ABCG2 and breast cancer: If SAF was tested toward a pair of wild-type and multidrug-resistant breast cancer cells (MDA-MB-231-pcDNA3 and MDA-MB-231-BCRP clone 23), it did not exhibit any cytotoxicity up to 100 μM (data not shown), confirming our assessments based on grouping the mean log10IC50 values for secalonic acid of the NCI cell lines according to the tumor type of the cell lines.