Combined Inhibition of Smoothened and the DNA Damage Checkpoint WEE1 Exerts Antitumor Activity in Cholangiocarcinoma

Cholangiocarcinoma (CCA) is characterized by resistance to chemotherapy and a poor prognosis. Therefore, treatments that can effectively suppress tumor growth are urgently needed. Aberrant activation of hedgehog (HH) signaling has been implicated in several cancers, including those of the hepatobiliary tract. However, the role of HH signaling in intrahepatic CCA (iCCA) has not been completely elucidated. In this study, we addressed the function of the main transducer Smoothened (SMO) and the transcription factors (TFs) GLI1 and GLI2 in iCCA. In addition, we evaluated the potential benefits of the combined inhibition of SMO and the DNA damage kinase WEE1. Transcriptomic analysis of 152 human iCCA samples showed increased expression of GLI1, GLI2, and Patched 1 (PTCH1) in tumor tissues compared with nontumor tissues. Genetic silencing of SMO, GLI1, and GLI2 inhibited the growth, survival, invasiveness, and self-renewal of iCCA cells. Pharmacologic inhibition of SMO reduced iCCA growth and viability in vitro, by inducing double-strand break DNA damage, leading to mitotic arrest and apoptotic cell death. Importantly, SMO inhibition resulted in the activation of the G2-M checkpoint and DNA damage kinase WEE1, increasing the vulnerability to WEE1 inhibition. Hence, the combination of MRT-92 with the WEE1 inhibitor AZD-1775 showed increased antitumor activity in vitro and in iCCA xenografts compared with single treatments. These data indicate that combined inhibition of SMO and WEE1 reduces tumor burden and may represent a strategy for the clinical development of novel therapeutic approaches in iCCA.

Criteria for preclinical models of cholangiocarcinoma: scientific and medical relevance

Cholangiocarcinoma (CCA) is a rare malignancy that develops at any point along the biliary tree. CCA has a poor prognosis, its clinical management remains challenging, and effective treatments are lacking. Therefore, preclinical research is of pivotal importance and necessary to acquire a deeper understanding of CCA and improve therapeutic outcomes. Preclinical research involves developing and managing complementary experimental models, from in vitro assays using primary cells or cell lines cultured in 2D or 3D to in vivo models with engrafted material, chemically induced CCA or genetically engineered models. All are valuable tools with well-defined advantages and limitations. The choice of a preclinical model is guided by the question(s) to be addressed; ideally, results should be recapitulated in independent approaches. In this Consensus Statement, a task force of 45 experts in CCA molecular and cellular biology and clinicians, including pathologists, from ten countries provides recommendations on the minimal criteria for preclinical models to provide a uniform approach. These recommendations are based on two rounds of questionnaires completed by 35 (first round) and 45 (second round) experts to reach a consensus with 13 statements. An agreement was defined when at least 90% of the participants voting anonymously agreed with a statement. The ultimate goal was to transfer basic laboratory research to the clinics through increased disease understanding and to develop clinical biomarkers and innovative therapies for patients with CCA.

Metabolic reprogramming in cholangiocarcinoma

Metabolic reprogramming is a hallmark of cancer and allows tumour cells to meet the increased energy demands required for rapid proliferation, invasion, and metastasis. Indeed, many tumour cells acquire distinctive metabolic and bioenergetic features that enable them to survive in resource-limited conditions, mainly by harnessing alternative nutrients. Several recent studies have explored the metabolic plasticity of cancer cells with the aim of identifying new druggable targets, while therapeutic strategies to limit the access to nutrients have been successfully applied to the treatment of some tumours. Cholangiocarcinoma (CCA), a highly heterogeneous tumour, is the second most common form of primary liver cancer. It is characterised by resistance to chemotherapy and poor prognosis, with 5-year survival rates of below 20%. Deregulation of metabolic pathways have been described during the onset and progression of CCA. Increased aerobic glycolysis and glutamine anaplerosis provide CCA cells with the ability to generate biosynthetic intermediates. Other metabolic alterations involving carbohydrates, amino acids and lipids have been shown to sustain cancer cell growth and dissemination. In this review, we discuss the complex metabolic rewiring that occurs during CCA development and leads to unique nutrient addiction. The possible role of therapeutic interventions based on metabolic changes is also thoroughly discussed.

Paclitaxel Restores Sensitivity to Chemotherapy in Preclinical Models of Multidrug-Resistant Intrahepatic Cholangiocarcinoma

The treatment of unresectable cholangiocarcinoma (CCA) is limited by the development of resistance to conventional first-line chemotherapy based on gemcitabine (GEM). In addition, a prior treatment with GEM frequently induces cross-resistance to other drugs employed in the second-line. Paclitaxel (PTX) is now emerging as an alternative option for the management of advanced/metastatic CCA. In the present work, we evaluate the antitumor activity of PTX in preclinical models of multidrug-resistant intrahepatic cholangiocarcinoma (iCCA). In vitro, PTX decreases tumor cell viability by affecting the cell cycle and inducing apoptosis and impairs the stem cell compartment. In vivo, a therapeutic regimen containing albumin-bound nanoparticle (Nab)-PTX overcomes drug resistance resulting in delayed tumor growth, impaired organization of the tumor vasculature, and reduced glucose uptake. Together, our results provide a rationale to consider PTX-based regimens in patients with iCCA who became refractory to conventional therapies.

Macrophage MerTK promotes profibrogenic cross-talk with hepatic stellate cells via soluble mediators

Background & Aims

Activation of Kupffer cells and recruitment of monocytes are key events in fibrogenesis. These cells release soluble mediators which induce the activation of hepatic stellate cells (HSCs), the main fibrogenic cell type within the liver. Mer tyrosine kinase (MerTK) signaling regulates multiple processes in macrophages and has been implicated in the pathogenesis of non-alcoholic steatohepatitis-related fibrosis. In this study, we explored if MerTK activation in macrophages influences the profibrogenic phenotype of HSCs.

Methods

Macrophages were derived from THP-1 cells or differentiated from peripheral blood monocytes towards MerTK⁺/CD206⁺/CD163⁺/CD209^- macrophages. The role of MerTK was assessed by pharmacologic and genetic inhibition. HSC migration was determined in Boyden chambers, viability was measured by the MTT assay, and proliferation was evaluated by the BrdU incorporation assay.

Results

Gas-6 induced MerTK phosphorylation and Akt activation in macrophages, and these effects were inhibited by UNC569. During polarization, MerTK⁺/CD206⁺/CD163⁺/CD209^- macrophages exhibited activation of STAT3, ERK1/2, p38 and increased expression of VEGF-A. Activation of MerTK in THP-1 macrophages induced a secretome which promoted a significant increase in migration, proliferation, viability and expression of profibrogenic factors in HSCs. Similarly, conditioned medium from MerTK⁺ macrophages induced a significant increase in cell migration, proliferation, STAT3 and p38 phosphorylation and upregulation of IL-8 expression in HSCs. Moreover, conditioned medium from Gas-6-stimulated Kupffer cells induced a significant increase in HSC proliferation. These effects were specifically related to MerTK expression and activity in macrophages, as indicated by pharmacologic inhibition and knockdown experiments.

Conclusions

MerTK activation in macrophages modifies the secretome to promote profibrogenic features in HSCs, implicating this receptor in the pathogenesis of hepatic fibrosis.

Lay summary

Fibrosis represents the process of scarring occurring in patients with chronic liver diseases. This process depends on production of scar tissue components by a specific cell type, named hepatic stellate cells, and is regulated by interaction with other cells. Herein, we show that activation of MerTK, a receptor present in a population of macrophages, causes the production of factors that act on hepatic stellate cells, increasing their ability to produce scar tissue.

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MerTK, a member of the TAM family of proteins, is highly expressed in MerTK⁺/CD206⁺/CD163⁺/CD209^- macrophages.

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In these macrophages, activation of MerTK induces phosphorylation of Akt, STAT3, ERK1/2, p38 and increased expression of VEGF-A.

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MerTK activation in macrophages modulates the secretome to promote the profibrogenic phenotype of human HSCs.

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Profibrogenic effects of macrophages expressing high levels of MerTK were blocked by knockdown or inhibition of MerTK.

The protease-inhibitor SerpinB3 as a critical modulator of the stem-like subset in human cholangiocarcinoma

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) is a form of primary liver cancer with limited therapeutic options. Recently, cancer stem cells (CSCs) have been proposed as a driving force of tumour initiation and dissemination, thus representing a crucial therapeutic target. The protease inhibitor SerpinB3 (SB3) has been identified in several malignancies including hepatocellular carcinoma. SB3 has been involved in the early events of hepatocarcinogenesis and is highly expressed in hepatic progenitor cells and in a mouse model of liver progenitor cell activation. However, only limited information on the possible role of SB3 in CCA stem-like compartment is available.

METHODS

Enrichment of CCA stem-like subset was performed by sphere culture (SPH) in CCA cell lines (CCLP1, HUCCT1, MTCHC01 and SG231). Quantitative RT-PCR and Western blotting were used to detect SB3 in both SPH and parental monolayer (MON) cells. Acquired CSC-like features were analysed using an endogenous and a paracrine in vitro model, with transfection of SB3 gene or addition of recombinant SB3 to cell medium respectively. SB3 tumorigenic role was explored in an in vivo mouse model of CCA by subcutaneous injection of SB3-transfected MON (MON^SB3+ ) cells in immune-deficient NOD-SCID/IL2Rg^null  (NSG) mice. SB3 expression in human CCA sections was investigated by immunohistochemistry. Overall survival (OS) and time to recurrence (TTR) analyses were carried out from a transcriptome database of 104 CCA patients.

RESULTS

SB3, barely detected in parental MON cells, was overexpressed in the same CCA cells grown as 3D SPH. Notably, MON^SB3+ showed significant overexpression of genes associated with stemness (CD24, CD44, CD133), pluripotency (c-MYC, NOTCH1, STAT3, YAP, NANOG, BMI1, KLF4, OCT4, SOX2), epithelial mesenchymal transition (β-catenin, SLUG) and extracellular matrix remodelling (MMP1, MMP7, MMP9, ADAM9, ADAM10, ADAM17, ITGB3). SB3-overexpressing cells showed superior spherogenic capacity and invasion ability compared to control. Importantly, MON^SB3+ exhibited activation of MAP kinases (ERK1/2, p38, JNK) as well as phosphorylation of NFκB (p65) in addition to up-regulation of the proto-oncogene β-catenin. All these effects were reversed after transient silencing of SB3. According to the in vitro finding, MON^SB3+ cells retained high tumorigenic potential in NSG mice. SB3 overexpression was observed in human CCA tissues and analysis of OS as well as TTR indicated a worse prognosis in SB3⁺ CCA patients.

CONCLUSION

These findings indicate a SB3 role in mediating malignant phenotype of CCA and identify a new therapeutic target.

Extracellular Signal-Regulated Kinase 5 Regulates the Malignant Phenotype of Cholangiocarcinoma Cells

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) is characterized by high resistance to chemotherapy and poor prognosis. Several oncogenic pathways converge on activation of extracellular signal-regulated kinase 5 (ERK5), whose role in CCA has not been explored. The aim of this study was to investigate the role of ERK5 in the biology of CCA.

APPROACH AND RESULTS

ERK5 expression was detected in two established (HuCCT-1 and CCLP-1) and two primary human intrahepatic CCA cell lines (iCCA58 and iCCA60). ERK5 phosphorylation was increased in CCA cells exposed to soluble mediators. In both HuCCT-1 and CCLP-1 cells, ERK5 was localized in the nucleus, and exposure to fetal bovine serum (FBS) further increased the amount of nuclear ERK5. In human CCA specimens, ERK5 mRNA expression was increased in tumor cells and positively correlated with portal invasion. ERK5 protein levels were significantly associated with tumor grade. Growth, migration, and invasion of CCA cells were decreased when ERK5 was silenced using specific short hairpin RNA (shRNA). The inhibitory effects on CCA cell proliferation, migration and invasion were recapitulated by treatment with small molecule inhibitors targeting ERK5. In addition, expression of the angiogenic factors VEGF and angiopoietin 1 was reduced after ERK5 silencing. Conditioned medium from ERK5-silenced cells had a lower ability to induce tube formation by human umbilical vein endothelial cells and to induce migration of myofibroblasts and monocytes/macrophages. In mice, subcutaneous injection of CCLP-1 cells silenced for ERK5 resulted in less frequent tumor development and smaller size of xenografts compared with cells transfected with nontargeting shRNA.

CONCLUSIONS

ERK5 is a key mediator of growth and migration of CCA cells and supports a protumorigenic crosstalk between the tumor and the microenvironment.

Mitochondrial oxidative metabolism contributes to a cancer stem cell phenotype in cholangiocarcinoma

BACKGROUND & AIMS

Little is known about the metabolic regulation of cancer stem cells (CSCs) in cholangiocarcinoma (CCA). We analyzed whether mitochondrial-dependent metabolism and related signaling pathways contribute to stemness in CCA.

METHODS

The stem-like subset was enriched by sphere culture (SPH) in human intrahepatic CCA cells (HUCCT1 and CCLP1) and compared to cells cultured in monolayer. Extracellular flux analysis was examined by Seahorse technology and high-resolution respirometry. In patients with CCA, expression of factors related to mitochondrial metabolism was analyzed for possible correlation with clinical parameters.

RESULTS

Metabolic analyses revealed a more efficient respiratory phenotype in CCA-SPH than in monolayers, due to mitochondrial oxidative phosphorylation. CCA-SPH showed high mitochondrial membrane potential and elevated mitochondrial mass, and over-expressed peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α, a master regulator of mitochondrial biogenesis. Targeting mitochondrial complex I in CCA-SPH using metformin, or PGC-1α silencing or pharmacologic inhibition (SR-18292), impaired spherogenicity and expression of markers related to the CSC phenotype, pluripotency, and epithelial-mesenchymal transition. In mice with tumor xenografts generated by injection of CCA-SPH, administration of metformin or SR-18292 significantly reduced tumor growth and determined a phenotype more similar to tumors originated from cells grown in monolayer. In patients with CCA, expression of PGC-1α correlated with expression of mitochondrial complex II and of stem-like genes. Patients with higher PGC-1α expression by immunostaining had lower overall and progression-free survival, increased angioinvasion and faster recurrence. In GSEA analysis, patients with CCA and high levels of mitochondrial complex II had shorter overall survival and time to recurrence.

CONCLUSIONS

The CCA stem-subset has a more efficient respiratory phenotype and depends on mitochondrial oxidative metabolism and PGC-1α to maintain CSC features.

LAY SUMMARY

The growth of many cancers is sustained by a specific type of cells with more embryonic characteristics, termed 'cancer stem cells'. These cells have been described in cholangiocarcinoma, a type of liver cancer with poor prognosis and limited therapeutic approaches. We demonstrate that cancer stem cells in cholangiocarcinoma have different metabolic features, and use mitochondria, an organelle located within the cells, as the major source of energy. We also identify PGC-1α, a molecule which regulates the biology of mitochondria, as a possible new target to be explored for developing new treatments for cholangiocarcinoma.

A Novel Multidrug-Resistant Cell Line from an Italian Intrahepatic Cholangiocarcinoma Patient

Simple Summary

Intrahepatic cholangiocarcinoma (ICC) has limited prognosis and therapies. The first-line gemcitabine-based therapy provided poor benefits in terms of survival due to the development of resistance. Gemcitabine-resistance mechanisms were studied on pancreatic cancer models or cell lines derived from ICC patients of Eastern countries. Since ICC has different etiology and genetic/molecular characteristics depending on the ethnicity, appropriate preclinical models that recapitulate their biology are required. Thus, we aimed to establish and characterize an Italian ICC cell line, named 82.3. Cells were isolated from a patient-derived xenograft. After one year, immunophenotypical, biological, genetic, molecular features, and in vivo tumorigenicity in NOD/SCID mice were investigated. Furthermore, 82.3 cells displayed resistance to gemcitabine, 5-fluorouracil, carboplatin, and oxaliplatin. This model could be exploited either to investigate drug resistance mechanisms or to test alternative drugs through the identification of suitable targets to overcome drug resistance.

Abstract

Chemotherapy resistance is a relevant clinical issue in tumor treatment, in particular in biliary tract carcinoma (BTC), for which there are no effective therapies, neither in the first nor in the second line. The development of chemoresistant cell lines as experimental models to investigate the mechanisms of resistance and identify alternative druggable pathways is mandatory. In BTC, in which genetics and biological behavior depend on the etiology, ethnicity, and anatomical site of origin, the creation of models that better recapitulate these characteristics is even more crucial. Here we have established and characterized an intrahepatic cholangiocarcinoma (iCCA) cell line derived from an Italian patient, called 82.3. Cells were isolated from a patient-derived xenograft (PDX) and, after establishment, immunophenotypic, biological, genetic, molecular characteristics, and tumorigenicity in vivo in NOD/SCID mice were investigated. 82.3 cells exhibited epithelial morphology and cell markers (EPCAM, CK7, and CK19); they also expressed different cancer stem markers (CD44, CD133, CD49b, CD24, Stro1, PAX6, FOXA2, OCT3/4), α–fetoprotein and under anchorage-independent and serum-free conditions were capable of originating cholangiospheres. The population doubling time was approximately 53 h. In vitro, they demonstrated a poor ability to migrate; in vivo, 82.3 cells retained their tumorigenicity, with a long latency period (16 weeks). Genetic identity using DNA fingerprinting analysis revealed 16 different loci, and the cell line was characterized by a complex hyperdiploid karyotype. Furthermore, 82.3 cells showed cross-resistance to gemcitabine, 5-fluorouracil, carboplatin, and oxaliplatin; in fact, their genetic profile showed that 60% of genes (n = 168), specific for drug resistance and related to the epithelial-mesenchymal transition, were deregulated in 82.3 cells compared to a control iCCA cell line sensitive to chemotherapeutics. RNA sequencing analysis revealed the enrichment for genes associated with epithelial to mesenchymal transition (EMT), vasculature development, and extracellular matrix (ECM) remodeling, underlining an aggressive phenotype. In conclusion, we have created a new iCCA cell line of Caucasian origin: this could be exploited as a preclinical model to study drug resistance mechanisms and to identify alternative therapies to improve the prognosis of this tumor type.

Establishment and characterization of a new spontaneously immortalized ER-/PR-/HER2+ human breast cancer cell line, DHSF-BR16

Invasive ductal carcinoma (IDC) constitutes the most frequent malignant cancer endangering women’s health. In this study, a new spontaneously immortalized breast cancer cell line, DHSF-BR16 cells, was isolated from the primary IDC of a 74-years old female patient, treated with neoadjuvant chemotherapy and disease-free 5-years after adjuvant chemotherapy. Primary breast cancer tissue surgically removed was classified as ER⁻/PR⁻/HER2⁺, and the same phenotype was maintained by DHSF-BR16 cells. We examined DHSF-BR16 cell morphology and relevant biological and molecular markers, as well as their response to anticancer drugs commonly used for breast cancer treatment. MCF-7 cells were used for comparison purposes. The DHSF-BR16 cells showed the ability to form spheroids and migrate. Furthermore, DHSF-BR16 cells showed a mixed stemness phenotype (i.e. CD44⁺/CD24^−/low), high levels of cytokeratin 7, moderate levels of cytokeratin 8 and 18, EpCAM and E-Cadh. Transcriptome analysis showed 2071 differentially expressed genes between DHSF-BR16 and MCF-7 cells (logFC > 2, p-adj < 0.01). Several genes were highly upregulated or downregulated in the new cell line (log2 scale fold change magnitude within − 9.6 to + 12.13). A spontaneous immortalization signature, mainly represented by extracellular exosomes-, plasma membrane- and endoplasmic reticulum membrane pathways (GO database) as well as by metabolic pathways (KEGG database) was observed in DHSF-BR16 cells. Also, these cells were more resistant to anthracyclines compared with MCF-7 cells. Overall, DHSF-BR16 cell line represents a relevant model useful to investigate cancer biology, to identify both novel prognostic and drug response predictive biomarkers as well as to assess new therapeutic strategies.

Cholangiocarcinoma 2020: the next horizon in mechanisms and management

Cholangiocarcinoma (CCA) includes a cluster of highly heterogeneous biliary malignant tumours that can arise at any point of the biliary tree. Their incidence is increasing globally, currently accounting for ~15% of all primary liver cancers and ~3% of gastrointestinal malignancies. The silent presentation of these tumours combined with their highly aggressive nature and refractoriness to chemotherapy contribute to their alarming mortality, representing ~2% of all cancer-related deaths worldwide yearly. The current diagnosis of CCA by non-invasive approaches is not accurate enough, and histological confirmation is necessary. Furthermore, the high heterogeneity of CCAs at the genomic, epigenetic and molecular levels severely compromises the efficacy of the available therapies. In the past decade, increasing efforts have been made to understand the complexity of these tumours and to develop new diagnostic tools and therapies that might help to improve patient outcomes. In this expert Consensus Statement, which is endorsed by the European Network for the Study of Cholangiocarcinoma, we aim to summarize and critically discuss the latest advances in CCA, mostly focusing on classification, cells of origin, genetic and epigenetic abnormalities, molecular alterations, biomarker discovery and treatments. Furthermore, the horizon of CCA for the next decade from 2020 onwards is highlighted.

Role of Chemokines in the Biology of Cholangiocarcinoma

Cholangiocarcinoma (CCA), a heterogeneous tumor with poor prognosis, can arise at any level in the biliary tree. It may derive from epithelial cells in the biliary tracts and peribiliary glands and possibly from progenitor cells or even hepatocytes. Several risk factors are responsible for CCA onset, however an inflammatory milieu nearby the biliary tree represents the most common condition favoring CCA development. Chemokines play a key role in driving the immunological response upon liver injury and may sustain tumor initiation and development. Chemokine receptor-dependent pathways influence the interplay among various cellular components, resulting in remodeling of the hepatic microenvironment towards a pro-inflammatory, pro-fibrogenic, pro-angiogenic and pre-neoplastic setting. Moreover, once tumor develops, chemokine signaling may influence its progression. Here we review the role of chemokines in the regulation of CCA development and progression, and the modulation of angiogenesis, metastasis and immune control. The potential role of chemokines and their receptors as possible biomarkers and/or therapeutic targets for hepatobiliary cancer is also discussed.

Free episomal and integrated HBV DNA in HBsAg-negative patients with intrahepatic cholangiocarcinoma

There is evidence that chronic hepatitis B virus (HBV) infection is associated with an increased risk of intrahepatic cholangiocarcinoma (ICC) development, and it has been hypothesized an etiological role of HBV in the development of this tumor. Very little is known about occult HBV infection (OBI) in ICC. Aims of the study were to investigate the OBI prevalence and to characterize the HBV molecular status at intrahepatic level in OBI-positive cases with ICC.

Frozen liver tumor specimens from 47 HBV surface-antigen-negative patients with ICC and 41 paired non-tumor liver tissues were tested for OBI by 4 different HBV-specific nested PCR. Covalently closed circular HBV DNA (HBV cccDNA) and viral integrations were investigated in OBI-positive cases.

HBV DNA was detected in tumor and/or non-tumor specimens from 29/47 (61.7%) ICC patients. HBV cccDNA was found in tissues from 5/17 (34.5%) cases examined. HBV integration was detected in 4/10 (40%) tumor tissues tested and involved HBx and HBV-core gene sequences in 3 and 1 cases, respectively. Viral integration occurred: (a) 9,367 nucleotides upstream of the cat-eye-syndrome critical region protein-5-isoform coding sequence; (b) within the cystinosin isoform-1-precursor gene; (c) within the thromboxane-A-synthase-1 gene; (d) within the ATPase phospholipid transporting 9B gene.

Occult HBV infection is highly prevalent in patients with ICC. Both free viral genomes and integrated HBV DNA can be present in these cases. These results suggest an involvement of HBV in the carcinogenic process leading to ICC development even in cases with occult infection.

Role of Myeloid-Epithelial-Reproductive Tyrosine Kinase and Macrophage Polarization in the Progression of Atherosclerotic Lesions Associated With Nonalcoholic Fatty Liver Disease

Recent lines of evidence highlight the involvement of myeloid-epithelial-reproductive tyrosine kinase (MerTK) in metabolic disease associated with liver damage. MerTK is mainly expressed in anti-inflammatory M2 macrophages where it mediates transcriptional changes including suppression of proinflammatory cytokines and enhancement of inflammatory repressors. MerTK is regulated by metabolic pathways through nuclear sensors including LXRs, PPARs, and RXRs, in response to apoptotic bodies or to other sources of cholesterol. Nonalcoholic fatty liver disease (NAFLD) is one of the most serious public health problems worldwide. It is a clinicopathological syndrome closely related to obesity, insulin resistance, and oxidative stress. It includes a spectrum of conditions ranging from simple steatosis, characterized by hepatic fat accumulation with or without inflammation, to nonalcoholic steatohepatitis (NASH), defined by hepatic fat deposition with hepatocellular damage, inflammation, and accumulating fibrosis. Several studies support an association between NAFLD and the incidence of cardiovascular diseases including atherosclerosis, a major cause of death worldwide. This pathological condition consists in a chronic and progressive inflammatory process in the intimal layer of large- and medium-sized arteries. The complications of advanced atherosclerosis include chronic or acute ischemic damage in the tissue perfused by the affected artery, leading to cellular death. By identifying specific targets influencing lipid metabolism and cardiovascular-related diseases, the present review highlights the role of MerTK in NAFLD-associated atherosclerotic lesions as a potential innovative therapeutic target. Therapeutic advantages might derive from the use of compounds selective for nuclear receptors targeting PPARs rather than LXRs regulating macrophage lipid metabolism and macrophage mediated inflammation, by favoring the expression of MerTK, which mediates an immunoregulatory action with a reduction in inflammation and in atherosclerosis.

Experimental models to unravel the molecular pathogenesis, cell of origin and stem cell properties of cholangiocarcinoma

Human cholangiocarcinoma (CCA) is an aggressive tumour entity arising from the biliary tree, whose molecular pathogenesis remains largely undeciphered. Over the last decade, the advent of high-throughput and cell-based techniques has significantly increased our knowledge on the molecular mechanisms underlying this disease while, at the same time, unravelling CCA complexity. In particular, it becomes clear that CCA displays pronounced inter- and intratumoural heterogeneity, which is presumably the consequence of the interplay between distinct tissues and cells of origin, the underlying diseases, and the associated molecular alterations. To better characterize these events and to design novel and more effective therapeutic strategies, a number of CCA experimental and preclinical models have been developed and are currently generated. This review summarizes the current knowledge and understanding of these models, critically underlining their translational usefulness and limitations. Furthermore, this review aims to provide a comprehensive overview on cells of origin, cancers stem cells and their dynamic interplay within CCA tissue.

Establishment and Characterization of a New Intrahepatic Cholangiocarcinoma Cell Line Resistant to Gemcitabine

Intrahepatic cholangiocarcinoma (ICC) is one of the most lethal liver cancers. Late diagnosis and chemotherapy resistance contribute to the scarce outfit and poor survival. Resistance mechanisms are still poorly understood. Here, we established a Gemcitabine (GEM) resistant model, the MT-CHC01R1.5 cell line, obtained by a GEM gradual exposure (up to 1.5 µM) of the sensitive counterpart, MT-CHC01. GEM resistance was irreversible, even at high doses. The in vitro and in vivo growth was slower than MT-CHC01, and no differences were highlighted in terms of migration and invasion. Drug prediction analysis suggested that Paclitaxel and Doxycycline might overcome GEM resistance. Indeed, in vitro MT-CHC01R1.5 growth was reduced by Paclitaxel and Doxycycline. Importantly, Doxycycline pretreatment at very low doses restored GEM sensitivity. To assess molecular mechanisms underlying the acquisition of GEM resistance, a detailed analysis of the transcriptome in MT-CHC01R1.5 cells versus the corresponding parental counterpart was performed. Transcriptomic analysis showed that most up-regulated genes were involved in cell cycle regulation and in the DNA related process, while most down-regulated genes were involved in the response to stimuli, xenobiotic metabolism, and angiogenesis. Furthermore, additional panels of drug resistance and epithelial to mesenchymal transition genes (n = 168) were tested by qRT-PCR and the expression of 20 genes was affected. Next, based on a comparison between qRT-PCR and microarray data, a list of up-regulated genes in MT-CHC01R1.5 was selected and further confirmed in a primary cell culture obtained from an ICC patient resistant to GEM. In conclusion, we characterized a new GEM resistance ICC model that could be exploited either to study alternative mechanisms of resistance or to explore new therapies.

Assessment of a High Sensitivity Method for Identification of IDH1 R132x Mutations in Tumors and Plasma of Intrahepatic Cholangiocarcinoma Patients

Hotspot codon 132 mutations (R132xIDH1m) are frequent in intrahepatic cholangiocarcinoma (ICC), are druggable by anti-IDH1m agents, and could represent a marker of disease progression. Developing an assay to identify R132xIDH1m would provide a useful tool to select patients benefitting from targeted treatments. We tested a quantitative real-time allele-specific polymerase chain reaction (qPCR)-based method to detect the main R132xIDH1m in an Italian ICC series (n = 61) of formalin-fixed paraffin-embedded (FFPE) samples, and on circulating-free DNA samples. The outcomes were compared with nested PCR/Sanger sequencing. Reconstitution experiments of plasmids harboring the different R132xIDH1m mixed with wild-type (WT) DNA demonstrated that qPCR is able to detect at least 2% of all mutated allele. High efficiency was also observed on patient-derived mutated DNA mixed with WT DNA (up to 10% and 0.3 ng of mutated template); qPCR detected 16.4% of mutated samples (one R132G, three R132C and six R132L) while nested PCR/Sanger sequencing only 8.2% (four R132L and one R132G). In a single patient with an R132C-mutated tumor, qPCR was also performed on plasma samples collected at four time-points, observing an increase correlating with disease progression. In conclusion, we developed a qPCR assay which could represent a fast, inexpensive and sensitive tool both for detection of R132xIDH1m in ICC samples and monitoring disease progression from liquid biopsy.

Iron Metabolism in Liver Cancer Stem Cells

Cancer stem cells (CSC) which have been identified in several tumors, including liver cancer, represent a particular subpopulation of tumor cells characterized by properties similar to those of adult stem cells. Importantly, CSC are resistant to standard therapies, thereby leading to metastatic dissemination and tumor relapse. Given the increasing evidence that iron homeostasis is deregulated in cancer, here we describe the iron homeostasis alterations in cancer cells, particularly in liver CSC. We also discuss two paradoxically opposite iron manipulation-strategies for tumor therapy based either on iron chelation or iron overload-mediated oxidant production leading to ferroptosis. A better understanding of iron metabolism modifications occurring in hepatic tumors and particularly in liver CSC cells may offer new therapeutic options for this cancer, which is characterized by increasing incidence and unfavorable prognosis.

The Role of Stroma in Cholangiocarcinoma: The Intriguing Interplay between Fibroblastic Component, Immune Cell Subsets and Tumor Epithelium

Cholangiocarcinoma (CCA) is a severe and mostly intractable adenocarcinoma of biliary epithelial cells. A typical feature of CCA is its highly desmoplastic microenvironment containing fibrogenic connective tissue and an abundance of immune cells (T lymphocytes, Natural Killer (NK) cells, and macrophages) infiltrating tumor epithelium. This strong desmoplasia is orchestrated by various soluble factors and signals, suggesting a critical role in shaping a tumor growth-permissive microenvironment that is responsible for CCA poor clinical outcome. Indeed stroma not only provides an abundance of factors that facilitate CCA initiation, growth and progression, but also a prejudicial impact on therapeutic outcome. This review will give an overview of tumor-stroma signaling in a microenvironment critically regulating CCA development and progression. Identification of CCA secreted factors by both the fibroblast component and immune cell subsets might provide ample opportunities for pharmacological targeting of this type of cancer.

Genomic perturbations reveal distinct regulatory networks in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma remains a highly heterogeneous malignancy that has eluded effective patient stratification to date. The extent to which such heterogeneity can be influenced by individual driver mutations remains to be evaluated. Here, we analyzed genomic (whole-exome sequencing, targeted exome sequencing) and epigenomic data from 496 patients and used the three most recurrently mutated genes to stratify patients (IDH, KRAS, TP53, "undetermined"). Using this molecular dissection approach, each subgroup was determined to possess unique mutational signature preferences, comutation profiles, and enriched pathways. High-throughput drug repositioning in seven patient-matched cell lines, chosen to reflect the genetic alterations specific for each patient group, confirmed in silico predictions of subgroup-specific vulnerabilities linked to enriched pathways. Intriguingly, patients lacking all three mutations ("undetermined") harbored the most extensive structural alterations, while isocitrate dehydrogenase mutant tumors displayed the most extensive DNA methylome dysregulation, consistent with previous findings.

CONCLUSION

Stratification of intrahepatic cholangiocarcinoma patients based on occurrence of mutations in three classifier genes (IDH, KRAS, TP53) revealed unique oncogenic programs (mutational, structural, epimutational) that influence pharmacologic response in drug repositioning protocols; this genome dissection approach highlights the potential of individual mutations to induce extensive molecular heterogeneity and could facilitate advancement of therapeutic response in this dismal disease. (Hepatology 2018).

Transcriptomic analysis and mutational status of IDH1 in paired primary-recurrent intrahepatic cholangiocarcinoma

Background

Effective target therapies for intrahepatic cholangiocarcinoma (ICC) have not been identified so far. One of the reasons may be the genetic evolution from primary (PR) to recurrent (REC) tumors. We aim to identify peculiar characteristics and to select potential targets specific for recurrent tumors.

Eighteen ICC paired PR and REC tumors were collected from 5 Italian Centers. Eleven pairs were analyzed for gene expression profiling and 16 for mutational status of IDH1. For one pair, deep mutational analysis by Next Generation Sequencing was also carried out. An independent cohort of patients was used for validation.

Results

Two class-paired comparison yielded 315 differentially expressed genes between REC and PR tumors. Up-regulated genes in RECs are involved in RNA/DNA processing, cell cycle, epithelial to mesenchymal transition (EMT), resistance to apoptosis, and cytoskeleton remodeling. Down-regulated genes participate to epithelial cell differentiation, proteolysis, apoptotic, immune response, and inflammatory processes. A 24 gene signature is able to discriminate RECs from PRs in an independent cohort; FANCG is statistically associated with survival in the chol-TCGA dataset. IDH1 was mutated in the RECs of five patients; 4 of them displayed the mutation only in RECs. Deep sequencing performed in one patient confirmed the IDH1 mutation in REC.

Conclusions

RECs are enriched for genes involved in EMT, resistance to apoptosis, and cytoskeleton remodeling. Key players of these pathways might be considered druggable targets in RECs. IDH1 is mutated in 30% of RECs, becoming both a marker of progression and a target for therapy.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4829-0) contains supplementary material, which is available to authorized users.

Stem-like plasticity and heterogeneity of circulating tumor cells: current status and prospect challenges in liver cancer

Poor prognosis and high recurrence remain leading causes of primary liver cancerassociated mortality. The spread of circulating tumor cells (CTCs) in the blood plays a major role in the initiation of metastasis and tumor recurrence after surgery. Nevertheless, only a subset of CTCs can survive, migrate to distant sites and establish secondary tumors. Consistent with cancer stem cell (CSC) hypothesis, stem-like CTCs might represent a potential source for cancer relapse and distant metastasis. Thus, identification of stem-like metastasis-initiating CTC-subset may provide useful clinically prognostic information. This review will emphasize the most relevant findings of CTCs in the context of stem-like biology associated to liver carcinogenesis. In this view, the emerging field of stem-like CTCs may deliver substantial contribution in liver cancer field in order to move to personalized approaches for diagnosis, prognosis and therapy.

Dysregulation of Iron Metabolism in Cholangiocarcinoma Stem-like Cells

Cholangiocarcinoma (CCA) is a devastating liver tumour arising from malignant transformation of bile duct epithelial cells. Cancer stem cells (CSC) are a subset of tumour cells endowed with stem-like properties, which play a role in tumour initiation, recurrence and metastasis. In appropriate conditions, CSC form 3D spheres (SPH), which retain stem-like tumour-initiating features. Here, we found different expression of iron proteins indicating increased iron content, oxidative stress and higher expression of CSC markers in CCA-SPH compared to tumour cells growing as monolayers. Exposure to the iron chelator desferrioxamine decreased SPH forming efficiency and the expression of CSC markers and stem-like genes, whereas iron had an opposite effect. Microarray profiles in CCA samples (n = 104) showed decreased H ferritin, hepcidin and ferroportin expression in tumours respect to surrounding liver, whereas transferrin receptor was up-regulated. Moreover, we found a trend toward poorer outcome in CCA patients with elevated expression of ferritin and hepcidin, two major proteins of iron metabolism. These findings, which represent the first evidence of a role for iron in the stem cell compartment as a novel metabolic factor involved in CCA growth, may have implications for a better therapeutic approach.

RNA-seq reveals distinctive RNA profiles of small extracellular vesicles from different human liver cancer cell lines

Liver cancer (LC) is one of the most common cancers and represents the third highest cause of cancer-related deaths worldwide. Extracellular vesicle (EVs) cargoes, which are selectively enriched in RNA, offer great promise for the diagnosis, prognosis and treatment of LC. Our study analyzed the RNA cargoes of EVs derived from 4 liver-cancer cell lines: HuH7, Hep3B, HepG2 (hepato-cellular carcinoma) and HuH6 (hepatoblastoma), generating two different sets of sequencing libraries for each. One library was size-selected for small RNAs and the other targeted the whole transcriptome. Here are reported genome wide data of the expression level of coding and non-coding transcripts, microRNAs, isomiRs and snoRNAs providing the first comprehensive overview of the extracellular-vesicle RNA cargo released from LC cell lines. The EV-RNA expression profiles of the four liver cancer cell lines share a similar background, but cell-specific features clearly emerge showing the marked heterogeneity of the EV-cargo among the individual cell lines, evident both for the coding and non-coding RNA species.

Abstract 2677: Role of CLEC4D in inflammation-driven liver carcinogenesis

Hepatocellular carcinoma (HCC) accounts for approximately 90% of all primary liver tumors and is the second most deadly cancer in the world. HCC commonly arises in a chronically damaged liver that contains large amounts of inflammation and fibrosis. Indeed, interactions among hepatocytes, stromal, and inflammatory cells create a complex microenvironment permissive to tumor development. Myeloid cells are crucial players in cancer-related inflammation. From transcriptional profiling of liver myeloid cells, we identified the gene encoding for the C-type lectin receptor CLEC4D as one of the genes upregulated during the inflammatory response that precedes cancer development in a spontaneous model of murine HCC. We hypothesized that CLEC4D may be involved in the molecular mechanisms that drive HCC pathogenesis. We used the murine model of diethylnitrosamine (DEN)-induced liver carcinogenesis and evaluated tumor growth in genetically modified mice lacking CLEC4D (CLEC4D KO mice), as compared to C57BL/6 wild type (WT) mice. We observed that tumor burden (number of tumors per mouse and tumor dimensions) was reduced in CLEC4D KO mice compared to WT mice. Gene expression analysis of tumor lesions showed that the tumor microenvironment of CLEC4D KO mice was less inflammatory. CLEC4D expression was then evaluated in surgical specimens and tissue microarrays from HCV+ HCC patients. CLEC4D-positive inflammatory cells (macrophages and granulocytes) were present both in the peritumor and in the tumor areas. The percentage of intratumor CLEC4D-positive cells inversely correlated with the degree of the lesion: CLEC4D expression was higher in dysplastic nodules compared to high grade HCCs. Our results indicate that the CLEC4D-dependent pathway contributes to the initiation and the progression of HCC. By targeting CLEC4D, we could modulate immune responses and provide an environment less favorable to tumor growth. An intervention at this level could represent a chemopreventive strategy to arrest the development of HCC in a cirrhotic liver.This work has been supported by Fondazione Cariplo, grant n° 2014-0962.

Citation Format: Elena Riboldi, Luca Di Tommaso, Nausicaa Clemente, Chiara Raggi, Elisa Forti, Simone Merlin, Fabio Pasqualini, Antonia Follenzi, Antonio Sica. Role of CLEC4D in inflammation-driven liver carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2677. doi:10.1158/1538-7445.AM2017-2677

Outcome of hepatitis B and C virus-associated hepatocellular carcinoma occurring after renal transplantation

Kidney transplant recipients (KTR) are subjected to immunosuppressive therapy that can enhance hepatitis B and C virus replication, leading to cirrhosis and hepatocellular carcinoma (HCC). The aim of this study was to assess the prevalence and outcome of HCC in KTR. Case-control study. Patients with chronic HBV and/or HCV infection who underwent kidney transplantation between 1976 and 2011 and subsequently developed HCC were compared to a control group of patients with chronic HBV and/or HCV infection, matched for gender and age at HCC diagnosis, who did not receive kidney transplantation. Among 2944 KTR, 330 had hepatitis B and/or C. Fourteen developed HCC, a period prevalence of 4.2%. Age at HCC diagnosis was 52.6 ± 6.5 years (53.5 ± 5.7 in controls, P=.76). Time between transplantation and HCC diagnosis was 16.7 ± 2.7 years. Six HCCs were related to HBV, six to HCV and two to co-infection with HBV and HCV. Immunosuppressive therapy was comparable in HBV, HCV and HBV+HCV patients. At diagnosis, 71% of patients met Milan criteria (65% in the control group, P=.4). Alpha-fetoprotein levels, tumour characteristics and treatment modalities were comparable between both groups. Patient survival 2 years after HCC diagnosis was 28% in KTR, compared to 68% in controls (P=.024). Survival after HCC diagnosis is significantly worse in KTR compared to nontransplanted patients with HBV and/or HCV. Prevention is crucial and should be based on viral eradication/suppression before or after transplantation.

Cholangiocarcinoma stem-like subset shapes tumor-initiating niche by educating associated macrophages

BACKGROUND & AIMS

A therapeutically challenging subset of cells, termed cancer stem cells (CSCs) are responsible for cholangiocarcinoma (CCA) clinical severity. Presence of tumor-associated macrophages (TAMs) has prognostic significance in CCA and other malignancies. Thus, we hypothesized that CSCs may actively shape their tumor-supportive immune niche.

METHODS

CCA cells were cultured in 3D conditions to generate spheres. CCA sphere analysis of in vivo tumorigenic-engraftment in immune-deficient mice and molecular characterization was performed. The in vitro and in vivo effect of CCA spheres on macrophage precursors was tested after culturing healthy donor cluster of differentiation (CD)14⁺ with CCA-sphere conditioned medium.

RESULTS

CCA spheres engrafted in 100% of transplanted mice and revealed a significant 20.3-fold increase in tumor-initiating fraction (p=0.0011) and a sustained tumorigenic potential through diverse xenograft-generations. Moreover, CCA spheres were highly enriched for CSC, liver cancer and embryonic stem cell markers both at gene and protein levels. Next, fluorescence-activated cell sorting analysis showed that in the presence of CCA sphere conditioned medium, CD14⁺ macrophages expressed key markers (CD68, CD115, human leukocyte antigen-D related, CD206) indicating that CCA sphere conditioned medium was a strong macrophage-activator. Gene expression profile of CCA sphere activated macrophages revealed unique molecular TAM-like features confirmed by high invasion capacity. Also, freshly isolated macrophages from CCA resections recapitulated a similar molecular phenotype of in vitro-educated macrophages. Consistent with invasive features, the largest CD163⁺ set was found in the tumor front of human CCA specimens (n=23) and correlated with a high level of serum cancer antigen 19.9 (n=17). Among mediators released by CCA spheres, only interleukin (IL)13, IL34 and osteoactivin were detected and further confirmed in CCA patient sera (n=12). Surprisingly, a significant association of IL13, IL34 and osteoactivin with sphere stem-like genes was provided by a CCA database (n=104). In vitro combination of IL13, IL34, osteoactivin was responsible for macrophage-differentiation and invasion, as well as for in vivo tumor-promoting effect.

CONCLUSION

CCA-CSCs molded a specific subset of stem-like associated macrophages thus providing a rationale for a synergistic therapeutic strategy for CCA-disease.

LAY SUMMARY

Immune plasticity represents an important hallmark of tumor outcome. Since cancer stem cells are able to manipulate stromal cells to their needs, a better definition of the key dysregulated immune subtypes responsible for cooperating in supporting tumor initiation may facilitate the development of new therapeutic approaches. Considering that human cholangiocarcinoma represents a clinical emergency, it is essential to move to predictive models in order to understand the adaptive process of macrophage component (imprinting, polarization and maintenance) engaged by tumor stem-like compartment.

Sex-Specific Effects of Prenatal Stress on Bdnf Expression in Response to an Acute Challenge in Rats: a Role for Gadd45β

Exposure to early adversities represents a major risk factor for psychiatric disorders. We have previously shown that exposure to prenatal stress (PNS) in rats alters the developmental expression of brain-derived neurotrophic factor (Bdnf) with a specific temporal profile. However, exposure to early-life stress is known to alter the ability to cope with challenging events later in life, which may contribute to the enhanced vulnerability to stress-related disorders. Since Bdnf is also an important player for activity-dependent plasticity, we investigated whether the exposure to PNS in rats could alter Bdnf responsiveness to an acute challenge at adulthood. We found that exposure to PNS produces significant changes in Bdnf responsiveness with brain region- and gender-specific selectivity. Indeed, exposure to an acute stress upregulates Bdnf expression in the prefrontal cortex, but not in the hippocampus, of control animals. Moreover, such modulatory activity is selectively impaired in PNS female rats, an effect that was associated with changes in the modulation of the DNA demethylase Gadd45β. Our results suggest that exposure to PNS may reprogram gene transcription through epigenetic mechanisms reducing the ability to cope under adverse conditions, a trait that is disrupted in psychiatric diseases.

Expert consensus document: Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

Cholangiocarcinoma (CCA) is a heterogeneous group of malignancies with features of biliary tract differentiation. CCA is the second most common primary liver tumour and the incidence is increasing worldwide. CCA has high mortality owing to its aggressiveness, late diagnosis and refractory nature. In May 2015, the "European Network for the Study of Cholangiocarcinoma" (ENS-CCA: www.enscca.org or www.cholangiocarcinoma.eu) was created to promote and boost international research collaboration on the study of CCA at basic, translational and clinical level. In this Consensus Statement, we aim to provide valuable information on classifications, pathological features, risk factors, cells of origin, genetic and epigenetic modifications and current therapies available for this cancer. Moreover, future directions on basic and clinical investigations and plans for the ENS-CCA are highlighted.

Impact of microenvironment and stem-like plasticity in cholangiocarcinoma: molecular networks and biological concepts

Clinical complexity, anatomic diversity and molecular heterogeneity of cholangiocarcinoma (CCA) represent a major challenge in the assessment of effective targeted therapies. Molecular and cellular mechanisms underlying the diversity of CCA growth patterns remain a key issue of clinical concern. Crucial questions comprise the nature of the CCA-origin, the initial target for cellular transformation as well as the relationship with the cancer stem cells (CSC) concept. Additionally, since CCA often develops in the context of an inflammatory milieu (cirrhosis and cholangitis), the stromal compartment or tumour microenvironment (TME) likely promotes initiation and progression of this malignancy, contributing to its heterogeneity. This review will emphasize the dynamic interplay between stem-like intrinsic and TME-extrinsic pathways, which may represent novel options for multi-targeted therapies in CCA.

Antitumor effects in hepatocarcinoma of isoform-selective inhibition of HDAC2

Histone deacetylase 2 (HDAC2) is a chromatin modifier involved in epigenetic regulation of cell cycle, apoptosis, and differentiation that is upregulated commonly in human hepatocellular carcinoma (HCC). In this study, we show that specific targeting of this HDAC isoform is sufficient to inhibit HCC progression. siRNA-mediated silencing of HDAC inhibited HCC cell growth by blocking cell-cycle progression and inducing apoptosis. These effects were associated with deregulation of HDAC-regulated genes that control cell cycle, apoptosis, and lipid metabolism, specifically, by upregulation of p27 and acetylated p53 and by downregulation of CDK6 and BCL2. We found that HDAC2 silencing in HCC cells also strongly inhibited PPARγ signaling and other regulators of glycolysis (ChREBPα and GLUT4) and lipogenesis (SREBP1C and FAS), eliciting a marked decrease in fat accumulation. Notably, systemic delivery of HDAC2 siRNA encapsulated in lipid nanoparticles was sufficient to blunt the growth of human HCC in a murine xenograft model. Our findings offer preclinical proof-of-concept for HDAC2 blockade as a systemic therapy for liver cancer.

Epigenetic reprogramming modulates malignant properties of human liver cancer

Reversal of DNA hypermethylation and associated gene silencing is an emerging cancer therapy approach. Here we addressed the impact of epigenetic alterations and cellular context on functional and transcriptional reprogramming of hepatocellular carcinoma (HCC) cells. Our strategy employed a 3-day treatment of established and primary human HCC-derived cell lines grown as a monolayer at various cell densities with the DNMT1 inhibitor zebularine (ZEB) followed by a 3D culture to identify cells endowed with self-renewal potential. Differences in self-renewal, gene expression, tumorigenicity, and metastatic potential of spheres at generations G1-G5 were examined. Transient ZEB exposure produced differential cell density-dependent responses. In cells grown at low density, ZEB caused a remarkable increase in self-renewal and tumorigenicity associated with long-lasting gene expression changes characterized by a stable overexpression of cancer stem cell-related and key epithelial-mesenchymal transition genes. These effects persisted after restoration of DNMT1 expression. In contrast, at high cell density, ZEB caused a gradual decrease in self-renewal and tumorigenicty, and up-regulation of apoptosis- and differentiation-related genes. A permanent reduction of DNMT1 protein using short hairpin RNA (shRNA)-mediated DNMT1 silencing rendered HCC cells insensitive both to cell density and ZEB effects. Similarly, WRL68 and HepG2 hepatoblastoma cells expressing low DNMT1 basal levels also possessed a high self-renewal, irrespective of cell density or ZEB exposure. Spheres formed by low-density cells treated with ZEB or shDNMT1 displayed a high molecular similarity which was sustained through consecutive generations, confirming the essential role of DNMT1 depletion in the enhancement of cancer stem cell properties.

CONCLUSION

These results identify DNA methylation as a key epigenetic regulatory mechanism determining the pool of cancer stem cells in liver cancer and possibly other solid tumors.

Methylation and liver cancer

Cancer evolution at all stages (including initiation, progression and invasion) is driven by both epigenetic abnormalities and genetic alterations. Epigenetics refer to any structural modification of genomic regions, which lead to modification in gene expression without alterations in DNA sequence. Progressive deregulation of epigenetic process is being increasingly recognized in liver carcinogenesis. This review will provide an overview of DNA methylation, one of the most commonly epigenetic events, which profoundly contributes to liver cancer initiation and progression. Furthermore, the recent advancements in the knowledge of epigenetic reprogramming underlying hepatic cancer stem cells will be highlighted.

Modeling pathogenesis of primary liver cancer in lineage-specific mouse cell types

BACKGROUND & AIMS

Human primary liver cancer is classified into biologically distinct subgroups based on cellular origin. Liver cancer stem cells (CSCs) have been recently described. We investigated the ability of distinct lineages of hepatic cells to become liver CSCs and the phenotypic and genetic heterogeneity of primary liver cancer.

METHODS

We transduced mouse primary hepatic progenitor cells, lineage-committed hepatoblasts, and differentiated adult hepatocytes with transgenes encoding oncogenic H-Ras and SV40LT. The CSC properties of transduced cells and their ability to form tumors were tested by standard in vitro and in vivo assays and transcriptome profiling.

RESULTS

Irrespective of origin, all transduced cells acquired markers of CSC/progenitor cells, side populations, and self-renewal capacity in vitro. They also formed a broad spectrum of liver tumors, ranging from cholangiocarcinoma to hepatocellular carcinoma, which resembled human liver tumors, based on genomic and histologic analyses. The tumor cells coexpressed hepatocyte (hepatocyte nuclear factor 4α), progenitor/biliary (keratin 19, epithelial cell adhesion molecule, A6), and mesenchymal (vimentin) markers and showed dysregulation of genes that control the epithelial-mesenchymal transition. Gene expression analyses could distinguish tumors of different cellular origin, indicating the contribution of lineage stage-dependent genetic changes to malignant transformation. Activation of c-Myc and its target genes was required to reprogram adult hepatocytes into CSCs and for tumors to develop. Stable knockdown of c-Myc in transformed adult hepatocytes reduced their CSC properties in vitro and suppressed growth of tumors in immunodeficient mice.

CONCLUSIONS

Any cell type in the mouse hepatic lineage can undergo oncogenic reprogramming into a CSC by activating different cell type-specific pathways. Identification of common and cell of origin-specific phenotypic and genetic changes could provide new therapeutic targets for liver cancer.

Abstract 2653: Direct oncogenic reprogramming of adult mouse hepatocytes into cancer stem cells

Objective: Primary human liver cancer (PLC), the third most lethal cancer worldwide, is classified into biologically distinct subgroups, which suggests origin from different hepatic lineage cells. The existence of cancer stem cells (CSCs) was reported in PLC, but the cellular origin of liver CSCs has not been elucidated. Our aim was to investigate the contribution of different hepatic lineage cells to the evolution of CSCs and the phenotypic and genetic heterogeneity of PLC. Methods: Three cell types at different levels of differentiation, including primary mouse hepatic progenitor cells (HPCs), lineage committed hepatoblasts (HBs) and terminally differentiated hepatocytes (AHs) were co-transduced with lentiviral vectors carrying oncogenic H-Ras-Luciferase/EGFP and SV40 large T (LT)-mCherry. CSC properties of FACS sorted H-Ras-EGFP+/SV40LT-mCherry+ cells were tested by standard in vitro and in vivo assays. Individual liver tumors derived from intrasplenic injection of transduced HPCs, HBs and AHs were subjected to immunohistochemistry and whole transcriptome profiling. Results: HPCs, HBs and AHs were susceptible to transformation albeit with a different efficiency as shown by the frequency of tumor initiating cells (1/7, 1/26 and 1/42, respectively). All transduced cells acquired similar attributes of liver CSCs in vitro as judged by self-renewal ability, expression of CSC marker CD133, CD24, CD44 and CD90 and high percentage of side population cells. HPC-, HB- and AH-initiated liver tumors commonly showed a multi-lineage differentiation expressing hepatocyte (HNFα), hepatic progenitor cell (EpCAM, cytokeratin 19, A6) and mesenchymal (vimentin) markers and resembled human PLC. Nevertheless, tumors displayed distinct morphophenotypes according to their cell-of origin: AH tumors showed predominantly hepatocellular carcinoma, HB tumors cholangicarcinoma and HPC tumors epithelial-mesenchymal transition (EMT)-like features. Gene expression analyses revealed the activation of EMT- and embryonic cell-related transcriptional programs in all tumors with the highest number of significant genetic changes in AH (2826) versus HB (574) and HPC tumors (906). Hierarchical clustering distinguished tumors of different cellular origin underscoring the contribution of lineage-stage-dependent genetic changes in malignant transformation. Notably, AH-derived tumors showed specific enrichment of c-Myc target genes. Stable knockdown of c-Myc in transformed AHs reduced their CSC properties and delayed tumor growth. Conclusions: Our results indicate that liver tumors with dominant CSC features can originate from any cell in the hepatocytic lineage. Identification of common and cell-of-origin specific phenotypic and genetic changes may provide novel therapeutic targets for treatment of PLC.

Citation Format: Agnes Holczbauer, Valentina M. Factor, Jesper B. Andersen, David E. Kleiner, Jens U. Marquardt, Chiara Raggi, Mitsuteru Kitade, Daekwan Seo, Akita Hirofumi, Marian E. Durkin, Snorri S. Thorgeirsson. Direct oncogenic reprogramming of adult mouse hepatocytes into cancer stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2653. doi:10.1158/1538-7445.AM2013-2653

Mesenchymal stem cells, aging and regenerative medicine

Tissue maintenance and regeneration is dependent on stem cells and increasing evidence has shown to decline with age. Stem cell based-aging is thought to influence therapeutic efficacy. Mesenchymal stromal cells (MSCs) are involved in tissue regeneration. Here, we discuss the effects of age-related changes on MSC properties considering their possible use in research or regenerative medicine.

Hepatocyte growth factor/c-met signaling is required for stem-cell-mediated liver regeneration in mice

Hepatocyte growth factor (HGF)/c-Met supports a pleiotrophic signal transduction pathway that controls stem cell homeostasis. Here, we directly addressed the role of c-Met in stem-cell-mediated liver regeneration by utilizing mice harboring c-met floxed alleles and Alb-Cre or Mx1-Cre transgenes. To activate oval cells, the hepatic stem cell (HSC) progeny, we used a model of liver injury induced by diet containing the porphyrinogenic agent, 3,5-diethocarbonyl-1,4-dihydrocollidine (DDC). Deletion of c-met in oval cells was confirmed in both models by polymerase chain reaction analysis of fluorescence-activated cell-sorted epithelial cell adhesion molecule (EpCam)-positive cells. Loss of c-Met receptor decreased the sphere-forming capacity of oval cells in vitro as well as reduced oval cell pool, impaired migration, and decreased hepatocytic differentiation in vivo, as demonstrated by double immunofluorescence using oval- (A6 and EpCam) and hepatocyte-specific (i.e. hepatocyte nuclear factor 4-alpha) antibodies. Furthermore, lack of c-Met had a profound effect on tissue remodeling and overall composition of HSC niche, which was associated with greatly reduced matrix metalloproteinase (MMP)9 activity and decreased expression of stromal-cell-derived factor 1. Using a combination of double immunofluorescence of cell-type-specific markers with MMP9 and gelatin zymography on the isolated cell populations, we identified macrophages as a major source of MMP9 in DDC-treated livers. The Mx1-Cre-driven c-met deletion caused the greatest phenotypic impact on HSCs response, as compared to the selective inactivation in the epithelial cell lineages achieved in c-Met(fl/fl); Alb-Cre(+/-) mice. However, in both models, genetic loss of c-met triggered a similar cascade of events, leading to the failure of HSC mobilization and death of the mice.

CONCLUSION

These results establish a direct contribution of c-Met in the regulation of HSC response and support a unique role for HGF/c-Met as an essential growth-factor-signaling pathway for regeneration of diseased liver.

Human hepatic cancer stem cells are characterized by common stemness traits and diverse oncogenic pathways

Epigenetic mechanisms play critical roles in stem cell biology by maintaining pluripotency of stem cells and promoting differentiation of more mature derivatives. If similar mechanisms are relevant for the cancer stem cell (CSC) model, then epigenetic modulation might enrich the CSC population, thereby facilitating CSC isolation and rigorous evaluation. To test this hypothesis, primary human cancer cells and liver cancer cell lines were treated with zebularine (ZEB), a potent DNA methyltransferase-1 inhibitor, and putative CSCs were isolated using the side population (SP) approach. The CSC properties of ZEB-treated and untreated subpopulations were tested using standard in vitro and in vivo assays. Whole transcriptome profiling of isolated CSCs was performed to generate CSC signatures. Clinical relevance of the CSC signatures was evaluated in diverse primary human cancers. Epigenetic modulation increased frequency of cells with CSC properties in the SP fraction isolated from human cancer cells as judged by self-renewal, superior tumor-initiating capacity in serial transplantations, and direct cell tracking experiments. Integrative transcriptome analysis revealed common traits enriched for stemness-associated genes, although each individual CSC gene expression signature exhibited activation of different oncogenic pathways (e.g., EGFR, SRC, and MYC). The common CSC signature was associated with malignant progression, which is enriched in poorly differentiated tumors, and was highly predictive of prognosis in liver and other cancers.

CONCLUSION

Epigenetic modulation may provide a tool for prospective isolation and in-depth analysis of CSC. The liver CSC gene signatures are defined by a pernicious interaction of unique oncogene-specific and common stemness traits. These data should facilitate the identifications of therapeutic tools targeting both unique and common features of CSCs.

Molecular targeting of CSN5 in human hepatocellular carcinoma: a mechanism of therapeutic response

Development of targeted therapy for hepatocellular carcinoma (HCC) remains a major challenge. We have recently identified an elevated expression of the fifth subunit of COP9 signalosome (CSN5) in early HCC as compared to dysplastic stage. In the present study, we explored the possibility of CSN5 being a potential therapeutic target for HCC. Our results show that CSN5 knockdown by small interfering (si) RNA caused a strong induction of apoptosis and inhibition of cell cycle progression in HCC cells in vitro. The downregulation of CSN5 was sufficient to interfere with CSN function as evidenced by the accumulation of neddylated Cullin1 and changes in the protein levels of CSN controlled substrates SKP2, p53, p27 and NF-kB, albeit to a different degree depending on the HCC cell line, which could account for the CSN5 knockdown phenotype. The transcriptomic analysis of CSN5 knockdown signature showed that the anti-proliferative effect was driven by a common subset of molecular alterations including downregulation of CDK6 and ITGB1, which were functionally interconnected with key oncogenic regulators MYC and TGFβ1 involved in the control of proliferation, apoptotic cell death and HCC progression. Consistent with microarray analysis, western blotting revealed that CSN5 depletion increased phosphorylation of Smad 2/3, key mediators of TGFβ1 signaling, decreased the protein levels of ITGB1, CDK6, and cyclin D1 and caused reduced expression of anti-apoptotic Bcl-2 while elevating the levels of pro-apoptotic Bak. A chemically modified variant of CSN5 siRNA was then selected for in vivo application based on the growth inhibitory effect and minimal induction of unwanted immune response. Systemic delivery of the CSN5 3/8 variant by stable-nucleic-acid-lipid-particles (SNALP) significantly suppressed the tumor growth in Huh7-luc⁺ orthotopic xenograft model. Taken together, these results indicate that CSN5 plays a pivotal role in HCC pathogenesis and maybe an attractive molecular target for systemic HCC therapy.

Abstract 2460: Tumorigenic potential is independent of sphere phenotype in liver cancer

Background: A phenotypic plasticity, a hallmark of embryonic development and cancer progression/metastasis, is dynamically regulated by extrinsic signals produced by niche and intrinsic cell autonomous mechanisms. Consequently, both cell microenvironment and genetic/epigenetic machinery play important roles in cell fate reprogramming.

Objective: In this study we aimed to evaluate the effects of environmental and/or epigenetic modulation on cancer stem cell (CSC) properties using a panel of human HCC cell lines.

Methods: Seven human hepatoma cell lines, including one primary HCC cell line, were plated at high (HD) and low density (LD) and grown in the presence or absence of DNA-methyltransferase inhibitor zebularine (Zeb) for 3 days. Thereafter cells were propagated in serum-free condition for evaluation of sphere-forming ability. Primary tumor-spheres were passaged every 10 days to generate passage 1 (P1) trough P7 spheres. Gene expression was examined by qRT-PCR and microarray analysis. Sphere tumorigenic capacity was evaluated in vivo after subcutaneous (s.c.) transplantation into NOD/SCID mice.

Results: Cells grown under LD failed to form spheres when placed in non-adherent growth conditions. In contrast, Zeb-treated LD (LDZ) cells were capable of forming clonal-expanding spherical colonies. Cells cultured at HD possessed a comparable sphere forming ability regardless of Zeb pre-treatment. However, despite the similar phenotype and size, spheres formed by LDZ and HD/HDZ cells possessed different self-renewal and tumorigenic potential in vitro and in vivo. Thus, LDZ spheres exhibited a considerably stronger induction of the stem cell-related genes (NANOG, OCT4, and BMI1) as well as epithelial-mesenchymal transition markers (β-catenin, ZEB1, VIM and SNA1) as compared to HD spheres. Furthermore, in serial sphere formation assay, only LDZ-spheres could retain a long term self-renewal while the sphere-forming ability of both HD- and HDZ-spheres was exhausted within the first three passages in vitro. In addition, cells dissociated from LDZ-spheres at P1 possessed higher tumorigenicity upon s.c. transplantation into NOD/SCID mice as compared to P1 HD-spheres, and only LDZ-spheres could propagate the tumor growth in vivo at later passages.

Conclusion: We describe functional tumor-sphere approach which offers an efficient tool to enrich for cells with CSC properties. By modulating either cell density and/or epigenome in hepatoma cell lines we selected for sphere-forming phenotype possessing a high tumor-initiating potential including a long-term ability for self-renew during serial sphere passaging and propagation of tumor growth in vivo. The global gene expression analysis is underway to characterize the molecular mechanisms responsible for maintaining CSC compartment in sphere-derived tumor clones.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2460. doi:10.1158/1538-7445.AM2011-2460

Abstract 2452: Generation of hepatocellular carcinomas with cancer stem cell properties from primary mouse hepatocytes

BACKGROUND: Current evidence suggests that hepatocellular carcinoma (HCC), the most common adult primary liver cancer, comprises biologically distinct subgroups including the recently identified hepatic progenitor cell- and cholangiocarcinoma (CC)-like subtypes. These observations support the notion that HCCs can be derived from different cells within the lineage from adult liver stem cell to hepatocyte.

AIM: We addressed two questions: (1) does the transforming potential of oncogenes depend on the stage of hepatocytic differentiation and (2) is the tumor phenotype determined by the stage of differentiation at which transformation occurs.

METHODS: Fetal (ED16.5) hepatocytes were purified by magnetic sorting and adult (3-month) hepatocytes were isolated by collagenase perfusion from C57BL/6 mice. Cells were transduced with lentiviral vectors carrying oncogenic H-Ras and SV40 large T (LT) together with GFP and mCherry fluorescent reporters. Double positive cells were sorted and injected into the spleen of NOD/SCID mice. Tumors larger than 3 mm derived from the transduced fetal (n=20) and adult hepatocytes (n=20) were macrodissected and subjected to histopathology evaluation, immunohistochemistry and transcriptome profiling. Cancer stem cell traits were examined by FACS analysis of lineage specific and cancer stem cell associated markers, side population and tumor sphere formation assays using cell lines established from fetal and adult hepatocyte-derived tumors.

RESULTS: Both fetal and adult hepatocytes co-transduced with oncogenic H-Ras/SV40LT produced liver tumors with similar growth characteristics and gave rise to lung metastases with 80% (8/10) and 63% (5/8) frequency, respectively. Histologically, fetal and adult hepatocyte-derived tumors were moderately-poorly differentiated HCCs with CC-like phenotype. All tumor cell lines were 100% positive for CK18, CK19, EpCam, A6, CD44, CD49f and CD29 and contained SP fraction (1-2%) as measured by FACS analysis regardless of the cell origin. CD133 was expressed at lower and variable levels in fetal (26.0±7.2%) and adult (46.1±9.1%) tumor cell lines. Both fetal and adult tumor cells possessed a sphere forming capacity which was maintained within 5 sphere generations. Unsupervised hierarchical clustering separated the fetal and adult tumors after log2 transformation by using corresponding normal samples as reference.

CONCLUSION: Our results suggest that the activation of certain oncogenic pathways may have more significant effect on the tumor phenotype than the stage of hepatocytic differentiation at which the transformation occurs. Oncogenic H-Ras and SV40LT are capable of inducing a cancer stem cell-like state in mature hepatocytes that displays characteristics of hepatic stem cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2452. doi:10.1158/1538-7445.AM2011-2452

Abstract 1644: siRNA targeting of cell cycle kinase Wee1 inhibits hepatocullar carconima growth in vitro and in vivo

Development of targeted therapy for hepatocellular carcinoma (HCC) remains a major challenge. Previously studies have shown that protein level and kinase activity of Wee1 are significantly elevated in HCC compared with surrounding cirrhotic tissues, although the underlying mechanisms are still unknown. Under normal conditions, Wee1 kinase plays an important role in maintaining G2 arrest through the inhibitory phosphorylation of cdc2 on Tyr-15. In the present study, we explored the possibility of Wee1 being a potential therapeutic target for HCC. To inactivate Wee1, three Wee1-specific small interfering (si) RNAs (Wee1-1, Wee1-2 and Wee1-3) were tested for growth inhibition in HCC cell lines as determined by MTT assay, FACS analysis and microscopy. To obtain insights into molecular changes caused by Wee1 silencing, global changes in gene expression were examined by illumina microarray. For in vivo evaluation of Wee1 as a therapeutic target, we employed orthotopic xenograft model using luciferase-expressing HCC reporter cell lines Huh7- and HepG2-luc+ and stable-nucleic-acid-lipid-particle (SNALP) as an optimal carrier of siRNA into liver.

Among the tested siRNA molecules, the Wee1-2siRNA was the most effective in inhibiting Huh7 and HepG2 cell growth (80% and 84%, respectively) which was paralleled by a similar decrease in the levels of target mRNA and protein. Wee1 knockdown by siRNA also caused a block in cell cycle progression and induced apoptosis of HCC cells. The comparison of gene expression profiles in HepG2 cells treated with either control siRNA or Wee1-2siRNA identified 506 differentially expressed genes (P &lt; 0.05 by bootstrap t-test). Genes functionally involved in cell proliferation, such as cdk2, cyclin B1, and Akt1, were down-regulated while cell cycle inhibitor p21 and tumor suppressor TSC2 were up-regulated. Western blotting showed that Wee1 silencing significantly increased the expression of p53 and p21 and decreased cyclin D1 protein levels in Wee1-deficient HepG2 cells, which could contribute to cell cycle arrest and induction of apoptosis. Wee1 5/6, a modified variant of Wee1-2siRNA, was then selected for in vivo application based on the growth inhibitory effect and minimal induction of unwanted immune response. Systemic delivery of Wee1 5/6 variant by SNALP significantly suppressed both Huh7 and HepG2 tumor growth in orthotopic xenograft model. In addition, administration of Wee1 5/6 SNALP increased the survival of mice bearing HepG2-derived tumors bearing mice in a dose-dependent manner. Taken together, these results indicate that Wee1 maybe an attractive molecular target for systemic HCC therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1644. doi:10.1158/1538-7445.AM2011-1644

An integrated genomic and epigenomic approach predicts therapeutic response to zebularine in human liver cancer

Epigenomic changes such as aberrant hypermethylation and subsequent atypical gene silencing are characteristic features of human cancer. Here, we report a comprehensive characterization of epigenomic modulation caused by zebularine, an effective DNA methylation inhibitor, in human liver cancer. Using transcriptomic and epigenomic profiling, we identified a zebularine response signature that classified liver cancer cell lines into two major subtypes with different drug responses. In drug-sensitive cell lines, zebularine caused inhibition of proliferation coupled with increased apoptosis, whereas drug-resistant cell lines showed up-regulation of oncogenic networks (for example, E2F1, MYC, and TNF) that drive liver cancer growth in vitro and in preclinical mouse models. Assessment of zebularine-based therapy in xenograft mouse models demonstrated potent therapeutic effects against tumors established from zebularine-sensitive but not zebularine-resistant liver cancer cells, leading to increased survival and decreased pulmonary metastasis. Integration of the zebularine gene expression and demethylation response signatures allowed differentiation of patients with hepatocellular carcinoma according to their survival and disease recurrence. This integrated signature identified a subclass of patients within the poor-survivor group that is likely to benefit from therapeutic agents that target the cancer epigenome.

Definition of ubiquitination modulator COP1 as a novel therapeutic target in human hepatocellular carcinoma

The development of targeted therapeutics for hepatocellular carcinoma (HCC) remains a major challenge. The ubiquitination modulator COP1 regulates p53 activity by ubiquitination and it is frequently overexpressed in human HCC. In this study, we tested the hypothesis that COP1 blockade by short interfering RNA (siRNA)-mediated inhibition could affect the course of HCC progression. The COP1 isoform COP1-1 was selected as the most effective target for siRNAs in terms of growth inhibition and apoptotic induction in several HCC cell lines. Growth inhibition occurred in HCC cells that retained wild-type p53 or expressed mutant p53 (Y220C or R249S), whereas p53-null Hep3B cells were resistant. Microarray expression analysis revealed that the antiproliferative effects of COP1 blockade were driven by a common subset of molecular alterations including a p53-associated functional network. In an orthotopic mouse xenograft model of HCC, systemic delivery of a modified COP1 siRNA by stable nucleic acid-lipid particles suppressed neoplastic growth in liver without unwanted immune responses. Our findings offer a first proof of principle that COP1 can be a promising target for systemic therapy of HCC.

Abstract 4297: Selective enrichment of liver cancer stem cell by DNA methyltransferase inhibition

Background: Evidence is growing that many solid cancers, including liver cancer, contain small subpopulations of cells with stem cell-like properties known as cancer stem cells (CSCs) that are responsible for maintaining and propagating a tumor. Major obstacles in the research on CSC biology are the paucity and lack of specific markers of CSC. We have recently shown that human liver CSC can be enriched by modulating the epigenome of liver cancer cell lines with zebularine (Zeb), a potent DNA methyltransferase inhibitor.

Objective: In this study we exploited the impact of epigenetic modulation of cancer epigenome by Zeb in conjunction with the ability of stem/progenitor cells to grow as non-adherent spheres in serum-free media to provide further enrichment of the CSC fraction.

Methods: Huh7 cells were plated in high (HD, 13×103cell/cm2) and low (LD, 2.7×103/cm2) density and treated with 100 µM Zeb for 3days. The sphere forming ability and serial sphere formation were investigated in Matrigel and suspension culture, respectively. CSC and pluripotency markers preferentially expressed in cells grown under sphere conditions were examined by qRT-PCR and surface markers by FACS.

Results: Huh7 cells grown under LD failed to form tumorspheres when placed in Matrigel or non-adherent growth conditions. In striking contrast, Zeb-treated low density cells were capable of forming spherical clonal-expanding colonies which showed the stem cell-like properties such as strong induction of the stem cell-related genes NANOG and OCT4 and did not express EpCAM. Cells grown at high density possessed a similar sphere forming ability regardless of Zeb pretreatment. However, morphological characterization revealed a predominance of smaller sized spheres suggesting reduced proliferation potential and/or differences in cell type of origin, with smaller spheres originating from the progenitors, and larger spheres from the stem cells. Consistent with this, HD spheres showed a smaller induction of NANOG and OCT4, expressed high levels of EpCAM and exhibited reduced self-renewal in serial sphere formation assay. The sphere forming ability of LD and HD cells was associated with a presence of a subpopulation of CD133-/cKit+ cells.

Conclusion: The described “double selective” approach offers an in vitro model to enrich for cells with cancer stem cell properties. Both cell density and epigenetic modulation were able to affect the sphere-forming potential of Huh7 cells. Further studies are needed to characterize this cell population in more detail, to clarify their tumorigenic potential and the capacity to propagate tumor growth in vivo.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4297.

Abstract 4181: Comparison of tumorigenic proficiency at different stages of hepatocyte differentiation

BACKGROUND: Current evidence suggests that any cell that can proliferate repeatedly is susceptible to neoplastic transformation. In the liver, these include all cells within the lineage from hepatoblast and adult liver stem cell to hepatocyte and cholangiocyte. Lentiviral vectors with their ability to transduce non-dividing cells are effective tools to introduce oncogenes at different stages of lineage commitment. AIM: To address whether (1) the transforming potential of defined oncogenes is dependent on the stage of hepatocytic differentiation and (2) the genotype and phenotype of developed tumors reflect the stage of differentiation. METHODS: To generate genetically defined liver carcinomas, constitutive lentiviral vectors were developed carrying oncogenic H-Ras and luciferase/EGFP double reporter as well as SV40 large T (LT) antigen and mCherry fluorescent reporter. The E-cadherin-positive hepatoblasts (ED16.5) and newborn (1day) hepatocytes as well as adult (3month) hepatocytes were transduced ex vivo by lentiviral vectors and FACS-sorted before intrasplenic transplantation into NOD/SCID mice. Liver tumors larger than 3mm derived from fetal (n=20), newborn (n=18) and adult hepatocytes (n=10) transfected with H-Ras and SV40 LT were macrodissected and subjected to immunohistochemistry and microarray analyses. RESULTS: Infection with H-Ras alone was not sufficient to transform hepatocytes at any state of differentiation. SV40 LT was capable to transform only fetal hepatocytes but not hepatocytes as judged by robust anchorage-independent growth in vitro and rapid tumor formation in vivo. The combination of activated H-Ras and SV40 LT significantly accelerated the tumor potential of all infected hepatocytes. In all cases, tumors resembled the histopathological subtypes of human hepatocellular carcinoma (HCC) albeit with variable degrees of malignancy. HCCs derived from hepatoblasts were more aggressive with a predominance of pseudoglandular component and more frequent extrahepatic growth. The pseudoglandular structures were strongly positive for cytokeratin 19 (CK19). Unsupervised hierarchical clustering of the expression profiles grouped the tumors according to CK19 associated gene expression signature with highest levels found in fetal- to lowest in adult hepatocyte-derived tumors. HCCs established from hepatoblasts were genetically more heterogeneous and clustered with tumors derived from both newborn and adult hepatocytes. CONCLUSIONS: There is a reciprocal relationship between the transforming potential of defined oncogenes and extent of commitment to hepatocyte lineage. Transformation of hepatocytes at the different stages of differentiation may induce a cancer stem cell-like phenotype that displays the markers characteristic of hepatic stem cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4181.