FOXM1 and breast cancer: Biotin-labeled M1-21 could bind to endogenous Foxm1 when incubated with the lysates of mouse breast cancer 4T1 cells (Fig. S18B) and as expected, M1-21 inhibited mouse 4T1 cells at a similar concentration (20 μM) inhibiting human MDA-MB-231 cells (Fig. S18C), suggesting that M1-21 could inhibit mouse cancers by targeting mouse Foxm1.