Figure 2.

ABCB1 inhibition potentiated response to chemotherapy in BXD-1425EPN. (a) Cytotoxic response of the BXD-1425EPN cell line to the chemotherapeutic drugs methotrexate, vincristine and etoposide was assessed by the stem cell relevant clonogenic assay to produce dose response curves (100% represents vehicle control). (b–d) The IC₅₀ concentrations for each drug were then recalculated in the presence of either the non-specific ABCB1 inhibitor verapamil (20 µM) or the selective ABCB1 inhibitor, vardenafil (10 µM). There was a significant potentiation of cytotoxic response represented by reduction in the IC₅₀ concentrations of methotrexate (b), vincristine (c) and etoposide (d) when combined with either inhibitor (*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.005, **** p ≤ 0.001).