LBH589 not only inhibited HDAC6 and enhanced 14-3-3�� acetylation, but also depleted HDAC6 to trigger the dissociation of PP1�� from HDAC6. LBH589 subsequently interfered in the regulation of the c-Raf-ERK signaling pathway, contributing to M phase cell cycle transition. In conclusion, this study suggests that HDAC6 may be a sensitive therapeutic target in the treatment of prostate cancer using LBH589 for clinical translation in future. As an initial attempt to investigate the cytotoxic effect of LBH589, four prostate cancer cell lines, LNCaP, PC-3, DU-145 and 22Rv1, were treated with various concentrations of LBH589 and cell viability was measured by MTT assay. In general, LBH589 ABT-263 Bcl-2 inhibitor showed potent growth VE-822 clinical trial inhibition effect on each cancer cell line in a dose- and time-dependent manner. Among the cell lines, LNCaP and PC-3 were the most sensitive and resistant to LBH589 treatment, respectively. Investigating the cell cycle profiles subsequent to LBH589 exposure, LBH589 treatment did not cause G2-M, but not G1, growth arrest in the four prostate cancer cell lines for 24 hours. LBH589-induced G2-M growth arrest was most prominent in PC-3 and LNCaP. Although LBH589 induced a comparable degree of G2-M arrest in LNCaP and PC-3 cells, the significant difference of apoptosis between these two cell lines under prolonged LBH589 exposure suggested that the underlying mechanisms involved might be different. A previous study has shown LBH589-mediated G2/M cellcycle arrest via down-regulation of Aurora A and B kinase in renal cell carcinoma. LBH589 treatment increased the same levels of histone H3 acetylation in both LNCaP and PC-3 cells, indicating that LBH589 was functional in both prostate cancer cell lines. However, down-regulation of Aurora A and B kinases by LBH589 was only observed in PC-3 cells but not in LNCaP cells. In order to investigate whether other hydroxamic acid derivatives had similar effects on LNCaP and PC-3 cells, two other HDACIs, SAHA and SBHA, were tested and showed that the down-regulation of Aurora A and B kinases only occurred in PC-3 cells but not in LNCaP. To further address the discrepancy between LNCaP and PC-3 cells under LBH589 treatment, two G2-M transition molecules Cdc2 and Cdc25C were compared. LBH589 decreased Cdc25C and phosphorylated Cdc2 levels in PC-3 cells but not in LNCaP cells. LBH589 also induced a band shift pattern of Cdc25C in LNCaP cells in a dose- and timedependent manner. The molecular mechanisms involved in the distinct LBH589- mediated effects between the two PCa cells were investigated.