Objective:To explore the effects and mechanism of glycogen synthase kinase 3β (GSK-3β3) inhibitor (2'Z,3'E)-6-bromo-indirubin-3'-oxime (BIO) on drug resistance in colon cancer cells.Methods:The colon cancer SW480 and SW620 cells were treated with BIO,5-fluorouracil (5-FU) and BIO/5-FU,separately.Cell cycle distribution,apoptosis level and efflux ability of rhodamine 123 (Rh123) were detected by flow cytometry.The protein expressions of P-glycoprotein (P-gp),multidrug resistance protein 2 (MRP2),thymidylate synthase (TS),β-catenin,E2F-1 and Bcl-2 were detected by Western blot.β-catenin and P-gp were stained with double immunofluorescence and observed under a confocal microscope.Results:BIO up-regulated β-catenin,P-gp,MRP2 and TS,enhanced the efflux ability of Rh123,decreased Bcl-2 protein and gave the opposite effect to E2F-1 protein in SW480 and SW620 cells.Furthermore,BIO significantly inhibited cell apoptosis,increased S and G2/M phase cells,and reduced the cell apoptosis induced by 5-FU in SW480 cells,whereas the effects were slight or not obvious in SW620 cells.Conclusion:GSK-3β was involved in drug resistance regulation,and activation of β-catenin and inhibition of E2F-1 may be the most responsible for the enhancement of 5-FU chemotherapy resistance induced by GSK-3β inhibitor BIO in colon cancer.