PCI 29732 inhibits the function of ABCG2 by competitively binding to the ATP-binding site of ABCG2 and enhances the anti-tumor efficacy of substrate chemotherapeutic agents. PCI 29732 (20 mg/kg; p.o.; every 3 d × 5 times) enhances the anticancer efficacy of Topotecan in the H460/MX20 cell xenograft nude mice model.