MHY219 is a novel HDAC inhibitor. MHY219 induces apoptosis via up-regulation of androgen receptor expression in human prostate cancer cells. MHY219 was shown to enhance the cytotoxicity on DU145 cells (IC50, 0.36 μM) when compared with LNCaP (IC50, 0.97 μM) and PC3 cells (IC50, 5.12 μM). MHY219 showed a potent inhibition of total HDAC activity when compared with SAHA. MHY219 increased histone H3 hyperacetylation and reduced the expression of class I HDACs (1, 2 and 3) in prostate cancer cells. MHY219 effectively increased the sub-G1 fraction of cells through p21 and p27 dependent pathways in DU145 cells. MHY219 significantly induced a G2/M phase arrest in DU145 and PC3 cells and arrested the cell cycle at G0/G1 phase in LNCaP cells. Furthermore, MHY219 effectively increased apoptosis in DU145 and LNCaP cells, but not PC3 cells, according to Annexin V/PI staining and Western blot analysis. These results indicate that MHY219 is a potent HDAC inhibitor that targets regulating mu......