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The mainstay of treatment for adult patients with gliomas, glioneuronal and neuronal tumors consists of combinations of surgery, radiotherapy, and chemotherapy. For many systemic cancers, targeted treatments are a part of the standard of care, however, the predictive significance of most of these targets in central nervous system (CNS) tumors remains less well-studied. Despite that, there is increasing use of advanced molecular diagnostics that identify potential targets, and tumor-agnostic regulatory approvals on targets also present in CNS tumors have been granted. This raises the question of when and for which targets it is meaningful to test in adult patients with CNS tumors. This evidence-based guideline reviews the evidence available for targeted treatment for alterations in the RAS/MAPK pathway (BRAF, NF1), in growth factor receptors (EGFR, ALK, fibroblast growth factor receptor (FGFR), neurotrophic tyrosine receptor kinase (NTRK), platelet-derived growth factor receptor alpha, and ROS1), in cell cycle signaling (CDK4/6, MDM2/4, and TSC1/2) and altered genomic stability (mismatch repair, POLE, high tumor mutational burden (TMB), homologous recombination deficiency) in adult patients with gliomas, glioneuronal and neuronal tumors. At present, targeted treatment for BRAF p.V600E alterations is to be considered part of the standard of care for patients with recurrent gliomas, pending regulatory approval. For approved tumor agnostic treatments for NTRK fusions and high TMB, the evidence for efficacy in adult patients with CNS tumors is very limited, and treatment should preferably be given within prospective clinical registries and trials. For targeted treatment of CNS tumors with FGFR fusions or mutations, clinical trials are ongoing to confirm modest activity so far observed in basket trials. For all other reviewed targets, evidence of benefit in CNS tumors is currently lacking, and testing/treatment should be in the context of available clinical trials.

Background Glioblastoma (GBM) is an aggressive brain cancer that typically results in death in the first 15 months after diagnosis. There have been limited advances in finding new treatments for GBM. In this study, we investigated molecular differences between patients with extremely short (≤ 9 months, Short term survivors, STS) and long survival (≥ 36 months, Long term survivors, LTS). Methods Patients were selected from an in-house cohort (GLIOTRAIN-cohort), using defined inclusion criteria (Karnofsky score > 70; age Results Transcriptomic analysis of tumour samples identified cilium gene signatures as enriched in LTS. Moreover, Immunohistochemical analysis confirmed the presence of cilia in the tumours of LTS. Notably, reverse phase protein array analysis (RPPA) demonstrated increased phosphorylated GAB1 (Y627), SRC (Y527), BCL2 (S70) and RAF (S338) protein expression in STS compared to LTS. Next, we identified 25 unique master regulators (MR) and 13 transcription factors (TFs) belonging to ontologies of integrin signalling and cell cycle to be upregulated in STS. Conclusion Overall, comparison of STS and LTS GBM patients, identifies novel biomarkers and potential actionable therapeutic targets for the management of GBM. Graphical abstract

In glioblastoma (GBM), tumour-associated microglia/macrophages (TAMs) represent the major cell type of the stromal compartment and contribute to tumour immune escape mechanisms. Thus, targeting TAMs is emerging as a promising strategy for immunotherapy. However, TAM heterogeneity and metabolic adaptation along GBM progression represent critical features for the design of effective TAM-targeted therapies. Here, we comprehensively study the cellular and molecular changes of TAMs in the GL261 GBM mouse model, combining single-cell RNA-sequencing with flow cytometry and immunohistological analyses along GBM progression and in the absence of Acod1 (also known as Irg1), a key gene involved in the metabolic reprogramming of macrophages towards an anti-inflammatory phenotype. Similarly to patients, we identify distinct TAM profiles, mainly based on their ontogeny, that reiterate the idea that microglia- and macrophage-like cells show key transcriptional differences and dynamically adapt along GBM stages. Notably, we uncover decreased antigen-presenting cell features and immune reactivity in TAMs along tumour progression that are instead enhanced in Acod1-deficient mice. Overall, our results provide insight into TAM heterogeneity and highlight a novel role for Acod1 in TAM adaptation during GBM progression. publishedVersion

Multiomic single nucleus RNA- and ATACseq profiling reveals regulators of glioma cell state diversity. The extensive intra- and intertumoral heterogeneity observed in glioma reflects the resistance to therapy and poor prognosis observed clinically. Single-cell sequencing studies have highlighted that glioma heterogeneity reflects the co-existence of cell subpopulations with distinct cell states. Prior studies have also shown that EGFR-amplifying extrachromosomal DNA (ecDNA) elements in IDH-wild-type gliomas can contribute to heterogeneity by driving oncogene amplification through long range chromatin contacts. However, single cell studies have largely focused on analyses of transcriptional profiles, and the epigenetic mechanisms underlying the contribution of ecDNA elements to tumor cell state diversity remain poorly understood. To further our understanding of the regulatory programs that contribute to transcriptional diversity and mediate the distribution of tumor cell states, we profiled primary-recurrent tumor pairs from 18 patient samples with multiomic single-nucleus RNA- and ATACseq, resulting in 86,135 cells identified with linked chromatin accessibility and gene expression profiles. Integrative clustering of the tumor cells identified tumor cell states ranging from a stem-like to differentiated- phenotype that were also associated with differences in chromatin accessibility and inferred transcription factor binding activity. Analyses of chromatin accessibility resulted in the identification of ecDNA, and integrative clustering of ecDNA+ cells highlighted distinct cell states with increased copy number burden, oncogene amplification, and differential chromatin accessibility. These results suggest that a better understanding of extrachromosomal contributions to tumor diversity would aid in development of more efficient therapies.

BACKGROUND Numerous epidemiological studies have highlighted the protective role of immunoglobulin E-mediated allergic diseases on glioblastoma (GBM) susceptibility and prognosis. However, the mechanistic explanations behind these phenomena remain unexplored. Our objective was to set up a preclinical model and investigate the mechanisms underlying such protection to improve our understanding of the crosstalk between immune system and brain tumor development. MATERIAL AND METHODS A mouse model of allergic airway inflammation (AAI) induced by repeated nasal instillation of House Dust Mite extract was initiated before intracranial implantation of GL261 glioma cells, in both immunocompetent (C57BL/6) and immunodeficient (RAG-KO) mice. Tumor take and tumor growth were monitored by MRI. Central (microglia) and peripheral (spleen, bone marrow) immune cells were characterized by flow cytometry. The response of microglia was further assessed by RNA sequencing. Impact of candidate genes on patient survival was characterized by Cox regression analysis using data from TCGA and CGGA. RESULTS Following AAI induction in C57BL/6 mice, engraftment of GL261 cells in the brain was delayed and tumor growth rate was reduced. This correlated with an increase in survival of the mice and was accompanied by increased effector memory T-cells in the circulation. Of note, the survival benefit was lost in RAG-KO mice devoid of adaptive immunity. At the level of the brain, we observed enhanced secretion of TNFα and IL6 in microglia ex vivo. AAI induced a transcriptional reprogramming of microglia towards a pro-inflammatory-like state. We identified an allergy-related microglia gene signature that is associated with improved prognosis of glioma patients. CONCLUSION Our results demonstrate that AAI limits both tumor take and GBM progression in mice, providing a preclinical model to study the role of allergic inflammation in GBM susceptibility and prognosis, respectively. At the functional level, we identify a potentiation of microglial and adaptive anti-tumoral immunity. Further investigations are warranted to shed light on the reciprocal crosstalk between microglial reprogramming and peripheral immunity in the context of allergies and brain tumors.

BACKGROUND Glioblastomas are among the most heterogeneous tumors, which hampers patient stratification and development of effective therapies. Glioblastomas create a dynamic ecosystem, where heterogeneous tumor cells interact with the tumor microenvironment to establish different niches. Upon tumor growth, Glioblastoma cells manifest remarkable plasticity and respond flexibly to selective pressures by transiting towards states favorable to the new tumor microenvitonment. How this phenotypic plasticity contributes to treatment resistance is currently less clear. The exact nature of treatment resistant, tolerant and sensitive Glioblastoma cells remains unresolved. Further studies at the single cell level are needed to reveal transient and long-term signatures of the resistant states. MATERIAL AND METHODS To investigate long-term phenotypic changes upon treatment at the single cell level we performed single cell RNA-seq (scRNA-seq) on the longitudinal patient-derived xenograft (PDOX) models derived from Glioblastoma patient tumors prior and after the standard-of-care treatment. In addition, direct treatment of PDOXs with temozolomide combined with scRNA-seq allowed revealing short-term transcriptomic changes both in tumor cells and in the mouse-derived cells forming tumor microenvironment. Advanced computational algorithms, including reference-free deconvolution methods, were applied to reveal treatment resistance signatures and master regulators of the identified treatment-resistant subpopulations. RESULTS We show that PDOX models recapitulate all the major cell types and transcriptional programs reported in Glioblastoma patient samples, providing clinically relevant models for investigating treatment resistance signatures of tumor cells and associated tumor microenvironment. Analysis of treatment naïve and treated Glioblastomas at the single cell level revealed presence of pre-existing treatment resistant states as well as newly established resistant subpopulatons. Certain transcriptomic changes are preserved long term, regardless of the lack of genetic evolution of the tumor cells. CONCLUSION Phenotypic plasticity is an important factor contributing to resistance mechanisms in Glioblastoma. Key molecular regulators of tumor cell plasticity towards treatment resistance states represent novel targets for future combinatory treatments.

Background Women represent an increasing proportion of the overall workforce in medicine but are underrepresented in leadership roles. Methods To explore gender inequalities and challenges in career opportunities, a web-based survey was conducted among the membership of the European Association of Neuro-Oncology and the Brain Tumor Group of the European Organisation for Research and Treatment of Cancer. Results A total of 228 colleagues responded to the survey: 129 women (median age 45 years; range, 25-66 years) and 99 men (median age 48 years; range, 24-81 years); 153 participants (67%) were married and 157 participants (69%) had at least 1 child. Women less often declared being married (60% vs 77%, P = .007) or having a child (63% vs 77%, P = .024). Men more frequently had a full-time position (88% vs 75%, P = .036). Women and men both perceived an underrepresentation of women in leadership positions. Half of participants agreed that the most important challenges for women are leading a team and obtaining a faculty position. Fewer women than men would accept such a position (42% vs 56%). The main reasons were limited time for career and an inappropriate work and life balance. Women specifically cited negative discrimination, limited opportunities, and lack of self-confidence. Discrimination of women at work was perceived by 64% of women vs 47% of men (P = .003). Conclusion Women are perceived as experiencing more difficulties in acquiring a leadership position. Personal preferences may account for an underrepresentation of women in leadership positions, but perceived gender inequalities extend beyond disparities of access to leadership.

Glioblastoma represents the most common primary malignancy of the central nervous system in adults and remains a largely incurable disease. The elucidation of disease subtypes based on mutational profiling, gene expression and DNA methylation has so far failed to translate into improved clinical outcomes. However, new knowledge emerging from the subtyping effort in the IDH-wild-type setting may provide directions for future precision therapies. Here, we review recent learnings in the field, and further consider how tumour microenvironment differences across subtypes may reveal novel contexts of vulnerability. We discuss recent treatment approaches and ongoing trials in the IDH-wild-type glioblastoma setting, and propose an integrated discovery stratagem incorporating multi-omics, single-cell technologies and computational approaches.

Purpose Glioblastoma (GBM) remains an incurable disease despite extensive treatment with surgical resection, irradiation, and temozolomide. In line with many other forms of aggressive cancers, GBM is currently under consideration as a target for immunotherapy. However, GBM tends to be nonimmunogenic and exhibits a microenvironment with few or no effector T cells, a relatively low nonsynonymous somatic mutational load, and a low predicted neoantigen burden. GBM also exploits a multitude of immunosuppressive strategies. Methods and Materials A number of immunotherapeutic approaches have been tested with disappointing results. A rationale exists to combine immunotherapy and radiation therapy, which can induce an immunogenic form of cell death with T-cell activation and tumor infiltration. Results Various immunotherapy agents, including immune checkpoint modulators, transforming growth factor beta receptor inhibitors, and indoleamine-2,3-dioxygenase inhibitors, have been evaluated with irradiation in preclinical GBM models, with promising results, and are being further tested in clinical trials. Conclusions This review aims to present the basic rationale behind this emerging complementary therapeutic approach in GBM, appraise the current preclinical and clinical data, and discuss the future challenges in improving the antitumor immune response.

Inevitable tumor recurrence and a poor median survival are frustrating reminders of the inefficacy of our current standard of care for patients with newly diagnosed glioblastoma (GBM), which includes surgery followed by radiotherapy and chemotherapy with the DNA alkylating agent temozolomide. Because resistance to genotoxic damage is achieved mainly through execution of the DNA damage response (DDR) and DNA repair pathways, knowledge of the changes in DNA repair and cell-cycle gene expression that occur during tumor development might help identify new targets and improve treatment. Here, we performed a gene expression analysis targeting components of the DNA repair and cell-cycle machineries in cohorts of paired tumor samples (i.e., biopsies from the same patient obtained at the time of primary tumor operation and at recurrence) from patients treated with radiotherapy or radiotherapy plus temozolomide. We identified and validated a 27-gene signature that resulted in the classification of GBM specimens into three groups, two of which displayed inverse expression profiles. Each group contained primary and recurrent samples, and the tumor at relapse frequently displayed a gene expression profile different from that of the matched primary biopsy. Within the groups that exhibited opposing gene expression profiles, the expression pattern of the gene signature at relapse was linked to progression-free survival. We provide experimental evidence that our signature exposes group-specific vulnerabilities against genotoxicants and inhibitors of the cell cycle and DDR, with the prospect of personalized therapeutic strategies. Significance: These findings suggest that classification of GBM tumors based on a DNA repair and cell-cycle gene expression signature exposes vulnerabilities to standard-of-care therapies and offers the potential for personalized therapeutic strategies.

BACKGROUND: Glioblastoma (GBM) is the most common primary brain tumor in adults with a median survival of approximately 15 months; therefore, more effective treatment options for GBM are required. To identify new drugs targeting GBMs, we performed a high-throughput drug screen using patient-derived neurospheres cultured to preferentially retain their glioblastoma stem cell (GSC) phenotype. METHODS: High-throughput drug screening was performed on GSCs followed by a dose-response assay of the 5 identified original “hits.” A PI3K/mTOR dependency to a proteasome inhibitor (carfilzomib), was confirmed by genetic and pharmacologic experiments. Proteasome Inhibition Response Signatures were derived from proteomic and bioinformatic analysis. Molecular mechanism of action was determined using three-dimensional (3D) GBM-organoids and preclinical orthotopic models. RESULTS: We found that GSCs were highly sensitive to proteasome inhibition due to an underlying dependency on an increased protein synthesis rate, and loss of autophagy, associated with PTEN loss and activation of the PI3K/mTOR pathway. In contrast, combinatory inhibition of autophagy and the proteasome resulted in enhanced cytotoxicity specifically in GSCs that did express PTEN. Finally, proteasome inhibition specifically increased cell death markers in 3D GBM-organoids, suppressed tumor growth, and increased survival of mice orthotopically engrafted with GSCs. As perturbations of the PI3K/mTOR pathway occur in nearly 50% of GBMs, these findings suggest that a significant fraction of these tumors could be vulnerable to proteasome inhibition. CONCLUSIONS: Proteasome inhibition is a potential synthetic lethal therapeutic strategy for GBM with proteasome addiction due to a high protein synthesis rate and autophagy deficiency.

Patient-derived cancer models are essential tools for studying tumor biology and for preclinical interventions. Although numerous clinical cancer trials are being conducted, many fail due to inappropriate selection of compounds at the preclinical stage. Therefore, better preclinical models are crucial for predicting successful clinical impact. Orthotropic patient-derived xenograft (PDOX) models are of particular importance for brain cancers, as they allow to better recapitulate the brain tumor environment and the blood brain barrier. We created a large collection of PDOXs from primary and recurrent gliomas with and without mutations in IDH1. PDOX models were based on 3D organoids, derived from mechanically minced patient material. Organoids were implanted in the brain of immunodeficient mice and further propagated by serial intracranial transplantations. High grade glioma PDOX models, starting with viable patient-derived organoids, have generally a high tumor take rate, a reproducible phenotype and tumor development time. PDOXs retain histopathological, genetic, epigenetic and transcriptomic features of patient tumors with no mouse-specific clonal evolution. Longitudinal PDOX models confirmed limited evolution of gliomas upon treatment observed in patient tumors. PDOX-derived standardized tumor organoid cultures enabled assessment of drug responses, which were validated in mice. PDOXs showed clinically relevant responses to Temozolomide and to targeted treatments such as EGFR and CDK4/6 inhibitors in (epi)genetically defined groups, according to MGMT promoter and EGFR/CDK status respectively. These data indicate that glioma PDOXs represent clinically relevant avatars for personalized treatment. The use of these models should lead to a more realistic evaluation of the efficacy of novel drugs, thereby increasing the success of clinical studies.

BACKGROUND: High-grade gliomas likely remodel the metabolic machinery to meet the increased demands for amino acids and nucleotides during rapid cell proliferation. Glycine, a non-essential amino acid and intermediate of nucleotide biosynthesis, may increase with proliferation. Non-invasive measurement of glycine by magnetic resonance spectroscopy (MRS) was evaluated as an imaging biomarker for assessment of tumor aggressiveness. METHODS: We measured glycine, 2-hydroxyglutarate (2HG), and other tumor-related metabolites in 35 glioma patients using an MRS sequence tailored for co-detection of glycine and 2HG in gadolinium-enhancing and non-enhancing tumor regions on 3T MRI. Glycine and 2HG concentrations as measured by MRS were correlated with tumor cell proliferation (MIB-1 labeling index), expression of mitochondrial serine hydroxymethyltransferase (SHMT2), and glycine decarboxylase (GLDC) enzymes, and patient overall survival. RESULTS: Elevated glycine was strongly associated with presence of gadolinium enhancement, indicating more rapidly proliferative disease. Glycine concentration was positively correlated with MIB-1, and levels higher than 2.5 mM showed significant association with shorter patient survival, irrespective of isocitrate dehydrogenase status. Concentration of 2HG did not correlate with MIB-1 index. A high glycine/2HG concentration ratio, >2.5, was strongly associated with shorter survival (P

Epithelial-to-mesenchymal transition (EMT) is supposed to be responsible for increased invasion and metastases in epithelial cancer cells. The activation of EMT genes has further been proposed to be important in the process of malignant transformation of primary CNS tumors. Since the cellular source and clinical impact of EMT factors in primary CNS tumors still remain unclear, we aimed at deciphering their distribution in vivo and clinico-pathological relevance in human gliomas. We investigated 350 glioma patients for the expression of the key EMT factors SLUG and TWIST by immunohistochemistry and immunofluorescence related to morpho-genetic alterations such as EGFR-amplification, IDH-1 (R132H) mutation and 1p/19q LOH. Furthermore, transcriptional cluster and survival analyses were performed. Our data illustrate that SLUG and TWIST are overexpressed in gliomas showing vascular proliferation such as pilocytic astrocytomas and glioblastomas. EMT factors are exclusively expressed by non-neoplastic pericytes/vessel-associated mural cells (VAMCs). They are not associated with patient survival but correlate with pericytic/VAMC genes in glioblastoma cluster analysis. In summary, the upregulation of EMT genes in pilocytic astrocytomas and glioblastomas reflects the level of activation of pericytes/VAMCs in newly formed blood vessels. Our results underscore that the negative prognostic potential of the EMT signature in the group of diffuse gliomas of WHO grade II-IV does most likely not derive from glioma cells but rather reflects the degree of proliferating mural cells thereby constituting a potential target for future alternative treatment approaches.

Leucine-rich repeats and immunoglobulin-like domains containing protein 1 (LRIG1) is an endogenous feedback regulator of receptor tyrosine kinases (RTKs) and was recently shown to inhibit growth of different types of malignancies. Additionally, this multifaceted RTK inhibitor was reported to be a tumor suppressor, a stem cell regulator, and a modulator of different cellular phenotypes. This mini-review provides a concise and up-to-date summary about the known functions of LRIG1 and its related family members, with a special emphasis on underlying molecular mechanisms and the opportunities for harnessing its therapeutic potential against cancer.

Glioblastoma (GBM), the most frequent and aggressive malignant primary brain tumor, is characterized by a highly invasive growth. In our previous study we showed that overexpression of Carboxypeptidase E (CPE) mitigated glioma cell migration. In the present study we aimed at deciphering the regulatory mechanisms of the secreted form of CPE (sCPE). By transcriptome analysis and inhibition of signaling pathways involved in the regulation of cell growth and motility, we discovered that overexpression of sCPE was accompanied by differential regulation of mRNAs connected to the motility-associated networks, among others FAK, PAK, Cdc42, integrin, STAT3 as well as TGF-β. Especially SLUG was downregulated in sCPE-overexpressing glioma cells, paralleled by reduced expression of matrix-metalloproteinases (MMP) and, in consequence, by decreased cell migration. Expression of SLUG was regulated by ERK since inhibition of ERK reverted sCPE-mediated SLUG downregulation and enhanced cell motility. In a mouse glioma model, overexpression of sCPE significantly prolonged survival. Our results implicate a novel role for sCPE that mainly affects the expression of motility-associated genes via several signal pathways.

Simple Summary Glioblastoma (GBM) is the most aggressive brain tumor and most resistant to therapy. The identification of novel predictive biomarkers or targets to counteract chemoresistance, requires a better understanding of the GBM primary response to therapy. The aim of our study was to assess the molecular response of GBM to the standard of care chemotherapy by temozolomide (TMZ). We established a comprehensive map of gene expression changes after treatment and discovered that GBM cells elicit a coordinated gene expression program after chemotherapy that differs between sensitive and resistant cells. We found that a novel class of genes expressed as long non-coding RNAs (lncRNAs) is involved in gene regulatory circuits in GBM and could represent novel markers of GBM patient prognosis. By shedding light on the involvement of the non-coding genome in GBM, our results may provide new mechanistic insight on lncRNAs and their importance in chemoresistance. Abstract Resistance to chemotherapy by temozolomide (TMZ) is a major cause of glioblastoma (GBM) recurrence. So far, attempts to characterize factors that contribute to TMZ sensitivity have largely focused on protein-coding genes, and failed to provide effective therapeutic targets. Long noncoding RNAs (lncRNAs) are essential regulators of epigenetic-driven cell diversification, yet, their contribution to the transcriptional response to drugs is less understood. Here, we performed RNA-seq and small RNA-seq to provide a comprehensive map of transcriptome regulation upon TMZ in patient-derived GBM stem-like cells displaying different drug sensitivity. In a search for regulatory mechanisms, we integrated thousands of molecular associations stored in public databases to generate a background “RNA interactome”. Our systems-level analysis uncovered a coordinated program of TMZ response reflected by regulatory circuits that involve transcription factors, mRNAs, miRNAs, and lncRNAs. We discovered 22 lncRNAs involved in regulatory loops and/or with functional relevance in drug response and prognostic value in gliomas. Thus, the investigation of TMZ-induced gene networks highlights novel RNA-based predictors of chemosensitivity in GBM. The computational modeling used to identify regulatory circuits underlying drug response and prioritizing gene candidates for functional validation is applicable to other datasets.

Malignant brain tumors remain uniformly fatal, even with the best-to-date treatment. For Glioblastoma (GBM), the most severe form of brain cancer in adults, the median overall survival is roughly over a year. New therapeutic options are urgently needed, yet recent clinical trials in the field have been largely disappointing. This is partially due to inappropriate preclinical model systems, which do not reflect the complexity of patient tumors. Furthermore, clinically relevant patient-derived models recapitulating the immune compartment are lacking, which represents a bottleneck for adequate immunotherapy testing. Emerging 3D organoid cultures offer innovative possibilities for cancer modeling. Here, we review available GBM organoid models amenable to a large variety of pre-clinical applications including functional bioassays such as proliferation and invasion, drug screening, and the generation of patient-derived orthotopic xenografts (PDOX) for validation of biological responses in vivo. We emphasize advantages and technical challenges in establishing immunocompetent ex vivo models based on co-cultures of GBM organoids and human immune cells. The latter can be isolated either from the tumor or from patient or donor blood as peripheral blood mononuclear cells (PBMCs). We also discuss the challenges to generate GBM PDOXs based on humanized mouse models to validate efficacy of immunotherapies in vivo. A detailed characterization of such models at the cellular and molecular level is needed to understand the potential and limitations for various immune activating strategies. Increasing the availability of immunocompetent GBM models will improve research on emerging immune therapeutic approaches against aggressive brain cancer.

BACKGROUND High grade glioma (HGG) patients develop resistance to standard treatment leading to disease progression and limited life expectancy. Recent advances in the molecular characterisation of treatment-naïve HGGs based on next generation sequencing and DNA methylation analyses have led to a better delineation of HGG-subtypes and identification of distinct genomic abnormalities opening opportunities for personalized treatment strategies. METHODS We collected 300 fresh glioma specimen with approximately 100 longitudinal samples of initial and recurrent tumors from 43 matched patients. We succeeded in generating a live-biobank of HGG patient-derived orthotopic xenografts (PDOX) and 3D tumor organoids that neatly recapitulates the mutational spectrum including structural DNA variations and methylation-based subtypes of gliomas. A highlight is the generation of 19 PDOXs of paired initial and relapse HGGs from 9 glioma patients, enabling high-throughput drug screens. We performed comprehensive molecular profiling using arrayCGH, DNA-methylation and targeted DNA sequencing on patient specimen and their derivatives, 3D tumor organoids and PDOXs. RESULTS Detailed analysis of the paired longitudinal samples indicated that PDOXs closely recapitulate the evolutionary trajectory of the parental tumors. Furthermore, targeted genomic sequencing of paired HGGs suggests that relapse tumors also accumulate somatic mutations in epigenetic effectors. Based on patient-derived material we carried out drug response screening on 3D tumor organoids using a compound library matching the majority of genes that were assessed with targeted sequencing. Differential drug responses between initial and recurrent tumors were observed and the prevailing primary drug response profiles were essentially recapitulad in the relapse setting. CONCLUSIONS Response assessment of treatment-naïve gliomas and their recurrences provides crucial information on the differential sensitivity between initial and relapsed HGGs and offers novel personalized therapeutic options for the relapse setting. Furthermore, in depth correlation of the profiled somatic molecular landscape with drug response will enable pharmacogenomic predictions of potential inhibitors in the clinical setting.

INTRODUCTION Aberrant regulation of receptor tyrosine kinase (RTK) activity is characteristic of Glioblastoma (GBM). However, RTK-based targeted therapies have been largely unsuccessful in GBM patients, partially due to the complexity and redundance of RTK signaling. LRIG1 (Leucine-rich Repeats and ImmunoGlobulindomains protein 1) is known as an endogenous inhibitor of epidermal growth factor receptor (EGFR) during health and disease, however its mechanism of action is poorly understood. We previously showed that the soluble form of LRIG1 potently inhibits of GBM growth in vivo, irrespective of EGFR expression level and status, suggesting the involvement of other RTKs. Here, we aimed to shed light on the molecular mechanisms underlying its anti-cancer activity. MATERIAL AND METHODS We generated a recombinant human soluble LRIG1 protein by expressing LRIG1 ectodomain in insect cells via baculovirus infection and subsequent His-tag purification. rh-sLRIG1 was applied in the medium of classical GBM cell lines, patient-derived GBM stem-like cells and patient-derived 3D tumor organoids. Using different cell-based assays, cell proliferation, invasion, cell morphology, as well as protein expression and protein-protein interactions were investigated. RESULTS We find that recombinant sLRIG1 efficiently reduces proliferation, invasion and viability of GBM cells and patient-derived organoids, and modulates cytoskeleton proteins and cell shape. In line with previous data, the effect of recombinant sLRIG1 is independent of EGFR expression. Interestingly sLRIG1 regulates several RTKs by direct protein downregulation, including AXL, while EGFR expression is not affected. At the molecular level, we find that sLRIG1 interferes with AXL dimerization, while no protein interaction with EGFR is detected. CONCLUSION We identify AXL as a novel LRIG1 target and provide evidence that sLRIG1-mediated RTK downregulation requires direct protein-protein interaction. These data pave the way for a potential therapeutic application of recombinant sLRIG1 in the inhibition of growth factor signaling in GBM.

Background Invasion and angiogenesis are major hallmarks of glioblastoma (GBM) growth. While invasive tumor cells grow adjacent to blood vessels in normal brain tissue, tumor cells within neovascularized regions exhibit hypoxic stress and promote angiogenesis. The distinct microenvironments likely differentially affect metabolic processes within the tumor cells. Methods In the present study, we analyzed gene expression and metabolic changes in a human GBM xenograft model that displayed invasive and angiogenic phenotypes. In addition, we used glioma patient biopsies to confirm the results from the xenograft model. Results We demonstrate that the angiogenic switch in our xenograft model is linked to a proneural-to-mesenchymal transition that is associated with upregulation of the transcription factors BHLHE40, CEBPB, and STAT3. Metabolic analyses revealed that angiogenic xenografts employed higher rates of glycolysis compared with invasive xenografts. Likewise, patient biopsies exhibited higher expression of the glycolytic enzyme lactate dehydrogenase A and glucose transporter 1 in hypoxic areas compared with the invasive edge and lower-grade tumors. Analysis of the mitochondrial respiratory chain showed reduction of complex I in angiogenic xenografts and hypoxic regions of GBM samples compared with invasive xenografts, nonhypoxic GBM regions, and lower-grade tumors. In vitro hypoxia experiments additionally revealed metabolic adaptation of invasive tumor cells, which increased lactate production under long-term hypoxia. Conclusions The use of glycolysis versus mitochondrial respiration for energy production within human GBM tumors is highly dependent on the specific microenvironment. The metabolic adaptability of GBM cells highlights the difficulty of targeting one specific metabolic pathway for effective therapeutic intervention.

Intratumoral heterogeneity is one of the major barriers in the treatment of many tumor types. In glioblastoma (GBM) – the most aggressive brain tumor - survival of patients following standard therapy has stagnated to an average of 14 months, largely due to the inherent heterogeneity and phenotypic plasticity. Patient-derived orthotopic xenografts (PDOX) are important tools for preclinical cancer studies. We have shown that they recapitulate histological and molecular features of patient tumors, thus producing more clinically relevant study outcomes when compared to other preclinical models. To understand the impact of treatment on intratumoral heterogeneity and interactions of tumor cells with the microenvironment, we applied single-cell RNA-seq in GBM PDOX models generated from naive and treatment exposed patient tumors. Here we show that PDOX models recapitulate all the major cell types and transcriptional programs reported in GBM patient samples. We demonstrate that GBM tumor cells occur in distinct phenotypic states dictated by microenvironmental cues and treatment-induced pressure. Non-neoplastic cells present within xenografts undergo transcriptomic adaptation similar to the GBM microenvironment in patients. Analysis of treated PDOXs and longitudinal PDOX models derived from patients prior and after treatment allows us to investigate short-term and stable long-term transcriptomic adaptations. We aim to reveal key molecular regulators enhancing tumor cell plasticity and resistance, that could be targeted in combinatory treatments. Our GBM PDOX models provide a platform for high-quality pre-clinical research and an improved clinical relevance in the development and testing of novel therapeutics.

Background: Standard-of-care for glioblastoma (GBM) includes surgery, radiation and temozolomide (TMZ). Nearly all tumors recur and 5-year survival is less than 3%. Unmethylated promoter status for O6-methylguanine-DNA-methyltransferase (MGMT) is a validated biomarker for TMZ-resistance. Second-line treatment with bevacizumab has failed to improve survival and GBMs escape treatment by inducing intratumor hypoxia. VAL-083 is a bi-functional DNA-targeting agent that readily crosses the blood-brain barrier and accumulates in brain tumor tissue. VAL-083 induces DNA interstrand crosslinks at N7-guanine, leading to double-strand breaks and cancer cell-death in GBM cells, independent of MGMT. VAL-083 is currently in Phase II clinical trial for the treatment of MGMT promoter unmethylated GBM, both recurrent and treatment-naïve (NCT02717962, NCT03050736), and it remains to be seen if it shows enhanced anti-tumor effect compared to TMZ. Based on its unique monosaccharide backbone structure, VAL-083 may also benefit from bevacizumab-induced GLUT transporter upregulation leading to enhanced uptake and anti-tumor activity. Methods: The cytotoxic effect of VAL-083 and TMZ was verified in 3D GBM organoids derived from 18 patient-derived orthotopic xenograft (PDOX) GBM models of different (epi)genetic background. Cell responses to drugs were calculated as the area under the curve (AUC). We further evaluated VAL-083 ability to decrease tumor growth in vivo in a MGMT-unmethylated, temozolomide-resistant recurrent GBM PDOX model. Mice were grouped into control, bevacizumab, VAL-083, and VAL-083+bevacizmab. Tumor progression was measured by MRI and histopathological assessment. Results: GBM organoids showed only partial response to TMZ. As expected, MGMT- methylated GBMs were less resistant in comparison to MGMT-unmethylated GBMs. VAL-083 was generally more effective than TMZ and response to VAL-083 was not dependent on MGMT promoter methylation status. Responses to TMZ and VAL-083 were comparable between treatment-naïve PDOXs and PDOXs derived from patients previously treated with TMZ and radiation. VAL-083 led to dramatic reduction of tumor growth in vivo (-83% for VAL-083 group, -90% for VAL-083 + bevacizumab). The analysis of tumor growth in time showed further reduction of tumor progression upon combined treatment. Histological assessment showed increased DNA damage (H2AX-P) in tumor cells. H2AX-P was only slightly increased in certain zones of the normal brain, close to meninges and subventricular zone, to a much lower extend in comparison to tumor cell, which was in line with the low toxicity of VAL-083. Citation Format: Anna Golebiewska, Anaïs Oudin, Virginie Baus, Ann-Christin Hau, Eliane Klein, Anne Steino, Jeffrey A. Bacha, Simone P. Niclou, Dennis M. Brown. Dianhydrogalactitol (VAL-083) exhibits strong efficacy in GBM tumors with different (epi)genetic background and treatment history [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5231.

It is well recognized that long term cell cultures are poor models to study human cancer, largely because of loss of clonal heterogeneity, accumulation or loss of genomic alterations and adaptation to a highly artificial environment. Patient-derived orthotopic xenografts (PDOX) based on organotypic three-dimensional tumor spheroids from human glioma samples are proposed to represent a reliable and clinically-relevant animal model. We have generated a living biobank of PDOX models from 34 glioma patients (grade III and IV), including longitudinal patient samples with matched recurrent tumors. Using an efficient orthotopic xenografting procedure we obtain an overall tumor take-rate of close to 80%. We show that our glioma PDOX retain the genetic and epigenetic profiles of primary patient biopsies throughout several generations of xenotransplantation. In particular they not only faithfully recapitulate gene amplification and expression of EGFR and EGFRvIII variant in a reproducible manner, also amplification and expression of rarer patient-specific EGFR variants is maintained. Overall genome-wide transcriptomic profiles of PDOX remain very similar to patient biopsies and correlate better with the GBM cohort of TCGA (538 GBM samples) than conventional cell lines. Observed differences at the transcriptomic level are largely based on the replacement of human to mouse stromal cells, which impacts on the molecular sub-classification of GBM. We conclude that glioma PDOX models closely reflect patient heterogeneity and treatment response, and thus represent appropriate avatars for reproducible pre-clinical trials. Furthermore, by combining profiling of the somatic mutational landscape with large-scale drug screening, PDOX-derived tumor organoids can elucidate druggable targets and tumor response profiles in a personalized patient-specific manner.

INTRODUCTION: The role of receptor tyrosine kinases (RTKs) in glioblastoma is widely acknowledged. However, therapies based on RTK targeting have been continuously unsuccessful in GBM patients, highlighting the complexity of RTK signaling and biology. LRIG1 (Leucine-rich Repeats and ImmunoGlobulin domains protein 1) was identified as an endogenous inhibitor of epidermal growth factor receptor (EGFR) and other RTKs, and was confirmed as a tumor suppressor in various cancer types. We previously identified the soluble form of LRIG1 as a potent inhibitor of GBM growth in vivo, irrespective of EGFR status. Here, we aim to shed light on the molecular mechanisms underlying its anti-cancer activity. MATERIAL AND METHODS: We used GBM cells overexpressing EGFRvIII, with or without soluble LRIG1 overexpression. In parallel, we generated a recombinant human soluble LRIG1 protein (rh-sLRIG1) by expressing LRIG1 ectodomain in insect cells via baculovirus infection and subsequent His-tag purification. rh-sLRIG1 was applied in the medium of classical GBM cell lines and patient-derived GBM stem-like cells. Applying a variety of cell-based assays, cell proliferation, migration, cell morphology, as well as protein expression and protein-protein interactions were investigated. RESULTS: We confirmed that sLRIG1 efficiently reduced proliferation and invasion capacities of GBM cells, and modulated cytoskeleton proteins and cell shape. Inhibition of cell proliferation by sLRIG1 was independent of EGFR expression levels in GBM cells and interestingly, rh-sLRIG1 treatment was associated with downregulation of AXL, which constitutes a newly-identified regulatory function of LRIG1. We are currently addressing the impact of the LRIG1-AXL signaling axis on GBM invasion and resistance to EGFR inhibition. CONCLUSION: We identified AXL as a novel LRIG1 target and provide evidence for the potential therapeutic application of recombinant sLRIG1 in the inhibition of growth factor signaling in GBM.

BACKGROUND: It is well recognized that long term cell cultures are poor models to study human cancer, largely because of loss of clonal heterogeneity, accumulation or loss of genomic alterations and adaptation to a highly artificial environment. Patient-derived orthotopic xenografts (PDOX) based on organotypic three-dimensional tumor spheroids from human glioma samples are proposed to represent a reliable and clinically-relevant animal model. METHODS: A living biobank of PDOX models from 34 glioma patients (grade III and IV), including longitudinal patient samples with matched recurrent tumors, were generated by intracranial grafting of organotypic tumor spheroids in immunedeficient mice. Genetic/epigenetic analyses on patient biopsies and corresponding PDOX included array comparative genomic hybridization, transcriptional profiling, targeted sequencing and methylation arrays. RESULTS: Using an efficient orthotopic xenografting procedure we obtain an overall tumor take-rate of close to 80%. We show that glioma PDOX retain the genetic and epigenetic profiles of primary patient biopsies throughout several generations of xenotransplantation. In particular they not only faithfully recapitulate gene amplification and expression of EGFR and EGFRvIII variant in a reproducible manner, also amplification and expression of rarer patient-specific EGFR variants is maintained. Overall genome-wide transcriptomic profiles of PDOXs remain very similar to patient biopsies and correlate better with the GBM cohort of TCGA (538 GBM samples) than conventional cell lines. Observed differences at the transcriptomic level are largely based on the replacement of human to mouse stromal cells, which impacts on the molecular sub-classification of GBM. CONCLUSION: We conclude that glioma PDOX models reflect patient heterogeneity and treatment response, and represent appropriate avatars for reproducible pre-clinical trials. Furthermore, by combining profiling of the somatic mutational landscape with large-scale drug screening, PDOX-derived tumor organoids can be applied to elucidate druggable targets and tumor response profiles in a personalized patient-specific manner.

Adult diffuse gliomas are a diverse group of brain neoplasms that inflict a high emotional toll on patients and their families. The Cancer Genome Atlas and similar projects have provided a comprehensive understanding of the somatic alterations and molecular subtypes of glioma at diagnosis. However, gliomas undergo significant cellular and molecular evolution during disease progression. We review the current knowledge on the genomic and epigenetic abnormalities in primary tumors and after disease recurrence, highlight the gaps in the literature, and elaborate on the need for a new multi-institutional effort to bridge these knowledge gaps and how the Glioma Longitudinal Analysis Consortium (GLASS) aims to systemically catalog the longitudinal changes in gliomas. The GLASS initiative will provide essential insights into the evolution of glioma toward a lethal phenotype, with the potential to reveal targetable vulnerabilities and, ultimately, improved outcomes for a patient population in need.

Standard treatments for glioblastoma (GBM) include surgery, radiation and chemotherapy with temozolomide (TMZ). Nearly all tumors recur and 5-year survival is less than 3%, largely due to chemoresistance. Cancer cells utilize DNA damage repair pathways to overcome cytotoxicity of chemotherapy. GBM tumors expressing O6-methylguanine-DNA-methyltransferase (MGMT) are resistant to TMZ and nitrosourea, and deficient DNA mismatch repair (MMR) confers resistance to TMZ and platinum agents. Alterations in p53, particularly gain-of-function mutations, are correlated with increased MGMT and poor prognoses in GBM. Second line anti-angiogenic treatment with bevacizumab has been implicated in increased chemoresistance and has not improved overall survival. Thus, refractory GBM is a significant clinical challenge and novel therapeutic strategies to overcome chemoresistance are essential. VAL-083 is a bi-functional alkylating agent that readily crosses the blood-brain barrier and has shown activity against GBM in prior NCI-sponsored clinical trials. A Phase I/II clinical trial studying VAL-083 in recurrent GBM, after TMZ and bevacizumab failure, suggested the potential of VAL-083 to offer a clinically meaningful survival benefit. The mechanism-of-action of VAL-083 differs from other alkylating agents, including TMZ and nitrosoureas, inducing interstrand cross-links at guanine-N7 causing DNA double-strand breaks and cancer cell death. VAL-083 activity is independent of MGMT and p53 status and it is active against TMZ-resistant GBM cancer stem cells. Recent findings that VAL-083 leads to irreversible S/G2-phase cell cycle arrest, propose synergy with S-phase specific chemotherapeutics, including topoisomerase and PARP inhibitors. VAL-083 persistently activates the homologous recombination (HR) DNA repair pathway and its potency is increased in HR-impaired cancer cells, suggesting increased VAL-083 cytotoxicity in HR-impaired tumors. Further, hypoxic cancer cells downregulate HR, proposing increased VAL-083 potency in hypoxic tumors. Bevacizumab increases intratumor hypoxia, presumably impairing HR, proposing VAL-083 as a treatment option in HR-deficient or hypoxic cancers following, or as part of combination with, bevacizumab. Here, we investigated cytotoxicity and DNA damage response of VAL-083 combinations by crystal violet, western blot and flow cytometry in a range of cancer cells, and MMR-related chemoresistance using lentiviral MLH1 and MSH2 vectors. The potency of VAL-083 in GBM was investigated under hypoxia either in vitro or in vivo as part of a combination treatment with bevacizumab. Our results demonstrate a distinct anti-cancer mechanism for VAL-083, enabling i) ability to overcome resistance to TMZ, platinum agents, and nitrosoureas, ii) increased potency in cancers with impaired HR, and iii) synergy with topoisomerase and PARP inhibitors.

It is well recognized that long term cell cultures are poor models to study human cancer, largely because of loss of clonal heterogeneity, accumulation or loss of genomic alterations and adaptation to a highly artificial environment. Patient-derived orthotopic xenografts (PDOX) based on organotypic three-dimensional tumor spheroids from human glioma samples are proposed to represent a reliable and clinically-relevant animal model. We have generated a living biobank of PDOX models from 34 glioma patients (grade III and IV), including longitudinal patient samples with matched recurrent tumors. Using an efficient orthotopic xenografting procedure we obtain an overall tumor take-rate of close to 80%. We show that our glioma PDOX retain the genetic and epigenetic profiles of primary patient biopsies throughout several generations of xenotransplantation. In particular they not only faithfully recapitulate gene amplification and expression of EGFR and EGFRvIII variant in a reproducible manner, also amplification and expression of rarer patient-specific EGFR variants is maintained. Overall genome-wide transcriptomic profiles of PDOX remain very similar to patient biopsies and correlate better with the GBM cohort of TCGA (538 GBM samples) than conventional cell lines. Observed differences at the transcriptomic level are largely based on the replacement of human to mouse stromal cells, which impacts on the molecular sub-classification of GBM. We conclude that glioma PDOX models closely reflect patient heterogeneity and treatment response, and thus represent appropriate avatars for reproducible pre-clinical trials. Furthermore, by combining profiling of the somatic mutational landscape with large-scale drug screening, PDOX-derived tumor organoids can elucidate druggable targets and tumor response profiles in a personalized patient-specific manner.

Background Glioblastoma ranks among the most lethal cancers, with current therapies offering only palliation. Paracrine vascular endothelial growth factor (VEGF) signaling has been targeted using anti-angiogenic agents, whereas autocrine VEGF/VEGF receptor 2 (VEGFR2) signaling is poorly understood. Bevacizumab resistance of VEGFR2-expressing glioblastoma cells prompted interrogation of autocrine VEGF-C/VEGFR2 signaling in glioblastoma. Methods Autocrine VEGF-C/VEGFR2 signaling was functionally investigated using RNA interference and exogenous ligands in patient-derived xenograft lines and primary glioblastoma cell cultures in vitro and in vivo. VEGF-C expression and interaction with VEGFR2 in a matched pre- and post-bevacizumab treatment cohort were analyzed by immunohistochemistry and proximity ligation assay. Results VEGF-C was expressed by patient-derived xenograft glioblastoma lines, primary cells, and matched surgical specimens before and after bevacizumab treatment. VEGF-C activated autocrine VEGFR2 signaling to promote cell survival, whereas targeting VEGF-C expression reprogrammed cellular transcription to attenuate survival and cell cycle progression. Supporting potential translational significance, targeting VEGF-C impaired tumor growth in vivo, with superiority to bevacizumab treatment. Conclusions Our results demonstrate VEGF-C serves as both a paracrine and an autocrine pro-survival cytokine in glioblastoma, promoting tumor cell survival and tumorigenesis. VEGF-C permits sustained VEGFR2 activation and tumor growth, where its inhibition appears superior to bevacizumab therapy in improving tumor control.

Introduction Animal models are essential tools for basic research and preclinical therapeutic interventions. Although numerous clinical cancer trials are being conducted, many fail due to inappropriate selection of compounds at the preclinical stage. Therefore better preclinical models are crucial for predicting successful clinical impact. Orthotropic PDX models are of particular importance for brain cancers, as they allow to better recapitulate the brain tumour environment and the blood brain barrier. Material and methods Glioblastoma PDX models were based on 3D organotypic spheroids, derived from mechanically minced patient material. Spheroids were implanted in the brain of immunodeficient mice and further propagated by serial intracranial transplantations. For detailed molecular characterisation each PDX was compared to its original patient tumour at the genetic, epigenetic and transcriptomic levels and intra-tumoral heterogeneity was addressed at the single cell level. We furthered performed proof-of-concept preclinical studies interfering with angiogenesis and autophagy. Results and discussions Our glioblastoma PDX models starting with viable patient-derived spheroids has a high tumour take rate and a reproducible phenotype and tumour development time. We observed three distinct histological tumour phenotypes: a highly ‘invasive’, a highly ‘angiogenic’ and an ‘intermediate’ phenotype which combines invasion and vascular abnormalities. Typical glioblastoma characteristics such as pseudopalisading necrosis, invasion or microvascular proliferation we maintained. PDXs retained the genetic and epigenetic profiles of patient tumours through several generations. Transcriptomic profiles of PDXs were similar to patient biopsies and correlated better with TCGA glioblastoma samples than conventional glioma cell lines. In vivo pharmacological inhibition of autophagy significantly increased survival of PDXs and combination treatment with bevacizumab showed a synergistic effect. Conclusion Here we show that glioblastoma PDXs represent a reliable and clinically-relevant animal model. The model can be applied for analyses at different molecular levels. Importantly, the PDXs can be applied for accurate reproducible pre-clinical trials, including personalised medicine-based treatments. The use of this model should lead to a more realistic evaluation of the efficacy of novel drugs, thereby increasing the success of clinical studies.

BACKGROUND Cellular heterogeneity has been well established within numerous cancer types, including malignant brain tumours. Initially, cancer stem cells (CSC) have been accounted for formation of phenotypic heterogeneity and tumor progression in glioblastoma (GBM). Recent data, however, suggest that CSCs may not represent a stable entity and intrinsic plasticity plays a key role in tumor adaptation to changing microenvironments. The question arises whether CSCs are a defined subpopulation of tumor cells or whether they represent a changing entity that any cancer cell can adopt depending on the environmental conditions. MATERIAL AND METHODS Intra-tumoral phenotypic heterogeneity was interrogated at the single cell transcriptomic and proteomic level in GBM patient-derived orthotopic xenografts (PDOXs) and stem-like cultures. Tumor cell subpopulations were further classified based on expression of four stem cell-associated membrane markers (CD133, CD15, A2B5 and CD44). The resulting 16 subpopulations were FACS isolated and functionally analyzed. Mathematical Markov modelling was applied to calculate state transitions between cell states. RESULTS GBM patient biopsies, PDOXs and stem-like cell cultures display remarkable stem cell-associated intra-tumoral heterogeneity. Independent of marker expression, all analysed tumor subpopulations carried stem-cell properties and had the capacity to recreate phenotypic heterogeneity. Mathematical modeling revealed a different propensity in reforming the original heterogeneity over time, which was independent of the proliferation index but linked to tumorigenic potential. Although subpopulations varied in their potential to adapt to new environments, all were able to reach a steady state microenvironment-specific equilibrium. CONCLUSION Our results suggest that phenotypic heterogeneity in GBM results from intrinsic plasticity allowing tumor cells to effectively adapt to new microenvironments. Cellular states are non-hierarchical, reversible and occur via stochastic state transitions of existing populations, striving towards an equilibrium instructed by the microenvironment. Our data provides evidence that CSCs do not represent a clonal entity defined by distinct functional properties and transcriptomic signatures, but rather a cellular state that is determined by environmental conditions, which has implications for the design of treatment strategies targeting CSC-like states.

BACKGROUND A major hallmark of glioblastoma (GBM) is its highly invasive capacity, contributing to its aggressive behaviour. Since invasive cells cannot be easily removed by surgery or irradiation, they are left behind and eventually result in lethal recurrence. Therefore, a better understanding of the invasion process and of the key molecular players underlying the invasive capacities of GBM may lead to the identification of new therapeutic targets for GBM patients. MATERIAL AND METHODS To identify candidate genes responsible for invasion, a genome-wide shRNA screen was performed in patient-derived GBM sphere cultures. The phenotype of the most promising candidate was validated in in vitro invasion assays, ex vivo brain slice cultures and in vivo orthotopic xenografts in mice. Gene knockdown in invasive GBM cell lines was compared with overexpression in non-invasive cells. RNA sequencing of knockdown cells, along with the generation of deletion constructs were applied to uncover the mechanisms regulating invasion. RESULTS Through a whole genome shRNA screen, a zinc-finger containing protein was identified as an invasion essential candidate gene. Knockdown of this gene confirmed a strong decrease in invasion capacity in two highly invasive GBM cell lines. In contrast, gene overexpression switched non-invasive GBM cells to an invasive phenotype. Deletion of either one or both zinc-finger motifs led to decreased invasion indicating that the two zinc-finger motifs are essential for regulating invasion. Mutation of the nuclear localisation signal resulted in retention of the protein in the cytoplasm and loss of the invasion phenotype demonstrating that the protein activity is required in the nucleus. Gene expression analyses revealed that invasion-related genes are significantly regulated by the candidate gene once it is localized in the nucleus. CONCLUSION We identified a zinc-finger containing protein as a novel driver of GBM invasion, presumably through a transcription factor activity resulting in the induction of an invasive transcriptional program. This protein and its downstream pathway may represent a novel promising target to overcome invasive capacities in GBM.

Background: Standard-of-care for glioblastoma (GBM) includes surgery, radiation and temozolomide (TMZ). Nearly all tumors recur and 5-year survival is less than 3%. Unmethylated promoter status for O6-methylguanine-DNA-methyltransferase (MGMT) is a validated biomarker for TMZ-resistance. Second-line treatment with bevacizumab has not only failed to improve survival, but has also been shown to induce intratumor hypoxia, which is implicated in increased chemoresistance. VAL-083 is a bi-functional DNA-targeting agent that readily crosses the blood-brain barrier and accumulates in brain tumor tissue. VAL-083 induces DNA double-strand breaks at N7-guanine and cancer cell-death in GBM cancer stem cells (CSCs) and non-CSCs, independent of MGMT. We have previously shown that bevacizumab treatment upregulates expression of glucose transporters GLUT-1/GLUT-3 on GBM cells. We hypothesized that, based on its unique monosaccharide backbone structure, VAL-083 may benefit from bevacizumab-induced GLUT transporter upregulation leading to enhanced VAL-083 uptake and anti-tumor activity. Methods: To investigate the in vivo anti-tumor effect of VAL-083+bevacizumab, we used a orthotopic patient-derived xenograft GBM model. All mice carried MGMT-unmethylated, temozolomide-resistant recurrent T16 GBM tumors as detected by MRI 35 days post-implantation. Mice were grouped into control, bevacizumab, VAL-083, and VAL-083+bevacizmab. Tumor progression was measured by MRI on days 49 and 56, and tumor growth rate was calculated for the entire study (day 35 vs. 56) and for the last 7 days (day 49 vs. 56). Results: Tumors were significantly smaller in VAL-083-treated mice both compared to control (-83%, p Conclusions: These results show strong in vivo anti-tumor efficacy of VAL-083 against MGMT-unmethylated, TMZ-resistant recurrent GBM. This effect was further augmented in combination with bevacizumab, providing rationale of clinical investigation of VAL-083 in combination with bevacizumab in the treatment of GBM. Citation Format: Anna Golebiewska, Anais Oudin, Anne Steino, Simone P. Niclou, Jeffrey Bacha, Dennis M. Brown. Dianhydrogalactitol (VAL-083) reduces glioblastoma tumor growth upon bevacizumab-induced hypoxia, in vivo [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 1051.

Background Deregulated growth factor signaling is a major driving force in the initiation and progression of glioblastoma. The tumor suppressor and stem cell marker Lrig1 is a negative regulator of the epidermal growth factor receptor (EGFR) family. Here, we addressed the therapeutic potential of the soluble form of Lrig1 (sLrig1) in glioblastoma treatment and the mechanism of sLrig1-induced growth inhibition. Methods With use of encapsulated cells, recombinant sLrig1 was locally delivered in orthotopic glioblastoma xenografts generated from freshly isolated patient tumors. Tumor growth and mouse survival were evaluated. The efficacy of sLrig1 and the affected downstream signaling was studied in vitro and in vivo in glioma cells displaying variable expression of wild-type and/or a constitutively active EGFR mutant (EGFRvIII). Results Continuous interstitial delivery of sLrig1 in genetically diverse patient-derived glioma xenografts led to strong tumor growth inhibition. Glioma cell proliferation in vitro and tumor growth in vivo were potently inhibited by sLrig1, irrespective of EGFR expression levels. Of importance, tumor growth was also suppressed in EGFRvIII-driven glioma. sLrig1 induced cell cycle arrest without changing total receptor level or phosphorylation. Affected downstream effectors included MAP kinase but not AKT signaling. Of importance, local delivery of sLrig1 into established tumors led to a 32% survival advantage in treated mice. Conclusions To our knowledge, this is the first report demonstrating that sLrig1 is a potent inhibitor of glioblastoma growth in clinically relevant experimental glioma models and that this effect is largely independent of EGFR status. The potent anti-tumor effect of sLrig1, in combination with cell encapsulation technology for in situ delivery, holds promise for future treatment of glioblastoma.

Brain metastasis is associated with a particular poor prognosis. Novel insight into the brain metastatic process is therefore warranted. Several preclinical models of brain tumor metastasis have been developed during the last 60 years, and they have in part revealed some of the mechanisms underlying the metastatic process. This review discusses mechanisms of brain metastasis with a key focus of the development of animal model systems. This includes the use of rodent, syngeneic brain metastasis models (spontaneous, chemically induced and genetically engineered models) and human xenotransplantation models (ectopic inoculation and orthotopic models). Current information indicates that none of these fully reflect tumor development seen in patients with metastatic disease. The various model systems used, however, have provided important insight into specific mechanisms of the metastatic process related to the brain. By combining the knowledge obtained from animal models, new important information on the molecular mechanisms behind metastasis will be obtained, leading to the future development of new therapeutic strategies.

IDH1R132H mutations are considered to play a key role in the development of low grade gliomas and secondary glioblastomas (GBM). Wild type IDH1 converts isocitrate to α-ketoglutarate (a-KG) while reducing NADP+, whereas IDH1R132H uses a-KG to generate high amounts of the oncometabolite D-2-hydroxyglutarate (D-2-HG). While the effects of D-2-HG have been subject to intense research, D-2-HG independent effects of IDH1R132H on energy homeostasis and redox status are insufficiently studied.

Despite surgical resection and genotoxic treatment with ionizing radiation and the DNA alkylating agent temozolomide (TMZ), glioblastoma (GBM) remains one of the most lethal cancers, due in great part to the action of DNA repair factors that drive resistance and lead to tumor relapse. Important features of these mechanisms include the inherent redundancy and complexity of the many DNA repair pathways activated as part of the DNA damage response (DDR) to DNA damage. Understanding how DNA repair mechanisms operate to remove lesions induced by TMZ in GBM cells and identifying novel pharmacological targets remain of vital importance in order to improve GBM treatment.

Animal models are essential tools for basic research and for preclinical therapeutic interventions. Although numerous clinical trials have been conducted, most fail due to inappropriate selection of the compounds at the preclinical stage. Therefore better preclinical models are crucial for achieving important clinical impact. Here we show that glioblastoma patient-derived xenografts (PDXs) based on organotypic spheroids represent a reliable and clinically-relevant animal model. Our PDX models are characterized by a tumor take rate close to 100% and a very reproducible tumor development time. We observe three distinct histological tumor phenotypes: a highly “invasive”, a highly “angiogenic” and an “intermediate” phenotype which combines invasion and vascular abnormalities. Typical glioblastoma characteristics such as pseudopalisading necrosis, invasion or microvascular proliferation are maintained. Interestingly, angiogenic features appear stronger in nude rats compared to immunodeficient mice.

Treatment of glioblastoma (GBM) includes surgery and chemoradiation with temozolomide. Due to chemoresistance, nearly all tumors recur and 5-year survival is less than 3%. Various treatments, including anti-angiogenic treatment with bevacizumab, nitrosoureas and topoisomerase inhibitors, have failed to improve overall survival in recurrent GBM (rGBM). GBM tumors expressing O6-methylguanine-DNA-methyltransferase (MGMT) are resistant to temozolomide and nitrosourea, and deficient DNA mismatch repair (MMR) confers secondary resistance to temozolomide. Our recent phase I/II trial in rGBM patients previously treated with temozolomide and bevacizumab, suggested that VAL-083 may offer a clinically meaningful survival benefit for rGBM patients. VAL-083 is a first-in-class bi-functional DNA-targeting agent that readily crosses the blood-brain barrier and accumulates in brain tumor tissue. The mechanism-of-action of VAL-083 differs from other alkylating agents and overcomes both MGMT- and MMR-related resistance to temozolomide, in vitro. VAL-083 rapidly induces interstrand cross-links at N7-guanine, causing DNA double-strand breaks and persistent activation of the homologous recombination (HR) DNA repair pathway. Furthermore, VAL-083 potency is increased in HR-deficient cancer cells, suggesting increased cytotoxicity in HR-impaired tumors. Hypoxic GBM cells downregulate HR activity, thus proposing increased VAL-083 potency in hypoxic tumors. Bevacizumab increases intratumor hypoxia, suggesting VAL-083 as a treatment option in HR-deficient or hypoxic cancers following, or as part of combination with, bevacizumab. The potency of VAL-083 as part of a combinatory treatment with bevacizumab was investigated in GBM models under hypoxia both in vitro and in vivo. Separately, we demonstrated that VAL-083 induces irreversible S/G2-phase cell-cycle arrest, thus proposing synergy with S-phase specific chemotherapeutics, including topoisomerase and PARP inhibitors. Here, we investigated cytotoxicity of VAL-083 combinations with various topoisomerase and PARP inhibitors in a range of cancer cells. Our results support the potential of VAL-083 to i) overcome resistance to temozolomide, and ii) display synergy as part of combinatory therapies with topoisomerase or PARP inhibitors.

Recent results from 2 double-blind, placebo-controlled phase III trials (RTOG 0825) and (AVAglio) for first-line treatment of glioblastoma patients with the VEGF antibody bevacizumab, showed similar results, related to overall and progression-free survival. The RTOG 0825 trial indicated, opposed to the AVAglio trial, that patients treated with bevacizumab showed a decline in global neurocognitive function compared to untreated patients, -a decline that was most obvious after prolonged treatment. At present, there is a considerably controversy related to these observations. In the present work we point at the possibility that bevacizumab treatment of the normal brain can reduce synaptic plasticity in the hippocampus. We believe that such a phenomenon may partly explain the reduced cognitive function observed in patients in the RTOG 0825 trial. Since the same effects were not clearly defined in the AVAglio trial, further studies on putative neurocognitive effects after bevacizumab treatment are warranted.

Standard-of-care for glioblastoma (GBM) includes surgery, radiation and temozolomide. Nearly all tumors recur and 5-year survival is less than 3%. Unmethylated promoter status for O(6)-methylguanine-DNA-methyltransferase (MGMT) is a validated biomarker for temozolomide-resistance. Second-line treatment with bevacizumab has not only failed to improve survival, but has also been shown to induce intratumor hypoxia, which is implicated in increased chemoresistance. VAL-083 is a bi-functional DNA-targeting agent that readily crosses the blood-brain barrier. VAL-083 targets N(7)-guanine, causing DNA double-strand breaks and cancer cell-death in GBM cancer stem cells (CSCs) and non-CSCs, independent of MGMT. We have previously shown that bevacizumab treatment upregulates expression of glucose transporters GLUT-1/GLUT-3 on GBM cells. We hypothesized that, based on its unique monosaccharide backbone structure, VAL-083 may benefit from bevacizumab-induced GLUT transporter upregulation leading to enhanced VAL-083 uptake and anti-tumor activity. Methods: To investigate the in vivo anti-tumor effect of VAL-083+bevacizumab, we used a orthotopic patient-derived xenograft GBM model. All mice carried MGMT-unmethylated, temozolomide-resistant recurrent T16 GBM tumors as detected by MRI 35 days post-implantation. Mice were grouped into control, bevacizumab, VAL-083, and VAL-083+bevacizmab. Tumor progression was measured by MRI on days 49 and 56, and tumor growth rate was calculated for the entire study (day 35 vs. 56) and for the last 7 days (day 49 vs. 56). Results: Tumors were significantly smaller in VAL-083-treated mice both compared to control (-83%, p

Counteracting high attrition rates in anticancer drug development and providing optimal therapeutic management of cancer patients require preclinical models that properly recapitulate the complexity and diversity of human tumours. Patient-derived cancer xenografts (PDXs), developed by transplanting human tumor fragments into immunodeficient mice, retain the idiosyncratic characteristics of different tumors from different patients. The possibility of population-scale correlations between therapeutic response in PDXs and extensive, multidimensional molecular annotation has enabled the identification of several sensitivity and resistance biomarkers in a number of different tumor types, with immediate clinical relevance. To effectively recapitulate and therapeutically interrogate through patient-derived models the heterogeneity that typifies human cancer, 13 European cancer centres and university hospitals joined forces in 2013 to start EurOPDX, an academic research consortium that now gathers 19 institutions throughout Europe and in the US. EurOPDX includes world-renowned experts at the forefront of research in basic, preclinical, translational and clinical oncology across multiple pathologies, and displays a wide range of expertise in technological platforms. The primary goal of the Consortium is to maximize exploitation of PDXs and other patient-derived cancer models for cancer research by: (i) integrating institutional collections into an organic, multicentre collection of patient-derived models, now reaching 2,000 subcutaneous and orthotopic models for 30+ different pathologies (www.europdx.eu); (ii) defining common operating procedures to improve and standardize molecular and pharmacologic characterization of the models; (iii) sharing models within and outside the consortium to perform collaborative precision oncology “xenopatient” trials, to discover predictive biomarkers, new targets, and new strategies to overcome drug resistance. Towards these objectives, the EC granted 5 million euros under the H2020 programme for a “EurOPDX Distributed Infrastructure for Research on patient-derived Xenografts" - EDIReX EU project n. 731105, starting on February 2018. By teaming up with other key academic, technological and SME partners, our goal with EDIReX is to establish a cutting-edge European infrastructure offering transnational access to PDX resources to academic and industrial cancer researchers, including the distribution of cryopreserved samples to third parties, the structured biobanking of user-developed models, and the performance of drug efficacy studies. We will provide an overview of the current achievements of the Consortium and the objectives of the EDIReX project. Citation Format: Enzo Medico, Mohamed Bentires-Alj, Andrew V. Biankin, Alejandra Bruna, Annette T. Byrne, Carlos Caldas, Robert B. Clarke, Georges Coukos, Olivier Elemento, Manuel Hidalgo, Giorgio Inghirami, Steven de Jong, Jos Jonkers, Ales Krenek, Eleonora Leucci, Gunhild Mari Maelandsmo, Michaela Th. Mayrhofer, Terrence F. Meehan, Simone P. Niclou, Pier Giuseppe Pelicci, Alejandro Piris-Gimenez, Leo Price, Sergio Roman-Roman, Livio Trusolino, Luca Vezzadini, Alberto Villanueva, Emilie Vinolo, on behalf of the EurOPDX Consortium. The EurOPDX EDIReX project: Towards a European research infrastructure on patient-derived cancer models [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 985.

Introduction To date there is no curative treatment available for patients with Glioblastoma (GBM). The cancer stem cell (CSC) hypothesis posits that GBMs rely on a small subpopulation of cells with stemness properties responsible for tumour progression and recurrence. Recent experimental data from GBM and other cancers however suggest that CSCs may not be a stable entity. The question arises whether such cells are a defined subpopulation of tumour cells or whether they represent a changing entity that any cancer cell can adopt depending on the environmental conditions. Material and methods Tumour cell subpopulations were classified based on their expression of four chosen cell membrane markers (CD133, CD15, A2B5 and CD44). The resulting 16 subpopulations were FACS isolated and analysed for self-renewal and ability to reform the original heterogeneous population in different environments. Mathematical Markov modelling was applied to calculate state transitions between cell states. Intra-tumoral heterogeneity was further interrogated at the single cell transcriptomic level. Results and discussions Similar to patient biopsies, we observed markers to be heterogeneously expressed in patient-derived GBM xenografts and stem-like cell cultures. All analysed tumour cell subpopulations carried stem-cell properties and had the capacity to adapt their marker expression profiles to give rise to the original subpopulations. Mathematical modelling revealed a different propensity in reforming the original heterogeneity over time, which was independent of the proliferation index but linked to tumorigenic potential. Although subpopulations varied in their potential to adapt to new environments, all were able to reach a steady state microenvironment-specific equilibrium. Conclusion Our results suggest that GBM CSCs do not represent a clonal entity defined by distinct functional properties and transcriptomic signatures, but rather a cellular state that is determined by environmental conditions. Cellular states are non-hierarchical, reversible and occur via stochastic state transitions of existing populations, striving towards an equilibrium instructed by the microenvironment. Our data provides evidence that stem cell-associated phenotypic heterogeneity in GBM is a result of intrinsic plasticity, which has important implications for the design of treatment strategies targeting cancer stem-like states.

The histopathological and molecular heterogeneity of glioblastomas represents a major obstacle for effective therapies. Glioblastomas do not develop autonomously, but evolve in a unique environment that adapts to the growing tumour mass and contributes to the malignancy of these neoplasms. Here, we show that patient-derived glioblastoma xenografts generated in the mouse brain from organotypic spheroids reproducibly give rise to three different histological phenotypes: (i) a highly invasive phenotype with an apparent normal brain vasculature, (ii) a highly angiogenic phenotype displaying microvascular proliferation and necrosis and (iii) an intermediate phenotype combining features of invasion and vessel abnormalities. These phenotypic differences were visible during early phases of tumour development suggesting an early instructive role of tumour cells on the brain parenchyma. Conversely, we found that tumour-instructed stromal cells differentially influenced tumour cell proliferation and migration in vitro, indicating a reciprocal crosstalk between neoplastic and non-neoplastic cells. We did not detect any transdifferentiation of tumour cells into endothelial cells. Cell type-specific transcriptomic analysis of tumour and endothelial cells revealed a strong phenotype-specific molecular conversion between the two cell types, suggesting co-evolution of tumour and endothelial cells. Integrative bioinformatic analysis confirmed the reciprocal crosstalk between tumour and microenvironment and suggested a key role for TGFβ1 and extracellular matrix proteins as major interaction modules that shape glioblastoma progression. These data provide novel insight into tumour-host interactions and identify novel stroma-specific targets that may play a role in combinatorial treatment strategies against glioblastoma.

Introduction:Despite surgical resection and genotoxic treatment with ionizing radiation (IR) and the DNA alkylating agent temozolomide (TMZ), glioblastoma remains one of the most lethal cancers, due in great part to the action of complex DNA repair mechanisms that drive resistance and tumour relapse. One such mechanism involves the DNA-repair protein O6-methylguanine-DNA methyltransferase (MGMT) which mediates the direct removal of O6-methylguanine, the most highly cytotoxic lesion induced by TMZ. Importantly, silencing of MGMT through promoter methylation, which is observed in about 40% of GBM patients, confers a small but significant survival benefit in patients treated with TMZ and IR compared to IR only. In addition to MGMT, several DNA repair pathways have been involved in the repair of TMZ-induced lesions. Understanding the molecular details of these mechanisms and identifying potential pharmacological targets have emerged as vital tasks to improve treatment. At the same time, deciphering the genetic and epigenetic alterations that shape the “DNA repair makeup” of GBM cells should help tailor therapy to individual patients.Approach and Results:We have undertaken complementary approaches to understand the molecular basis behind chemoresistance, tumour progression and relapse in GBM patients. Firstly, we have measured the mRNA expression levels of a selection of DNA repair and cell cycle factors in paired, primary and recurrent GBM biopsies from patients treated or not with TMZ. Classification of the deregulated genes led to the identification of a gene signature that segregated 3 groups of biopsies. Inspection of these groups suggests that one route to tumour progression is associated with profound alterations in cell cycle genes as well as genes encoding crucial DNA repair factors. We have further exploited our differential gene expression analysis to learn how cancer cells modulate the expression of specific pathways in response to glioblastomagenesis and genotoxic treatment, and propose novel therapeutic strategies based on the inhibition of DNA repair factors. Lastly, we have carried out a large-scale shRNA screen of DNA repair/chromatin factors to identify those gene silencings that sensitize GBM cells to TMZ, as well as synthetic lethal interactions with MGMT. We are currently validating the most promising candidates in vitro as well as in vivo, using orthotopic xenograft models of GBM.