Tobias Martens

A Novel One-Armed Anti-c-Met Antibody Inhibits Glioblastoma Growth In vivo

Purpose: Expression of the receptor tyrosine kinase c-Met and its ligand scatter factor/hepatocyte growth factor (SF/HGF) are strongly increased in glioblastomas, where they promote tumor proliferation, migration, invasion, and angiogenesis. We used a novel one-armed anti-c-Met antibody to inhibit glioblastoma growth in vivo. Experimental Design: U87 glioblastoma cells (c-Met and SF/HGF positive) or G55 glioblastoma cells (c-Met positive and SF/HGF negative) were used to generate intracranial orthotopic xenografts in nude mice. The one-armed 5D5 (OA-5D5) anti-c-Met antibody was infused intratumorally using osmotic minipumps. Following treatment, tumor volumes were measured and tumors were analyzed histologically for extracellular matrix (ECM) components and proteases relevant to tumor invasion. Microarray analyses were done to determine the effect of the antibody on invasion-related genes. Results: U87 tumor growth, strongly driven by SF/HGF, was inhibited >95% with OA-5D5 treatment. In contrast, G55 tumors, which are not SF/HGF driven, did not respond to OA-5D5, suggesting that the antibody can have efficacy in SF/HGF-activated tumors. In OA-5D5-treated U87 tumors, cell proliferation was reduced >75%, microvessel density was reduced >90%, and apoptosis was increased >60%. Furthermore, OA-5D5 treatment decreased tumor cell density >2-fold, with a consequent increase in ECM deposition and increased immunoreactivity for laminin, fibronectin, and tenascin. Microarray studies showed no incresae in these ECM factors, rather down-regulation of urokinase-type plasminogen activator and matrix metalloproteinase 16 in glioblastoma cells treated with OA-5D5. Conclusions: Local treatment with OA-5D5 can almost completely inhibit intracerebral glioblastoma growth when SF/HGF is driving tumor growth. The mechanisms of tumor inhibition include antiproliferative, antiangiogenic, and proapoptotic effects.

Molecular classification of diffuse cerebral WHO grade II/III gliomas using genome- and transcriptome-wide profiling improves stratification of prognostically distinct patient groups

Abstract Cerebral gliomas of World Health Organization (WHO) grade II and III represent a major challenge in terms of histological classification and clinical management. Here, we asked whether large-scale genomic and transcriptomic profiling improves the definition of prognostically distinct entities. We performed microarray-based genome- and transcriptome-wide analyses of primary tumor samples from a prospective German Glioma Network cohort of 137 patients with cerebral gliomas, including 61 WHO grade II and 76 WHO grade III tumors. Integrative bioinformatic analyses were employed to define molecular subgroups, which were then related to histology, molecular biomarkers, including isocitrate dehydrogenase 1 or 2 (IDH1/2) mutation, 1p/19q co-deletion and telomerase reverse transcriptase (TERT) promoter mutations, and patient outcome. Genomic profiling identified five distinct glioma groups, including three IDH1/2 mutant and two IDH1/2 wild-type groups. Expression profiling revealed evidence for eight transcriptionally different groups (five IDH1/2 mutant, three IDH1/2 wild type), which were only partially linked to the genomic groups. Correlation of DNA-based molecular stratification with clinical outcome allowed to define three major prognostic groups with characteristic genomic aberrations. The best prognosis was found in patients with IDH1/2 mutant and 1p/19q co-deleted tumors. Patients with IDH1/2 wild-type gliomas and glioblastoma-like genomic alterations, including gain on chromosome arm 7q (+7q), loss on chromosome arm 10q (−10q), TERT promoter mutation and oncogene amplification, displayed the worst outcome. Intermediate survival was seen in patients with IDH1/2 mutant, but 1p/19q intact, mostly astrocytic gliomas, and in patients with IDH1/2 wild-type gliomas lacking the +7q/−10q genotype and TERT promoter mutation. This molecular subgrouping stratified patients into prognostically distinct groups better than histological classification. Addition of gene expression data to this genomic classifier did not further improve prognostic stratification. In summary, DNA-based molecular profiling of WHO grade II and III gliomas distinguishes biologically distinct tumor groups and provides prognostically relevant information beyond histological classification as well as IDH1/2 mutation and 1p/19q co-deletion status.

A distinct subset of glioma cell lines with stem cell-like properties reflects the transcriptional phenotype of glioblastomas and overexpresses CXCR4 as therapeutic target

Glioblastomas contain stem‐like cells that can be maintained in vitro using specific serum‐free conditions. We investigated whether glioblastoma stem‐like (GS) cell lines preserve the expression phenotype of human glioblastomas more closely than conventional glioma cell lines. Expression profiling revealed that a distinct subset of GS lines, which displayed a full stem‐like phenotype (GSf), mirrored the expression signature of glioblastomas more closely than either other GS lines or cell lines grown in serum. GSf lines are highly tumorigenic and invasive in vivo, express CD133, grow spherically in vitro, are multipotent and display a Proneural gene expression signature, thus recapitulating key functional and transcriptional aspects of human glioblastomas. In contrast, GS lines with a restricted stem‐like phenotype exhibited expression signatures more similar to conventional cell lines than to original patient tumors, suggesting that the transcriptional resemblance between GS lines and tumors is associated with different degrees of “stemness”. Among markers overexpressed in patient tumors and GSf lines, we identified CXCR4 as a potential therapeutic target. GSf lines contained a minor population of CXCR4hi cells, a subfraction of which coexpressed CD133 and was expandable by hypoxia, whereas conventional cell lines contained only CXCR4lo cells. Convection‐enhanced local treatment with AMD3100, a specific CXCR4 antagonist, inhibited the highly invasive growth of GS xenografts in vivo and cell migration in vitro. We thus demonstrate the utility of GSf lines in testing therapeutic agents and validate CXCR4 as a target to block the growth of invasive tumor‐initiating glioma stem cells in vivo.

Inhibition of glioblastoma growth in a highly invasive nude mouse model can be achieved by targeting epidermal growth factor receptor but not vascular endothelial growth factor receptor-2.

Purpose: Major shortcomings of traditional mouse models based on xenografted human glioblastoma cell lines are that tumor cells do not invade and that genetic alterations, such as amplification of the epidermal growth factor receptor (EGFR) gene, are not maintained. Such models are thus of limited value for preclinical studies. We established a highly invasive model to evaluate the effect of antibodies against EGFR (cetuximab) and vascular endothelial growth factor receptor-2 (antibody DC101). Experimental Design: After short-term culture, glioblastoma spheroids were implanted into the brains of nude mice. Animals were treated either i.c. with cetuximab or i.p. with DC101. Tumor burden was determined histologically using image analysis of 36 different landmark points on serial brain sections. Results: Invasive xenografts were obtained from nine different glioblastomas. Three of seven cases treated with cetuximab responded with significant tumor growth inhibition, whereas four did not. All responsive tumors were derived from glioblastomas exhibiting EGFR amplification and expression of the truncated EGFRvIII variant, which were maintained in the xenografts. All nonresponsive tumors lacked EGFR amplification and EGFRvIII expression. The proportion of apoptotic cells was increased, whereas proliferation and invasion were decreased in responsive tumors. None of four xenograft cases treated with DC101 responded to treatment, and the diffusely invading tumors grew independent of angiogenesis. Conclusions: Inhibition of glioblastoma growth and invasion can be achieved using i.c. delivery of an anti-EGFR antibody, but tumor response depends on the presence of amplified and/or mutated EGFR. Antiangiogenic treatment with DC101 is not effective against diffusely invading tumors.

Glioblastoma Stem–like Cell Lines with Either Maintenance or Loss of High-Level EGFR Amplification, Generated via Modulation of Ligand Concentration

Purpose: Despite the high incidence of epidermal growth factor receptor (EGFR) gene amplification and rearrangement in glioblastomas, no suitable cell line exists that preserves these alterations in vitro and is tumorigenic in immunocompromised mice. On the basis of previous observations that glioblastoma cells cultured with serum lose the EGFR amplification rapidly and that EGF can inhibit the growth of EGFR-amplified tumor cells, we hypothesized that serum-free and EGF-free culture conditions could promote maintenance of the EGFR amplification. Experimental Design: Cells from EGFR-amplified glioblastomas were taken into culture using neural stem cell conditions with modifications, including varying oxygen concentrations and omission of routine EGF supplementation. Results: High-level EGFR amplification was rapidly lost in 5 glioblastoma cultures supplemented with EGF, whereas it was preserved in cultures from the same tumors established without EGF. Cultures from 2 glioblastomas developed into pairs of cell lines, with either stable maintenance or irreversible loss of high-level EGFR amplification in the majority of cells. One EGFR-amplified cell line preserved expression of the receptor variant EGFRvIII. Cell lines with high-level EGFR amplification/EGFRvIII expression formed highly aggressive tumors in nude mice, whereas nonamplified cell lines were either nontumorigenic or grew significantly more slowly. In contrast, nonamplified cell lines proliferated faster in vitro. All cell lines responded to erlotinib, with inhibition of receptor activation and proliferation but partly different effects on downstream signaling and migration. Conclusions: Isogenic glioblastoma cell lines maintaining stable differences in EGFR/EGFRvIII status can be derived by varying exposure to EGF ligand and reflect the intratumoral genetic heterogeneity. Clin Cancer Res; 18(7); 1901–13. ©2012 AACR.

A Phase II, Randomized, Study of Weekly APG101+Reirradiation versus Reirradiation in Progressive Glioblastoma

Purpose: Preclinical data indicate anti-invasive activity of APG101, a CD95 ligand (CD95L)–binding fusion protein, in glioblastoma. Experimental Design: Patients (N = 91) with glioblastoma at first or second progression were randomized 1:2 between second radiotherapy (rRT; 36 Gy; five times 2 Gy per week) or rRT+APG101 (400 mg weekly i.v.). Patient characteristics [N = 84 (26 patients rRT, 58 patients rRT+APG101)] were balanced. Results: Progression-free survival at 6 months (PFS-6) rates were 3.8% [95% confidence interval (CI), 0.1–19.6] for rRT and 20.7% (95% CI, 11.2–33.4) for rRT+APG101 (P = 0.048). Median PFS was 2.5 (95% CI, 2.3–3.8) months and 4.5 (95% CI, 3.7–5.4) months with a hazard ratio (HR) of 0.49 (95% CI, 0.27–0.88; P = 0.0162) adjusted for tumor size. Cox regression analysis adjusted for tumor size revealed a HR of 0.60 (95% CI, 0.36–1.01; P = 0.0559) for rRT+APG101 for death of any cause. Lower methylation levels at CpG2 in the CD95L promoter in the tumor conferred a stronger risk reduction (HR, 0.19; 95% CI, 0.06–0.58) for treatment with APG101, suggesting a potential biomarker. Conclusions: CD95 pathway inhibition in combination with rRT is an innovative concept with clinical efficacy. It warrants further clinical development. CD95L promoter methylation in the tumor may be developed as a biomarker. Clin Cancer Res; 20(24); 6304–13. ©2014 AACR.

Hypoxia and oxygenation induce a metabolic switch between pentose phosphate pathway and glycolysis in glioma stem-like cells

Fluctuations in oxygen tension during tissue remodeling impose a major metabolic challenge in human tumors. Stem-like tumor cells in glioblastoma, the most common malignant brain tumor, possess extraordinary metabolic flexibility, enabling them to initiate growth even under non-permissive conditions. We identified a reciprocal metabolic switch between the pentose phosphate pathway (PPP) and glycolysis in glioblastoma stem-like (GS) cells. Expression of PPP enzymes is upregulated by acute oxygenation but downregulated by hypoxia, whereas glycolysis enzymes, particularly those of the preparatory phase, are regulated inversely. Glucose flux through the PPP is reduced under hypoxia in favor of flux through glycolysis. PPP enzyme expression is elevated in human glioblastomas compared to normal brain, especially in highly proliferative tumor regions, whereas expression of parallel preparatory phase glycolysis enzymes is reduced in glioblastomas, except for strong upregulation in severely hypoxic regions. Hypoxia stimulates GS cell migration but reduces proliferation, whereas oxygenation has opposite effects, linking the metabolic switch to the “go or grow” potential of the cells. Our findings extend Warburg’s observation that tumor cells predominantly utilize glycolysis for energy production, by suggesting that PPP activity is elevated in rapidly proliferating tumor cells but suppressed by acute severe hypoxic stress, favoring glycolysis and migration to protect cells against hypoxic cell damage.

RON receptor tyrosine kinase in human gliomas: expression, function, and identification of a novel soluble splice variant

Malignant gliomas are incurable because of their diffuse infiltration of the surrounding brain. The recepteur d’origine nantais (RON) receptor tyrosine kinase is highly expressed in several epithelial cancer types and mediates tumorigenic, pro‐invasive as well as metastatic effects. Analyzing RON expression in human gliomas, we found that different splice variants with known oncogenic activity are expressed in glioblastomas (GBM). In addition, the RON ligand macrophage‐stimulating protein (MSP) is secreted by cultured GBM cells. MSP showed no mitogenic effect on GBM cells but displayed significant chemotactic activity for several GBM cell lines. We identified a novel splice variant, RONΔ90, which is generated by a transcript missing exon 6. As a result of a frameshift, translation is terminated in exon 7, resulting in a truncated soluble protein. RONΔ90 transcripts are expressed in normal human brain as well as in low grade astrocytomas but only in approximately 50% of highly malignant astrocytomas. In addition, RONΔ90 is detectable in supernatants of GBM cell lines. We cloned the RONΔ90 cDNA, and purified the recombinant protein from transfected cells. RONΔ90 inhibited MSP‐induced phosphorylation of cellular RON and also attenuated basal activation levels. In addition, RONΔ90 inhibited MSP‐induced glioma cell migration as well as random motility. To conclude, RONΔ90 is a novel soluble receptor variant with antagonistic activity that may act as a physiological modulator of RON signaling. The expression of several oncogenic RON splice variants in malignant gliomas suggests that these could represent candidate targets for treatment with agents inhibiting RON activity.

Vascular events after transsylvian selective amygdalohippocampectomy and impact on epilepsy outcome

Epilepsy surgery is a standard treatment option for medically intractable temporal lobe epilepsy. Selective amygdalohippocampectomy (SAH) and anterior temporal lobectomy (ATL) are two of the standard surgical procedures in these cases. We conducted a retrospective analysis of patients treated with SAH via a modified transsylvian approach in our epilepsy center between 2008 and 2011, and we analyzed the impact of adjacent procedure‐related infarctions on seizure outcome in these patients.

Inhibition of intracerebral glioblastoma growth by targeting the insulin-like growth factor 1 receptor involves different context-dependent mechanisms

BACKGROUND Signaling by insulin-like growth factor 1 receptor (IGF-1R) can contribute to the formation and progression of many diverse tumor types, including glioblastoma. We investigated the effect of the IGF-1R blocking antibody IMC-A12 on glioblastoma growth in different in vivo models. METHODS U87 cells were chosen to establish rapidly growing, angiogenesis-dependent tumors in the brains of nude mice, and the GS-12 cell line was used to generate highly invasive tumors. IMC-A12 was administered using convection-enhanced local delivery. Tumor parameters were quantified histologically, and the functional relevance of IGF-1R activation was analyzed in vitro. RESULTS IMC-A12 treatment inhibited the growth of U87 and GS-12 tumors by 75% and 50%, respectively. In GS-12 tumors, the invasive tumor extension and proliferation rate were significantly reduced by IMC-A12 treatment, while apoptosis was increased. In IMC-A12-treated U87 tumors, intratumoral vascularization was markedly decreased, and tumor cell proliferation was moderately reduced. Flow cytometry showed that <2% of U87 cells but >85% of GS-12 cells expressed IGF-1R. Activation of IGF-1R by IGF-1 and IGF-2 in GS-12 cells was blocked by IMC-A12. Both ligands stimulated GS-12 cell proliferation, and IGF-2 also stimulated migration. IMC-A12 inhibited these stimulatory effects and increased apoptosis. In U87 cells, stimulation with either ligand had no functional effect. CONCLUSIONS IGF-1R blockade can inhibit glioblastoma growth by different mechanisms, including direct effects on the tumor cells as well as indirect anti-angiogenic effects. Hence, blocking IGF-1R may be useful to target both the highly proliferative, angiogenesis-dependent glioblastoma core component as well as the infiltrative periphery.