Oligodeoxyribonucleotide phosphorothioate fluxes and localization in hematopoietic cells

An antisense oligonucleotide phosphorothioate, previously shown to inhibit HIV-1 viral expression in chronically infected H9 cells, was fluorescently labeled to study oligonucleotide fluxes and localization within living cells. Observations based on flow cytometry and fluorescence microscopy show the following: within around 0.5-2 h, an apparent steady-state distribution of the oligonucleotide is achieved in which the intracellular oligonucleotide concentration is less than that present in the external medium; following oligonucleotide uptake and resuspension of the cells in oligonucleotide-free medium, an oligonucleotide efflux, with a time constant similar to that for uptake, is observed (although a significant fraction of the phosphorothioate remains within the cell); cellular uptake as a function of the external oligonucleotide concentration is nonlinear, being more efficient at lower concentrations (less than 2 microM); and a predominant oligonucleotide localization within the cell nucleus and perinuclear organelles is observed.