Dyes providing increased sensitivity in flow‐cytometric dye‐efflux assays for multidrug resistance

Abstract

In an effort to improve detection of P‐glycoprotein‐mediated multidrug resistance (mdr), several dyes were compared to rhodamine 123 (R123) in efflux assays. Two dyes (SY‐38 and SY‐3150) were found that provided better sensitivity. These dyes were effluxed by a cell line known to be mdr‐positive (P388/R84) but not by an mdr‐negative cell line (P388). Efflux was blocked by both verapamil and cyclosporine A. Efflux from KG1a cells was less than from P388/R84, just as has been seen with R123 and daunomycin. In further experiments, a model system was used to demonstrate two‐color immunofluorescence plus efflux measurements. This was done using a sequential staining method. A procedure was devised that, at least for this model system, allowed single‐step staining with both dye and antibody. The sensitivity of the efflux measurement was slightly compromised by using this one‐step staining method. © 1995 Wiley‐Liss, Inc. Copyright © 1995 Wiley‐Liss, Inc.