Marked enhancement in gene expression by targeting the human insulin receptor

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.

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.

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.

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.