MTT cell proliferation assays. (a) Cytotoxicity of eupatorin in MDA-MB-468 cells and MCF-10A cells. (b) Decrease of eupatorin cytotoxicity in MDA-MB-468 cells after addition of acacetin. (c) Cytotoxicity of acacetin in MDA-MB-468 cells and MCF-10A cells. (d) Cytotoxicity of cirsiliol in MDA-MB-468 cells and MCF-10A cells. Cells were plated into 96-well plates and treated with 10-3 to 100 μM eupatorin, acacetin, or cirsiliol (as described in Materials and methods) and allowed to grow for 96 hours. For the inhibition experiment, acacetin was used at a final concentration of 1.5 μM. Error bars represent mean ± standard deviation (SD) for n = 4 determinations. MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.