Compounds 74 and 75 are cytotoxic against a broad range of human breast cancer, colorectal carcinoma, glioma, lymphoblastoma, and mouse melanoma cell lines as well as several drug‐resistant phenotypes, either with P‐glycoprotein and BCRP (ABC transporters) overexpressed, p53 deleted, or EGFR or B‐RAF mutation‐activated. Here, ABCG2 is linked to breast cancer.