Mediators of glioblastoma resistance and invasion during antivascular endothelial growth factor therapy.

PURPOSE: Vascular endothelial growth factor (VEGF) has been identified as a critical regulator of angiogenesis. Currently, several different strategies are being used to target the VEGF-VEGF receptor signal transduction pathway in glioblastoma. Although anti-VEGF therapy seems be effective in normalizing abnormal tumor vasculature, leading to an enhanced response to radiation and chemotherapy, tumors eventually become resistant to the therapy and adopt a highly infiltrative and invasive phenotype. EXPERIMENTAL DESIGN: In the present study, we evaluated the effects of anti-VEGF therapy (bevacizumab) on glioblastoma invasion both in vitro and in vivo and evaluated the angiogenesis- and invasion-related mediators of developed resistance to this therapy. RESULTS: We found that glioblastoma tumors escaped from antiangiogenic treatment by (a) reactivating angiogenesis through up-regulation of other proangiogenic factors and (b) invading normal brain areas, which was seen in association with up-regulation of matrix metalloproteinase (MMP)-2, MMP-9, and MMP-12; secreted protein, acidic, cysteine-rich; and tissue inhibitor of metalloproteinase 1. In addition to the paracrine effects of VEGF on endothelial cells, autocrine VEGF signaling seemed to regulate glioblastoma invasion because anti-VEGF therapy increased tumor invasiveness in vitro. CONCLUSIONS: Collectively, these findings reinforce the importance of VEGF in regulating tumor invasion and identify potential mediators of resistance to targeted VEGF therapy. These results will be important for developing novel combination therapies to overcome this resistance phenotype.

Differential expression of 12 histone deacetylase (HDAC) genes in astrocytomas and normal brain tissue: class II and IV are hypoexpressed in glioblastomas.

BACKGROUND: Glioblastoma is the most lethal primary malignant brain tumor. Although considerable progress has been made in the treatment of this aggressive tumor, the clinical outcome for patients remains poor. Histone deacetylases (HDACs) are recognized as promising targets for cancer treatment. In the past several years, HDAC inhibitors (HDACis) have been used as radiosensitizers in glioblastoma treatment. However, no study has demonstrated the status of global HDAC expression in gliomas and its possible correlation to the use of HDACis. The purpose of this study was to evaluate and compare mRNA and protein levels of class I, II and IV of HDACs in low grade and high grade astrocytomas and normal brain tissue and to correlate the findings with the malignancy in astrocytomas. METHODS: Forty-three microdissected patient tumor samples were evaluated. The histopathologic diagnoses were 20 low-grade gliomas (13 grade I and 7 grade II) and 23 high-grade gliomas (5 grade III and 18 glioblastomas). Eleven normal cerebral tissue samples were also analyzed (54 total samples analyzed). mRNA expression of class I, II, and IV HDACs was studied by quantitative real-time polymerase chain reaction and normalized to the housekeeping gene beta-glucuronidase. Protein levels were evaluated by western blotting. RESULTS: We found that mRNA levels of class II and IV HDACs were downregulated in glioblastomas compared to low-grade astrocytomas and normal brain tissue (7 in 8 genes, p < 0.05). The protein levels of class II HDAC9 were also lower in high-grade astrocytomas than in low-grade astrocytomas and normal brain tissue. Additionally, we found that histone H3 (but not histone H4) was more acetylated in glioblastomas than normal brain tissue. CONCLUSION: Our study establishes a negative correlation between HDAC gene expression and the glioma grade suggesting that class II and IV HDACs might play an important role in glioma malignancy. Evaluation of histone acetylation levels showed that histone H3 is more acetylated in glioblastomas than normal brain tissue confirming the downregulation of HDAC mRNA in glioblastomas.

Gene expression profile analysis of primary glioblastomas and non-neoplastic brain tissue: identification of potential target genes by oligonucleotide microarray and real-time quantitative PCR.

The prognosis of glioblastomas is still extremely poor and the discovery of novel molecular therapeutic targets can be important to optimize treatment strategies. Gene expression analyses comparing normal and neoplastic tissues have been used to identify genes associated with tumorigenesis and potential therapeutic targets. We have used this approach to identify differentially expressed genes between primary glioblastomas and non-neoplastic brain tissues. We selected 20 overexpressed genes related to cell cycle, cellular movement and growth, proliferation and cell-to-cell signaling and analyzed their expression levels by real time quantitative PCR in cDNA obtained from microdissected fresh tumor tissue from 20 patients with primary glioblastomas and from 10 samples of non-neoplastic white matter tissue. The gene expression levels were significantly higher in glioblastomas than in non-neoplastic white matter in 18 out of 20 genes analyzed: P < 0.00001 for CDKN2C, CKS2, EEF1A1, EMP3, PDPN, BNIP2, CA12, CD34, CDC42EP4, PPIE, SNAI2, GDF15 and MMP23b; and NFIA (P: 0.0001), GPS1 (P: 0.0003), LAMA1 (P: 0.002), STIM1 (P: 0.006), and TASP1 (P: 0.01). Five of these genes are located in contiguous loci at 1p31-36 and 2 at 17q24-25 and 8 of them encode surface membrane proteins. PDPN and CD34 protein expression were evaluated by immunohistochemistry and they showed concordance with the PCR results. The present results indicate the presence of 18 overexpressed genes in human primary glioblastomas that may play a significant role in the pathogenesis of these tumors and that deserve further functional investigation as attractive candidates for new therapeutic targets.