The percentage of P-gp⁺ cells in oligonucleotide-treated K562/ADM cells (5 μmol/L) after incubation with oligonucleotide-free medium. After random (▧), MDR1-S (▧), and MDR1-AS (▪) treatment, these cells were incubated with oligonucleotide-free medium for 1 to 10 days, and measurement of P-gp using fluorescence microscopy was performed. The results are expressed as the percentage of treated cells compared with the untreated control, and represent the mean of two experiments.