Highly efficient transfection into primary cultured mouse hepatocytes by use of cation-liposomes: an application for immunization

Miniaturization of gene transfection assays in 384- and 1536-well microplates

The miniaturization of gene transfer assays to either 384- or 1536-well plates greatly economizes the expense and allows much higher throughput when transfecting immortalized and primary cells compared with more conventional 96-well assays. To validate the approach, luciferase and green fluorescent protein (GFP) reporter gene transfer assays were developed to determine the influence of cell seeding number, transfection reagent to DNA ratios, transfection time, DNA dose, and luciferin dose on linearity and sensitivity. HepG2, CHO, and NIH 3T3 cells were transfected with polyethylenimine (PEI)-DNA in both 384- and 1536-well plates. The results established optimal transfection parameters in 384-well plates in a total assay volume of 35μl and in 1536-well plates in a total assay volume of 8μl. A luciferase assay performed in 384-well plates produced a Z' score of 0.53, making it acceptable for high-throughput screening. Primary hepatocytes were harvested from mouse liver and transfected with PEI DNA and calcium phosphate DNA nanoparticles in 384-well plates. Optimal transfection of primary hepatocytes was achieved on as few as 250cellsperwell in 384-well plates, with CaPO4 proving to be 10-fold more potent than PEI.

Gene transfection of multicellular spheroid of hepatocytes on an artificial substrate

The handling of hepatocytes, a major cell population in the liver, is an important technique in both liver tissue engineering and hepatology. However, these cells are so fragile that it has been impossible to harvest hepatocytes with high viability from tissue culture dishes after a period of culture in vitro. In this study, we employed an artificial substrate for transfection of multilayer hepatocytes and harvested these cells with high viability after transfection. Hepatocytes cultured on an amphiphilic artificial substrate form multilayer aggregates (spheroids) in the presence of growth factors during gene transfection with cation liposomes. Compared to cells cultured on a collagen-coated plate, these spheroids are easily harvested with high viability by pipetting in EDTA solution. In addition, these spheroids rapidly spread on collagen after transfer from the artificial substrate, demonstrating that hepatocytes in the center of the spheroids were viable. Epidermal growth factor (EGF) increased the transfection efficiency into hepatocytes while hepatocyte growth factor (HGF) alone did not increase the efficiency. However, HGF synergestically increased the effect of EGF on transfection. Interestingly, this transfection required the process of spheroid formation because the gene was not transfected once the spheroid formation completed or under conditions where hepatocytes did not form spheroids. This method using spheroidal hepatocytes for in vitro transfection is promising for the development of ex vivo gene therapy.

Gene Expression in Primary Cultured Mouse Hepatocytes with a Cationic Liposomal Vector, TFL-3: Comparison with Rat Hepatocytes

We recently reported that a cationic liposomal vector, TFL-3, could be used to achieve significant gene expression in primary cultured rat hepatocytes (Nguyen et al., Biol. Pharm. Bull., 26, 880-885 (2003)). A combination of hepatocyte transplantation and hepatocyte-targeted gene transfer represents a potentially important strategy for expanding treatment options for liver disease. A widely applied approach to support cross-species is necessary before human applications can be realized. Therefore, in this study, we examined the utility of TFL-3 in another species of rodent hepatocytes, namely mouse hepatocytes. Gene expression in mouse hepatocytes by TFL-3 was successful and the level was higher than those in rat hepatocytes that we recently reported on. Interestingly, it appears that both the degree and rate of gene expression were dependent on the incubation time prior to lipofection as well as on the density of cells per dish, but these parameters were independent of the amount of pDNA associated with the cells. These significantly suggest that the culture time prior to and following lipofection, which are related to the biological condition of the cells, may be one of major factors that affect gene expression in hepatocytes and non- or less dividing cells.

Adsorption and desorption behaviors of cationic liposome-DNA complexes upon lipofection in inside and outside biomembrane models using a dynamic quasi-elastic laser scattering method

The dynamic behaviors of cationic liposome-DNA complexes in inside and outside biomembrane models upon lipofection were investigated using the time-resolved quasi-elastic laser scattering (QELS) method. Inside and outside biomembrane models with similar phospholipid compositions to those in living cells were formed at a tetradecane/phosphate buffered saline (TD/PBS) interface. Cationic liposome-DNA complexes were injected into the buffer subphase, and their adsorption/desorption behaviors at the biomembrane models were monitored through changes in the interfacial tension. We found that the adsorption rate of the complexes increased 2.6 times more in the outside model than in the inside one. The adsorption rate of DNA alone did not show a remarkable difference from one side to the other; however, the adsorption rate of the cationic liposome alone showed a similar tendency to that of the liposome-DNA complex. These results indicated that the difference in lipid composition induced a different dynamic behavior of exogenous biomolecules and that the cationic liposomes played an important role in the faster incorporation of DNA into cells upon lipofection.

Factors that affect the efficiency of cell transfection by immunoporation

Immunoporation is a recently discovered method that is able to transfect various human cell lines efficiently by targeting the cell surface antigens with antibody-coated beads. For this particular study, HL60, a cell line difficult to transfect by other methods, was used as a model to define the various parameters of the cell membrane that determine the efficiency of this method. The level of antigen expression on the cell surface was the first parameter to be analyzed and experiments indicated that there is a close correlation between the level of expression of surface antigens and the efficiency of immunoporation. The mixing speed, the bead to cell ratio, and the mixing time were all found to affect the ability of the antigen-coated beads to pull holes in the cells and it was found that for HL60 cells the optimum mixing speed was 40 rpm and the bead to cell ratio was 20:1 using a mixing time of 6 h.

Culture time-dependent gene expression in isolated primary cultured rat hepatocytes by transfection with the cationic liposomal vector TFL-3

The development of a carrier system that enables the transfer of a functional exogenous gene to non- or less frequently dividing mammalian cells is essential for increasing the available options for the treatment of various diseases. The issue of whether TFL-3, a recently developed cationic liposome, can be successfully used to achieve gene expression in primary cultured rat hepatocytes was examined. The hepatocytes were transfected for 4 h with plasmid DNA (pDNA) in TFL-3 at various time points after 4-h preculture. The transfection efficiency was determined at various times posttransfection with pDNA coding for chloramphenicol acetyltransferase (CAT), luciferase, or beta-galactosidase. The amount of intranuclear pDNA present, as a consequence of the lipofection, was also quantitatively determined. Successful lipofections were observed for all pDNA tested, and the efficiencies were superior to that of commercially available LIPOFECTAMINE under our experimental conditions. The degree and rate of gene expression were dependent on incubation time prior to lipofection as well as on the density of the cells per dish, but this relationship did not hold for the amount of gene delivered to the nuclei. These results indicate that TFL-3 could be a useful vector for achieving sufficient gene expression in rat hepatocytes and suggest that the culture time prior to and following lipofection, which is related to the biological condition of the cells, may be one major factor affecting efficient gene expression in nondividing cells.

Analysis of differential lipofection efficiency in primary and established myoblasts

In this study we have compared the process of lipid-mediated transfection in primary and established myoblasts, in an attempt to elucidate the mechanisms responsible for the scarce transfectability of the former. We determined the metabolic stability of cytoplasmically injected and lipofected DNA in primary and established myoblasts and carried out a comparative time course analysis of luciferase reporter-gene expression and DNA stability. The efficiency of the transcription-translation machinery of the two cell types was compared by intranuclear injection of naked plasmid DNA encoding luciferase. Subcellular colocalization of fluorescein-labeled lipopolyplexes with specific endosomal and lysosomal markers was performed by confocal microscopy to monitor the intracellular trafficking of plasmid DNA during transfection. The metabolic stability of plasmid DNA was similar in primary and established myoblasts after both lipofection and cytoplasmic injection. In both cell types, lipofection had no detectable effect on the rate of cell proliferation. Confocal analysis showed that nuclear translocation of transfected DNA coincided with localization in a compartment devoid of endosome- or lysosome-specific marker proteins. The residency time of plasmid DNA in this compartment differed for primary and established myoblasts. Our findings suggest that the lower transfectability of primary myoblasts is mostly due to a difference in the intracellular delivery pathway that correlates with more rapid delivery of internalized complex to the lysosomal compartment.

Transferrin receptor-mediated gene transfer to the corneal endothelium

BACKGROUND

The application of gene therapy to prevent allograft rejection requires the development of noninflammatory vectors. We have therefore investigated the use of a nonviral system, transferrin-mediated lipofection, to transfer genes into the cornea with the aim of preventing corneal graft rejection.

METHODS

Rabbit and human corneas were cultured ex vivo and transfected with either lipofection alone or in conjunction with transferrin. The efficiency of transfection, localization, and kinetics of marker gene expression were determined. Strategies to increase gene expression, using chloroquine and EDTA, were investigated. In addition to a marker gene, a gene construct encoding viral interleukin 10 (vIL-10) was transfected and its functional effects were examined in vitro.

RESULTS

Transferrin, liposome, and DNA were demonstrated to interact with each other, forming a complex. This complex was found to deliver genes selectively to the endothelium of corneas resulting in gene expression. Treatment of corneas with chloroquine and EDTA increased the transfection efficiency eight-fold and threefold, respectively. We also demonstrated that constructs encoding vIL-10 could be delivered to the endothelium. Secreted vIL-10 was shown to be functionally active by inhibition of a mixed lymphocyte reaction.

CONCLUSIONS

Our data indicate that transferrin-mediated lipofection is a comparatively efficient nonviral method for delivering genes to the corneal endothelium. Its potential for use in preventing graft rejection is shown by the ability of this system to induce vIL-10 expression at secreted levels high enough to be functional.

Transformation of malaria parasites by the spontaneous uptake and expression of DNA from human erythrocytes

The uptake and expression of extracellular DNA has been established as a mechanism for horizontal transfer of genes between bacterial species. Such transfer can support acquisition of advantageous elements, including determinants that affect the interactions between infectious organisms and their hosts. Here we show that erythrocyte-stage Plasmodium falciparum malaria parasites spontaneously take up DNA from the host cell cytoplasm into their nuclei. We have exploited this finding to produce levels of reporter expression in P.falciparum that are substantially improved over those obtained by electroporation protocols currently used to transfect malaria parasites. Parasites were transformed to a drug-resistant state when placed into cell culture with erythrocytes containing a plasmid encoding the human dihydrofolate reductase sequence. The findings reported here suggest that the malaria genome may be continually exposed to exogenous DNA from residual nuclear material in host erythrocytes.

Safe and efficient gene transfer into porcine hepatocytes using Sendai virus-cationic liposomes for bioartificial liver support

Establishment of a bioartificial liver support system using genetically modified hepatocytes is a potential approach to improve the treatment of severe liver failure. We describe the development of an efficient ex vivo method of gene transfer into a large number of porcine hepatocytes using hemagglutinating virus of Japan (HVJ)-liposome. The transfection efficiency of HVJ-liposome into isolated porcine hepatocytes attached to microcarrier beads was evaluated by beta-galactosidase (beta-gal) staining, fluorescence activated cell sorting analysis for beta-gal and luciferase assay, respectively. To examine the function and cellular damage of transduced hepatocytes, we used enzyme-linked immunosorbent assay for porcine albumin synthesis, lidocaine clearance test (P-450 activity), aspartate aminotransferase, and lactic dehydrogenase release assays. The optimal conditions for gene transfer into the beads-attached hepatocytes using HVJ-liposome included 4 microg of deoxyribonucleic acid with 200 microg of lipid/2 x 105 cells and exposure duration of 90 min. Under these conditions, beta-gal and luciferase genes were transduced to 2.5 x 108 isolated porcine hepatocytes following attachment to the beads. Positive beta-gal staining was observed in more than 30% of the beads-attached hepatocytes. The gene transfer activity of HVJ-liposome method determined by luciferase activities was about 100-fold of that of the lipofection method. Transfected porcine hepatocytes remained functional without any significant cell damage. Our results demonstrated that HVJ-liposome mediated gene transfer into microcarrier-attached porcine hepatocytes is an efficient and nontoxic method suitable for a bioartificial liver support sytem.

Cell delivery, intracellular trafficking and expression of an integrin-mediated gene transfer vector in tracheal epithelial cells

The mechanism of cell entry and intracellular fate of a gene transfer vector composed of a receptor-targeting, DNA-condensing peptide, RGD-oligolysine, a luciferase encoding plasmid DNA (pDNA) and a cationic liposome was examined. We demonstrate by confocal microscopy, electron microscopy and subcellular fractionation that the major mechanism of entry of the vector is endocytic. The vector complex rapidly (5 min) internalizes into early endosomes, then late endosomes and lysosomes. Entry involves, at least in part, clathrin-coated pit-mediated endocytosis since different conditions or drugs known to influence this pathway modify both uptake of pDNA and its expression. The observed increase in expression with addition of a lip some correlated with an increase in the rate of transfer of the pDNA to lysosomes, a decrease in intracellular recycling and exocytosis of the pDNA and an increase in the amount of pDNA in the nuclear fraction. Trafficking within the cell involved endosome fusion and the acid environment of the endosomes-lysosomes was beneficial for expression. After 30 min both the peptide and pDNA localized to the nucleus and the amount of intact pDNA in the nuclear fraction was highest with liposome and peptide. A better understanding of the cellular mechanisms by which vectors transfer to and traffic in cells should help design improved vectors.

Expression of vascular endothelial growth factor promotes colonization, vascularization, and growth of transplanted hepatic tissues in the mouse

A complex vascular network forms an important component of the liver architecture. This network is essential for the supply of oxygen and nutrients to cells and delivery of molecules for metabolic exchange. In this study, we attempted to construct a vascular network in transplanted hepatic tissues and examined the effect of such network on tissue formation. Primary hepatocytes of adult mice were transfected with vascular endothelial growth factor (VEGF) gene in vitro then transplanted with collagen beads intraperitoneally in mice. VEGF-transfected hepatocytes secreted sufficient protein of the transgene in vitro to induce proliferation of endothelial cells. In vivo, VEGF-transfected hepatocytes formed a large number of colonies and developed a significant vascular network in established tissues compared with control tissues. In addition, hepatocytes of VEGF-transfected, established tissues proliferated and formed a substantial parenchymal region. These hepatocytes were also functional as confirmed by the production of albumin. Our results suggested that VEGF expression conferred not only the formation of a vascular network but also promoted tissue formation. Our study showed that ex vivo gene transfection into hepatocytes is a useful method for the induction of liver reconstitution in vivo.

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.

Novel pyridinium surfactants for efficient, nontoxic in vitro gene delivery

Novel, double-chained pyridinium compounds have been developed that display highly efficient DNA transfection properties. The transfection efficiency of several of these compounds is enhanced by an order of magnitude, when compared with the transfection efficiency accomplished with the widely used cationic lipid system, lipofectin. Most importantly, the pyridinium compounds were found to be essentially nontoxic toward cells. Using various reporter genes, such as beta-galactosidase and pNEO (a gene construct that renders cells resistent to antibiotic derivatives of neomycin like G418), we demonstrate that the enhanced efficiency relates to the fact that a relative higher number of cells in the population is transfected (approximately 50% in the case of COS cells) by the pyridinium derivatives, whereas the delivery of DNA per cell is also enhanced. Furthermore, application of the pyridinium derivatives shows little cellular preference in their ability to transfect cells. By systematically modifying the structure of the pyridinium amphiphile, i.e., by changing either the headgroup structure or the alkyl chains, some insight was obtained that may lead to unraveling the mechanism of amphiphile-mediated transfection, and thus to protocols that further optimize the carrier properties of the amphiphile. Our results reveal that unsaturated alkyl chains enhance the transfection properties of the pyridinium-based amphiphiles. Preliminary experiments suggest that the structure-dependent improvement of transfection efficiency, when comparing pyridinium derivatives with lipofectin, likely relates to the mechanism of delivery rather than the packaging of the amphiphile/DNA complex.

In vitro studies of liposome-mediated gene transfer into head and neck cancer cell lines

The 5-year survival rate of patients with squamous cell carcinoma of the head and neck (HNSCC) has remained poor despite innovative surgery and new radiation and chemotherapeutic strategies. In such patients, gene therapy relying on the modification of tumor cells by gene transfer may have great potential as a new treatment modality in the therapy of HNSCC. In the present study we developed an in vitro model to show the efficacy and technical feasibility of cationic liposome-mediated gene transfer into HNSCC. Five adherent squamous cell carcinoma cell lines were transfected with SV40- or CMV-promoter-driven CAT (chloramphenicol-acetyl-transferase)-expression plasmids using DOTAP as the liposome carrier. The level of CAT expression was shown to correlate directly with the amount of transfected DNA and could be measured by a CAT-enzyme-linked immunosorbent assay. The results of gene transfer by liposome-DNA complexes obtained for all cell lines showed a dose-dependent efficacy correlating to the amount of DOTAP employed. The data demonstrate the successful in vitro transfection of epithelial cell lines with DNA, suggesting its usefulness as a new tool for head and neck cancer therapy in vivo.

Parameters influencing the introduction of plasmid DNA into cells by the use of synthetic amphiphiles as a carrier system

Parameters that affect cellular transfection as accomplished by introducing DNA via carriers composed of cationic synthetic amphiphiles, have been investigated, with the aim to obtain insight into the mechanism of DNA translocation. Such insight may be exploited in optimizing carrier properties of synthetic amphiphiles for molecules other than nucleic acids. In the present work, the interaction of vesicles composed of the cationic amphiphile dioleyloxy-propyl-trimethylammonium chloride (DOTMA) with cultured cells was examined. The results show that optimal transfection is dependent on the concentration of lipid, which determines the efficiency of vesicle interaction with the target cell membrane, as well as the toxicity of the amphiphiles towards the cell. A low lipid/DNA ratio prevents the complex from interacting with the cell surface, whereas at a relatively high amphiphile concentration the complex becomes toxic. Translocation efficiency is independent of the initial vesicle size but is affected by the size of the DNA. An incubation time of the DNA/amphiphile complex and cells of approx. 2-4 h is required for obtaining efficient transfection. In conjunction with observations on DNA/amphiphile complex-induced hemolysis of erythrocytes, a mechanism of DNA-entry is proposed which involves translocation of the nucleic acids through pores across the membranes rather than delivery via fusion or endocytosis. Dioleoylphosphatidylethanolamine, a phospholipid frequently used in a mixture with DOTMA ('lipofectin') strongly facilitates this pore formation. Translocation of the DNA is effectively prevented when the cells are pretreated with Ca2+ or pronase. These observations suggest that Ca(2+)-sensitive cell surface proteins play a role in amphiphile-mediated DNA translocation.