Plasticity of ovarian cancer cell SKOV3ip and vasculogenic mimicry in vivo

[Vasculogenic mimicry]

Anti-angiogenic drugs are used as an established approach of malignant neoplasms therapy. It has been established that the development of the phenomenon of vasculogenic mimicry - a specific variant of tumor neoangiogenesis, which is formed in highly aggressive solid tumors, is associated with a decrease in the effectiveness of antitumor therapy. This review highlights the mechanisms of development of vasculogenic mimicry in malignant neoplasms, which is one of the alternative options for tumor blood supply. In the formation of vasculogenic mimicry, an important role is assigned to the tumor microenvironment, primarily tumor-associated macrophages and fibroblasts. The signaling pathways that regulate the formation of vasculogenic mimicry channels in tumors have been characterized. The prospects for a targeted impact on molecular targets that initiate and promote vasculogenic mimicry, the impact on which can increase the effectiveness of antitumor therapy, are shown. The review discusses experimental studies of the mechanisms of vasculogenic mimicry formation in malignant neoplasms and the prospects for targeted action on molecules that are components of signaling cascades involved in the development of this model of neoangiogenesis.

Vandetanib alters the tumoricidal capacity of human breast cancer stem cells via inhibiting vasculogenic capacity

Introduction

The inhibition of vascularization into tumor stroma as well as dynamic cell growth is the center of attention. Here, we aimed to examine the role of vandetanib on angiogenesis capacity of breast cancer stem cell (CSCs).

Methods

MDA-MB-231 cells were exposed to different doses of vandetanib and survival rate was monitored. Stimulatory effects of vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and epidermal growth factor (EGF) were evaluated in vandetanib-treated MDA-MB-231 cells. In vitro tubulogenesis capacity was studied on the Matrigel surface. The synergistic effects of vandetanib on cell survival were also assessed after PI3K and/or Wnt3a inhibition. Vascular endothelial (VE)-cadherin, matrix metalloproteinase-2 (MMP-2), -9, Wnt3a, and p-Akt/Akt ratio were measured using western blotting.

Results

Vandetanib reduced survival rate in a dose-dependent manner (P<0.05). Proliferative effects associated with VEGF, FGF, and EGF were blunted in these cells pre-exposed to vandetanib (P<0.05). The microcirculation pattern's triple-negative breast cancer (TNBC) was suppressed by 1, 5 µM of vandetanib (P<0.05). Hence 1, 5 µM of vandetanib potentially decreased the population of CD24- cells. 1 and 5 µM of vandetanib inhibited cell proliferation by blocking PI3K and Wnt3a pathways and decreased the p-Akt/Akt ratio, Wnta3 protein levels (P<0.05). 1 and 5 µM vandetanib combined with PI3K inhibitor diminished metastatic markers including, MMP-2, and MMP-9. The concurrent treatment (PI3K, inhibitor+ 1, 5 µM vandetanib) also considerably reduced epithelial-mesenchymal transition (EMT) markers such as VE-cadherin (P<0.05).

Conclusion

Vandetanib suppressed vasculogenic mimicry (VM) networking through blunting stemness properties, coincided with suppression of VE-cadherin in CSCs.

PAX2 induces vascular‑like structures in normal ovarian cells and ovarian cancer

In adult tissue, the paired box 2 (PAX2) protein is expressed in healthy oviductal, but not normal ovarian surface epithelial cells. PAX2 is expressed in a subset of cases of serous ovarian carcinoma; however, the role of PAX2 in the initiation and progression of ovarian cancer remains unknown. The aim of the present study was to determine the biological effects of PAX2 expression in normal and cancerous epithelial cells. By culturing the normal and cancerous ovarian cells that express PAX2 in 3D culture and staining the cells with vasculogenic mimicry markers such as CD31 and PAS, it was shown that PAX2 overexpression in both normal and cancerous ovarian epithelial cells induced formation of vascular-like structures both in vitro and in vivo. These results indicated a potential role of PAX2 in ovarian cancer progression by increasing the presence of vascular-like structures to promote the supply of nutrients to tumor cells and facilitate cancer cell proliferation and invasion.

Divergent Metabolic Effects of Metformin Merge to Enhance Eicosapentaenoic Acid Metabolism and Inhibit Ovarian Cancer In Vivo

Metformin is being actively repurposed for the treatment of gynecologic malignancies including ovarian cancer. We investigated if metformin induces analogous metabolic changes across ovarian cancer cells. Functional metabolic analysis showed metformin caused an immediate and sustained decrease in oxygen consumption while increasing glycolysis across A2780, C200, and SKOV3ip cell lines. Untargeted metabolomics showed metformin to have differential effects on glycolysis and TCA cycle metabolites, while consistent increased fatty acid oxidation intermediates were observed across the three cell lines. Metabolite set enrichment analysis showed alpha-linolenic/linoleic acid metabolism as being most upregulated. Downstream mediators of the alpha-linolenic/linoleic acid metabolism, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were abundant in all three cell lines. EPA was more effective in inhibiting SKOV3 and CaOV3 xenografts, which correlated with inhibition of inflammatory markers and indicated a role for EPA-derived specialized pro-resolving mediators such as Resolvin E1. Thus, modulation of the metabolism of omega-3 fatty acids and their anti-inflammatory signaling molecules appears to be one of the common mechanisms of metformin's antitumor activity. The distinct metabolic signature of the tumors may indicate metformin response and aid the preclinical and clinical interpretation of metformin therapy in ovarian and other cancers.

Histochemical Staining of Vasculogenic Mimicry

Vasculogenic mimicry (VM) describes a new tumor microvascular paradigm of non-endothelial cells, where aggressive cancer cells independent of angiogenesis acquire the ability to fluid-conducting vessels. VM shows worse 5-year overall survival in cancer that suggesting that VM could be a promising surgical and effective adjuvant therapy strategy in prognostics of metastatic cancer patients. The current chapter is a comprehensive review on "Main Staining Methods and Protocols in Vasculogenic Mimicry." Here, we provide most up-to-date and detailed information upon microscopy and histology protocols for the identification and understanding of VM process in both in vitro and in vivo.

IL-1β Promotes Vasculogenic Mimicry of Breast Cancer Cells Through p38/MAPK and PI3K/Akt Signaling Pathways

Vasculogenic mimicry (VM), a micro vessel-like structure formed by the cancer cells, plays a pivotal role in cancer malignancy and progression. Interleukin-1 beta (IL-1β) is an active pro-inflammatory cytokine and elevated in many tumor types, including breast cancer. However, the effect of IL-1β on the VM of breast cancer has not been clearly elucidated. In this study, breast cancer cells (MCF-7 and MDA-MB-231) were used to study the effect of IL-1β on the changes that can promote VM. The evidence for VM stimulated by IL-1β was acquired by analyzing the expression of VM-associated biomarkers (VE-cadherin, VEGFR-1, MMP-9, MMP-2, c-Fos, and c-Jun) via western blot, immunofluorescent staining, and Immunohistochemistry (IHC). Additionally, morphological evidence was collected via Matrigel-based cord formation assay under normoxic/hypoxic conditions and microvessel examination through Hematoxylin and Eosin staining (H&E). Furthermore, the STRING and Gene Ontology database was also used to analyze the VM-associated interacting molecules stimulated by IL-β. The results showed that the expression of VM biomarkers was increased in both MCF-7 and MDA-MB-231 cells after IL-1β treatment. The increase in VM response was observed in IL-1β treated cells under both normoxia and hypoxia. IL-1β also increased the activation of transcription factor AP-1 complex (c-Fos/c-Jun). The bioinformatics data indicated that p38/MAPK and PI3K/Akt signaling pathways were involved in the IL-1β stimulation. It was further confirmed by the downregulated expression of VM biomarkers and reduced formation of the intersections upon the addition of the signaling pathway inhibitors. The study suggests that IL-1β stimulates the VM and its associated events in breast cancer cells via p38/MAPK and PI3K/Akt signaling pathways. Aiming the VM-associated molecular targets promoted by IL-1β may offer a novel anti-angiogenic therapeutic strategy to control the aggressiveness of breast cancer cells.

Angiogenesis and vasculogenic mimicry as therapeutic targets in ovarian cancer

Tumor angiogenesis is an essential process for growth and metastasis of cancer cells as it supplies tumors with oxygen and nutrients. During tumor angiogenesis, many pro-angiogenic factors are secreted by tumor cells to induce their own vascularization via activation of pre-existing host endothelium. However, accumulating evidence suggests that vasculogenic mimicry (VM) is a key alternative mechanism for tumor vascularization when tumors are faced with insufficient supply of oxygen and nutrients. VM is a tumor vascularization mechanism in which tumors create a blood supply system, in contrast to tumor angiogenesis mechanisms that depend on pre-existing host endothelium. VM is closely associated with tumor progression and poor prognosis in many cancers. Therefore, inhibition of VM may be a promising therapeutic strategy and may overcome the limitations of anti-angiogenesis therapy for cancer patients. In this review, we provide an overview of the current anti-angiogenic therapies for ovarian cancer and the current state of knowledge regarding the links between microRNAs and the VM process, with a focus on the mechanism that regulates associated signaling pathways in ovarian cancer. Moreover, we discuss the potential for VM as a therapeutic strategy against ovarian cancer.

Reducing the structure bias of RNA-Seq reveals a large number of non-annotated non-coding RNA

The study of RNA expression is the fastest growing area of genomic research. However, despite the dramatic increase in the number of sequenced transcriptomes, we still do not have accurate estimates of the number and expression levels of non-coding RNA genes. Non-coding transcripts are often overlooked due to incomplete genome annotation. In this study, we use annotation-independent detection of RNA reads generated using a reverse transcriptase with low structure bias to identify non-coding RNA. Transcripts between 20 and 500 nucleotides were filtered and crosschecked with non-coding RNA annotations revealing 111 non-annotated non-coding RNAs expressed in different cell lines and tissues. Inspecting the sequence and structural features of these transcripts indicated that 60% of these transcripts correspond to new snoRNA and tRNA-like genes. The identified genes exhibited features of their respective families in terms of structure, expression, conservation and response to depletion of interacting proteins. Together, our data reveal a new group of RNA that are difficult to detect using standard gene prediction and RNA sequencing techniques, suggesting that reliance on actual gene annotation and sequencing techniques distorts the perceived architecture of the human transcriptome.

Vascular mimicry: changing the therapeutic paradigms in cancer

Cancer is a major problem in the health system, and despite many efforts to effectively treat it, none has yet been fully successful. Angiogenesis and metastasis are considered as major challenges in the treatment of various cancers. Researchers have struggled to succeed with anti-angiogenesis drugs for the effective treatment of cancer, although new challenges have emerged in the treatment with the emergence of resistance to anti-angiogenesis and anti-metastatic drugs. Numerous studies have shown that different cancers can resist anti-angiogenesis drugs in a new process called vascular mimicry (VM). The studies have revealed that cells resistant to anti-angiogenesis cancer therapies are more capable of forming VMs in the in vivo and in vitro environment, although there is a link between the presence of VM and poor clinical outcomes. Given the importance of the VM in the challenges facing cancer treatment, researchers are trying to identify factors that prevent the formation of these structures. In this review article, it is attempted to provide a comprehensive overview of the molecules and main signaling pathways involved in VM phenomena, as well as the agents currently being identified as anti-VM and the role of VM in response to treatment and prognosis of cancer patients.

Paradigms of vascularization in melanoma: Clinical significance and potential for therapeutic targeting

Melanoma is the most aggressive form of skin cancer. Malignant melanoma in particular has a poor prognosis and although treatment has improved, drug resistance continues to be a challenge. Angiogenesis, the formation of blood vessels from existing microvessels, precedes the progression of melanoma from a radial growth phase to a malignant phenotype. In addition, melanoma cells can form networks of vessel-like fluid conducting channels through vasculogenic mimicry (VM). Both angiogenesis and VM have been postulated to contribute to the development of resistance to treatment and to enable metastasis. Also, the metastatic spread of melanoma is highly dependent on lymphangiogenesis, the formation of lymphatic vessels from pre-existing vessels. Interestingly, the design and clinical testing of drugs that target VM and lymphangiogenesis lag behind that of angiogenesis inhibitors. Despite this, antiangiogenic drugs have not significantly improved the overall survival of melanoma patients, thus necessitating the targeting of alternative mechanisms. In this article, I review the roles of the three paradigms of tissue perfusion, namely, angiogenesis, VM and lymphangiogenesis, in promoting melanoma progression and metastasis. This article also explores the latest development and potential opportunities in the therapeutic targeting of these processes.

Vasculogenic mimicry in carcinogenesis and clinical applications

Distinct from classical tumor angiogenesis, vasculogenic mimicry (VM) provides a blood supply for tumor cells independent of endothelial cells. VM has two distinct types, namely tubular type and patterned matrix type. VM is associated with high tumor grade, tumor progression, invasion, metastasis, and poor prognosis in patients with malignant tumors. Herein, we discuss the recent studies on the role of VM in tumor progression and the diverse mechanisms and signaling pathways that regulate VM in tumors. Furthermore, we also summarize the latest findings of non-coding RNAs, such as lncRNAs and miRNAs in VM formation. In addition, we review application of molecular imaging technologies in detection of VM in malignant tumors. Increasing evidence suggests that VM is significantly associated with poor overall survival in patients with malignant tumors and could be a potential therapeutic target.

Targeting vasculogenic mimicry by phytochemicals: A potential opportunity for cancer therapy

Vasculogenic mimicry (VM) is regarded as a process where very aggressive cancer cells generate vascular-like patterns without the presence of endothelial cells. It is considered as the main mark of malignant cancer and has pivotal role in cancer metastasis and progression in various types of cancers. On the other hand, resistance to the antiangiogenesis therapies leads to the cancer recurrence. Therefore, development of novel chemotherapies and their combinations is urgently needed for abolition of VM structures and also for better tumor therapy. Hence, identifying compounds that target VM structures might be superior therapeutic factors for cancers treatment and controlling the recurrence and metastasis. In recent times, naturally occurring compounds, especially phytochemicals have obtained great attention due to their safe properties. Phytochemicals are also capable of targeting VM structure and also their main signaling pathways. Consequently, in this review article, we illustrated key signaling pathways in VM, and the phytochemicals that affect these structures including curcumin, genistein, lycorine, luteolin, columbamine, triptolide, Paris polyphylla, dehydroeffusol, jatrorrhizine hydrochloride, grape seed proanthocyanidins, resveratrol, isoxanthohumol, dehydrocurvularine, galiellalactone, oxacyclododecindione, brucine, honokiol, ginsenoside Rg3, and norcantharidin. The recognition of these phytochemicals and their safety profile may lead to new therapeutic agents' development for VM elimination in different types of tumors.

Class I histone deacetylase inhibitor suppresses vasculogenic mimicry by enhancing the expression of tumor suppressor and anti-angiogenesis genes in aggressive human TNBC cells

Triple-negative breast cancer (TNBC) cells form angiogenesis-independent vessel-like structures to survive, known as vasculogenic mimicry (VM), contributing to a poor prognosis for cancer patients. Nuclear localized class I histone deacetylases (HDACs) enzymes, particularly HDACs 1, 2, 3 deacetylate chromatin histones, are overexpressed in cancers and epigenetically regulate the expression of genes involved in cancer initiation and progression. The specific HDAC inhibitor, entinostat, has been shown to attenuate tumor progression and metastasis in TNBC. In this study, we hypothesized that entinostat would enhance the expression of anti-angiogenic and tumor suppressor genes and would thus suppress VM structures in TNBC cells in a 3D Matrigel cell culture preclinical model. Our data indicated that invasive triple-negative MDA-MB-231, LM2-4 and BT-549 breast cancer cells, but not poorly invasive luminal MCF-7 cells, efficiently underwent matrix-associated VM formation. Approximately 80% of TNBC cells with the stem cell phenotype potential formed vessel-like structures when mixed with Matrigel and cultured in the low attachment tissue culture plate. The molecular mechanisms of VM formation are rather complex, while angiogenesis inhibitor genes are downregulated and pro-angiogenesis genes are upregulated in VM-forming cells. Our data revealed that treatment of the TNBC VM phenotype cells with entinostat epigenetically led to the re-expression of the anti-angiogenic genes, serpin family F member 1 (SERPINF1) and thrombospondin 2 (THBS2), and to that of the tumor suppressor genes, phosphatase and tensin homolog (PTEN) and p21, and reduced VM structures. We also found that treatment of the TNBC VM phenotype cells with entinostat downregulated the expression of vascular endothelial growth factor A (VEGF-A), and that of the epithelial-mesenchymal transition (EMT)-related genes, Vimentin and β-catenin. METABIRC and TCGA breast cancer cohort mRNA expression data analysis revealed that a high expression of the anti-angiogenesis-associated genes, THBS2, SERPINF1 and serpin family B member 5 (SERPINB5), and of the tumor suppressor gene, PTEN, was associated with a better overall survival (OS) of breast cancer patients. Taken together, the findings of this study demonstrate that HDACs 1, 2, 3 partly contribute to VM formation in TNBC cells; thus, HDACs may be an important therapeutic target for TNBC.

Hsp90β promotes aggressive vasculogenic mimicry via epithelial-mesenchymal transition in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a typical hypervascular solid tumor. Vasculogenic mimicry (VM) formed by aggressive tumor cells to mimic vasculogenic networks plays an important role in the tumor malignancy of HCC. Hsp90β promotes endothelial cell-dependent angiogenesis in HCC. However, the relationship between Hsp90β and VM formation is unclear. In this study, we found that Hsp90β is positively correlated with VM and EMT marker proteins in HCC tissues and promotes tube formation, cell migration, and invasion in vitro. Hsp90β interacts with Twist1 and promotes its deubiquitination and stabilization to nuclear translocation and enhances the VE-cadherin promoter activity. Results of in vitro analysis indicate that Hsp90β enhances the tumor VM in tumor-burdened mice, and the Hsp90 inhibitor NVP-BEP800 suppresses VM formation by releasing Hsp90β and Twist1 interaction. This study provides a potential antitumor therapy for inhibiting VM by targeting Hsp90β in HCC.

Chitinase 3 like 1 (CHI3L1) promotes vasculogenic mimicry formation in cervical cancer

Vasculogenic mimicry (VM) is an alternative microvascular system which tumour cells orchestrate, independent of endothelial cell-mediated angiogenesis. VM develops tumour vascular networks that correlate with tumour growth, metastasis, and short survival time of patients with a number of cancers. However, little is known regarding VM in the vascularisation of cervical cancer. Chitinase 3 like 1 (CHI3L1) has been previously reported to display the ability to induce angiogenesis in cervical cancer. Here, we explored a pathological role of CHI3L1 in tumour cell-mediated vascularisation. Sixty-six samples of cervical cancer were collected to examine CHI3L1 expression and VM formation using immunohistochemistry and CD34-periodic acid-Schiff (PAS) dual staining. CHI3L1 expression was significantly correlated with formation of tumour cell-associated vascular channels in the absence of endothelial cells (p=0.031). Interestingly, tumour samples lacking VM were positively correlated with non-metastasis (p=0.035). Patients with VM positive tumours tended to have decreased overall survival (OS) compared to those with VM negative samples (43.9 versus 64.6 months, p=0.079). In addition, recombinant CHI3L1 enhanced cervical cancer cell lines to form tube-like structures, supporting the notion that CHI3L1 mediates VM in cervical cancer. Our present data reveal the crucial role of CHI3L1 in the formation of VM, which may contribute to tumour aggressiveness. Therefore, targeting CHI3L1 may be a valuable strategy for the reduction of cervical cancer vascularisation and metastasis.

Evolving Significance and Future Relevance of Anti-Angiogenic Activity of mTOR Inhibitors in Cancer Therapy

mTOR inhibitors have demonstrated remarkable anti-tumor activity in experimental models, mainly by reducing cancer cell growth and tumor angiogenesis. Their use in cancer patients as monotherapy has, however, generated only limited benefits, increasing median overall survival by only a few months. Likewise, in other targeted therapies, cancer cells develop resistance mechanisms to overcome mTOR inhibition. Hence, novel therapeutic strategies have to be designed to increase the efficacy of mTOR inhibitors in cancer. In this review, we discuss the present and future relevance of mTOR inhibitors in cancer therapy by focusing on their effects on tumor angiogenesis.

Role of X‑linked inhibitor of apoptosis‑associated factor‑1 in vasculogenic mimicry in ovarian cancer

X-linked inhibitor of apoptosis‑associated factor 1 (XAF1) was identified as a novel X-linked inhibitor of apoptosis (XIAP) binding partner that may reverse the anti‑apoptotic effect of XIAP. Previous studies have revealed that XAF1 serves an important role in cancer angiogenesis. Vasculogenic mimicry (VM) describes the formation of fluid‑conducting channels by highly invasive and genetically dysregulated tumor cells. VM is critical for tumor blood supply and is associated with aggressive actions and metastasis. The aim of present study was to investigate the potential association between XAF1 expression with VM of ovarian cancer, and evaluate the role of XAF1 in tumor cell migration and invasion of SKOV3 cells. VM structure and XAF1 expression were detected in 94 tissue samples of advanced epithelial ovarian cancer (EOC). Invasion and migration of the SKOV3 human ovarian carcinoma cell line were identified by Transwell assay. It was revealed that the presence of VM was associated with high grade advanced ovarian cancer. Reduced XAF1 expression was significantly associated with presence of VM. Overexpression of XAF1 significantly reduced invasion and migration of SKOV3 cells, and inhibited vascular endothelial growth factor protein expression. Furthermore, vasculature was suppressed by overexpression of XAF1 in vivo in xenograft models. In conclusion, XAF1 expression was associated with VM in ovarian cancer, suggesting a potential role of XAF1 in the formation of VM in EOC. These findings may facilitate the development of novel therapeutic agents for the treatment of ovarian cancer.

Vasculogenic mimicry signaling revisited: focus on non-vascular VE-cadherin

Vasculogenic mimicry (VM) is a blood supply system independent of endothelial vessels in tumor cells from different origins. It reflects the plasticity of aggressive tumor cells that express vascular cell markers and line tumor vasculature. The presence of VM is associated with a high tumor grade, short survival, invasion and metastasis. Endothelial cells (ECs) express various members of the cadherin superfamily, in particular vascular endothelial (VE-) cadherin, which is the main adhesion receptor of endothelial adherent junctions. Aberrant extra-vascular expression of VE-cadherin has been observed in certain cancer types associated with VM. In this review we focus on non-endothelial VE-cadherin as a prominent factor involved in the acquisition of tubules-like structures by aggressive tumor cells and we summarize the specific signaling pathways, the association with trans-differentiation and stem-like phenotype and the therapeutic opportunities derived from the in-depth knowledge of the peculiarities of the biology of VE-cadherin and other key components of VM.

Involvement of human chorionic gonadotropin in regulating vasculogenic mimicry and hypoxia-inducible factor-1α expression in ovarian cancer cells

BACKGROUND

Human chorionic gonadotropin (hCG) can play a crucial role in angiogenesis. In the present study, we focused on hCG to gain insight into its potential effects on vasculogenic mimicry (VM) in ovarian cancer cells.

METHODS

Ovarian cancer OVCAR-3 cells were incubated with different concentrations of recombinant hCG in 3-dimensional cultures. VM was identified by morphological observations and vascular endothelial cell marker detection in OVCAR-3 cells. Expression of hCG, hypoxia-inducible factor-1α (HIF-1α), and the endothelial cell markers CD31, VEGF, and factor VIII were detected by reverse transcription polymerase chain reaction and western blotting. The effect of hCG on endothelial cell-marker expression in ovarian cancer cells was further explored using small interfering RNA (siRNA) and plasmid-based approaches.

RESULTS

Incubation of OVCAR-3 cells with recombinant hCG induced vessel-like network formation, which was accompanied by significant elevation of vascular marker expression. Attenuation of hCG expression by siRNA in OVCAR-3 cells suppressed the expression of endothelial cell markers and HIF-1α by tumour cells. Overexpression of hCG in OVCAR-3 cells resulted in increased expression of endothelial cell markers and HIF-1α.

CONCLUSIONS

HCG was crucial for changing the phenotype of OVCAR-3 cells to endothelial-like cells. The effect of hCG induction on VM in ovarian cancer cells is potentially associated with HIF-1α.

Establishment and Characterization of Orthotopic Mouse Models for Human Uveal Melanoma Hepatic Colonization

Uveal melanoma (UM) is a rare type of melanoma, although it is the most common primary ocular malignant tumor in adults. Nearly one-half the patients with primary UM subsequently develop systemic metastasis, preferentially to the liver. Currently, no treatment is effective for UM hepatic metastasis, and the prognosis is universally poor. The main challenge in designing a treatment strategy for UM hepatic metastasis is the lack of suitable animal models. We developed two orthotopic mouse models for human UM hepatic metastases: direct hepatic implantation model (intrahepatic dissemination model) and splenic-implantation model (hematogenous dissemination model) and investigated the tumorgenesis in the liver. A human UM cell line, established from a hepatic metastasis and nonobese diabetic severe combined immunodeficient γ mice, were used for development of in vivo tumor models. In the direct hepatic implantation model, a localized tumor developed in the liver in all cases and intrahepatic dissemination was subsequently seen in about one-half of cases. However, in the splenic implantation model, multiple hepatic metastases were observed after splenic implantation. Hepatic tumors subsequently seeded intra-abdominal metastasis; however, lung metastases were not seen. These findings are consistent with those observed in human UM hepatic metastases. These orthotopic mouse models offer useful tools to investigate the biological behavior of human UM cells in the liver.

An HCG-rich microenvironment contributes to ovarian cancer cell differentiation into endothelioid cells in a three-dimensional culture system

We investigated the expression of human chorionic gonadotropin (HCG) and its effects on vasculogenic mimicry (VM) formation in ovarian cancer cells under normoxic and hypoxic conditions in three-dimensional matrices preconditioned by an endothelial-trophoblast cell co-culture system. The co-culture model was established using human umbilical vein endothelial cells (HUVECs) and HTR-8 trophoblast cells in a three-dimensional culture system. The co-cultured cells were removed with NH4OH, and ovarian cancer cells were implanted into the preconditioned matrix. VM was identified morphologically and by detecting vascular markers expressed by cancer cells. The specificity of the effects of exogenous HCG in the microenvironment was assessed by inhibition with a neutralizing anti-HCG antibody. HCG siRNA was used to knock down endogenous HCG expression in OVCAR-3 ovarian cancer cells. HTR-8 cells 'fingerprinted' HUVECs to form capillary-like tube structures in co-cultures. In the preconditioned HCG-rich microenvironment, the number of vessel-like network structures formed by HCG receptor-positive OVCAR-3 cells and the expression levels of CD31, VEGF and factor VIII were significantly increased. The preconditioned HCG-rich microenvironment significantly increased the expression of hypoxia inducible factor-1α (HIF‑1α) and VM formation in OVCAR-3 cells under hypoxic conditions. Treatment with a neutralizing anti-HCG antibody but not HCG siRNA significantly inhibited the formation of vessel-like network structures. HCG in the microenvironment contributes to OVCAR-3 differentiation into endothelioid cells in three-dimensional matrices preconditioned with an endothelial-trophoblast cell co-culture system. HCG may synergistically enhance hypoxia-induced vascular markers and HIF-1α expression. These findings would provide perspectives on new therapeutic targets for ovarian cancer.

Advanced research on vasculogenic mimicry in cancer

Vasculogenic mimicry (VM) is a brand-new tumour vascular paradigm independent of angiogenesis that describes the specific capacity of aggressive cancer cells to form vessel-like networks that provide adequate blood supply for tumour growth. A variety of molecule mechanisms and signal pathways participate in VM induction. Additionally, cancer stem cell and epithelial-mesenchymal transitions are also shown to be implicated in VM formation. As a unique perfusion way, VM is associated with tumour invasion, metastasis and poor cancer patient prognosis. Due to VM's important effects on tumour progression, more VM-related strategies are being utilized for anticancer treatment. Here, with regard to the above aspects, we make a review of advanced research on VM in cancer.

Pivotal role of pervasive neoplastic and stromal cells reprogramming in circulating tumor cells dissemination and metastatic colonization

Reciprocal interactions between neoplastic cells and their microenvironment are crucial events in carcinogenesis and tumor progression. Pervasive stromal reprogramming and remodeling that transform a normal to a tumorigenic microenvironment modify numerous stromal cells functions, status redox, oxidative stress, pH, ECM stiffness and energy metabolism. These environmental factors allow selection of more aggressive cancer cells that develop important adaptive strategies. Subpopulations of cancer cells acquire new properties associating plasticity, stem-like phenotype, unfolded protein response, metabolic reprogramming and autophagy, production of exosomes, survival to anoikis, invasion, immunosuppression and therapeutic resistance. Moreover, by inducing vascular transdifferentiation of cancer cells and recruiting endothelial cells and pericytes, the tumorigenic microenvironment induces development of tumor-associated vessels that allow invasive cells to gain access to the tumor vessels and to intravasate. Circulating cancer cells can survive in the blood stream by interacting with the intravascular microenvironment, extravasate through the microvasculature and interact with the metastatic microenvironment of target organs. In this review, we will focus on many recent paradigms involved in the field of tumor progression.

A new perspective of vasculogenic mimicry: EMT and cancer stem cells (Review)

Vasculogenic mimicry (VM), a new pattern of tumor microcirculation, is important for the growth and progression of tumors. Epithelial-mesenchymal transition (EMT) is pivotal in malignant tumor progression and VM formation. With increasing knowledge of cancer stem cell (CSC) phenotypes and functions, increasing evidence suggests that CSCs are involved in VM formation. Recent studies have indicated that EMT is relevant to the acquisition and maintenance of stem cell-like characteristics. Thus, in this review we discuss the correlation between CSCs, EMT and VM formation.

HER2/neu expression correlates with vasculogenic mimicry in invasive breast carcinoma

Vasculogenic mimicry (VM) refers to the condition in which tumour cells mimic endothelial cells to form extracellular matrix-rich tubular channels. VM is more extensive in more aggressive tumours. The human epidermal growth factor receptor 2 (HER2) gene is amplified in 20–30% of human breast cancers and has been implicated in mediating aggressive tumour growth and metastasis. However, thus far, there have been no data on the role of HER2 in VM formation. Immunohistochemical and histochemical double-staining methods were performed to display VM in breast cancer specimens. Transfection in MCF7 cells was performed and clones were selected by G418. The three-dimensional Matrigel culture was used to evaluate VM formation in the breast cancer cell line. According to statistical analysis, VM was related to the presence of a positive nodal status and advanced clinical stage. The positive rate of VM increased with increased HER2 expression. In addition, cases with HER2 3+ expression showed significantly greater VM channel count than those in other cases. The exogenous HER2 overexpression in MCF-7 cells induced vessel-like VM structures on the Matrigel and increased the VM mediator vascular endothelial (VE) cadherin. Our data provide evidence for a clinically relevant association between HER2 and VM in human invasive breast cancer. HER2 overexpression possibly induces VM through the up-regulation of VE cadherin. Understanding the key molecular events may provide therapeutic intervention strategies for HER2+ breast cancer.

Tumor cell vasculogenic mimicry: from controversy to therapeutic promise

In 1999, The American Journal of Pathology published an article entitled "Vascular channel formation by human melanoma cells in vivo and in vitro: vasculogenic mimicry," by Maniotis and colleagues, which ignited a spirited debate for several years and earned distinction as a citation classic. Tumor cell vasculogenic mimicry (VM) refers to the plasticity of aggressive cancer cells forming de novo vascular networks, which thereby contribute to perfusion of rapidly growing tumors, transporting fluid from leaky vessels, and/or connecting with the constitutional endothelial-lined vasculature. The tumor cells capable of VM share a plastic, transendothelial phenotype, which may be induced by hypoxia. Since VM was introduced as a novel paradigm for melanoma tumor perfusion, many studies have contributed new findings illuminating the underlying molecular pathways supporting VM in a variety of tumors, including carcinomas, sarcomas, glioblastomas, astrocytomas, and melanomas. Facilitating the functional plasticity of tumor cell VM are key proteins associated with vascular, stem cell, and hypoxia-related signaling pathways, each deserving serious consideration as potential therapeutic targets and diagnostic indicators of the aggressive, metastatic phenotype.

Molecular pathways: vasculogenic mimicry in tumor cells: diagnostic and therapeutic implications

Tumor cell vasculogenic mimicry (VM) describes the functional plasticity of aggressive cancer cells forming de novo vascular networks, thereby providing a perfusion pathway for rapidly growing tumors, transporting fluid from leaky vessels, and/or connecting with endothelial-lined vasculature. The underlying induction of VM seems to be related to hypoxia, which may also promote the plastic, transendothelial phenotype of tumor cells capable of VM. Since its introduction in 1999 as a novel paradigm for melanoma tumor perfusion, many studies have contributed new insights into the underlying molecular pathways supporting VM in a variety of tumors, including melanoma, glioblastoma, carcinomas, and sarcomas. In particular, critical VM-modulating genes are associated with vascular (VE-cadherin, EphA2, VEGF receptor 1), embryonic and/or stem cell (Nodal, Notch4), and hypoxia-related (hypoxia-inducible factor, Twist1) signaling pathways. Each of these pathways warrants serious scrutiny as potential therapeutic, vascular targets, and diagnostic indicators of plasticity, drug resistance, and the aggressive metastatic phenotype.

Role of hCG in vasculogenic mimicry in OVCAR-3 ovarian cancer cell line

OBJECTIVES

Vasculogenic mimicry (VM) is induced by hypoxia in 3-dimensional culture of ovarian cancer cells. By using this 3D model system, we explored the expression of human chorionic gonadotropin (hCG) and its effects on VM formation in ovarian cancer cell line OVCAR-3 both under normoxic and hypoxic conditions.

METHODS

Vasculogenic mimicry was identified by morphological observation and detection of vascular cell marker expressed by OVCAR-3. Potential formation of tumor channels was observed by light microscopy and scanning electron microscopy. Expression of vascular cell marker CD31, vascular endothelial growth factor, and Factor VIII were detected by flow cytometry, immunochemistry, and Western blot. Expression of hCG was investigated by enzyme-linked immunosorbent assay, chemiluminescence immunoassay, real-time polymerase chain reaction (PCR), and Western blot. Expression of hypoxia-inducible factor-1α (HIF-1α) was detected by real-time PCR, Western blot, and blocked by small interference RNA. Incubation of OVCAR-3 with recombinant hCG was used to evaluate its effect on VM formation. The specificity of the effect of hCG was assessed by inhibition with the neutralizing anti-hCG antibody.

RESULTS

OVCAR-3 cells formed vessel-like network structures and expressed vascular marker significantly under hypoxia in 3D. The expression level of hCG under hypoxia was significantly higher than that under normoxia. Attenuating hypoxia-inducible factor (HIF)-1α expression via small interference RNA resulted in a significantly decreased hCG expression in OVCAR-3, which indicated that the effect of hypoxia on hCG expression was mediated through HIF-1α. Treatment of OVCAR-3 with 5000 mU/mL hCG resulted in the presence of tumor cell-lined vasculature and significant elevation in vascular marker expression, even under normoxia. Expression level of vascular marker and HIF-1α in OVCAR-3 increased in response to hCG treatment in a dose-dependent manner. The effect of hCG was inhibited by the neutralizing anti-hCG antibody.

CONCLUSIONS

Human chorionic gonadotropin has the potential to induce VM in OVCAR-3. Human chorionic gonadotropin might have synergistic hypoxia-induced effect on vascular marker and HIF-1α expression.

IRX1 influences peritoneal spreading and metastasis via inhibiting BDKRB2-dependent neovascularization on gastric cancer

The overexpression of IRX1 gene correlates with the growth arrest in gastric cancer. Furthermore, overexpression of IRX1 gene suppresses peritoneal spreading and long distance metastasis. To explore the precise mechanisms, we investigated whether restoring IRX1 expression affects the angiogenesis or vasculogenic mimicry (VM). Human umbilical vein endothelial cells (HUVECs) and chick embryo and SGC-7901 gastric cancer cells were used for angiogenesis and VM analysis. Small interfering RNA was used for analyzing the function of BDKRB2, a downstream target gene of IRX1. As results, the remarkable suppression on peritoneal spreading and pulmonary metastasis of SGC-7901 cells by IRX1 transfectant correlates to reduced angiogenesis as well as VM formation. Using the supernatant from SGC-7901/IRX1 cells, we found a strong inhibiting effect on angiogenesis both in vitro and in chick embryo. SGC-7901/IRX1 cells revealed strong inhibiting effect on VM formation too. By gene-specific RNA interference for BDKRB2, or its effector PAK1, we got an effective inhibition on tube formation, cell proliferation, cell migration and invasion in vitro. In conclusion, enforcing IRX1 expression effectively suppresses peritoneal spreading and pulmonary metastasis via anti-angiogenesis and anti-VM mechanisms, in addition to previously found cell growth and invasion. BDKRB2 and its downstream effector might be potential targets for anti-cancer strategy.

Contribution of cancer stem cells to tumor vasculogenic mimicry

Vasculogenic mimicry (VM), a newly-defined pattern of tumor blood supply, provides a special passage without endothelial cells and is conspicuously different from angiogenesis and vasculogenesis. The biological features of the tumor cells that form VM remain unknown. Cancer stem cells (CSCs) are believed to be tumor-initiating cells, capable of self-renewal and multipotent differentiation, which resemble normal stem cells in phenotype and function. Recently CSCs have been shown to contribute to VM formation as well as angiogenesis. These findings challenge the previous understanding of the cellular basis of VM formation. In this review, we present evidence for participation of CSCs in VM formation. We also discuss the potential mechanisms and possible interaction of CSCs with various elements in tumor microenvironment niche. Based on the importance of VM in tumor progression, it constitutes a novel therapeutic target for cancer.

Endothelial-like cells derived directly from human tumor xenografts

Tumor-associated endothelial cells (TAECs) harboring various genomic abnormalities have been described in human cancers although their origins remain obscure. We generated 4 human cancer cell lines tagged with multiple markers, grew them as xenografts, and characterized their TAECs. Depending on their tumor of origin, 5-40% of TAECs reproducibly expressed all tags. Tagged TAECs (tTAECS) were morphologically, immunologically and functionally similar, although not identical, to normal endothelial cells (ECs) and contained only human chromosomes. tTAECs underwent a senescent-like proliferative arrest after several in vitro passages, but could be immortalized by telomerase, thus allowing us to show that the retention of the EC phenotype was of long-term duration. In contrast, nonimmortalized tTAECs could be propagated in vivo where they incorporated into the tumor neo-vasculature. Although consistent with previous reports that some tumor cells may undergo "vasculogenic mimicry" (VM), the tumor-derived endothelial-like cells described here appear distinctly different. Moreover, their properties and behaviors are more durable than expected for cells undergoing VM, are not the result of fusions between ECs and tumor cells, and are cell autonomous. These findings could have significant implications for therapies that target tumor angiogenesis.

The proliferation, apoptosis, invasion of endothelial-like epithelial ovarian cancer cells induced by hypoxia

BACKGROUND

Epithelial ovarian cancer is one of the most malignant cancers in women because metastasis occurs in the most of patients by the time of diagnosis. Cancer cells have strong capacity to form angiogenesis or vasculogenic mimicry, which plays the major role in its malignant phenotype. Vasculogenic mimicry might contribute to the failure of the angiogenesis-targeted therapy strategies. Under the microenvironment of the tumor, hypoxia is the most common phenomena because of the vast energy and oxygen consuming. In the present study, the endothelial-like cells induced by hypoxia from SKOV-3 and ES-2 ovarian cancer cells were harvested to investigate the changes in their biological behaviors.

METHODS

The endothelial-like cells from SKOV-3 and ES-2 cells were harvested by laser capture microdissection. The biological behaviors of the endothelial-like cells, including proliferation, cell cycle, apoptosis, invasion and telomerase activity were determined by MTT, FCM, Transwell chamber and TRAP-ELISA methods. HIF-1α is the most important factor for the behavior changes under hypoxic condition. Some other genes relative to biological behaviors are also changes following the changes of HIF-1α. In order to elucidate the underlying mechanisms for these changes by hypoxia, the relative genes expressions including HIF-1α, CyclinD1, Flk-1, VEGF, p53 and V-src were determined by real-time PCR.

RESULTS

SKOV-3 and ES-2 cells were resistant to hypoxia by adoption of proliferation, apoptosis, differentiation and invasion. Combined with other studies, the more poorly cancer cells differentiate, the more strongly cells are resistant to hypoxia, the more possible to form vasculogenic mimicry. The changes in the expression of HIF-1α, and HIF-1α-dependent VEGF, Flk-1, Cyclin D1, and HIF-1α-independent p53 have been involved in this process.

CONCLUSIONS

HIF-1α took an important role in the behavioral changes of SKOV-3 and ES-2 cells by hypoxia. At the same time, other mechanisms were also involved in this process.

Molecular regulation of vasculogenic mimicry in tumors and potential tumor-target therapy

“Vasculogenic mimicry (VM)”, is a term that describes the unique ability of highly aggressive tumor cells to express a multipotent, stem cell-like phenotype, and form a pattern of vasculogenic-like networks in three-dimensional culture. As an angiogenesis-independent pathway, VM and/or periodic acid-schiff-positive patterns are associated with poor prognosis in tumor patients. Moreover, VM is resistant to angiogenesis inhibitors. Here, we will review the advances in research on biochemical and molecular signaling pathways of VM in tumors and on potential anti-VM therapy strategy.

Immunohistochemistry in the evaluation of neovascularization in tumor xenografts

Angiogenesis, or neovascularization, is known to play an important role in the neoplastic progression leading to metastasis. CD31 or Factor VIII-related antigen (F VIII RAg) immunohistochemistry is widely used in experimental studies for quantifying tumor neovascularization in immunocompromised animal models implanted with transformed human cell lines. Quantification, however, can be affected by variations in the methodology used to measure vascularization including antibody selection, antigen retrieval (AR) pretreatment, and evaluation techniques. To examine this further, we investigated the microvessel density (MVD) and the intensity of microvascular staining among five different human tumor xenografts and a mouse syngeneic tumor using anti-CD31 and F VIII RAg immunohistochemical staining. Different AR methods also were evaluated. Maximal retrieval of CD31 was achieved using 0.5 M Tris (pH 10) buffer, while maximum retrieval of F VIII RAg was achieved using 0.05% pepsin treatment of tissue sections. For each optimized retrieval condition, anti-CD31 highlighted small vessels better than F VIII RAg. Furthermore, the MVD of CD31 was significantly greater than that of F VIII RAg decorated vessels (p<0.001). The choice of antibody and AR method has a significant affect on immunohistochemical findings when studying angiogenesis. One also must use caution when comparing studies in the literature that use different techniques and reagents.

Thalidomide influences growth and vasculogenic mimicry channel formation in melanoma

AIMS

To observe the effects of thalidomide on melanoma tumor growth and blood supply patterns in C57 mice.

METHODS

Thirty mice inoculated subcutaneously with B16F10 cells were randomly divided into the treatment group and the control group. Thalidomide was administered once a day at a dose of 200 mg/kg for the treatment group starting on the fifth day after inoculation, and an equivalent volume of 0.5% carboxylmethyl cellulose was administered similarly in the control group. The diameter of the tumors was measured daily after inoculation until the mice were sacrificed on the 19th day. The different blood supply patterns were counted after immunohistochemical and PAS histochemical double-Staining. VEGF, NF-kappaB, PCNA, MMP-2 and MMP-9 expression in tumor tissue was also assessed.

RESULTS

The tumor volume(P = 0.019) and the number of vasculogenic mimicry(P = 0.03) and mosaic vessels(P = 0.004) in the treatment group were significantly decreased compared with the control group. VEGF(P = 0.004), NF-kappaB(P = 0.009), PCNA(P = 0.002), MMP-2 (P = 0.000), MMP-9(P = 0.002) protein expression and MMP-2(P = 0.000) and MMP-9(P = 0.000) mRNA in the treatment group were significantly lower than those in the control groups.

CONCLUSION

Thalidomide inhibits vasculogenic mimicry channel and mosaic vessels formation in melanoma through the regulation of vasculogenic factors, and it can induce necrosis of melanoma cells, which may be related with the NF-kappaB signaling pathway.