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Aggressive tumor cells can obtain the ability to transdifferentiate into cells with endothelial features and thus form vasculogenic networks. This phenomenon, called vasculogenic mimicry (VM), is associated with increased tumor malignancy and poor clinical outcome. To identify novel key molecules implicated in the process of vasculogenic mimicry, microarray analysis was performed to compare gene expression profiles of aggressive (VM+) and non-aggressive (VM−) cells derived from Ewing sarcoma and breast carcinoma. We identified the CD44/c-Met signaling cascade as heavily relevant for vasculogenic mimicry. CD44 was at the center of this cascade, and highly overexpressed in aggressive tumors. Both CD44 standard isoform and its splice variant CD44v6 were linked to increased aggressiveness in VM. Since VM is most abundant in Ewing sarcoma tumors functional analyses were performed in EW7 cells. Overexpression of CD44 allowed enhanced adhesion to its extracellular matrix ligand hyaluronic acid. CD44 expression also facilitated the formation of vasculogenic structures in vitro, as CD44 knockdown experiments repressed migration and vascular network formation. From these results and the observation that CD44 expression is associated with vasculogenic structures and blood lakes in human Ewing sarcoma tissues, we conclude that CD44 increases aggressiveness in tumors through the process of vasculogenic mimicry.

Aggressive tumor cells can adopt an endothelial cell‐like phenotype and contribute to the formation of a tumor vasculature, independent of tumor angiogenesis. This adoptive mechanism is referred to as vascular mimicry and it is associated with poor survival in cancer patients. To what extent tumor cells capable of vascular mimicry phenocopy the angiogenic cascade is still poorly explored. Here, we identify pericytes as important players in vascular mimicry. We found that pericytes are recruited by vascular mimicry‐positive tumor cells in order to facilitate sprouting and to provide structural support of the vascular‐like networks. The pericyte recruitment is mediated through platelet‐derived growth factor (PDGF)‐B. Consequently, preventing PDGF‐B signaling by blocking the PDGF receptors with either the small tyrosine kinase inhibitor imatinib or blocking antibodies inhibits vascular mimicry and tumor growth. Collectively, the current study identifies an important role for pericytes in the formation of vascular‐like structures by tumor cells. Moreover, the mechanism that controls the pericyte recruitment provides therapeutic opportunities for patients with aggressive vascular mimicry‐positive cancer types. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

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In developmental angiogenesis, pericytes are recruited by PDGF-B-expressing endothelial cells to remodel, stabilize and support the immature blood vessel. In a process called vasculogenic mimicry (VM) highly aggressive tumor cells gain the unique ability to dedifferentiate into multiple cellular phenotypes, and obtain endothelial-like characteristics. This process can lead to the formation of vasculogenic-like matrix-embedded networks, i.e. vascular-like structures, contributing to circulation. The presence of VM is associated with increased tumor malignancy. Interestingly, also the expression of PDGF in tumor cells has been demonstrated to be associated with an increased grade of malignancy. As plastic, highly aggressive tumor cells form vasculogenic-like structures resembling immature vessels, we hypothesize that plastic tumor cells engaged in VM also functionally resemble endothelial cells by seeking structural support. We demonstrate that plastic, aggressive melanoma cells transcribe and secrete PDGF-B, while in poorly aggressive melanoma cells, PDGF-B is absent. Myofibroblasts, acquired from the human vena saphena, cultured in the presence of plastic tumor cell conditioned medium display an activated phenotype. Additionally, in vitro analysis of 3D-culture on Matrigel demonstrated the functional contribution of myofibroblasts to plastic tumor cells as they structurally support the VM-characteristic networks formed. Immunohistochemical analysis of a series of cutaneous melanoma tissues showed a gradient PDGF-B staining towards the outer surface of the nest structures, i.e. the tumor cells aligning the VM-characteristic matrix networks. Consistent with the above described data, we observed staining for alpha-smooth muscle actin (α-SMA), a pericyte-specific marker, within the VM-characteristic matrix networks, thereby revealing the presence of pericytes inside these networks. Together our results demonstrate that highly aggressive, VM-positive tumor cells do not solely resemble endothelial cells phenotypically, but also actively behave like endothelial cells by producing PDGF-B and attracting structural support to their immature structures. The current findings suggest that targeting of pericytes may have an unexpected anti-tumor activity through affecting vasculogenic mimicry. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5158. doi:10.1158/1538-7445.AM2011-5158