Spencer Kong

Biological barriers to cellular delivery of lipid-based DNA carriers.

Although lipid-based DNA delivery systems are being assessed in gene therapy clinical trials, many investigators in this field are concerned about the inefficiency of lipid-based gene transfer technology, a criticism directed at all formulations used to enhance transfer of plasmid expression vectors. It is important to recognize that many approaches have been taken to improve transfection efficiency, however because of the complex nature of the formulation technology being developed, it has been extremely difficult to define specific carrier attributes that enhance transfection. We believe that these optimization processes are flawed for two reasons. First, a very defined change in formulation components affects the physical and chemical characteristics of the carrier in many ways. As a consequence, it has not been possible to define structure/activity relationships. Second, the primary endpoint used to assess plasmid delivery has been transgene expression, an activity that is under the control of cellular processes that have nothing to do with delivery. Gene expression following administration of a plasmid expression vector involves a number of critical steps: (i) DNA protection, (ii) binding to a specific cell population, (iii) DNA transfer across the cell membrane, (iv) release of DNA into the cytoplasm, (v) transport through the cell and across the nuclear membrane as well as (vi) transcription and translation of the gene. The objective of this review is to describe lipid-based DNA carrier systems and the attributes believed to be important in regulating the transfection activity of these formulations. Although membrane destabilization activity of the lipid-based carriers plays an important role, we suggest here that a critical element required for efficient transfection is dissociation of lipids bound to the plasmid expression vector following internalization.

The role of interactions between O2, H2O2, · OH, e− and O2− in free radical damage to biological systems☆

Abstract The occurrence of the Haber-Weiss reaction and other interactions between free radicals has been investigated in the effects of mixtures of free radicals on the permeability of resealed erythrocyte ghosts and on the activity of membrane-bound glyceraldehyde-3-phosphate dehydrogenase. The following mixtures were found to induce damage greater than that which could be accounted for by the independent actions of the constituent free radicals: (i) · OH + H 2 O 2 , and (ii) · OH + H 2 O 2 + O 2 − . In contrast, the following mixtures were found to induce less damage than that predicted on the basis of independent actions of constituent free radicals: (i) H 2 O 2 + O 2 − , and (ii) oxidizing radicals ( · OH, H 2 O 2 ) + reducing radicals ( e − , H · ). These results suggest a Haber-Weiss-like interaction between H 2 O 2 and O 2 − and an interaction between H 2 O 2 and · OH to produce a species more potent than either in causing increased permeability. The decrease in damage observed in the simultaneous presence of oxidizing and reducing radicals suggests an antagonistic effect by which each tends to moderate damage by the other. Inactivation of glyceraldehyde-3-phosphate dehydrogenase was found to be more sensitive to radiation than permeability by an order of magnitude, while permeability was more sensitive to the enhancement of damage by oxygen. Comparison of the effectiveness of free radical scavengers in inhibiting the increase in permeability caused by free radicals showed the following order of effectiveness, expressed in terms of percentage protection: formate (90%) > nitrogen (65%) > catalase (60%) > dismutase (32%), and with respect to enzymatic inactivation, nitrogen (100%) > formate (77%) > dismutase (48%) > catalase (44%). The relative rates observed anaerobically and aerobically in the presence and absence of the above scavengers suggest that (at least in the case of radiation damage to the membranes of erythrocyte ghost cells) the “oxygen effect” is due to the interaction of oxygen with e − and H., producing O 2 − which aggravates damage under conditions which allow consequent Haber-Weiss-like reactions. The further increase in damage when oxygen concentration is raised yet higher is due to the interaction of oxygen with the sites of initial damage.

Efficient Delivery of Antennapedia Homeodomain Fused to CTL Epitope with Liposomes into Dendritic Cells Results in the Activation of CD8+ T Cells

The in vivo induction of a CTL response using Antennapedia homeodomain (AntpHD) fused to a poorly immunogenic CTL epitope requires that the Ag is given in presence of SDS, an unacceptable adjuvant for human use. In the present report, we developed a hybrid CTL epitope delivery system consisting of AntpHD peptide vector formulated in liposomes as an alternative approach to bypass the need for SDS. It is proposed that liposomes will prevent degradation of the Ag in vivo and will deliver AntpHD recombinant peptide to the cytosol of APCs. We show in this work that dendritic cells incubated with AntpHD-fused peptide in liposomes can present MHC class I-restricted peptide and induce CTL response with a minimal amount of Ag. Intracellular processing studies have shown that encapsulated AntpHD recombinant peptide is endocytized before entering the cytosol, where it is processed by the proteasome complex. The processed liposomal peptides are then transported to the endoplasmic reticulum. The increase of the CTL response induced by AntpHD-fused peptide in liposomes correlates with this active transport to the class I-processing pathway. In vivo studies demonstrated that positively charged liposomes increase the immunogenicity of AntpHD-Cw3 when injected s.c. in mice in comparison to SDS. Moreover, addition of CpG oligodeoxynucleotide immunostimulatory sequences further increase the CD8+ T cell response. This strategy combining lipid-based carriers with AntpHD peptide to target poorly immunogenic Ags into the MHC class I processing pathway represents a novel approach for CTL vaccines that may have important applications for development of cancer vaccines.

Analysis of Cationic Liposome-mediated Interactions of Plasmid DNA with Murine and Human Melanoma Cells in Vitro

Lipid-based DNA transfer formulations are typically selected on the basis of in vitro transfection studies where the activity of specific formulations is defined by transgene expression. It is unclear, however, whether expression is directly related to the efficiency of DNA transfer. In an attempt to correlate DNA transfer with transgene expression, we used a simple assay consisting of measuring DNA (3H-plasmid encoding for β-galactosidase) binding to murine (B16/BL6) and human (KZ) melanoma cells in vitro at 4 and 37 °C. The difference in cell association at these temperatures was assumed to be a consequence of DNA uptake, an assumption that was confirmed by protease removal of cell surface-associated DNA. DNA associated with B16/BL6 melanoma cells (up to 30 ng or 12% of the added DNA) following incubation with dioleoyldimethylammonium chloride/dioleoylphosphatidylethanolamine (DOPE) liposome-DNA aggregates was comparable to that achieved with 1,2-dioleoyloxypropyl-3-trimethylammonium bromide/DOPE or dimethyldioctadecylammonium bromide/DOPE liposomes; however, transgene expression was 2- and 5-fold less for the latter two formulations, respectively. Similarly, equivalent amounts of DNA delivery were achieved with B16/BL6 and KZ melanoma cells, yet the level of transgene expression in the KZ cells was undetectable. It was demonstrated that the lack of transgene expression was not a consequence of cell-specific differences in DNA degradation.

Lipid/DNA complexes as an intermediate in the preparation of particles for gene transfer: an alternative to cationic liposome/DNA aggregates

Abstract When cationic liposomes are mixed with plasmid DNA an aggregation reaction occurs. The heterogeneous membrane structures which arise following this reaction are dependent on liposomal lipid composition, liposome/DNA ratio as well as the presence of added salts or proteins. The resulting structures are also unstable, resulting in time dependent changes in the physical attributes of the aggregates. Pharmaceutical development of the liposome/DNA aggregates will be challenging because of these factors. For these reasons we have pursued development of alternative lipid-based systems as a vehicle for gene transfer. The pivotal step that led to development of these novel systems was the identification and isolation of a hydrophobic cationic lipid/DNA complex. This complex can be used as an intermediate in the preparation of well-defined particles. The hydrophobic lipid/DNA complex and the liposome/DNA aggregates are both formed as a consequence of multivalent electrostatic interactions. In contrast to the liposome/DNA aggregates, however, we believe that the particles formed when using lipid/DNA complex intermediates are a consequence of hydrophobic interactions.

Oxazole yellow homodimer YOYO-1-labeled DNA: a fluorescent complex that can be used to assess structural changes in DNA following formation and cellular delivery of cationic lipid DNA complexes

To improve transfection efficiency following delivery of plasmid expression vectors using lipid-based carriers, it is crucial to define structural characteristics of the lipid/DNA complexes that optimize transgene expression. Due to its strong affinity for DNA and high quantum yield, the fluorescent DNA intercalator YOYO-1 was used as a tool to assess changes in DNA that occur following lipid binding and cell delivery. In this study, the stability of the dye/DNA complex following binding of poly-L-lysine or monocationic lipids is characterized. More than 98% of the fluorescence measured for a defined DNA/YOYO-1 complex was lost when DNA was condensed using poly-L-lysine. This loss in fluorescence could be attributed to displacement of bound dye. In contrast, more than 30% of the fluorescence of the dye-labeled DNA was retained after formation of cationic lipid/DNA complexes. Significantly, the results illustrate differences in structural changes cationic lipids and PLL exert on plasmid DNA. The fluorescent lipid/DNA complex was used to assess DNA delivery to murine B16/BL6 cells in vitro. An assay relying on fluorescence resonance energy transfer between bound YOYO-1 and propidium iodide was used to distinguish between DNA attached to the cell surface and internalized DNA.

15 Targeted Gene Transfer

The overall goal of gene therapy is to cure or stabilize a disease process that results from the production of a mutant protein (for example, the chloride channel protein important in cystic fibrosis) or overproduction of a normal protein (such as the products of certain oncogenes). We can achieve this goal by replacing the defective gene or by reducing the overexpression of the target gene using an antisense strategy, thus reducing the production of the diseasepromoting protein (1,2). For either method, it is critical to transfer DNA into target cells in a concentration high enough to be effective in modifying the disease. DNA must be delivered to the desired cell population in an intact state, whereby it can be efficiently transcribed and ultimately translated. The method of gene transfer must be highly efficient and nontoxic, and the delivery system must be relatively easy to prepare and administer (3). There is a great deal of optimism surrounding the development of gene therapy as an effective strategy for management of many different human diseases. The active agent used to procure gene therapy is likely to consist of oligonucleotides, ribozymes, or a DNA sequence that can be transcribed into a message capable of eliciting a therapeutic response. Unlike conventional small-molecule therapeutics however, gene therapy requires the use of a carrier system to deliver the active agent directly into the target cell population.