TY - JOUR T1 - Co-expression of ABCB1 and ABCG2 in a Cell Line Model Reveals Both Independent and Additive Transporter Function JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.118.086181 SP - dmd.118.086181 AU - Andrea N. Robinson AU - Bethelihem G. Tebase AU - Sonia C. Francone AU - Lyn M. Huff AU - Hanna Kozlowski AU - Dominique Cossari AU - Jung-Min Lee AU - Dominic Esposito AU - Robert W. Robey AU - Michael M. Gottesman Y1 - 2019/01/01 UR - http://dmd.aspetjournals.org/content/early/2019/05/02/dmd.118.086181.abstract N2 - Although overexpression of multiple ATP-binding cassette transporters has been reported in clinical samples, few studies have examined how co-expression of multiple transporters affected resistance to chemotherapeutic drugs. We therefore examined how co-expression of ABCB1 (P-glycoprotein) and ABCG2 contribute to drug resistance in a cell line model. HEK-293 cells were transfected with vector encoding full-length ABCB1, ABCG2, or a bicistronic vector containing both genes, each under the control of a separate promoter. Cells transfected with both transporters (B1/G2 cells) demonstrated high levels of both transporters and uptake of both the ABCB1-specific substrate rhodamine 123 and the ABCG2-specific substrate pheophorbide a was reduced when examined by flow cytometry. B1/G2 cells were also cross-resistant to the ABCB1 substrate doxorubicin, the ABCG2 substrate topotecan, as well as mitoxantrone and the cell cycle checkpoint kinase 1 inhibitor prexasertib, both of which were found to be substrates of both ABCB1 and ABCG2. When B1/G2 cells were incubated with both rhodamine 123 and pheophorbide a, transport of both compounds was observed, suggesting that ABCB1 and ABCG2, when co-expressed, can function independently to transport substrates. ABCB1 and ABCG2 also functioned additively to transport the common fluorescent substrates mitoxantrone and BODIPY®-prazosin, as it was necessary to inhibit both transporters to prevent efflux from B1/G2 cells. ABCG2 expression was also found to decrease the efficacy of the ABCB1 inhibitor tariquidar in B1/G2 cells. Thus, ABCB1 and ABCG2 can independently and additively confer resistance to substrates, underscoring the need to inhibit multiple transporters when they are co-expressed.SIGNIFICANCE STATEMENT N/A ER -