Objective To investigate the in vitro anti-proliferation effect of a histone deacetylase inhibitor,chidamide,on a cutaneous malignant melanoma cell line,A375.Methods Cultured A375 cells were treated with different concentrations of chidamide(5,10,50,100,500 μmol/L)and aichostatin A (TSA)(0.1,0.25,0.5,1.0 μmol/L),respectively,for various durations(24,48,72,96,120 hours).Subsequently,cell proliferation,apoptosis and cell cycle were detected by MTT assay,annexin Vfluorescein isothiocyanate and propidium iodide double staining,and DNA ploid analysis,respectively.Results The proliferation of A375 cells was inhibited in a dose-dependent manner by chidamide of 5-500μmol/L and TSA of 0.1-1 μmol/L,and in a time-dependent manner from 0 to 120 hours after the beginning of trealment with ehidamide of 5-500μmol/L and TSA of 0.25-1μmol/L.The 48-hour 50% growth inhibition concentration(IC50)of ehidamide and TSA on A375 cells was about 250 μmol/L and 0.7μmol/L,respectively.After 48-hour treatment,the apoptosis mte was 80.27%±3.06%,79.53%±5.70%,83.13%±6.90%in A375 cells treated with chidamide of 62.5,125,250 μmol/L,respectively,16.27%±2.46%,28.83%±2.55%,83.40%±8.65%in those treated with TSA of 0.175,0.35,0.7 μmol/L,respectively,10.43%±0.96%in ontreated cells;a statistical increase was noticed in chidamide-treated cells and TSA-treated cells vs.untreated cells(all P＜0.001).A positive correlation was observed between the apoptosis rate and concentrations of TSA(r=0.955,P=0.000).Cell cycle analysis indicated that treatment with chidamide induced cell cycle arrest in G0/G1 phase,with the cell proportion in G0/G1 phase being 76.30%±6.06%,82.79%±0.74%,88.91%±5.29%in A375 cells treated with chidamide of 62.5,125,250μmol/L,respectively,versus 38.73%±3.36%in untreated cells.While after 48-hour treatment with TSA of 0.35 and 0.7 μmol/L,the proportion of cells in G2/M phases was 25.15%±2.71%and 58.71%±3.45%,respectively,compared to 15.73%±0.23%in untreated cells(P＜0.01).Conclusion Chidamide and TSA could induce cell cycle arrest and apoptosis,as well as inhibit the growth of A375 ceils in vitro.