Figure 3. Inhibitory ability of known P-glycoprotein (P-gp) inhibitors correlates with sensitizing Halaven (HAL)-treated KBV20C cells. A: KBV20C cells were grown on 6-well plates and treated with different micromolar concentrations (indicated as suffix) of verapamil (VER), mitotane (Mit), or piperine (Pip) alone and in combination with 50 ng/ml HAL, or with 0.1% dimethylsulfoxide (DMSO) (Con). After 1 day, all cells were observed using an inverted microscope at ×50 magnification. B: KBV20C cells were grown on 6-well plates and treated with 10 μM verapamil, 20 μM curcumin, 200 μM fumagillin, 100 μM piperine, 50 μM mitotane, 5 μM tesmilifene, 60 μM sulindac, 100 μM probenecid, 100 μM indomethacin, 10 μM C-4, or 0.1% DMSO (Con). After 24 h, all cells were stained with calcein-AM, as described in the Materials and Methods section. The stained cells were subsequently examined by FACS analysis.