Vascular gene expression patterns are conserved in primary and metastatic brain tumors.

Malignant primary glial and secondary metastatic brain tumors represent distinct pathological entities. Nevertheless, both tumor types induce profound angiogenic responses in the host brain microvasculature that promote tumor growth. We hypothesized that primary and metastatic tumors induce similar microvascular changes that could function as conserved angiogenesis based therapeutic targets. We previously isolated glioma endothelial marker genes (GEMs) that were selectively upregulated in the microvasculature of proliferating glioblastomas. We sought to determine whether these genes were similarly induced in the microvasculature of metastatic brain tumors. RT-PCR and quantitative RT-PCR were used to screen expression levels of 20 candidate GEMs in primary and metastatic clinical brain tumor specimens. Differentially regulated GEMs were further evaluated by immunohistochemistry or in situ hybridization to localize gene expression using clinical tissue microarrays. Thirteen GEMs were upregulated to a similar degree in both primary and metastatic brain tumors. Most of these genes localize to the cell surface (CXCR7, PV1) or extracellular matrix (COL1A1, COL3A1, COL4A1, COL6A2, MMP14, PXDN) and were selectively expressed by the microvasculature. The shared expression profile between primary and metastatic brain tumors suggests that the molecular pathways driving the angiogenic response are conserved, despite differences in the tumor cells themselves. Anti-angiogenic therapies currently in development for primary brain tumors may prove beneficial for brain metastases and vice versa.

Characterization of TEM1/endosialin in human and murine brain tumors.

BACKGROUND: TEM1/endosialin is an emerging microvascular marker of tumor angiogenesis. We characterized the expression pattern of TEM1/endosialin in astrocytic and metastatic brain tumors and investigated its role as a therapeutic target in human endothelial cells and mouse xenograft models. METHODS: In situ hybridization (ISH), immunohistochemistry (IH) and immunofluorescence (IF) were used to localize TEM1/endosialin expression in grade II-IV astrocytomas and metastatic brain tumors on tissue microarrays. Changes in TEM1/endosialin expression in response to pro-angiogenic conditions were assessed in human endothelial cells grown in vitro. Intracranial U87MG glioblastoma (GBM) xenografts were analyzed in nude TEM1/endosialin knockout (KO) and wildtype (WT) mice. RESULTS: TEM1/endosialin was upregulated in primary and metastatic human brain tumors, where it localized primarily to the tumor vasculature and a subset of tumor stromal cells. Analysis of 275 arrayed grade II-IV astrocytomas demonstrated TEM1/endosialin expression in 79% of tumors. Robust TEM1/endosialin expression occurred in 31% of glioblastomas (grade IV astroctyomas). TEM1/endosialin expression was inversely correlated with patient age. TEM1/endosialin showed limited co-localization with CD31, alphaSMA and fibronectin in clinical specimens. In vitro, TEM1/endosialin was upregulated in human endothelial cells cultured in matrigel. Vascular Tem1/endosialin was induced in intracranial U87MG GBM xenografts grown in mice. Tem1/endosialin KO vs WT mice demonstrated equivalent survival and tumor growth when implanted with intracranial GBM xenografts, although Tem1/endosialin KO tumors were significantly more vascular than the WT counterparts. CONCLUSION: TEM1/endosialin was induced in the vasculature of high-grade brain tumors where its expression was inversely correlated with patient age. Although lack of TEM1/endosialin did not suppress growth of intracranial GBM xenografts, it did increase tumor vascularity. The cellular localization of TEM1/endosialin and its expression profile in primary and metastatic brain tumors support efforts to therapeutically target this protein, potentially via antibody mediated drug delivery strategies.

Plasmalemmal vesicle associated protein-1 (PV-1) is a marker of blood-brain barrier disruption in rodent models.

BACKGROUND: Plasmalemmal vesicle associated protein-1 (PV-1) is selectively expressed in human brain microvascular endothelial cells derived from clinical specimens of primary and secondary malignant brain tumors, cerebral ischemia, and other central nervous system (CNS) diseases associated with blood-brain barrier breakdown. In this study, we characterize the murine CNS expression pattern of PV-1 to determine whether localized PV-1 induction is conserved across species and disease state. RESULTS: We demonstrate that PV-1 is selectively upregulated in mouse blood vessels recruited by brain tumor xenografts at the RNA and protein levels, but is not detected in non-neoplastic brain. Additionally, PV-1 is induced in a mouse model of acute ischemia. Expression is confined to the cerebovasculature within the region of infarct and is temporally regulated. CONCLUSION: Our results confirm that PV-1 is preferentially induced in the endothelium of mouse brain tumors and acute ischemic brain tissue and corresponds to blood-brain barrier disruption in a fashion analogous to human patients. Characterization of PV-1 expression in mouse brain is the first step towards development of rodent models for testing anti-edema and anti-angiogenesis therapeutic strategies based on this molecule.