A novel hydroxysuberamide derivative potentiates MG132-mediated anticancer activity against human hormone refractory prostate cancers--the role of histone deacetylase and endoplasmic reticulum stress.

ABSTRACT

BACKGROUND: Histone deacetylase (HDAC) inhibitors are successful for treatment of advanced cutaneous T-cell lymphoma but only show modest effect in solid tumors. Approaches for HDAC inhibitors to improve activity against solid tumors are necessary. METHODS: Sulforhodamine B assay and flow cytometric analysis detected cell proliferation and cell-cycle progression, respectively. Protein expression was determined by Western blotting. Comet assay and DNA end-binding activity of Ku proteins detected DNA damage and DNA repair activity, respectively. siRNA technique was used for knockdown of specific cellular target. RESULTS: WJ25591 displayed inhibitory activity against HDAC1 and cell proliferation in human hormone-refractory prostate cancers PC-3 and DU-145. WJ25591 caused an arrest of cell-cycle at both G1- and G2-phase and increased protein expressions of p21 and cyclin E, followed by cell apoptosis. WJ25591-induced Bcl-2 down-regulation and activation of caspase-9, -8, and -3, suggesting apoptotic execution through both intrinsic and extrinsic apoptotic pathways. WJ25591 also significantly inhibited DNA repair activity but not directly induced DNA damage. Moreover, the proteasome inhibitor MG-132 dramatically sensitized WJ25591-induced cell apoptosis. The siRNA technique demonstrated that endoplasmic reticulum (ER) stress, in particular CHOP/GADD153 up-regulation, contributed to the synergistic effect. CONCLUSIONS: The data suggest that WJ25591 inhibited HDAC activity, leading to cell-cycle arrest and inhibition of DNA repair. Caspase cascades are subsequently triggered to execute cell apoptosis. MG-132 dramatically sensitizes WJ25591-mediated apoptosis, at least partly, through ER stress response. The data also reveal that combination of HDAC inhibitors and proteasome inhibitors may be a potential strategy against hormone-refractory prostate cancers.