Expression of mRNA and functional activity of ABC protein transporters in SP and MP cells. (A) Expression of mRNA of ABCG2 (BCRP) and ABCB1 (MDR/Pgp) in sorted SP and MP cells of MM (OPM1, KMS-11, OCIMy5, RPMI-Dox40, and RPMI-MR20) cell lines, as determined by QuantiGene Plex assay system. Fluorescence intensity of ABC transporters was normalized to fluorescence intensity of the housekeeping gene GAPDH. All experiments were performed in triplicate, P < .05, t test, statistical significance. (B) Efflux of Rh123, ie, functional activity of P-glycoprotein transporter (left column) and Mitoxantrone, ie, functional activity of BCRP1 transporter (right column) in SP and MP cells. MM cell lines (OPM1, KMS-11, OCIMy5, RPMI-MR20, and RPMI-Dox40) were dual stained with either Rh123 and Hoechst 33342 or Mitoxantrone and Hoechst 33342: SP cells (gray) and MP cells (black). Data are representative of 3 independent experiments; all experiments were performed in triplicate.