Cationic lipids, lipoplexes and intracellular delivery of genes

Fliposomes: pH-Sensitive Liposomes Containing a trans-2-morpholinocyclohexanol-Based Lipid That Performs a Conformational Flip and Triggers an Instant Cargo Release in Acidic Medium

Incorporation of a pH-sensitive conformational switch into a lipid structure enables a drastic conformational flip upon protonation that disrupts the liposome membrane and causes rapid release of cargo specifically in areas of increased acidity. pH-sensitive liposomes containing the amphiphile (1) with trans-2-morpholinocyclohexanol conformational switch, a phospholipid, and a PEG-lipid conjugate were constructed and characterized. The optimized composition—1/POPC/PEG-ceramide (50/4/5)—could be stored at 4 °C and pH 7.4 for up to 1.5 years, and was stable in blood serum in vitro after 48 h at 37 °C. Liposomes loaded with ANTS/DPX or methotrexate demonstrated an unusually quick content release (in a few seconds) at pH below 5.5, which was independent of inter-liposome contact. The pH-titration curve for the liposome leakage paralleled the curve for the acid-induced conformational flip of 1 studied by ¹H-NMR. Freeze-fracture electron microscopy images showed budding and division of the bilayer at pH 5.5. A plausible mechanism of pH-sensitivity involves an acid-triggered conformational flip of 1, shortening of lipid tails, and membrane perturbations, which cause the content leakage. The methotrexate-loaded liposomes demonstrated much higher cytotoxicity in HeLa cells than the free drug indicating that they can serve as viable drug delivery systems.

The role of counterions in the membrane-disruptive properties of pH-sensitive lysine-based surfactants

Surfactants are among the most versatile and widely used excipients in pharmaceuticals. This versatility, together with their pH-responsive membrane-disruptive activity and low toxicity, could also enable their potential application in drug delivery systems. Five anionic lysine-based surfactants which differ in the nature of their counterion were studied. Their capacity to disrupt the cell membrane was examined under a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model for endosomal membranes. The surfactants showed pH-sensitive hemolytic activity and improved kinetics at the endosomal pH range. Low concentrations resulted in negligible hemolysis at physiological pH and high membrane lytic activity at pH 5.4, which is in the range characteristic of late endosomes. With increasing concentration, the surfactants showed an enhanced capacity to lyse cell membranes, and also caused significant membrane disruption at physiological pH. This observation indicates that, at high concentrations, surfactant behavior is independent of pH. The mechanism of surfactant-mediated membrane destabilization was addressed, and scanning electron microscopy studies were also performed to evaluate the effects of the compounds on erythrocyte morphology as a function of pH. The in vitro cytotoxicity of the surfactants was assessed by MTT and NRU assays with the 3T3 cell line. The influence of different types of counterion on hemolytic activity and the potential applications of these surfactants in drug delivery are discussed. The possibility of using pH-sensitive surfactants for endosome disruption could hold great promise for intracellular drug delivery systems in future therapeutic applications.

Understanding the mechanism of protamine in solid lipid nanoparticle-based lipofection: the importance of the entry pathway

The aim of our study was to evaluate the effect of protamine on the transfection capacity of solid lipid nanoparticles (SLNs) by correlating it to the internalization mechanisms and intracellular trafficking of the vectors. Vectors were prepared with SLN, DNA, and protamine. ARPE-19 and HEK-293 cells were used for the evaluation of the formulations. Protamine induced a 6-fold increase in the transfection of SLNs in retinal cells due to the presence of nuclear localization signals (NLS), its protection capacity, and a shift in the internalization mechanism from caveolae/raft-mediated to clathrin-mediated endocytosis. However, protamine produced an almost complete inhibition of transfection in HEK-293 cells. In spite of the high DNA condensation capacity of protamine and its content in NLS, this does not always lead to an improvement in cell transfection since it may impair some of the limiting steps of the transfection processes.

In vitro and in vivo mRNA delivery using lipid-enveloped pH-responsive polymer nanoparticles

Biodegradable core--shell structured nanoparticles with a poly(β-amino ester) (PBAE) core enveloped by a phospholipid bilayer shell were developed for in vivo mRNA delivery with a view toward delivery of mRNA-based vaccines. The pH-responsive PBAE component was chosen to promote endosome disruption, while the lipid surface layer was selected to minimize toxicity of the polycation core. Messenger RNA was efficiently adsorbed via electrostatic interactions onto the surface of these net positively charged nanoparticles. In vitro, mRNA-loaded particle uptake by dendritic cells led to mRNA delivery into the cytosol with low cytotoxicity, followed by translation of the encoded protein in these difficult-to-transfect cells at a frequency of ~30%. Particles loaded with mRNA administered intranasally (i.n.) in mice led to the expression of the reporter protein luciferase in vivo as soon as 6 h after administration, a time point when naked mRNA given i.n. showed no expression. At later time points, luciferase expression was detected in naked mRNA-treated mice, but this group showed a wide variation in levels of transfection, compared to particle-treated mice. This system may thus be promising for noninvasive delivery of mRNA-based vaccines.

In vitro skin permeation of hinokitiol loaded in vesicles composed of behenyltrimethylammonium chloride and stearic acid

INTRODUCTION

Behenyltrimethylammonium chloride (BTAC) and stearic acid (SA) could be associated with each other through salt bridges, and the associated BTAC/SA could build bilayer vesicles with the aid of hinokitiol (HKL).

METHOD

The vesicles were prepared by a precipitation method and used to enhance the skin permeation of HKL.

RESULTS

In case the molar ratio of BTAC/SA/HKL was 1/1/0, no vesicle was observed on transmission electron microscope photos. When the molar ratio of BTAC/SA/HKL was 1/1/0.4, vesicle was observed together with some agglomerates. When the content of HKL increased to the ratios of 1/1/0.8 and 1/1/1.2, vesicles were exclusively observed. In vitro fluxes for 18 hours through hairless mouse skin of HKL dissolved in alcoholic solutions were less than 1 mg/cm2/h. Whereas the fluxes of HKL encapsulated in the vesicles were about three times higher than that of HKL in the alcoholic solutions.

CONCLUSION

The vesicles could be used for the hair growth promotion.

Chitosan-coated liposomes for intracellular oligonucleotides delivery: characteristics and cell uptake behavior

Surface modification of liposomes with polymer to optimize drug delivery was well developed recently. The objective of the present work was to evaluate the feasibility of chitosan-coated liposomes (CSLP) as vehicles for anti-sense oligodeoxynucleotides (ASON). CSLP was obtained by adding chitosan dropwise to liposomes under magnetic stirring. The effect of chitosan content on size, zeta potential, and coating efficiency was investigated, which showed that chitosan increased the size and zeta potential of CSLP, and the coating efficiency increased with chitosan content increasing. Agarose gel electrophoresis was employed to evaluate the loading efficiency of CSLP for ASON, from which one could see ASON was completely combined to CSLP when the mass ratio of total lipids:ASON was more than 50:1. MTT assay showed that CSLP took on very low cytotoxicity, which is much lower than chitosan. At last, cell uptake behavior was investigated by a flow cytometer, which showed that CSLP enhanced significantly the COS7 cells uptake of ASON. All the results indicated that the CSLP could be a promising non-viral ASON vehicle.

Metodologie per il trasferimento genico

L’esito di qualsiasi approccio di terapia genica, sia che esso preveda l’inoculazione del materiale genetico direttamente in vivo sia che venga effettuato ex vivo nelle cellule prelevate dal paziente, dipende strettamente dall’efficienza con cui gli acidi nucleici con funzione terapeutica vengono internalizzati dalle cellule bersaglio. Di fatto, l’efficienza del trasferimento genico probabilmente rappresenta a tutt’oggi il parametro più importante che ancora limita le applicazioni di terapia genica, o comunque ne condiziona il successo.

Biological responses towards cationic peptides and drug carriers

In drug development, major resources are invested into the development of cellular delivery systems to increase the effectiveness of a large array of potential therapeutics, such as proteins and oligonucleotides. These carriers comprise cell-penetrating peptides (CPPs), cationic lipids and cationic polymers. In recent years, evidence has been accumulating that these carriers not only act as mere pharmacokinetic modifiers but also interfere with cellular processes in various ways. In this review, we present an overview of the biological side effects associated with carrier systems. The focus will be on CPPs, which have been explored for a diverse set of cargos. Reported activities range from an induction of receptor internalization to the generation of reactive oxygen species. Ultimately, cell-penetrating molecules with such biological side effects might evolve into new bioactive agents that combine delivery capacity and pharmacophore in a single molecular entity. First examples for such molecules will be presented.

Liposomes for use in gene delivery

Liposomes have a wide array of uses that have been continuously expanded and improved upon since first being observed to self-assemble into vesicular structures. These arrangements can be found in many shapes and sizes depending on lipid composition. Liposomes are often used to deliver a molecular cargo such as DNA for therapeutic benefit. The lipids used to form such lipoplexes can be cationic, anionic, neutral, or a mixture thereof. Herein physical packing parameters and specific lipids used for gene delivery will be discussed, with lipids classified according to overall charge.

Highly fluorescent magnetic quantum dot probe with superior colloidal stability

A magnetic quantum dot (MQD) based cellular nanoprobe, composed of a magnetic oxide nanoparticle component and a quantum dot component, has been synthesized and used for both imaging and separation. The successful synthesis is based on a reverse micelle based polyacrylate coating in the presence of component nanoparticles, followed by their functionalization via conjugation chemistry.

Non-covalent association of folate to lipoplexes: a promising strategy to improve gene delivery in the presence of serum

The success of gene therapy depends on the efficient delivery of therapeutic genes into target cells in vitro and in vivo. Non-viral vectors, such as cationic liposome-DNA complexes (lipoplexes), have been used for numerous gene delivery applications, although their efficacy is still limited, particularly when compared to that of viral vectors. In this work, we assessed the efficacy of a new gene delivery system generated by non-covalent association of folate to lipoplexes (FA-associated lipoplexes) in two different cancer cell lines (SCC-VII and TSA cells). Association of FA with liposomes composed of DOTAP and cholesterol, and subsequent complexation with DNA greatly increased transfection efficiency above that obtained with plain lipoplexes in both cell lines. The addition of 40μg of FA to lipoplexes was optimal for transfection and allowed to overcome the inhibitory effect induced by the presence of serum. Notably, the biological activity of the FA-associated complexes was even significantly improved under these conditions. Transfection activity mediated by FA-associated lipoplexes was compared with that by FA-conjugated lipoplexes, and the results showed that electrostatic association of FA to the lipoplexes led to considerably higher levels of biological activity than that involving covalent coupling of FA. Moreover, FA-associated lipoplexes confer greater DNA protection than FA-conjugated lipoplexes. To our knowledge, this is the first study reporting the characterization and application of FA-associated lipoplexes in gene delivery and showing their greater efficacy than that of FA-conjugated lipoplexes. Overall, the results obtained in the present work constitute a strong indication that the developed FA-associated lipoplexes are promising candidates for in vivo gene delivery.

Methods for Gene Delivery

The success of any gene transfer procedure, either through in vivo inoculation of the genetic material or after gene transfer into the patient’s cells ex vivo, strictly depends upon the efficiency of nucleic acid internalization by the target cells. As a matter of fact, making gene transfer more efficient continues to represent the most relevant challenge to the clinical success of gene therapy.

Poly-N-acetyl glucosamine gel matrix as a non-viral delivery vector for DNA-based vaccination

Intramuscular administration of plasmid DNA vaccines is one of the main delivery approaches that can generate antigen specific T cell responses. However, major limitations of the intramuscular delivery strategy are the low level of myocyte transfection, resulting in a minimal level of protein expression; the inability to directly target antigen presenting cells, in particular dendritic cells, which are critical for establishment of efficacious antigen-specific immune responses. Although several viral vectors have been designed to improve plasmid DNA delivery, they have limitations, including the generation of neutralizing antibodies in addition to lacking the simplicity and versatility required for universal clinical application. We have developed an inexpensive non-viral delivery vector based on the polysaccharide polymer poly-N-acetyl glucosamine with the capability to target dendritic cells. This vector is fully biocompatible, biodegradable, and nontoxic. The advantage of the application of this delivery system relative to other approaches is discussed.

Use of total reflection X-ray fluorescence (TRXF) for the quantification of DNA binding to lipid monolayers at the air-water interface

To use the TRXF technique for the quantification of DNA binding to monolayers at the air-water interface, DNA from salmon testes was labeled by covalently bound bromine. For this purpose, an analytical procedure for the quantification of bromine in labeled DNA with a detection limit of 10-20 μg was developed. It was found that the pH of the solution has a strong influence on the yield of brominated DNA (BrDNA) when Br(2) is used as a reagent. Much higher degrees of bromination can be achieved at pH 5 than at pH 7. A degree of bromination above a threshold of 2 to 3% (bromine per base) leads to the cross linking of BrDNA with the formation of an insoluble gel during the precipitation procedure. Finally, a reaction scheme with N-bromosuccinimide (NBS) that avoids precipitation has been established. Succinimide and some bromide ions remain in the solution as byproducts. However, these bromide ions are not competitive with BrDNA for binding at positively charged monolayers. Therefore, a new method for binding studies of model DNA to Langmuir monolayers at the air-water interface has been established. An important result of these studies is the finding that higher salt concentrations (representing physiological conditions) lead to an increased amount of adsorbed DNA. This can be explained by the decrease in the effective charge of the DNA molecules with decreasing Debye screening length.

The benefit of hydrophobic domain asymmetry on the efficacy of transfection as measured by in vivo imaging

We, and others, have observed that the structure of cationic lipids appears to have a significant effect on the transfection efficacy of optimized nucleic acid/cationic lipid complexes (lipoplexes) used for in vitro and in vivo gene delivery and expression. Although there are many in vitro comparisons of lipid reagents for gene delivery, few comparisons have been made in vivo. We previously reported the effects of changes in hydrophobic domain chain length and chain asymmetry, changes in headgroup composition, and counterion exchange. We have observed in our own work over many years the apparent superiority of asymmetric versus symmetric hydrocarbon domains for otherwise similar lipids. In this investigation we use in vivo whole animal brain imaging to evaluate the contribution of symmetric versus asymmetric hydrophobic domains on what we previously determined to be optimal chain lengths for in vitro transfections. We specifically investigated several glycerol-based lipids; however, the rare reports of asymmetric non-glycerol-based lipids also support our observations. We found that asymmetric, two-chain cationic lipids of 14 to 18 carbons perform significantly better in vivo, as analyzed by whole animal imaging, than the paired symmetric lipids.

Monolayers of mixture of alkylaminomethyl rutin and lecithin at the air/water interface

A compound of flavonol-based biosurfactant, as C(8)-substituted alkylaminomethyl rutin (DAMR) for a potential pharmaceutical or agrochemical use, was prepared experimentally. The surface behavior of DAMR and its mixture with lecithin from soybean (SL) had been studied. DAMR, regarded as a pseudo-amphoteric character, exhibits both liquid-condensed (LC) and liquid-expanded (LE) phases while SL is in the form of the LE phase only. The phase parameters of DAMR (including A(limt), pi(coll)) are observed to strongly depend on both the subphase temperature and the pH, which regulate the degree of ionization. In addition, the observed positive deviation calculated from excess Gibbs free energies of the DAMR-SL system suggests a repulsive interaction between DAMR and SL at all X(DAMR) values. Also the interaction parameter is found to increase linearly with surface pressure, regardless of composition. Notably, the relationship of logarithmic activity coefficient vs. X(DAMR)(2) reveals that the molecular interaction of DAMR-SL can be adequately simulated using a simple regular mixture model. Importantly, lower C(S)(-1) values of this mixture than those with pure DAMR and SL denote weak elasticity of mixed monolayers with values of X(DAMR) of 0.2-0.8, indicating that the direct addition of DAMR may exert a somewhat adverse influence on SL membranes.

Immune response induced by a linear DNA vector: influence of dose, formulation and route of injection

Previously, minimalistic, immunogenetically defined gene expression (MIDGE) vectors were developed as effective and sophisticated carriers for DNA vaccination. Here we evaluate the influence of dose, formulation and delivery route on the immune response after vaccination with MIDGE-Th1 vectors encoding hepatitis B virus surface antigen (HBsAg). An HBsAg-specific IgG1 and IgG2a antibody response was induced in a dose-dependent manner, whereas the IgG2a/IgG1 ratio was independent of the injected DNA dose. Formulation of MIDGE-HBsAg-Th1 with the cationic pyridinium amphiphile SAINT-18 significantly increased antibody levels of IgG1 and IgG2a compared to the unformulated vector. In contrast, SAINT-18 had neither a significant effect on the IgG2a/IgG1 ratio nor on the type and strength of cellular immunity. Overall, the strongest immune response was generated after intradermal injection, followed by intramuscular and subcutaneous (s.c.) injection. The results show that the formulation of MIDGE-Th1 with SAINT-18 increased the efficacy of the MIDGE-Th1 DNA vaccine and is therefore a suitable approach to improve the efficacy of DNA vaccines also in large animals and humans.

Nanotechnology solutions for mucosal immunization

The current prevalence of infectious diseases in many developing regions of the world is a serious burden, impacting both the general health as well as economic growth of these communities. Additionally, treatment with conventional medication becomes increasingly challenging due to emergence of new and drug resistant strains jeopardizing the progress made in recent years towards control and elimination of certain types of infectious diseases. Thus, from a public health perspective, prevention such as through immunization by vaccination, which has proven to be most effective, might be the best alternative to prevent and combat infectious diseases in these regions. To achieve this, development of wide-scale immunization programs become necessary including vaccines that can easily and widely be distributed, stored and administered. Mucosal vaccines offer great potential since they can be administered via oral or intranasal delivery route which does not require trained personnel, avoids the use of needles and improves overall patient compliance and acceptance. However, it necessitates the implementation of specific immunization strategies to improve their efficacy. Application of nanotechnology to design and create particle mediated delivery systems that can efficiently encapsulate vaccine components for protection of the sensitive payload, target the mucosal immune system and incorporate mucosal adjuvants maximizing immune response is key strategy to improve the effectiveness of mucosal vaccines.

Comparative gene transfer between cationic and thiourea lipoplexes

BACKGROUND

We have previously developed lipopolythiourea lipids as neutral DNA condensing agents for systemic gene delivery. Optimization of the lipopolythiourea structure led to efficient transfecting agents. To further evaluate these lipids, we investigated the internalization process of the thiourea lipoplexes and their intracellular mechanism of transfection versus that of cationic lipoplexes.

METHODS

The MTT test was used for cytotoxicity assessment. Transfection efficiency was determined by luciferase read-out. Permeation to propidium iodide and enhanced green fluorescent protein was evaluated by flow cytometry. Kinetics of internalization and DNA release were monitored by confocal microscopy with labelled DNA. Endocytosis inhibitors were used to study the mechanisms of lipoplex internalization.

RESULTS

Although thiourea/DNA complexes exhibit an almost similar level of transfection compared to that of cationic complexes, the thiourea lipoplexes were shown to be six-fold less internalized. Complexes were able to permeabilize the cytoplasmic membrane to 30 kDa molecules. Finally, DNA was shown to be released in less than 10 min in the cellular cytoplasm versus 30 min for cationic lipoplexes.

CONCLUSIONS

Despite a weaker internalization compared to cationic lipids, the thiourea lipoplexes were able to transfect cells at a similar level as a result of its greater ability to destabilize the cytoplasmic membrane and release DNA.

Fusogenic activity of cationic lipids and lipid shape distribution

Addition of co-lipids into cationic lipid formulations is considered as promoting cell delivery of DNA by enhancing fusion processes with cell membranes. Here, by combining FRET and confocal microscopy, we demonstrate that some cationic lipids do not require a co-lipid to fuse efficiently with cells. These cationic lipids are able to self-organize into bilayers that are stable enough to form liposomes, while presenting some destabilizing properties reminiscent of the conically shaped fusogenic co-lipid, DOPE. We therefore analyzed the resident lipid structures in cationic bilayers by molecular dynamics simulations, clustering the individual lipid structures into populations of similarly shaped molecules, as opposed to the classical approach of using the static packing parameter to define the lipid shapes. Comparison of fusogenic properties with these lipid populations suggests that the ratio of cylindrical versus conical lipid populations correlates with the ability to fuse with cell membranes.

DC-Chol/DOPE cationic liposomes: a comparative study of the influence factors on plasmid pDNA and siRNA gene delivery

Cationic liposomes (CLs) composed of 3beta-[N-(N',N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) and dioleoylphosphatidylethanolamine (DOPE) (DC-Chol/DOPE liposomes) have been classified as one of the most efficient gene delivery systems. Our study aims to examine the effect of the molar ratio of DC-Chol/DOPE, PEGylation and serum on the pDNA (plasmid pDNA) and siRNA (small interfering RNA) transfection of DC-Chol/DOPE liposomes. The results showed that the most efficient DC-Chol/DOPE liposomes for pDNA or siRNA delivery were at a 1:2 or 1:1 molar ratio of DC-Chol/DOPE, respectively. The transfection efficiency of DC-Chol/DOPE liposomes increased along with increased weight ratio of DC-Chol/siRNA. However, the pDNA transfection efficiency decreased along with increased weight ratio of DC-Chol/pDNA from 3/1. As expected, PEGylation decreased siRNA and pDNA transfection efficiency of DC-Chol/DOPE liposomes. In PEGylated DC-Chol/DOPE liposomes, increased weight ratio of DC-Chol/pDNA from 3/1 did not lead to higher pDNA transfection efficiency, whereas increased weight ratio of DC-Chol/siRNA resulted in increased siRNA transfection efficiency. Furthermore, the serum did not significantly inhibit the pDNA and siRNA transfection efficiency of DC-Chol/DOPE liposomes. In conclusion, our results elucidated the influence factors of DC-Chol/DOPE liposome transfection and would reveal that siRNA and pDNA transfection mechanisms were different in DC-Chol/DOPE liposomes.

Fluorescence methods for evaluating lipoplex-mediated gene delivery

The biological activity of cationic liposome/DNA complexes ("lipoplexes") is strongly dependent on their ability to protect DNA and to interact with cells, including binding to the cell surface, internalization via endocytosis and cytoplasmic delivery of the DNA. In this chapter, we describe a number of methods and procedures to study these processes, based on the use of fluorescent probes.

Lyophilized HER2-specific PEGylated immunoliposomes for active siRNA gene silencing

The development of a tumor-specific immunoliposome delivering small interfering RNA (siRNA) represents a practical way in cancer gene therapy. In this study, we developed PEGylated 3beta-[N-(N', N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol)/dioleoylphosphatidyl ethanolamine (DOPE) immunoliposomes conjugated with the Fab' of recombinant humanized anti-HER2 monoclonal antibody (PIL) for siRNA delivery. The results demonstrated that the lyophilized PIL (LPIL) prepared by the lyophilization/rehydration method possessed a significantly enhanced HER1 gene, a model target, silencing ability compared with PIL in HER2-overexpressing SK-BR3 cells. Among a series of LPIL with different PEGylation degree, LPIL containing 2.5%PEG (2.5%PEG LPIL) showed the best HER1 gene silencing activity. Confocal microscope studies demonstrated that 2.5%PEG LPIL could specifically bind to SK-BR3 cells and were sequentially internalized into them. Using RhoA as a cancer therapeutic target, 2.5%PEG LPIL entrapping anti-RhoA siRNA could specifically silence RhoA expression and inhibit cell invasion in SK-BR3 cells. In conclusion, these finding demonstrated the potential use of 2.5%PEG LPIL in specifically delivering siRNA to HER2-overexpressing cancers.

Novel cholesterol-based cationic lipids for gene delivery

Gene therapy based on gene delivery is a promising strategy for the treatment of human disease. Here we present data on structure/biological activity of new biodegradable cholesterol-based cationic lipids with various heterocyclic cationic head groups and linker types. Enhanced accumulation of nucleic acids in the cells mediated by the lipids was demonstrated by fluorescent microscopy and flow cytometry. Light scattering and atomic force microscopy were used to find structure/transfection activity correlations for the lipids. We found that the ability of the lipids to stimulate intracellular accumulation of the oligodeoxyribonucleotides and plasmid DNA correlates well with their ability to form in solution lipid/NA complexes of sizes that do not exceed 100 nm. Screening of the lipids revealed the most promising transfection agents both in terms of low toxicity and efficient delivery: cholesterol-based lipids with positively charged pyridine and methyl imidazole head groups and either the ester or carbamate linker.

Nonviral gene delivery: principle, limitations, and recent progress

Gene therapy is becoming a promising therapeutic modality for the treatment of genetic and acquired disorders. Nonviral approaches as alternative gene transfer vehicles to the popular viral vectors have received significant attention because of their favorable properties, including lack of immunogenicity, low toxicity, and potential for tissue specificity. Such approaches have been tested in preclinical studies and human clinical trials over the last decade. Although therapeutic benefit has been demonstrated in animal models, gene delivery efficiency of the nonviral approaches remains to be a key obstacle for clinical applications. This review focuses on existing and emerging concepts of chemical and physical methods for delivery of therapeutic nucleic acid molecules in vivo. The emphasis is placed on discussion about problems associated with current nonviral methods and recent efforts toward refinement of nonviral approaches.

The density of GM1-enriched lipid rafts correlates inversely with the efficiency of transfection mediated by cationic liposomes

Although cationic liposome-mediated transfection has become a standard procedure, the mechanistic details of the process are unknown. It has been suggested that endocytic uptake of lipoplexes is efficient, and transfectability is largely determined by later steps. In this article, we stained GM1-enriched membrane microdomains, a subclass of lipid rafts, with subunit B of cholera toxin and correlated transfection efficiency with their density by quantitatively evaluating microscopic images. We found a strong anticorrelation between the density of GM1-enriched membrane microdomains and the efficacy of transfection monitored by measuring the expression level of GFP in different cell lines transfected by lipofection using two different transfection agents. These findings imply that GM1-enriched membrane microdomains interfere with the process of lipofection. The blocked step must be endocytosis since the accumulation of fluorescently labeled plasmids was lower in cells with high content of GM1-enriched membrane microdomains. Such a correlation was not observed in cells transfected by electroporation. By comparing the efficiency of lipofection in several cell lines we found that those with a high density of GM1-enriched membrane microdomains were the most resistant to transfection. We conclude that the inhibition of lipofection by GM1-enriched membrane microdomains is a general rule, and that endocytosis of lipoplexes can be rate limiting in cells with high density of GM1-enriched membrane rafts.

Archaeal tetraether bipolar lipids: Structures, functions and applications

Archaea have developed specific tools permitting life under harsh conditions and archaeal lipids are one of these tools. This microreview describes the particular features of tetraether-type archaeal lipids and their potential applications in biotechnology. Natural and synthetic tetraether lipid structures as well as their applications in drug/gene delivery, vaccines and proteoliposomes or as lipid films are reviewed.

Gene delivery via DNA incorporation within a biomimetic apatite coating

Integrating inductivity with conductivity in a material may advance tissue engineering. An organic/inorganic hybrid was developed by incorporating plasmid DNA encoding for the beta-gal gene complexed with Lipofectamine 2000 (DNA-Lipoplex) within apatite via coprecipitation. It was hypothesized that this system will result in enhanced transfection efficiency compared to DNA-Lipoplexes adsorbed to the mineral surface and DNA coprecipitated without Lipofectamine 2000. PLGA films were cast onto glass slips and apatite and DNA were coprecipitated in modified simulated body fluid (mSBF). DNA-Lipoplex presence in mineral, DNA-Lipoplex stability (vs. coprecipitation time), and transfection efficiency (determined with C3H10T1/2 cells) as a function of coprecipitation time, DNA-Lipoplex concentration, and DNA incorporation method were studied. DNA-Lipoplex presence and spatial distribution on apatite were confirmed through fluorescence. Transfection efficiency was highest for 6h of DNA-Lipoplex coprecipitation. Differences in transfection efficiency were found between the DNA concentrations, with the highest efficiency for coprecipitation being 40 microg/ml (p < or = 0.009 relative to other coprecipitation concentrations). Significant differences in transfection efficiency existed between incorporation methods (p < 0.05) with the highest efficiency for DNA-Lipoplex coprecipitation. This hybrid material system not only integrates inductivity provided by the DNA and conductivity provided by the apatite, but it also has significant implications in non-viral gene delivery due to its ability to increase transfection efficiency.

Physico-chemical characteristics of lipoplexes influence cell uptake mechanisms and transfection efficacy

Background

Formulation of DNA/cationic lipid complexes (lipoplexes) designed for nucleic acid delivery mostly results in positively charged particles which are thought to enter cells by endocytosis. We recently developed a lipoplex formulation called Neutraplex that allows preparation of both cationic and anionic stable complexes with similar lipid content and ultrastructure.

Methodology/Principal Findings

To assess whether the global net charge could influence cell uptake and activity of the transported oligonucleotides (ON), we prepared lipoplexes with positive and negative charges and compared: (i) their physicochemical properties by zeta potential analysis and dynamic light scattering, (ii) their cell uptake by fluorescence microscopy and flow cytometry, and (iii) the biological activity of the transported ON using a splicing correction assay. We show that positively or negatively charged lipoplexes enter cells cells using both temperature-dependent and -independent uptake mechanisms. Specifically, positively charged lipoplexes predominantly use a temperature-dependent transport when cells are incubated OptiMEM medium. Anionic lipoplexes favour an energy-independent transport and show higher ON activity than cationic lipoplexes in presence of serum. However, lipoplexes with high positive global net charge and OptiMEM medium give the highest uptake and ON activity levels.

Conclusions

These findings suggest that, in addition to endocytosis, lipoplexes may enter cell via a temperature-independent mechanism, which could be mediated by lipid mixing. Such characteristics might arise from the specific lipoplex ultrastructure and should be taken into consideration when developing lipoplexes designed for in vivo or ex vivo nucleic acid transfer.

Polyelectrolyte-induced aggregation of liposomes: a new cluster phase with interesting applications

Different charged colloidal particles have been shown to be able to self-assemble, when mixed in an aqueous solvent with oppositely charged linear polyelectrolytes, forming long-lived finite-size mesoscopic aggregates. On increasing the polyelectrolyte content, with the progressive reduction of the net charge of the primary polyelectrolyte-decorated particles, larger and larger clusters are observed. Close to the isoelectric point, where the charge of the adsorbed polyelectrolytes neutralizes the original charge of the particles' surface, the aggregates reach their maximum size, while beyond this point any further increase of the polyelectrolyte-particle charge ratio causes the formation of aggregates whose size is progressively reduced. This re-entrant condensation behavior is accompanied by a significant overcharging. Overcharging, or charge inversion, occurs when more polyelectrolyte chains adsorb on a particle than are needed to neutralize its original charge so that, eventually, the sign of the net charge of the polymer-decorated particle is inverted. The stability of the finite-size long-lived clusters that this aggregation process yields results from a fine balance between long-range repulsive and short-range attractive interactions, both of electrostatic nature. For the latter, besides the ubiquitous dispersion forces, whose supply becomes relevant only at high ionic strength, the main contribution appears due to the non-uniform correlated distribution of the charge on the surface of the polyelectrolyte-decorated particles ('charge-patch' attraction). The interesting phenomenology shown by these system has a high potential for biotechnological applications, particularly when the primary colloidal particles are bio-compatible lipid vesicles. Possible applications of these systems as multi-compartment vectors for the simultaneous intra-cellular delivery of different pharmacologically active substances will be briefly discussed.