Cell survival was measured with resazurin and with neutral red. ATP level was assayed with luciferin/luciferase kit. Luteolin transport was measured by an original method described in the paper.
3-BP (10–200 μM) induced a decrease of ATP level after 1-h incubation in all cell lines studied, more drastically in ABCB1-overexpressing cells. 50 and 200 μM 3-BP significantly decreased cell viability; the effect was more pronounced for ABCB1-overexpressing cells. PSC833, inhibitor of ABCB1, ameliorated the toxic effect of 3-BP on MDCK-II ABCB1 cells and MDCK-II cells. 3-BP inhibited luteolin transport in MDCK-II ABCG2 cells.
These results indicate that 3-BP shows selective toxicity against ABCB1- but not ABCG2-overexpressing cells, apparently due to enhanced ATP depletion but in a manner independent of the transport activity of Pgp, suggesting a novel mechanism of hypersensitivity of ABCB1-overexpressing cells to 3-BP.