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Glioblastoma is the most common primary malignant brain tumor in adults with an overall survival of only 14.6 months. Hypoxia is known to play a role in tumor aggressiveness but the influence of hypoxia on the immune microenvironment is not fully understood. The aim of this study was to investigate the expression of immune-related proteins in normoxic and hypoxic tumor areas by digital spatial profiling. Tissue samples from 10 glioblastomas were stained with a panel of 40 antibodies conjugated to photo-cleavable oligonucleotides. The free oligo-tags from normoxic and hypoxic areas were hybridized to barcodes for digital counting. Differential expression patterns were validated by Ivy Glioblastoma Atlas Project (GAP) data and an independent patient cohort. We found that CD44, Beta-catenin and B7-H3 were upregulated in hypoxia, whereas VISTA, CD56, KI-67, CD68 and CD11c were downregulated. PD-L1 and PD-1 were not affected by hypoxia. Focusing on the checkpoint-related markers CD44, B7-H3 and VISTA, our findings for CD44 and VISTA could be confirmed with Ivy GAP RNA sequencing data. Immunohistochemical staining and digital quantification of CD44, B7-H3 and VISTA in an independent cohort confirmed our findings for all three markers. Additional stainings revealed fewer T cells and high but equal amounts of tumor-associated microglia and macrophages in both hypoxic and normoxic regions. In conclusion, we found that CD44 and B7-H3 were upregulated in areas with hypoxia whereas VISTA was downregulated together with the presence of fewer T cells. This heterogeneous expression should be taken into consideration when developing novel therapeutic strategies.

Glioblastomas (GBM) are highly infiltrative tumors and despite intensive treatment tumor recurrence is inevitable. The immune microenvironment in recurrent GBM is poorly characterized, but it is potentially influenced by therapeutic interventions with surgery, radiotherapy, and chemotherapy. The aim of this study was to obtain a deeper insight in the immune microenvironment in primary and recurrent GBM. Primary and recurrent glioblastoma samples from 18 patients were identified and expression profiling of 770 myeloid innate immune-related markers was performed. Leukemia inhibitory factor and pentraxin 3 were expressed at lower levels in recurrent tumors. Using in silico data and immunohistochemical staining, this was validated for pentraxin 3. Both high leukemia inhibitory factor and pentraxin 3 expression appeared to be associated with shorter survival in primary and recurrent GBM using in silico data. In primary GBM, gene set analysis also showed higher expression of genes involved in metabolism, extracellular matrix remodeling and complement activation, whereas genes involved in T cell activation and checkpoint signaling were expressed at higher levels in recurrent GBM. The reduced level of pentraxin 3 in recurrent glioblastomas and the gene set analysis results suggest an altered microenvironment in recurrent GBM that might be more active.

The tyrosine kinase receptor c-Met has been suggested to be involved in crucial parts of glioma biology like tumor stemness, growth and invasion. The aim of this study was to investigate the prognostic value of c-Met in a population-based glioma patient cohort. Tissue samples from 238 patients with WHO grade I, II, III and IV tumors were analyzed using immunohistochemical staining and advanced image analysis. Strong c-Met expression was found in tumor cells, blood vessels, and peri-necrotic areas. At the subcellular level, c-Met was identified in the cytoplasm and in the cell membrane. Measurements of high c-Met intensity correlated with high WHO grade (p = 0.006) but no association with survival was observed in patients with WHO grade II (p = 0.09) or III (p = 0.17) tumors. High expression of c-Met was associated with shorter overall survival in patients with glioblastoma multiforme (p = 0.03). However the prognostic effect of c-Met in glioblastomas was time-dependent and only observed in patients who survived more than 8.5 months, and not within the first 8.5 months after diagnosis. This was significant in multivariate analysis (HR 1.99, 95 % CI 1.29-3.08, p = 0.002) adjusted for treatment and the clinical variables age (HR 1.01, 95 % CI 0.99-1.03, p = 0.30), performance status (HR 1.34, 95 % CI 1.17-1.53, p < 0.001), and tumor crossing midline (HR 1.28, 95 % CI 0.79-2.07, p = 0.29). In conclusion, this study showed that high levels of c-Met holds unfavorable prognostic value in glioblastomas.

SUMMARY The therapeutic paradigm of gliomas is changing from a general approach towards an individualized and targeted approach. Accordingly, the search for prognostic and predictive biomarkers, as well as the demand for quantitative, feasible and robust methods for biomarker analysis increases. We find that software classifiers can identify and quantify the expression of a given biomarker within different subcellular compartments and that such classifiers can exclude frequently occurring nontumor cells, thereby avoiding potential bias. The use of a quantitative approach provides a continuous measurement of the expression, allowing establishment of new cut-points and identification of patients with specific prognoses. However, some pitfalls must be noted. This article focuses on benefits and pitfalls of novel approaches for quantifying protein biomarkers in gliomas.

Gliomas are highly infiltrative tumors incurable with surgery. Although surgery removes the bulk tumor, tumor cells in the periphery are left behind resulting in tumor relapses. The aim of the present study was to characterize the phenotype of tumor cells in the periphery focusing on tumor stemness, proliferation and chemo-resistance. This was investigated in situ in patient glioma tissue as well as in orthotopic glioblastoma xenografts. We identified 26 gliomas having the R132 mutation in Isocitrate DeHydrogenase 1 (mIDH1). A double immunofluorescence approach identifying mIDH1 positive tumor cells and a panel of markers was used. The panel comprised of six stem cell-related markers (CD133, Musashi-1, Bmi-1, Sox-2, Nestin and Glut-3), a proliferation marker (Ki-67) as well as a chemo-resistance marker (MGMT). Computer-based automated classifiers were designed to measure the mIDH1 positive nucleus area-fraction of the chosen markers. Moreover, orthotopic glioblastoma xenografts from five different patient-derived spheroid cultures were obtained and the tumor cells identified by human specific immunohistochemical markers. The results showed that tumor cells in the periphery of patient gliomas expressed stem cell markers, however for most markers at a significantly lower level than in the tumor core. The Ki-67 level was slightly reduced in the periphery, whereas the MGMT level was similar. In orthotopic glioblastoma xenografts all markers showed similar levels in the core and periphery. In conclusion tumor cells in the periphery of patient gliomas have a stem cell phenotype, although it is less pronounced than in the tumor core. Novel therapies aiming at preventing recurrence should therefore take tumor stemness into account. Migrating cells in orthotopic glioblastoma xenografts preserve expression and stem cell markers. The orthotopic model therefore has a promising translational potential.

Glioblastoma is the most frequent and malignant primary brain tumor. The standard treatment includes surgery, radiation and chemotherapy. The limited efficacy of the current treatment has been explained by the existence of treatment-resistant stem-like tumor cells. The aim of this study was to investigate the short-term effects of radiation of spheroids containing tumor-initiating stem-like cells. We used a patient-derived glioblastoma stem cell enriched culture (T76) and the standard glioblastoma cell line U87. Primary spheroids were irradiated with doses between 2 and 50 Gy and assessed after two and five days. We found a small reduction in primary spheroid size after radiation and an associated small increase in uptake of the cell death marker propidium iodide. Using immunohistochemistry, P53 expression was found to be significantly increased, whereas the Ki-67 proliferation index was significantly reduced. Both number and size of secondary spheroids formed after radiation were significantly reduced. In a limiting dilution assay, the spheroid formation capacity upon irradiation was higher for T76 compared to U87, but for both T76 and U87 irradiation led to a reduced spheroid formation capacity. Gene expression analysis of nine stem cell- and two hypoxia-related genes did not reveal any upregulation after radiation. In conclusion, this study suggests that a major short-term effect of radiation is pronounced reduction of tumor cell proliferation. We found no upregulation of stem cell-related genes. This may suggest a limited effect of targeting these genes within the first days after radiation therapy.

Gliomas are highly infiltrative tumors incurable with surgery. Although surgery removes the bulk tumor, tumor cells in the periphery are left behind resulting in tumor relapses. The aim of the present study was to characterize the phenotype of tumor cells in the periphery focusing on tumor stemness, proliferation and chemoresistance. This was investigated in situ in patient glioma tissue as well as in orthotopic glioblastoma xenografts. We identified 26 gliomas having the R132 mutation in Isocitrate DeHydrogenase 1 (mIDH1). A double immunofluorescence approach identifying mIDH1 positive tumor cells and a panel of markers was used. The panel comprised of five different stem cell markers (CD133, Musashi-1, Bmi-1, Sox-2 and Nestin), the proliferation marker Ki-67 as well as MGMT. Computer-based automated classifiers were designed to measure the mIDH1 positive nucleus area-fraction of the chosen markers. Moreover orthotopic glioblastoma xenografts from five different patient-derived spheroid cultures were obtained. A double immunofluorescence approach identifying vimentin positive tumor cells and the same panel of markers were used, except MGMT since most tumors were MGMT methylated. The results showed that tumor cells in the periphery of patient gliomas expressed stem cell markers, however at a significantly lower level than in the tumor core. The Ki-67 level was significantly reduced, whereas the reduction in the MGMT level did not reach significance. In orthotopic glioblastoma xenografts same results were obtained for Sox-2, Nestin and Ki-67, where as the other markers were expressed at the same level in core and periphery. In conclusion tumor cells in the periphery of patient gliomas displayed reduced but to a large degree preserved stemness and proliferation. Novel therapies aiming at preventing recurrence should therefore take tumor stemness into account. Orthotopic glioblastoma xenografts to a large degree mimic patient tumors and therefore have a promising translational potential.

2088 Background: C-met is a tyrosine kinase receptor involved in growth, invasiveness and malignant progression in glioblastoma multiforme (GBM). Activation of the C-met pathway increases resistance towards DNA damage in glioma cell lines and it has been shown that an orally administrated C-met kinase inhibitor inhibits intracranial glioma growth in immunodeficient mice, suggesting that C-met is a potential target in glioma treatment. The purpose of the present study was to investigate the prognostic value of C-met in GBMs and subsequently correlate the prognostic value to known clinical variables, identified in a population-based cohort. Methods: Tissue samples from 186 GBM patients were analyzed using immunohistochemical staining and advanced quantitative image analysis. This provided continuous measurements based on staining intensity. Results: Median intensity was 70.8 (range 15.5-200.1). When divided at the median C-met was not prognostic. Further exploration showed that dichotomizing at an intensity of 75 (60% vs. 40%), high levels of C-met were associated with poor survival. However; C-met is a time-dependent factor and no prognostic effect was observed within the first 8.5 months after diagnosis (HR 0.97, 95% CI 0.62-1.51, p = 0.892). After 8.5 months, patients with high levels of C-met had a significantly poorer survival as compared to patients with low levels (HR 2.06, 95% CI 1.33-3.18, p = 0.001). This was significant in multivariate analysis adjusted for clinical variables; C-met (HR 1.89, 95% CI 1.22-2.93, p = 0.004), age (HR 1.02, 95% CI 1.00-1.03, p = 0.037), performance status (HR1.55, 95% CI 1.38-1.74, p = 0.004), and tumor crossing midline (HR 1.72, 955 CI 0.75-3.92, p = 0.201). Interestingly; C-met was only prognostic in patients who received post-surgical treatment, whereas no effect was observed in the 31 patients who underwent surgery only (HR 0.54, 95% CI 0.26-1.15, p = 0.113). Conclusions: Using advanced quantitative image analysis, we found that C-met was an independent prognostic factor of poor survival in GBMs. The effect did not appear within the first 8.5 months after the diagnosis and it was only seen in patients who received post-surgical treatment.