Glioblastoma stem cell differentiation into endothelial cells evidenced through live-cell imaging

Tumor microenvironment of cancer stem cells: Perspectives on cancer stem cell targeting

There are few tumor cell subpopulations with stem cell characteristics in tumor tissue, defined as cancer stem cells (CSCs) or cancer stem-like cells (CSLCs), which can reconstruct neoplasms with malignant biological behaviors such as invasiveness via self-renewal and unlimited generation. The microenvironment that CSCs depend on consists of various cellular components and corresponding medium components. Among these factors existing at a variety of levels and forms, cytokine networks and numerous signal pathways play an important role in signaling transduction. These factors promote or maintain cancer cell stemness, and participate in cancer recurrence, metastasis, and resistance. This review aims to summarize the recent molecular data concerning the multilayered relationship between CSCs and CSC-favorable microenvironments. We also discuss the therapeutic implications of targeting this synergistic interplay, hoping to give an insight into targeting cancer cell stemness for tumor therapy and prognosis.

Cancer Stem Cells from Definition to Detection and Targeted Drugs

Cancers remain the second leading cause of mortality in the world. Preclinical and clinical studies point an important role of cancer/leukaemia stem cells (CSCs/LSCs) in the colonisation at secondary organ sites upon metastatic spreading, although the precise mechanisms for specific actions are still not fully understood. Reviewing the present knowledge on the crucial role of CSCs/LSCs, their plasticity, and population heterogeneity in treatment failures in cancer patients is timely. Standard chemotherapy, which acts mainly on rapidly dividing cells, is unable to adequately affect CSCs with a low proliferation rate. One of the proposed mechanisms of CSC resistance to anticancer agents is the fact that these cells can easily shift between different phases of the cell cycle in response to typical cell stimuli induced by anticancer drugs. In this work, we reviewed the recent studies on CSC/LSC alterations associated with disease recurrence, and we systematised the functional assays, markers, and novel methods for CSCs screening. This review emphasises CSCs' involvement in cancer progression and metastasis, as well as CSC/LSC targeting by synthetic and natural compounds aiming at their elimination or modulation of stemness properties.

Molecular prognostic of nine parthanatos death-related genes in glioma, particularly in COL8A1 identification

Post-operative progression and chemotherapy resistance are the main causes of treatment failure in glioma patients. There is a lack of ideal prediction models for post-operative glioma patient progression and drug sensitivity. We aimed to develop a prognostic model of parthanatos mRNA biomarkers for glioma outcomes. A total of 11 parthanatos genes were obtained from ParthanatosCluster database. ConsensusClusterPlus and R "Limma" package were used to cluster The Cancer Genome Atlas (TCGA)-glioma cohort and analyze the differential mRNAs. Univariate Cox regression analysis, random survival forest model, and least absolute shrinkage and selection operator (LASSO) regression analysis were used to determine the nine ParthanatosScore prognostic genes combination. ParthanatosScore was verified by 656 patients and 979 patients in TCGA and CGCA-LGG/GBM datasets. Differences in genomic mutations, tumor microenvironments, and functional pathways were assessed. Drug response prediction was performed using pRRophetic. Kaplan-Meier survival analysis was analyzed. Finally, COL8A1 was selected to evaluate its potential biological function and drug sensitivity of temozolomide and AZD3759 in glioma cells. ParthanatosScore obtained a combination of nine glioma prognostic genes, including CD58, H19, TNFAIP6, FTLP3, TNFRSF11B, SFRP2, LOXL1, COL8A1, and FABP5P7. In the TCGA-LGG/GBM dataset, glioma prognosis was poor in high ParthanatosScore. Low-score glioma patients were sensitive to AZD3759_1915, AZD5582_1617, AZD8186_1918, Dasatinib_1079, and Temozolomide_1375, while high-score patients were less sensitive to these drugs. Compared with HA cells, COL8A1 was significantly over-expressed in LN229 and U251 cells. Silencing COL8A1 inhibited the malignant characterization of LN229 and U251 cells. Temozolomide and AZD3759 also promoted parthanatos gene expression in glioma cells. Temozolomide and AZD3759 inhibited COL8A1 expression and cell viability and promoted apoptosis in glioma cells and PGM cells. ParthanatosScore can accurately predict clinical prognosis and drug sensitivity after glioma surgery. Silencing COL8A1 inhibited the malignant characterization. Temozolomide and AZD3759 inhibited COL8A1 expression and cell viability and promoted apoptosis and parthanatos gene expression, which is a target to improve glioma.

Glioblastoma Therapy: Past, Present and Future

Glioblastoma (GB) stands out as the most prevalent and lethal form of brain cancer. Although great efforts have been made by clinicians and researchers, no significant improvement in survival has been achieved since the Stupp protocol became the standard of care (SOC) in 2005. Despite multimodality treatments, recurrence is almost universal with survival rates under 2 years after diagnosis. Here, we discuss the recent progress in our understanding of GB pathophysiology, in particular, the importance of glioma stem cells (GSCs), the tumor microenvironment conditions, and epigenetic mechanisms involved in GB growth, aggressiveness and recurrence. The discussion on therapeutic strategies first covers the SOC treatment and targeted therapies that have been shown to interfere with different signaling pathways (pRB/CDK4/RB1/P16ink4, TP53/MDM2/P14arf, PI3k/Akt-PTEN, RAS/RAF/MEK, PARP) involved in GB tumorigenesis, pathophysiology, and treatment resistance acquisition. Below, we analyze several immunotherapeutic approaches (i.e., checkpoint inhibitors, vaccines, CAR-modified NK or T cells, oncolytic virotherapy) that have been used in an attempt to enhance the immune response against GB, and thereby avoid recidivism or increase survival of GB patients. Finally, we present treatment attempts made using nanotherapies (nanometric structures having active anti-GB agents such as antibodies, chemotherapeutic/anti-angiogenic drugs or sensitizers, radionuclides, and molecules that target GB cellular receptors or open the blood-brain barrier) and non-ionizing energies (laser interstitial thermal therapy, high/low intensity focused ultrasounds, photodynamic/sonodynamic therapies and electroporation). The aim of this review is to discuss the advances and limitations of the current therapies and to present novel approaches that are under development or following clinical trials.

IFITM3 promotes glioblastoma stem cell-mediated angiogenesis via regulating JAK/STAT3/bFGF signaling pathway

Interferon-induced transmembrane protein 3 (IFITM3) has been previously verified to be an endosomal protein that prevents viral infection. Recent findings suggested IFITM3 as a key factor in tumor invasion and progression. To clarify the role and molecular mechanism of IFITM3 in Glioblastoma multiforme (GBM) progression, we investigated the expression of IFITM3 in glioma datasets culled from The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA). Primary GBM stem cells (GSCs) were cultured and identified in vitro. Loss-of-function and gain-of-function experiments were established by using shRNAs and lentiviral vectors targeting IFITM3. Co-culture system of GSCs and vascular endothelial cells was constructed in a Transwell chamber. Tube formation and spheroid-based angiogenesis assays were performed to determine the angiogenic capacity of endothelial cells. Results revealed that IFITM3 is elevated in GBM samples and predictive of adverse outcome. Mechanistically, GSCs-derived IFITM3 causes activation of Jak2/STAT3 signaling and leads to robust secretion of bFGF into tumor environment, which eventually results in enhanced angiogenesis. Taken together, these evidence indicated IFITM3 as an essential factor in GBM angiogenesis. Our findings provide a new insight into mechanism by which IFITM3 modulates GBM angiogenesis.

Collagen and derivatives-based materials as substrates for the establishment of glioblastoma organoids

Glioblastoma (GBM) is a common primary brain malignancy known for its ability to invade the brain, resistance to chemotherapy and radiotherapy, tendency to recur frequently, and unfavorable prognosis. Attempts have been undertaken to create 2D and 3D models, such as glioblastoma organoids (GBOs), to recapitulate the glioma microenvironment, explore tumor biology, and develop efficient therapies. However, these models have limitations and are unable to fully recapitulate the complex networks formed by the glioma microenvironment that promote tumor cell growth, invasion, treatment resistance, and immune escape. Therefore, it is necessary to develop advanced experimental models that could better simulate clinical physiology. Here, we review recent advances in natural biomaterials (mainly focus on collagen and its derivatives)-based GBO models, as in vitro experimental platforms to simulate GBM tumor biology and response to tested drugs. Special attention will be given to 3D models that use collagen, gelatin, further modified derivatives, and composite biomaterials (e.g., with other natural or synthetic polymers) as substrates. Application of these collagen/derivatives-constructed GBOs incorporate the physical as well as chemical characteristics of the GBM microenvironment. A perspective on future research is given in terms of current issues. Generally, natural materials based on collagen/derivatives (monomers or composites) are expected to enrich the toolbox of GBO modeling substrates and potentially help to overcome the limitations of existing models.

Vasculogenic mimicry-associated novel gene signature predicted prognosis and response to immunotherapy in lung adenocarcinoma

BACKGROUNDS

It was highlighted by recent studies on the biological significance of vasculogenic mimicry (VM) in tumorigenicity and progression. However, it is unclear whether VM also plays a potential role in immune regulation and tumor microenvironment (TME) formation.

METHODS

To identify patterns of VM alterations and VM-associated genetic features in non-small cell lung adenocarcinoma, we have screened 309 VM regulators and performed consensus molecular typing by the NMF algorithm. The ssGSEA and CIBORSORT algorithms were employed to measure the relative infiltration of distinct immune cell subpopulations. Individual tumors with immune responses were evaluated for alteration patterns of VM with typing-based differential genes.

RESULTS

In 490 LUAD samples, two distinctive VM alteration patterns connected to different clinical outcomes and biochemical pathways were established. TME characterization showed that the observed VM patterns were primarily saturated with cell proliferation and metabolic pathways and higher in immune cell infiltration of the C1 type. Vasculogenic mimicry-related genes (VMRG) risk scores were constructed to divide patients with lung adenocarcinoma into subgroups with high and low scores. Patients with lower scores had better immunological scores and longer survival times. Upon further investigation, higher scores were positively correlated with higher tumor mutation burden (TMB), M1-type macrophages and immune checkpoint molecules. Nevertheless, in two other immunotherapy cohorts, individuals with lower scores had enhanced immune responses and long-lasting therapeutic benefits. Finally, we monitored the ANLN gene from the VMRG model, which was highly expressed in lung adenocarcinoma tissues and negatively correlated with prognosis; it was also highly expressed in lung adenocarcinoma cell lines, and knockdown of ANLN elicited low expression of VEGFA, MMP2 and MMP9.

CONCLUSION

This study highlights that VM modifications are significantly associated with the diversity and complexity of TME, revealing new features of the immune microenvironment in lung adenocarcinoma and providing a new strategy for immunotherapy. Screening ANLN as a critical target for vasculogenic mimicry in lung adenocarcinoma provides a novel perspective for the targeted treatment of lung adenocarcinoma.

Molecular mechanisms of Thrombospondin-2 modulates tumor vasculogenic mimicry by PI3K/AKT/mTOR signaling pathway

Vasculogenic mimicry (VM) differs from the classical tumor angiogenesis model. VM does not depend on endothelial cells; instead, highly aggressive tumor cells mimic endothelial cells to form a vascular-like channel structure. VM mediated by tumor cells is significantly and positively associated with a poor prognosis and low survival rates in patients with highly aggressive cancer. In the treatment of highly aggressive malignancies, the presence of VM is considered an important reason for the unsatisfactory clinical efficacy of anti-tumor-angiogenesis therapy (e.g., therapy targeting vascular endothelial growth factor A). Many targeted therapeutic drugs based on traditional tumor blood vessels have been used clinically. Although some progress has been made in certain tumors, problems such as drug resistance have restricted the expected therapeutic effects. Thrombospondin 2 (THBS2) is one of the most important genes associated with angiogenesis, and this gene exerts angiogenesis-related functions through the PI3K/AKT signaling pathway. Although the PI3K/AKT/mTOR signaling pathway is closely related to the progression of VM, the mechanism by which the promising biomarker THBS2 participates in and regulates tumor VM by activating the PI3K/AKT/mTOR signaling pathway is unclear. In this review, we analyze the monomer structure and biological activity of THBS2, the structure and potential synthesis mechanisms of VM, and the complex mechanisms between THBS2, the PI3K/AKT/mTOR signaling pathway, and VM.

Glioblastoma Vascular Plasticity Limits Effector T-cell Infiltration and Is Blocked by cAMP Activation

Glioblastoma (GBM) is the deadliest form of brain cancer. It is a highly angiogenic and immunosuppressive malignancy. Although immune checkpoint blockade therapies have revolutionized treatment for many types of cancer, their therapeutic efficacy in GBM has been far less than expected or even ineffective. In this study, we found that the genomic signature of glioma-derived endothelial cells (GdEC) correlates with an immunosuppressive state and poor prognosis of patients with glioma. We established an in vitro model of GdEC differentiation for drug screening and used this to determine that cyclic adenosine monophosphate (cAMP) activators could effectively block GdEC formation by inducing oxidative stress. Furthermore, cAMP activators impaired GdEC differentiation in vivo, normalized the tumor vessels, and altered the tumor immune profile, especially increasing the influx and function of CD8+ effector T cells. Dual blockade of GdECs and PD-1 induced tumor regression and established antitumor immune memory. Thus, our study reveals that endothelial transdifferentiation of GBM shapes an endothelial immune cell barrier and supports the clinical development of combining GdEC blockade and immunotherapy for GBM. See related Spotlight by Lee et al., p. 1300.

The Role of Hypoxia and Cancer Stem Cells in Development of Glioblastoma

Glioblastoma multiform (GBM) is recognized as the most malignant brain tumor with a high level of hypoxia, containing a small population of glioblastoma stem like cells (GSCs). These GSCs have the capacity of self-renewal, proliferation, invasion and recapitulating the parent tumor, and are major causes of radio-and chemoresistance of GBM. Upregulated expression of hypoxia inducible factors (HIFs) in hypoxia fundamentally contributes to maintenance and progression of GSCs. Therefore, we thoroughly reviewed the currently acknowledged roles of hypoxia-associated GSCs in development of GBM. In detail, we recapitulated general features of GBM, especially GSC-related features, and delineated essential responses resulted from interactions between GSC and hypoxia, including hypoxia-induced signatures, genes and pathways, and hypoxia-regulated metabolic alterations. Five hypothesized GSC niches are discussed and integrated into one comprehensive concept: hypoxic peri-arteriolar niche of GSCs. Autophagy, another protective mechanism against chemotherapy, is also closely related to hypoxia and is a potential therapeutic target for GBM. In addition, potential causes of therapeutic resistance (chemo-, radio-, surgical-, immuno-), and chemotherapeutic agents which can improve the therapeutic effects of chemo-, radio-, or immunotherapy are introduced and discussed. At last, as a potential approach to reverse the hypoxic microenvironment in GBM, hyperbaric oxygen therapy (HBOT) might be an adjuvant therapy to chemo-and radiotherapy after surgery. In conclusion, we focus on demonstrating the important role of hypoxia on development of GBM, especially by affecting the function of GSCs. Important advantages have been made to understand the complicated responses induced by hypoxia in GBM. Further exploration of targeting hypoxia and GSCs can help to develop novel therapeutic strategies to improve the survival of GBM patients.

Investigating Trans-differentiation of Glioblastoma Cells in an In Vitro 3D Model of the Perivascular Niche

Glioblastoma multiforme (GBM) is the deadliest form of brain cancer, responsible for over 50% of adult brain tumors. A specific region within the GBM environment is known as the perivascular niche (PVN). This area is defined as within approximately 100 μm of vasculature and plays an important role in the interactions between endothelial cells (ECs), astrocytes, GBM cells, and stem cells. We have designed a 3D in vitro model of the PVN comprising either collagen Type 1 or HyStem-C, human umbilical vein ECs (HUVECs), and LN229 (GBM) cells. HUVECs were encapsulated within the hydrogels to form vascular networks. After 7 days, LN229 cells were co-cultured to investigate changes in both cell types. Over a 14 day culture period, we measured alterations in HUVEC networks, the contraction of the hydrogels, trans-differentiation of LN229 cells, and the concentrations of two chemokines; CXCL12 and TGF-β. Increased cellular proliferation ranging from 10- to 16-fold was exhibited in co-cultures from days 8 to 14. This was accompanied with a decrease in the height of hydrogels of up to 68%. These changes in the biomaterial scaffold indicate that LN229-HUVEC interactions promote changes to the matrix. TGF-β and CXCL12 secretion increased approximately 2-2.6-fold each from day 8 to 14 in all co-cultures. The expression of CXCL12 correlated with cell colocalization, indicating a chemotactic role in enabling the migration of LN229 cells toward HUVECs in co-cultures. von Willebrand factor (vWF) was co-expressed with glial fibrillary acidic protein (GFAP) in up to 15% of LN229 cells after 24 h in co-culture. Additionally, when LN229 cells were co-cultured with human brain microvascular ECs, the percentages of GFAP⁺/vWF⁺ cells were up to 20% higher than that in co-cultures with HUVECs in collagen (2.2 mg/mL) and HyStem-C gels on day 14. The expression of vWF indicates the early stages of trans-differentiation of LN229 cells to an EC phenotype. Designing in vitro models of trans-differentiation may provide additional insights into how vasculature and cellular phenotypes are altered in GBM.

Resolving the lineage relationship between malignant cells and vascular cells in glioblastomas

Glioblastoma multiforme (GBM), a highly malignant and heterogeneous brain tumor, contains various types of tumor and non-tumor cells. Whether GBM cells can trans-differentiate into non-neural cell types, including mural cells or endothelial cells (ECs), to support tumor growth and invasion remains controversial. Here we generated two genetic GBM models de novo in immunocompetent mouse brains, mimicking essential pathological and molecular features of human GBMs. Lineage-tracing and transplantation studies demonstrated that, although blood vessels in GBM brains underwent drastic remodeling, evidence of trans-differentiation of GBM cells into vascular cells was barely detected. Intriguingly, GBM cells could promiscuously express markers for mural cells during gliomagenesis. Furthermore, single-cell RNA sequencing showed that patterns of copy number variations (CNVs) of mural cells and ECs were distinct from those of GBM cells, indicating discrete origins of GBM cells and vascular components. Importantly, single-cell CNV analysis of human GBM specimens also suggested that GBM cells and vascular cells are likely separate lineages. Rather than expansion owing to trans-differentiation, vascular cell expanded by proliferation during tumorigenesis. Therefore, cross-lineage trans-differentiation of GBM cells is very unlikely to occur during gliomagenesis. Our findings advance understanding of cell lineage dynamics during gliomagenesis, and have implications for targeted treatment of GBMs.

Characteristics of vasculogenic mimicry and tumour to endothelial transdifferentiation in human glioblastoma: a systematic review

BACKGROUND

Glioblastoma, the most common primary malignant brain tumour in adults, is a highly vascular tumour characterised by abnormal angiogenesis. Additional mechanisms of tumour vascularisation have also been reported in glioblastoma, including the formation of tumour cell-derived vessels by vasculogenic mimicry (VM) or the transdifferentiation of tumour cells to endothelial cells. VM and endothelial transdifferentiation have frequently been reported as distinct processes, however, the use of both terms to describe a single process of vascularisation also occurs. Some overlapping characteristics have also been reported when identifying each process. We therefore aimed to determine the markers consistently attributed to VM and endothelial transdifferentiation in the glioblastoma literature.

METHODS

Ovid MEDLINE and Ovid Embase were searched for studies published between January 1999 and July 2021 that assessed VM or tumour to endothelial transdifferentiation in human glioblastoma. The online systematic review tool Covidence was used for screening and data extraction. Extracted data included type of tumour-derived vasculature reported, methods and techniques used, and markers investigated. Studies were grouped based on type of vasculature reported for further assessment.

RESULTS

One hundred and thirteen of the 419 unique records identified were included for analysis. VM was reported in 64/113 studies, while tumour to endothelial transdifferentiation was reported in 16/113 studies. The remaining studies used both terms to describe a single process, did not define the process that occurred, or concluded that neither VM nor endothelial transdifferentiation occurred. Absence of CD34 and/or CD31 in vascular structures was the most common indicator of VM, while expression of CD34 and/or CD31, in addition to various other endothelial, stem cell or tumour cell markers, indicated tumour to endothelial transdifferentiation.

CONCLUSION

Cells derived from tumour to endothelial transdifferentiation express typical endothelial markers including CD34 and CD31, while tumour cells contributing to VM lack CD34 and CD31 expression. Additional tumour markers are required to identify transdifferentiation in glioblastoma tissue, and this process requires further characterisation.

Differential regulation of H3K9/H3K14 acetylation by small molecules drives neuron-fate-induction of glioma cell

Differentiation therapy using small molecules is a promising strategy for improving the prognosis of glioblastoma (GBM). Histone acetylation plays an important role in cell fate determination. Nevertheless, whether histone acetylation in specific sites determines GBM cells fate remains to be explored. Through screening from a 349 small molecule-library, we identified that histone deacetylase inhibitor (HDACi) MS-275 synergized with 8-CPT-cAMP was able to transdifferentiate U87MG GBM cells into neuron-like cells, which were characterized by cell cycle arrest, rich neuron biomarkers, and typical neuron electrophysiology. Intriguingly, acetylation tags of histone 3 at lysine 9 (H3K9ac) were decreased in the promoter of multiple oncogenes and cell cycle genes, while ones of H3K9ac and histone 3 at lysine 14 (H3K14ac) were increased in the promoter of neuron-specific genes. We then compiled a list of genes controlled by H3K9ac and H3K14ac, and proved that it is a good predictive power for pathologic grading and survival prediction. Moreover, cAMP agonist combined with HDACi also induced glioma stem cells (GSCs) to differentiate into neuron-like cells through the regulation of H3K9ac/K14ac, indicating that combined induction has the potential for recurrence-preventive application. Furthermore, the combination of cAMP activator plus HDACi significantly repressed the tumor growth in a subcutaneous GSC-derived tumor model, and temozolomide cooperated with the differentiation-inducing combination to prolong the survival in an orthotopic GSC-derived tumor model. These findings highlight epigenetic reprogramming through H3K9ac and H3K14ac as a novel approach for driving neuron-fate-induction of GBM cells.

Double Immunohistochemical Staining on Formalin-Fixed Paraffin-Embedded Tissue Samples to Study Vascular Co-option

Vascular co-option is a non-angiogenic mechanism whereby tumor growth and progression move on by hijacking the pre-existing and nonmalignant blood vessels and is employed by various tumors to grow and metastasize.The histopathological identification of co-opted blood vessels is complex, and no specific markers were defined, but it is critical to develop new and possibly more effective therapeutic strategies. Here, in glioblastoma, we show that the co-opted blood vessels can be identified, by double immunohistochemical staining, as weak CD31⁺ vessels with reduced P-gp expression and proliferation and surrounded by highly proliferating and P-gp- or S100A10-expressing tumor cells. Results can be quantified by the Aperio Colocalization algorithm, which is a valid and robust method to handle and investigate large data sets.

Differential P-Glycoprotein/CD31 Expression as Markers of Vascular Co-Option in Primary Central Nervous System Tumors

BACKGROUND

Vascular co-option is one of the main features of brain tumor progression. It is identified using histopathological analysis, but no antibody-specific markers were found, and no universally accepted histological features were defined.

METHODS

We employed double immunohistochemical stainings for CD31, P-gp, S100A10, and mitochondria on formalin-fixed, paraffin-embedded human samples of IDH-WT glioblastoma, IDH-mutant astrocytoma, and meningioma to study vascular co-option across different brain tumors and across normal, peritumoral, and intratumoral areas using the Aperio colocalization algorithm, which is a valid and robust method to handle and investigate large data sets.

RESULTS

The results have shown that (i) co-opted vessels could be recognized by the presence of metabolically overactive (evaluated as mitochondria expression) and P-gp⁺ or S100A10⁺ tumor cells surrounding CD31⁺ endothelial cells; (ii) vascular co-option occurs in the intratumoral area of meningioma and astrocytoma; and (iii) vascular co-option is prevalent in peritumoral glioblastoma area.

CONCLUSIONS

The described approach identifies new markers for cellular components of the vessel wall and techniques that uncover the order and localization of vascularization mechanisms, which may contribute to developing new and possibly more effective therapeutic strategies.

Inter and intra-tumor heterogeneity of paediatric type diffuse high-grade gliomas revealed by single-cell mass cytometry

Paediatric-type diffuse high-grade gliomas (PDHGG) are aggressive tumors affecting children and young adults, with no effective treatment. These highly heterogeneous malignancies arise in different sites of the Central Nervous System (CNS), carrying distinctive molecular alterations and clinical outcomes (inter-tumor heterogeneity). Moreover, deep cellular and molecular profiling studies highlighted the coexistence of genetically and phenotypically different subpopulations within the same tumor mass (intra-tumor heterogeneity). Despite the recent advances made in the field, the marked heterogeneity of PDHGGs still impedes the development of effective targeted therapies and the identification of suitable biomarkers. In order to fill the existing gap, we used mass cytometry to dissect PDHGG inter- and intra-heterogeneity. This is one of the most advanced technologies of the "-omics" era that, using antibodies conjugated to heavy metals, allows the simultaneous measurement of more than 40 markers at single-cell level. To this end, we analyzed eight PDHGG patient-derived cell lines from different locational and molecular subgroups. By using a panel of 15 antibodies, directly conjugated to metals or specifically customized to detect important histone variants, significant differences were highlighted in the expression of the considered antigens. The single-cell multiparametric approach realized has deepened our understanding of PDHGG, confirming a high degree of intra- and inter-tumoral heterogeneity and identifying some antigens that could represent useful biomarkers for the specific PDHGG locational or molecular subgroups.

Glioblastoma-Specific Strategies of Vascularization: Implications in Anti-Angiogenic Therapy Resistance

Angiogenesis has long been implicated as a crucial process in GBM growth and progression. GBM can adopt several strategies to build up its abundant and aberrant vasculature. Targeting GBM angiogenesis has gained more and more attention in anti-cancer therapy, and many strategies have been developed to interfere with this hallmark. However, recent findings reveal that the effects of anti-angiogenic treatments are temporally limited and that tumors become refractory to therapy and more aggressive. In this review, we summarize the GBM-associated neovascularization processes and their implication in drug resistance mechanisms underlying the transient efficacy of current anti-angiogenic therapies. Moreover, we describe potential strategies and perspectives to overcome the mechanisms adopted by GBM to develop resistance to anti-angiogenic therapy as new potential therapeutic approaches.

Prrx1 promotes resistance to temozolomide by upregulating ABCC1 and inducing vasculogenic mimicry in glioma

Gliomas are the most common primary brain tumors with dismal prognoses. Temozolomide (TMZ), the frontline therapeutic agent for gliomas, has shown limited clinical benefit primarily due to the acquired chemoresistance. Although growing evidence has suggested that the multi-drug resistance phenotype and abnormal vascular microenvironment are responsible for the intrinsic and extrinsic TMZ resistance, the molecular mechanism of TMZ resistance remains to be elucidated. In this study, we found Paired-related homeobox 1 (Prrx1) was an independent prognostic factor for the efficacy of chemotherapy-based postoperative treatment. Silencing Prrx1 markedly enhanced the TMZ-induced cytotoxicity both in vitro and in vivo. We also demonstrated that Prrx1 increased the expression of ABCC1, a member of ATP-Binding Cassette (ABC) transporter protein family, through binding to the promoter region of ABCC1 gene and initiating its transcription. Silencing ABCC1 mitigated the TMZ resistance induced by Prrx1. Furthermore, Prrx1 facilitates the formation of vasculogenic mimicry (VM), a critical extrinsic mechanism for glioma TMZ resistance. Collectively, our findings supported the critical role of Prrx1 in TMZ resistance via intrinsic and extrinsic mechanism. Targeting Prrx1 might represent a feasible strategy to overcome therapeutic resistance in glioma.

M2-like tumor-associated macrophages transmit exosomal miR-27b-3p and maintain glioblastoma stem-like cell properties

There is growing evidence supporting the implications of exosomes-shuttled microRNAs (miRs) in the phenotypes of glioblastoma stem cells (GSCs), whilst the role of exosomal miR-27b-3p remains to be established. Herein, the aim of this study was to investigate the effect of M2 tumor-associated macrophage (TAM)-derived exosomal miR-27b-3p on the function of GSCs. Clinical glioblastoma (GBM) specimens were obtained and GSCs and M2-TAMs were isolated by fluorescence-activated cell sorting (FACS), and exosomes were separated from M2-TAMs. It was observed that M2-TAM-derived exosomes promoted the stem-like properties of GSCs. Gain- and loss- of function assays were then conducted to explore the effects of exosomal miR-27b-3p and the miR-27b-3p/MLL4/PRDM1 axis on GSC phenotypes. A xenograft tumor model of GBM was further established for in vivo substantiation. Inhibition of miR-27b-3p in M2-TAMs reduced exosomal miR-27b-3p transferred into GSCs and consequently diminished GSC viability in vitro and tumor-promoting effects of GSCs in vivo. The interaction among miR-27b-3p, mixed linked leukemia 4 (MLL4), positive regulatory domain I (PRDM1) was validated by dual-luciferase and ChIP assays. MLL4 positively regulated PRDM1 expression by inducing methylation in the PRDM1 enhancer region and ultimately reduced IL-33 expression. miR-27b-3p targeted MLL4/PRDM1 to activate IL-33 and maintain the stem-like function of GSCs. In conclusion, our study elucidated that M2-TAM-derived exosomal miR-27b-3p enhanced the tumorigenicity of GSCs through the MLL4/PRDM1/IL-33 axis.

[Latest Research Findings on the Role of Non-Tumor Cells in Glioma Microenvironment]

As the tumor cell-centered treatment strategies cannot curb the malignant progression of glioblastoma effectively, the therapeutic effect of glioblastoma is still not satisfactory. In addition to glioma cells, glioma microenvironment (GME) comprises massive numbers of non-tumor cells and soluble cytokines. The non-tumor cells include endothelial cells, pericytes, microglia/macrophages, mesenchymal cells, astrocytes, neurons, etc. These non-tumor cell components, together with glioma cells, form one organism which regulates the progression of glioma. Considerable progress has been been in research on GME, which will be conducive to the development of non-tumor cell targeted therapies and and improvements in the prognosis of glioma patients. Herein, we summarized the interaction of glioma cells with endothelial cells, pericytes, microglia/macrophages, astrocytes, neurons and mesenchymal cells, a topic that has been extensively researched, as well as the corresponding translational studies. We also discussed the potential challenges and opportunities of developing glioma treatments based on tumor microenvironment.

The Vascular Microenvironment in Glioblastoma: A Comprehensive Review

Glioblastoma multiforme, the deadliest primary brain tumor, is characterized by an excessive and aberrant neovascularization. The initial expectations raised by anti-angiogenic drugs were soon tempered due to their limited efficacy in improving the overall survival. Intrinsic resistance and escape mechanisms against anti-VEGF therapies evidenced that tumor angiogenesis is an intricate multifaceted phenomenon and that vessels not only support the tumor but exert indispensable interactions for resistance and spreading. This holistic review covers the essentials of the vascular microenvironment of glioblastoma, including the perivascular niche components, the vascular generation patterns and the implicated signaling pathways, the endothelial–tumor interrelation, and the interconnection between vessel aberrancies and immune disarrangement. The revised concepts provide novel insights into the preclinical models and the potential explanations for the failure of conventional anti-angiogenic therapies, leading to an era of new and combined anti-angiogenic-based approaches.

Disruption of β-catenin-mediated negative feedback reinforces cAMP-induced neuronal differentiation in glioma stem cells

Accumulating evidence supports the existence of glioma stem cells (GSCs) and their critical role in the resistance to conventional treatments for glioblastoma multiforme (GBM). Differentiation therapy represents a promising alternative strategy against GBM by forcing GSCs to exit the cell cycle and reach terminal differentiation. In this study, we demonstrated that cAMP triggered neuronal differentiation and compromised the self-renewal capacity in GSCs. In addition, cAMP induced negative feedback to antagonize the differentiation process by activating β-catenin pathway. Suppression of β-catenin signaling synergized with cAMP activators to eliminate GSCs in vitro and extended the survival of animals in vivo. The cAMP/PKA pathway stabilized β-catenin through direct phosphorylation of the molecule and inhibition of GSK-3β. The activated β-catenin translocated into the nucleus and promoted the transcription of APELA and CARD16, which were found to be responsible for the repression of cAMP-induced differentiation in GSCs. Overall, our findings identified a negative feedback mechanism for cAMP-induced differentiation in GSCs and provided potential targets for the reinforcement of differentiation therapy for GBM.

P4HA1 Regulates CD31 via COL6A1 in the Transition of Glioblastoma Stem-Like Cells to Tumor Endothelioid Cells

Glioblastoma multiforme (GBM) is a common intracranial malignancy characterized by abundant and aberrant vasculature. The efficiency of existing antivascular treatments remains unsatisfactory. The transition of glioblastoma stem-like cells (GSCs) into tumor endothelioid cells (ECs) has been thought to cause glioma neovascularization and anti-angiogenesis tolerance, but the mechanisms regulating glioma transdifferentiation remains unclear. Our previous study found that P4HA1 regulates GSCs vascular mimicry in a hypoxic microenvironment, but the detailed molecular mechanism has not been determined. In this study, candidate protein COL6A1 was screened by mass spectrometry. In vitro experiments show that P4HA1 regulates the expression of CD31 via COL6A1, with the levels of expression of P4HA1, COL6A1 and the vascular endothelial molecular markers CD31 showing positive correlations in vivo assay. Altering the expression of P4HA1 in GSCs altered the expression of COL6A1 and CD31, thereby inducing glioma angiogenesis. In conclusion, this study revealed that the P4HA1/COL6A1 axis modulates the transdifferentiation process of GSCs into ECs. Interrupting this signaling axis can inhibit glioma angiogenesis, suggesting that this axis may be a novel target for antivascular therapy in patients with glioma.

PDGF-R inhibition induces glioblastoma cell differentiation via DUSP1/p38MAPK signalling

Glioblastoma (GBM) is the most common and fatal primary brain tumour in adults. Considering that resistance to current therapies leads to limited response in patients, new therapeutic options are urgently needed. In recent years, differentiation therapy has been proposed as an alternative for GBM treatment, with the aim of bringing cancer cells into a post-mitotic/differentiated state, ultimately limiting tumour growth. As an integral component of cancer development and regulation of differentiation processes, kinases are potential targets of differentiation therapies. The present study describes how the screening of a panel of kinase inhibitors (KIs) identified PDGF-Rα/β inhibitor CP-673451 as a potential differentiation agent in GBM. We show that targeting PDGF-Rα/β with CP-673451 in vitro triggers outgrowth of neurite-like processes in GBM cell lines and GBM stem cells (GSCs), suggesting differentiation into neural-like cells, while reducing proliferation and invasion in 3D hyaluronic acid hydrogels. In addition, we report that treatment with CP-673451 improves the anti-tumour effects of temozolomide in vivo using a subcutaneous xenograft mouse model. RNA sequencing and follow-up proteomic analysis revealed that upregulation of phosphatase DUSP1 and consecutive downregulation of phosphorylated-p38^MAPK can underlie the pro-differentiation effect of CP-673451 on GBM cells. Overall, the present study identifies a potential novel therapeutic option that could benefit GBM patients in the future, through differentiation of residual GSCs post-surgery, with the aim to limit recurrence and improve quality of life.

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.

ITGA5 Predicts Dual-Drug Resistance to Temozolomide and Bevacizumab in Glioma

AIMS

Anti-angiotherapy (Bevacizumab) is currently regarded as a promising option for glioma patients who are resistant to temozolomide (TMZ) treatment. But ongoing clinical research failed to meet therapeutic expectations. This study aimed to explore the pivotal genetic feature responsible for TMZ and Bevacizumab resistance in glioma patients.

METHODS

We downloaded the transcriptomic and methylation data of glioma patients from The Cancer Genome Atlas (TCGA), Chinese Glioma Genome Atlas (CGGA), and Gene Expression Omnibus (GEO) databases and grouped these patients into resistant and non-resistant groups based on their clinical profiles. Differentially expressed genes and pathways were identified and exhibited with software in R platform. A TMZ-resistant cell line was constructed for validating the expression change of the candidate gene, ITGA5. An ITGA5-overexpressing cell line was also constructed to investigate its biological function using the CCK8 assay, Western blot, periodic acid-Schiff (PAS) staining, and transcriptional sequencing.

RESULTS

Change of the cell morphology and polarity was closely associated with TMZ mono-resistance and TMZ/Bevacizumab dual resistance in glioma patients. The expression level of ITGA5 was effective in determining drug resistance and the outcome of glioma patients, which is regulated by methylation on two distinct sites. ITGA5 was augmented in TMZ-resistant glioma cells, while overexpressing ITGA5 altered the cell-promoted TMZ resistance through enhancing vascular mimicry (VM) formation correspondingly.

CONCLUSIONS

Both the epigenetic and transcriptional levels of ITGA5 are effective in predicting TMZ and Bevacizumab resistance, indicating that ITGA5 may serve as a predictor of the treatment outcomes of glioma patients.

A tale of two multi-focal therapies for glioblastoma: An antibody targeting ELTD1 and nitrone-based OKN-007

Glioblastoma (GBM) is the most common primary malignant brain tumour in adults. Despite a multimodal treatment response, survival for GBM patients remains between 12 and 15 months. Anti‐ELTD1 antibody therapy is effective in decreasing tumour volumes and increasing animal survival in an orthotopic GBM xenograft. OKN‐007 is a promising chemotherapeutic agent that is effective in various GBM animal models and is currently in two clinical trials. In this study, we sought to compare anti‐ELTD1 and OKN‐007 therapies, as single agents and combined, against bevacizumab, a commonly used therapeutic agent against GBM, in a human G55 xenograft mouse model. MRI was used to monitor tumour growth, and immunohistochemistry (IHC) was used to assess tumour markers for angiogenesis, cell migration and proliferation in the various treatment groups. OKN and anti‐ELTD1 treatments significantly increased animal survival, reduced tumour volumes and normalized the vasculature. Additionally, anti‐ELTD1 was also shown to significantly affect other pro‐angiogenic factors such as Notch1 and VEGFR2. Unlike bevacizumab, anti‐ELTD1 and OKN treatments did not induce a pro‐migratory phenotype within the tumours. Anti‐ELTD1 treatment was shown to be as effective as OKN therapy. Both OKN and anti‐ELTD1 therapies show promise as potential single‐agent multi‐focal therapies for GBM patients.

LOXL1-AS1 communicating with TIAR modulates vasculogenic mimicry in glioma via regulation of the miR-374b-5p/MMP14 axis

At present, growing evidence indicates that long non‐coding RNAs (lncRNAs) participate in the progression of glioma. The function of LOXL1‐AS1 in vasculogenic mimicry (VM) in glioma remains unclear. First, the expressions of TIAR, the lncRNA LOXL1‐AS1, miR‐374b‐5p and MMP14 were examined by qRT‐PCR and Western blot in both, glioma tissues and glioma cell lines. Proliferation, migration, invasion and tube formation assays were conducted to evaluate the roles of TIAR, LOXL1‐AS1, miR‐374b‐5p and MMP14 in malignant cellular behaviours in glioma cells. A nude mouse xenograft model and dual staining for CD34 and PAS were used to assess whether VM was affected by TIAR, LOXL1‐AS1 or miR‐374b‐5p in vivo. In this study, low levels of TIAR and high levels of LOXL1‐AS1 were found in glioma cells and tissues. TIAR downregulated the expression of LOXL1‐AS1 by destabilizing it. LOXL1‐AS1 acted like a miRNA sponge towards miR‐374b‐5p so that downregulation of the former greatly inhibited cell proliferation, migration, invasion and VM. Additionally, miR‐374b‐5p overexpression repressed malignant biological behaviours and VM in glioma by modifying MMP14. In summary, we demonstrated that TIAR combined with LOXL1‐AS1 modulates VM in glioma via the miR‐374b‐5p/MMP14 axis, revealing novel targets for glioma therapy.

Discovery of novel ID2 antagonists from pharmacophore-based virtual screening as potential therapeutics for glioma

Glioma, especially the most aggressive type glioblastoma multiforme, is a malignant cancer of the central nervous system with a poor prognosis. Traditional treatments are mainly surgery combined with radiotherapy and chemotherapy, which is still far from satisfactory. Therefore, it is of great clinical significance to find new therapeutic agents. Serving as an inhibitor of differentiation, protein ID2 (inhibitor of DNA binding 2) plays an important role in neurogenesis, neovascularization and malignant development of gliomas. It has been shown that ID2 affects the malignant progression of gliomas through different mechanisms. In this study, a pharmacophore-based virtual screening was carried out and 16 hit compounds were purchased for pharmacological evaluations on their ID2 inhibitory activities. Based on the cytotoxicity of these small-molecule compounds, two compounds were shown to effectively inhibit the viability of glioma cells in the micromolar range. Among them, AK-778-XXMU was chosen for further study due to its better solubility in water. A SPR (Surface Plasma Resonance) assay proved the high affinity between AK-778-XXMU and ID2 protein with the K_D value as 129 nM. The plausible binding mode of ID2 was studied by molecular docking and it was found to match AGX51 very well in the same binding site. Subsequently, the cancer-suppressing potency of the compound was characterized both in vitro and in vivo. The data demonstrated that compound AK-778-XXMU is a potent ID2 antagonist which has the potential to be developed as a therapeutic agent against glioma.

Coaxially Bioprinted Cell-Laden Tubular-Like Structure for Studying Glioma Angiogenesis

Glioblastomas are the most frequently diagnosed and one of the most lethal primary brain tumors, and one of their key features is a dysplastic vascular network. However, because the origin of the tumor blood vessels remains controversial, an optimal preclinical tumor model must be established to elucidate the tumor angiogenesis mechanism, especially the role of tumor cells themselves in angiogenesis. Therefore, shell-glioma cell (U118)-red fluorescent protein (RFP)/core-human umbilical vein endothelial cell (HUVEC)-green fluorescent protein (GFP) hydrogel microfibers were coaxially bioprinted. U118–RFP and HUVEC–GFP cells both exhibited good proliferation in a three-dimensional (3D) microenvironment. The secretability of both vascular endothelial growth factor A and basic fibroblast growth factor was remarkably enhanced when both types of cells were cocultured in 3D models. Moreover, U118 cells promoted the vascularization of the surrounding HUVECs by secreting vascular growth factors. More importantly, U118–HUVEC-fused cells were found in U118–RFP/HUVEC–GFP hydrogel microfibers. Most importantly, our results indicated that U118 cells can not only recruit the blood vessels of the surrounding host but also directly transdifferentiate into or fuse with endothelial cells to participate in tumor angiogenesis in vivo. The coaxially bioprinted U118–RFP/HUVEC–GFP hydrogel microfiber is a model suitable for mimicking the glioma microenvironment and for investigating tumor angiogenesis.

Preclinical Evaluation of Sodium Selenite in Mice: Toxicological and Tumor Regression Studies after Striatum Implantation of Human Glioblastoma Stem Cells

Glioblastoma (GBM) is the most aggressive malignant glioma, with a very poor prognosis; as such, efforts to explore new treatments and GBM’s etiology are a priority. We previously described human GBM cells (R2J-GS) as exhibiting the properties of cancer stem cells (growing in serum-free medium and proliferating into nude mice when orthotopically grafted). Sodium selenite (SS)—an in vitro attractive agent for cancer therapy against GBM—was evaluated in R2J-GS cells. To go further, we launched a preclinical study: SS was given orally, in an escalation-dose study (2.25 to 10.125 mg/kg/day, 5 days on, 2 days off, and 5 days on), to evaluate (1) the absorption of selenium in plasma and organs (brain, kidney, liver, and lung) and (2) the SS toxicity. A 6.75 mg/kg SS dose was chosen to perform a tumor regression assay, followed by MRI, in R2J-GS cells orthotopically implanted in nude mice, as this dose was nontoxic and increased brain selenium concentration. A group receiving TMZ (5 mg/kg) was led in parallel. Although not reaching statistical significance, the group of mice treated with SS showed a slower tumor growth vs. the control group (p = 0.08). No difference was observed between the TMZ and control groups. We provide new insights of the mechanisms of SS and its possible use in chemotherapy.

Environmental interplay: Stromal cells and biomaterial composition influence in the glioblastoma microenvironment

Glioblastoma multiforme (GBM) is the most deadly form of brain cancer. Recurrence is common, and established therapies have not been able to significantly extend overall patient survival. One platform through which GBM research can progress is to design biomimetic systems for discovery and investigation into the mechanisms of invasion, cellular properties, as well as the efficacy of therapies. In this review, 2D and 3D GBM in vitro cultures will be discussed. We focus on the effects of biomaterial properties, interactions between stromal cells, and vascular influence on cancer cell survival and progression. This review will summarize critical findings in each of these areas and how they have led to a more comprehensive scientific understanding of GBM. STATEMENT OF SIGNIFICANCE: Glioblastoma multiforme (GBM) is the most deadly form of brain cancer. Recurrence is common, and established therapies have not been able to significantly extend overall patient survival. One platform through which GBM research can progress is to design biomimetic systems for discovery and investigation into the mechanisms of invasion, cellular properties, as well as the efficacy of therapies. In this review, 2D and 3D GBM in vitro cultures will be discussed. We focus on the effects of biomaterial properties, interactions between stromal cells and vascular influence on cancer cell survival and progression. This review will summarize critical findings in each of these areas and how they have lead to a more comprehensive scientific understanding of GBM.

Targeting S1PR1 May Result in Enhanced Migration of Cancer Cells in Bladder Carcinoma

Clinical bladder tumor histological analysis shows that high expression of S1PR1 is associated with poor patient prognosis. However, there are no studies that describe the underlying mechanism. To investigate the relative distribution and actual function of S1PR1 in bladder tumors, we analyzed multiple clinical databases in combination with tumor purity and immune cell infiltration simulations, as well as databases of well-defined histological phenotypes of bladder cancer, and single-cell sequencing of adjacent normal tissues and bladder tumors, and further compared them with bladder cancer cell lines. The results showed that S1PR1 expression was generally higher in normal tissues than in bladder cancer tissues, and its distribution was mainly in endothelial cells or immune cells. The association between high S1PR1 expression and poor prognosis may be due to tumor invasion of adjacent normal tissues, where highly expressed S1PR1 may affect prognostic interpretation. The effect of S1PR1 itself on cancer cells was associated with cell adhesion, and in bladder cancer cells, S1PR1 expression was negatively correlated with cell motility. Moreover, the use of FTY-720 will cause an increased metastatic ability of bladder cancer cells. In conclusion, we suggest that the use of S1PR1-specific inhibition as a synergistic treatment requires more observation and consideration.

A Magnetic T7 Peptide&AS1411 Aptamer-Modified Microemulsion for Triple Glioma-Targeted Delivery of Shikonin and Docetaxel

Glioma-targeted drug delivery is a hugely challenging task because of the multibarrier in the brain. In this study, we report a magnetic T7 peptide&AS1411 aptamer-modified microemulsion for triple glioma-targeted delivery of shikonin and docetaxel (Fe3O4@T7/AS1411/DTX&SKN-M). Such a system comprises two tumor-targeted ligands (T7 peptide and AS1411 aptamer), ultra-small superparamagnetic iron oxide nanoparticle (Fe3O4), and shikonin&docetaxel-coloaded microemulsion (SKN&DTX-M). Fe3O4@T7/AS1411/DTX&SKN-M is capable of stably circulating in the blood, accumulating around the brain under an external magnetic field, distributing inside the glioma via the affinity to nucleolin/transferrin receptor, and retarding the growth of orthotopic glioma. Fe3O4@T7/AS1411/DTX&SKN-M encapsulated Fe3O4 nanoparticles in the core to obtain the superparamagnetism, which did not influence the main surface properties. Introducing 6% (wt%) of DSPE-PEG2000-T7 and 180 nM of AS1411 collaboratively enhanced the murine glioma (G422) cellular uptake of Fe3O4@T7/AS1411/DTX&SKN-M and thereby achieved the strongest antiproliferation among all the groups. Notably, the drug distribution at the brain sites of orthotopic Luc-G422 glioma tumor-bearing nude mice treated with Fe3O4@T7/AS1411/DTX&SKN-M was overwhelming among all the treatments. Most importantly, Fe3O4@T7/AS1411/DTX&SKN-M not only significantly reduced the luminescence signal at the brain areas of orthotopic Luc-G422 glioma mice but also prolonged the overall survival period. The enhancement of anti-glioma efficacy was associated with down-regulating the population of CD133- and CD44-positive cells within the tumors. In summary, such a triple glioma-targeted delivery of shikonin and docetaxel using combinational magnetism and T7/AS1411 modification strategies provides a promising method for synergistic and precise glioma therapy.

Dual role of WNT5A in promoting endothelial differentiation of glioma stem cells and angiogenesis of glioma derived endothelial cells

Glioma is a devastating cancer with a rich vascular network. No anti-angiogenic treatment is available for prolonging the overall survival of glioma patients. Recent studies have demonstrated that the endothelial differentiation of glioma stem cells (GSCs) into glioma-derived endothelial cells (GDECs) may be a novel target for anti-angiogenic therapy in glioma; however, the underlying mechanisms of this process remain unknown. Here, we report that wingless-related integration site (WNT) family member 5A (WNT5A) plays significant roles in GSC endothelial differentiation and GDECs angiogenesis. WNT5A is preferentially secreted by GDECs, and inhibition of WNT5A suppresses angiogenesis and tumorigenesis in GDECs. Silencing of WNT5A in GDECs also disrupts the impact of GDECs on stimulating GSC endothelial differentiation. Frizzled-4 is a receptor that mediates the effect of WNT5A on GSC endothelial differentiation and angiogenesis of GDECs via GSK3β/β-catenin/epithelial-mesenchymal transition signalling. The shWNT5A@cRGD-DDD liposomes, targeting WNT5A, exert anti-angiogenic effects in vivo. In this study, we identified that WNT5A has a dual functional role in modulating the endothelial differentiation of GSCs and angiogenesis of GDECs, indicating that WNT5A is a potential target for anti-angiogenesis-based therapeutics in glioma.

Tumor-associated hematopoietic stem and progenitor cells positively linked to glioblastoma progression

Brain tumors are typically immunosuppressive and refractory to immunotherapies for reasons that remain poorly understood. The unbiased profiling of immune cell types in the tumor microenvironment may reveal immunologic networks affecting therapy and course of disease. Here we identify and validate the presence of hematopoietic stem and progenitor cells (HSPCs) within glioblastoma tissues. Furthermore, we demonstrate a positive link of tumor-associated HSPCs with malignant and immunosuppressive phenotypes. Compared to the medullary hematopoietic compartment, tumor-associated HSPCs contain a higher fraction of immunophenotypically and transcriptomically immature, CD38- cells, such as hematopoietic stem cells and multipotent progenitors, express genes related to glioblastoma progression and display signatures of active cell cycle phases. When cultured ex vivo, tumor-associated HSPCs form myeloid colonies, suggesting potential in situ myelopoiesis. In experimental models, HSPCs promote tumor cell proliferation, expression of the immune checkpoint PD-L1 and secretion of tumor promoting cytokines such as IL-6, IL-8 and CCL2, indicating concomitant support of both malignancy and immunosuppression. In patients, the amount of tumor-associated HSPCs in tumor tissues is prognostic for patient survival and correlates with immunosuppressive phenotypes. These findings identify an important element in the complex landscape of glioblastoma that may serve as a target for brain tumor immunotherapies.

A deeper knowledge of the immune cell profile within the brain cancer tumor microenvironment (TM) could identify targets to improve immunotherapy efficacy. Here, in glioblastoma, the authors find haematopoietic stem and progenitor cells in the TM, which are associated with poor prognosis and increased immunosuppression.

Nestin+/CD31+ cells in the hypoxic perivascular niche regulate glioblastoma chemoresistance by upregulating JAG1 and DLL4

BACKGROUND

Failure of glioblastoma (GBM) therapy is often ascribed to different types of glioblastoma stem-like cell (GSLC) niche; in particular, a hypoxic perivascular niche (HPVN) is involved in GBM progression. However, the cells responsible for HPVNs remain unclear.

METHODS

Immunostaining was performed to determine the cells involved in HPVNs. A hypoxic chamber and 3-dimensional (3D) microfluidic chips were designed to simulate a HPVN based on the pathological features of GBM. The phenotype of GSLCs was evaluated by fluorescence scanning in real time and proliferation and apoptotic assays. The expression of JAG1, DLL4, and Hes1 was determined by immunostaining, ELISA, Western blotting, and quantitative PCR. Their clinical prognostic significance in GBM HPVNs and total tumor tissues were verified by clinical data and The Cancer Genome Atlas databases.

RESULTS

Nestin+/CD31+ cells and pericytes constitute the major part of microvessels in the HPVN, and the high ratio of nestin+/CD31+ cells rather than pericytes are responsible for the poor prognosis of GBM. A more real HPVN was simulated by a hypoxic coculture system in vitro, which consisted of 3D microfluidic chips and a hypoxic chamber. Nestin+/CD31+ cells in the HPVN were derived from GSLC transdifferentiation and promoted GSLC chemoresistance by providing more JAG1 and DLL4 to induce downstream Hes1 overexpression. Poor GBM prognosis correlated with Hes1 expression of tumor cells in the GBM HPVN, and not with total Hes1 expression in GBM tissues.

CONCLUSIONS

These results highlight the critical role of nestin+/CD31+ cells in HPVNs that acts in GBM chemoresistance and reveal the distinctive prognostic value of these molecular markers in HPVNs.

Tumor Vessels Fuel the Fire in Glioblastoma

Glioblastoma, a subset of aggressive brain tumors, deploy several means to increase blood vessel supply dedicated to the tumor mass. This includes typical program borrowed from embryonic development, such as vasculogenesis and sprouting angiogenesis, as well as unconventional processes, including co-option, vascular mimicry, and transdifferentiation, in which tumor cells are pro-actively engaged. However, these neo-generated vascular networks are morphologically and functionally abnormal, suggesting that the vascularization processes are rather inefficient in the tumor ecosystem. In this review, we reiterate the specificities of each neovascularization modality in glioblastoma, and, how they can be hampered mechanistically in the perspective of anti-cancer therapies.

In Vitro Glioblastoma Models: A Journey into the Third Dimension

Simple Summary

In this review, the thorny issue of glioblastoma models is addressed, with a focus on 3D in vitro models. In the first part of the manuscript, glioblastoma features and classification are recapitulated, in order to highlight the major critical aspects that should be taken into account when choosing a glioblastoma 3D model. In the second part of the review, the 3D models described in the literature are critically discussed, considering the advantages, disadvantages, and feasibility for each experimental model, in the light of the potential issues that researchers want to address.

Abstract

Glioblastoma multiforme (GBM) is the most lethal primary brain tumor in adults, with an average survival time of about one year from initial diagnosis. In the attempt to overcome the complexity and drawbacks associated with in vivo GBM models, together with the need of developing systems dedicated to screen new potential drugs, considerable efforts have been devoted to the implementation of reliable and affordable in vitro GBM models. Recent findings on GBM molecular features, revealing a high heterogeneity between GBM cells and also between other non-tumor cells belonging to the tumoral niche, have stressed the limitations of the classical 2D cell culture systems. Recently, several novel and innovative 3D cell cultures models for GBM have been proposed and implemented. In this review, we first describe the different populations and their functional role of GBM and niche non-tumor cells that could be used in 3D models. An overview of the current available 3D in vitro systems for modeling GBM, together with their major weaknesses and strengths, is presented. Lastly, we discuss the impact of groundbreaking technologies, such as bioprinting and multi-omics single cell analysis, on the future implementation of 3D in vitro GBM models.

Heterogeneous Expression of Proangiogenic and Coagulation Proteins in Gliomas of Different Histopathological Grade

Brain gliomas are characterized by remarkably intense invasive growth and the ability to create new blood vessels. Angiogenesis is a key process in the progression of these tumors. Coagulation and fibrinolysis factors play a role in promoting angiogenesis. The aim of the study was to evaluate the expression of proangiogenic proteins (VEGF and bFGF) and hemostatic proteins (TF, fibrinogen, fibrin, D-dimers) associated with neoplastic cells and vascular endothelial cells in brain gliomas of various degrees of malignancy. Immunohistochemical tests were performed using the ABC method with the use of mono- and polyclonal antibodies. The obtained results indicated that both neoplastic cells and vascular endothelial cells in gliomas of various degrees of malignancy are characterized by heterogeneous expression of proteins of the hemostatic system and angiogenesis markers. The strongest expression of proangiogenic factors and procoagulant factors was demonstrated in gliomas of higher-grade malignancy.

The adaptive transition of glioblastoma stem cells and its implications on treatments

Glioblastoma is the most malignant tumor occurring in the human central nervous system with overall median survival time <14.6 months. Current treatments such as chemotherapy and radiotherapy cannot reach an optimal remission since tumor resistance to therapy remains a challenge. Glioblastoma stem cells are considered to be responsible for tumor resistance in treating glioblastoma. Previous studies reported two subtypes, proneural and mesenchymal, of glioblastoma stem cells manifesting different sensitivity to radiotherapy or chemotherapy. Mesenchymal glioblastoma stem cells, as well as tumor cells generate from which, showed resistance to radiochemotherapies. Besides, two metabolic patterns, glutamine or glucose dependent, of mesenchymal glioblastoma stem cells also manifested different sensitivity to radiochemotherapies. Glutamine dependent mesenchymal glioblastoma stem cells are more sensitive to radiotherapy than glucose-dependent ones. Therefore, the transition between proneural and mesenchymal subtypes, or between glutamine-dependent and glucose-dependent, might lead to tumor resistance to radiochemotherapies. Moreover, neural stem cells were also hypothesized to participate in glioblastoma stem cells mediated tumor resistance to radiochemotherapies. In this review, we summarized the basic characteristics, adaptive transition and implications of glioblastoma stem cells in glioblastoma therapy.

Neural crest cell-derived pericytes act as pro-angiogenic cells in human neocortex development and gliomas

Central nervous system diseases involving the parenchymal microvessels are frequently associated with a ‘microvasculopathy’, which includes different levels of neurovascular unit (NVU) dysfunction, including blood–brain barrier alterations. To contribute to the understanding of NVU responses to pathological noxae, we have focused on one of its cellular components, the microvascular pericytes, highlighting unique features of brain pericytes with the aid of the analyses carried out during vascularization of human developing neocortex and in human gliomas. Thanks to their position, centred within the endothelial/glial partition of the vessel basal lamina and therefore inserted between endothelial cells and the perivascular and vessel-associated components (astrocytes, oligodendrocyte precursor cells (OPCs)/NG2-glia, microglia, macrophages, nerve terminals), pericytes fulfil a central role within the microvessel NVU. Indeed, at this critical site, pericytes have a number of direct and extracellular matrix molecule- and soluble factor-mediated functions, displaying marked phenotypical and functional heterogeneity and carrying out multitasking services. This pericytes heterogeneity is primarily linked to their position in specific tissue and organ microenvironments and, most importantly, to their ontogeny. During ontogenesis, pericyte subtypes belong to two main embryonic germ layers, mesoderm and (neuro)ectoderm, and are therefore expected to be found in organs ontogenetically different, nonetheless, pericytes of different origin may converge and colonize neighbouring areas of the same organ/apparatus. Here, we provide a brief overview of the unusual roles played by forebrain pericytes in the processes of angiogenesis and barriergenesis by virtue of their origin from midbrain neural crest stem cells. A better knowledge of the ontogenetic subpopulations may support the understanding of specific interactions and mechanisms involved in pericyte function/dysfunction, including normal and pathological angiogenesis, thereby offering an alternative perspective on cell subtype-specific therapeutic approaches.

Neural crest cell-derived pericytes act as pro-angiogenic cells in human neocortex development and gliomas

Central nervous system diseases involving the parenchymal microvessels are frequently associated with a ‘microvasculopathy’, which includes different levels of neurovascular unit (NVU) dysfunction, including blood–brain barrier alterations. To contribute to the understanding of NVU responses to pathological noxae, we have focused on one of its cellular components, the microvascular pericytes, highlighting unique features of brain pericytes with the aid of the analyses carried out during vascularization of human developing neocortex and in human gliomas. Thanks to their position, centred within the endothelial/glial partition of the vessel basal lamina and therefore inserted between endothelial cells and the perivascular and vessel-associated components (astrocytes, oligodendrocyte precursor cells (OPCs)/NG2-glia, microglia, macrophages, nerve terminals), pericytes fulfil a central role within the microvessel NVU. Indeed, at this critical site, pericytes have a number of direct and extracellular matrix molecule- and soluble factor-mediated functions, displaying marked phenotypical and functional heterogeneity and carrying out multitasking services. This pericytes heterogeneity is primarily linked to their position in specific tissue and organ microenvironments and, most importantly, to their ontogeny. During ontogenesis, pericyte subtypes belong to two main embryonic germ layers, mesoderm and (neuro)ectoderm, and are therefore expected to be found in organs ontogenetically different, nonetheless, pericytes of different origin may converge and colonize neighbouring areas of the same organ/apparatus. Here, we provide a brief overview of the unusual roles played by forebrain pericytes in the processes of angiogenesis and barriergenesis by virtue of their origin from midbrain neural crest stem cells. A better knowledge of the ontogenetic subpopulations may support the understanding of specific interactions and mechanisms involved in pericyte function/dysfunction, including normal and pathological angiogenesis, thereby offering an alternative perspective on cell subtype-specific therapeutic approaches.

Dissecting the mechanism of temozolomide resistance and its association with the regulatory roles of intracellular reactive oxygen species in glioblastoma

Glioblastoma is the most common primary malignant brain tumor that is usually considered fatal even with treatment. This is often a result for tumor to develop resistance. Regarding the standard chemotherapy, the alkylating agent temozolomide is effective in disease control but the recurrence will still occur eventually. The mechanism of the resistance is various, and differs in terms of innate or acquired. To date, aberrations in O⁶-methylguanine-DNA methyltransferase are the clear factor that determines drug susceptibility. Alterations of the other DNA damage repair genes such as DNA mismatch repair genes are also known to affect the drug effect. Together these genes have roles in the innate resistance, but are not sufficient for explaining the mechanism leading to acquired resistance. Recent identification of specific cellular subsets with features of stem-like cells may have role in this process. The glioma stem-like cells are known for its superior ability in withstanding the drug-induced cytotoxicity, and giving the chance to repopulate the tumor. The mechanism is complicated to administrate cellular protection, such as the enhancing ability against reactive oxygen species and altering energy metabolism, the important steps to survive. In this review, we discuss the possible mechanism for these specific cellular subsets to evade cancer treatment, and the possible impact to the following treatment courses. In addition, we also discuss the possibility that can overcome this obstacle.

In vitro biomimetic models for glioblastoma-a promising tool for drug response studies

The poor response of glioblastoma to current treatment protocols is a consequence of its intrinsic drug resistance. Resistance to chemotherapy is primarily associated with considerable cellular heterogeneity, and plasticity of glioblastoma cells, alterations in gene expression, presence of specific tumor microenvironment conditions and blood-brain barrier. In an attempt to successfully overcome chemoresistance and better understand the biological behavior of glioblastoma, numerous tri-dimensional (3D) biomimetic models were developed in the past decade. These novel advanced models are able to better recapitulate the spatial organization of glioblastoma in a real time, therefore providing more realistic and reliable evidence to the response of glioblastoma to therapy. Moreover, these models enable the fine-tuning of different tumor microenvironment conditions and facilitate studies on the effects of the tumor microenvironment on glioblastoma chemoresistance. This review outlines current knowledge on the essence of glioblastoma chemoresistance and describes the progress achieved by 3D biomimetic models. Moreover, comprehensive literature assessment regarding the influence of 3D culturing and microenvironment mimicking on glioblastoma gene expression and biological behavior is also provided. The contribution of the blood-brain barrier as well as the blood-tumor barrier to glioblastoma chemoresistance is also reviewed from the perspective of 3D biomimetic models. Finally, the role of mathematical models in predicting 3D glioblastoma behavior and drug response is elaborated. In the future, technological innovations along with mathematical simulations should create reliable 3D biomimetic systems for glioblastoma research that should facilitate the identification and possibly application in preclinical drug testing and precision medicine.

Pathogenetic Features and Current Management of Glioblastoma

Glioblastoma (GBM) is the most common form of primary malignant brain tumor with a devastatingly poor prognosis. The disease does not discriminate, affecting adults and children of both sexes, and has an average overall survival of 12-15 months, despite advances in diagnosis and rigorous treatment with chemotherapy, radiation therapy, and surgical resection. In addition, most survivors will eventually experience tumor recurrence that only imparts survival of a few months. GBM is highly heterogenous, invasive, vascularized, and almost always inaccessible for treatment. Based on all these outstanding obstacles, there have been tremendous efforts to develop alternative treatment options that allow for more efficient targeting of the tumor including small molecule drugs and immunotherapies. A number of other strategies in development include therapies based on nanoparticles, light, extracellular vesicles, and micro-RNA, and vessel co-option. Advances in these potential approaches shed a promising outlook on the future of GBM treatment. In this review, we briefly discuss the current understanding of adult GBM's pathogenetic features that promote treatment resistance. We also outline novel and promising targeted agents currently under development for GBM patients during the last few years with their current clinical status.

The Strange Case of Jekyll and Hyde: Parallels Between Neural Stem Cells and Glioblastoma-Initiating Cells

During embryonic development, radial glial precursor cells give rise to neural lineages, and a small proportion persist in the adult mammalian brain to contribute to long-term neuroplasticity. Neural stem cells (NSCs) reside in two neurogenic niches of the adult brain, the hippocampus and the subventricular zone (SVZ). NSCs in the SVZ are endowed with the defining stem cell properties of self-renewal and multipotent differentiation, which are maintained by intrinsic cellular programs, and extrinsic cellular and niche-specific interactions. In glioblastoma, the most aggressive primary malignant brain cancer, a subpopulation of cells termed glioblastoma stem cells (GSCs) exhibit similar stem-like properties. While there is an extensive overlap between NSCs and GSCs in function, distinct genetic profiles, transcriptional programs, and external environmental cues influence their divergent behavior. This review highlights the similarities and differences between GSCs and SVZ NSCs in terms of their gene expression, regulatory molecular pathways, niche organization, metabolic programs, and current therapies designed to exploit these differences.

ADAMTS1 Supports Endothelial Plasticity of Glioblastoma Cells with Relevance for Glioma Progression

Gliomas in general and the more advanced glioblastomas (GBM) in particular are the most usual tumors of the central nervous system with poor prognosis. GBM patients develop resistance to distinct therapies, in part due to the existence of tumor cell subpopulations with stem-like properties that participate in trans-differentiation events. Within the complex tumor microenvironment, the involvement of extracellular proteases remains poorly understood. The extracellular protease ADAMTS1 has already been reported to contribute to the plasticity of cancer cells. Accordingly, this basic knowledge and the current availability of massive sequencing data from human gliomas, reinforced the development of this work. We first performed an in silico study of ADAMTS1 and endothelial markers in human gliomas, providing the basis to further assess these molecules in several primary glioblastoma-initiating cells and established GBM cells with the ability to acquire an endothelial-like phenotype. Using a co-culture approach of endothelial and GBM cells, we noticed a relevant function of ADAMTS1 in GBM cells leading the organization of endothelial-like networks and, even more significantly, we found a blockade of the formation of tumor-spheres and a deficient response to hypoxia in the absence of ADAMTS1. Our data support a chief role of this protease modulating the phenotypic plasticity of GBM.