Drug efflux transport properties of 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) and its fluorescent free acid, BCECF.

2',7'-Bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) is a fluorescent probe used to examine multidrug resistance-associated protein (MRP) transporter activity in cells. BCECF is introduced into the cell as the nonfluorescent membrane permeable acetoxymethyl ester, BCECF-AM, where it is hydrolyzed to the membrane impermeable BCECF. The lipophilic nature of BCECF-AM suggests it may be a substrate for other drug efflux transporters such as P-glycoprotein (P-gp) and the breast cancer resistance protein (BCRP). To assess the drug efflux transporter interactions of BCECF-AM and BCECF, accumulation studies were examined in various drug efflux-expressing cells. Inhibition of P-gp, BCRP, and/or MRP produced distinct changes in the time-dependent accumulation of BCECF in the cells. Treatment with GF120918 produced an immediate and sustained effect throughout the entire time course examined. Fumitremorgin C only affected BCECF accumulation at the early time points, whereas the impact of indomethacin on BCECF accumulation was observed only at the latter time points. Permeability studies in bovine brain microvessel endothelial cells indicated an increased basolateral-to-apical transport of BCECF, which could be reduced in the presence of either indomethacin or GF120918. These results indicate that the intracellular accumulation and transcellular permeability of BCECF are sensitive to a variety of drug efflux interactions. These results likely reflect an interaction of the ester form with P-gp and BCRP during the initial accumulation process, and an interaction of the free acid form with MRP after hydrolysis in the cell.