Efficient delivery of a Bcl-2-specific antisense oligodeoxyribonucleotide (G3139) via transferrin receptor-targeted liposomes

A novel transferrin receptor (TfR)-targeted liposomal formulation was synthesized and evaluated for the delivery of a phosphorothioate antisense oligodeoxyribonucleotide (ODN) (G3139, oblimerson sodium, or Genasense (TM)) to Bcl-2 in K562 leukemia cells. Liposomes composed of DC-Chol/egg PC/PEG-DSPE (25:73.5:1.5, mol/mol/mol) were loaded with G3139 with high efficiency (70-80%). To prepare targeted liposomes, transferrin was first coupled to PEG-DSPE and then incorporated into the bilayer by post-insertion. The liposomes had a mean diameter of 100 to 150 nm and exhibited colloidal stability for up to 8 weeks. Uptake of Tf-conjugated G3139-containing liposomes in TfR positive K562 cells was found to be more efficient than that of the non-targeted control formulation and could be blocked by excess free Tf. Treatment with Tf-conjugated liposomes resulted in Bcl-2 protein downregulation in K562 cells that was approximately 2-fold greater than with non-targeted liposomes (p < 0.05) and 10-fold greater than with free G3139. Treatment with 2 mu M G3139 in Tf-conjugated liposomes resulted in > 80% reduction in Bcl-2 transcript. In addition, Tf-conjugated liposomal G3139-sensitized K562 cells to daunorubicin, lowering IC50 from 1.8 mu M to 0.18 mu M. In conclusion, Tf-conjugated liposomes are effective delivery vehicles for G3139 antisense oligos in TfR positive K562 cells and warrant further investigation as an in vivo oligo delivery vehicle. (c) 2006 Elsevier B.V. All rights reserved.