(A–D) Dose-related inhibition of growth by carboplatin, Nutlin-3a, and the 1:1 combination in MDA-MB-231, TMD231 and MDA-MB-468 TNBC cells and MCF-7 breast cancer cells following 5 day proliferation assays. (E–H) IC50 values of carboplatin and Nutlin-3a were determined at the indicated dose-ratios and analyzed by isobolograms. Individual isobole points which lie below the diagonal line of additivity indicate synergism, points on the line indicate additivity, and points above the line indicate antagonism. Each point represents the mean of three experiments. Vertical and horizontal lines indicate ±1 SD and are absent when less than the size of the point.