Especially,

the combination of HDAC inhibitor with conventional chemotherapy is expected to have a synergistic effect, because the mechanism of action is different from those of conventional chemotherapeutic regimens. Valproic acid (VPA), which has long been used clinically for treatment of epilepsy and bipolar disorder without significant toxicity, causes hyperacetylation of the N-terminal tails of histones H3 and H4 in vitro and in vivo and inhibits HDAC activity, probably by binding to the catalytic center and thereby blocking substrate access [18, 19]. VPA inhibits both class I and II HDACs, with high potency for Epigenetics inhibitor class I HDACs [20]. Earlier studies indicated that p21WAF1, one of the target genes induced by VPA, affects differentiation and decreases tumor cell growth [21, 22]. Another PXD101 report focused on the apoptotic activity of VPA [23]. However, the detailed mechanism of apoptosis by VPA has not been elucidated. On the other hand, recent evidence suggests that HDAC inhibitors also enhance the acetylation of non-histone proteins, such as p53, c-Jun, and α-tubulin [24–26]. It is possible that VPA increases acetylation of non-histone proteins in relation with apoptosis. However, no reports

have focused on the therapeutic potential of VPA in gastric cancer. The present study was performed to investigate the anticancer mechanism of action of VPA by analyzing the expression of cell cycle regulatory proteins and apoptosis-modulating proteins in a scirrhous gastric cancer cell line. In addition to acetylation of histones, PRKACG the possibility

LY2606368 in vivo that acetylation of the non-histone protein α-tubulin contributes to inhibition of tumor growth was also examined. Paclitaxel (PTX) is an anticancer agent, which stabilizes polymerized microtubules and enhances microtubule assembly, and thus arrests the cell cycle in G0/G1 and G2/M phases, leading to cell death [27], and has been used for peritoneal dissemination of ovarian and gastric cancer [4, 28]. As tubulin is a target molecule of PTX, combination of VPA with PTX has the potential to show synergistic effects. In the present study, we also evaluated the synergistic effects of PTX with VPA on a scirrhous gastric cancer cell line. The mechanisms of these anticancer effects of VPA, which are different from conventional chemotherapy, may provide a new strategy to improve the clinical outcome of gastric cancer patients. Methods Materials VPA was purchased from Sigma-Aldrich Co. (Japan). PTX was kindly provided by Bristol-Myers Squibb Company (Japan). Cell lines and cell culture OCUM-2MD3, a highly peritoneal-seeding cell line derived from human scirrhous gastric cancer, was kindly provided by the Department of Surgical Oncology of Osaka City University of Medicine.