Proteoglycans mediate cationic liposome-DNA complex-based gene delivery in vitro and in vivo

Dengue virus binding to human leukocyte cell lines: receptor usage differs between cell types and virus strains

Monocyte macrophages (Mphi) are thought to be the principal target cells for the dengue viruses (DV), the cause of dengue fever and hemorrhagic fever. Cell attachment is mediated by the virus envelope (E) protein, but the host-cell receptors remain elusive. Currently, candidate receptor molecules include proteins, Fc receptors, glycosaminoglycans (GAGs) and lipopolysaccharide binding CD14-associated molecules. Here, we show that in addition to Mphi, cells of the T- and B-cell lineages, and including cells lacking GAGs, can bind and become infected with DV. The level of virus binding varied widely between cell lines and, notably, between virus strains within a DV serotype. The latter difference may be ascribable to one or more amino acid differences in domain II of the E protein. Heparin had no significant effect on DV binding, while heparinase treatment of cells in all cases increased DV binding, further supporting the contention that GAGs are not required for DV binding and infection of human cells. In contrast to a recent report, we found that lipopolysaccharide (LPS) had either no effect or enhanced DV binding to, and infection of, various human leukocyte cell lines, while in all virus-cell combinations, depletion of Ca(2+)/Mg(2+) enhanced DV binding. This argues against involvement of beta(2) integrins in virus-host cell interactions, a conclusion in accord with the demonstration of three virus binding membrane proteins of < 75 kDa. Collectively, the results of this study question the purported exclusive importance of the E protein domain III in DV binding to host cells and point to a far more complex interaction between various target cells and, notably, individual DV strains.

Atomic force microscopy imaging of DNA-cationic liposome complexes optimised for gene transfection into neuronal cells

BACKGROUND

Cationic liposomes represent an important gene delivery system due to their low immunogenicity, but are relatively inefficient, with optimisation of DNA-liposome complexes (lipoplexes) for transfection necessary for each cell type of interest. There have been few studies examining optimisation in neuronal cell types or determining how the structure of lipoplexes affects transfection efficiency.

METHODS

Four commercially available cationic liposome formulations were used to optimise transfection efficiency in neuronal cells. The DNA to liposome ratio and the amount of DNA used in transfections were varied. Transfection efficiency was determined by the percentage of cells positive for the micro-galactosidase reporter gene product. The structure of lipoplexes was studied using atomic force microscopy. Lipoplexes were characterised further using dynamic light scattering to determine size and fluorescence techniques to show DNA compaction.

RESULTS

Optimal transfection conditions were found to differ between immortalised cell lines and primary cells. High transfection efficiencies in immortalised cell lines were achieved predominantly with multivalent cationic liposomes while primary neuronal cells showed optimal transfection efficiency with monovalent cationic liposomes. The structure of lipoplexes was observed with atomic force microscopy and showed globular complexes for multivalent cationic liposomes, while monovalent liposomes gave less compact structures. In support of this finding, high levels of DNA compaction with multivalent liposomes were observed using fluorescence quenching measurements for all DNA to liposome ratios tested. One monovalent liposome showed increasing levels of compaction with increasing liposome amount. Dynamic light scattering showed little change in complex size when the different lipoplexes were studied.

CONCLUSIONS

Optimisation of transfection efficiency was different for cell lines and primary neurons. Immortalised cells showed optimal transfection with multivalent liposomes while primary neurons showed optimal transfection with monovalent liposomes. The charge ratio of the monovalent liposome was below one, suggesting a different mechanism of lipoplex binding and uptake in primary neurons. The structure of lipoplexes, as

An optimized amphiphilic cationic peptide as an efficient non-viral gene delivery vector

BACKGROUND

Due to their chemical definition and reduced size, the use of peptides as gene delivery systems is gaining interest as compared to the more common polymeric non-viral vectors. To achieve gene transfer efficiencies that would make peptides a realistic alternative to existing methods, we have evaluated and attempted to concert those properties with a direct impact on the activity of the system. These considerations have led to the design, synthesis and characterization of a 23-residue cationic peptide which we term RAWA.

METHODS

We have characterized RAWA biophysically and functionally. Biophysical studies include evaluation of DNA condensation and membrane perturbing activities. DNA transfer activity has been evaluated in cell culture at controlled DNA-to-peptide stoichiometries, using a luciferase gene as reporter. Requirements for additional effectors such as chloroquine and peptide cofactors have also been considered.

RESULTS

RAWA displays in vitro DNA condensing activity similar to that of protamines, reaching maximum effect at a peptide-to-DNA molar charge ratio (CR) of 4 (+/-). The reduced membrane perturbing activity diminishes its cytotoxic potential. In COS-7 cells, transfection efficiency with RAWA peptiplexes, compares favorably with well-recognized systems, including Lipofectamine Plus, Superfect, GenePorter and FuGene. The peptide-associated activity between free and DNA-bound species has been mapped by analyzing dependency on chloroquine treatment. The lack of significant serum inhibition and low toxicity make this system advantageous for potential in vivo application. A ternary complex including the acid-triggered fusogenic JTS-1 peptide is presented as a potential strategy for further in vivo studies.

CONCLUSIONS

We have developed a gene delivery system based on an amphipathic cationic peptide with improved DNA condensation ability and reduced cytotoxicity, which maintains membrane binding and perturbing activities. Observed efficiency with this molecule is very high and compares favorably with currently available transfection systems.

Characteristics and biodistribution of cationic liposomes and their DNA complexes

We have developed some novel liposome formulations for gene transfection. The formulations consisting of O,O'-ditetradecanoyl-N-(alpha-trimethyl ammonio acetyl) diethanolamine chloride (DC-6-14) as a cationic lipid, phospholipid and cholesterol showed effective gene transfection activity in cultured cells with serum and in vivo, i.e., intraperitoneal injection in mice. In this report, the physicochemical characteristics and biodistribution of the liposomes containing DC-6-14 (DC-6-14 liposomes) as a drug (gene) carrier for gene therapy were investigated in vitro and in vivo. DC-6-14 liposome-DNA complexes were usually thought to have positive surface charge. However, depending on the ratio of DNA to liposomes, zeta-potential of the complexes became negative. The diameter of the complexes also depended on the DNA-liposome ratio, and showed a maximum when their surface potential was neutral. When biodistribution of the complexes was determined after intravenous injection, positively charged complexes showed an immediate lung accumulation. On the other hand, negatively charged complexes did not show lung accumulation. These results have suggested that biodistribution of the DNA-liposome complexes, prepared with DC-6-14 liposomes, depends on their surface charge. Therefore, some surface modification of DC-6-14 liposomes may improve the biodistribution and hence the targetability of their DNA complexes.

Noninvasive gene targeting to the brain

Gene therapy of the brain is hindered by the presence of the blood-brain barrier (BBB), which prevents the brain uptake of bloodborne gene formulations. Exogenous genes have been expressed in the brain after invasive routes of administration, such as craniotomy or intracarotid arterial infusion of noxious agents causing BBB disruption. The present studies describe the expression of an exogenous gene in brain after noninvasive i.v. administration of a 6- to 7-kb expression plasmid encoding either luciferase or beta-galactosidase packaged in the interior of neutral pegylated immunoliposomes. The latter are conjugated with the OX26 mAb to the rat transferrin receptor, which enables targeting of the plasmid DNA to the brain via the endogenous BBB transferrin receptor. Unlike cationic liposomes, this neutral liposome formulation is stable in blood and does not result in selective entrapment in the lung. Luciferase gene expression in the brain peaks at 48 h after a single i.v. administration of 10 microg of plasmid DNA per adult rat, a dose that is 30- to 100-fold lower than that used for gene expression in rodents with cationic liposomes. beta-Galactosidase histochemistry demonstrated gene expression throughout the central nervous system, including neurons, choroid plexus epithelium, and the brain microvasculature. In conclusion, widespread gene expression in the brain can be achieved by using a formulation that does not employ viruses or cationic liposomes, but instead uses endogenous receptor-mediated transport pathways at the BBB.

Lipopolycationic telomers for gene transfer: synthesis and evaluation of their in vitro transfection efficiency

We report on the synthesis of a series of lipopolyamine telomers I-14,n, I-18,n, and II-18,n and on their in vitro gene-transfer capability. Their structure consists of a polyamine polar moiety, including n primary amine functions (from 1 to 70), connected to a hydrophobic moiety, including two hydrocarbon C14 or C18 chains, through a mercaptopropanoyl or mercaptoglyceryl unit and an amide or ether function. They were obtained by telomerization of N-[2-[(BOC)aminoethyl]]acrylamide with N,N-ditetradecyl- and N,N-dioctadecylpropanamide-3-thiol and rac-1,2-dioctadecyloxypropane-3-thiol, respectively, then BOC deprotection. For N/P ratios (N = number of telomer amine equivalents; P = number of DNA phosphates) from 0.8 to 10, these lipopolyamines condensed DNA, with or without the use of DOPE, forming lipopolyplexes or teloplexes of mean sizes less than 200 nm. Some trends, structure-activity and structure-toxicity relationships, were established to achieve both highest in vitro transfection levels and cell viability. Thus, DNA formulations based on telomers I-14,20 and I-18,20 and for N/P ratios lower than 5 led to the most efficient teloplex formulations for plasmid delivery to lung epithelial A549 cells.

Heparan sulfate glycosaminoglycans are involved in adenovirus type 5 and 2-host cell interactions

Gene therapy vectors derived from subgroup C adenoviruses of the serotype 5 (Ad5) and 2 (Ad2) resulted in inefficient infection of well differentiated respiratory cells, both in vitro and in vivo. The level of expression and localization of the primary receptor for Ad5 and Ad2, termed CAR, do not completely explain why the infection efficiency varies greatly in different experimental conditions. The possibility that additional receptors like proteoglycans are involved in the infection of Ad5 and Ad2 was investigated, because several pathogenic microorganisms use heparan sulfate-glycosaminoglycans (HS-GAGs) as coreceptors for multistep attachment to target cells. The HS-GAG analog heparin decreased Ad5- and Ad2-mediated infection and binding starting from the concentration of 0.1 microgram/ml, up to a maximum of 50%. A similar reduction in Ad5 binding and infection was obtained by treatment of cells with heparin lyases I, II, and III but not with chondroitin ABC lyase. The effect of heparin on Ad5 binding has not been observed in surface GAG-defective Raji cells and after treating A549 cells with heparin lyases I, II,and III. The binding of Ad5 was completely abolished when both CAR was blocked with RmcB antibody and HS-GAGs were competitively inhibited by heparin. Parallel experiments demonstrate that HS-GAGs are irrelevant to binding and infection of the subgroup B adenovirus type 3. Collectively, these results demonstrate for the first time that HS-GAGs expressed on the cell surface are involved in the binding of Ad5 and Ad2 to host cells.

Systemic linear polyethylenimine (L-PEI)-mediated gene delivery in the mouse

BACKGROUND

Several nonviral vectors including linear polyethylenimine (L-PEI) confer a pronounced lung tropism to plasmid DNA when injected into the mouse tail vein in a nonionic solution.

METHODS

and results We have optimized this route by injecting 50 microg DNA with excess L-PEI (PEI nitrogen/DNA phosphate = 10) in a large volume of 5% glucose (0.4 ml). In these conditions, 1-5% of lung cells were transfected (corresponding to 2 ng luciferase/mg protein), the other organs remaining essentially refractory to transfection (1-10 pg luciferase/mg protein). beta-Galactosidase histochemistry confirmed alveolar cells, including pneumocytes, to be the main target, thus leading to the puzzling observation that the lung microvasculature must be permeable to cationic L-PEI/DNA particles of ca 60 nm. A smaller injected volume, premixing of the complexes with autologous mouse serum, as well as removal of excess free L-PEI, all severely decreased transgene expression in the lung. Arterial or portal vein delivery did not increase transgene expression in other organs.

CONCLUSIONS

These observations suggest that effective lung transfection primarily depends on the injection conditions: the large nonionic glucose bolus prevents aggregation as well as mixing of the cationic complexes and excess free L-PEI with blood. This may favour vascular leakage in the region where the vasculature is dense and fragile, i.e. around the lung alveoli. Cationic particles can thus reach the epithelium from the basolateral side where their receptors (heparan sulphate proteoglycans) are abundant.

Mechanisms and kinetics of liposome-cell interactions

Although the possibility of targeting drugs to specific tissues and cells, as well as facilitating their uptake and cytoplasmic delivery has rendered liposomes a versatile drug carrier system with numerous potential applications in medicine, the molecular mechanisms of liposome-cell interactions are not understood well. Here we have reviewed the early and current concepts of liposome-cell interactions, including possible liposome receptors. Uptake of liposomes by cells can be modified by the lipid composition, particularly by the inclusion of steric stabilizers such as PEG-conjugated lipids. Such modifications also alter the circulation time and biodistribution of liposomes, which can thus be tailored for particular applications. The intracellular fate of encapsulated molecules can be modified by the use of pH-sensitive liposomes which can also be sterically stabilized. Cationic liposomes that can undergo lipid mixing with cellular membranes can deliver complexed DNA to cells, but most likely via an endocytotic process. Kinetic analysis of liposome-cell interactions can elucidate the numbers of liposome receptors of several types and the corresponding binding constants. It is likely that liposomes bind to different cell surface receptors on different cells, and that they utilize more than one type of receptor on a particular cell. The kinetic analysis also provides the rate constants of endocytosis and the percentages of liposomes that are bound or endocytosed.

Intracellular accumulation of secreted proteoglycans inhibits cationic lipid-mediated gene transfer. Co-transfer of glycosaminoglycans to the nucleus

Molecules secreted by potential target cells may interfere with cationic lipid-mediated gene transfer. This has been studied using human lung fibroblasts and human epidermoid lung cancer cells. Secreted cell medium components caused a substantial decrease both in the uptake of cationic lipid-DNA complexes (2-4-fold) and in reporter gene expression (100-1000-fold). Metabolic labeling of the cell medium showed that especially [35S]sulfate-labeled macromolecules competed with DNA for binding to the cationic lipid. Release of DNA from the cationic lipid by cell medium components was demonstrated by an ethidium bromide intercalation assay. In the presence of the cationic lipid, the secreted macromolecules were internalized by the cells. By enzymatic digestions, it was shown that the competing macromolecules consist of chondroitin/dermatan sulfate and heparan sulfate proteoglycans and that the effects on transfection were mediated by the polyanionic glycosaminoglycan portion of the proteoglycan. Accordingly, pretreatment of cell medium with the polycationic peptide protamine sulfate abrogated the inhibitory effects on gene transfer. Fluorescence microscopy studies revealed that heparan sulfate, internalized as a complex with cationic lipids, accumulated in the cell nuclei. These results support the view that the lack of specificity of this type of gene transfer vehicle is a major hindrance to efficient and safe in vivo administration.

Lipoplex-mediated gene delivery to the lung occurs within 60 minutes of intravenous administration

We have defined the critical time period for gene delivery in the lung after intravenous administration of cationic lipoplex. We accomplished this through the displacement of intravenously injected cationic lipoplexes from the lungs by the subsequent administration of anionic liposomes. When reporter gene-bearing lipoplexes were injected intravenously and followed by anionic liposomes 5 min later, reporter gene expression was reduced up to 400-fold compared with animals into which lipoplex alone was administered. Administration of anionic liposomes 60-90 min after lipoplex injection yielded no significant reduction in lung transfection. When lipoplexes were disrupted 5 min after administration, the pulmonary distribution of the cationic lipid and DNA components was reduced by 80%. Lipids subsequently accumulated primarily in the liver, while the plasmid DNA constituent distributed into the blood and liver. As the interval between lipoplex and anionic liposome injection increased, the degree of lipoplex displacement from the lung decreased to such a point that, 60 min after lipoplex injection, the anionic liposome injection did not displace significant quantities of the lipoplex. We conclude that cationic lipid-DNA complexes can be disrupted in vivo via the administration of anionic liposomes; moreover, we have employed this phenomenon to demonstrate that transfectionally active DNA is taken up within 60 min of systemic lipoplex administration.

Comparative transfection studies of human ovarian carcinoma cells in vitro, ex vivo and in vivo with poly(2-(dimethylamino)ethyl methacrylate)-based polyplexes

BACKGROUND

Poly(2-(dimethylamino)ethyl methacrylate) (p(DMAEMA)) can be used successfully for in vitro transfection of different cell lines, including the OVCAR-3 human ovarian carcinoma cell line. The aim of this study was to investigate whether it is possible to transfect OVCAR-3 cells in vivo with polyplexes containing p(DMAEMA).

METHODS

In order to understand the generally observed gap between in vitro and in vivo transfection, we gradually went from in vitro to in vivo transfection of OVCAR-3 cells, while keeping the exposure conditions the same, as far as possible. To find the reason for the negligible degree of in vivo transfection, in vitro cultured OVCAR-3 cells were transfected in the presence of peritoneal ascites fluid. Next, the influence of hyaluronic acid, one of the ascites components, on the transfection efficiency was studied.

RESULTS

P(DMAEMA)-containing polyplexes can transfect OVCAR-3 cells in vitro with an overall transfection efficiency of 10%. Cells grown in vivo can be transfected ex vivo with p(DMAEMA)/plasmid complexes with an overall transfection efficiency of approximately 1-2%. When transfection complexes are injected i.p. into nude mice bearing OVCAR-3 cells in the peritoneal cavity, the degree of in vivo transfection efficiency achieved is negligible. In vitro cultured OVCAR-3 cells were also transfected with polyplexes in the presence of peritoneal ascites fluid. The results indicate that one or more components of ascites had a negative effect on the transfection efficiency of p(DMAEMA)-containing polyplexes. To elucidate which component(s) of ascites may have interfered, the influence of hyaluronic acid, one of the ascites components, on the transfection efficiency was studied. The outcome suggests that hyaluronic acid may have induced a negative effect on the transfection capability of p(DMAEMA)-containing polyplexes.

CONCLUSION

P(DMAEMA) is an efficient transfectant in vitro and ex vivo. However, transfected cells were not detected in vivo which may be caused by a negative influence of components of the ascites fluid.