Radiation sensitization of glioblastoma by cilengitide has unanticipated schedule-dependency.

We investigated whether cilengitide could amplify the antitumor effects of radiotherapy in an orthotopic rat glioma xenograft model. Cilengitide is a specific inhibitor of alphav series integrins, and acts as an antiangiogenic. U251 human glioma cells express alphavbeta3 and alphavbeta5 integrins. We used in vitro assays of adhesion and growth of tumor and endothelial cells to evaluate cytotoxicity and the potential for cilengitide to enhance radiation toxicity. Treatment was then evaluated in an orthotopic model to evaluate synergy with therapeutic radiation in vivo. In vitro, cilengitide blocked cell adhesion, but did not influence the effects of radiation on U251 cells; cilengitide strongly amplified radiation effects on endothelial cell survival. In vivo, radiotherapy prolonged the survival of U251 tumor-bearing rats from 50 to over 110 days. Cotreatment with cilengitide and radiation dramatically amplified the effects of radiation, producing survival over 200 days and triggering an enhanced apoptotic response and suppression of tumor growth by histology at necropsy. Signaling pathways activated in the tumor included NFkappab, a documented mediator of cellular response to radiation. Because cilengitide has a short plasma half-life (t((1/2)) approximately 20 min), antiangiogenic scheduling typically uses daily injections. We found that a single dose of cilengitide (4 mg/kg) given between 4 and 12 hr prior to radiation was sufficient to produce the same effect. Our results demonstrate that blockade of alphav integrins mediates an unanticipated rapid potentiation of radiation, and suggests possible clinical translation for glioma therapy.

Glioma cells on the run - the migratory transcriptome of 10 human glioma cell lines.

BACKGROUND: Glioblastoma multiforme (GBM) is the most common primary intracranial tumor and despite recent advances in treatment regimens, prognosis for affected patients remains poor. Active cell migration and invasion of GBM cells ultimately lead to ubiquitous tumor recurrence and patient death. To further understand the genetic mechanisms underlying the ability of glioma cells to migrate, we compared the matched transcriptional profiles of migratory and stationary populations of human glioma cells. Using a monolayer radial migration assay, motile and stationary cell populations from seven human long term glioma cell lines and three primary GBM cultures were isolated and prepared for expression analysis. RESULTS: Gene expression signatures of stationary and migratory populations across all cell lines were identified using a pattern recognition approach that integrates a priori knowledge with expression data. Principal component analysis (PCA) revealed two discriminating patterns between migrating and stationary glioma cells: i) global down-regulation and ii) global up-regulation profiles that were used in a proband-based rule function implemented in GABRIEL to find subsets of genes having similar expression patterns. Genes with up-regulation pattern in migrating glioma cells were found to be overexpressed in 75% of human GBM biopsy specimens compared to normal brain. A 22 gene signature capable of classifying glioma cultures based on their migration rate was developed. Fidelity of this discovery algorithm was assessed by validation of the invasion candidate gene, connective tissue growth factor (CTGF). siRNA mediated knockdown yielded reduced in vitro migration and ex vivo invasion; immunohistochemistry on glioma invasion tissue microarray confirmed up-regulation of CTGF in invasive glioma cells. CONCLUSION: Gene expression profiling of migratory glioma cells induced to disperse in vitro affords discovery of genomic signatures; selected candidates were validated clinically at the transcriptional and translational levels as well as through functional assays thereby underscoring the fidelity of the discovery algorithm.

MAP-ing glioma invasion: mitogen-activated protein kinase kinase 3 and p38 drive glioma invasion and progression and predict patient survival.

Although astrocytic brain tumors do not metastasize systemically, during tumorigenesis glioma cells adopt an invasive phenotype that is poorly targeted by conventional therapies; hence, glioma patients die of recurrence from the locally invasive tumor population. Our work is aimed at identifying and validating novel therapeutic targets and biomarkers in invasive human gliomas. Transcriptomes of invasive glioma cells relative to stationary cognates were produced from a three-dimensional spheroid in vitro invasion assay by laser capture microdissection and whole human genome expression microarrays. Qualitative differential expression of candidate invasion genes was confirmed by quantitative reverse transcription-PCR, clinically by immunohistochemistry on tissue microarray, by immunoblotting on surgical specimens, and on two independent gene expression data sets of glial tumors. Cell-based assays and ex vivo brain slice invasion studies were used for functional validation. We identify mitogen-activated protein kinase (MAPK) kinase 3 (MKK3) as a key activator of p38 MAPK in glioma; MKK3 activation is strongly correlated with p38 activation in vitro and in vivo. We further report that these members of the MAPK family are strong promoters of tumor invasion, progression, and poor patient survival. Inhibition of either candidate leads to significantly reduced glioma invasiveness in vitro. Consistent with the concept of synthetic lethality, we show that inhibition of invasion by interference with these genes greatly sensitizes arrested glioma cells to cytotoxic therapies. Our findings therefore argue that interference with MKK3 signaling through a novel treatment combination of p38 inhibitor plus temozolomide heightens the vulnerability of glioma to chemotherapy.

Increased fibroblast growth factor-inducible 14 expression levels promote glioma cell invasion via Rac1 and nuclear factor-kappaB and correlate with poor patient outcome.

Glial tumors progress to malignant grades by heightened proliferation and relentless dispersion throughout the central nervous system. Understanding genetic and biochemical processes that foster these behaviors is likely to reveal specific and effective targets for therapeutic intervention. Our current report shows that the fibroblast growth factor-inducible 14 (Fn14), a member of the tumor necrosis factor (TNF) receptor superfamily, is expressed at high levels in migrating glioma cells in vitro and invading glioma cells in vivo. Forced Fn14 overexpression stimulates glioma cell migration and invasion, and depletion of Rac1 by small interfering RNA inhibits this cellular response. Activation of Fn14 signaling by the ligand TNF-like weak inducer of apoptosis (TWEAK) stimulates migration and up-regulates expression of Fn14; this TWEAK effect requires Rac1 and nuclear factor-kappaB (NF-kappaB) activity. The Fn14 promoter region contains NF-kappaB binding sites, which mediate positive feedback causing sustained overexpression of Fn14 and enduring glioma cell invasion. Furthermore, Fn14 gene expression levels increase with glioma grade and inversely correlate with patient survival. These results show that the Fn14 cascade operates as a positive feedback mechanism for elevated and sustained Fn14 expression. Such a feedback loop argues for aggressive targeting of the Fn14 axis as a unique and specific driver of glioma malignant behavior.