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Glioblastoma (GBM) is the most aggressive malignant primary brain tumor in adults, with a median survival of 14.6 months. Recent efforts have focused on identifying clinically relevant subgroups to improve our understanding of pathogenetic mechanisms and patient stratification. Concurrently, the role of immune cells in the tumor microenvironment has received increasing attention, especially T cells and tumor-associated macrophages (TAM). The latter are a mixed population of activated brain-resident microglia and infiltrating monocytes/monocyte-derived macrophages, both of which express ionized calcium-binding adapter molecule 1 (IBA1). This study investigated differences in immune cell subpopulations among distinct transcriptional subtypes of GBM. Human GBM samples were molecularly characterized and assigned to Proneural, Mesenchymal or Classical subtypes as defined by NanoString nCounter Technology. Subsequently, we performed and analyzed automated immunohistochemical stainings for TAM as well as specific T cell populations. The Mesenchymal subtype of GBM showed the highest presence of TAM, CD8+, CD3+ and FOXP3+ T cells, as compared to Proneural and Classical subtypes. High expression levels of the TAM-related gene AIF1, which encodes the TAM-specific protein IBA1, correlated with a worse prognosis in Proneural GBM, but conferred a survival benefit in Mesenchymal tumors. We used our data to construct a mathematical model that could reliably identify Mesenchymal GBM with high sensitivity using a combination of the aforementioned cell-specific IHC markers. In conclusion, we demonstrated that molecularly distinct GBM subtypes are characterized by profound differences in the composition of their immune microenvironment, which could potentially help to identify tumors amenable to immunotherapy.

Microglial cells are considered as sensors of brain pathology by detecting any sign of brain lesions, infections, or dysfunction and can influence the onset and progression of neurological diseases. They are capable of sensing their neuronal environment via many different signaling molecules, such as neurotransmitters, neurohormones and neuropeptides. The neuropeptide VGF has been associated with many metabolic and neurological disorders. TLQP21 is a VGF-derived peptide and has been shown to signal via C3aR1 and C1qBP receptors. The effect of TLQP21 on microglial functions in health or disease is not known. Studying microglial cells in acute brain slices, we found that TLQP21 impaired metabotropic purinergic signaling. Specifically, it attenuated the ATP-induced activation of a K+conductance, the UDP-stimulated phagocytic activity, and the ATP-dependent laser lesion-induced process outgrowth. These impairments were reversed by blocking C1qBP, but not C3aR1 receptors. While microglia in brain slices from male mice lack C3aR1 receptors, both receptors are expressed in primary cultured microglia. In addition to the negative impact on purinergic signaling, we found stimulating effects of TLQP21 in cultured microglia, which were mediated by C3aR1 receptors: it directly evoked membrane currents, stimulated basal phagocytic activity, evoked intracellular Ca2+transient elevations, and served as a chemotactic signal. We conclude that TLQP21 has differential effects on microglia depending on C3aR1 activation or C1qBP-dependent attenuation of purinergic signaling. Thus, TLQP21 can modulate the functional phenotype of microglia, which may have an impact on their function in health and disease.SIGNIFICANCE STATEMENTThe neuropeptide VGF and its peptides have been associated with many metabolic and neurological disorders. TLQP21 is a VGF-derived peptide that activates C1qBP receptors, which are expressed by microglia. We show here, for the first time, that TLQP21 impairs P2Y-mediated purinergic signaling and related functions. These include modulation of phagocytic activity and responses to injury. As purinergic signaling is central for microglial actions in the brain, this TLQP21-mediated mechanism might regulate microglial activity in health and disease. We furthermore show that, in addition to C1qBP, functional C3aR1 responses contribute to TLQP21 action on microglia. However, C3aR1 responses were only present in primary cultures but notin situ, suggesting that the expression of these receptors might vary between different microglial activation states.

Medulloblastoma, which is the most common malignant paediatric brain tumour, has a 70% survival rate, but standard treatments often lead to devastating life-long side effects and recurrence is fatal. One of the emerging strategies in the search for treatments is to determine the roles of tumour microenvironment cells in the growth and maintenance of tumours. The most attractive target is tumour-associated macrophages (TAMs), which are abundantly present in the Sonic Hedgehog (SHH) subgroup of medulloblastoma. Here, we report an unexpected beneficial role of TAMs in SHH medulloblastoma. In human patients, decreased macrophage number is correlated with significantly poorer outcome. We confirm macrophage anti-tumoural behaviour in both ex vivo and in vivo murine models of SHH medulloblastoma. Taken together, our findings suggest that macrophages play a positive role by impairing tumour growth in medulloblastoma, in contrast to the pro-tumoural role played by TAMs in glioblastoma, another common brain tumour., The Sonic Hedgehog subgroup of medulloblastoma are characterised by the high infiltration of tumour-associated macrophages (TAMs). Here, the authors show that TAM numbers in patients are associated with better prognosis and that, consistently, in a murine model of medulloblastoma, these TAMs have anti-tumoural properties.

Patients with glioma whose tumors carry a mutation in isocitrate dehydrogenase 1 (IDH1 R132H ) are younger at diagnosis and live longer. IDH1 mutations co-occur with other molecular lesions, such as 1p/19q codeletion, inactivating mutations in the tumor suppressor protein 53 (TP53 ) gene, and loss-of-function mutations in alpha thalassemia/mental retardation syndrome X-linked gene ( ATRX ). All adult low-grade gliomas (LGGs) harboring ATRX loss also express the IDH1 R132H mutation. The current molecular classification of LGGs is based, partly, on the distribution of these mutations. We developed a genetically engineered mouse model harboring IDH1 R132H , TP53 and ATRX inactivating mutations, and activated NRAS G12V. Previously, we established that ATRX deficiency, in the context of wild-type IDH1, induces genomic instability, impairs nonhomologous end-joining DNA repair, and increases sensitivity to DNA-damaging therapies. In this study, using our mouse model and primary patient-derived glioma cultures with IDH1 mutations, we investigated the function of IDH1 R132H in the context of TP53 and ATRX loss. We discovered that IDH1 R132H expression in the genetic context of ATRX and TP53 gene inactivation (i) increases median survival in the absence of treatment, (ii) enhances DNA damage response (DDR) via epigenetic up-regulation of the ataxia-telangiectasia–mutated (ATM) signaling pathway, and (iii) elicits tumor radioresistance. Accordingly, pharmacological inhibition of ATM or checkpoint kinases 1 and 2, essential kinases in the DDR, restored the tumors’ radiosensitivity. Translation of these findings to patients with IDH1 132H glioma harboring TP53 and ATRX loss could improve the therapeutic efficacy of radiotherapy and, consequently, patient survival.

Glioblastoma is the most common and most aggressive primary brain tumour. Standard of care consists of surgical resection followed by radiotherapy and concomitant and maintenance temozolomide (temozolomide/radiotherapy→temozolomide). Corticosteroids are commonly used perioperatively to control cerebral oedema and are frequently continued throughout subsequent treatment, notably radiotherapy, for amelioration of side effects. The effects of corticosteroids such as dexamethasone on cell growth in glioma models and on patient survival have remained controversial. We performed a retrospective analysis of glioblastoma patient cohorts to determine the prognostic role of steroid administration. A disease-relevant mouse model of glioblastoma was used to characterize the effects of dexamethasone on tumour cell proliferation and death, and to identify gene signatures associated with these effects. A murine anti-VEGFA antibody was used in parallel as an alternative for oedema control. We applied the dexamethasone-induced gene signature to The Cancer Genome Atlas glioblastoma dataset to explore the association of dexamethasone exposure with outcome. Mouse experiments were used to validate the effects of dexamethasone on survival in vivo Retrospective clinical analyses identified corticosteroid use during radiotherapy as an independent indicator of shorter survival in three independent patient cohorts. A dexamethasone-associated gene expression signature correlated with shorter survival in The Cancer Genome Atlas patient dataset. In glioma-bearing mice, dexamethasone pretreatment decreased tumour cell proliferation without affecting tumour cell viability, but reduced survival when combined with radiotherapy. Conversely, anti-VEGFA antibody decreased proliferation and increased tumour cell death, but did not affect survival when combined with radiotherapy. Clinical and mouse experimental data suggest that corticosteroids may decrease the effectiveness of treatment and shorten survival in glioblastoma. Dexamethasone-induced anti-proliferative effects may confer protection from radiotherapy- and chemotherapy-induced genotoxic stress. This study highlights the importance of identifying alternative agents such as vascular endothelial growth factor antagonists for managing oedema in glioblastoma patients. Beyond the established adverse effect profile of protracted corticosteroid use, this analysis substantiates the request for prudent and restricted use of corticosteroids in glioblastoma.

Diffuse intrinsic pontine glioma (DIPG) is an aggressive brain tumour, being the leading cause of paediatric death caused by cancer. Despite all the advances made regarding effective therapies, the survival is dismal. Our lab has engineered the oncolytic virus Delta-24-ACT armed with the costimulatory ligand 41BBL in order to increase the antitumoral effect of the adenovirus. 41BB is a costimulatory receptor which promotes the expansion of activated T cells and the generation and maintenance of CD8 T memory cells. Therefore, we propose the use of Delta-24-ACT as a therapeutic approach for DIPG tumours. We observed that Delta-24-ACT is able to infect and replicate in NP53 and PDGFB-driven, two DIPG murine cell lines. Furthermore, 41BBL is expressed in the membranes of the infected cells and results with immunogenic cell death as shown by the different DAMPs. Injection of Delta-24-ACT in DIPG model was safe, showed no sign of toxicity and led to a significantly increase in the median overall survival, generating anti-glioma memory in long-term survivors. Mechanistic experiments, showed an increase of T cell infiltration (mainly CD8), decrease of proliferating cells and a reduction of the number of vessels in FFPE brain samples in the treated mice. We are currently performing nanostring analyses to assess the changes in the transcriptional immune phenotype of treated versus control mice. In summary, our data suggest that Delta-24-ACT is safe and induces a potent antitumor immune response in DIPG models mainly based in the activation of CD8 lymphocytes recruited by the viral activity.

The rise in population aging worldwide is causing an unparalleled increase in death from many cancers, including glioblastoma (GBM). Here, we have explored the impact of aging and rejuvenation on GBM tumorigenesis. Compared with neuro-inflammatory old GBM, young GBM displayed elevated neuronal/synaptic signaling via brain-derived neurotrophic factor (BDNF) and SLIT and NTRK like-family member 6 (SLITRK6), promoting favorable survival rates. These effects were attributed to the rise in nicotinamide adenine dinucleotide (NAD+) levels, as brain rejuvenation by parabiosis or administration of nicotinamide mononucleotide (NMN) in mice elicited a younger phenotype with activated neuronal/synaptic signaling and improved outcomes. Our data indicate that age-associated NAD+ loss contributes to the highly aggressive GBM by the shift from neuronal/synaptic activity to neuro-inflammation in the elderly brain. These findings have therapeutic and preventive implications in GBM and provide mechanistic insights into the exacerbation of GBM tumorigenesis by aging.

Mutation in isocitrate dehydrogenase (mIDH) is the main genetic lesion that defines clinical glioma subtypes and prognosis. This gain of function mutation is associated with the production of the oncometabolite, R-2-hydroxyglutarate, that inhibits α-ketoglutarate dependent enzymes such as TET2 and the Jumonji-C domain containing demethylases. The resultant epigenetic modifications elicit profound effects on the tumor biology and on the glioma-infiltrating immune cells. Here, we report that in genetically engineered mouse glioma models(1), IDH1 mutation caused an expansion of tumor infiltration granulocytes. Upon phenotypic and functional characterization, we uncovered that granulocytes in mIDH1 glioma express low level of immunosuppressive molecules and did not inhibit T-cell function. Single-cell sequencing revealed that these granulocytes are heterogeneous and composed of three distinct populations; neutrophils, pre-neutrophils, and a small fraction of immunosuppressive PMN-MDSCs. Moreover, primary human gliomas showed a higher cellular fraction exhibiting the PMN-MDSCs gene signature in wtIDH1 tumors than the mIDH1 tumors. The mechanism by which mIDH1 mediates non-immune suppressive granulocytes expansion involves epigenetic reprogramming which leads to enhanced expression of granulocyte colony-stimulating factor (G-CSF) in stem-like cells. High G-CSF gene expression is correlated with favorable patient outcome solely in LGG-astrocytoma with mIDH1. Thus, G-CSF represents a potential therapeutic that can be harnessed to improve immunotherapeutic responses in wild type IDH1 glioma patients.

Oncolytic viruses have become promising therapeutic candidates to treat gliomas. Our group has developed Delta-24-ACT, an oncolytic adenovirus armed with the positive costimulatory ligand 4-1BBL which is capable to trigger the activation of T cells and thereby increase their antitumor immune response. Here we evaluate the anti-glioma effect of Delta-24-ACT alone or in combination with an immune checkpoint inhibitor. We observed that Delta-24-ACT was able to infect and kill murine glioma (GL261-5 and CT-2A) and also human glioma cell lines (U87-MG and U251-MG), while maintaining its replication in the latter. Of importance, Delta-24-ACT infection resulted in 4-1BBL expression on the membrane of glioma cells. Moreover, this ligand was functional and was able to stimulate CD8 lymphocytes in vitro, suggesting the potential of Delta-24-ACT to trigger an effective immune response. Furthermore, in vivo Delta-24-ACT showed anti-tumour effect in two murine glioma models by significantly increasing the median survival time and leading to long-term survivors. Mechanistic studies demonstrated an increase of the T cell infiltration and the activation of different immune cell populations by flow cytometry and a decrease of proliferative cells and tumour vessels by immunohistochemistry on FFPE brain samples. Importantly, the infiltrating lymphocytes also showed signs of exhaustion increasing the amount of IL-10 and the expression of PD-1. To overcome this exhaustion we combined Delta-24-ACT with an anti-PD-1 antibody. Evaluation of this combination in vivo further increased the median survival time of treated tumor-bearing mice and resulted in 50% long-term survivors. Rechallenge studies with the same cell line showed that combination treatment effectively protected these animals of developing tumors and therefore, the acquisition of immune memory. In summary, our data demonstrated that Delta-24-ACT induces a potent anti-tumour effect in vitro and in vivo as a result of the recruitment of immune cell populations modulating the immunosuppressive tumour microenvironment of glioma.

A pathologic hallmark of glioblastoma (GBM), the most common and deadly primary brain tumor in adults, is pseudopalisading necrotic regions in which ischemic conditions are found. Ischemic microenvironments characterized by low oxygen, restricted glucose, and acidic pH due to poor blood supply occurs in both solid tumors and non-neoplastic tissue injury. Modeling these physiologically relevant ischemic conditions within glioblastoma in vitro, we identified chromodomain helicase DNA binding protein 7 (CHD7) as a novel ischemia-regulated gene. CHD7 is an epigenetic reader that controls neural stem cell maintenance and is mutated in CHARGE syndrome, a developmental disorder associated with cranial nerve abnormalities. CHD7 mRNA expression was consistently suppressed in multiple patient-derived xenograft brain tumor lines in response to ischemic conditions, and lower expression of CHD7 correlates with poor GBM patient survival. These microenvironment-mediated decreases in CHD7 protein and mRNA levels observed in glioblastoma were also mirrored in neural progenitor cells in vitro, and CHD7 levels were reduced in the perinecrotic niche of GBM patient and xenograft tissue sections. Genetic targeting of CHD7 increased angiogenesis in vitro in association with differential regulation of angiogenesis associated genes as determined in RNA sequencing analysis. Although targeting CHD7 in orthotopically implanted xenograft brain tumor models did not affect survival outcomes in mice, we observed marked differences in blood vessel architecture and organization, suggesting a major role for CHD7 in regulating vessel formation within these tumors. Together, our data provide insight into the molecular responses to ischemia that regulate angiogenesis.

Glioblastoma (GBM) remains the deadliest of all primary brain tumors with very few effective treatment options. Recently, we reported that high AXL expression is correlated with poor prognosis in GBM patients and demonstrated the therapeutic benefits of targeting AXL, a member of TAM receptor tyrosine kinase family using a novel small molecule inhibitor, BGB324 in immunocompetent mouse GBM models and xenografts of patient-derived glioma stem cells(GSCs). The promise of BGB324 in tumor burden management prompted us to develop a clinical trial with BGB324 as a single agent therapeutic with the goal to extend it as a combinatorial therapy in the future. Our surgical PK/PD clinical trial with BGB324 in recurrent GBM has been approved by the Brain Malignancy Steering Committee at the National Cancer Institute. Study treatment will consist of 2 cohorts of adult GBM patients, one (Group A) receiving the treatment pre-operatively and the other (Group B) receiving no treatment at all prior to surgery. First 5 patients recruited to Group A will be checked for the desired intra-tumoral drug concentration achieved to continue the trial. Group A will be supplemented by an additional 5 patients bringing the number to n=10 in each arm of the trial. Following surgical resection, patients in both cohorts will receive BGB324 daily in 21-day cycles. Treatment will be continued unless patients exhibit significant toxicity or substantial tumor progression. Our preclinical findings show the upregulation of AXL and its role in apoptosis induction in mesenchymal GBM as well as its association with MLK4, a serine threonine kinase we previously characterized as a mesenchymal GSC molecular target. Inhibition of phosphorylation of AXL and concomitant NF-kB activation in mesenchymal GSCs was found to be the nodal target of the drug action. An up-to-date information of the trial will be presented in detail.

Mitochondrial utilization of the carbohydrate fuel for energy production is required for postnatal cerebellar development., While deregulation of mitochondrial metabolism and cytosolic glycolysis has been well recognized in tumor cells, the role of coordinated mitochondrial oxidation and cytosolic fermentation of pyruvate, a key metabolite derived from glucose, in physiological processes is not well understood. Here, we report that knockout of PTPMT1, a mitochondrial phosphoinositide phosphatase, completely blocked postnatal cerebellar development. Proliferation of granule cell progenitors, the most actively replicating cells in the developing cerebellum, was only moderately decreased, and proliferation of Purkinje cell progenitors did not seem to be affected in knockout mice. In contrast, generation of functional Bergmann glia from multipotent precursor cells (radial glia), which is essential for cerebellar corticogenesis, was totally disrupted. Moreover, despite a low turnover rate, neural stem cells were impaired in self-renewal in knockout mice. Mechanistically, loss of PTPMT1 decreased mitochondrial aerobic metabolism by limiting utilization of pyruvate, which resulted in bioenergetic stress in neural precursor/stem cells but not in progenitor or mature cells, leading to cell cycle arrest through activation of the AMPK-p19/p21 pathway. This study suggests that mitochondrial oxidation of the carbohydrate fuel is required for postnatal cerebellar development, and identifies a bioenergetic stress–induced cell cycle checkpoint in neural precursor/stem cells.

While diffuse intrinsic pontine glioma (DIPG), the most common pediatric brainstem tumor, exhibits transient responsiveness to radiation (XRT), overall survival is

Glioblastoma (GBM) is a lethal disease with no effective therapies available. We previously observed upregulation of the TAM (Tyro-3, Axl, and Mer) receptor tyrosine kinase family member AXL in mesenchymal GBM and showed that knockdown of AXL induced apoptosis of mesenchymal, but not proneural, glioma sphere cultures (GSC). In this study, we report that BGB324, a novel small molecule inhibitor of AXL, prolongs the survival of immunocompromised mice bearing GSC-derived mesenchymal GBM-like tumors. We show that protein S (PROS1), a known ligand of other TAM receptors, was secreted by tumor-associated macrophages/microglia and subsequently physically associated with and activated AXL in mesenchymal GSC. PROS1-driven phosphorylation of AXL (pAXL) induced NFκB activation in mesenchymal GSC, which was inhibited by BGB324 treatment. We also found that treatment of GSC-derived mouse GBM tumors with nivolumab, a blocking antibody against the immune checkpoint protein PD-1, increased intratumoral macrophages/microglia and activation of AXL. Combinatorial therapy with nivolumab plus BGB324 effectively prolonged the survival of mice bearing GBM tumors. Clinically, expression of AXL or PROS1 was associated with poor prognosis for patients with GBM. Our results suggest that the PROS1–AXL pathway regulates intrinsic mesenchymal signaling and the extrinsic immune microenvironment, contributing to the growth of aggressive GBM tumors. Significance: These findings suggest that development of combination treatments of AXL and immune checkpoint inhibitors may provide benefit to patients with GBM. Cancer Res; 78(11); 3002–13. ©2018 AACR.

Background Depending on the level, differentiation state, and tumor stage, reactive nitrogen and oxygen species inhibit or increase cancer growth and tumor initiating cell maintenance. The rate-limiting enzyme in a pathway that can regulate reactive species production but has not been thoroughly investigated in glioblastoma (GBM; grade IV astrocytoma) is guanosine triphosphate (GTP) cyclohydrolase 1 (GCH1). We sought to define the role of GCH1 in the regulation of GBM growth and brain tumor initiating cell (BTIC) maintenance. Methods We examined GCH1 mRNA and protein expression in patient-derived xenografts, clinical samples, and glioma gene expression datasets. GCH1 levels were modulated using lentiviral expression systems, and effects on cell growth, self-renewal, reactive species production, and survival in orthotopic patient-derived xenograft models were determined. Results GCH1 was expressed in GBMs with elevated but not exclusive RNA and protein levels in BTICs in comparison to non-BTICs. Overexpression of GCH1 in GBM cells increased cell growth in vitro and decreased survival in an intracranial GBM mouse model. In converse experiments, GCH1 knockdown with short hairpin RNA led to GBM cell growth inhibition and reduced self-renewal in association with decreased CD44 expression. GCH1 was critical for controlling reactive species balance, including suppressing reactive oxygen species production, which mediated GCH1 cell growth effects. In silico analyses demonstrated that higher GCH1 levels in glioma patients correlate with higher glioma grade, recurrence, and worse survival. Conclusions GCH1 expression in established GBMs is pro-tumorigenic, causing increased growth due, in part, to promotion of BTIC maintenance and suppression of reactive oxygen species.

There is a growing recognition that gliomas are complex tumors composed of neoplastic and non-neoplastic cells, which each individually contribute to cancer formation, progression and response to treatment. The majority of the non-neoplastic cells are tumor-associated macrophages (TAMs), either of peripheral origin or representing brain-intrinsic microglia, that create a supportive stroma for neoplastic cell expansion and invasion. TAMs are recruited to the glioma environment, have immune functions, and can release a wide array of growth factors and cytokines in response to those factors produced by cancer cells. In this manner, TAMs facilitate tumor proliferation, survival and migration. Through such iterative interactions, a unique tumor ecosystem is established, which offers new opportunities for therapeutic targeting.

DDX6 (p54/RCK) is a human RNA helicase with central roles in mRNA decay and translation repression. To help our understanding of how DDX6 performs these multiple functions, we conducted the first unbiased, large-scale study to map the DDX6-centric protein-protein interactome using immunoprecipitation and mass spectrometry. Using DDX6 as bait, we identify a high-confidence and high-quality set of protein interaction partners which are enriched for functions in RNA metabolism and ribosomal proteins. The screen is highly specific, maximizing the number of true positives, as demonstrated by the validation of 81% (47/58) of the RNA-independent interactors through known functions and interactions. Importantly, we minimize the number of indirect interaction partners through use of a nuclease-based digestion to eliminate RNA. We describe eleven new interactors, including proteins involved in splicing which is an as-yet unknown role for DDX6. We validated and characterized in more detail the interaction of DDX6 with Nuclear fragile X mental retardation-interacting protein 2 (NUFIP2) and with two previously uncharacterized proteins, FAM195A and FAM195B (here referred to as granulin-1 and granulin-2, or GRAN1 and GRAN2). We show that NUFIP2, GRAN1, and GRAN2 are not P-body components, but re-localize to stress granules upon exposure to stress, suggesting a function in translation repression in the cellular stress response. Using a complementary analysis that resolved DDX6’s multiple complex memberships, we further validated these interaction partners and the presence of splicing factors. As DDX6 also interacts with the E3 SUMO ligase TIF1β, we tested for and observed a significant enrichment of sumoylation amongst DDX6’s interaction partners. Our results represent the most comprehensive screen for direct interaction partners of a key regulator of RNA life cycle and localization, highlighting new stress granule components and possible DDX6 functions—many of which are likely conserved across eukaryotes.

// Xi Feng 1 , Frank Szulzewsky 2,* , Alexan Yerevanian 1,3,* , Zhihong Chen 1 , David Heinzmann 1,4 , Rikke Darling Rasmussen 1 , Virginia Alvarez-Garcia 1 , Yeonghwan Kim 5 , Bingcheng Wang 6 , Ilaria Tamagno 1 , Hao Zhou 7 , Xiaoxia Li 7 , Helmut Kettenmann 2 , Richard M. Ransohoff 1,8 and Dolores Hambardzumyan 1 1 Department of Neurosciences at Cleveland Clinic, Cleveland, Ohio, USA 2 Cellular Neurosciences, Max Delbruck Center for Molecular Medicine, Berlin, Germany 3 Case Western Reserve University School of Medicine, Cleveland, Ohio, USA 4 Department of Cardiology at Tubingen University School of Medicine, Tubingen, Germany 5 Department of Stem Cell Biology and Regenerative Medicine, Cleveland, Ohio, USA 6 Rammelkamp Center for Research, MetroHealth Center, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA 7 Department of Immunology at Cleveland Clinic, Cleveland, Ohio, USA 8 Neuroinflammation Research Center, Cleveland Clinic, Cleveland, Ohio, USA * These authors have contributed equally to this work Correspondence to: Dolores Hambardzumyan, email: // Keywords : CX3CR1/CX3CL1 signaling, glioblastoma, microglia, monocyte Received : January 19, 2015 Accepted : March 10, 2015 Published : March 30, 2015 Abstract The most abundant populations of non-neoplastic cells in the glioblastoma (GBM) microenvironment are resident microglia, macrophages and infiltrating monocytes from the blood circulation. The mechanisms by which monocytes infiltrate into GBM, their fate following infiltration, and their role in GBM growth are not known. Here we tested the hypothesis that loss of the fractalkine receptor CX3CR1 in microglia and monocytes would affect gliomagenesis. Deletion of Cx3cr1 from the microenvironment resulted in increased tumor incidence and shorter survival times in glioma-bearing mice. Loss of Cx3cr1 did not affect accumulation of microglia/macrophages in peri-tumoral areas, but instead indirectly promoted the trafficking of CD11b + CD45 hi CX3CR1 low Ly-6C hi Ly-6G - F4/80 -/low circulating inflammatory monocytes into the CNS, resulting in their increased accumulation in the perivascular area. Cx3cr1-deficient microglia/macrophages and monocytes demonstrated upregulation of IL1β expression that was inversely proportional to Cx3cr1 gene dosage. The Proneural subgroup of the TCGA GBM patient dataset with high IL1β expression showed shorter survival compared to patients with low IL1β. IL1β promoted tumor growth and increased the cancer stem cell phenotype in murine and human Proneural glioma stem cells (GSCs). IL1β activated the p38 MAPK signaling pathway and expression of monocyte chemoattractant protein (MCP-1/CCL2) by tumor cells. Loss of Cx3cr1 in microglia in a monocyte-free environment had no impact on tumor growth and did not alter microglial migration. These data suggest that enhancing signaling to CX3CR1 or inhibiting IL1β signaling in intra-tumoral macrophages can be considered as potential strategies to decrease the tumor-promoting effects of monocytes in Proneural GBM.

Glioblastoma (GBM) is a lethal disease without effective therapies. Previously we reported that the TAM receptor tyrosine kinase family member AXL is upregulated in mesenchymal GBM and its knockdown induces apoptosis of mesenchymal but not proneural glioma sphere cultures (GSCs). In this study, we report that BGB324, a novel small molecule inhibitor for AXL, prolongs the survival of immunocompromised mice bearing mesenchymal GSC-derived GBM-like intracranial tumors by inhibition of AXL activation in tumor cells. Mechanistically, we identified that protein S (PROS1), known as a ligand for other TAM receptors, is secreted by tumor-associated macrophages, thereby physically associates and activates AXL in mesenchymal GSCs. The PROS1-driven phosphorylation of AXL resulted in the NF-kB activation in mesenchymal GSCs and this activation was eliminated by BGB324 treatment. In addition, BGB324 downregulated the immune checkpoint protein PD-L1 both in vitro and in vivo. Combination of BGB324 with Nivolumab - the neutralizing antibody for PD-1 (a receptor for PD-L1) was effective to prolong the survival of immunocompetent mice bearing syngeneic GBM models. Clinically, both AXL and PROS1 expression indicated poorer prognosis of GBM patients. These data suggest that the PROS1/AXL pathway regulates intrinsic mesenchymal signaling as well as extrinsic immune microenvironment, contributing to the growth of aggressive GBM tumors. To translate the pre-clinical data to human GBM patients, we designed a surgical PK/PD clinical trial with BGB324 for recurrent GBM and this trial is currently under review by the Brain Malignancy Steering Committee in the National Cancer Institute.

NOTCH1 signalling contributes to defective remyelination by impairing differentiation of oligodendrocyte progenitor cells (OPCs). Here we report that IL-17 stimulation induces NOTCH1 activation in OPCs, contributing to Th17-mediated demyelinating disease. Mechanistically, IL-17R interacts with NOTCH1 via the extracellular domain, which facilitates the cleavage of NOTHC1 intracellular domain (NICD1). IL-17-induced NOTCH1 activation results in the interaction of IL-17R adaptor Act1 with NICD1, followed by the translocation of the Act1–NICD1 complex into the nucleus. Act1–NICD1 are recruited to the promoters of several NOTCH1 target genes (including STEAP4, a metalloreductase important for inflammation and cell proliferation) that are specifically induced in the spinal cord by Th17 cells. A decoy peptide disrupting the IL-17RA–NOTCH1 interaction inhibits IL-17-induced NOTCH1 activation and attenuates Th17-mediated experimental autoimmune encephalitis (EAE). Taken together, these findings demonstrate critical crosstalk between the IL-17 and NOTCH1 pathway, regulating Th17-induced inflammatory and proliferative genes to promote demyelinating disease., NOTCH signalling stimulates oligodendrocyte progenitor cell proliferation but how this regulates demyelinating disease is unclear. Here, the authors show that an IL-17 adaptor protein, Act1, interacts with the C-terminal fragment of NOTCH1 (NICD) to activate cell proliferation and an inflammatory response.

Sir, We appreciate the interest of Drs Clement and Champ in our article, which provided overall compelling evidence for a negative impact of corticosteroid medication on survival in patients with glioblastoma. …

In glioblastoma (GBM), tumor-associated macrophages (TAM) represent up to one half of the cells of the tumor mass, including both infiltrating macrophages and resident brain microglia. In an effort to delineate the temporal and spatial dynamics of TAM composition during gliomagenesis, we used genetically engineered and GL261-induced mouse models in combination with CX3CR1GFP/WT;CCR2RFP/WT double knock-in mice. Using this approach, we demonstrated that CX3CR1LoCCR2Hi monocytes were recruited to the GBM, where they transitioned to CX3CR1HiCCR2Lo macrophages and CX3CR1HiCCR2− microglia-like cells. Infiltrating macrophages/monocytes constituted approximately 85% of the total TAM population, with resident microglia accounting for the approximately 15% remaining. Bone marrow–derived infiltrating macrophages/monocytes were recruited to the tumor early during GBM initiation, where they localized preferentially to perivascular areas. In contrast, resident microglia were localized mainly to peritumoral regions. RNA-sequencing analyses revealed differential gene expression patterns unique to infiltrating and resident cells, suggesting unique functions for each TAM population. Notably, limiting monocyte infiltration via genetic Ccl2 reduction prolonged the survival of tumor-bearing mice. Our findings illuminate the unique composition and functions of infiltrating and resident myeloid cells in GBM, establishing a rationale to target infiltrating cells in this neoplasm. Cancer Res; 77(9); 2266–78. ©2017 AACR.

Purpose: Bevacizumab, a humanized monoclonal antibody to VEGF, is used routinely in the treatment of patients with recurrent glioblastoma (GBM). However, very little is known regarding the effects of bevacizumab on the cells in the perivascular space in tumors. Experimental Design: Established orthotopic xenograft and syngeneic models of GBM were used to determine entry of monoclonal anti-VEGF-A into, and uptake by cells in, the perivascular space. Based on the results, we examined CD133+ cells derived from GBM tumors in vitro. Bevacizumab internalization, trafficking, and effects on cell survival were analyzed using multilabel confocal microscopy, immunoblotting, and cytotoxicity assays in the presence/absence of inhibitors. Results: In the GBM mouse models, administered anti-mouse-VEGF-A entered the perivascular tumor niche and was internalized by Sox2+/CD44+ tumor cells. In the perivascular tumor cells, bevacizumab was detected in the recycling compartment or the lysosomes, and increased autophagy was found. Bevacizumab was internalized rapidly by CD133+/Sox2+-GBM cells in vitro through macropinocytosis with a fraction being trafficked to a recycling compartment, independent of FcRn, and a fraction to lysosomes. Bevacizumab treatment of CD133+ GBM cells depleted VEGF-A and induced autophagy thereby improving cell survival. An inhibitor of lysosomal acidification decreased bevacizumab-induced autophagy and increased cell death. Inhibition of macropinocytosis increased cell death, suggesting macropinocytosis of bevacizumab promotes CD133+ cell survival. Conclusions: We demonstrate that bevacizumab is internalized by Sox2+/CD44+-GBM tumor cells residing in the perivascular tumor niche. Macropinocytosis of bevacizumab and trafficking to the lysosomes promotes CD133+ cell survival, as does the autophagy induced by bevacizumab depletion of VEGF-A. Clin Cancer Res; 23(22); 7059–71. ©2017 AACR.

In response to neurodegeneration, the adult mammalian brain activates a cellular cascade that results in reactive astro- and microgliosis. The mechanism through which astrocytes become reactive and the physiological consequences of their activation in response to neurodegeneration is complex. While the activation and proliferation of astrocytes has been shown to occur during massive neuronal cell death, the functional relationship between these two events has not been clearly elucidated. Here we show that in response to Kainic acid- (KA) induced neurodegeneration, the mitogen sonic hedgehog (SHH) is upregulated in reactive astrocytes. SHH activity peaks at 7 days and is accompanied by increased Gli activity and elevated proliferation in several cell types. To determine the functional role of SHH-Gli signaling following KA lesions, we used a pharmacological approach to show that SHH secreted by astrocytes drives the activation and proliferation of astrocytes and microglia. The consequences of SHH-Gli signaling in KA-induced lesions appear to be independent of the severity of neurodegeneration.

The tumour vascular microenvironment supports tumorigenesis not only by supplying oxygen and diffusible nutrients but also by secreting soluble factors that promote tumorigenesis. Here we identify a feedforward mechanism in which endothelial cells (ECs), in response to tumour-derived mediators, release angiocrines driving aberrant vascularization and glioblastoma multiforme (GBM) progression through a hypoxia-independent induction of hypoxia-inducible factor (HIF)-1α. Phosphorylation of profilin-1 (Pfn-1) at Tyr 129 in ECs induces binding to the tumour suppressor protein von Hippel-Lindau (VHL), and prevents VHL-mediated degradation of prolyl-hydroxylated HIF-1α, culminating in HIF-1α accumulation even in normoxia. Elevated HIF-1α induces expression of multiple angiogenic factors, leading to vascular abnormality and tumour progression. In a genetic model of GBM, mice with an EC-specific defect in Pfn-1 phosphorylation exhibit reduced tumour angiogenesis, normalized vasculature and improved survival. Moreover, EC-specific Pfn-1 phosphorylation is associated with tumour aggressiveness in human glioma. These findings suggest that targeting Pfn-1 phosphorylation may offer a selective strategy for therapeutic intervention of malignant solid tumours.

Diffuse infiltrative invasion is a major cause for the dismal prognosis of glioblastoma (GBM), but the underlying mechanisms remain incompletely understood. Using human glioblastoma stem cells (GSCs) that recapitulate the invasive propensity of primary GBM, we find that EphA2 critically regulates GBM invasion in vivo. EphA2 was expressed in all seven GSC lines examined, and overexpression of EphA2 enhanced intracranial invasion. The effects required Akt-mediated phosphorylation of EphA2 on serine 897. In vitro the Akt-EphA2 signaling axis is maintained in the absence of ephrin-A ligands and is disrupted upon ligand stimulation. To test whether ephrin-As in tumor microenvironment can regulate GSC invasion, the newly established Efna1;Efna3;Efna4 triple knockout mice (TKO) were used in an ex vivo brain slice invasion assay. We observed significantly increased GSC invasion through the brain slices of TKO mice relative to wild type littermates. Mechanistically EphA2 knockdown suppressed stem properties of GSCs, causing diminished self-renewal, reduced stem marker expression and decreased tumorigenicity. In a subset of GSCs, the reduced stem properties were associated with lower Sox2 expression. Overexpression of EphA2 promoted stem properties in a kinase-independent manner and increased Sox2 expression. In addition to suppressing invasion, disrupting Akt-EphA2 crosstalk attenuated stem marker expression and neurosphere formation while having minimal effects on tumorigenesis, suggesting that the Akt-EphA2 signaling axis contributes to the stem properties. Taken together, the results show that EphA2 endows invasiveness of GSCs in vivo in cooperation with Akt and contributes to the maintenance of stem properties.

Glioblastoma is the most common and aggressive primary brain tumor characterized by a dismal prognosis despite aggressive treatment regimens. A hallmark of glioblastoma is aberrant angiogenesis that results in disruption of the blood-brain barrier. This drives glioblastoma-associated cerebral edema caused by leakage of serum from the blood into the brain. Typically, edema is managed by the corticosteroid dexamethasone which is known to normalize the blood brain barrier. Various groups have also demonstrated beneficial effects following normalization of the blood-brain barrier with anti-angiogenic therapies such as cediranib and bevacizumab. Interleukin 1 (IL-1) signaling inhibition, however, has not been investigated in this context despite evidence that it modulates blood-brain barrier integrity in other neuroinflammatory conditions. In this work, we demonstrate that IL-1 signaling does not impact the production of VEGF by bone marrow-derived macrophages and microglia in vitro. Moreover, we demonstrate no effect of dexamethasone treatment on VEGF levels in murine PDGFB-driven glioblastoma generated with RCAS/tv-a technology in vivo. This suggests that the restoration of blood-brain barrier integrity by dexamethasone is VEGF-independent. Dexamethasone is shown here, however, to downregulate both IL-1α and IL-1β expression in vivo and in vitro. Genetic ablation of IL-1β and subsequent MRI analysis is shown to reduce formation of edema in vivo, allowing mice to survive with larger tumors than wildtype controls. Serial sectioning of the tumor, and histological reconstruction of the total volume post-euthanasia confirms these results. Genetic ablation of IL-1R1 in vivo is shown to reduce blood-brain barrier permeability in a Hoechst dye-based vessel leakage assay. Future experiments will elucidate if these effects can be attributed to altered angiogenesis or regulation of endothelial cell junction molecules. Regardless, this work outlines IL-1 signaling as a promising therapeutic target to modulate blood-brain barrier integrity and serve as an alternative to dexamethasone for the treatment of glioblastoma-associated cerebral edema.

The GBM microenvironment is composed of numerous non-neoplastic cells, among which tumor-associated myeloid cells (TAMs) are the most abundant. TAMs are constituted of several different cell types, including brain microglia and bone-marrow-derived infiltrating cells, which can be further divided into inflammatory monocytes, monocyte-derived macrophages, and polymorphnuclear neutrophils. These myeloid cells are believed to promote tumor growth and immune evasion by expressing immune checkpoint proteins. Remarkable progress has been made in treating lung cancer and melanoma by using immune-checkpoint inhibitors; however, mixed results were obtained for its application in GBM. To examine how molecular-subtypes of GBM influence the composition and immunosuppression of tumor-associated myeloid cells, we used the RCAS/tv-a system, a somatic cell-specific gene transfer system, to generate de novo murine GBM (mGBM). By manipulating different known human oncogenic-driver mutations such as overexpressing PDGFB or EGFRVIII, or silencing NF1, we generated Proneural (PN), Classical (CL) and Mesenchymal (MES) GBMs respectively, which phenotypically resemble their human counterparts. We found that the majority (80%) of tumor-infiltrating myeloid cells in PN GBM are bone-marrow derived macrophages, whereas this number is significantly less in CL and MES mGBM. Interestingly, unique to MES, there is a significant presence (16%) of neutrophils in these tumors than in other subtypes (4%). Further characterization for subtype-specific expression of PD-L1, a druggable immune checkpoint molecule, by flow cytometry shows that MES has the highest expression of PD-L1 (Mean Fluorescent Intensity=13,000 ± 3,000), whereas the expression is lower (MFI=8,100 ± 2,000) in PN and lowest (MFI=5,900 ± 2,000) in CL. The current effort is devoted to examining how myeloid cells isolated from different subtypes can differentially suppress T cell functions; and how mice carry these subtypes respond to anti-PD-L1 therapy. Our findings illuminate the unique composition and functions of tumor-associated myeloid cells in different GBM subtypes, establishing a rationale to target these cells in this heterogeneous neoplasm.

Anti-angiogenic therapy of glioblastoma with bevacizumab, a vascular endothelial growth factor-A (VEGFA) blocking antibody, may accelerate tumor cell invasion and induce alternative angiogenic pathways. We investigated the roles of the pro-angiogenic receptor APLNR and its cognate ligand apelin in VEGFA/VEGFR2 anti-angiogenic therapy against distinct subtypes of glioblastoma. In proneural glioblastoma, apelin levels were downregulated by VEGFA or VEGFR2 blockade by use of bevacizumab or ramucirumab, respectively. A central role for apelin/APLNR in controlling glioblastoma vascularization was corroborated in a serial implantation model of the angiogenic switch that occurs in human glioblastoma. Apelin and APLNR are broadly expressed in human glioblastoma, and knockdown or knockout of APLN in orthotopic models of proneural or classical glioblastoma subtypes massively reduced glioblastoma vascularization as compared with controls. What is more, direct infusion of the bioactive peptide apelin-13 was able to rescue this vascular loss-of-function phenotype, demonstrating the specific control of tumor vascularization by apelin/APLNR signaling. While high levels of apelin correlated with reduced tumor cell invasiveness, the reduction in apelin expression led to accelerated glioblastoma cell invasion. Analysis of stereotactic glioblastoma biopsies from patients as well as from in vitro and in vivo experiments revealed increased dissemination of APLNR-positive tumor cells when apelin levels were reduced. Most interestingly, application of apelin-F13A, a mutant APLNR ligand, blocked both tumor angiogenesis and glioblastoma cell invasion. Furthermore, co-targeting VEGFR2 and APLNR synergistically improved survival of mice bearing proneural glioblastoma. In summary, we show that apelin/APLNR signaling controls glioblastoma angiogenesis and invasion directly, and that both pathological features are blunted by apelin-F13A. We suggest that apelin-F13A can improve the efficiency and reduce the side effects of established anti-angiogenic treatments for distinct glioblastoma subtypes.

Pediatric high-grade gliomas (pHGG) account for the most cancer-related deaths in children, as there are no effective therapies available. It is known tumor associated macrophages (TAM) can make up 30–40% of the total tumor cell mass in adult high-grade gliomas, promoting tumor growth and immune evasion. This raises the question of whether pHGGs possess a distinct constituency of TAMs due to their unique genetic and epigenetic landscapes. To uncover the composition and behavior of TAMs in pHGG we utilize RCAS/tva, a somatic cell-type specific gene transfer system which allows us to recapitulate all major subtypes of pHGG in newborn immunocompetent mice, including histone wild-type and histone-mutant tumors. We combine RCAS-H3.3K27M, RCAS-H3.3G34R/V, or RCAS-H3.3WT along with their driver mutations such as RCAS-shp53 and RCAS-PDGFA or RCAS-PDGFB. These tumors are induced in Nestin-positive cells, each in their respective locations found in the human population. Tumors driven by PDGFB have a significantly lower median survival compared to PDGFA-driven tumors and have increased infiltration of lymphocytes and TAMs, specifically inflammatory monocytes. In vitro bone marrow derived monocyte and microglial cultures demonstrate the BMDM population is most responsible for the production of inflammatory chemokines and angiogenic factors in the tumor microenvironment. We performed histological analyses on over 40 human patient samples to determine the role of the stromal population in TAM infiltration. Matched human samples were also utilized for pan-cancer immune profiling with NanoString to further characterize the innate and adaptive immune microenvironments. These analyses indicate DIPG/K27M tumors have a higher immune cell infiltrate compared to G34R/V and histone wildtype tumors. Further, we observe higher infiltration of T-cell populations in pHGGs compared to adult HGGs, suggesting these tumors may be amenable to immunotherapy despite being considered “immune cold.” These studies provide the critical foundation needed for the development of novel therapeutics targeting these tumors.

The GBM microenvironment is composed of numerous non-neoplastic cells, among which tumor-associated myeloid cells (TAMs) are the most abundant. TAMs are constituted of several different cell types, including brain microglia and bone-marrow-derived infiltrating cells, which can be further divided into inflammatory monocytes, monocyte-derived macrophages, and polymorphnuclear neutrophils. These myeloid cells are believed to promote tumor growth and immune evasion by expressing immune checkpoint proteins. Remarkable progress has been made in treating lung cancer and melanoma by using immune-checkpoint inhibitors; however, mixed results were obtained for its application in GBM. To examine how molecular-subtypes of GBM influence the composition and immunosuppression of tumor-associated myeloid cells, we used the RCAS_tv-a system, a somatic cell-specific gene transfer system, to generate de novo murine GBM (mGBM). By manipulating different known human oncogenic-driver mutations such as overexpressing PDGFB or EGFRVIII, or silencing NF1, we generated Proneural (PN), Classical (CL) and Mesenchymal (MES) GBMs respectively, which phenotypically resemble their human counterparts. We found that the majority (80%) of tumor-infiltrating myeloid cells in PN GBM are bone-marrow derived macrophages, whereas this number is significantly less in CL and MES mGBM. Interestingly, unique to MES, there is a significant presence (16%) of neutrophils in these tumors than in other subtypes (4%). Further characterization for subtype-specific expression of PD-L1, a druggable immune checkpoint molecule, by flow cytometry shows that MES has the highest expression of PD-L1), whereas the expression is lower in PN and CL subtypes. Treating GBM-bearing mice with anti-PDL1 antibodies did not prolong their survival. Concurrent treatment of irradiation and anti-PDL1 antibody did not confer significant survival advantage either compared to controls. These results reflect the unsuccessful trails of recent human clinical studies; however, it also emphasizes the importance of understanding the mechanism of resistance in GBM immunotherapy before effective immune treatment can be established. Our immunocompetent mouse models provide indispensable tools for these studies. Note: This abstract was not presented at the meeting. Citation Format: Zhihong Chen, Cameron J. Hurting, Ben Gabanic, Jyothi Murukuti, Dolores Hambardzumyan. Genetic driver-mutations define composition and properties of tumor-associated myeloid cells in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1100.

Pediatric high-grade gliomas (pHGG) drastically differ from their adult counterparts in terms of genetic and epigenetic alterations, suggesting they may also differ in the constituency of their tumor microenvironment. It is known tumor associated macrophages (TAMs) can constitute up to 30–40% of the total tumor cell mass in adult high-grade gliomas, yet little is known for pHGGs. This raises the question of whether pHGGs possess a distinct constituency of TAMs due to their unique genetic and epigenetic landscapes. To uncover the composition and behavior of TAMs in pHGG we utilize RCAS/tva, a somatic cell-type specific gene transfer system in which we administer RCAS-PDGFA or RCAS-PDGFB to Nestin-positive cells in the brain of immunocompetent Cdkn2a knockout mice. We observe PDGFB-driven tumors have a significantly lower median survival compared to PDGFA-driven tumors. PDGFB tumors also have increased infiltration of TAMs, made evident by immunohistochemical staining for IBA1. Flow cytometry indicates the increased number of TAMs is due to bone-marrow derived inflammatory monocytes, not the microglial population. Unsupervised clustering and principle component analysis indicates these tumors possess distinct expression profiles. Several chemokines and receptors are highly expressed in PDGFB tumors such as Ccl2, Ccl3, and Ccl7, suggesting chemokine mediated infiltration of TAMs may be occurring. To study PDGF signaling and TAM infiltration in human pHGGs, we stained over 40 tumors for IBA1, PDGF-receptors, and PDGF-ligands. There is a positive correlation between PDGFRβ, PDGFB, and CD31 staining with IBA1, suggesting a stromal role exists for the infiltration of TAMs. Current in vivo studies are being conducted to determine if TAM infiltration can be inhibited by genetically or pharmacologically targeting chemokine signaling pathways. In vivo and in vitro studies are also being performed to determine which cell types are the main sources of chemokines and inflammatory molecules are in the microenvironment.

Based on the clonal evolution theory of cancer formation, a single cell within a tissue gains a cancer-driving mutation and thus a growth advantage. From this expanded cellular mass, another cell gains a new mutation allowing this newly mutated cell to gain new competitive advantage and to expand in number (thus clonal expansion). Another clone then emerges. Eventually all required mutations are gained, and a cancer forms. Consequently, while a primary lesion may harbor divergent subclones, all the subclones within the primary cancer as well as all metastatic growths in secondary organs share at least the very first oncogenic mutation that initiates the primary cancer. However, by tracking genetically marked mammary epithelial cells that suffered the initiating oncogenic mutation—and their neighboring mammary cells that did not-in several mouse models of human breast cancer, we found that genetically unrelated mammary epithelial cells can be colluded by neighboring mutated cells to disseminate, and that they can even undergo de novo tumorigenic transformation and form distant metastases. Therefore, clonally unrelated epithelial cells may contribute to cancer progression and to the heterogeneity of the systemic disease. The non-linear cancer spread has important implications in cancer prevention, treatment, and therapeutic resistance.

Glioblastomas (GBM) are one of the most recalcitrant brain tumors because of their aggressive invasive growth and resistance to therapy. They are highly heterogeneous malignancies at both the molecular and histological levels. Specific histological hallmarks including pseudopalisading necrosis and microvascular proliferation distinguish GBM from lower-grade gliomas, and make GBM one of the most hypoxic as well as angiogenic tumors. These microanatomical compartments present specific niches within the tumor microenvironment that regulate metabolic needs, immune surveillance, survival, invasion as well as cancer stem cell maintenance. Here we review features and functions of the distinct GBM niches, detail the different cell constituents and the functional status of the vasculature, and discuss prospects of therapeutically targeting GBM niche constituents.

Antibiotics, though remarkably useful, can also cause certain adverse effects. We detected that treatment of adult mice with antibiotics decreases hippocampal neurogenesis and memory retention. Reconstitution with normal gut flora (SPF) did not completely reverse the deficits in neurogenesis unless the mice also had access to a running wheel or received probiotics. In parallel to an increase in neurogenesis and memory retention, both SPF-reconstituted mice that ran and mice supplemented with probiotics exhibited higher numbers of Ly6C(hi) monocytes in the brain than antibiotic-treated mice. Elimination of Ly6C(hi) monocytes by antibody depletion or the use of knockout mice resulted in decreased neurogenesis, whereas adoptive transfer of Ly6C(hi) monocytes rescued neurogenesis after antibiotic treatment. We propose that the rescue of neurogenesis and behavior deficits in antibiotic-treated mice by exercise and probiotics is partially mediated by Ly6C(hi) monocytes.

Glioblastoma (GBM) is the most common and aggressive type of primary malignant brain tumor in adults. Despite therapy with maximal safe surgical resection, radiation and temozolomide, prognosis remains poor at 14.6 months. Hence, there is an urgent need for developing novel therapeutic agents. In GBMs, the balance of angiogenic growth factors is skewed toward pro-angiogenesis and VEGF is identified as the key growth factor responsible for neovasculature. Targeting angiogenesis is hypothesized to arrest tumor growth and hence VEGF is an attractive therapeutic target.The purpose of this review is to discuss VEGF pathway inhibitors, their efficacy as monotherapy or in combination with other drugs, the effects on the radiographic response/assessment for GBMs, mechanisms of resistance and associated biomarkers. A short summary of angiogenesis and of the biological characteristics of angiogenesis will also be provided to enhance the understanding of VEGF pathway inhibitors.Therapeutic targeting of VEGF has lead to improvements in progression-free survival in GBM patients without any change in the overall survival. VEGF-targeted therapy remains a promising therapeutic opportunity if improvements in biomarkers, imaging techniques and rational combination therapy are used to help advance the clinical efficacy of this approach.

Within high-grade gliomas, the precise identities and functional roles of stem-like cells remain unclear. In the normal neurogenic niche, ID (Inhibitor of DNA-binding) genes maintain self-renewal and multipotency of adult neural stem cells. Using PDGF- and KRAS-driven murine models of gliomagenesis, we show that high Id1 expression (Id1(high)) identifies tumor cells with high self-renewal capacity, while low Id1 expression (Id1(low)) identifies tumor cells with proliferative potential but limited self-renewal capacity. Surprisingly, Id1(low) cells generate tumors more rapidly and with higher penetrance than Id1(high) cells. Further, eliminating tumor cell self-renewal through deletion of Id1 has modest effects on animal survival, while knockdown of Olig2 within Id1(low) cells has a significant survival benefit, underscoring the importance of non-self-renewing lineages in disease progression.

Medulloblastoma (MB), the most common pediatric brain tumor, has a 70% survival rate but standard treatments often lead to devastating life-long side effects, and recurrence is fatal. MB was classified based on molecular and genetic profiles and resulted in four distinct subgroups. The most common subclass of MB is SHH, which accounts for approximately 30% of cases. This class has been successfully modeled in vivo in murine models, which closely recapitulate human disease, providing a convenient and relevant model system for analyzing the SHH MB subclass in vivo. To better understand the mechanisms of tumor growth and recurrence, recent attention has been focused on determining the composition and role of non-tumor cells comprising the tumor microenvironment (TME). Tumor-associated macrophages (TAM) are a key component of the TME that could have two opposite effects on tumor. TAMs can help tumors to evade the immune system by suppressing other immune cell functions, and contribute to tumor growth by promoting angiogenesis. On the other hand, they could suppress tumor growth and delay tumor development. Recently, it was reported that of the subgroups, human SHH MB has the greatest number of TAMs, as well as increased expression of macrophage-associated genes. However, to date, there are no studies addressing the functional role of TAMs in SHH MB. In this work, we demonstrate a functional role of TAMs in both in vitro and in vivo models. We show that reduction of macrophage numbers leads to increased animal mortality in a murine model of SHH MB. Further investigation of the TME and TAMs in MB has the potential to elucidate immune system involvement in the disease and lead to development of novel treatment options.

Glioblastoma-associated microglia and macrophages/monocytes (GAMs) constitute the most abundant type of immune cells in glioblastoma. To date there is still insufficient knowledge about the expression profiles and activation states of these cells. We have previously performed RNA-Seq and microarray on CD11b+ freshly isolated human and mouse GAMs. Here we combine this data with analysis from published whole tumor TCGA data to identify new myeloid-derived transcripts in glioblastoma. We first re-analyzed our previously published human GAMs RNA-Seq dataset for genes that are at least 4-fold up regulated in comparison to naïve microglia and displayed an absolute log2 expression greater than 7. Subsequently, we queried the TCGA glioblastoma dataset to identify genes that showed a high correlation to the myeloid markers CD68, CD14, and AIF1. We found that the expression of IBSP, FCGBP, MARCO, RNASE1, CTSL, SPP1, and GPNMB significantly correlated with the expression of the different myeloid markers. In addition, the correlation was the highest in the proneural subtype samples, which have previously been shown to harbor the highest percentage of myeloid cells. Three of these genes (Spp1, Ctsl, and Gpnmb) were also highly expressed in murine GAMs. Finally, we performed immunofluorescence stainings for CTSL and GPNMB in human GBM samples and PDGF-driven mouse tumors and could show that both proteins were highly abundant in IBA1+ myeloid cells in both human and mouse samples. Conclusively, we have identified several new myeloid-specific genes in glioblastoma that might pose potential new targets. Subsequent studies will be necessary to evaluate the role of these genes in glioblastoma.

Pediatric high-grade gliomas (pHGG) account for the most cancer-related deaths in children under the age of 19 years old. Recent advances have demonstrated that pHGGs drastically differ from their adult counterparts in terms of genetic and epigenetic alterations, suggesting they may also differ in the constituency of their tumor microenvironment. It is now known tumor associated macrophages (TAMs) can make up 30–40% of the total tumor cell mass in adult high-grade gliomas and play important roles in immune suppression and tumor promotion. This raises the question of whether pHGGs possess a distinct constituency of TAMs due to their unique genetic and epigenetic landscapes. To uncover the composition and behavior of TAMs in pHGG we utilize RCAS/tva, a somatic cell-type specific gene transfer system in which we administer RCAS-PDGFA or RCAS-PDGFB to simulate PDGF receptor activation in immune-competent new-born mice. We found that PDGFB-driven tumors have a significantly lower median survival compared to PDGFA-driven tumors. PDGFB-driven tumors also have increased infiltration of TAMs, made evident by immunohistochemical staining for IBA1. Flow cytometry analysis indicates the increased number of TAMs is due to an increased inflammatory monocyte population, but not due to the microglial population. We hypothesize these findings are attributable to the additional activation of the stromal population by PDGFB, as it can activate both PDGFRα and PDGFRβ while PDGFA only activates PDGFRα. Gene expression analysis indicates that several chemokines, chemokine receptors, macrophage, and immune markers are differentially expressed between PDGFB and -A tumor types. To establish correlations between PDGF signaling and TAM infiltration in human pediatric tumor samples, we stained 37 tumors for IBA1, PDGF-receptors, and PDGF-ligands. A positive correlation exists between high PDGFRb and PDGFB staining with high IBA1. Further studies will be done to discern the effects of increased TAM infiltration and the mechanisms driving enhanced tumor malignancy.

Diffuse intrinsic pontine glioma (DIPG), the most common pediatric brainstem tumor, is associated with a dismal prognosis with almost no survivors within two years of diagnosis. It is unamenable to surgical resection, is not responsive to conventional chemotherapy, and responds only temporarily to radiation therapy (XRT). Recent publications identified carboxy (C)-terminal truncating mutations of PPM1D, which encodes the protein WIP1, in up to 25% of DIPGs. WIP1 is a serine/threonine protein phosphatase that plays an important role in DNA damage response (DDR). Prior publications show that most, but not all, PPM1D C-terminal mutants function in a dominant negative fashion to promote tumor growth in cancer models. We hypothesized that PPM1D mutation promotes DIPG growth, and WIP1 inhibition suppresses tumor proliferation. We further hypothesized that, due to its key role in DDR, WIP1 inhibition enhances the antitumor effects of XRT. Using Sanger sequencing, we identified de novo mutation of PPM1D in the C-terminus of multiple patient-derived DIPG cell lines. We also stably introduced clinically relevant PPM1D mutations, which we identified in DIPGs resected from patients, into a PPM1D wild-type DIPG cell line, DIPG VI, as well as into DIPG cells derived from a DIPG mouse model. Using trypan blue exclusion, bioluminescence, and immunofluorescence detection of markers of proliferation and cell death, in the presence or absence of PPM1D knockdown or pharmacologic WIP1 inhibition, and/or following XRT exposure, we measured proliferation of DIPG VI, DIPG VI L513X, a cell line with stable expression of a mutant PPM1D, and DIPG7, a cell line with a de novo PPM1D mutation. We also assayed proliferation in organotypic brain slice cultures derived from symptomatic immunocompromised mice orthotopically xenografted with DIPG cells and of DIPG cells embedded within the brainstem of organotypic brain slices derived from immunocompetent mice. Finally, we orthotopically xenografted DIPG cells into the early post-natal (P0-2) brainstem of immunodeficient mice, treated mice with vehicle or with a small-molecule WIP1 inhibitor, and measured effects on survival, as well as proliferation in tumor cells post-necropsy. Under cell culture conditions, expression of PPM1D mutants promoted tumor cell proliferation in wild-type PPM1D murine and human DIPG cells. Conversely, PPM1D knockdown significantly suppressed DIPG cell proliferation, especially in PPM1D mutated DIPG cells. Similarly, treatment with a small-molecule WIP1 inhibitor suppressed the growth of PPM1D-mutated, but not PPM1D wild-type DIPG cells, in neurosphere cultures, on immunocompetent organotypic brain slices, and on organotypic brain slices derived from symptomatic, orthotopic, xenografted mice. WIP1 inhibition had similar effects on growth inhibition to XRT alone and augmented the antiproliferative and proapoptotic effects of XRT in vitro. Mice bearing an orthotopic xenograft of PPM1D-mutated human DIPG cells, DIPG7, died of disease earlier than mice xenografted with PPM1D wild-type human DIPG cells, DIPG VI. Treatment of mice bearing orthotopically, xenografted DIPG7 cells with a WIP1 inhibitor via a continuous 14-day infusion into the lateral ventricles resulted in a significant reduction in proliferation of tumor cells. In summary, our results show that C-terminal mutated PPM1D is oncogenic in DIPG, promoting proliferation and reduced survival in vivo. WIP1 inhibition suppresses growth and increases the radiosensitivity of PPM1D-mutated DIPG. These results suggest that WIP1 is a druggable target alone and in combination with XRT in DIPG. Further studies will examine the PPM1D-mediated mechanisms of tumorigenesis and treatment responsiveness in DIPG in order to develop clinically viable treatment paradigms that target PPM1D-mutated tumors. Citation Format: Mwangala P. Akamandisa, Kai Nie, Jing Wen, Rita Nahta, Dolores Hambardzumyan, Robert C. Castellino. Mechanisms of PPM1D-mediated tumorigenesis in diffuse intrinsic pontine glioma (DIPG) [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B05.

Glioblastoma (GBM), or grade IV astrocytoma, is a deadly disease due in part to the high degree of intratumoral heterogeneity that contributes to treatment failures. Previous studies have shown the importance of reactive species balances, partially controlled by the coupling of nitric oxide synthases (NOS) with their cofactor, in maintenance of glioma stem cell (GSC) phenotype as well as survival of cancer cells in general. In this study, we investigated the roles of GTP cyclohydrolase 1 (GCH1), which is the first and rate-limiting enzyme of the pathway producing of NOS cofactor producing pathway, in GBM stem cell phenotypes via redox balances. We found that GCH1 RNA and protein expression were increased in GSCs in comparison to non-GSCs, but that GCH1 was not exclusive to the GSC fraction. Indeed, GCH1 was elevated in GBM in comparison to normal brain. Overexpression of GCH1 in GBM cells increased cell growth in vitro and neurosphere-forming capability and decreased survival in an intracranial GBM mouse model. In contrast, GCH1 knockdown with short hairpin RNA in GBM cells led to growth inhibition in vitro as well as increased survival in animal models. GCH1 increased CD44 expression and was upregulated in the detrimental mesenchymal GBM subtype in which CD44 served as a marker. Mechanistically, we found that the expression of GCH1 increased BH4 production, as well as augmented multiple antioxidant pathways, including the expression of PARK7, was critical for controlling reactive species balance, including suppressing reactive oxygen species production. In silico analyses demonstrated that higher GCH1 levels in glioma patients correlate with higher glioma grade, recurrence and worse survival. Together, our data suggest that upregulation of GCH1 in GSCs promotes tumor maintenance and is a key regulator of reactive oxygen species in GBM, and GCH1 pathway is a potential target for therapy. Citation Format: Anh N. Tran, Kiera Walker, David G. Harrison, Wei Chen, James Mobley, Lauren Hocevar, James R. Hackney, Randee Sedaka, Jennifer Pollock, Matthew S. Goldberg, Dolores Hambardzumyan, Sara J. Cooper, G Yancey Gillespie, Anita B. Hjelmeland. Glioblastoma, cancer stem cells, and reactive species balances: A case for GTP cyclohydrolase 1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 163.

Originally identified as an oncogene activated by amplification in squamous cell carcinomas, several lines of evidence now suggest that squamous cell carcinoma-related oncogene (SCCRO; aka DCUN1D1) may play a role in the pathogenesis of a wide range of human cancers including gliomas. SCCRO's oncogenic function is substantiated by its ectopic expression, resulting in transformation of cells in culture and xenograft formation in nude mice. The aim of this study was to assess the in vivo oncogenicity of SCCRO in a murine model. Ubiquitous expression of SCCRO resulted in early embryonic lethality. Because SCCRO overexpression was detected in human gliomas, its in vivo oncogenic activity was assessed in an established murine glioma model. Conditional expression of SCCRO using a replication-competent ASLV long terminal repeat with splice acceptor/nestin-(tumor virus-A) tv-a model system was not sufficient to induce tumor formation in a wild-type genetic background, but tumors formed with increasing frequency and decreasing latency in facilitated background containing Ink4a deletion alone or in combination with PTEN loss. Ectopic expression of SCCRO in glial progenitor cells resulted in lower-grade gliomas in Ink4a-/- mice, whereas its expression in Ink4a-/-/PTEN-/- background produced high-grade glioblastoma-like lesions that were indistinguishable from human tumors. Expression of SCCRO with platelet-derived growth factor-beta (PDGF-β) resulted in an increased proportion of mice forming glioblastoma-like tumors compared with those induced by PDGF-β alone. This work substantiates SCCRO's function as an oncogene by showing its ability to facilitate malignant transformation and carcinogenic progression in vivo and supports a role for SCCRO in the pathogenesis of gliomas and other human cancers.

Brainstem gliomas (BSG) are a rare group of central nervous system tumors that arise mostly in children and usually portend a particularly poor prognosis. We report the development of a genetically engineered mouse model of BSG using the RCAS/tv-a system and its implementation in preclinical trials. Using immunohistochemistry, we found that platelet-derived growth factor (PDGF) receptor α is overexpressed in 67% of pediatric BSGs. Based on this observation, we induced low-grade BSGs by overexpressing PDGF-B in the posterior fossa of neonatal nestin tv-a mice. To generate high-grade BSGs, we overexpressed PDGF-B in combination with Ink4a-ARF loss, given that this locus is commonly lost in high-grade pediatric BSGs. We show that the likely cells of origin for these mouse BSGs exist on the floor of the fourth ventricle and cerebral aqueduct. Irradiation of these high-grade BSGs shows that although single doses of 2, 6, and 10 Gy significantly increased the percent of terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling (TUNEL)–positive nuclei, only 6 and 10 Gy significantly induce cell cycle arrest. Perifosine, an inhibitor of AKT signaling, significantly induced TUNEL-positive nuclei in this high-grade BSG model, but in combination with 10 Gy, it did not significantly increase the percent of TUNEL-positive nuclei relative to 10 Gy alone at 6, 24, and 72 hours. Survival analysis showed that a single dose of 10 Gy significantly prolonged survival by 27% (P = 0.0002) but perifosine did not (P = 0.92). Perifosine + 10 Gy did not result in a significantly increased survival relative to 10 Gy alone (P = 0.23). This PDGF-induced BSG model can serve as a preclinical tool for the testing of novel agents. Cancer Res; 70(6); 2548–57

SummaryeNOS expression is elevated in human glioblastomas and correlated with increased tumor growth and aggressive character. We investigated the potential role of nitric oxide (NO) activity in the perivascular niche (PVN) using a genetic engineered mouse model of PDGF-induced gliomas. eNOS expression is highly elevated in tumor vascular endothelium adjacent to perivascular glioma cells expressing Nestin, Notch, and the NO receptor, sGC. In addition, the NO/cGMP/PKG pathway drives Notch signaling in PDGF-induced gliomas in vitro, and induces the side population phenotype in primary glioma cell cultures. NO also increases neurosphere forming capacity of PDGF-driven glioma primary cultures, and enhances their tumorigenic capacity in vivo. Loss of NO activity in these tumors suppresses Notch signaling in vivo and prolongs survival of mice. This mechanism is conserved in human PDGFR amplified gliomas. The NO/cGMP/PKG pathway's promotion of stem cell-like character in the tumor PVN may identify therapeutic targets for this subset of gliomas.

During development, proliferation of cerebellar granule neuron precursors (CGNP), candidate cells-of-origin for the pediatric brain tumor medulloblastoma, requires signaling by Sonic hedgehog (Shh) and insulin-like growth factor (IGF), the pathways of which are also implicated in medulloblastoma. One of the consequences of IGF signaling is inactivation of the mammalian target of rapamycin (mTOR)–suppressing tuberous sclerosis complex (TSC), comprised of TSC1 and TSC2, leading to increased mRNA translation. We show that mice, in which TSC function is impaired, display increased mTOR pathway activation, enhanced CGNP proliferation, glycogen synthase kinase-3α/β (GSK-3α/β) inactivation, and cytoplasmic localization of the cyclin-dependent kinase inhibitor p27Kip1, which has been proposed to cause its inactivation or gain of oncogenic functions. We observed the same characteristics in wild-type primary cultures of CGNPs in which TSC1 and/or TSC2 were knocked down, and in mouse medulloblastomas induced by ectopic Shh pathway activation. Moreover, Shh-induced mouse medulloblastomas manifested Akt-mediated TSC2 inactivation, and the mutant TSC2 allele synergized with aberrant Shh signaling to increase medulloblastoma incidence in mice. Driving exogenous TSC2 expression in Shh-induced medulloblastoma cells corrected p27Kip1 localization and reduced proliferation. GSK-3α/β inactivation in the tumors in vivo and in primary CGNP cultures was mTOR-dependent, whereas p27Kip1 cytoplasmic localization was regulated upstream of mTOR by TSC2. These results indicate that a balance between Shh mitogenic signaling and TSC function regulating new protein synthesis and cyclin-dependent kinase inhibition is essential for the normal development and prevention of tumor formation or expansion. [Cancer Res 2009;69(18):7224–34]

SummaryIn normal brain, the side population (SP) phenotype is generated by ABC transporter activity and identifies stem cell and endothelial cell subpopulations by dye exclusion. By drug efflux, the ABCG2 transporter provides chemoresistance in stem cells and contributes to the blood brain barrier (BBB) when active in endothelial cells. We investigated the SP phenotype of mouse and human gliomas. In glioma endothelial cells, ABC transporter function is impaired, corresponding to disruption of the BBB in these tumors. By contrast, the SP phenotype is increased in nonendothelial cells that form neurospheres and are highly tumorigenic. In this cell population, Akt, but not its downstream target mTOR, regulates ABCG2 activity, and loss of PTEN increases the SP. This Akt-induced ABCG2 activation results from its transport to the plasma membrane. Temozolomide, the standard treatment of gliomas, although not an ABCG2 substrate, increases the SP in glioma cells, especially in cells missing PTEN.

Several recent reports have provided evidence that cancer is initiated by a rare fraction of cells called "cancer stem cells" which are multipotent, self-renewing subset of the tumor. However, several issues regarding the biology and techniques of isolating these cells from solid tumors remain to be clarified. In addition, experimental data supports two possibilities for glioma cell of origin. First, that stem cells or early progenitors are transformed and show variable differentiation of their progeny during tumor development. Second, that more differentiated glia are transformed by genetic events that lead to a loss of differentiation maintenance. In human gliomas, these two theories are not mutually exclusive. In this review we will summarize both theories, and highlight outstanding issues that remain to be resolved.