Fig. 9

EP13 and 2-DG act synergistically to kill breast cancer cells. MDA-MB-231 (a, d), Hs578T (b, e), and MCF-7 (c, f) cells were treated for 72 h with increasing concentrations of EP13 and 2-DG used alone or in combination at a constant ratio of 1/1. Cell numbers were determined by crystal violet staining. Data were analysed by Compusyn software to determine the combination index (CI) according to the Chou Talalay method (a, b, c). The CI value is given for each total dose corresponding to the addition of the concentration value of EP13 and 2-DG used in combination (a total dose of 2 corresponds to treatment with 1 µM EP13 and 1 mM 2-DG). The area between the dashed lines (0.9 < CI < 1.1) is related to an additive effect. A CI > 1.1 indicates an antagonistic effect, and a CI < 0.9 indicates a synergistic effect. The isobologram analysis shows the effect (Fa: fraction affected corresponding to the cell number decrease (%)) of the combination of the two compounds versus their effect when used alone (d, e, f). The diagonal line joins the individual doses of EP13 and 2-DG on the x- and y-axes to achieve a 25%, 50% or 75% cancer cell number decrease (Fa). The symbols show the dose of each compound used in combination to achieve similar effects. Data points below the line of additivity indicate synergy, and data points above denote antagonism