Identification of tumor-initiating cells in a canine hepatocellular carcinoma cell line

Establishment and characterization of six canine hepatocellular carcinoma cell lines

Background

Hepatocellular carcinoma (HCC) is the most common malignant liver tumor in dogs. Although surgical resection is a major treatment option for canine HCC, there are no distinct strategies for unresectable tumor subtypes or adjuvant chemotherapy for tumors with positive margins. We aimed to establish and characterize novel HCC cell lines from canine patients.

Methods

The cellular morphology, general growth features and tumorigenicity of the established cell lines were evaluated. We also examined the sensitivity of the cell lines to multi-target tyrosine kinase inhibitors (TKIs).

Results

We established novel canine HCC cell lines from hepatic tumors and an additional kidney tumor of six canine patients. All cell lines showed colony forming and migratory ability. KU-cHCC-001 and KU-cHCC-001-Kidney, two cell lines exhibiting high epithelial-mesenchymal transition characteristics, showed tumorigenicity in xenografted mice. Toceranib, a veterinary TKI that targets vascular endothelial growth factor (VEGFR)/platelet-derived growth factor receptor (PDGFR)/c-kit, effectively inhibited the mitogen-activated protein kinase pathway and induced apoptosis. The established canine HCC cell lines showed greater sensitivity to toceranib than to sorafenib, a first-line treatment for human HCC targeting RAF/VEGFR/PDGFR. Sorafenib showed improved anti-tumor effects when co-treated with SCH772984, an extracellular signal-regulated kinase inhibitor.

Conclusion

Our study suggests new therapeutic strategies for canine HCC, and these cell lines are valuable research materials for understanding HCC tumor biology in both humans and dogs.

Machine learning determines stemness associated with simple and basal-like canine mammary carcinomas

Simple and complex carcinomas are the most common type of malignant Canine Mammary Tumors (CMTs), with simple carcinomas exhibiting aggressive behavior and poorer prognostic. Stemness is an ability associated with cancer initiation, malignancy, and therapeutic resistance, but is still few elucidated in canine mammary tumor subtypes. Here, we first validated, using CMT samples, a previously published canine one-class logistic regression machine learning algorithm (OCLR) to predict stemness (mRNAsi) in canine cancer cells. Then, using the canine mRNAsi, we observed that simple carcinomas exhibit higher stemness than complex carcinomas and other histological subtypes. Also, we confirmed that stemness is higher and associated with basal-like CMTs and with NMF2 metagene signature, a tumor-specific DNA-repair metagene signature. Using correlation analysis, we selected the top 50 genes correlated with higher stemness, and the top 50 genes correlated with lower stemness and further performed a gene set enrichment analysis to observe the biological processes enriched for these genes. Finally, we suggested two promise stemness-associated targets in CMTs, POLA2 and APEX1, especially in simple carcinomas. Thus, our work elucidates stemness as a potential mechanism behind the aggressiveness and development of canine mammary tumors, especially in simple carcinomas, describing evidence of a promising strategy to target this disease.

mTOR pathway as a potential therapeutic target for cancer stem cells in canine mammary carcinoma

Mammary adenocarcinoma, the most common cancer in female dogs, often exhibits the lymph node and lung metastases and has a higher mortality rate. However, mammary adenocarcinoma has no established treatment, except early surgical excision. Canine mammary carcinoma has many common features with human mammary carcinoma, including clinical characteristics, heterogeneity, and genetic aberrations, making it an excellent spontaneous tumor model for human breast cancer. Diverse cancers comprised heterogeneous cell populations originating from cancer stem cells (CSCs) with self-renewal ability. Therefore, in addition to conventional therapy, therapeutic strategies targeting CSCs are essential for cancer eradication. The present study aimed to extract inhibitors of canine mammary CSCs that suppress their self-renewal ability. Sphere-formation assay, which evaluates self-renewal ability, was performed for the canine mammary cancer cell lines CTBp and CNMp. The spheres formed in this assay were used in inhibitor library screening, which identified various signaling pathways such as proteosome, stress inducer, and mammalian target of rapamycin (mTOR). The present study focused on the mTOR signaling pathway. Western blotting showed higher levels of phosphorylated mTOR in sphere-forming CTBp and CNMp cells than in adherent cells. Drug sensitivity examination using the mTOR inhibitors everolimus and temsirolimus revealed dose-dependent reductions in viability among both sphere-forming cells and adherent cells. Expression of phosphorylated mTOR in adherent and sphere-forming cells decreased by everolimus and temsirolimus treatment. In mice transplanted with CTBp-derived spheres, everolimus treatment significantly decreased tumor volume compared to control. These results reveal that the mTOR signaling pathway may be a potential to be a therapeutic target in both cancer cells and CSCs. Novel therapeutic strategies for canine mammary carcinoma are expected to benefit to human breast carcinoma as well.

Visualizing the cancer stem-like properties of canine tumour cells with low proteasome activity

Cancer stem-like cells (CSCs) cause treatment failure in various tumours; however, establishing CSC-targeted therapies has been hampered by difficulties in the identification and isolation of this small sub-population of cells. Recent studies have revealed that tumour cells with low proteasome activity display a CSC phenotype that can be utilized to image CSCs in canines. This study visualizes and reveals the CSC-like properties of tumour cells with low proteasome activity in HMPOS (osteosarcoma) and MegTCC (transitional cell carcinoma), which are canine cell lines. The parent cells were genetically engineered to express ZsGreen1, a fluorescent protein connected to the carboxyl-terminal degron of canine ornithine decarboxylase that accumulates with low proteasome activity (ZsG⁺ cells). ZsG⁺ cells were imaged and the mode of action of this system was confirmed using a proteasome inhibitor (MG-132), which increased the ZsGreen1 fluorescence intensity. The CSC-like properties of ZsG⁺ cells were evaluated on the basis of cell divisions, cell cycle, the expression of CSC markers and tumourigenicity. ZsG⁺ cells underwent asymmetric divisions and had a low percentage of G0/G1 phase cells; moreover, ZsG⁺ cells expressed CSC markers such as CD133 and showed a large tumourigenic capability. In histopathological analysis, ZsG⁺ cells were widely distributed in the tumour samples derived from ZsG⁺ cells and in the proliferative regions of the tumours. The results of this study indicate that visualized canine tumour cells with low proteasome activity have a CSC-like phenotype and that this visualization system can be utilized to identify and isolate canine CSCs.

An Update on Molecular Pathways Regulating Vasculogenic Mimicry in Human Osteosarcoma and Their Role in Canine Oncology

Canine tumors are valuable comparative models for human counterparts, especially to explore novel biomarkers and to understand pathways and processes involved in metastasis. Vasculogenic mimicry (VM) is a unique property of malignant cancer cells which promote metastasis. Thus, it represents an opportunity to investigate both the molecular mechanisms and the therapeutic targets of a crucial phenotypic malignant switch. Although this biological process has been largely investigated in different human cancer types, including osteosarcoma, it is still largely unknown in veterinary pathology, where it has been mainly explored in canine mammary tumors. The presence of VM in human osteosarcoma is associated with poor clinical outcome, reduced patient survival, and increased risk of metastasis and it shares the main pathways involved in other type of human tumors. This review illustrates the main findings concerning the VM process in human osteosarcoma, search for the related current knowledge in canine pathology and oncology, and potential involvement of multiple pathways in VM formation, in order to provide a basis for future investigations on VM in canine tumors.

Sphere-forming cells display stem cell-like characteristics and increased xCT expression in a canine hepatocellular carcinoma cell line

Hepatocellular carcinoma (HCC) is the most common type of canine primary liver tumor; however, most chemotherapies against HCC are ineffective due to resistance to anticancer agents. Sphere-forming cells are considered to act as cancer stem cells for various types of solid tumors and have been established for many canine tumor cell lines, yet no studies have reported sphere-forming cells for canine HCC. In this study, we established sphere-forming cells from a canine HCC cell line (AZACH). These cells displayed increased stem cell marker mRNA expression (Nanog, Sox2, c-Myc, and Klf4), aldehyde dehydrogenase activity, and chemoresistance against mitoxantrone, gemcitabine, and doxorubicin. In addition, sphere-forming cells exhibited higher xCT expression and lower intracellular reactive oxygen species levels than adherent cells. Treatment with sulfasalazine, a xCT-specific inhibitor, reduced sphere formation efficiency. Together, these results indicate that sphere-forming cells derived from a canine HCC cell line have similar characteristics to cancer stem cells and that their increased xCT expression and associated resistance to oxidative stress contribute toward sphere formation.

Metabolite profiling in sphere-forming cells from canine mammary adenocarcinoma cell lines using gas chromatography-mass spectrometry

Cancer consists of heterogeneous cells that contain a small population of cells that possess stem cell properties; these cells, referred to as cancer stem cells (CSCs) or tumor-initiating cells, are involved in tumor progression and metastasis. Using a sphere-forming assay, canine mammary CSCs were found to be similar to human breast CSCs. Metabolic reprogramming has been recognized as a hallmark of various cancers. However, the significance of cellular metabolism in CSCs remains unclear. The aim of this study was to define the metabolic characteristics of CSCs derived from canine mammary tumors and gain an understanding of the maintenance of stemness. We identified metabolite profiles of canine mammary adenocarcinoma cell lines using gas chromatography-mass spectrometry. Metabolites were extracted from both adherent and sphere-forming cells derived from three cell lines. Sphere-forming cells were separated from adherent cells using an orthogonal, partial least-squares discriminant analysis. Sphere-forming cells were found to contain high levels of the amino acids alanine, glycine and proline compared with adherent cells. They also had high levels of palmitoleate, palmitate and dihomo-gamma-linolenic acid compared with adherent cells. In a sphere-forming assay, palmitate increased the number of spheres for all cell lines. These results indicate that the sphere-forming cells derived from canine mammary adenocarcinoma cell lines have specific metabolic profiles that may be useful for the development of CSC-specific therapies targeting metabolic pathways and potential stemness biomarkers; these results also clarify the maintenance of stemness in canine mammary CSCs.

Transforming growth factor-β decreases side population cells in hepatocellular carcinoma in vitro

Hepatocellular carcinoma (HCC) can result from hepatitis B or C infection, fibrosis or cirrhosis. Transforming growth factor-β (TGF-β) is one of the main growth factors associated with fibrosis or cirrhosis progression in the liver, but its role is controversial in hepatocarcinogenesis. In the present study, the effect of TGF-β on the HCC Huh-7 and Huh-Bat cell lines was evaluated. To study the effect of TGF-β, Huh-7 and Huh-Bat cells were treated with TGF-β and a TGF-β receptor inhibitor (SB431542). Cell survival, cell cycle, numbers of side population (SP) cells and expression of the cancer stem cell marker cluster of differentiation (CD)133, epithelial-mesenchymal transition markers (E-cadherin, α-smooth muscle actin and vimentin) and TGF-β-regulated proteins [phospho-c-Jun N-terminal kinase (p-JNK), p-c-Jun and p-smad2] were investigated. TGF-β treatment resulted in decreased cell survival with a targeted effect on SP cells. Expression of CD133 and vimentin was upregulated by treatment with the TGF-β receptor antagonist SB431542, but not with TGF-β. By contrast, TGF-β induced accumulation of cells at G0/G1, and upregulated expression of p-JNK, p-c-Jun and p-smad2. However, these effects were blocked when cells were treated with TGF-β plus SB431542, indicating the specificity of the TGF-β effect. The present results indicated that TGF-β has anticancer effects mediated by survival inhibition of cancer stem cells, which may be developed as a novel therapy for HCC.

Modulation of fatty acid metabolism and immune suppression are features of in vitro tumour sphere formation in ontogenetically distinct dog cancers

Non-adherent, 3-dimensional sphere formation is used as an in vitro surrogate to evaluate cellular potential for tumour initiation and self-renewal. To determine if a shared molecular program underlies the capacity for sphere formation by cells originating from diverse tumour types, we characterized molecular and functional properties of 10 independent cell lines derived from 3 ontogenetically distinct dog cancers: hemangiosarcoma, osteosarcoma and glial brain tumours. Genome-wide gene expression profiling identified tumour-of-origin-dependent patterns of adjustment to sphere formation in a uniform culture condition. However, expression of the stem/progenitor markers CD34 and CD117, resistance to cytotoxic drugs and dye efflux (side population assays) showed no association with these gene expression profiles. Instead, primary sphere-forming capacity was inversely correlated with the ability to reform secondary spheres, regardless of tumour ontogeny. Primary sphere formation seemed to be proportional to the number of pre-existing cells with sphere-forming capacity in the cell lines. Cell lines where secondary sphere formation was more proficient than primary sphere formation showed enrichment of genes involved in fatty acid synthesis and immunosuppressive cytokines. In contrast, cell lines where secondary sphere formation was approximately equivalent to or less proficient than primary sphere formation showed upregulation of CD40 and enrichment of genes involved in fatty acid oxidation. Our data suggest that in vitro sphere formation is associated with upregulation of gene clusters involved in metabolic and immunosuppressive functions, which might be necessary for self-renewal and for tumour initiation and/or tumour propagation in vivo.

Soluble factors from adipose tissue-derived mesenchymal stem cells promote canine hepatocellular carcinoma cell proliferation and invasion

The potential effects of adipose tissue-derived mesenchymal stem cells (AT-MSCs) on the growth and invasion of canine tumours including hepatocellular carcinoma (HCC) are not yet understood. Moreover in humans, the functional contribution of AT-MSCs to malignancies remains controversial. The purpose of this study was to investigate the effects of AT-MSCs on the proliferation and invasion of canine HCC cells in vitro. The effect of AT-MSCs on mRNA levels of factors related to HCC progression were also evaluated. Conditioned medium from AT-MSCs (AT-MSC-CM) significantly enhanced canine HCC cell proliferation and invasion. Moreover, mRNA expression levels of transforming growth factor-beta 1, epidermal growth factor A, hepatocyte growth factor, platelet-derived growth factor-beta, vascular endothelial growth factor, and insulin-like growth factor 2 were 2.3 ± 0.4, 2.0 ± 0.5, 5.7 ± 1.9, 1.7 ± 0.2, 2.1 ± 0.4, and 1.4 ± 0.3 times higher, respectively (P < 0.05). The mRNA expression level of MMP-2 also increased (to 4.0 ± 1.2 times control levels) in canine HCC cells co-cultured with AT-MSCs, but MMP-9 mRNA significantly decreased (to 0.5 ± 0.1 times control levels). These findings suggest that soluble factors from AT-MSCs promote the proliferation and invasion of canine HCC cells.

In vitro and in vivo characterization of stem-like cells from canine osteosarcoma and assessment of drug sensitivity

Cancer stem cell (CSC) self-renewing and drug resistance cause treatment failure and tumor recurrence. Osteosarcoma is an aggressive bone tumor characterized by biological and molecular heterogeneity, possibly dependent on CSCs. CSC identification in osteosarcoma and their efficient targeting are still open questions. Spontaneous canine osteosarcoma shares clinical and biological features with the human tumors, representing a model for translational studies. We characterized three CSC-enriched canine osteosarcoma cultures. In serum-free conditions, these CSC cultures grow as anchorage-independent spheroids, show mesenchymal-like properties and in vivo tumorigenicity, recapitulating the heterogeneity of the original osteosarcoma. Osteosarcoma CSCs express stem-related factors (Sox2, Oct4, CD133) and chemokine receptors and ligands (CXCR4, CXCL12) involved in tumor proliferation and self-renewal. Standard drugs for osteosarcoma treatment (doxorubicin and cisplatin) affected CSC-enriched and parental primary cultures, showing different efficacy within tumors. Moreover, metformin, a type-2 diabetes drug, significantly inhibits osteosarcoma CSC viability, migration and self-renewal and, in co-treatment with doxorubicin and cisplatin, enhances drug cytotoxicity. Collectively, we demonstrate that canine osteosarcoma primary cultures contain CSCs exhibiting distinctive sensitivity to anticancer agents, as a reliable experimental model to assay drug efficacy. We also provide proof-of-principle of metformin efficacy, alone or in combination, as pharmacological strategy to target osteosarcoma CSCs.

Identification of rhodamine 123-positive stem cell subpopulations in canine hepatocellular carcinoma cells

The majority of cases of chemotherapy for hepatocellular carcinoma (HCC) are not effective in human or veterinary medicine due to resistance against anticancer agents. In human medicine, hepatocellular carcinoma stem cells (HCSCs) were recently identified as cytokeratin 19 (CK19)-, cluster of differentiation (CD)-44-, and CD133-positive. However, there are few previous reports regarding canine HCSC (cHCSC). Additionally, to the best of our knowledge, the chemoresistance against anticancer agents of these cHCSCs has not been investigated. In the present study staining of cHCSCs was performed with rhodamine 123, a low-toxicity fluorescent dye for mitochondria, by flow cytometry. There were two subpopulations in the HCC cell line defined by their higher (Rho^Hi) and lower (Rho^Lo) fluorescence intensity of rhodamine 123. The Rho^Hi subpopulation demonstrated a higher Nanog gene expression, sphere-forming ability, and chemoresistance against gemcitabine. However, there was no significant difference between Rho^Hi and Rho^Lo regarding the proliferation rate and chemoresistance against mitoxantrone and doxorubicin. The present results indicate that the expression of rhodamine 123 identifies different stem cell subpopulations in a canine HCC cell line.

Identification of tumor-initiating cells derived from two canine rhabdomyosarcoma cell lines

Cancer stem cells or tumor-initiating cells (TICs) are a small subpopulation of cells that have the capacity to self-renew, differentiate and initiate tumors. These cells may function in tumor initiation, aggression and recurrence. Whether spheres derived from canine rhabdomyosarcoma cells have stem cell-like properties is unclear. We induced sphere formation in the canine rhabdomyosarcoma cell lines, CMS-C and CMS-J, and characterized the spheres in vitro and in vivo. Sphere-forming cells were more resistant to vincristine, mitoxantrone and doxorubicin than adherent cells. Xenograft transplantation demonstrated that 1 × 10³ sphere-forming cells derived from CMS-C were sufficient for tumor formation. The sphere assay showed that the sphere-forming cells were present in these tumors. These results suggest that the spheres derived from canine rhabdomyosarcoma cells may possess characteristics of TICs. This study provides the foundation for elucidating the contribution of TICs to rhabdomyosarcoma tumorigenesis.

Monoclonal Antibodies 13A4 and AC133 Do Not Recognize the Canine Ortholog of Mouse and Human Stem Cell Antigen Prominin-1 (CD133)

The pentaspan membrane glycoprotein prominin-1 (CD133) is widely used in medicine as a cell surface marker of stem and cancer stem cells. It has opened new avenues in stem cell-based regenerative therapy and oncology. This molecule is largely used with human samples or the mouse model, and consequently most biological tools including antibodies are directed against human and murine prominin-1. Although the general structure of prominin-1 including its membrane topology is conserved throughout the animal kingdom, its primary sequence is poorly conserved. Thus, it is unclear if anti-human and -mouse prominin-1 antibodies cross-react with their orthologs in other species, especially dog. Answering this issue is imperative in light of the growing number of studies using canine prominin-1 as an antigenic marker. Here, we address this issue by cloning the canine prominin-1 and use its overexpression as a green fluorescent protein fusion protein in Madin-Darby canine kidney cells to determine its immunoreactivity with antibodies against human or mouse prominin-1. We used immunocytochemistry, flow cytometry and immunoblotting techniques and surprisingly found no cross-species immunoreactivity. These results raise some caution in data interpretation when anti-prominin-1 antibodies are used in interspecies studies.

Curcumin Suppresses Phthalate-Induced Metastasis and the Proportion of Cancer Stem Cell (CSC)-like Cells via the Inhibition of AhR/ERK/SK1 Signaling in Hepatocellular Carcinoma

Recent evidence indicating that phthalates promote cancer development, including cell proliferation, migration, and invasion, has raised public health concerns. Here, we show that bis(2-ethylhexyl) phthalate promotes the migration, invasion, and epithelial-mesenchymal transition of hepatocellular carcinoma cells. In addition, bis(2-ethylhexyl) phthalate increased the proportion of cancer stem cell (CSC)-like cells and stemness maintenance in vitro as well as tumor growth and metastasis in vivo. The various activities of curcumin, including anticancer, anti-inflammation, antioxidation, and immunomodulation, have been investigated extensively. Curcumin suppressed phthalate-induced cell migration, invasion, and epithelial-mesenchymal transition, decreased the proportion of CSC-like cells in hepatocellular carcinoma cell lines in vitro, and inhibited tumor growth and metastasis in vivo. We also reveal that curcumin suppressed phthalate-induced migration, invasion, and CSC-like cell maintenance through inhibition of the aryl hydrocarbon receptor/ERK/SK1/S1P3 signaling pathway. Our results suggest that curcumin may be a potential antidote for phthalate-induced cancer progression.

The potential role of COX-2 in cancer stem cell-mediated canine mammary tumor initiation: an immunohistochemical study

Increasing evidence suggests that cancer stem cells (CSCs) are responsible for tumor initiation and maintenance. Additionally, it is becoming apparent that cyclooxygenase (COX) signaling is associated with canine mammary tumor development. The goals of the present study were to investigate COX-2 expression patterns and their effect on CSC-mediated tumor initiation in primary canine mammary tissues and tumorsphere models using immunohistochemistry. Patterns of COX-2, CD44, octamer-binding transcription factor (Oct)-3/4, and epidermal growth factor receptor (EGFR) expression were examined in malignant mammary tumor (MMT) samples and analyzed in terms of clinicopathological characteristics. COX-2 and Oct-3/4 expression was higher in MMTs compared to other histological samples with heterogeneous patterns. In MMTs, COX-2 expression correlated with tumor malignancy features. Significant associations between COX-2, CD44, and EGFR were observed in low-differentiated MMTs. Comparative analysis showed that the levels of COX-2, CD44, and Oct-3/4 expression varied significantly among TSs of three histological grades. Enhanced COX-2 staining was consistently observed in TSs. Similar levels of staining intensity were found for CD44 and Oct-3/4, but EGFR expression was weak. Our findings indicate the potential role of COX-2 in CSC-mediated tumor initiation, and suggest that COX-2 inhibition may help treat canine mammary tumors by targeting CSCs.

In vitro and in vivo antiproliferative activity of metformin on stem-like cells isolated from spontaneous canine mammary carcinomas: translational implications for human tumors

Background

Cancer stem cells (CSCs) are considered the cell subpopulation responsible for breast cancer (BC) initiation, growth, and relapse. CSCs are identified as self-renewing and tumor-initiating cells, conferring resistance to chemo- and radio-therapy to several neoplasias. Nowadays, th (about 10mM)e pharmacological targeting of CSCs is considered an ineludible therapeutic goal. The antidiabetic drug metformin was reported to suppress in vitro and in vivo CSC survival in different tumors and, in particular, in BC preclinical models. However, few studies are available on primary CSC cultures derived from human postsurgical BC samples, likely because of the limited amount of tissue available after surgery. In this context, comparative oncology is acquiring a relevant role in cancer research, allowing the analysis of larger samples from spontaneous pet tumors that represent optimal models for human cancer.

Methods

Isolation of primary canine mammary carcinoma (CMC) cells and enrichment in stem-like cell was carried out from fresh tumor specimens by culturing cells in stem-permissive conditions. Phenotypic and functional characterization of CMC-derived stem cells was performed in vitro, by assessment of self-renewal, long-lasting proliferation, marker expression, and drug sensitivity, and in vivo, by tumorigenicity experiments. Corresponding cultures of differentiated CMC cells were used as internal reference. Metformin efficacy on CMC stem cell viability was analyzed both in vitro and in vivo.

Results

We identified a subpopulation of CMC cells showing human breast CSC features, including expression of specific markers (i.e. CD44, CXCR4), growth as mammospheres, and tumor-initiation in mice. These cells show resistance to doxorubicin but were highly sensitive to metformin in vitro. Finally, in vivo metformin administration significantly impaired CMC growth in NOD-SCID mice, associated with a significant depletion of CSCs.

Conclusions

Similarly to the human counterpart, CMCs contain stem-like subpopulations representing, in a comparative oncology context, a valuable translational model for human BC, and, in particular, to predict the efficacy of antitumor drugs. Moreover, metformin represents a potential CSC-selective drug for BC, as effective (neo-)adjuvant therapy to eradicate CSC in mammary carcinomas of humans and animals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1235-8) contains supplementary material, which is available to authorized users.