In the present study, multi-factorial drug-resistant cancer cell lines such as leukemia CEM/ADR5000 cells over-expressing P-gp, breast adenocarcinoma MDA-MB-231-BCRP clone 23 expressing BCRP, EGFR-transfected U87MG.ΔEGFR glioblastoma cells and p53 knockout HCT116 (p53−/−) colon cancer cells (Efferth et al. 2003a; Kuete et al. 2013a, b, 2014c; Kimmig et al. 1990; Gillet et al. 2004; Doyle et al. 1998) were used to determine the cytotoxicity the selected plant extracts. Here, PGP is linked to glioblastoma.