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

Target delivery of small interfering RNAs with vitamin E-coupled nanoparticles for treating hepatitis C

RNA interference (RNAi) represents a promising strategy for the treatment of HCV infection. However, the development of an effective system for in vivo delivery of small interfering RNA (siRNA) to target organ remains a formidable challenge. Here, we develop a unique nanoparticle platform (VE-DC) composed of α-tocopherol (vitamin E) and cholesterol-based cationic liposomes (DOTAP-Chol) for systemic delivery of siRNAs to the liver. A HCV-replicable cell line, Huh7.5.1-HCV, and a transient HCV core expressing cell line, Huh7.5.1-Core, were constructed and used to assess the in vitro anti-HCV activity of VE-DC/siRNAs. A transient in vivo HCV model was also constructed by hydrodynamic injection of pCDNA3.1(+)-3FLAG-Core (pCore-3FLAG) plasmid expressing core protein or pGL3-5′UTR-luciferase (pGL3-5′UTR-luc) plasmid expressing luciferase driven by HCV 5′UTR. Nanoscale VE-DC/siRNA was intravenously injected to assess the liver-targeting property as well as antiviral activity. The nanoscale VE-DC effectively exerted an anti-HCV activity in the in vitro cell models. Post-administration of VE-DC/siRNAs also effectively delivered siRNAs to the liver, suppressing core protein production and firefly luciferase activity, without inducing an innate immunity response or off-target and toxicity effects. The VE-DC platform has high potential as a vehicle for delivery of siRNAs to the liver for gene therapy for targeting hepatitis C.

Novel cholesterol-based cationic lipids as transfecting agents of DNA for efficient gene delivery

The design, synthesis and biological evaluation of the cationic lipid gene delivery vectors based on cholesterol and natural amino acids lysine or histidine are described. Cationic liposomes composed of the newly synthesized cationic lipids 1a or 1b and neutral lipid DOPE (1,2-dioleoyl-l-α-glycero-3-phosphatidyl-ethanolamine) exhibited good transfection efficiency. pEGFP-N₁ plasmid DNA was transferred into 293T cells by cationic liposomes formed from cationic lipids 1a and 1b, and the transfection activity of the cationic lipids was superior (1a) or parallel (1b) to that of the commercially available 3β-[N-(N',N'-dimethylaminoethyl)-carbamoyl] cholesterol (DC-Chol) derived from the same cholesterol backbone with different head groups. Combined with the results of agarose gel electrophoresis, transfection experiments with various molar ratios of the cationic lipids and DOPE and N/P (+/−) molar charge ratios, a more effective formulation was formed, which could lead to relatively high transfection efficiency. Cationic lipid 1a represents a potential agent for the liposome used in gene delivery due to low cytotoxicity and impressive gene transfection activity.

Peptide amphiphile containing arginine and fatty acyl chains as molecular transporters

Peptide amphiphiles (PAs) are promising tools for the intracellular delivery of numerous drugs. PAs are known to be biodegradable systems. Here, four PA derivatives containing arginine and lysine conjugated with fatty acyl groups with different chain lengths, namely, PA1: R-K(C14)-R, PA2: R-K(C16)-R, PA3: K(C14)-R-K(C14), and PA4: K(C16)-R-K(C16), where C16 = palmitic acid and C14 = myristic acid, were synthesized through Fmoc chemistry. Flow cytometry studies showed that, among all synthesized PAs, only K(C16)-R-K(C16), PA4 was able to enhance the cellular uptake of a fluorescence-labeled anti-HIV drug 2',3'-dideoxy-3'-thiacythidine (F'-3TC, F' = fluorescein) and a biologically important phosphopeptide (F'-PEpYLGLD) in human leukemia cells (CCRF-CEM) after 2 h incubation. For example, the cellular uptake of F'-3TC and F'-PEpYLGLD was enhanced approximately 7.1- and 12.6-fold in the presence of the PA4 compared to those of the drugs alone. Confocal microscopy of F'-3TC and F'-PEpYLGLD loaded PA4 in live cells showed significantly higher intracellular localization than the drug alone in human ovarian cells (SK-OV-3) after 2 h incubation. The high-performance liquid chromatography (HPLC) results showed that loading of Dox by the peptide amphiphile was 56% after 24 h. The loaded Dox was released (34%) within 48 h intracellularly. The circular dichrosim (CD) results exhibited that the secondary structure of the peptide was changed upon interactions with Dox. Mechanistic studies revealed that endocytosis is the major pathway of the internalization. These studies suggest that PAs containing the appropriate sequence of amino acids, chain length, charge, and hydrophobicity can be used as cellular delivery tools for transporting drugs and biomolecules.

Potential implications of nanoparticle characterization on in vitro and in vivo gene delivery

Nanoparticles are rapidly emerging as therapeutic delivery vectors defined by size-dependent properties. They offer several advantages over the traditional drug-delivery systems and medical diagnostics but also pose considerable challenges for systemic applications. Gene delivery is one of the important applications of nanotechnology. Usually, the nanoparticles employed for gene delivery are either formed by condensation of DNA with preformed cationic polymers or by polymerization of monomeric units thereby entrapping DNA in it. The physicochemical properties such as size, shape, surface morphology have been found to have significant influence on the gene-delivery efficacy of nanoparticles. Furthermore, when administered in vitro and in vivo, the efficiency of nanoparticles depends on a wide variety of other parameters, that is, transfection conditions, time of exposure, cell type and so forth. In this review, the potential role of characterization of nanoparticles physicochemical properties on the in vitro and in vivo gene delivery efficacy of nanoparticles is discussed.

Slow release and delivery of antisense oligonucleotide drug by self-assembled peptide amphiphile nanofibers

Antisense oligonucleotides provide a promising therapeutic approach for several disorders including cancer. Chemical stability, controlled release, and intracellular delivery are crucial factors determining their efficacy. Gels composed of nanofibrous peptide network have been previously suggested as carriers for controlled delivery of drugs to improve stability and to provide controlled release, but have not been used for oligonucleotide delivery. In this work, a self-assembled peptide nanofibrous system is formed by mixing a cationic peptide amphiphile (PA) with Bcl-2 antisense oligodeoxynucleotide (ODN), G3139, through electrostatic interactions. The self-assembly of PA-ODN gel was characterized by circular dichroism, rheology, atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM images revealed establishment of the nanofibrous PA-ODN network. Due to the electrostatic interactions between PA and ODN, ODN release can be controlled by changing PA and ODN concentrations in the PA-ODN gel. Cellular delivery of the ODN by PA-ODN nanofiber complex was observed by using fluorescently labeled ODN molecule. Cells incubated with PA-ODN complex had enhanced cellular uptake compared to cells incubated with naked ODN. Furthermore, Bcl-2 mRNA amounts were lower in MCF-7 human breast cancer cells in the presence of PA-ODN complex compared to naked ODN and mismatch ODN evidenced by quantitative RT-PCR studies. These results suggest that PA molecules can control ODN release, enhance cellular uptake and present a novel efficient approach for gene therapy studies and oligonucleotide based drug delivery.

Improvements in transfection efficiency with chitosan modified poly(DL-lactide-co-glycolide) nanospheres prepared by the emulsion solvent diffusion method, for gene delivery

This study sought to evaluate the in vitro transfection efficiency of plasmid DNA (pDNA)-loaded chitosan-modified poly(DL-lactide-co-glycolide) nanospheres (CS-PLGA NS) in a gene-delivery system. Using the emulsion solvent diffusion (ESD) method, pDNA-loaded PLGA NS was prepared and the surface of the PLGA NS was modified by binding to CS. Gene transfection ability of CS-PLGA NS was examined in A549 cells. The luciferase gene was used as a reporter gene. The pattern of luciferase activity by pDNA-loaded CS-PLGA NS was initially weak, but gradually grew stronger before decreasing activity. These phenomena should be in accordance with the sustained-release profile of pDNA from PLGA NS in the cytosol and the pDNA protection against DNase. Positively charged CS-PLGA NS was found, by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay, not to exhibit cytotoxicity on A549 cells. These results suggest that CS-PLGA NS are potential contributors to efficient pDNA delivery due to their increased interactions with cells and lack of cytotoxic effects.

Emerging links between surface nanotechnology and endocytosis: impact on nonviral gene delivery

Significant effort continues to be exerted toward the improvement of transfection mediated by nonviral vectors. These endeavors are often focused on the design of particulate carriers with properties that encourage efficient accumulation at the membrane surface, particle uptake, and endosomal escape. Despite its demonstrated importance in successful nonviral transfection, relatively little investigation has been done to understand the pressures driving internalized vectors into favorable nondegradative endocytic pathways. Improvements in transfection efficiency have been noted for complexes delivered with a substrate-mediated approach, but the reasons behind such enhancements remain unclear. The phenotypic changes exhibited by cells interacting with nano- and micro-featured substrates offer hints that may explain these effects. This review describes nanoscale particulate and substrate parameters that influence both the uptake of nonviral gene carriers and the endocytic phenotype of interacting cells, and explores the molecular links that may mediate these interactions. Substrate-mediated control of endocytosis represents an exciting new design parameter that will guide the creation of efficient transgene carriers.

Chitosan-modified poly(D,L-lactide-co-glycolide) nanospheres for improving siRNA delivery and gene-silencing effects

Chitosan (CS) surface-modified poly(d,l-lactide-co-glycolide) (PLGA) nanospheres (NS) for a siRNA delivery system were evaluated in vitro. siRNA-loaded PLGA NS were prepared by an emulsion solvent diffusion (ESD) method, and the physicochemical properties of NS were investigated. The level of targeted protein expression and siRNA uptake were examined in A549 cells. CS-modified PLGA NS exhibited much higher encapsulation efficiency than unmodified PLGA NS (plain-PLGA NS). CS-modified PLGA NS showed a positive zeta potential, while plain-PLGA NS were negatively charged. siRNA uptake studies by observation with confocal leaser scanning microscopy (CLSM) indicated that siRNA-loaded CS-modified PLGA NS were more effectively taken up by the cells than plain-PLGA NS. The efficiencies of different siRNA preparations were compared at the level of targeted protein expression. The gene-silencing efficiency of CS-modified PLGA NS was higher and more prolonged than those of plain-PLGA NS and naked siRNA. This result correlated with the CLSM studies, which may have been due to higher cellular uptake of CS-modified PLGA NS due to electrostatic interactions. It was concluded that CS-modified PLGA NS containing siRNA could provide an effective siRNA delivery system.

"Soft" calcium crosslinks enable highly efficient gene transfection using TAT peptide

PURPOSE

Typically, low molecular weight cationic peptides or polymers exhibit poor transfection efficiency due to an inability to condense plasmid DNA into small nanoparticles. Here, efficient gene delivery was attained using TAT/pDNA complexes containing calcium crosslinks.

METHODS

Electrostatic complexes of pDNA with TAT or PEI were studied with increasing calcium concentration. Gel electrophoresis was used to determine DNA condensation. The morphology of the complexes was probed by transmission electron microscopy. Transfection efficiency was assessed using a luciferase reporter plasmid. The accessibility of phosphate and amine groups within complexes was evaluated to determine the effect of calcium on structure.

RESULTS

TAT/pDNA complexes were condensed into small, 50-100 nm particles by optimizing the concentration of calcium. Complexes optimized for small size also exhibited higher transfection efficiency than PEI polyplexes in A549 cells. TAT and TAT complexes displayed negligible cytotoxicity up to 5 mg/mL, while PEI exhibited high cytotoxicity, as expected. Probing the TAT-Ca/pDNA structure suggested that calcium interacted with both phosphate and amine groups to compact the complexes; however, these "soft" crosslinks could be competitively disrupted to facilitate DNA release.

CONCLUSION

Small and stable TAT-Ca/pDNA complexes were obtained via "soft" calcium crosslinks leading to sustained gene expression levels higher than observed for control PEI gene vectors. TAT-Ca/pDNA complexes were stable, maintaining particle size and transfection efficiency even in the presence of 10% of FBS. TAT-Ca complexes offer an effective vehicle offering potential for translatable gene delivery.

Antitumor activity and prolonged survival by carbon-nanotube-mediated therapeutic siRNA silencing in a human lung xenograft model

Carbon nanotubes are novel nanomaterials that are thought to offer potential benefits to a variety of biomedical and clinical applications. In this study, the treatment of a human lung carcinoma model in vivo using siRNA sequences leading to cytotoxicity and cell death is carried out using either cationic liposomes (DOTAP:cholesterol) or amino-functionalized multi-walled carbon nanotubes (MWNT - NH(+)(3)). Validation for the most cytotoxic siRNA sequence using a panel of human carcinoma and murine cells reveals that the proprietary siTOX sequence is human specific and can lead to significant cytotoxic activities delivered both by liposome or MWNT - NH(+)(3) in vitro. A comparative study using both types of vector indicates that only MWNT - NH(+)(3):siRNA complexes administered intratumorally can elicit delayed tumor growth and increased survival of xenograft-bearing animals. siTOX delivery via the cationic MWNT - NH(+)(3) is biologically active in vivo by triggering an apoptotic cascade, leading to extensive necrosis of the human tumor mass. This suggests that carbon-nanotube-mediated delivery of siRNA by intratumoral administration leads to successful and statistically significant suppression of tumor volume, followed by a concomitant prolongation of survival of human lung tumor-bearing animals. The direct comparison between carbon nanotubes and liposomes demonstrates the potential advantages offered by carbon nanotubes for the intracellular delivery of therapeutic agents in vivo. The present work may act as the impetus for further studies to explore the therapeutic capacity of chemically functionalized carbon nanotubes to deliver siRNA directly into the cytoplasm of target cells and achieve effective therapeutic silencing in various disease indications where local delivery is feasible or desirable.

Vault nanoparticles containing an adenovirus-derived membrane lytic protein facilitate toxin and gene transfer

Nonviral methods of gene delivery possess several advantages over that of viral-based vectors, including having increased safety. However, the ability to achieve effective transport of therapeutic molecules across host cell membranes via nonviral methods remains a significant goal. Cell-derived nanoparticles known as vaults have been proposed as novel candidate transfer vehicles for various foreign molecules. Recombinant vault particles enter cells via macropinocytosis or phagocytosis but lack demonstrable membrane penetrating activity. To explore the feasibility of improving vault penetration into target cells, we incorporated the membrane lytic domain of adenovirus protein VI (pVI) into the interior of recombinant vault particles via fusion to the vault poly(ADP-ribose) polymerase (VPARP) interaction domain. The membrane lytic activity of the pVI domain was retained upon incorporation into vault particles. Moreover, internalization of vault-pVI complexes into murine macrophages promoted co-delivery of a soluble ribotoxin or a cDNA plasmid encoding GFP. These findings indicate that vault particles can be modified to enhance cell transfer of selected biomolecules.

Very long chain N4, N9 -diacyl spermines: non-viral lipopolyamine vectors for efficient plasmid DNA and siRNA delivery

PURPOSE

To study the effect of increasing the chain length over C-18 and varying the oxidation level in synthesized N4, N9-diacyl spermines on DNA and siRNA formulation, and then to compare their transfection efficiency in cell lines

METHODS

The five novel very long chain N4, N9-diacyl polyamines: N4, N9-[diarachidoyl, diarachidonoyl, dieicosenoyl, dierucoyl and dinervonoyl]-1,12-diamino-4,9-diazadodecane were synthesized. The abilities of these novel compounds to condense DNA and to form nanoparticles were studied using ethidium bromide fluorescence quenching and nanoparticle characterization techniques. Transfection efficiency was studied in FEK4 primary skin cells and in an immortalized cancer cell line (HtTA), and compared with the non-liposomal transfection formulation Lipogen, N4, N9-dioleoyl-1,12-diamino-4,9-diazadodecane. Also, the abilities of these compounds to condense siRNA and to form nanoparticles were studied using a RiboGreen intercalation assay and their abilities to deliver siRNA into cells were studied in FEK4 and HtTA cells using fluorescein-labelled Label IT(R) RNAi Delivery Control, a sequenced 21-mer from Mirus.

RESULTS

We show efficient pEGFP and siRNA formulation and delivery to primary skin and cancer cell lines.

CONCLUSIONS

Adding two C20 or C22 chains, both mono-cis-unsaturated, N4, N9-dieicosenoyl spermine and N4, N9-dierucoyl spermine, gave efficient siRNA delivery vectors, even in the presence of serum, comparable to TransIT-TKO and with excellent cell viability.

Establishing chitosan coated PLGA nanosphere platform loaded with wide variety of nucleic acid by complexation with cationic compound for gene delivery

The purpose of this paper was to establish the surface modified poly(d,l-lactide-co-glycolide) (PLGA) nanosphere platform with chitosan (CS) for gene delivery by using the emulsion solvent diffusion (ESD) method. The advantages of this method are a simple process under mild conditions without sonication. This method requires essentially dissolving both polymer and drug in the organic solvent. Therefore a hydrophilic drug such as nucleic acid is hardly applied to the ESD method. Nucleic acid can easily form an ion-complex with cationic compound, which can be dissolved in the organic solvent. Thereafter, nucleic acid solubility for organic solution can increase by complexation with cationic compound. We used DOTAP as a cationic compound to increase the loading efficiency of nucleic acid. By coating the PLGA nanospheres with CS, the loading efficiency of nucleic acid in the modified nanospheres increased significantly. The release profile of nucleic acid from PLGA nanospheres exhibited sustained release after initial burst. The PLGA nanospheres coated with chitosan reduced the initial burst of nucleic acid release and prolonged the drugs releasing at later stage. Chitosan coated PLGA nanosphere platform was established to encapsulate satisfactorily wide variety of nucleic acid for an acceptable gene delivery system.

Varying the unsaturation in N4,N9-dioctadecanoyl spermines: nonviral lipopolyamine vectors for more efficient plasmid DNA formulation

PURPOSE

The aim of the study is to analyze the effect of varying the degree of unsaturation in synthesized N4,N9-dioctadecanoyl spermines on DNA condensation and then to compare their transfection efficiency in cell culture.

METHODS

The N4,N9-di-C18 lipopolyamines-saturated (stearoyl), C9-cis- (oleoyl), and C9,12-di-cis- (linoleoyl)-were synthesized from the naturally occurring polyamine spermine. The ability of these novel compounds to condense DNA and form nanoparticles was studied using ethidium bromide fluorescence quenching and nanoparticle characterization techniques. Transfection efficiency was studied in several primary skin cells (FEK4, FCP4, FCP5, FCP7, and FCP8) and in an immortalized cancer cell line (HtTA) and was compared with the commercially available nonliposomal transfection formulation Transfectam (dioctadecylamidoglycyl spermine), which also contains two saturated C18 lipid chains.

RESULTS

N4,N9-Dilinoleoyl spermine (C18, di-cis-9,12) is efficient at circular plasmid DNA (pEGFP) condensation and gives the most effective transfection in a series of primary skin cells and cancer cell lines at low charge ratios of 5.5 (+/-ammonium/phosphate).

CONCLUSIONS

The dienoic fatty acyl spermine conjugate N4,N9-dilinoleoyl spermine efficiently condenses DNA and achieves the highest transfection levels among the studied lipopolyamines in cultured cells.

Towards improved gene delivery: Flip of cationic lipids in highly polarized liposomes

Hyperpolarization of cationic liposomes improves their stability in the presence of human serum albumin.

Analytical and biological characterization of supercoiled plasmids purified by various chromatographic techniques

Supercoiled plasmids are an important component of gene-based delivery vehicles. A number of production methods for clinical applications have been developed, each resulting in very high-quality product with low levels of residual contaminants. There is, however, no consensus on the optimal methods to characterize plasmid quality, and further, to determine if these methods are predictive of either product stability or biological activity. We have produced two plasmids using four production purification methodologies based on PolyFlo and hydrophobic interaction chromatography (HIC), either alone or in tandem processes. In each case, the product was analyzed using standard molecular biological methods. We also performed a number of biophysical analyses such as dynamic light scattering (DLS), circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Minimal differences were detected among the preparations based on the more standard molecular biological methods. Some small differences were detected, however, using biophysical techniques, particularly FTIR and DSC, which may reflect small variations in plasmid tertiary structure and thermal stability. Stability after heat exposure at 60 degrees C, exposure to fetal bovine serum and long-term storage at 4 degrees C varied between plasmids. One plasmid showed no difference in stability depending on the production process, but the other showed significant differences. Evaluation in vivo in models for gene immunization and gene therapy showed significant differences in the response depending on the method of purification. Preparations using a tandem process of PolyFlo used in two separation modes provided higher biological activity compared to a tandem HIC/PolyFlo process or either resin used alone in a single column process. These data indicate that the process by which supercoiled plasmids are made can influence plasmid stability and biological activity and emphasize the need for more rigorous methods to evaluate supercoiled plasmids as gene-delivery vehicles.

Induction of apoptosis in A549 human lung cancer cells by all-trans retinoic acid incorporated in DOTAP/cholesterol liposomes

All-trans retinoic acid (ATRA) has been shown to exert anti-cancer activities in a number of types of cancer cells. However, it has been reported that many NSCLC exhibited resistance to ATRA treatment. In the present study, we hypothesized that intracellular delivery of ATRA would overcome the ATRA resistance in A549 cells. Here, we investigated the induction of apoptosis by ATRA incorporated in cationic liposomes composed of DOTAP/cholesterol in A549 human lung cancer cells, which are insensitive (resistant) to the growth inhibitory effects of ATRA. The zeta potentials of DOTAP/cholesterol liposomes and DSPC/cholesterol liposomes were about +50 and -3 mV. In A549 cells, [(3)H]ATRA incorporated in DOTAP liposomes showed increased cellular association compared with [(3)H]ATRA or [(3)H]ATRA incorporated in DSPC/cholesterol liposomes. ATRA incorporated in DOTAP/cholesterol liposomes showed much higher cytotoxic effects and apoptosis-inducing activity compared with ATRA or ATRA incorporated in DSPC/cholesterol liposomes. The enhanced expression of TIG3 mRNA tumor suppressor gene by ATRA incorporation into DOTAP/cholesterol liposomes might partly explain the mechanism of enhanced cytotoxicity and/or apoptosis. These observations provide valuable information to help in the design of differentiation therapy by ATRA in non-small cell lung carcinoma.

New perfluorinated polycationic dimerizable detergents for the formulation of monomolecular DNA nanoparticles and their in vitro transfection efficiency

We describe the synthesis of new perfluorinated dimerizable detergents which contain a tricationic or tetracationic (linear or branched spermine, respectively) polar head, and report on their cmc, their ability to condense DNA into cationic monomolecular DNA nanoparticles as well as on the in vitro transfection efficiency of these nanoparticles. Such cationic nanoparticles were prone to display efficient cell transfection properties as a result of increased contact to the anionic cell surface and internalization by endocytosis, low size compatible with improved intracellular diffusion and nuclear pore crossing, and the presence of amine function of low pK(a) for their endosomal escape. The challenge was to design polymerizable polycationic detergents that display a cmc high enough for the monomer to perform monomolecular DNA condensation (as cationic particles) and low enough for the dimer to form stable nanoparticles capable of efficient cell transfection. Although we succeeded in formulating small-sized cationic monomolecular DNA nanoparticles (<40 nm) with these dimerizable perfluorinated spermine-based detergents for N/P ratios of up to 5 (N=number of detergent amine equivalents/P=number of DNA phosphate equivalents), these small-sized cationic nanoparticles proved to be poor non-specific transfection agents in vitro, even in the presence of chloroquine. Their poor transfection potential could be due more likely to Brownian motion which prevents these very small-sized particles from sedimentation and adsorption onto the adherent cell monolayer, and, consequently, from proteoglycan-triggered endocytosis.

A method to evaluate the effect of liposome lipid composition on its interaction with the erythrocyte plasma membrane

Lipid aggregates are considered promising carriers for macromolecules and toxic drugs. In order to fulfill this function, aggregates should have properties that ensure the efficient delivery of their cargo to the desired location. One of these properties is their stability in blood when accumulating in the targeted tissue. This stability may be affected by a number of factors, including enzymatic activity, protein adsorption, and non-specific lipid exchange between the aggregate and morphological blood components. Since blood cells in the majority consist of erythrocytes, their interaction with aggregates should be carefully analyzed. In this paper, we present a method that allows the exchange of lipid between liposomes and the erythrocyte plasma membrane to be evaluated. The extent of this exchange was measured in terms of the toxicity of a cationic lipid (DOTAP) incorporated into the liposome lipid bilayer, evaluated by plasma membrane mechanical properties. After liposomes were formed from DOTAP/PC or DOTAP/PE mixtures, erythrocyte plasma membranes were destabilized in a manner dependent on DOTAP concentration. A constant quantity of DOTAP mixed with various proportions of SM caused no such effect, indicating very limited lipid exchange with the cell membrane for such liposome formulations.

A stopped-flow kinetic study of the assembly of nonviral gene delivery complexes

Stopped-flow circular dichroism and fluorescence spectroscopy are used to characterize the assembly of complexes consisting of plasmid DNA bound to the cationic lipids dimethyldioctadecylammonium bromide and 1, 2-dioleoyl- 3-trimethylammonium-propane and a series of polyamidoamine dendrimers. The kinetics of complexation determined from the stopped-flow circular dichroism measurements suggests complexation occurs within 50 ms. Further analysis, however, was precluded by the presence of mixing (shear) artifacts. Stopped-flow fluorescence employing the high-affinity DNA dyes Hoechst 33258 and YOYO-1 was able to resolve two sequential steps in the assembly of complexes that are assigned to binding/dehydration and condensation events. The rates of each process were determined over the temperature range of 10-50 degrees C and activation energies were determined from the slope of Arrhenius plots. The behavior of polyamidoamine dendrimers can be separated into two classes based on their differing binding modes: generation 2 and the larger generations (G4, G7, and G9). The larger generations have activation energies for binding that follow the trend G4 > G7 > G9. The activation energies for condensation (compaction) of complexes composed of these same dendrimers have the opposite trend G9 > G7 > G4. It is postulated that a balance between a more energetically favorable condensation and less favorable binding may prove beneficial in enhancing gene delivery.

Structure/Function Relationships of Polyamidoamine/DNA Dendrimers as Gene Delivery Vehicles

PAMAM dendrimers are members of a class of polyamine polymers that demonstrate significant gene delivery ability. In this study, a selection of PAMAM dendrimers, spanning a range of sizes (generations 2, 4, 7, and 9) and transfection efficiencies, are characterized by various biophysical methods to search for structural properties that correlate with transfection. Measurements of colloidal properties (size and zeta potential) as a function of charge ratio reveal that highly transfecting dendrimer/DNA complexes have size/zeta potential values between 4 and 8. Circular dichroism (CD) and FTIR spectroscopy of complexes confirm the DNA component remains in B form when associated with all dendrimer generations up to a 5:1 charge ratio (+/-). Isothermal titration calorimetry and differential scanning calorimetry detect changes that are related to polymer structure and charge ratio but do not directly correlate with transfection efficiency. Despite DNA structural and stability changes detected by CD, FTIR, DSC, and ITC that are similar to those seen with other cationic delivery vehicles [e.g., cationic lipids, peptoids/lipitoids, peptides, polyethyleneimines (PEIs), etc.], clear correlations with transfection activity are not readily apparent. This may be due, at least in part, to the heterogeneity of the complexes.