Abstract 1533: Sunitinib reverses ABCG2/BCRP-mediated multidrug resistance by inhibiting its efflux activity

Abstract

Abstract Background and objective: Overexpression of ATP-binding cassette (ABC) transporters, which play a key role in the development of multidrug resistance (MDR), is a significant impediment to successful cancer treatment. Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we investigated in vitro the possible interaction of sunitinib with the major members of the ABC transporters: P-glycoprotein (P-gp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), breast cancer resistance protein (BCRP, ABCG2) and lung-resistance protein (LRP). Methods: Cytotoxicity tests were performed using the MTT assay; The intracellular accumulation of doxorubicin and rhodamine 123 (Rho123) was analysed by flow cytometry; Membrane vesicles were prepared by the nitrogen cavitation and transport assays were performed using the rapid filtration method to confirm the effect of sunitinib on the transporter activity of ABCG2; Western Blotting was used to determine the protein expression; and reverse transcription-PCR was used to assess the expression of ABCG2 at mRNA level. Results: The IC50 concentration for parental cell line S1 to topotecan or doxorubicin were 0.135 ± 0.056 µM and 0.165 ± 0.009 µM, respectively; However, the concentration of topotecan or doxorubicin required to inhibit ABCG2- overexpressing cell line S1-M1-80 by 50% was about 5.132 ± 2.024 and 6.845 ± 1.035 µM; Coincubation with 2.5 sunitinib, the concentrations required to inhibit the growth of S1-M1-80 cells by 50% for topotecan was 0.091 ± 0.012 µM, and for doxorubicin was 0.181 ± 0.037 µM, respectively. Sunitinib potently reverses ABCG2-mediated resistance to topotecan and doxorubicin in vitro and has no significant reversal effect on ABCB1-, ABCC1- and LRP-mediated drug resistance, although a small synergetic effect was observed in combining sunitinib and conventional chemotherapeutic agents in ABCB1-overexpressing MCF-7/adr and parental sensitive MCF-7 cells, ABCC1-overexpressing C-A120 and parental sensitive KB-3-1 cells. Sunitinib significantly increased intracellular accumulation of rhodamine 123 and doxorubicin and remarkably inhibited the efflux of rhodamine-123 in ABCG2-overexpressing cells, and also profoundly inhibited the transport of [3H]-methotrexate by ABCG2. However, sunitinib did not affect the expression of ABCG2 at mRNA or protein levels. In addition, sunitinib did not block the phosphorylation of Akt and Erk1/2 in ABCG2-overexpressing or parental sensitive cells. Conclusions: Sunitinib reverses ABCG2-mediated MDR through inhibiting the drug efflux function of ABCG2. These findings may be useful for cancer combinational therapy with sunitinib in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1533.