Lipid-based systems for the intracellular delivery of genetic drugs

Lipoplexes' Structure, Preparation, and Role in Managing Different Diseases

Lipid-based vectors are becoming promising alternatives to traditional therapies over the last 2 decades specially for managing life-threatening diseases like cancer. Cationic lipids are the most prevalent non-viral vectors utilized in gene delivery. The increasing number of clinical trials about lipoplex-based gene therapy demonstrates their potential as well-established technology that can provide robust gene transfection. In this regard, this review will summarize this important point. These vectors however have a modest transfection efficiency. This limitation can be partly addressed by using functional lipids that provide a plethora of options for investigating nucleic acid-lipid interactions as well as in vitro and in vivo nucleic acid delivery for biomedical applications. Despite their lower gene transfer efficiency, lipid-based vectors such as lipoplexes have several advantages over viral ones: they are less toxic and immunogenic, can be targeted, and are simple to produce on a large scale. Researchers are actively investigating the parameters that are essential for an effective lipoplex delivery method. These include factors that influence the structure, stability, internalization, and transfection of the lipoplex. Thorough understanding of the design principles will enable synthesis of customized lipoplex formulations for life-saving therapy.

Defining the EM-signature of successful cell-transfection

In this report, we describe the architecture of Lipofectamine 2000 and 3000 transfection- reagents, as they appear inside of transfected cells, using classical transmission electron microscopy (EM). We also demonstrate that they provoke consistent structural changes after they have entered cells, changes that not only provide new insights into the mechanism of action of these particular transfection-reagents, but also provide a convenient and robust method for identifying by EM which cells in any culture have been successfully transfected. This also provides clues to the mechanism(s) of their toxic effects, when they are applied in excess. We demonstrate that after being bulk-endocytosed by cells, the cationic spheroids of Lipofectamine remain intact throughout the entire time of culturing, but escape from their endosomes and penetrate directly into the cytoplasm of the cell. In so doing, they provoke a stereotypical recruitment and rearrangement of endoplasmic reticulum (ER), and they ultimately end up escaping into the cytoplasm and forming unique 'inclusion-bodies.' Once free in the cytoplasm, they also invariably develop dense and uniform coatings of cytoplasmic ribosomes on their surfaces, and finally, they become surrounded by 'annulate' lamellae' of the ER. In the end, these annulate-lamellar enclosures become the ultrastructural 'signatures' of these inclusion-bodies, and serve to positively and definitively identify all cells that have been effectively transfected. Importantly, these new EM-observations define several new and unique properties of these classical Lipofectamines, and allow them to be discriminated from other lipoidal or particulate transfection-reagents, which we find do not physically break out of endosomes or end up in inclusion bodies, and in fact, provoke absolutely none of these 'signature' cytoplasmic reactions.

Extracellular Vesicles Released by Genetically Modified Macrophages Activate Autophagy and Produce Potent Neuroprotection in Mouse Model of Lysosomal Storage Disorder, Batten Disease

Over the recent decades, the use of extracellular vesicles (EVs) has attracted considerable attention. Herein, we report the development of a novel EV-based drug delivery system for the transport of the lysosomal enzyme tripeptidyl peptidase-1 (TPP1) to treat Batten disease (BD). Endogenous loading of macrophage-derived EVs was achieved through transfection of parent cells with TPP1-encoding pDNA. More than 20% ID/g was detected in the brain following a single intrathecal injection of EVs in a mouse model of BD, ceroid lipofuscinosis neuronal type 2 (CLN2) mice. Furthermore, the cumulative effect of EVs repetitive administrations in the brain was demonstrated. TPP1-loaded EVs (EV-TPP1) produced potent therapeutic effects, resulting in efficient elimination of lipofuscin aggregates in lysosomes, decreased inflammation, and improved neuronal survival in CLN2 mice. In terms of mechanism, EV-TPP1 treatments caused significant activation of the autophagy pathway, including altered expression of the autophagy-related proteins LC3 and P62, in the CLN2 mouse brain. We hypothesized that along with TPP1 delivery to the brain, EV-based formulations can enhance host cellular homeostasis, causing degradation of lipofuscin aggregates through the autophagy-lysosomal pathway. Overall, continued research into new and effective therapies for BD is crucial for improving the lives of those affected by this condition.

Nucleotides Entrapped in Liposome Nanovesicles as Tools for Therapeutic and Diagnostic Use in Biomedical Applications

The use of nucleotides for biomedical applications is an old desire in the scientific community. As we will present here, there are references published over the past 40 years with this intended use. The main problem is that, as unstable molecules, nucleotides require some additional protection to extend their shelf life in the biological environment. Among the different nucleotide carriers, the nano-sized liposomes proved to be an effective strategic tool to overcome all these drawbacks related to the nucleotide high instability. Moreover, due to their low immunogenicity and easy preparation, the liposomes were selected as the main strategy for delivery of the mRNA developed for COVID-19 immunization. For sure this is the most important and relevant example of nucleotide application for human biomedical conditions. In addition, the use of mRNA vaccines for COVID-19 has increased interest in the application of this type of technology to other health conditions. For this review article, we will present some of these examples, especially focused on the use of liposomes to protect and deliver nucleotides for cancer therapy, immunostimulatory activities, enzymatic diagnostic applications, some examples for veterinarian use, and the treatment of neglected tropical disease.

Toward Contactless Biology: Acoustophoretic DNA Transfection

Acoustophoresis revolutionized the field of container-less manipulation of liquids and solids by enabling mixing procedures which avoid contamination and loss of reagents due to the contact with the support. While its applications to chemistry and engineering are straightforward, additional developments are needed to obtain reliable biological protocols in a contactless environment. Here, we provide a first, fundamental step towards biological reactions in air by demonstrating the acoustophoretic DNA transfection of mammalian cells. We developed an original acoustophoretic design capable of levitating, moving and mixing biological suspensions of living mammalians cells and of DNA plasmids. The precise and sequential delivery of the mixed solutions into tissue culture plates is actuated by a novel mechanism based on the controlled actuation of the acoustophoretic force. The viability of the contactless procedure is tested using a cellular model sensitive to small perturbation of neuronal differentiation pathways. Additionally, the efficiency of the transfection procedure is compared to standard, container-based methods for both single and double DNA transfection and for different cell types including adherent growing HeLa cancer cells, and low adhesion neuron-like PC12 cells. In all, this work provides a proof of principle which paves the way to the development of high-throughput acoustophoretic biological reactors.

Spherulites: onion-like vesicles as nanomedicines

Spherulites are onion-like structures composed of phospholipids and excipients. Initially discovered in an academic laboratory, these autoassembled nano-objects have been developed further by the start-up Capsulis (Bordeaux, France), and commercialized for veterinary and dermatological applications. Owing to economical strategies, the development of these objects have not been pursued, however, they are very interesting systems, which should be exploited further. The autoassembly of amphiphiles followed by a shear stress allows the formation of nano- to micrometer range nanoparticles, which could be interesting either for systemic or local delivery. Small molecules to macromolecules have been encapsulated in spherulites in the nanometer range. All have shown promising results. Hence, spherulite-encapsulated oligonucleotides have shown increased cell internalization. DNA was shown to be encapsulated in these neutral nanoparticles. Proof-of-concept of protein encapsulation was obtained leading to immune stimulation. This review summarizes the different ways to obtain spherulites, the results of the various investigations performed to date and indicates the limits and the interests of theses nanocarriers and proposes future prospects.

The emperor's new dystrophin: finding sense in the noise

Targeted dystrophin exon removal is a promising therapy for Duchenne muscular dystrophy (DMD); however, dystrophin expression in some reports is not supported by the associated data. As in the account of 'The Emperor's New Clothes', the validity of such claims must be questioned, with critical re-evaluation of available data. Is it appropriate to report clinical benefit and induction of dystrophin as dose dependent when the baseline is unclear? The inability to induce meaningful levels of dystrophin does not mean that dystrophin expression as an end point is irrelevant, nor that induced exon skipping as a strategy is flawed, but demands that drug safety and efficacy, and study parameters be addressed, rather than questioning the strategy or the validity of dystrophin as a biomarker.

Next generation delivery system for proteins and genes of therapeutic purpose: why and how?

Proteins and genes of therapeutic interests in conjunction with different delivery systems are growing towards new heights. "Next generation delivery systems" may provide more efficient platform for delivery of proteins and genes. In the present review, snapshots about the benefits of proteins or gene therapy, general procedures for therapeutic protein or gene delivery system, and different next generation delivery system such as liposome, PEGylation, HESylation, and nanoparticle based delivery have been depicted with their detailed explanation.

Calcium phosphate nanoparticles: second-generation nonviral vectors in gene therapy

Adverse effects of viral vectors, instability of naked DNA, cytotoxicity and low transfection of cationic lipids, cationic polymers and other synthetic vectors are currently severe limitations in gene therapy. In addition to targeting a specific cell type, an ideal nonviral vector must manifest an efficient endosomal escape, render sufficient protection of DNA in the cytosol and help provide an easy passage of cytosolic DNA to the nucleus. Virus-like size calcium phosphate nanoparticles have been found to overcome many of these limitations in delivering genes to the nucleus of specific cells. This review has focused on some applications of DNA-loaded calcium phosphate nanoparticles as nonviral vectors in gene delivery, and their potential use in gene therapy, as well as highlighting the mechanistic studies to probe the reason for high transfection efficiency of the vector. It has been demonstrated that calcium ions play an important role in endosomal escape, cytosolic stability and enhanced nuclear uptake of DNA through nuclear pore complexes. The special role of exogenous calcium ions to overcome obstacles in practical realization of this field suggests that calcium phosphate nanoparticles are not 'me too' synthetic vectors and can be designated as second-generation nonviral vectors for gene therapy.

Liposomal drug delivery systems: from concept to clinical applications

The first closed bilayer phospholipid systems, called liposomes, were described in 1965 and soon were proposed as drug delivery systems. The pioneering work of countless liposome researchers over almost 5 decades led to the development of important technical advances such as remote drug loading, extrusion for homogeneous size, long-circulating (PEGylated) liposomes, triggered release liposomes, liposomes containing nucleic acid polymers, ligand-targeted liposomes and liposomes containing combinations of drugs. These advances have led to numerous clinical trials in such diverse areas as the delivery of anti-cancer, anti-fungal and antibiotic drugs, the delivery of gene medicines, and the delivery of anesthetics and anti-inflammatory drugs. A number of liposomes (lipidic nanoparticles) are on the market, and many more are in the pipeline. Lipidic nanoparticles are the first nanomedicine delivery system to make the transition from concept to clinical application, and they are now an established technology platform with considerable clinical acceptance. We can look forward to many more clinical products in the future.

Intracellular trafficking pathways involved in the gene transfer of nano-structured calcium phosphate-DNA particles

Nano-structured calcium phosphate (NanoCaP) particles have been proven to be a powerful means of non-viral gene delivery. In order to better understand the mechanisms through which NanoCaPs-mediated mammalian cell transfection is achieved, we have sought to define the intracellular trafficking pathways involved in the cellular uptake and intracellular processing of these particles. Previous work has indicated that NanoCaP-DNA complexes are most likely internalized via endocytosis, however the subsequent pathways involved have not been determined. Through the use of specific inhibitors, we show that endocytosis of NanoCaP particles is both clathrin- and caveolae-dependent, and suggest that the caveolaer mechanism is the major contributor. We demonstrate colocalization of NanoCaP-pDNA complexes with known markers of both clathrin-coated and caveolar vesicles. Furthermore, through the use of quantitative flow cytometry, we present the first work in which the percent internalization of CaP-DNA complexes into cells is quantified. The overall goal of this research is to foster the continued improvement of NanoCaP-based gene delivery strategies.

A covalently stabilized lipid-polycation-DNA (sLPD) vector for antisense oligonucleotide delivery

Antisense oligonucleotide G3139 is designed for Bcl-2 downregulation and is known to induce toll-like receptor activation. Novel stabilized lipid-polycation-DNA (sLPD) nanoparticles were constructed and evaluated for the delivery of G3139 to human carcinoma KB cells and for bioactivity in vivo. Polyethylenimine (PEI) was incorporated as a DNA condensing agent. The lipid composition used was DOTAP/DDAB/Chol/TPGS/linoleic acid/hexadecenal at molar ratios of 30/30/34/1/5/0.2. The nanoparticles were stabilized by the formation of a reversible covalent bond between the aldehyde group on the cis-11-hexadecenal and amines on the PEI. When sLPDs were used to transfect KB cells, 90.4% Bcl-2 downregulation was observed, compared to no significant downregulation by free G3139 and 54.6% downregulation by nonstabilized LPD-G3139. The sLPDs were then evaluated for therapeutic efficacy in mice bearing KB subcutaneous tumors and were found to trigger a strong antitumor response, inhibiting tumor growth and prolonging survival with 72% increase in lifespan (ILS). Consistent with previous reports on other G3139 nanoparticles, the increased antitumor activities of sLPDs in vivo were found to be associated with increased cytokine induction rather than Bcl-2 downregulation, suggesting an immunological mechanism.

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.

Development of lipidoid-siRNA formulations for systemic delivery to the liver

RNA interference therapeutics afford the potential to silence target gene expression specifically, thereby blocking production of disease-causing proteins. The development of safe and effective systemic small interfering RNA (siRNA) delivery systems is of central importance to the therapeutic application of siRNA. Lipid and lipid-like materials are currently the most well-studied siRNA delivery systems for liver delivery, having been utilized in several animal models, including nonhuman primates. Here, we describe the development of a multicomponent, systemic siRNA delivery system, based on the novel lipid-like material 98N(12)-5(1). We show that in vivo delivery efficacy is affected by many parameters, including the formulation composition, nature of particle PEGylation, degree of drug loading, and biophysical parameters such as particle size. In particular, small changes in the anchor chain length of poly(ethylene glycol) (PEG) lipids can result in significant effects on in vivo efficacy. The lead formulation developed is liver targeted (>90% injected dose distributes to liver) and can induce fully reversible, long-duration gene silencing without loss of activity following repeat administration.

Cationic liposomes as non-viral carriers of gene medicines: resolved issues, open questions, and future promises

The clinical success of gene therapy is critically dependent on the development of efficient and safe gene delivery reagents, popularly known as "transfection vectors." The transfection vectors commonly used in gene therapy are mainly of two types: viral and non-viral. The efficiencies of viral transfection vectors are, in general, superior to their non-viral counterparts. However, the myriads of potentially adverse immunogenic aftermaths associated with the use of viral vectors are increasingly making the non-viral gene delivery reagents as the vectors of choice. Among the existing arsenal of non-viral gene delivery reagents, the distinct advantages associated with the use of cationic transfection lipids include their: (a) robust manufacture; (b) ease in handling and preparation techniques; (c) ability to inject large lipid:DNA complexes; and (d) low immunogenic response. The present review highlights the major achievements in the area of designing efficacious cationic transfection lipids, some of the more recent advances in the field of cationic liposomes-mediated gene transfer and targeted gene delivery, some unresolved issues and challenges in liposomal gene delivery, and future promises of cationic liposomes as gene-carriers in non-viral gene therapy.

Wanted and unwanted properties of surface PEGylated nucleic acid nanoparticles in ocular gene transfer

Ocular gene therapy may offer new hope for severe eye diseases. Many of these ocular diseases are due to a gene defect in the retina, a multi-layered sensory tissue that lines the back of the eye. However, it is well known that the blood-retina barrier and sclera prevent hydrophilic and high molecular weight drugs to reach the retina after systemic or topical application. Therefore, intravitreal injection of non-viral nucleic acid nanoparticles has been considered as a safe and promising approach in ocular gene transfer. However, after intravitreal injection the non-viral nucleic acid nanoparticles should be stable and mobile in the vitreous. In this overview we focus on the behavior of non-viral nucleic acid nanoparticles (lipoplexes) in vitreous and on PEGylation strategies that improve their behavior in vitreous, but that do not affect their transfection capacity.

Properties of Mixed DOTAP−DPPC Bilayer Membranes as Reported by Differential Scanning Calorimetry and Dynamic Light Scattering Measurements

We have investigated the effect of a cationic lipid [DOTAP] on both the thermotropic phase behavior and the structural organization of aqueous dispersions of dipalmitoyl-phosphatidylcholine [DPPC] by means of high-sensitivity differential scanning calorimetry and dynamic light scattering measurements. We find that the incorporation of increasing quantities of DOTAP progressively reduces the temperature and the enthalpy of the gel-to-liquid crystalline transition. We are further showing that, in mixed DOTAP-DPPC systems, the reduction of the phase transition temperature is accompanied by a reduction of the average size of the structures present in the aqueous mixtures, whatever the DOTAP concentration is. These results, which extend a previous investigation by Campbell et al. (Campbell, R. B.; Balasubramanian, S. V.; Straubinger, R. M.; Biochim. Biosphys. Acta 2001, 27, 1512.) limited to a DOTAP concentration below 20 mol %, confirm that the insertion of cationic head groups in zwitterionic phosphatidylcholine bilayers facilitates the formation of stable, relatively small, unilamellar vesicles. This self-assembling restructuring from an aqueous multilamellar structure toward a liposomal phase is favored by decreasing the phospholipid phase transition temperature and by increasing the temperature of the system. This reduction of the average size and the appearance of a stable liposomal phase is also promoted by a heating and cooling thermal treatment.

Optimization and delivery of plasmid DNA for vaccination

Vaccination with DNA is one of the most promising novel immunization techniques against a variety of pathogens and tumors, for which conventional vaccination regimens have failed. DNA vaccines are able to stimulate both arms of the immune system simultaneously, without carrying the safety risks associated with live vaccines, therefore representing not only an alternative to conventional vaccines but also significant progress in the prevention and treatment of fatal diseases and infections. However, translation of the excellent results achieved in small animals to similar success in primates or large animals has so far proved to be a major hurdle. Moreover, biosafety issues, such as the removal of antibiotic resistance genes present in plasmid DNA used for vaccination, remain to be addressed adequately. This review describes strategies to improve the design and production of conventional plasmid DNA, including an overview of safety and regulatory issues. It further focuses on novel systems for the optimization of plasmid DNA and the development of diverse plasmid DNA delivery systems for vaccination purposes.

Nanostructured calcium phosphates (NanoCaPs) for non-viral gene delivery: Influence of the synthesis parameters on transfection efficiency

Calcium phosphate (CaP) based approaches remain an attractive option for delivering plasmid DNA (pDNA) into cultured cells. However, despite their appeal, current synthesis methodologies typically yield lower, less consistent transfection efficiencies when compared to viral approaches. Therefore, we report here a novel method to consistently synthesize efficient, nano-sized, mono-dispersed CaP-pDNA particles; accomplished by optimizing both the stoichiometry (Ca/P ratio) of the CaP particles as well as the mode in which the calcium and phosphate precursor solutions are mixed. Our results indicate that calcium and phosphate precursors when mixed in a controlled and regulated manner reproducibly result in nano-sized particles that consistently yield higher transfection efficiencies when compared to particles synthesized via manual mixing (a two-fold increase was observed). Also, maximum transfection efficiencies in both HeLa and MC3T3-E1 cells lines were obtained when a Ca/P ratio between 100 and 300 was used. Particles synthesized within this optimum Ca/P ratio range were between 25 and 50 nm. Our data suggests that these maximized transfection efficiencies were obtained because these particles not only effectively condensed (70% efficient) but also efficiently bound (90% efficient) the pDNA. In addition, X-ray diffraction and Fourier transform infrared spectroscopy analyses confirmed that all of the synthesized CaP structures exhibited the hydroxyapatite phase.

Ultra-low sized cross-linked polyvinylpyrrolidone nanoparticles as non-viral vectors for in vivo gene delivery

In principle, the technique of gene delivery involves taking complete or parts of genes that can code specific message and delivering them to selected cells in the body. Such a transfer of plasmid DNA into mammalian cells has posed major challenges for gene therapy. This study shows the encapsulation of a plasmid DNA in cross-linked polyvinylpyrrolidone (PVP) nanoparticles of size less than 100 nm. This kind of encapsulation provides complete protection to the plasmid DNA from external DNase environment and generates the hope that the resulting formulation can be developed into a potential vector for effective gene delivery. In order to check this potentially, the reporter gene pSVbeta-gal was encapsulated and in vitro transfection efficiency of this system was found to be nearly 80% compared to the commercially available transfection reagent Polyfect. Further, in vivo biodistribution studies indicated that this system could be used safely for effective gene delivery.

Cell Biological and Biophysical Aspects of Lipid-mediated Gene Delivery

Cationic lipids are conceptually and methodologically simple tools to deliver nucleic acids into the cells. Strategies based on cationic lipids are viable alternatives to viral vectors and are becoming increasingly popular owing to their minimal toxicity. The first-generation cationic lipids were built around the quaternary nitrogen primarily for binding and condensing DNA. A large number of lipids with variations in the hydrophobic and hydrophilic region were generated with excellent transfection efficiencies in vitro. These cationic lipids had reduced efficiencies when tested for gene delivery in vivo. Efforts in the last decade delineated the cell biological basis of the cationic lipid gene delivery to a significant detail. The application of techniques such as small angle X-ray spectroscopy (SAXS) and fluorescence microscopy, helped in linking the physical properties of lipid:DNA complex (lipoplex) with its intracellular fate. This biological knowledge has been incorporated in the design of the second-generation cationic lipids. Lipid-peptide conjugates (peptoids) are effective strategies to overcome the various cellular barriers along with the lipoplex formulations methodologies. In this context, cationic lipid-mediated gene delivery is considerably benefited by the methodologies of liposome-mediated drug delivery. Lipid mediated gene delivery has an intrinsic advantage of being a biomimetic platform on which considerable variations could be built to develop efficient in vivo gene delivery protocols.

Cationic liposomes for gene delivery

Cationic liposome-DNA complexes (lipoplexes) constitute a potentially viable alternative to viral vectors for the delivery of therapeutic genes. This review will focus on various parameters governing lipoplex biological activity, from their mode of formation to in vivo behaviour. Particular emphasis is given to the mechanism of interaction of lipoplexes with cells, in an attempt to dissect the different barriers that need to be surpassed for efficient gene expression to occur. Aspects related to new trends in the formulation of lipid-based gene delivery systems aiming at overcoming some of their limitations will be covered. Finally, examples illustrating the potential of cationic liposomes in clinical applications will be provided.

Stearylated octaarginine and artificial virus-like particles for transfection of siRNA into primary rat neurons

RNA interference (RNAi) provides a powerful experimental tool for sequence-specific gene silencing, allowing efficient analysis of gene function in a multitude of cell types. However, application of RNAi in primary mammalian neurons has been limited by low-transfection efficiency and considerable toxicity of conventional transfection methods. In this study, we evaluated a peptide-mediated and a polymer/lipid-based cellular delivery method for siRNA into rat primary neurons and compared the results with a commonly used liposomal transfection reagent. Stearylated octaarginine (Stearyl-R8) was used as polypeptide and artificial virus-like particles (AVPs) were used as a combined liposomal-polymeric vector, since both reagents have been previously shown to successfully transfect DNA into cell lines. Stearyl-R8 and AVPs both promoted siRNA transfection into primary hippocampal neurons via the endosomal pathway. SiRNA-mediated gene silencing could be effectively induced in primary neuron cultures. In comparison with the commonly used cationic liposome transfection agent, both novel reagents were less detrimental to cell metabolic activity. We conclude that these novel transfection methods yield performances comparable to cationic liposome-mediated transfection for siRNA, while being less cytotoxic in primary neurons. Stearyl-R8 and AVPs may therefore represent novel and more cost-efficient alternatives to conventional siRNA-transfection reagents.

Polyethylenimine-based antisense oligodeoxynucleotides of IL-4 suppress the production of IL-4 in a murine model of airway inflammation

BACKGROUND

Interleukin-4 (IL-4) plays a crucial role as an inflammatory mediator in allergic asthma via inducing Th2 inflammation and IgE synthesis. To develop an effective therapeutic agent which specifically inhibits production of IL-4, antisense oligodeoxynucleotides (AS-ODNs) against murine IL-4 mRNA were generated and complexed with polyethylenimine (PEI) to improve intracellular delivery.

METHODS

AS-ODNs were generated against the translation initiation region of murine IL-4 mRNA, and complexed with linear PEI. In vitro efficacy of AS-ODNs/PEI complexes was tested by measuring IL-4 production in the D10.G4.1 cell line, and cytotoxicity was tested by XTT assay. Physicochemical properties of polyplexes were examined using atomic force microscopy (AFM) and DNase I protection assay. In vivo effects of IL-4 AS-ODNs/PEI complexes were tested in a murine model of airway inflammation. IL-4 concentrations in the bronchoalveolar lavage (BAL) fluid and circulating IgE levels were measured by ELISA, and histological analysis of lung tissues was performed.

RESULTS

IL-4 AS-ODNs/PEI complexes were spheres with an average diameter of 98 nm and resistant to DNase I-mediated degradation. IL-4 AS-ODNs/PEI complexes showed up to 35% inhibition of IL-4 production in D10.G4.1 cells without causing any toxicity, while naked ODNs gave less than 1% reduction. Furthermore, IL-4 AS-ODNs/PEI complexes were effective in suppressing secretion of IL-4 (up to 30% reduction) in the BAL fluid in an ovalbumin-sensitized murine model of airway inflammation. Circulating IgE levels were decreased, and airway inflammation was alleviated by treatment with IL-4 AS-ODNs polyplexes.

CONCLUSIONS

These data demonstrate that complexation of IL-4 AS-ODNs with PEI provides a potential therapeutic tool in controlling inflammation associated with allergic asthma, and further presents an opportunity to the development of clinical therapy based on combination of multiple AS-ODNs of cytokines and/or signaling effectors involved in Th2 inflammation and eosinophilia.

Cell-specific targeting of lipid-based carriers for ODN and DNA

It is well recognized that there is an urgent need for non-toxic systemically applicable vectors for biologically active nucleotides to fully exploit the current potential of molecular medicine in gene therapy. Cell-specific targeting of non-viral lipid-based carriers for ODN and DNA is a prerequisite to attain the concentration of nucleic acids required for therapeutic efficacy in the target tissue. In this review we will address the most promising approaches to selective targeting of liposomal nucleic acid carriers in vivo. In addition, the routes of entry and intracellular processing of these carrier systems are discussed as well as physiological factors potentially interfering with the biological and/or therapeutic activity of their nucleotide pay-load.

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.

Entrapment of small molecules and nucleic acid-based drugs in liposomes

In the past two decades there have been major advances in the development of liposomal drug delivery systems suitable for applications ranging from cancer chemotherapy to gene therapy. In general, an optimized system consists of liposomes with a diameter of approximately 100 nm that possess a long circulation lifetime (half-life >5 h). Such liposomes will circulate sufficiently long to take advantage of a phenomenon known as disease site targeting, wherein liposomes accumulate at sites of disease, such as tumors, as a result of the leaky vasculature and reduced blood flow exhibited by the diseased tissue. The extended circulation lifetime is achieved by the use of saturated lipids and cholesterol or by the presence of PEG-containing lipids. This chapter will focus on the methodology required for the generation of two very different classes of liposomal carrier systems: those containing conventional small molecular weight (usually anticancer) drugs and those containing larger genetic (oligonucleotide and plasmid DNA) drugs. Initially, we will examine the encapsulation of small, weakly basic drugs within liposomes in response to transmembrane pH and ion gradients. Procedures will be described for the formation of large unilamellar vesicles (LUVs) by extrusion methods and for loading anticancer drugs into LUVs in response to transmembrane pH gradients. Three methods for generating transmembrane pH gradients will be discussed: (1) the use of intravesicular citrate buffer, (2) the use of transmembrane ammonia gradients, and (3) ionophore-mediated generation of pH gradients via transmembrane ion gradients. We will also discuss the loading of doxorubicin into LUVs by formation of drug-metal ion complexes. Different approaches are required for encapsulating macromolecules within LUVs. Plasmid DNA can be encapsulated by a detergent-dialysis approach, giving rise to stabilized plasmid-lipid particles, vectors with potential for systemic gene delivery. Antisense oligonucleotides can be spontaneously entrapped upon electrostatic interaction with ethanol-destabilized cationic liposomes, giving rise to small multilamellar systems known as stabilized antisense-lipid particles (SALP). These vectors have the potential to regulate gene expression.

pDNA loaded calcium phosphate nanoparticles: highly efficient non-viral vector for gene delivery

Nanoparticles of calcium phosphate encapsulating plasmid DNA (pDNA) of size 100-120 nm in diameter were prepared. XRD studies of these nanoparticles showed them to be crystalline in nature having hydroxyapatite structure. The maximum loading of pDNA and its release from nanoparticles were studied using gel electrophoresis. The time dependent size measurement of these particles demonstrated that these particles show strong aggregational behaviour in aqueous dispersion. Calcium phosphate nanoparticles were found to be dissolved even in low acidic buffer (pH 5.0) releasing the pDNA, which suggested that DNA release from these particles in the endosomal compartment was possible. In vitro transfection efficiency of these calcium phosphate nanoparticles was found to be higher than that of the commercial transfecting reagent Polyfect.

Spontaneously formed monodisperse biomimetic unilamellar vesicles: the effect of charge, dilution, and time

Using small-angle neutron scattering and dynamic light scattering, we have constructed partial structural phase diagrams of lipid mixtures composed of the phosphatidylcholines dimyristoyl and dihexanoyl doped with calcium ions (Ca2+) and/or the negatively charged lipid, dimyristoyl phosphatidylglycerol (DMPG). For dilute solutions (lipid concentration < or =1 wt %), spontaneously forming unilamellar vesicles (ULVs) were found, and their polydispersity was determined to be approximately 20%. The stability of the Ca2+- or DMPG-doped ULVs was monitored over a period of 4 days and their structural parameters (e.g., average outer radius, <Ro>) were found to be insensitive to the lipid concentration (Clp). However, doping the dimyristoyl/dihexanoyl system with both Ca2+ and DMPG resulted in ULVs whose <Ro> was found to be Clp dependent. The <Ro> of DMPG-doped ULVs remained unchanged over an extended period of time (at least 4 days), a good indication of their stability.

Transfection of “naked” siRNA results in endosomal uptake and metabolic impairment in cultured neurons

RNA interference is rapidly becoming a powerful tool for gene silencing in mammalian cells. Introduction of siRNA into primary cells, however, remains one of the major difficulties of this novel technique. Using cationic lipid-based transfection reagents satisfactory transfection results are observed in cell lines, but low transfection efficiency and cytotoxicity limit applications in primary cells, especially primary neurons. The application of "naked" siRNA has been previously used successfully in nematodes and mammals in vivo. We therefore evaluated the effects of non-cationic-lipid-based siRNA application to primary hippocampal neuron cultures. "Naked" siRNA was bound to the cell surface and was taken up into endosomes. No significant silencing effect of endogenous or reporter genes was observed, rather application of "naked" siRNA was accompanied by a moderate downregulation of metabolic activity in culture. We postulate that endosomal degradation of "naked" siRNA in neurons prevents the induction of significant RNAi-mediated mRNA-downregulation and is accompanied by a global impairment of the cell metabolism. Transfection methods circumventing the endosomal pathway therefore might prove useful for siRNA transduction of primary neurons.

A Multi-Model Approach to Nucleic Acid-Based Drug Development

With the advent of functional genomics and the shift of interest towards sequence-based therapeutics, the past decades have witnessed intense research efforts on nucleic acid-mediated gene regulation technologies. Today, RNA interference is emerging as a groundbreaking discovery, holding promise for development of genetic modulators of unprecedented potency. Twenty-five years after the discovery of antisense RNA and ribozymes, gene control therapeutics are still facing developmental difficulties, with only one US FDA-approved antisense drug currently available in the clinic. Limited predictability of target site selection models is recognized as one major stumbling block that is shared by all of the so-called complementary technologies, slowing the progress towards a commercial product. Currently employed in vitro systems for target site selection include RNAse H-based mapping, antisense oligonucleotide microarrays, and functional screening approaches using libraries of catalysts with randomized target-binding arms to identify optimal ribozyme/DNAzyme cleavage sites. Individually, each strategy has its drawbacks from a drug development perspective. Utilization of message-modulating sequences as therapeutic agents requires that their action on a given target transcript meets criteria of potency and selectivity in the natural physiological environment. In addition to sequence-dependent characteristics, other factors will influence annealing reactions and duplex stability, as well as nucleic acid-mediated catalysis. Parallel consideration of physiological selection systems thus appears essential for screening for nucleic acid compounds proposed for therapeutic applications. Cellular message-targeting studies face issues relating to efficient nucleic acid delivery and appropriate analysis of response. For reliability and simplicity, prokaryotic systems can provide a rapid and cost-effective means of studying message targeting under pseudo-cellular conditions, but such approaches also have limitations. To streamline nucleic acid drug discovery, we propose a multi-model strategy integrating high-throughput-adapted bacterial screening, followed by reporter-based and/or natural cellular models and potentially also in vitro assays for characterization of the most promising candidate sequences, before final in vivo testing.

Liposome-complexed adenoviral gene transfer in cancer cells expressing various levels of coxsackievirus and adenovirus receptor

PURPOSE

Loss of coxsackievirus and adenovirus receptor (CAR) is frequently observed in malignant cancer, hampering adenoviral gene therapy approaches. Complexing adenovirus with cationic liposomes can increase adenoviral transgene expression, particularly in cells with CAR-deficiency. We investigated whether other factors such as lipid composition might be involved in determining the efficiency of liposome-complexed adenoviral gene transfer in cancer cells.

MATERIAL AND METHODS

Human cancer cell lines with different expression levels of CAR were infected with a GFP transgene. The efficiency of transgene expression was assessed by determining GFP expression using FACS analysis.

RESULTS

The efficiency of liposome-complexed adenoviral gene transfer was dependent on the lipid composition constituting liposomes. Polyethylene glycol (PEG)-containing liposomes were most effective in increasing liposome-complexed adenoviral gene transfer. In CAR-deficient cells, use of PEG-containing liposomes enhanced adenoviral gene transfer, whereas in CAR-expressing cells enhancement varied depending on cell type. In some CAR-expressing cells, the effect of liposome complexing was even comparable to that in CAR-deficient cells. Increased adenoviral transgene expression following complexing with PEG-containing liposomes correlated with liposome uptake in cancer cells.

CONCLUSIONS

Liposome-complexed adenoviral gene transfer appears to depend on lipid composition and the level of liposome uptake by cancer cells, in addition to CAR levels. Our study suggest that these multiple factors should be considered in designing liposome-complexed adenoviral vectors to improve outcomes of current adenoviral cancer gene therapies.

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.

Anionic polyethyleneglycol lipids added to cationic lipoplexes increase their plasmatic circulation time

Cationic liposomes have been widely sensed as good DNA compacting delivery agents. Although their use generally met with encouraging results in vitro, the results in vivo were rather disappointing, as they strongly interact with the blood components before they can reach the therapeutic target. Polyethyleneglycol (PEG) shielding has been proposed as a way to alleviate this effect, but was still found unsatisfactory in most instances for systemic administration. We demonstrate here that the insertion of anionic functions between the lipid part and the PEG, at a correct distance to favor electrostatic interactions with the outer cationic layer of the lipoplexes, provides not only a decrease in the mean peripheral charge of the lipoplex (zeta potential), but also a greater colloidal stability of the particles in the presence of serum. Transfection in the lung is also decreased with negatively charged PEG shielding, although no significant changes are observed in the tumor. This encouraging new approach should consequently be combined with active extra-cellular receptor targeting to achieve the desired delivery of the therapeutic DNA to tumor tissues.

Mesenchymal stem cells, MG63 and HEK293 transfection using chitosan-DNA nanoparticles

Chitosan-DNA nanoparticles were synthesized from the complexation of the cationic polymer with a ss-gal DNA plasmid, in order to study the efficacy of chitosan to develop a non-viral gene delivery system that can be optimized for efficient gene therapy. The optimal binding conditions were determined with the fluorescamine and PicoGreen assays. DNA distribution within the nanoparticle was visualized by electron transmission microscopy, while the size and morphology were assessed by atomic force microscopy. The transfection potential was evaluated for the first time on human mesenchymal stem cells (MSCs), on human osteosarcoma cells (MG63) and on human embryonic kidney cells (HEK293). The LipofectAMINE(TM) 2000 (LF) reagent was used in comparison. The effect of chitosan-DNA nanoparticles on cell viability was illustrated with the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. The nanoparticles formed are of a diameter inferior to 100nm with a homogenous distribution of DNA. The transfection of HEK293 cells is superior to that seen with MG63 cells and MSCs, however not surpassing that seen with LF. Minimal cytotoxicity is seen with the polyplexes compared to greater than 50% toxicity with LF. These results suggest that chitosan-DNA nanoparticles have favorable characteristics for non-viral gene delivery, are cell type dependent and not cytotoxic.

New cationic lipids form channel-like pores in phospholipid bilayers

Two representatives of a new class of cationic lipids were found to have high pore-forming activity in planar bilayer membranes. These molecules, called BHHD-TADC and BHTD-TADC, have qualitatively similar effects on phospholipid membranes. Addition of 2.5-5 micro M of either of them to the membrane bathing solutions resulted in formation of long-lived anion-selective pores with conductance in the range 0.1-2 nS in 0.1 M KCl. Pore formation was found to be dependent on the potential applied to the membrane. When negative potential was applied to membrane at the side of addition, the rate of pore formation was much lower compared to when the positive potential was applied. Dependence of pore formation on compound concentration was highly nonlinear, indicating that this process requires assembly of molecules in the membrane. Addition of any of these compounds on both sides of the membrane increased the efficiency of pore formation by one to two orders of magnitude. Pore formation was strongly pH dependent. Although pores were formed with high efficiency at pH 6.5, only occasional fluctuations of membrane conductance were observed at pH 7.5. Possible mechanisms of new compounds biological activity are discussed.

Calcium phosphate nanoparticles as novel non-viral vectors for targeted gene delivery

Calcium phosphate nanoparticles present a unique class of non-viral vectors, which can serve as efficient and alternative DNA carriers for targeted delivery of genes. In this study we report the design and synthesis of ultra-low size, highly monodispersed DNA doped calcium phosphate nanoparticles of size around 80 nm in diameter. The DNA encapsulated inside the nanoparticle is protected from the external DNase environment and could be used safely to transfer the encapsulated DNA under in vitro and in vivo conditions. Moreover, the surface of these nanoparticles could be suitably modified by adsorbing a highly adhesive polymer like polyacrylic acid followed by conjugating the carboxylic groups of the polymer with a ligand such as p-amino-1-thio-beta-galactopyranoside using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride as a coupling agent. We have demonstrated in our studies that these surface modified calcium phosphate nanoparticles can be used in vivo to target genes specifically to the liver.

The transfection of Jurkat T-leukemic cells by use of pH sensitive immunoliposomes

A gene transfer vector has been developed utilising anionic liposomes as a carrier of plasmid DNA (pEGlacZ, 7.6 kb) to transfect CD3+ T lymphocytes (Jurkat cells). The plasmid DNA that contained the Escherichia coli beta-galactosidase reporter gene was condensed using poly-l-lysine of molecular mass 20,700 (PLK99) to form a polyplex which was interacted with several anionic liposome formulations to form lipopolyplexes. The liposome formulations where based on dioleoylphosphatidylethanolamine (DOPE) in combination with cholesterol and dioleoylphosphatidylcholine (DOPC) and oleic acid, or dimyristoylphosphatidylethanolamine (DMPE). For targeting to the Jurkat cells distearoylphosphatidylethanolamine (DSPE) linked to poly (ethylene glycol) molecular mass 2,000 and coupled to anti-CD3 antibody was incorporated. The polyplexes and lipopolyplexes were characterised in terms of size, zeta potential, agarose gel electrophoresis and electron microscopy and the permeability of the lipopolyplexes to liposome-encapsulated glucose was determined. The polyplexes consisted of a mixed population of rod-like structures (53-160 nm long and 23-31 nm diameter) and spheres (18-30 nm diameter). The lipopolyplexes retained a permeability barrier although were more permeable to glucose than their component liposomes. The poly-l-lysine condensing agent was still susceptible to pronase digestion suggesting that the polyplex was associated with the outer surface of the liposome. The lipopolyplexes with lipid composition DOPE/cholesterol/OA/DSPE-PEG2000 anti-CD3+ PLK99-plasmid DNA had significant gene transfer activity, as monitored by beta-galactosidase expression, that depended on the charge ratio of the component polyplex and the lipid/DNA weight ratio. The anti-CD3 antibody, the liposomal lipid and pH sensitivity were essential for transfection activity.