Nuclear localization and antisense effect of PNA internalized by ASGP-R-mediated endocytosis with protein/DNA conjugates

In order for peptide nucleic acids (PNAs) to be effective as therapeutic agents, methods for cellular delivery must be developed. Here we demonstrate spontaneous nuclear localization and antisense effects of peptide nucleic acids (PNAs) delivered to hepatic cells through asialoglycoprotein receptor-mediated endocytosis. Asialofetuin conjugates with DNA oligonucleotides (AF/DNA) complementary to the PNA of interest were designed as cell-specific delivery vectors. PNAs hybridized to the asialofetuin-oligonucleotide conjugates were internalized into murine primary hepatocytes and human HepG2 hepatocarcinoma cells effectively through receptor-mediated endocytosis in vitro. After a 4-h incubation, PNAs were largely localized in the nuclei of the cells; the mechanisms involved are still unclear. More than 70% inhibition of telomerase activity was observed when PNAs complementary to the RNA template of human telomerase were delivered to HepG2 cells using AF/DNA. The PNAs were stably associated with the AF/DNA conjugates in 50% serum at 37 °C for at least 3 h. The PNAs were spontaneously released from the conjugate through a strand exchange mechanism when complementary nucleic acid was added. The complexation of PNAs with the AF/DNA conjugates resulted in delivery of PNAs to liver after intravenous injection into mice. The present study indicates that conjugation to a natural proteinous ligand can be used as a non-toxic vector for cellular delivery of oligonucleotide analogs.