The multidrug transporter ABCB1 (MDR1, Pgp) plays an important role in the absorption,
distribution, metabolism, and elimination of a wide range of pharmaceutical compounds.
Functional investigation of the ABCB1 expression is also essential in many diseases,
including drug-resistant cancer, inflammatory conditions, or Alzheimer disease. In
this study, we examined the potential interaction of the ABCB1 multidrug transporter
with a group of commercially available viability dyes that are generally considered
not to penetrate into intact cells. Here, we demonstrate that the slow cellular accumulation
of TO-PRO™-1 (TP1) or TO-PRO™-3 (TP3) was strongly inhibited by ABCB1-dependent dye
extrusion. TP1/3 dye accumulation was not affected by the presence of ABCC1 or ABCG2,
while this uptake was increased to the level in the ABCB1-negative cells by a specific
P-glycoprotein inhibitor, Tariquidar. We suggest that TP compounds can be used as
highly sensitive, selective, non-toxic, and stable dyes to examine the functional
expression and properties of the ABCB1 multidrug transporter, especially in microplate-based
high-throughput flow cytometry assays. In addition, we demonstrate the applicability
of the TP dyes to efficiently select and separate even a very low number of Pgp-expressing
intact cells.
