Selective inhibitor of multidrug resistance-associated protein 1 (MRP1) and P-glycoprotein (P-gp). Increases the sensitivity of MRP1-overexpressing tumor cells (MCF7/VP) to doxorubicin (Cat. No. 2252), vincristine (Cat. No. 1257) and etoposide (Cat. No. 1226) by 3.8-, 14.6- and 11.6-fold respectively. Increases the efficacy of vincristine and etoposide in murine models of neuroblastoma in vivo. Does not sensitize MRP2, MRP3, MRP4 or MRP5 transporters to known substrates.