Importance of liposome complexing volume in transfection optimization

Advancing nonviral gene delivery: lipid- and surfactant-based nanoparticle design strategies

Gene therapy is a technique utilized to treat diseases caused by missing, defective or overexpressing genes. Although viral vectors transfect cells efficiently, risks associated with their use limit their clinical applications. Nonviral delivery systems are safer, easier to manufacture, more versatile and cost effective. However, their transfection efficiency lags behind that of viral vectors. Many groups have dedicated considerable effort to improve the efficiency of nonviral gene delivery systems and are investigating complexes composed of DNA and soft materials such as lipids, polymers, peptides, dendrimers and gemini surfactants. The bottom-up approach in the design of these nanoparticles combines components essential for high levels of transfection, biocompatibility and tissue-targeting ability. This article provides an overview of the strategies employed to improve in vitro and in vivo transfection, focusing on the use of cationic lipids and surfactants as building blocks for nonviral gene delivery systems.

Induction of human alveolar epithelial cell growth factor receptors by dendrimeric nanostructures

Although nonviral dendrimeric nanostructures have been widely used as gene delivery systems, key questions about target cells responses to these nanostructures are yet to be answered. Here, we report the responsiveness of A431 and A549 cells upon treatment with polypropylenimine diaminobutane (DAB) dendrimers nanosystems. Complexation of DAB dendrimers with DNA reduced the zeta potential of nanostructures, but increased their size. Fluorescence microscopy revealed high transfection efficiency in both cell lines treated with DAB dendrimers with induced cytotoxicity evidenced by MTT assay. The A549 cells showed upregulation of epidermal growth factor receptor (EGFR) and its downstream signalling biomolecule Akt kinase upon treatment with DAB dendrimers, while no changes were observed in A431 cells. Based on our findings, the biological impacts of these nanosystems appeared to be cell dependent. Thus, the biological responses of target cells should be taken into account when these nanostructures are used as gene delivery system.

Characterization of the interaction between P143 and LEF-3 from two different baculovirus species: Choristoneura fumiferana nucleopolyhedrovirus LEF-3 can complement Autographa californica nucleopolyhedrovirus LEF-3 in supporting DNA replication

The baculovirus protein P143 is essential for viral DNA replication in vivo, likely as a DNA helicase. We have demonstrated that another viral protein, LEF-3, first described as a single-stranded DNA binding protein, is required for transporting P143 into the nuclei of insect cells. Both of these proteins, along with several other early viral proteins, are also essential for DNA replication in transient assays. We now describe the identification, nucleotide sequences, and transcription patterns of the Choristoneura fumiferana nucleopolyhedrovirus (CfMNPV) homologues of p143 and lef-3 and demonstrate that CfMNPV LEF-3 is also responsible for P143 localization to the nucleus. We predicted that the interaction between P143 and LEF-3 might be critical for cross-species complementation of DNA replication. Support for this hypothesis was generated by substitution of heterologous P143 and LEF-3 between two different baculovirus species, Autographa californica nucleopolyhedrovirus and CfMNPV, in transient DNA replication assays. The results suggest that the P143-LEF-3 complex is an important baculovirus replication factor.

Polyion complex micelles from plasmid DNA and poly(ethylene glycol)-poly(L-lysine) block copolymer as serum-tolerable polyplex system: physicochemical properties of micelles relevant to gene transfection efficiency

Polyion complex (PIC) micelles composed of the poly(ethylene glycol)-poly(L-lysine) (PEG-PLL) block copolymer and plasmid DNA (pDNA) were investigated in this study from a physicochemical viewpoint to get insight into the structural feature of the PIC micellar vector system to show practical gene transfection efficacy particularly under serum-containing medium. The residual ratio (r) of the lysine units in PEG-PLL to the phosphate units of pDNA in the system significantly affects the size of the PIC micelles evaluated from dynamic light scattering, being decreased from approximately 120 to 80 nm with an increase in the r value for the region with r > or = 1.0. The zeta potential of the complexes slightly increased with r in the same region, yet maintained a very small absolute value and leveled off to a few mV at r approximately 2.0. These results suggest that the micelles are most likely to take the core-shell structure with dense PEG palisades surrounding the PIC core to compartmentalize the condensed pDNA. Furthermore, an increasing r value in the region of r > or = 1 induces a rearrangement of the stoichiometric complex formed at r=1.0 to the non-stoichiometric complex composed of the excess block copolymer. The association number of pDNA and the block copolymer in the micelle was estimated from the apparent micellar molecular weight determined by static light scattering measurements, indicating that a single pDNA molecule was incorporated in each of the micelles prepared from the PEG (Mw=12,000 g/mol)-PLL (polymerization degree of PLL segment: 48) (12-48) block copolymer at r=2.0. These 12-48/pDNA micelles showed a gene expression comparable to the lipofection toward cultured 293 cells, though 100 microM chloroquine was required in the transfection medium. Notably, even in the presence of serum, the PIC micelles achieved appreciable cellular association to attain a high gene expression, which is in sharp contrast with the drastic decrease in the gene expression for lipoplex system in the presence of serum. A virus-comparable size (approximately 100 nm) with a serum-tolerable property of the PIC micelles indeed suggests their promising feasibility as non-viral gene-vector systems used for clinical gene therapy.

The use of fluorescence resonance energy transfer to monitor dynamic changes of lipid-DNA interactions during lipoplex formation

Fluorescence resonance energy transfer (FRET) was used to monitor interactions between Cy3-labeled plasmid DNA and NBD-labeled cationic liposomes. FRET data show that binding of cationic liposomes to DNA occurs immediately upon mixing (within 1 min), but FRET efficiencies do not stabilize for 1-5 h. The time allowed for complex formation has effects on in vitro luciferase transfection efficiencies of DOPE-based lipoplexes; i.e., lipoplexes prepared with a 1-h incubation have much higher transfection efficiencies than samples with 1-min or 5-h incubations. The molar charge ratio of DOTAP to negatively charged phosphates in the DNA (DOTAP+/DNA-) also affected the interaction between liposomes and plasmid DNA, and interactions stabilized more rapidly at higher charge ratios. Lipoplexes formulated with DOPE were more resistant to high ionic strength than complexes formulated with cholesterol. Taken together, our data demonstrate that lipid-DNA interactions and in vitro transfection efficiencies are strongly affected by the time allowed for complex formation. This effect is especially evident in DOPE-based lipoplexes, and suggests that the time allowed for lipoplex formation is a parameter that should be carefully controlled in future studies.

Biochemical and biophysical characteristics of lipoplexes pertinent to solid tumour gene therapy

Cationic liposomes have become the reagent of choice for transfer of nucleic acids such as plasmids and oligodeoxynucleotides to cells in culture and in vivo. Whilst these reagents have several advantages over other forms of nucleic acid transfer methods, toxicity remains a significant problem, especially in vivo. Recent studies have also highlighted the immunostimulatory nature of these cationic vesicles when complexed to plasmid DNA, a phenomenon that may be harnessed for efficacious usage against tumours. Current research in this dynamic technological field is aimed at the development of cationic lipids that have negligible toxic effects and enhanced transfection capabilities.

Expression of beta-galactosidase gene and endothelial nitric oxide synthase gene in rat vascular smooth muscle cells after in vitro lipotransfection

The aim of this study was to optimize the conditions for in vitro lipotransfection of rat vascular smooth muscle cells (VSMC) with bacterial beta-galactosidase gene and bovine endothelial nitric oxide synthase (ecNOS) gene. Transfection efficiency of four liposomes: Transfectam, Lipofectin, Unifectin-10, and Maxifectin was compared. The best results (efficiency 1-5%) were obtained with Maxifectin, when transfections were performed in VSMC cultures being at 50% confluency, with 1 microg DNA and 10 microl liposome per well, and when the liposome/DNA complexes were coincubated with the cells for 24 h. This method allowed detection of the transgene activity 12 h after the beginning of the transfection, with maximum values between the second and fourth days. The expression of the potentially therapeutic ecNOS gene was evidenced by confirmation of ecNOS mRNA generation, indirect detection of active ecNOS protein and by measurement of nitrite ion accumulation in the medium from the transfected cell cultures.

Lipoplexes and tumours. A review

The need for genotherapy to refocus its attention on to laboratory evaluation of better methods rather than proceeding to the clinic with semi-apt tools for genetic transfer has been highlighted in clinical study reports documented to date. Quintessential for tumour genotherapy is the ability to target abnormal cells, hence reducing exposure of normal cells to genetic material whilst maximizing gene dosage to tumour cells. This becomes increasingly important as genotherapy establishes itself in the clinic alongside the older modes of treatment. This review has discussed the applicability of lipoplexes for genotherapy of solid tumours. Lipoplexes have been used extensively for gene transfer into cells, such as cancerous cells, deficient for a certain gene product. While cationic liposomes have many advantages over other forms of delivery mechanisms, several problems hinder their use in-vivo. A closer examination of the physical limitations of current lipoplex preparations, the development and testing of novel formulations, combined with more attention to the cellular processes of cell membrane breaching and nuclear entry, may enhance gene delivery. Essential for tumour genotherapy is the ability to target these lipoplexes into tumour sites whilst reducing gene dosage to other normal tissues. Development of a better lipofection agent may indeed require a collaboration of the fields of physiology, cell biology, molecular biology, biochemistry, chemistry and membrane physics.

Lipoplex size is a major determinant of in vitro lipofection efficiency

The inhibition effect of serum on the transfection efficiency of cationic liposome-DNA complexes (lipoplexes) is a major obstacle to the application of this gene delivery vector both in vitro and in vivo. The size of the lipoplexes, as they are presented to targeted cells, is found to be the major determinant of their effectiveness in transfection. The transfection efficiency and the cell association and uptake of lipoplexes with CHO cells was found to increase with increasing lipoplex size. The influence on the transfection efficiency of lipoplexes by their cationic lipid:DNA ratios, types of liposomes, incubation time in polyanion containing media, and time of serum addition, are mediated mainly through size. Lipoplexes at a 2:1 charge ratio grow in size in media containing polyanions. The size growth may be arrested by adding serum to the incubation media. By using large lipoplexes, especially those made from multilamellar vesicles, the serum inhibition effect may be overcome.

Phosphate-enhanced transfection of cationic lipid-complexed mRNA and plasmid DNA

Cationic lipid-mediated gene transfer has been shown to be a competent albeit inefficient mechanism of promoting cellular gene transfer. One way to improve the efficacy of cationic lipid-mediated transgene expression is to optimize conditions for complex formation between the lipids and nucleic acids. In this report we describe the beneficial effects of using phosphate buffer to precondition lipofectin (a 1:1 (w/w) mixture of N-[1-(2,3-dioleyloxy)propyl]-n,n, n-trimethylammonium chloride (DOTMA), and dioleoyl phosphatidylethanolamine (DOPE)) prior to complexing with plasmid DNA or mRNA. Under such optimized conditions we studied the kinetics of DNA- and RNA-mediated transgene expression in a human osteosarcoma cell line (HOS). Preincubation of lipofectin in phosphate buffer resulted in up to 26- and 56-fold increases in luciferase expression from plasmid DNA and mRNA, respectively. Addition of chloroquine (50 microM), which enhanced plasmid-mediated gene delivery 3-fold, was synergistic with phosphate resulting in an additional 46-fold increase in luciferase expression. The preincubation with phosphate shortened both the time required for cellular uptake and the time to achieve maximal transgene expression. Optimal transfection was achieved in the presence of 30-80 mM phosphate, at pH 5.6-6.8 under which the phosphate anion is divalent. The effect of phosphate anion was specific in that monovalent Cl- and acetate anions were not stimulatory. These results demonstrate that divalent phosphate anion plays a stimulatory role during complex formation and transfection when cationic lipids come in contact with negatively charged nucleic acids and cell membranes. These findings delineate specific conditions which dramatically enhance transfection efficiency for both DNA and mRNA, and provide an effective procedure for gene transfection studies.

Enhanced anticancer therapy mediated by specialized liposomes

It has been a central aim of experimental and clinical therapeutics to deliver therapeutic agents as close as possible to, or if possible within, a diseased cell. Such targeting achieves two major aims of drug delivery, the maximum dose of therapeutic agent to the diseased cell and avoidance of uptake by and, usually, accompanying side-effects to normal, healthy cells. Conventional liposomes, originally used for studies in membrane biophysics and biochemistry, have been used in therapy for the past two decades. However, when applied to deliver drugs into cells, conventional liposomes proved inefficient and so novel unconventional or specialized liposomes are constantly being prepared to enhance cell-specific delivery in-vivo. One possible way of achieving better targeting is combination of the positive attributes of more than one specialized type of liposome into one vesicle. Although a limited number of studies has examined the combined effect of such dual-specialty liposomes, more studies are warranted using appropriate models. Liposomes are composed of one, a few, or many concentric bilayer membranes which alternate with aqueous spaces. The drugs are encapsulated within the aqueous internal volume if they are hydrophilic or in the lipid bilayers if they are hydrophobic (Kim 1993). Liposomes range in size from 25 nm to more than 20 microns (Sugarman & Perez-Soler 1992). Depending on their solubility and method of formulation antimicrobial, cytotoxic and other conventional drugs, hormones, antigens, enzymes, genetic material, viruses and bacteria can be incorporated in either the aqueous or hydrophobic phase. This review discusses the types and characteristics of non-conventional liposomes used in various modes of cancer therapy, mainly chemotherapy and gene therapy. It concludes with suggestions on improving these novel liposomal to effect better targeting to cancer cells.