Abstract A040: Reactive oligodendrocytes promote glioblastoma progression through CCL5/CCR5-mediated glioma stem cell maintenance

Background: Glioblastoma (GBM) is associated with poor survival (1 year-34.6% and 5 year-4.75%) and affects approximately 13,000 patients per year. Standard treatment consists of surgical resection, external beam radiation therapy, adjuvant chemotherapy with temozolomide and tumor treating fields. Nonetheless, despite a heavy investment in therapy, all patients eventually succumb to their disease. Hypoxic regions are common in GBM and are implicated in maintenance of glioma stem cells (GSCs), promoting angiogenesis and therapeutic resistance. Recently, we and others have shown that lysine-specific histone demethylase 1A (KDM1A) is overexpressed in GBM and GSCs. However, the role of KDM1A and its functions in hypoxic response remains unknown. The objective of this study is to elucidate the functional role of KDM1A in hypoxia and test the efficacy of novel KDM1A inhibitors on hypoxia-mediated functions in GBM. Methods: The expression of KDM1A following hypoxia induction was determined in vitro by Western blotting and qRT-PCR. The expression of KDM1A in GBM tissue was examined by immunohistochemistry (IHC). KDM1A knockout cells were generated using CRISPR/Cas9 system and knockdown cells were generated using KDM1A shRNA lentiviral particles. The effect of KDM1A knockdown or treatment with KDM1A inhibitors NCL-1 and NCD-38 on stemness and self-renewal of primary patient-derived GBM cells was examined using neurosphere formation and extreme limiting dilution assays. Interaction of KDM1A with hypoxia inducible factor 1α (HIF-1α) was examined by immunoprecipitation (IP). The role of KDM1A on HIF target genes was determined using qRT-PCR and HRE-reporter activity. Mouse orthotopic xenografts models were used for preclinical evaluation of KDM1A inhibitors. Results: Western blot analysis revealed that KDM1A expression is induced in primary GBM cells following hypoxia. IHC analysis demonstrated elevated expression of KDM1A in hypoxic regions in human GBM tissues as well as mouse GBM xenografts. IP analysis demonstrated that KDM1A interacts with HIF-1α. Cell viability assays revealed that NCD-38 is more potent in reducing the cell viability of primary GBM cells compared to other KDM1A inhibitors. KDM1A knockdown or KDM1A inhibitor treatment significantly reduced the HIF- target gene expression including VEGF, PGK, CAIX, and HRE-Luc reporter activity in GBM cells. Further, hypoxia mediated cell proliferation and self-renewal ability of GSCs was compromised in KDM1A knockdown and KDM1A inhibitor-treated cells. Further, knockdown of KDM1A or treatment with KDM1A inhibitor significantly reduced the in vivo tumor growth and improved survival in orthotopic models. Conclusions: Our results demonstrate that KDM1A plays a critical role in hypoxia response and inhibition of KDM1A is a novel therapeutic approach for the treatment of GBM. Citation Format: Gangadhara R. Sareddy, Suryavathi Viswanadhapalli, Mei Zhou, Yiliao Luo, Xiaonan Li, Jinyou Liu, Aleksandra Gruslova, Takayoshi Suzuki, Andrew Brenner. The lysine demethylase KDM1A inhibition attenuates hypoxic responses in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2422.

Glioblastoma (GBM) is an aggressive brain tumor with poor prognosis, marked by extensive necrosis and enrichment of tumor-associated macrophages (TAMs) and glioma stem cells (GSCs) in peri-necrotic regions. Analysis of Ivy-GAP and single-cell RNA-seq data revealed elevated Hippo pathway transcriptional activity in the hypoxic peri-necrotic niche despite low expression of canonical stemness factors like SOX2, OLIG2, and FOXM1. We hypothesize that Hippo activation supports GSC maintenance through hypoxia and TAM-derived cytokines. In patient-derived GBM neurospheres, 1% hypoxia increased nuclear YAP1/TAZ and CYR61 expression. Zyxin (Zyx), a potential upstream regulator, was upregulated and phosphorylated under hypoxia. AKT, previously known to phosphorylate Zyx and be regulated by hypoxia, was also activated, suggesting hypoxia promotes Zyx phosphorylation and YAP/TAZ nuclear translocation via AKT. AKT inhibition with Capivasertib reduced Zyx phosphorylation and Hippo transcription in hypoxia. Conditioned media from primary macrophages activated Hippo signaling in GBM cells. NicheNetR identified TGF-β1 as a hypoxia-specific TAM-derived cytokine promoting malignant gene programs. Exogenous TGF-β1 increased CYR61, while TGFBR2 expression is elevated under hypoxia. Blocking TGFBR2 with inhibitor LY2109761 abolished TGF-β1-induced Hippo activation. Hypoxia and TGF-β1 synergistically enhanced GSC maintenance in limiting dilution assays. In vivo, pharmacologic inhibition of YAP/TAZ with Verteporfin or genetic TAZ knockdown in the RCAS/tv-a mouse model reduced tumor burden and prolonged survival. Flow cytometry confirmed decreased CD133+/CD44+ GSCs in TAZ-deficient tumors. These results demonstrate hypoxia and TGF-β1 signaling to activate YAP/TAZ-driven Hippo signaling, promoting GSC maintenance in the peri-necrotic GBM niche.

Despite advances in biology and therapeutic modalities, existence of highly tumorigenic glioma stem-like cells (GSCs) makes glioblastomas (GBMs) invincible. N6-methyl adenosine (m6A), one of the abundant mRNA modifications catalyzed by methyltransferase-like 3 and 14 (METTL3/14), influences various events in RNA metabolism. Here, we report the crucial role of METTL3-mediated m6A modification in GSC (neurosphere) maintenance and dedifferentiation of glioma cells. METTL3 expression is elevated in GSC and attenuated during differentiation. RNA immunoprecipitation studies identified SOX2 as a bonafide m6A target of METTL3 and the m6A modification of SOX2 mRNA by METTL3 enhanced its stability. The exogenous overexpression of 3'UTR-less SOX2 significantly alleviated the inhibition of neurosphere formation observed in METTL3 silenced GSCs. METTL3 binding and m6A modification in vivo required intact three METTL3/m6A sites present in the SOX2-3'UTR. Further, we found that the recruitment of Human antigen R (HuR) to m6A-modified RNA is essential for SOX2 mRNA stabilization by METTL3. In addition, we found a preferential binding by HuR to the m6A-modified transcripts globally. METTL3 silenced GSCs showed enhanced sensitivity to γ-irradiation and reduced DNA repair as evidenced from the accumulation of γ-H2AX. Exogenous overexpression of 3'UTR-less SOX2 in METTL3 silenced GSCs showed efficient DNA repair and also resulted in the significant rescue of neurosphere formation from METTL3 silencing induced radiosensitivity. Silencing METTL3 inhibited RasV12 mediated transformation of mouse immortalized astrocytes. GBM tumors have elevated levels of METTL3 transcripts and silencing METTL3 in U87/TIC inhibited tumor growth in an intracranial orthotopic mouse model with prolonged mice survival. METTL3 transcript levels predicted poor survival in GBMs which are enriched for GSC-specific signature. Thus our study reports the importance of m6A modification in GSCs and uncovers METTL3 as a potential molecular target in GBM therapy.

BackgroundA major contributing factor to glioblastoma (GBM) development and progression is its ability to evade the immune system by creating an immune-suppressive environment, where GBM-associated myeloid cells, including resident microglia and peripheral monocyte-derived macrophages, play critical pro-tumoral roles. However, it is unclear whether recruited myeloid cells are phenotypically and functionally identical in GBM patients and whether this heterogeneity is recapitulated in patient-derived orthotopic xenografts (PDOXs). A thorough understanding of the GBM ecosystem and its recapitulation in preclinical models is currently missing, leading to inaccurate results and failures of clinical trials.MethodsHere, we report systematic characterization of the tumor microenvironment (TME) in GBM PDOXs and patient tumors at the single-cell and spatial levels. We applied single-cell RNA sequencing, spatial transcriptomics, multicolor flow cytometry, immunohistochemistry, and functional studies to examine the heterogeneous TME instructed by GBM cells. GBM PDOXs representing different tumor phenotypes were compared to glioma mouse GL261 syngeneic model and patient tumors.ResultsWe show that GBM tumor cells reciprocally interact with host cells to create a GBM patient-specific TME in PDOXs. We detected the most prominent transcriptomic adaptations in myeloid cells, with brain-resident microglia representing the main population in the cellular tumor, while peripheral-derived myeloid cells infiltrated the brain at sites of blood–brain barrier disruption. More specifically, we show that GBM-educated microglia undergo transition to diverse phenotypic states across distinct GBM landscapes and tumor niches. GBM-educated microglia subsets display phagocytic and dendritic cell-like gene expression programs. Additionally, we found novel microglial states expressing cell cycle programs, astrocytic or endothelial markers. Lastly, we show that temozolomide treatment leads to transcriptomic plasticity and altered crosstalk between GBM tumor cells and adjacent TME components.ConclusionsOur data provide novel insights into the phenotypic adaptation of the heterogeneous TME instructed by GBM tumors. We show the key role of microglial phenotypic states in supporting GBM tumor growth and response to treatment. Our data place PDOXs as relevant models to assess the functionality of the TME and changes in the GBM ecosystem upon treatment.Graphical

Background: Glioblastoma (GBM) patients face a dismal prognosis, with median survival of ~15 months and 5-year survival rate of 6.8%. Standard of care includes surgical resection, external beam radiation therapy, and adjuvant chemotherapy with temozolomide (TMZ). Unfortunately, all GBM patients succumb to their disease. Glioma stem cells (GSCs), a GBM subpopulation, possess enhanced DNA repair that contributes to chemoradiotherapy resistance. The epigenetic modifier lysine-specific histone demethylase 1A (KDM1A/LSD1) is overexpressed in GBM and emerging studies show KDM1A is implicated in DNA damage response. This study aims to determine the significance of KDM1A to promote DNA repair in GSCs. We hypothesize KDM1A inhibition augments therapeutic efficacy of TMZ via attenuation of DNA repair pathways. Methods: Patient-derived GSCs were obtained via IRB-approved protocol from patient samples at UT Health San Antonio. KDM1A knockdown and knockout cells were generated by transduction of validated KDM1A-specific shRNA or gRNA, respectively. Brain bioavailability of KDM1A inhibitor NCD38 was established using LS-MS/MS. Effect of combination KDM1A knockdown or inhibition with TMZ was studied using cell viability, neurosphere, and self-renewal assays. Mechanistic studies were conducted using CUT&Tag-seq, RNA-seq, immunofluorescence, comet, Western blotting, RT-qPCR, homologous recombination (HR), and non-homologous end-joining (NHEJ) reporter assays. In vivo efficacy of KDM1A knockdown or inhibitor alongside TMZ was determined using orthotopic murine GBM models. Results: GBM patient data sets showed KDM1A is elevated in recurrent GBM versus primary tumors. KDM1A knockdown, knockout, or pharmacological inhibition increased efficacy of TMZ in reducing cell viability and self-renewal of GSCs. Pharmacokinetic studies demonstrated KDM1A inhibitor NCD38 is readily brain penetrable. CUT&Tag-seq studies showed KDM1A is enriched at the promoters of DNA repair genes. RNA-seq studies confirmed that KDM1A inhibition reduced expression of DNA repair-related genes. RT-qPCR and Western blotting validated downregulation of DNA double-strand break repair genes. Knockdown, knockout, or inhibition of KDM1A attenuated HR and NHEJ-mediated DNA repair capacity. Immunofluorescence and comet assay demonstrated increased TMZ-mediated DNA damage in NCD38-treated GSCs. Importantly, KDM1A knockdown or inhibition enhanced efficacy of TMZ and significantly improved survival of mice bearing orthotopic GBM tumors. Conclusions: Our results provide compelling evidence KDM1A is essential for DNA repair in GSCs and KDM1A inhibition sensitizes GBM to TMZ via attenuation of DNA repair pathways. These findings suggest combination therapy of KDM1A inhibitor NCD38 with TMZ is a potential novel therapeutic strategy to improve GBM outcomes. Citation Format: Salvador Alejo, Bridgitte Palacios, Prabhakar Pitta Venkata, He Yi, Wenjing Li, Jessica Johnson, Sridharan Jayamohan, Weixing Zhao, Siyuan Zheng, Takayoshi Suzuki, Rajeshwar R. Tekmal, Andrew Brenner, Ratna K. Vadlamudi, Gangadhara R. Sareddy. Lysine-specific histone demethylase 1A (KDM1A/LSD1) inhibition attenuates DNA double-strand break repair and augments efficacy of temozolomide in glioblastoma [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 6263.

BACKGROUND Glioblastoma (GB) is one of the deadliest types of human cancer. Despite a very aggressive treatment regime, including resection of the tumor, radiation, and chemotherapy, the recurrence rate is more than 90%. Recurrence is mostly caused by the regrowth of highly invasive and resistant cells that have spread from the tumor bulk and are not removed by resection. To develop an effective therapeutic approach, we need to better understand the underlying molecular and cellular mechanisms of GB chemoradiation resistance and tumor spreading. MATERIAL AND METHODS To dynamically follow the changes occurring in GB post-therapy and investigate its relationship with vascular microenvironment, we employed multiple bulk and single-cell RNA-Seq analyses, phosphoproteome, in vitro and in vivo real-time imaging, organotypic cultures and functional assays, digital pathology, and spatial transcriptomics on patient material or preclinical models of GB. RESULTS We demonstrated that chemoradiation and the brain vasculature induce a transition to a functional cell state, which we named VC-Resist. This cell state is midway through the transcriptomic axis between proneural and mesenchymal GB cells and is closer to the AC/MES-like state. Better cell survival, G2M-arrest, activation of senescence/stemness pathways make this GB cell state more resistant to therapy. Notably, these persister GB cells are highly vessel co-opting, allowing homing to the perivascular niche, which, in turn, increases their transition to this cell state and resistance to therapy. Molecularly, the transition to the VC-Resist cell state is driven by FGF-FGFR1 signaling, which leads to the activation of DNA damage repair and YAP1 pathways. CONCLUSION These findings demonstrate that the perivascular niche and GB cell plasticity jointly generate a vicious loop that leads to resistance to therapy and brain infiltration during GB recurrence. SUPPORT This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 (Grant Agreement No. 805225), the INSERM-CNRS ATIP-Avenir grant, the NanoTheRad grant from Paris-Saclay University, Fondation ARC pour la recherche sur le cancer, Campus France and Canceropole Ile-de-France (2022-1-EMERG-06-ICR-1).

IntroductionOverexpression of epidermal growth factor (EGFR) drives glioblastoma (GBM) cell invasion and tumour progression. EGFR has been a major therapeutic target in GBM. However, clinical trials were disappointing, and we are still missing molecular basis to explain these poor results. In other solid tumours, extracellular matrix proteins found in the tumour microenvironment and their heterodimeric integrin receptors trigger resistance to EGFR targeted therapy. We recently established that the fibronectin receptor, α5β1 integrin is a pertinent therapeutic target in GBM. Therefore, we seek to evaluate whether α5β1 integrin is involved in therapy targeting EGFR in GBM.Material and methodsWe used GBM cell line (U87) overexpressing or down expressing α5 integrin subunit. EGFR was inhibited by clinically approved tyrosine kinase inhibitors (TKIs) (gefitinib, erlotinib, lapatinib). For cell motility assays, we performed spheroid dissemination assays, in 2D and 3D environment and chemotaxis assays through Boyden chambers. We also evaluated the impact of integrin expression on cell clonogenicity and cell grow th (2D, spheroids) in presence of EGFR inhibitors. Confocal microscopy confirmed integrin, EGFR and endosomes markers localization. Protein colocalization in early-endosomes was confirmed by confocal image analysis and dSTORM super-resolution.Results and discussionsWe showed that loss of integrin α5 expression increased U87 cell sensitivity to TKIs in spheroid cell evasion assays but did not affect TKIs efficiency on chemotaxis, cell growth (2D or 3D) or cell clonogenicity. EGFR is thus critical for cell dissemination from GBM tumour spheroïds and overexpression of α5 integrin can circumvent EGFR inhibition by TKIs. Using confocal imaging, we showed that TKIs provoked a massive relocalization of integrin and EGFR in Rab5, EEA1 or LRP1 positive endosomes. Dynamic studies confirmed that TKIs increased EGFR receptor endocytosis. By colocalization studies and super-resolution dSTORM imaging, we clearly showed that in intracellular vesicules integrin and EGFR are in close proximity, suggesting a potential interaction.ConclusionWe showed in GBM cells that α5β1 integrin expression triggers resistance to EGFR-targeting TKIs and that TKIs alter EGFR and integrin membrane trafficking. These data point out the potential importance of integrin and EGFR endocytosis and trafficking in GBM resistance to TKIs.

Patients with glioblastoma almost always suffer a recurrence of an aggressive treatment resistant tumour and succumb within months highlighting the need to develop treatment options for recurrent glioblastoma. One potential target is prostate specific membrane antigen (PSMA) expressed on the new vessels in primary glioblastoma tumours. This study compared the expression of PSMA in primary and recurrent glioblastoma tumours. Formalin-fixed paraffin-embedded sections of primary and matched recurrent tumours from 13 patients with glioblastoma were processed for PSMA immunohistochemical labelling. PSMA expression was scored from digitally scanned sections using a categorical system (Total PSMA expression = PSMA label intensity (0–3) x percent PSMA-positive blood vessels). Little PSMA labelling was observed in any adjacent ‘unaffected’ brain tissue. PSMA was localised to blood vessels including those displaying microvascular proliferation in 12/13 primary and 9/13 recurrent glioblastoma tumours. Total PSMA expression scores ranged from 0 – 230 (maximum score = 300) and was divided into low and high expression based on a median split (median = 57) of PSMA expression across all tumours. Regression analysis showed a significant difference in PSMA expression between primary and recurrent glioblastoma (p = 0.04) with PSMA being highly expressed in ~70% of primary and only 31% of recurrent glioblastoma. Three cases displayed high expression in both primary and recurrent glioblastoma and one case had no PSMA expression at all. In conclusion, whilst higher expression of PSMA was detected in more primary tumours, 70%+ of all primary and recurrent tumours expressed PSMA to some extent adding evidence that this may be a useful target for treatment of glioblastoma. Larger cohorts and other techniques for detecting PSMA are needed to provide further evidence for PSMA’s utility as a target and to further define which glioblastoma patients are most likely to benefit from this approach.

Brain cancer is the 10th leading cause of death in United States with increasing primary tumor morbidity and secondary brain metastasis morbidity. Glioblastoma (GBM) is most lethal brain tumor with less than 5% 5 years survival rate marked by significant resistance to majority of therapies targeting tumor cells or tumor microenvironment. Here we shown one approach to convert aggressive GBM cells to immunogenic tumor cells by knockout FGL2 in GBM cells to evoke efficient anti-tumor immunosurvilliance. FGL2 is an immunosuppressive molecule and its expression level is strongly correlated with glioma grade and poor diagnosis. FGL2 from GBM cells, but not from host cells, is essential for immune evasion dependent GBM progression using both preclinical GBM and brain metastatic tumor models. Knockout FGL2 in GBM cells completely abolish tumor progression of GBM models challenged with low or high number of tumor cells in immunocompetent mice and protect mice from tumor rechallenge in periphery. This eradication effect is impaired in immune deficient mice and CD8+ T cells depleted mice, but not in FGL2KO mice, showing the necessarily of immune system to eliminate FGL2KO tumor cells and the requirement of FGL2 in tumor cells to evade immunosurvilliance. To understand how the systemic CD8+ T cell-dependent anti-tumor response and memory was induced by FGL2KO GBM cells, we studied the impact of FGL2KO tumor cells on dendritic cells (DCs) which control immune response via its critical role in the generation of effective cytotoxic T lymphocyte (CTL) responses. Knockout FGL2 in GBM cells induced CD8a+/CD103+ DCs accumulation in brain in vivo; DCs proliferation and CD103+ DCs induction in vitro. In agreement with this discovery, knockout Batf3, a key transcription factor regulating CD8a+/CD103+ DCs, reverse the impact of FGL2KO in GBM cell in vivo. By molecule analysis, a novel signaling pathway was revealed that knockout FGL2 in GBM cells induce NF-κ B activation, and this activation induced Batf3 and associated CD103 expression in DCs. Therefore, target specific molecule in GBM cells, such as knockout FGL2, can convert aggressive GBM cells to immunogenic cells, pointing to new approach for immune therapy. Citation Format: Jun Yan, Qingnan Zhao, Konrad Gabrusiewicz, Ling-Yuan Kong, Longfei Huo, Xueqing Xia, Jun Wei, Jingda Xu, Eric Davis, Amy B. Heimberger, Shulin Li. CRISPR9-mediated FGL2-KO in tumor cells impairs tumor progression in brain and triggers antitumor immune memory systematically via NF-κB dependent Batf3 expression in DCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5746.

Glioblastoma (GBM) is a prevalent and refractory type of brain tumor. Over the past two decades, there have been minimal advancements in GBM therapy. The current standard treatment involves surgical excision followed by radiation and chemotherapy. Compared to other tumors, GBM is more challenging to treat due to the presence of glioma stem-like cells (GSCs) and the blood–brain barrier, resulting in an extremely low survival rate. Mitochondria play a critical role in tumor respiration, metabolism, and multiple signaling pathways involved in tumor formation, progression, and cell apoptosis. Consequently, mitochondria represent promising targets for developing novel anticancer agents, including those targeting oxidative phosphorylation, reactive oxygen species (ROS), mitochondrial transfer, and mitophagy. This review outlines the mitochondrial-related therapeutic targets in GBM, highlighting the potential of mitochondria as a target for GBM treatment.

Circadian regulator CLOCK promotes tumor angiogenesis in glioblastoma.

Mitochondrial transfer in the central nervous system occurs from astrocytes to neurons in stroke. Mitochondrial exchange has also been reported among tumor cells in glioblastoma (GBM), the most common primary brain tumor. However, the role of mitochondrial transfer from non-neoplastic cells in the surrounding microenvironment to GBM remains poorly understood. We hypothesized that mitochondrial transfer from these non-neoplastic to GBM cells supports tumor metabolism and growth. Using transgenic mice expressing fluorophore-tagged mitochondria, we found that ~50% of orthotopically-implanted mouse GBM cells acquire host mitochondria. Brain-resident cells, mainly astrocytes, but not infiltrating immune cells were the primary mitochondrial donors in vivo and in vitro. Mitochondrial transfer also occurred from immortalized human astrocytes to a broad array of patient-derived xenograft (PDX) models of GBM in vitro at rates of 15-35%. GBM cells that acquired mitochondria expressed higher levels of the ATP-synthase subunit ATP5A and produced more ATP, while metabolomics revealed upregulated amino acid metabolism in recipient cells. In vivo, mouse GBM cells that acquired mitochondria were more likely to be in G2/M proliferative cell cycle phases. We observed a similar effect in PDX that acquired astrocyte mitochondria from co-cultures in vitro. To mechanistically link increased proliferation specifically to mitochondrial transfer, we isolated astrocyte mitochondria by differential centrifugation and found that addition and uptake of cell-free mitochondria in human GBM cells recapitulated the increased proliferation. Using sorted mouse and human GBM cells with/without astrocyte mitochondrial acquisition, we further found that mitochondrial transfer promoted in vitro self-renewal and in vivo tumorigenicity, leading to significant reduction in survival and increased penetrance in orthotopic GBM models. Transfer in mouse and human systems was contact-dependent and was abrogated by physical separation of donor and recipient cells by transwell inserts. We visualized contact-dependent transfer across actin-based intercellular connections consistent with previously reported microtubes. We confirmed the critical role of actin and the actin-associated protein, growth-associated protein 43 (GAP43) in facilitating mitochondrial transfer by showing that pharmacologic inhibition and genetic knockdown (respectively) significantly decreased the rate of mitochondrial transfer. Taken together, mitochondrial transfer comprises a fundamental, protumorigenic mechanism of GBM, enhancing metabolic activity and driving tumor cell proliferation. Further elucidating the molecular machinery regulating astrocyte mitochondrial transfer and its downstream protumorigenic effects will lead to therapeutic opportunities targeting this understudied tumor microenvironment interaction. Citation Format: Dionysios C. Watson, Defne Bayik, Simon Storevik, Shannon S. Moreino, Samuel S. Sprowls, Gauravi Deshpande, Palavalasa Sravya, Costas A. Lyssiotis, Daniel R. Wahl, Hrvoje Miletic, Justin D. Lathia. Mitochondrial transfer from astrocytes drives glioblastoma tumorigenicity [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 331.

The therapeutic resistance of gliomas is, at least in part, due to stemlike glioma cells (SLGCs), which self-renew, generate the bulk of tumor cells, and sustain tumor growth. SLGCs from glioblastomas (GB) have been studied in cell cultures or mouse models, whereas little is known about SLGCs from lower grade gliomas. To compare cell and organotypic slice cultures from GBs and lower grade gliomas and study the maintenance of SLGCs. Cells and tissue slices from astrocytomas, oligodendrogliomas, oligoastrocytomas, and GBs were cultivated in (1) serum-free medium supplemented with the growth factors epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), (2) medium containing 10% serum plus EGF and bFGF (F+GF medium), or (3) medium containing 10% fetal calf serum (F medium). Maintenance of cells and cytoarchitecture was addressed, using several candidate SLGC markers (Nestin, Sox2, CD133, CD44, CD49f/integrin α6, and Notch) as well as CD31 (endothelial cells), ionized calcium-binding adapter molecule 1 (microglia), and vimentin. Cell vitality was determined. SLGCs were present in tissue slices from lower and higher grade gliomas. Preservation of the cytoarchitecture in slices was possible for >3 weeks. Maintenance of SLGCs required the presence of EGF/bFGF in cell and slice cultures, in which F+GF appeared superior to N medium. Constraints were observed regarding the preservation of the microglia but not of the endothelial cells. Maintenance of the microglia was improved by addition of the cytokine macrophage colony-stimulating factor. Medium supplemented with serum and growth factors EGF, bFGF, and macrophage colony-stimulating factor permits the preservation of SLGCs and non-SLGCs in the original glioma microenvironment.

BackgroundThe current standard of care for Glioblastoma Multiforme (GBM) consists of fractionated focal irradiation with concomitant temozolomide (TMZ) chemotherapy. A promising strategy to increase the efficacy of TMZ is through interference with the DNA damage repair machinery, by poly(ADP-ribose) polymerase protein inhibition(PARPi). The objective of the present study was to investigate the therapeutic benefit of combination therapy in patient-derived glioma stem-like cells (GSC).MethodsCombination therapy feasibility was tested on established GBM cell lines U373 and T98. We developed an in vitro drug-screening assay based on GSC cultures derived from a panel of primary patient tissue samples (n = 20) to evaluate the effect of PARPi (ABT-888) monotherapy and combination therapy with TMZ. Therapeutic effect was assessed by viability, double stranded breaks, apoptosis and autophagy assays and longitudinal microscopic cell monitoring was performed. O-6-methylguanine-DNA methyltransferase (MGMT) status was determined by methylation assay and protein expression by western blots.ResultsPARPi monotherapy was found to decrease viability by more than 25% in 4 of the 20 GSCs (20%) at 10 μM. TMZ monotherapy at 50 μM and 100 μM was effective in 12 and 14 of the 20 GSCs, respectively. TMZ resistance to 100 μM was found in 7 of 8 MGMT protein positive cultures. Potentiation of TMZ therapy through PARPi was found in 90% (n = 20) of GSCs, of which 6 were initially resistant and 7 were sensitive to TMZ monotherapy. Increased induction of double stranded breaks and apoptosis were noted in responsive GSCs. There was a trend noted, albeit statistically insignificant, of increased autophagy both in western blots and accumulation of autophagosomes.ConclusionPARPi mediated potentiation of TMZ is independent of TMZ sensitivity and can override MGMT(-) mediated resistance when administered simultaneously. Response to combination therapy was associated with increased double strand breaks induction, and coincided by increased apoptosis and autophagy. PARPi addition potentiates TMZ treatment in primary GSCs. PARPi could potentially enhance the therapeutic efficacy of the standard of care in GBM.

Glioblastoma multiforme (GBM) is the most frequent primary brain tumor in adults with a 5-year survival rate of 5% despite intensive research efforts. The poor prognosis is due, in part, to aggressive invasion into the surrounding brain parenchyma. Invasion is a complex process mediated by cell-intrinsic pathways, extrinsic microenvironmental cues, and biophysical cues from the peritumoral stromal matrix. Recent data have attributed GBM invasion to the glioma stem-like cell (GSC) subpopulation. GSCs are slowly dividing, highly invasive, therapy resistant, and are considered to give rise to tumor recurrence. GSCs are localized in a heterogeneous cellular niche, and cross talk between stromal cells and GSCs cultivates a fertile environment that promotes GSC invasion. Pro-migratory soluble factors from endothelial cells, astrocytes, macrophages, microglia, and non-stem-like tumor cells can stimulate peritumoral invasion of GSCs. Therefore, therapeutic efforts designed to target the invasive GSCs may enhance patient survival. In this review, we summarize the current understanding of extrinsic pathways and major stromal and immune players facilitating GSC maintenance and survival.