RESUMEN
Several polycations such as polylysine polymers are efficient transfection agents due to their capacity to bind DNA at physiological pH. By linking a ligand for a cell surface receptor to the polycation domain, a selective delivery of polyanionic compounds such as oligodeoxynucleotides (ODNs) without cell membrane-disruption can be achieved. Therefore, we aimed to develop this strategy to improve the uptake of oligomers in cancer cells. In particular, cationic polymers polylysine were covalently linked to a molecule of Folic Acid (FA) to deliver complexed ODNs in human melanoma (M-14) cells which express FA receptors. Since in these cells c-myc oncogene seems to play a crucial role in tumor growth, we used a c-myc antisense ODNs (15mer base antisense c-myc ODNs phosphorothioate) to inhibit its expression. The cellular uptake of the complexed ODNs was improved compared to the cellular uptake of free ODNs with a significant decrease in the intracellular c-myc protein level, resulting in a reduction of the growth rate and colony-forming capacity of the cells. No such effect was observed when ODNs in scrambled sequences were administered under the same experimental conditions. The efficacy of the uptake of the complex is receptor-related since a Transferrin-polylysine carrier produced no significant biological effects (in melanoma cells the Fe uptake is mediated by an oxidoreductase present in the cell membrane and not by Transferrin receptor pathway). Our results demonstrate that: a) By choosing the appropriate ligand for the membrane receptor present on the target cells, selective targeting of ODNs can be achieved. b) The uptake of the ODNs can be improved by receptor-mediated endocytosis. c) In a model system the complexed ODNs are capable of impairing gene product synthesis and function.