Isolation and Culture of Glioblastoma Brain Tumor Stem Cells

Epigenetic and molecular coordination between HDAC2 and SMAD3-SKI regulates essential brain tumour stem cell characteristics

Histone deacetylases are important epigenetic regulators that have been reported to play essential roles in cancer stem cell functions and are promising therapeutic targets in many cancers including glioblastoma. However, the functionally relevant roles of specific histone deacetylases, in the maintenance of key self-renewal and growth characteristics of brain tumour stem cell (BTSC) sub-populations of glioblastoma, remain to be fully resolved. Here, using pharmacological inhibition and genetic loss and gain of function approaches, we identify HDAC2 as the most relevant histone deacetylase for re-organization of chromatin accessibility resulting in maintenance of BTSC growth and self-renewal properties. Furthermore, its specific interaction with the transforming growth factor-β pathway related proteins, SMAD3 and SKI, is crucial for the maintenance of tumorigenic potential in BTSCs in vitro and in orthotopic xenograft models. Inhibition of HDAC2 activity and disruption of the coordinated mechanisms regulated by the HDAC2-SMAD3-SKI axis are thus promising therapeutic approaches for targeting BTSCs.

Chemical genomics reveals targetable programs of human cancers rooted in pluripotency

Overlapping principles of embryonic and tumor biology have been described, with recent multi-omics campaigns uncovering shared molecular profiles between human pluripotent stem cells (hPSCs) and adult tumors. Here, using a chemical genomic approach, we provide biological evidence that early germ layer fate decisions of hPSCs reveal targets of human cancers. Single-cell deconstruction of hPSCs-defined subsets that share transcriptional patterns with transformed adult tissues. Chemical screening using a unique germ layer specification assay for hPSCs identified drugs that enriched for compounds that selectively suppressed the growth of patient-derived tumors corresponding exclusively to their germ layer origin. Transcriptional response of hPSCs to germ layer inducing drugs could be used to identify targets capable of regulating hPSC specification as well as inhibiting adult tumors. Our study demonstrates properties of adult tumors converge with hPSCs drug induced differentiation in a germ layer specific manner, thereby expanding our understanding of cancer stemness and pluripotency.

Neurosurgical Approaches to Brain Tissue Harvesting for the Establishment of Cell Cultures in Neural Experimental Cell Models

In recent decades, cell biology has made rapid progress. Cell isolation and cultivation techniques, supported by modern laboratory procedures and experimental capabilities, provide a wide range of opportunities for in vitro research to study physiological and pathophysiological processes in health and disease. They can also be used very efficiently for the analysis of biomaterials. Before a new biomaterial is ready for implantation into tissues and widespread use in clinical practice, it must be extensively tested. Experimental cell models, which are a suitable testing ground and the first line of empirical exploration of new biomaterials, must contain suitable cells that form the basis of biomaterial testing. To isolate a stable and suitable cell culture, many steps are required. The first and one of the most important steps is the collection of donor tissue, usually during a surgical procedure. Thus, the collection is the foundation for the success of cell isolation. This article explains the sources and neurosurgical procedures for obtaining brain tissue samples for cell isolation techniques, which are essential for biomaterial testing procedures.

Glioblastoma Contains Topologically Distinct Proliferative and Metabolically Defined Subpopulations of Nestin- and Glut1-Expressing Cells

The difficulty in treatment of glioblastoma is a consequence of its natural infiltrative growth and the existence of a population of therapy-resistant glioma cells that contribute to growth and recurrence. To identify cells more likely to have these properties, we examined the expression in tumor specimens of several protein markers important for glioma progression including the intermediate filament protein, Nestin (NES), a glucose transporter (Glut1/SLC2A1), the glial lineage marker, glial fibrillary acidic protein, and the proliferative indicator, Ki-67. We also examined the expression of von Willebrand factor, a marker for endothelial cells as well as the macrophage/myeloid markers CD163 and CD15. Using a multicolor immunofluorescence and hematoxylin and eosin staining approach with archival formalin-fixed, paraffin embedded tissue from primary, recurrent, and autopsy IDH1 wildtype specimens combined with high-resolution tissue image analysis, we have identified highly proliferative NES(+)/Glut1(-) cells that are preferentially perivascular. In contrast, Glut1(+)/NES(-) cells are distant from blood vessels, show low proliferation, and are preferentially located at the borders of pseudopalisading necrosis. We hypothesize that Glut1(+)/NES(-) cells would be naturally resistant to conventional chemotherapy and radiation due to their low proliferative capacity and may act as a reservoir for tumor recurrence.

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.

Calcium Channels in Adult Brain Neural Stem Cells and in Glioblastoma Stem Cells

The brain of adult mammals, including humans, contains neural stem cells (NSCs) located within specific niches of which the ventricular-subventricular zone (V-SVZ) is the largest one. Under physiological conditions, NSCs proliferate, self-renew and produce new neurons and glial cells. Several recent studies established that oncogenic mutations in adult NSCs of the V-SVZ are responsible for the emergence of malignant primary brain tumors called glioblastoma. These aggressive tumors contain a small subpopulation of cells, the glioblastoma stem cells (GSCs), that are endowed with proliferative and self-renewal abilities like NSCs from which they may arise. GSCs are thus considered as the cells that initiate and sustain tumor growth and, because of their resistance to current treatments, provoke tumor relapse. A growing body of studies supports that Ca²⁺ signaling controls a variety of processes in NSCs and GSCs. Ca²⁺ is a ubiquitous second messenger whose fluctuations of its intracellular concentrations are handled by channels, pumps, exchangers, and Ca²⁺ binding proteins. The concerted action of the Ca²⁺ toolkit components encodes specific Ca²⁺ signals with defined spatio-temporal characteristics that determine the cellular responses. In this review, after a general overview of the adult brain NSCs and GSCs, we focus on the multiple roles of the Ca²⁺ toolkit in NSCs and discuss how GSCs hijack these mechanisms to promote tumor growth. Extensive knowledge of the role of the Ca²⁺ toolkit in the management of essential functions in healthy and pathological stem cells of the adult brain should help to identify promising targets for clinical applications.

Brain Tumor Stem Cell Dependence on Glutaminase Reveals a Metabolic Vulnerability through the Amino Acid Deprivation Response Pathway

Cancer cells can metabolize glutamine to replenish TCA cycle intermediates, leading to a dependence on glutaminolysis for cell survival. However, a mechanistic understanding of the role that glutamine metabolism has on the survival of glioblastoma (GBM) brain tumor stem cells (BTSC) has not yet been elucidated. Here, we report that across a panel of 19 GBM BTSC lines, inhibition of glutaminase (GLS) showed a variable response from complete blockade of cell growth to absolute resistance. Surprisingly, BTSC sensitivity to GLS inhibition was a result of reduced intracellular glutamate triggering the amino acid deprivation response (AADR) and not due to the contribution of glutaminolysis to the TCA cycle. Moreover, BTSC sensitivity to GLS inhibition negatively correlated with expression of the astrocytic glutamate transporters EAAT1 and EAAT2. Blocking glutamate transport in BTSCs with high EAAT1/EAAT2 expression rendered cells susceptible to GLS inhibition, triggering the AADR and limiting cell growth. These findings uncover a unique metabolic vulnerability in BTSCs and support the therapeutic targeting of upstream activators and downstream effectors of the AADR pathway in GBM. Moreover, they demonstrate that gene expression patterns reflecting the cellular hierarchy of the tissue of origin can alter the metabolic requirements of the cancer stem cell population. SIGNIFICANCE: Glioblastoma brain tumor stem cells with low astrocytic glutamate transporter expression are dependent on GLS to maintain intracellular glutamate to prevent the amino acid deprivation response and cell death.

Myc targeted CDK18 promotes ATR and homologous recombination to mediate PARP inhibitor resistance in glioblastoma

PARP inhibitors (PARPis) have clinical efficacy in BRCA-deficient cancers, but not BRCA-intact tumors, including glioblastoma (GBM). We show that MYC or MYCN amplification in patient-derived glioblastoma stem-like cells (GSCs) generates sensitivity to PARPi via Myc-mediated transcriptional repression of CDK18, while most tumors without amplification are not sensitive. In response to PARPi, CDK18 facilitates ATR activation by interacting with ATR and regulating ATR-Rad9/ATR-ETAA1 interactions; thereby promoting homologous recombination (HR) and PARPi resistance. CDK18 knockdown or ATR inhibition in GSCs suppressed HR and conferred PARPi sensitivity, with ATR inhibitors synergizing with PARPis or sensitizing GSCs. ATR inhibitor VE822 combined with PARPi extended survival of mice bearing GSC-derived orthotopic tumors, irrespective of PARPi-sensitivity. These studies identify a role of CDK18 in ATR-regulated HR. We propose that combined blockade of ATR and PARP is an effective strategy for GBM, even for low-Myc GSCs that do not respond to PARPi alone, and potentially other PARPi-refractory tumors.

PARP inhibitors are mainly used to treat BRCA1/2 mutated cancers. Here, the authors show that MYC amplified glioblastomas are sensitive to PARP inhibition due to CDK18 repression, which impairs ATR regulated homologous recombination repair, and that ATR inhibition sensitises glioblastomas to PARP inhibition.