Expression of VEGFR3 in glioma endothelium correlates with tumor grade

Recent advances and future directions on small molecule VEGFR inhibitors in oncological conditions

"A journey of mixed emotions" is a quote that best describes the progress chart of vascular endothelial growth factor receptor (VEGFR) inhibitors as cancer therapeutics in the last decade. Exhilarated with the Food and Drug Administration (FDA) approvals of numerous VEGFR inhibitors coupled with the annoyance of encountering the complications associated with their use, drug discovery enthusiasts are on their toes with an unswerving determination to enhance the rate of translation of VEGFR inhibitors from preclinical to clinical stage. The recently crafted armory of VEGFR inhibitors is a testament to their growing dominance over other antiangiogenic therapies for cancer treatment. This review perspicuously underscores the earnest attempts of the researchers to extract the antiproliferative potential of VEGFR inhibitors through the design of mechanistically diverse structural assemblages. Moreover, this review encompasses sections on structural/molecular properties and physiological functions of VEGFR, FDA-approved VEGFR inhibitors, and hurdles restricting the activity range/clinical applicability of VEGFR targeting antitumor agents. In addition, tactics to overcome the limitations of VEGFR inhibitors are discussed. A clear-cut viewpoint transmitted through this compilation can provide practical directions to push the cart of VEGFR inhibitors to advanced-stage clinical investigations in diverse malignancies.

Unlocking Hope: Anti-VEGFR inhibitors and their potential in glioblastoma treatment

PURPOSE

This systematic review summarizes evidence of VEGFR gene mutations and VEGF/VEGFR protein expression in glioblastoma multiforme (GBM) patients, alongside the efficacy and safety of anti-VEGFR tyrosine kinase inhibitors (TKIs) for GBM treatment.

METHODS

A comprehensive literature review was conducted using PubMed up to August 2023. Boolean operators and MeSH term "glioma," along with specific VEGFR-related keywords, were utilized following thorough examination of existing literature.

RESULTS

VEGFR correlates with glioma grade and GBM progression, presenting a viable therapeutic target. Regorafenib and axitinib show promise among studied TKIs. Other multi-targeted TKIs (MTKI) and combination therapies exhibit potential, albeit limited by blood-brain barrier penetration and toxicity. Combining treatments like radiotherapy and enhancing BBB penetration may benefit patients. Further research is warranted in patient quality of life and biomarker-guided selection.

CONCLUSION

While certain therapies hold promise for GBM, future research should prioritize personalized medicine and innovative strategies for improved treatment outcomes.

The VEGFs/VEGFRs system in Alzheimer's and Parkinson's diseases: Pathophysiological roles and therapeutic implications

The vascular endothelial growth factors (VEGFs) and their cognate receptors (VEGFRs), besides their well-known involvement in physiological angiogenesis/lymphangiogenesis and in diseases associated to pathological vessel formation, play multifaceted functions in the central nervous system (CNS). In addition to shaping brain development, by controlling cerebral vasculogenesis and regulating neurogenesis as well as astrocyte differentiation, the VEGFs/VEGFRs axis exerts essential functions in the adult brain both in physiological and pathological contexts. In this article, after describing the physiological VEGFs/VEGFRs functions in the CNS, we focus on the VEGFs/VEGFRs involvement in neurodegenerative diseases by reviewing the current literature on the rather complex VEGFs/VEGFRs contribution to the pathogenic mechanisms of Alzheimer's (AD) and Parkinson's (PD) diseases. Thereafter, based on the outcome of VEGFs/VEGFRs targeting in animal models of AD and PD, we discuss the factual relevance of pharmacological VEGFs/VEGFRs modulation as a novel and potential disease-modifying approach for these neurodegenerative pathologies. Specific VEGFRs targeting, aimed at selective VEGFR-1 inhibition, while preserving VEGFR-2 signal transduction, appears as a promising strategy to hit the molecular mechanisms underlying AD pathology. Moreover, therapeutic VEGFs-based approaches can be proposed for PD treatment, with the aim of fine-tuning their brain levels to amplify neurotrophic/neuroprotective effects while limiting an excessive impact on vascular permeability.

Molecular and Circulating Biomarkers in Patients with Glioblastoma

Glioblastoma is the most aggressive malignant tumor of the central nervous system with a low survival rate. The difficulty of obtaining this tumor material represents a major limitation, making the real-time monitoring of tumor progression difficult, especially in the events of recurrence or resistance to treatment. The identification of characteristic biomarkers is indispensable for an accurate diagnosis, the rigorous follow-up of patients, and the development of new personalized treatments. Liquid biopsy, as a minimally invasive procedure, holds promise in this regard. The purpose of this paper is to summarize the current literature regarding the identification of molecular and circulating glioblastoma biomarkers and the importance of their integration as a valuable tool to improve patient care.

Cediranib, a pan-inhibitor of vascular endothelial growth factor receptors, inhibits proliferation and enhances therapeutic sensitivity in glioblastoma cells

AIMS

Glioblastoma (GB) is the most aggressive type of brain tumor. Rapid progression, active angiogenesis, and therapy resistance are major reasons for its high mortality. Elevated expression of members of the vascular endothelial growth factor (VEGF) family suggests that anti-VEGF therapies may be potent anti-glioma therapeutic approaches. Here, we evaluated the anti-tumor activity of cediranib, a pan inhibitor of the VEGF receptors, on GB cells.

MATERIALS AND METHODS

Anti-proliferative effects of cediranib were determined using MTT, crystal-violet staining, clonogenic and anoikis resistance assays. Apoptosis induction was assessed by Annexin V/PI staining and Western blot analysis and aggressive abilities of GB cells were investigated using cell migration/invasion assays and zymography. Small-interfering RNA (siRNA)-mediated Knockdown was used to study resistance mechanisms. The anti-proliferative and apoptotic effects of cediranib in combination with radiotherapy, temozolomide, bevacizumab were also evaluated using MTT, Annexin V/PI staining and Western blot analysis for cleaved PARP-1.

KEY FINDINGS

Cediranib reduced GB cell proliferation, induced apoptotic cell death and inhibited the aggressive abilities of GB cells. Cediranib synergistically increased the anti-proliferative and apoptotic effects of radiotherapy and bevacizumab and augmented the sensitivity of GB cells to temozolomide chemotherapy. In addition, knockdown of MET and AKT potentiated cediranib sensitivity in cediranib-resistant GB cells.

SIGNIFICANCE

These findings suggest that cediranib, alone or in combination with other therapeutics, is a promising strategy for the treatment of GB and provide a rationale for further investigation of the therapeutic potential of cediranib for the treatment of this fatal malignancy.

Advanced MRI assessment of non-enhancing peritumoral signal abnormality in brain lesions

Evaluation of Central Nervous System (CNS) focal lesions has been classically made focusing on the assessment solid or enhancing component. However, the assessment of solitary peripherally enhancing lesions where the differential diagnosis includes High-Grade Gliomas (HGG) and metastasis, is usually challenging. Several studies have tried to address the characteristics of peritumoral non-enhancing areas, for better characterization of these lesions. Peritumoral hyperintense T2/FLAIR signal abnormality predominantly contains infiltrating tumor cells in HGG whereas CNS metastasis induce pure vasogenic edema. In addition, the accurate determination of the real extension of HGG is critical for treatment selection and outcome. Conventional MRI sequences are limited in distinguishing infiltrating neoplasm from vasogenic edema. Advanced MRI sequences like Diffusion Weighted Imaging (DWI), Diffusion Tensor Imaging (DTI), Perfusion Weighted Imaging (PWI) and MR spectroscopy (MRS) have all been utilized for this aim with acceptable results. Other advanced MRI approaches, less explored for this task such as Arterial Spin Labelling (ASL), Diffusion Kurtosis Imaging (DKI), T2 relaxometry or Amide Proton Transfer (APT) are also showning promising results in this scenario. In this article, we will discuss the physiopathological basis of peritumoral T2/FLAIR signal abnormality and review potential applications of advanced MRI sequences for its evaluation.

The Hippo-TAZ axis mediates vascular endothelial growth factor C in glioblastoma-derived exosomes to promote angiogenesis

Glioblastoma (GBM) is one of the most highly vascularized human cancers. The role of exosomes in cancer angiogenesis has attracted recent interest. However, proangiogenic biomolecules transported by exosomes to facilitate angiogenesis in GBM have not yet been identified. Here, we found a specific 120-kDa isoform of vascular endothelial growth factor (VEGF) in GBM-derived exosomes and confirmed it as VEGF-C. By binding to VEGF receptor 2 (VEGFR2), VEGF-C from GBM-derived exosomes showed a strong stimulatory effect on tafazzin (TAZ) expression in endothelial cells by inhibiting the Hippo signaling pathway, which eventually stimulates endothelial cell viability, migration, and tubulation. In human glioma samples, the expression of VEGF-C in tumor cells positively correlated with TAZ expression in endothelial cells. We further demonstrated that an inhibitor of exosomal release had a cooperative inhibitory effect with bevacizumab on GBM xenograft subcutaneous tumor growth and angiogenesis. Taken together, our findings revealed a novel VEGF-C isoform in GBM-derived exosomes with a role in angiogenesis and highlighted the importance of recognizing its unique signaling pathway when considering drug treatment strategies for GBM.

The immunohistochemical landscape of the VEGF family and its receptors in glioblastomas

Background

Angiogenesis is one of the hallmarks of cancer. This complex mechanism of tumor progression provides tumors cells with essential nutrients. There have been a limited number of investigations of markers of angiogenesis in Glioblastomas (GBMs), and most previous studies have focused on VEGF-A. Recent evidence suggests that there is a complex lymphatic system in central nervous system (CNS), which suggests VEGF-C and VEGF–D as interesting biomarker candidates. This study was designed to evaluate the expressions of VEGF-A, −C, −D and their co-receptors, VEGFR-1, VEGFR-2, and VEGFR-3 by immunohistochemistry (IHC) using a series of GBMs. In addition, we evaluate any putative correlations between IHC expression levels of VEGF and clinical data of patients.

Methods

Tumor samples of 70 GBM patients (64 isocitrate dehydrogenase-1 wildtype (wtIDH-1) and 6 mutant (mutIDH-1)) were assessed by IHC using tissue microarray platforms for VEGF subunits and their co-receptors. The medical records were reviewed for clinical and therapeutic data.

Results

All VEGF subunits and receptors were highly expressed in GBMs: 57 out of 62 (91.9%), 53 out of 56 (94.6%) and 55 out of 63 cases (87.3%) showed VEGF-A, VEGF-C and -D imunoexpression, respectively. Interestingly, we had found both nuclear and cytoplasmic localization of VEGF-C staining in GBM tumor cells. The frequency of immunoexpression of VEGF receptors was the following: VEGFR-1, 65 out of 66 cases (98.5%); VEGFR-2, 63 out of 64 cases (98.4%); VEGFR-3, 49 out of 50 cases (90.0%). There were no significant differences in the patient overall survival (OS) related to the VEGF staining. A weak and monotonous correlation was observed between VEGF and its cognate receptors. The pattern of VEGF IHC was found to be similar when GBM mutIDH-1 subtypes were compared to wtIDH-1.

Conclusion

Both VEGF-C and –D, together with their receptors, were found to be overexpressed in the majority GBMs, and the IHC expression levels did not correlate with OS or IDH status. To understand the significance of the interactions and increased expression of VEGF-C, VEGF-D, VEGFR-2, and VEGFR-3 axis in GBM requires more extensive studies. Also, functional assays using a larger series of GBM is also necessary to better address the biological meaning of nuclear VEGF-C expression in tumor cells.

Formation of new lymphatic vessels in glioma: An immunohistochemical analysis

We investigated the distribution and formation of new lymphatic vessels in gliomas. Specimens from seven glioma cases were analyzed by immunohistochemical staining for CD34, lymphatic endothelial hyaluronic acid receptor 1 (LYVE‐1), prospero‐related homeobox 1 (Prox1), nestin, and hypoxia‐inducible factor 1α (HIF‐1α). Three types of vessels were observed in glioma specimens: LYVE‐1⁺ lymphatic vessels, CD34⁺ blood vessels, and LYVE‐1⁺/CD34⁺ blood vessels. Prox1⁺/LYVE‐1⁺ cells were distributed in some lymphatic vessels as well as among vascular endothelial cells and glioma cells. Nestin⁺ cells were scattered throughout the gliomas, and some lymphatic cells also expressed nestin. HIF‐1α⁺ Prox1⁺ cells were widely distributed within the glioma specimens. The present immunohistochemical analysis revealed upregulation of Prox1 and HIF‐1α in some glioma tissues as well as the differentiation of nestin⁺ tumor stem cells into LYVE‐1⁺ lymphatic vessels.

VEGF-C sustains VEGFR2 activation under bevacizumab therapy and promotes glioblastoma maintenance

Background

Glioblastoma ranks among the most lethal cancers, with current therapies offering only palliation. Paracrine vascular endothelial growth factor (VEGF) signaling has been targeted using anti-angiogenic agents, whereas autocrine VEGF/VEGF receptor 2 (VEGFR2) signaling is poorly understood. Bevacizumab resistance of VEGFR2-expressing glioblastoma cells prompted interrogation of autocrine VEGF-C/VEGFR2 signaling in glioblastoma.

Methods

Autocrine VEGF-C/VEGFR2 signaling was functionally investigated using RNA interference and exogenous ligands in patient-derived xenograft lines and primary glioblastoma cell cultures in vitro and in vivo. VEGF-C expression and interaction with VEGFR2 in a matched pre- and post-bevacizumab treatment cohort were analyzed by immunohistochemistry and proximity ligation assay.

Results

VEGF-C was expressed by patient-derived xenograft glioblastoma lines, primary cells, and matched surgical specimens before and after bevacizumab treatment. VEGF-C activated autocrine VEGFR2 signaling to promote cell survival, whereas targeting VEGF-C expression reprogrammed cellular transcription to attenuate survival and cell cycle progression. Supporting potential translational significance, targeting VEGF-C impaired tumor growth in vivo, with superiority to bevacizumab treatment.

Conclusions

Our results demonstrate VEGF-C serves as both a paracrine and an autocrine pro-survival cytokine in glioblastoma, promoting tumor cell survival and tumorigenesis. VEGF-C permits sustained VEGFR2 activation and tumor growth, where its inhibition appears superior to bevacizumab therapy in improving tumor control.

Laser Capture Microdissection and RNA-Seq Analysis: High Sensitivity Approaches to Explain Histopathological Heterogeneity in Human Glioblastoma FFPE Archived Tissues

Laser capture microdissection (LCM) coupled with RNA-seq is a powerful tool to identify genes that are differentially expressed in specific histological tumor subtypes. To better understand the role of single tumor cell populations in the complex heterogeneity of glioblastoma, we paired microdissection and NGS technology to study intra-tumoral differences into specific histological regions and cells of human GBM FFPE tumors. We here isolated astrocytes, neurons and endothelial cells in 6 different histological contexts: tumor core astrocytes, pseudopalisading astrocytes, perineuronal astrocytes in satellitosis, neurons with satellitosis, tumor blood vessels, and normal blood vessels. A customized protocol was developed for RNA amplification, library construction, and whole transcriptome analysis of each single portion. We first validated our protocol comparing the obtained RNA expression pattern with the gene expression levels of RNA-seq raw data experiments from the BioProject NCBI database, using Spearman's correlation coefficients calculation. We found a good concordance for pseudopalisading and tumor core astrocytes compartments (0.5 Spearman correlation) and a high concordance for perineuronal astrocytes, neurons, normal, and tumor endothelial cells compartments (0.7 Spearman correlation). Then, Principal Component Analysis and differential expression analysis were employed to find differences between tumor compartments and control tissue and between same cell types into distinct tumor contexts. Data consistent with the literature emerged, in which multiple therapeutic targets significant for glioblastoma (such as Integrins, Extracellular Matrix, transmembrane transport, and metabolic processes) play a fundamental role in the disease progression. Moreover, specific cellular processes have been associated with certain cellular subtypes within the tumor. Our results are promising and suggest a compelling method for studying glioblastoma heterogeneity in FFPE samples and its application in both prospective and retrospective studies.

Increased Expression of Vascular Endothelial Growth Factor-D Following Brain Injury

Alterations in the expression of the vascular endothelial growth factors (VEGF) A and B occur during blood–brain barrier (BBB) breakdown and angiogenesis following brain injury. In this study, the temporal and spatial expression of VEGF-D and VEGF receptors-2 and -3 (VEGFR-2 and VEGFR-3, respectively) was determined at the mRNA and protein level in the rat cortical cold-injury model over a period of 0.5 to 6 days post-injury. In order to relate endothelial VEGF-D protein expression with BBB breakdown, dual labeling immunofluorescence was performed using antibodies to VEGF-D and to fibronectin, a marker of BBB breakdown. In control rats, VEGF-D signal was only observed in scattered perivascular macrophages in the cerebral cortex. The upregulation of VEGF-D mRNA expression was observed in the injury site between days 0.5 to 4, coinciding with the period of BBB breakdown and angiogenesis. At the protein level, intracerebral vessels with BBB breakdown to fibronectin in the lesion on days 0.5 to 4 failed to show endothelial VEGF-D. Between days 0.5 to 6, an increased VEGF-D immunoreactivity was noted in the endothelium of pial vessels overlying the lesion site, in neutrophils, macrophages, and free endothelial cells within the lesion. The upregulation of VEGFR-2 and -3 mRNA and protein expression was observed early post-injury on day 0.5. Although there was concurrent expression of VEGF-A, VEGF-B, and VEGF-D post-injury, differences in their spatial expression during BBB breakdown and angiogenesis suggest that they have specific and separate roles in these processes.

Extracellular matrix differences in glioblastoma patients with different prognoses

Glioblastoma is the most common malignant central nervous system tumor. Patient outcome remains poor despite the development of therapy and increased understanding of the disease in the past decades. Glioma cells invade the peritumoral brain, which results in inevitable tumor recurrence. Previous studies have demonstrated that the extracellular matrix (ECM) is altered in gliomas and serves a major role in glioma invasion. The present study focuses on differences in the ECM composition of tumors in patients with poor and improved prognosis. The mRNA and protein expression of 16 invasion-associated ECM molecules was determined using reverse trascription-quantitiative polymerase chain reaction and immunohistochemistry, respectively. Clinical factors of patients with different prognoses was also analyzed. It was determined that age and postoperative Karnofsky performance score were associated with patient survival. Furthermore, Fms-related tyrosine kinase 4/vascular endothelial growth factor receptor 3 (FLT4/VEGFR3), murine double minute 2 (MDM2) and matrix metallopeptidase 2 (MMP2) mRNA levels were significantly different between the two prognostic groups. Additionally, brevican, cluster of differentiation 44, hyaluronan mediated motility receptor, integrin-αV and -β1, and MDM2 protein expression were indicated to be significantly different in immunohistochemistry slides. Using the expression profile, including the invasion spectrum of the samples, it was possible to identify the prognostic group of the sample with high efficacy, particularly in cases with poor prognosis. In conclusion, it was determined that ECM components exhibit different expression levels in tumors with different prognoses and thus the invasion spectrum can be used as a prognostic factor in glioblastoma.

Blockade of vascular endothelial growth factor receptors by tivozanib has potential anti-tumour effects on human glioblastoma cells

Glioblastoma (GBM) remains one of the most fatal human malignancies due to its high angiogenic and infiltrative capacities. Even with optimal therapy including surgery, radiotherapy and temozolomide, it is essentially incurable. GBM is among the most neovascularised neoplasms and its malignant progression associates with striking neovascularisation, evidenced by vasoproliferation and endothelial cell hyperplasia. Targeting the pro-angiogenic pathways is therefore a promising anti-glioma strategy. Here we show that tivozanib, a pan-inhibitor of vascular endothelial growth factor (VEGF) receptors, inhibited proliferation of GBM cells through a G2/M cell cycle arrest via inhibition of polo-like kinase 1 (PLK1) signalling pathway and down-modulation of Aurora kinases A and B, cyclin B1 and CDC25C. Moreover, tivozanib decreased adhesive potential of these cells through reduction of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Tivozanib diminished GBM cell invasion through impairing the proteolytic cascade of cathepsin B/urokinase-type plasminogen activator (uPA)/matrix metalloproteinase-2 (MMP-2). Combination of tivozanib with EGFR small molecule inhibitor gefitinib synergistically increased sensitivity to gefitinib. Altogether, these findings suggest that VEGFR blockade by tivozanib has potential anti-glioma effects in vitro. Further in vivo studies are warranted to explore the anti-tumour activity of tivozanib in combinatorial approaches in GBM.

Anticalins directed against vascular endothelial growth factor receptor 3 (VEGFR-3) with picomolar affinities show potential for medical therapy and in vivo imaging

Members of the vascular endothelial growth factor receptor (VEGFR) family play a central role in angiogenesis as well as lymphangiogenesis and are crucial for tumor growth and metastasis. In particular, VEGFR-3 expression is induced in endothelial cells during tumor angiogenesis. We report the design of anticalins that specifically recognize the ligand-binding domains 1 and 2 of VEGFR-3. To this end, a library of the lipocalin 2 scaffold with 20 randomized positions distributed across its binding site was subjected to phage display selection and enzyme linked immunosorbent assay (ELISA) screening using the VEGF-C binding fragment (D1-2) or the entire extracellular region (D1-7) of VEGFR-3 as target proteins. Promising anticalin candidates were produced in Escherichia coli and biochemically characterized. Three variants with different receptor binding modes were identified, and two of them were optimized with regard to target affinity as well as folding efficiency. The resulting anticalins show dissociation constants down to the single-digit picomolar range. Specific recognition of VEGFR-3 on cells was demonstrated by immunofluorescence microscopy. Competitive binding versus VEGF-C was demonstrated for two of the anticalins with Ki values in the low nanomolar range. Based on these data, VEGFR-3 specific anticalins provide promising reagents for the diagnosis and/or therapeutic intervention of tumor-associated vessel growth.

The gain-of-function GLI1 transcription factor TGLI1 enhances expression of VEGF-C and TEM7 to promote glioblastoma angiogenesis

We recently discovered that truncated glioma-associated oncogene homolog 1 (TGLI1) is highly expressed in glioblastoma (GBM) and linked to increased GBM vascularity. The mechanisms underlying TGLI1-mediated angiogenesis are unclear. In this study, we compared TGLI1- with GLI1-expressing GBM xenografts for the expression profile of 84 angiogenesis-associated genes. The results showed that expression of six genes were upregulated and five were down-regulated in TGLI1-carrying tumors compared to those with GLI1. Vascular endothelial growth factor-C (VEGF-C) and tumor endothelial marker 7 (TEM7) were selected for further investigations because of their significant correlations with high vascularity in 135 patient GBMs. TGLI1 bound to both VEGF-C and TEM7 gene promoters. Conditioned medium from TGLI1-expressing GBM cells strongly induced tubule formation of brain microvascular endothelial cells, and the induction was prevented by VEGF-C/TEM7 knockdown. Immunohistochemical analysis of 122 gliomas showed that TGLI1 expression was positively correlated with VEGF-C, TEM7 and microvessel density. Analysis of NCBI Gene Expression Omnibus datasets with 161 malignant gliomas showed an inverse relationship between tumoral VEGF-C, TEM7 or microvessel density and patient survival. Together, our findings support an important role that TGLI1 plays in GBM angiogenesis and identify VEGF-C and TEM7 as novel TGLI1 target genes of importance to GBM vascularity.

Differential expression of PDGFRB and EGFR in microvascular proliferation in glioblastoma

Glioblastoma (GBM) is the highly malignant glioma and exhibits microvascular proliferation. PCR mRNA arrays and immunohistochemical stains on tissue microarray demonstrated that the expression level of PDGFRB in GBM microvascular proliferation was significantly higher than that in GBM tumor cells while the expression level of EGFR was lower in microvascular proliferation than in GBM tumor cells. PDGFRB protein was selectively expressed in pericytes in GBM microvascular proliferation. By analyzing The Cancer Genome Atlas (TCGA) datasets for GBM, it was found that genomic DNA alterations were the main reason for the high expression of EGFR in GBM tumor cells. Our miRNA microarray data showed that microRNAs (miRNAs) (miR-193b-3p, miR-518b, miR-520f-3p, and miR-506-5p) targeting PDGFRB were downregulated in microvascular proliferation, which might be the most likely reason for the high expression of PDGFRB in GBM microvascular proliferation. The increase of several miRNAs (miR-133b, miR-30b-3p, miR-145-5p, and miR-146a-5p) targeting EGFR in GBM microvascular proliferation was one of the reasons for the lack of expression of EGFR in GBM microvascular proliferation. These findings implicated that miRNAs, such as miR-506, miR-133b, miR-145, and miR-146a, that target PDGFRB or EGFR, might be potential therapeutic agents for GBM. A new generation of targeted therapeutic agents against both EGFR and PDGFRB might be developed in the future.

Upregulation of miR-107 Inhibits Glioma Angiogenesis and VEGF Expression

MicroRNAs can function as oncogenes or tumor suppressors in glioma. Previously, we showed that miR-107 inhibits glioma cell proliferation, migration, and invasion. Since tumor growth and invasion are closely related to angiogenesis, we further examined the role of miR-107 in glioma angiogenesis. In a co-culture of glioma cells and human brain microvascular endothelial cells (HBMVEC), overexpression of miR-107 in glioma cells led to the inhibition of HBMVEC proliferation, migration, and tube formation ability. ELISA, RT-PCR, and western blot assays revealed that upregulation of miR-107 in glioma cells inhibits VEGF expression. Our findings collectively support the critical involvement of miR-107 in glioma cell angiogenesis and highlight its potential as a therapeutic target for glioma.

ID3 contributes to the acquisition of molecular stem cell-like signature in microvascular endothelial cells: its implication for understanding microvascular diseases

While significant progress has been made to advance our knowledge of microvascular lesion formation, yet the investigation of how stem-like cells may contribute to the pathogenesis of microvascular diseases is still in its infancy. We assessed whether the inhibitor of DNA binding and differentiation 3 (ID3) contributes to the acquisition of a molecular stem cell-like signature in microvascular endothelial cells. The effects of stable ID3 overexpression and SU5416 treatment - a chemical inducer of microvascular lesions, had on the stemness signature were determined by flow cytometry, immunoblot, and immunohistochemistry. Continuous ID3 expression produced a molecular stemness signature consisting of CD133(+) VEGFR3(+) CD34(+) cells. Cells exposed to SU5416 showed positive protein expression of ID3, VEGFR3, CD34 and increased expression of pluripotent transcription factors Oct-4 and Sox-2. ID3 overexpressing cells supported the formation of a 3-D microvascular lesion co-cultured with smooth muscle cells. In addition, in vivo microvascular lesions from SuHx rodent model showed an increased expression of ID3, VEGFR3, and Pyk2 similar to SU5416 treated human endothelial cells. Further investigations into how normal and stem-like cells utilize ID3 may open up new avenues for a better understanding of the molecular mechanisms which are underlying the pathological development of microvascular diseases.

The indolinone MAZ51 induces cell rounding and G2/M cell cycle arrest in glioma cells without the inhibition of VEGFR-3 phosphorylation: involvement of the RhoA and Akt/GSK3β signaling pathways

MAZ51 is an indolinone-based molecule originally synthesized as a selective inhibitor of vascular endothelial growth factor receptor (VEGFR)-3 tyrosine kinase. This study shows that exposure of two glioma cell lines, rat C6 and human U251MG, to MAZ51 caused dramatic shape changes, including the retraction of cellular protrusions and cell rounding. These changes were caused by the clustering and aggregation of actin filaments and microtubules. MAZ51 also induced G2/M phase cell cycle arrest. This led to an inhibition of cellular proliferation, without triggering significant cell death. These alterations induced by MAZ51 occurred with similar dose- and time-dependent patterns. Treatment of glioma cells with MAZ51 resulted in increased levels of phosphorylated GSK3β through the activation of Akt, as well as increased levels of active RhoA. Interestingly, MAZ51 did not affect the morphology and cell cycle patterns of rat primary cortical astrocytes, suggesting it selectively targeted transformed cells. Immunoprecipitation–western blot analyses indicated that MAZ51 did not decrease, but rather increased, tyrosine phosphorylation of VEGFR-3. To confirm this unanticipated result, several additional experiments were conducted. Enhancing VEGFR-3 phosphorylation by treatment of glioma cells with VEGF-C affected neither cytoskeleton arrangements nor cell cycle patterns. In addition, the knockdown of VEGFR-3 in glioma cells did not cause morphological or cytoskeletal alterations. Furthermore, treatment of VEGFR-3-silenced cells with MAZ51 caused the same alterations of cell shape and cytoskeletal arrangements as that observed in control cells. These data indicate that MAZ51 causes cytoskeletal alterations and G2/M cell cycle arrest in glioma cells. These effects are mediated through phosphorylation of Akt/GSK3β and activation of RhoA. The anti-proliferative activity of MAZ51 does not require the inhibition of VEGFR-3 phosphorylation, suggesting that it is a potential candidate for further clinical investigation for treatment of gliomas, although the precise mechanism(s) underlying its effects remain to be determined.

Differences in vascular endothelial growth factor receptor expression and correlation with the degree of enhancement in medulloblastoma

OBJECT

Vascular endothelial growth factor (VEGF) is the major proangiogenic factor in many solid tumors. Vascular endothelial growth factor receptor (VEGFR) is expressed in abundance in pediatric patients with medulloblastoma and is associated with tumor metastasis, poor prognosis, and proliferation. Gadolinium enhancement on MRI has been suggested to have prognostic significance for some tumors. The association of VEGF/VEGFR and Gd enhancement in medulloblastoma has never been closely examined. The authors therefore sought to evaluate whether Gd-enhancing medulloblastomas have higher levels of VEGFR and CD31. Outcomes and survival in patients with enhancing and nonenhancing tumors were also compared.

METHODS

A retrospective analysis of patients with enhancing, nonenhancing, and partially enhancing medulloblastomas was performed. Primary end points included risk stratification, extent of resection, and perioperative complications. A cohort of 3 enhancing and 3 nonenhancing tumors was selected for VEGFR and CD31 analysis as well as microvessel density measurements.

RESULTS

Fifty-eight patients were analyzed, and 20.7% of the medulloblastomas in these patients were nonenhancing. Enhancing medulloblastomas exhibited strong VEGFR1/2 and CD31 expression relative to nonenhancing tumors. There was no significant difference in perioperative complications or patient survival between the 2 groups.

CONCLUSIONS

These results suggest that in patients with medulloblastoma the presence of enhancement on MRI may correlate with increased vascularity and angiogenesis, but does not correlate with worse patient prognosis in the short or long term.

Circulating proteins as potential biomarkers of sunitinib and interferon-α efficacy in treatment-naïve patients with metastatic renal cell carcinoma

PURPOSE

We investigated potential biomarkers of efficacy in a phase III trial of sunitinib versus interferon-alpha (IFN-α), first-line in metastatic renal cell carcinoma (mRCC), by analyzing plasma levels of vascular endothelial growth factor (VEGF)-A, VEGF-C, soluble VEGF receptor-3 (sVEGFR-3) and interleukin (IL)-8.

METHODS

Seven hundred and fifty mRCC patients were randomized to oral sunitinib 50 mg/day in repeated cycles of a 4-week on/2-week off schedule or IFN-α 9 million units subcutaneously thrice weekly. Plasma samples collected from a subset of 63 patients on days 1 and 28 of cycles 1-4 and at end of treatment were analyzed by ELISA.

RESULTS

Baseline characteristics of biomarker-evaluated patients in sunitinib (N = 33) and IFN-α (N = 30) arms were comparable to their respective intent-to-treat populations. By univariate Cox regression analysis, low baseline soluble protein levels were associated with lower risk of progression/death (all P < 0.05): in both treatment arms, baseline VEGF-A and IL-8 were associated with overall survival (OS) and baseline VEGF-C with progression-free survival (PFS); in the sunitinib arm, baseline VEGF-A was associated with PFS and baseline sVEGFR-3 with PFS and OS; in the IFN-α arm, baseline IL-8 was associated with PFS. In multivariate analysis, baseline sVEGFR-3 and IL-8 remained independent predictors of OS in the sunitinib arm, while no independent predictors of outcome remained in the IFN-α arm. Pharmacodynamic changes were not associated with PFS or OS for any plasma protein investigated.

CONCLUSIONS

Our findings suggest that, in mRCC, baseline VEGF-A and IL-8 may have prognostic value, while baseline sVEGFR-3 may predict sunitinib efficacy.

Collaborative overexpression of matrix metalloproteinase-1 and vascular endothelial growth factor-C predicts adverse prognosis in patients with gliomas

BACKGROUND AND AIM

Matrix metalloproteinase-1 (MMP-1), a member of the MMP family of zinc-dependent endopeptidases, has been detected to be strongly expressed in gliomas with high tumor grade and to be correlated with increased tumor invasiveness. Vascular endothelial growth factor-C (VEGF-C), which is able to induce MMP-1 transcription, has been found to be upregulated in glioblastoma compared to low grade gliomas and non-neoplastic brain. The aim of the present study was to investigate the clinical significance of the co-expression of MMP-1 and VEGF-C in glioma patients on determining the prognosis.

METHODS

One hundred and sixteen glioma patients (26 World Health Organization (WHO) grade I, 30 WHO grade II, 30 WHO grade III, and 30 WHO grade IV) and 15 non-neoplastic brain specimens acquired from 15 patients undergoing surgery for epilepsy as control were collected. Immunohistochemistry was used to evaluate the expression of MMP-1 and VEGF-C in glioma and non-neoplastic brain tissues. The correlations of collaborative MMP-1 and VEGF-C expression with selected clinicopathologic parameters and clinical outcome of glioma patients were also assessed.

RESULTS

Both MMP-1 and VEGF-C expression were significantly higher in glioma tissues compared to non-neoplastic brain tissues (both P<0.001). Of 116 glioma patients, 68 (58.62%) overexpressed MMP-1 and VEGF-C simultaneously. In addition, combined MMP-1 and VEGF-C expression was significantly associated with WHO grade (P<0.001) and Karnofsky performance status (KPS) score (P=0.01). Moreover, glioma patients expressing both MMP-1 and VEGF-C exhibited markedly poorer overall survival (P<0.001). According to the multivariate analyses, collaborative overexpression of MMP-1 and VEGF-C was found to be an independent prognostic factor for overall survival (P=0.009).

CONCLUSIONS

Our data demonstrated for the first time that overexpression of both MMP-1 and VEGF-C may be an independent poor prognostic factor in gliomas, suggesting the interaction between MMP-1 and VEGF-C collaboratively stimulated advanced tumor progression and adverse outcome. Inhibiting both MMP-1 and VEGF-C could be a novel therapeutic approach for gliomas.

Glioma stem cells and immunotherapy for the treatment of malignant gliomas

Stem cell research has led to the discovery of glioma stem cells (GSCs), and because these cells are resistant to chemotherapy and radiotherapy, analysis of their properties has been rapidly pursued for targeted treatment of malignant glioma. Recent studies have also revealed complex crosstalk between GSCs and their specialized environment (niche). Therefore, targeting not only GSCs but also their niche may be a principle for novel therapies of malignant glioma. One possible novel strategy for targeting GSCs and their niches is immunotherapy with different antitumor mechanism(s) from those of conventional therapy. Recent clinical studies of immunotherapy using peptide vaccines and antibodies have shown promising results. This review describes the recent findings related to GSCs and their niches, as well as immunotherapies for glioma, followed by discussion of immunotherapies that target GSCs for the treatment of malignant glioma.

Evaluation of 18F-labeled targeted perfluorocarbon-filled albumin microbubbles as a probe for microUS and microPET in tumor-bearing mice

OBJECTIVE

In this study, albumin-shelled, targeted MBs (tMBs) were first demonstrated with the expectation of visualization of biodistribution of albumin-shelled tMBs. The actual biodistribution of albumin-shelled tMBs is of vital importance either for molecular imaging or for drug delivery.

MOTIVATION

Recently, albumin microbubbles (MBs) have been studied for drug and gene delivery in vitro and in vivo through cavitation. Targeted lipid-shelled MBs have been applied for ultrasound molecular imaging and conjugated with radiolabeled antibodies for whole-body biodistribution evaluations. The novelty of the work is that, in addition to the lipid tMBs, the albumin tMBs was also applied in biodistribution detection.

METHODS

Multimodality albumin-shelled, (18)F-SFB-labeled VEGFR2 tMBs were synthesized, and their characteristics in mice bearing MDA-MB-231 human breast cancer were investigated with micro-positron-emission tomography (microPET) and high-frequency ultrasound (microUS).

RESULTS

Albumin-shelled MBs can be labeled with (18)F-SFB directly and conjugated with antibodies for dual molecular imaging. The albumin-shelled tMBs show a lifetime in 30min in the blood pool and a highly specific adherence to tumor vessels in mice bearing human breast cancer.

CONCLUSIONS

From the evaluations of whole-body biodistribution, the potential of the dual molecular imaging probe for drug or gene delivery in animal experiments with albumin shelled MBs has been investigated.

VEGF-C, VEGF-D and VEGFR-3 expression in peripheral neuroblastic tumours

AIMS

More than 50% of neuroblastomas (NBs) present with haematogenous and/or lymphatic metastasis; however, little is known about the clinicopathological significance in NBs of the key lymphangiogenesis growth factors vascular endothelial growth factor (VEGF)-C and VEGF-D and the receptor VEGFR-3.

METHODS AND RESULTS

Ninety-three NBs and nine ganglioneuromas (GNs) were immunostained for VEGF-C, VEGF-D and VEGFR-3. VEGF-C and VEGF-D were present in 76% and 82% of the NBs, respectively. There was no significant difference in VEGF-C expression between NBs and GNs. VEGF-D expression was significantly higher in NBs compared with GNs and in MYCN-amplified NBs. VEGFR-3 tumoral cell expression (VEGFR-3c), present in 48% of the NBs, was significantly higher in NBs from children ≥ 18 months at presentation and those belonging to a high-risk group. VEGFR-3 lymphovascular density was increased significantly in NBs compared with GNs and in NBs associated with adverse clinicopathological and biological factors. Lymphovascular invasion, assessed in VEGFR-3-stained vessels, was present in ∼50% of NBs. Cox regression analyses demonstrated that VEGFR-3c expression was associated with a significantly shorter event-free survival and that its effect was independent of the important pathological variable, mitosis-karyorrhexis index.

CONCLUSIONS

VEGF-D and VEGFR-3 up-regulation support tumour progression in NB and VEGFR-3c may provide a useful prognostic marker in NBs.

Phage displayed peptides/antibodies recognizing growth factors and their tyrosine kinase receptors as tools for anti-cancer therapeutics

The basic idea of displaying peptides on a phage, introduced by George P. Smith in 1985, was greatly developed and improved by McCafferty and colleagues at the MRC Laboratory of Molecular Biology and, later, by Barbas and colleagues at the Scripps Research Institute. Their approach was dedicated to building a system for the production of antibodies, similar to a naïve B cell repertoire, in order to by-pass the standard hybridoma technology that requires animal immunization. Both groups merged the phage display technology with an antibody library to obtain a huge number of phage variants, each of them carrying a specific antibody ready to bind its target molecule, allowing, later on, rare phage (one in a million) to be isolated by affinity chromatography. Here, we will briefly review the basis of the technology and the therapeutic application of phage-derived bioactive molecules when addressed against key players in tumor development and progression: growth factors and their tyrosine kinase receptors.

Vascular endothelial growth factor receptor 2 (VEGFR-2) signalling activity in paediatric pilocytic astrocytoma is restricted to tumour endothelial cells

AIMS

Tumours depend on angiogenesis for enhanced tumour cell survival and progression. Vascular endothelial growth factor receptor (VEGFR) signalling plays a major part in this process. Previously, we evaluated tyrosine kinase activity in paediatric brain tumour tissue lysates using a peptide microarray containing 144 different tyrosine kinase peptide substrates. When applied to paediatric pilocytic astrocytoma tissue, this analysis revealed extensive phosphorylation of VEGFR-derived peptides. The aim of the current study was to validate this result and determine the presence of VEGFR-2 activity in paediatric pilocytic astrocytoma as the main VEGFR in terms of mitogenic signalling. In addition, the localization of VEGFR1-3 mRNA expression was assessed.

METHODS

VEGFR-2 phosphorylation was determined by adopting a proximity ligation assay approach. Enrichment of endothelial markers and VEGFRs in tumour endothelium was determined by quantitative polymerase chain reaction (qPCR) analysis of laser-microdissected blood vessels.

RESULTS

Proximity ligation assays on tumour cryosections showed the presence of phosphorylation of VEGFR-2, which primarily localized to vascular endothelium. qPCR analysis of endothelial markers and VEGFRs showed a 13.6-fold average enrichment of VEGFR-2 expression in the laser-microdissected endothelium compared to whole tumour. Also the expression of VEGFR-1 and -3 was highly enriched in the endothelium fraction with an average fold-enrichment of 16.5 and 50.8 respectively.

CONCLUSIONS

Phosphorylated VEGFR-2 is detected on endothelial cells in paediatric pilocytic astrocytoma. Furthermore, endothelial cells are the main source of VEGFR1-3 mRNA expression. This suggests a crucial role for VEGF/VEGFR-induced angiogenesis in the progression and maintenance of these tumours.

Expression and cellular distribution of vascular endothelial growth factor-C system in cortical tubers of the tuberous sclerosis complex

Cortical tubers are malformations of cortical development in patients with tuberous sclerosis complex (TSC), and highly associated with pediatric intractable epilepsy. Recent evidence has shown that signaling mediated through vascular endothelial growth factor-C (VEGF-C) and its receptors, VEGFR-2 and VEGFR-3, has direct effects on both neurons and glial cells. To understand the potential role of VEGF-C system in the pathogenesis of cortical tubers, we investigated the expression patterns of VEGF-C signaling in cortical tubers compared with age-matched normal control cortex (CTX). We found that VEGF-C, VEGFR-2 and VEGFR-3 were clearly upregulated in tubers at both the mRNA and protein levels, compared with CTX. The in situ hybridization and immunostaining results demonstrated that VEGF-C, VEGFR-2 and VEGFR-3 were highly expressed in dysplastic neurons (DNs), giant cells (GCs) and reactive astrocytes within tubers. Most DNs/GCs expressing VEGF-C and its receptors co-labeled with neuronal rather than astrocytic markers, suggesting a neuronal lineage. In addition, protein levels of Akt-1, p-Bad and ERK1/2, the important downstream factors of the VEGF-C pathway, were significantly increased in cortical tubers, indicating involvement of VEGF-C-dependent prosurvival signaling in cortical tubers. Taken together, our results suggest a putative role for the VEGF-C signaling pathway in the pathogenesis of cortical tubers.

Mechanism-related circulating proteins as biomarkers for clinical outcome in patients with unresectable hepatocellular carcinoma receiving sunitinib

Background

Several proteins that promote angiogenesis are overexpressed in hepatocellular carcinoma (HCC) and have been implicated in disease pathogenesis. Sunitinib has antiangiogenic activity and is an oral multitargeted inhibitor of vascular endothelial growth factor receptors (VEGFRs)-1, -2, and -3, platelet-derived growth factor receptors (PDGFRs)-α and -β, stem-cell factor receptor (KIT), and other tyrosine kinases. In a phase II study of sunitinib in advanced HCC, we evaluated the plasma pharmacodynamics of five proteins related to the mechanism of action of sunitinib and explored potential correlations with clinical outcome.

Methods

Patients with advanced HCC received a starting dose of sunitinib 50 mg/day administered orally for 4 weeks on treatment, followed by 2 weeks off treatment. Plasma samples from 37 patients were obtained at baseline and during treatment and were analyzed for vascular endothelial growth factor (VEGF)-A, VEGF-C, soluble VEGFR-2 (sVEGFR-2), soluble VEGFR-3 (sVEGFR-3), and soluble KIT (sKIT).

Results

At the end of the first sunitinib treatment cycle, plasma VEGF-A levels were significantly increased relative to baseline, while levels of plasma VEGF-C, sVEGFR-2, sVEGFR-3, and sKIT were significantly decreased. Changes from baseline in VEGF-A, sVEGFR-2, and sVEGFR-3, but not VEGF-C or sKIT, were partially or completely reversed during the first 2-week off-treatment period. High levels of VEGF-C at baseline were significantly associated with Response Evaluation Criteria in Solid Tumors (RECIST)-defined disease control, prolonged time to tumor progression (TTP), and prolonged overall survival (OS). Baseline VEGF-C levels were an independent predictor of TTP by multivariate analysis. Changes from baseline in VEGF-A and sKIT at cycle 1 day 14 or cycle 2 day 28, and change in VEGF-C at the end of the first off-treatment period, were significantly associated with both TTP and OS, while change in sVEGFR-2 at cycle 1 day 28 was an independent predictor of OS.

Conclusions

Baseline plasma VEGF-C levels predicted disease control (based on RECIST) and were positively associated with both TTP and OS in this exploratory analysis, suggesting that this VEGF family member may have utility in predicting clinical outcome in patients with HCC who receive sunitinib.

Trial registration

ClinicalTrials.gov: NCT00247676

VEGFR-3/Flt-4 mediates proliferation and chemotaxis in glial precursor cells

Neuronal and vascular cells share common chemical signals. Vascular endothelial growth factor (VEGF)-C and -D and their receptor VEGFR-3/Flt-4 mediate lymphangiogenesis, but they occur also in the brain. Quantitative RT-PCR of mouse brain tissues and cultivated cells showed that the VEGFR-3 gene is highest transcribed in postnatal brain and in glial precursor cells whereas VEGF-C and -D are variably produced by different neuronal and glial cells. In neurospheres (neural stem cells) VEGFR-3 was induced by differentiation with platelet-derived growth factor (PDGF). In functional studies with an A2B5- and nestin-positive, O4-negative murine glial precursor cell line, VEGF-C and -D stimulated phosphorylation of the kinases Erk1/2; this signal transduction was inhibited by UO126. Both peptides induced the proliferation of glial precursor cells which could be inhibited by UO126. Furthermore, VEGF-D considerably enhanced their migration into an open space in a wound-healing assay. These results show that VEGF-C/-D together with its receptor VEGFR-3 provides an auto-/paracrine growth and chemotactic system for glial precursors in the developing brain.

Biology of angiogenesis and invasion in glioma

Treatment of adult brain tumors, in particular glioblastoma, remains a significant clinical challenge, despite modest advances in surgical technique, radiation, and chemotherapeutics. The formation of abnormal, dysfunctional tumor vasculature and glioma cell invasion along white matter tracts are believed to be major components of the inability to treat these tumors effectively. Recent insight into the fundamental processes governing glioma angiogenesis and invasion provide a renewed hope for development of novel strategies aimed at reducing the morbidity of this uniformly fatal disease. In this review, we discuss background biology of the blood brain barrier and its pertinence to blood vessel formation and tumor invasion. We will then focus our attention on the biology of glioma angiogenesis and invasion, and the key mediators of these processes. Last, we will briefly discuss recent and ongoing clinical trials targeting mediators of angiogenesis or invasion in glioma patients. The findings provide a renewed hope for those endeavoring to improve treatment of patients with glioma by providing a novel set of rational targets for translational drug discovery.

Angiogenesis as a therapeutic target in malignant gliomas

Currently, adult glioblastoma (GBM) patients have poor outcomes with conventional cytotoxic treatments. Because GBMs are highly angiogenic tumors, inhibitors that target tumor vasculature are considered promising therapeutic agents in these patients. Encouraging efficacy and tolerability in preliminary clinical trials suggest that targeting angiogenesis may be an effective therapeutic strategy in GBM patients. However, the survival benefits observed to date in uncontrolled trials of antiangiogenic agents have been modest, and several obstacles have limited their effectiveness. This article reviews the rationale for antiangiogenic agents in GBM, their potential mechanisms of action, and their clinical development in GBM patients. Although challenges remain with this approach, ongoing studies may improve upon the promising initial benefits already observed in GBM patients.

Genome-wide discovery of functional transcription factor binding sites by comparative genomics: the case of Stat3

The identification of direct targets of transcription factors is a key problem in the study of gene regulatory networks. However, the use of high throughput experimental methods, such as ChIP-chip and ChIP-sequencing, is limited by their high cost and strong dependence on cellular type and context. We developed a computational method for the genome-wide identification of functional transcription factor binding sites based on positional weight matrices, comparative genomics, and gene expression profiling. The method was applied to Stat3, a transcription factor playing crucial roles in inflammation, immunity and oncogenesis, and able to induce distinct subsets of target genes in different cell types or conditions. A newly generated positional weight matrix enabled us to assign affinity scores of high specificity, as measured by EMSA competition assays. Phylogenetic conservation with 7 vertebrate species was used to select the binding sites most likely to be functional. Validation was carried out on predicted sites within genes identified as differentially expressed in the presence or absence of Stat3 by microarray analysis. Twelve of the fourteen sites tested were bound by Stat3 in vivo, as assessed by Chromatin Immunoprecipitation, allowing us to identify 9 Stat3 transcriptional targets. Given its high validation rate, and the availability of large transcription factor-dependent gene expression datasets obtained under diverse experimental conditions, our approach appears to be a valid alternative to high-throughput experimental assays for the discovery of novel direct targets of transcription factors.

The angiopoietin 1/angiopoietin 2 balance as a prognostic marker in primary glioblastoma multiforme

OBJECT

In the present study, the authors analyzed the ANGPT1/ANGPT2 balance in the context of therapeutic outcome in 62 patients with primary glioblastomas multiforme (GBMs).

METHODS

The tumor tissue used was obtained in adult patients who underwent neurosurgical debulking. Microvessel density was assessed by morphometric analysis. Double immunostaining for Ki 67/CD34 and cleaved caspase-3/CD34 was used to investigate the proliferation and apoptotic fraction of both endothelial and tumor cells. The expression of VEGFs (A-D) was evaluated on immunohistochemistry. To measure tumor vascular stabilization, the ANGPT1/ANGPT2 mRNA balance was determined using real-time reverse transcriptase polymerase chain reaction.

RESULTS

Within the hypoxic perinecrotic tumor area, the apoptotic fraction of endothelial cells was positively correlated with VEGFA expression (p < 0.001). Higher levels of VEGFA correlated with greater proliferation of endothelial cells in the intermediate tumor area (p = 0.031). Vascular endothelial growth factor D was significantly more highly expressed within the perinecrotic tumor area compared with the intermediate tumor area (p < 0.001). Multivariate analysis showed a significant association between the ANGPT1/ANGPT2 balance and the survival time of patients with GBMs (p = 0.035).

CONCLUSIONS

The results of the present study suggest that the ANGPT1/ANGPT2 balance has prognostic value in patients with primary GBMs. The authors' findings support the need for further studies of the feasibility of antiangiogenic therapy in primary GBMs, with a special focus on the normalization of tumor vasculature.

Angiogenesis in gliomas

Angiogenesis, the sprouting of new blood vessels from preexisting blood vessels, is a hallmark of glioma progression. Malignant gliomas are among the most lethal tumors with a very dismal prognosis, despite advances in standard therapy, including surgery, radiation, and chemotherapy. The median survival of patients with malignant gliomas has changed little in the last few years and is still measured in months. In an attempt to develop new therapeutic strategies and identify the molecular mechanism involved in glioma growth and progression, there has been extraordinary scientific interest in the past 2 decades in angiogenic responses associated with gliomas. This chapter focuses on the molecular mechanism of glioma angiogenesis and summarizes some of the therapeutic approaches based on antiangiogenesis.

New molecular targets in angiogenic vessels of glioblastoma tumours

Antiangiogenesis approaches have the potential to be particularly effective in the treatment of glioblastoma tumours. These tumours exhibit extremely high levels of neovascularisation, which may contribute to their extremely aggressive behaviour, not only by providing oxygenation and nutrition, but also by establishing a leaky vasculature that lacks a blood-brain barrier. This leaky vasculature enables migration of tumour cells, as well as the build up of fluid, which exacerbates tissue damage due to increased intracranial pressure. Here, we discuss the considerable progress that has been made in the identification of the pro- and antiangiogenic factors produced by glioblastoma tumours and the effects of these molecules in animal models of the disease. The safety and efficacy of some of these approaches have now been demonstrated in clinical trials. However, the ability of tumours to overcome these therapies and to re-establish angiogenesis requires further clinical research regarding potential multimodality therapies, as well as basic research into the regulation of angiogenesis by as yet unidentified factors. Optimisation of noninvasive procedures for monitoring of angiogenesis would greatly facilitate such research.

Presence of pluripotent CD133+ cells correlates with malignancy of gliomas

BACKGROUND

Presence of CD133(+) cancer stem cells has been demonstrated within glioblastoma multiforme (GBM), the most malignant phenotype of gliomas (WHO grade IV). Since GBM frequently develops from low grade gliomas (WHO grade II) we assessed a possible qualitative or quantitative correlation of CD133(+) cells and glioma grade to get new insights in gliomagenesis.

RESULTS

The amount of CD133(+) cells within the bulk tumor mass, analyzed by immunostaining and Western blotting, showed a clear quantitative correlation with glioma grade (WHO degrees II, III and IV). Most of CD133(+) cells were arranged in clusters frequently associated to tumor vessels. Protein analysis revealed high cellular coexpression of CD133 with Musashi-I but not CD34 indicating a neural, i.e. local origin of these cells. In vitro, no differences in stem cell properties concerning self-renewal and multi-lineage differentiation have been found for CD133(+) cells isolated from gliomas of different grades.

CONCLUSIONS

These findings indicate a solely quantitative correlation of glioma grade with the presence of neural CD133(+) cells within tumors supporting the concept of a CD133(+) stem cell dependent gliomagenesis.

Prognostic molecular markers with no impact on decision-making: the paradox of gliomas based on a prospective study

This study assessed the prognostic value of several markers involved in gliomagenesis, and compared it with that of other clinical and imaging markers already used. Four-hundred and sixteen adult patients with newly diagnosed glioma were included over a 3-year period and tumour suppressor genes, oncogenes, MGMT and hTERT expressions, losses of heterozygosity, as well as relevant clinical and imaging information were recorded. This prospective study was based on all adult gliomas. Analyses were performed on patient groups selected according to World Health Organization histoprognostic criteria and on the entire cohort. The endpoint was overall survival, estimated by the Kaplan–Meier method. Univariate analysis was followed by multivariate analysis according to a Cox model. p14^ARF, p16^INK4A and PTEN expressions, and 10p 10q23, 10q26 and 13q LOH for the entire cohort, hTERT expression for high-grade tumours, EGFR for glioblastomas, 10q26 LOH for grade III tumours and anaplastic oligodendrogliomas were found to be correlated with overall survival on univariate analysis and age and grade on multivariate analysis only. This study confirms the prognostic value of several markers. However, the scattering of the values explained by tumour heterogeneity prevents their use in individual decision-making.

Glioblastoma multiforme: an emerging paradigm of anti-VEGF therapy

BACKGROUND

Adults with malignant glioma, especially the most common subtype, glioblastoma multiforme, have an unacceptably poor outcome with current therapies. Malignant gliomas are amongst the most angiogenic of cancers, and VEGF is the dominant angiogenic mediator in these tumors.

OBJECTIVE

To summarize the clinical experience of VEGF-directed treatment for malignant glioma.

METHODS

We reviewed the completed, ongoing and planned clinical trials evaluating anti-VEGF strategies for malignant glioma patients.

RESULTS/CONCLUSIONS

Recent studies incorporating anti-VEGF agents plus cytotoxic therapy among recurrent malignant glioma patients have achieved unprecedented improvements in radiographic response, time to progression and survival. Furthermore, acceptable toxicity was observed. Hence, a major current focus in neuro-oncology is to further develop antiangiogenic strategies for this desperate patient population.