2.5. ABCG2 Transporter Activity Assay

Cells were implanted in 60-mm dishes and allowed to grow for 2 days. Cells were incubated with ABCG2 substrate pheophorbide a (Pha, 500 nM) alone or in combination with ABCG2 inhibitor Ko143 (1μM) for 4 h in the complete medium. Cells were rinsed with PBS after the incubation and trypsinized. Cells were resuspended in PBS and measured with a FACSCalibur flow cytometer for fluorescence in the FL3 channel. Fluorescence after Pha in combination with Ko143 was normalized to that after Pha treatment alone to indicate the ABCG2 activity.