Nuclear accumulation of exogenous DNA fragments in viable cells mediated by FGF-2 and DNA release upon cellular injury

Blood-brain barrier transport of non-viral gene and RNAi therapeutics

The development of gene- and RNA interference (RNAi)-based therapeutics represents a challenge for the drug delivery field. The global brain distribution of DNA genes, as well as the targeting of specific regions of the brain, is even more complicated because conventional delivery systems, i.e. viruses, have poor diffusion in brain when injected in situ and do not cross the blood-brain barrier (BBB), which is only permeable to lipophilic molecules of less than 400 Da. Recent advances in the "Trojan Horse Liposome" (THL) technology applied to the transvascular non-viral gene therapy of brain disorders presents a promising solution to the DNA/RNAi delivery obstacle. The THL is comprised of immunoliposomes carrying either a gene for protein replacement or small hairpin RNA (shRNA) expression plasmids for RNAi effect, respectively. The THL is engineered with known lipids containing polyethyleneglycol (PEG), which stabilizes its structure in vivo in circulation. The tissue target specificity of THL is given by conjugation of approximately 1% of the PEG residues to peptidomimetic monoclonal antibodies (MAb) that bind to specific endogenous receptors (i.e. insulin and transferrin receptors) located on both the BBB and the brain cellular membranes, respectively. These MAbs mediate (a) receptor-mediated transcytosis of the THL complex through the BBB, (b) endocytosis into brain cells and (c) transport to the brain cell nuclear compartment. The present review presents an overview of the THL technology and its current application to gene therapy and RNAi, including experimental models of Parkinson's disease and brain tumors.

Marked enhancement in gene expression by targeting the human insulin receptor

BACKGROUND

Exogenous genes can be delivered to cells without viral vectors using an "artificial virus" comprised of nonviral plasmid DNA encapsulated in the interior of 85 nm pegylated immunoliposomes (PIL). The liposomes are targeted to cells with receptor-specific targeting ligands such as receptor-specific peptidomimetic monoclonal antibodies.

METHODS

The levels of luciferase gene expression in human or rat glioma cells are measured after targeting the PIL-encapsulated plasmid DNA via the human insulin receptor, the human epidermal growth factor receptor, or the rat transferrin receptor. The luciferase expression plasmids were either derived from pCEP4, which contains the Epstein-Barr nuclear antigen-1/oriP replication system, or from pGL2, which lacks this system for episomal replication of plasmid DNA.

RESULTS

Depending on the plasmid construct used and the receptor targeted, the peak luciferase gene expression varied more than 200-fold from 1.8 +/- 0.1 to 419 +/- 31 pg luciferase per mg cell protein. With the same plasmid, the peak level of gene expression following delivery to the cell via the human insulin receptor was 100-200-fold higher than gene expression following delivery via either the epidermal growth factor receptor or the transferrin receptor. There was no gene expression if the targeting ligand on the PIL was replaced with a nonspecific isotype control antibody.

CONCLUSIONS

The extent to which an exogenous gene is expressed within a cell via a nonviral, receptor-mediated gene transfer technology is determined by the receptor specificity of the targeting ligand. The highest levels of gene expression are obtained after targeting the insulin receptor, and this may derive from the nuclear targeting properties of this receptor system.

Stem cells and the philosopher's stone

Stem cell biology is now one of the most exciting and rapidly advancing areas of scientific endeavor. Promises of cures of a wide variety of diseases by specific replacement of damaged or malfunctional tissues by use of totipotent or multipotent stem cells is on the horizon in clinical practice. Stem cells derived from the embryo and from adult tissues have been shown to have extensive potentials for self-renewal and differentiation. In addition, the plasticities of phenotype exhibited in vivo by some of these cell populations challenge the doctrine of irreversibility of cell commitment after particular developmental stages. This brief review considers certain aspects of these recent findings of the many unexpected potentials of stem cells to differentiate into alternative processes, and their potential value for use in tissue reconstruction procedures are prominent areas that require further study. Rigorous investigation of these topics will lead to realistic approaches in the future for stem cell therapy in a variety of human diseases and other clinical problems.

Receptor-mediated delivery of an antisense gene to human brain cancer cells

BACKGROUND

The goal of this work was the development of a gene targeting technology that will enable the delivery of therapeutic genes to brain cancer cells in vivo following intravenous administration. High-grade brain gliomas overexpress the epidermal growth factor receptor (EGFR) and EGFR antisense gene therapy could reduce the growth of EGFR-dependent gliomas.

METHODS

A human EGFR antisense gene driven by the SV40 promoter in a non-viral plasmid carrying elements that facilitate extra-chromosomal replication was packaged in the interior of 85 nm pegylated immunoliposomes (PILs). The PILs were targeted to U87 human glioma cells with the 83-14 murine monoclonal antibody (MAb) to the human insulin receptor (HIR).

RESULTS

Confocal fluorescent microscopy demonstrated that the unconjugated HIR MAb is rapidly internalized by the glioma cells. Endocytosis followed by entry into the nucleus was also demonstrated for the HIR MAb conjugated PILs carrying fluorescein-labeled plasmid DNA. The PILs delivered exogenous genes to virtually all cells in culture, based on beta-galactosidase histochemistry. The targeting of a luciferase gene to the U87 cells with the PILs resulted in luciferase levels in excess of 150 pg/mg protein after 72 h of incubation. The level of luciferase gene expression in the U87 cells achieved with the PIL gene targeting system was comparable to that with lipofectamine. Targeting the EGFR antisense gene to U87 glioma cells with the PILs resulted in more than 70% reduction in [(3)H]thymidine incorporation into the cells; this was paralleled by a 79% reduction in the level of immunoreactive EGFR.

CONCLUSION

The present work describes the targeting of an EGFR antisense gene to human brain cancer cells, which results in a 70-80% inhibition in cancer cell growth. PILs provide a new approach to gene targeting that is effective in vivo following intravenous administration without viral vectors.