Abstract: BACKGROUND ＆ AIM: To study the in vitro anti_tumor effect of 6_epi_ ophiobolin K、ophiobolin K and ophiobolin G from microorganisms. MATERIALS AND METHODS: The effects of the three compounds on the proliferation of six human tumor cell lines were investigated by MTT method with IC50, and the inhibitory activities of the three compounds against cathepsin B were assayed for evaluation of anti_tumor invasiveness and metastasis in vitro. RESULTS: Compared with negative control, 6_epi_ophiobolin K,ophiobolin K and ophiobolin G showed significant inhibitory activities to Hct_15,Hct_116,MDA_MB_231,MCF_7,A549 and K562 cell lines. 6_epi_ophiobolin K to the above tumor cell lines demons trated IC50 of 5.70,3.60,28.00,8.40,2.00 and 3.10 μg/ml, respectively. Ophiobolin K showed IC50 of 1.40、0.81、4.26、3.70,0.91 and 1.10 μg/ml,respectively,while Ophiobolin G revealed IC50 of 4.10,4.60,26.10,17.10,6.70 and 6.10 μg/ml,respecfively.All three compounds have moderate inhibitory activities to athepsin B with the IC50 of 46,26 and 23 μg/ml,respectively. CONCLUSION: The three compounds all had anti_proliferative effects on tumor cell lines.

Key words: ophiobolin, cathepsin B, anti_tumor