Sensitization of ABCG2-overexpressing cells to conventional chemotherapeutic agent by sunitinib was associated with inhibiting the function of ABCG2.

Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we evaluated the possible interaction of sunitinib with P-glycoprotein (P-gp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), breast cancer resistance protein (BCRP, ABCG2) and lung-resistance protein (LRP) in vitro. Our results showed that sunitinib completely reverse drug resistance mediated by ABCG2 at a non-toxic concentration of 2.5muM 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 and methotrexate by ABCG2 in ABCG2-overexpressing cells, and also profoundly inhibited the transport of [(3)H]-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. Overall, we conclude that 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.