Efficient delivery of an antisense oligodeoxyribonucleotide formulated in folate receptor-targeted liposomes.

BACKGROUND

Folate receptors (FRs) are cellular surface markers for numerous solid tumors and myeloid leukemias. The aim of this study was to develop an antisense oligodeoxyribonucleotide (ODN) carrier targeting FR-overexpressing cancer cells using folate (FA) as the targeting moiety. G3139, a phosphorothioate antisense ODN against human bcl2 mRNA, was evaluated in this study.

MATERIALS AND METHODS

G3139-containing liposomes were prepared using an ethanol dilution method. For the targeted formulation, 0.5 mol% of folate-PEG-DSPE was incorporated as a targeting ligand into cationic liposomes composed of DC-Chol/egg PC/PEG-DSPE at 25:65:10 mol/mol. Particle size and surface charge were measured and cellular uptake was assessed by fluorescence microscopy and flow cytometry. The ODN-containing formulations were evaluated in FR+ KB cells for Bcl2 down-regulation measured by Western blot. The cytotoxicity of the formulations was determined by MTT assay.

RESULTS

The G3139-containing liposomes had an average diameter of 80-90 nm with high ODN entrapment efficiency (70-80%). Incorporation of the folate ligand did not significantly alter the particle size and entrapment efficiency. The formulation exhibited colloidal stability in a serum-containing environment. In uptake studies, the folate-targeted formulation showed ligand concentration-dependent uptake that was up to 6-fold more efficient than that of the non-targeted formulation (p < 0.05). The uptake could be blocked by an excess amount of free folate, thus indicating an FR-dependent mechanism.

CONCLUSION

FR-targeted G3139-containing liposomes showed promising transfection activity in KB cells. FR-targeted formulations were capable of specific targeting to FR-overexpressing cell lines and optimizing the amount of folate ligand in the liposomal formulation can result in more efficient antisense delivery.