Figure 2

Clonogenic survival analysis of MB cells treated with etoposide in the presence of ABCB1 inhibitors. The left panel shows the effect of increasing etoposide concentrations on clonogenic survival (100% representing solvent control). The middle and right panels represent clonogenic survival in the presence of etoposide (IC₅₀ concentrations derived from dose–response data) in combination with VPL (10 and 20 μM) or vardenafil (5 and 10 μM) respectively. (A) MED1 clonogenic survival is significantly inhibited in cells co-treated with etoposide and VPL or vardenafil (unpaired student’s t-test, ٭٭٭P < 0.0001 in all cases). (B) There was also a significant increase in etoposide cytotoxicity in DAOY cells when combined with VPL and vardenafil (unpaired student’s t-test, ٭٭P < 0.001; ٭P = 0.02). (C) No significant inhibition was observed in the MED3 cell line. Data represent mean ± SEM of n ≥ 3 experiments, each experiment was performed in duplicate.