Glioblastoma Brain Tumor-initiating Cells Research Articles

Cell-specific cross-talk proteomics reveals cathepsin B signaling as a driver of glioblastoma malignancy near the subventricular zone.

Glioblastoma (GBM) is the most prevalent and aggressive malignant primary brain tumor. GBM proximal to the lateral ventricles (LVs) is more aggressive, potentially because of subventricular zone contact. Despite this, cross-talk between GBM and neural stem/progenitor cells (NSC/NPCs) is not well understood. Using cell-specific proteomics, we show that LV-proximal GBM prevents neuronal maturation of NSCs through induction of senescence. In addition, GBM brain tumor-initiating cells (BTICs) increase expression of cathepsin B (CTSB) upon interaction with NPCs. Lentiviral knockdown and recombinant protein experiments reveal that both cell-intrinsic and soluble CTSB promote malignancy-associated phenotypes in BTICs. Soluble CTSB stalls neuronal maturation in NPCs while promoting senescence, providing a link between LV-tumor proximity and neurogenesis disruption. Last, we show LV-proximal CTSB up-regulation in patients, showing the relevance of this cross-talk in human GBM biology. These results demonstrate the value of proteomic analysis in tumor microenvironment research and provide direction for new therapeutic strategies in GBM.

Abstract 1273: Glioblastoma brain tumor-initiating cells are protected from hypoxia when co-cultured with normal human astrocytes revealing a potential role for mitochondrial transfer via tunneling nanotubes

Abstract Background: Glioblastoma (GBM) has a median survival of <2 years and generally recurs within 6 months of treatment due to the development of chemo- and radiotherapy (RT) resistance. Tunneling nanotubes (TNTs) serve as intercellular conduits for establishing robust, tumor-promoting networks within the hypoxic tumor microenvironment. TNTs are provoked by hypoxia and can passage organelles like mitochondria, i.e., between astrocytes and stem-like brain tumor-initiating cells (BTICs). This is theorized to expand resistance properties to other cell types, as well as facilitate metabolic rescue in damaged cancer cells. We investigated the mitochondrial uptake (MU) abilities of RT-sensitive or RT-resistant BTICs from normal human astrocytes (NHAs) under hypoxic conditions. Methods: We used a Cytation5 Cell Imager to quantify MU by BTICs from NHAs in direct contact under normal (20%) or hypoxic oxygen tensions (5%). We obtained RT-sensitive (JX14P) patient-derived xenograft BTICs and generated a paired acquired-resistant (JX14P-RT) line. This was achieved by implanting primary tumors into flanks of athymic nude mice and serially treating with 6 fractions of 2Gy over 14 days for multiple passages until the median doubling time was halved. Cells were plated at a 1:1 ratio on Geltrex for 18h and exposed to 5% or 20% oxygen in serum-free media. NHAs were pre-labeled with a GFP-mitochondria tracker and BTICs were infected with a mCherry lentivirus. BTIC-MU was determined by quantifying double-positive cells in whole-well images. Viability was determined using CellTiterGlo, n = 4. Results: Time-lapse imaging revealed GFP-mitochondria transfer from NHAs to BTIC cells via TNTs stimulated by hypoxic conditions. We measured overall MU and cell viability in both BTIC lines. JX14P co-cultured with NHAs trended toward an increased MU (cell fraction) in hypoxia (Hyp) compared to Normoxia (Norm) (Norm = 32.61 ± 13, Hyp = 44.83 ± 5, P>0.167). JX14P exhibit higher cell viability (RLU) in hypoxia when mono- or co-cultured with NHAs (Mono: Norm = 10275 ± 901, Hyp = 12599 ± 579, P<0.0039, Co: Norm = 5415 ± 664, Hyp = 8341 ± 700, P<0.0001). JX14P-RT co-cultured with NHAs show a trend for more MU in hypoxia compared to Normoxia (Norm = 25.90 ± 12, Hyp = 38.12 ± 12, P>0.167). Compared to monoculture, JX14PRT exhibits higher cell viability in co-culture with NHAs under hypoxia (Mono: Norm = 9721 ± 255, Hyp = 10011 ± 1462, P>0.998, Co: Norm = 4928 ± 664, Hyp = 7805 ± 944, P<0.005). Conclusions: RT-sensitive or -resistant BTICs cocultured with NHAs exhibit increased cell viability under acute hypoxia compared to Normoxia with a trend toward increased MU. Results indicate a potential protective effect following direct interaction with NHAs under hypoxia. We are further exploring metabolic changes in each cell type following mitochondrial exchange. Citation Format: Lauren C. Nassour-Caswell, Nicholas J. Eustace, Christian T. Stackhouse, Hasan Alrefai, Patricia H. Hicks, Taylor L. Schanel, Joshua C. Anderson, Andee M. Beierle, Christopher D. Willey. Glioblastoma brain tumor-initiating cells are protected from hypoxia when co-cultured with normal human astrocytes revealing a potential role for mitochondrial transfer via tunneling nanotubes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1273.

A CD133-AKT-Wnt signaling axis drives glioblastoma brain tumor-initiating cells.

Mechanistic insight into signaling pathways downstream of surface receptors has been revolutionized with integrated cancer genomics. This has fostered current treatment modalities, namely immunotherapy, to capitalize on targeting key oncogenic signaling nodes downstream of a limited number of surface markers. Unfortunately, rudimentary mechanistic understanding of most other cell surface proteins has reduced the clinical utility of these markers. CD133 has reproducibly been shown to correlate with disease progression, recurrence, and poor overall survivorship in the malignant adult brain tumor, glioblastoma (GBM). Using several patient-derived CD133high and CD133low GBMs we describe intrinsic differences in determinants of stemness, which we owe to a CD133-AKT-Wnt signaling axis in which CD133 functions as a putative cell surface receptor for AKT-dependent Wnt activation. These findings may have implications for personalized oncology trials targeting PI3K/AKT or Wnt as both pathways may be activated independent of their canonical drivers, leading to treatment resistance and disease relapse.

Bmi1 regulates human glioblastoma stem cells through activation of differential gene networks in CD133+ brain tumor initiating cells.

Glioblastoma (GBM) is the most aggressive adult brain cancer, with a 15month median survivorship attributed to the existence of treatment-refractory brain tumor initiating cells (BTICs). In order to better understand the mechanisms regulating the tumorigenic properties of this population, we studied the role of the polycomb group member BMI1 in our patient-derived GBM BTICs and its relationship with CD133, a well-established marker of BTICs. Using gain and loss-of-function studies for Bmi1 in neural stem cells (NSCs) and patient-derived GBM BTICs respectively, we assessed in vitro self-renewal and in vivo tumor formation in these two cell populations. We further explored the BMI1 transcriptional regulatory network through RNA sequencing of different GBM BTIC populations that were knocked down for Bmi1. There is a differential role of BMI1 in CD133-positive cells, notably involving cell metabolism. In addition, we identified pivotal targets downstream of BMI1 in CD133+ cells such as integrin alpha 2 (ITGA2), that may contribute to regulating GBM stem cell properties. Our work sheds light on the association of three genes with CD133-BMI1 circuitry, their importance as downstream effectors of the BMI1 signalling pathway, and their potential as future targets for tackling GBM treatment-resistant cell populations.

PS2 - 217 Treatment of Glioblastoma Brain Tumor-Initiating Cells with Microglial and Macrophage-Derived Cytokines

The most common brain cancer, glioblastoma (GBM), also has the worst five-year survival rates of all cancers. This is due in part to cancer stem cells, known as brain tumor initiating cells (BTICs), which initiate GBM and are resistant to current therapies. Thus, it is important to study therapeutics targeting BTICs. Innate immune cells, microglia and macrophages (MMs), are also important GBM-associated cells. GBM influences MMs to promote tumor growth. However, my research group discovered that an old drug, amphotericin B, re-stimulates MMs to secrete cytokines that inhibit BTIC self-renewal (Nature Neurosci 17:46-55, 2014). Hence, I hypothesize these cytokines are potential GBM treatments. Methods: Twenty genetically diverse BTIC lines were exposed to interleukin-8 (IL8), monocyte chemoattractant protein-1 (MCP1), and tumor necrosis factor-alpha (TNF), the cytokines secreted most abundantly by amphotericin-stimulated MMs. Assays for proliferation, differentiation, apoptosis, and cell cycle arrest were performed. BTICs were then co-cultured with human GBM-derived MMs stimulated with TNF. Lastly, the relationship between TNF receptors (TNFR1/2) and presumed BTICs was determined in frozen human GBM sections by immunofluorescence. Results: TNF had the most potent inhibitory effect on BTIC proliferation. Also, TNF was able to increase BTIC differentiation, and induce apoptosis and G1 cell cycle arrest. In MM-BTIC co-culture, TNF stimulated MMs to decrease sphere formation. Interestingly, in human GBM tissue TNFR1 co-labeled with OLIG2, a major transcription factor expressed in presumed BTICs, implicating TNF as a BTIC-specific treatment. Conclusion: TNF is a promising candidate for the treatment of GBM.

Small molecule epigenetic screen identifies novel EZH2 and HDAC inhibitors that target glioblastoma brain tumor-initiating cells.

Glioblastoma (GBM) is the most lethal and aggressive adult brain tumor, requiring the development of efficacious therapeutics. Towards this goal, we screened five genetically distinct patient-derived brain-tumor initiating cell lines (BTIC) with a unique collection of small molecule epigenetic modulators from the Structural Genomics Consortium (SGC). We identified multiple hits that inhibited the growth of BTICs in vitro, and further evaluated the therapeutic potential of EZH2 and HDAC inhibitors due to the high relevance of these targets for GBM. We found that the novel SAM-competitive EZH2 inhibitor UNC1999 exhibited low micromolar cytotoxicity in vitro on a diverse collection of BTIC lines, synergized with dexamethasone (DEX) and suppressed tumor growth in vivo in combination with DEX. In addition, a unique brain-penetrant class I HDAC inhibitor exhibited cytotoxicity in vitro on a panel of BTIC lines and extended survival in combination with TMZ in an orthotopic BTIC model in vivo. Finally, a combination of EZH2 and HDAC inhibitors demonstrated synergy in vitro by augmenting apoptosis and increasing DNA damage. Our findings identify key epigenetic modulators in GBM that regulate BTIC growth and survival and highlight promising combination therapies.

Abstract LB-207: mTORC2/Akt signaling is modulated by noncanonical mitochondrial Notch1/PINK1 interaction in myc-amplified medulloblastoma tumorigenesis

Abstract Medulloblastoma is known to be the most malignant pediatric brain tumor. The armamentarium of targeted therapies to currently treat medulloblastoma and similar pediatric central nervous system malignancies is extremely limited, often necessitating the need to combat such tumors with modified regimens of therapeutic options designed originally to target adult neoplasms. Given such limited therapies, a budding focus on the role of mitochondrial dysregulation in the tumorigenesis of such pathologies merits consideration. Mitochondria are known to play fundamental roles in multiple processes conserved across eukaryotic species. Aside from their key role in energy production through oxidative phosphorylation, the organelles also serve as the sites of essential metabolic pathways, redox regulation, calcium homeostasis, apoptosis, and cell fate determination and differentiation. Recently, we documented the role of noncanonical Notch signaling and mitochondrial involvement in adult glioblastoma brain tumor-initiating cells (Lee KS et al., Genes and Development, 2013). Although the canonical Notch pathway and is generally well-characterized, involving the ligand-induced cleavage of Notch for transcriptional regulation, only more recently has credible evidence surfaced documenting the role of a second noncanonical pathway, where Notch can function independently of ligand and transcription through a mechanism that remains to be fully elucidated. The regulatory self-renewal versus differentiation choice of Drosophila and mammalian human neural stem cells requires Notch signaling, and in our work, we found noncanonical Notch pathway interaction with PTEN-induced putative kinase 1 (PINK1) to influence mitochondrial function, activating mTORC2/Akt signaling. siRNA-induced knockdown preferentially impaired the maintenance of Drosophila and human glioblastoma cancer stem cell-like tumor-forming cells to a far greater degree than normal stem cell counterparts. Further experiments have elucidated similar findings of increased Notch1/PINK1 mitochondrial interaction and mTORC2/Akt activity in patient-derived Group 3 (myc-amplified) medulloblastoma primary lines to levels greater than normal or glioblastoma samples. Additionally these medulloblastoma samples appear to be more susceptible to siRNA-induced knockdown of PINK1 than their counterparts. In vivo experiments are ongoing to address the role of mitochondrial Notch1/Pink1 interaction in tumor initiation and its targeting by small molecule inhibitors. Such results underscore the importance of mitochondria in both normal and cancer stem cell biology, a highly conserved mechanism across species, with exciting implications for the treatment of pediatric central nervous system malignancies. Citation Format: Abdullah H. Feroze, Kyu-Sun Lee, Sharareh Gholamin, Zhihao Wu, Irving Weissman, Bingwei Lu, Siddhartha S. Mitra, Samuel Cheshier. mTORC2/Akt signaling is modulated by noncanonical mitochondrial Notch1/PINK1 interaction in myc-amplified medulloblastoma tumorigenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-207. doi:10.1158/1538-7445.AM2014-LB-207

Mesenchymal stem cells from human fat engineered to secrete BMP4 are nononcogenic, suppress brain cancer, and prolong survival.

Glioblastoma is the most common adult primary malignant intracranial cancer. It is associated with poor outcomes because of its invasiveness and resistance to multimodal therapies. Human adipose-derived mesenchymal stem cells (hAMSC) are a potential treatment because of their tumor tropism, ease of isolation, and ability to be engineered. In addition, bone morphogenetic protein 4 (BMP4) has tumor-suppressive effects on glioblastoma and glioblastoma brain tumor-initiating cells (BTIC), but is difficult to deliver to brain tumors. We sought to engineer BMP4-secreting hAMSCs (hAMSCs-BMP4) and evaluate their therapeutic potential on glioblastoma. The reciprocal effects of hAMSCs on primary human BTIC proliferation, differentiation, and migration were evaluated in vitro. The safety of hAMSC use was evaluated in vivo by intracranial coinjections of hAMSCs and BTICs in nude mice. The therapeutic effects of hAMSCs and hAMSCs-BMP4 on the proliferation and migration of glioblastoma cells as well as the differentiation of BTICs, and survival of glioblastoma-bearing mice were evaluated by intracardiac injection of these cells into an in vivo intracranial glioblastoma murine model. hAMSCs-BMP4 targeted both the glioblastoma tumor bulk and migratory glioblastoma cells, as well as induced differentiation of BTICs, decreased proliferation, and reduced the migratory capacity of glioblastomas in vitro and in vivo. In addition, hAMSCs-BMP4 significantly prolonged survival in a murine model of glioblastoma. We also demonstrate that the use of hAMSCs in vivo is safe. Both unmodified and engineered hAMSCs are nononcogenic and effective against glioblastoma, and hAMSCs-BMP4 are a promising cell-based treatment option for glioblastoma.

GBM secretome induces transient transformation of human neural precursor cells

Glioblastoma (GBM) is the most aggressive primary brain tumor in humans, with a uniformly poor prognosis. The tumor microenvironment is composed of both supportive cellular substrates and exogenous factors. We hypothesize that exogenous factors secreted by brain tumor initiating cells (BTICs) could predispose normal neural precursor cells (NPCs) to transformation. When NPCs are grown in GBM-conditioned media, and designated as "tumor-conditioned NPCs" (tcNPCs), they become highly proliferative and exhibit increased stem cell self-renewal, or the unique ability of stem cells to asymmetrically generate another stem cell and a daughter cell. tcNPCs also show an increased transcript level of stem cell markers such as CD133 and ALDH and growth factor receptors such as VEGFR1, VEGFR2, EGFR and PDGFRα. Media analysis by ELISA of GBM-conditioned media reveals an elevated secretion of growth factors such as EGF, VEGF and PDGF-AA when compared to normal neural stem cell-conditioned media. We also demonstrate that tcNPCs require prolonged or continuous exposure to the GBM secretome in vitro to retain GBM BTIC characteristics. Our in vivo studies reveal that tcNPCs are unable to form tumors, confirming that irreversible transformation events may require sustained or prolonged presence of the GBM secretome. Analysis of GBM-conditioned media by mass spectrometry reveals the presence of secreted proteins Chitinase-3-like 1 (CHI3L1) and H2A histone family member H2AX. Collectively, our data suggest that GBM-secreted factors are capable of transiently altering normal NPCs, although for retention of the transformed phenotype, sustained or prolonged secretome exposure or additional transformation events are likely necessary.