Rapamycin sensitivity of the MDA-MB-468 breast cancer cell line. (A) MDA-MB-468 cells were treated with rapamycin at various concentrations. SRB assay was performed 5 days later. The assay results shown are the mean (± standard deviation) of three independent experiments. (B) 2 × 103 MDA-MB-468 cells were plated in 60-mm plates in triplicate and treated with DMSO or 100 nM rapamycin. Two weeks later, cell colonies were stained with crystal violet, and the plates were scanned and colonies quantitated. The results shown are the mean (± standard deviation) for three plates. (C) Mice with established MDA-MB-468 tumor xenografts received DMSO or rapamycin (15 mg/kg) intraperitoneally once a week for 3 weeks. The tumor volumes were then measured using calipers every other day and presented as the mean (± standard error of the mean). Solid line, rapamycin; dashed line, DMSO. * P < 0.05.