Abstract
Multidrug resistance (MDR), mediated by highly expressed ABC transporters, is one of the most important mechanisms in tumor cells. Breast cancer resistance protein (BCRP) is a member of the ABC transporter family. This transporter expels different kinds of lipophilic anticancer drugs, which have diffused into the cells. In this study, 96-well plate based assays and flow cytometry analysis were employed to screen natural products for BCRP inhibition. The beta-carboline alkaloid harmine inhibited BCRP in a BCRP overexpressing breast cancer cell line (MDA-MB-231). Harmine reduced resistance to the anticancer drugs mitoxantrone and camptothecin mediated by BCRP and might be an interesting new reversal agent. Harmine did not inhibit P-glycoprotein (P-gp) mediated drug efflux.