solution containing phosphate-buffered saline, a plasmid, plasmid complex, or polyethylenimine/plasmid, and liposome microbubbles was injected via a tail vein with (study) or without (control) transthoracic ultrasound irradiation. The efficiency of reporter gene transfer was determined by detection of luciferase activity or microscopy, and histologic investigations of the tissue specimens were performed.

RESULTS

Ultrasound-targeted microbubble destruction significantly increased luciferase activity in vivo compared to plasmids and microbubbles alone (P < .001). More importantly, the increase in transgene expression was significantly related to ultrasound-targeted microbubble destruction in the presence of polyethylenimine (P < .001). In addition, fluorescein expression was present in all sections that received ultrasound-targeted microbubble destruction. The fluorescent reporter genes and luciferase plasmid all had similar results. Regardless of ultrasound exposure, expression in other organs was close to a background level except for the liver and lung. Hematoxylin-eosin staining showed no notable myocardial injury or death in control and treated mice.

CONCLUSIONS

An atraumatic targeted gene delivery technique based on ultrasound-targeted microbubble destruction and polyethylenimine has been developed to transfect cardiomyocytes in vivo. If a suitable target gene is added, the novel technique could be highly effective in many kinds of heart disease.

Interaction of poly(ethylenimine)-DNA polyplexes with mitochondria: implications for a mechanism of cytotoxicity

Poly(ethylenimine) (PEI) and PEI-based systems have been widely studied for use as nucleic acid delivery vehicles. However, many of these vehicles display high cytotoxicity, rendering them unfit for therapeutic use. By exploring the mechanisms that cause cytotoxicity, and through understanding structure-function relationships between polymers and intracellular interactions, nucleic acid delivery vehicles with precise intracellular properties can be tailored for specific function. Previous research has shown that PEI is able to depolarize mitochondria, but the exact mechanism as to how depolarization is induced remains elusive and therefore is the focus of the current study. Potential mechanisms for mitochondrial depolarization include direct mitochondrial membrane permeabilization by PEI or PEI polyplexes, activation of the mitochondrial permeability transition pore, and interference with mitochondrial membrane proton pumps, specifically Complex I of the electron transport chain and F(0)F(1)-ATPase. Herein, confocal microscopy and live cell imaging showed that PEI polyplexes do colocalize to some degree with mitochondria early in transfection, and the degree of colocalization increases over time. Cyclosporin a was used to prevent activation of the mitochondrial membrane permeability transition pore, and it was found that early in transfection cyclosporin a was unable to prevent the loss of mitochondrial membrane potential. Further studies done using rotenone and oligomycin to inhibit Complex I of the electron transport chain and F(0)F(1)-ATPase, respectively, indicate that both of these mitochondrial proton pumps are functioning during PEI transfection. Overall, we conclude that direct interaction between polyplexes and mitochondria may be the reason why mitochondrial function is impaired during PEI transfection.

Aerosolized BC-819 inhibits primary but not secondary lung cancer growth

Despite numerous efforts, drug based treatments for patients suffering from lung cancer remains poor. As a promising alternative, we investigated the therapeutic potential of BC-819 for the treatment of lung cancer in mouse tumor models. BC-819 is a novel plasmid DNA which encodes for the A-fragment of Diphtheria toxin and has previously been shown to successfully inhibit tumor growth in human clinical study of bladder carcinoma. In a first set of experiments, we examined in vitro efficacy of BC-819 in human lung cancer cell-lines NCI-H460, NCI-H358 and A549, which revealed >90% reduction of cell growth. In vivo efficacy was examined in an orthotopic mouse xenograft lung cancer model and in a lung metastasis model using luminescent A549-C8-luc adenocarcinoma cells. These cells resulted in peri- and intra-bronchiolar tumors upon intrabronchial application and parenchymal tumors upon intravenous injection, respectively. Mice suffering from these lung tumors were treated with BC-819, complexed to branched polyethylenimine (PEI) and aerosolized to the mice once per week for a period of 10 weeks. Using this regimen, growth of intrabronchially induced lung tumors was significantly inhibited (p = 0.01), whereas no effect could be observed in mice suffering from lung metastasis. In summary, we suggest that aerosolized PEI/BC-819 is capable of reducing growth only in tumors arising from the luminal part of the airways and are therefore directly accessible for inhaled BC-819.

Polyethylenimines for RNAi-mediated gene targeting in vivo and siRNA delivery to the lung

RNA interference (RNAi) is a promising strategy to inhibit the expression of pathologically relevant genes, which show aberrant (over-)expression, e.g. in tumors or other pathologies. The induction of RNAi relies on small interfering RNAs (siRNAs), which trigger the specific mRNA degradation. Their instability and poor delivery into target tissues including the lung, however, so far severely limits the therapeutic use of siRNAs and requires the development of nanoscale delivery systems. Polyethylenimines (PEIs) are synthetic polymers, which are able to form non-covalent complexes with siRNAs. These nanoscale complexes ('nanoplexes') allow the protection of siRNAs from nucleolytic degradation, their efficient cellular uptake through endocytosis and intracellular release through the 'proton sponge effect'. Chemical modifications of PEIs as well as the coupling of cell/tissue-specific ligands are promising approaches to increase the biocompatibility, specificity and efficacy of PEI-based nanoparticles. This review article gives a comprehensive overview of pre-clinical in vivo studies on the PEI-mediated delivery of therapeutic siRNAs in various animal models. It discusses the chemical properties of PEIs and PEI modifications, and their influences on siRNA knockdown efficacy, on adverse effects of the polymer or the nanoplex and on siRNA biodistribution in vivo. Beyond systemic application, PEI-based complexation allows the local siRNA application to the lung. Biodistribution studies demonstrate cellular uptake of PEI-complexed, but not of naked siRNAs in the lung with little systemic availability of the siRNAs, indicating the usefulness of this approach for the targeting of genes, which are pathologically relevant in lung tumors or lung metastases. Taken together, (i) PEI and PEI derivatives may represent an efficient delivery platform for siRNAs, (ii) siRNA-mediated induction of RNAi is a promising approach for the knockdown of pathologically relevant genes, and (iii) when sufficiently addressing biocompatibility issues, the locoregional delivery of PEI/siRNA complexes may become an attractive therapeutic strategy for the treatment of lung diseases with little systemic side effects.

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.

Magnetic aerosol targeting of nanoparticles to cancer: nanomagnetosols

Inhalation of aerosols represents the most frequently used drug delivery method for the treatment of lung diseases. To further improve drug efficacy in the lungs, it may be advantageous to control aerosol deposition and target aerosols to diseased or disease-causing lung tissue and cellular structures in order to maximize drug potency and minimize side effects in unaffected tissue. We have recently investigated a novel method which brings aerosol delivery to an advanced level of specificity by making use of magnetic gradient fields to direct magnetizable aerosol droplets containing superparamagnetic iron oxide nanoparticles (SPION) specifically to desired regions of the lungs in mice. In this chapter, we will present a detailed description of this procedure for application in mice.

Reducible poly(oligo-D-arginine) for enhanced gene expression in mouse lung by intratracheal injection

Nonarginine (D-R9) has been reported to be one of the most efficacious protein transduction domains (PTDs) for the intracellular cargo delivery such as DNA, RNA, proteins, and particles. Although oligoarginines are capable of forming polyplex with DNA by electrostatic interaction, the length of oligoarginine can affect the toxicity and gene expression. The reducible poly(oligo-D-arginine) (rPOA) composed of the Cys-(D-R9)-Cys repeating unit forming disulfide bonds between terminal cysteinyl-thiol groups of short peptides was hypothesized to show efficient gene transfection without toxicity. The reducible high molecular weight poly(oligo-D-arginine) may fragment into the Cys-(D-R9)-Cys in cellular environments such as cytosol, cell surface, endosomes, and lysosomes, and enhance DNA transfection efficiency. In the present study, in vitro stability, cytotoxicity, and transfection efficiency of DNA/poly(oligo-D-arginine) polyplex were evaluated. In addition, in vivo delivery of DNA into the lung was performed by intratracheal injection of DNA/poly(oligo-D-arginine) polyplex. The in vivo study with rPOA showed higher level of gene expression than PEI, sustaining for 1 week without toxicity. Reducible high molecular weight poly(oligo-D-arginine) based on R9 PTD is a very promising nonviral gene carrier for lung diseases by efficiently condensing, stabilizing, and transfecting DNA.

CpG-free plasmid DNA prevents deterioration of pulmonary function in mice

Nonviral gene vectors have been shown to be therapeutically effective in various animal models of inherited and acquired lung diseases. Although an acute unmethylated CG dinucleotide (CpG)-mediated inflammatory response has been previously observed for first-generation plasmids, its effect on pulmonary function has not been investigated to date. Here, we present data on lung functional parameters together with histopathology, cellular and inflammatory events in response to pulmonary administration of DNA-containing particles. We show that aerosol delivery of polyethylenimine gene vectors containing a first-generation CpG-rich plasmid induced an inflammatory response which was associated with a decrease in lung compliance. In contrast to these observations, aerosol application of CpG-free plasmid DNA prevented immune response and impairment of pulmonary function. These results demonstrate that aerosol delivery of CpG-free plasmid DNA is critical to avoid alteration of pulmonary function. Therefore, we suggest to use CpG-free pDNA for gene delivery to the lungs in future.

Non-viral vectors in cystic fibrosis gene therapy: recent developments and future prospects

Gene therapy has been proposed for a wide range of human diseases but few have received the level of attention over such a prolonged period as cystic fibrosis (CF) with over 20 clinical studies undertaken. Following a 10-year interval, clinical trials of an aerosolisable non-viral gene transfer agent have recently been initiated by researchers in the United Kingdom. Here we review the rationale and requirements for effective gene therapy for CF lung disease. The previous non-viral gene therapy trials are discussed and the prospects for the current leading non-viral formulations for CF gene therapy are considered. Factors affecting the selection and design of the plasmid DNA molecule, likely to be of central importance to clinical efficacy, are reviewed and we describe the potential merits of the formulation that has been selected for the forthcoming UK trials.

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.

REV1 is implicated in the development of carcinogen-induced lung cancer

The somatic mutation hypothesis of cancer predicts that reducing the frequency of mutations induced by carcinogens will reduce the incidence of cancer. To examine this, we developed an antimutator strategy based on the manipulation of the level of a protein required for mutagenic bypass of DNA damage induced by the ubiquitous carcinogen benzo[a]pyrene. The expression of this protein, REV1, was reduced in mouse cells using a vector encoding a gene-specific targeting ribozyme. In the latter cells, mutagenesis induced by the activated form of benzo[a]pyrene was reduced by >90%. To examine if REV1 transcripts could be lowered in vivo, the plasmid was complexed with polyethyleneimine, a nonviral cationic polymer, and delivered to the lung via aerosol. The endogenous REV1 transcript in the bronchial epithelium as determined by quantitative real-time PCR in laser capture microdissected cells was reduced by 60%. There was a significant decrease in the multiplicity of carcinogen-induced lung tumors from 6.4 to 3.7 tumors per mouse. Additionally, REV1 inhibition completely abolished tumor formation in 27% of the carcinogen-exposed mice. These data support the central role of the translesion synthesis pathway in the development of lung cancer. Further, the selective modulation of members of this pathway presents novel potential targets for cancer prevention. The somatic mutation hypothesis of cancer predicts that the frequency of cancers will also be reduced.

Electroporation enhances reporter gene expression following delivery of naked plasmid DNA to the lung

BACKGROUND

Existing methods of non-viral airway gene transfer suffer from low levels of efficiency. Electroporation has been used to enhance gene transfer in a range of tissues. Here we assess the usefulness of electroporation for enhancing gene transfer in the lungs of mice and sheep.

METHODS

Naked plasmid DNA (pDNA) expressing either luciferase or green fluorescent protein (GFP) was delivered to mouse lungs by instillation. Following surgical visualisation, the lungs were directly electroporated and the level and duration of luciferase activity was assessed and cell types that were positive for GFP were identified in lung cryosections. Naked pDNA was nebulised to the sheep lung and electrodes attached to the tip of a bronchoscope were used to electroporate airway segment bifurcations, Luciferase activity was assessed in electroporated and control non-electroporated regions, after 24 h.

RESULTS

Following delivery of naked pDNA to the mouse lung, electroporation resulted in up to 400-fold higher luciferase activity than naked pDNA alone when luciferase was under the control of a cytomegalovirus (CMV) promoter. Following delivery of a plasmid containing the human polyubiquitin C (UbC) promoter, electroporation resulted in elevated luciferase activity for at least 28 days. Visualisation of GFP indicated that electroporation resulted in increased GFP detection compared with non-electroporated controls. In the sheep lung electroporation of defined sites in the airways resulted in luciferase activity 100-fold greater than naked pDNA alone.

CONCLUSIONS

These results indicate that electroporation can be used to enhance gene transfer in the lungs of mice and sheep without compromising the duration of expression.

Use of ultrasound to enhance nonviral lung gene transfer in vivo

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

Targeting of the glucocorticoid hormone receptor with plasmid DNA comprising glucocorticoid response elements improves nonviral gene transfer efficiency in the lungs of mice

BACKGROUND

It has been previously demonstrated that plasmid DNA transport into the nucleus could be increased by transcription factor binding. We chose the glucocorticoid responsive element (GRE) which binds to the glucocorticoid receptor (GR), a transcription factor which is shuttled into the nucleus upon ligand binding such as dexamethasone.

METHODS

We cloned two, four, and eight repetitive sequences of the GRE into the reporter plasmid pEGFPLuc. Binding of the pEGFPLuc-GRE to the GR was examined by electrophoretic mobility shift assay (EMSA) experiments. GR expression in bronchiolar and alveolar epithelial cells was confirmed by Western blotting. Intracellular trafficking of GR was examined using a fusion protein of cyano-fluorescent protein (CFP) and GR. Transfection efficiencies of pEGFPLuc compared to pEGFPLucGRE(2-8) were examined in vitro and in vivo upon tail vein injection of cationic liposome gene vectors containing dexamethasone (safeplexes) and aerosol application of polyethylenimine (PEI)-pDNA particles.

RESULTS

Binding of GRE containing plasmids to the GR was shown in EMSA experiments and intranuclear shuttling of CFP-GR after ligand stimulation was confirmed. Enhanced gene transfer efficiency of pEGFPLucGRE(2) in vitro was only observed on confluent cells. A 2.5-fold increase in gene expression in the lungs of mice after tail vein injection of pEGFPLucGRE(2) complexed with safeplexes compared with pEGFPLuc was observed. PEI-mediated aerosol gene delivery of pEGFPLucGRE(2) was 4.7-fold higher than pEGFPLuc only after intraperitoneal dexamethasone.

CONCLUSION

The results suggest that inclusion of GRE sequences into plasmid DNA vectors combined with dexamethasone application could improve transgene expression in the lungs in vivo.

Aerosol gene delivery to the murine lung is mouse strain dependent

The cationic polymer polyethylenimine (PEI) has been previously demonstrated to efficiently deliver genes to the lungs of mice in vivo via nebulization. Although within these studies various mouse strains were used in individual experiments, no direct comparison of gene delivery to different mouse strains via aerosol application has been published to date. With respect to the widespread use of mice as animal models of inherited and acquired diseases, such data could be of relevance to select the most appropriate mouse genetic background for preclinical mouse models. We investigated PEI-based aerosol gene delivery in two commonly used mouse strains, BALB/c and NMRI, and mixed 129/Sv x C57BL/6 mice. Gene expression in BALB/c mice was significantly 3.2- and 3.8-fold higher than in NMRI and 129/Sv x C57BL/6 mice, respectively. Lung deposition rates of radioactively labeled plasmid DNA (I(123)) complexed with PEI were not significantly different between each of the mouse strains. The kinetics of pDNA clearance from the lungs of BALB/c mice was slightly faster than from NMRI mice. Whereas gene expression increased until day 3 after treatment, the levels of pDNA decreased over the same period of time. Repeated aerosol application in a 3-day time interval could maintain gene expression at high levels compared with a single application. Furthermore, PEI-pDNA aerosol application led to reproducible gene expression in independent experiments. These data suggest that the genetic background of mice could be important for nonviral aerosol gene delivery which should be considered in transgenic animal mouse models of inherited and acquired diseases for aerosol gene delivery studies.

Transfection of multiple pulmonary cell types following intravenous injection of PEI-DNA in normal and CFTR mutant mice

BACKGROUND

The polycationic vector polyethylenimine (PEI) has been shown to be a powerful agent for transfecting the mouse lung after injection of plasmid-based polyplexes through the tail vein. These findings raise therapeutic prospects for a number of lung conditions. For such potentials to be realised, the precise identity of the transfected cells remains to be determined; however, so far, no ultrastructural analysis has been performed on PEI-transfected lungs. The definition of which pulmonary cells are transfected is particularly critical for certain pulmonary diseases which might require transfection of defined cell types such as epithelial cells for cystic fibrosis (CF).

METHODS

Here, we use a combination of light and electron microscopy to determine which cells are transfected in the lung after PEI-mediated gene delivery through the intravenous route. Furthermore, we extend the same experimental setting to a mouse model of CF to provide proof of principle that this approach can be used in genetic models of the disease.

RESULTS

We show that within 18-20 h after injection through the tail vein, DNA/PEI complexes have already crossed the capillary barrier resulting in high levels of expression of reporter genes in the lungs. Transgene expression is observed in endothelial cells, in type I and type II pneumocytes, and in septal cells. Coexpression of the transgene and of the endogenous CF transmembrane conductance regulator (CFTR) gene is observed in some of the targeted epithelial cells. Levels and sites of expression are similar in normal and in CFTR-mutant mice.

CONCLUSIONS

The results demonstrate that PEI-mediated gene delivery leads to transfection of epithelial cells beyond the endothelial barrier and show that this method can be used for lung gene delivery in CF fragile mutant mice.

Human-specific cystic fibrosis transmembrane conductance regulator antibodies detect in vivo gene transfer to ovine airways

A panel of 11 human cystic fibrosis transmembrane conductance regulator (hCFTR) antibodies were tested in ovine nasal, tracheal, and bronchial epithelial brushings. Two of these, G449 (polyclonal) and MATG1104 (monoclonal), recognized hCFTR but did not cross react with endogenous sheep CFTR. This specificity allows immunologic detection of hCFTR expressed in gene transfer studies in sheep against the background of endogenous ovine CFTR, thus enhancing the value of the sheep as a model animal in which to study CFTR gene transfer. Studies on mixed populations of human and sheep nasal epithelial cells showed that detection of hCFTR by these two antibodies was possible even at the lowest proportion of human cells (1:100). The hCFTR gene was delivered in vivo by local instillation using polyethylenimine-mediated gene transfer to the ventral surface of the ovine trachea and hCFTR mRNA and protein levels scored in a blinded fashion. Despite abundant hCFTR mRNA expression, the number of cells expressing hCFTR protein detectable by G449 was low (approximately 0.006-0.05%). Immunohistochemistry for hCFTR in animals treated by whole-lung aerosol demonstrated positive cells in sections of tracheal epithelium and in distal conducting airways. The strategic use of hCFTR-specific antibodies supports the utility of the normal sheep as a model for hCFTR gene transfer studies.

Aerosolized nanogram quantities of plasmid DNA mediate highly efficient gene delivery to mouse airway epithelium

The lung is an important target of gene therapeutic interventions. In contrast to intratracheal instillation, inhalation would be the most practical route of administration in clinical applications. Here we show that aerosolized nanogram quantities of pDNA complexed to PEI (350 ng) yielded transfection levels 15-fold higher than a 140-fold higher dose (50 microg) of the same vector applied directly to the lungs of mice via intratracheal intubation. An important efficacy parameter is the osmolarity of the aerosol and not biophysical properties of the nebulized vector. Vectors formulated and nebulized in hypoosmotic distilled water yielded 57- and 185-fold higher expression levels than those in isotonic 5% glucose or Hepes-buffered saline, respectively. Pretreatment of mice with nebulized indomethacin, which prevents water-induced airway alteration, resulted in lower gene expression, whereas pretreatment with EGTA or polidocanol, which modulate tight-junction activity, had no effect. These results, together with histological analysis of regional lung deposition and gene expression, suggest that a temporary water-induced hypoosmotic shock permeabilizes the epithelium sufficiently to allow vector uptake. The so far observed inefficiency of nonviral gene delivery to the airways may be the result of an inappropriate method of vector administration.