The role of dioleoyl phosphatidylethanolamine in cationic liposome mediated gene transfer

High density of octaarginine stimulates macropinocytosis leading to efficient intracellular trafficking for gene expression

The mechanism of the arginine-rich peptide-mediated cellular uptake is currently a controversial issue. Several factors, including the type of peptide, the nature of the cargo, and the linker between them, appear to affect uptake. One of the less studied factors, which may affect the uptake mechanism, is the effect of peptide density on the surface of the cargo. Here, we examined the mechanism of cellular uptake and intracellular trafficking of liposomes modified with different densities of the octaarginine (R8) peptide. Liposomes modified with a low R8 density were taken up mainly through clathrin-mediated endocytosis, leading to extensive lysosomal degradation, whereas those modified with a high R8 density were taken up mainly through macropinocytosis and were less subject to lysosomal degradation. Furthermore, the high density R8-liposomes were able to stimulate the macropinocytosis-mediated uptake of other particles. When plasmid DNA was condensed and encapsulated in R8-liposomes, the levels of gene expression were three orders of magnitude higher for the high density liposomes. The enhanced gene expression by the high density R8-liposomes was highly impaired by blocking uptake through macropinocytosis. The different extents of gene expression from different densities of the R8 peptide on the liposomes could be explained principally by the existence of an intracellular trafficking route, but not by the uptake amount, of internalized liposomes. These results show that the density of the R8 peptide on liposomes determines the uptake mechanism and that this is directly linked to intracellular trafficking, resulting in different levels of gene expression.

Structural variation of cationic lipids: minimum requirement for improved oligonucleotide delivery into cells

In vivo transfection efficiency (TE) using cationic liposome/oligonucleotide (ODN) complexes is often hampered by interactions with serum components. Novel cationic lipids with different hydroxyethyl or dihydroxypropyl ammonium backbones, esterified hydrocarbon chains and hydroxy substituents have been synthesized and applied in cationic liposome formulations with and without the helper lipid DOPE (1:1, m/m). Their properties for cellular ODN delivery were determined using fluorescently labeled ODNs (F-ODNs). Cationic lipids with hydrocarbon chains esterified to non-glycerol backbones in non-vicinal configuration were completely ineffective in nuclear ODN-delivery. Instead, an increased cytoplasmic localization of F-ODNs was observed. Cationic lipids equipped with only one hydrocarbon were completely incompetent for cellular ODN delivery. In the absence of serum, all cationic lipids tested with hydrocarbon chains in vicinal configuration esterified to a glycerol backbone (the respective N-(1,2-diacyl-dihydroxypropyl)-N,N,N-trimethyl-ammoniumchlorides or N-(1,2-diacyl-dihydroxypropyl)-N(hydroxyethyl)-N,N-dimethyl-ammoniumchlorides as well as N-(1,2-diacyl-dihydroxypropyl)-N(1,2-dihydroxypropyl)-N,N-dimethyl-ammoniumchlorides with lauroyl, myristoyl, palmitoyl, stearoyl and erucoyl chains) were able to transfect cells when combined with DOPE (20-80% nuclear fluorescence). Remarkably, only the analog esterified with two myristoyl chains was equally effective even in the absence of DOPE. By adding hydroxy groups to the N-alkyl residue, TE under serum conditions was improved yielding transfection rates of 55%, 75% and 90% for 0, 1 or 2 substituted hydroxy groups, respectively. For plasmid DNA, different requirements were identified. Again, the analog with two myristoyl chains was most effective but only in the presence of DOPE. However, the addition of hydroxy groups had no influence on the TE in the presence of serum.

Gene therapy in the cornea

Technological advances in the field of gene therapy has prompted more than three hundred phase I and phase II gene-based clinical trials for the treatment of cancer, AIDS, macular degeneration, cardiovascular, and other monogenic diseases. Besides treating diseases, gene transfer technology has been utilized for the development of preventive and therapeutic vaccines for malaria, tuberculosis, hepatitis A, B and C viruses, AIDS, and influenza. The potential therapeutic applications of gene transfer technology are enormous. The cornea is an excellent candidate for gene therapy because of its accessibility and immune-privileged nature. In the last two decades, various viral vectors, such as adeno, adeno-associated, retro, lenti, and herpes simplex, as well as non-viral methods, were examined for introducing DNA into corneal cells in vitro, in vivo and ex vivo. Most of these studies used fluorescent or non-fluorescent marker genes to track the level and duration of transgene expression in corneal cells. However, limited studies were directed to evaluate prospects of gene-based interventions for corneal diseases or disorders such as allograft rejection, laser-induced post-operative haze, herpes simplex keratitis, and wound healing in animal models. We will review the successes and obstacles impeding gene therapy approaches used for delivering genes into the cornea.

The role of dioleoylphosphatidylethanolamine (DOPE) in targeted gene delivery with mannosylated cationic liposomes via intravenous route

We have previously reported that mannosylated cationic liposome consisting with the mannosylated cationic cholesterol derivative Man-C4-Chol (Man) and dioleoylphosphatidylethanolamine (DOPE) (Man/DOPE) could deliver DNA to the liver by intravenous administration via mannose receptor-mediated endocytosis, however, rapid degradation in lysosomes might be a rate-limiting step in its gene transfection. In this study, we tried to evaluate the role of DOPE in in vivo gene transfer by comparing its transfection efficacy with mannosylated liposomes composed of Man and dioleoylphosphatidylcholine (DOPC) (Man/DOPC). In vitro studies showed that the cellular association of both liposome/pCMV-Luc complexes was almost the same, although Man/DOPE complex showed about 10-fold higher transfection activity than Man/DOPC complex. After intraportal administration into mice, Man/DOPE complex showed higher gene expression than Man/DOPC complex, suggesting that DOPE improves intracellular trafficking in target cells under in vivo conditions. An intravenous administration study demonstrated that Man/DOPE complex was accumulated in the liver more efficiently and achieved a higher gene expression in the liver than Man/DOPC complex. Thus, we conclude that the property of DOPE in mannosylated liposomes contributes to the efficient gene expression in the target site through enhanced distribution to the target site and intracellular sorting in the target cells under in vivo conditions.

Role of clathrin- and caveolae-mediated endocytosis in gene transfer mediated by lipo- and polyplexes

We investigated the effects of inhibitors of clathrin-mediated endocytosis (chlorpromazine and K(+) depletion) and of caveolae-mediated uptake (filipin and genistein) on internalization of FITC-poly-l-lysine-labeled DOTAP/DNA lipoplexes and PEI/DNA polyplexes by A549 pneumocytes and HeLa cells and on the transfection efficiencies of these complexes with the luciferase gene. Uptake of the complexes was assayed by fluorescence-activated cell sorting. Lipoplex internalization was inhibited by chlorpromazine and K(+) depletion but unaffected by filipin and genistein. In contrast, polyplex internalization was inhibited by all four inhibitors. We conclude that lipoplex uptake proceeds only by clathrin-mediated endocytosis, while polyplexes are taken up by two mechanisms, one involving caveolae and the other clathrin-coated pits. Transfection by lipoplexes was entirely abolished by blocking clathrin-mediated endocytosis, whereas inhibition of the caveolae pathway had no effect. By contrast, transfection mediated by polyplexes was completely blocked by genistein and filipin but was unaffected by inhibitors of clathrin-mediated endocytosis. Fluorescence colocalization studies with a lysosomal marker, AlexaFluor-dextran, revealed that polyplexes taken up by clathrin-mediated endocytosis are targeted to the lysosomal compartment for degradation, while the polyplexes internalized via caveolae escape this compartment, permitting efficient transfection.

Interaction of cationic lipid vesicles with model cell membranes--as determined by neutron reflectivity

Transfection of cells by DNA (for the purposes of gene therapy) can be effectively engineered through the use of cationic lipid/DNA "lipoplexes", although the transfection efficiency of these lipoplexes is sensitive to the neutral "helper" lipid included. Here, neutron reflectivity has been used to investigate the role of the helper lipid present during the interaction of cationic lipid vesicles with model cell membranes. Dimethyldioctadecylammonium bromide (DDAB) vesicles were formed with two different helper lipids, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) and cholesterol, and the interaction of these vesicles with a supported phospholipid bilayer was determined. DOPE-containing vesicles were found to interact faster with the membrane than those containing cholesterol, and vesicles containing either of the neutral helper lipids were found to interact faster than when DDAB alone was present. The interaction between the vesicles and the membrane was characterized by an exchange of lipid between the membrane and the lipid aggregates in solution; the deposition of vesicle bilayers on the surface of the membrane was not apparent.

Preparation and characterization of chitosan and trimethyl-chitosan-modified poly-(epsilon-caprolactone) nanoparticles as DNA carriers

The purpose of this research was to prepare poly-(epsilon-caprolactone) (PCL) particles by an emulsion-diffusion-evaporation method using a blend of poly-(vinyl alcohol) and chitosan derivatives as stabilizers. The chitosan derivatives used were chitosan hydrochloride and trimethyl chitosans (TMC) with varying degrees of quaternization. Particle characteristics-size, zeta potential, surface morphology, cytotoxicity, and transfection efficiency-were investigated. The developed method yields PCL nanoparticles in the size range of 250 to 300 nm with a positive surface charge (2.5 to 6.8 mV). The cytotoxicity was found to be moderate and virtually independent of the stabilizers' concentration with the exception of the highly quaternized TMC (degree of substitution 66%) being significantly more toxic. In immobilization experiments with gel electrophoresis, it could be shown that these cationic nanoparticles (NP) form stable complexes with DNA at a NP:DNA ratio of 3:1. These nanoplexes showed a significantly higher transfection efficiency on COS-1 cells than naked DNA.

Formation and intracellular trafficking of lipoplexes and polyplexes

Cationic lipid/DNA lipoplexes and cationic polymer/DNA polyplexes represent an attractive alternative to viral vectors for cell transfection in vitro and in vivo but still suffer from a relatively low efficiency. Optimization of their transfection efficiency may be attempted by using a trial and error approach consisting of synthesizing and testing a large number of derivatives. On the other hand, rational design of highly efficient cationic lipids and polymers requires a deeper understanding of the interactions between the vector and the DNA as well as the cellular pathways and mechanisms involved in DNA entry into the cell and ultimately the nucleus. In the present review, the pathways and mechanisms involved in lipoplex- and polyplex-mediated transfection are comparatively addressed and unresolved questions are highlighted.

Novel molecular approaches to cystic fibrosis gene therapy

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

N4,N9-dioleoyl spermine is a novel nonviral lipopolyamine vector for plasmid DNA formulation

PURPOSE

To study the effect of synthesized N4,N9-dioleoyl spermine on DNA condensation and then measure its transfection efficiency in cell culture.

METHODS

The lipopolyamine was synthesized from the naturally occurring polyamine spermine. The ability of this novel compound to condense DNA was studied using ethidium bromide fluorescence quenching and light scattering assays. Transfection efficiency was studied in primary skin cells (FEK4) and in an immortalized cancer cell line (HtTA), and compared with the commercially available transfection formulations Lipofectin and Lipofectamine.

RESULTS

The synthesized N4,N9-dioleoyl spermine formula is efficient at condensing calf thymus and circular plasmid DNA and effectively transfects both primary skin cells and cancer cell lines at low charge ratios of (+/- ammonium/phosphate) 2.5.

CONCLUSIONS

N4,N9-Dioleoyl spermine condenses DNA and achieves high transfection levels in cultured cells.

DNA-loaded bacterial ghosts efficiently mediate reporter gene transfer and expression in macrophages

There is a demand for efficient and safe DNA delivery vehicles mediating gene transfer and expression. We present bacterial ghosts as a novel platform technology for DNA delivery and targeting of macrophages. Bacterial ghosts are cell envelopes of gram-negative bacteria that are devoid of the cytoplasmic content. Escherichia coli ghosts were loaded with plasmid DNA and linear double-stranded DNA. Confocal laser scanning microscopy and flow cytometry confirmed that the DNA localized to the inner lumen of bacterial ghosts and was not associated with the outer surface of the bacteria. Up to approximately 6000 plasmids could be loaded per single ghost and the amount of loaded DNA correlated with the DNA concentration used for loading. E. coli ghosts loaded with plasmids encoding the enhanced green fluorescent protein (EGFP) targeted efficiently murine macrophages (RAW264.7) and mediated effective gene transfer. The EGFP was expressed by more than 60% of the macrophages as measured by flow cytometry detecting the green fluorescence and immunocytochemical staining with antibodies specific for EGFP.

Transfection with different colloidal systems: comparison of solid lipid nanoparticles and liposomes

Cationic solid lipid nanoparticles (SLN) for gene transfer are formulated using the same cationic lipids as for liposomal transfection agents. To investigate the differences and similarities in structure and performance between SLN and liposomes, a SLN preparation (S1), its counterpart formulation without matrix lipid (L1), a commercially available liposomal preparation (DLTR)--all based on the cationic lipid DOTAP--and a liposomal formulation that additionally contained the helper lipid dioleoylphosphatidylethanolamine (DOPE) (Escort) were compared. Photon correlation spectroscopy (PCS) showed that the SLN were smaller in diameter than the corresponding liposomes (88 vs. 148 nm) and atomic force microscopy (AFM) supported the expected structural differences. Desoxy ribonuclein acid (DNA) binding differed only marginally. Surprisingly, reporter gene expression was comparable between all DOTAP based formulations (S1, L1, DLTR), surpassed only by the DOPE containing liposomes (Escort). In conclusion, cationic lipid composition seems to be more dominant for in vitro transfection performance than the kind of colloidal structure it is arranged in. Hence, cationic SLN extend the range of highly potent non-viral transfection agents by one with favourable and distinct technological properties. Further SLN optimisation should be facilitated by the accumulated knowledge about cationic lipids in liposomal formulations.

Delivery systems for pulmonary gene therapy

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

Nonbilayer phase of lipoplex–membrane mixture determines endosomal escape of genetic cargo and transfection efficiency

Cationic lipids are widely used for gene delivery, and inclusion of dioleoylphosphatidylethanolamine (DOPE) as a helper lipid in cationic lipid-DNA formulations often promotes transfection efficacy. To investigate the significance of DOPE's preference to adopt a hexagonal phase in the mechanism of transfection, the properties and transfection efficiencies of SAINT-2/DOPE lipoplexes were compared to those of lipoplexes containing lamellar-phase-forming dipalmitoylphosphatidylethanolamine (DPPE). After interaction with anionic vesicles, to simulate lipoplex-endosomal membrane interaction, SAINT-2/DOPE lipoplexes show a perfect hexagonal phase, whereas SAINT-2/DPPE lipoplexes form a mixed lamellar-hexagonal phase. The transition to the hexagonal phase is crucial for dissociation of DNA or oligonucleotides (ODN) from the lipoplexes. However, while the efficiencies of nucleic acid release from either complex were similar, SAINT-2/DOPE lipoplexes displayed a two- to threefold higher transfection efficiency or nuclear ODN delivery. Interestingly, rupture of endosomes following a cellular incubation with ODN-containing SAINT-2/DPPE complexes dramatically improved nuclear ODN delivery to a level that was similar to that observed for SAINT-2/DOPE complexes. Our data demonstrate that although hexagonal phase formation in lipoplexes is a prerequisite for nucleic acid release from the complex, it appears highly critical for accomplishing efficient translocation of nucleic acids across the endosomal membrane into the cytosol for transport to the nucleus.

Cationic lipid–DNA complexes for non-viral gene therapy: relating supramolecular structures to cellular pathways

Cationic liposomes (CLs) are used as nonviral vectors in worldwide human clinical trials of gene therapy. Among other advantages, lipid-DNA complexes have the ability to transfer very large genes into cells, but their efficiency is much lower than that of viruses. Recent studies combining structural and biological techniques are beginning to unravel the relationship between the distinctly structured CL-DNA complexes and their transfection efficiency. Most CL-DNA complexes form a multilayered structure with DNA sandwiched between the cationic lipids (lamellar complexes, LalphaC). On rare occasions, an inverted hexagonal structure (HIIC) is observed. An important recent insight is that the membrane charge density (sigmaM) of the CL-vector is a universal parameter governing the transfection efficiency of LalphaC (but not HIIC) complexes. This has led to a new model of the cellular uptake of LalphaC complexes through activated fusion with endosomal membranes. Surface-functionalised complexes with poly(ethylene glycol)-lipids, potentially suitable for transfection invivo, have also been investigated, and the novel aspects of these complexes are discussed.

Quantitative aspects of endocytic activity in lipid-mediated transfections

Variation in transfection efficiency observed in different cell-types is poorly understood. To investigate the influence of endocytic activity on lipid-mediated transfections, we have monitored both the processes in 12 different cell-types. The endocytic activity shows a strong positive correlation (P < 0.01), with transfection efficiency. Treatment with wortmannin resulted in cell-type-dependent inhibition of transfection. Studies on M-phase cells by confocal microscopy show that compared to interphase cells, uptake of cationic liposomes was substantially reduced. In addition, transfection efficiency of cells in mitotic phase was inhibited by >70% compared to controls. Our study based on several cell-types demonstrates for the first time that quantitative aspects of endocytosis have decisive influence on the overall process of lipid-mediated transgene expression.

Cell Tagging with Clinically Approved Iron Oxides: Feasibility and Effect of Lipofection, Particle Size, and Surface Coating on Labeling Efficiency

PURPOSE

To evaluate the effect of lipofection, particle size, and surface coating on labeling efficiency of mammalian cells with superparamagnetic iron oxides (SPIOs).

MATERIALS AND METHODS

Institutional Review Board approval was not required. Different human cell lines (lung and breast cancer, fibrosarcoma, leukocytes) were tagged by using carboxydextran-coated SPIOs of various hydrodynamic diameters (17-65 nm) and a dextran-coated iron oxide (150 nm). Cells were incubated with increasing concentrations of iron (0.01-1.00 mg of iron [Fe] per milliliter), including or excluding a transfection medium (TM). Cellular iron uptake was analyzed qualitatively at light and electron microscopy and was quantified at atomic emission spectroscopy. Cell visibility was assessed with gradient- and spin-echo magnetic resonance (MR) imaging. Effects of iron concentration in the medium and of lipofection on cellular SPIO uptake were analyzed with analysis of variance and two-tailed Student t test, respectively.

RESULTS

Iron oxide uptake increased in a dose-dependent manner with higher iron concentrations in the medium. The TM significantly increased the iron load of cells (up to 2.6-fold, P < .05). For carboxydextran-coated SPIOs, larger particle size resulted in improved cellular uptake (65 nm, 4.37 microg +/- 0.08 Fe per 100 000 cells; 17 nm, 2.14 microg +/- 0.06 Fe per 100 000 cells; P < .05). Despite larger particle size, dextran-coated iron oxides did not differ from large carboxydextran-coated particles (150 nm, 3.81 microg +/- 0.46 Fe per 100 000 cells; 65 nm, 4.37 microg +/- 0.08 Fe per 100 000 cells; P > .05). As few as 10 000 cells could be detected with clinically available MR techniques by using this approach.

CONCLUSION

Lipofection-based cell tagging is a simple method for efficient cell labeling with clinically approved iron oxide-based contrast agents. Large particle size and carboxydextran coating are preferable for cell tagging with endocytosis- and lipofection-based methods.

Evaluation of nuclear transfer and transcription of plasmid DNA condensed with protamine by microinjection: The use of a nuclear transfer score

In the present study, the nuclear delivery of a green fluorescence protein (GFP)-encoding pDNA condensed by protamine was investigated in terms of trans-gene expression after cytoplasmic (E(cyt)) and nuclear (E(nuc)) microinjection. To compare the nuclear transfer process, a novel parameter; the nuclear transfer (NT) score was introduced. The E(cyt) value for protamine/pDNA particles increased in a charge ratio-dependent manner. The calculated NT score showed that this increase results from an enhancement in nuclear transfer efficiency, which was also quantitatively confirmed by a recently developed confocal image-assisted three-dimensionally integrated quantification (CIDIQ) method. Moreover, E(nuc) for protamine/pDNA particles was significantly higher than that for poly-L-lysine/pDNA particles, suggesting that pDNA, when condensed with protamine, is more accessible to intra-nuclear transcription. Collectively, protamine is an excellent DNA condenser, with bi-functional advantages: improvement in nuclear delivery and efficient intra-nuclear transcription.

New effects in polynucleotide release from cationic lipid carriers revealed by confocal imaging, fluorescence cross-correlation spectroscopy and single particle tracking

We report on new insights into the mechanisms of short single and double stranded oligonucleotide release from cationic lipid complexes (lipoplexes), used in gene therapy. Specifically, we modeled endosomal membranes using giant unilamellar vesicles and investigated the roles of various individual cellular phospholipids in interaction with lipoplexes. Our approach uses a combination of confocal imaging, fluorescence cross-correlation spectroscopy and single particle tracking, revealing several new aspects of the release: (a) phosphatidylserine and phosphatidylethanolamine are equally active in disassembling lipoplexes, while phosphatidylcholine and sphingomyelin are inert; (b) in contrast to earlier findings, phosphatidylethanolamine alone, in the absence of anionic phosphatidylserine triggers extensive release; (c) a double-stranded DNA structure remains well preserved after release; (d) lipoplexes exhibited preferential binding to transient lipid domains, which appear at the onset of lipoplex attachment to originally uniform membranes and vanish after initiation of polynucleotide release. The latter effect is likely related to phosphatidyleserine redistribution in membranes due to lipoplex binding. Real time tracking of single DOTAP/DOPE and DOTAP/DOPC lipoplexes showed that both particles remained compact and associated with membranes up to 1-2 min before fusion, indicating that a more complex mechanism, different from suggested earlier rapid fusion, promotes more efficient transfection by DOTAP/DOPE complexes.

Dioleoyl phosphatidylethanolamine and PEG-lipid conjugates modify DNA delivery mediated by 1,4-dihydropyridine amphiphiles

Complexes of amphiphilic cationic 1,4-dihydropyridines with DNA (lipoplexes) can be used for nonviral gene delivery. In order to achieve serum-resistant transfection system, DOPE and PEG-lipid conjugates were used to modify 1,4-dihydropyridine amphiphile DHP-12 complexes with DNA. The ability to bind DNA was examined by ethidium bromide displacement assay. Cellular uptake, transfection efficacy and intracellular trafficking of the lipoplexes were assessed using FACS, betagalactosidase gene transfection and confocal laser microscopy, respectively. Cytotoxicity was determined by MTT assay. DHP-12 lipoplexes that included DOPE showed enhanced cell uptake and transfection efficacy both in the absence and presence of serum. PEG-lipid conjugates, in contrast, impaired transfection. In conclusion, combination of DHP-12 with DOPE appears to be a promising transfection system.

Pyridinium cationic lipids in gene delivery: an in vitro and in vivo comparison of transfection efficiency versus a tetraalkylammonium congener

Cationic lipids provide a promising alternative to the use of viruses for delivering genes therapeutically. Among the several classes of lipidic vectors, those bearing a heterocyclic cationic head have shown important advantages, such as low cytotoxicity and improved efficiency across different cell lines. We recently reported a simple and efficient strategy for obtaining pyridinium cationic lipids, starting from pyrylium salts and primary amines. The present study is aimed to compare the cellular toxicity and transfection efficiency generated by the pyridinium polar head versus the tetramethylammonium one on several tumor cell lines and also in experimental animals, delivered via intratumor injections. Thus, the lead compound 1-(2,3-dioleoyloxypropyl)-2,4,6-trimethylpyridinium lipid (2Oc), coformulated with different helper lipids in various molar ratios, was tested against its ammonium congener DOTAP-a standard transfection reagent. The results revealed that when formulated with cholesterol at 1:1 molar ratio, the pyridinium lipid 2Oc was able to transfect several cancer cell lines with similar or better efficiency than its tetraalkylammonium congener DOTAP, while producing lower cytotoxicity. The NCI-H23 lung cancer cell line was found to be the most susceptible to be transfected. Therefore, we designed an in vivo assay based on this type of carcinoma in nude mice, which were injected intratumoral with 2Oc- and DOTAP-based lipoplexes. The red fluorescent protein reporter revealed that the pyridinium cationic lipid was superior to its tetraalkylammonium congener, transfecting the tissue on a higher area and with higher efficiency. These encouraging findings, together with the simple and efficient synthetic strategy, lay the foundation for further development of pyridinium lipids for gene therapy with improved transfection efficiency in vivo and even further reduced cytotoxicity.

“Diffusible‐PEG‐Lipid Stabilized Plasmid Lipid Particles”

Many viral and non-viral gene transfer systems suffer from common pharmacological issues that limit their utility in a systemic context. By application of the liposomal drug delivery paradigm, many of the limitations of the first generation non-viral delivery systems can be overcome. Encapsulation in small, long-circulating particles called stabilized plasmid lipid particles (SPLP) results in enhanced accumulation at disease sites and selective protein expression. This work compares the detergent dialysis method of SPLP manufacture with an alternative method, spontaneous vesicle formation by ethanol dilution. The pharmacology of SPLP, as determined by monitoring lipid label and quantitative real time PCR, is also presented.

Biophysical and biochemical properties of a binary lipid mixture for DNA transfection

The phase and miscibility behavior of a triple-chain phosphatidylcholine (TPHPC) and a single-chain surfactant (CTAB) were investigated in aqueous dispersions and in monolayers at the air/water interface. CTAB can be incorporated in the TPHPC monolayer because of its complementary molecule shape and reduces the tilt angle of TPHPC. The type of phases and the phase sequence (L2 - LS) are the same in the pure TPHPC monolayer and in the TPHPC/CTAB (80:20 mol:mol) mixture. No indication of any ordering of adsorbed DNA was observed. In the aqueous dispersions, TPHPC exhibits an inverted hexagonal phase above the chain melting. The addition of 30 mol% CTAB leads to the appearance of a lamellar Lalpha phase. The binding of DNA to the mixture is obvious but this is accompanied by a separation of the two lipids what is supported by monolayer experiments. The system has no long-term stability. The main reason seems to be not only the stronger interaction of DNA with CTAB, but also especially the unexpected weak interaction between CTAB and TPHPC. The transfection efficiency is lower compared with lipofectamine. The main disadvantage of this system is the cytotoxicity of CTAB, which could not be lowered by incorporation of CTAB in the TPHPC bilayer.

Lipoplex Structures and Their Distinct Cellular Pathways

Cationic liposomes (CLs) are used as non-viral vectors in worldwide clinical trials of gene therapy. Among other advantages, CL-DNA complexes have the ability to transfer very large genes into cells. However, since the understanding of their mechanisms of action is still incomplete, their transfection efficiencies remain low compared to those of viruses. We describe recent studies which have started to unravel the relationship between the distinct structures and physicochemical properties of CL-DNA complexes and their transfection efficiency by combining several techniques: synchrotron X-ray diffraction for structure determination, laser-scanning confocal microscopy to probe the interactions of CL-DNA particles with cells, and luciferase reporter-gene expression assays to measure transfection efficiencies in mammalian cells. Most CL-DNA complexes form a multilayered structure with DNA sandwiched between the cationic lipids (lamellar complexes, L(alpha)(C)). Much more rarely, an inverted hexagonal structure (H(II)(C)) with single DNA strands encapsulated in lipid tubules is observed. An important recent insight is that the membrane charge density sigma(M) of the CL-vector, rather than, for example, the charge of the cationic lipid, is a universal parameter governing the transfection efficiency of L(alpha)(C) complexes. This has led to a new model of the intracellular release of L(alpha)(C) complexes, through activated fusion with endosomal membranes. In contrast to L(alpha)(C) complexes, H(II)(C) complexes exhibit no dependence on sigma(M), since their structure leads to a distinctly different mechanism of cell entry. Surface-functionalized complexes with poly(ethyleneglycol)-lipids (PEG-lipids), potentially suitable for transfection in vivo, have also been investigated, and the novel aspects of these complexes are discussed.

Polycationic lipids inhibit the pro-inflammatory response to LPS

Lipopolysaccharide (LPS) is a major component of the outer membrane of Gram-negative bacteria. As such, it signals monocytes, macrophages and neutrophils to up-regulate phagocytic functions and to release pro-inflammatory cytokines. Despite the established role of CD14 as the main LPS receptor, the precise nature of the LPS signalling complex and its compartmentalization remain unknown. Interactions of LPS with other cell surface molecules such as TLR-4 and MD-2, and its subsequent internalization are required for LPS signalling. Here, we show that the polycationic lipid LipoFectamine causes inhibition of the LPS-induced MAPK activation and lack of pro-inflammatory cytokine production, despite proper localization of CD14 within lipid rafts and massive LPS internalization. The ability of LipoFectamine to inhibit LPS induced pro-inflammatory responses may be due to uncoupling of CD14 from TLR-4/MD-2 in the LPS signalling complex of mouse macrophages/microglial cells, as suggested by inhibition of LPS-induced concomitant internalization of these surface molecules. Thus, LipoFectamine may be a useful tool to dissect the molecular interactions leading to LPS signalling, and identifies a potential therapeutic strategy for LPS clearance.

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

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

Dynamic properties of an oriented lipid/DNA complex studied by neutron scattering

The formation of lipid-DNA (CL-DNA) complexes called lipoplexes, proposed as DNA vectors in gene therapy, is obtained by adding DNA to a solution containing liposomes composed of cationic and neutral lipids. The structural and dynamic properties of such lipoplexes are determined by a coupling between the electrostatic interactions and the elastic parameters of the lipid mixture. An attempt to achieve a better understanding of the structure-dynamics relationship is reported herein. In particular, an elastic neutron scattering investigation of DOTAP-DOPC (dioleoyl trimethylammonium propane-dioleoyl phosphatidylcoline) complexed with DNA is described. Proton dynamics in this oriented CL-DNA lipoplex is found to be strongly dependent upon DNA concentration. Our results show that a substantial modification of the membrane dynamics is accompanied by the balancing of the total net charge inside the complex, together with the consequent displacement of interlayer water molecules.

Cationic compounds used in lipoplexes and polyplexes for gene delivery

Gene transfer represents an important advance in the treatment of both genetic and acquired diseases. Many cationic lipids and cationic polymers naturally occurred or synthesized have been used for gene transfer. They have the advantages over viral gene transfer as non-immunogenic, easy to produce and not oncogenic. These cationic compounds, however, have the major limitations of inefficient transfection and toxicity to cells. For overcoming these problems, many new cationic compounds were developed since the first cationic lipid, DOTMA, was found usage in gene therapy. This article reviews cationic lipids for gene therapy from chemistry viewpoint and we classify these compounds as monovalent cationic lipids, polyvalent cationic lipids, cationic polymers, guanidine containing compounds, cationic peptides and cholesterol containing compounds, and hope to provide suggestions on the development of this variety of cationic compounds through the discussion.

In vitro detection of mdr1 mRNA in murine leukemia cells with 111In-labeled oligonucleotide

PURPOSE

The feasibility of intracellular mdr1 mRNA expression detection with radiolabeled antisense oligonucleotide (ODN) was investigated in the murine leukemia cell line, P388/S, and its subclonal, adriamycin-resistant cell line, P388/R.

METHODS

The expression level of mdr1 mRNA was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Existence of the multidrug resistance (MDR) phenomenon was assessed via cellular uptake of 99mTc-sestamibi (MIBI), a known substrate for P-glycoprotein. A 15-mer phosphorothioate antisense ODN complementary to the sequences located at -1 to 14 of mdr1 mRNA and its corresponding sense ODN were conjugated with the cyclic anhydride of diethylene triamine penta-acetic acid (cDTPA) via an amino group linked to the terminal phosphate at the 5' end at pH 8-9. The DTPA-ODN complexes at concentrations of 0.1-17.4 microM were reacted with 111InCl3 at pH 5 for 1 h. The hybridization affinity of labeled ODN was evaluated with size-exclusion high-performance liquid chromatography following incubation with the complementary sequence. Cellular uptake of labeled ODN was examined in vitro. Furthermore, enhancing effects of synthetic lipid carriers (Transfast) on transmembrane delivery of ODN were assessed.

RESULTS

P388/R cells displayed intense mdr1 mRNA expression in comparison with P388/S cells. 99mTc-MIBI uptake in P388/S cells was higher than that in P388/R cells. Specific radioactivity up to 1,634 MBq/nmol was achieved via elevation of added radioactivity relative to ODN molar amount. The hybridization affinity of antisense 111In-ODN was preserved at approximately 85% irrespective of specific activity. Cellular uptake of antisense 111In-ODN did not differ from that of sense 111In-ODN in either P388/S cells or P388/R cells. However, lipid carrier incorporation significantly increased transmembrane delivery of 111In-ODN; moreover, specific uptake of antisense 111In-ODN was demonstrated in P388/R cells.

CONCLUSION

Radiolabeling of ODN at high specific radioactivity and specific uptake of antisense 111In-ODN in drug-resistant cells may facilitate future gene imaging of mdr1 mRNA.

An overview of current delivery systems in cancer gene therapy

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

Cell type-specific gene expression, mediated by TFL-3, a cationic liposomal vector, is controlled by a post-transcription process of delivered plasmid DNA

The issue of whether the TFL-3, a recently developed cationic liposome, achieves efficient gene expression in different mammalian cell lines (NIH/3T3, LLC, A431 and HeLa cells) was examined. The issue of whether gene expression is related to the amount of plasmid DNA (pDNA) delivered in cells or nuclei following transfection was also examined. The cells were transfected for 1h with pDNA/TFL-3 lipoplexes, and the transfection efficiency was determined by means of a luciferase activity assay. The amount of intracellular and intranuclear pDNA following the transfection was also quantitatively determined. Successful transgene expressions in all cell lines we tested were observed under our experimental conditions, suggesting that the TFL-3 represents a suitable nonviral vector system for the successful gene expression in mammalian cells in vitro. The degree and rate of gene expression were dependent on the type of cells used as well as the incubation time after transfection, but these parameters were independent of the amount of gene delivered to cells and nuclei. These results suggest that TFL-3 mediated gene expression is largely controlled by the process of post-transcription of the delivered pDNA, and not by the process of cellular entry of pDNA and cytoplasmic trafficking of pDNA into nuclei, which is dependent on the cell type. Therefore, the results obtained here clearly suggest that the cell type-specific improvement in transcription efficiency of pDNA and translation of the derived mRNA, together with an improved delivery system to enhance the nuclear delivery of pDNA, is necessary to achieve efficient transgene expression in mammalian cells.

Characterization of DNA/lipid complexes by fluorescence resonance energy transfer

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

Polyfection as Nonviral Gene Transfer Method —Design of Novel Nonviral Vector Using α-Cyclodextrin—

Due to the growing concerns over the toxicity and immunogenicity of viral DNA delivery systems, DNA delivery via nonviral routes has become more desirable and advantageous. In particular, polycation complexes with DNA (polyplex) are attractive nonviral vectors. To design novel polycationic vectors, we prepared polyamidoamine starburst dendrimer (dendrimer) conjugates with three cyclodextrins (CDE conjugates) and three generations (G2, G3, and G4) of dendrimers. Of seven CDE conjugates, an alpha-CDE conjugate (G3) with an average degree of substitution (DS) of alpha-CyD of 2.4 [alpha-CDE conjugate (G3, DS 2.4)] showed greater gene transfer activity than dendrimers and other alpha-CDE conjugates with less cytotoxicity. These results suggest the potential use of alpha-CDE conjugate (G3, DS 2.4) as a polycationic vector in vitro and in vivo. Herein, I review a recent polyfection method, with special focus on alpha-CDE conjugate (G3, DS 2.4).

Enhancement of immune responses by DNA vaccination through targeted gene delivery using mannosylated cationic liposome formulations following intravenous administration in mice

The present study investigated the potency of the mannosylated cationic liposomes (Man liposomes) that we have developed in novel DNA vaccine carrier. Ovalbumin (OVA) was selected as a model antigen for vaccination; accordingly, OVA-encoding pDNA (pCMV-OVA) was constructed to evaluate DNA vaccination. The potency of the Man liposome/pCMV-OVA complex was compared with naked pCMV-OVA and that complexed with DC-Chol liposomes. In cultured mouse peritoneal macrophages, MHC class I-restricted antigen presentation of the Man liposome/pCMV-OVA complex was significantly higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. After intravenous administration, OVA mRNA expression and MHC class I-restricted antigen presentation on CD11c+ cells and inflammatory cytokines, such as TNF-alpha, IL-12, and IFN-gamma, that can enhance the Th1 response of the Man liposome/pCMV-OVA complex were higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. Also, the spleen cells from mice immunized by intravenous administration of the Man liposome/pCMV-OVA complex showed the highest proliferation response and IFN-gamma secretion. These findings suggest that the targeted delivery of DNA vaccine by Man liposomes is a potent vaccination method for DNA vaccine therapy.

Improving lipoplex-mediated gene transfer into C6 glioma cells and primary neurons

The development of methodologies for gene transfer into the central nervous system is crucial for gene therapy of neurological disorders. In this study, different cationic liposome formulations were used to transfer DNA into C6 glioma cells and primary hippocampal and cortical neurons by varying the nature of the helper lipid (DOPE, Chol) or a mixture of DOPE and cholesterol (Chol) associated to DOTAP. In addition, the effect of the lipid/DNA (+/-) charge ratio, the association of the ligand transferrin to the lipoplexes, and the stage of differentiation of the primary cells on the levels of transfection activity, transfection efficiency, and duration of gene expression were evaluated. Mechanistic studies were also performed to investigate the route of delivery of the complexes into neurons. Our results indicate that DOTAP:Chol (1:1 mol ratio) was the best formulation to transfer a reporter gene into C6 glioma cells, primary hippocampal neurons, and primary cortical neurons. The use of transferrin-associated lipoplexes resulted in a significant enhancement of transfection activity, as compared to plain lipoplexes, which can be partially attributed to the promotion of their internalization mediated by transferrin. While for hippocampal neurons the levels of luciferase gene expression are very low, for primary cortical neurons the levels of transgene expression are high and relatively stable, although only 4% of the cells has been transfected. The stage of cell differentiation revealed to be critical to the levels of gene expression. Consistent with previous findings on the mechanisms of cell internalization, the experiments with inhibitors of the endocytotic pathway clearly indicate that transferrin-associated lipoplexes are internalized into primary neurons by endocytosis. Promising results were obtained in terms of the levels and duration of gene expression, particularly in cortical neurons when transfected with the Tf-associated lipoplexes, this finding suggesting the usefulness of these lipid-based carriers to deliver genes within the CNS.

Improving anti-angiogenic therapy via selective delivery of cationic liposomes to tumour vasculature

In the past three decades, two very important findings regarding tumour vasculature have been made. Firstly, it has been known a solid tumour has to establish an adequate blood supply to grow beyond a critical mass. Secondly, it has been proven that the tumour vasculature is relatively more aberrant, dynamic and permeable than healthy host tissue. This review discusses the potential of delivering therapeutic nucleic acids to tumour vasculature using cationic liposomes, vehicles recently demonstrated to be selectively delivered to tumour vasculature.

Synergism in gene delivery by small PEIs and three different nonviral vectors

We have reported earlier that a combination of low-molecular weight polyethylenimines (PEIs) with the cationic liposome, Dosper, results in a synergistic increase in the transfection efficiency. Now we have investigated whether this synergism is a general mechanism seen with other transfection reagents as well. Therefore, we have combined the low-molecular weight PEIs (MW 700 and 2000) with Dotap (a monocationic liposome), Lipofectamine (a combination of neutral and polycationic liposome), and Superfect (a dendrimer). The highest synergism was achieved with Lipofectamine and PEIs in the SMC cells, or with Dotap and PEIs in the C6 cells. Superfect did not induce any synergism. The combinations did not cause any changes in DNA condensing ability measured with ethidium bromide exclusions. The proton pump inhibitor, bafilomycin A1, had similar effects in both cell lines. Interestingly, the combination of Dosper (a positive control) and PEI caused the most effective transfection synergism in the presence of serum, although Lipofectamine, with or without PEIs, was a very potent reagent demonstrating the best transfection efficiency in the absence of serum. It is suggested that the PEI/Dosper-mediated synergism in the transfection efficiency may be a general mechanism for liposomal transfection reagents, although the effects can vary depending on cell lines.

Compositional effects of cationic lipid/DNA delivery systems on transgene expression in cell culture

Studies of the contribution of various physical properties of cationic lipid/DNA complexes (CLDCs) to their observed transgene expression in vitro were conducted using cationic liposomes composed of the cationic lipids 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and dimethyldioctadecylammonium bromide (DDAB), with or without equimolar amounts of cholesterol (CHOL) or 1,2-dioleoylphosphatidylethanolamine (DOPE). The relative degree of luciferase expression by CLDCs is dependent on a complex relationship between net charge of the CLDC as well as previously reported properties, such as membrane fluidity and curvature of the cationic bilayer. Assessments were made of the role of these physical properties on CLDC stability in the extracellular medium, the extent of DNA cellular association, and membrane disruption activity. The efficiency of luciferase expression from negatively charged CLDCs is greatly improved by incorporation of DOPE. This result correlates with enhanced resistance to inhibition of gene delivery by heparan sulfate, increased cellular association of DNA, and enhanced membrane disruption activity. Luciferase expression by positively charged CLDCs is greatly reduced by incorporating equimolar amounts of CHOL and DOPE. This result occurs is in spite of increased resistance to heparan sulfate-mediated inhibition of gene delivery, increased DNA cellular association, and enhanced membrane disruption activity. The observed CLDC compositional effects on luciferase expression along with observed effects on the delivery process suggest that a better understanding of the kinetics and specific routes of gene delivery is necessary.

Cationic Vesicles Consisting of 1,2-Dioleoyl-3-Trimethylammonium Propane (DOTAP) and Phosphatidylcholines and Their Interaction with Erythrocyte Membrane

We studied the formation and stability of vesicles consisting of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and phosphatidylcholines by electron spin resonance (ESR) analysis and observation of their hemolytic activities. In contrast with previous findings on dimethyldialkylammoniums, DOTAP formed vesicles at 37 degrees C with phosphatidylcholines containing either saturated acyl chains such as dimyristoylphosphatidylcholine (DMPC) or unsaturated acyl chains such as dilinoleoylphosphatidylcholine (DLPC). Phosphatidylcholines made the bilayer more rigid and significantly reduced the hemolytic activity of DOTAP. In the presence of equimolar concentration of DOTAP and phosphatidylcholines, formation of tightly aggregated structures of several erythrocytes was observed, as previously reported for the vesicles containing dimethyldipalmitylammonium. These findings indicate that DOTAP vesicles were stabilized by phosphatidylcholines with either saturated acyl chains or unsaturated acyl chains, and the interaction with the lipid bilayer of biological membranes as cationic vesicles became prominent with minimal membrane damage by DOTAP monomers.

Effect of oligopeptides on gene expression: comparison of DNA/peptide and DNA/peptide/liposome complexes

Plasmid DNA is known to form complexes with a variety of cationic peptides and lipids, which have been explored as possible carriers for DNA transfection in mammalian cells. We synthesized oligopeptides consisting of nine amino acid residues including lysine (K), tryptophan (W), and cysteine (C), and also their symmetrical dimmers with a disulfide bond as possible carriers. The pDNA(pGL3)/oligopeptide complexes generally showed poor transfection efficiencies but little cytotoxicity for HeLa S3. The ternary system of pDNA/oligopeptide/liposome containing cationic liposomes formulated from the cholesterol derivative (DMB-Chol) and dioleoylphosphatidylethanolamine (DOPE) showed 10(4)-10(5)-fold greater effective gene expression (10(8)-10(9) level, RLU/min/mg protein) than those of the corresponding pDNA/oligopeptide complexes. In the presence of 10% serum, the ternary complexes were maintained at 10(7) levels. The ethidium bromide exclusion studies showed the ternary complexes have much greater affinity to pDNA than the corresponding pDNA/oligopeptide complexes. Plasmid sensitivity against DNase I degradation showed that the ternary complexes were well protected from the digestion. Synthetic oligopeptides are active as potential enhancers for DOPE-containing cationic liposome-mediated transfection. These findings have implications for successful in vivo transfection.

A model for the analysis of nonviral gene therapy

Further understanding of the mechanisms involved in cellular and intracellular delivery of transgene is needed to produce clinical applications of gene therapy. The compartmental and computational model designed in this work is integrated with data from previous experiments to quantitatively estimate rate constants of plasmid translocation across cellular barriers in transgene delivery in vitro. The experimental conditions between two cellular studies were held constant, varying only the cell type, to investigate how the rates differed between cell lines. Two rate constants were estimated per barrier for active transport and passive diffusion. Translocation rates of intact plasmid across the cytoplasmic and nuclear barriers varied between cell lines. CV1 cells were defined by slower rates (0.23 h(-1) cytoplasmic, 0.08 h(-1) nuclear) than those of the HeLa cells (1.87 h(-1) cytoplasmic, 0.45 h(-1) nuclear). The nuclear envelope was identified as a rate-limiting barrier by comparing the rate of intact plasmid translocation at each barrier. Slower intact plasmid translocation in CV1 cells was correlated with a reduced absolute capacity for transgene efficiency in comparison with HeLa cells. HeLa cells were three times more efficient than CV1 cells at producing green fluorescent protein per intact plasmid delivered to the nucleus. Mathematical modeling coordinated with experimental studies can provide detailed, quantitative understanding of nonviral gene therapy.

The use of fluorescence resonance energy transfer to monitor dynamic changes of lipid-DNA interactions during lipoplex formation

Fluorescence resonance energy transfer (FRET) was used to monitor interactions between Cy3-labeled plasmid DNA and NBD-labeled cationic liposomes. FRET data show that binding of cationic liposomes to DNA occurs immediately upon mixing (within 1 min), but FRET efficiencies do not stabilize for 1-5 h. The time allowed for complex formation has effects on in vitro luciferase transfection efficiencies of DOPE-based lipoplexes; i.e., lipoplexes prepared with a 1-h incubation have much higher transfection efficiencies than samples with 1-min or 5-h incubations. The molar charge ratio of DOTAP to negatively charged phosphates in the DNA (DOTAP+/DNA-) also affected the interaction between liposomes and plasmid DNA, and interactions stabilized more rapidly at higher charge ratios. Lipoplexes formulated with DOPE were more resistant to high ionic strength than complexes formulated with cholesterol. Taken together, our data demonstrate that lipid-DNA interactions and in vitro transfection efficiencies are strongly affected by the time allowed for complex formation. This effect is especially evident in DOPE-based lipoplexes, and suggests that the time allowed for lipoplex formation is a parameter that should be carefully controlled in future studies.

Three-dimensional imaging of lipid gene-carriers: membrane charge density controls universal transfection behavior in lamellar cationic liposome-DNA complexes

Cationic liposomes (CLs) are used worldwide as gene vectors (carriers) in nonviral clinical applications of gene delivery, albeit with unacceptably low transfection efficiencies (TE). We present three-dimensional laser scanning confocal microscopy studies revealing distinct interactions between CL-DNA complexes, for both lamellar L(alpha)(C) and inverted hexagonal H(II)(C) nanostructures, and mouse fibroblast cells. Confocal images of L(alpha)(C) complexes in cells identified two regimes. For low membrane charge density (sigma(M)), DNA remained trapped in CL-vectors. By contrast, for high sigma(M), released DNA was observed in the cytoplasm, indicative of escape from endosomes through fusion. Remarkably, firefly luciferase reporter gene studies in the highly complex L(alpha)(C)-mammalian cell system revealed an unexpected simplicity where, at a constant cationic to anionic charge ratio, TE data for univalent and multivalent cationic lipids merged into a single curve as a function of sigma(M), identifying it as a key universal parameter. The universal curve for transfection by L(alpha)(C) complexes climbs exponentially over approximately four decades with increasing sigma(M) below an optimal charge density (sigma(M)(*)), and saturates for at a value rivaling the high transfection efficiency of H(II)(C) complexes. In contrast, the transfection efficiency of H(II)(C) complexes is independent of sigma(M). The exponential dependence of TE on sigma(M) for L(alpha)(C) complexes, suggests the existence of a kinetic barrier against endosomal fusion, where an increase in sigma(M) lowers the barrier. In the saturated TE regime, for both L(alpha)(C) complexes and H(II)(C), confocal microscopy reveals the dissociation of lipid and DNA. However, the lipid-released DNA is observed to be in a condensed state, most likely with oppositely charged macro-ion condensing agents from the cytoplasm, which remain to be identified. Much of the observed bulk of condensed DNA may be transcriptionally inactive and may determine the current limiting factor to transfection by cationic lipid gene vectors.

Nuclear localisation sequence templated nonviral gene delivery vectors: investigation of intracellular trafficking events of LMD and LD vector systems

The impact of a peptide that contains a nuclear localisation sequence (NLS) on intracellular DNA trafficking was studied. We used the adenoviral core peptide mu and an SV40 NLS peptide to condense plasmid DNA (pDNA) prior to formulation with 3beta-[N-(N', N'-dimethylaminoethane)carbamoyl]cholesterol/dioleoyl-L-alpha-phosphatidyl ethanolamine (DC-Chol/DOPE) liposomes to give LMD and LND vectors, respectively. Fluorescent-labelled lipid and peptides plus dye-labelled pDNA components were used to investigate gene delivery in dividing and S-phase growth-arrested cells. Confocal microscopic analyses reveal little difference in intracellular trafficking events. Strikingly, mu peptide associates with nuclei and nucleoli of cells within less than 15 mins incubation of LMD with cells, which suggests that mu peptide has an NLS function. These NLS properties were confirmed by cloning of a mu-beta-galactosidase fusion protein that localises in the nuclei of cells after cytosolic translation. In dividing cells both LMD and LND deliver pDNA(Cy3) to nuclei within 30-45 min incubation with cells. By contrast, pDNA is detected only in the cytoplasm in growth-arrested cells over the period of time investigated, and not in the nuclei. LD systems prepared from DC-Chol/DOPE cationic liposomes and pDNA(Cy3) behave similarly to LMD systems, which suggests that mu peptide is unable to influence trafficking events in this current LMD formulation, in spite of its strong NLS capacity. We further describe the effect of polyethyleneglycol (PEG) on cellular uptake. "Stealth" systems obtained by post-coating LMD particles with fluorescent-labelled PEG molecules (0.5, 5 and 10 mol % fluorescein-PEG(5000)-N-hydroxysuccinimide) were prepared and shown to be internalised rapidly (mins) by cells, without detectable transgene expression. This result indicates that PEG blocks intracellular trafficking of pDNA.

Photochemically enhanced gene delivery with cationic lipid formulations

Entrapment and degradation of transfecting DNA in endocytic vesicles often hampers the use of lipidic vectors for gene delivery purposes. Photochemical internalisation (PCI) is a technology for achieving light-induced release of DNA trapped inside these vesicles, and therefore represents a way of overcoming the endocytic membrane barrier and improving gene transfer. The technology is based on utilising photosensitizers which localise in the membranes of endocytic vesicles, causing photochemical damages that rupture the vesicles upon illumination. The purpose of this work was to study the effect of PCI on transfection mediated by the cationic lipid N-(2-aminoethyl)-N,N-dimethyl-2,3-bis(tetradecyloxy)-1-propanaminium bromide (betaAE-DMRIE), with or without the helper lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). It was shown that PCI has no effect on betaAE-DMRIE mediated transfection, whereas it significantly enhances transfection mediated by the combination of betaAE-DMRIE and DOPE. The effect of PCI was highly dependent on the timing of illumination relative to the time of DNA delivery, both regarding the sequence of, and the time between, these two treatments.

Lipoplexes with alkylphospholipid as new helper lipid for efficient in vitro and in vivo gene transfer in tumor therapy

To improve liposomal gene transfer we investigated the influence of membrane-interacting alkylphospholipids (APLs) on gene transfer efficiency in vitro and in vivo using the LacZ reporter gene and the cytosine deaminase (CD) suicide gene. Liposomes were first optimized concerning the kind and amount of APL and the additional liposome components. Thus, an up to 270% increase in the transfer efficiency of the LacZ gene into HCT15 and HCT116 human colon carcinoma cells could be obtained in vitro compared to lipofectin-mediated transfection by using a lipoplex consisting of tetradecylphosphocholine/dimethyldioctadecylamine/cholesterol/dioleylphosphoethanolamine-liposomes and the pSV40-betaGal-plasmid. The in vivo experiments revealed that alkylphospholipid-lipoplexes (APL-LPs) were similarly effective in the transfer of the LacZ gene into colon carcinoma as formulations consisting of lipofectin. Using the CD-gene in combination with APL-LPs resulted in a significantly stronger inhibition of C26 colon carcinoma growth compared to lipofectin-mediated gene transfer following treatment of mice with the prodrug 5-fluorocytosine. The results of this study demonstrate for the first time that the utilization of membrane-active APLs as component of the liposomal part of lipoplexes enhances the efficacy of gene therapy in vitro and in vivo.

Cationic liposome-mediated gene delivery: biophysical study and mechanism of internalization

To identify factors affecting cationic liposome-mediated gene delivery efficiency, we studied the relationship between the biophysical characteristics of liposome/DNA complexes (lipoplexes) at different (+/-) charge ratios, their structures as monitored by atomic force microscopy (AFM), and their mechanism(s) of internalization into the cells. Significant changes were observed in the particle size and zeta potential of liposomes and their structures assessed by AFM upon addition of DNA, which depended on (+/-) charge ratios. AFM images showed that lipoplexes were formed from extensively fused and apparently homogeneous lipid particles encapsulating DNA. Lipoplexes were found to internalize the cells through the endocytosis pathway. Lipoplex-cell fusion was found to occur mainly at the plasma membrane level; however, this lipoplex-cell membrane fusion was found to be essential for the uptake of the large particles. A new perspective for the internalization of large lipoplex particles into cytoplasm is discussed.

Barriers to nonviral gene delivery

The use of various synthetic lipids and polymers to deliver DNA for gene therapy applications has been the subject of intense examination for the last 15 years. Our understanding of the processes involved in the delivery of DNA, although still limited, can be described in terms of specific physical and chemical barriers encountered along the delivery pathway. Successful engagement of this pathway involves avoiding inactivation in the extracellular compartment and initial favorable interactions with the cell surface. Internalization of the delivery system by endocytosis results in a poorly defined endosomal trafficking process which, if not escaped, leads to degradation of the therapeutic DNA in lysosomes. For the small fraction of material that is able to escape this vesicular trafficking pathway, the cytosol provides additional physical and metabolic barriers to further trafficking to the nucleus. Finally, nuclear uptake has been demonstrated to be a significant barrier to gene delivery. In this review, we outline in greater detail the various processes involved in each step and describe various formulation variables that have been explored to overcome these delivery barriers to nonviral gene delivery.

Surface charge density determines the efficiency of cationic gemini surfactant based lipofection

The efficiencies of the binary liposomes composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine and cationic gemini surfactant, (2S,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide as transfection vectors, were measured using the enhanced green fluorescent protein coding plasmid and COS-1 cells. Strong correlation between the transfection efficiency and lipid stoichiometry was observed. Accordingly, liposomes with X(SR-1) > or = 0.50 conveyed the enhanced green fluorescent protein coding plasmid effectively into cells. The condensation of DNA by liposomes with X(SR-1) > 0.50 was indicated by static light scattering and ethidium bromide intercalation assay, whereas differential scanning calorimetry and fluorescence anisotropy of diphenylhexatriene revealed stoichiometry dependent reorganization in the headgroup region of the liposome bilayer, in alignment with our previous Langmuir-balance study. Surface charge density and the organization of positive charges appear to determine the mode of interaction of DNA with (2S,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide/1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes, only resulting in DNA condensation when X(SR-1) > 0.50. Condensation of DNA in turn seems to be required for efficient transfection.