FOXM1 and breast cancer: In order to develop breast cancer cells with acquired resistance to our FOXM1 inhibitors, ER-positive (MCF7) and triple negative (MDA-MB-231) breast cancer cells were exposed to increasing concentrations of inhibitor (NB73 or NB115) over a 6 to 9-month period, until we reached a point where cells grew well and maintained good viability in a maintenance dose of 10 μM compound.