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Abstract
ABCG2 overexpression has been linked to resistance to topoisomerase inhibitors, leading us to examine the potential interaction between ABCG2 and becatecarin.
Interaction with ABCG2 was determined by ATPase assay, competition of [125I]iodoarylazidoprazosin (IAAP) photolabeling and flow cytometry. Cellular resistance was measured in 4-day cytotoxicity assays. ABCG2 expression was measured by fluorescent-substrate transport assays and immunoblot.
Becatecarin competed [125I]-IAAP labeling of ABCG2, stimulated ATPase activity and, at concentrations greater than 10 μM, inhibited ABCG2-mediated transport. Becatecarin-selected A549 Bec150 lung carcinoma cells were 3.1-, 15-, 8-, and 6.8-fold resistant to becatecarin, mitoxantrone, SN-38 and topotecan, respectively. A549 Bec150 cells transported the ABCG2 substrates pheophorbide a, mitoxantrone and BODIPY-prazosin and displayed increased staining with the anti-ABCG2 antibody 5D3 compared to parental cells. Increased ABCG2 expression was confirmed by immunoblot.
Our results suggest that becatecarin is transported by ABCG2 and can induce ABCG2 expression in cancer cells.