Bodipy-FL-verapamil: a fluorescent probe for the study of multidrug resistance proteins.

Most of the substances used as fluorescent probes to study drug transport and the effect of efflux blockers in multidrug resistant cells have many drawbacks, such as toxicity, unspecific background, accumulation in mitochondria. New fluorescent compounds, among which Bodipy-FL-verapamil (BV), have been therefore proposed as more useful tools. The uptake of BV has been evaluated by cytofluorimetry and fluorescence microscopy using cell lines that overexpress P-glycoprotein (P388/ADR and LLC-PK(1)/ADR) or MRP (multidrug resistance-related protein) (PANC-1) and clinical specimens from patients. The effect of specific inhibitors for P-glycoprotein (verapamil and vinblastine) or MRP (MK571 and probenecid) has been also studied. BV intracellular concentrations were significantly lower in the two P-glycoprotein overexpressing cell lines in comparison with the parental lines. In addition, verapamil and vinblastine increased the intracellular concentrations of the dye; MK571 and probenecid, two MRP inhibitors, increased BV levels in PANC-1 cells, that express this protein. These findings were confirmed in clinical specimens from patients. Fluorescence microscopy revealed a faint fluorescence emission in P-glycoprotein or MRP expressing cell lines; however, treatment with specific inhibitors significantly increased the fluorescence. BV is a useful tool for studying multidrug resistance proteins with different techniques such as cytofluorimetry and fluorescence microscopy, but does not discriminate between P-glycoprotein and MRP. In comparison with other classic fluorescent probes, the assay with this dye is extremely rapid, simple, not toxic for cells, devoid of fluorescent background, and can be useful in the clinical settings.