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

Application of lipids and plasmid design for gene delivery to mammalian cells

Cationic lipids are widely used for in vitro gene transfer due to their efficiency. The major challenges for the improvement of in vivo cationic lipid-mediated gene delivery reside in the design of more biocompatible lipoplexes mimicking viral-mediated gene delivery and in understanding the fate of the lipoplexes within the cells.

Biodistribution and gene expression of lipid/plasmid complexes after systemic administration

The objectives of this study were to investigate the influence of physicochemical properties of lipid/plasmid complexes on in vivo gene transfer and biodistribution characteristics. Formulations based on 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) and novel biodegradable cationic lipids, such as ethyl dioleoyl phosphatidylcholine (EDOPC), ethyl palmitoyl myristyl phosphatidylcholine (EPMPC), myristyl myristoyl carnitine ester (MMCE), and oleyl oleoyl L-carnitine ester (DOLCE), were assessed for gene expression after tail vein injection of lipid/plasmid complexes in mice. Gene expression was influenced by cationic lipid structure, cationic lipid-to-colipid molar ratios, plasmid-to-lipid charge ratios, and precondensation liposome size. Detectable levels of human growth hormone (hGH) in serum, human factor IX (hFIX) in plasma, and chloramphenicol acetyltransferase (CAT) in the lung and liver were observed with positively charged lipid/plasmid complexes prepared from 400-nm extruded liposomes with a cationic lipid-to-colipid ratio of 4:1 (mol/mol). Intravenous administration of lipid/CAT plasmid complexes resulted in distribution of plasmid DNA mainly to the lung at 15 min after injection. Plasmid DNA accumulation in the liver increased with time up to 24 hr postinjection. There was a 10-fold decrease in the amount of plasmid DNA in the lung at 15 min after injection, when the lipid/plasmid complex charge ratio was decreased from 3:1 to 0.5:1 (+/-). Bright fluorescent aggregates were evident in in vivo-transfected lung with the positively charged pCMV-CAT/DOLCE:dioleyl phosphatidylethanolamine (DOPE) (1:1, mol/mol) complexes, while more discrete punctate fluorescence was observed with a 4:1 molar ratio of cationic lipid:colipid formulations. Preinjection of polyanions such as plasmid, dextran sulfate, polycytidic acid, and polyinosinic acid decreased hGH expression, whereas the preinjection of both positively charged and neutral liposomes had no effect on hGH serum levels. Of the cationic lipids tested, DOLCE was found to be the most effective potentially biodegradable cationic lipid. A correlation between gene expression and cationic lipid:colipid ratios and lipid-to-plasmid charge ratio was also observed for DOTMA- and DOLCE-based formulations.

Isolated lung liposome-mediated gene transfer produces organ-specific transgenic expression

BACKGROUND

Gene therapy is a promising strategy for the treatment of inoperable pulmonary tumors and rejection after lung transplantation. However, unlike ex vivo administration, intravenous in vivo transfection lacks organ specificity and has a limited duration of expression. The objectives of this study were to limit transfection to a single lung and to increase the duration of gene expression in vivo.

METHODS

Sixteen male Fisher rats were anesthetized and divided into two groups. Animals in group I (n = 7) received an intrajugular administration of 1,320 microg of chloramphenicol acetyl transferase (CAT) complementary DNA complexed with cationic liposomes. Animals in group II (n = 9) received 660 microg of CAT complementary DNA complexed with cationic liposomes into the pulmonary artery of an isolated left lung over 10 minutes. After 40 minutes of incubation, the lung was flushed with 10 mL of normal saline solution, and the perfusate was suctioned through a left pulmonary venotomy. The circulation to the left lung was then restored. After 48 hours, the animals were divided into subgroups (a and b) and CAT activity was assessed in the lungs, hearts, livers, and kidneys of groups Ia (n = 3) and IIa (n = 5). After 21 days, CAT activity was assessed in the left lungs of groups Ib (n = 4) and IIb (n = 4).

RESULTS

After 48 hours, animals that had received intravenous administration of CAT cDNA showed strong expression in the lungs and hearts and negligible expression in the livers and kidneys. In contrast, animals in group IIa, which had received isolated left lung perfusion of CAT cDNA showed expression only in the left lung. After 21 days, the left lungs of animals in group Ib, which had received intravenous administration of CAT complementary DNA, showed no CAT expression, but the left lungs of animals in group IIb, which had received isolated left lung perfusion of CAT complementary DNA, exhibited strong CAT expression.

CONCLUSIONS

Compared with intravenous administration, isolated lung liposome-mediated gene transfer provides prolonged organ-specific gene expression. This provides a useful model to study the effects of gene therapy on pulmonary tumors, which may have further application when gene therapy is used in clinical practice.

Effective treatment of early endobronchial cancer with regional administration of liposome-p53 complexes

BACKGROUND

Lung cancer originates in a diffusely damaged bronchial epithelium as a result of sequential and cumulative genetic alterations. We investigated the feasibility of in vivo gene replacement in endobronchial precancerous and cancerous cells by a regionally administered nonviral delivery system.

METHODS

After evaluating the in vitro transfection efficiency and cytotoxicity of a variety of cationic liposome-p53 formulations, a specific formulation, DP3-p53, was selected for further in vitro and in vivo evaluation. The ability of DP3-p53 to introduce the p53 gene in the normal bronchial epithelium was studied in transgenic mice that lack the p53 gene. The therapeutic effect of DP3-p53 administered intratracheally was studied in two nude mouse models of endobronchial human lung cancer by use of H358 (p53-null) and H322 (p53-mutant) cells.

RESULTS

DP3-p53 was able to effectively introduce and express the p53 gene and induce G1 arrest and apoptosis in H358 cells in vitro and to introduce and transcribe the p53 gene in the bronchial epithelium of transgenic mice that lack the p53 gene in vivo. In therapeutic experiments using groups of four or five mice each, administration of five intratracheal doses of DP3-p53 (2 microg or 8 microg DNA per dose) on days 4, 8, 12, 16, and 20 after intratracheal tumor inoculation significantly inhibited lung tumor formation and prolonged by approximately twofold the survival of mice bearing H358 or H322 endobronchial tumor cells in contrast to the survival among untreated mice and mice treated with the DP3-empty vector (P = .007 [two-sided logrank test] for mice bearing H358 cells and P = .008 [two-sided logrank test] for those bearing H322 cells).

CONCLUSIONS/IMPLICATIONS

Liposome-based p53 delivery through the airways is a potentially effective strategy for the treatment of early endobronchial cancer. These results have important implications for the gene therapy and prevention of human lung cancer.

Efficiency of cationic lipid-mediated transfection of polarized and differentiated airway epithelial cells in vitro and in vivo

Systematic analysis of a large number of different cationic lipids has led to the identification of novel structures (GL-67) and formulations of cationic lipid:plasmid DNA (pDNA) complexes that facilitate high levels of gene expression in lungs of mice. However, despite significant improvement in gene transfer activity, we show here that the efficiency of GL-67-mediated gene transduction of intact airway epithelia is still relatively low. Administration of GL-67:pCF1-CFTR (encoding the cystic fibrosis transmembrane conductance regulator) complexes into the nasal epithelium of cystic fibrosis (CF) transgenic mice resulted only in marginal correction of the ion transport defects. Measurements of nasal potential differences (PD) showed no correction of the sodium (Na+) transport defect, and only partial restitution of the chloride (Cl-) transport defect was achieved in a small proportion of the animals after perfusion of the nasal epithelium with the complexes. Furthermore, in contrast to results obtained following instillation of GL-67:pDNA complexes into the lungs of mice, perfusion of GL-67:pDNA into the nasal epithelium resulted only in a moderate enhancement of gene transduction activity relative to that attained with naked pDNA alone. To determine the basis for this low efficiency of transfection, a series of studies was conducted to identify some of the barriers governing cationic lipid-mediated gene transfer to the airway epithelium. We show here that the transfection activity of GL-67 was affected by the polarization, differentiation, and proliferative state of the cells. Diminished transfection activity was observed with nonmitotic, highly polarized and differentiated airway epithelial cells. This observed reduction in gene expression with nonmitotic cells was determined to be due in part to inefficient nuclear translocation of the pDNA from the cytoplasm. Together these data indicate that much improvement in the ability of cationic lipids to transfect polarized and differentiated airway epithelial cells is a necessary prerequisite for effective cationic lipid-mediated gene therapy of airway diseases such as CF.

Free liposomes enhance the transfection activity of DNA/lipid complexes in vivo by intravenous administration

Factors that regulate the transfection efficiency of cationic lipid-based carriers are still largely unknown. We have shown in a previous report [F. Liu, H.W. Qi, L. Huang, D. Liu, Factors controlling the efficiency of cationic lipid-mediated transfection in vivo via intravenous administration, Gene Ther., 4 (1997) 517-523. ] that the transfection efficiency, to the lung, of a lipid formulation composed of N-[1-(2,3-dioleoyloxy)propyl-N,N, N-trimethylammonium chloride (DOTMA) and Tween 80 is directly proportional to the ratio of DOTMA to DNA. In this study, we investigated the mechanism underlying the high cationic lipid to DNA ratio dependent transfection activity. Specifically, we have examined the role of free cationic liposomes in affecting the transfection efficiency of the DNA/lipid complexes in vivo by intravenous administration. The data show that greater transfection activity of DNA/lipid complexes in the lung at a higher cationic lipid to DNA ratio is due to the function of free liposomes present in the DNA/lipid mixture. Free liposomes enhance the transfection activity of DNA/lipid complexes by increasing the retention time of DNA and decreasing transgene degradation in different organs. In addition to DOTMA liposomes, liposomes composed of 1,2-dioleoyl-3-trimethylammonium propane chloride (DOTAP) and 3beta[N-(N', N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) also enhance the level of gene expression in animals transfected by DNA/DOTMA complexes. These results suggest that inclusion of free liposomes into the DNA/lipid complexes may be important in achieving an optimal transfection activity in vivo.

Lipitoids--novel cationic lipids for cellular delivery of plasmid DNA in vitro

BACKGROUND

Although synthetic nonviral vectors hold promise for the delivery of plasmid DNA, their gene-transfer efficiencies are far from matching those of viruses. To systematically investigate the structure-activity relationship of cationic lipids, a small library of cationic lipid-peptoid conjugates (lipitoids) was synthesized. The compounds were evaluated for their ability to form complexes with plasmid DNA and to mediate DNA transfer in vitro.

RESULTS

Lipid-peptoid conjugates were conveniently prepared in high yield using solid-phase synthesis. Several lipitoids condensed plasmid DNA into 100 nm spherical particles and protected the DNA and DNase digestion. A subset of lipitoids with a repeated (aminoethyl, neutral, neutral) sidechain trimer motif conjugated with dimyristoyl phosphatidyl-ethanolamine (DMPE) mediated DNA transfer with high efficiency.

CONCLUSIONS

Automated solid-phase synthesis of cationic lipids allowed the rapid synthesis of a diverse set of transfection reagents. The most active compound DMPE-(Nae-Nmpe-Nmpe)3 (Nae, N-aminoethyl glycine; Nmpe, N-p-methoxyphenethyl-glycine) is more efficient than lipofectin or DMRIE-C (two commercial cationic lipid transfection reagents) and is active in the presence and absence of serum. The activity in the presence of serum suggests potential for applications in vivo.

Aerosol delivery of lipid:DNA complexes to lungs of rhesus monkeys

PURPOSE

The potential use of aerosol delivery for non-viral gene therapy was tested by nebulization of lipid:DNA complexes to the lungs of rhesus monkeys.

METHODS

Four female rhesus monkeys were dosed with lipid:DNA formulations via aerosol inhalation, where the DNA coded for the human Cystic Fibrosis Transmembrane Conductance Regulator (hCFTR) protein. Delivery of DNA was determined in lung samples by polymerase chain reaction (PCR) by qualitative and quantitative methods. Transgene specific messenger RNA was measured by reverse transcriptase PCR (RT-PCR) and protein expression and localization were evaluated by immunohistochemistry (IHC).

RESULTS

Approximately four mg of DNA, complexed with cationic lipid 1.2-dimyristoyl-sn-glycero-3-ethylphosphatidylcholine (EDMPC) and cholesterol were delivered to the lungs of animals by airjet nebulizer. Three days after dosing, tissue samples from the lung were collected and shown to have vector specific DNA, RNA and the presence of CFFR protein. Specifically, the hCFTR protein was distributed widely, although non-uniformly, throughout airway epithelium being located on the apical surface of epithelial cells. Importantly, no adverse clinical effects were observed and the lungs showed no histological abnormalities or signs of acute inflammation.

CONCLUSIONS

This study shows that lipid:DNA formulations based on EDMPC and cholesterol can be administered to primates by nebulization resulting in measurable expression of the hCFTR protein. The absence of inflammation is also encouraging and such systems may have utility for delivery of genes to the lungs for the treatment of a variety of pulmonary diseases including cystic fibrosis.

Transgene expression kinetics after transfection with cationic phosphonolipids in hematopoietic non adherent cells

Cationic lipids are considered to be capable of efficiently and safely mediating DNA transfer into cells, although expression is transient. A new family of cationic lipids, called phosphonolipids, has been developed, with the relationship between the hydrophobic domain of the lipid molecules and the significant enhancement of transduction efficiency in a non-adherent cell line characterised in the present study. The kinetics of transfection efficiency were also investigated. Our results demonstrate that the peak of the transient expression of these reporter genes mediated by cationic lipids occurred within 3 to 14 days, depending on the aliphatic chain length of the complex used and on its formulation in the presence or absence of DOPE. Furthermore, the kinetics of transgene expression were found to differ in adherent and non-adherent cells. These results were obtained using three different techniques: CPRG, luminescence, and FACS-gal, and were in agreement with electron microscopy studies. We thus hypothesized that the plasma membrane composition of cells could affect the efficiency of transfection with cationic lipids. Our results suggest that phosphonolipids constitute a promising class of compounds for gene transfer protocols, and that galenic optimization should improve and modify the transfection efficiency of these DNA-lipid complexes.

Airway delivery of cationic lipid: DNA complexes for cystic fibrosis

Cationic lipids are under active consideration as gene delivery vehicles for cystic fibrosis. Initial studies have shown cationic lipids to be effective agents of gene transfer to epithelial cells in vitro. Instillation of these vectors into animal models has led to widely different degrees of transfection of the airway epithelia. Newer generations of cationic lipids, with dramatically improved transfection efficiencies, appear to result in mostly alveolar gene delivery. Aerosol delivery of cationic lipid-DNA complexes has resulted in variable transfection of the airways in animal models. Initial human clinical trials using intranasal instillation have shown variable low levels of expression, accompanied by little toxicity. Recent developments in the formulation of cationic lipid-DNA complexes have resulted in an ability to aerosolize high concentrations of the complex, and should permit an evaluation of the efficacy of these delivery vehicles when aerosolized into cystic fibrosis patients.

Chemistry and cellular aspects of cationic facial amphiphiles

A series of compounds containing a bile acid core and a polyamine side chain have been synthesized to evaluate their ability to promote the uptake of DNA into cells. These compounds differ from conventional cationic lipids because they contain a positively charged chain attached to a facial amphiphile rather than to a hydrophobic moiety. Formulations of several of the designed compounds were found to dramatically increase the cellular uptake of both plasmid and oligonucleotide DNA. Moreover, initial experiments have shown that some of the compounds promote plasmid gene expression in various tissues after introduction into animals. These results have provided interesting information about structure-activity relationships as well as clues to the mechanism of action that may lead to further improvements in the design.

Gene transfer with lipospermines and polyethylenimines

It is an obvious and basic principle that to be efficient, gene therapy requires effective gene transfer followed by adequate gene expression. However, getting DNA, a pro-drug, into the cell and into the nucleus, remains a crucially limiting factor. Even recombinant viral methods still show poor performances in clinical situations and non-viral methods are considered classically to be of yet lower efficiency. Here, we consider the mode of action, the nature of the complexes formed with DNA and the transfection potentials of two categories of inert, cationic vectors, the lipospermines and polyethylenimine. Both are among the best vectors currently available for in vitro work. Moreover, polyethylenimine is proving to be a versatile and effective carrier for different in vivo situations, especially for delivering genes into the mammalian brain.

Strategies of gene transfer to the kidney

Kidney targeted gene transfer has been a realistic goal for many researchers since 1991, but unfortunately, to date there is no reliable gene transfer technique for gene therapy of renal diseases. However, at the experimental level, several in vivo gene transfer methods have attempted to target certain renal structures, for example, the HVJ-liposome method and renal perfusion of adenovirus for glomerular cells, intravenous injection of oligonucleotides (ODNs) for proximal tubule, intra-arterial injection of adenovirus followed by cold incubation with a vasodilator for interstitial vasculature of the outer medulla, and adenoviral injection into the renal pelvis for the inner medullary collecting duct. As an ex vivo gene transfer method targeting the glomerulus, the transfusion of genetically-modified mesangial cells has been attempted. Implantation of genetically-modified tubular epithelial cells into the subcapsular region has been employed for ex vivo transfection to the interstitium. Gene therapy has focused particularly on the transplanted kidney, where an exogenous gene can transferred in advance. In the future, an inducible system and individual cell targeting strategy should be developed. The improvement of gene transfer techniques, especially vectors for delivering genes, is crucial. The potential application of gene transfer technologies is enormous while the therapeutic approaches have just begun to be explored. Therapeutic interventions of the process of progression of glomerulonephritis in the rat have been directed towards inhibiting the actions of growth factors. Obviously, molecular biological intervention is coming of age and there is a tremendous excitement over its potential. We believe that gene transfer techniques will become common tools for the dissection of molecular aspects of diseases and possibly for gene therapy in the field of nephrology.

Cationic lipid-mediated gene transfer: effect of serum on cellular uptake and intracellular fate of lipopolyamine/DNA complexes

Most of the cationic lipids used for gene transfer experiments drastically lose their efficiency in the presence of serum. We used a cationic lipid with a spermine head group and its fluorescent analog to study the cellular uptake and the intracellular fate of lipoplexes in the presence and absence of serum. We found that the amount of DNA and lipid taken up by the cells was not related to the efficacy of the gene transfer. When the lipofection was performed in the presence of serum, lipoplexes were contained within small intracellular vesicles. In the absence of serum, the vesicles were larger and heterogeneous in size and shape. By analysis of their size distribution, we showed that lipoplexes preformed in the absence of serum tended to aggregate. This aggregation was inhibited in the presence of serum. We used a carbonate formulation that led to the preformation of large particles: those large particles gave a high lipofection efficiency in the presence of serum and their intracellular distribution was identical to that observed in the absence of serum.

Aerosolization of cationic lipid:pDNA complexes--in vitro optimization of nebulizer parameters for human clinical studies

Previously, we have described the optimization of the aerosol delivery of a nonviral gene therapy vector to the lungs of rodents (Eastman et al., 1997b). Although aerosolizing cationic lipid:pDNA complexes into a whole-body exposure chamber resulted in high levels of reporter gene expression in the lungs of BALB/c mice, the conditions employed were not optimal for the delivery of lipid:pDNA complexes to the lungs of human patients. That is, the consumption rate of the material in the nebulizer, and thus the delivery time, were very slow and the aerosol was delivered in a continuous flow. Here we describe in vitro experiments used to develop a cationic lipid:pDNA aerosol with characteristics more suitable for delivery to the lungs of humans, as a necessary prerequisite for conducting a clinical study with human cystic fibrosis patients. Using cascade impactors and all-glass impingers, we have screened several commercially available nebulizers for their ability to deliver intact, respirable, active lipid:pDNA complexes in the shortest time possible, and have identified the Pari LC Jet Plus nebulizer as the optimal nebulizer that meets these criteria. Using this nebulizer in an intermittent mode to mimic breath actuation, consumption rates of approximately 0.6 ml/min of the cationic lipid:pDNA complexes (6 mM cationic lipid:8 mM pDNA) were obtained. The plasmid DNA remained intact and the complexes were shown to maintain activity throughout the nebulization run. Based on measurements of the nebulized dose and the mass median aerodynamic diameter, we calculate a delivered dose of approximately 22 micromol (7.2 mg) of pDNA for each 8 ml of cationic lipid:pDNA complex aerosolized to the lungs of a human patient. This dose should be sufficient to test the clinical efficacy of cationic lipid-mediated gene delivery for the treatment of cystic fibrosis.

Ex vivo liposome-mediated gene transfer to lung isografts

OBJECTIVE

Gene therapy is a promising strategy to modify ischemia-reperfusion injury and rejection after transplantation. We evaluated variables that may affect ex vivo gene transfer to rat lung isografts.

METHODS

Left lungs were harvested and perfused via the pulmonary vein with chloramphenicol acetyltransferase complementary deoxyribonucleic acid complexed with cationic liposomes. Several variables were examined: (1) Influence of temperature: In group I (n = 4), grafts were stored for 4 hours at 23 degrees C and transplanted. Chloramphenicol acetyltransferase activity was assessed on postoperative day 2. In groups II and III (n = 4), grafts were stored at 10 degrees and 4 degrees C, respectively. Arterial oxygen tension and inflammatory infiltrate were also determined. (2) Influence of storage time: Grafts were preserved at 10 degrees C for 1, 2, 3, 4 (n = 4), and 10 hours (n = 5). chloramphenicol acetyltransferase activity was assessed on postoperative day 2. (3) Rapidity and duration of transgene expression: Grafts were preserved at 10 degrees C for 1 hour and then transplanted. Chloramphenicol acetyltransferase activity was assessed 2, 4, 6, 12, and 24 hours and 2, 7, 14, 21, and 28 days after implantation.

RESULTS

Chloramphenicol acetyltransferase expression was apparently less in lungs transfected at 4 degrees C than in those transfected at 10 degrees and 23 degrees C. Storage for 1 hour at 10 degrees C was sufficient to yield significant expression. Increasing the exposure time to 10 hours did not increase toxicity. There were no differences in arterial oxygen tension between transfected and nontransfected lungs. Chloramphenicol acetyltransferase expression was detected for at least 28 days.

CONCLUSION

Ex vivo liposome-mediated transfection of lung isografts can be achieved after a short time of cold storage, with minimal toxicity.

Transfection of myoblasts in primary culture with isomeric cationic cholesterol derivatives

Transfection of satellite cells from dog muscle (myoblasts) in primary culture has been optimized with respect to the position of the cholesteryl moiety along the polyamine chain of spermidine or spermine. Spermidine or spermine were derivatized with cholesterylchloroformate giving rise to three isomers in the case of spermidine and two isomers for spermine that were separated by reversed-phase high-performance liquid chromatography (rp-HPLC). The position of the cholesteryl moiety was assigned by 13C-NMR and coelution with synthetic isomers of defined structure. The isomeric cationic lipids were evaluated for their transfection activity in myoblasts from dog muscle and a human lung epithelial cell line (A549) using plasmid DNA expressing the luciferase reporter gene. The results showed that the position of the cholesteryl moiety is of critical importance for efficient transfection of myoblasts in primary culture with isomers having a derivatized secondary amine being significantly more effective than those with a derivatized primary amine. On the contrary, differences in the A549 cell line were less pronounced and did not follow the same pattern. The results show that slight structural differences between cationic lipids lead to significantly different transfection efficiencies for myoblasts in primary culture. This may also represent an advantage in view of cell or organ targeting.

Successful in vivo and ex vivo transfection of pulmonary artery segments in lung isografts

OBJECTIVE

Gene transfer to lung grafts may be useful in ameliorating ischemia-reperfusion injury and rejection. Efficient gene transfection to the whole organ may prove problematic. Proximal pulmonary artery endothelial transfection might provide beneficial downstream effects on the whole graft. The aim of this study was to determine the feasibility of transfecting proximal pulmonary artery segments in lung isografts.

METHODS

Male Fischer rats were divided into six groups. In vivo transfection: In group I (n = 7), a proximal segment of the left pulmonary artery was isolated and injected with saline solution by means of a catheter inserted through the right ventricle. After an exposure period of 20 minutes, clamps were removed and blood flow was restored. In group II (n = 7), the isolated arterial segments were injected with adenovirus carrying the Escherichia coli LacZ gene encoding for beta-galactosidase. Ex vivo transfection: In group III (n = 5), arterial segments were injected ex vivo with saline solution and in group IV (n = 5) with the adenovirus construct. In group V (n = 6), arteries were injected with saline solution and in group VI (n = 11) with liposome chloramphenicol acetyl transferase cDNA. In groups I to IV, animals were killed on postoperative day 3 and transgene expression was assessed by Bluo-Gal staining. In groups V and VI, animals were killed on postoperative day 2 and transgene expression was assessed by chloramphenicol acetyl transferase activity assay.

RESULTS

Transgene expression was detected grossly and microscopically in endothelial and smooth muscle cells of pulmonary artery segments from all surviving animals of groups II and IV. In group VI, chloramphenicol acetyl transferase activity was significant in all assessed arterial segments.

CONCLUSION

Significant transgene expression is observed in proximal pulmonary artery segments after both in vivo and ex vivo exposure.

Liposome-mediated gene transfer to lung isografts

OBJECTIVES

Our objective were to determine the feasibility, efficacy, and safety of in vivo and ex vivo liposome-mediated gene transfer to lung isografts.

METHODS

Fischer rats were divided into three main groups: (1) Nontransplant setting: Liposome-chloramphenicol acetyl transferase cDNA was intravenously injected, and lungs were harvested at different time points: 2, 6, 12, and 24 hours; 2, 5, 8, and 21 days (n = 3). Chloramphenicol acetyl transferase activity was determined in lungs, hearts, livers, and kidneys. The distribution and type of transfected cells were evaluated by in situ hybridization. Lung toxicity was assessed by arterial oxygen tension, histology, and tumor necrosis factor-alpha levels. (2) In vivo graft transfection: Left lungs were transplanted 6 hours, 4 hours, and 15 minutes after intravenous injection and were assessed for chloramphenicol acetyl transferase activity and arterial oxygen tension on postoperative day 2. (3) Ex vivo graft transfection: Grafts were infused ex vivo with either 660 micrograms (n = 3) or 330 micrograms (n = 3) of DNA complexed to liposomes and stored at 10 degrees C for 4 hours. Chloramphenicol acetyl transferase activity was assessed 44 hours after transplantation.

RESULTS

Transgene expression was detected in endothelial cells, macrophages, and interstitial cells. Chloramphenicol acetyl transferase activity was present as early as 2 hours, increased significantly between 6 hours and 8 days, and then decreased to minimal levels by 21 days. Chloramphenicol acetyl transferase activity was greatest in donor lungs and hearts and minimal in livers and kidneys. Arterial oxygen tension was normal in treated animals. Inflammation was minimal, and tumor necrosis factor-alpha levels increased only sevenfold in treated animals.

CONCLUSION

In vivo and ex vivo liposome-mediated gene transfer to lung isografts allows significant transgene expression with minimal effects on graft function.

Strategies for correcting the delta F508 CFTR protein-folding defect

Many human diseases arise as a result of mutations within genes encoding essential proteins. In many cases, the mutations are not so severe as to render the protein biologically inactive. Rather, the mutations oftentimes result in only subtle protein-folding abnormalities. In the case of the CFTR protein, a mutation leading to the loss of a single amino acid is responsible for the diseased state in the majority of individuals with cystic fibrosis. Here the newly synthesized mutant CFTR protein, missing a phenylalanine residue at position 508 (delta F508 CFTR), is unable to transit from the endoplasmic reticulum to the plasma membrane, where it functions as a regulator of chloride transport. All of the available evidence indicate that the newly synthesized delta F508 CFTR protein adopts a slightly altered conformation and therefore is retained at the level of the endoplasmic reticulum, ostensibly by the actions of the cellular quality control system. Because the mutant protein is capable of functioning as a chloride channel, developing ways to elicit its release out of the ER and to the plasma membrane has important clinical implications. Herein, we discuss our recent studies showing that the protein-folding defect associated with the delta F508 CFTR mutation, as well as a number of other temperature-sensitive mutations, can be overcome by strategies designed to influence protein folding inside the cell. Specifically we show that a number of low-molecular-weight compounds, all of which are known to stabilize proteins in their native conformation, are effective in rescuing the folding and/or processing defects associated with different mutations that oftentimes lead to human disease.

Efficient gene transduction by Epstein-Barr-virus-based vectors coupled with cationic liposome and HVJ-liposome

We show here a novel non-viral strategy to transduce human cells by using an EBV-based vector system. The EBV-based vectors, the plasmid vectors carrying EBV oriP (origin for plasmid replication) and EBNA (EBV nuclear antigen) 1 gene from EBV genome, were combined with 2 gene delivery systems, i.e., cationic liposome and HVJ-liposome. By both methods, EBV-based vectors could be more efficiently transfected into HeLa cells than non-EBV, conventional plasmid vectors. When human primary fibroblasts were transfected, EBV-based vectors coupled with cationic liposome but HVJ-liposome resulted in successful gene transduction, while human bone marrow cells were transduced with both HVJ-liposome- and cationic liposome-EBV vectors. These results suggest the potential applications of the EBV-based vector system for gene therapy.

Comparison of DNA-lipid complexes and DNA alone for gene transfer to cystic fibrosis airway epithelia in vivo

Cationic lipids show promise as vectors for transfer of CFTR cDNA to airway epithelia of patients with cystic fibrosis (CF). However, previous studies have not compared the effect of DNA-lipid to DNA alone. Recently, we developed a formulation of plasmid encoding CFTR (pCF1-CFTR) and cationic lipid (GL-67:DOPE) that generated greater gene transfer in mouse lung than previously described DNA-lipid vectors. Therefore, we tested the hypothesis that DNA-lipid complexes were more effective than DNA alone at transferring CFTR cDNA to airway epithelia in vivo. We administered complexes of DNA-lipid to one nostril and DNA alone to the other nostril in a randomized, double-blind study. Electrophysiologic measurements showed that DNA-lipid complexes partially corrected the Cl- transport defect. Importantly, the pCF1-CFTR plasmid alone was at least as effective as complexes of DNA with lipid. Measurements of vector-specific CFTR transcripts also showed gene transfer with both DNA-lipid and DNA alone. These results indicate that nonviral vectors can transfer CFTR cDNA to airway epithelia and at least partially restore the Cl- transport defect characteristic of CF. However, improvements in the overall efficacy of gene transfer are required to develop a treatment for CF.

Characterization of cationic liposome-mediated gene transfer in vivo by intravenous administration

Physicochemical properties of the cationic liposomes, including structure of the cationic lipid-to-DNA ratio, liposome particle size, and inclusion of the helper lipids, were studied for their effect on the level, site, and duration time of gene expression in vivo by intravenous administration. Using a cytomegalovirus (CMV)-driven gene expression system containing either the luciferase or green fluorescence protein gene as a reporter and two cationic lipids [N-(2,3-dioleoyloxy)propyl-N,N,N-trimethylammonium chloride (DOTMA) and 1,2-dioleoyloxy-3-trimethylammonium propane (DOTAP)], we demonstrated in vivo by a single intravenous injection of DNA/liposome complexes into mice, that cationic liposomes are capable of transfecting cells in organs such as the lung, heart, liver, spleen, and kidney. Transfection efficiency is determined mainly by the structure of the cationic lipid and the ratio of cationic lipid to DNA. Although the presence of cholesterol in DOTAP liposomes did not affect transfection activity, inclusion of dioleoylphosphatidylethanolamine (DOPE) into either DOTAP or DOTMA liposomes significantly decreases liposome transfection activity in vivo. Results form time course show that gene expression in different organs is transient, with a peak level between 4 and 24 hr, dropping to less than 1% of the peak level by day 4. Experiments with repeated injections showed that the peak level of gene expression could be regained by subsequent injection.

Toward development of a non-viral gene therapeutic

Gene therapy is an emerging field that has reached the early clinical stages of development for some disease states. However, the demonstration of safety in animals and the introduction of gene-based formulations in humans hides the fact that numerous developmental and basic research questions remain. This article highlights progress and emerging issues in the area of liposome-based non-viral gene delivery. The colloidal nature of these formulations render them complicated at the physico-chemical and biological levels. Instrumentation and methodologies need to be developed to better understand the subtleties of plasmid DNA, complexing agents, delivery mode and the route of entry into the cell and the nucleus. Major hurdles to entry include membrane binding, endosomal release, nuclear uptake and decomplexation. Each 'stage' is poorly understood but numerous approaches are being directed to increase cellular delivery. These research efforts, coupled with sensible formulation research and a multi-disciplinary, long-term effort, are necessary for success.

Cationic lipid-based gene delivery systems: pharmaceutical perspectives

Gene delivery systems are designed to control the location of administered therapeutic genes within a patient's body. Successful in vivo gene transfer may require (i) the condensation of plasmid and its protection from nuclease degradation, (ii) cellular interaction and internalization of condensed plasmid, (iii) escape of plasmid from endosomes (if endocytosis is involved), and (iv) plasmid entry into cell nuclei. Expression plasmids encoding a therapeutic protein can be, for instance, complexed with cationic liposomes or micelles in order to achieve effective in vivo gene transfer. A thorough knowledge of pharmaceutics and drug delivery, bio-engineering, as well as cell and molecular biology is required to design optimal systems for gene therapy. This mini-review provides a critical discussion on cationic lipid-based gene delivery systems and their possible uses as pharmaceuticals.

Improved DNA: liposome complexes for increased systemic delivery and gene expression

To increase cationic liposome-mediated intravenous DNA delivery extruded DOTAP:cholesterol liposomes were used to form complexes with DNA, resulting in enhanced expression of the chloramphenicol acetyltransferase gene in most tissues examined. The DNA:liposome ratio, and mild sonication, heating, and extrusion steps used for liposome preparation were crucial for improved systemic delivery. Size fractionation studies showed that maximal gene expression was produced by a homogeneous population of DNA:liposome complexes between 200 to 450 nm in size. Cryo-electron microscopy examination demonstrates that the DNA:liposome complexes have a novel morphology, and that the DNA is condensed on the interior of invaginated liposomes between two lipid bilayers. This structure could account for the high efficiency of gene delivery in vivo and for the broad tissue distribution of the DNA:liposome complexes. Ligands can be placed on the outside of this structure to provide for targeted gene delivery.

Structure of in-serum transfecting DNA-cationic lipid complexes

Noticeable modifications of in-serum transfection efficiency of dioctadecylamidoglycyl-spermine (DOGS)-DNA complexes are observed, depending on DNA condensation conditions. The structures of the complexes are studied, keeping in mind the variability of lipid polymorphism, by cryo-transmission electron microscopy and X-ray diffraction. By increasing both pH and ionic strength, well-organised lamellar structures with a period of 65 A replace supramicellar aggregates. A relationship between the structures and their in-vitro transfection activity is established. Efficiency in the presence of serum is maintained when a lamellar arrangement is involved.

Basis of pulmonary toxicity associated with cationic lipid-mediated gene transfer to the mammalian lung

Studies have indicated that although abundant levels of transgene expression could be achieved in the lungs of mice instilled with cationic lipid:pDNA complexes, the efficiency of gene transfer is low. As a consequence, a relatively large amount of the complex will need to be administered to the human lungs to achieve therapeutic efficacy for indications such as cystic fibrosis. Because all cationic lipids exhibit some level of cytotoxicity in vitro, we assessed the safety profile of one such cationic lipid, GL-67, following administration into the lungs of BALB/c mice. Dose-dependent pulmonary inflammation was observed that was characterized by infiltrates of neutrophils, and, to a lesser extent, macrophages and lymphocytes. The lesions in the lung were multifocal in nature and were manifested primarily at the junction of the terminal bronchioles and alveolar ducts. The degree of inflammation abated with time and there were no apparent permanent fibrotic lesions, even in animals that were treated at the highest doses. Analysis of the individual components of the complex revealed that the pulmonary inflammation was primarily cationic lipid-mediated with a minor contribution from the neutral co-lipid DOPE. Associated with the lesions in the lungs were elevated levels of the pro-inflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) that peaked at days 1-2 post-instillation but resolved to normal limits by day 14. Total cell counts, primarily of neutrophils, were also significantly elevated in the bronchoalveolar lavage fluids of GL-67:pDNA-treated mice between days 1 and 3 but returned to normal limits by day 14. No specific immune responses were detected against the cationic lipid or plasmid DNA in mice that had been either instilled or immunized with the individual components or complex, nor was there any evidence of complement activation. These studies indicate that a significant improvement in the potency of cationic lipid:pDNA formulations is desirable to minimize the toxicity associated with cationic lipids.

A concentrated and stable aerosol formulation of cationic lipid:DNA complexes giving high-level gene expression in mouse lung

Advances in gene therapy vectors and techniques hold promise for treatment of many inherited and acquired diseases. For lung indications, especially those involving the epithelium, delivery of the gene therapy vehicle ideally will involve the use of an aerosol. Aerosol delivery of transgenes using cationic lipids is currently limited by the ability to generate highly concentrated formulations of lipid:DNA complexes that are stable and retain their activity following aerosolization. We have examined many of the variables inherent in aerosolizing cationic lipid gene delivery vehicles and have devised a new formulation that incorporates small amounts of a polyethylene glycol-containing lipid. This formulation has allowed the preparation of concentrated dispersions of cationic lipid:plasmid DNA (pDNA) complexes (> 20 mM pDNA) at approximately 10-fold higher concentrations than previously reported. Most of the pDNA in these formulations was bound to the lipid component and thereby protected from nebulizer-induced shearing; the pDNA also maintained full biological activity both in vitro and in vivo. This new formulation thus represents a significant improvement over current methods to prepare concentrated, active cationic lipid gene delivery vectors, and provides a new tool with which to test gene transfer to the lung.

Optimization of plasmid vectors for high-level expression in lung epithelial cells

Nonviral gene therapy approaches use a plasmid vector to express the desired transgene. We have systematically examined several regulatory elements within plasmid vectors that govern gene expression, e.g., the promoter, enhancer, intron, and polyadenylation signal, by constructing a series of plasmids that differed only in the particular sequence element being evaluated. Of the several promoters and polyadenylation signal sequences that were tested, the human cytomegalovirus (CMV) immediate early gene promoter and the addition of polyadenylation signal sequences from the bovine growth hormone (BGH) gene or rabbit beta-globin gene produced the highest levels of expression in vitro. The inclusion of a hybrid intron 3 to the promoter further increased expression 1.6-fold. The addition of a region of the CMV enhancer 5' to several weak promoters increased expression 8- to 67-fold, and co-transfection with a second plasmid encoding a chimeric transcription factor also enhanced expression. On the basis of these results, the CMV promoter, the hybrid intron, and the BGH polyadenylation signal were selected for consistent high level expression in vitro and in the mouse lung. However, expression was transient, with greater than 60% loss of activity in the first 7 days. This transient expression was not specific to CMV promoter-containing plasmids, because plasmids containing other heterologous promoters showed a similar profile of transient expression in vivo. These comparative analyses begin to provide a basis for the development of optimized expression plasmids for gene therapy of lung diseases.

Analysis of recombinant adeno-associated virus packaging and requirements for rep and cap gene products

Adeno-associated virus (AAV) is a human parvovirus currently being developed as a vector for gene therapy applications. Because the gene transfer vector commonly retains only the AAV terminal repeats, propagation of recombinant AAV (rAAV) requires that the viral replication (Rep) and capsid (Cap) proteins be supplied in trans. In an effort to optimize the production of these vectors, a panel of helper plasmids was constructed to determine if expression of the rep and/or cap genes is a limiting factor for rAAV packaging. Expression of the Rep and Cap proteins was increased by replacing the endogenous AAV promoters, p5 and p40, with the Rous sarcoma virus (RSV) long terminal repeat (LTR) and the cytomegalovirus immediate-early promoter, respectively. Increased synthesis of the Cap proteins resulted in an approximately 10-fold increase in the yield of rAAV, indicating that production of capsid proteins is one limiting factor for rAAV packaging. Expression of the rep gene from the RSV LTR not only failed to increase the yield of rAAV but also prevented activation of p40 transcription with adenovirus infection, resulting in a reduced level of capsid protein synthesis.

Tissue distribution of the cytofectin component of a plasmid-DNA/cationic lipid complex following intravenous administration in mice

Allovectin-7 is a gene therapy agent that consists of plasmid DNA (pDNA) encoding the human HLA-B7 class I and beta2-microglobulin genes (VCL-1005), complexed with the cationic lipid DMRIE Br and DOPE. A tritiated version of the cytofectin component, DMRIE Br, was synthesized by regiospecific isotope incorporation to a very high specific activity. The 3H-labeled DMRIE/DOPE mixture was complexed with VCL-1005 to produce a radiolabeled version of Allovectin-7. The VCL-1005/3H-DMRIE/DOPE complex was administered intravenously to mice, and the tissue distribution of radioactivity was analyzed 24 hr later. Excretion of radioisotope was monitored for 96 hr post dosing. At 24 hr post administration, a tissue distribution for the radioisotope of liver >> spleen > lung >> heart > brain approximately muscle approximately blood was observed. During the 96-hr period post dose, very little administered radioactivity (<17%) was excreted and the majority of the isotope (83%) remained in the animal. This is the first report on the biodistribution of the cytofectin component of a pDNA-cationic lipid complex for which the distribution of the plasmid component has also been reported.

Optimization of formulations and conditions for the aerosol delivery of functional cationic lipid:DNA complexes

We have examined several variables inherent in aerosolizing cationic lipid:DNA complexes using a jet nebulizer and thereby have optimized the delivery of functional complexes. Maximal aerosol transfer efficiency of cationic lipid:pDNA complexes was quantitated and shown to require the presence of at least 25 mM NaCL as an excipient. This is possibly related to effects on the measured zeta potentials of the complex, which indicate that the complexes are more highly charged in solutions of physiological ionic strength than in solutions of low ionic strength. Inclusion of saline also resulted in retention of the starting lipid to plasmid DNA (pDNA) ratio following nebulization. These data were used to design in vitro aerosolization experiments with tissue culture cells that resulted in the identification of a cationic lipid:pDNA ratio of 0.75:1 (mol:mol) as being optimal for aerosolization. This formulation largely protected pDNA from shear degradation during nebulization and produced a respirable aerosol droplet size (1-3 microns). It was tested further in a mouse model and shown to result in the dose-dependent transfection of mouse lungs, generating the equivalent of several picograms of reporter gene activity per mouse lung. The results of these experiments have provided a set of optimal conditions for nebulizing cationic lipid:pDNA complexes that can be used as a starting point for the further evaluation of aerosol delivery of these nonviral gene delivery vectors in vivo.

Cationic phosphonolipids as non viral vectors for DNA transfection in hematopoietic cell lines and CD34+ cells

The ability to transfer genes into a hematopoietic stem cell and to achieve regulation of their expression in lymphoid or myeloid lineages should open many new therapeutic opportunities. Besides gene transfer mediated by virus vectors like retrovirus or adenovirus, non viral systems have the theoretical advantage of being safe and easy to manage. We developed a new family of cationic lipids called phosphonolipids, synthesized 24 new molecules, and then in a first step we tested their potential to transfer genes in human hematopoietic cell lines (K562 and TF1). A LacZ plasmid under the control of a strong viral promoter was used as a reporter gene and a FACS-Gal assay and a quantitative test CPRG assay evaluated the beta gal expression. The targeted cells were analyzed 48 hours after transfection. The present work shows that seven novel molecules display a high transfer efficiency. One of them is nine-fold more efficient than the commercially available cationic lipids. The results obtained ex vivo on CD34 cells with the FACS-Gal assay show that at day 10 after transfection, 45 percent of cells are expressing gal.