α5-GABAA receptors negatively regulate MYC-amplified medulloblastoma growth

Phytochemical Modulation of Ion Channels in Oncologic Symptomatology and Treatment

Modern chemotherapies offer a broad approach to cancer treatment but eliminate both cancer and non-cancer cells indiscriminately and, thus, are associated with a host of side effects. Advances in precision oncology have brought about new targeted therapeutics, albeit mostly limited to a subset of patients with an actionable mutation. They too come with side effects and, ultimately, 'self-resistance' to the treatment. There is recent interest in the modulation of ion channels, transmembrane proteins that regulate the flow of electrically charged molecules in and out of cells, as an approach to aid treatment of cancer. Phytochemicals have been shown to act on ion channels with high specificity regardless of the tumor's genetic profile. This paper explores the use of phytochemicals in cancer symptom management and treatment.

GABA(A) receptor activation drives GABARAP-Nix mediated autophagy to radiation-sensitize primary and brain-metastatic lung adenocarcinoma tumors

In non-small cell lung cancer (NSCLC) treatment, targeted therapies benefit only a subset of NSCLC, while radiotherapy responses are not durable and toxicity limits therapy. We find that a GABA(A) receptor activator, AM-101, impairs viability and clonogenicity of NSCLC primary and brain metastatic cells. Employing an ex vivo 'chip', AM-101 is as efficacious as the chemotherapeutic docetaxel, which is used with radiotherapy for advanced-stage NSCLC. In vivo , AM-101 potentiates radiation, including conferring a survival benefit to mice bearing NSCLC intracranial tumors. GABA(A) receptor activation stimulates a selective-autophagic response via multimerization of GABA(A) Receptor-Associated Protein (GABARAP), stabilization of mitochondrial receptor Nix, and utilization of ubiquitin-binding protein p62. A targeted-peptide disrupting Nix binding to GABARAP inhibits AM-101 cytotoxicity. This supports a model of GABA(A) receptor activation driving a GABARAP-Nix multimerization axis triggering autophagy. In patients receiving radiotherapy, GABA(A) receptor activation may improve tumor control while allowing radiation dose de-intensification to reduce toxicity.

Highlights

Activating GABA(A) receptors intrinsic to lung primary and metastatic brain cancer cells triggers a cytotoxic response. GABA(A) receptor activation works as well as chemotherapeutic docetaxel in impairing lung cancer viability ex vivo . GABA(A) receptor activation increases survival of mice bearing lung metastatic brain tumors.A selective-autophagic response is stimulated by GABA(A) receptor activation that includes multimerization of GABARAP and Nix.Employing a new nanomolar affinity peptide that abrogates autophagosome formation inhibits cytotoxicity elicited by GABA(A) receptor activation.

Malignancies in Prader-Willi Syndrome: Results From a Large International Cohort and Literature Review

CONTEXT

Prader-Willi syndrome (PWS) is a complex disorder combining hypothalamic dysfunction, neurodevelopmental delay, hypotonia, and hyperphagia with risk of obesity and its complications. PWS is caused by the loss of expression of the PWS critical region, a cluster of paternally expressed genes on chromosome 15q11.2-q13. As life expectancy of patients with PWS increases, age-related diseases like malignancies might pose a new threat to health.

OBJECTIVE

To investigate the prevalence and risk factors of malignancies in patients with PWS and to provide clinical recommendations for cancer screening.

METHODS

We included 706 patients with PWS (160 children, 546 adults). We retrospectively collected data from medical records on past or current malignancies, the type of malignancy, and risk factors for malignancy. Additionally, we searched the literature for information about the relationship between genes on chromosome 15q11.2-q13 and malignancies.

RESULTS

Seven adults (age range, 18-55 years) had been diagnosed with a malignancy (acute lymphoblastic leukemia, intracranial hemangiopericytoma, melanoma, stomach adenocarcinoma, biliary cancer, parotid adenocarcinoma, and colon cancer). All patients with a malignancy had a paternal 15q11-13 deletion. The literature review showed that several genes on chromosome 15q11.2-q13 are related to malignancies.

CONCLUSION

Malignancies are rare in patients with PWS. Therefore, screening for malignancies is only indicated when clinically relevant symptoms are present, such as unexplained weight loss, loss of appetite, symptoms suggestive of paraneoplastic syndrome, or localizing symptoms. Given the increased cancer risk associated with obesity, which is common in PWS, participation in national screening programs should be encouraged.

The Neurodevelopmental and Molecular Landscape of Medulloblastoma Subgroups: Current Targets and the Potential for Combined Therapies

Medulloblastoma is the most common malignant pediatric brain tumor and is associated with significant morbidity and mortality in the pediatric population. Despite the use of multiple therapeutic approaches consisting of surgical resection, craniospinal irradiation, and multiagent chemotherapy, the prognosis of many patients with medulloblastoma remains dismal. Additionally, the high doses of radiation and the chemotherapeutic agents used are associated with significant short- and long-term complications and adverse effects, most notably neurocognitive delay. Hence, there is an urgent need for the development and clinical integration of targeted treatment regimens with greater efficacy and superior safety profiles. Since the adoption of the molecular-based classification of medulloblastoma into wingless (WNT) activated, sonic hedgehog (SHH) activated, group 3, and group 4, research efforts have been directed towards unraveling the genetic, epigenetic, transcriptomic, and proteomic profiles of each subtype. This review aims to delineate the progress that has been made in characterizing the neurodevelopmental and molecular features of each medulloblastoma subtype. It further delves into the implications that these characteristics have on the development of subgroup-specific targeted therapeutic agents. Furthermore, it highlights potential future avenues for combining multiple agents or strategies in order to obtain augmented effects and evade the development of treatment resistance in tumors.

GABAergic signaling beyond synapses: an emerging target for cancer therapy

Traditionally, γ-aminobutyric acid (GABA) is best known for its role as a primary inhibitory neurotransmitter reducing neuronal excitability in the mammalian central nervous system (CNS), thereby producing calming effects. However, an emerging body of data now supports a function for GABA beyond neurotransmission as a potent factor regulating cancer cell growth and metastasis, as well as the antitumor immune response, by shaping the tumor microenvironment (TME). Here, we review the current knowledge on GABA's effects on the function of tumor cells, tumor-immune interactions, and the underlying molecular mechanisms. Since altered GABAergic signaling is now recognized as a feature of certain types of solid tumors, we also discuss the potential of repurposing existing GABAergic agents as a new class of anticancer therapy.

GABAergic signaling as a potential therapeutic target in cancers

GABA is the most common inhibitory neurotransmitter in the vertebrate central nervous system. Synthesized by glutamic acid decarboxylase, GABA could specifically bind with two GABA receptors to transmit inhibition signal stimuli into cells: GABAA receptor and GABAB receptor. In recent years, emerging studies revealed that GABAergic signaling not only participated in traditional neurotransmission but was involved in tumorigenesis as well as regulating tumor immunity. In this review, we summarize the existing knowledge of the GABAergic signaling pathway in tumor proliferation, metastasis, progression, stemness, and tumor microenvironment as well as the underlying molecular mechanism. We also discussed the therapeutical advances in targeting GABA receptors to provide the theoretical basis for pharmacological intervention of GABAergic signaling in cancer treatment especially immunotherapy.

Case report: Somatic mutations in microtubule dynamics-associated genes in patients with WNT-medulloblastoma tumors

Medulloblastoma (MB) is the most common pediatric brain tumor which accounts for about 20% of all pediatric brain tumors and 63% of intracranial embryonal tumors. MB is considered to arise from precursor cell populations present during an early brain development. Most cases (~70%) of MB occur at the age of 1-4 and 5-9, but are also infrequently found in adults. Total annual frequency of pediatric tumors is about 5 cases per 1 million children. WNT-subtype of MB is characterized by a high probability of remission, with a long-term survival rate of about 90%. However, in some rare cases there may be increased metastatic activity, which dramatically reduces the likelihood of a favorable outcome. Here we report two cases of MB with a histological pattern consistent with desmoplastic/nodular (DP) and classic MB, and genetically classified as WNT-MB. Both cases showed putative causal somatic protein truncating mutations identified in microtubule-associated genes: ARID2, TUBB4A, and ANK3.

HOXA5 inhibits the proliferation of extrahepatic cholangiocarcinoma cells by enhancing MXD1 expression and activating the p53 pathway

Homeobox A5 (HOXA5) is a transcription factor in mammalian and can regulate cell differentiation, proliferation, and apoptosis as well as tumorigenesis. However, little is known on whether and how HOXA5 can regulate the malignant behaviors of cholangiocarcinoma. The methylation levels of HOXA5 were evaluated by methylation microarray and bisulfite sequencing PCR. HOXA5 expression in tissue samples was examined by immunohistochemistry and Western blot. The proliferation of tumor cells was assessed by CCK-8, EdU, and nude mouse tumorigenicity assays. The invasion, apoptosis and cell cycling of tumor cells were evaluated by Wound healing assay and flow cytometry. The interaction between HOXA5 and the MXD1 promoter was examined by CUT & Tag assay, luciferase reporter assay and chromatin immunoprecipitation. Hypermethylation in the HOXA5 promoter down-regulated HOXA5 expression in extrahepatic cholangiocarcinoma (ECCA) tissues, which was correlated with worse overall survival. HOXA5 overexpression significantly inhibited the proliferation and tumor growth. HOXA5 overexpression enhanced MXD1 expression by directly binding to the MXD1 promoter in ECCA cells. MXD1 overexpression inhibited the proliferation and tumor growth while MXD1 silencing abrogated the HOXA5-mediated proliferation inhibition. HOXA5 overexpression increased p53 protein expression in an MXD1-dependent manner. HOXA5 and MXD1 acted as tumor suppressors to inhibit the mitosis of ECCA cells by enhancing the p53 signaling. Our findings may uncover molecular mechanisms by which the HOXA5/MXD1 axis regulates the progression of ECCA, suggesting that the HOXA5/MXD1 may be therapeutic targets for ECCA.

An integrative analysis of DNA methylation and gene expression to predict lung adenocarcinoma prognosis

Background: Abnormal DNA methylation of gene promoters is an important feature in lung adenocarcinoma (LUAD). However, the prognostic value of DNA methylation remains to be further explored. Objectives. We sought to explore DNA methylation characteristics and develop a quantifiable criterion related to DNA methylation to improve survival prediction for LUAD patients.

Methods: Illumina Human Methylation450K array data, level 3 RNA-seq data and corresponding clinical information were obtained from TCGA. Cox regression analysis and the Akaike information criterion were used to construct the best-prognosis methylation signature. Receiver operating characteristic curve analysis was used to validate the prognostic ability of the DNA methylation-related feature score. qPCR was used to measure the transcription levels of the identified genes upon methylation.

Results: We identified a set of DNA methylation features composed of 11 genes (MYEOV, KCNU1, SLC27A6, NEUROD4, HMGB4, TACR3, GABRA5, TRPM8, NLRP13, EDN3 and SLC34A1). The feature score, calculated based on DNA methylation features, was independent of tumor recurrence and TNM stage in predicting overall survival. Of note, the combination of this feature score and TNM stage provided a better overall survival prediction than either of them individually. The transcription levels of all the hypermethylated genes were significantly increased after demethylation, and the expression levels of 3 hypomethylated proteins were significantly higher in tumor tissues than in normal tissues, as indicated by immunohistochemistry data from the Human Protein Atlas. Our results suggested that these identified genes with prognostic features were regulated by DNA methylation of their promoters.

Conclusion: Our studies demonstrated the potential application of DNA methylation markers in the prognosis of LUAD.

Ligand-Gated Ion Channels as Targets for Treatment and Management of Cancers

Ligand-gated ion channels are an ionotropic receptor subtype characterized by the binding of an extracellular ligand, followed by the transient passage of ions through a transmembrane pore. Ligand-gated ion channels are commonly subcategorized into three superfamilies: purinoreceptors, glutamate receptors, and Cys-loop receptors. This classification is based on the differing topographical morphology of the receptors, which in turn confers functional differences. Ligand-gated ion channels have a diverse spatial and temporal expression which implicate them in key cellular processes. Given that the transcellular electrochemical gradient is finely tuned in eukaryotic cells, any disruption in this homeostasis can contribute to aberrancies, including altering the activity of pro-tumorigenic molecular pathways, such as the MAPK/ERK, RAS, and mTOR pathways. Ligand-gated ion channels therefore serve as a potential targetable system for cancer therapeutics. In this review, we analyze the role that each of the three ligand-gated ion channel superfamilies has concerning tumor proliferation and as a target for the treatment of cancer symptomatology.

The Nervous System Contributes to the Tumorigenesis and Progression of Human Digestive Tract Cancer

Tumors of the gastrointestinal tract are one of the highest incidences of morbidity and mortality in humans. Recently, a growing number of researchers have indicated that nerve fibers and nerve signals participate in tumorigenesis. The current overarching view based on the responses to therapy revealed that tumors are partly promoted by the tumor microenvironment (TME), endogenous oncogenic factors, and complex systemic processes. Homeostasis of the neuroendocrine-immune axis (NEI axis) maintains a healthy in vivo environment in humans, and dysfunction of the axis contributes to various cancers, including the digestive tract. Interestingly, nerves might promote tumor development via multiple mechanisms, including perineural invasion (PNI), central level regulation, NEI axis effect, and neurotransmitter induction. This review focuses on the association between digestive tumors and nerve regulation, including PNI, the NEI axis, stress, and neurotransmitters, as well as on the potential clinical application of neurotherapy, aiming to provide a new perspective on the management of digestive cancers.

Therapeutically leveraging GABAA receptors in cancer

γ-aminobutyric acid or GABA is an amino acid that functionally acts as a neurotransmitter and is critical to neurotransmission. GABA is also a metabolite in the Krebs cycle. It is therefore unsurprising that GABA and its receptors are also present outside of the central nervous system, including in immune cells. This observation suggests that GABAergic signaling impacts events beyond brain function and possibly human health beyond neurological disorders. Indeed, GABA receptor subunits are expressed in pathological disease states, including in disparate cancers. The role that GABA and its receptors may play in cancer development and progression remains unclear. If, however, those cancers have functional GABA receptors that participate in GABAergic signaling, it raises an important question whether these signaling pathways might be targetable for therapeutic benefit. Herein we summarize the effects of modulating Type-A GABA receptor signaling in various cancers and highlight how Type-A GABA receptors could emerge as a novel therapeutic target in cancer.

Medulloblastoma uses GABA transaminase to survive in the cerebrospinal fluid microenvironment and promote leptomeningeal dissemination

Medulloblastoma (MB) is a malignant pediatric brain tumor arising in the cerebellum. Although abnormal GABAergic receptor activation has been described in MB, studies have not yet elucidated the contribution of receptor-independent GABA metabolism to MB pathogenesis. We find primary MB tumors globally display decreased expression of GABA transaminase (ABAT), the protein responsible for GABA metabolism, compared with normal cerebellum. However, less aggressive WNT and SHH subtypes express higher ABAT levels compared with metastatic G3 and G4 tumors. We show that elevated ABAT expression results in increased GABA catabolism, decreased tumor cell proliferation, and induction of metabolic and histone characteristics mirroring GABAergic neurons. Our studies suggest ABAT expression fluctuates depending on metabolite changes in the tumor microenvironment, with nutrient-poor conditions upregulating ABAT expression. We find metastatic MB cells require ABAT to maintain viability in the metabolite-scarce cerebrospinal fluid by using GABA as an energy source substitute, thereby facilitating leptomeningeal metastasis formation.

Outcome and molecular analysis of young children with choroid plexus carcinoma treated with non-myeloablative therapy: results from the SJYC07 trial

Background

Choroid plexus carcinoma (CPC) is a rare and aggressive tumor of infancy without a clear treatment strategy. This study describes the outcomes of children with CPC treated on the multi-institutional phase 2 SJYC07 trial and reports on the significance of clinical and molecular characteristics.

Methods

Eligible children <3 years-old with CPC were postoperatively stratified to intermediate-risk (IR) stratum if disease was localized or high-risk (HR) stratum, if metastatic. All received high-dose methotrexate-containing induction chemotherapy. IR-stratum patients received focal irradiation as consolidation whereas HR-stratum patients received additional chemotherapy. Consolidation was followed by oral antiangiogenic maintenance regimen. Survival rates and potential prognostic factors were analyzed.

Results

Thirteen patients (median age: 1.41 years, range: 0.21-2.93) were enrolled; 5 IR, 8 HR. Gross-total resection or near-total resection was achieved in ten patients and subtotal resection in 3. Seven patients had TP53-mutant tumors, including 4 who were germline carriers. Five patients experienced progression and died of disease; 8 (including 5 HR) are alive without progression. The 5-year progression-free survival (PFS) and overall survival rates were 61.5 ± 13.5% and 68.4 ± 13.1%. Patients with TP53-wild-type tumors had a 5-year PFS of 100% as compared to 28.6 ± 17.1% for TP53-mutant tumors (P = .012). Extent of resection, metastatic status, and use of radiation therapy were not significantly associated with survival.

Conclusions

Non-myeloablative high-dose methotrexate-containing therapy with maximal surgical resection resulted in long-term PFS in more than half of patients with CPC. TP53-mutational status was the only significant prognostic variable and should form the basis of risk-stratification in future trials.

A Benzodiazepine Ligand with Improved GABAA Receptor α5-Subunit Selectivity Driven by Interactions with Loop C

The family of GABA_A receptors is an important drug target group in the treatment of sleep disorders, anxiety, epileptic seizures, and many others. The most frequent GABA_A receptor subtype is composed of two α-, two β-, and one γ2-subunit, whereas the nature of the α-subunit critically determines the properties of the benzodiazepine binding site of those receptors. Nearly all of the clinically relevant drugs target all GABA_A receptor subtypes equally. In the past years, however, drug development research has focused on studying α5-containing GABA_A receptors. Beyond the central nervous system, α5-containing GABA_A receptors in airway smooth muscles are considered as an emerging target for bronchial asthma. Here, we investigated a novel compound derived from the previously described imidazobenzodiazepine SH-053-2'F-R-CH3 (SH53d-ester). Although SH53d-ester is only moderately selective for α5-subunit-containing GABA_A receptors, the derivative SH53d-acid shows superior (>40-fold) affinity selectivity and is a positive modulator. Using two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes and radioligand displacement assays with human embryonic kidney 293 cells, we demonstrated that an acid group as substituent on the imidazobenzodiazepine scaffold leads to large improvements of functional and binding selectivity for α5β3γ2 over other αxβ3γ2 GABA_A receptors. Atom level structural studies provide hypotheses for the improved affinity to this receptor subtype. Mutational analysis confirmed the hypotheses, indicating that loop C of the GABA_A receptor α-subunit is the dominant molecular determinant of drug selectivity. Thus, we characterize a promising novel α5-subunit-selective drug candidate. SIGNIFICANCE STATEMENT: In the current study we present the detailed pharmacological characterization of a novel compound derived from the previously described imidazobenzodiazepine SH-053-2'F-R-CH3. We describe its superior (>40-fold) affinity selectivity for α5-containing GABA_A receptors and show atom-level structure predictions to provide hypotheses for the improved affinity to this receptor subtype. Mutational analysis confirmed the hypotheses, indicating that loop C of the GABA_A receptor α-subunit is the dominant molecular determinant of drug selectivity.

A Targeted Bioinformatics Assessment of Adrenocortical Carcinoma Reveals Prognostic Implications of GABA System Gene Expression

Adrenocortical carcinoma (ACC) is a rare but deadly cancer for which few treatments exist. Here, we have undertaken a targeted bioinformatics study of The Cancer Genome Atlas (TCGA) ACC dataset focusing on the 30 genes encoding the γ-aminobutyric acid (GABA) system—an under-studied, evolutionarily-conserved system that is an emerging potential player in cancer progression. Our analysis identified a subset of ACC patients whose tumors expressed a distinct GABA system transcriptome. Transcript levels of ABAT (encoding a key GABA shunt enzyme), were upregulated in over 40% of tumors, and this correlated with several favorable clinical outcomes including patient survival; while enrichment and ontology analysis implicated two cancer-related biological pathways involved in metastasis and immune response. The phenotype associated with ABAT upregulation revealed a potential metabolic heterogeneity among ACC tumors associated with enhanced mitochondrial metabolism. Furthermore, many GABA_A receptor subunit-encoding transcripts were expressed, including two (GABRB2 and GABRD) prognostic for patient survival. Transcripts encoding GABA_B receptor subunits and GABA transporters were also ubiquitously expressed. The GABA system transcriptome of ACC tumors is largely mirrored in the ACC NCI-H295R cell line, suggesting that this cell line may be appropriate for future functional studies investigating the role of the GABA system in ACC cell growth phenotypes and metabolism.

Melanoma Cell Intrinsic GABAA Receptor Enhancement Potentiates Radiation and Immune Checkpoint Inhibitor Response by Promoting Direct and T Cell-Mediated Antitumor Activity

PURPOSE

Most patients with metastatic melanoma show variable responses to radiation therapy and do not benefit from immune checkpoint inhibitors. Improved strategies for combination therapy that leverage potential benefits from radiation therapy and immune checkpoint inhibitors are critical.

METHODS AND MATERIALS

We analyzed metastatic melanoma tumors in the TCGA cohort for expression of genes coding for subunits of type A γ-aminobutyric acid (GABA) receptor (GABA_AR), a chloride ion channel and major inhibitory neurotransmitter receptor. Electrophysiology was used to determine whether melanoma cells possess intrinsic GABA_AR activity. Melanoma cell viability studies were conducted to test whether enhancing GABA_AR mediated chloride transport using benzodiazepine-impaired viability. A syngeneic melanoma mouse model was used to assay the effect of benzodiazepine on tumor volume and its ability to potentiate radiation therapy or immunotherapy. Treated tumors were analyzed for changes in gene expression by RNA sequencing and presence of tumor-infiltrating lymphocytes by flow cytometry.

RESULTS

Genes coding for subunits of GABA_ARs express functional GABA_ARs in melanoma cells. By enhancing GABA_AR-mediated anion transport, benzodiazepines depolarize melanoma cells and impair their viability. In vivo, benzodiazepine alone reduces tumor growth and potentiates radiation therapy and α-PD-L1 antitumor activity. The combination of benzodiazepine, radiation therapy, and α-PD-L1 results in near complete regression of treated tumors and a potent abscopal effect, mediated by increased infiltration of polyfunctional CD8⁺ T cells. Treated tumors show expression of cytokine-cytokine receptor interactions and overrepresentation of p53 signaling.

CONCLUSIONS

This study identifies an antitumor strategy combining radiation and/or an immune checkpoint inhibitor with modulation of GABA_ARs in melanoma using benzodiazepine.

An oncolytic measles virus-sensitive Group 3 medulloblastoma model in immune-competent mice

Background

Oncolytic measles virus (MV) is effective in xenograft models of many tumor types in immune-compromised mice. However, no murine cell line exists that is tumorigenic, grows in immune-competent mice, and is killed by MV. The lack of such a model prevents an examination of the effect of the immune system on MV oncotherapy.

Methods

Cerebellar stem cells from human CD46-transgenic immunocompetent mice were transduced to express Sendai virus C-protein, murine C-Myc, and Gfi1b proteins. The resultant cells were injected into the brain of NSG mice, and a cell line, called CSCG, was prepared from the resulting tumor.

Results

CSCG cells are highly proliferative, and express stem cell markers. These cells are permissive for replication of MV and are killed by the virus in a dose- and time-dependent manner. CSCG cells form aggressive tumors that morphologically resemble medulloblastoma when injected into the brains of immune-competent mice. On the molecular level, CSCG tumors overexpress natriuretic peptide receptor 3 and gamma-aminobutyric acid type A receptor alpha 5, markers of Group 3 medulloblastoma. A single intratumoral injection of MV‒green fluorescent protein resulted in complete tumor regression and prolonged survival of animals compared with treatments with phosphate buffered saline (P = 0.0018) or heat-inactivated MV (P = 0.0027).

Conclusions

This immune-competent model provides the first platform to test therapeutic regimens of oncolytic MV for Group 3 medulloblastoma in the presence of anti-measles immunity. The strategy presented here can be used to make MV-sensitive murine models of any human tumor for which the driving mutations are known.

Modulating native GABAA receptors in medulloblastoma with positive allosteric benzodiazepine-derivatives induces cell death

PURPOSE

Pediatric brain cancer medulloblastoma (MB) standard-of-care results in numerous comorbidities. MB is comprised of distinct molecular subgroups. Group 3 molecular subgroup patients have the highest relapse rates and after standard-of-care have a 20% survival. Group 3 tumors have high expression of GABRA5, which codes for the α5 subunit of the γ-aminobutyric acid type A receptor (GABAAR). We are advancing a therapeutic approach for group 3 based on GABAAR modulation using benzodiazepine-derivatives.

METHODS

We performed analysis of GABR and MYC expression in MB tumors and used molecular, cell biological, and whole-cell electrophysiology approaches to establish presence of a functional 'druggable' GABAAR in group 3 cells.

RESULTS

Analysis of expression of 763 MB tumors reveals that group 3 tumors share high subgroup-specific and correlative expression of GABR genes, which code for GABAAR subunits α5, β3 and γ2 and 3. There are ~ 1000 functional α5-GABAARs per group 3 patient-derived cell that mediate a basal chloride-anion efflux of 2 × 109 ions/s. Benzodiazepines, designed to prefer α5-GABAAR, impair group 3 cell viability by enhancing chloride-anion efflux with subtle changes in their structure having significant impact on potency. A potent, non-toxic benzodiazepine ('KRM-II-08') binds to the α5-GABAAR (0.8 µM EC50) enhancing a chloride-anion efflux that induces mitochondrial membrane depolarization and in response, TP53 upregulation and p53, constitutively phosphorylated at S392, cytoplasmic localization. This correlates with pro-apoptotic Bcl-2-associated death promoter protein localization.

CONCLUSION

GABRA5 expression can serve as a diagnostic biomarker for group 3 tumors, while α5-GABAAR is a therapeutic target for benzodiazepine binding, enhancing an ion imbalance that induces apoptosis.

Decrease of Nibrin expression in chronic hypoxia is associated with hypoxia-induced chemoresistance in some brain tumour cells

Background

Solid tumours are less oxygenated than normal tissues. This is called tumour hypoxia and leads to resistance to radiotherapy and chemotherapy. The molecular mechanisms underlying such resistance have been investigated in a range of tumour types, including the adult brain tumours glioblastoma, yet little is known for paediatric brain tumours. Medulloblastoma (MB) is the most common malignant brain tumour in children. We aimed to elucidate the impact of hypoxia on the sensitivity of MB cells to chemo- and radiotherapy.

Methods

We used two MB cell line (D283-MED and MEB-Med8A) and a widely used glioblastoma cell line (U87MG) for comparison. We applied a range of molecular and cellular techniques to measure cell survival, cell cycle progression, protein expression and DNA damage combined with a transcriptomic micro-array approach in D283-MED cells, for global gene expression analysis in acute and chronic hypoxic conditions.

Results

In D283-MED and U87MG, chronic hypoxia (5 days), but not acute hypoxia (24 h) induced resistance to chemotherapy and X-ray irradiation. This acquired resistance upon chronic hypoxia was present but less pronounced in MEB-Med8A cells. Using transcriptomic analysis in D283-MED cells, we found a large transcriptional remodelling upon long term hypoxia, in particular the expression of a number of genes involved in detection and repair of double strand breaks (DSB) was altered. The levels of Nibrin (NBN) and MRE11, members of the MRN complex (MRE11/Rad50/NBN) responsible for DSB recognition, were significantly down-regulated. This was associated with a reduction of Ataxia Telangiectasia Mutated (ATM) activation by etoposide, indicating a profound dampening of the DNA damage signalling in hypoxic conditions. As a consequence, p53 activation by etoposide was reduced, and cell survival enhanced. Whilst U87MG shared the same dampened p53 activity, upon chemotherapeutic drug treatment in chronic hypoxic conditions, these cells used a different mechanism, independent of the DNA damage pathway.

Conclusion

Together our results demonstrate a new mechanism explaining hypoxia-induced resistance involving the alteration of the response to DSB in D283-MED cells, but also highlight the cell type to cell type diversity and the necessity to take into account the differing tumour genetic make-up when considering re-sensitisation therapeutic protocols.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5476-9) contains supplementary material, which is available to authorized users.

Molecular markers and potential therapeutic targets in non-WNT/non-SHH (group 3 and group 4) medulloblastomas

Childhood medulloblastomas (MB) are heterogeneous and are divided into four molecular subgroups. The provisional non-wingless-activated (WNT)/non-sonic hedgehog-activated (SHH) category combining group 3 and group 4 represents over two thirds of all MBs, coupled with the highest rates of metastases and least understood pathology. The molecular era expanded our knowledge about molecular aberrations involved in MB tumorigenesis, and here, we review processes leading to non-WNT/non-SHH MB formations.

The heterogeneous group 3 and group 4 MBs frequently harbor rare individual genetic alterations, yet the emerging profiles suggest that infrequent events converge on common, potentially targetable signaling pathways. A mutual theme is the altered epigenetic regulation, and in vitro approaches targeting epigenetic machinery are promising. Growing evidence indicates the presence of an intermediate, mixed signature group along group 3 and group 4, and future clarifications are imperative for concordant classification, as misidentifying patient samples has serious implications for therapy and clinical trials.

To subdue the high MB mortality, we need to discern mechanisms of disease spread and recurrence. Current preclinical models do not represent the full scale of group 3 and group 4 heterogeneity: all of existing group 3 cell lines are MYC-amplified and most mouse models resemble MYC-activated MBs. Clinical samples provide a wealth of information about the genetic divergence between primary tumors and metastatic clones, but recurrent MBs are rarely resected. Molecularly stratified treatment options are limited, and targeted therapies are still in preclinical development. Attacking these aggressive tumors at multiple frontiers will be needed to improve stagnant survival rates.

RNAi screening of subtracted transcriptomes reveals tumor suppression by taurine-activated GABAA receptors involved in volume regulation

To identify coding and non-coding suppressor genes of anchorage-independent proliferation by efficient loss-of-function screening, we have developed a method for enzymatic production of low complexity shRNA libraries from subtracted transcriptomes. We produced and screened two LEGO (Low-complexity by Enrichment for Genes shut Off) shRNA libraries that were enriched for shRNA vectors targeting coding and non-coding polyadenylated transcripts that were reduced in transformed Mouse Embryonic Fibroblasts (MEFs). The LEGO shRNA libraries included ~25 shRNA vectors per transcript which limited off-target artifacts. Our method identified 79 coding and non-coding suppressor transcripts. We found that taurine-responsive GABA_A receptor subunits, including GABRA5 and GABRB3, were induced during the arrest of non-transformed anchor-deprived MEFs and prevented anchorless proliferation. We show that taurine activates chloride currents through GABA_A receptors on MEFs, causing seclusion of cell volume in large membrane protrusions. Volume seclusion from cells by taurine correlated with reduced proliferation and, conversely, suppression of this pathway allowed anchorage-independent proliferation. In human cholangiocarcinomas, we found that several proteins involved in taurine signaling via GABA_A receptors were repressed. Low GABRA5 expression typified hyperproliferative tumors, and loss of taurine signaling correlated with reduced patient survival, suggesting this tumor suppressive mechanism operates in vivo.

Tumor-suppressing effects of microRNA-612 in bladder cancer cells by targeting malic enzyme 1 expression

The present study investigated the possible tumor-suppressing function of microRNA (miR)-612 and the underlying molecular mechanism of its action in bladder cancer in vitro and in vivo. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was carried out to quantify the expression levels of miR-612 in bladder cancer tissues and cell lines. The data demonstrated that the level of miR-612 expression was significantly reduced in bladder cancer tissues and cell lines, as compared with that in non-cancerous tissues and cells. Reduced miR-612 expression was associated with advanced tumor, lymph node and metastasis stages, and with distant metastasis of bladder cancer. A functional study revealed that transfection of cells with an miR-612 mimic suppressed bladder cancer cell growth, colony formation, migration, invasion and epithelial-mesenchymal transition. Bioinformatics analysis identified that miR-612 targeted the expression of malic enzyme 1 (ME1), and this was confirmed by western blot and luciferase reporter assay results. Furthermore, the ME1 expression levels were inversely associated with miR-612 expression in bladder cancer tissue specimens. In addition, knockdown of ME1 expression using ME1 siRNA mimicked the effect of ectopic miR-612 overexpression in bladder cancer cells in terms of tumor cell growth, migration and invasion. By contrast, ME1 overexpression weakened the inhibitory effect of the miR-612 mimic in bladder cancer cells. In conclusion, the present study demonstrated that miR-612 may function as a tumor suppressor in bladder cancer by targeting ME1 expression.

Medulloblastoma: experimental models and reality

Medulloblastoma is the most frequent malignant brain tumor in childhood, but it may also affect infants, adolescents, and young adults. Recent advances in the understanding of the disease have shed light on molecular and clinical heterogeneity, which is now reflected in the updated WHO classification of brain tumors. At the same time, it is well accepted that preclinical research and clinical trials have to be subgroup-specific. Hence, valid models have to be generated specifically for every medulloblastoma subgroup to properly mimic molecular fingerprints, clinical features, and responsiveness to targeted therapies. This review summarizes the availability of experimental medulloblastoma models with a particular focus on how well these models reflect the actual disease subgroup. We further describe technical advantages and disadvantages of the models and finally point out how some models have successfully been used to introduce new drugs and why some medulloblastoma subgroups are extraordinary difficult to model.

Functional analysis of HOXA10 and HOXB4 in human medulloblastoma cell lines

Medulloblastoma (MB) is a malignant childhood brain tumor which at molecular level is classified into at least four major subtypes: WNT, SHH, group C and group D differing in response to treatment. Previous studies have associated changes in expression levels and activation of certain HOX genes with MB development. In the present study, we investigate the role of HOX genes in two attributes acquired by tumor cells: migration and proliferation potential, as well as, in vivo tumorigenic potential. We analyzed UW402, UW473, DAOY and ONS-76 human pediatric MB cell lines and cerebellum primary cultures. Two-color microarray-based gene expression analysis was used to identify differentially expressed HOX genes. Among the various HOX genes significantly overexpressed in DAOY and ONS-76 cell lines compared to UW402 and UW473 cell lines, HOXA10 and HOXB4 were selected for further analysis. The expression levels of these HOX genes were validated by real-time PCR. A mouse model was used to study the effect of the HOXA10 and HOXB4 genes on the in vivo tumorigenic potential and the in vitro proliferative and migration potential of MB cell lines. Our results show that the inhibition of HOXA10 in DAOY cell line led to increased in vitro cell migration while in vitro cell proliferation or in vivo tumorigenic potential were unaffected. We also observed that induced expression of HOXB4 in the UW473 cell line significantly reduced in vitro cell proliferation and migration capability of UW473 cells with no effect on the in vivo tumorigenicity. This suggests that HOXA10 plays a role in migration events and the HOXB4 gene is involved in proliferation and migration processes of medulloblastoma cells, however, it appears that these genes are not essential for the tumorigenic process of these cells.

Neuronal Activity in Ontogeny and Oncology

The nervous system plays a central role in regulating the stem cell niche in many organs, and thereby pivotally modulates development, homeostasis, and plasticity. A similarly powerful role for neural regulation of the cancer microenvironment is emerging. Neurons promote the growth of cancers of the brain, skin, prostate, pancreas, and stomach. Parallel mechanisms shared in development and cancer suggest that neural modulation of the tumor microenvironment may prove a universal theme, although the mechanistic details of such modulation remain to be discovered for many malignancies. We review here what is known about the influences of active neurons on stem cell and cancer microenvironments across a broad range of tissues, and we discuss emerging principles of neural regulation of development and cancer.

First In Vivo Testing of Compounds Targeting Group 3 Medulloblastomas Using an Implantable Microdevice as a New Paradigm for Drug Development

Medulloblastoma is the most common childhood malignant brain tumor. The most lethal medulloblastoma subtype exhibits a high expression of the GABAA receptor α5 subunit gene and MYC amplification. New benzodiazepines have been synthesized to function as α5-GABAA receptor ligands. To compare their efficacy with that of standard-of-care treatments, we have employed a newly developed microscale implantable device that allows for high-throughput localized intratumor drug delivery and efficacy testing. Microdoses of each drug were delivered into small distinct regions of tumors, as confirmed by tissue mass spectrometry, and the local drug effect was determined by immunohistochemistry. We have identified a benzodiazepine derivative, KRM-II-08, as a new potent inhibitor in several α5-GABAA receptor expressing tumor models. This is the first instance of in vivo testing of several benzodiazepine derivatives and standard chemotherapeutic drugs within the same tumor. Obtaining high-throughput drug efficacy data within a native tumor microenvironment as detailed herein, prior to pharmacological optimization for bioavailability or safety and without systemic exposure or toxicity, may allow for rapid prioritization of drug candidates for further pharmacological optimization.

In vitro models of medulloblastoma: Choosing the right tool for the job

The recently-defined four molecular subgroups of medulloblastoma have required updating of our understanding of in vitro models to include molecular classification and risk stratification features from clinical practice. This review seeks to build a more comprehensive picture of the in vitro systems available for modelling medulloblastoma. The subtype classification and molecular characterisation for over 40 medulloblastoma cell-lines has been compiled, making it possible to identify the strengths and weaknesses in current model systems. Less than half (18/44) of established medulloblastoma cell-lines have been subgrouped. The majority of the subgrouped cell-lines (11/18) are Group 3 with MYC-amplification. SHH cell-lines are the next most common (4/18), half of which exhibit TP53 mutation. WNT and Group 4 subgroups, accounting for 50% of patients, remain underrepresented with 1 and 2 cell-lines respectively. In vitro modelling relies not only on incorporating appropriate tumour cells, but also on using systems with the relevant tissue architecture and phenotype as well as normal tissues. Novel ways of improving the clinical relevance of in vitro models are reviewed, focusing on 3D cell culture, extracellular matrix, co-cultures with normal cells and organotypic slices. This paper champions the establishment of a collaborative online-database and linked cell-bank to catalyse preclinical medulloblastoma research.

SMARCA4/Brg1 coordinates genetic and epigenetic networks underlying Shh-type medulloblastoma development

Recent large-scale genomic studies have classified medulloblastoma into four subtypes: Wnt, Shh, Group 3 and Group 4. Each is characterized by specific mutations and distinct epigenetic states. Previously, we showed that a chromatin regulator SMARCA4/Brg1 is required for Gli-mediated transcription activation in Sonic hedgehog (Shh) signaling. We report here that Brg1 controls a transcriptional program that specifically regulates Shh-type medulloblastoma growth. Using a mouse model of Shh-type medulloblastoma, we deleted Brg1 in precancerous progenitors and primary or transplanted tumors. Brg1 deletion significantly inhibited tumor formation and progression. Genome-wide expression analyses and binding experiments indicate that Brg1 specifically coordinates with key transcription factors including Gli1, Atoh1 and REST to regulate the expression of both oncogenes and tumor suppressors that are required for medulloblastoma identity and proliferation. Shh-type medulloblastoma displays distinct H3K27me3 properties. We demonstrate that Brg1 modulates activities of H3K27me3 modifiers to regulate the expression of medulloblastoma genes. Brg1-regulated pathways are conserved in human Shh-type medulloblastoma, and Brg1 is important for the growth of a human medulloblastoma cell line. Thus, Brg1 coordinates a genetic and epigenetic network that regulates the transcriptional program underlying the Shh-type medulloblastoma development.

Identification of alsterpaullone as a novel small molecule inhibitor to target group 3 medulloblastoma

Advances in the molecular biology of medulloblastoma revealed four genetically and clinically distinct subgroups. Group 3 medulloblastomas are characterized by frequent amplifications of the oncogene MYC, a high incidence of metastasis, and poor prognosis despite aggressive therapy. We investigated several potential small molecule inhibitors to target Group 3 medulloblastomas based on gene expression data using an in silico drug screen. The Connectivity Map (C-MAP) analysis identified piperlongumine as the top candidate drug for non-WNT medulloblastomas and the cyclin-dependent kinase (CDK) inhibitor alsterpaullone as the compound predicted to have specific antitumor activity against Group 3 medulloblastomas. To validate our findings we used these inhibitors against established Group 3 medulloblastoma cell lines. The C-MAP predicted drugs reduced cell proliferation in vitro and increased survival in Group 3 medulloblastoma xenografts. Alsterpaullone had the highest efficacy in Group 3 medulloblastoma cells. Genomic profiling of Group 3 medulloblastoma cells treated with alsterpaullone confirmed inhibition of cell cycle-related genes, and down-regulation of MYC. Our results demonstrate the preclinical efficacy of using a targeted therapy approach for Group 3 medulloblastomas. Specifically, we provide rationale for advancing alsterpaullone as a targeted therapy in Group 3 medulloblastoma.

Pediatric brain tumor cell lines

Pediatric brain tumors as a group, including medulloblastomas, gliomas, and atypical teratoid rhabdoid tumors (ATRT) are the most common solid tumors in children and the leading cause of death from childhood cancer. Brain tumor-derived cell lines are critical for studying the biology of pediatric brain tumors and can be useful for initial screening of new therapies. Use of appropriate brain tumor cell lines for experiments is important, as results may differ depending on tumor properties, and can thus affect the conclusions and applicability of the model. Despite reports in the literature of over 60 pediatric brain tumor cell lines, the majority of published papers utilize only a small number of these cell lines. Here we list the approximately 60 currently-published pediatric brain tumor cell lines and summarize some of their central features as a resource for scientists seeking pediatric brain tumor cell lines for their research.