To explore down-regulating IDO1 expression ability of small-molecule inhibitors in tumor cells,twenty-five novel berberine(BBR)analogues with various substituents on positions 3 and 9 were synthesized and examined for repression of IFN-γ-induced IDO1 promoter activity.Structure-activity relationship(SAR)indicated that tertiary carbon,quaternary carbon or rigid structure substitutions at the 9-position might be beneficial for enhancing inhibitory potency.Among them,compounds 2f,2i,2n,2o and 8b exhibited satisfactory activities,with inhibition rate of 71–90%compared with that of BBR.Preliminary mechanism study revealed that compounds 2i and 2n inhibited IFN-γ-induced IDO1 expression through activating AMPK and subsequent inhibition of STAT1 phosphorylation.Furthermore,both of them exhibited anticancer activity by enhancing the specific lysis of NK cells to A549 cells,rather than through cytotoxic effects.The discoveries in this study represent a new mechanism in the antitumor action of BBR derivatives and may have implications for development of clinical cancer immunotherapy.