Coexpression of ABCB1 and ABCG2 in a Cell Line Model Reveals Both Independent and Additive Transporter Function

Abstract

Although overexpression of multiple ATP-binding cassette transporters has been reported in clinical samples, few studies have examined how coexpression of multiple transporters affected resistance to chemotherapeutic drugs. We therefore examined how coexpression of ABCB1 (P-glycoprotein) and ABCG2 contributes to drug resistance in a cell line model. HEK293 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 ABCG2specific 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 coexpressed, 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 coexpressed.

In vivo characterization of [18F]AVT-011 as a radiotracer for PET imaging of multidrug resistance

“…These results are consistent with functional redundancy between ABCB1A/ B and ABCG2 at the blood-brain barrier in limiting brain uptake of dual ABCB1/ABCG2 substrates [29], and with previous reports on the brain uptake of other ABC transporter substrate radiotracers [30,31]. While [ 18 F]AVT-011's lack of selectivity may be undesirable for imaging transporter function in certain pathophysiological conditions [11], its dual substrate property may be beneficial for imaging MDR mediated by ABC transporters in tumors because ABCB1 and ABCG2 are often co-expressed [1], and can independently and additively contribute to MDR [32]. While the higher brain uptake of [ 18 F]AVT-011 in wildtype and Abcg2 −/− mice after tariquidar administration could have resulted from changes in perfusion, this possibility is unlikely for two reasons.…”

Reversal Effect of ALK Inhibitor NVP-TAE684 on ABCG2-Overexpressing Cancer Cells

“…At present, various specific and nonspecific inhibitors of ABCG2 have been found. FTC is a mycotoxin isolated from Aspergillus fumigatus (39,40). It can specifically sensitize chemotherapeutic agents to MDR mediated by ABCG2.…”

Aberrant DNA Methylation of ABC Transporters in Cancer

“…In some cancers, e.g., leukemia, ABCB1 and ABCG2 are commonly co-expressed. However, ABCB1 and ABCG2 have been found to function independently and additively in a cell line model expressing high levels of both ABC transporters [ 76 ].…”