Detailed analysis of structures and formulations of cationic lipids for efficient gene transfer to the lung

Structure-function relationship research of glycerol backbone-based cationic lipids for gene delivery

Transfection activities of two series of synthetic glycerol backbone-based cationic lipids were studied as gene delivery carriers. The variable length of hydrocarbon chains, diverse quaternary ammonium heads, different linkage, as well as alternative anion combined with them allowed to find how these factors affect cationic lipids on their gene delivery performance. The structure-function relationship of the synthetic glycerol backbone-based cationic lipids was discussed, and the transfection efficiency of some of the cationic liposomes was superior or parallel to that of two commercial transfection agents.

In vivo imaging of gene transfer to the respiratory tract

Imaging of in vivo gene expression using luciferase expression in various organs has been used for several years. In contrast to other organs, in vivo imaging of the lung, particularly after non-viral gene transfer has not been extensively studied. The aim of this study was to address several questions: (1) Does in vivo light emission correlate with standard tissue homogenate-based luciferase detection in a dose-dependent manner? Recombinant Sendai virus (SeV) transduces airway epithelial cells very efficiently and was used to address this question, (2) Is the sensitivity of the assay sufficient to detect non-viral gene transfer? We treated mice with SeV-Lux vector using our standard "sniffing" protocol, a method that predominantly results in lung deposition. Dose-related in vivo light emission was visible in all animals. Importantly, there was a significant correlation (r>0.90, p<0.0001) between the in vivo and ex vivo assays in both the left and right lung. We next transfected the nasal epithelium via nasal perfusion or the lungs ("sniffing") of mice with a luciferase plasmid (pCIKLux) complexed to the cationic lipid GL67 (n=25-27/group) and imaged luciferase expression in vivo 24h after transfection. Gene expression was detectable in both organs. Correlation between the in vivo and ex vivo assays was significant (r=0.52, p<0.005) in the left, but not the right lung. The correlation in the nose was weaker (r=0.45, p<0.05). To our knowledge these studies show for the first time that this non-invasive method of assessing pulmonary gene transfer is viable for evaluating non-viral gene transfer agents.

Cationic liposomes as non-viral carriers of gene medicines: resolved issues, open questions, and future promises

The clinical success of gene therapy is critically dependent on the development of efficient and safe gene delivery reagents, popularly known as "transfection vectors." The transfection vectors commonly used in gene therapy are mainly of two types: viral and non-viral. The efficiencies of viral transfection vectors are, in general, superior to their non-viral counterparts. However, the myriads of potentially adverse immunogenic aftermaths associated with the use of viral vectors are increasingly making the non-viral gene delivery reagents as the vectors of choice. Among the existing arsenal of non-viral gene delivery reagents, the distinct advantages associated with the use of cationic transfection lipids include their: (a) robust manufacture; (b) ease in handling and preparation techniques; (c) ability to inject large lipid:DNA complexes; and (d) low immunogenic response. The present review highlights the major achievements in the area of designing efficacious cationic transfection lipids, some of the more recent advances in the field of cationic liposomes-mediated gene transfer and targeted gene delivery, some unresolved issues and challenges in liposomal gene delivery, and future promises of cationic liposomes as gene-carriers in non-viral gene therapy.

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.

A Poly(β-Amino Ester) of Spermine and Poly(ethylene Glycol) Diacrylate as a Gene Carrier

Vectors are vital aspect of gene delivery system which decides the success of gene therapy. Efficient transfection with minimum or no toxicity, are two principal aims of any gene delivery system. In this our study, we rationally developed biodegradable water soluble poly(ßamino ester) (PAE) based on spermine (SPR) and poly (ethylene glycol) (PEG), by Michael-type addition reaction and further studied for its potential as a gene carrier. Confirmation of synthesized PAE was done by proton NMR spectroscopy. In gel retardation assay, the PAEs have shown good DNA binding ability over wide range of polyplexes. The addition of PEG over SPR resulted in a novel PAE with higher degree of safety and transfection efficiency as compared with polyethylenimine 25K (PEI) when studied in 293T human kidney carcinoma cells.

Novel cationic lipophilic peptides for oligodeoxynucleotide delivery

In search of new oligodeoxynucleotide (ODN) delivery agents, we evaluated novel peptides derived from core peptide H-GLRILLLKV-OH (CP). CP is a fragment designed from the T-cell antigen receptor (TCR) alpha-chain transmembrane sequence. CP was able to enter cells including T-cells and inhibited interleukin-2 (IL-2) production. To examine the effect of increased lipophilicity on cellular uptake and activity of CP, a lipoamino acid (2-aminododecanoic acid) was incorporated into peptide CP resulting in 2-aminodecanoyl-CP (LP). The toxicity of CP and LP was assessed by measuring the haemolytic activity. Neither compound caused any haemolysis of red blood cells. We have also compared the biological activities of the CP and LP. Using a T-cell antigen presentation assay, the more lipophilic LP caused greater inhibition of IL-2 production than the parent CP in the antigen stimulated T-cells. The LP also showed increased permeability than CP in the Caco-2 cell assay. We utilised the enhanced cell permeability property of LP in oligodeoxynucleotide ODN1 delivery. Isothermal titration calorimetry (ITC) suggested that CP and LP complex with ODN1 in a 12:1 (CP:ODN1) and 15:1 (LP:ODN1) ratio. These complexes were then transfected into human retinal pigment epithelial cells. The level of transfection was measured by the decreased production of the protein human vascular endothelial growth factor (hVEGF). The results revealed greater transfection efficiency for both CP and LP (47%, 55% more inhibition) compared to commercially available transfection agent cytofectin GSV. These results suggested that the CP and particularly its lipophilic analogue LP have the potential to be used as oligodeoxynucleotide delivery systems.

Nonviral gene delivery: what we know and what is next

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

Ethanol enhanced in vivo gene delivery with non-ionic polymeric micelles inhalation

Modifications of both carriers and host barriers have been investigated for efficient inhalation gene delivery to lung. Here we used a biocompatible, non-ionic poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) (PEO-PPO-PEO) polymeric micelles (PM) as a carrier and combined it with ethanol to enhance membrane penetration of delivered DNA. The inhalation delivery with six 100 microg doses of pCMV-Lac Z with PM co-formulated with 10%-40% ethanol to nude mice in 2 days at 8 h interval was performed. The beta-galatosidase (beta-Gal) activity was assessed using chlorophenol red-beta-d galactopyranoside (CPRG) and X-gal staining for quantitative and qualitative analysis in tissues. The results showed that beta-Gal activity was significantly increased by 38% in lung around bronchioles when inhalation with PM and 10% ethanol was given. The 10% ethanol also increased the intracellular apparent permeability by 42% in stomach and by 141% in intestine at 48 h after the first dosage of delivery. Also delivery of DNA encoding a functional human cystic fibrosis transmembrane protein (CFTR) using the same inhalation delivery method co-formulated with 10% ethanol, an increased expression of CFTR in lung was detected by immunostaining. We concluded that 10% ethanol co-formulated with the PM system could enhance inhaled gene delivery to airway and gastrointestinal (GI) tract.

Bile acid-oligopeptide conjugates interact with DNA and facilitate transfection

Bile acids conjugated to oligoarginine-containing peptides (BACs) form complexes with DNA based on the electrostatic interactions between negatively charged phosphate groups of the nucleic acid and the positively charged side chain guanidinium groups of the oligoarginine in the BACs. Charge neutralization of both components and subsequent increases of the net positive charge of the complex combined with the water-soluble lipophilic nature of the bile acid results in changes in the physicochemistry and biological properties of the complexes. We have examined the relationship of a series of 13 BACs on their interaction with circular plasmid DNA (pDNA). The formation of soluble, low-density and insoluble, high-density complexes was analyzed using several methods. The formation of high-density complexes was dependent on the DNA concentration, and was enhanced by increasing the BAC to pDNA charge ratio. Several of the BAC:pDNA complexes demonstrated exclusion of the DNA-intercalator Hoechst 33258 from pDNA, and were also protected from DNase activity. Several BAC conjugates interacted with pDNA to form nanometer-sized particles suitable for cell transfection in vitro. Five of the 13 BACs were transfection competent as single agents, and 11 of the 13 BACs showed enhancement of transfection in combination with DOPE containing liposomes or silica nanoparticles.

Identification of transfected cell types following non-viral gene transfer to the murine lung

BACKGROUND

Identification of the cell types transfected following gene transfer is an important factor in the selection of appropriate gene transfer agents (GTAs). Due to the relatively low gene expression mediated by non-viral GTAs, current methodologies for the detection and identification of transfected cells in the lung have proven insensitive and unreliable. We have investigated the use of the green fluorescent protein (GFP) to identify transfected cells in a mouse lung model.

METHODS

Direct visualisation of GFP fluorescence in frozen histological sections was used in conjunction with a panel of cell type specific antibodies to investigate the distribution and level of gene expression in mouse lungs following instillation of non-viral GTAs.

RESULTS

Despite considerable tissue autofluorescence, dose-dependent expression of GFP was detected following instillation of as little as 25 microg naked plasmid DNA (pDNA). Naked pDNA and pDNA complexed with polyethylenimine appeared to transfect mainly ciliated cells and Clara cells of the conducting airway, whereas expression mediated by pDNA complexed with the cationic lipid GL67 was found predominantly in type I pneumocytes.

CONCLUSIONS

Direct visualisation of GFP expression was used to detect transfected cell types in the mouse lung. In contrast with observations made using beta-galactosidase as a reporter, gene expression from several non-viral GTAs was readily demonstrated and no false GFP-positive cells were ever detected in untreated lung tissues. Lung delivery of different GTAs resulted in GFP expression in different cell types, confirming the importance of identification of transfected cells when screening and selecting GTAs for disease targets.

Cell Biological and Biophysical Aspects of Lipid-mediated Gene Delivery

Cationic lipids are conceptually and methodologically simple tools to deliver nucleic acids into the cells. Strategies based on cationic lipids are viable alternatives to viral vectors and are becoming increasingly popular owing to their minimal toxicity. The first-generation cationic lipids were built around the quaternary nitrogen primarily for binding and condensing DNA. A large number of lipids with variations in the hydrophobic and hydrophilic region were generated with excellent transfection efficiencies in vitro. These cationic lipids had reduced efficiencies when tested for gene delivery in vivo. Efforts in the last decade delineated the cell biological basis of the cationic lipid gene delivery to a significant detail. The application of techniques such as small angle X-ray spectroscopy (SAXS) and fluorescence microscopy, helped in linking the physical properties of lipid:DNA complex (lipoplex) with its intracellular fate. This biological knowledge has been incorporated in the design of the second-generation cationic lipids. Lipid-peptide conjugates (peptoids) are effective strategies to overcome the various cellular barriers along with the lipoplex formulations methodologies. In this context, cationic lipid-mediated gene delivery is considerably benefited by the methodologies of liposome-mediated drug delivery. Lipid mediated gene delivery has an intrinsic advantage of being a biomimetic platform on which considerable variations could be built to develop efficient in vivo gene delivery protocols.

Dendrons with spermine surface groups as potential building blocks for nonviral vectors in gene therapy

This paper investigates a series of dendrons based on the Newkome dendritic scaffold that displays a naturally occurring polyamine (spermine) on their surface. These dendrons have previously been shown to interact with DNA in a generation dependent manner with the more highly branched dendrons exhibiting a strong multivalency effect for the spermine surface groups. In this paper, we investigate the ability of these dendrons to transfect DNA into cells (human breast carcinoma cells, MDA-MB-231, and murine myoblast cells, C2C12) as determined by the luciferase assay. Although the dendrons are unable to transfect DNA in their own right, they are capable of delivering DNA in vitro when administered with chloroquine, which assists with escape from endocytic vesicles. The cytotoxicity of the dendrons was determined using the XTT assay, and it was shown that the dendrons were nontoxic either alone or in the presence of DNA. However, when administered with DNA and chloroquine, the most highly branched dendron did exhibit some cytotoxicity. This paper elucidates the relationship between in vitro transfection efficiency and toxicity. While transfection efficiencies are modest, the low toxicity of the dendrons, both in their own right, and in the presence of DNA, provides encouragement that this type of building block, which has a relatively high affinity for DNA, will provide a useful starting point for the further synthetic development of more effective gene transfection agents.

Cationic liposomes for gene delivery

Cationic liposome-DNA complexes (lipoplexes) constitute a potentially viable alternative to viral vectors for the delivery of therapeutic genes. This review will focus on various parameters governing lipoplex biological activity, from their mode of formation to in vivo behaviour. Particular emphasis is given to the mechanism of interaction of lipoplexes with cells, in an attempt to dissect the different barriers that need to be surpassed for efficient gene expression to occur. Aspects related to new trends in the formulation of lipid-based gene delivery systems aiming at overcoming some of their limitations will be covered. Finally, examples illustrating the potential of cationic liposomes in clinical applications will be provided.

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

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

Characteristics of transcription-regulatory elements for gene expression from plasmid vectors in human trophoblast cell lines

Nonviral gene delivery systems are useful for basic research in trophoblasts. In these systems, gene expression is regulated by a cassette of regulatory elements within the plasmid, and the transcriptional activity differs among cell lines. In the present study, we used BeWo and JAR human trophoblast cell lines to systematically compare the transcriptional activities of several expression cassettes and those of a control plasmid made up of a simian virus 40 (SV40) promoter, a polyadenylation (PA) signal, and an enhancer. We also found that insertion of intron elements enhanced transcriptional activities in the following order: intron A>hybrid beta-globin-immunoglobin intron>no intron. Of several PA signals tested including those from SV40, bovine growth hormone, and the minimal rabbit beta-globin, the latter had the highest transcriptional activities (3.9- and 26-fold over control plasmid in BeWo and JAR cells, respectively). Addition of a second enhancer increased the transcriptional activity in these cells. We also found that gene expression level can be controlled by selecting the expression cassette. These results should be useful for further transgene experiments in BeWo and JAR cells.

Nondisruptive, sequence-specific coupling of fluorochromes to plasmid DNA

A method to attach a fluorochrome sequence-specifically to supercoiled plasmid DNA (pDNA) without perturbing transgene expression would provide an invaluable aid in a variety of applications requiring probes for the intracellular tracking of transfected pDNA. Here we report a method to couple commercially available fluorochromes covalently and sequence-specifically to pDNA using a peptide nucleic acid (PNA) as a linker molecule. The terminal cysteine thiol group on the PNA peptide backbone is reacted with a maleimide moiety on the fluorochrome to produce a fluorescent conjugate which is in turn hybridized to a plasmid expression vector containing an 11-bp target sequence. Spectroscopic evaluation and an electrophoretic mobility shift assay showed that the pDNA hybridized to one PNA-fluorochrome conjugate molecule. The fluorescence signal comigrated with pDNA on acrylamide gels, confirming the stable attachment of the fluorescent conjugate to the pDNA. The utility of one of the conjugates, PNA-Oregon green 488/pCMVbeta-DTS, to probe pDNA transport across the nuclear envelope, a significant barrier to gene transfer, was undertaken using a digitonin-permeabilized HeLa cell assay. The PNA-Oregon green 488/pCMVbeta-DTS conjugate is able to efficiently traverse the nuclear membrane of the permeabilized cells, accumulating in the nuclei within 30 min and reaching maximal levels by 1h. When transfected into HeLa cells, the PNA-Oregon green 488/pCMVbeta-DTS conjugate retained 55% of the native plasmid's biological activity, as determined by a beta-galactosidase assay. Thus, this method allows for the sequence-specific coupling of commercially available fluorochromes to DNA expression vectors while retaining biological function.

Inefficient cationic lipid-mediated siRNA and antisense oligonucleotide transfer to airway epithelial cells in vivo

BACKGROUND

The cationic lipid Genzyme lipid (GL) 67 is the current "gold-standard" for in vivo lung gene transfer. Here, we assessed, if GL67 mediated uptake of siRNAs and asODNs into airway epithelium in vivo.

METHODS

Anti-lacZ and ENaC (epithelial sodium channel) siRNA and asODN were complexed to GL67 and administered to the mouse airway epithelium in vivo Transfection efficiency and efficacy were assessed using real-time RT-PCR as well as through protein expression and functional studies. In parallel in vitro experiments were carried out to select the most efficient oligonucleotides.

RESULTS

In vitro, GL67 efficiently complexed asODNs and siRNAs, and both were stable in exhaled breath condensate. Importantly, during in vitro selection of functional siRNA and asODN we noted that asODNs accumulated rapidly in the nuclei of transfected cells, whereas siRNAs remained in the cytoplasm, a pattern consistent with their presumed site of action. Following in vivo lung transfection siRNAs were only visible in alveolar macrophages, whereas asODN also transfected alveolar epithelial cells, but no significant uptake into conducting airway epithelial cells was seen. SiRNAs and asODNs targeted to beta-galactosidase reduced betagal mRNA levels in the airway epithelium of K18-lacZ mice by 30% and 60%, respectively. However, this was insufficient to reduce protein expression. In an attempt to increase transfection efficiency of the airway epithelium, we increased contact time of siRNA and asODN using the in vivo mouse nose model. Although highly variable and inefficient, transfection of airway epithelium with asODN, but not siRNA, was now seen. As asODNs more effectively transfected nasal airway epithelial cells, we assessed the effect of asODN against ENaC, a potential therapeutic target in cystic fibrosis; no decrease in ENaC mRNA levels or function was detected.

CONCLUSION

This study suggests that although siRNAs and asODNs can be developed to inhibit gene expression in culture systems and certain organs in vivo, barriers to nucleic acid transfer in airway epithelial cells seen with large DNA molecules may also affect the efficiency of in vivo uptake of small nucleic acid molecules.

Successful in vivo tumor targeting of prostate-specific membrane antigen with a highly efficient J591/PEI/DNA molecular conjugate

We have utilized a novel polyethylenimine (PEI)/DNA-betagal vector to investigate the specificity and efficiency of immuno-targeting prostate-specific membrane antigen (PSMA). Coupling of the PSMA-specific monoclonal antibody, J591, to the vector was facilitated via the high-affinity interaction between phenyl(di)boronic acid and salicylhydroxamic acid molecules. Highly efficient gene delivery by this prostate cancer (PCA)-targeted J591/polyethylene glycol (PEG)/PEI/DNA-betagal vector was demonstrated in PSMA-positive cells relative to controls, resulting in significant growth inhibition in vitro when the J591/PEG/PEI/DNA-p53 was used. Competition with free antibody resulted in about 90% reduction in both J591 internalization and betagal gene delivery, indicating specificity for PSMA-positive cells. More importantly, testing the efficiency of the J591/PEG/PEI/DNA-betagal targeting vector in an orthotopic PCA model in nude mice resulted in up to a 20-fold increase in gene delivery over the untargeted vector controls. The in vivo organ distribution profile also revealed betagal expression predominantly in the tumor, which was more than 1 log higher than the next highest level of expression in the lung. Furthermore, with the targeted vector containing the gene for yellow fluorescent protein or biotinylated J591, we further demonstrate in vivo that vector-mediated gene delivery is specific for both tumor cells and tumor-associated neovasculature in PSMA-positive tumors. These results suggest the potential for further optimization of this novel vector in the context of therapeutic gene delivery.

Gene Therapy for Lung Diseases

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

Identification and characterization of a novel peptide ligand of epidermal growth factor receptor for targeted delivery of therapeutics

Epidermal growth factor receptor (ErbB1, EGFR) is overexpressed in a variety of human cancer cells. It has been considered as a rational target for drug delivery. To identify novel ligands with specific binding capabilities to EGFR, we screened a phage display peptide library and found an enriched phage clone encoding the amino acid sequence YHWYGYTPQNVI (designated as GE11). Competitive binding assay and Scatchard analysis revealed that GE11 peptide bound specifically and efficiently to EGFR with a dissociation constant of approximately 22 nM, but with much lower mitogenic activity than with EGF. We showed that the peptides were internalized preferentially into EGFR highly expressing cells, and they accumulated in EGFR overexpressing tumor xenografts after i.v. delivery in vivo. In gene delivery studies, GE11-conjugated polyethylenimine (PEI) vectors were less mitogenic, but still quite efficient at transfecting genes into EGFR highly expressing cells and tumor xenografts. Taken together, GE11 is a potentially safe and efficient targeting moiety for selective drug delivery systems mediated through EGFR.

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.

Kanamycin A-derived cationic lipids as vectors for gene transfection

Cationic lipids nowadays constitute a promising alternative to recombinant viruses for gene transfer. We have recently explored the transfection potential of a new class of lipids based upon the use of aminoglycosides as cationic polar headgroups. The encouraging results obtained with a first cholesterol derivative of kanamycin A prompted us to investigate this family of vectors further, by modulating the constituent structural units of the cationic lipid. For this study, we have investigated the transfection properties of a series of new derivatives based on a kanamycin A scaffold. The results primarily confirm that aminoglycoside-based lipids are efficient vectors for gene transfection both in vitro and in vivo (mouse airways). Furthermore, a combination of transfection and physicochemical data revealed that some modifications of the constitutive subunits of kanamycin A-based vectors were associated with substantial changes in their transfection properties.

Transient siRNA-Mediated Attenuation of Liver Expression from an α-Galactosidase a Plasmid Reduces Subsequent Humoral Immune Responses to the Transgene Product in Mice

Hepatocytes are an effective depot for protein production from gene therapy vectors. However, when gene transfer vectors or their delivery induces hepatic inflammation, adaptive immune responses against the transgene product can ensue. In BALB/c mice, hydrodynamic delivery of a CMV-driven plasmid DNA (pDNA) bearing human alpha-galactosidase A (alphagal) to the liver generated antibodies against alphagal. This humoral immune response was more robust in a transgenic knockout for alphagal, the Fabry mouse. The antibody response could be attenuated in both mouse strains by using a promoter more restricted to hepatocytes. In an attempt to reduce further the humoral responses to alphagal, expression from the transgene was attenuated by using siRNA during the period of initial delivery-associated liver inflammation. In both mouse models and with both promoters, codelivering an alphagal siRNA resulted in a 2 log decrease in initial expression that then increased over the next few weeks to levels generated by the pDNA alone. This strategy led to both attenuated antibodies and an immune status approximating "tolerance" to alphagal. Importantly, in the Fabry mouse, an alphagal siRNA together with a hepatocyte-restricted promoter gave minimal anti-alphagal antibodies and profound tolerance, suggesting that such an approach might have clinical utility for genetic diseases.

Novel molecular approaches to cystic fibrosis gene therapy

Gene therapy holds promise for the treatment of a range of inherited diseases, such as cystic fibrosis. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of cystic fibrosis pulmonary disease has proved elusive. There are many reasons for this lack of progress, both macroscopically in terms of airway defence mechanisms and at the molecular level with regard to effective cDNA delivery. This review of approaches to cystic fibrosis gene therapy covers these areas in detail and highlights recent progress in the field. For gene therapy to be effective in patients with cystic fibrosis, the cDNA encoding the cystic fibrosis transmembrane conductance regulator protein must be delivered effectively to the nucleus of the epithelial cells lining the bronchial tree within the lungs. Expression of the transgene must be maintained at adequate levels for the lifetime of the patient, either by repeat dosage of the vector or by targeting airway stem cells. Clinical trials of gene therapy for cystic fibrosis have demonstrated proof of principle, but gene expression has been limited to 30 days at best. Results suggest that viral vectors such as adenovirus and adeno-associated virus are unsuited to repeat dosing, as the immune response reduces the effectiveness of each subsequent dose. Nonviral approaches, such as cationic liposomes, appear more suited to repeat dosing, but have been less effective. Current work regarding non-viral gene delivery is now focused on understanding the mechanisms involved in cell entry, endosomal escape and nuclear import of the transgene. There is now increasing evidence to suggest that additional ligands that facilitate endosomal escape or contain a nuclear localization signal may enhance liposome-mediated gene delivery. Much progress in this area has been informed by advances in our understanding of the mechanisms by which viruses deliver their genomes to the nuclei of host cells.

The therapeutic potential of the human cystic fibrosis transmembrane conductance regulator gene

The cloning of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), mutations of which are responsible for the clinical onset of cystic fibrosis (CF), along with progress in understanding the interplay between CFTR functions and the CF cellular phenotype have prompted many investigators to explore the therapeutic potential of CFTR gene delivery to airway cells in CF patients. In the last four years, a large number of Phase I clinical trials have been started. The results from the very first trials, although mixed, showed that it was possible to transfer and express the CFTR gene, and in certain cases restore the functional electrophysiological properties of the diseased CF cells. These initial trials have been fundamental in encouraging more basic research on vector design to improve the safety and efficiency of persistent CFTR gene transfer, and to introduce novel ways of administration and new techniques to assess the potential therapeutic efficacy of functional gene expression. New Phase I clinical trials based on novel protocol design were therefore initiated.

Airway gene transfer using cationic emulsion as a mucosal gene carrier

BACKGROUND

Delivery of genes to airway mucosa would be a very valuable method for gene therapy and vaccination. However, there have been few reports on suitable gene delivery systems for administration. In this study, we use a cationic emulsion system, which is physically stable and facilitates the transfer of genes in the presence of up to 90% serum, as a mucosal gene carrier.

METHODS AND RESULTS

Cationic lipid emulsion was formulated with squalene and 1,2-dioleoyl-sn-glycero-3-trimethylammoniumpropane (DOTAP) as major components. Emulsions formed stable complexes with DNA and protected and transferred DNA to target cells against DNase I digestion in the presence of mucosal destabilizers such as heparin sulfate (a polysaccharide of the glycosaminoglycan family in mucosa) and Newfectan (a natural lung extract of bovine) in an in vitro system. In contrast, commercial liposomes and counter liposomes, made with an identical lipid composition of emulsions, failed. After in vivo intranasal instillation, the cationic emulsion showed at least 200 times better transfection activity than the liposomal carriers in both nasal tissue and lung.

CONCLUSIONS

These findings show that cationic emulsions can mediate gene transfection into airway epithelium, making it a good choice for transferring therapeutic genes and for genetic vaccination against an pathogenic infection via an airway route.

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.

Progress towards gene therapy for cystic fibrosis

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

Delivery systems for pulmonary gene therapy

Delivery of therapeutic genes to the lungs is an attractive strategy to correct a variety of pulmonary dysfunctions such as cystic fibrosis, alpha-1 antitrypsin deficiency, pulmonary hypertension, asthma, and lung cancer. Different delivery routes such as intratracheal instillation, aerosol and intravenous injection have been utilized with varying degrees of efficiency. Both viral and non-viral vectors, with their respective strengths and weaknesses, have achieved significant levels of transgene expression in the lungs. However, the application of gene therapy for the treatment of pulmonary disease has been handicapped by various barriers to the delivery vectors such as serum proteins during intravenous delivery, and surfactant proteins and mucus in the airway lumen during topical application of therapeutic genes. Immune and cytokine responses against the delivery vehicle are also major problems encountered in pulmonary gene therapy. Despite these shortcomings much progress has been made to enhance the efficiency, as well as lower the toxicity of gene therapy vehicles in the treatment of pulmonary disorders such as cystic fibrosis, lung cancer and asthma.

Detection of plasmid DNA vectors following gene transfer to the murine airways

Non-viral gene therapy is being considered as a treatment for cystic fibrosis. In clinical studies and in studies using the mouse airways as a model, current formulations result in only transient transgene expression. A number of reasons for this have been proposed including the loss of plasmid DNA from cells. The aim of these studies was to investigate why transgene expression from non-viral vectors is transient in the mouse lung. Plasmid DNA encoding the luciferase reporter gene was complexed with the cationic lipid GL67 and delivered to the mouse airways. The persistence of plasmid DNA in the mouse lungs was investigated using quantitative PCR and Southern hybridization. Results showed that intact plasmid DNA persisted in the mouse lung in the absence of any detectable luciferase activity. The de novo methylation of plasmid DNA in vivo was investigated as a potential cause of this transient gene expression but results suggested that plasmid DNA does not become de novo methylated in the mouse lung. Therefore processes other than the loss of plasmid DNA from the lung or the de novo methylation of plasmid DNA vectors must be responsible for the transient transgene expression.

A defective nontransmissible recombinant Sendai virus mediates efficient gene transfer to airway epithelium in vivo

Recombinant Sendai virus (SeV)-mediated gene transfer to differentiated airway epithelial cells has shown to be very efficient, because of its ability to overcome the intra- and extracellular barriers known to limit gene delivery. However, this virus is transmission competent and therefore unlikely to be suitable for use in clinical trials. A nontransmissible, replication-competent recombinant SeV has recently been developed by deleting the envelope Fusion (F) protein gene (SeV/DeltaF). Here we show that SeV/DeltaF is able to mediate beta-galactosidase reporter gene transfer to the respiratory tract of mice in vivo, as well as to human nasal epithelial cells in vitro. Further, in an ex vivo model of differentiated airway epithelium, SeV/DeltaF gene transfer was not importantly inhibited by native mucus. When compared to the transmission-competent SeV in vivo, no difference in gene expression was observed at the time of peak expression. The development of an F-defective nontransmissible SeV, which can still efficiently mediate gene transfer to the airway epithelium, represents the first important step towards the use of a cytoplasmic RNA viral vector in clinical trials of gene therapy.

A realistic chance for gene therapy in the near future

The expanding knowledge of the genetic and cellular mechanisms of human diseases in the post-genomic era coupled with the development of different vector systems to efficiently transfer genes to a variety of cell types and organs in vivo gave rise to the concept of gene therapy as a promising therapeutic option for genetic and acquired diseases. Gene therapy has been the focus of both enthusiasm and critique in the past years. Major progress has been achieved in evaluating gene therapy in clinical trials. However, a number of hurdles must still be overcome to make gene therapy safe and applicable for human diseases. Increased knowledge of the interaction of the gene therapy vehicles with the host has resulted in modifications of existing and the development of new vector systems, as well as adjustments of future clinical applications. Adeno-associated virus vectors, retrovirus- and lentivirus-based vectors show great promise for the correction of monogenic diseases. Correction of the genetic defect can be attempted by either in vivo administration to directly target a diseased organ or by administration of ex vivo genetically modified cells, e.g., bone marrow stem cells. The lack of persistent expression and the immune responses of the host have limited the use of adenovirus vectors for the permanent correction of monogenic diseases. However, the ease of production and the number of cell types and organs that can be efficiently infected make adenovirus-based vectors a promising tool for applications where permanent gene expression is not the therapeutic goal or where the induction of immune responses is the desired response, as for genetic vaccines. Overall, gene therapy remains promising for the correction of genetic as well as acquired disorders, where permanent or transient expression of a gene product will be therapeutic.

Polymers for DNA delivery

Nucleic acid delivery has many applications in basic science, biotechnology, agriculture, and medicine. One of the main applications is DNA or RNA delivery for gene therapy purposes. Gene therapy, an approach for treatment or prevention of diseases associated with defective gene expression, involves the insertion of a therapeutic gene into cells, followed by expression and production of the required proteins. This approach enables replacement of damaged genes or expression inhibition of undesired genes. Following two decades of research, there are two major methods for delivery of genes. The first method, considered the dominant approach, utilizes viral vectors and is generally an efficient tool of transfection. Attempts, however, to resolve drawbacks related with viral vectors (e.g., high risk of mutagenicity, immunogenicity, low production yield, limited gene size, etc.), led to the development of an alternative method, which makes use of non-viral vectors. This review describes non-viral gene delivery vectors, termed "self-assembled" systems, and are based on cationic molecules, which form spontaneous complexes with negatively charged nucleic acids. It introduces the most important cationic polymers used for gene delivery. A transition from in vitro to in vivo gene delivery is also presented, with an emphasis on the obstacles to achieve successful transfection in vivo.

Keratinocyte growth factor therapy in murine oleic acid-induced acute lung injury

Alveolar type II (ATII) cell proliferation and differentiation are important mechanisms in repair following injury to the alveolar epithelium. KGF is a potent ATII cell mitogen, which has been demonstrated to be protective in a number of animal models of lung injury. We have assessed the effect of recombinant human KGF (rhKGF) and liposome-mediated KGF gene delivery in vivo and evaluated the potential of KGF as a therapy for acute lung injury in mice. rhKGF was administered intratracheally in male BALB/c mice to assess dose response and time course of proliferation. SP-B immunohistochemistry demonstrated significant increases in ATII cell numbers at all rhKGF doses compared with control animals and peaked 2 days following administration of 10 mg/kg rhKGF. Protein therapy in general is very expensive, and gene therapy has been suggested as a cheaper alternative for many protein replacement therapies. We evaluated the effect of topical and systemic liposome-mediated KGF-gene delivery on ATII cell proliferation. SP-B immunohistochemistry showed only modest increases in ATII cell numbers following gene delivery, and these approaches were therefore not believed to be capable of reaching therapeutic levels. The effect of rhKGF was evaluated in a murine model of OA-induced lung injury. This model was found to be associated with significant alveolar damage leading to severe impairment of gas exchange and lung compliance. Pretreatment with rhKGF 2 days before intravenous OA challenge resulted in significant improvements in PO2, PCO2, and lung compliance. This study suggests the feasibility of KGF as a therapy for acute lung injury.

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.

KLN-5: a safe monocationic lipophosphoramide to transfect efficiently haematopoietic cell lines and human CD34+ cells

The safe and efficient delivery of nucleic acids into haematopoietic stem cells (HSCs) has a wide range of therapeutic applications. Although viruses are being used in most clinical trials owing to their high transfection efficacy, recent results highlight many concerns about their use. Synthetic transfection reagents, in contrast, have the advantage of being safe and easy to manage while their low transfection efficiency remains a hurdle that needs to be addressed before they can be widely used. Using information on transfection mechanisms, a new family of monocationic lipids called lipophosphoramides was synthesized. Their efficiency to transfer genes into haematopoietic cell lines (K562, Jurkat and Daudi) and CD34+ cells was assessed. In this study, we report that one of these new compounds, KLN-5, leads to more efficient transfection activity than one of our previously most efficient reagents (EG-308) and the commercially available monocationic lipids (DC-CHOL and DOTAP/DOPE) (P<0.05). In addition, only a slight toxicity related to the chemical structure of the new compounds is observed. Moreover, we show that KLN-5 can successfully carry the transgene into haematopoietic progenitor cells (CD34+). These results demonstrate that synthetic transfection reagents represent a viable alternative to viruses and could have potential practical utility in a number of applications.

Synthesis, characterization and transfection activity of new saturated and unsaturated cationic lipids

We synthesized new cationic lipids, analogue to N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) and 1,2-dimyristyloxypropyl-3-dimethyl-hydroxyethylammonium bromide (DMRIE), in order to compare those containing a dodecyl chain with those having a relatively long chain with two or five double bonds, such as squalenyl and dihydrofarnesyl derivatives, or complex saturated structures, such as squalane derivatives. The fusogenic helper lipid dioleoylphosphatidylethanolamine (DOPE) was added to cationic lipids to form a stable complex. Liposomes composed of 50:50 w/w cationic lipid/DOPE were prepared and incubated with plasmidic DNA at various charge ratios and the diameter and zeta potential of the complexes were measured. The surface charge of the DNA/lipid complexes can be controlled by adjusting the cationic lipid/DNA ratio. Finally, we tested the in vitro transfection efficiency of the cationic lipid/DNA complexes using different cell lines. The transfection efficiency was highest for the dodecyloxy derivative containing a single hydroxyethyl group in the head, followed by the dodecyloxy and the farnesyloxy trimethylammonium derivatives. Instead the C27 squalenyl and C27 squalanyl derivatives resulted inactive.

Contribution of Toll-like receptor 9 signaling to the acute inflammatory response to nonviral vectors

Immunostimulatory CpG motifs have been implicated as a major contributor to the acute inflammatory response associated with nonviral vectors, most prominently seen after systemic delivery of cationic lipid-plasmid DNA (pDNA) complexes. We have shown previously that complexes containing pDNA vectors that have been largely depleted of CpG motifs have significantly reduced acute toxicity when delivered systemically. However, several CpGs remain in these vectors and the toxicity is not negligible, especially at higher doses of complex. To determine the maximal reduction in the acute toxic response that could be achieved by eliminating CpG signaling, we injected cationic lipid-pDNA complexes into transgenic mice that are deficient in Toll-like receptor 9 (TLR9), which is the receptor that recognizes immunostimulatory CpG motifs. We observed significantly decreased adverse hematological changes and liver damage in TLR9(-/-) mice compared to normal mice and increased survival at higher doses of complex. However, a pronounced loss of lymphocytes and platelets was still observed in the TLR9(-/-) mice at higher doses. We also measured the toxicity in normal mice of systemically delivered complexes containing non-CpG oligonucleotides. Although serum transaminase levels were reduced, a loss of lymphocytes and platelets akin to that seen in the TLR9(-/-) mice was observed. Taken together, these findings suggest that signaling through TLR9 contributes to the majority but not all of the toxic responses associated with systemic delivery of cationic lipid-pDNA complexes.

An overview of current delivery systems in cancer gene therapy

The main objective in gene therapy is the development of efficient, non-toxic gene carriers that can encapsulate and deliver foreign genetic materials into specific cell types such as cancerous cells. During the past two decades, enormous research in the area of gene delivery has been conducted worldwide, in particular for cancer gene therapy application. Viral vectors are biological systems derived from naturally evolved viruses capable of transferring their genetic materials into the host cells. Many viruses including retrovirus, adenovirus, herpes simplex virus (HSV), adeno-associated virus (AAV) and pox virus have been modified to eliminate their toxicity and maintain their high gene transfer capability. The limitations associated with viral vectors, however, in terms of their safety, particularly immunogenicity, and in terms of their limited capacity of transgenic materials, have encouraged researchers to increasingly focus on non-viral vectors as an alternative to viral vectors. Non-viral vectors are generally cationic in nature. They include cationic polymers such as poly(ethylenimine) (PEI) and poly(L-lysine) (PLL), cationic peptides and cationic liposomes. The newly described liposomal preparation LPD (liposomes/protamine/DNA), for example, has shown superiority over conventional liposomes/DNA complexes (lipoplexes). Although non-viral vectors are less efficient than viral ones, they have the advantages of safety, simplicity of preparation and high gene encapsulation capability. This article reviews the most recent studies highlighting the advantages and the limitations of various types of gene delivery systems used in cancer gene therapy.

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

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

Polyethyleneimine-based gene therapy by inhalation

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

Characterization of DNA/lipid complexes by fluorescence resonance energy transfer

Fluorescence resonance energy transfer (FRET) is a potential method for the characterization of DNA-cationic lipid complexes (lipoplexes). In this work, we used FRET models assuming a multilamellar lipoplex arrangement. The application of these models allows the determination of the distance between the fluorescent intercalator on the DNA and a membrane dye on the lipid, and/or the evaluation of encapsulation efficiencies of this liposomal vehicle. The experiments were carried out in 1,2-dioleoyl-3-trimethylammonium-propane/pUC19 complexes with different charge ratios. We used 2-(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (DPH-PC) and 2-(4,4-difluoro-5-octyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (BODIPY-PC) as membrane dyes, and ethidium bromide (EtBr) and BOBO-1 as DNA intercalators. In cationic complexes (charge ratios (+/-) >or= 2), we verified that BOBO-1 remains bound to DNA, and FRET occurs to the membrane dye. This was also confirmed by anisotropy and lifetime measurements. In complexes with all DNA bound to the lipid (charge ratio (+/-) = 4), we determined 27 A as the distance between the donor and acceptor planes (half the repeat distance for a multilamellar arrangement). In complexes with DNA unbound to the lipids (charge ratio (+/-) = 0.5 and 2), we calculated the encapsulation efficiencies. The presented FRET methodology is, to our knowledge, the first procedure allowing quantification of lipid-DNA contact.

Effects of intramyocardial pVEGF165 delivery on regional myocardial blood flow: evidence for a spatial ‘delivery–efficacy’ mismatch

The aim of this study was to determine the effects of direct intramyocardial pVEGF165 gene transfer on regional myocardial blood flow in a porcine model of chronic myocardial ischaemia. Pigs underwent placement of an ameroid constrictor around the left circumflex coronary artery. After 3 weeks, animals received direct intramyocardial injections of pVEGF165 (20 x 50 microl at 1 microg/microl, n=11) or a plasmid vector encoding chloramphenicol acetyltransferase (20 x 50 microl at 1 microg/microl, n=11) into a specified target area (TA) of the left lateral wall. At 3 weeks after gene transfer, animals underwent final evaluation including a systematic assessment of regional myocardial blood flow (MBF) under resting and stress conditions. In all, 20 animals (10 per group) reached final studies. There was no change in mean arterial blood pressure or Rentrop collateral score from gene delivery to final studies in either group, nor were there differences between study groups. MBF was significantly higher in the areas adjacent to the TA in the VEGF group under resting (P<0.001) and stress conditions (P<0.05). In addition, pVEGF165 gene transfer abolished flow differences between the adjacent areas and the septum. MBF was not different between study groups in the TA, the anterior wall, or the septum. In conclusion, direct intramyocardial pVEGF165 gene transfer significantly improves myocardial blood flow. However, this effect is limited to the myocardial segments adjacent to the area of gene delivery. These data, therefore, demonstrate a spatial 'delivery-efficacy' mismatch with implications for myocardial gene delivery sites and detection of treatment effects in vivo.

New cationic lipids for gene transfer with high efficiency and low toxicity: T-shape cholesterol ester derivatives

New degradable cationic ester lipids with 'T-shape' configurations were synthesized and tested for gene delivery carrier. Their transfection efficiency and toxicity were compared with commercially available cationic lipids, DOTMA, DOSPA, and DC-Chol. They showed efficient transfection activity and almost no toxicity on mammalian cell lines. Their ester bond degradation was monitored by (1)H NMR.