BIOLOGICAL EFFECTS AND CELLULAR UPTAKE OF C-MYC ANTISENSE OLIGONUCLEOTIDES AND THEIR CATIONIC LIPOSOME COMPLEXES

The biological effects and cellular uptake of human c-myc antisense ol igonucleotides and their liposome complexes were investigated in vitro using human promonocytic leukemia U937 cells. Antisense phosphorothio ate oligonucleotides (S-Oligo) significantly inhibited the growth of U 937 cells in a dose-dependent manner. However, no significant effect o n cell proliferation was observed with unmodified phosphodiester (P-Ol igo) and partially phosphorothioated (PS3-Oligo) oligonucleotides with an antisense sequence and S-Oligo with sense and G-quartet control se quences. In cellular uptake experiments, radiolabeled S-Oligo was take n up by U937 cells more than P-Oligo and PS3-Oligo, Similar results we re obtained in mouse peritoneal macrophages used for comparison. Confo cal microscopic studies demonstrated a significant distribution of FIT C-labeled oligonucleotides on the cell surface and in the cytoplasm in a punctate pattern, but not in the nucleus. When complexed with catio nic liposomes, cellular uptake of FITC-labeled P-Oligo or S-Oligo was significantly increased and the fluorescence was located mainly in the nucleus, indicating that the uptake and intracellular pharmacokinetic s of both oligonucleotides can be modified by complexation. An inhibit ory effect of the complexes was observed at a dose which is ineffectiv e in the case of the oligonucleotides alone. However, this effect was also associated with cytotoxicity of the cationic liposomes, suggestin g that optimization of this formulation will be necessary to achieve a more efficient delivery of the oligonucleotides to U937 cells.