【Objective】 To study the cytotoxic activity of brazilein against human breast cancer MCF-7 cells and its action mechanism. 【Methods】 MTT assay was used to detect the cytotoxic activity of brazilein against MCF-7 cells and immortalized breast epithelial MCF10A cells. The apoptosis was determined by Annexin V-FITC/PI staining and flow cytometry analysis. Mitochondrial membrane potentia was indicated by DiOC6 staining. The Western blotting was performed to detect wanted protein. 【Results】 Brazilein exerted potent cytotoxicity to human breast cancer MCF-7 cells

and the IC50 values was (7.15 ± 0.43) μmol/L. However

the IC50 values of brazilein against the MCF10A cells was (33.56 ± 2.87) μmol/L. After treatment with 0

7.5

15

30 μmol/L brazilein for 48 h

the percent of apoptosis was elevated from (3.37 ± 0.66)% to (16.8 ± 1.27)%

(31.31 ± 4.22)%

(51.23 ± 5.55)%

respectively. Brazilein decrease the level of mitochondrial membrane potentia in a dose-dependent manner

as detected by DiOC6 staining. Western blotting showed that brazilein released cyto-c to cytoplasm and following cleaved caspase-9 protein. The further study showed that brazilein down-regulated survivin in protein level by Western blot analysis. 【Conclusion】 Brazilein induced apoptosis though a mitochondria-dependent pathway

and which was related to the down-regulation of survivin protein.