Cellular uptake of phosphorothioate oligodeoxynucleotides is negatively affected by cell density in a transformed rat tracheal epithelial cell line: implication for antisense approaches.

Antisense oligodeoxynucleotides have been used to specifically inhibit the expression of a variety of genes. In the process of testing phosphorothioate oligodeoxynucleotides (S-oligos) as specific inhibitors of transforming growth factor alpha synthesis, we observed that the efficiency of cellular uptake of S-oligos was not constant throughout the culture period but decreased as the cell densities increased. Our data suggest that the mechanism by which oligonucleotides enter cells is negatively affected by increased cell density. These results emphasize the importance of determining uptake kinetics before designing and interpreting antisense experiments using phosphorothioate oligonucleotides.