Endothelial-like cells derived directly from human tumor xenografts

Polyphyllin I suppresses the formation of vasculogenic mimicry via Twist1/VE-cadherin pathway

Vasculogenic mimicry (VM) is a functional microcirculation pattern formed by aggressive tumor cells and is related to the metastasis and poor prognosis of many cancer types, including hepatocellular carcinoma (HCC). Thus far, no effective drugs have been developed to target VM. In this study, patients with liver cancer exhibited reduced VM in tumor tissues after treatment with Rhizoma Paridis. Polyphyllin I (PPI), which is the main component of Rhizoma Paridis, inhibited VM formation in HCC lines and transplanted hepatocellular carcinoma cells. Molecular mechanism analysis showed that PPI impaired VM formation by blocking the PI3k-Akt-Twist1-VE-cadherin pathway. PPI also displayed dual effects on Twist1 by inhibiting the transcriptional activation of the Twist1 promoter and interfering with the ability of Twist1 to bind to the promoter of VE-cadherin, resulting in VM blocking. This study is the first to report on the clinical application of the VM inhibitor. Results may contribute to the development of novel anti-VM drugs in clinical therapeutics.

Involvement of the Integrin α1β1 in the Progression of Colorectal Cancer

Integrins are a family of heterodimeric glycoproteins involved in bidirectional cell signaling that participate in the regulation of cell shape, adhesion, migration, survival and proliferation. The integrin α1β1 is known to be involved in RAS/ERK proliferative pathway activation and plays an important role in fibroblast proliferation. In the small intestine, the integrin α1 subunit is present in the crypt proliferative compartment and absent in the villus. We have recently shown that the integrin α1 protein and transcript (ITGA1) are present in a large proportion of colorectal cancers (CRC) and that their expression is controlled by the MYC oncogenic factor. Considering that α1 subunit/ITGA1 expression is correlated with MYC in more than 70% of colon adenocarcinomas, we postulated that the integrin α1β1 has a pro-tumoral contribution to CRC. In HT29, T84 and SW480 CRC cells, α1 subunit/ITGA1 knockdown resulted in a reduction of cell proliferation associated with an impaired resistance to anoikis and an altered cell migration in HT29 and T84 cells. Moreover, tumor development in xenografts was reduced in HT29 and T84 sh-ITGA1 cells, associated with extensive necrosis, a low mitotic index and a reduced number of blood vessels. Our results show that α1β1 is involved in tumor cell proliferation, survival and migration. This finding suggests that α1β1 contributes to CRC progression.

A mesenchymal glioma stem cell profile is related to clinical outcome

Recent studies have demonstrated a relationship between the expression of stem cell-associated genes and relapses in glioblastoma (GBM), suggesting a key role for tumor stem cells in this process. Although there is increasing interest in this field, glioma stem cells (GSCs) are still poorly characterized, their 'stemness' state and factors maintaining these properties remain largely unknown. We performed an expression profiling analysis of pluripotency in gliomaspheres derived from 11 patients. Comparative analysis between GSCs and H1 and H9 human embryonic stem cells as well as H9-derived neural stem cells indicates major variations in gene expression of pluripotency factors Nanog and OCT4, but a stable pattern for SOX2 suggesting its important function in maintaining pluripotency in GSCs. Our results also showed that all GSC lines have the capacity to commit to neural differentiation and express mesenchymal or endothelial differentiation markers. In addition, hierarchical clustering analysis revealed two groups of GSCs reflecting their heterogeneity and identified COL1A1 and IFITM1 as the most discriminating genes. Similar patterns have been observed in tumors from which gliomaspheres have been established. To determine whether this heterogeneity could be clinically relevant, the expression of both genes was further analyzed in an independent cohort of 30 patients with GBM and revealed strong correlation with overall survival. In vitro silencing of COL1A1 and IFTM1 confirmed the effect of these mesenchymal-associated genes on cell invasion and gliomasphere initiation. Our results indicate that COL1A1 and IFITM1 genes could be considered for use in stratifying patients with GBM into subgroups for risk of recurrence at diagnosis, as well as for prognostic and therapeutic evolution.

Metronomic chemotherapy and anti-angiogenesis: can upgraded pre-clinical assays improve clinical trials aimed at controlling tumor growth?

Metronomic chemotherapy, which is continuously administered systemically at close to non-toxic doses, targets the endothelial cells (ECs) that are proliferating during tumor angiogenesis. This leads to harmful effects of an even greatly increased number contiguous tumor cells. Although pre-clinical studies of angiogenesis-related EC features in vitro and of the anti-angiogenic and anti-tumor effects in vivo of metronomic chemotherapy have provided valuable insights, clinical trials with this type of therapy have been less successful in inhibiting tumor growth. One possible reason for the apparent disconnect between the pre-clinical and clinical outcomes is that most of the currently used experimental angiogenesis assays and tumor models are incapable of yielding data that can be translated readily into the clinical setting. Many of the assays used suffer from unintentional artifactual effects, e.g., oxidative stress in vitro, and inflammation in vivo, which reduces the sensitivity and discriminatory power of the assays. Co-treatment with an antioxidant or the inclusion of antioxidants in the vehicle often significantly affects the angiogenesis-modulating outcome of metronomic mono-chemotherapy in vivo. This ‘metronomic chemotherapy vehicle factor’ merits further study, as do the observations of antagonistic effects following metronomic treatment with a combination of standard chemotherapeutic drugs in vivo.

Rapid in vitro derivation of endothelium directly from human cancer cells

The development of an independent blood supply by a tumor is essential for maintaining growth beyond a certain limited size and for providing a portal for metastatic dissemination. Host-derived endothelial cells (ECs) residing in and compromising the tumor vasculature originate via distinct processes known as sprouting angiogenesis and vasculogenesis. More recently ECs originating directly from the tumor cells themselves have been described although the basis for this phenomenon remains poorly understood. Here we describe in vitro conditions that allow lung and ovarian cancer cells to undergo a rapid and efficient transition into ECs that are indistinguishable from those obtained in vivo. A variety of methods were used to establish that the acquired phenotypes and behaviors of these tumor-derived ECs (TDECs) closely resemble those of authentic ECs. Xenografts arising from co-inoculated in vitro-derived TDECs and tumor cells were also more highly vascularized than control tumors; moreover, their blood vessels were on average larger and frequently contained admixtures of host-derived ECs and TDECs derived from the initial inoculum. These results demonstrate that cancer cells can be manipulated under well-defined in vitro conditions to initiate a tumor cell-to-EC transition that is largely cell-autonomous, highly efficient and closely mimics the in vivo process. These studies provide a suitable means by which to identify and perhaps modify the earliest steps in TDEC generation.

Endothelial Progenitors Exist within the Kidney and Lung Mesenchyme

The renal endothelium has been debated as arising from resident hemangioblast precursors that transdifferentiate from the nephrogenic mesenchyme (vasculogenesis) and/or from invading vessels (angiogenesis). While the Foxd1-positive renal cortical stroma has been shown to differentiate into cells that support the vasculature in the kidney (including vascular smooth muscle and pericytes) it has not been considered as a source of endothelial cell progenitors. In addition, it is unclear if Foxd1-positive mesenchymal cells in other organs such as the lung have the potential to form endothelium. This study examines the potential for Foxd1-positive cells of the kidney and lung to give rise to endothelial progenitors. We utilized immunofluorescence (IF) and fluorescence-activated cell sorting (FACS) to co-label Foxd1-expressing cells (including permanently lineage-tagged cells) with endothelial markers in embryonic and postnatal mice. We also cultured FACsorted Foxd1-positive cells, performed in vitro endothelial cell tubulogenesis assays and examined for endocytosis of acetylated low-density lipoprotein (Ac-LDL), a functional assay for endothelial cells. Immunofluorescence and FACS revealed that a subset of Foxd1-positive cells from kidney and lung co-expressed endothelial cell markers throughout embryogenesis. In vitro, cultured embryonic Foxd1-positive cells were able to differentiate into tubular networks that expressed endothelial cell markers and were able to endocytose Ac-LDL. IF and FACS in both the kidney and lung revealed that lineage-tagged Foxd1-positive cells gave rise to a significant portion of the endothelium in postnatal mice. In the kidney, the stromal-derived cells gave rise to a portion of the peritubular capillary endothelium, but not of the glomerular or large vessel endothelium. These findings reveal the heterogeneity of endothelial cell lineages; moreover, Foxd1-positive mesenchymal cells of the developing kidney and lung are a source of endothelial progenitors that are likely critical to patterning the vasculature.

Hypoxia-induced expression of VE-cadherin and filamin B in glioma cell cultures and pseudopalisade structures

Most of our knowledge regarding glioma cell biology comes from cell culture experiments. For many years the standards for glioma cell culture were the use of cell lines cultured in the presence of serum and 20 % O2. However, in vivo, normoxia in many brain areas is in close to 3 % O2. Hence, in cell culture, the experimental value referred as the norm is hyperoxic compared to any brain physiological value. Likewise, cells in vivo are not usually exposed to serum, and low-passaged glioma neurosphere cultures maintained in serum-free medium is emerging as a new standard. A consequence of changing the experimental normoxic standard from 20 % O2 to the more brain physiological value of 3 % O2, is that a 3 % O2 normoxic reference point enabled a more rigorous characterization of the level of regulation of genes by hypoxia. Among the glioma hypoxia-regulated genes characterized using this approach we found VE-cadherin that is required for blood vessel formation, and filamin B a gene involved in endothelial cell motility. Both VE-cadherin and filamin B were found expressed in pseudopalisades, a glioblastoma pathognomonic structure made of hypoxic migrating cancer cells. These results provide additional clues on the role played by hypoxia in the acquisition of endothelial traits by glioma cells and on the functional links existing between pseudopalisades, hypoxia, and tumor progression.

Inherent phenotypic plasticity facilitates progression of head and neck cancer: endotheliod characteristics enable angiogenesis and invasion

The presence of the EMT (epithelial-mesenchymal transition), EndMT (endothelial-mesenchymal transition) and VM (vasculogenic mimicry) demonstrates the multidirectional extent of phenotypic plasticity in cancers. Previous findings demonstrating the crosstalk between head and neck squamous cell carcinoma (HNSCC) and vascular endothelial growth factor (VEGF) imply that HNSCC cells share some functional commonalities with endothelial cells. Our current results reveal that cultured HNSCC cells not only possess endothelial-specific markers, but also display endotheliod functional features including low density lipoprotein uptake, formation of tube-like structures on Matrigel and growth state responsiveness to VEGF and endostatin. HNSCC cell subpopulations are also highly responsive to transforming growth factor-β1 and express its auxiliary receptor, endoglin. Furthermore, the endotheliod characteristics observed in vitro recapitulate phenotypic features observed in human HNSCC tumors. Conversely, cultured normal human oral keratinocytes and intact or ulcerated human oral epithelia do not express comparable endotheliod characteristics, which imply that assumption of endotheliod features is restricted to transformed keratinocytes. In addition, this phenotypic state reciprocity facilitates HNSCC progression by increasing production of factors that are concurrently pro-proliferative and pro-angiogenic, conserving cell energy stores by LDL internalization and enhancing cell mobility. Finally, recognition of this endotheliod phenotypic transition provides a solid rationale to evaluate the antitumorigenic potential of therapeutic agents formerly regarded as exclusively angiostatic in scope.

The radiosensitivity of endothelial cells isolated from human breast cancer and normal tissue in vitro

We developed a novel method for harvesting endothelial cells from blood vessels of freshly obtained cancer and adjacent normal tissue of human breast, and compared the response of the cancer-derived endothelial cells (CECs) and normal tissue-derived endothelial cells (NECs) to ionizing radiation. In brief, when tissues were embedded in Matrigel and cultured in endothelial cell culture medium (ECM) containing growth factors, endothelial cells grew out of the tissues. The endothelial cells were harvested and cultured as monolayer cells in plates coated with gelatin, and the cells of 2nd-5th passages were used for experiments. Both CECs and NECs expressed almost the same levels of surface markers CD31, CD105 and TEM-8 (tumor endothelial marker-8), which are known to be expressed in angiogenic endothelial cells, i.e., mitotically active endothelial cells. Furthermore, both CECs and NECs were able to migrate into experimental wound in the monolayer culture, and also to form capillary-like tubes on Matrigel-coated plates. However, the radiation-induced suppressions of migration and capillary-like tube formations were greater for CECs than NECs from the same patients. In addition, in vitro clonogenic survival assays demonstrated that CECs were far more radiosensitive than NECs. In summary, we have developed a simple and efficient new method for isolating endothelial cells from cancer and normal tissue, and demonstrated for the first time that endothelial cells of human breast cancer are significantly more radiosensitive than their normal counterparts from the same patients.

In vivo evolution of tumor-derived endothelial cells

The growth of a malignant tumor beyond a certain, limited size requires that it first develop an independent blood supply. In addition to providing metabolic support, this neovasculature also allows tumor cells to access the systemic circulation, thus facilitating metastatic dissemination. The neovasculature may originate either from normal blood vessels in close physical proximity to the tumor and/or from the recruitment of bone marrow-derived endothelial cell (EC) precursors. Recent studies have shown that human tumor vasculature ECs may also arise directly from tumor cells themselves and that the two populations have highly similar or identical karyotypes. We now show that, during the course of serial in vivo passage, these tumor-derived ECs (TDECs) progressively acquire more pronounced EC-like properties. These include higher-level expression of EC-specific genes and proteins, a greater capacity for EC-like behavior in vitro, and a markedly enhanced propensity to incorporate into the tumor vasculature. In addition, both vessel density and size are significantly increased in neoplasms derived from mixtures of tumor cells and serially passaged TDECs. A comparison of early- and late-passage TDECs using whole-genome single nucleotide polymorphism profiling showed the latter cells to have apparently evolved by a process of clonal expansion of a population with a distinct pattern of interstitial chromosomal gains and losses affecting a relatively small number of genes. The majority of these have established roles in vascular development, tumor suppression or epithelial-mesenchymal transition. These studies provide direct evidence that TDECs have a strong evolutionary capacity as a result of their inherent genomic instability. Consequently such cells might be capable of escaping anti-angiogenic cancer therapies by generating resistant populations.

Neovascularization after irradiation: what is the source of newly formed vessels in recurring tumors?

Local relapse of tumors after radiation therapy remains a challenge in oncology. To devise rational approaches for preventing this relapse, we have to improve our understanding of how new vessels form in previously irradiated tumors. We propose that tumor regrowth after local irradiation is dependent on blood vessel formation by local endothelial cells without the need for recruitment of endothelial precursor cells from distant nonirradiated tissues or bone marrow. We also suggest that infiltrating myeloid bone marrow-derived cells promote survival of local endothelial cells during the early period after irradiation and angiogenesis during the later stage of tumor regrowth, both via paracrine mechanisms.