Probiotics in Health and Disease: Distinct Roles of Different Strains in Natural Killer Cell Activation and Regulation.

Elucidating the role of probiotic bacteria in health and disease perhaps constitutes one of the most exciting and fastest growing fields in medicine as we uncover the beneficial roles of these bacteria in many disease processes including cancer. We and others have reported previously that probiotic bacteria play a significant role in the activation of many cells including the cancer fighting natural killer (NK) cells. NK cells are the key immune effectors which control tumor growth and metastasis due to their ability to mediate direct cytotoxicity and/or differentiation of cancer stem cells/undifferentiated tumors through secreted and membrane bound interferon-gamma and tumor necrosis factor-alpha. In this review, we present an overview of recent studies from our laboratory and those of the others on their beneficial effects on immune cell function in particular on NK cells. In addition, we also highlight the current understanding of the role of probiotics in enhancement of the effectiveness of cancer therapeutics. Moreover, we discuss the functional impairment of cancer patients' NK cells and the role of probiotics in reversal of such functional impairment. NK cell-based immuno-therapies in combination with well-selected strains of probiotic bacteria may probably represent one of the best adjunct therapeutic approaches to prevent and treat cancer in the future.

Upregulation of Cathepsin X in Glioblastoma: Interplay with γ-Enolase and the Effects of Selective Cathepsin X Inhibitors.

Glioblastoma (GBM) is the most common and deadly primary brain tumor in adults. Understanding GBM pathobiology and discovering novel therapeutic targets are critical to finding efficient treatments. Upregulation of the lysosomal cysteine carboxypeptidase cathepsin X has been linked to immune dysfunction and neurodegenerative diseases, but its role in cancer and particularly in GBM progression in patients is unknown. In this study, cathepsin X expression and activity were found to be upregulated in human GBM tissues compared to low-grade gliomas and nontumor brain tissues. Cathepsin X was localized in GBM cells as well as in tumor-associated macrophages and microglia. Subsequently, potent irreversible (AMS36) and reversible (Z7) selective cathepsin X inhibitors were tested in vitro. Selective cathepsin X inhibitors decreased the viability of patient-derived GBM cells as well as macrophages and microglia that were cultured in conditioned media of GBM cells. We next examined the expression pattern of neuron-specific enzyme γ-enolase, which is the target of cathepsin X. We found that there was a correlation between high proteolytic activity of cathepsin X and C-terminal cleavage of γ-enolase and that cathepsin X and γ-enolase were colocalized in GBM tissues, preferentially in GBM-associated macrophages and microglia. Taken together, our results on patient-derived material suggest that cathepsin X is involved in GBM progression and is a potential target for therapeutic approaches against GBM.

Brain malignancies: Glioblastoma and brain metastases.

Brain, the major organ of the central nervous system controls and processes most of body activities. Therefore, the most aggressive brain tumor - glioblastoma and metastases from other organs to the brain are lethal leaving the patients with very short time of survival. The brain tissue landscape is very different from any other tissues and the specific microenvironment, comprising stem cells niches and blood-brain barrier, significantly influences the low rate of glioblastoma metastasis out of the brain, but better accommodates brain-invading cancer. In contrast to low frequency (0.5%) of all glioblastoma metastases, 10%-45% of other primary cancers do metastasize to the brain. This review addresses general cellular and molecular pathways that are to some extent similar in both types of metastases, involving circulating tumor cells (CTCs) with cancer stem cells (CSCs) characteristics, and metastatic niches. The invasion is a dynamic process involving reversible epithelial-to-mesenchymal (EMT) cell process, creating a transient gradient state that is inter-connected with epigenetic plasticity of the metastasizing (m)CSCs. These cells can switch between stationary, low proliferating/dormant state to a migratory, mesenchymal-like state. Settling in their respective niches as dormant CSCs in the secondary organ is a common feature in all types of metastases. In glioblastoma metastasis, the malignant mGSC cells express markers of mesenchymal GSC subtype (MES-GSC), such as CD44 and YK-40 and their major obstacle seems to be propagating in the in various organs' microenvironments, different from the niches that home GSCs in the primary glioblastoma. Focusing on one stromal component in the glioblastoma niches, the mesenchymal stem cells (MSCs), we report herein on their differential effects on glioblastoma cells, highly depending on their genetic subtype. On the other hand, in brain metastases, the major hindrance to metastatic progression of mCSCs seem to be crossing the blood-brain-barrier. Novel therapeutic approaches for brain metastases from various cancer types are advancing slowly, and the general trends involve targeting metastatic sub-clones and selective determinants of their niches. The update on the four most common brain metastases from lung, breast, melanoma and colorectal carcinoma is presented.

Multiple Defects of Natural Killer Cells in Cancer Patients: Anarchy, Dysregulated Systemic Immunity, and Immunosuppression in Metastatic Cancer.

We have previously demonstrated that natural killer (NK) cells are the main immune effectors that can mediate selection and differentiation of different cancer stem cells and undifferentiated tumors via lysis and secreted or membrane-bound interferon-γ and tumor necrosis factor-α, respectively. This leads to growth inhibition and tumor metastasis curtailment. In this review, we present an overview of our findings on NK cell biology and its significance in selection and differentiation of stem-like tumors using in vitro and in vivo studies conducted in nonobese diabetic/severe combined immunodeficiency (scid)/interleukin-Rγ--, humanized-bone-marrow/liver/thymus (hu-BLT) mice, and those of human cancer patients. Moreover, we present recent advances in NK cell expansion and therapeutic delivery and discuss the superiority of allogeneic supercharged NK cells over their autologous counterparts for cancer treatment. We review potential loss of NK cell numbers and function at neoplastic and preneoplastic stages of tumorigenesis as a potential mechanism for pancreatic cancer induction and progression. We believe that NK cells should be placed highly in the armamentarium of tumor immunotherapy due to their indispensable role in targeting cancer stem-like/poorly differentiated tumors and a variety of other key NK cell functions that are discussed in this report, including their role in CD8+ T-cell expansion and targeting gene knockout or dedifferentiated tumors. The combination of allogeneic supercharged NK cells and other immunotherapeutic strategies such as oncolytic viruses, antibody-dependent cellular cytotoxicity-inducing antibodies, checkpoint inhibitors, chimeric antigen receptor (CAR)-T cells and CAR-NK cells, chemotherapeutics, and radiotherapeutic strategies can be used for optimal eradication of tumors.

TRIM28 Selective Nanobody Reduces Glioblastoma Stem Cell Invasion.

Glioblastoma (GB), is the most common and aggressive malignant primary brain tumour in adults. Intra- and inter-tumour heterogeneity, infiltrative GB cell invasion and presence of therapy-resistant GB stem cells (GSCs) represent major obstacles to favourable prognosis and poor therapy response. Identifying the biomarkers of the most aggressive tumour cells and their more efficient targeting strategies are; therefore, crucial. Recently, transcription factor TRIM28 has been identified as a GB biomarker and, in this study, we have shown high expression of TRIM28 in GB and in low grade gliomas as well as higher expression in GSCs vs. differentiated GB cells, although in both cases not significant. We demonstrated significant in vitro inhibition of GB cells and GSCs invasiveness and spread in zebrafish brains in vivo by anti-TRIM28 selective nanobody NB237. TRIM28 was also enriched in GB (tumour) core and associated with the expression of stem cell genes, but was not prognostic for overall survival. However, based on the above results, we conclude that TRIM28 nanobody NB237 offers a new opportunity as a GB therapeutic tool.

CCR5-Mediated Signaling Is Involved in Invasion of Glioblastoma Cells in Its Microenvironment.

The chemokine CCL5/RANTES is a versatile inflammatory mediator, which interacts with the receptor CCR5, promoting cancer cell interactions within the tumor microenvironment. Glioblastoma is a highly invasive tumor, in which CCL5 expression correlates with shorter patient survival. Using immunohistochemistry, we identified CCL5 and CCR5 in a series of glioblastoma samples and cells, including glioblastoma stem cells. CCL5 and CCR5 gene expression were significantly higher in a cohort of 38 glioblastoma samples, compared to low-grade glioma and non-cancerous tissues. The in vitro invasion of patients-derived primary glioblastoma cells and glioblastoma stem cells was dependent on CCL5-induced CCR5 signaling and is strongly inhibited by the small molecule CCR5 antagonist maraviroc. Invasion of these cells, which was enhanced when co-cultured with mesenchymal stem cells (MSCs), was inhibited by maraviroc, suggesting that MSCs release CCR5 ligands. In support of this model, we detected CCL5 and CCR5 in MSC monocultures and glioblastoma-associated MSC in tissue sections. We also found CCR5 expressing macrophages were in close proximity to glioblastoma cells. In conclusion, autocrine and paracrine cross-talk in glioblastoma and, in particular, glioblastoma stem cells with its stromal microenvironment, involves CCR5 and CCL5, contributing to glioblastoma invasion, suggesting the CCL5/CCR5 axis as a potential therapeutic target that can be targeted with repositioned drug maraviroc.

Cathepsin K cleavage of SDF-1α inhibits its chemotactic activity towards glioblastoma stem-like cells.

Glioblastoma (GBM) is the most aggressive primary brain tumor with poor patient survival that is at least partly caused by malignant and therapy-resistant glioma stem-like cells (GSLCs) that are protected in GSLC niches. Previously, we have shown that the chemo-attractant stromal-derived factor-1α (SDF-1α), its C-X-C receptor type 4 (CXCR4) and the cysteine protease cathepsin K (CatK) are localized in GSLC niches in glioblastoma. Here, we investigated whether SDF-1α is a niche factor that through its interactions with CXCR4 and/or its second receptor CXCR7 on GSLCs facilitates their homing to niches. Furthermore, we aimed to prove that SDF-1α cleavage by CatK inactivates SDF-1α and inhibits the invasion of GSLCs. We performed mass spectrometric analysis of cleavage products of SDF-1α after proteolysis by CatK. We demonstrated that CatK cleaves SDF-1α at 3 sites in the N-terminus, which is the region of SDF-1α that binds to its receptors. Confocal imaging of human GBM tissue sections confirmed co-localization of SDF-1α and CatK in GSLC niches. In accordance, 2D and 3D invasion experiments using CXCR4/CXCR7-expressing GSLCs and GBM cells showed that SDF-1α had chemotactic activity whereas CatK cleavage products of SDF-1α did not. Besides, CXCR4 inhibitor plerixafor inhibited invasion of CXCR4/CXCR7-expressing GSLCs. In conclusion, CatK can cleave and inactivate SDF-1α. This implies that CatK activity facilitates migration of GSLCs out of niches. We propose that activation of CatK may be a promising strategy to prevent homing of GSLCs in niches and thus render these cells sensitive to chemotherapy and radiation.

Adipose tissue stem cell-derived hepatic progenies as an in vitro model for genotoxicity testing.

The problem of the currently used routine genotoxicity tests is relatively low predictivity of in vitro tests for in vivo genotoxicity and carcinogenicity. An important reason is considered to be inadequate expression of xenobiotic-metabolizing enzymes in indicator cell lines. The aim of our study was to generate metabolically active differentiated hepatic progenies (hDHP) from human adipose tissue-derived mesenchymal stem cells (hASC) for genotoxicity testing. hDHP, generated using a three-step hepatic differentiation procedure, expressed hepatic properties such as glycogen storage and albumin secretion. The results of the comet assay demonstrated comparable sensitivity of hASC and hDHP to detect DNA damage induced by a direct acting genotoxic agent tert-butylhydroperoxide. Exposure to model indirect acting genotoxins benzo(a)pyrene, aflatoxin B1, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine did not induce DNA damage in hASC, while hDHP cells detected DNA damage induced by benzo(a)pyrene and aflatoxin B1, indicating their metabolic activity. The gene and protein expression analysis confirmed the presence of key enzymes involved in metabolism of the three genotoxins in hDHP cells. Moreover, the exposure of hDHP to the model pro-carcinogens altered the expression of selected metabolic genes. hDHP were further immortalized with hTERT transfection, resulting in a stable cell line that can be matured to metabolically active hDHP ready for genotoxicity testing in only 2 weeks. The advantage of these immortalized cells is their prolonged replicative life span and consequently limitless supply of hDHP cells. We conclude that hDHP cells have a great potential for the application in the routine genotoxicity testing and are therefore worth further investigations.

Proteases and cytokines as mediators of interactions between cancer and stromal cells in tumours.

Proteolytic enzymes are highly relevant in different processes of cancer progression. Their interplay with other signalling molecules such as cytokines represents important regulation of multicellular cross-talk. In this review, we discuss protease regulation mechanisms of cytokine signalling in various types of cancer. Additionally, we highlight the reverse whereby cytokines have an impact on protease expression in an autocrine and paracrine manner, representing complex feedback mechanisms among multiple members of these two protein families. The relevance of the protease-cytokine axis is illustrated in glioblastoma, where interactions between normal mesenchymal stem cells and cancer cells play an important role in this very malignant form of brain cancer.

Glioblastoma-mesenchymal stem cell communication modulates expression patterns of kinin receptors: Possible involvement of bradykinin in information flow.

The most aggressive subtype of brain tumors is glioma WHO grade IV, the glioblastoma (GBM). The present work aims to elucidate the role of kinin receptors in interactions between GBM cells and mesenchymal stem cells (MSC). The GBM cell line U87-MG was stably transfected to express dsRed protein, single cell cloned, expanded, and cultured with MSC, both in the direct co-cultures (DC) and indirect co-cultures (IC) at equal cell number ratio for 72 h. Up- and down-regulation of matrix metalloproteases (MMP)-9 expression in U87-MG and MSC cells, respectively, in direct co-culture points to possible MSC participation in tumor invasion. MMP9 expression is in line with significantly increased expression of kinin B1 (B1R) and B2 receptor (B2R) in U87-MG cells and their decreased levels in MSC, as confirmed by quantitative assessment using flow cytometric analysis. Similarly, in indirect cultures (IC), lacking the contact between GBM and MSC cells, an increase of B1 and B2 receptor expression was again noted in U87-MG cells, and no significant changes in kinin receptors in MSC was observed. Functionality of kinin-B1 and B2 receptors was evidenced by stimulation of intracellular calcium fluxes by their respective agonists, des-Arg9-bradykinin (DBK) and bradykinin (BK). Moreover, BK showed a feedback control on kinin receptor expression in mono-cultures, direct and indirect co-cultures. The treatment with BK resulted in down-regulation of B1 and B2 receptors in MSC, with simultaneous up-regulation of these receptors in U87-MG cells, suggesting that functions of BK in information flow between these cells is important for tumor progression and invasion. © 2015 International Society for Advancement of Cytometry.

Imaging of human glioblastoma cells and their interactions with mesenchymal stem cells in the zebrafish (Danio rerio) embryonic brain.

BACKGROUND: An attractive approach in the study of human cancers is the use of transparent zebrafish (Danio rerio) embryos, which enable the visualization of cancer progression in a living animal. MATERIALS AND METHODS: We implanted mixtures of fluorescently labeled glioblastoma (GBM) cells and bonemarrow-derived mesenchymal stem cells (MSCs) into zebrafish embryos to study the cellular pathways of their invasion and the interactions between these cells in vivo. RESULTS: By developing and applying a carbocyanine-dye-compatible clearing protocol for observation of cells in deep tissues, we showed that U87 and U373 GBM cells rapidly aggregated into tumor masses in the ventricles and midbrain hemispheres of the zebrafish embryo brain, and invaded the central nervous system, often using the ventricular system and the central canal of the spinal cord. However, the GBM cells did not leave the central nervous system. With co-injection of differentially labeled cultured GBM cells and MSCs, the implanted cells formed mixed tumor masses in the brain. We observed tight associations between GBM cells and MSCs, and possible cell-fusion events. GBM cells and MSCs used similar invasion routes in the central nervous system. CONCLUSIONS: This simple model can be used to study the molecular pathways of cellular processes in GBM cell invasion, and their interactions with various types of stromal cells in double or triple cell co-cultures, to design anti-GBM cell therapies that use MSCs as vectors.

Melanoma antigens in pediatric medulloblastoma contribute to tumor heterogeneity and species-specificity of group 3 tumors.

Background: Medulloblastoma (MB) is the most malignant childhood brain cancer. Group 3 MB subtype accounts for about 25% of MB diagnoses and is associated with the most unfavorable outcomes. Herein, we report that more than half of group 3 MB tumors express melanoma antigens (MAGEs), which are potential prognostic and therapeutic markers. MAGEs are tumor antigens, expressed in several types of adult cancers and associated with poorer prognosis and therapy resistance; however, their expression in pediatric cancers is mostly unknown. The aim of this study was to determine whether MAGEs are activated in pediatric MB. Methods: To determine MAGE frequency in pediatric MB, we obtained formalin-fixed paraffin-embedded tissue (FFPE) samples of 34 patients, collected between 2008 - 2015, from the Children's Medical Center Dallas pathology archives and applied our validated reverse transcription quantitative PCR (RT-qPCR) assay to measure the relative expression of 23 MAGE cancer-testis antigen genes. To validate our data, we analyzed several published datasets from pediatric MB patients and patient-derived orthotopic xenografts, totaling 860 patients. We then examined how MAGE expression affects the growth and oncogenic potential of medulloblastoma cells by CRISPR-Cas9- and siRNA-mediated gene depletion. Results: Our RT-qPCR analysis suggested that MAGEs were expressed in group 3/4 medulloblastoma. Further mining of bulk and single-cell RNA-sequencing datasets confirmed that 50-75% of group 3 tumors activate a subset of MAGE genes. Depletion of MAGEAs, B2, and Cs alter MB cell survival, viability, and clonogenic growth due to decreased proliferation and increased apoptosis. Conclusions: These results indicate that targeting MAGEs in medulloblastoma may be a potential therapeutic option for group 3 medulloblastomas. Key Points: Several Type I MAGE CTAs are expressed in >60% of group 3 MBs. Type I MAGEs affect MB cell proliferation and apoptosis. MAGEs are potential biomarkers and therapeutic targets for group 3 MBs. Importance of the Study: This study is the first comprehensive analysis of all Type I MAGE CTAs ( MAGEA , -B , and -C subfamily members) in pediatric MBs. Our results show that more than 60% of group 3 MBs express MAGE genes, which are required for the viability and growth of cells in which they are expressed. Collectively, these data provide novel insights into the antigen landscape of pediatric MBs. The activation of MAGE genes in group 3 MBs presents potential stratifying and therapeutic options.

New Insights in ATP Synthesis as Therapeutic Target in Cancer and Angiogenic Ocular Diseases.

Lactate and ATP formation by aerobic glycolysis, the Warburg effect, is considered a hallmark of cancer. During angiogenesis in non-cancerous tissue, proliferating stalk endothelial cells (ECs) also produce lactate and ATP by aerobic glycolysis. In fact, all proliferating cells, both non-cancer and cancer cells, need lactate for the biosynthesis of building blocks for cell growth and tissue expansion. Moreover, both non-proliferating cancer stem cells in tumors and leader tip ECs during angiogenesis rely on glycolysis for pyruvate production, which is used for ATP synthesis in mitochondria through oxidative phosphorylation (OXPHOS). Therefore, aerobic glycolysis is not a specific hallmark of cancer but rather a hallmark of proliferating cells and limits its utility in cancer therapy. However, local treatment of angiogenic eye conditions with inhibitors of glycolysis may be a safe therapeutic option that warrants experimental investigation. Most types of cells in the eye such as photoreceptors and pericytes use OXPHOS for ATP production, whereas proliferating angiogenic stalk ECs rely on glycolysis for lactate and ATP production. (J Histochem Cytochem XX.XXX-XXX, XXXX).

Anti-Vimentin Nanobody Decreases Glioblastoma Cell Invasion In Vitro and In Vivo.

PURPOSE: Glioblastoma (GBM) is the most common primary brain tumour and one of the deadliest cancers. In addition to late diagnosis and inadequate treatment, the extremely low survival rate is also due to the lack of appropriate therapeutic biomarkers and corresponding therapeutic agents. One of the potential therapeutic biomarkers is the intermediate filament vimentin, which is associated with epithelial-mesenchymal transition (EMT). The purpose of this study was to analyse the effect of the anti-vimentin nanobody Nb79 on cell invasion in vitro and in vivo. To further our understanding of the mechanism of action, we investigated the association between Nb79 and EMT in GBM and GBM stem cells by analysing the expression levels of key EMT-related proteins. METHODS: The expression of vimentin in glioma tissues and cells was determined by RT-qPCR. An invasion assay was performed on differentiated glioblastoma cell line U-87 MG and stem cell line NCH421k in vitro as well as in vivo in zebrafish embryos. The effect of Nb79 on expression of EMT biomarkers beta-catenin, vimentin, ZEB-1 and ZO1 was determined by Western blot and immunocytochemistry. RESULTS: Our study shows that vimentin is upregulated in glioblastoma tissue compared to lower grade glioma and non-tumour brain tissue. We demonstrated that treatment with Nb79 reduced glioblastoma cell invasion by up to 64% in vitro and up to 21% in vivo. In addition, we found that the tight junction protein ZO-1 had higher expression on the cell membrane, when treated with inhibitory anti-vimentin Nb79 compared to control. CONCLUSION: In conclusion, our results suggest that anti-vimentin nanobody Nb79 is a promising tool to target glioblastoma cell invasion.

Infiltrating natural killer cells bind, lyse and increase chemotherapy efficacy in glioblastoma stem-like tumorospheres.

Glioblastomas remain the most lethal primary brain tumors. Natural killer (NK) cell-based therapy is a promising immunotherapeutic strategy in the treatment of glioblastomas, since these cells can select and lyse therapy-resistant glioblastoma stem-like cells (GSLCs). Immunotherapy with super-charged NK cells has a potential as antitumor approach since we found their efficiency to kill patient-derived GSLCs in 2D and 3D models, potentially reversing the immunosuppression also seen in the patients. In addition to their potent cytotoxicity, NK cells secrete IFN-γ, upregulate GSLC surface expression of CD54 and MHC class I and increase sensitivity of GSLCs to chemotherapeutic drugs. Moreover, NK cell localization in peri-vascular regions in glioblastoma tissues and their close contact with GSLCs in tumorospheres suggests their ability to infiltrate glioblastoma tumors and target GSLCs. Due to GSLC heterogeneity and plasticity in regards to their stage of differentiation personalized immunotherapeutic strategies should be designed to effectively target glioblastomas.

The Cytotoxic Effects of Cannabidiol and Cannabigerol on Glioblastoma Stem Cells May Mostly Involve GPR55 and TRPV1 Signalling.

Glioblastoma (GBM) is one of the most aggressive cancers, comprising 60-70% of all gliomas. The large G-protein-coupled receptor family includes cannabinoid receptors CB1, CB2, GPR55, and non-specific ion receptor protein transporters TRPs. First, we found up-regulated CNR1, GPR55, and TRPV1 expression in glioma patient-derived tissue samples and cell lines compared with non-malignant brain samples. CNR1 and GPR55 did not correlate with glioma grade, whereas TRPV1 negatively correlated with grade and positively correlated with longer overall survival. This suggests a tumour-suppressor role of TRPV1. With respect to markers of GBM stem cells, preferred targets of therapy, TRPV1 and GPR55, but not CNR1, strongly correlated with different sets of stemness gene markers: NOTCH, OLIG2, CD9, TRIM28, and TUFM and CD15, SOX2, OCT4, and ID1, respectively. This is in line with the higher expression of TRPV1 and GPR55 genes in GSCs compared with differentiated GBM cells. Second, in a panel of patient-derived GSCs, we found that CBG and CBD exhibited the highest cytotoxicity at a molar ratio of 3:1. We suggest that this mixture should be tested in experimental animals and clinical studies, in which currently used Δ9-tetrahydrocannabinol (THC) is replaced with efficient and non-psychoactive CBG in adjuvant standard-of-care therapy.

Cell Biology Meets Cell Metabolism: Energy Production Is Similar in Stem Cells and in Cancer Stem Cells in Brain and Bone Marrow.

Energy production by means of ATP synthesis in cancer cells has been investigated frequently as a potential therapeutic target in this century. Both (an)aerobic glycolysis and oxidative phosphorylation (OXPHOS) have been studied. Here, we review recent literature on energy production in glioblastoma stem cells (GSCs) and leukemic stem cells (LSCs) versus their normal counterparts, neural stem cells (NSCs) and hematopoietic stem cells (HSCs), respectively. These two cancer stem cell types were compared because their niches in glioblastoma tumors and in bone marrow are similar. In this study, it became apparent that (1) ATP is produced in NSCs and HSCs by anaerobic glycolysis, whereas fatty acid oxidation (FAO) is essential for their stem cell fate and (2) ATP is produced in GSCs and LSCs by OXPHOS despite the hypoxic conditions in their niches with FAO and amino acids providing its substrate. These metabolic processes appeared to be under tight control of cellular regulation mechanisms which are discussed in depth. However, our conclusion is that systemic therapeutic targeting of ATP production via glycolysis or OXPHOS is not an attractive option because of its unwanted side effects in cancer patients.

Proteases Regulate Cancer Stem Cell Properties and Remodel Their Microenvironment.

Proteolytic activity is perturbed in tumors and their microenvironment, and proteases also affect cancer stem cells (CSCs). CSCs are the therapy-resistant subpopulation of cancer cells with tumor-initiating capacity that reside in specialized tumor microenvironment niches. In this review, we briefly summarize the significance of proteases in regulating CSC activities with a focus on brain tumor glioblastoma. A plethora of proteases and their inhibitors participate in CSC invasiveness and affect intercellular interactions, enhancing CSC immune, irradiation, and chemotherapy resilience. Apart from their role in degrading the extracellular matrix enabling CSC migration in and out of their niches, we review the ability of proteases to modulate CSC properties, which prevents their elimination. When designing protease-oriented therapies, the multifaceted roles of proteases should be thoroughly investigated.

Immunotherapy of Glioblastoma: Current Strategies and Challenges in Tumor Model Development.

Glioblastoma is the most common brain malignant tumor in the adult population, and immunotherapy is playing an increasingly central role in the treatment of many cancers. Nevertheless, the search for effective immunotherapeutic approaches for glioblastoma patients continues. The goal of immunotherapy is to promote tumor eradication, boost the patient's innate and adaptive immune responses, and overcome tumor immune resistance. A range of new, promising immunotherapeutic strategies has been applied for glioblastoma, including vaccines, oncolytic viruses, immune checkpoint inhibitors, and adoptive cell transfer. However, the main challenges of immunotherapy for glioblastoma are the intracranial location and heterogeneity of the tumor as well as the unique, immunosuppressive tumor microenvironment. Owing to the lack of appropriate tumor models, there are discrepancies in the efficiency of various immunotherapeutic strategies between preclinical studies (with in vitro and animal models) on the one hand and clinical studies (on humans) on the other hand. In this review, we summarize the glioblastoma characteristics that drive tolerance to immunotherapy, the currently used immunotherapeutic approaches against glioblastoma, and the most suitable tumor models to mimic conditions in glioblastoma patients. These models are improving and can more precisely predict patients' responses to immunotherapeutic treatments, either alone or in combination with standard treatment.

Energy Metabolism in IDH1 Wild-Type and IDH1-Mutated Glioblastoma Stem Cells: A Novel Target for Therapy?

Cancer is a redox disease. Low levels of reactive oxygen species (ROS) are beneficial for cells and have anti-cancer effects. ROS are produced in the mitochondria during ATP production by oxidative phosphorylation (OXPHOS). In the present review, we describe ATP production in primary brain tumors, glioblastoma, in relation to ROS production. Differentiated glioblastoma cells mainly use glycolysis for ATP production (aerobic glycolysis) without ROS production, whereas glioblastoma stem cells (GSCs) in hypoxic periarteriolar niches use OXPHOS for ATP and ROS production, which is modest because of the hypoxia and quiescence of GSCs. In a significant proportion of glioblastoma, isocitrate dehydrogenase 1 (IDH1) is mutated, causing metabolic rewiring, and all cancer cells use OXPHOS for ATP and ROS production. Systemic therapeutic inhibition of glycolysis is not an option as clinical trials have shown ineffectiveness or unwanted side effects. We argue that systemic therapeutic inhibition of OXPHOS is not an option either because the anti-cancer effects of ROS production in healthy cells is inhibited as well. Therefore, we advocate to remove GSCs out of their hypoxic niches by the inhibition of their binding to niches to enable their differentiation and thus increase their sensitivity to radiotherapy and/or chemotherapy.