Intracellular accumulation of DOX

The intracellular accumulation of DOX was examined by measuring the fluorescence intensity of DOX. The K562 or K562/DOX cells were seeded in 6-well plates at 5×10⁵ cells/well. After 24 h, the cells were pre-treated for 48 h at 37°C with 5% CO_2. and then 2 ml DOX (4 µM) was added to each well, followed by incubation at 37°C for 60 min in the dark. Following incubation, the cells were immediately washed with ice-cold PBS three times and lysed with RIPA lysis buffer, and the fluorescent signal of the cells was detected with a multimode microplate reader (TriStar2; Berthold Bio) using a 595-nm long band-pass filter.