DOTAP cationic liposomes prefer relaxed over supercoiled plasmids

A fluorescence-based assay for Trichomonas vaginalis drug screening

BACKGROUND

The emergence and spread of drug resistance in Trichomonas vaginalis parasites has become an important concern in trichomoniasis treatment. Fast and reliable growth assessment is critical for validating in vitro drug susceptibility and high-throughput screening of newly developed drugs.

METHODS

Modified media without yeast extract were evaluated for their ability to support the growth of T. vaginalis parasites. The potential of the nucleic acid-binding dye SYBR Green I for detecting T. vaginalis drug resistance was characterized, and seeding parasite concentration and incubation time were optimized. The fluorescence assay based on SYBR Green I was further validated in four T. vaginalis isolates with different susceptibilities to the antibiotics metronidazole, tinidazole, ornidazole and secnidazole, and compared with the traditional method that detects minimum lethal concentrations (MLCs).

RESULTS

A modified medium consisting of RPMI 1640 and Tryptone Plus as replacements for yeast extract and tryptone, respectively, in traditional trypticase-yeast extract-maltose (TYM) medium exhibited similar performance as TYM medium in maintaining T. vaginalis growth, while it showed much lower background fluorescent signals. The T. vaginalis SYBR Green I-based fluorescence (TSF) drug assay was found to have to satisfy one of two conditions to demonstrate the 50% inhibitory concentration of metronidazole for the sensitive isolate TV-334: (i) a seeding density of 3 × 104 parasites/ml and an incubation time of 48 h; or (ii) a seeding density of 1 × 104 parasites/ml and an incubation time of 72 h. Subsequent validation experiments revealed that the 48-h incubation/3 × 104 parasites/ml seeding density condition had a greater sensitivity to detect drug resistance than the 72-h condition. The TSF assay also exhibited high efficiency in identifying parasite drug resistance, as evidenced by its strong correlation with the standard MLC assay results (P = 0.003).

CONCLUSIONS

This study presents a robust TSF assay that has the potential to facilitate high-throughput, automated in vitro anti-trichomoniasis susceptibility testing for drug resistance monitoring and drug development. In comparison to the standard MLC method, this assay offers the advantages of reduced labor and elimination of subjective examination.

Segregation of Dispersed Silica Nanoparticles in Microfluidic Water-in-Oil Droplets: A Kinetic Study

Dispersed negatively charged silica nanoparticles segregate inside microfluidic water-in-oil (W/O) droplets that are coated with a positively charged lipid shell. We report a methodology for the quantitative analysis of this self-assembly process. By using real-time fluorescence microscopy and automated analysis of the recorded images, kinetic data are obtained that characterize the electrostatically-driven self-assembly. We demonstrate that the segregation rates can be controlled by the installment of functional moieties on the nanoparticle's surface, such as nucleic acid and protein molecules. We anticipate that our method enables the quantitative and systematic investigation of the segregation of (bio)functionalized nanoparticles in microfluidic droplets. This could lead to complex supramolecular architectures on the inner surface of micrometer-sized hollow spheres, which might be used, for example, as cell containers for applications in the life sciences.

Lipid- and polymer-based plexes as therapeutic carriers for bioactive molecules

Recently, promising strategies of plexes include the complexation of nucleic acids with lipids (lipoplexes) and different kinds of polymers (polyplexes) for delivery of actives and genetic material in abnormal conditions like cancer, cystic fibrosis and genetic disorders. The present review article focuses on the comparative aspects of lipoplexes and polyplexes associated with molecular structure, cellular transportation and formulation aspects. The major advantages of lipoplexes and polyplexes over conventional liposomes involve non-immunogenic viral gene transfer, facile manufacturing and preservation of genetic material encapsulated within the nanocarriers. Lipoplexes and polyplexes enhance the transfection of DNA into the cell by stepwise electrostatic cationic-anionic interaction with DNA backbones. The ease and cost-effective formation of complexes extend their applications in the treatment of cancer and genetic disorders. Lipoplexes and polyplexes necessitate intensive research in the fields of quality, toxicity and methods of preparation for commercialization.

Cationic Liposomes: A Flexible Vaccine Delivery System for Physicochemically Diverse Antigenic Peptides

PURPOSE

Personalized peptide-based cancer vaccines will be composed of multiple patient specific synthetic long peptides (SLPs) which may have various physicochemical properties. To formulate such SLPs, a flexible vaccine delivery system is required. We studied whether cationic liposomes are suitable for this purpose.

METHODS

Fifteen SIINFEKL T cell epitope-containing SLPs, widely differing in hydrophobicity and isoelectric point, were separately loaded in cationic liposomes via the dehydration-rehydration method. Particle size and polydispersity index (PDI) were measured via dynamic light scattering (DLS), and zeta potential with laser Doppler electrophoresis. Peptide loading was fluorescently determined and the immunogenicity of the formulated peptides was assessed in co-cultures of dendritic cells (DCs) and CD8⁺ T-cells in vitro.

RESULTS

All SLPs were loaded in cationic liposomes by using three different loading method variants, depending on the SLP characteristics. The fifteen liposomal formulations had a comparable size (< 200 nm), PDI (< 0.3) and zeta potential (22-30 mV). Cationic liposomes efficiently delivered the SLPs to DCs that subsequently activated SIINFEKL-specific CD8⁺ T-cells, indicating improved immunological activity of the SLPs.

CONCLUSION

Cationic liposomes can accommodate a wide range of different SLPs and are therefore a potential delivery platform for personalized cancer vaccines.

Mg2+-induced DNA compaction, condensation, and phase separation in gene delivery vehicles based on zwitterionic phospholipids: a dynamic light scattering and surface-enhanced Raman spectroscopic study

Despite the significant efforts towards applying improved non-destructive and label-free measurements of biomolecular structures of lipid-based gene delivery vectors, little is achieved in terms of their structural relevance in gene transfections. Better understanding of structure-activity relationships of lipid-DNA complexes and their gene expression efficiencies thus becomes an essential issue. Raman scattering offers a complimentary measurement technique for following the structural transitions of both DNA and lipid vesicles employed for their transfer. This work describes the use of SERS coupled with light scattering approaches for deciphering the bioelectrochemical phase formations between nucleic acids and lipid vesicles within lipoplexes and their surface parameters that could influence both the uptake of non-viral gene carriers and the endocytic routes of interacting cells. As promising non-viral alternatives of currently employed risky viral systems or highly cytotoxic cationic liposomes, complexations of both nucleic acids and zwitterionic lipids in the presence of Mg²⁺ were studied applying colloidal Ag nanoparticles. It is shown that the results could be employed in further conformational characterizations of similar polyelectrolyte gene delivery systems.

Lipid nanocapsules functionalized with polyethyleneimine for plasmid DNA and drug co-delivery and cell imaging

The paper reports on the preparation of lipid nanocapsules (LNCs) functionalized with poly(ethyleneimine) (PEI) moieties and their successful use as drug and gene delivery systems. The cationic LNCs were produced by a phase inversion process with a nominal size of 25 nm and subsequently modified with PEI chains using a transacylation reaction. The functionalization process allowed good control over the nanoscale particle size (26.2 ± 3.9 nm) with monodisperse size characteristics (PI < 0.2) and positive surface charge up to +18.7 mV. The PEI-modified LNCs (LNC25-T) displayed good buffering capacity. Moreover, the cationic LNC25-T were able to condense DNA and form complexes via electrostatic interactions in a typical weight ratio-dependent relationship. It was found that the mean diameter of LNC25-T/pDNA complexes increased to ∼40-50 nm with the LNC25-T/pDNA ratio from 1 to 500. Gel electrophoresis and cell viability experiments showed that the LNC25-T/pDNA complexes had high stability with no cytotoxicity due to the anchored PEI polymers on the surface of LNCs. Finally, the transfection efficiency of the LNC25-T/pDNA complexes was studied and evaluated on HEK cell lines in comparison with free PEI/pDNA polyplexes. The combination of cationic LNCs with pDNA exhibited more than a 2.8-fold increase in transfection efficiency compared to the standard free PEI/pDNA polyplexes at the same PEI concentrations. Moreover, we have demonstrated that LNC25-T/pDNA loaded with a hydrophobic drug, paclitaxel, showed high drug efficacy. The high transfection efficiency combined with the potential of simultaneous co-delivery of hydrophobic drugs, relatively small size of LNC25-T/pDNA complexes, and fluorescence imaging can be crucial for gene therapy, as small particle sizes may be more favorable for in vivo studies.

Gold nanoparticles electroporation enhanced polyplex delivery to mammalian cells

Nonviral methods have been explored as the replacement of viral systems for their low toxicity and immunogenicity. However, they have yet to reach levels competitive to their viral counterparts. In this paper, we combined physical and chemical methods to improve the performance of polyplex delivery of DNA and small interfering RNA. Specifically, gold nanoparticles (AuNPs) were used to carry polyplex (a chemical approach) while electroporation (a physical approach) was applied for fast and direct cytosolic delivery. In this hybrid approach, cationic polymer molecules condense and/or protect genetic probes as usual while AuNPs help fix polycations to reduce their cytotoxicity and promote the transfection efficiency of electroporation. AuNPs of various sizes were first coated with polyethylenimine, which were further conjugated with DNA plasmids or small interfering RNA molecules to form AuNPs-polyplex. The hybrid nanoparticles were then mixed with cells and introduced into cell cytosol by electroporation. The delivery efficiency was evaluated with both model anchor cells (i.e., NIH/3T3) and suspension cells (i.e., K562), together with their impact on cell viability. We found that AuNP-polyplex showed 1.5∼2 folds improvement on the transfection efficiency with no significant increase of toxicity when compared to free plasmid delivery by electroporation alone. Such a combination of physical and chemical delivery concept may stimulate further exploration in the delivery of various therapeutic materials for both in vitro and in vivo applications.

Topical drug delivery to retinal pigment epithelium with microfluidizer produced small liposomes

Drug delivery from topically instilled eye drops to the posterior segment of the eye has long been one of the greatest challenges of ocular drug development. We developed methods of liposome preparation utilizing a microfluidizer to achieve adjustable nanoparticle size (even less than 80 nm) and high loading capacity of plasmid DNA. The microfluidizing process parameters were shown to affect the size of the liposomes. Higher operating pressures and passage for at least 10 times through the microfluidizer produced small liposomes with narrow size distribution. The liposomes were physically stable for several months at +4°C. In vivo distribution of the optimized liposome formulations in the rat eyes was investigated with confocal microscopy of the histological specimens. Transferrin was used as a targeting ligand directed to retinal pigment epithelium. Size dependent distribution of liposomes to different posterior segment tissues was seen. Liposomes with the diameter less than 80 nm permeated to the retinal pigment epithelium whereas liposomes with the diameter of 100 nm or more were distributed to the choroidal endothelium. Active targeting was shown to be necessary for liposome retention to the target tissue. In conclusion, these microfluidizer produced small liposomes in eye drops are an attractive option for drug delivery to the posterior segment tissues of the eye.

In vitro performance of lipid-PLGA hybrid nanoparticles as an antigen delivery system: lipid composition matters

Due to the many beneficial properties combined from both poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and liposomes, lipid-PLGA hybrid NPs have been intensively studied as cancer drug delivery systems, bio-imaging agent carriers, as well as antigen delivery vehicles. However, the impact of lipid composition on the performance of lipid-PLGA hybrid NPs as a delivery system has not been well investigated. In this study, the influence of lipid composition on the stability of the hybrid NPs and in vitro antigen release from NPs under different conditions was examined. The uptake of hybrid NPs with various surface charges by dendritic cells (DCs) was carefully studied. The results showed that PLGA NPs enveloped by a lipid shell with more positive surface charges could improve the stability of the hybrid NPs, enable better controlled release of antigens encapsulated in PLGA NPs, as well as enhance uptake of NPs by DC.

Contribution of syndecans to lipoplex-mediated gene delivery

The long awaited breakthrough of gene therapy significantly depends on the in vivo efficiency of targeted intracellular delivery. Hidden details of cellular uptake present a great hurdle for non-viral gene delivery with liposomes. Growing scientific evidence supports the involvement of polyanionic cell surface carbohydrates in cellular internalization of cationic liposomes. Syndecans, a highly conserved family of transmembrane heparan sulfate proteoglycans serve attachment sites for great variety of cationic ligands including growth factors, cytokines and even parasites. In the present study we quantitatively measured the contribution of various syndecan isoforms to liposome-mediated gene transfer. The obtained data show the superiority of syndecan-4, the ubiquitously expressed isoform of the syndecan family, in cellular uptake of liposomes. Applied mutational analysis demonstrated that gene delivery could be abolished by mutating the glycosaminoglycan attachment site of syndecans, highlighting the importance of polyanionic heparan sulfate side chains in the attachment of cationic liposomes. Blocking sulfation of syndecans also diminished gene delivery, a finding that confirms the essential role of polyanionic charges in binding cationic liposomes. Mutating other parts of the syndecan extracellular domain, including the cell-binding domain, had clearly smaller effect on liposome internalization. Mutational analyses also revealed that superiority of syndecan-4 in liposome-mediated gene delivery is significantly influenced by its cytoplasmic domain that orchestrates signaling pathways leading to macropinocytosis. In summary our study present a mechanistic insight into syndecan-mediated macropinocytic uptake of lipoplexes and highlights syndecan-4 as a superior target for cationic liposomes.

Factors affecting DNA binding and stability of association to cationic liposomes

Lipoplexes are complexes formed between cationic liposomes (L(+)) and polyanionic nucleic acids (P(-)). They are commonly used in vitro and in vivo as a nucleic acid delivery system. Our study aims are to investigate how DOTAP-based cationic liposomes, which vary in their helper lipid (cholesterol or DOPE) and in media of different ionic strengths affect the degree, mode of association and degree of condensation of pDNA. This was determined by ultracentrifugation and gel electrophoresis, methods based on different physical principles. In addition, the degree of pDNA condensation was also determined using the ethidium bromide (EtBr) intercalation assay. The results suggest that for cationic lipid compositions (DOTAP/DOPE and DOTAP/cholesterol), 1.5 M NaCl, but not 0.15 M NaCl, both prevent lipoplex formation and/or induce partial dissociation between lipid and DNA of preformed lipoplexes. The higher the salt concentration the greater is the similarity of DNA condensation (monitored by EtBr intercalation) between lipoplex DNA and free DNA. As determined by ultracentrifugation and agarose gel electrophoresis, 30-90% of the DNA is uncondensed. SDS below its critical micellar concentration (CMC) induced "de-condensation" of DNA without its physical release (assessed by ultracentrifugation) for both DOTAP/DOPE and DOTAP/cholesterol lipoplexes. As was assessed by agarose gel electrophoresis SDS induced release of 50-60% of DNA from the DOTAP/cholesterol lipoplex but not from the DOTAP/DOPE lipoplex. This study shows that there are conditions under which DNA is still physically associated with the cationic lipids but undergoes unwinding to become less condensed. We also proved that the helper lipid affects level and strength of the L(+) and DNA(-) electrostatic association; these interactions are weaker for DOTAP/cholesterol than for DOTAP/DOPE, despite the fact that the positive charge and surface pH of DOTAP/cholesterol and DOTAP/DOPE are similar.

In vitro reporter gene transfection via plasmid DNA delivered by metered dose inhaler

Aerosolised DNA administration could potentially advance the treatment of inheritable lung diseases, lung malignancies and provide genetic immunisation against infection. Jet nebulisation, the current standard for introducing DNA formulations into the lung, is inherently inefficient. Pressurised metered dose inhalers (pMDIs) offer a potentially more efficacious and convenient alternative, especially for repeat administration. We aim to modify a novel low-energy nanotechnology process to prepare surfactant-coated pDNA nanoparticles for pulmonary gene delivery via a pMDI. Water-in-oil microemulsions containing green fluorescent protein reporter plasmid were snap-frozen and lyophilised. Lyophilised pDNA, in some cases following a surfactant wash, was incorporated into pMDIs with hydrofluoroalkane 134a (HFA134a) propellant and ethanol as cosolvent. To assess biological functionality, A549 human lung epithelial cells were exposed to aerosolised pDNA particles in the presence of dioleoyl-trimethylammonium propane (DOTAP). Transfection studies demonstrated that pDNA biological functionality was maintained following aerosolisation. In vitro toxicity assays (MTT) showed no significant cell viability loss following aerosolised pDNA treatment. We have demonstrated that pDNA particles can be incorporated into an HFA134a formulation and aerosolised using a standard valve and actuator. Particles prepared by this novel process have potential for stable and efficient delivery of pDNA to the lower respiratory tract via standard pMDI technology.

The Effect of Electroporation Type Pulsed Electric Fields on DNA in Aqueous Solution

Electroporation is a physical phenomenon in which pulsed electric fields applied across a cell produce transient (reversible) or permanent (irreversible) permeabilization of the cell membrane. Irreversible electroporation is an important method of sterilization in the food industry and it is becoming an important minimally invasive tissue ablation technique in medicine. Motivated by recent observations of apoptosis like marker stains in irreversibly electroporated cells we performed a study on the effects of electroporation type electric pulses on the integrity of naked DNA in solution. Using gel electrophoresis analyses we show that pulses of the irreversible electroporation type have the ability to affect the naked DNA in solution. It is found that some electric parameters that lead to cell death by irreversible electroporation also cause changes in the naked DNA exposed to the same procedure. Our analysis tentatively suggests that some electroporation type electric pulses cause nicks in the DNA molecule. Therefore, it is possible that the mechanisms of cell death in irreversible electroporation also include damages to the DNA. However, this work did not investigate the possible effects of electroporation induced electrode corrosion byproducts, such as Al3+ ions on DNA integrity; which should be also studied in the future. In general, since electroporation phenomena based applications are widely used in medicine and biotechnology, the current study suggests that further research into the effects of electroporation type electric pulses on the DNA are warranted.

A theoretical and experimental approach to the compaction process of DNA by dioctadecyldimethylammonium bromide/zwitterionic mixed liposomes

The compaction of DNA by cationic liposomes constituted by a mixture of a cationic lipid, dioctadecyldimethylammonium bromide (DODAB), and a zwitterionic lipid, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), has been evaluated by means of experimental studies (electrophoretic mobility, conductometry, cryogenic electron transmission microscopy or cryo-TEM, and fluorescence spectroscopy) as well as theoretical calculations. This information reveals that DODAB/DOPE and DODAB/DLPC liposomes are mostly spherical and unilamellar, with a mean diameter of around 70 and 61 nm, respectively, a bilayer thickness of 4.5 nm, and gel-to-fluid transition temperatures, T(m), of around 19 and 28 degrees C, respectively. Their positively charged surfaces efficiently compact the negatively charged DNA by means of a strong entropically driven surface interaction that yields DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes as confirmed by zeta potential and ethidium bromide fluorescence intercalation assays. These experiments have permitted as well the evaluation of the different microenvironments of varying polarity of the DNA helix, liposomes, and/or lipoplexes. DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes have been characterized by isoneutrality ratios (L/D)(phi) of around 4.7 and 4.8, respectively, a more fluid membrane than that of the parent liposomes, and T(m) around 24 and 28 degrees C, respectively, as revealed by fluorescence anisotropy. Cryo-TEM micrographs reveal a rich scenario of nanostructures and morphologies, from unilamellar DNA-coated liposomes to multilamellar lipoplexes passing through cluster-like structures. Phase diagrams (aggregation and re-entrant condensation phenomena), calculated by means of a phenomenological theory, have confirmed the experimental concentration domains and the isoneutrality conditions. The influence of helper lipid in the compaction process, as well as the optimum choice among those herein chosen, has been analyzed.

Effect of ionic strength and presence of serum on lipoplexes structure monitorized by FRET

Background

Serum and high ionic strength solutions constitute important barriers to cationic lipid-mediated intravenous gene transfer. Preparation or incubation of lipoplexes in these media results in alteration of their biophysical properties, generally leading to a decrease in transfection efficiency. Accurate quantification of these changes is of paramount importance for the success of lipoplex-mediated gene transfer in vivo.

Results

In this work, a novel time-resolved fluorescence resonance energy transfer (FRET) methodology was used to monitor lipoplex structural changes in the presence of phosphate-buffered saline solution (PBS) and fetal bovine serum. 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/pDNA lipoplexes, prepared in high and low ionic strength solutions, are compared in terms of complexation efficiency. Lipoplexes prepared in PBS show lower complexation efficiencies when compared to lipoplexes prepared in low ionic strength buffer followed by addition of PBS. Moreover, when serum is added to the referred formulation no significant effect on the complexation efficiency was observed. In physiological saline solutions and serum, a multilamellar arrangement of the lipoplexes is maintained, with reduced spacing distances between the FRET probes, relative to those in low ionic strength medium.

Conclusion

The time-resolved FRET methodology described in this work allowed us to monitor stability and characterize quantitatively the structural changes (variations in interchromophore spacing distances and complexation efficiencies) undergone by DOTAP/DNA complexes in high ionic strength solutions and in presence of serum, as well as to determine the minimum amount of potentially cytotoxic cationic lipid necessary for complete coverage of DNA. This constitutes essential information regarding thoughtful design of future in vivo applications.

Cholesteryl cytofectins with primary amino head groups transfect transformed human epithelial cell lines efficiently

Two novel cholesterol-based cytofectins containing primary amino head groups, glycylcholesteryl formylhydrazide (MS10) and beta-alanylcholesterylformylhydrazide (MS11), have been prepared and incorporated into unilamellar cationic liposomes in equimolar amounts with dioleoylphosphatidylethanolamine (DOPE) as colipid. Stable lipoplexes were formed with pGL3 DNA which afforded protection to the DNA from serum nuclease digestion. Packing of the DNA was shown by ethidium displacement to be more effective in MS11 lipoplexes. High transfection levels in three human transformed epithelial cell lines HeLa (cervical), SNO (esophageal), HepG2 (hepatocyte-derived), and the murine fibroblast line NIH-3T3 were achieved by both lipoplexes at liposome: DNA ratios of 6:1 and 7:1 ((w)/(w)) corresponding to +/- charge ratios of 1.6:1 and 1.9:1. MS11 lipoplexes, in particular, afforded high transfection activities in the presence of fetal bovine serum.

Liposome/DNA systems: correlation between association, hydrophobicity and cell viability

Small unilamellar vesicles associated with plasmid DNA showed maximum association efficiency for a cationic mixture of egg phosphatidylcholine (EPC):1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE):di-1,2-dioleoyl-3-trimethyl ammonium propane (DOTAP) (16:8:1 molar ratio) [65%], followed by neutral lipids EPC:1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE):cholesterol (Chol) (2:2:1 molar ratio) [30%], and a polymerized formulation 1,2-bis(10,12-tricosadiynoyl)sn-glycero-3-phosphocholine (DC8,9PC):DMPE:Chol (2:2:1 molar ratio) [11%]. The hydrophobicity factor (HF) for these formulations followed the trend DC8,9PC:DMPE:CHOL < EPC:DMPE:Chol < EPC:DOPE DOTAP, and DNA association did not alter this trend. Results suggest that the higher the HF value, the more fluid the membrane and the higher the efficiency of DNA association. On the other hand, no differences were observed in cell toxicity with lipids up to 1 mg/ml in VERO cells.

Serum-free transfection of CHO-cells with tailor-made unilamellar vesicles

At present, a number of transfection techniques are available to introduce foreign DNA into cells, but still minimal intrusion or interference with normal cell physiology, low toxicity, reproducibility, cost efficiency and successful creation of stable transfectants are highly desirable properties for improved transfection techniques.For all previous transfection experiments done in our labs, using serum-free cultivated host cell lines, an efficiency value of approximately 0.1% for selection of stable cell lines has not been exceeded, consequently we developed and improved a transfection system based on defined liposomes, so-called large unilamellar vesicles, consisting of different lipid compositions to facilitate clone selection and increase the probability for creation of recombinant high-production clones. DNA and DOTAP/DOPE or CHEMS/DOPE interact by electrostatic means forming so-called lipoplexes (Even-Chen and Barenholz 2000) and the lipofection efficiency of those lipoplexes has been determined via confocal microscopy.In addition, the expression of the EGFP was determined by FACS to investigate transient as well as stable transfection and the transfection efficiency of a selection of different commercially available transfection reagents and kits has been compared to our tailor-made liposomes.

Gene delivery by aminofullerenes: structural requirements for efficient transfection

A series of aminofullerenes that share a common structural motif have been synthesized and subjected to a systematic investigation of structure activity relationship regarding their ability for transient transfection and cytotoxicity. DNA-binding tests indicated that any water-soluble fullerene-bearing amino group would bind to double-stranded DNA. For these molecules to be effective transfection reagents, however, they require additional structural features. First, the molecule must be capable of producing submicrometer-sized fullerene/DNA aggregates that can be internalized into mammalian cells through endocytosis. Second, the molecule must be capable of releasing DNA as the aggregates are transferred into the cytoplasm. This can be achieved in at least two ways: by loss of the DNA-binding amino groups from the fullerene core, and by transformation of the amino groups to neutral groups such as amides. The screening experiments led us to identify the best reagent, a tetrapiperidinofullerene, that can be synthesized in two steps from fullerene, piperazine, and molecular oxygen, and that is more efficient at transfection than a commonly used lipid-based transfection reagent.

Characterization of the interplay between the main factors contributing to lipoplex-mediated transfection in cell cultures

Transfection efficiency of lipoplex-mediated gene delivery is multifactorial. However, the mode of interaction between the factors which affect transfection is not fully understood. To help fill this deficiency we evaluated the effect of the interplay between several variables that affect transfection efficiency in cell cultures. For this, we applied the Analysis of Variance Model with Fixed Effects and Repeated Measures to assess the data. The variables studied include: two different genes, Luc, and human growth hormone (hGH), in three different plasmids (two of which contain the luciferase (Luc) gene, but different promoter-enhancer regions (CMV and H19) and one plasmid coding hGH with a S16 promoter); three topoisoforms of pDNA (supercoiled (SC), open circular (OC), and closed circular (CC)); three cationic lipid compositions, all based on the monocationic lipid DOTAP (100% DOTAP, DOTAP/DOPE 1 : 1, and DOTAP/cholesterol 1 : 1, all ratios are mole ratios); two DNA-/L+ charge ratios (0.2 and 0.5); and two cell lines (NIH 3T3 and MBT-2). Our statistical analysis confirmed that the cell type, the gene used for transfection, the promoter type, the type of helper lipid, and DNA-/DOTAP+ charge ratio, all affect transfection efficiency in a statistically significant manner. The most efficient lipoplex formulation in both cell lines was that based on DOTAP (without helper lipid), having CC plasmid DNA. We suggest that for obtaining the most transfection-efficient lipoplex one should select the best topoisoform of pDNA for each particular cell type, and complex it with cationic liposomes having optimal lipid composition.

Mild surfection of neural cells, especially motoneurons, in primary culture and cell lines

Of all cell types, motoneurons (MNs), are possibly the most difficult to maintain in culture, since their development and survival is conditioned by many factors that are still in the course of identification. This may also be the reason why they are difficult to transfect. We succeed to transfect these fragile cells with lipoplex [DOTAP:PC (10:1)-pGFP]-precoated coverslips. Here, we report that this original method, also termed 'surfection' does not perturbate MN development and survival while giving important transfection yield (15%). Lipofectamine 2000 and other well-known auxiliary lipids (DOPE, Chol) give lower surfection yields. The use of (DOTAP:PC)-based lipid vector also can be extended to several neural and non-neural cell lines with appreciable transfection yield such as a glial cell line (GCL) derived from rat spinal cord (65%), HeLa S3 (60%), COS-7 (30%) and HEK 293 cells (20%). The efficiency of DOTAP:PC (10:1) and Lipofectamine 2000 vectors in our surfection method are compared on standard HeLa S3 cell lines. Lipofectamine 2000 (72%) is slightly better than DOTAP:PC (10:1) (60%). However, the surfection method improved the efficiency of Lipofectamine 2000 itself (72%) as compared to the classical (62%) approach. In summary we have developed an original standard surfection protocol for both MN primary cultures and cell lines, thus simplifying laboratory practice; moreover, Lipofectamine 2000 used in this surfection method is more efficient for the cell lines than the manufacturer-recommended method. We emphasize that our method particularly spares fragile cells like MNs from injure and therefore, might be applied to other fragile cell type in primary cultures.

A cationic cytofectin with long spacer mediates favourable transfection in transformed human epithelial cells

The synthesis and transfection potential of a novel cationic cholesterol cytofectin with a dimethylamino head group and a long 12 atom, 15A spacer incorporating relatively polar amido and dicarbonyl hydrazine linkages are reported. Thus N,N-dimethylaminopropylamidosuccinylcholesterylformylhydrazide (MS09) in equimolar admixture with dioleoylphosphatidylethanolamine (DOPE) forms stable unilamellar liposomes (80-150 nm) which cluster into very effective transfecting, serum nuclease-resistant, lipoplexes with DNA (180-200 nm) at a liposome+/DNA- molar charge ratio of 2.8:1 (12:1, w/w). Gel retardation and ethidium displacement assays confirmed that DNA was fully liposome-associated and maximally compacted at this ratio. Transfection levels in three human transformed epithelial cell lines, as established by luciferase transgene activity, was found to be optimal at this charge ratio and in the following order: cervical carcinoma (HeLa)>oesophageal carcinoma (SNO)>hepatoblastoma (HepG2). Activity in the murine fibroblast line NIH-3T3 was comparable to that in HepG2 cells. MS09 lipoplexes achieved approximately three-times and two-times greater activity than Lipofectin complexes in HeLa and SNO cells, respectively, whilst comparable levels were recorded in HepG2 and NIH-3T3 cells. MS09 lipoplexes were well tolerated by HepG2, HeLa and SNO cells with cell numbers found to be 80, 85 and 75% of untreated cultures, respectively, at the optimal transfection concentration. These lipoplexes also exhibited high activity in the presence of 10% foetal bovine serum (FBS) in HeLa (17% inhibition) and HepG2 (33% inhibition) cells.

Effect of “helper lipid” on lipoplex electrostatics

Lipoplexes, which are complexes between cationic liposomes (L+) and nucleic acids, are commonly used as a nucleic acid delivery system in vitro and in vivo. This study aimed to better characterize cationic liposome and lipoplex electrostatics, which seems to play a major role in the formation and the performance of lipoplexes in vitro and in vivo. We characterized lipoplexes based on two commonly used monocationic lipids, DOTAP and DMRIE, and one polycationic lipid, DOSPA--each with and without helper lipid (cholesterol or DOPE). Electrical surface potential (Psi0) and surface pH were determined using several surface pH-sensitive fluorophores attached either to a one-chain lipid (4-heptadecyl hydroxycoumarin (C17HC)) or to the primary amino group of the two-chain lipids (1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-carboxyfluorescein (CFPE) and 1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-7-hydroxycoumarin) (HC-DOPE). Zeta potentials of the DOTAP-based cationic liposomes and lipoplexes were compared with Psi0 determined using C17HC. The location and relatively low sensitivity of fluorescein to pH changes explains why CFPE is the least efficient in quantifying the differences between the various cationic liposomes and lipoplexes used in this study. The fact that, for all cationic liposomes studied, those containing DOPE as helper lipid have the least positive Psi0 indicates neutralization of the cationic charge by the negatively-charged phosphodiester of the DOPE. Zeta potential is much less positively charged than Psi0 determined by C17HC. The electrostatics affects size changes that occurred to the cationic liposomes upon lipoplex formation. The largest size increase (based on static light scattering measurements) for all formulations occurred at DNA-/L+ charge ratios 0.5-1. Comparing the use of the one-chain C17HC and the two-chain HC-DOPE for monitoring lipoplex electrostatics reveals that both are suitable, as long as there is no serum (or other lipidic assemblies) present in the medium; in the latter case, only the two-chain HC-DOPE gives reliable results. Increasing NaCl concentrations decrease surface potential. Neutralization by DNA is reduced in a NaCl-concentration-dependent manner.

Biophysical characterization of anionic lipoplexes

Transfection efficiency of liposomal gene delivery vectors depends on an optimal balance in the electro-chemical and structural properties of the transfection-capable complexes. We have recently reported a novel anionic lipoplex DNA delivery system composed of a ternary complex of endogenous occurring non-toxic anionic lipids, physiological Ca2+ cations, and plasmid DNA encoding a gene of interest with high transfection efficiency and low toxicity. In this work, we investigate the electro-chemical and structural properties anionic lipoplexes and compare them with those of Ca2+-DNA complexes. Biophysical characterization is used to explain the transfection efficiency of anionic lipoplexes in mammalian CHO-K1 cells. Circular dichroism and fluorescence spectroscopy showed that the plasmid DNA underwent conformational transition from native B-DNA to Z-DNA due to compaction and condensation upon Ca2+-mediated complexation with anionic liposomes. Zeta potential measurements and gel electrophoresis studies demonstrated that Ca2+ interaction with plasmid DNA during the formation of lipoplexes also led to increased association of supercoiled plasmid DNA with the lipoplexes, leading to charge neutralization which is expected to facilitate transfection. However, even 10-fold higher concentrations of Ca2+ alone (in the absence of the anionic liposomes) were unable to induce these changes in plasmid DNA molecules. A model explaining the possible mechanism of anionic lipoplex formation and the correlation of high transfection efficiency to biophysical properties was proposed. These studies confirm the utility of biophysical studies to identify optimal formulation conditions to design efficient liposomal gene delivery vectors.

New multivalent cationic lipids reveal bell curve for transfection efficiency versus membrane charge density: lipid-DNA complexes for gene delivery

BACKGROUND

Gene carriers based on lipids or polymers-rather than on engineered viruses-constitute the latest technique for delivering genes into cells for gene therapy. Cationic liposome-DNA (CL-DNA) complexes have emerged as leading nonviral vectors in worldwide gene therapy clinical trials. To arrive at therapeutic dosages, however, their efficiency requires substantial further improvement.

METHODS

Newly synthesized multivalent lipids (MVLs) enable control of headgroup charge and size. Complexes comprised of MVLs and DNA have been characterized by X-ray diffraction and ethidium bromide displacement assays. Their transfection efficiency (TE) in L-cells was measured with a luciferase assay.

RESULTS

Plots of TE versus the membrane charge density (sigmaM, average charge/unit area of membrane) for the MVLs and monovalent 2,3-dioleyloxypropyltrimethylammonium chloride (DOTAP) merge onto a universal, bell-shaped curve. This bell curve leads to the identification of three distinct regimes, related to interactions between complexes and cells: at low sigmaM, TE increases with increasing sigmaM; at intermediate sigmaM, TE exhibits saturated behavior; and unexpectedly, at high sigmaM, TE decreases with increasing sigmaM.

CONCLUSIONS

Complexes with low sigmaM remain trapped in the endosome. In the high sigmaM regime, accessible for the first time with the new MVLs, complexes escape by overcoming a kinetic barrier to fusion with the endosomal membrane (activated fusion), yet they exhibit a reduced level of efficiency, presumably due to the inability of the DNA to dissociate from the highly charged membranes in the cytosol. The intermediate, optimal regime reflects a compromise between the opposing demands on sigmaM for endosomal escape and dissociation in the cytosol.

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.

The role of organ vascularization and lipoplex-serum initial contact in intravenous murine lipofection

Following intravenous administration of cationic lipid-DNA complexes (lipoplexes) into mice, transfection (lipofection) occurs predominantly in the lungs. This was attributed to high entrapment of lipoplexes in the extended lung vascular tree. To determine whether lipofection in other organs could be enhanced by increasing the degree of vascularization, we used a transgenic mouse model with tissue-specific angiogenesis in liver. Tail vein injection of N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethylammonium chloride (DOTAP)/cholesterol lipoplexes resulted in increased lipoplex entrapment in hypervascularized liver but did not boost luciferase expression, suggesting that lipoplex delivery is not a sufficient condition for efficient organ lipofection. Because the intravenously injected lipoplexes migrated within seconds to lungs, we checked whether the effects of immediate contact with serum correlate with lung lipofection efficiency of different DOTAP-based formulations. Under conditions mimicking the injection environment, the lipoplex-serum interaction was strongly dependent on helper lipid and ionic strength: lipoplexes prepared in 150 mM NaCl or lipoplexes with high (>33 mol%) cholesterol were found to aggregate immediately. This aggregation process was irreversible and was inversely correlated with the percentage of lung cells that took up lipoplexes and with the efficiency of lipofection. No other structural changes in serum were observed for cholesterol-based lipoplexes. Dioleoyl phosphatidylethanolamine-based lipoplexes were found to give low expression, apparently because of an immediate loss of integrity in serum, without lipid-DNA dissociation. Our study suggests that efficient in vivo lipofection is the result of cross-talk between lipoplex composition, interaction with serum, hemodynamics, and target tissue "susceptibility" to transfection.

The Structural Organization of Cationic Lipid-DNA Complexes

The interaction of cationic liposomes with supercoiled plasmid DNA results in a major rearrangement of each component to form compact multilamellar structures comprised of alternating layers of two-dimensional arrays of DNA sandwiched between lipid bilayers. Fluorescence resonance energy transfer was used to estimate the distance of closest approach of DNA to the lipid bilayers in these complexes. The effect of several compositional variables on this distance, including the ratio of cationic lipid to DNA, and the charge density, intrinsic curvature, and fluidity of the lipid bilayer were examined. Additionally, the effect of ionic strength was studied. For complexes prepared at or above a 3:1 charge ratio (+/-), the observed distance of closest approach was found to be in agreement with the intercalation of DNA between lipid bilayers. As the charge ratio was decreased, a monotonic increase in the distance was observed with a maximum observed at 0.5:1. Correlations between differences in the proximity of DNA to the lipid bilayer and the hydrodynamic size of the complexes were also found. A model based on these observations and previous reports suggests the formation of discrete populations of complexes below a charge ratio of 0.5:1 and above 3:1. The structure of the negatively charged complexes is consistent with DNA extending from the surface of the particles, whereas those possessing excess positive charge were multilamellar aggregates with the DNA effectively condensed between lipid bilayers. Complexes between these two states consist of weighted fractions of these two species.

Lipoplex-induced hemagglutination: potential involvement in intravenous gene delivery

We report a study aiming to characterize the interaction of blood and blood components with lipoplexes under conditions relevant to in vivo intravenous transfection. In this study we focus on the interaction of lipoplexes with red blood cells (RBC). It was found that no significant hemolysis occurred during several hours' incubation using lipoplex compositions and lipoplex/red blood cell ratios in the range commonly used for in vivo transfection. However, the interaction of RBC with lipoplexes resulted in massive agglutination, which occurs irrespective of the type of cationic lipid or helper lipid. Agglutination was also induced by polyplexes (such as dendrimer/DNA complexes) and lipoplexes in the presence of spermidine or protamine sulfate (the latter induced hemagglutination by itself). DSPE-PEG(2000) inserted into the lipoplexes inhibits hemagglutination somewhat. In order to understand the effect of serum on the agglutination better, plasma was separated into its high molecular weight components (HMWC, >14 kDa) and its low molecular weight components (LMWC, < or = 14 kDa). These fractions were characterized for their level of proteins, primary amino groups, osmotic pressure, and electrical conductivity, and compared with saline (0.15 M NaCl). It was found that both LMWC and HMWC inhibit agglutination by themselves, although whole serum demonstrates better hemagglutination inhibition than each fraction separately. The inhibitory effect of the serum (or plasma) is explained by its effect on the electrostatics of the lipoplexes, reducing their positive charge, as was demonstrated using fluorescein-phosphatidylethanolamine-labeled lipoplexes. The effect of LMWC was related to ionic strength and was equal to the effect of 0.15 M NaCl. The level of agglutination was reduced with increasing lipoplex DNA(-)/cationic lipid(+) (DNA(-)/L(+)) ratio. However, at the low DNA(-)/L(+) ratio needed to achieve significant in vivo transfection after i.v. administration, massive agglutination occurred. These data suggest that i.v. administration of lipoplexes and polyplexes may lead to RBC agglutination, and the agglutinates formed may explain the localization of lipoplexes and expression of their transgenes in the lungs.

Phase behavior, DNA ordering, and size instability of cationic lipoplexes. Relevance to optimal transfection activity

Mechanisms of cationic lipid-based nucleic acid delivery are receiving increasing attention, but despite this the factors that determine high or low activity of lipoplexes are poorly understood. This study is focused on the fine structure of cationic lipid-DNA complexes (lipoplexes) and its relevance to transfection efficiency. Monocationic (N-(1-(2,3-dioleoyloxy)propyl),N,N,N-trimethylammonium chloride, N-(1-(2,3-dimyristyloxypropyl)-N,N-dimethyl-(2-hydroxyethyl)ammonium bromide) and polycationic (2,3-dioleyloxy-N-[2(sperminecarboxamido)ethyl]-N,N-dimethyl-1-propanammonium trifluoroacetate) lipid-based assemblies, with or without neutral lipid (1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine, cholesterol) were used to prepare lipoplexes of different L(+)/DNA(-) charge ratios. Circular dichroism, cryogenic-transmission electron microscopy, and static light scattering were used for lipoplex characterization, whereas expression of human growth hormone or green fluorescent protein was used to quantify transfection efficiency. All monocationic lipids in the presence of inverted hexagonal phase-promoting helper lipids (1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine, cholesterol) induced appearance of Psi(-) DNA, a chiral tertiary DNA structure. The formation of Psi(-) DNA was also dependent on cationic lipid-DNA charge ratio. On the other hand, monocationic lipids either alone or with 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine as helper lipid, or polycationic 2,3-dioleyloxy-N-[2(sperminecarboxamido)ethyl]-N,N-dimethyl-1-propanammonium trifluoroacetate-based assemblies, neither of which promotes a lipid-DNA hexagonal phase, did not induce the formation of Psi(-) DNA. Parallel transfection studies reveal that the size and phase instability of the lipoplexes, and not the formation of Psi(-) DNA structure, correlate with optimal transfection.

Dystrophin expression in muscle following gene transfer with a fully deleted ("gutted") adenovirus is markedly improved by trans-acting adenoviral gene products

Helper-dependent adenoviruses (HDAd) are Ad vectors lacking all or most viral genes. They hold great promise for gene therapy of diseases such as Duchenne muscular dystrophy (DMD), because they are less immunogenic than E1/E3-deleted Ad (first-generation Ad or FGAd) and can carry the full-length (Fl) dystrophin (dys) cDNA (12 kb). We have compared the transgene expression of a HDAd (HDAdCMVDysFl) and a FGAd (FGAdCMV-dys) in cell culture (HeLa, C2C12 myotubes) and in the muscle of mdx mice (the mouse model for DMD). Both vectors encoded dystrophin regulated by the same cytomegalovirus (CMV) promoter. We demonstrate that the amount of dystrophin expressed was significantly higher after gene transfer with FGAdCMV-dys compared to HDAdCMVDysFl both in vitro and in vivo. However, gene transfer with HDAdCMVDysFl in the presence of a FGAd resulted in a significant increase of dystrophin expression indicating that gene products synthesized by the FGAd increase, in trans, the amount of dystrophin produced. This enhancement occurred in cell culture and after gene transfer in the muscle of mdx mice and dystrophic golden retriever (GRMD) dogs, another animal model for DMD. The E4 region of Ad is required for the enhancement, because no increase of dystrophin expression from HDAdCMVDysFl was observed in the presence of an E1/E4-deleted Ad in vitro and in vivo. The characterization of these enhancing gene products followed by their inclusion into an HDAd may be required to produce sufficient dystrophin to mitigate the pathology of DMD by HDAd-mediated gene transfer.