Specific inhibition of influenza virus RNA polymerase and nucleoprotein genes expression by liposomally endocapsulated antisense phosphorothioate oligonucleotides: penetration and localization of oligonucleotides in clone 76 cells.

Liposomally encapsulated phosphorothioate oligonucleotides with four target sites (PB1, PB2, PA, and NP) were synthesized and tested for inhibitory effects by a CAT-ELISA assay using the clone 76 cell line. The liposomally encapsulated phosphorothioate oligonucleotides (S-ODNs) complementary to the sites of the PB2-AUG and PA-AUG initiation codons showed highly inhibitory effects. Displacement of the target AUG initiation codon sequence to the 3'-end, 5'-end, and/or center sites on the antisense phosphorothioate oligonucleotides was studied with regard to the inhibition of influenza virus RNA polymerases and NP. The antisense phosphorothioate oligonucleotide containing the AUG initiation codon at the center site of the oligonucleotide had the highest inhibitory effects. The liposomally encapsulated phosphorothioate oligonucleotides exhibited higher inhibitory activity than the free oligonucleotides. Observation of clone 76 cells treated with the endocapsulated antisense phosphodiester oligonucleotide, FITC-ODNs-PB2-T3, by a confocal laser scanning microscope, revealed diffuse fluorescence, apparently within the cytoplasm. Interestingly, the endocapsulated antisense phosphorothioate oligonucleotide, FITC-S-ODNs-PB2-T3 accumulated in the nuclear region of clone 76 cells. However, weak fluorescence was observed in the endosomes and in the cytoplasms of the clone 76 cells treated with the free antisense phosphorothioate oligonucleotides.