Mechanisms of temozolomide resistance in glioblastoma - a comprehensive review

The landscape of circRNAs in gliomas temozolomide resistance: Insights into molecular pathways

As the deadliest type of primary brain tumor, gliomas represent a significant worldwide health concern. Circular RNA (circRNA), a unique non-coding RNA molecule, seems to be one of the most alluring target molecules involved in the pathophysiology of many kinds of cancers. CircRNAs have been identified as prospective targets and biomarkers for the diagnosis and treatment of numerous disorders, particularly malignancies. Recent research has established a clinical link between temozolomide (TMZ) resistance and certain circRNA dysregulations in glioma tumors. CircRNAs may play a therapeutic role in controlling or overcoming TMZ resistance in gliomas and may provide guidance for a novel kind of individualized glioma therapy. To address the biological characteristics of circRNAs and their potential to induce resistance to TMZ, this review has highlighted and summarized the possible roles that circRNAs may play in molecular pathways of drug resistance, including the Ras/Raf/ERK PI3K/Akt signaling pathway and metabolic processes in gliomas.

Albumin-Based Microneedles for Spatiotemporal Delivery of Temozolomide and Niclosamide to Resistant Glioblastoma

Glioblastoma (GBM) is the most common and aggressive malignant brain tumor. Standard therapy includes maximal surgical resection, radiotherapy, and adjuvant temozolomide (TMZ) administration. However, the rapid development of TMZ resistance and the impermeability of the blood-brain barrier (BBB) significantly hinder the therapeutic efficacy. Herein, we developed spatiotemporally controlled microneedle patches (BMNs) loaded with TMZ and niclosamide (NIC) to overcome GBM resistance. We found that hyaluronic acid (HA) increased the viscosity of bovine serum albumin (BSA) and evidenced that concentrations of BSA/HA exert an impact degradation rates exposure to high-temperature treatment, showing that the higher BSA/HA concentrations result in slower drug release. To optimize drug release rates and ensure synergistic antitumor effects, a 15% BSA/HA solution constituting the bottoms of BMNs was chosen to load TMZ, showing sustained drug release for over 28 days, guaranteeing long-term DNA damage in TMZ-resistant cells (U251-TR). Needle tips made from 10% BSA/HA solution loaded with NIC released the drug within 14 days, enhancing TMZ's efficacy by inhibiting the activity of O6-methylguanine-DNA methyltransferase (MGMT). BMNs exhibit superior mechanical properties, bypass the BBB, and gradually release the drug into the tumor periphery, thus significantly inhibiting tumor proliferation and expanding median survival in mice. The on-demand delivery of BMNs patches shows a strong translational potential for clinical applications, particularly in synergistic GBM treatment.

Triggering of endoplasmic reticulum stress via ATF4-SPHK1 signaling promotes glioblastoma invasion and chemoresistance

Despite advances in therapies, glioblastoma (GBM) recurrence is almost inevitable due to the aggressive growth behavior of GBM cells and drug resistance. Temozolomide (TMZ) is the preferred drug for GBM chemotherapy, however, development of TMZ resistance is over 50% cases in GBM patients. To investigate the mechanism of TMZ resistance and invasive characteristics of GBM, analysis of combined RNA-seq and ChIP-seq was performed in GBM cells in response to TMZ treatment. We found that the PERK/eIF2α/ATF4 signaling was significantly upregulated in the GBM cells with TMZ treatment, while blockage of ATF4 effectively inhibited cell migration and invasion. SPHK1 expression was transcriptionally upregulated by ATF4 in GBM cells in response to TMZ treatment. Blockage of ATF4-SPHK1 signaling attenuated the cellular and molecular events in terms of invasive characteristics and TMZ resistance. In conclusion, GBM cells acquired chemoresistance in response to TMZ treatment via constant ER stress. ATF4 transcriptionally upregulated SPHK1 expression to promote GBM cell aggression and TMZ resistance. The ATF4-SPHK1 signaling in the regulation of the transcription factors of EMT-related genes could be the underlying mechanism contributing to the invasion ability of GBM cells and TMZ resistance. ATF4-SPHK1-targeted therapy could be a potential strategy against TMZ resistance in GBM patients.

Evaluating the Base Excision Repair Inhibitor TRC102 and Temozolomide for Patients with Recurrent Glioblastoma in the Phase 2 Adult Brain Tumor Consortium Trial BERT

PURPOSE

Patients with glioblastoma (GBM) have a dismal prognosis. Although the DNA alkylating agent temozolomide (TMZ) is the mainstay of chemotherapy, therapeutic resistance rapidly develops in patients. Base excision repair inhibitor TRC102 (methoxyamine) reverses TMZ resistance in preclinical glioma models. We aimed to investigate the efficacy and safety of oral TRC102+TMZ in recurrent GBM (rGBM).

PATIENTS AND METHODS

A preregistered (NCT02395692), nonrandomized, multicenter, phase 2 clinical trial (BERT) was planned and conducted through the Adult Brain Tumor Consortium (ABTC-1402). Arm 1 included patients with bevacizumab-naïve GBM at the first recurrence, with the primary endpoint of response rates. If sufficient activity was identified, a second arm was planned for the bevacizumab-refractory patients. The secondary endpoints were overall survival (OS), progression-free survival (PFS), PFS at 6 months (PFS6), and toxicity.

RESULTS

Arm 1 enrolled 19 patients with a median of two treatment cycles. Objective responses were not observed; hence, arm 2 did not open. The median OS was 11.1 months [95% confidence interval (CI), 8.2-17.9]. The median PFS was 1.9 months (95% CI, 1.8-3.7). The PFS6 was 10.5% (95% CI, 1.3%-33.1%). Most toxicities were grades 1 and 2, with two grade 3 lymphopenias and one grade 4 thrombocytopenia. Two patients with PFS ≥ 17 months and OS > 32 months were deemed "extended survivors." RNA sequencing of tumor tissue, obtained at diagnosis, demonstrated significantly enriched signatures of DNA damage response (DDR), chromosomal instability (CIN70, CIN25), and cellular proliferation (PCNA25) in "extended survivors."

CONCLUSIONS

These findings confirm the safety and feasibility of TRC102+TMZ in patients with rGBM. They also warrant further evaluation of combination therapy in biomarker-enriched trials enrolling GBM patients with baseline hyperactivated DDR pathways.

UBE2D3 regulated by WTAP-mediated m6A modification inhibits temozolomide chemosensitivity in glioblastoma

To explore how the ubiquitin-conjugating enzyme E2D3 (UBE2D3) influences temozolomide (TMZ) resistance in glioblastoma (GBM), and to clarify the association between UBE2D3 and WTAP. The UBE2D3 protein expression in GBM tissues were detected using immunohistochemistry (IHC) through tissue microarrays. The potential pathways of UBE2D3 in TCGA-GBM were predicted via Gene Set Enrichment Analysis (GSEA). To investigate UBE2D3's role in TMZ resistance, GBM cells were transduced with UBE2D3 shRNA or overexpression lentivirus, followed by assessments of CCK-8, flow cytometry, comet assay, and western blot analysis. Furthermore, a subcutaneous tumor model was established in nude mice using U87 cells transduced with interfering lentivirus to observe tumor growth and assess cell apoptosis using TUNEL staining. Mechanically, m6A content analysis, m6A methylated RNA immunoprecipitation quantitative PCR, reporter gene assay, mRNA stability measurements, RNA immunoprecipitation, quantitative Real-Time PCR, and Western blot assays were carried out to verify the role of WTAP/IGF2BP1 in regulating UBE2D3 expression. UBE2D3 exhibited elevated expression levels in GBM tissues compared with normal brain tissues and was associated with the DNA repair signaling pathway. In both in vitro and in vivo studies, it was demonstrated that TMZ treatment combined with reduced UBE2D3 expression further suppressed U87 cell viability and tumor growth, with a notable increase in apoptosis rate and DNA damage. Conversely, the overexpression of UBE2D3 had the opposite impact. Furthermore, our findings revealed that WTAP promotes the m6A modification of UBE2D3 via an IGF2BP1-dependent mechanism. The WTAP-IGF2BP1 axis regulates UBE2D3 stability in an m6A-dependent manner, influencing tumor malignancy and TMZ chemosensitivity in GBM via the DNA repair signaling pathway.

Gene expression profiling and the isocitrate dehydrogenase mutational landscape of temozolomide‑resistant glioblastoma

Glioblastoma multiforme (GBM) is an aggressive brain cancer that occurs more frequently than other brain tumors. The present study aimed to reveal a novel mechanism of temozolomide resistance in GBM using bioinformatics and wet lab analyses, including meta-Z analysis, Kaplan-Meier survival analysis, protein-protein interaction (PPI) network establishment, cluster analysis of co-expressed gene networks, and hierarchical clustering of upregulated and downregulated genes. Next-generation sequencing and quantitative PCR analyses revealed downregulated [tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 1 (TIE1), calcium voltage-gated channel auxiliary subunit α2Δ1 (CACNA2D1), calpain 6 (CAPN6) and a disintegrin and metalloproteinase with thrombospondin motifs 6 (ADAMTS6)] and upregulated [serum amyloid (SA)A1, SAA2, growth differentiation factor 15 (GDF15) and ubiquitin specific peptidase 26 (USP26)] genes. Different statistical models were developed for these genes using the Z-score for P-value conversion, and Kaplan-Meier plots were constructed using several patient cohorts with brain tumors. The highest number of nodes was observed in the PPI network was for ADAMTS6 and TIE1. The PPI network model for all genes contained 35 nodes and 241 edges. Immunohistochemical staining was performed using isocitrate dehydrogenase (IDH)-wild-type or IDH-mutant GBM samples from patients and a significant upregulation of TIE1 (P<0.001) and CAPN6 (P<0.05) protein expression was demonstrated in IDH-mutant GBM in comparison with IDH-wild-type GBM. Structural analysis revealed an IDH-mutant model demonstrating the mutant residues (R132, R140 and R172). The findings of the present study will help the future development of novel biomarkers and therapeutics for brain tumors.

Naringin and temozolomide combination suppressed the growth of glioblastoma cells by promoting cell apoptosis: network pharmacology, in-vitro assays and metabolomics based study

Introduction: Glioblastoma, which affects a large number of patients every year and has an average overall lifespan of around 14.6 months following diagnosis stands out as the most lethal primary invasive brain tumor. Currently, surgery, radiation, and chemotherapy with temozolomide (TMZ) are the three major clinical treatment approaches. However, the ability to treat patients effectively is usually limited by TMZ resistance. Naringin, a bioflavonoid with anti-cancer, antioxidant, metal-chelating, and lipid-lowering effects, has emerged as a promising therapeutic option. Methods: To explore the targets and pathways of naringin and TMZ in glioblastoma network pharmacology, cell line-based ELISA, flow cytometry, immunocytochemistry, western blotting, and LC-HRMS based metabolomics study were used. Results: The findings through the network pharmacology suggested that the key targets of naringin in the chemosensitization of glioblastoma would be Poly [ADP-ribose] polymerase 1 (PARP-1), O-6-Methylguanine-DNA Methyltransferase (MGMT), and caspases. The functional enrichment analysis revealed that these targets were significantly enriched in important pathways such as p53 signaling, apoptosis, and DNA sensing. Further, the results of the in-vitro study in U87-MG and T98-G glioblastoma cells demonstrated that TMZ and naringin together significantly reduced the percentage of viability and inhibited the DNA repair enzymes PARP-1 and MGMT, and PI3K/AKT which led to chemosensitization and, in turn, induced apoptosis, which was indicated by increased p53, caspase-3 expression and decreased Bcl2 expression. Additionally, a metabolomics study in T98-G glioblastoma cells using liquid chromatography high-resolution mass spectrometry (LC-HRMS) revealed downregulation of C8-Carnitine (-2.79), L-Hexanoylcarnitine (-4.46), DL-Carnitine (-2.46), Acetyl-L-carnitine (-3.12), Adenine (-1.3), Choline (-2.07), Propionylcarnitine (-1.69), Creatine (-1.33), Adenosine (-0.84), Spermine (-1.42), and upregulation of Palmitic Acid (+1.03) and Sphingosine (+0.89) in the naringin and TMZ treatment groups. Discussion: In conclusion, it can be said that naringin in combination with TMZ chemosensitized TMZ antiglioma response and induced apoptosis in tumor cells.

Temporal and regional expression changes and co-staining patterns of metabolic and stemness-related markers during glioblastoma progression

Glioblastomas (GBMs) are characterized by high heterogeneity, involving diverse cell types, including those with stem-like features contributing to GBM's malignancy. Moreover, metabolic alterations promote growth and therapeutic resistance of GBM. Depending on the metabolic state, antimetabolic treatments could be an effective strategy. Against this background, we investigated temporal and regional expression changes and co-staining patterns of selected metabolic markers [pyruvate kinase muscle isozyme 1/2 (PKM1/2), glucose transporter 1 (GLUT1), monocarboxylate transporter 1/4 (MCT1/4)] in a rodent model and patient-derived samples of GBM. To understand the cellular sources of marker expression, we also examined the connection of metabolic markers to markers related to stemness [Nestin, Krüppel-like factor 4 (KLF4)] in a regional and temporal context. Rat tumour biopsies revealed a temporally increasing expression of GLUT1, higher expression of MCT1/4, Nestin and KLF4, and lower expression of PKM1 compared to the contralateral hemisphere. Patient-derived tumours showed a higher expression of PKM2 and Nestin in the tumour centre vs. edge. Whereas rare co-staining of GLUT1/Nestin was found in tumour biopsies, PKM1/2 and MCT1/4 showed a more distinct co-staining with Nestin in rats and humans. KLF4 was mainly co-stained with GLUT1, MCT1 and PKM1/2 in rat and human tumours. All metabolic markers yielded individual co-staining patterns among themselves. Co-staining mainly occurred later in tumour progression and was more pronounced in tumour centres. Also, positive correlations were found amongst markers that showed co-staining. Our results highlight a link between metabolic alterations and stemness in GBM progression, with complex distinctions depending on studied markers, time points and regions.

Selective regulation of chemosensitivity in glioblastoma by phosphatidylinositol 3-kinase beta

Resistance to chemotherapies such as temozolomide is a major hurdle to effectively treat therapy-resistant glioblastoma. This challenge arises from the activation of phosphatidylinositol 3-kinase (PI3K), which makes it an appealing therapeutic target. However, non-selectively blocking PI3K kinases PI3Kα/β/δ/γ has yielded undesired clinical outcomes. It is, therefore, imperative to investigate individual kinases in glioblastoma's chemosensitivity. Here, we report that PI3K kinases were unequally expressed in glioblastoma, with levels of PI3Kβ being the highest. Patients deficient of O6-methylguanine-DNA-methyltransferase (MGMT) and expressing elevated levels of PI3Kβ, defined as MGMT-deficient/PI3Kβ-high, were less responsive to temozolomide and experienced poor prognosis. Consistently, MGMT-deficient/PI3Kβ-high glioblastoma cells were resistant to temozolomide. Perturbation of PI3Kβ, but not other kinases, sensitized MGMT-deficient/PI3Kβ-high glioblastoma cells or tumors to temozolomide. Moreover, PI3Kβ-selective inhibitors and temozolomide synergistically mitigated the growth of glioblastoma stem cells. Our results have demonstrated an essential role of PI3Kβ in chemoresistance, making PI3Kβ-selective blockade an effective chemosensitizer for glioblastoma.

The tumour microenvironment, treatment resistance and recurrence in glioblastoma

The adaptability of glioblastoma (GBM) cells, encouraged by complex interactions with the tumour microenvironment (TME), currently renders GBM an incurable cancer. Despite intensive research, with many clinical trials, GBM patients rely on standard treatments including surgery followed by radiation and chemotherapy, which have been observed to induce a more aggressive phenotype in recurrent tumours. This failure to improve treatments is undoubtedly a result of insufficient models which fail to incorporate components of the human brain TME. Research has increasingly uncovered mechanisms of tumour-TME interactions that correlate to worsened patient prognoses, including tumour-associated astrocyte mitochondrial transfer, neuronal circuit remodelling and immunosuppression. This tumour hijacked TME is highly implicated in driving therapy resistance, with further alterations within the TME and tumour resulting from therapy exposure inducing increased tumour growth and invasion. Recent developments improving organoid models, including aspects of the TME, are paving an exciting future for the research and drug development for GBM, with the hopes of improving patient survival growing closer. This review focuses on GBMs interactions with the TME and their effect on tumour pathology and treatment efficiency, with a look at challenges GBM models face in sufficiently recapitulating this complex and highly adaptive cancer.

Oncolytic viral therapy for gliomas: Advances in the mechanisms and approaches to delivery

Glioma is a diverse category of tumors originating from glial cells encompasses various subtypes, based on the specific type of glial cells involved. The most aggressive is glioblastoma multiforme (GBM), which stands as the predominant primary malignant tumor within the central nervous system in adults. Despite the application of treatment strategy, the median survival rate for GBM patients still hovers around 15 months. Oncolytic viruses (OVs) are artificially engineered viruses designed to selectively target and induce apoptosis in cancer cells. While clinical trials have demonstrated encouraging results with intratumoral OV injections for some cancers, applying this approach to GBM presents unique challenges. Here we elaborate on current trends in oncolytic viral therapy and their delivery methods. We delve into the various methods of delivering OVs for therapy, exploring their respective advantages and disadvantages and discussing how selecting the optimal delivery method can enhance the efficacy of this innovative treatment approach.

Emerging role of MYB transcription factors in cancer drug resistance

Decades ago, the viral myeloblastosis oncogene v-myb was identified as a gene responsible for the development of avian leukemia. However, the relevance of MYB proteins for human cancer diseases, in particular for solid tumors, remained basically unrecognized for a very long time. The human family of MYB transcription factors comprises MYB (c-MYB), MYBL2 (b-MYB), and MYBL1 (a-MYB), which are overexpressed in several cancers and are associated with cancer progression and resistance to anticancer drugs. In addition to overexpression, the presence of activated MYB-fusion proteins as tumor drivers was described in certain cancers. The identification of anticancer drug resistance mediated by MYB proteins and their underlying mechanisms are of great importance in understanding failures of current therapies and establishing new and more efficient therapy regimens. In addition, new drug candidates targeting MYB transcription factor activity and signaling have emerged as a promising class of potential anticancer therapeutics that could tackle MYB-dependent drug-resistant cancers in a more selective way. This review describes the correlation of MYB transcription factors with the formation and persistence of cancer resistance to various approved and investigational anticancer drugs.

Diethyldithiocarbamate-ferrous oxide nanoparticles inhibit human and mouse glioblastoma stemness: aldehyde dehydrogenase 1A1 suppression and ferroptosis induction

The development of effective therapy for eradicating glioblastoma stem cells remains a major challenge due to their aggressive growth, chemoresistance and radioresistance which are mainly conferred by aldehyde dehydrogenase (ALDH)1A1. The latter is the main stemness mediator via enhancing signaling pathways of Wnt/β-catenin, phosphatidylinositol 3-kinase/AKT, and hypoxia. Furthermore, ALDH1A1 mediates therapeutic resistance by inactivating drugs, stimulating the expression of drug efflux transporters, and detoxifying reactive radical species, thereby apoptosis arresting. Recent reports disclosed the potent and broad-spectrum anticancer activities of the unique nanocomplexes of diethyldithiocarbamate (DE, ALDH1A1 inhibitor) with ferrous oxide nanoparticles (FeO NPs) mainly conferred by inducing lipid peroxidation-dependent non-apoptotic pathways (iron accumulation-triggered ferroptosis), was reported. Accordingly, the anti-stemness activity of nanocomplexes (DE-FeO NPs) was investigated against human and mouse glioma stem cells (GSCs) and radioresistant GSCs (GSCs-RR). DE-FeO NPs exhibited the strongest growth inhibition effect on the treated human GSCs (MGG18 and JX39P), mouse GSCs (GS and PDGF-GSC) and their radioresistant cells (IC50 ≤ 70 and 161 μg/mL, respectively). DE-FeO NPs also revealed a higher inhibitory impact than standard chemotherapy (temozolomide, TMZ) on self-renewal, cancer repopulation, chemoresistance, and radioresistance potentials. Besides, DE-FeO NPs surpassed TMZ regarding the effect on relative expression of all studied stemness genes, as well as relative p-AKT/AKT ratio in the treated MGG18, GS and their radioresistant (MGG18-RR and GS-RR). This potent anti-stemness influence is primarily attributed to ALDH1A1 inhibition and ferroptosis induction, as confirmed by significant elevation of cellular reactive oxygen species and lipid peroxidation with significant depletion of glutathione and glutathione peroxidase 4. DE-FeO NPs recorded the optimal LogP value for crossing the blood brain barrier. This in vitro novel study declared the potency of DE-FeO NPs for collapsing GSCs and GSCs-RR with improving their sensitivity to chemotherapy and radiotherapy, indicating that DE-FeO NPs may be a promising remedy for GBM. Glioma animal models will be needed for in-depth studies on its safe effectiveness.

RAPID resistance to BET inhibitors is mediated by FGFR1 in glioblastoma

Bromodomain and extra-terminal domain (BET) proteins are therapeutic targets in several cancers including the most common malignant adult brain tumor glioblastoma (GBM). Multiple small molecule inhibitors of BET proteins have been utilized in preclinical and clinical studies. Unfortunately, BET inhibitors have not shown efficacy in clinical trials enrolling GBM patients. One possible reason for this may stem from resistance mechanisms that arise after prolonged treatment within a clinical setting. However, the mechanisms and timeframe of resistance to BET inhibitors in GBM is not known. To identify the temporal order of resistance mechanisms in GBM we performed quantitative proteomics using multiplex-inhibitor bead mass spectrometry and demonstrated that intrinsic resistance to BET inhibitors in GBM treatment occurs rapidly within hours and involves the fibroblast growth factor receptor 1 (FGFR1) protein. Additionally, small molecule inhibition of BET proteins and FGFR1 simultaneously induces synergy in reducing GBM tumor growth in vitro and in vivo. Further, FGFR1 knockdown synergizes with BET inhibitor mediated reduction of GBM cell proliferation. Collectively, our studies suggest that co-targeting BET and FGFR1 may dampen resistance mechanisms to yield a clinical response in GBM.

TAK1 inhibition leads to RIPK1-dependent apoptosis in immune-activated cancers

Poor survival and lack of treatment response in glioblastoma (GBM) is attributed to the persistence of glioma stem cells (GSCs). To identify novel therapeutic approaches, we performed CRISPR/Cas9 knockout screens and discovered TGFβ activated kinase (TAK1) as a selective survival factor in a significant fraction of GSCs. Loss of TAK1 kinase activity results in RIPK1-dependent apoptosis via Caspase-8/FADD complex activation, dependent on autocrine TNFα ligand production and constitutive TNFR signaling. We identify a transcriptional signature associated with immune activation and the mesenchymal GBM subtype to be a characteristic of cancer cells sensitive to TAK1 perturbation and employ this signature to accurately predict sensitivity to the TAK1 kinase inhibitor HS-276. In addition, exposure to pro-inflammatory cytokines IFNγ and TNFα can sensitize resistant GSCs to TAK1 inhibition. Our findings reveal dependency on TAK1 kinase activity as a novel vulnerability in immune-activated cancers, including mesenchymal GBMs that can be exploited therapeutically.

On the Importance of Acidity in Cancer Cells and Therapy

Cancer cells are associated with high glycolytic activity, which results in acidification of the tumor microenvironment. The occurrence of this stressful condition fosters tumor aggressiveness, with the outcome of invasiveness and metastasis that are linked to a poor clinical prognosis. Acidosis can be both the cause or consequence of alterations in the functions and expressions of transporters involved in intracellular acidity regulation. This review aims to explore the origin of acidity in cancer cells and the various mechanisms existing in tumors to resist, survive, or thrive in the acidic environment. It highlights the difficulties in measuring the intracellular pH evolution that impedes our understanding of the many regulatory and feedback mechanisms. It finally presents the consequences of acidity on tumor development as well as the friend or foe role of acidity in therapy.

In vivo C6 glioma models: an update and a guide toward a more effective preclinical evaluation of potential anti-glioblastoma drugs

Glioblastoma multiform (GBM) is the most common primary brain tumor with a poor prognosis and few therapeutic choices. In vivo, tumor models are useful for enhancing knowledge of underlying GBM pathology and developing more effective therapies/agents at the preclinical level, as they recapitulate human brain tumors. The C6 glioma cell line has been one of the most widely used cell lines in neuro-oncology research as they produce tumors that share the most similarities with human GBM regarding genetic, invasion, and expansion profiles and characteristics. This review provides an overview of the distinctive features and the different animal models produced by the C6 cell line. We also highlight specific applications of various C6 in vivo models according to the purpose of the study and offer some technical notes for more convenient/repeatable modeling. This work also includes novel findings discovered in our laboratory, which would further enhance the feasibility of the model in preclinical GBM investigations.

KDM5B predicts temozolomide-resistant subclones in glioblastoma

Adaptive plasticity to the standard chemotherapeutic temozolomide (TMZ) leads to glioblastoma progression. Here, we examine early stages of this process in patient-derived cellular models, exposing the human lysine-specific demethylase 5B (KDM5B) as a prospective indicator for subclonal expansion. By integration of a reporter, we show its preferential activity in rare, stem-like ALDH1A1+ cells, immediately increasing expression upon TMZ exposure. Naive, genetically unmodified KDM5Bhigh cells phosphorylate AKT (pAKT) and act as slow-cycling persisters under TMZ. Knockdown of KDM5B reverses pAKT levels, simultaneously increasing PTEN expression and TMZ sensitivity. Pharmacological inhibition of PTEN rescues the effect. Interference with KDM5B subsequent to TMZ decreases cellular vitality, and clonal tracing with DNA barcoding demonstrates high individual levels of KDM5B to predict subclonal expansion already before TMZ exposure. Thus, KDM5Bhigh treatment-naive cells preferentially contribute to the dynamics of drug resistance under TMZ. These findings may serve as a cornerstone for future biomarker-assisted clinical trials.

Dual blockade of EGFR and PI3K signaling pathways offers a therapeutic strategy for glioblastoma

BACKGROUND

Glioblastoma multiforme (GBM) is a devastating disease that lacks effective drugs for targeted therapy. Previously, we found that the third-generation epidermal growth factor receptor (EGFR) inhibitor AZD-9291 persistently blocked the activation of the ERK pathway but had no inhibitory effect on the phosphoinositide 3-kinase (PI3K)/Akt pathway. Given that the PI3K inhibitor GDC-0084 is being evaluated in phase I/II clinical trials of GBM treatment, we hypothesized that combined inhibition of the EGFR/ERK and PI3K/Akt pathways may have a synergistic effect in the treatment of GBM.

METHODS

The synergistic effects of cotreatment with AZD-9291 and GDC-0084 were validated using cell viability assays in GBM and primary GBM cell lines. Moreover, the underlying inhibitory mechanisms were assessed through colony formation, EdU proliferation, and cell cycle assays, as well as RNA-seq analyses and western blot. The therapeutic effects of the drug combination on tumor growth and survival were investigated in mice bearing tumors using subcutaneously or intracranially injected LN229 xenografts.

RESULTS

Combined treatment with AZD-9291 and GDC-0084 synergistically inhibited the proliferation and clonogenic survival, as well as induced cell cycle arrest of GBM cells and primary GBM cells, compared to monotherapy. Moreover, AZD-9291 plus GDC-0084 combination therapy significantly inhibited the growth of subcutaneous tumors and orthotopic brain tumor xenografts, thus prolonging the survival of tumor-bearing mice. More importantly, the combination of AZD-9291 and GDC-0084 simultaneously blocked the activation of the EGFR/MEK/ERK and PI3K/AKT/mTOR signaling pathways, thereby exerting significant antitumor activity.

CONCLUSION

Our findings demonstrate that the combined blockade of the EGFR/MEK/ERK and PI3K/AKT/mTOR pathways is more effective against GBM than inhibition of each pathway alone, both in vitro and in vivo. Our results suggest that AZD-9291 combined with GDC-0084 may be considered as a potential treatment strategy in future clinical trials. Video Abstract.

Gene signatures associated with prognosis and chemotherapy resistance in glioblastoma treated with temozolomide

Background: Glioblastoma (GBM) prognosis remains extremely poor despite standard treatment that includes temozolomide (TMZ) chemotherapy. To discover new GBM drug targets and biomarkers, genes signatures associated with survival and TMZ resistance in GBM patients treated with TMZ were identified. Methods: GBM cases in The Cancer Genome Atlas who received TMZ (n = 221) were stratified into subgroups that differed by median overall survival (mOS) using network-based stratification to cluster patients whose somatic mutations affected genes in similar modules of a gene interaction network. Gene signatures formed from differentially mutated genes in the subgroup with the longest mOS were used to confirm their association with survival and TMZ resistance in independent datasets. Somatic mutations in these genes also were assessed for an association with OS in an independent group of 37 GBM cases. Results: Among the four subgroups identified, subgroup four (n = 71 subjects) exhibited the longest mOS at 18.3 months (95% confidence interval: 16.2, 34.1; p = 0.0324). Subsets of the 86 genes that were differentially mutated in this subgroup formed 20-gene and 8-gene signatures that predicted OS in two independent datasets (Spearman's rho of 0.64 and 0.58 between actual and predicted OS; p < 0.001). Patients with mutations in five of the 86 genes had longer OS in a small, independent sample of 37 GBM cases, but this association did not reach statistical significance (p = 0.07). Thirty-one of the 86 genes formed signatures that distinguished TMZ-resistant GBM samples from controls in three independent datasets (area under the curve ≥ 0.75). The prognostic and TMZ-resistance signatures had eight genes in common (ANG, BACH1, CDKN2C, HMGA1, IFI16, PADI4, SDF4, and TP53INP1). The latter three genes have not been associated with GBM previously. Conclusion: PADI4, SDF4, and TP53INP1 are novel therapy and biomarker candidates for GBM. Further investigation of their oncologic functions may provide new insight into GBM treatment resistance mechanisms.

Cyanine Dye Conjugation Enhances Crizotinib Localization to Intracranial Tumors, Attenuating NF-κB-Inducing Kinase Activity and Glioma Progression

Glioblastoma (GBM) is a highly aggressive form of brain cancer with a poor prognosis and limited treatment options. The ALK and c-MET inhibitor Crizotinib has demonstrated preclinical therapeutic potential for newly diagnosed GBM, although its efficacy is limited by poor penetration of the blood brain barrier. Here, we identify Crizotinib as a novel inhibitor of nuclear factor-κB (NF-κB)-inducing kinase, which is a key regulator of GBM growth and proliferation. We further show that the conjugation of Crizotinib to a heptamethine cyanine dye, or a near-infrared dye (IR-Crizotinib), attenuated glioma cell proliferation and survival in vitro to a greater extent than unconjugated Crizotinib. Moreover, we observed increased IR-Crizotinib localization to orthotopic mouse xenograft GBM tumors, which resulted in impaired tumor growth in vivo. Overall, IR-Crizotinib exhibited improved intracranial chemotherapeutic delivery and tumor localization with concurrent inhibition of NIK and noncanonical NF-κB signaling, thereby reducing glioma growth in vitro, as well as in vivo, and increasing survival in a preclinical rodent model.

Silencing of Dicer enhances dacarbazine resistance in melanoma cells by inhibiting ADSL expression

Dacarbazine (DTIC) is the primary first-line treatment for advanced-stage metastatic melanoma; thus, DTIC resistance is poses a major challenge. Therefore, investigating the mechanism underlying DTIC resistance must be investigated. Dicer, a type III cytoplasmic endoribonuclease, plays a pivotal role in the maturation of miRNAs. Aberrant Dicer expression may contribute to tumor progression, clinical aggressiveness, and poor prognosis in various tumors. Dicer inhibition led to a reduction in DTIC sensitivity and an augmentation in stemness in melanoma cells. Clinical analyses indicated a low Dicer expression level as a predictor of poor prognosis factor. Metabolic alterations in tumor cells may interfere with drug response. Adenylosuccinate lyase (ADSL) is a crucial enzyme in the purine metabolism pathway. An imbalance in ADSL may interfere with the therapeutic efficacy of drugs. We discovered that DTIC treatment enhanced ADSL expression and that Dicer silencing significantly reduced ADSL expression in melanoma cells. Furthermore, ADSL overexpression reversed Dicer silencing induced DTIC resistance and cancer stemness. These findings indicate that Dicer-mediated ADSL regulation influences DTIC sensitivity and stemness in melanoma cells.

Tumor treating fields for the treatment of glioblastoma: Current understanding and future perspectives

Background

This review focuses on the recently published evidence on tumor treating fields (TTFields) administered alone or in combination with locoregional and systemic options for treating glioblastoma (GBM) in the past ten years. The aim is to critically summarize the novelty and results obtained with this innovative tool, which is becoming part of the armamentarium of neurosurgeons and neuro-oncologists.

Methods

A comprehensive search and analysis were conducted on pivotal studies published in the past ten years. Furthermore, all completed clinical trials, whose results were published on clinicaltrials.gov, were examined and included in the present review, encompassing both recurrent (r) and newly diagnosed (n) GBM. Finally, an additional examination of the ongoing clinical trials was also conducted.

Results

Recent trials have shown promising results both in patients with nGBM and rGBM/progressive (rGBM), leading to Food and Drug Administration approval in selected patients and the Congress of Neurological Surgeons to include TTFields into current guidelines on the management of GBM (P100034/S001-029). Recently, different randomized trials have demonstrated promising results of TTFields in combination with standard treatment of n- and rGBM, especially when considering progression-free and overall survival, maintaining a low rate of mild to moderate adverse events.

Conclusion

Optimal outcomes were obtained in nGBM and progressive disease. A possible future refinement of TTFields could significantly impact the treatment of rGBM and the actual standard of care for GBM, given the better safety profile and survival effects.

Local delivery of doxorubicin prodrug via lipid nanocapsule-based hydrogel for the treatment of glioblastoma

Glioblastoma (GBM) recurrences appear in most cases around the resection cavity borders and arise from residual GBM cells that cannot be removed by surgery. Here, we propose a novel treatment that combines the advantages of nanomedicine and local drug delivery to target these infiltrating GBM cells. We developed an injectable lipid nanocapsule (LNC)-based formulation loaded with lauroyl-doxorubicin prodrug (DOXC12). Firstly, we demonstrated the efficacy of intratumoral administration of DOXC12 in GL261 GBM-bearing mice, which extended mouse survival. Then, we formulated an injectable hydrogel by mixing the appropriate amount of prodrug with the lipophilic components of LNC. We optimized the hydrogel by incorporating cytidine-C16 (CytC16) to achieve a mechanical stiffness adapted for an application in the brain post-surgery (DOXC12-LNCCL). DOXC12-LNCCL exhibited high DOXC12 encapsulation efficiency (95%) and a size of approximately 60 nm with sustained drug release for over 1 month in vitro. DOXC12-LNCCL exhibited enhanced cytotoxicity compared to free DOXC12 (IC50 of 349 and 86 nM, respectively) on GL261 GBM cells and prevented the growth of GL261 spheroids cultured on organotypic brain slices. In vivo, post-surgical treatment with DOXC12-LNCCL significantly improved the survival of GL261-bearing mice. The combination of this local treatment with the systemic administration of anti-inflammatory drug ibuprofen further delayed the onset of recurrences. In conclusion, our study presents a promising therapeutic approach for the treatment of GBM. By targeting residual GBM cells and reducing the inflammation post-surgery, we present a new strategy to delay the onset of recurrences in the gap period between surgery and standard of care therapy.

From signalling pathways to targeted therapies: unravelling glioblastoma's secrets and harnessing two decades of progress

Glioblastoma, a rare, and highly lethal form of brain cancer, poses significant challenges in terms of therapeutic resistance, and poor survival rates for both adult and paediatric patients alike. Despite advancements in brain cancer research driven by a technological revolution, translating our understanding of glioblastoma pathogenesis into improved clinical outcomes remains a critical unmet need. This review emphasises the intricate role of receptor tyrosine kinase signalling pathways, epigenetic mechanisms, and metabolic functions in glioblastoma tumourigenesis and therapeutic resistance. We also discuss the extensive efforts over the past two decades that have explored targeted therapies against these pathways. Emerging therapeutic approaches, such as antibody-toxin conjugates or CAR T cell therapies, offer potential by specifically targeting proteins on the glioblastoma cell surface. Combination strategies incorporating protein-targeted therapy and immune-based therapies demonstrate great promise for future clinical research. Moreover, gaining insights into the role of cell-of-origin in glioblastoma treatment response holds the potential to advance precision medicine approaches. Addressing these challenges is crucial to improving outcomes for glioblastoma patients and moving towards more effective precision therapies.

RNA cytosine methyltransferase NSUN5 promotes protein synthesis and tumorigenic phenotypes in glioblastoma

Glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor in adults. The standard treatment achieves a median overall survival for GBM patients of only 15 months. Hence, novel therapies based on an increased understanding of the mechanistic underpinnings of GBM are desperately needed. In this study, we show that elevated expression of 28S rRNA (cytosine-C(5))-methyltransferase NSUN5, which methylates cytosine 3782 of 28S rRNA in GBM cells, is strongly associated with the poor survival of GBM patients. Moreover, we demonstrate that overexpression of NSUN5 increases protein synthesis in GBM cells. NSUN5 knockdown decreased protein synthesis, cell proliferation, sphere formation, migration, and resistance to temozolomide in GBM cell lines. NSUN5 knockdown also decreased the number and size of GBM neurospheres in vitro. As a corollary, mice harboring U251 tumors wherein NSUN5 was knocked down survived longer than mice harboring control tumors. Taken together, our results suggest that NSUN5 plays a protumorigenic role in GBM by enabling the enhanced protein synthesis requisite for tumor progression. Accordingly, NSUN5 may be a hitherto unappreciated target for the treatment of GBM.

A co-formulation of interferons alpha2b and gamma distinctively targets cell cycle in the glioblastoma-derived cell line U-87MG

BACKGROUND

HeberFERON is a co-formulation of α2b and γ interferons, based on their synergism, which has shown its clinical superiority over individual interferons in basal cell carcinomas. In glioblastoma (GBM), HeberFERON has displayed promising preclinical and clinical results. This led us to design a microarray experiment aimed at identifying the molecular mechanisms involved in the distinctive effect of HeberFERON compared to the individual interferons in U-87MG model.

METHODS

Transcriptional expression profiling including a control (untreated) and three groups receiving α2b-interferon, γ-interferon and HeberFERON was performed using an Illumina HT-12 microarray platform. Unsupervised methods for gene and sample grouping, identification of differentially expressed genes, functional enrichment and network analysis computational biology methods were applied to identify distinctive transcription patterns of HeberFERON. Validation of most representative genes was performed by qPCR. For the cell cycle analysis of cells treated with HeberFERON for 24 h, 48 and 72 h we used flow cytometry.

RESULTS

The three treatments show different behavior based on the gene expression profiles. The enrichment analysis identified several mitotic cell cycle related events, in particular from prometaphase to anaphase, which are exclusively targeted by HeberFERON. The FOXM1 transcription factor network that is involved in several cell cycle phases and is highly expressed in GBMs, is significantly down regulated. Flow cytometry experiments corroborated the action of HeberFERON on the cell cycle in a dose and time dependent manner with a clear cellular arrest as of 24 h post-treatment. Despite the fact that p53 was not down-regulated, several genes involved in its regulatory activity were functionally enriched. Network analysis also revealed a strong relationship of p53 with genes targeted by HeberFERON. We propose a mechanistic model to explain this distinctive action, based on the simultaneous activation of PKR and ATF3, p53 phosphorylation changes, as well as its reduced MDM2 mediated ubiquitination and export from the nucleus to the cytoplasm. PLK1, AURKB, BIRC5 and CCNB1 genes, all regulated by FOXM1, also play central roles in this model. These and other interactions could explain a G2/M arrest and the effect of HeberFERON on the proliferation of U-87MG.

CONCLUSIONS

We proposed molecular mechanisms underlying the distinctive behavior of HeberFERON compared to the treatments with the individual interferons in U-87MG model, where cell cycle related events were highly relevant.

Computational modeling and synthesis of pyridine variants of benzoyl-phenoxy-acetamide with high glioblastoma cytotoxicity and brain tumor penetration

Glioblastomas are highly aggressive brain tumors for which therapeutic options are very limited. In a quest for new anti-glioblastoma drugs, we focused on specific structural modifications to the benzoyl-phenoxy-acetamide (BPA) structure present in a common lipid-lowering drug, fenofibrate, and in our first prototype glioblastoma drug, PP1. Here, we propose extensive computational analyses to improve the selection of the most effective glioblastoma drug candidates. Initially, over 100 structural BPA variations were analyzed and their physicochemical properties, such as water solubility (- logS), calculated partition coefficient (ClogP), probability for BBB crossing (BBB_SCORE), probability for CNS penetration (CNS-MPO) and calculated cardiotoxicity (hERG), were evaluated. This integrated approach allowed us to select pyridine variants of BPA that show improved BBB penetration, water solubility, and low cardiotoxicity. Herein the top 24 compounds were synthesized and analyzed in cell culture. Six of them demonstrated glioblastoma toxicity with IC50 ranging from 0.59 to 3.24 µM. Importantly, one of the compounds, HR68, accumulated in the brain tumor tissue at 3.7 ± 0.5 µM, which exceeds its glioblastoma IC50 (1.17 µM) by over threefold.

Downregulation of long noncoding RNA TP73-AS1 expression confers resistance to temozolomide in human glioblastoma cells

Glioblastoma multiforme (GBM), the most aggressive primary malignant brain tumor, is resistant to conventional radiotherapies and chemotherapies, including temozolomide (TMZ). Overcoming GBM resistance to the chemotherapeutic agent TMZ poses an important therapeutic problem. This study established an association between the long noncoding RNA TP73-AS1 and TMZ sensitivity regulation in human GBM cells (U87MG). Transcriptomic analysis revealed that TP73-AS1 expression was reduced in TMZ-resistant U87MGRT100 cells compared to that in parental U87MG cells. Additionally, TP73-AS1 knockdown in parental U87MG cells decreased their sensitivity to TMZ. Overall, these findings suggest that TP73-AS1 functions as a regulator of TMZ sensitivity in GBM cells.

Tyrphostin A9 attenuates glioblastoma growth by suppressing PYK2/EGFR-ERK signaling pathway

PURPOSE

Glioblastoma (GBM) is a fatal primary brain tumor with extremely poor clinical outcomes. The anticancer efficiency of tyrosine kinase inhibitors (TKIs) has been shown in GBM and other cancer, with limited therapeutic outcomes. In the current study, we aimed to investigate the clinical impact of active proline-rich tyrosine kinase-2 (PYK2) and epidermal growth factor receptor (EGFR) in GBM and evaluate its druggability by a synthetic TKI-Tyrphostin A9 (TYR A9).

METHODS

The expression profile of PYK2 and EGFR in astrocytoma biopsies (n = 48) and GBM cell lines were evaluated through quantitative PCR, western blots, and immunohistochemistry. The clinical association of phospho-PYK2 and EGFR was analyzed with various clinicopathological features and the Kaplan-Meier survival curve. The phospho-PYK2 and EGFR druggability and subsequent anticancer efficacy of TYR A9 was evaluated in GBM cell lines and intracranial C6 glioma model.

RESULTS

Our expression data revealed an increased phospho-PYK2, and EGFR expression aggravates astrocytoma malignancy and is associated with patients' poor survival. The mRNA and protein correlation analysis showed a positive association between phospho-PYK2 and EGFR in GBM tissues. The in-vitro studies demonstrated that TYR A9 reduced GBM cell growth, cell migration, and induced apoptosis by attenuating PYK2/EGFR-ERK signaling. The in-vivo data showed TYR A9 treatment dramatically reduced glioma growth with augmented animal survival by repressing PYK2/EGFR-ERK signaling.

CONCLUSION

Altogether, this study report that increased phospho-PYK2 and EGFR expression in astrocytoma was associated with poor prognosis. The in-vitro and in-vivo evidence underlined translational implication of TYR A9 by suppressing PYK2/EGFR-ERK modulated signaling pathway. The schematic diagram displayed proof of concept of the current study indicating activated PYK2 either through the Ca2+/Calmodulin-dependent protein kinase II (CAMKII) signaling pathway or autophosphorylation at Tyr402 induces association to the SH2 domain of c-Src that leads to c-Src activation. Activated c-Src in turn activates PYK2 at other tyrosine residues that recruit Grb2/SOS complex and trigger ERK½ activation. Besides, PYK2 interaction with c-Src acts as an upstream of EGFR transactivator that can activate the ERK½ signaling pathway, which induces cell proliferation and cell survival by increasing anti-apoptotic proteins or inhibiting pro-apoptotic proteins. TYR A9 treatment attenuate GBM cell proliferation and migration; and induce GBM cell death by inhibiting PYK2 and EGFR-induced ERK activation.

Unraveling the therapeutic mechanisms of dichloroacetic acid in lung cancer through integrated multi-omics approaches: metabolomics and transcriptomics

Objective: The aim of this study was to investigate the molecular mechanisms underlying the therapeutic effects of dichloroacetic acid (DCA) in lung cancer by integrating multi-omics approaches, as the current understanding of DCA's role in cancer treatment remains insufficiently elucidated. Methods: We conducted a comprehensive analysis of publicly available RNA-seq and metabolomic datasets and established a subcutaneous xenograft model of lung cancer in BALB/c nude mice (n = 5 per group) treated with DCA (50 mg/kg, administered via intraperitoneal injection). Metabolomic profiling, gene expression analysis, and metabolite-gene interaction pathway analysis were employed to identify key pathways and molecular players involved in the response to DCA treatment. In vivo evaluation of DCA treatment on tumor growth and MIF gene expression was performed in the xenograft model. Results: Metabolomic profiling and gene expression analysis revealed significant alterations in metabolic pathways, including the Warburg effect and citric acid cycle, and identified the MIF gene as a potential therapeutic target in lung cancer. Our analysis indicated that DCA treatment led to a decrease in MIF gene expression and an increase in citric acid levels in the treatment group. Furthermore, we observed a potential interaction between citric acid and the MIF gene, suggesting a novel mechanism underlying the therapeutic effects of DCA in lung cancer. Conclusion: This study underscores the importance of integrated omics approaches in deciphering the complex molecular mechanisms of DCA treatment in lung cancer. The identification of key metabolic pathways and the novel finding of citric acid elevation, together with its interaction with the MIF gene, provide promising directions for the development of targeted therapeutic strategies and improving clinical outcomes for lung cancer patients.

Zinc finger and SCAN domain-containing 18 suppresses the proliferation, self-renewal, and drug resistance of glioblastoma cells

Elucidation of cellular and molecular mechanisms key to glioblastoma growth, self-renewal, survival, and metastasis is important for developing novel therapeutic strategies. In this study, the expression and function of zinc finger and SCAN domain-containing 18 (ZSCAN18) in human glioblastoma cell lines were characterized. Compared with normal astrocytes, ZSCAN18 was significantly down-regulated in all tested glioblastoma cell lines, with the LN-229 cell line having the lowest ZSCAN18 expression. Lentivirus-mediated ZSCAN18 overexpression suppressed glioblastoma cell proliferation, sphere formation, and SOX2 and OCT4 expression, implying the negative role of ZSCAN18 in glioblastoma development. ZSCAN18 overexpression enhanced the sensitivity of glioblastoma cells to Temozolomide. The glioblastoma implantation model showed a consistent inhibitory effect of ZSCAN18 on the proliferation and self-renewal of glioblastoma cells in vivo. Notably, ZSCAN18 overexpression resulted in the down-regulation of glioma-associated oncogene homolog 1 (GLI1) which is the terminal component of the Hedgehog signaling. Lentivirus-mediated GLI1 overexpression restored the proliferation and promoted the resistance of glioblastoma cells to Temozolomide. However, GLI1 overexpression did not affect the self-renewal of ZSCAN18-overexpressing glioblastoma cells. Taken together, this research uncovers the role of ZSCAN18 in regulating glioblastoma cell growth and maintenance. ZSCAN18 could be a potential glioblastoma biomarker.

A receptor-mediated landscape of druggable and targeted nanomaterials for gliomas

Gliomas are the most common type of brain cancer, and among them, glioblastoma multiforme (GBM) is the most prevalent (about 60% of cases) and the most aggressive type of primary brain tumor. The treatment of GBM is a major challenge due to the pathophysiological characteristics of the disease, such as the presence of the blood-brain barrier (BBB), which prevents and regulates the passage of substances from the bloodstream to the brain parenchyma, making many of the chemotherapeutics currently available not able to reach the brain in therapeutic concentrations, accumulating in non-target organs, and causing considerable adverse effects for the patient. In this scenario, nanocarriers emerge as tools capable of improving the brain bioavailability of chemotherapeutics, in addition to improving their biodistribution and enhancing their uptake in GBM cells. This is possible due to its nanometric size and surface modification strategies, which can actively target nanocarriers to elements overexpressed by GBM cells (such as transmembrane receptors) related to aggressive development, drug resistance, and poor prognosis. In this review, an overview of the most frequently overexpressed receptors in GBM cells and possible approaches to chemotherapeutic delivery and active targeting using nanocarriers will be presented.

Barriers to overcoming immunotherapy resistance in glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor, known for its poor prognosis and high recurrence rate. Current standard of care includes surgical resection followed by combined radiotherapy and chemotherapy. Although immunotherapies have yielded promising results in hematological malignancies, their successful application in GBM remains limited due to a host of immunosuppressive factors unique to GBM. As a result of these roadblocks, research efforts have focused on utilizing combinatorial immunotherapies that target networks of immune processes in GBM with promising results in both preclinical and clinical trials, although limitations in overcoming the immunosuppressive factors within GBM remain. In this review, we aim to discuss the intrinsic and adaptive immune resistance unique to GBM and to summarize the current evidence and outcomes of engineered and non-engineered treatments targeted at overcoming GBM resistance to immunotherapy. Additionally, we aim to highlight the most promising strategies of targeted GBM immunotherapy combinatorial treatments and the insights that may directly improve the current patient prognosis and clinical care.

UBE2T Promotes Temozolomide Resistance of Glioblastoma Through Regulating the Wnt/β-Catenin Signaling Pathway

Purpose

Patients with glioblastoma (GBM) have poor prognosis and limited therapeutic options, largely because of chemoresistance to temozolomide (TMZ) treatment. Ubiquitin conjugating enzyme E2 T (UBE2T) plays a key role in regulating the malignancy of various tumors, including GBM; however, its role in TMZ resistance of GBM has not been elucidated. The purpose of this study was to clarify the role of UBE2T in mediating TMZ resistance and investigate the specific underlying mechanism.

Methods

Western blotting was used to detect the protein levels of UBE2T and Wnt/β-catenin-related factors. CCK-8, flow cytometry, and colony formation assays were used to examine the effect of UBE2T on TMZ resistance. Wnt/β-catenin signaling pathway activation was inhibited using XAV-939, and a xenograft mouse model was generated to clarify the function of TMZ in vivo.

Results

UBE2T knockdown sensitized GBM cells to TMZ treatment, whereas UBE2T overexpression promoted TMZ resistance. The specific UBE2T inhibitor, M435-1279, increased the sensitivity of GBM cells to TMZ. Mechanistically, our results demonstrated that UBE2T induces β-catenin nuclear translocation and increases the protein levels of downstream molecules, including survivin and c-Myc. Inhibition of Wnt/β-catenin signaling using XAV-939 blocked TMZ resistance due to UBE2T overexpression in GBM cells. In addition, UBE2T was shown to facilitate TMZ resistance by inducing Wnt/β-catenin signaling pathway activation in a mouse xenograft model. Combined treatment with TMZ and UBE2T inhibitor achieved superior tumor growth suppression relative to TMZ treatment alone.

Conclusion

Our data reveal a novel role of UBE2T in mediating TMZ resistance of GBM cells via regulating Wnt/β-catenin signaling. These findings indicate that targeting UBE2T has promising potential to overcome TMZ resistance of GBM.

EZH2-Myc driven glioblastoma elicited by cytomegalovirus infection of human astrocytes

Mounting evidence is identifying human cytomegalovirus (HCMV) as a potential oncogenic virus. HCMV has been detected in malignant gliomas. EZH2 and Myc play a potential oncogenic role, correlating with the glioma grade. Herewith, we present the first experimental evidence for HCMV as a reprogramming vector, straight through the dedifferentiation of mature human astrocytes, and generation of CMV-Elicited Glioblastoma Cells (CEGBCs) possessing glioblastoma-like traits. HCMV counterparts the progression of the perceived cellular and molecular mechanisms succeeding the transformation and invasion processes with CEGBCs involved in spheroid formation and invasiveness. Glioblastoma multiforme (GBM) biopsies were characterized by an elevated EZH2 and Myc expression, possessing a strong positive correlation between the aforementioned markers in the presence of HCMV. From GBM tissues, we isolated HCMV clinical strains that transformed HAs toward CEGBCs exhibiting upregulated EZH2 and Myc. Spheroids generated from CEGBCs possessed invasion potential and were sensitive to EZH2 inhibitor, ganciclovir, and temozolomide triple therapy. HCMV clinical strains transform HAs and fit with an HCMV-induced glioblastoma model of oncogenesis, and supports the tumorigenic properties of Myc and EZH2 which might be highly pertinent in the pathophysiology of astrocytic brain tumors and thereby paving the way for new therapeutic strategies.

Tumor Treating Fields (TTFields) increase the effectiveness of temozolomide and lomustine in glioblastoma cell lines

PURPOSE

Tumor Treating Fields (TTFields) are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression, ultimately leading to cell death. TTFields therapy is approved for treatment of newly-diagnosed glioblastoma (GBM) concurrent with maintenance temozolomide (TMZ). Recently, the benefit of TMZ in combination with lomustine (CCNU) was demonstrated in patients with O⁶-methylguanine DNA methyltransferase (MGMT) promoter methylation. The addition of adjuvant TTFields to TMZ plus CCNU further improved patient outcomes, leading to a CE mark for this regimen. The current in vitro study aimed to elucidate the mechanism underlying the benefit of this treatment protocol.

METHODS

Human GBM cell lines with different MGMT promoter methylation statuses were treated with TTFields, TMZ, and CCNU, and effectiveness was tested by cell count, apoptosis, colony formation, and DNA damage measurements. Expression levels of relevant DNA-repair proteins were examined by western blot analysis.

RESULTS

TTFields concomitant with TMZ displayed an additive effect, irrespective of MGMT expression levels. TTFields concomitant with CCNU or with CCNU plus TMZ was additive in MGMT-expressing cells and synergistic in MGMT-non-expressing cells. TTFields downregulated the FA-BRCA pathway and increased DNA damage induced by the chemotherapy combination.

CONCLUSIONS

The results support the clinical benefit demonstrated for TTFields concomitant with TMZ plus CCNU. Since the FA-BRCA pathway is required for repair of DNA cross-links induced by CCNU in the absence of MGMT, the synergy demonstrated in MGMT promoter methylated cells when TTFields and CCNU were co-applied may be attributed to the BRCAness state induced by TTFields.

Computational modeling and synthesis of Pyridine variants of Benzoyl-Phenoxy-Acetamide with high glioblastoma cytotoxicity and brain tumor penetration

Glioblastomas are highly aggressive brain tumors for which therapeutic options are very limited. In a quest for new anti-glioblastoma drugs, we focused on specific structural modifications of benzoyl-phenoxy-acetamide (BPA) present in a common lipid-lowering drug, fenofibrate, and in our first prototype glioblastoma drug, PP1. Here, we propose extensive computational analyses to improve selection of the most effective glioblastoma drug candidates. Initially over 100 structural BPA variations were analyzed and their physicochemical properties such as water solubility (-logS), calculated partition coefficient (ClogP), probability for BBB crossing (BBB_SCORE), probability for CNS penetration (CNS-MPO) and calculated cardiotoxicity (hERG), were evaluated. This integrated approach allowed us to select pyridine variants of BPA that show improved BBB penetration, water solubility, and low cardiotoxicity. Herein the top 24 compounds were synthesized and analyzed in cell culture. Six of them demonstrated glioblastoma toxicity with IC50 ranging from 0.59 to 3.24mM. Importantly, one of the compounds, HR68, accumulated in the brain tumor tissue at 3.7+/-0.5mM, which exceeds its glioblastoma IC50 (1.17mM) by over 3-fold.

Cell Cycle-Related FAM64A Could be Activated by TGF-β Signaling to Promote Glioma Progression

Gliomas are aggressive brain tumors characterized by uncontrolled cell proliferation. FAM64A, a cell cycle-related gene, has been found to promote cell proliferation in various tumors, including gliomas. However, the regulatory mechanism and clinical significance of FAM64A in gliomas remain unclear. In this study, we investigated FAM64A expression in gliomas with different grades and constructed FAM64A silenced cell lines to study its functions. Our results demonstrated that FAM64A was highly expressed in glioblastoma (P < 0.001) and associated with a poor prognosis (P < 0.001). Expression profiles at the single-cell resolution indicated FAM64A could play a role in a cell-cycle-dependent way to promote glioma cell proliferation. We further observed that FAM64A silencing in glioma cells resulted in disrupted proliferation and migration ability, and increased cell accumulation in the G2/M phase (P = 0.034). Additionally, TGF-β signaling upregulates FAM64A expression, and SMAD4 and FAM64A co-localize in high-grade glioma tissues. We found FAM64A knockdown inhibited TGF-β-induced epithelial-mesenchymal transition in glioma. Our findings suggest that FAM64A could serve as a diagnostic and therapeutic target in gliomas.

Urinary 8-hydroxy-2'-deoxyguanosine levels are elevated in patients with IDH1-wildtype glioblastoma and are associated with tumor recurrence in gliomas

2021 World Health Organization (WHO) Central Nervous System (CNS) Tumor Classification includes molecular diagnostic parameters such as isocitrate dehydrogenase (IDH) mutation or 1p19q codeletion status, in addition to the classical histological classification. Several studies have revealed that patients with IDH1 mutation have a longer survival rate compared to wildtype individuals. In glioma cells, increased oxidative stress has been identified. However, till now, the relation between oxidative stress levels and IDH1 mutation status in those patients was not examined. Therefore, the aim of this study was to investigate the urinary levels of oxidatively induced DNA damage products, 8-hydroxy-2'- deoxyguanosine (8-OH-dG), (5'R) and (5'S)-8,5'-cyclo-2'-deoxyadenosines (R-cdA and S-cdA) as reliable oxidative stress markers in patients with IDH1-wildtype (n = 20) and IDH1-mutant (n = 22) glioma. Absolute quantification of 8-OH-dG, R-cdA and S-cdA was achieved by liquid chromatography-tandem mass spectrometry with isotope dilution. The levels of 8-OH-dG were significantly greater in IDH1-wildtype glioma patients than those in IDH1-mutant ones (p = 0.017). No statistically significant difference was observed for R-cdA and S-cdA levels. 8-OH-dG levels were positively correlated with patients' tumor recurrence in all patients (r = 0.382, p = 0.014). The mutation status of glioma is well correlated with oxidative stress. Examination of noninvasively measured oxidative DNA damage products along with IDH1 mutation status in glioma patients, might be particularly important in terms of evaluating and monitoring the effectiveness of treatment.

Mechanical nanosurgery of chemoresistant glioblastoma using magnetically controlled carbon nanotubes

Glioblastoma (GBM) is the most common and aggressive primary brain cancer. Despite multimodal treatment including surgery, radiotherapy, and chemotherapy, median patient survival has remained at ~15 months for decades. This situation demands an outside-the-box treatment approach. Using magnetic carbon nanotubes (mCNTs) and precision magnetic field control, we report a mechanical approach to treat chemoresistant GBM. We show that GBM cells internalize mCNTs, the mobilization of which by rotating magnetic field results in cell death. Spatiotemporally controlled mobilization of intratumorally delivered mCNTs suppresses GBM growth in vivo. Functionalization of mCNTs with anti-CD44 antibody, which recognizes GBM cell surface-enriched antigen CD44, increases mCNT recognition of cancer cells, prolongs mCNT enrichment within the tumor, and enhances therapeutic efficacy. Using mouse models of GBM with upfront or therapy-induced resistance to temozolomide, we show that mCNT treatment is effective in treating chemoresistant GBM. Together, we establish mCNT-based mechanical nanosurgery as a treatment option for GBM.

A combination of metformin and epigallocatechin gallate potentiates glioma chemotherapy in vivo

Glioma is the most devastating high-grade tumor of the central nervous system, with dismal prognosis. Existing treatment modality does not provide substantial benefit to patients and demands novel strategies. One of the first-line treatments for glioma, temozolomide, provides marginal benefit to glioma patients. Repurposing of existing non-cancer drugs to treat oncology patients is gaining momentum in recent years. In this study, we investigated the therapeutic benefits of combining three repurposed drugs, namely, metformin (anti-diabetic) and epigallocatechin gallate (green tea-derived antioxidant) together with temozolomide in a glioma-induced xenograft rat model. Our triple-drug combination therapy significantly inhibited tumor growth in vivo and increased the survival rate (50%) of rats when compared with individual or dual treatments. Molecular and cellular analyses revealed that our triple-drug cocktail treatment inhibited glioma tumor growth in rat model through ROS-mediated inactivation of PI3K/AKT/mTOR pathway, arrest of the cell cycle at G1 phase and induction of molecular mechanisms of caspases-dependent apoptosis.In addition, the docking analysis and quantum mechanics studies performed here hypothesize that the effect of triple-drug combination could have been attributed by their difference in molecular interactions, that maybe due to varying electrostatic potential. Thus, repurposing metformin and epigallocatechin gallate and concurrent administration with temozolomide would serve as a prospective therapy in glioma patients.

Changes in calpain-2 expression during glioblastoma progression predisposes tumor cells to temozolomide resistance by minimizing DNA damage and p53-dependent apoptosis

BACKGROUND

Glioblastoma multiforme (GBM) is characterized by an unfavorable prognosis for patients affected. During standard-of-care chemotherapy using temozolomide (TMZ), tumors acquire resistance thereby causing tumor recurrence. Thus, deciphering essential molecular pathways causing TMZ resistance are of high therapeutic relevance.

METHODS

Mass spectrometry based proteomics were used to study the GBM proteome. Immunohistochemistry staining of human GBM tissue for either calpain-1 or -2 was performed to locate expression of proteases. In vitro cell based assays were used to measure cell viability and survival of primary patient-derived GBM cells and established GBM cell lines after TMZ ± calpain inhibitor administration. shRNA expression knockdowns of either calpain-1 or calpain-2 were generated to study TMZ sensitivity of the specific subunits. The Comet assay and ɣH2AX signal measurements were performed in order to assess the DNA damage amount and recognition. Finally, quantitative real-time PCR of target proteins was applied to differentiate between transcriptional and post-translational regulation.

RESULTS

Calcium-dependent calpain proteases, in particular calpain-2, are more abundant in glioblastoma compared to normal brain and increased in patient-matched initial and recurrent glioblastomas. On the cellular level, pharmacological calpain inhibition increased the sensitivities of primary glioblastoma cells towards TMZ. A genetic knockdown of calpain-2 in U251 cells led to increased caspase-3 cleavage and sensitivity to neocarzinostatin, which rapidly induces DNA strand breakage. We hypothesize that calpain-2 causes desensitization of tumor cells against TMZ by preventing strong DNA damage and subsequent apoptosis via post-translational TP53 inhibition. Indeed, proteomic comparison of U251 control vs. U251 calpain-2 knockdown cells highlights perturbed levels of numerous proteins involved in DNA damage response and downstream pathways affecting TP53 and NF-κB signaling. TP53 showed increased protein abundance, but no transcriptional regulation.

CONCLUSION

TMZ-induced cell death in the presence of calpain-2 expression appears to favor DNA repair and promote cell survival. We conclude from our experiments that calpain-2 expression represents a proteomic mode that is associated with higher resistance via "priming" GBM cells to TMZ chemotherapy. Thus, calpain-2 could serve as a prognostic factor for GBM outcome.

The dark side of mRNA translation and the translation machinery in glioblastoma

Among the different types of cancer affecting the central nervous system (CNS), glioblastoma (GB) is classified by the World Health Organization (WHO) as the most common and aggressive CNS cancer in adults. GB incidence is more frequent among persons aged 45–55 years old. GB treatments are based on tumor resection, radiation, and chemotherapies. The current development of novel molecular biomarkers (MB) has led to a more accurate prediction of GB progression. Moreover, clinical, epidemiological, and experimental studies have established genetic variants consistently associated with the risk of suffering GB. However, despite the advances in these fields, the survival expectancy of GB patients is still shorter than 2 years. Thus, fundamental processes inducing tumor onset and progression remain to be elucidated. In recent years, mRNA translation has been in the spotlight, as its dysregulation is emerging as a key cause of GB. In particular, the initiation phase of translation is most involved in this process. Among the crucial events, the machinery performing this phase undergoes a reconfiguration under the hypoxic conditions in the tumor microenvironment. In addition, ribosomal proteins (RPs) have been reported to play translation-independent roles in GB development. This review focuses on the research elucidating the tight relationship between translation initiation, the translation machinery, and GB. We also summarize the state-of-the-art drugs targeting the translation machinery to improve patients’ survival. Overall, the recent advances in this field are shedding new light on the dark side of translation in GB.

Involvement of cell shape and lipid metabolism in glioblastoma resistance to temozolomide

Temozolomide (TMZ) has been used as standard-of-care for glioblastoma multiforme (GBM), but the resistance to TMZ develops quickly and frequently. Thus, more studies are needed to elucidate the resistance mechanisms. In the current study, we investigated the relationship among the three important phenotypes, namely TMZ-resistance, cell shape and lipid metabolism, in GBM cells. We first observed the distinct difference in cell shapes between TMZ-sensitive (U87) and resistant (U87R) GBM cells. We then conducted NMR-based lipid metabolomics, which revealed a significant increase in cholesterol and fatty acid synthesis as well as lower lipid unsaturation in U87R cells. Consistent with the lipid changes, U87R cells exhibited significantly lower membrane fluidity. The transcriptomic analysis demonstrated that lipid synthesis pathways through SREBP were upregulated in U87R cells, which was confirmed at the protein level. Fatostatin, an SREBP inhibitor, and other lipid pathway inhibitors (C75, TOFA) exhibited similar or more potent inhibition on U87R cells compared to sensitive U87 cells. The lower lipid unsaturation ratio, membrane fluidity and higher fatostatin sensitivity were all recapitulated in patient-derived TMZ-resistant primary cells. The observed ternary relationship among cell shape, lipid composition, and TMZ-resistance may be applicable to other drug-resistance cases. SREBP and fatostatin are suggested as a promising target-therapeutic agent pair for drug-resistant glioblastoma.

The PYK2 inhibitor PF-562271 enhances the effect of temozolomide on tumor growth in a C57Bl/6-Gl261 mouse glioma model

BACKGROUND

The development of resistance to temozolomide (TMZ), a standard chemotherapeutic, limits the effective treatment of glioblastoma (GBM). Focal adhesion kinase (FAK) and proline rich tyrosine kinase 2 (Pyk2) regulate proliferation and invasion of GBM cells. We found that TMZ activates FAK and Pyk2 signaling in GBM. We hypothesized that pharmacological inhibitors of Pyk2/FAK together with TMZ can enhance the inhibitory effect of TMZ on tumor growth and dispersal and improve the treatment outcome.

METHODS

Primary human GBM cell cultures and a C57Bl/6-GL261 mouse glioma implantation model were used. Pyk2 (Tyr579/580) and FAK (Tyr925) phosphorylation was analyzed by western blotting. Viability, cell cycle, migration, invasion and invadopodia formation were investigated in vitro. Animal survival, tumor size and invasion, TUNEL apoptotic cell death and the Ki67 proliferation index were evaluated in vivo upon treatment with TMZ (50 mg/kg, once/day, orally) and the Pyk2/FAK inhibitor PF-562271 (once/daily, 50 mg/kg, orally) vs. TMZ monotherapy.

RESULTS

In vitro studies revealed significantly reduced viability, cell cycle progression, invasion and invadopodia with TMZ (100 µM) + PF-562271 (16 nM) compared with TMZ alone. In vivo studies demonstrated that combinatorial treatment led to prominent reductions in tumor size and invasive margins, extensive signs of apoptosis and a reduced proliferation index, together with a 15% increase in the survival rate in animals, compared with TMZ monotherapy.

CONCLUSION

TMZ + PF-562271 eliminates TMZ-related Pyk2/FAK activation in GBM and improves the treatment efficacy.

Enhancing Anti-Cancer Therapy with Selective Autophagy Inhibitors by Targeting Protective Autophagy

Autophagy is a process of eliminating damaged or unnecessary proteins and organelles, thereby maintaining intracellular homeostasis. Deregulation of autophagy is associated with several diseases including cancer. Contradictory dual roles of autophagy have been well established in cancer. Cytoprotective mechanism of autophagy has been extensively investigated for overcoming resistance to cancer therapies including radiotherapy, targeted therapy, immunotherapy, and chemotherapy. Selective autophagy inhibitors that directly target autophagic process have been developed for cancer treatment. Efficacies of autophagy inhibitors have been tested in various pre-clinical cancer animal models. Combination therapies of autophagy inhibitors with chemotherapeutics are being evaluated in clinal trials. In this review, we will focus on genetical and pharmacological perturbations of autophagy-related proteins in different steps of autophagic process and their therapeutic benefits. We will also summarize combination therapies of autophagy inhibitors with chemotherapies and their outcomes in pre-clinical and clinical studies. Understanding of current knowledge of development, progress, and application of cytoprotective autophagy inhibitors in combination therapies will open new possibilities for overcoming drug resistance and improving clinical outcomes.

TRPML2 Mucolipin Channels Drive the Response of Glioma Stem Cells to Temozolomide and Affect the Overall Survival in Glioblastoma Patients

The survival of patients with glioblastoma (GBM) is poor. The main cause is the presence of glioma stem cells (GSCs), exceptionally resistant to temozolomide (TMZ) treatment. This last may be related to the heterogeneous expression of ion channels, among them TRPML2. Its mRNA expression was evaluated in two different neural stem cell (NS/PC) lines and sixteen GBM stem-like cells by qRT-PCR. The response to TMZ was evaluated in undifferentiated or differentiated GSCs, and in TRPML2-induced or silenced GSCs. The relationship between TRPML2 expression and responsiveness to TMZ treatment was evaluated by MTT assay showing that increased TRPML2 mRNA levels are associated with resistance to TMZ. This research was deepened by qRT-PCR and western blot analysis. PI3K/AKT and JAK/STAT pathways as well as ABC and SLC drug transporters were involved. Finally, the relationship between TRPML2 expression and overall survival (OS) and progression-free survival (PFS) in patient-derived GSCs was evaluated by Kaplan-Meier analysis. The expression of TRPML2 mRNA correlates with worse OS and PFS in GBM patients. Thus, the expression of TRPML2 in GSCs influences the responsiveness to TMZ in vitro and affects OS and PFS in GBM patients.

Nucleobase-modified nucleosides and nucleotides: Applications in biochemistry, synthetic biology, and drug discovery

. DNA is often referred to as the "molecule of life" since it contains the genetic blueprint for all forms of life on this planet. The core building blocks composing DNA are deoxynucleotides. While the deoxyribose sugar and phosphate group are ubiquitous, it is the composition and spatial arrangement of the four natural nucleobases, adenine (A), cytosine (C), guanine (G), and thymine (T), that provide diversity in the coding information present in DNA. The ability of DNA to function as the genetic blueprint has historically been attributed to the formation of proper hydrogen bonding interactions made between complementary nucleobases. However, recent chemical and biochemical studies using nucleobase-modified nucleotides that contain "non-hydrogen bonding" functional groups have challenged many of the dogmatic views for the necessity of hydrogen-bonding interactions for DNA stability and function. Based on years of exciting research, this area has expanded tremendously and is thus too expansive to provide a comprehensive review on the topic. As such, this review article provides an opinion highlighting how nucleobase-modified nucleotides are being applied in diverse biomedical fields, focusing on three exciting areas of research. The first section addresses how these analogs are used as mechanistic probes for DNA polymerase activity and fidelity during replication. This section outlines the synthetic logic and medicinal chemistry approaches used to replace hydrogen-bonding functional groups to examine the contributions of shape/size, nucleobase hydrophobicity, and pi-electron interactions. The second section extends these mechanistic studies to provide insight into how nucleobase-modified nucleosides are used in synthetic biology. One example is through expansion of the genetic code in which changing the composition of DNA makes it possible to site-specifically incorporate unnatural amino acids bearing unique functional groups into enzymes and receptors. The final section describes results of pre-clinical studies using nucleobase-modified nucleosides as potential therapeutic agents against diseases such as cancer.

Characterization of EGFR-reprogrammable temozolomide-resistant cells in a model of glioblastoma

Temozolomide (TMZ) resistance is a major clinical challenge for glioblastoma (GBM). O⁶-methylguanine-DNA methyltransferase (MGMT) mediated DNA damage repair is a key mechanism for TMZ resistance. However, MGMT-null GBM patients remain resistant to TMZ, and the process for resistance evolution is largely unknown. Here, we developed an acquired TMZ resistant xenograft model using serial implantation of MGMT-hypermethylated U87 cells, allowing the extraction of stable, TMZ resistant (TMZ-R) tumors and primary cells. The derived tumors and cells exhibited stable multidrug resistance both in vitro and in vivo. Functional experiments, as well as single-cell RNA sequencing (scRNA-seq), indicated that TMZ treatment induced cellular heterogeneity including quiescent cancer stem cells (CSCs) in TMZ-R tumors. A subset of these were labeled by NES⁺/SOX2⁺/CADM1⁺ and demonstrated significant advantages for drug resistance. Further study revealed that Epidermal Growth Factor Receptor (EGFR) deficiency and diminished downstream signaling may confer this triple positive CSCs subgroup’s quiescent phenotypes and chemoresistance. Continuous EGF treatment improved the chemosensitivity of TMZ-R cells both in vitro and in vivo, mechanically reversing cell cycle arrest and reduced drug uptake. Further, EGF treatment of TMZ-R tumors favorably normalized the response to TMZ in combination therapy. Here, we characterize a unique subgroup of CSCs in MGMT-null experimental glioblastoma, identifying EGF + TMZ therapy as a potential strategy to overcome cellular quiescence and TMZ resistance, likely endowed by deficient EGFR signaling.