Abstract: BACKGROUND ＆ AIM： The inhibitory effect of arsenic trioxide (As2O3) on human breast cancer MDA_MB_468 cells and the change of syk expression. MATERIALS AND METHODS: After treatment with various concentrations of As2O3, MDA_MB_468 cells proliferation was assessed by using methyl thiazolyl tetrazolium(MTT) method. The morphologic changes of MDA_MB_468 cells were examined with light microscope. After treated with As2O3 , cell cycle distribution and expression of Syk protein were measured by flow cytometry(FCM). Expression of syk mRNA was eveluated with RT_PCR. RESULTS: As2O3 inhibited the proliferation of MDA_MB_468 cells significantly, and in a time and dose_dependent manner (P<0.05). After treatment with As2O3, MDA_MB_468 cell cycle was arrested in the S＋G2/M phase. MDA_MB_468 cells expressed syk mRNA, As2O3 enhanced syk mRNA and Syk protein expression of MDA_MB_468 cells. CONCLUSIONS: As2O3 may inhibit the proliferation of MDA_MB_468 cells by enhancing the expression of syk.

Key words: arsenic trioxide, human breast cancer cell, MDA_MB_468 cell, apoptosis, syk