Cholangiocarcinoma (CCA) is a highly invasive and metastatic form of carcinoma with bleak prognosis due to limited therapies, frequent relapse, and chemotherapy resistance. There is an urgent need to identify the molecular regulators of CCA in order to develop novel therapeutics and advance diseases diagnosis. Many cellular proteins including histones may undergo a series of enzyme-mediated post-translational modifications including acetylation, methylation, phosphorylation, sumoylation, and crotonylation. Histone deacetylases (HDACs) play an important role in regulating epigenetic maintenance and modifications of their targets, which in turn exert critical impacts on chromatin structure, gene expression, and stability of proteins. As such, HDACs constitute a group of potential therapeutic targets for CCA. The aim of this review was to summarize the role that HDACs perform in regulating epigenetic changes, tumor development, and their potential as therapeutic targets for CCA.

Secreted Protein, Acidic and Rich in Cysteine (SPARC) is a matricellular protein involved in many biological processes and found over-expressed in cirrhotic livers. By mean of a genetic approach we herein provide evidence from different in vivo liver disease models suggesting a profibrogenic role for SPARC. Two in vivo models of liver fibrosis, based on TAA administration and bile duct ligation, were developed on SPARC wild-type (SPARC^+/+) and knock-out (SPARC^−/−) mice. Hepatic SPARC expression was analyzed by qPCR. Fibrosis was assessed by Sirius Red staining, and the maturation state of collagen fibers was analyzed using polarized light. Necroinflammatory activity was evaluated by applying the Knodell score and liver inflammatory infiltration was characterized by immunohistochemistry. Hepatic stellate cell activation was assessed by α-SMA immunohistochemistry. In addition, pro-fibrogenic genes and inflammatory cytokines were measured by qPCR and/or ELISA. Liver gene expression profile was analyzed in SPARC^−/− and SPARC^+/+ mice using Affymetrix Mouse Gene ST 1.0 array. SPARC expression was found induced in fibrotic livers of mouse and human. SPARC^−/− mice showed a reduction in the degree of inflammation, mainly CD4+ cells, and fibrosis. Consistently, collagen deposits and mRNA expression levels were decreased in SPARC^−/− mice when compared to SPARC^+/+ mice; in addition, MMP-2 expression was increased in SPARC^−/− mice. A reduction in the number of activated myofibroblasts was observed. Moreover, TGF-β1 expression levels were down-regulated in the liver as well as in the serum of TAA-treated knock-out animals. Ingenuity Pathway Analysis (IPA) analysis suggested several gene networks which might involve protective mechanisms of SPARC deficiency against liver fibrogenesis and a better established machinery to repair DNA and detoxify from external chemical stimuli. Overall our data suggest that SPARC plays a significant role in liver fibrogenesis. Interventions to inhibit SPARC expression are suggested as promising approaches for liver fibrosis treatment.

Cholangiocytes, the epithelial cells lining the biliary tree in the liver, express primary cilia that can detect several kinds of environmental signals and then transmit this information into the cell. We have reported that cilia are significantly reduced in cholangiocarcinoma (CCA) and that the experimental deciliation of normal cells induces a malignant‐like phenotype with increased proliferation, anchorage‐independent growth, invasion, and migration. Here, we tested the hypothesis that the chemosensory function of cholangiocyte primary cilia acts as a mechanism for tumor suppression. We found that in the presence of extracellular nucleotides cilia‐dependent chemosensation of the nucleotides inhibited migration and invasion in normal ciliated cholangiocytes through a P2Y11 receptor and liver kinase B1 (LKB1)–phosphatase and tensin homolog–AKT–dependent mechanism. In contrast, in normal deciliated cholangiocytes and CCA cells, the nucleotides induced the opposite effects, i.e., increased migration and invasion. As activation of LKB1 through a cilia‐dependent mechanism was required for the nucleotide‐mediated inhibitory effects on migration and invasion, we attempted to activate LKB1 directly, independent of ciliary expression, using the compound hesperidin methyl chalcone (HMC). We found that HMC induced activation of LKB1 in both ciliated and deciliated cells in vitro , resulting in the inhibition of migration and proliferation. Furthermore, using a rat syngeneic orthotopic CCA model, we found that HMC inhibited tumor growth in vivo . Conclusion: These findings highlight the importance of the chemosensory function of primary cilia for the control of migration and invasion and suggest that, by directly activating LKB1 and bypassing the need for primary cilia, it is possible to emulate this chemosensory function in CCA cells; these data warrant further studies evaluating the possibility of using HMC as therapy for CCA.

This work identifies novel targets against primary ciliary disassembly that can lead to new cholangiocarcinoma therapeutic strategies. Furthermore, ciliary loss has been described in different tumors, increasing the significance of our research.