Receptor-targeted co-transport of DNA and magnetic resonance contrast agents

BACKGROUND

Ligand molecules conjugated to polylysine can be electrostatically bound to DNA and can bind receptors or antigens on the surface of cells, delivering the DNA into specific cells and tissues. Several researchers have used this approach to generate non-viral vehicles for the efficient delivery of DNA to specific cells. We have attempted to adopt this general approach to the cell-specific delivery of magnetic contrast agents for use in magnetic resonance imaging (MRI).

RESULTS

We have synthesized a new class of agents capable of both transfecting genes into cells and enhancing the contrast of the targeted cells for MRI. DNA is used both to encode a marker gene and as a molecular scaffold, which electrostatically binds polylysine conjugated to transferrin, an iron uptake protein, and polylysine modified with gadolinium chelated to diethylenetriaminepetaacetic acid. When cells displaying the transferrin receptor are treated with these particles, high levels of gene expression are observed, higher than with control particles composed only of transferrin, polylysine and DNA. The treated cells show specific MRI contrast enhancement, which did not require expression of the marker gene.

CONCLUSIONS

The development of this class of particles permits the use of novel protocols by which genes for genetic therapy and agents for MRI contrast are co-transported. These protocols may allow non-invasive MRI monitoring of DNA delivery for gene therapy in real time.

Transfection of folate-polylysine DNA complexes: evidence for lysosomal delivery

We are utilizing the folate receptor for the intracellular delivery of DNA. In this study, a folate-poly-L-lysine (FPLL) conjugate was synthesized and equilibrated with plasmid DNA encoding the firefly luciferase gene. The FPLL-DNA complexes were added to KB cells treated with chloroquine. Luciferase activity of cells incubated with FPLL-DNA was 6-fold higher than of cells exposed to poly-L-lysine (PLL)-DNA. The addition of free folic acid competitively inhibited the enhancement of gene expression. Removal of chloroquine from the media significantly inhibited transfection efficiency of FPLL-DNA complexes. We conclude that FPLL-DNA complexes are delivered into KB cells via folate receptor-mediated endocytosis and likely follow a lysosomal pathway into the cytoplasm.