2.5. Flow cytometry-based substrate efflux assay

The ABCB1 substrate rhodamine 123 (Rh123) efflux assay was performed as previously described7. Briefly, MDA435/LCC6 or MDA435/LCC6 MDR1 cells were incubated with Rh123 (0.5 μg/mL) alone or co-incubated with individual POPs at 10 μmol/L, verapamil at 50 μmol/L and PSC833 at 0.4 μmol/L (ABCB1 inhibitors as positive controls), respectively, at 37 °C for 30 min. After a 1 h Rh123-free efflux, fluorescence retention in the cells was measured by an LSRFortessa Cell Analyzer.