An integrin-targeted non-viral vector for pulmonary gene therapy

Physiological Barriers and Strategies of Lipid-Based Nanoparticles for Nucleic Acid Drug Delivery

Lipid-based nanoparticles (LBNPs) are currently the most promising vehicles for nucleic acid drug (NAD) delivery. Although their clinical applications have achieved success, the NAD delivery efficiency and safety are still unsatisfactory, which are, to a large extent, due to the existence of multi-level physiological barriers in vivo. It is important to elucidate the interactions between these barriers and LBNPs, which will guide more rational design of efficient NAD vehicles with low adverse effects and facilitate broader applications of nucleic acid therapeutics. This review describes the obstacles and challenges of biological barriers to NAD delivery at systemic, organ, sub-organ, cellular, and subcellular levels. The strategies to overcome these barriers are comprehensively reviewed, mainly including physically/chemically engineering LBNPs and directly modifying physiological barriers by auxiliary treatments. Then the potentials and challenges for successful translation of these preclinical studies into the clinic are discussed. In the end, a forward look at the strategies on manipulating protein corona (PC) is addressed, which may pull off the trick of overcoming those physiological barriers and significantly improve the efficacy and safety of LBNP-based NADs delivery.

Directing the Way-Receptor and Chemical Targeting Strategies for Nucleic Acid Delivery

Nucleic acid therapeutics have shown great potential for the treatment of numerous diseases, such as genetic disorders, cancer and infections. Moreover, they have been successfully used as vaccines during the COVID-19 pandemic. In order to unfold full therapeutical potential, these nano agents have to overcome several barriers. Therefore, directed transport to specific tissues and cell types remains a central challenge to receive carrier systems with enhanced efficiency and desired biodistribution profiles. Active targeting strategies include receptor-targeting, mediating cellular uptake based on ligand-receptor interactions, and chemical targeting, enabling cell-specific delivery as a consequence of chemically and structurally modified carriers. With a focus on synthetic delivery systems including polyplexes, lipid-based systems such as lipoplexes and lipid nanoparticles, and direct conjugates optimized for various types of nucleic acids (DNA, mRNA, siRNA, miRNA, oligonucleotides), we highlight recent achievements, exemplified by several nucleic acid drugs on the market, and discuss challenges for targeted delivery to different organs such as brain, eye, liver, lung, spleen and muscle in vivo.

Targeting of Polyelectrolyte RNA Complexes to Cell Surface Integrins as an Efficient Cytoplasmic Transfection Mechanism

This is the first demonstration of receptor-mediated delivery of mRNA and establishes a new approach to gene therapy. Messenger RNA (mRNA) provides a promising alternative to plasmid DNA as a genetic material for delivery in non-viral gene therapy strategies. Since it does not require access to the nucleus and is less dependent on the cell cycle for expression, mRNA delivered using cationic lipids or short cationic polymers can be effectively translated within target cells. In this study, mRNA formed discrete nanoparticles following self assembly with a range of cationic polymers. Based on transfection activities, the low molecular weight polycations were more efficient than high molecular weight, while protamine and polyethylenimine were far more efficient than poly(L-lysine). Receptor-mediated delivery of mRNA was demonstrated using the synthetic polyamino acid (K)16GACDCRGDCFCA designed to promote cell entry following interaction with cell surface αυ integrins. RGD-bearing mRNA complexes showed very high levels of expression, reaching over 60% transduction of B16F10 cells.

Gene delivery from supercharged coiled-coil protein and cationic lipid hybrid complex

A lipoproteoplex comprised of an engineered supercharged coiled-coil protein (CSP) bearing multiple arginines and the cationic lipid formulation FuGENE HD (FG) was developed for effective condensation and delivery of nucleic acids. The CSP was able to maintain helical structure and self-assembly properties while exhibiting binding to plasmid DNA. The ternary CSP·DNA(8:1)·FG lipoproteoplex complex demonstrated enhanced transfection of β-galactosidase DNA into MC3T3-E1 mouse preosteoblasts. The lipoproteoplexes showed significant increases in transfection efficiency when compared to conventional FG and an mTat·FG lipopolyplex with a 6- and 2.5-fold increase in transfection, respectively. The CSP·DNA(8:1)·FG lipoproteoplex assembled into spherical particles with a net positive surface charge, enabling efficient gene delivery. These results support the application of lipoproteoplexes with protein engineered CSP for non-viral gene delivery.

The use of CpG-free plasmids to mediate persistent gene expression following repeated aerosol delivery of pDNA/PEI complexes

Aerosol gene therapy offers great potential for treating acquired and inherited lung diseases. For treatment of chronic lung diseases such as cystic fibrosis, asthma and emphysema, non-viral gene therapy will likely require repeated administration to maintain transgene expression in slowly dividing, or terminally differentiated, lung epithelial cells. When complexed with plasmid DNA (pDNA), the synthetic polymer, 25 kDa branched Polyethylenimine (PEI), can be formulated for aerosol delivery to the lungs. We show that pDNA/PEI aerosol formulations can be repeatedly administered to airways of mice on at least 10 occasions with no detectable toxicity. Interestingly, peak reporter gene activity upon repeated delivery was significantly reduced by up to 75% compared with a single administration, despite similar pDNA lung deposition at each subsequent aerosol exposure. Although the precise mechanism of inhibition is unknown, it is independent of mouse strain, does not involve an immune response, and is mediated by PEI. Importantly, using a dosing interval of 56 days, delivery of a fourth-generation, CpG-free plasmid generated high-level, sustained transgene expression, which was further boosted at subsequent administrations. Together these data indicate that pDNA/PEI aerosol formulations offer a versatile platform for gene delivery to the lung resulting in sustained transgene expression suitable for treatment of chronic lung diseases.

Nebulisation of receptor-targeted nanocomplexes for gene delivery to the airway epithelium

Background

Gene therapy mediated by synthetic vectors may provide opportunities for new treatments for cystic fibrosis (CF) via aerosolisation. Vectors for CF must transfect the airway epithelium efficiently and not cause inflammation so they are suitable for repeated dosing. The inhaled aerosol should be deposited in the airways since the cystic fibrosis transmembrane conductance regulator gene (CFTR) is expressed predominantly in the epithelium of the submucosal glands and in the surface airway epithelium. The aim of this project was to develop an optimised aerosol delivery approach applicable to treatment of CF lung disease by gene therapy.

Methodology

The vector suspension investigated in this study comprises receptor-targeting peptides, cationic liposomes and plasmid DNA that self-assemble by electrostatic interactions to form a receptor-targeted nanocomplex (RTN) of approximately 150 nm with a cationic surface charge of +50 mV. The aerodynamic properties of aerosolised nanocomplexes produced with three different nebulisers were compared by determining aerosol deposition in the different stages of a Next Generation Pharmaceutical Impactor (NGI). We also investigated the yield of intact plasmid DNA by agarose gel electrophoresis and densitometry, and transfection efficacies in vitro and in vivo.

Results

RTNs nebulised with the AeroEclipse II BAN were the most effective, compared to other nebulisers tested, for gene delivery both in vitro and in vivo. The biophysical properties of the nanocomplexes were unchanged after nebulisation while the deposition of RTNs suggested a range of aerosol aerodynamic sizes between 5.5 µm–1.4 µm cut off (NGI stages 3–6) compatible with deposition in the central and lower airways.

Conclusions

RTNs showed their ability at delivering genes via nebulisation, thus suggesting their potential applications for therapeutic interventions of cystic fibrosis and other respiratory disorders.

In vitro and in vivo studies of local arterial gene delivery and transfection using lipopolyplexes-embedded stents

Gene-eluting stents can have profound impact in the treatment of coronary restenosis, especially when the encoded protein can re-endothelialize the arterial lumen. In this study, we have examined gene delivery in vitro and in vivo using poly(beta-amino ester) (PbAE) precondensed plasmid DNA-containing cationic liposomes or lipopolyplexes (LPP) immobilized on stainless steel meshes and stents using gelatin coatings. In vitro studies using LPP-immobilized on 50 mm round meshes using type A and B gelatin coatings showed that LPP were efficiently internalized in human aortic smooth muscle cells (SMC) over time, leading to green fluorescent protein (GFP) expression. Type B gelatin coating was found to be more effective in intracellular delivery and transgene expression efficiency and, as such, was used for stent coating. In vivo studies, carried out in iliac artery restenosis model in New Zealand white rabbits, also showed GFP expression in arterial tissues after 24 h of implantation. Based on these encouraging preliminary results, LPP-based formulations can serve as a safe and effective nonviral gene delivery system for effective treatment of coronary restenosis.

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.

DNA as therapeutics; an update

Human gene therapy is the introduction of new genetic material into the cells of an individual with the intention of producing a therapeutic benefit for the patient. Deoxyribonucleic acid and ribonucleic acid are used in gene therapy. Over time and with proper oversight, human gene therapy might become an effective weapon in modern medicine's arsenal to help fight diseases such as cancer, acquired immunodeficiency syndrome, diabetes, high blood pressure, coronary heart disease, peripheral vascular disease, neurodegenerative diseases, cystic fibrosis, hemophilia and other genetic disorders. Gene therapy trials in humans are of two types, somatic and germ line gene therapy. There are many ethical, social, and commercial issues raised by the prospects of treating patients whose consent is impossible to obtain. This review summarizes deoxyribonucleic acid-based therapeutics and gene transfer technologies for the diseases that are known to be genetic in origin. Deoxyribonucleic acid-based therapeutics includes plasmids, oligonucleotides for antisense and antigene applications, deoxyribonucleic acid aptamers and deoxyribonucleic acidzymes. This review also includes current status of gene therapy and recent developments in gene therapy research.

Escape from the matrix: multiple mechanisms for fibroblast activation in pulmonary fibrosis

Lung fibrosis is a recognized feature of many chronic lung diseases and is central to the pathogenesis of idiopathic pulmonary fibrosis, a disease that carries a prognosis worse than many cancers. Current research into this condition is defining the key pathways of activation either in resident fibroblasts, matrix-producing cells derived from circulating fibrocytes, or epithelial cells that appear to transdifferentiate to fibroblast-like cells. The downstream signaling pathways are also being delineated as well as the gene interactions leading to altered cell phenotype. These studies have led to an appreciation that multiple pathways, including inflammatory and coagulation cascades, are involved in the pathogenesis of idiopathic pulmonary fibrosis. As these facts come to light, we are exploring promising new approaches to treat fibroses and halt the inexorable progression that is a feature of these disorders. This article reviews these findings and our current concepts of the key molecular events leading to tissue damage and excessive matrix deposition in lung fibrosis. It also highlights the need for new studies to delineate alternative pathogenetic mechanisms and integrate these pathways so we have a framework to better understand their importance in individual patients.

Progress in developing cationic vectors for non-viral systemic gene therapy against cancer

Initially, gene therapy was viewed as an approach for treating hereditary diseases, but its potential role in the treatment of acquired diseases such as cancer is now widely recognized. The understanding of the molecular mechanisms involved in cancer and the development of nucleic acid delivery systems are two concepts that have led to this development. Systemic gene delivery systems are needed for therapeutic application to cells inaccessible by percutaneous injection and for multi-located tumor sites, i.e. metastases. Non-viral vectors based on the use of cationic lipids or polymers appear to have promising potential, given the problems of safety encountered with viral vectors. Using these non-viral vectors, the current challenge is to obtain a similarly effective transfection to viral ones. Based on the advantages and disadvantages of existing vectors and on the hurdles encountered with these carriers, the aim of this review is to describe the "perfect vector" for systemic gene therapy against cancer.

Regulation of matrix turnover: fibroblasts, forces, factors and fibrosis

Fibroblasts are multifunctional cells that are responsible for matrix homoeostasis, continuously synthesizing and degrading a diverse group of extracellular molecules and their receptors. Rates of turnover of matrix molecules and the proteases that degrade them are normally under the control of diverse chemical and mechanical cues, with cytokines, growth factors, proteases, lipid mediators and mechanical forces playing roles. The maintenance of this homoeostasis is vital to the preservation of normal tissue function and is clearly lost in chronic diseases of the joints, skin and internal organs where destruction and excessive deposition is seen. Current research is focusing on defining the key pathways of activation either in resident fibroblasts, matrix-producing cells derived from circulating fibrocytes, or from transdifferentiation of resident cells. The common downstream signalling pathways are also being defined, as well as the gene interactions leading to altered cell phenotype. The present article reviews these findings and our current concepts of the key molecular events leading to tissue damage and excessive matrix deposition in tissue fibrosis. These studies are leading to an appreciation of the complexity of events with multiple pathways involved, but, as the facts emerge, we are finding promising new ways to treat fibrosis and halt the inexorable progression that is a feature of so many fibrotic and remodelling disorders.

Analysis and optimization of the cationic lipid component of a lipid/peptide vector formulation for enhanced transfection in vitro and in vivo

We have previously described a lipopolyplex formulation comprising a mixture of a cationic peptide with an integrin-targeting motif (K16GACRRETAWACG) and Lipofectin, a liposome consisting of DOTMA and DOPE in a 1:1 ratio. The high transfection efficiency of the mixture involved a synergistic interaction between the lipid/peptide components. The aim of this study was to substitute the lipid component of the lipopolyplex to optimize transfection further and to seek information on the structure-activity relationship of the lipids in the lipopolyplex. Symmetrical cationic lipids with diether linkages that varied in alkyl chain length were formulated into liposomes and then incorporated into a lipopolyplex by mixing with an integrin-targeting peptide and plasmid DNA. Luciferase transfections were performed of airway epithelial cells and fibroblasts in vitro and murine lung airways in vivo. The biophysical properties of lipid structures and liposome formulations and their potential effects on bilayer membrane fluidity were determined by differential scanning calorimetry and calcein-release assays. Shortening the alkyl tail from C18 to C16 or C14 enhanced lipopolyplex and lipoplex transfection in vitro but with differing effects. The addition of DOPE enhanced transfection when formulated into liposomes with saturated lipids but was more variable in its effects with unsaturated lipids. A substantial improvement in transfection efficacy was seen in murine lung transfection with unsaturated lipids with 16 carbon alkyl tails. The optimal liposome components of lipopolyplex and lipoplex vary and represent a likely compromise between their differing structural and functional requirements for complex formation and endosomal membrane destabilization.

PEGylated J591 mAb loaded in PLGA-PEG-PLGA tri-block copolymer for targeted delivery: In vitro evaluation in human prostate cancer cells

J591 monoclonal antibody (mAb) has high affinity for prostate specific membrane antigen (PSMA) on prostate cancer (PCA) cells. We coupled polyethylene glycol-J591 (PEGylated J591) to a salicyl hydroxamic acid (SHA)-derivatized polyethylenimine (PEI)/DNA-betagal vector to investigate the specificity and efficiency of targeting PSMA in PCA cells through encapsulation. Coupling was facilitated via the high affinity interaction between phenyl(di)boronic acid (PDBA) and SHA molecules yielding J591/PEG/PEI/DNA-betagal polyplex. After encapsulation with poly(d,l-lactic-co-glycolic acid)-b-polyethylene glycol-b-poly(d,l-lactic-co-glycolic acid) (PLGA-PEG-PLGA) tri-block copolymer, 8-10-fold increment of gene transfection levels were attained at the optimum concentration of 0.25% (w/v) using Pluronic F68 tri-block copolymer as a control. The enhanced transfection efficiency was attributed to increased internalization and uptake of the radiolabeled plasmid in the presence of PLGA-PEG-PLGA tri-block copolymer. The release of plasmid DNA (pDNA) from microparticles containing SHA-PEI-complexed pDNA showed little initial burst release followed by a 5% release over 48 h. The release accelerated thereafter and approximately 60% was released after 28 days. Deconvolution confocal microscopy showed polyplex/microparticle formulation localized in the cell nucleus as opposed to the polyplex without PLGA-PEG-PLGA indicating that an optimal concentration of PLGA-PEG-PLGA tri-block copolymer can be utilized to enhance endocytic process of J591-mediated targeting of PCA cells.

Application to Vascular Adventitia of a Nonviral Vector for TIMP-1 Gene Therapy to Prevent Intimal Hyperplasia

Somatic gene transfer continues to have potential for the study and therapy of cardiovascular disease. We have developed a modular, self-assembling, nonviral system consisting of Lipofectin, integrin-targeting peptides, and plasmid DNA (LID) and we have applied this to a model of vascular injury, rat carotid angioplasty. Marker gene studies identified transfection of adventitial cells after vector delivery to that layer. Human tissue inhibitor of metalloproteinase-1 (hTIMP-1) was tested as a therapeutic gene product after direct application to the exposed adventitial layer. Vascular LID.hTIMP-1 transfection was confirmed by polymerase chain reaction and gene expression by immunohistochemistry at 7 days. Neointimal areas were 0.160 +/- 0.078 and 0.225 +/- 0.052 mm(2) for LID.hTIMP-1-transfected (n = 14) and LID.pCI-transfected (n = 12) vessels, respectively, at 14 days, and 0.116 +/- 0.068 mm(2) (n = 14) and 0.194 +/- 0.095 mm(2) (n = 14), respectively, at 28 days, representing a 29 and 40% reduction in neointimal hyperplasia at 14 and 28 days, respectively, after balloon dilatation. Neointima-to-media ratios were similarly reduced. In addition, expansile remodeling after balloon injury was inhibited at 14 days, the area within the external elastic lamina being 0.50 +/- 0.02 and 0.61 +/- 0.02 mm(2) in LID.hTIMP-1- and LID.pCI-transfected arteries, respectively (p < 0.0005). We have demonstrated an effective system of therapeutic gene transfer, particularly targeting the arterial adventitia, where transfer of genes involved in matrix remodeling and cell migration may be useful.

The Nuclear Pore Complex: The Gateway to Successful Nonviral Gene Delivery

One of the limiting steps in the efficiency of nonviral gene delivery is transport of genetic material across the nuclear membrane. Trafficking of nuclear proteins from the cytoplasm into the nucleus occurs via the nuclear pore complex and is mediated by nuclear localization signals and their nuclear receptors. Several strategies employing this transport mechanism have been designed and explored to improve nonviral gene delivery. In this article, we review the mechanism of nuclear import through the nuclear pore complex and the strategies used to facilitate nuclear import of exogenous DNA and improve gene expression.

Synthetic, self-assembly ABCD nanoparticles; a structural paradigm for viable synthetic non-viral vectors

Gene therapy research is still in trouble owing to a paucity of acceptable vector systems to deliver nucleic acids to patients for therapy. Viral vectors are efficient but may be too dangerous. Synthetic non-viral vectors are inherently safer but are currently not efficient enough to be clinically viable. The solution for gene therapy lies with improved synthetic non-viral vectors systems. This review is focused on synthetic cationic liposome/micelle-based non-viral vector systems and is a critical review written to illustrate the increasing importance of chemistry in gene therapy research. This review should be of primary interest to synthetic chemists and biomedical researchers keen to appreciate emerging technologies, but also to biological scientists who remain to be convinced about the relevance of chemistry to biology.

Tumor-specific gene delivery mediated by a novel peptide-polyethylenimine-DNA polyplex targeting aminopeptidase N/CD13

We have developed a novel polyethylenimine (PEI)-DNA vector formulation that is capable of efficient tumor-specific delivery after intravenous administration to nude mice. To further increase the specificity of delivery, we have attached the peptide CNGRC to the vector, which is specific for aminopeptidase N (CD13). The strategy for coupling this peptide to PEI was based on a novel method involving the strong affinity between phenyl(di)boronic acid (PDBA) and salicylhydroxamic acid (SHA) as well as a polyethylene glycol (PEG) linker to reduce steric hindrance between the vector and the peptide. In vitro assessment of targeting by the CNGRC/PEG/PEI/DNA vector carrying a beta-galactosidase (beta-Gal)-expressing plasmid showed as much as a 5-fold increase in transduction, relative to the untargeted PEG/PEI/DNA-betagal vector, of CD13-positive lung cancer, fibrosarcoma, bladder cancer, and human umbilical vein endothelial cells. Competition with free peptide resulted in up to a 90% reduction in delivery, indicating that gene delivery was specific for CD13-positive cells. Intravenous administration of the CNGRC/PEG/PEI/DNA-betagal vector to nude mice bearing subcutaneous tumors resulted in as much as a 12-fold increase in beta-Gal expression in tumors as compared with expression in either lungs or tumors from animals treated with the original PEI/DNA-betagal vector. In vivo transduction analysis using the CNGRC/PEG/PEI/DNA vector to target the intravenous delivery of a yellow fluorescence protein (YFP)-expressing plasmid to subcutaneous H1299 tumors confirmed delivery of YFP to both tumor cells and tumor endothelial cells. The use of this peptide to further increase tumor-specific delivery mediated by our novel PEI/DNA vector now provides a basis for developing tumor-targeted gene therapies for use in the clinical treatment of cancer.

Lipid Mixing between Lipoplexes and Plasma Lipoproteins Is a Major Barrier for Intravenous Transfection Mediated by Cationic Lipids

It has been previously shown that transfection activity of cationic liposome/DNA lipoplexes delivered systemically is drastically inhibited by lipoproteins (Tandia, B. M., Vandenbranden, M., Wattiez, R., Lakhdar, Z., Ruysschaert, J. M., and Elouahabi, A. (2003) Mol Ther. 8, 264-273). In this work, we have compared the binding/uptake and transfection activities of DOTAP (N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride) and diC14-amidine (3-tetradecylamino-N-tert-butyl-N'-tetra-decylpropionamidine)-containing lipoplexes in the presence or absence of purified low density lipoproteins and high density lipoprotein. Binding/uptake of both lipoplexes by the mouse lung endothelial cell line was inhibited to a similar extent in the presence of lipoproteins. In contrast, transfection activity of diC14-amidine-containing lipoplexes was almost completely inhibited (approximately by 95%), whereas approximately 40% transfection activity of DOTAP-containing lipoplexes was preserved in the presence of lipoproteins. Interestingly, the ability of lipoproteins to inhibit the transfection efficiency of lipoplexes was well correlated with their ability to undergo lipid mixing with the cationic lipid bilayer as revealed by fluorescence resonance energy transfer assay. Incubation of lipoplexes with increased doses of lipoproteins resulted in enhanced lipid mixing and reduced transfection activity of the lipoplexes in mouse lung endothelial cells. The role of lipid mixing in transfection was further demonstrated using lipid-mixing inhibitor, lyso-phosphatidylcholine, or activator (dioleoylphosphatidylethanolamine). Incorporation of Lyso-PC into diC14-amidine-containing lipoplexes completely abolished their capacity to undergo lipid mixing with lipoproteins and allowed them to reach a high transfection efficiency in the presence of lipoproteins. On the other hand, the incorporation of dioleoylphosphatidylethanolamine into DOTAP/DNA lipoplex activated lipid mixing with the lipoproteins and was shown to be detrimental toward the transfection activity of these lipoplexes. Taken together, these results indicate that fusion of lipoplexes with lipoproteins is a limiting factor for in vivo transfection.

What Role Can Chemistry Play in Cationic Liposome‐Based Gene Therapy Research Today?

Gene therapy research is still in trouble owing to a paucity of acceptable vector systems to deliver nucleic acids to patients for therapy. Viral vectors are efficient but may be too dangerous for routine clinical use. Synthetic non-viral vectors are inherently much safer but are currently not efficient enough to be clinically viable. The solution for gene therapy lies with improved synthetic non-viral vectors based upon well-found platform technologies and a thorough understanding of the barriers to efficient gene delivery and expression (transfection) relevant to clinical applications of interest. Here we introduce and interpret synthetic non-viral vector systems through the ABCD nanoparticle structural paradigm that represents, in our view, an appropriate lens through which to view all synthetic, non-viral vector systems applicable to in vitro use or in vivo applications and gene therapy. Our intention in introducing this paradigm is to shift the focus of organic and physical chemists away from the design of yet another cytofectin, and instead encourage them to appreciate the wider challenges presented by the need to produce tool kits of meaningful chemical components from which to assemble viable, tailor-made nanoparticles for in vivo applications and gene therapy, both now and in the future.

Toxicity of Cationic Lipid‐DNA Complexes

As with any conventional drug, the body's response to cationic lipid-DNA complexes is highly dependent on both the dose administered and the route of delivery. At relatively low doses there is little to no effect on organ function or tissue architecture, but at higher doses, acute inflammation and tissue damage can occur that is sometimes quite profound. Of the two most common routes of delivery, intravenous (IV) or intrapulmonary, IV administration tends to cause more severe adverse effects and can be lethal at higher doses of complex. Both routes activate an innate immune response that includes the induction of proinflammatory cytokines and immune cell activation, a major portion of which has been attributed to the presence of immunostimulatory CpG motifs within the plasmid DNA vector. Removing CpGs from the plasmid vector reduces several, but not all of the acute inflammatory responses to cationic lipid-DNA complexes. Therefore, other strategies are required to improve the therapeutic potential of these vectors, such as transient immune suppression, aerosolization of the complex, and novel formulations that have increased efficiency of transduction and decreased interaction with immune cells.

Functional delivery of large genomic DNA to human cells with a peptide-lipid vector

BACKGROUND

Nonviral gene transfer vectors have the potential to deliver much larger DNA constructs than current viral vectors but suffer from a low transfection efficiency. The LID vector, composed of Lipofectin (L), an integrin-targeting peptide (I) and DNA (D), is a highly efficient synthetic vector, both in vitro and in vivo, which may allow the transfer of genomic loci for gene therapy.

METHODS

Transfection efficiencies were quantitated using the green fluorescent protein (GFP) reporter. Expression of a large genomic locus (NBS1 [Nijmegen breakage syndrome], encoding nibrin) was assessed by immunofluorescence.

RESULTS

We report a systematic study of the parameters influencing delivery of BAC-based plasmids ranging in size from 12 to 242 kb using the LID vector. We showed 60% of cells were transfected with the smaller plasmids while plasmids up to 242 kb were consistently delivered to over 10% of cells. The number of transfected cells was related to number of plasmids in the transfection complex independent of plasmid size. Atomic force microscopy showed that LID particle size increased with plasmid size consistent with one plasmid molecule per particle. When LID vectors were used to deliver the NBS1 gene as a 143 kb construct to primary NBS cells, at least 57% of cells expressing GFP also expressed functional nibrin.

CONCLUSIONS

We show that LID vectors represent a promising tool for the transfer of complete genomic loci.

DNA delivery from an intravascular stent with a denatured collagen-polylactic-polyglycolic acid-controlled release coating: mechanisms of enhanced transfection

We previously demonstrated that DNA-polylactic-polyglycolic acid (PLGA)-coated stents can deliver genes to the arterial wall with reporter expression involving 1% of neointimal cells. The present study investigated a novel formulation utilizing denatured collagen in DNA-stent coatings; denatured collagen was hypothesized to enhance gene transfer due to adhesion molecule interactions and actin-related mechanisms. Arterial smooth muscle cells (SMCs) cultivated on denatured collagen had significantly greater plasmid DNA (beta-galactosidase) transfection than SMC grown on native collagen (18.3+/-1.2 vs 1.0+/-0.1%, P<0.001). The denatured-collagen effect was completely blocked with anti-alpha(v)beta(3) integrin antibody. SMCs cultivated on native collagen supplemented with tenascin-C (TN-C), a protein recognized by alpha(v)beta(3) integrins, showed a 33-fold increase in transfection compared to control (P<0.001); this effect was also blocked with anti-alpha(v)beta(3) antibody. We observed that cells grown on denatured collagen had marked F-actin-enriched stress fibers and intense perinuclear G actin, compared to those grown on native collagen, which demonstrated F-actin-enriched focal adhesions without perinuclear G-actin localization. Cytochalasin-D, an F actin depolymerizing agent, caused significantly increased SMC transfection in cells cultivated on native collagen compared to control cells (18.0+/-1.8 vs 3.02+/-0.9%, P<0.001) further supporting the view that actin-related cytoskeletal changes influence transfection. A denatured-collagen-PLGA composite vascular stent coating similarly resulted in increased plasmid DNA green fluorescent protein (GFP) expression compared to controls (P<0.001) in SMC cultures; the increased transfection was blocked by anti-alpha(v)beta(3) antibody. Pig coronary studies comparing denatured-collagen-PLGA-coated stents containing plasmid DNA (encoding GFP) to coated stents without DNA demonstrated 10.8% of neointimal cells transfected; this level of expression was almost an order of magnitude greater than previously reported with a DNA delivery stent. It is concluded that denatured collagen incorporated into plasmid DNA-stent coating formulations may increase the level of gene expression in vitro and in vivo because of integrin-related mechanisms and associated changes in the arterial smooth muscle cell actin cytoskeleton.

Identification of human plasma proteins that bind to cationic lipid/DNA complex and analysis of their effects on transfection efficiency: implications for intravenous gene transfer

Interaction of cationic lipid/DNA complex with the plasma is a limiting step for the cationic lipid-mediated intravenous gene transfer and expression process. Most of the plasma components that interact with the complex and inhibit its transfection efficiency are still unknown. In the present work, human plasma proteins and lipoproteins that bind to a cationic lipid/DNA complex were isolated on a sucrose density gradient and identified by 2-D gel electrophoresis. Protein binding did not result in complex dissociation or DNA degradation. The effects of several complex-binding plasma components on the transfection efficiency were studied using lung endothelial cells cultured in vitro. Lipoprotein particles caused a drastic loss of the transfection efficiency of the complex. Surprisingly, fibrinogen was found to activate the transfection process. The roles of these complex-binding plasma components on the complex uptake efficiency were quantitatively assessed using radiolabeled plasmid DNA and qualitatively evaluated using fluorescence microscopy. A good correlation was found between the effects of the complex-binding plasma components on the transfection and on cell uptake efficiencies. In contrast to what was generally believed, our data suggest that disruption of the complex does not occur when it is in contact with the plasma and therefore could not be responsible for the loss of transfection activity. Instead, coating of complexes with plasma components seems to be responsible for reduced uptake by cells, which in turn results in reduced transfection.

Repeated intrathecal administration of plasmid DNA complexed with polyethylene glycol-grafted polyethylenimine led to prolonged transgene expression in the spinal cord

Gene delivery into the spinal cord provides a potential approach to the treatment of spinal cord traumatic injury, amyotrophic lateral sclerosis, and spinal muscular atrophy. These disorders progress over long periods of time, necessitating a stable expression of functional genes at therapeutic levels for months or years. We investigated in this study the feasibility of achieving prolonged transgene expression in the rat spinal cord through repeated intrathecal administration of plasmid DNA complexed with 25 kDa polyethylenimine (PEI) into the lumbar subarachnoid space. With a single injection, DNA/PEI complexes could provide transgene expression in the spinal cord 40-fold higher than naked plasmid DNA. The transgene expression at the initial level persisted for about 5 days, with a low-level expression being detectable for at least 8 weeks. When repeated dosing was tested, a 70% attenuation of gene expression was observed following reinjection at a 2-week interval. This attenuation was associated with apoptotic cell death and detected even using complexes containing a noncoding DNA that did not mediate any gene expression. When each component of the complexes, PEI polymer or naked DNA alone, were tested in the first dosing, no reduction was found. Using polyethylene glycol (PEG)-grafted PEI for DNA complexes, no attenuation of gene expression was detected after repeated intrathecal injections, even in those rats receiving three doses, administered 2 weeks apart. Lumbar puncture is a routine and relatively nontraumatic clinical procedure. Repeated administration of DNA complexed with PEG-grafted PEI through this less invasive route may prolong the time span of transgene expression when needed, providing a viable strategy for the gene therapy of spinal cord disorders.

Polycation liposome-mediated gene transfer in vivo

The polycation liposome (PCL), a recently developed gene transfer system, is simply prepared by a modification of liposomes with cetylated polyethylenimine (PEI), and shows remarkable transgene efficiency with low cytotoxicity. In the present study, we investigated the applicability of PCLs for in vivo gene transfer, since the PCL-mediated transgene efficiency was found to be maintained in the presence of serum. PCLs composed of dioleoylphosphatidylethanolamine (DOPE) with 5 mol% cetyl PEI (PEI average mr. wt. 1800), were superior for transfection to those of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (2:1 as molar ratio) with 5 mol% cetyl PEI in vitro, although the latter PCLs were more efficient for gene transfer in vivo. PCL-DNA complexes were injected into mice via a tail or the portal vein, with the DNA being a plasmid encoding green fluorescent protein (GFP) or luciferase; and the expression was monitored qualitatively or quantitatively, respectively. Tail vein injection resulted in high expression of both GFP and luciferase genes in lung, and portal vein injection resulted in high expression of both genes in the liver. Concerning the gene delivery efficiency, the PCL was found to be superior to PEI or cetyl PEI alone. The optimal conditions for in vivo transfection with PCLs were also examined.

Formation of LID vector complexes in water alters physicochemical properties and enhances pulmonary gene expression in vivo

There is currently an urgent need to develop efficient gene-delivery systems for the lung that are free of inflammatory effects. The LID vector is a synthetic gene delivery system, comprised of lipofectin (L), an integrin-targeting peptide (I) and DNA (D) that has previously been shown to have high transfection efficiency in the lung. We have assessed the effect of alternative methods of complex preparation on structural features of the complex, levels and duration of reporter gene expression and the host response to the LID vector. We have demonstrated that making the complex in water affects the structure of the LID complexes making them smaller and more stable with a more cationic surface charge than complexes prepared in phosphate-buffered saline (PBS). When the LID vector was constituted in water and instilled intratracheally into the lungs of mice there was a 10-fold increase in luciferase activity compared with preparation in PBS. Furthermore, luciferase activity was still evident 1 week following vector instillation. This enhancement may be because of altered complex structure, although effects of the hypotonic vector solution on the lung cannot be excluded. The inflammatory effects of instilling the LID vector in water were minimal, even after three administrations of the LID vector, with only mild alterations in cytokine and broncho-alveolar lavage fluid (BALF) cell profiles. These results demonstrate that the LID vector can generate high, and prolonged, levels of gene expression in the lung from small quantities of DNA and that careful attention to synthetic polyplex structure may be important to optimize efficiency of gene expression in vivo.