Fagaridine chloride (84) exhibits potent cytotoxicity against several cancer cell lines (e.g., CCRF-CEM cells, CEM/ADR5000 cells, MDA-MB-231-pcDNA3 cells, MDA-MB-231-BCRP clone 23 cells, HCT-116p53 +/+, HCT-116p53−/− cells, U87.MG cells and counterparts U87.MGΔEGFR, and HepG2 cells). This evidence concerns the gene ABCG2 and cancer.