Effect of a histone deacetylase inhibitor on antitumor effect of gemcitabine to focus the gene network of ingenuity pathways analysis.

Abstract

230 Background: Histone deacetylase (HDAC) is strongly associated with epigenetic regulation and carcinogenesis, and its inhibitors induce the differentiation or apoptosis of cancer cells. Valproic acid (VPA) is one of the clinically available HDAC inhibitors. We previously showed that VPA augmented antitumor effect of GEM in choalngiocarcinoma cell line (2010 GI Symposium); this time, we performed microarray analysis and Ingenuity Pathways Analysis (IPA) to identify the systematic mechanism of the augmentative effect of VPA. Methods: Human cholangiocarcinoma cell line (HuCCT1) was used. The anticancer effects of VPA or gemcitabine (GEM), and the effects of VPA combined with GEM were studied by MTT assay. We divided the following four groups: control group, VPA group, GEM group, VPA plus GEM combination group. The gene expressions of p21, HDAC, VEGF, and HIF-1 were evaluated by RT-PCR. And, the microarray analysis was performed, the genes were picked up using Gene Spring GX10, and then IPA was performed. Results: In GEM alone group, no effect of GEM was observed in dose of 5 mm, and 16% of proliferation-inhibitory effects were observed in dose of 10 nm. In VPA alone group, no effect of VPA was observed in dose of 0.5 mm, and 12%, 35%, and 67% of proliferation-inhibitory effects were observed in dose of 1.0, 5.0, and 10mm, respectively. GEM (5 nm) and VPA (0.5 mm) reduced by 23%, which significantly augmented the anticancer effect of GEM alone or VPA alone (p<0.01). Furthermore, GEM combined with VPA upregulated the p21 expression compared with single agent (p<0.05). And, in regard to microarray analysis, we analyzed in 28,869 genes. The 24 genes were picked up with the comparison between VPA group and VPA plus GEM combination group using Gene Spring GX10, and the gene network of the cellular development containing the gene relevant to the differentiation of cancer cell, HLA-DR, was formed with IPA. Conclusions: VPA augmented the effects of anticancer agents in a cholangiocarcinoma cell line. Such effects may be owing to the gene network of the cellular development. HDAC inhibitor may have the effect of the differentiation of cancer cell. No significant financial relationships to disclose.