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Malignant gliomas are uniformly lethal tumors whose morbidity is mediated in large part by the angiogenic response of the brain to the invading tumor. This profound angiogenic response leads to aggressive tumor invasion and destruction of surrounding brain tissue as well as blood-brain barrier breakdown and life-threatening cerebral edema. To investigate the molecular mechanisms governing the proliferation of abnormal microvasculature in malignant brain tumor patients, we have undertaken a cell-specific transcriptome analysis from surgically harvested nonneoplastic and tumor-associated endothelial cells. SAGE-derived endothelial cell gene expression patterns from glioma and nonneoplastic brain tissue reveal distinct gene expression patterns and consistent up-regulation of certain glioma endothelial marker genes across patient samples. We define the G-protein-coupled receptor RDC1 as a tumor endothelial marker whose expression is distinctly induced in tumor endothelial cells of both brain and peripheral vasculature. Further, we demonstrate that the glioma-induced gene, PV1, shows expression both restricted to endothelial cells and coincident with endothelial cell tube formation. As PV1 provides a framework for endothelial cell caveolar diaphragms, this protein may serve to enhance glioma-induced disruption of the blood-brain barrier and transendothelial exchange. Additional characterization of this extensive brain endothelial cell gene expression database will provide unique molecular insights into vascular gene expression.

In an effort to study the importance of stromal involvement in angiogenesis, we developed a novel, multicellular model that utilizes three of the primary cell types involved in tumor angiogenesis.Fluorescently labeled human microvascular endothelial cells (HMVECs), 10T1/2 cells and myofibroblasts were incubated in the presence of a three-dimensional tumor cell cluster resuspended in collagen and embedded in Matrigel.HMVECs cultured in the presence of a human SKOV-3 ovarian carcinoma tumor cell cluster, surrounded the tumor cell cluster, while myofibroblasts invaded the cluster, localizing within the tumor cell mass. In contrast, 10T1/2 cells, a pluripotent mouse mesenchymal cell line with pericyte-like properties, did not demonstrate the same invasive phenotype. HMVECs cultured in the presence of myofibroblasts invaded the tumor cell cluster and colocalized with the myofibroblasts as demonstrated by fluorescent microscopy and immunohistochemistry. The angiogenesis inhibitors SU6668 and paclitaxel inhibited stromal invasion, while a broad-spectrum matrix metalloproteinase inhibitor did not.This model emphasizes the critical interaction between endothelial cells and myofibroblasts and provides a more complete in vitro model for studying angiogenesis and tumor progression.

Identification of appropriate models for in vivo and in vitro preclinical testing of inhibitors of tumor angiogenesis and progression is vital to the successful development of anticancer therapeutics. Although the focus is on human molecular targets, most preclinical in vivo efficacy testing occurs in mice. The goal of the current studies was to identify a murine endothelial cell line to model tumor endothelium for studying the antiangiogenic activity of therapeutic compounds in vitro. In situ hybridization was performed on three s.c. grown syngeneic murine tumors (B16 melanoma, Lewis lung carcinoma, and CT26 colon carcinoma) to assess expression of murine homologs of human tumor endothelial cell markers in the vasculature of these tumor models. Seven murine endothelial cell lines were characterized for expression of the murine homologs of recognized endothelial cell surface markers as well as for tumor endothelial cell surface markers. The seven murine endothelial cell lines had similar generation times and five of the seven lines were able to form tubes on Matrigel. Real-time-PCR and flow cytometry analysis were used to evaluate relative mRNA and protein expression of murine homologs of several recognized endothelial cell surface markers in the seven cell lines. The expression of the mRNA for the murine homologs of five tumor endothelial cell surface markers was also evaluated. The 2H11 cell line expressed all five of the tumor endothelial cell surface markers as well as several well-recognized endothelial cells markers. The 2H11 cell line responds to known and novel antiangiogenic agents by inhibition of proliferation and tube formation. These cells can be used in in vitro angiogenesis assays for evaluating the potential antiangiogenic properties and interspecies cross-reactivity of novel compounds.