Objective  This work aims to investigate the effect of PXDIOI, a novel potent histone deacetylase inhibitor, on the cell proliferation, cycle arrest and apoptosis of human breast cancer cell line MCF-7 and to preliminarily explore its molecular mechanism.

  Methods  MCF-7 cells were cultured in RPMI 1640 medium supplemented with 10%fetal bovin serum and were treated with PXDIOI at varying concentrations.The methyl thiazolyl tetrazolium(MTT) assay and clonogenic assay were used to measure cell proliferation. Morphological changes of cells were observed by fluorescent microscope after staining by Hoechst33342.Flow cytometer was used to analyze the cell cycle arrest rates(PI staining) and the cell apoptotic rates(AnnexinV-FITC/PI double-staining).The protein expressions of p21, CyclinB1, PARP, Bcl-2 and Bax were detected by Western blot.

  Results  PXD101 was used to inhibit the proliferation of the MCF-7 cell line in a dose and time-dependent manner.Fluorescence microscope showed there were nuclear fragmentation and apoptosis bodies in the cells.Flow cytometric analysis indicated that PXD101 induced MCF-7 cells in G ₂/M phase were significantly increased.After MCF-7 cells exposed to different concentrations of PXD101, i.e., 0, 0.1, 1 and 10μmol/L, for 24 h, the ratio of G₂/ M-phase cells was(12.66±1.55)%, (20.63±1.32)%, (23.20±1.82)%and(32.19±2.37)%respectively(P < 0.05).The rates of apoptotic cells were also significantly increased, compared with the control group(P < 0.05).PXDIOI could up-regulate the protein expression of p21 and down-regulate the expression of CyclinBl.The cleavage of PARP and the expression of pro-apoptosis protein Bax were increased while the anti-apoptosis protein Bcl-2 was decreased.

  Conclusion  PXD101 in vitro can significantly inhibit the proliferation and can induce cell cycle arrest and apoptosis on human breast cancer MCF-7 cell line in a dose-dependent manner.PXD101 may become a new anti-tumor drug for human breast cancer.