Human Medulloblastoma Cell Lines Research Articles

Abstract 3156: Unveiling the functional role of HDGFRP3 in pediatric medulloblastoma: Implications for growth, progression, and radioresistance

Abstract Introduction: Medulloblastoma (MB) is the most common malignant brain cancer in children. Although long-term survival has improved in recent years, only a modest percentage of patients survive high-risk disease. The quality of life for those who survive is substantially reduced due to the high toxicity associated with the radiation and chemotherapy. Therefore, identification of safe and potent therapeutic approaches that can sensitize the therapy response in MB without inducing toxicity will lead to more efficient treatment of MB patients. We recently discovered that targeting HDGFRP3, a protein highly expressed in MB, and can block MB growth and improve the efficacy of radiation therapy. HDGFRP3 is a multifaceted protein that plays important roles in diverse cellular processes. Our investigation sheds light on the functional role of HDGFRP3 in MB, focusing on its involvement in growth, progression, and radioresistance where we report HDGFRP3 as a novel oncogenic driver of these processes. Methods: Human MB cell lines (DAOY, D556, D425, and HDMB03) were purchased from the American Type Culture Collection and cultured in standard medium. MB cancer cells were transfected with siRNA specific to HDGFRP3. These knockdown cells were analyzed for cell viability, migration, invasion, colony formation, stemness, cell cycle, apoptosis assays for functional role assessment. Real-time qPCR and western blotting were performed to validate the downstream targets of HDGFRP3 in MB models. Results: Our findings demonstrate that HDGFRP3 functions as an oncogene in MB, as its overexpression promotes cancer growth, while its depletion results in decreased tumor growth in MB models. Furthermore, we provide evidence that HDGFRP3 knockdown results in decreased migratory potential of MB cells as well as a reduction in stemness. Interestingly, HDGFRP3 depletion improved the efficacy of standard of care radiation in multiple MB models. At present, in vivo studies are validate the oncogenic role of HDGFRP3 in preclinical animal models of MB. Conclusions: In conclusion, our data suggests HDGFRP3 facilitates MB growth, progression, stemness as well as resistance to radiation therapy. Our comprehensive investigation into HDGFRP3's functional role in MB presented here provides valuable insights into its potential as a therapeutic target and opens avenues for further research into novel treatment strategies for the pediatric brain tumors. Citation Format: Saif S. Nirzhor, Prabhakar Pitta Venkata, Shahad Abdulsahib, Panneerdoss Subbarayalu, Santosh Timilsina, Manjeet K. Rao. Unveiling the functional role of HDGFRP3 in pediatric medulloblastoma: Implications for growth, progression, and radioresistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3156.

Nanodiamond Effects on Cancer Cell Radiosensitivity: The Interplay between Their Chemical/Physical Characteristics and the Irradiation Energy

Nanoparticles are being increasingly studied to enhance radiation effects. Among them, nanodiamonds (NDs) are taken into great consideration due to their low toxicity, inertness, chemical stability, and the possibility of surface functionalization. The objective of this study is to explore the influence of the chemical/physical properties of NDs on cellular radiosensitivity to combined treatments with radiation beams of different energies. DAOY, a human radioresistant medulloblastoma cell line was treated with NDs—differing for surface modifications [hydrogenated (H-NDs) and oxidized (OX-NDs)], size, and concentration—and analysed for (i) ND internalization and intracellular localization, (ii) clonogenic survival after combined treatment with different radiation beam energies and (iii) DNA damage and apoptosis, to explore the nature of ND–radiation biological interactions. Results show that chemical/physical characteristics of NDs are crucial in determining cell toxicity, with hydrogenated NDs (H-NDs) decreasing either cellular viability when administered alone, or cell survival when combined with radiation, depending on ND size and concentration, while OX-NDs do not. Also, irradiation at high energy (γ-rays at 1.25 MeV), in combination with H-NDs, is more efficient in eliciting radiosensitisation when compared to irradiation at lower energy (X-rays at 250 kVp). Finally, the molecular mechanisms of ND radiosensitisation was addressed, demonstrating that cell killing is mediated by the induction of Caspase-3-dependent apoptosis that is independent to DNA damage. Identifying the optimal combination of ND characteristics and radiation energy has the potential to offer a promising therapeutic strategy for tackling radioresistant cancers using H-NDs in conjunction with high-energy radiation.

The Sonic hedgehog pathway inhibitor GDC0449 induces autophagic death in human Medulloblastoma Daoy cells

ABSTRACT Medulloblastoma (MB) is a frequently occurring malignant brain tumor in children, and many of these tumors are identified by the abnormal activation of the Sonic Hedgehog (SHH) pathway. Although the Shh inhibitor GDC0449 initially shows some effectiveness in certain tumors, they eventually recur due to drug resistance mechanisms, highlighting the need for new treatment options. In this study, we explore whether GDC0449 induces autophagy in the human MB cell lines. To investigate the ultrastructural pathology changes of GDC0449-treated Daoy and D283 cells, we employed Transmission Electron Microscopy (TEM) technology to identify the expression of autophagic vacuoles. Our results indicate that GDC0449 only increases autophagy in Daoy cells by increasing the LC3-II/LC3-I ratio and autophagosome formation.We also analyzed Beclin1, LC3, Bax, and Cleaved-caspase3 protein and mRNA expression levels of autophagic and apoptotic markers using fluorescence confocal microscopy, RT-PCR, and Western blot. We found that cell autophagy and apoptosis increased in a dose-dependent manner with GDC0449 treatment. Additionally, we observed increased mammalian target of rapamycin (mTOR) phosphorylation and decreased protein kinase B (AKT/PKB), Ribosomal Protein S6, eIF4E-binding protein (4EBP1) phosphorylation in GDC0449-treated Daoy cells. It was observed that inhibiting autophagy using Beclin1 siRNA significantly blocked the apoptosis-inducing effects of GDC0449, suggesting that GDC0449 mediates its apoptotic effects by inducing autophagy.Our data suggests that GDC0449 inhibits the growth of human MB Daoy cells by autophagy-mediated apoptosis. The mechanism of GDC0449-induced autophagy in Daoy cells may be related to the inhibition of the PI3K/AKT/mTOR signaling pathway.

MDB-33. REST AND USP37 CONTROL THE MTORC1-AUTOPHAGY AXIS IN MEDULLOBLASTOMA BY REGULATING RAPTOR DEGRADATION

Abstract The RE1 Silencing Transcription Factor (REST) is a repressor of neurogenesis. Its expression is elevated in the pediatric brain tumor medulloblastoma (MB) and correlates with poor patient prognosis. RNAseq analyses of MB tumors identified significant differences in the expression of genes associated with autophagy between high- and low-REST expressing samples. Microscopy and biochemical analyses of isogenic high- and low-REST human MB cell lines confirmed REST-dependent changes in autophagy, suggesting that REST controls the process. We had previously shown that REST regulates the activity of the mammalian target of rapamycin complex 2 (mTORC2). However, whether REST controls the mTORC1 pathway, a negative regulator for autophagy, is still unknown. mTORC1 is known to block autophagy initiation by phosphorylation of UNC51-like autophagy activating kinases (ULK)1/2 and the Phosphatidyl Kinase 3 subunit C3 (PIK3C3) to prevent global expression of lysosomal and autophagy genes through Transcription Factor EB (TFEB) phosphorylation. The above findings led us to investigate if REST controls autophagy through modulation of mTORC1 activity in MBs and to understand the underlying mechanisms. Biochemical studies demonstrated that REST elevation promotes proteasomal degradation of Raptor, a key regulatory sub-unit of the mTOR1 complex, to induce autophagy. Specifically, we discovered that Raptor is a novel substrate of the deubiquitylase USP37, which we previously identified as a REST-target gene product. These data show that REST drives autophagy by silencing USP37, destabilizing Raptor, and blocking mTORC1 activity. Finally, the pharmacological blockade of autophagy caused a decline in MB cell growth in a REST-dependent manner, indicating that REST-dependent autophagy is a pro-survival mechanism in MBs.

Investigation of Bioactivity of Estragole Isolated from Basil Plant on Brain Cancer Cell Lines Using Nuclear Method.

In recent years, there has been a significant increase in studies investigating the potential use of plant-origin products in the treatment and diagnosis of different types of cancer. In this study, Estragole (EST) was isolated from basil leaves via ethanolic extraction using an 80% ethanol concentration. The isolation process was performed using the High Performance Liquid Chromatography (HPLC) method. The EST isolated from the basil plant was radiolabeled with 131I using the iodogen method. Quality control studies of the radiolabeled EST (131IEST) were carried out by using Thin Layer Radio Chromatography (TLRC). Next, in vitro cell, culture studies were done to investigate the bio-affinity of plant-originated EST labeled with 131I on human medulloblastoma (DAOY) and human glioblastoma-astrocytoma (U-87 MG) cell lines. Finally, the cytotoxicity of EST was determined, and cell uptake of 131I-EST was investigated on cancer cell lines by incorporation studies. As a result of these studies, it has been shown that 131I-EST has a significant uptake on the brain cells. This result is very satisfying, and it has encouraged us to do in vivo studies for the molecule in the future.

IGFBP2 promotes proliferation and cell migration through STAT3 signaling in Sonic hedgehog medulloblastoma

Medulloblastoma (MB) is the most common pediatric brain malignancy and is divided into four molecularly distinct subgroups: WNT, Sonic Hedgehog (SHHp53mut and SHHp53wt), Group 3, and Group 4. Previous reports suggest that SHH MB features a unique tumor microenvironment compared with other MB groups. To better understand how SHH MB tumor cells interact with and potentially modify their microenvironment, we performed cytokine array analysis of culture media from freshly isolated MB patient tumor cells, spontaneous SHH MB mouse tumor cells and mouse and human MB cell lines. We found that the SHH MB cells produced elevated levels of IGFBP2 compared to non-SHH MBs. We confirmed these results using ELISA, western blotting, and immunofluorescence staining. IGFBP2 is a pleiotropic member of the IGFBP super-family with secreted and intracellular functions that can modulate tumor cell proliferation, metastasis, and drug resistance, but has been understudied in medulloblastoma. We found that IGFBP2 is required for SHH MB cell proliferation, colony formation, and cell migration, through promoting STAT3 activation and upregulation of epithelial to mesenchymal transition markers; indeed, ectopic STAT3 expression fully compensated for IGFBP2 knockdown in wound healing assays. Taken together, our findings reveal novel roles for IGFBP2 in SHH medulloblastoma growth and metastasis, which is associated with very poor prognosis, and they indicate an IGFBP2-STAT3 axis that could represent a novel therapeutic target in medulloblastoma.

Euxanthone Suppresses the Proliferation, Migration and Invasion of Human Medulloblastoma Cells by Inhibiting the RANK/RANKL Pathway

Background: Euxanthone is a plant-based flavonoid that is mostly isolated from a Chinese medicinal plant, Polygala caudate. This study was designed to evaluate the anticancer effects of euxanthone against human medulloblastoma cells. Materials and Methods: Cell viability was evaluated by CCK-8 and EdU assays. Apoptotic cell percentage was determined by annexin V/PI assay. The mRNA expression was determined by qRT-PCR. Wound healing and transwell assays were used to assess cell migration and invasion. Results: The results revealed aberrant activation of RANK/RANKL pathway in human medulloblastoma tissues and cell lines. Euxanthone suppressed the proliferation of the D425 medulloblastoma cells with comparatively lower cytotoxic effects against the normal human cerebellar granule cells. The IC50 of euxanthone against the D425 cells was found to be 10 µM. Interestingly, silencing of receptor activator of nuclear factor kβ (RANK) could also suppress the proliferation of the D425 cells via induction of apoptosis. Nonetheless, overexpression of RANK could abolish the cytotoxic effects of euxanthone on the D425 cells. Finally, wound-heal and transwell assay showed that euxanthone suppressed the migration and invasion of the D425 medulloblastoma cells. Conclusion: Collectively, the results revealed the anticancer effects of euxanthone against human medulloblastoma cells via RANK/RANKL pathway. These results suggest the potential of euxanthone as a lead molecule in the development of chemotherapy for medulloblastoma.

Targeting H3K27me3 demethylase to inhibit Shh signaling and cholesterol metabolism in medulloblastoma growth.

Previously we uncovered the epigenetic regulation of medulloblastoma that low levels of H3K27me3 are required for Shh target gene expression and medulloblastoma growth. Since Jmjd3, an H3K27me3 demethylase, is responsible for maintaining low H3K27me3 at Shh target genes, targeting Jmjd3 could be an efficient way to inhibit Shh signaling and medulloblastoma growth. Here we show that the small molecule GSK-J4, an inhibitor of Jmjd3, significantly inhibited the expression of Shh target genes in Shh responsive cell models and primary cerebellar granule neuron precursors. GSK-J4 also significantly reduced the growth of primary Shh medulloblastoma cultures. Treating human medulloblastoma cell line DaoY by GSK-J4 led to cell cycle arrest at G0/G1 phase with decreased cells in S-phase. Tumor cell proliferation was significantly inhibited by GSK-J4 treatment. Gene expression analyses showed that GSK-J4 additionally constrained the expression of key genes in cholesterol biosynthesis. Our results highlight the possibility that targeting H3K27me3 demethylase Jmjd3 with GSK-J4 to inhibit Shh signaling and cholesterol metabolism is a potential application to treat Shh medulloblastoma.

CD155 is a putative therapeutic target in medulloblastoma.

Medulloblastoma is the most common pediatric malignant brain tumor, consisting of four molecular subgroups (WNT, SHH, Group 3, Group 4) and 12 subtypes. Expression of the cell surface poliovirus receptor (PVR), CD155, is necessary for entry of the viral immunotherapeutic agent, PVSRIPO, a polio:rhinovirus chimera. CD155, physiologically expressed in the mononuclear phagocytic system, is widely expressed ectopically in solid tumors. The objective of this study is to elucidate CD155 expression as both a receptor for PVSRIPO and a therapeutic target in medulloblastoma. PVR mRNA expression was determined in several patient cohorts and human medulloblastoma cell lines. Patient samples were also analyzed for CD155 expression using immunohistochemistry and cell lines were analyzed using Western Blots. CD155 was blocked using a monoclonal antibody and cell viability, invasion, and migration were assessed. PVR mRNA expression was highest in the WNT subgroup and lowest in Group 4. PVR expression in the subgroups of medulloblastoma were similar to other pediatric brain and non-brain tumors. PVR expression was largely not associated with subgroup or subtype. Neither PVR protein expression intensity nor frequency were associated with overall survival. PVR expression was elevated in Group 3 patients with metastases but there was no difference in paired primary and metastatic medulloblastoma. Blocking PVR resulted in dose-dependent cell death, decreased invasion in vitro, and modestly inhibited cell migration. CD155 is expressed across medulloblastoma subgroups and subtypes. Blocking CD155 results in cell death and decreased cellular invasion. This study provides rationale for CD155-targeting agents including PVSRIPO and antibody-mediated blockade of CD155.

PATH-09. Liquid biopsy of cerebrospinal fluid enables detecting and monitoring ofMYC/MYCN amplification in pediatric CNS malignancies

Abstract In the era of precision oncology, rapid molecular profiling as well as continuous monitoring of response to treatment or relapse are of increasing importance. We investigated digital droplet (dd)PCR for cerebrospinal fluid (CSF) derived cell-free (cf)DNA detection as a new method for rapid diagnosing of MYC/MYCN amplification in CNS malignancies - a patient collective with a dismal prognosis. Wet lab validated ddPCR probes for MYC were first investigated in D425 cells, a human medulloblastoma cell line with confirmed MYC amplification. Results of the methylation array of patients with stored CSF/serum samples (-80°C) were screened for patients with MYC/MYCN amplification. Five patients with medulloblastoma (group 3/4) and MYC-amplification and one patient with a diffuse glioma and MYCN-amplification were included in this study. ddPCR was performed on cfDNA isolated from CSF or serum. MYC amplification was detected by ddPCR in 28/33 (85%) CSF samples, with 4/5 negative samples being from one patient, and only one sample showing an unsuccessful analysis. MYC amplification was detectable in all longitudinal samples in 4/5 patients. 1/1 sample from the patient with MYCN amplific ation was positive in ddPCR. We were not able to detect MYC amplification in serum samples. Importantly, a turn-around time of only six hours from sample thawing/acquisition to result generation was easily achievable. Concluding, detection of MYC/MYCN-amplification in CSF by ddPCR is feasible in the clinical setting and allows for a rapid molecular diagnosis. MYC-amplification was constantly detectable in 4/5 patients with longitudinal CSF samples, which is in-line with the tumor burden our patients suffered from. Interestingly, the detectability in the patient’s serum was low, presumably due to the lower percentage of cell-free tumor (ct)DNA in serum when compared to CSF. Our results render ddPCR as a promising tool for bed-side molecular diagnosis and disease monitoring.

494 Enhanced Senescence Phenotype In Human Medulloblastoma via Protein Phosphatase 2A Inhibition and Radiation Therapy

INTRODUCTION: Medulloblastoma is the most common malignant pediatric brain tumor. Radiation(RT) is a part of standard care but causes significant neurocognitive impairment. Strategies to sensitize RT is critical to improving the quality of life and long-term survival of patients. Previous studies show that inhibition of protein-phosphatase 2A(PP2A)–a ubiquitous serine/threonine phosphatase–enhanced sensitivity to RT in multiple brain tumor xenografts. However, the mechanism behind enhanced radio-cytotoxicity is poorly understood. We hypothesize that PP2A inhibition combined with RT will increase cytoplasmic double-stranded DNA (dsDNA) and induce cGAS-cGAMP-STING signaling, promoting cellular senescence and thereby decreasing tumor growth. METHODS: D425-WT, a human group-3 medulloblastoma cell line, was used to generate a CRISPR sgPP2A knock out, D425-KO. We radiated WT and KO cells in vitro, quantified dsDNA in cytoplasmic extract using dsDNA Assay kit, and measured cGAMP levels in whole cell lysate using ELISA. Through FACS, we quantified the proportion of b-gal-expressing senescent cells. We measured protein expression of senescence markers (p21, p16, g-h2aX) by Western blot(WB). Finally, we injected D425 WT or KO cells orthotopically into cerebellum of nude NU/J mice followed by RT (10Gy) 3 days post-injection and monitored survival. RESULTS: In response to RT, D425-KO compared to WT showed significant increase in cytoplasmic dsDNA and intracellular cGAMP--a cyclic di-nucleotide STING agonist. There was also an increase in b-gal+ senescent cells and senescence markers expression in WB. In vivo, PP2AKO alone extended longevity, but PP2AKO with RT further prolonged survival compared to KO or RT alone. CONCLUSION: PP2A inhibition enhances RT induced cytosolic dsDNA damage and STING activation, promoting cellular senescence in vitro and sensitivity to RT in vivo.

MiR-497 promotes the migration and invasion of human medulloblast Daoy cell line through targeted regulation of ARHGDIA in vitro

ObjectivesTo further investigate the effects of miR-497 on the biological behavior of human medulloblastoma cell line in vitro. MethodsHuman medulloblastoma cell lines, Daoy and D341, were used in this study, and the miR-497 expression in the cells was measured by Quantitative PCR with fluorescence. The Daoy cells were divided into the mimics group (Daoy cells treated with mimics), inhibitor group (Daoy cells treated with inhibitor), normal Daoy cells, ARHGDIA siRNA group (Daoy cells transfected with ARHGDIA siRNA), ARHGDIA control group (Daoy cells did not receive any treatment), and negative control group (normal cells transfected with ARHGDIA siRNA). The expression of miR-497 and ARHGDIA mRNA was measured by Quantitative PCR with fluorescence, while the level of ARHGDIA protein was measured by Western blot. The binding capability of ARHGDIA and miR-497 was assessed by luciferase assay, the migration of cells was assessed by wound healing assay, and the invasion of cells was assessed by Transwell assay. ResultsCompared to D341 cells, the miR-497 level was significantly higher in the Daoy cells (P < 0.01). The dual-luciferase reporter assay showed that miR-497 targets ARHGDIA. Transfecting the normal Daoy cells with miR-497 mimics significantly reduced the expression of ARHGDIA protein (P < 0.05), while transfecting normal Daoy cells with miR-497 inhibitor significantly increased the expression of ARHGDIA protein (P < 0.05). Consequently, the migration and invasion capability of cells increased significantly after transfection with miR-497 mimic (P < 0.05), and decreased significantly after transfection with miR-497 inhibitor (P < 0.05). In addition, the migration and invasion capabilities of the cells also increased significantly after transfection with ARHGDIA siRNA (P < 0.05). ConclusionsmiR-497/ARHGDIA axis participates in the in vitro migration and invasion of human medulloblastoma cell lines.

Cytotoxic effects and tolerability of gemcitabine and axitinib in a xenograft model for c-myc amplified medulloblastoma

Medulloblastoma is the most common high-grade brain tumor in childhood. Medulloblastomas with c-myc amplification, classified as group 3, are the most aggressive among the four disease subtypes resulting in a 5-year overall survival of just above 50%. Despite current intensive therapy regimens, patients suffering from group 3 medulloblastoma urgently require new therapeutic options. Using a recently established c-myc amplified human medulloblastoma cell line, we performed an in-vitro-drug screen with single and combinatorial drugs that are either already clinically approved or agents in the advanced stage of clinical development. Candidate drugs were identified in vitro and then evaluated in vivo. Tumor growth was closely monitored by BLI. Vessel development was assessed by 3D light-sheet-fluorescence-microscopy. We identified the combination of gemcitabine and axitinib to be highly cytotoxic, requiring only low picomolar concentrations when used in combination. In the orthotopic model, gemcitabine and axitinib showed efficacy in terms of tumor control and survival. In both models, gemcitabine and axitinib were better tolerated than the standard regimen comprising of cisplatin and etoposide phosphate. 3D light-sheet-fluorescence-microscopy of intact tumors revealed thinning and rarefication of tumor vessels, providing one explanation for reduced tumor growth. Thus, the combination of the two drugs gemcitabine and axitinib has favorable effects on preventing tumor progression in an orthotopic group 3 medulloblastoma xenograft model while exhibiting a favorable toxicity profile. The combination merits further exploration as a new approach to treat high-risk group 3 medulloblastoma.

Steroidal alkaloids isolated from Veratrum grandiflorum Loes. as novel Smoothened inhibitors with anti-proliferation effects on DAOY medulloblastoma cells

Constitutive activation of Hedgehog (Hh) pathway is intimately related with the occurrence and development of several malignancies, such as medulloblastoma (MB) and other tumors. Therefore, small molecular inhibitors of Hh pathway are urgently needed. In this study, three new steroidal alkaloids, ⊿5 (20R, 24R) 23-oxo-24-methylsolacongetidine, ⊿5 (20S, 24R) 23-oxo-24-methylsolacongetidine and veralinine 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-D-glucopyranoside, together with six known alkaloids, 20-epi-verazine, verazine, protoverine 15-(l)-2′-methylbutyrate, jervine, veramarine and β1-chaconine, were isolated and determined from Veratrum grandiflorum Loes. The dual-luciferase bioassay indicated that all compounds exhibited significant inhibitions of Hh pathway with IC50 values of 0.72–14.31 μM against Shh-LIGHT 2 cells. To determine whether these Hh pathway inhibitors act with the Smoothened (Smo) protein, which is an important oncoprotein and target for this pathway, BODIPY-cyclopamine (BC) competitive binding assay was preferentially performed. Compared with BC alone, all compounds obviously reduced the fluorescence intensities of BC binding with Smo in Smo-overexpression HEK293T cells through fluorescence microscope and flow cytometer. By directly interacting with Smo, it revealed that they were actually novel natural Smo inhibitors. Then, their anti-tumor effects were investigated against the human MB cell line DAOY, which is a typical pediatric brain tumor cells line with highly expressed Hh pathway. Interestingly, most of compounds had slight proliferation inhibitions on DAOY cells after treatment for 24 h same as vismodegib, while β1-chaconine showed the strongest inhibitory effect on the growth of DAOY with IC50 value of 5.35 μM. In conclusion, our studies valuably provide several novel natural Smo inhibitors for potential targeting treatment of Hh-dependent tumors.

Deficiency of Ku Induces Host Cell Exploitation in Human Cancer Cells.

Cancer metastasis is the major cause of death from cancer (Massague and Obenauf, 2016; Steeg, 2016). The extensive genetic heterogeneity and cellular plasticity of metastatic tumors set a prime barrier for the current cancer treatment protocols (Boumahdi and de Sauvage, 2020). In addition, acquired therapy resistance has become an insurmountable obstacle that abolishes the beneficial effects of numerous anti-cancer regimens (De Angelis et al., 2019; Boumahdi and de Sauvage, 2020). Here we report that deficiency of Ku leads to the exploitation of host cells in human cancer cell line models. We found that, upon conditional deletion of XRCC6 that codes for Ku70, HCT116 human colorectal cancer cells gain a parasitic lifestyle that is characterized by the continuous cycle of host cell exploitation. We also found that DAOY cells, a human medulloblastoma cell line, innately lack nuclear Ku70/Ku86 proteins and utilize the host-cell invasion/exit mechanism for maintenance of their survival, similarly to the Ku70 conditionally-null HCT116 cells. Our study demonstrates that a functional loss of Ku protein promotes an adaptive, opportunistic switch to a parasitic lifestyle in human cancer cells, providing evidence for a previously unknown mechanism of cell survival in response to severe genomic stress. We anticipate that our study will bring a new perspective for understanding the mechanisms of cancer cell evolution, leading to a shift in the current concepts of cancer therapy protocols directed to the prevention of cancer metastasis and therapy resistance.

Novel Glutamine Antagonist JHU395 Suppresses MYC-Driven Medulloblastoma Growth and Induces Apoptosis.

Medulloblastoma is the most common malignant pediatric brain tumor. Amplification of c-MYC is a hallmark of a subset of poor-prognosis medulloblastoma. MYC upregulates glutamine metabolism across many types of cancer. We modified the naturally occurring glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON) by adding 2 promoeities to increase its lipophilicity and brain penetration creating the prodrug isopropyl 6-diazo-5-oxo-2-(((phenyl (pivaloyloxy) methoxy) - carbonyl) amino) hexanoate, termed JHU395. This prodrug was shown to have a 10-fold improved CSF-to-plasma ratio and brain-to-plasma ratio relative to DON. We hypothesized that JHU395 would have superior cell penetration compared with DON and would effectively and more potently kill MYC-expressing medulloblastoma. JHU395 treatment caused decreased growth and increased apoptosis in multiple human high-MYC medulloblastoma cell lines at lower concentrations than DON. Parenteral administration of JHU395 in Nu/Nu mice led to the accumulation of micromolar concentrations of DON in brain. Treatment of mice bearing orthotopic xenografts of human MYC-amplified medulloblastoma with JHU395 increased median survival from 26 to 45 days compared with vehicle control mice (p < 0.001 by log-rank test). These data provide preclinical justification for the ongoing development and testing of brain-targeted DON prodrugs for use in medulloblastoma.

The Expression of the Cancer-Associated lncRNA Snhg15 Is Modulated by EphrinA5-Induced Signaling.

The Eph receptor tyrosine kinases and their respective ephrin-ligands are an important family of membrane receptors, being involved in developmental processes such as proliferation, migration, and in the formation of brain cancer such as glioma. Intracellular signaling pathways, which are activated by Eph receptor signaling, are well characterized. In contrast, it is unknown so far whether ephrins modulate the expression of lncRNAs, which would enable the transduction of environmental stimuli into our genome through a great gene regulatory spectrum. Applying a combination of functional in vitro assays, RNA sequencing, and qPCR analysis, we found that the proliferation and migration promoting stimulation of mouse cerebellar granule cells (CB) with ephrinA5 diminishes the expression of the cancer-related lncRNA Snhg15. In a human medulloblastoma cell line (DAOY) ephrinA5 stimulation similarly reduced SNHG15 expression. Computational analysis identified triple-helix-mediated DNA-binding sites of Snhg15 in promoters of genes found up-regulated upon ephrinA5 stimulation and known to be involved in tumorigenic processes. Our findings propose a crucial role of Snhg15 downstream of ephrinA5-induced signaling in regulating gene transcription in the nucleus. These findings could be potentially relevant for the regulation of tumorigenic processes in the context of glioma.

Microsecond Pulsed Electric Fields: An Effective Way to Selectively Target and Radiosensitize Medulloblastoma Cancer Stem Cells

Cancer stem cells constitute an endless reserve for the maintenance and progression of tumors, and they could be the reason for conventional therapy failure. New therapeutic strategies are necessary to specifically target them. In this context, microsecond pulsed electric fields have been selected to expose D283Med cells, a human medulloblastoma cell line resulted to be rich in cancer stem cells, and normal human astrocytes. We analyzed invitro different endpoints at different times after microsecond pulsed electric field exposure, such as permeabilization, reactive oxygen species generation, cell viability/proliferation, cell cycle, and clonogenicity, as well as the expression of different genes involved in cell cycle, apoptosis, and senescence. Furthermore, the response of D283Med cells exposed to microsecond pulsed electric fields was validated invivo in a heterotopic mouse xenograft model. Our invitro results showed that a specific pulse protocol (ie, 0.3 MV/m, 40 μs, 5 pulses) was able to induce irreversible membrane permeabilization and apoptosis exclusively in medulloblastoma cancer stem cells. In the surviving cells, reactive oxygen species generation was observed, together with a transitory G2/M cell-cycle arrest with a senescence-associated phenotype via the upregulation of GADD45A. Invivo results, after pulsed electric field exposure, demonstrated a significant tumor volume reduction with no eradication of tumor mass. In conjunction, we verified the efficacy of electric pulse pre-exposure followed by ionizing irradiation invivo to enable complete inhibition of tumor growth. Our data reveal novel therapeutic options for the targeting of medulloblastoma cancer stem cells, indicating nonionizing pulsed electric field pre-exposure as an effective means to overcome the radioresistance of cancer stem cells.

Small-molecule screen reveals synergy of cell cycle checkpoint kinase inhibitors with DNA-damaging chemotherapies in medulloblastoma.

Medulloblastoma (MB) consists of four core molecular subgroups with distinct clinical features and prognoses. Treatment consists of surgery, followed by radiotherapy and cytotoxic chemotherapy. Despite this intensive approach, outcome remains dismal for patients with certain subtypes of MB, namely, MYC-amplified Group 3 and TP53-mutated SHH. Using high-throughput assays, six human MB cell lines were screened against a library of 3208 unique compounds. We identified 45 effective compounds from the screen and found that cell cycle checkpoint kinase (CHK1/2) inhibition synergistically enhanced the cytotoxic activity of clinically used chemotherapeutics cyclophosphamide, cisplatin, and gemcitabine. To identify the best-in-class inhibitor, multiple CHK1/2 inhibitors were assessed in mice bearing intracranial MB. When combined with DNA-damaging chemotherapeutics, CHK1/2 inhibition reduced tumor burden and increased survival of animals with high-risk MB, across multiple different models. In total, we tested 14 different models, representing distinct MB subgroups, and data were validated in three independent laboratories. Pharmacodynamics studies confirmed central nervous system penetration. In mice, combination treatment significantly increased DNA damage and apoptosis compared to chemotherapy alone, and studies with cultured cells showed that CHK inhibition disrupted chemotherapy-induced cell cycle arrest. Our findings indicated CHK1/2 inhibition, specifically with LY2606368 (prexasertib), has strong chemosensitizing activity in MB that warrants further clinical investigation. Moreover, these data demonstrated that we developed a robust and collaborative preclinical assessment platform that can be used to identify potentially effective new therapies for clinical evaluation for pediatric MB.

MT1 and MT2 melatonin receptors play opposite roles in brain cancer progression.

Primary brain tumors remain among the deadliest of all cancers. Glioma grade IV (glioblastoma), the most common and malignant type of brain cancer, is associated with a 5-year survival rate of < 5%. Melatonin has been widely reported as an anticancer molecule, and we have recently demonstrated that the ability of gliomas to synthesize and accumulate this indolamine in the surrounding microenvironment negatively correlates with tumor malignancy. However, our understanding of the specific effects mediated through the activation of melatonin membrane receptors remains limited. Thus, here we investigated the specific roles of MT1 and MT2 in gliomas and medulloblastomas. Using the MT2 antagonist DH97, we showed that MT1 activation has a negative impact on the proliferation of human glioma and medulloblastoma cell lines, while MT2 activation has an opposite effect. Accordingly, gliomas have a decreased mRNA expression of MT1 (also known as MTNR1A) and an increased mRNA expression of MT2 (also known as MTNR1B) compared to the normal brain cortex. The MT1/MT2 expression ratio negatively correlates with the expression of cell cycle-related genes and is a positive prognostic factor in gliomas. Notably, we showed that functional selective drugs that simultaneously activate MT1 and inhibit MT2 exert robust anti-tumor effects in vitro and in vivo, downregulating the expression of cell cycle and energy metabolism genes in glioma stem-like cells. Overall, we provided the first evidence regarding the differential roles of MT1 and MT2 in brain tumor progression, highlighting their relevance as druggable targets. KEY MESSAGES: • MT1 impairs while MT2 promotes the proliferation of glioma and medulloblastoma cell lines. • Gliomas have a decreased expression of MT1 and an increased expression of MT2 compared to normal brain cortex. • Tumors with a high MT1/MT2 expression ratio have significantly better survival rates. • Functional selective drugs that simultaneously activate MT1 and inhibit MT2 downregulate the expression of cell cycle and energy metabolism genes in glioma stem-like cells and exert robust anti-tumor effects in vivo.