AIM:To investigate the therapeutic effect of raddeanin A(RA)on prostate cancer xenograft mouse model,and to explore its potential mechanisms.METHODS:(1)Western blot analysis was used to investigate the effects of different concentrations(0,0.5,1,2 and 4 μmol/L)of RA on the expression of programmed cell death li-gand 1(PD-L1)protein in prostate cancer cell lines PC-3,DU145 and RM-1.(2)Thirty C57BL/6J mice were randomly divided into blank group,low-dose RA group,and high-dose RA group,with 10 mice in each group.The mice in low-and high-dose RA groups were intraperitoneally injected with 2 and 4 mg/kg RA continuously for 24 d,respectively.Mouse body weight was recorded,and tumor volume and weight were measured.Immunohistochemistry experiments were con-ducted to detect the expression of Ki67 and PD-L1 proteins in mouse tumor tissues.Flow cytometry was used to determine the percentages of CD8+T cells,CD4+T cells and regulatory T cells(Treg),as well as the levels of interferon-γ(IFN-γ)and granzyme B(GzmB)in tumor tissues.RESULTS:Treatment with RA significantly reduced the expression of PD-L1 in PC-3,DU145 and RM-1 cells(P<0.05 or P<0.01).In vivo experiments showed that RA treatment led to significant decreases in tumor volume and weight(P<0.05 or P<0.01).Additionally,the expression levels of Ki67 and PD-L1 in tu-mor tissues were significantly reduced(P<0.05 or P<0.01).Furthermore,RA treatment significantly increased the per-centages of CD8+T cells and CD4+T cells within mouse tumors,elevated the levels of IFN-γ and GzmB,and reduced the number of activated Treg(P<0.05 or P<0.01).CONCLUSION:The RA exhibits potent inhibitory effects on tumor growth in a prostate cancer xenograft mouse model.Its mechanism may be associated with the inhibition of PD-L1 expres-sion,increased infiltration of tumor-infiltrating T cells,and suppression of Treg.