Controllable gene therapy pharmaceutics of non-viral gene delivery systems

In vitro gene expression by cationized derivatives of an artificial protein with repeated RGD sequences, Pronectin

The objective of this study is to investigate the efficiency of a non-viral gene carrier with RGD sequences, Pronectin F(+) for gene transfection. The Pronectin F(+) was cationized by introducing ethylenediamine (Ed), spermidine (Sd), and spermine (Sm) to the hydroxyl groups while the corresponding gelatin derivative was prepared similarly because gelatin also has one RGD sequence per molecule. The zeta potential and molecular size of Pronectin F(+) and gelatin derivatives were examined before and after polyion complexation with a plasmid DNA of luciferase. When complexed with the plasmid DNA at the Pronectin F(+)/plasmid DNA mixing ratio of 50, the complex exhibited a zeta potential of about 10 mV, which is similar to that of the gelatin derivative-plasmid DNA complex. Irrespective of the type of Pronectin F(+) and gelatin derivatives, their complexation enabled the apparent molecular size of plasmid DNA to reduce to about 200 nm, the size decreasing with the increased derivative/plasmid DNA weight mixing ratio. The rat gastric mucosal (RGM)-1 cells treated with both complexes exhibited significantly stronger luciferase activities than free plasmid DNA although the enhanced extent was significant for the Sm derivative compared with the corresponding Ed and Sd derivatives. Cell attachment was enhanced by the Pronectin F(+) derivative to a significant high extent compared with the gelatin derivative. The amount of plasmid DNA internalized into the cells was enhanced by the complexation with every Pronectin F(+) derivative compared with the gelatin derivative. For both of Pronectin F(+) and gelatin carriers, the buffering capacity of Sm derivatives was higher than that of Ed and Sd derivatives and comparable to that of polyethyleneimine. It is likely that the high efficiency of gene transfection for the Sm derivative is due to the superior buffering effect. We conclude that the Sm derivative of Pronectin F(+) is promising as a non-viral vector of gene transfection.

Liver targeting of plasmid DNA by pullulan conjugation based on metal coordination

Liver targeting of plasmid DNA was achieved through conjugation of pullulan derivatives with chelate residues based on metal coordination. Triethylenetetramine (Ti), diethylenetriamine pentaacetic acid (DTPA), and spermine (Sm) were chemically introduced to pullulan, a polysaccharide with an inherent affinity for the liver, to obtain various pullulan-Ti, pullulan-DTPA, and pullulan-Sm derivatives. Irrespective of the type of pullulan derivatives, intravenous injection of the pullulan derivatives-plasmid DNA conjugates with Zn2+ coordination significantly enhanced the level of gene expression only in the liver to a significant greater extent than that of free plasmid DNA. The enhanced gene expression by the pullulan-DTPA-plasmid DNA conjugate was specific to the liver and the level was significantly higher than that of the pullulan-DTPA-plasmid DNA mixture. The level of gene expression depended on the percentage of chelate residue introduced, the mixing ratio of the plasmid DNA-DTPA residue in conjugate preparation, and the plasmid DNA dose. The gene expression induced by the conjugate lasted over 12 days after injection. A fluorescent-microscopic study revealed that the plasmid DNA was localized at the liver after injection of the pullulan-DTPA-plasmid DNA conjugate with Zn2+ coordination. Pre-injection of both arabinogalactan and galactosylated albumin suppressed significantly the liver level of gene expression, in contrast to that of mannosylated albumin, indicating that the plasmid DNA in the conjugate was transfected at hepatocytes. We conclude that the Zn2+-coordinated pullulan conjugation is a promising way to enable the plasmid DNA to target to the liver for gene expression as well as to prolong the time duration of gene expression

Real time monitoring of lipoplex molar mass, size and density

Time-resolved multiangle laser light scattering (TR-MALLS) is used to monitor the temporal variation of DNA/cationic liposome lipoplex molar masses and geometric sizes throughout the complexation process. The measured molar masses and geometric sizes are in turn used to estimate lipoplex density. The DNA/cationic lipid charge ratio is found to be the primary factor governing lipoplex formation kinetics and the final lipoplex molar mass, geometric size and density. Charge ratios near unity lead to a growing kinetic regime in which initially formed primary lipoplexes undergo further aggregation eventually forming large molar mass lipoplexes of high density, while charge ratios very far from unity yield low molar mass lipoplexes of lower density. It is also noted that solvent composition can play a significant role in the lipoplex formation process with lipoplexes formed in ion-containing media being larger and denser than those formed in dextrose solution.

A thermodynamic study of cationic polymer-plasmid DNA complexes by highly-sensitive differential scanning calorimetry

The characteristics of polymer-DNA complexes formed by positively-negatively charged interaction have a great influence on their transfection potential. Since the limit changes in thermal transitions which were hardly measured in conventional calorimetry, now in this study they have been successfully carried out by highly-sensitive differential scanning calorimetry for better understanding the pDMAEMA-plasmid DNA complexing process. Thermal behaviors of plasmid DNA, polymer and their formed complexes were recorded to give insights into their conformational changes when temperature was raised. In results, the supercoiled or open-circular plasmid DNA is not thermal reversible indicated by the decrease of denaturation peak and disappearance of DNA conformational transition related to its twist status at 50-70 degrees C. The cationic polymer is thermally stable by showing reversible transition peaks after two heating processes. For the cationic polymer-plasmid DNA complexes, electrostatic forces lead to a higher denaturation temperature of plasmid DNA and transition temperature of polymer. Also, heat can cause a topological change in plasmid DNA and then change their mutual complexation capacity.

Cationized human serum albumin as a non-viral vector system for gene delivery? Characterization of complex formation with plasmid DNA and transfection efficiency

Cationized human serum albumin (cHSA) could serve as a potential non-viral vector system for gene delivery. Native human serum albumin was cationized by covalent coupling of hexamethylenediamine to the carboxyl groups resulting in a shift of the isoelectric point from pH 4-5 to 7-9. The cationized albumin underwent spontaneous self-assembly with DNA as demonstrated by retardation of CMV-nlacZ plasmid in agarose gel electrophoresis. Photon correlation spectroscopy showed a decrease of complex size with increasing cHSA/plasmid ratios. Under optimized conditions complexes were formed with 230-260 nm mean diameter and a homogenous, narrow size distribution. At room temperature complexes were stable in 0.9% sodium chloride solution pH 7.4 for 1 h without aggregation. Process parameters such as albumin concentration, incubation time, temperature, pH, order of reagent addition, the presence of bivalent ions and the ionic strength of the complexation medium all influenced the complex size. Confocal laser scanning microscopy showed interactions of a Texas Red labeled cationized albumin with cell membranes of ECV 304 cells and an enhanced endocytic uptake compared to native albumin. The potential for introducing exogeneous DNA into cells was shown using NIH 3T3 fibroblasts. Successful, albeit low reporter gene expression could be achieved in the presence of chloroquine. Under in vitro conditions no toxic effect could be observed. In conclusion, cationized albumin may have promise as a non-toxic vector for gene delivery, especially for DNA vaccination.

Statistical modelling of the formulation variables in non-viral gene delivery systems

Traditionally, optimisation of a gene delivery formulation utilises a study design that involves altering only one formulation variable at any one time whilst keeping the other variables constant. As gene delivery formulations become more complex, e.g. to include multiple cellular and sub-cellular targeting elements, there will be an increasing requirement to generate and analyse data more efficiently and allow examination of the interaction between variables. This study aims to demonstrate the utility of multifactorial design, specifically a Central Composite Design, in modelling the responses size, zeta potential and in vitro transfection efficiency of some prototypic non-viral gene delivery vectors. i.e. cationic liposome-pDNA complexes, and extending the application of the design strategy to more complex vectors, i.e. tri-component lipid:polycation:DNA (LPD). The modelled predictions of how the above responses change as a function of formulation show consistency with an extensive literature base of data obtained using more traditional approaches, and highlight the robustness and utility of the Central Composite Design in examining key formulation variables in non-viral gene delivery systems. The approach should be further developed to maximise the predictive impact of data across the full range of pharmaceutical sciences.

Liposome-mediated DNA vaccination: the effect of vesicle composition

Liposome-entrapped DNA has been shown to enhance the potency of DNA vaccines, possibly by facilitating uptake of the plasmid by antigen-presenting cells (APC). In this paper, we have investigated the influence of the liposomal composition and surface charge on such potency. Plasmid DNA pRc/CMV HBS encoding the S (small) region of hepatitis B surface antigen was entrapped within cationic liposomes of various compositions and surface charges with high efficiency (88-97% of the amount used) by the dehydration-rehydration method that generates dehydration-rehydration vesicles (DRV). Cryo-electron microscopy revealed that DNA-containing DRV (DRV(DNA)) were multilamellar. In immunisation studies, female Balb/c mice were given two to four intramuscular injections of 10 microg naked or liposome-entrapped pRc/CMV HBS and bled at time intervals. Results indicate that the lipid composition of the DRV(DNA) influences the strength of the humoural response (immunoglobulin (Ig)G subclasses) with inclusion of dioleoyl phosphatidylethanolamine (DOPE) or phosphatidylethanolamine (PE) in the liposomal structure contributing to greater responses. DRV(DNA) in which the DOPE or PE were omitted or substituted with cholesterol led to significant reduction of humoural responses against the encoded antigen. Replacing phosphatidylcholine (PC) in the DRV(DNA) with the high-melting distearoyl phosphatidylcholine also contributed to lower responses. In other experiments, IgG responses were monitored in mice immunised with pRc/CMV HBS entrapped in DRV composed of PC and DOPE as before but incorporating increasing amounts of DOTAP (1-16 micromol). Maximal IgG responses were observed at 10 weeks after the first of four injections and suggested a trend of higher responses when 4 or 8 micromol DOTAP was present in the DRV(DNA) formulation. Cell-mediated immunity (measured in terms of endogenous antigen-specific splenic interferon-gamma) in mice immunised with pRc/CMV HBS entrapped in liposomes composed of PC, DOPE and DOTAP (16:8:4 molar ratio) was much greater than in animals treated with naked plasmid. These results indicate that liposome-mediated DNA immunisation is more effective than the use of naked DNA, and also suggest that the presence of fusogenic phosphatidylethanolamine in DRV in conjunction with a low-melting phosphatidylcholine and an appropriate content of cationic lipid might contribute to more effective liposomal DNA vaccines. The notion that liposomes improve immune responses to the plasmid-encoded vaccine by facilitating the latter's uptake by APC was supported by the observation that in Balb/c mice injected intramuscularly with liposome-entrapped pCMV. Enhanced green fluorescent protein, expression of the gene in terms of fluorescence intensity in the draining lymph nodes, was much greater than in animals treated with the naked plasmid.

Cationic lipid-DNA complexes in gene delivery: from biophysics to biological applications

Great expectations from the application of gene therapy approaches to human disease have been impaired by the unsatisfactory clinical progress observed. Among others, the use of an efficient carrier for nucleic acid-based medicines is considered to be a determinant factor for the successful application of this promising therapeutic strategy. The drawbacks associated with the use of viral vectors, namely those related with safety problems, have prompted investigators to develop alternative methods for gene delivery, cationic lipid-based systems being the most representative. This review focuses on the various parameters that are considered to be crucial to optimize the use of cationic lipid-DNA complexes for gene therapy purposes. Particular emphasis is devoted to the analysis of the different stages involved in the transfection process, from the biophysical aspects underlying the formation of the complexes to the different biological barriers that need to be surpassed for gene expression to occur.

Determination of protection from serum nuclease activity by DNA-polyelectrolyte complexes using an electrophoretic method

Polyelectrolyte complexes between cationic polymers and DNA have emerged as potential nonviral vectors for DNA delivery. For successful in vivo delivery, methods for analyzing their ability to prevent digestion of the DNA payload by serum nucleases are essential. We report here a simple assay to determine degradation of DNA in these complexes using standard electrophoretic techniques. The assay is based on a high pH buffer which can dissociate the complexes under standard electrophoretic conditions. This assay can be used qualitatively to determine the time taken for degradation to occur. Alternatively, with a standard gel analysis program it can be used quantitatively to investigate rates of DNA degradation from complexes in the presence of serum nucleases. We have shown that it can distinguish between different formulations with the same polymer, and also to distinguish between the time taken to degradation and the rates of degradation of DNA in complexes formed with two structurally related, linear polyamidoamine polymers. The assay could also distinguish between the time to degradation using poly-l-lysine complexes, although these were less well dissociated by the electrophoresis buffer, and could not be analyzed quantitatively. This assay will be of value in investigating and developing polyelectrolyte formulations for parenteral administration.

Gene therapy in heart disease

Application of gene therapy to the field of cardiovascular disorders has been the subject of intensive work over the recent period. Gene therapy for cardiovascular disorders is now fast developing with most therapies being devoted to the consequences (ischemia) rather than the causes of atherosclerotic diseases. Recent human clinical trials have shown that injection of naked DNA encoding vascular endothelial growth factor promotes collateral vessel development in patients with critical limb ischemia or chronic myocardial ischemia. Promising studies in animals have also fueled enthusiasm for treatment of human restenosis by gene therapy, but clinical applications are warranted. Application of gene transfer to other cardiovascular diseases will require the coordinated development of a variety of new technologies, as well as a better definition of cellular and gene targets.

Gene medicine : a new field of molecular medicine

Gene therapy has emerged as a new concept of therapeutic strategies to treat diseases which do not respond to the conventional therapies. The principle of gene therapy is to introduce genetic materials into patient cells to produce therapeutic proteins in these cells. Gene therapy is now at the stage where a number of dinical trials have been carried out to patients with gene-deficiency disease or cancer. Genetic materials for gene therapy are generally composed of gene expression system and gene delivery system. For the dinical application of gene therapy in a way which conventional drugs are used, researches have been focused on the design of gene delivery system which can offer high transfection efficiency with minimal toxicity. Currently, viral delivery systems generally provide higher transfection efficiency compared with non-viral delivery systems while non-viral delivery systems are less toxic, less immunogenic and manufacturable in large scale compared with viral systems. Recently, novel strategies towards the design of new non-viral delivery system, combination of viral and non-viral delivery systems and targeted delivery system have been extensively studied. The continued effort in this area will lead us to develop gene medicine as 'gene as a drug' in the near future.

Monitoring DNA/poly-L-lysine polyplex formation with time-resolved multiangle laser light scattering

Nonviral DNA complexes show promise as alternative and attractive gene delivery vectors for treating genetic diseases. Nonviral DNA complexes are typically formed by combining DNA with various condensing/complexing agents such as lipids, polyelectrolytes, polymers, polypeptides, and surfactants in solution. DNA/poly-L-lysine polyplex formation kinetics are probed by time-resolved multiangle laser light scattering (TR-MALLS), which yields the time evolution of the supramolecular complex mass and geometric size. Primary polyplexes whose geometric size is smaller than individual DNA molecules in solution are formed very rapidly upon mixing DNA and poly-L-lysine. Over time, these primary polyplexes aggregate into larger structures whose ultimate size is determined primarily by the relative concentrations of DNA and poly-L-lysine. This final polyplex size varies with the DNA/poly-L-lysine mass ratio in a non-monotonic fashion, with the maximum polyplex size occurring at a DNA/poly-L-lysine mass ratio of approximately two to three (charge ratio near unity). The utility of TR-MALLS for monitoring the temporal evolution of DNA loading and supramolecular complex size growth (mean square radius and molar mass) throughout the DNA/poly-L-lysine polyplex formation process is demonstrated. The polyplex DNA loading and size, both geometric and molar mass, are key to understanding the transfection process and for developing optimal gene therapy vectors.

Novel cationic amphiphilic 1,4-dihydropyridine derivatives for DNA delivery

In order to find new efficient and safe agents for gene delivery, we have designed and synthesized nine novel single- and double-charged amphiphiles on the base of 1,4-dihydropyridine (1,4-DHP) ring. Some biophysical properties of the amphiphilic dihydropyridines and their complexes with DNA were examined. We investigated the transfer of beta-galactosidase gene into fibroblasts (CV1-P) and retinal pigment epithelial (D 4O7) cell lines in vitro. The structure-property relationships of the compounds were investigated in various ways. The net surface charges of 1,4-DHP liposomes were highly positive (25-49 mV). The double-charged compounds condensed DNA more efficiently than single-charged and the condensation increases with the increasing +/- charge ratio between the carrier and DNA. Double-charged compounds showed also buffering properties at endosomal pH and these compounds were more efficient in transfecting the cells, but transfection efficiency of amphiphiles was cell type-dependent. The length of alkyl chains in double-charged compounds affected the transfection efficacy. The most active amphiphile (compound VI) was double-charged and had two C(12) alkyl chains. At optimal charge ratio (+/- 4), it was 2.5 times more effective than PEI 25 and 10 times better than DOTAP, known efficient polymeric and liposomal transfection agents. Formulation of amphiphiles with DOPE did not change their activities. Our data demonstrate some important effects of amphiphile structure on biophysics and activity. The data also suggest that cationic amphiphilic 1,4-DHP derivatives may find use as DNA delivery system.

Polymer chemical structure is a key determinant of physicochemical and colloidal properties of polymer-DNA complexes for gene delivery

Polyplexes are now emerging as potentially useful vectors for gene therapy. To improve our understanding of how the chemical structure of the polymer affects the properties of these systems, a series of structurally related polymers, the linear poly(amidoamine)s (PAAs), have been examined for their abilities to form complexes with DNA. Structure-dependent differences in DNA binding are shown by gel electrophoretic retardation of DNA and thermal transition analyses. Two PAAs, NG28 and NG30, stand out as having high affinity DNA binding characteristics, similar to the model homopolypeptide, poly-L-lysine. In addition, differences in complex formation, particle size and surface charge are displayed for the different polymer-DNA systems. Electron microscopy studies showed that the polymers condensed DNA into similar unit structures but only complexes with NG30 did not undergo agglomeration. This was attributed to an excess of complexed polymer forming a shell of uncomplexed polymer chain segments around a condensed DNA-polymer core. The transfection activities of these polymer complexes differ greatly, and some of these differences can be explained in a multifactorial way by the physicochemical and colloidal properties. It is concluded that polymer chemical structure dictates the apparent affinity of DNA binding, and also several of the important colloidal characteristics of the resulting complexes.

Delivering DNA with polymer matrices: applications in tissue engineering and gene therapy

DNA delivery from polymers is currently being applied to the multidisciplinary science of gene therapy and tissue engineering. This is motivated by the potential of treating a wide range of diseases and the provision of alternatives to tissue and organ transplantation. The combination of these fields involves the incorporation of genes into polymeric matrices that can be injected or implanted to promote tissue regeneration. This review presents an overview of current and developing polymer systems for gene delivery and tissue engineering.

Gene transfer by cationic surfactants is essentially limited by the trapping of the surfactant/DNA complexes onto the cell membrane: a fluorescence investigation

The interaction between complexes of plasmid DNA with cetyltrimethylammonium bromide (CTAB) and L929 fibroblasts was first examined using confocal microscopy. The complexes labeled with the DNA intercalator, YOYO-1, were found to be trapped onto the external face of the plasma membrane; a feature that may constitute a major limiting step in transfection. Moreover, since no cytotoxic effect appeared in these conditions, we further inferred that the CTAB molecules remained bound to the DNA. The interaction of the complexes with the membranes was best modeled with neutral vesicles. From anisotropy thermotropic curves of DPHpPC-labeled vesicles and fluorescence resonance energy transfer measurements between these vesicles and YOYO-labeled complexes, we evidenced that the binding of the complexes to the vesicle surface opened the micelle-like domains and unwound DNA. However, DNA was not released but remained stably bound via electrostatic interactions to the CTAB molecules incorporated in the external liposome leaflet. Consequently, the large diameter of the unwound plasmid DNA is likely the major factor that precludes its internalization into the cells by endocytosis. In contrast, anionic vesicles that mimic the cytoplasmic facing monolayer of the plasma membrane rapidly released DNA from the complex. This may explain the previously reported high transfection efficiency of DNA complexed with liposomes composed of neutral lipids and cationic surfactants, since the latter may destabilize the endosomal membrane and induce the release of DNA in the cytoplasm.

Effects of physicochemical characteristics of poly(2-(dimethylamino)ethyl methacrylate)-based polyplexes on cellular association and internalization

The cationic polymer poly(2-(dimethylamino)ethyl methacrylate) (p(DMAEMA)) is able to efficiently bind and condense DNA and to mediate transfection of a variety of cell types. In this study, fluorescence activated cell sorting (FACS), confocal laser fluorescence microscopy (CSLM) and electron microscopy (EM) techniques were used to investigate in vitro the cellular interaction of p(DMAEMA)-based polyplexes with human ovarian carcinoma cells (OVCAR-3). Cellular association and subsequent internalization only occurred when the polyplexes exhibited a positive zeta potential. Small-sized polyplexes have an advantage over large-sized complexes regarding cellular entry. The effect of the presence of tertiary amine groups versus the presence of quatenary amine groups was evaluated by comparing p(DMAEMA) with its quaternary ammonium analogue poly(2-(trimethylamino)ethyl methacrylate) (p(TMAEMA)). The combined cellular interaction and transfection results suggest that the latter polymer does not have an intrinsic endosomal escape property, in contrast to the 'proton sponge' effect proposed for p(DMAEMA). PEGylation of p(DMAEMA) effectively shielded the surface charge and yielded a notably lower degree of cellular interaction. Data on the effects of the presence of endocytosis inhibitors and an endosome-disruptive peptide in the culture medium on the cellular interaction and transfection activity of p(DMAEMA)-based polyplexes support endocytosis as being the principal pathway for intracellular delivery of plasmid. Both the CLSM and EM studies did not reveal the presence of polyplexes or plasmid outside the endocytic vesicles or within the nucleus, suggesting that intracellular trafficking from the endosomes to the nucleus is a very inefficient process.

Effect of DNA complexation and freeze-drying on the physicochemical characteristics of cationic liposomes

We describe the use of saccharides, such as sorbitol, mannitol, sucrose, maltodextrin, and dextran, as cyoprotectants for freeze-drying cationic liposomes. Saccharides can protect liposomes either by interacting with phospholipid headgroups or by forming an amorphous glass surrounding the vesicles, thus preventing aggregation, mechanical rupture of membrane, fusion of liposomes, and drug leakage. We have particularly considered liposome characteristics, such as size, zeta potential, and ability in complexing DNA, before and after freeze-drying. Our study indicates that cationic liposomes are able to maintain liposome characteristics after lyophilization and rehydration and maintain the ability to complex DNA even if the strength of the interaction forces was of lower intensity with respect to liposomes before lyophilization.

Physical stability and in-vitro gene expression efficiency of nebulised lipid-peptide-DNA complexes

The lower respiratory tract provides a number of disease targets for gene therapy. Nebulisation is the most practical system for the aerosolisation of non-viral gene delivery systems. The aerosolisation process represents a significant challenge to the maintenance of the physical stability and biological activity of the gene vector. In this study we investigate the role of a condensing polycationic peptide on the stability and efficiency of nebulised lipid-DNA complexes. Complexes prepared from the cationic lipid 1, 2-dioleoyl-3-trimethylammonium propane (DOTAP) and plasmid DNA (pDNA) at mass (w/w) ratios of 12:1, 6:1 and 3:1, and complexes prepared from DOTAP, the polycationic peptide, protamine, and pDNA (LPD) at 3:2:1 w/w ratio were nebulised using a Pari LC Plus jet nebuliser. Samples from the nebuliser reservoir (pre- and post-nebulisation) and from the aerosol mist were collected and investigated for changes, including: particle diameter, retention of in-vitro transfection activity and the relative concentration and nature of the complexed pDNA remaining after the nebulisation procedure. The process of jet nebulisation adversely affected the physical stability of lipid:pDNA complexes with only those formulated at 12:1 w/w DOTAP:pDNA able to maintain their pre-nebulisation particle size distribution (145+/-3 nm pre-nebulisation vs. 142+/-2 nm aerosol mist) and preserve significant pDNA integrity in the reservoir (35% of pre-nebulisation pDNA band intensity). The LPD complexes were smaller (102+/-1 nm pre-nebulisation vs. 113+/-2 nm aerosol mist) with considerably greater retention of pDNA integrity in the reservoir (90% of pre-nebulisation pDNA band intensity). In contrast the concentration of pDNA in the aerosol mist for both the 12:1 w/w DOTAP:pDNA and LPD complexes were significantly reduced (10 and 12% of pre-nebulised values, respectively). Despite reduced pDNA concentration the transfection (% cells transfected) mediated by aerosol mist for the nebulised complexes was comparatively efficient (LPD aerosol mist 26 vs. 40% for pre-nebulised complex; the respective values for 12: 1 w/w DOTAP:pDNA were 12 vs. 28%). The physical stability and biological activity of nebulised lipid:pDNA complexes can be improved by inclusion of a condensing polycationic peptide such as protamine. The incorporation of the peptide precludes the use of potentially toxic excesses of lipid and charge and may act as a platform for the covalent attachment of peptide signals mediating sub-cellular targetting.

Gene expression in an intact ex-vivo skin tissue model following percutaneous delivery of cationic liposome-plasmid DNA complexes

The skin represents an attractive site for the localised gene therapy of dermatological pathologies and as a potential antigen bioreactor following transdermal delivery. Potential also exists for the gene therapy of skin as a cosmetic intervention. The most exploited non-viral gene delivery system involves the complexation of cationic liposomes with plasmid DNA (pDNA) to form lipid:pDNA vectors that protect the DNA from nuclease-mediated degradation and improve transgene-cell interactions. Despite numerous studies examining the potential for these vectors in delivering genes to a variety of keratinocyte models, investigations into the topical application of such complexes to intact skin tissue is limited. This ex-vivo study, conducted with intact skin tissue derived from hairless mice, provides quantitative confirmation that topical administration of cationic lipid:pDNA complexes can mediate uptake and expression of reporter pDNA (33-fold higher compared with control) in viable epidermal tissue. The ex-vivo study design provides for intact skin tissue that has not been subjected to depilatory procedures of potential detriment to stratum corneum barrier function, and can be utilised for the quantitative and efficient examination of a potentially wide range of non-viral gene vectors designed for epidermal expression.

Pharmaceutical and biological properties of poly(amino acid)/DNA polyplexes

Physicochemical properties of polyplexes formed between pRSVlacZ and poly(amino acid)s were investigated as a paradigm of more complex, synthetic virus-like, DNA delivery systems, that are of interest to many gene delivery laboratories. We observed the interaction between polymer and DNA using ethidium exclusion, and determined the size distributions and the zeta potentials of polyplexes. We correlated these properties with their fundamental interactions with cultured B16 murine melanoma cells, and the resulting efficiency of transfection. A variety of poly(amino acid)s each condensed DNA to produce particles with mean hydrodynamic diameters of approximately 100 nm (a typical span of a population was 80-120nm). Poly(amino acid) polyplexes were unstable in electrolyte solutions such as cell culture media. The apparent particle size increased in electrolyte, depending on the charge ratio, to diameters up to 700 nm. This was thought to be due to aggregation, since neutral particles were most sensitive. When the charge ratio (+/-) exceeded unity polyplexes had positive zeta potentials (which peaked at approximately +30 mV), bound non-specifically to cells, were internalised and in the presence of an endosomolytic agent were able to transfect cells. Though all cationic poly(amino acid)s investigated formed polyplexes with similar physical properties, their biological properties were significantly different. Polyplexes prepared with poly-L-ornithine were the most effective transfection agents, but poly(lys-co-ala, 1: 1) systems appeared to be inactive. This may reflect the differences in uncoupling of DNA and polymer, which is expected to be necessary for passage through the nuclear pore. Uncoupling of polycation and DNA was investigated by exposing the complexes to dextran sulphate. Release of DNA was detected by increased fluorescence at 600 nm in the presence of ethidium. Release of DNA was incomplete from polyplexes formed with high molecular weight polylysine. This may explain the lower levels of transfection observed with high molecular weight polylysine. The significance of these observations for design of advanced non-viral gene delivery systems is discussed.

Mechanisms of gene transfer mediated by lipoplexes associated with targeting ligands or pH-sensitive peptides

Association of a targeting ligand such as transferrin, or an endosome disrupting peptide such as GALA, with cationic liposome-DNA complexes ('lipoplexes') results in a significant enhancement of transfection of several cell types (Simões S et al, Gene Therapy 1998; 5: 955-964). Although these strategies can overcome some of the barriers to gene delivery by lipoplexes, the mechanisms by which they actually enhance tranfection is not known. In studies designed to establish the targeting specificity of transferrin, we found that apo-transferrin enhances transfection to the same extent as transferrin, indicating that internalization of the lipoplexes is mostly independent of transferrin receptors. These observations were reinforced by results obtained from competitive inhibition studies either by preincubating the cells with an excess of free ligand or with various 'receptor-blocking' lipoplexes. Transfection of cells in the presence of drugs that interfere with the endocytotic pathway provided additional insights into the mechanisms of gene delivery by transferrin- or GALA-lipoplexes. Our results indicate that transferrin-lipoplexes deliver transgenes by endocytosis primarily via a non-receptor-mediated mechanism, and that acidification of the endosomes is partially involved in this process.

Preparation and characterization of cationic microspheres for gene delivery

The production and characterization of cationic microparticles based on Eudragit RS and cationic agents (i.e. a cationic acrylic polymer and three different cationic surfactants) for the delivery of nucleic acids is here described. It was found that morphological and dimensional characteristics of microparticles were influenced by the type and concentration of cationic agent employed and by some experimental parameters such as stirring speed, emulsifying agent and type of rotor. The desoxiribonucleotide Defibrotide (DFT) was associated with positively charged microparticles and its in vitro release kinetics from microparticles were determined. A study of the in vitro toxicity of cationic microparticles on cultured human cell line K562 was also performed, demonstrating that DDAB(18) microparticles display very low cytotoxicity.

Pharmaceutical perspectives of nonviral gene therapy

The use of nonviral plasmid-based gene medicines represents an attractive in vivo gene transfer strategy that is simple and lacks many risks that are inherent to viral systems. Commercialization of gene medicines requires a thorough analysis of business opportunities, unmet clinical needs, competitive products under development, and issues related to intellectual property. Synthetic gene delivery systems are designed to control the location of a gene within the body by affecting distribution and access of a gene expression system to the target cell, and/or recognition by a cell surface receptor and uptake followed by intracellular and nuclear translocation. Plasmid-based gene expression systems are designed to control the level, fidelity, and duration of in vivo production of a therapeutic gene product. This review will provide insights into the potentials of plasmid-based gene therapy and critical evaluation of gene delivery sciences and clinical applications of gene medicines.

DNA complexes with block and graft copolymers of N-(2-hydroxypropyl)methacrylamide and 2-(trimethylammonio)ethyl methacrylate

Block and graft copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) with 2-(trimethylammonio)ethyl methacrylate (TMAEM) were synthesized for the preparation of polyelectrolyte complexes with calf thymus DNA intended for targeted delivery of genes in vivo. In this study, the effects of the poly(HPMA) content of copolymers on the parameters of the interpolyelectrolyte complexes is investigated. Static and dynamic light scattering methods were used as a main tool for characterization. The ability of the copolymers to condense DNA was studied by the ethidium bromide displacement method. The stability of the complexes against precipitation in 0.15 M NaCl and the resistance of the complexed DNA to the action of nucleases was also studied. It was found that the presence of poly(HPMA) in the copolymers has not significantly affected the ability of poly(TMAEM) parts of the copolymers to form complexes with DNA, but has an effect on molecular parameters and aggregation (precipitation) of the complexes. The size of the complexes increases with increasing poly(HPMA) content while their apparent molecular weight decreases. The complex stability against precipitation in 0.15 M NaCl strongly depends on the amount of poly(HPMA) in the copolymer structure. The presence of a sufficiently high content of poly(HPMA) is a prerequisite for achieving good stability. The structure of the complexes changes with increasing poly(HPMA) content from soft balls to the polymer coil. The density of the complexes decreases with increasing poly(HPMA) content independently of the copolymer structure. The DNA complexes of all copolymers showed very good nuclease stability.

Gene transfer by DNA-gelatin nanospheres

A DNA and gelatin nanoparticle coacervate containing chloroquine and calcium, and with the cell ligand transferrin covalently bound to the gelatin, has been developed as a gene delivery vehicle. In this study, the coacervation conditions which resulted in the formation of distinct nanoparticles are defined. Nanospheres formed within a narrow range of DNA concentrations and achieved incorporation of more than 98% of the DNA in the reaction. Crosslinking of gelatin to stabilize the particles does not effect the electrophoretic mobility of the DNA. DNA in the nanosphere is partially resistant to digestion with concentrations of DNase I that result in extensive degradation of free DNA but is completely degraded by high concentrations of DNase. Optimum cell transfection by nanosphere DNA required the presence of calcium and nanospheres containing transferrin. The biological integrity of the nanosphere DNA was demonstrated with a model system utilizing DNA encoding the cystic fibrosis transport regulator (CFTR). Transfection of cultured human tracheal epithelial cells (9HTEo) with nanospheres containing this plasmid resulted in CFTR expression in over 50% of the cells. Moreover, human bronchial epithelial cells (IB-3-1) defective in CFTR-mediated chloride transport were complemented with effective transport activity when transfected with nanospheres containing the CFTR transgene.

Lipid fusion in oligonucleotide and gene delivery with cationic lipids

Delivery of oligonucleotides and genes to their intracellular targets is a prerequisite for their successful use in medical therapy. Cationic liposomes are among the most commonly used and promising delivery systems for oligonucleotides and genes. Lipid fusion plays an important role in the cationic liposome-mediated delivery of these compounds. Fusion is involved in the complex formation between the nucleotides and the lipids, in the interactions between extracellular materials with the complexes, as well as in the intracellular trafficking of the delivery system and its load. Since lipid fusion is such a crucial factor in polynucleotide delivery, its controlled use is important for the success in oligonucleotide and DNA delivery. In this article we are reviewing the current knowledge on lipid fusion phenomena associated with the delivery of oligonucleotides and genes.

Biodistribution and gene expression of lipid/plasmid complexes after systemic administration

The objectives of this study were to investigate the influence of physicochemical properties of lipid/plasmid complexes on in vivo gene transfer and biodistribution characteristics. Formulations based on 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) and novel biodegradable cationic lipids, such as ethyl dioleoyl phosphatidylcholine (EDOPC), ethyl palmitoyl myristyl phosphatidylcholine (EPMPC), myristyl myristoyl carnitine ester (MMCE), and oleyl oleoyl L-carnitine ester (DOLCE), were assessed for gene expression after tail vein injection of lipid/plasmid complexes in mice. Gene expression was influenced by cationic lipid structure, cationic lipid-to-colipid molar ratios, plasmid-to-lipid charge ratios, and precondensation liposome size. Detectable levels of human growth hormone (hGH) in serum, human factor IX (hFIX) in plasma, and chloramphenicol acetyltransferase (CAT) in the lung and liver were observed with positively charged lipid/plasmid complexes prepared from 400-nm extruded liposomes with a cationic lipid-to-colipid ratio of 4:1 (mol/mol). Intravenous administration of lipid/CAT plasmid complexes resulted in distribution of plasmid DNA mainly to the lung at 15 min after injection. Plasmid DNA accumulation in the liver increased with time up to 24 hr postinjection. There was a 10-fold decrease in the amount of plasmid DNA in the lung at 15 min after injection, when the lipid/plasmid complex charge ratio was decreased from 3:1 to 0.5:1 (+/-). Bright fluorescent aggregates were evident in in vivo-transfected lung with the positively charged pCMV-CAT/DOLCE:dioleyl phosphatidylethanolamine (DOPE) (1:1, mol/mol) complexes, while more discrete punctate fluorescence was observed with a 4:1 molar ratio of cationic lipid:colipid formulations. Preinjection of polyanions such as plasmid, dextran sulfate, polycytidic acid, and polyinosinic acid decreased hGH expression, whereas the preinjection of both positively charged and neutral liposomes had no effect on hGH serum levels. Of the cationic lipids tested, DOLCE was found to be the most effective potentially biodegradable cationic lipid. A correlation between gene expression and cationic lipid:colipid ratios and lipid-to-plasmid charge ratio was also observed for DOTMA- and DOLCE-based formulations.

A physicochemical approach for predicting the effectiveness of peptide-based gene delivery systems for use in plasmid-based gene therapy

Novel synthetic peptides, based on carrier peptide analogs (YKAKnWK) and an amphipathic peptide (GLFEALLELLESLWELLLEA), have been formulated with DNA plasmids to create peptide-based gene delivery systems. The carrier peptides are used to condense plasmids into nanoparticles with a hydrodynamic diameter (DH) ranging from 40 to 200 nm, which are sterically stable for over 100 h. Size and morphology of the carrier peptide/plasmid complex have been determined by photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM), respectively. The amphipathic peptide is used as a pH-sensitive lytic agent to facilitate release of the plasmid from endosomes after endocytosis of the peptide/plasmid complex. Hemolysis assays have shown that the amphipathic peptide destabilizes lipid bilayers at low pH, mimicking the properties of viral fusogenic peptides. However, circular dichroism studies show that unlike the viral fusion peptides, this amphipathic peptide loses some of its alpha-helical structure at low pH in the presence of liposomes. The peptide-based gene delivery systems were tested for transfection efficiency in a variety of cell lines, including 14-day C2C12 mouse myotubes, using gene expression systems containing the beta-galactosidase reporter gene. Transfection data demonstrate a correlation between in vitro transfection efficiency and the combination of several physical properties of the peptide/plasmid complexes, including 1) DNA dose, 2) the zeta potential of the particle, 3) the requirement of both lytic and carrier peptides, and 4) the number of lysine residues associated with the carrier peptide. Transfection data on 14-day C2C12 myotubes utilizing the therapeutic human growth hormone gene formulated in an optimal peptide gene delivery system show an increase in gene expression over time, with a maximum in protein levels at 96 h (approximately 18 ng/ml).

Receptor-mediated targeted drug or toxin delivery

The new approach to the treatment of cancer or to immunomodulation is drug targeting. Cellular uptake of drugs bound to a targeting carrier or to a targetable polymeric carrier is mostly restricted to receptor-mediated endocytosis. Factors that influence the efficiency of receptor-mediated uptake of targeted drug conjugate are the affinity of the targeting moieties, the affinity and nature of the target antigen, density of the target antigen, the epitope of the target antigen, the type of cell target, the rate of endocytosis, the route of internalization of the ligand-receptor complex, the ability of the drug or toxin to release from its targeted carrier, the ability of the drug or toxin to escape from a vesicular compartment into the cytosol, the affinity of the carrier to the drug and the concentration of the carrier. Targeted chemotherapy is also significantly influenced by the antigenic modulation and/or immunoselection of tumor cells. The binding of drug (toxin) to targetable polymeric carrier considerably decreases unwanted side toxicity.

The efficiency of antioxidants delivered by liposomal transfer

Phenolic antioxidants of the hydroxychroman class, alpha-tocopherol (alpha-TOC) and 2,2,5,6,7-pentamethyl-6-hydroxychroman (PMHC), and the hindered phenols 2,3-dihydro-5-hydroxy-2,2,4-trimethylnaphtho[1,2-b]furan (NFUR), 2,6-di-tert-butyl-4-methoxyphenol (DBHA), and 2,6-di-tert-butyl-4-methyl phenol (BHT), were delivered into oxidizable (ACCEPTOR) liposomes of dilinoleoylphosphatidylcholine (DLPC) or 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC) from saturated DONOR liposomes of dimyristoylphosphatidylcholine (DMPC) by liposomal transfer. The antioxidant activities, k(inh), by the inhibited oxygen uptake method were compared with the k(inh)s determined when the antioxidants were introduced into the liposomes by coevaporation from organic solvents. The peroxidations were initiated using either thermal initiators, water-soluble azo-bis-amidinopropane hydrochloride (ABAP), lipid-soluble azo-bis-2,4-dimethylvaleronitrile (ADVN) and di-tert-butylhyponitrite (DBHN), or the photoinitiator benzophenone. The antioxidants PMHC, NFUR, DBHA, and BHT transferred rapidly between liposomes, but several hours of incubation were needed to transfer alpha-TOC. The average k(inh)s in liposomes, in the relative order NFUR approximately DBHA > PMHC > BHT approximately alpha-TOC, were markedly lower than known values in organic solvent. k(inh) values in liposomes appear to be controlled by effects of hydrogen bonding with water and by restricted diffusion of antioxidants, especially in the case of alpha-TOC. Product studies of the hydroperoxides formed during inhibited oxygen consumption were carried out. The cis,trans/trans,trans (c,t/t,t) product ratios of the 9- and 13-hydroperoxides formed from PLPC during inhibited peroxidation by PMHC were similar for both the coevaporated and liposomal transfer procedures. The c,t/t,t ratio for the same concentration of alpha-TOC, 1.52, compares to a value of 1.69 for PMHC at the start of the inhibition period. The higher c,t/t,t ratio observed for NFUR in DLPC, which varied between values of 7.0 at the start of the inhibition to about 1.8 after the break in the induction period, is a reflection of the increased hydrogen atom donating ability of the antioxidant plus the increased concentration of oxidizable lipid provided by DLPC.

Biomedical applications of nanotechnology--implications for drug targeting and gene therapy

Colloidal particles in the nanometre size range (less than 1 micron in diameter) can be engineered to provide opportunities for the site-specific delivery of drugs after injection into the general circulation or lymphatic systems. Targets include the liver (both Kupffer cells and hepatocytes), endothelial cells, sites of inflammation and lymph nodes. The size and surface of the particle are crucial factors in targeting, and the attachment of cell-specific ligands can lead to increased selectivity. The applications of such particle engineering are discussed in relation to conventional drugs as well as the emerging area of gene therapy.