PGP and breast cancer: Neferine increased R123 uptake in all drug-resistant cell lines (paclitaxel-resistant MCF-7, doxorubicin-resistant MCF-7 breast cancer cells, paclitaxel-resistant A549 lung cancer cells and paclitaxel-resistant HCT8 colon cancer cells) in a comparable manner, as the well-known P-gp inhibitor verapamil did.