Antisense c-myc Oligodeoxyribonucleotide Cellular Uptake

Antisense oligonucleotides have therapeutic potential as inhibitors of gene expression. However, the mechanism by which an intact oligonucleotide reaches the intracellular site of action is unknown. In this study, we use an Oligodeoxyribonucleotide 21-mer complementary to the translation initiation codon of the c-myc proto-oncogene to study the mechanism of oligonucleotide uptake and internalization into Rauscher Red 5-1.5 cells. We find trypsin-sensitive and trypsin-insensitive surface binding, in addition to internalization. Uptake is partially energy dependent and inhibited by charged molecules, including DNA, ATP, a random sequence oligonucleotide, and dextran sulfate. Uptake does not appear to occur via a traditional receptor-mediated uptake pathway because chloro-quine, monensin, and phenylarsine oxide pretreatment does not significantly decrease internalization. An anion channel inhibitor, SITS, and the salts, NaCl, Na₂SO₄, and NH₄Cl, significantly decrease oligonucleotide uptake. Whether uptake occurs via a channel or a novel uptake mechanism is still unknown. A model is proposed which reasonably simulates the experimental data.