The fluorescent probe Bodipy-FL-verapamil is a substrate for both P-glycoprotein and multidrug resistance-related protein (MRP)-1.

Several fluorescent probes have been used in functional studies to analyze drug transport in multidrug-resistant cells by fluorescent microscopy. Because many of these molecules have some drawbacks, such as toxicity, nonspecific background, or accumulation in mitochondria, new fluorescent compounds have been proposed as more useful tools. Among these substances, Bodipy-FL-Verapamil, a fluorescent conjugate of the drug efflux blocker verapamil, has been used to study P-glycoprotein activity in different cell types. In this study we tested by fluorescent microscopy the accumulation of Bodipy-FL-Verapamil in cell lines that overexpress either P-glycoprotein (P-gp) or multidrug resistance-related protein 1 (MRP1). Expression of P-gp and MRP1 was evaluated at the mRNA level by RT-PCR technique and at the protein level by flow cytometric analysis using C219 and MRP-m6 monoclonal antibodies. Results indicate that Bodipy-FL-Verapamil is actually a substrate for both proteins. As a consequence, any conclusion about P-gp activity obtained by the use of Bodipy-FL-Verapamil as fluorescent tracer should be interpreted with caution.