Abstract 1266: Co-expression of P-glycoprotein and ABCG2 in a cell line model reveals both independent and cooperative transporter function

Abstract

Abstract Although overexpression of multiple ATP-binding cassette transporters has been reported in clinical samples, few studies have examined how expression of multiple transporters might confer resistance to chemotherapy drugs. We therefore examined how P-glycoprotein (P-gp, encoded by the ABCB1 gene) 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 vector containing both genes under the control of a separate promoter. Cells transfected to express both transporters (B1/G2 cells) expressed high levels of both transporters and were able to transport both the P-gp-specific substrate rhodamine 123 and the ABCG2 specific substrate pheophorbide a when examined by flow cytometry. B1/G2 cells were also cross-resistant to the P-gp substrate doxorubicin, the ABCG2 substrate topotecan as well as mitoxantrone, a substrate of both transporters. The checkpoint inhibitor prexasertib was also found to be a substrate of both P-gp and ABCG2. When B1/G2 cells were incubated with both rhodamine 123 and pheophorbide a, transport of both compounds was observed, suggesting that P-gp and ABCG2 can function independently to transport substrates. P-gp and ABCG2 were also found to function cooperatively 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. This was also true in 3-day cytotoxicity assays with mitoxantrone and prexasertib. Thus, P-gp and ABCG2 can independently and cooperatively confer resistance to substrates, underscoring the need to inhibit multiple transporters when they are coexpressed. Citation Format: Andrea Robinson, Robert Robey, Michael Gottesman. Co-expression of P-glycoprotein and ABCG2 in a cell line model reveals both independent and cooperative transporter function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1266.