Microtubule-associated NAV3 regulates invasive phenotypes in glioblastoma cells

Glioblastomas are aggressive brain tumors for which effective therapy is still lacking, resulting in dismal survival rates. These tumors display significant phenotypic plasticity, harboring diverse cell populations ranging from tumor core cells to dispersed, highly invasive cells. Neuron navigator 3 (NAV3), a microtubule-associated protein affecting microtubule growth and dynamics, is downregulated in various cancers, including glioblastoma, and has thus been considered a tumor suppressor. In this study, we challenge this designation and unveil distinct expression patterns of NAV3 across different invasion phenotypes. Using glioblastoma cell lines and patient-derived glioma stem-like cell cultures, we disclose an upregulation of NAV3 in invading glioblastoma cells, contrasting with its lower expression in cells residing in tumor spheroid cores. Furthermore, we establish an association between low and high NAV3 expression and the amoeboid and mesenchymal invasive phenotype, respectively, and demonstrate that overexpression of NAV3 directly stimulates glioblastoma invasive behavior in both 2D and 3D environments. Consistently, we observed increased NAV3 expression in cells migrating along blood vessels in mouse xenografts. Overall, our results shed light on the role of NAV3 in glioblastoma invasion, providing insights into this lethal aspect of glioblastoma behavior.

Organelle adaptations in response to mechanical forces during tumour dissemination

Cell migration plays a pivotal role in various biological processes including cancer dissemination and successful metastasis, where the role of mechanical signals is increasingly acknowledged. This review focuses on the intricate mechanisms through which cancer cells modulate their migratory strategies via organelle adaptations in response to the extracellular matrix (ECM). Specifically, the nucleus and mitochondria emerge as pivotal mediators in this process. These organelles serve as sensors, translating mechanical stimuli into rapid metabolic alterations that sustain cell migration. Importantly, prolonged exposure to such stimuli can induce transcriptional or epigenetic changes, ultimately enhancing metastatic traits. Deciphering the intricate interplay between ECM properties and organelle adaptations not only advances our understanding of cytoskeletal dynamics but also holds promise for the development of innovative anti-metastatic therapeutic strategies.

Dissecting TGF-β-induced glioblastoma invasion with engineered hyaluronic acid hydrogels

Glioma stem cells (GSCs) contribute to rapid cellular invasion in glioblastoma (GBM). Transforming growth factor-β (TGF-β) has been strongly implicated in supporting key GSC functions, including stemness, immunosuppression, and resistance. Although TGF-β is well-known as a driver of cancer invasion, how TGF-β supports the invasion of GSCs is not well understood. Progress in understanding mechanisms of TGF-β-driven invasion in GSC-derived tumors has been limited by an absence of three-dimensional (3D) culture systems that support TGF-β-stimulated invasion. Here, we show that 3D hyaluronic acid (HA) matrices can address this need. We perform bioinformatic analysis of human glioma datasets, which reveals progressive enrichment of TGF-β-related gene expression with increasingly aggressive glioma grade and GBM subtype. We then experimentally screen the invasion of a panel of human GSC spheroids through a set of 3D matrix systems, including collagen I, Matrigel, and HA, and find that only HA recapitulates TGF-β-induced invasion. We then show that GSCs differ in their ability to invade HA in a way that can be predicted from TGF-β receptor 2 expression and SMAD2 phosphorylation. GSC spheroid invasion depends strongly on the presence of RGD peptides on the HA backbone but is surprisingly independent of matrix metalloprotease degradability. Finally, we demonstrate that TGF-β stimulates invasion through SMAD-dependent signaling, consistent with recent observations that TGF-β/SMAD signals drive tumor microtube formation and invasion. Our work supports further development of HA as a matrix platform for dissecting contributions of TGF-β and other cytokines to GBM invasion and screening of cytokine-dependent invasion in human tumors.

Supramaximal resection: retrospective study on IDH-wildtype Glioblastomas based on the new RANO-Resect classification

BACKGROUND

The prognostic value of the extent of resection in the management of Glioblastoma is a long-debated topic, recently widened by the 2022 RANO-Resect Classification, which advocates for the resection of the non-enhancing disease surrounding the main core of tumors (supramaximal resection, SUPR) to achieve additional survival benefits. We conducted a retrospective analysis to corroborate the role of SUPR by the RANO-Resect Classification in a single center, homogenous cohort of patients.

METHODS

Records of patients operated for WHO-2021 Glioblastomas at our institution between 2007 and 2018 were retrospectively reviewed; volumetric data of resected lesions were computed and classified by RANO-Resect criteria. Survival and correlation analyses were conducted excluding patients below near-total resection.

RESULTS

117 patients met the inclusion criteria, encompassing 45 near-total resections (NTR), 31 complete resections (CR), and 41 SUPR. Median progression-free and overall survival were 11 and 15 months for NTR, 13 and 17 months or CR, 20 and 24 months for SUPR, respectively (p < 0.001), with inverse correlation observed between survival and FLAIR residual volume (r -0.28). SUPR was not significantly associated with larger preoperative volumes or higher rates of postoperative deficits, although it was less associated with preoperative neurological deficits (OR 3.37, p = 0.003). The impact of SUPR on OS varied between MGMT unmethylated (HR 0.606, p = 0.044) and methylated (HR 0.273, p = 0.002) patient groups.

CONCLUSIONS

Results of the present study support the validity of supramaximal resection by the new RANO-Resect classification, also highlighting a possible surgical difference between tumors with methylated and unmethylated MGMT promoter.

Exploring prognostic factors and treatment strategies for long-term survival in pleomorphic xanthoastrocytoma patients

Pleomorphic xanthoastrocytomas (PXA) are rare, accounting for < 1% of all astrocytomas. Literature on the clinical course and treatment outcomes of PXAs is limited. The study aimed to determine prognosis and treatment strategies for PXAs. Patients who had PXAs surgery between 2000-2021 were retrospectively analyzed for demographics and radiological characteristics. Initial and salvage treatment outcomes were recorded. Overall, 40 and 9 patients had grade 2 and 3 PXAs; their 5-year progression-free survival (PFS) rates were 75.8% and 37.0%, respectively (p = 0.003). Univariate analysis revealed that strong T1 enhancement (p = 0.036), infiltrative tumor margins (p < 0.001), peritumoral edema (p = 0.003), WHO grade (p = 0.005), and gross total resection (p = 0.005) affected the PFS. Multivariate analysis revealed that the WHO grade (p = 0.010) and infiltrative tumor margins (p = 0.008) influenced the PFS. The WHO grade (p = 0.027) and infiltrative tumor margins (p = 0.027) also affected the overall survival (OS). Subgroup analysis for grade 2 PXAs revealed no significant associations between adjuvant radiation therapy and the PFS and OS. This study highlighted the heterogeneous nature of PXAs and its impact on patient prognosis. Infiltrative tumor margins emerged as a key prognostic factor. Our findings have emphasized the prognostic relevance of radiological features and the need for larger studies on comprehensive management.

The STEMRI trial: Magnetic resonance spectroscopy imaging can define tumor areas enriched in glioblastoma stem-like cells

Despite maximally safe resection of the magnetic resonance imaging (MRI)-defined contrast-enhanced (CE) central tumor area and chemoradiotherapy, most patients with glioblastoma (GBM) relapse within a year in peritumoral FLAIR regions. Magnetic resonance spectroscopy imaging (MRSI) can discriminate metabolic tumor areas with higher recurrence potential as CNI+ regions (choline/N-acetyl-aspartate index >2) can predict relapse sites. As relapses are mainly imputed to glioblastoma stem-like cells (GSCs), CNI+ areas might be GSC enriched. In this prospective trial, 16 patients with GBM underwent MRSI/MRI before surgery/chemoradiotherapy to investigate GSC content in CNI-/+ biopsies from CE/FLAIR. Biopsy and derived-GSC characterization revealed a FLAIR/CNI+ sample enrichment in GSC and in gene signatures related to stemness, DNA repair, adhesion/migration, and mitochondrial bioenergetics. FLAIR/CNI+ samples generate GSC-enriched neurospheres faster than FLAIR/CNI-. Parameters assessing biopsy GSC content and time-to-neurosphere formation in FLAIR/CNI+ were associated with worse patient outcome. Preoperative MRI/MRSI would certainly allow better resection and targeting of FLAIR/CNI+ areas, as their GSC enrichment can predict worse outcomes.

Unravelling the Glioblastoma Tumour Microenvironment: Can Aptamer Targeted Delivery Become Successful in Treating Brain Cancers?

The key challenges to treating glioblastoma multiforme (GBM) are the heterogeneous and complex nature of the GBM tumour microenvironment (TME) and difficulty of drug delivery across the blood-brain barrier (BBB). The TME is composed of various neuronal and immune cells, as well as non-cellular components, including metabolic products, cellular interactions, and chemical compositions, all of which play a critical role in GBM development and therapeutic resistance. In this review, we aim to unravel the complexity of the GBM TME, evaluate current therapeutics targeting this microenvironment, and lastly identify potential targets and therapeutic delivery vehicles for the treatment of GBM. Specifically, we explore the potential of aptamer-targeted delivery as a successful approach to treating brain cancers. Aptamers have emerged as promising therapeutic drug delivery vehicles with the potential to cross the BBB and deliver payloads to GBM and brain metastases. By targeting specific ligands within the TME, aptamers could potentially improve treatment outcomes and overcome the challenges associated with larger therapies such as antibodies.

Optimizing maximum resection of glioblastoma: Raman spectroscopy versus 5-aminolevulinic acid

OBJECTIVE

The objective of this study was to assess and compare the potential of 5-aminolevulinic acid (5-ALA) and Raman spectroscopy (RS) in detecting tumor-infiltrated brain in patients with glioblastoma (GBM).

METHODS

Between July 2020 and October 2021, the authors conducted a prospective clinical trial with 15 patients who underwent neurosurgical treatment of newly diagnosed and histologically verified GBM. A solid contrast-enhancing tumor core and peritumoral tissue were investigated intraoperatively for cancer cells by using 5-ALA and RS to achieve pathology-tailored maximum resection. In each case, a minimum of 10 biopsies were sampled from navigation-guided areas. Two neuropathologists examined the biopsies for the presence of neoplastic cells. The detection performance of 5-ALA and RS alone and in combination was assessed. Pre- and postoperative MRI, Karnofsky Performance Status (KPS), and National Institutes of Health Stroke Scale (NIHSS) scores were compared, and median progression-free survival (PFS) was evaluated.

RESULTS

A total of 185 biopsy samples were harvested from the contrast-enhancing tumor core (n = 19) and peritumoral tissue (n = 166). In the tumor core, 5-ALA and RS each showed a sensitivity of 100%. In the peritumoral tissue, 5-ALA was less sensitive than RS in detecting cancer (46% vs 69%) but showed higher specificity (81% vs 57%). When the two methods were combined, the accuracy of tumor detection was increased by about 10%. Pathology-tailored resection led to a 52% increase in resection volume comparing the volume of preoperative contrast enhancement with the postoperative resection cavity on MRI (p = 0.0123). Eloquent brain involvement prevented gross-total resection in 4 patients. Four weeks after surgery, mean KPS (p = 0.7637) and NIHSS scores (p = 0.3146) were not significantly different from preoperative values. Of the 13 patients who had received postoperative chemoradiotherapy, 4 did not show any progression after a median follow-up of 14 months. The remaining 9 patients had a median PFS of 8 months.

CONCLUSIONS

According to the study data, RS is capable of detecting tumor-infiltrated brain with higher sensitivity but lower specificity than the current standard of 5-ALA. With further technological and workflow advancements, RS in combination with protoporphyrin IX fluorescence may contribute to pathology-tailored glioma resection in the future.

Transmembrane water-efflux rate measured by magnetic resonance imaging as a biomarker of the expression of aquaporin-4 in gliomas

The water-selective channel protein aquaporin-4 (AQP4) contributes to the migration and proliferation of gliomas, and to their resistance to therapy. Here we show, in glioma cell cultures, in subcutaneous and orthotopic gliomas in rats, and in glioma tumours in patients, that transmembrane water-efflux rate is a sensitive biomarker of AQP4 expression and can be measured via conventional dynamic-contrast-enhanced magnetic resonance imaging. Water-efflux rates correlated with stages of glioma proliferation as well as with changes in the heterogeneity of intra-tumoural and inter-tumoural AQP4 in rodent and human gliomas following treatment with temozolomide and with the AQP4 inhibitor TGN020. Regions with low water-efflux rates contained higher fractions of stem-like slow-cycling cells and therapy-resistant cells, suggesting that maps of water-efflux rates could be used to identify gliomas that are resistant to therapies.

Main Manuscript for Cell migration simulator-based biomarkers for glioblastoma

Glioblastoma is the most aggressive malignant brain tumor with poor survival due to its invasive nature driven by cell migration, with unclear linkage to transcriptomic information. Here, we applied a physics-based motor-clutch model, a cell migration simulator (CMS), to parameterize the migration of glioblastoma cells and define physical biomarkers on a patient-by-patient basis. We reduced the 11-dimensional parameter space of the CMS into 3D to identify three principal physical parameters that govern cell migration: motor number - describing myosin II activity, clutch number - describing adhesion level, and F-actin polymerization rate. Experimentally, we found that glioblastoma patient-derived (xenograft) (PD(X)) cell lines across mesenchymal (MES), proneural (PN), classical (CL) subtypes and two institutions (N=13 patients) had optimal motility and traction force on stiffnesses around 9.3kPa, with otherwise heterogeneous and uncorrelated motility, traction, and F-actin flow. By contrast, with the CMS parameterization, we found glioblastoma cells consistently had balanced motor/clutch ratios to enable effective migration, and that MES cells had higher actin polymerization rates resulting in higher motility. The CMS also predicted differential sensitivity to cytoskeletal drugs between patients. Finally, we identified 11 genes that correlated with the physical parameters, suggesting that transcriptomic data alone could potentially predict the mechanics and speed of glioblastoma cell migration. Overall, we describe a general physics-based framework for parameterizing individual glioblastoma patients and connecting to clinical transcriptomic data, that can potentially be used to develop patient-specific anti-migratory therapeutic strategies generally.

A Simple 3D Cell Culture Method for Studying the Interactions between Human Mesenchymal Stromal/Stem Cells and Patients Derived Glioblastoma

We have developed a 3D biosphere model using patient-derived cells (PDCs) from glioblastoma (GBM), the major form of primary brain tumors in adult, plus cancer-activated fibroblasts (CAFs), obtained by culturing mesenchymal stem cells with GBM conditioned media. The effect of MSC/CAFs on the proliferation, cell-cell interactions, and response to treatment of PDCs was evaluated. Proliferation in the presence of CAFs was statistically lower but the spheroids formed within the 3D-biosphere were larger. A treatment for 5 days with Temozolomide (TMZ) and irradiation, the standard therapy for GBM, had a marked effect on cell number in monocultures compared to co-cultures and influenced cancer stem cells composition, similar to that observed in GBM patients. Mathematical analyses of spheroids growth and morphology confirm the similarity with GBM patients. We, thus, provide a simple and reproducible method to obtain 3D cultures from patient-derived biopsies and co-cultures with MSC with a near 100% success. This method provides the basis for relevant in vitro functional models for a better comprehension of the role of tumor microenvironment and, for precision and/or personalized medicine, potentially to predict the response to treatments for each GBM patient.

Conventional MRI-Derived Biomarkers of Adult-Type Diffuse Glioma Molecular Subtypes: A Comprehensive Review

The introduction of molecular criteria into the classification of diffuse gliomas has added interesting practical implications to glioma management. This has created a new clinical need for correlating imaging characteristics with glioma genotypes, also known as radiogenomics or imaging genomics. Although many studies have primarily focused on the use of advanced magnetic resonance imaging (MRI) techniques for radiogenomics purposes, conventional MRI sequences remain the reference point in the study and characterization of brain tumors. A summary of the conventional imaging features of glioma molecular subtypes should be useful as a tool for daily diagnostic brain tumor management. Hence, this article aims to summarize the conventional MRI features of glioma molecular subtypes in light of the recent literature.

Pathophysiological roles of integrins in gliomas from the perspective of glioma stem cells

Glioblastoma is the most common primary intracranial tumor and is also one of the most malignant central nervous system tumors. Its characteristics, such as high malignancy, abundant tumor vasculature, drug resistance, and recurrence-prone nature, cause great suffering to glioma patients. Furthermore, glioma stem cells are the primordial cells of the glioma and play a central role in the development of glioma. Integrins—heterodimers composed of noncovalently bound a and ß subunits—are highly expressed in glioma stem cells and play an essential role in the self-renewal, differentiation, high drug resistance, and chemo-radiotherapy resistance of glioma stem cells through cell adhesion and signaling. However, there are various types of integrins, and their mechanisms of function on glioma stem cells are complex. Therefore, this article reviews the feasibility of treating gliomas by targeting integrins on glioma stem cells.

Alpha2beta1 Integrin Polymorphism in Diffuse Astrocytoma Patients

Integrins are heterodimeric transmembrane glycoproteins resulting from the non-covalent association of an α and β chain. The major integrin receptor for collagen/laminin, α2β1 is expressed on a wide variety of cell types and plays an essential role in the adhesion of normal and tumor cells to the extracellular matrix. Integrin-triggered signaling pathways promote the invasion and survival of glioma cells by modifying the brain microenvironment. In this study, we investigated the association of a specific genetic polymorphism of integrin α2β1 with the incidence of diffusely infiltrating astrocytoma and the progression of these tumors. Single-nucleotide polymorphism in intron 7 of the integrin ITGA2 gene was examined in 158 patients and 162 controls using polymerase chain reaction and restriction enzyme analysis. The ITGA2 genotype +/+ (with a BglII restriction site in both alleles) exhibited higher frequency in grade II astrocytoma compared to control (P = 0.02) whereas the genotype -/- (lacking the BglII site) correlated with the poorest survival rate (P = 0.04). In addition, in silico analyses of ITGA2 expression from low-grade gliomas (LGG, n = 515) and glioblastomas (GBM, n = 159) indicated that the higher expression of ITGA2 in LGG was associated with poor overall survival (P &lt; 0.0001). However, the distribution of integrin ITGA2 BglII genotypes (+/+, +/-, -/-) was not significantly different between astrocytoma subgroups III and IV (P = 0.65, 0.24 and 0.33; 0.29, 0.48, 0.25, respectively) compared to control. These results suggest a narrow association between the presence of this SNP and indicate that further studies with larger samples are warranted to analyze the relation between tumor grade and overall survival, highlighting the importance of determining these polymorphisms for prognosis of astrocytomas.

Glioblastoma Microenvironment: From an Inviolable Defense to a Therapeutic Chance

Glioblastoma is an aggressive tumor and is associated with a dismal prognosis. The availability of few active treatments as well as the inexorable recurrence after surgery are important hallmarks of the disease. The biological behavior of glioblastoma tumor cells reveals a very complex pattern of genomic alterations and is partially responsible for the clinical aggressiveness of this tumor. It has been observed that glioblastoma cells can recruit, manipulate and use other cells including neurons, glial cells, immune cells, and endothelial/stromal cells. The final result of this process is a very tangled net of interactions promoting glioblastoma growth and progression. Nonetheless, recent data are suggesting that the microenvironment can also be a niche in which glioblastoma cells can differentiate into glial cells losing their tumoral phenotype. Here we summarize the known interactions between micro-environment and glioblastoma cells highlighting possible therapeutic implications.

PNJ scaffolds promote microenvironmental regulation of glioblastoma stem-like cell enrichment and radioresistance

Glioblastoma (GBM) brain tumors contain a subpopulation of self-renewing multipotent Glioblastoma stem-like cells (GSCs) that are believed to drive the near inevitable recurrence of GBM. We previously engineered temperature responsive scaffolds based on the polymer poly(N-isopropylacrylamide-co-Jeffamine M-1000 acrylamide) (PNJ) for the purpose of enriching GSCs in vitro from patient-derived samples. Here, we used PNJ scaffolds to study microenvironmental regulation of self-renewal and radiation response in patient-derived GSCs representing classical and proneural subtypes. GSC self-renewal was regulated by the composition of PNJ scaffolds and varied with cell type. PNJ scaffolds protected against radiation-induced cell death, particularly in conditions that also promoted GSC self-renewal. Additionally, cells cultured in PNJ scaffolds exhibited increased expression of the transcription factor HIF2α, which was not observed in neurosphere culture, providing a potential mechanistic basis for differences in radio-resistance. Differences in PNJ regulation of HIF2α in irradiated and untreated conditions also offered evidence of stem plasticity. These data show PNJ scaffolds provide a unique biomaterial for evaluating dynamic microenvironmental regulation of GSC self-renewal, radioresistance, and stem plasticity.

Wnt and PI3K/Akt/mTOR Survival Pathways as Therapeutic Targets in Glioblastoma

Glioblastoma (GBM) is a devastating type of brain tumor, and current therapeutic treatments, including surgery, chemotherapy, and radiation, are palliative at best. The design of effective and targeted chemotherapeutic strategies for the treatment of GBM require a thorough analysis of specific signaling pathways to identify those serving as drivers of GBM progression and invasion. The Wnt/β-catenin and PI3K/Akt/mTOR (PAM) signaling pathways are key regulators of important biological functions that include cell proliferation, epithelial–mesenchymal transition (EMT), metabolism, and angiogenesis. Targeting specific regulatory components of the Wnt/β-catenin and PAM pathways has the potential to disrupt critical brain tumor cell functions to achieve critical advancements in alternative GBM treatment strategies to enhance the survival rate of GBM patients. In this review, we emphasize the importance of the Wnt/β-catenin and PAM pathways for GBM invasion into brain tissue and explore their potential as therapeutic targets.

AI and High-Grade Glioma for Diagnosis and Outcome Prediction: Do All Machine Learning Models Perform Equally Well?

Radiomic models outperform clinical data for outcome prediction in high-grade gliomas (HGG). However, lack of parameter standardization limits clinical applications. Many machine learning (ML) radiomic models employ single classifiers rather than ensemble learning, which is known to boost performance, and comparative analyses are lacking in the literature. We aimed to compare ML classifiers to predict clinically relevant tasks for HGG: overall survival (OS), isocitrate dehydrogenase (IDH) mutation, O-6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation, epidermal growth factor receptor vIII (EGFR) amplification, and Ki-67 expression, based on radiomic features from conventional and advanced magnetic resonance imaging (MRI). Our objective was to identify the best algorithm for each task. One hundred fifty-six adult patients with pathologic diagnosis of HGG were included. Three tumoral regions were manually segmented: contrast-enhancing tumor, necrosis, and non-enhancing tumor. Radiomic features were extracted with a custom version of Pyradiomics and selected through Boruta algorithm. A Grid Search algorithm was applied when computing ten times K-fold cross-validation (K=10) to get the highest mean and lowest spread of accuracy. Model performance was assessed as AUC-ROC curve mean values with 95% confidence intervals (CI). Extreme Gradient Boosting (xGB) obtained highest accuracy for OS (74,5%), Adaboost (AB) for IDH mutation (87.5%), MGMT methylation (70,8%), Ki-67 expression (86%), and EGFR amplification (81%). Ensemble classifiers showed the best performance across tasks. High-scoring radiomic features shed light on possible correlations between MRI and tumor histology.

RhoGTPase Signalling in Cancer Progression and Dissemination

Rho GTPases are a family of small G proteins that regulate a wide array of cellular processes related to their key roles controlling the cytoskeleton. On the other hand, cancer is a multi-step disease caused by the accumulation of genetic mutations and epigenetic alterations, from the initial stages of cancer development when cells in normal tissues undergo transformation, to the acquisition of invasive and metastatic traits, responsible for a large number of cancer related deaths. In this review, we discuss the role of Rho GTPase signalling in cancer in every step of disease progression. Rho GTPases contribute to tumour initiation and progression, by regulating proliferation and apoptosis, but also metabolism, senescence and cell stemness. Rho GTPases play a major role in cell migration, and in the metastatic process. They are also involved in interactions with the tumour microenvironment and regulate inflammation, contributing to cancer progression. After years of intensive research, we highlight the importance of relevant models in the Rho GTPase field, and we reflect on the therapeutic opportunities arising for cancer patients.

Glioblastoma radiomics to predict survival: Diffusion characteristics of surrounding nonenhancing tissue to select patients for extensive resection

BACKGROUND AND PURPOSE

Glioblastoma (GBM) is an aggressive primary CNS neoplasm with poor overall survival (OS) despite standard of care. On MRI, GBM is usually characterized by an enhancing portion (CET) (surgery target) and a nonenhancing surrounding (NET). Extent of resection is a long debated issue in GBM, with recent evidence suggesting that both CET and NET should be resected in <65 years old patients, regardless of other risk factors (i.e., molecular biomarkers). Our aim was to test a radiomic model for patient survival stratification in <65 years old patients, by analyzing MRI features of NET, to aid tumor resection.

METHODS

Sixty-eight <65 years old GBM patients, with extensive CET resection, were selected. Resection was evaluated by manually segmenting CET on volumetric T1-weighted MRI pre and postsurgery (within 72 h). All patients underwent the same treatment protocol including chemoradiation. NET radiomic features were extracted with a custom version of Pyradiomics. Feature selection was performed with principal component analysis (PCA) and its effect on survival tested with Cox regression model. Twelve months OS discrimination was tested by t-test followed by logistic regression. Statistical significance was set at p<0.05. The most relevant features were identified from the component matrix.

RESULTS

Five PCA components (PC1-5) explained 90% of the variance. PC5 resulted significant in the Cox model (p = 0.002; exp(B) = 0.686), at t-test (p = 0.002) and logistic regression analysis (p = 0.006). Apparent diffusion coefficient (ADC)-based features were the most significant for patient survival stratification.

CONCLUSIONS

ADC radiomic features on NET predict survival after standard therapy and could be used to improve patient selection for more extensive surgery.

The inverse paradigm and the ancestral cell of IDH-wildtype glioblastoma

Rethinking IDH-wildtype glioblastoma through its unique features can help researchers find innovative and effective treatments. It is currently emerging that, after decades of therapeutic impasse, some traditional concepts regarding IDH-wildtype glioblastoma need to be supplemented and updated to overcome therapeutic resistance. Indeed, multiple clinical aspects and recent indirect and direct experimental data are providing evidence that the supratentorial brain parenchyma becomes entirely and quiescently micro-infiltrated long before primary tumor bulk growth. Furthermore, they are indicating that the known micro-infiltration that occurs during the IDH-wildtype glioblastoma growth and evolution is not at the origin of distant relapses. It follows that the ubiquitous supratentorial brain parenchyma micro-infiltration as a source for the development of widespread distant recurrences is actually due to the silent stage that precedes tumor growth rather than to the latter. All this implies that, in addition to the heterogeneity of the primary bulk, there is a second crucial cause of therapeutic resistance that has never hitherto been identified and challenged. In this regard, the ancestral founder cancer stem cell (CSC) appears as the key cell that can link the two causes of resistance.

Rationale and Clinical Implications of Fluorescein-Guided Supramarginal Resection in Newly Diagnosed High-Grade Glioma

Current standard of care for glioblastoma is surgical resection followed by temozolomide chemotherapy and radiation. Recent studies have demonstrated that >95% extent of resection is associated with better outcomes, including prolonged progression-free and overall survival. The diffusely infiltrative pattern of growth in gliomas results in microscopic extension of tumor cells into surrounding brain parenchyma that makes complete resection unattainable. The historical goal of surgical management has therefore been maximal safe resection, traditionally guided by MRI and defined as removal of all contrast-enhancing tumor. Optimization of surgical resection has led to the concept of supramarginal resection, or removal beyond the contrast-enhancing region on MRI. This strategy of extending the cytoreductive goal targets a tumor region thought to be important in the recurrence or progression of disease as well as resistance to systemic and local treatment. This approach must be balanced against the risk of impacting eloquent regions of brain and causing permanent neurologic deficit, an important factor affecting overall survival. Over the years, fluorescent agents such as fluorescein sodium have been explored as a means of more reliably delineating the boundary between tumor core, tumor-infiltrated brain, and surrounding cortex. Here we examine the rationale behind extending resection into the infiltrative tumor margins, review the current literature surrounding the use of fluorescein in supramarginal resection of gliomas, discuss the experience of our own institution in utilizing fluorescein to maximize glioma extent of resection, and assess the clinical implications of this treatment strategy.

Radiomics-based neural network predicts recurrence patterns in glioblastoma using dynamic susceptibility contrast-enhanced MRI

Glioblastoma remains the most devastating brain tumor despite optimal treatment, because of the high rate of recurrence. Distant recurrence has distinct genomic alterations compared to local recurrence, which requires different treatment planning both in clinical practice and trials. To date, perfusion-weighted MRI has revealed that perfusional characteristics of tumor are associated with prognosis. However, not much research has focused on recurrence patterns in glioblastoma: namely, local and distant recurrence. Here, we propose two different neural network models to predict the recurrence patterns in glioblastoma that utilizes high-dimensional radiomic profiles based on perfusion MRI: area under the curve (AUC) (95% confidence interval), 0.969 (0.903-1.000) for local recurrence; 0.864 (0.726-0.976) for distant recurrence for each patient in the validation set. This creates an opportunity to provide personalized medicine in contrast to studies investigating only group differences. Moreover, interpretable deep learning identified that salient radiomic features for each recurrence pattern are related to perfusional intratumoral heterogeneity. We also demonstrated that the combined salient radiomic features, or "radiomic risk score", increased risk of recurrence/progression (hazard ratio, 1.61; p = 0.03) in multivariate Cox regression on progression-free survival.

Quantitative mapping of individual voxels in the peritumoral region of IDH-wildtype glioblastoma to distinguish between tumor infiltration and edema

PURPOSE

The peritumoral region (PTR) in glioblastoma (GBM) represents a combination of infiltrative tumor and vasogenic edema, which are indistinguishable on magnetic resonance imaging (MRI). We developed a radiomic signature by using imaging data from low grade glioma (LGG) (marker of tumor) and PTR of brain metastasis (BM) (marker of edema) and applied it on the GBM PTR to generate probabilistic maps.

METHODS

270 features were extracted from T1-weighted, T2-weighted, and apparent diffusion coefficient maps in over 3.5 million voxels of LGG (36 segments) and BM (45 segments) scanned in a 1.5T MRI. A support vector machine classifier was used to develop the radiomics model from approximately 50% voxels (downsampled to 10%) and validated with the remaining. The model was applied to over 575,000 voxels of the PTR of 10 patients with GBM to generate a quantitative map using Platt scaling (infiltrative tumor vs. edema).

RESULTS

The radiomics model had an accuracy of 0.92 and 0.79 in the training and test set, respectively (LGG vs. BM). When extrapolated on the GBM PTR, 9 of 10 patients had a higher percentage of voxels with a tumor-like signature over radiological recurrence areas. In 7 of 10 patients, the areas under curves (AUC) were > 0.50 confirming a positive correlation. Including all the voxels from the GBM patients, the infiltration signature had an AUC of 0.61 to predict recurrence.

CONCLUSION

A radiomic signature can demarcate areas of microscopic tumors from edema in the PTR of GBM, which correlates with areas of future recurrence.

Image-based personalization of computational models for predicting response of high-grade glioma to chemoradiation

High-grade gliomas are an aggressive and invasive malignancy which are susceptible to treatment resistance due to heterogeneity in intratumoral properties such as cell proliferation and density and perfusion. Non-invasive imaging approaches can measure these properties, which can then be used to calibrate patient-specific mathematical models of tumor growth and response. We employed multiparametric magnetic resonance imaging (MRI) to identify tumor extent (via contrast-enhanced T1-weighted, and T2-FLAIR) and capture intratumoral heterogeneity in cell density (via diffusion-weighted imaging) to calibrate a family of mathematical models of chemoradiation response in nine patients with unresected or partially resected disease. The calibrated model parameters were used to forecast spatially-mapped individual tumor response at future imaging visits. We then employed the Akaike information criteria to select the most parsimonious member from the family, a novel two-species model describing the enhancing and non-enhancing components of the tumor. Using this model, we achieved low error in predictions of the enhancing volume (median: - 2.5%, interquartile range: 10.0%) and a strong correlation in total cell count (Kendall correlation coefficient 0.79) at 3-months post-treatment. These preliminary results demonstrate the plausibility of using multiparametric MRI data to inform spatially-informative, biologically-based predictive models of tumor response in the setting of clinical high-grade gliomas.

A role for GLUT3 in glioblastoma cell invasion that is not recapitulated by GLUT1

The multifaceted roles of metabolism in invasion have been investigated across many cancers. The brain tumor glioblastoma (GBM) is a highly invasive and metabolically plastic tumor with an inevitable recurrence. The neuronal glucose transporter 3 (GLUT3) was previously reported to correlate with poor glioma patient survival and be upregulated in GBM cells to promote therapeutic resistance and survival under restricted glucose conditions. It has been suggested that the increased glucose uptake mediated by GLUT3 elevation promotes survival of circulating tumor cells to facilitate metastasis. Here we suggest a more direct role for GLUT3 in promoting invasion that is not dependent upon changes in cell survival or metabolism. Analysis of glioma datasets demonstrated that GLUT3, but not GLUT1, expression was elevated in invasive disease. In human xenograft derived GBM cells, GLUT3, but not GLUT1, elevation significantly increased invasion in transwell assays, but not growth or migration. Further, there were no changes in glycolytic metabolism that correlated with invasive phenotypes. We identified the GLUT3 C-terminus as mediating invasion: substituting the C-terminus of GLUT1 for that of GLUT3 reduced invasion. RNA-seq analysis indicated changes in extracellular matrix organization in GLUT3 overexpressing cells, including upregulation of osteopontin. Together, our data suggest a role for GLUT3 in increasing tumor cell invasion that is not recapitulated by GLUT1, is separate from its role in metabolism and survival as a glucose transporter, and is likely broadly applicable since GLUT3 expression correlates with metastasis in many solid tumors.

The distribution of liver cancer stem cells correlates with the mechanical heterogeneity of liver cancer tissue

The survival of cancer stem cells is usually limited to a specific tumor microenvironment, and this microenvironment plays a vital role in the development of tumors. The mechanical properties of the microenvironment differ in different regions of solid tumors. However, in solid tumors, whether the distribution of cancer stem cells relates to the mechanical microenvironment of different regions is still unclear. In this study, we undertook a biophysical and biochemical assessment of the changes in the mechanical properties of liver tissue during the progression of liver cancer and explored the distribution of liver cancer stem cells in liver cancer tissues. Our analysis confirmed previous observations that the stiffness of liver tissue gradually increased with the progress of fibrosis. In liver cancer tissues, we found obvious mechanical heterogeneity: the core of the tumor was soft, the invasive front tissue was the hardest, and the para-cancer tissue was in an intermediate state. Interestingly, the greatest number of liver cancer stem cells was found in the invasive front part of the tumor. We finally established that stroma stiffness correlated with the number of liver cancer stem cells. These findings indicate that the distribution of liver cancer stem cells correlates with the mechanical heterogeneity of liver cancer tissue. This result provides a theoretical basis for the development of targeted therapies against the mechanical microenvironment of liver cancer stem cells.

Radiomic prediction models for the level of Ki-67 and p53 in glioma

OBJECTIVE

To identify glioma radiomic features associated with proliferation-related Ki-67 antigen and cellular tumour antigen p53 levels, common immunohistochemical markers for differentiating benign from malignant tumours, and to generate radiomic prediction models.

METHODS

Patients with glioma, who were scanned before therapy using standard brain magnetic resonance imaging (MRI) protocols on T1 and T2 weighted imaging, were included. For each patient, regions-of-interest (ROI) were drawn based on tumour and peritumoral areas (5/10/15/20 mm), and features were identified using feature calculations, and used to create and assess logistic regression models for Ki-67 and p53 levels.

RESULTS

A total of 92 patients were included. The best area under the curve (AUC) for the Ki-67 model was 0.773 for T2 weighted imaging in solid glioma (sensitivity, 0.818; specificity, 0.833), followed by a less reliable AUC of 0.773 (sensitivity, 0.727; specificity 0.667) in 20-mm peritumoral areas. The highest AUC for the p53 model was 0.709 (sensitivity, 1; specificity, 0.4) for T2 weighted imaging in 10-mm peritumoral areas.

CONCLUSION

Using T2-weighted imaging, the prediction model for Ki-67 level in solid glioma tissue was better than the p53 model. The 20-mm and 10-mm peritumoral areas in the Ki-67 and p53 model, respectively, showed predictive effects, suggesting value in further research into areas without conventional MRI features.

Immunohistochemical Analysis of DNA Repair- and Drug-Efflux-Associated Molecules in Tumor and Peritumor Areas of Glioblastoma

Glioblastoma (GBM), the most commonly occurring primary tumor arising within the central nervous system, is characterized by high invasiveness and poor prognosis. In spite of the improvement in surgical techniques, along with the administration of chemo- and radiation therapy and the incessant investigation in search of prospective therapeutic targets, the local recurrence that frequently occurs within the peritumoral brain tissue makes GBM the most malignant and terminal type of astrocytoma. In the current study, we investigated both GBM and peritumoral tissues obtained from 55 hospitalized patients and the expression of three molecules involved in the onset of resistance/unresponsiveness to chemotherapy: O6-methylguanine methyltransferase (MGMT), breast cancer resistance protein (BCRP1), and A2B5. We propose that the expression of these molecules in the peritumoral tissue might be crucial to promoting the development of early tumorigenic events in the tissue surrounding GBM as well as responsible for the recurrence originating in this apparently normal area and, accordingly, for the resistance to treatment with the standard chemotherapeutic regimen. Notably, the inverse correlation found between MGMT expression in peritumoral tissue and patients’ survival suggests a prognostic role for this protein.

Intratumoral Distribution of Lactate and the Monocarboxylate Transporters 1 and 4 in Human Glioblastoma Multiforme and Their Relationships to Tumor Progression-Associated Markers

(1) Background: Metabolic reprogramming has been postulated to be one of the hallmarks of cancer, thus representing a promising therapeutic target also in glioblastoma multiforme (GBM). Hypoxic tumor cells produce lactate, and monocarboxylate transporters (MCTs) play an important role in its distribution; (2) Methods: We examined the distribution of lactate by multi voxel magnetic resonance spectroscopic imaging and ELISA in glioblastoma multiforme (GBM) patients. In addition, we investigated the expression and cellular localization of MCT1, MCT4, and of several markers connected to tumor progression by quantitative PCR and immunofluorescence double-staining in human GBM ex vivo tissues; (3) Results: The highest lactate concentration was found at the center of the vital parts of the tumor. Three main GBM groups could be distinguished according to their regional gene expression differences of the investigated genes. MCT1 and MCT4 were found on cells undergoing epithelial to mesenchymal transition and on tumor stem-like cells. GBM cells revealing an expression of cellular dormancy markers, showed positive staining for MCT4; (4) Conclusion: Our findings indicate the existence of individual differences in the regional distribution of MCT1 and MCT4 and suggest that both transporters have distinct connections to GBM progression processes, which could contribute to the drug resistance of MCT-inhibitors.

High gene expression levels of VEGFA and CXCL8 in the peritumoral brain zone are associated with the recurrence of glioblastoma: A bioinformatics analysis

The present study aimed to identify differentially regulated genes between the peritumoral brain zone (PBZ) and tumor core (TC) of glioblastoma (GBM), to elucidate the underlying molecular mechanisms and provide a target for the treatment of tumors. The GSE13276 and GSE116520 datasets were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) for the PBZ and TC were obtained using the GEO2R tool. The bioinformatics and evolutionary genomics online tool Venn was used to identify common DEGs between the two datasets. The Database for Annotation, Visualization, and Integrated Discovery online tool was used to analyze enriched pathways of the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The Search Tool for the Retrieval of Interacting Genes/Proteins online tool was used to construct a protein-protein interaction (PPI) network of DEGs. Hub genes were identified using Cytohubba, a plug-in for Cytoscape. The Gene Expression Profiling Interactive Analysis (GEPIA) database was utilized to perform survival analysis. In total, 75 DEGs, including 12 upregulated and 63 downregulated genes, were identified. In the GO term analysis, these DEGs were mainly enriched in ‘regulation of angiogenesis’ and ‘central nervous system development’. Furthermore, in the KEGG pathway analysis, the DEGs were mainly enriched in ‘bladder cancer’ and ‘endocytosis’. When filtering the results of the PPI network analysis using Cytohubba, a total of 10 hub genes, including proteolipid protein 1, myelin associated oligodendrocyte basic protein, contactin 2, myelin oligodendrocyte glycoprotein, myelin basic protein, myelin associated glycoprotein, SRY-box transcription factor 10, C-X-C motif chemokine ligand 8 (CXCL8), vascular endothelial growth factor A (VEGFA) and plasmolipin, were identified. These hub genes were further subjected to GO term and KEGG pathway analysis, and were revealed to be enriched in ‘central nervous system development’, ‘bladder cancer’ and ‘rheumatoid arthritis’. These hub genes were used to perform survival analysis using the GEPIA database, and it was determined that VEGFA and CXCL8 were significantly associated with a reduction in the overall survival of patients with GBM. In conclusion, the results suggest that the recurrence of GBM is associated with high gene expression levels VEGFA and CXCL8, and the development of the central nervous system.

Hypoxia Can Induce Migration of Glioblastoma Cells Through a Methylation-Dependent Control of ODZ1 Gene Expression

The transmembrane protein ODZ1 has been associated with the invasive capacity of glioblastoma (GBM) cells through upregulation of RhoA/ROCK signaling, but the mechanisms triggering the ODZ1 pathway remain elusive. In addition, it is widely accepted that hypoxia is one of the main biological hallmarks of the GBM microenvironment and it is associated with treatment resistance and poor prognosis. Here we show that hypoxic tumor regions express higher levels of ODZ1 and that hypoxia induces ODZ1 expression in GBM cells by regulating the methylation status of the ODZ1 promoter. Hypoxia-induced upregulation of ODZ1 correlates with higher migration capacity of GBM cells that is drastically reduced by knocking down ODZ1. In vitro methylation of the promoter decreases its transactivation activity and we found a functionally active CpG site at the 3'end of the promoter. This site is hypermethylated in somatic neural cells and mainly hypomethylated in GBM cells. Mutagenesis of this CpG site reduces the promoter activity in response to hypoxia. Overall, we identify hypoxia as the first extracellular activator of ODZ1 expression and describe that hypoxia controls the levels of this migration-inducer, at least in part, by regulating the methylation status of the ODZ1 gene promoter.

Dissecting and rebuilding the glioblastoma microenvironment with engineered materials

Glioblastoma (GBM) is the most aggressive and common form of primary brain cancer. Several decades of research have provided great insight into GBM progression; however, the prognosis remains poor with a median patient survival time of ~ 15 months. The tumour microenvironment (TME) of GBM plays a crucial role in mediating tumour progression and thus is being explored as a therapeutic target. Progress in the development of treatments targeting the TME is currently limited by a lack of model systems that can accurately recreate the distinct extracellular matrix composition and anatomic features of the brain, such as the blood-brain barrier and axonal tracts. Biomaterials can be applied to develop synthetic models of the GBM TME to mimic physiological and pathophysiological features of the brain, including cellular and ECM composition, mechanical properties, and topography. In this Review, we summarize key features of the GBM microenvironment and discuss different strategies for the engineering of GBM TME models, including 2D and 3D models featuring chemical and mechanical gradients, interfaces and fluid flow. Finally, we highlight the potential of engineered TME models as platforms for mechanistic discovery and drug screening as well as preclinical testing and precision medicine.

Molecular and Clinical Insights into the Invasive Capacity of Glioblastoma Cells

The invasive capacity of GBM is one of the key tumoral features associated with treatment resistance, recurrence, and poor overall survival. The molecular machinery underlying GBM invasiveness comprises an intricate network of signaling pathways and interactions with the extracellular matrix and host cells. Among them, PI3k/Akt, Wnt, Hedgehog, and NFkB play a crucial role in the cellular processes related to invasion. A better understanding of these pathways could potentially help in developing new therapeutic approaches with better outcomes. Nevertheless, despite significant advances made over the last decade on these molecular and cellular mechanisms, they have not been translated into the clinical practice. Moreover, targeting the infiltrative tumor and its significance regarding outcome is still a major clinical challenge. For instance, the pre- and intraoperative methods used to identify the infiltrative tumor are limited when trying to accurately define the tumor boundaries and the burden of tumor cells in the infiltrated parenchyma. Besides, the impact of treating the infiltrative tumor remains unclear. Here we aim to highlight the molecular and clinical hallmarks of invasion in GBM.

Transcriptomic analysis reveals that BMP4 sensitizes glioblastoma tumor-initiating cells to mechanical cues

The poor prognosis of glioblastoma (GBM) is associated with a highly invasive stem-like subpopulation of tumor-initiating cells (TICs), which drive recurrence and contribute to intra-tumoral heterogeneity through differentiation. These TICs are better able to escape extracellular matrix-imposed mechanical restrictions on invasion than their more differentiated progeny, and sensitization of TICs to extracellular matrix mechanics extends survival in preclinical models of GBM. However, little is known about the molecular basis of the relationship between TIC differentiation and mechanotransduction. Here we explore this relationship through a combination of transcriptomic analysis and studies with defined-stiffness matrices. We show that TIC differentiation induced by bone morphogenetic protein 4 (BMP4) suppresses expression of proteins relevant to extracellular matrix signaling and sensitizes TIC spreading to matrix stiffness. Moreover, our findings point towards a previously unappreciated connection between BMP4-induced differentiation, mechanotransduction, and metabolism. Notably, stiffness and differentiation modulate oxygen consumption, and inhibition of oxidative phosphorylation influences cell spreading in a stiffness- and differentiation-dependent manner. Our work integrates bioinformatic analysis with targeted molecular measurements and perturbations to yield new insight into how morphogen-induced differentiation influences how GBM TICs process mechanical inputs.

Mechanical Durotactic Environment Enhances Specific Glioblastoma Cell Responses

Background: A hallmark of glioblastoma is represented by their ability to widely disperse throughout the brain parenchyma. The importance of developing new anti-migratory targets is critical to reduce recurrence and improve therapeutic efficacy. Methods: Polydimethylsiloxane substrates, either mechanically uniform or presenting durotactic cues, were fabricated to assess GBM cell morphological and dynamical response with and without pharmacological inhibition of NNMII contractility, of its upstream regulator ROCK and actin polymerization. Results: Glioma cells mechanotactic efficiency varied depending on the rigidity compliance of substrates. Morphologically, glioma cells on highly rigid and soft bulk substrates displayed bigger and elongated aggregates whereas on durotactic substrates the same cells were homogeneously dispersed with a less elongated morphology. The durotactic cues also induced a motility change, cell phenotype dependent, and with cells being more invasive on stiffer substrates. Pharmacological inhibition of myosin or ROCK revealed a rigidity-insensitivity, unlike inhibition of microfilament contraction and polymerization of F-actin, suggesting that alternative signalling is used to respond to durotactic cues. Conclusions: The presence of a distinct mechanical cue is an important factor in cell migration. Together, our results provide support for a durotactic role of glioma cells that acts through actomyosin contractility to regulate the aggressive properties of GBM cells.

The vitamin K-dependent factor, protein S, regulates brain neural stem cell migration and phagocytic activities towards glioma cells

Malignant gliomas are the most common primary brain tumors. Due to both their invasive nature and resistance to multimodal treatments, these tumors have a very high percentage of recurrence leading in most cases to a rapid fatal outcome. Recent data demonstrated that neural stem/progenitor cells possess an inherent ability to migrate towards glioma cells, track them in the brain and reduce their growth. However, mechanisms involved in these processes have not been explored in-depth. In the present report, we investigated interactions between glioma cells and neural stem/progenitor cells derived from the subventricular zone, the major brain stem cell niche. Our data show that neural stem/progenitor cells are attracted by cultured glioma-derived factors. Using multiple approaches, we demonstrate for the first time that the vitamin K-dependent factor protein S produced by glioma cells is involved in tumor tropism through a mechanism involving the tyrosine kinase receptor Tyro3 that, in turn, is expressed by neural stem/progenitor cells. Neural stem/progenitor cells decrease the growth of both glioma cell cultures and clonogenic population. Cultured neural stem/progenitor cells also engulf, by phagocytosis, apoptotic glioma cell-derived fragments and this mechanism depends on the exposure of phosphatidylserine eat-me signal and is stimulated by protein S. The disclosure of a role of protein S/Tyro3 axis in neural stem/progenitor cell tumor-tropism and the demonstration of a phagocytic activity of neural stem/progenitor cells towards dead glioma cells that is regulated by protein S open up new perspectives for both stem cell biology and brain physiopathology.

Pathological and Molecular Features of Glioblastoma and Its Peritumoral Tissue

Glioblastoma (GBM) is one of the most aggressive and lethal human brain tumors. At present, GBMs are divided in primary and secondary on the basis of the mutational status of the isocitrate dehydrogenase (IDH) genes. In addition, IDH1 and IDH2 mutations are considered crucial to better define the prognosis. Although primary and secondary GBMs are histologically indistinguishable, they retain distinct genetic alterations that account for different evolution of the tumor. The high invasiveness, the propensity to disperse throughout the brain parenchyma, and the elevated vascularity make these tumors extremely recidivist, resulting in a short patient median survival even after surgical resection and chemoradiotherapy. Furthermore, GBM is considered an immunologically cold tumor. Several studies highlight a highly immunosuppressive tumor microenvironment that promotes recurrence and poor prognosis. Deeper insight into the tumor immune microenvironment, together with the recent discovery of a conventional lymphatic system in the central nervous system (CNS), led to new immunotherapeutic strategies. In the last two decades, experimental evidence from different groups proved the existence of cancer stem cells (CSCs), also known as tumor-initiating cells, that may play an active role in tumor development and progression. Recent findings also indicated the presence of highly infiltrative CSCs in the peritumoral region of GBM. This region appears to play a key role in tumor growing and recurrence. However, until recently, few studies investigated the biomolecular characteristics of the peritumoral tissue. The aim of this review is to recapitulate the pathological features of GBM and of the peritumoral region associated with progression and recurrence.

Glioblastoma Unique Features Drive the Ways for Innovative Therapies in the Trunk-branch Era

Glioblastoma multiforme is a solid tumor with particular aspects due to its organ of origin and its development modalities. The brain is very sensitive to oxygen and glucose deprivation and it is the only organ that cannot be either transplanted or entirely removed. Furthermore, many clues and recent indirect experimental evidence indicate that the micro-infiltration of the whole brain parenchyma occurs in very early stages of tumor bulk growth or likely even before. As a consequence, the primary glioblastoma (IDH-wildtype, WHO 2016) is the only tumor where the malignant (i.e. distantly infiltrating the organ of origin) and deadly (i.e. leading cause to patient’s death) phases coincide and overlap in one single phase of its natural history. To date, the prognosis of optimally treated glioblastoma patients remains dismal despite recent fundamental progress in neurosurgical techniques which are enabling better maximal safe resection and survival outcome. Intratumor variegated heterogeneity of glioblastoma bulk due to trunk-branch evolution and very early micro-infiltration and settlement of neoplastic cells in the entire brain parenchyma are the reasons for resistance to current therapeutic treatments. With the aim of future innovative and effective therapies, this paper deals with the unique glioblastoma features, the appropriate research methods as well as the strategies to follow to overcome current causes of resistance.

EGFRvIII Is Expressed in Cellular Areas of Tumor in a Subset of Glioblastoma

Epidermal growth factor receptor variant III (EGFRvIII) is a tumor-specific cell surface antigen often expressed in glioblastoma and has drawn much attention as a possible therapeutic target. We performed immunohistochemistry on histology sections of surgical specimens taken from 67 cases with glioblastoma, isocitrate dehydrogenase-wild type, and evaluated the morphological characteristics and distribution of the EGFRvIII-positive tumor cells. We then evaluated the localization of EGFRvIII-expression within the tumor and peritumoral areas. EGFRvIII immunopositivity was detected in 15 specimens taken from 13 patients, including two recurrent specimens taken from the same patient at relapse. Immunofluorescence staining demonstrated that EGFRvIII-positive cells were present in cells positive for glial fibrillary acidic protein (GFAP), and some showed astrocytic differentiation with multiple fine processes and others did not shown. The EGFRvIII-positive cells were located in cellular areas of the tumor, but not in the invading zone. In the two recurrent cases, EGFRvIII-positive cells were markedly decreased in one case and retained in the other. With regard to overall survival, univariate analysis indicated that EGFRvIII-expression in patients with glioblastoma was not significantly associated with a favorable outcome. Double-labeling immunofluorescence staining of EGFRvIII and GFAP showed that processes of large, well differentiated, GFAP-positive glia extend to and surround less differentiated, EGFRvIII-positive glial cells in cellular areas of tumor. However, in the tumor periphery, EGFRvIII-positive tumor cells were not observed. This finding suggests that EGFRvIII is involved in tumor proliferation, but that invading glioma cells lose their EGFRvIII expression.

Not Everyone Fits the Mold: Intratumor and Intertumor Heterogeneity and Innovative Cancer Drug Design and Development

Disruptive innovations in medicine are game-changing in nature and bring about radical shifts in the way we understand human diseases, their treatment, and/or prevention. Yet, disruptive innovations in cancer drug design and development are still limited. Therapies that cure all cancer patients are in short supply or do not exist at all. Chief among the causes of this predicament is drug resistance, a mechanism that is much more dynamic than previously understood. Drug resistance has limited the initial success experienced with biomarker-guided targeted therapies as well. A major contributor to drug resistance is intratumor heterogeneity. For example, within solid tumors, there are distinct subclones of cancer cells, presenting profound complexity to cancer treatment. Well-known contributors to intratumor heterogeneity are genomic instability, the microenvironment, cellular genotype, cell plasticity, and stochastic processes. This expert review explains that for oncology drug design and development to be more innovative, we need to take into account intratumor heterogeneity. Initially thought to be the preserve of cancer cells, recent evidence points to the highly heterogeneous nature and diverse locations of stromal cells, such as cancer-associated fibroblasts (CAFs) and cancer-associated macrophages (CAMs). Distinct subpopulations of CAFs and CAMs are now known to be located immediately adjacent and distant from cancer cells, with different subpopulations exerting different effects on cancer cells. Disruptive innovation and precision medicine in clinical oncology do not have to be a distant reality, but can potentially be achieved by targeting these spatially separated and exclusive cancer cell subclones and CAF subtypes. Finally, we emphasize that disruptive innovations in drug discovery and development will likely come from drugs whose effect is not necessarily tumor shrinkage.

Tropomyosin Tpm 2.1 loss induces glioblastoma spreading in soft brain-like environments

INTRODUCTION

The brain is a very soft tissue. Glioblastoma (GBM) brain tumours are highly infiltrative into the surrounding healthy brain tissue and invasion mechanisms that have been defined using rigid substrates therefore may not apply to GBM dissemination. GBMs characteristically lose expression of the high molecular weight tropomyosins, a class of actin-associating proteins and essential regulators of the actin stress fibres and focal adhesions that underpin cell migration on rigid substrates.

METHODS

Here, we investigated how loss of the high molecular weight tropomyosins affects GBM on soft matrices that recapitulate the biomechanical architecture of the brain.

RESULTS

We find that Tpm 2.1 is down-regulated in GBM grown on soft substrates. We demonstrate that Tpm 2.1 depletion by siRNA induces cell spreading and elongation in soft 3D hydrogels, irrespective of matrix composition. Tpm 1.7, a second high molecular weight tropomyosin is also down-regulated when cells are cultured on soft brain-like surfaces and we show that effects of this isoform are matrix dependent, with Tpm 1.7 inducing cell rounding in 3D collagen gels. Finally, we show that the absence of Tpm 2.1 from primary patient-derived GBMs correlates with elongated, mesenchymal invasion.

CONCLUSIONS

We propose that Tpm 2.1 down-regulation facilitates GBM colonisation of the soft brain environment. This specialisation of the GBM actin cytoskeleton organisation that is highly suited to the soft brain-like environment may provide novel therapeutic targets for arresting GBM invasion.

Transcriptome profiling reveals PDZ binding kinase as a novel biomarker in peritumoral brain zone of glioblastoma

PURPOSE

Peritumoural brain zone (PT) of glioblastoma (GBM) is the area where tumour recurrence is often observed. We aimed to identify differentially regulated genes between tumour core (TC) and PT to understand the underlying molecular characteristics of infiltrating tumour cells in PT.

METHODS

17 each histologically characterised TC and PT tissues of GBM along with eight control tissues were subjected to cDNA Microarray. PT tissues contained 25-30% infiltrating tumour cells. Data was analysed using R Bioconductor software. Shortlisted genes were validated using qRT-PCR. Expression of one selected candidate gene, PDZ Binding Kinase (PBK) was correlated with patient survival, tumour recurrence and functionally characterized in vitro using gene knock-down approach.

RESULTS

Unsupervised hierarchical clustering showed that TC and PT have distinct gene expression profiles compared to controls. Further, comparing TC with PT, we observed a significant overlap in gene expression profile in both, despite PT having fewer infiltrating tumour cells. qRT-PCR for 13 selected genes validated the microarray data. Expression of PBK was higher in PT as compared to TC and recurrent when compared to newly diagnosed GBM tumours. PBK knock-down showed a significant reduction in cell proliferation, migration and invasion with increase in sensitivity to radiation and Temozolomide treatment.

CONCLUSIONS

We show that several genes of TC are expressed even in PT contributing to the vulnerability of PT for tumour recurrence. PBK is identified as a novel gene up-regulated in PT of GBM with a strong role in conferring aggressiveness, including radio-chemoresistance, thus contributing to recurrence in GBM tumours.

RND1 regulates migration of human glioblastoma stem-like cells according to their anatomical localization and defines a prognostic signature in glioblastoma

Despite post-operative radio-chemotherapy, glioblastoma systematically locally recurs. Tumors contacting the periventricular zone (PVZ) show earlier and more distant relapses than tumors not contacting the PVZ. Since glioblastoma stem-like cells (GSCs) have been proposed to play a major role in glioblastoma recurrence, we decided to test whether GSC migration properties could be different according to their anatomical location (PVZ+/PVZ–). For that purpose, we established paired cultures of GSCs from the cortical area (CT) and the PVZ of glioblastoma patient tumors. We demonstrated that PVZ GSCs possess higher migration and invasion capacities than CT GSCs. We highlighted specific transcriptomic profiles in PVZ versus CT populations and identified a down-regulation of the RhoGTPase, RND1 in PVZ GSCs compared to CT GSCs. Overexpression of RND1, dramatically inhibited PVZ GSC migration and conversely, downregulation of RND1 increased CT GSC migration. Additionally, transcriptomic analyses also revealed a down-regulation of RND1 in glioblastoma compared to normal brain. Using the glioblastoma TCGA database, low levels of RND1 were also shown to correlate with a decreased overall survival of patients. Finally, based on signaling pathways activated in patients with low levels of RND1, we identified an RND1^low signature of six genes (MET, LAMC1, ITGA5, COL5A1, COL3A1, COL1A2) that is an independent prognostic factor in glioblastoma. These findings contribute to explain the shorter time to progression of patients with PVZ involvement and, point out genes that establish the RND1^low signature as key targets genes to impede tumor relapse after treatment.

Endothelium-induced three-dimensional invasion of heterogeneous glioma initiating cells in a microfluidic coculture platform

Glioblastoma (GBM) is a highly invasive primary brain tumor that displays cellular heterogeneity, which is composed of glioma initiating cells (GICs) and their differentiated progeny. GICs play an important role in driving aggressive invasion. In particular, the interaction between GICs and blood vessels is critical because blood vessels are known to serve as routes for the invasion of GICs. However, the effect of endothelial cells on the three-dimensional (3D) invasion process of GICs as well as the spatial relationship between GICs and their differentiated progeny remains unclear. Here, we utilized a microfluidic device to recapitulate the 3D brain tumor microenvironments constituted by human umbilical vein endothelial cells (HUVECs) and type I collagen. Using the device, we found that HUVECs promoted the 3D invasion of heterogeneous glioma cell populations into type I collagen gel. The invasion induced by HUVECs was predominantly preceded by cells positive for nestin, a neural stem cell marker. In contrast, cells positive for tubulin β3 (TUBB3), a differentiated cell marker, rarely preceded invasion. In addition, HUVECs induced the upregulation of TUBB3 in GICs. Finally, we found that the genes associated with invasion, such as integrins α2 and β3, were significantly upregulated in the presence of HUVECs. These results as well as the experimental approach provide valuable knowledge for the development of effective therapeutic strategies targeting the aggressive invasion of GBM.

Biomimetic models to examine microenvironmental regulation of glioblastoma stem cells

Glioblastoma multiforme (GBM), a malignant brain tumor, is the deadliest form of human cancer with low survival rates because of its highly invasive nature. In recent years, there has been a growing appreciation for the role that glioblastoma stem cells (GSCs) play during tumorigenesis and tumor recurrence of GBM. GSCs are a specialized subset of GBM cells with stem cell-like features that contribute to tumor initiation and therapeutic resistance. Thus, to enhance therapeutic efficiency and improve survival, targeting GSCs and their microenvironmental niche appears to be a promising approach. To develop this approach, understanding GSC-microenvironment interactions is crucial. This review discusses various biomimetic model systems to understand the impact of biophysical, biochemical, and cellular microenvironmental cues on GSC behaviors. These models include two-dimensional or matrix-free environment models, engineered biomaterial-based three-dimensional models, co-culture models, and mouse and rat in vivo models. These systems have been used to study the effects of biophysical factors, modulation of signaling pathways, extracellular matrix components, and culture conditions on the GSC phenotype. The advantages and disadvantages of these model systems and their impact in the field of GSC research are discussed.

The pro-tumorigenic effects of metabolic alterations in glioblastoma including brain tumor initiating cells

De-regulated cellular energetics is an emerging hallmark of cancer with alterations to glycolysis, oxidative phosphorylation, the pentose phosphate pathway, lipid oxidation and synthesis and amino acid metabolism. Understanding and targeting of metabolic reprogramming in cancers may yield new treatment options, but metabolic heterogeneity and plasticity complicate this strategy. One highly heterogeneous cancer for which current treatments ultimately fail is the deadly brain tumor glioblastoma. Therapeutic resistance, within glioblastoma and other solid tumors, is thought to be linked to subsets of tumor initiating cells, also known as cancer stem cells. Recent profiling of glioblastoma and brain tumor initiating cells reveals changes in metabolism, as compiled here, that may be more broadly applicable. We will summarize the profound role for metabolism in tumor progression and therapeutic resistance and discuss current approaches to target glioma metabolism to improve standard of care.

PREX1 integrates G protein-coupled receptor and phosphoinositide 3-kinase signaling to promote glioblastoma invasion

A defining feature of the brain cancer glioblastoma is its highly invasive nature. When glioblastoma cells are isolated from patients using serum free conditions, they accurately recapitulate this invasive behaviour in animal models. The Rac subclass of Rho GTPases has been shown to promote invasive behaviour in glioblastoma cells isolated in this manner. However the guanine nucleotide exchange factors responsible for activating Rac in this context have not been characterized previously. PREX1 is a Rac guanine nucleotide exchange factor that is synergistically activated by binding of G protein αγ subunits and the phosphoinositide 3-kinase pathway second messenger phosphatidylinositol 3,4,5 trisphosphate. This makes it of particular interest in glioblastoma, as the phosphoinositide 3-kinase pathway is aberrantly activated by mutation in almost all cases. We show that PREX1 is expressed in glioblastoma cells isolated under serum-free conditions and in patient biopsies. PREX1 promotes the motility and invasion of glioblastoma cells, promoting Rac-mediated activation of p21-associated kinases and atypical PKC, which have established roles in cell motility. Glioblastoma cell motility was inhibited by either inhibition of phosphoinositide 3-kinase or inhibition of G protein βγ subunits. Motility was also inhibited by the generic dopamine receptor inhibitor haloperidol or a combination of the selective dopamine receptor D2 and D4 inhibitors L-741,626 and L-745,870. This establishes a role for dopamine receptor signaling via G protein βγ subunits in glioblastoma invasion and shows that phosphoinositide 3-kinase mutations in glioblastoma require a context of basal G protein–coupled receptor activity in order to promote this invasion.

The extent of edema and tumor synchronous invasion into the subventricular zone and corpus callosum classify outcomes and radiotherapy strategies of glioblastomas

BACKGROUND AND PURPOSE

Irradiating glioblastoma preoperative edema (PE) remains controversial. We investigated the associations between tumors' PE extent with invasion into synchronous subventricular zone and corpus callosum (sSVZCC) and treatment outcomes to provide the clinical evidence for radiotherapy decision-making.

MATERIAL AND METHODS

Extensive PE (EPE) was defined as PE extending ≥2 cm from the tumor edge and extensive progressive disease (EPD) as tumors spreading ≥2 cm from the preoperative tumor edge along PE. The survival and progression patterns were analyzed according to EPE and sSVZCC invasion.

RESULTS

In total, 136 patients were followed for a median of 74.9 (range, 47.6-102.1) months. The median overall survival and progression-free survival were 19.7 versus 28.6 months (p = 0.005) and 11.0 versus 17.4 months (p = 0.011) in patients with EPE+ versus EPE-, and were 18.7 versus 25.4 months (p = 0.021) and 10.7 versus 14.6 months (p = 0.020) in those with sSVZCC+ versus sSVZCC-. The EPD rates for tumors with EPE-/sSVZCC-, EPE-/sSVZCC+, EPE+/sSVZCC-, and EPE+/sSVZCC+ were 2.8%, 7.1%, 37.0%, and 71.9%, respectively. In EPE+/sSVZCC+, tumor migration was associated with the PE extending along the corpus callosum (77.8%) and subventricular zone (50.0%).

CONCLUSIONS

Our results support the need for developing individualized irradiation strategies for glioblastomas according to EPE and sSVZCC.