The dual mTOR kinase inhibitor TAK228 inhibits tumorigenicity and enhances radiosensitization in diffuse intrinsic pontine glioma

Dual targeting of histone deacetylases and MYC as potential treatment strategy for H3-K27M pediatric gliomas

Diffuse midline gliomas (DMGs) are aggressive and fatal pediatric tumors of the central nervous system that are highly resistant to treatments. Lysine to methionine substitution of residue 27 on histone H3 (H3-K27M) is a driver mutation in DMGs, reshaping the epigenetic landscape of these cells to promote tumorigenesis. H3-K27M gliomas are characterized by deregulation of histone acetylation and methylation pathways, as well as the oncogenic MYC pathway. In search of effective treatment, we examined the therapeutic potential of dual targeting of histone deacetylases (HDACs) and MYC in these tumors. Treatment of H3-K27M patient-derived cells with Sulfopin, an inhibitor shown to block MYC-driven tumors in vivo, in combination with the HDAC inhibitor Vorinostat, resulted in substantial decrease in cell viability. Moreover, transcriptome and epigenome profiling revealed synergistic effect of this drug combination in downregulation of prominent oncogenic pathways such as mTOR. Finally, in vivo studies of patient-derived orthotopic xenograft models showed significant tumor growth reduction in mice treated with the drug combination. These results highlight the combined treatment with PIN1 and HDAC inhibitors as a promising therapeutic approach for these aggressive tumors.

Related mechanisms, current treatments, and new perspectives in meningioma

Meningiomas are non-glial tumors that are the most common primary brain tumors in adults. Although meningioma can possibly be cured with surgical excision, variations in atypical/anaplastic meningioma have a high recurrence rate and a poor prognosis. As a result, it is critical to develop novel therapeutic options for high-grade meningiomas. This review highlights the current histology of meningiomas, prevalent genetic and molecular changes, and the most extensively researched signaling pathways and therapies in meningiomas. It also reviews current clinical studies and novel meningioma treatments, including immunotherapy, microRNAs, cancer stem cell methods, and targeted interventions within the glycolysis pathway. Through the examination of the complex landscape of meningioma biology and the highlighting of promising therapeutic pathways, this review opens the way for future research efforts aimed at improving patient outcomes in this prevalent intracranial tumor entity.

Deep-targeted gene sequencing reveals ARID1A mutation as an important driver of glioblastoma

AIMS

To investigate the key factors influencing glioma progression and the emergence of treatment resistance by examining the intrinsic connection between mutations in DNA damage and repair-related genes and the development of chemoresistance in gliomas.

METHODS

We conducted a comprehensive analysis of deep-targeted gene sequencing data from 228 glioma samples. This involved identifying differentially mutated genes across various glioma grades, assessing their functions, and employing I-TASSER for homology modeling. We elucidated the functional changes induced by high-frequency site mutations in these genes and investigated their impact on glioma progression.

RESULTS

The analysis of sequencing mutation results of deep targeted genes in integration revealed that ARID1A gene mutation occurs frequently in glioblastoma and alteration of ARID1A could affect the tolerance of glioma cells to temozolomide treatment. The deletion of proline at position 16 in the ARID1A protein affected the stability of binding of the SWI/SNF core subunit BRG1, which in turn affected the stability of the SWI/SNF complex and led to altered histone modifications in the CDKN1A promoter region, thereby affecting the biological activity of glioma cells, as inferred from modeling and protein interaction analysis.

CONCLUSION

The ARID1A gene is a critical predictive biomarker for glioma. Mutations at the ARID1A locus alter the stability of the SWI/SNF complex, leading to changes in transcriptional regulation in glioma cells. This contributes to an increased malignant phenotype of GBM and plays a pivotal role in mediating chemoresistance.

Transcriptional Regulation of Protein Synthesis by Mediator Kinase in MYC-driven Medulloblastoma

MYC-driven medulloblastoma (MB) is a highly aggressive cancer type with poor prognosis and limited treatment options. Through CRISPR-Cas9 screening across MB cell lines, we identified the Mediator-associated kinase CDK8 as the top dependence for MYC-driven MB. Loss of CDK8 markedly reduces MYC expression and impedes MB growth. Mechanistically, we demonstrate that CDK8 depletion suppresses ribosome biogenesis and mRNA translation. CDK8 regulates occupancy of phospho-Polymerase II at specific chromatin loci facilitating an epigenetic alteration that promotes transcriptional regulation of ribosome biogenesis. Additionally, CDK8-mediated phosphorylation of 4EBP1 plays a crucial role in initiating eIF4E-dependent translation. Targeting CDK8 effectively suppresses cancer stem and progenitor cells, characterized by increased ribosome biogenesis activity. We also report the synergistic inhibition of CDK8 and mTOR in vivo and in vitro . Overall, our findings establish a connection between transcription and translation regulation, suggesting a promising therapeutic approach targets multiple points in the protein synthesis network for MYC-driven MB.

Therapeutically targeting the unique disease landscape of pediatric high-grade gliomas

Pediatric high-grade gliomas (pHGG) are a rare yet devastating malignancy of the central nervous system's glial support cells, affecting children, adolescents, and young adults. Tumors of the central nervous system account for the leading cause of pediatric mortality of which high-grade gliomas present a significantly grim prognosis. While the past few decades have seen many pediatric cancers experiencing significant improvements in overall survival, the prospect of survival for patients diagnosed with pHGGs has conversely remained unchanged. This can be attributed in part to tumor heterogeneity and the existence of the blood-brain barrier. Advances in discovery research have substantiated the existence of unique subgroups of pHGGs displaying alternate responses to different therapeutics and varying degrees of overall survival. This highlights a necessity to approach discovery research and clinical management of the disease in an alternative subtype-dependent manner. This review covers traditional approaches to the therapeutic management of pHGGs, limitations of such methods and emerging alternatives. Novel mutations which predominate the pHGG landscape are highlighted and the therapeutic potential of targeting them in a subtype specific manner discussed. Collectively, this provides an insight into issues in need of transformative progress which arise during the management of pHGGs.

Different Impacts of DNA-PK and mTOR Kinase Inhibitors in Combination with Ionizing Radiation on HNSCC and Normal Tissue Cells

Despite substantial advancements in understanding the pathomechanisms of head and neck squamous cell carcinoma (HNSCC), effective therapy remains challenging. The application of kinase inhibitors (KIs) in HNSCC, specifically mTOR and DNA-PK inhibitors, can increase radiosensitivity and therefore presents a promising strategy when used simultaneously with ionizing radiation (IR) in cancer treatment. Our study focused on the selective DNA-PK-inhibitor AZD7648; the selective mTOR-inhibitor Sapanisertib; and CC-115, a dual inhibitor targeting both mTOR and DNA-PK. The impact of these KIs on HNSCC and normal tissue cells was assessed using various analytical methods including cell death studies, cell cycle analysis, real-time microscopy, colony-forming assays and immunohistochemical staining for γH2AX and downstream mTOR protein p-S6. We detected a strong inhibition of IR-induced DNA double-strand break (DSB) repair, particularly in AZD7648-treated HNSCC, whereas normal tissue cells repaired DNA DSB more efficiently. Additionally, AZD7648 + IR treatment showed a synergistic decline in cell proliferation and clonogenicity, along with an elevated G2/M arrest and cell death in the majority of HNSCC cell lines. CC-115 + IR treatment led to an elevation in G2/M arrest, increased cell death, and a synergistic reduction in cell proliferation, though the effect was notably lower compared to the AZD7648 + IR- treated group. Sapanisertib led to a high cellular toxicity in both HNSCC and normal tissue cells, even in non-irradiated cells. Regarding cell proliferation and the induction of apoptosis and necrosis, Sapanisertib + IR was beneficial only in HPV+ HNSCC. Overall, this study highlights the potential of AZD7648 as a radiosensitizing agent in advanced-stage HPV-positive and negative HNSCC, offering a promising therapeutic strategy. However, the dual mTOR/DNA-PK-I CC-115 did not provide a distinct advantage over the use of selective KIs in our investigations, suggesting limited benefits for its application in KI + IR therapy. Notably, the selective mTOR-inhibitor Sapanisertib was only beneficial in HPV+ HNSCC and should not be applied in HPV- cases.

PRMT5 inhibition shows in vitro efficacy against H3K27M-altered diffuse midline glioma, but does not extend survival in vivo

H3K27-altered Diffuse Midline Glioma (DMG) is a universally fatal paediatric brainstem tumour. The prevalent driver mutation H3K27M creates a unique epigenetic landscape that may also establish therapeutic vulnerabilities to epigenetic inhibitors. However, while HDAC, EZH2 and BET inhibitors have proven somewhat effective in pre-clinical models, none have translated into clinical benefit due to either poor blood-brain barrier penetration, lack of efficacy or toxicity. Thus, there remains an urgent need for new DMG treatments. Here, we performed wider screening of an epigenetic inhibitor library and identified inhibitors of protein arginine methyltransferases (PRMTs) among the top hits reducing DMG cell viability. Two of the most effective inhibitors, LLY-283 and GSK591, were targeted against PRMT5 using distinct binding mechanisms and reduced the viability of a subset of DMG cells expressing wild-type TP53 and mutant ACVR1. RNA-sequencing and phenotypic analyses revealed that LLY-283 could reduce the viability, clonogenicity and invasion of DMG cells in vitro, representing three clinically important phenotypes, but failed to prolong survival in an orthotopic xenograft model. Together, these data show the challenges of DMG treatment and highlight PRMT5 inhibitors for consideration in future studies of combination treatments.

Intra-promoter switch of transcription initiation sites in proliferation signaling-dependent RNA metabolism

Global changes in transcriptional regulation and RNA metabolism are crucial features of cancer development. However, little is known about the role of the core promoter in defining transcript identity and post-transcriptional fates, a potentially crucial layer of transcriptional regulation in cancer. In this study, we use CAGE-seq analysis to uncover widespread use of dual-initiation promoters in which non-canonical, first-base-cytosine (C) transcription initiation occurs alongside first-base-purine initiation across 59 human cancers and healthy tissues. C-initiation is often followed by a 5' terminal oligopyrimidine (5'TOP) sequence, dramatically increasing the range of genes potentially subjected to 5'TOP-associated post-transcriptional regulation. We show selective, dynamic switching between purine and C-initiation site usage, indicating transcription initiation-level regulation in cancers. We additionally detail global metabolic changes in C-initiation transcripts that mark differentiation status, proliferative capacity, radiosensitivity, and response to irradiation and to PI3K-Akt-mTOR and DNA damage pathway-targeted radiosensitization therapies in colorectal cancer organoids and cancer cell lines and tissues.

Decoding Diffuse Midline Gliomas: A Comprehensive Review of Pathogenesis, Diagnosis and Treatment

Diffuse midline gliomas (DMGs) are a group of aggressive CNS tumors, primarily affecting children and young adults, which have historically been associated with dismal outcomes. As the name implies, they arise in midline structures in the CNS, primarily in the thalamus, brainstem, and spinal cord. In more recent years, significant advances have been made in our understanding of DMGs, including molecular features, with the identification of potential therapeutic targets. We aim to provide an overview of the most recent updates in the field of DMGs, including classification, molecular subtypes, diagnostic techniques, and emerging therapeutic strategies including a review of the ongoing clinical trials, thus providing the treating multidisciplinary team with a comprehensive understanding of the current landscape and potential therapeutic strategies for this devastating group of tumors.

Radiotherapy and radio-sensitization in H3K27M -mutated diffuse midline gliomas

BACKGROUND

H3^K27M mutated diffuse midline gliomas (DMGs) are extremely aggressive and the leading cause of cancer-related deaths in pediatric brain tumors with 5-year survival <1%. Radiotherapy is the only established adjuvant treatment of H3^K27M DMGs; however, the radio-resistance is commonly observed.

METHODS

We summarized current understandings of the molecular responses of H3^K27M DMGs to radiotherapy and provide crucial insights into current advances in radiosensitivity enhancement.

RESULTS

Ionizing radiation (IR) can mainly inhibit tumor cell growth by inducing DNA damage regulated by the cell cycle checkpoints and DNA damage repair (DDR) system. In H3K27M DMGs, the aberrant genetic and epigenetic changes, stemness genotype, and epithelial-mesenchymal transition (EMT) disrupt the cell cycle checkpoints and DDR system by altering the associated regulatory signaling pathways, which leads to the development of radio-resistance.

CONCLUSIONS

The advances in mechanisms of radio-resistance in H3^K27M  DMGs promote the potential targets to enhance the sensitivity to radiotherapy.

Developing H3K27M mutant selective radiosensitization strategies in diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is a rare but highly lethal pediatric and adolescent tumor located in the pons of the brainstem. DIPGs harbor unique and specific pathological and molecular alterations, such as the hallmark lysine 27-to-methionine (H3K27M) mutation in histone H3, which lead to global changes in the epigenetic landscape and drive tumorigenesis. While fractionated radiotherapy, the current standard of care, improves symptoms and delays tumor progression, DIPGs inevitably recur, and despite extensive efforts chemotherapy-driven radiosensitization strategies have failed to improve survival. Advances in our understanding of the role of epigenetics in the cellular response to radiation-induced DNA damage, however, offer new opportunities to develop combinational therapeutic strategies selective for DIPGs expressing H3K27M. In this review, we provide an overview of preclinical studies that explore potential radiosensitization strategies targeting the unique epigenetic landscape of H3K27M mutant DIPG. We further discuss opportunities to selectively radiosensitize DIPG through strategic inhibition of the radiation-induced DNA damage response. Finally, we discuss the potential for using radiation to induce anti-tumor immune responses that may be potentiated in DIPG by radiosensitizing-therapeutic strategies.

Drugging Hijacked Kinase Pathways in Pediatric Oncology: Opportunities and Current Scenario

Childhood cancer is considered rare, corresponding to ~3% of all malignant neoplasms in the human population. The World Health Organization (WHO) reports a universal occurrence of more than 15 cases per 100,000 inhabitants around the globe, and despite improvements in diagnosis, treatment and supportive care, one child dies of cancer every 3 min. Consequently, more efficient, selective and affordable therapeutics are still needed in order to improve outcomes and avoid long-term sequelae. Alterations in kinases' functionality is a trademark of cancer and the concept of exploiting them as drug targets has burgeoned in academia and in the pharmaceutical industry of the 21st century. Consequently, an increasing plethora of inhibitors has emerged. In the present study, the expression patterns of a selected group of kinases (including tyrosine receptors, members of the PI3K/AKT/mTOR and MAPK pathways, coordinators of cell cycle progression, and chromosome segregation) and their correlation with clinical outcomes in pediatric solid tumors were accessed through the R2: Genomics Analysis and Visualization Platform and by a thorough search of published literature. To further illustrate the importance of kinase dysregulation in the pathophysiology of pediatric cancer, we analyzed the vulnerability of different cancer cell lines against their inhibition through the Cancer Dependency Map portal, and performed a search for kinase-targeted compounds with approval and clinical applicability through the CanSAR knowledgebase. Finally, we provide a detailed literature review of a considerable set of small molecules that mitigate kinase activity under experimental testing and clinical trials for the treatment of pediatric tumors, while discuss critical challenges that must be overcome before translation into clinical options, including the absence of compounds designed specifically for childhood tumors which often show differential mutational burdens, intrinsic and acquired resistance, lack of selectivity and adverse effects on a growing organism.

Dual Targeting of EGFR and MTOR Pathways Inhibits Glioblastoma Growth by Modulating the Tumor Microenvironment

Glioblastoma's (GBM) aggressive growth is driven by redundant activation of a myriad of signaling pathways and genomic alterations in tyrosine kinase receptors, such as epidermal growth factor receptor (EGFR), which is altered in over 50% of cases. Single agents targeting EGFR have not proven effective against GBM. In this study, we aimed to identify an effective anti-tumor regimen using pharmacogenomic testing of patient-derived GBM samples, in culture and in vivo. High-throughput pharmacological screens of ten EGFR-driven GBM samples identified the combination of erlotinib (EGFRi) and MLN0128 (a mammalian target of rapamycin inhibitor, or MTORi) as the most effective at inhibiting tumor cell viability. The anti-tumor activity of erlonitib+MLN0128 was synergistic and produced inhibition of the p-EGFR, mitogen-activated protein kinase (MAPK), and Phosphoinositide 3-kinase (PI3K) pathways in culture. Using an orthotopic murine model of GBM, we show that erlotinib+MLN0128 inhibited tumor growth in vivo and significantly prolonged the survival of tumor-bearing mice. Expression profiling of tumor tissues from treated mice revealed a unique gene signature induced by erlotinib+MLN0128, consisting of downregulation of immunosuppressive chemokines in the tumor microenvironment, including C-C motif chemokine ligand 2 (CCL2) and periostin. Lower periostin levels resulted in the inhibition of Iba1+ (tumor-promoting) macrophage infiltration of GBM xenografts. Taken together, our results demonstrate that pharmacological co-targeting of EGFR and MTOR using clinically available drugs represents an effective treatment paradigm for EGFR-driven GBMs, acting both by inhibiting tumor cell growth and modulating the immune tumor microenvironment.

Advances and Clinical Trials Update in the Treatment of Diffuse Intrinsic Pontine Gliomas

BACKGROUND

Diffuse intrinsic pontine gliomas (DIPGs) are high-grade gliomas (HGGs) that occur primarily in children, and represent a leading cause of death in pediatric patients with brain tumors with a median overall survival of only 8-11 months.

SUMMARY

While these lesions were previously thought to behave similarly to adult HGG, emerging data have demonstrated that DIPG is a biologically distinct entity from adult HGG frequently driven by mutations in the histone genes H3.3 and H3.1 not found in adult glioma. While biopsy of DIPG was historically felt to confer unacceptable risk of morbidity and mortality, multiple studies have demonstrated that stereotactic biopsy of DIPG is safe, allowing not only for improved understanding of DIPG but also forming the basis for protocols for personalized medicine in DIPG. However, current options for personalized medicine in DIPG are limited by the lack of efficacious targeted therapies for the mutations commonly found in DIPG. Multiple treatment modalities including targeted therapies, immunotherapy, convection-enhanced delivery, and focused ultrasound are in various stages of investigation.

KEY MESSAGE

Increasing frequency of biopsy for DIPG has identified distinct driving mutations that may serve as therapeutic targets. Novel treatment modalities are under investigation.

Venetoclax cooperates with ionizing radiation to attenuate Diffuse Midline Glioma tumor growth

PURPOSE

Tumor relapse after radiation therapy (RT) is a major hurdle in treating pediatric H3K27M-mutant diffuse midline gliomas (DMGs). RT-induced stress increases association of BCL2 family of proteins with BH3 pro-apoptotic activators preventing apoptosis. We hypothesized that inhibition of RT-induced BCL2 with a clinically relevant inhibitor, venetoclax, will block BCL2 activity leading to increased apoptosis. BCL2 has never been implicated in DMG as a RT-induced resistant mechanism.

EXPERIMENTAL DESIGN

We performed an integrated genomic analysis to determine genes responsible for radioresistance and a targeted drug screen to identify drugs that synergize with radiation in DMG. Effect of venetoclax on radiation-na�ve and 6Gy radiation on cells was evaluated by studying cell death, changes in BCL2 phosphorylation, reactive oxygen species (ROS), and apoptosis, as well as BCL2 association with BH3 apoptosis initiators. The efficacy of combining venetoclax with radiation was evaluated in vivo using orthotopic xenograft models.

RESULTS

BCL2 was identified as a key regulator of tumor growth after radiation in DMGs. Radiation sensitizes DMGs to venetoclax treatment independent of p53 status. Venetoclax as a monotherapy was not cytotoxic to DMG cells. Post-radiation venetoclax treatment significantly increased cell death, reduced BCL2-BIM association and augmented mitochondrial ROS leading to increased apoptosis. Combining venetoclax with RT significantly enhanced the survival of mice with DMG tumors.

CONCLUSIONS

This study shows that venetoclax impedes the anti-apoptotic function of radiation-induced BCL2 in DMG leading to increased apoptosis. Results from these pre-clinical studies demonstrate the potential use of the BCL2 inhibitor, venetoclax, combined with RT for pediatric DMG.

Novel Repositioning Therapy for Drug-Resistant Glioblastoma: In Vivo Validation Study of Clindamycin Treatment Targeting the mTOR Pathway and Combination Therapy with Temozolomide

Simple Summary

Given the significant costs and lengthy timelines of drug development and clinical trials, drug repositioning is a promising alternative to find effective treatments for brain tumors quickly and inexpensively. In the present study, using a simple drug screen of macrolides, we found that clindamycin (CLD) had cytotoxic effects on glioblastoma (GBM) cells. Further studies showed the inhibition of the mammalian target of rapamycin (mTOR) pathway as the key mechanism of action. Interestingly, we found that co-treatment with temozolomide (TMZ), the alkylating agent considered as standard therapy in GBM, enhanced these effects and proposed the inhibition of O6-methylguanine-DNA methyltransferase (MGMT) protein by CLD as a potential mechanism for this combination effect.

Abstract

Multimodal therapy including surgery, radiation treatment, and temozolomide (TMZ) is performed on glioblastoma (GBM). However, the prognosis is still poor and there is an urgent need to develop effective treatments to improve survival. Molecular biological analysis was conducted to examine the signal activation patterns in GBM specimens and remains an open problem. Advanced macrolides, such as azithromycin, reduce the phosphorylation of p70 ribosomal protein S6 kinase (p70S6K), a downstream mammalian target of rapamycin (mTOR) effector, and suppress the proliferation of T-cells. We focused on its unique profile and screened for the antitumor activity of approved macrolide antibiotics. Clindamycin (CLD) reduced the viability of GBM cells in vitro. We assessed the effects of the candidate macrolide on the mTOR pathway through Western blotting. CLD attenuated p70S6K phosphorylation in a dose-dependent manner. These effects on GBM cells were enhanced by co-treatment with TMZ. Furthermore, CLD inhibited the expression of the O6-methylguanine-DNA methyltransferase (MGMT) protein in cultured cells. In the mouse xenograft model, CLD and TMZ co-administration significantly suppressed the tumor growth and markedly decreased the number of Ki-67 (clone MIB-1)-positive cells within the tumor. These results suggest that CLD suppressed GBM cell growth by inhibiting mTOR signaling. Moreover, CLD and TMZ showed promising synergistic antitumor activity.

Experimental murine models of brainstem gliomas

As an intractable central nervous system (CNS) tumor, brainstem gliomas (BGs) are one of the leading causes of pediatric death by brain tumors. Owing to the risk of surgical resection and the little improvement in survival time after radiotherapy and chemotherapy, there is an urgent need to find reliable model systems to better understand the regional pathogenesis of the brainstem and improve treatment strategies. In this review, we outline the evolution of BG murine models, and discuss both their advantages and limitations in drug discovery.

Therapeutic Targets in Diffuse Midline Gliomas-An Emerging Landscape

Simple Summary

Diffuse midline gliomas (DMGs) remain one of the most devastating childhood brain tumour types, for which there is currently no known cure. In this review we provide a summary of the existing knowledge of the molecular mechanisms underlying the pathogenesis of this disease, highlighting current analyses and novel treatment propositions. Together, the accumulation of these data will aid in the understanding and development of more effective therapeutic options for the treatment of DMGs.

Abstract

Diffuse midline gliomas (DMGs) are invariably fatal pediatric brain tumours that are inherently resistant to conventional therapy. In recent years our understanding of the underlying molecular mechanisms of DMG tumorigenicity has resulted in the identification of novel targets and the development of a range of potential therapies, with multiple agents now being progressed to clinical translation to test their therapeutic efficacy. Here, we provide an overview of the current therapies aimed at epigenetic and mutational drivers, cellular pathway aberrations and tumor microenvironment mechanisms in DMGs in order to aid therapy development and facilitate a holistic approach to patient treatment.

PKI-587 enhances radiosensitization of hepatocellular carcinoma by inhibiting the PI3K/AKT/mTOR pathways and DNA damage repair

Radiation is an important therapeutic strategy for hepatocellular (HCC). In this study, we evaluated the role of the dual PI3K/mTOR inhibitor, PKI-587, on radiosensitization of HCC and its possible mechanism. MTT, colony formation, flow cytometry, and immunofluorescence were used to analyze the proliferation, cell cycle, formation of residual γ-H2AX foci, and apoptosis of HCC cells. A SK-Hep1 xenograft HCC model was used to assess the effects of PKI-587 in combination with ionizing radiation in vivo. The activation levels of PI3K/AKT/mTOR and DNA damage repair pathways and their downstream effector molecules were detected with Western blot. It was found that PKI-587 sensitized HCC cells to radiation by increasing DNA damage, enhancing G0/G1 cell-cycle arrest, and inducing apoptosis. In vivo, the combination of radiation with PKI-587 significantly inhibited tumor growth. These findings suggest the usefulness of PKI-587 on radiosensitization of HCC cells by inhibiting the PI3K/AKT/mTOR and DNA damage repair pathways. The combination of ionizing radiation and PKI-587 may be a strategy to improve the efficacy of treating HCC.

Translation Initiation Machinery as a Tumor Selective Target for Radiosensitization

Towards improving the efficacy of radiotherapy, one approach is to target the molecules and processes mediating cellular radioresponse. Along these lines, translational control of gene expression has been established as a fundamental component of cellular radioresponse, which suggests that the molecules participating in this process (i.e., the translational machinery) can serve as determinants of radiosensitivity. Moreover, the proteins comprising the translational machinery are often overexpressed in tumor cells suggesting the potential for tumor specific radiosensitization. Studies to date have shown that inhibiting proteins involved in translation initiation, the rate-limiting step in translation, specifically the three members of the eIF4F cap binding complex eIF4E, eIF4G, and eIF4A as well as the cap binding regulatory kinases mTOR and Mnk1/2, results in the radiosensitization of tumor cells. Because ribosomes are required for translation initiation, inhibiting ribosome biogenesis also appears to be a strategy for radiosensitization. In general, the radiosensitization induced by targeting the translation initiation machinery involves inhibition of DNA repair, which appears to be the consequence of a reduced expression of proteins critical to radioresponse. The availability of clinically relevant inhibitors of this component of the translational machinery suggests opportunities to extend this approach to radiosensitization to patient care.

Unbiased Proteomic and Phosphoproteomic Analysis Identifies Response Signatures and Novel Susceptibilities After Combined MEK and mTOR Inhibition in BRAFV600E Mutant Glioma

The mitogen-activated protein kinase pathway is one of the most frequently altered pathways in cancer. It is involved in the control of cell proliferation, invasion, and metabolism, and can cause resistance to therapy. A number of aggressive malignancies, including melanoma, colon cancer, and glioma, are driven by a constitutively activating missense mutation (V600E) in the v-Raf murine sarcoma viral oncogene homolog B (BRAF) component of the pathway. Mitogen-activated protein kinase kinase (MEK) inhibition is initially effective in targeting these cancers, but reflexive activation of mammalian target of rapamycin (mTOR) signaling contributes to frequent therapy resistance. We have previously demonstrated that combination treatment with the MEK inhibitor trametinib and the dual mammalian target of rapamycin complex 1/2 inhibitor TAK228 improves survival and decreases vascularization in a BRAFV600E mutant glioma model. To elucidate the mechanism of action of this combination therapy and understand the ensuing tumor response, we performed comprehensive unbiased proteomic and phosphoproteomic characterization of BRAFV600E mutant glioma xenografts after short-course treatment with trametinib and TAK228. We identified 13,313 proteins and 30,928 localized phosphosites, of which 12,526 proteins and 17,444 phosphosites were quantified across all samples (data available via ProteomeXchange; identifier PXD022329). We identified distinct response signatures for each monotherapy and combination therapy and validated that combination treatment inhibited activation of the mitogen-activated protein kinase and mTOR pathways. Combination therapy also increased apoptotic signaling, suppressed angiogenesis signaling, and broadly suppressed the activity of the cyclin-dependent kinases. In response to combination therapy, both epidermal growth factor receptor and class 1 histone deacetylase proteins were activated. This study reports a detailed (phospho)proteomic analysis of the response of BRAFV600E mutant glioma to combined MEK and mTOR pathway inhibition and identifies new targets for the development of rational combination therapies for BRAF-driven tumors.

Radiosensitization in Pediatric High-Grade Glioma: Targets, Resistance and Developments

Pediatric high-grade gliomas (pHGG) are the leading cause of cancer-related death in children. These epigenetically dysregulated tumors often harbor mutations in genes encoding histone 3, which contributes to a stem cell-like, therapy-resistant phenotype. Furthermore, pHGG are characterized by a diffuse growth pattern, which, together with their delicate location, makes complete surgical resection often impossible. Radiation therapy (RT) is part of the standard therapy against pHGG and generally the only modality, apart from surgery, to provide symptom relief and a delay in tumor progression. However, as a single treatment modality, RT still offers no chance for a cure. As with most therapeutic approaches, irradiated cancer cells often acquire resistance mechanisms that permit survival or stimulate regrowth after treatment, thereby limiting the efficacy of RT. Various preclinical studies have investigated radiosensitizers in pHGG models, without leading to an improved clinical outcome for these patients. However, our recently improved molecular understanding of pHGG generates new opportunities to (re-)evaluate radiosensitizers in these malignancies. Furthermore, the use of radio-enhancing agents has several benefits in pHGG compared to other cancers, which will be discussed here. This review provides an overview and a critical evaluation of the radiosensitization strategies that have been studied to date in pHGG, thereby providing a framework for improving radiosensitivity of these rapidly fatal brain tumors.

Advanced Pediatric Diffuse Pontine Glioma Murine Models Pave the Way towards Precision Medicine

Diffuse intrinsic pontine gliomas (DIPGs) account for ~15% of pediatric brain tumors, which invariably present with poor survival regardless of treatment mode. Several seminal studies have revealed that 80% of DIPGs harbor H3K27M mutation coded by HIST1H3B, HIST1H3C and H3F3A genes. The H3K27M mutation has broad effects on gene expression and is considered a tumor driver. Determination of the effects of H3K27M on posttranslational histone modifications and gene regulations in DIPG is critical for identifying effective therapeutic targets. Advanced animal models play critical roles in translating these cutting-edge findings into clinical trial development. Here, we review current molecular research progress associated with DIPG. We also summarize DIPG animal models, highlighting novel genomic engineered mouse models (GEMMs) and innovative humanized DIPG mouse models. These models will pave the way towards personalized precision medicine for the treatment of DIPGs.

TORC1/2 kinase inhibition depletes glutathione and synergizes with carboplatin to suppress the growth of MYC-driven medulloblastoma

Medulloblastoma is the most common malignant pediatric brain tumor. Tumors having high levels of c-MYC have the worst clinical prognosis, with only a minority of patients surviving. To address this unmet clinical need, we generated a human neural stem cell model of medulloblastoma that recapitulated the most aggressive subtype phenotypically and by mRNA expression profiling. An in silico analysis of these cells identified mTOR inhibitors as potential therapeutic agents. We hypothesized that the orally bioavailable TORC1/2 kinase inhibitor TAK228 would have activity against MYC-driven medulloblastoma. TAK228 inhibited mTORC1/2, decreased cell growth and caused apoptosis in high-MYC medulloblastoma cell lines. Comprehensive metabolic profiling of medulloblastoma orthotopic xenografts showed upregulation of glutathione compared to matched normal brain. TAK228 suppressed glutathione production. Because glutathione is required to detoxify platinum-containing chemotherapy, we hypothesized that TAK228 would cooperate with carboplatin in medulloblastoma. TAK228 synergized with carboplatin to inhibit cell growth and induce apoptosis and extended survival in orthotopic xenografts of high-MYC medulloblastoma. Brain-penetrant TORC1/2 inhibitors and carboplatin may be an effective combination therapy for high-risk medulloblastoma.

Gemcitabine and Selected mTOR Inhibitors in Uterine Sarcomas and Carcinosarcoma Cells- an Isobolographic Analysis

Introduction: mTOR inhibitors are anticancer agents affecting mTOR/AKT/PI3K pathway that is one of the most important in human cancer cells. Hyperactivation of mTOR/AKT/PI3K and overexpression of this pathway members are frequently reported in uterine sarcoma and carcinosarcoma. Present study is aimed to assess the activity of the two mTOR inhibitors (rapamycin - RAP and sapanisertib - MLN) as a single agent and combined with gemcitabine (GEM, one of substances commonly used in systemic anticancer treatment) in uterine sarcoma and carcinosarcoma in vitro models. Material and methods: SK-UT-1 and SK-UT1-B (uterine carcinosarcoma), MES-SA (leiomyosarcoma) and ESS-1 (endometrial stromal sarcoma) cell lines were used. An MTT assay was performed to examine the cytotoxicity of RAP, MLN and mixtures: RAP+MLN, RAP+GEM, MLN+GEM against these cells. The interactions between tested compounds were assessed in isobolographic analysis. Results and conclusions: Carcinosarcoma cell lines (both SK-UT-1 and SK-UT-1B) do not respond to RAP and respond relatively weakly to MLN treatment. Additive and supraadditive effects were noted for combined treatment with GEM and MLN. Endometrial stromal sarcoma cell line (ESS-1) occured to be sensitive to both RAP and MLN, but the response was stronger for MLN. Additive effect of all tested drug combinations was observed for ESS-1. Leiomyosarcoma cell line (MES-SA) was found sensitive to both mTOR inhibitors. Additive effects in combinations of GEM, RAP and MLN were observed, what makes them promising for future preclinical and clinical trials. Additivity with slight tendency towards antagonism between GEM and MLN observed in MES-SA cell line is unexpected finding and might prompt the mechanistic research aimed to explain this phenomenon.

Radio-Resistance and DNA Repair in Pediatric Diffuse Midline Gliomas

Malignant gliomas (MG) are among the most prevalent and lethal primary intrinsic brain tumors. Although radiotherapy (RT) is the most effective nonsurgical therapy, recurrence is universal. Dysregulated DNA damage response pathway (DDR) signaling, rampant genomic instability, and radio-resistance are among the hallmarks of MGs, with current therapies only offering palliation. A subgroup of pediatric high-grade gliomas (pHGG) is characterized by H3K27M mutation, which drives global loss of di- and trimethylation of histone H3K27. Here, we review the most recent literature and discuss the key studies dissecting the molecular biology of H3K27M-mutated gliomas in children. We speculate that the aberrant activation and/or deactivation of some of the key components of DDR may be synthetically lethal to H3K27M mutation and thus can open novel avenues for effective therapeutic interventions for patients suffering from this deadly disease.

Improving the Efficacy of Tumor Radiosensitization Through Combined Molecular Targeting

Chemoradiation, either alone or in combination with surgery or induction chemotherapy, is the current standard of care for most locally advanced solid tumors. Though chemoradiation is usually performed at the maximum tolerated doses of both chemotherapy and radiation, current cure rates are not satisfactory for many tumor entities, since tumor heterogeneity and plasticity result in chemo- and radioresistance. Advances in the understanding of tumor biology, a rapidly growing number of molecular targeting agents and novel technologies enabling the in-depth characterization of individual tumors, have fuelled the hope of entering an era of precision oncology, where each tumor will be treated according to its individual characteristics and weaknesses. At present though, molecular targeting approaches in combination with radiotherapy or chemoradiation have not yet proven to be beneficial over standard chemoradiation treatment in the clinical setting. A promising approach to improve efficacy is the combined usage of two targeting agents in order to inhibit backup pathways or achieve a more complete pathway inhibition. Here we review preclinical attempts to utilize such dual targeting strategies for future tumor radiosensitization.

Improving long-term survival in diffuse intrinsic pontine glioma

INTRODUCTION

Diffuse intrinsic pontine glioma (DIPG) is an almost universally fatal pediatric brain cancer. There has been no improvement in event-free survival (EFS) or overall survival (OS) despite immense effort through a multitude of clinical trials to find a cure. Recently, there has been a surge in the knowledge of DIPG biology, including the discovery of a recurrent H3F3A mutation in over 80% of these tumors.

AREAS COVERED

The authors review the most recent approaches to diagnosis and treatment of DIPG including chemotherapy, biologics, surgical approaches, and immunotherapy.

EXPERT OPINION

The authors propose four main opportunities to improve long-term survival. First, patients should be enrolled in scientifically sound clinical trials that include molecularly profiling either via stereotactic biopsy or liquid biopsy. Second, clinical trials should include more innovative endpoints other than traditional EFS and OS such as MRI/PET imaging findings combined with surrogates of activity (e.g. serial liquid biopsies) to better ascertain biologically active treatments. Third, innovative clinical trial approaches are needed to help allow for the rapid development of combination therapies to be tested. Finally, effort should be concentrated on reversing the effects of the histone mutation, as this malfunctioning development program seems to be key to DIPG relentlessness.

Pediatric high-grade glioma: aberrant epigenetics and kinase signaling define emerging therapeutic opportunities

INTRODUCTION

Supratentorial pediatric high-grade gliomas (pHGGs) are aggressive malignancies that lack effective treatment options. Deep genomic sequencing by multiple groups has revealed that the primary alterations unique to pHGGs occur in epigenetic and kinase genes. These mutations, fusions, and deletions present a therapeutic opportunity by use of small molecules targeting epigenetic modifiers and kinases that contribute to pHGG growth.

METHODS

Using a targeted search of the pre-clinical literature and clinicaltrials.gov for kinase and epigenetic pathways in pHGG, we collectively describe how these mechanisms are being targeted in pre-clinical animal models and in current clinical trials, as well as propose unexplored therapeutic possibilities for future investigations.

RESULTS

Relevant pHGG kinases are targetable by several FDA-approved or clinical-stage kinase inhibitors, including altered BRAF/MET/NTRK/ALK and wild-type PI3K/EGFR/PDGFR/VEGF/AXL. Epigenetic proteins implicated in pHGG are also clinically targetable and include histone erasers, writers and readers such as HDACs, demethylases LSD1/JMJD3, methyltransferase EZH2, chromatin reader bromodomains, and chromatin remodeler subunit BMI-1. Crosstalk between these pathways can occur involving kinases such as EGFR and AMPK interacting with epigenetic modifiers such as HDACs or EZH2. Single agent trial results of kinase inhibitors or epigenetic targets alone are underwhelming and hampered by poor pharmacokinetics, adaptive resistance, and broad inclusion criteria.

CONCLUSIONS

The genetic and phenotypic diversity of pHGGs is now well characterized after large-scale sequencing studies on patient tissue. However, clinical treatment paradigms have not yet shifted in response to this information. Combination therapies targeting multiple kinases or epigenetic targets may hold more promise, especially if attempted in selected patient populations with hemispheric pHGG tumors and relevant targeted therapeutic biomarkers.

PD-L1 Inhibitor Regulates the miR-33a-5p/PTEN Signaling Pathway and Can Be Targeted to Sensitize Glioblastomas to Radiation

Glioblastoma (GBM) is the most common and lethal brain tumor in adults. Ionizing radiation (IR) is a standard treatment for GBM patients and results in DNA damage. However, the clinical efficacy of IR is limited due to therapeutic resistance. The programmed death ligand 1 (PD-L1) blockade has a shown the potential to increase the efficacy of radiotherapy by inhibiting DNA damage and repair responses. The miR-33a-5p is an essential microRNA that promotes GBM growth and self-renewal. In this study, we investigated whether a PD-L1 inhibitor (a small molecule inhibitor) exerted radio-sensitive effects to impart an anti-tumor function in GBM cells by modulating miR-33a-5p. U87 MG cells and U251 cells were pretreated with PD-L1 inhibitor. The PD-L1 inhibitor-induced radio-sensitivity in these cells was assessed by assaying cellular apoptosis, clonogenic survival assays, and migration. TargetScan and luciferase assay showed that miR-33a-5p targeted the phosphatase and tensin homolog (PTEN) 3′ untranslated region. The expression level of PTEN was measured by western blotting, and was also silenced using small interfering RNAs. The levels of DNA damage following radiation was measured by the presence of γ-H₂AX foci, cell cycle, and the mRNA of the DNA damage-related genes, BRCA1, NBS1, RAD50, and MRE11. Our results demonstrated that the PD-L1 inhibitor significantly decreased the expression of the target gene, miR-33a-5p. In addition, pretreatment of U87 MG and U251 cells with the PD-L1 inhibitor increased radio-sensitivity, as indicated by increased apoptosis, while decreased survival and migration of GBM cells. Mir-33a-5p overexpression or silencing PTEN in U87 MG and U251 cells significantly attenuated PD-L1 radiosensitive effect. Additionally, PD-L1 inhibitor treatment suppressed the expression of the DNA damage response-related genes, BRCA1, NBS1, RAD50, and MRE11. Our results demonstrated a novel role for the PD-L1 inhibitor in inducing radio- sensitivity in GBM cells, where inhibiting miR-33a-5p, leading to PTEN activated, and inducing DNA damage was crucial for antitumor immunotherapies to treat GBM.

Diffuse intrinsic pontine glioma: molecular landscape and emerging therapeutic targets

PURPOSE OF REVIEW

Diffuse intrinsic pontine glioma (DIPG) is a fatal childhood brainstem malignancy. Despite advances in understanding of the molecular underpinnings of the tumor in the past decade, the dismal prognosis of DIPG has thus far remained unchanged. This review seeks to highlight promising therapeutic targets within three arenas: DIPG cell-intrinsic vulnerabilities, immunotherapeutic approaches to tumor clearance, and microenvironmental dependencies that promote tumor growth.

RECENT FINDINGS

Promising therapeutic strategies from recent studies include epigenetic modifying agents such as histone deacetylase inhibitors, bromodomain and extra-terminal motif (BET) protein inhibitors, and CDK7 inhibitors. Tumor-specific immunotherapies are emerging. Key interactions between DIPG and normal brain cells are coming to light, and targeting critical microenvironmental mechanisms driving DIPG growth in the developing childhood brain represents a new direction for therapy.

SUMMARY

Several DIPG treatment strategies are being evaluated in early clinical trials. Ultimately, we suspect that a multifaceted therapeutic approach utilizing cell-intrinsic, microenvironmental, and immunotherapeutic targets will be necessary for eradicating DIPG.

The autophagy reaction in the human umbilical cord: a potential marker for estimating fetal nutrition and neonatal growth

Objective: To assess the induction of autophagy in the human umbilical cord for physiological adaptation against starvation.Methods: The expression of autophagy-related proteins (LC3-II, p62) in umbilical cord tissues from 40 neonates was assessed by Western blotting. The correlation between the expression of autophagy-related proteins and maternal findings (height, weight, body mass index [BMI]), placental weight, neonatal findings (gestational age, height, weight, Apgar score at 1 min and 5 min), and the pH of the umbilical arterial blood were analyzed using Spearman's rank correlation coefficient test (p values of <.05 were considered significant). Venous blood findings (pH, pCO₂, glucose, total protein, albumin, and lactic acid) were also evaluated in 16 neonates admitted to the NICU.Results: The expression of LC3-II was positively correlated with serum total protein (ρ = 0.564, p = .023). The p62 level was also correlated with maternal BMI (ρ = 0.376, p = .017), the neonatal Apgar score at 1 min (ρ = 0.331 p = .037), total protein (ρ = 0.588, p = .017), and albumin (ρ = 0.552, p = .027) positively. A multiple linear regression analysis that included clinical parameters related to fetal nutrition and neonatal growth revealed that serum total protein was significantly associated with both LC3-II (p = .024) and p62 (p = .034) in the umbilical cord.Conclusion: The LC3-II or p62 expression in the umbilical cord may suggest the autophagy reaction for the homeostasis of protein or amino acid metabolism in the perinatal period.

Combination Therapy With Charged Particles and Molecular Targeting: A Promising Avenue to Overcome Radioresistance

Radiotherapy plays a central role in the treatment of cancer patients. Over the past decades, remarkable technological progress has been made in the field of conventional radiotherapy. In addition, the use of charged particles (e.g., protons and carbon ions) makes it possible to further improve dose deposition to the tumor, while sparing the surrounding healthy tissues. Despite these improvements, radioresistance and tumor recurrence are still observed. Although the mechanisms underlying resistance to conventional radiotherapy are well-studied, scientific evidence on the impact of charged particle therapy on cancer cell radioresistance is restricted. The purpose of this review is to discuss the potential role that charged particles could play to overcome radioresistance. This review will focus on hypoxia, cancer stem cells, and specific signaling pathways of EGFR, NFκB, and Hedgehog as well as DNA damage signaling involving PARP, as mechanisms of radioresistance for which pharmacological targets have been identified. Finally, new lines of future research will be proposed, with a focus on novel molecular inhibitors that could be used in combination with charged particle therapy as a novel treatment option for radioresistant tumors.

MGMT Expression Contributes to Temozolomide Resistance in H3K27M-Mutant Diffuse Midline Gliomas

Diffuse midline gliomas (DMGs) show resistance to many chemotherapeutic agents including temozolomide (TMZ). Histone gene mutations in DMGs trigger epigenetic changes including DNA hypomethylation, one of which is a frequent lack of O6-methyl-guanine-DNA methyltransferase (MGMT) promoter methylation, resulting in increased MGMT expression. We established the NGT16 cell line with HIST1H3B K27M and ACVR1 G328E gene mutations from a DMG patient and used this cell line and other DMG cell lines with H3F3A gene mutation (SF7761, SF8628, JHH-DIPG1) to analyze MGMT promoter methylation, MGMT protein expression, and response to TMZ. Three out of 4 DMG cell lines (NGT16, SF8628, and JHH-DIPG1) had unmethylated MGMT promoter, increased MGMT expression, and showed resistance to TMZ treatment. SF7761 cells with H3F3A gene mutation showed MGMT promoter methylation, lacked MGMT expression, and sensitivity to TMZ treatment. NGT16 line showed response to ALK2 inhibitor K02288 treatment in vitro. We confirmed in vitro that MGMT expression contributes to TMZ resistance in DMG cell lines. There is an urgent need to develop new strategies to treat TMZ-resistant DMGs.

TP53 Pathway Alterations Drive Radioresistance in Diffuse Intrinsic Pontine Gliomas (DIPG)

PURPOSE

Diffuse intrinsic pontine gliomas (DIPG) are the most severe pediatric brain tumors. Although accepted as the standard therapeutic, radiotherapy is only efficient transiently and not even in every patient. The goal of the study was to identify the underlying molecular determinants of response to radiotherapy in DIPG.

EXPERIMENTAL DESIGN

We assessed in vitro response to ionizing radiations in 13 different DIPG cellular models derived from treatment-naïve stereotactic biopsies reflecting the genotype variability encountered in patients at diagnosis and correlated it to their principal molecular alterations. Clinical and radiologic response to radiotherapy of a large cohort of 73 DIPG was analyzed according to their genotype. Using a kinome-wide synthetic lethality RNAi screen, we further identified target genes that can sensitize DIPG cells to ionizing radiations.

RESULTS

We uncover TP53 mutation as the main driver of increased radioresistance and validated this finding in four isogenic pairs of TP53^WT DIPG cells with or without TP53 knockdown. In an integrated clinical, radiological, and molecular study, we show that TP53^MUT DIPG patients respond less to irradiation, relapse earlier after radiotherapy, and have a worse prognosis than their TP53^WT counterparts. Finally, a kinome-wide synthetic lethality RNAi screen identifies CHK1 as a potential target, whose inhibition increases response to radiation specifically in TP53^MUT cells.

CONCLUSIONS

Here, we demonstrate that TP53 mutations are driving DIPG radioresistance both in patients and corresponding cellular models. We suggest alternative treatment strategies to mitigate radioresistance with CHK1 inhibitors. These findings will allow to consequently refine radiotherapy schedules in DIPG.

A low dose of AZD8055 enhances radiosensitivity of nasopharyngeal carcinoma cells by activating autophagy and apoptosis

Activation of the PI3K/mTOR pathways is significantly correlated with a poor prognosis in nasopharyngeal carcinoma (NPC). Inhibition of these pathways was reported to be effective in restoring radiosensitivity. In this study, the activity of the novel ATP-competitive, orally bioavailable mTOR inhibitor AZD8055 was found to inhibit the phosphorylated mTOR and NPC cells proliferation. The IC50 doses in CNE1 and CNE2 cell lines were 60 and 100 nanomolar, respectively. AZD8055 significantly enhanced the inhibitions of cell growth and colony formation induced by irradiation (P < 0.05 for all). AZD8055 at the IC50 doses prolonged G2/M arrest (P < 0.05) and promoted the apoptosis (P < 0.01) induced by irradiation and autophagy in NPC cells. Blocking autophagy weaken the cell growth inhibition and decreased apoptosis induced by AZD8055 combined with irradiation. Treatment with AZD8055 at 5, 10 and 20 mg/kg/d significantly enhanced NPC cell radiosensitivity in vivo and significantly induced apoptosis and autophagy in tumor tissues, Neither 5 nor 20 mg/kg/d AZD8055 induced significantly pro-apoptosis bax expressions in mouse livers and kidneys. 5 mg/kg/d produced good radiosensitivity but had little impact on body weight. We concluded that AZD8055 was a promising candidate radiosensitizer for NPC.

Preclinical therapeutic targets in diffuse midline glioma

Diffuse midline gliomas (DMG) are rapidly fatal tumors of the midbrain in children, characterized by a diffuse growing pattern and high levels of intrinsic resistance to therapy. The location of these tumors, residing behind the blood-brain barrier (BBB), and the limited knowledge about the biology of these tumors, has hindered the development of effective treatment strategies. However, the introduction of diagnostic biopsies and the implementation of autopsy protocols in several large centers world-wide has allowed for a detailed characterization of these rare tumors. This has resulted in the identification of novel therapeutic targets, as well as major advances in understanding the biology of DMG in relation to therapy resistance. We here provide an overview of the cellular pathways and tumor-specific aberrations that have been targeted in preclinical DMG research, and discuss the advantages and limitations of these therapeutic strategies in relation to therapy resistance and BBB-penetration. Therewith, we aim to provide researchers with a framework for successful preclinical therapy development.

ALK2 inhibitors display beneficial effects in preclinical models of ACVR1 mutant diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is a lethal childhood brainstem tumour, with a quarter of patients harbouring somatic mutations in ACVR1, encoding the serine/threonine kinase ALK2. Despite being an amenable drug target, little has been done to-date to systematically evaluate the role of ACVR1 in DIPG, nor to screen currently available inhibitors in patient-derived tumour models. Here we show the dependence of DIPG cells on the mutant receptor, and the preclinical efficacy of two distinct chemotypes of ALK2 inhibitor in vitro and in vivo. We demonstrate the pyrazolo[1,5-a]pyrimidine LDN-193189 and the pyridine LDN-214117 to be orally bioavailable and well-tolerated, with good brain penetration. Treatment of immunodeprived mice bearing orthotopic xenografts of H3.3K27M, ACVR1R206H mutant HSJD-DIPG-007 cells with 25 mg/kg LDN-193189 or LDN-214117 for 28 days extended survival compared with vehicle controls. Development of ALK2 inhibitors with improved potency, selectivity and advantageous pharmacokinetic properties may play an important role in therapy for DIPG patients.

Transient Inhibition of mTORC1 Signaling Ameliorates Irradiation-Induced Liver Damage

Recurrent liver cancer after surgery is often treated with radiotherapy, which induces liver damage. It has been documented that activation of the TGF-β and NF-κB signaling pathways plays important roles in irradiation-induced liver pathologies. However, the significance of mTOR signaling remains undefined after irradiation exposure. In the present study, we investigated the effects of inhibiting mTORC1 signaling on irradiated livers. Male C57BL/6J mice were acutely exposed to 8.0 Gy of X-ray total body irradiation and subsequently treated with rapamycin. The effects of rapamycin treatment on irradiated livers were examined at days 1, 3, and 7 after exposure. The results showed that 8.0 Gy of irradiation resulted in hepatocyte edema, hemorrhage, and sinusoidal congestion along with a decrease of ALB expression. Exposure of mice to irradiation significantly activated the mTORC1 signaling pathway determined by pS6 and p-mTOR expression via western blot and immunostaining. Transient inhibition of mTORC1 signaling by rapamycin treatment consistently accelerated liver recovery from irradiation, which was evidenced by decreasing sinusoidal congestion and increasing ALB expression after irradiation. The protective role of rapamycin on irradiated livers might be mediated by decreasing cellular apoptosis and increasing autophagy. These data suggest that transient inhibition of mTORC1 signaling by rapamycin protects livers against irradiation-induced damage.

Inhibition of enhancer of zest homologue 2 is a potential therapeutic target for high-MYC medulloblastoma

MYC amplification is common in Group 3 medulloblastoma and is associated with poor survival. Group 3 and Group 4 medulloblastomas are also known to have elevated levels of histone H3-lysine 27-tri-methylation (H3K27me3), at least in part due to high expression of the H3K27 methyltransferase enhancer of zest homologue 2 (EZH2), which can be regulated by MYC. We therefore examined whether MYC expression is associated with elevated EZH2 and H3K27me3 in medulloblastoma, and if high-MYC medulloblastomas are particularly sensitive to pharmacological EZH2 blockade. Western blot analysis of low (DAOY, UW228, CB SV40) and high (DAOY-MYC, UW228-MYC, CB-MYC, D425) MYC cell lines showed that higher levels of EZH2 and H3K27me3 were associated with elevated MYC. In fixed medulloblastoma samples examined using immunohistochemistry, most MYC positive tumors also had high H3K27me3, but many MYC negative ones did as well, and the correlation was not statistically significant. All high MYC lines tested were sensitive to the EZH2 inhibitor EPZ6438. Many low MYC lines also grew more slowly in the presence of EPZ6438, although DAOY-MYC cells responded more strongly than parent DAOY cultures with lower MYC levels. We find that higher MYC levels are associated with increased EZH2, and pharmacological blockade of EZH2 is a potential therapeutic strategy for aggressive medulloblastoma with elevated MYC.

Cutting Edge Therapeutic Insights Derived from Molecular Biology of Pediatric High-Grade Glioma and Diffuse Intrinsic Pontine Glioma (DIPG)

Pediatric high-grade glioma (pHGG) and brainstem gliomas are some of the most challenging cancers to treat in children, with no effective therapies and 5-year survival at ~2% for diffuse intrinsic pontine glioma (DIPG) patients. The standard of care for pHGG as a whole remains surgery and radiation combined with chemotherapy, while radiation alone is standard treatment for DIPG. Unfortunately, these therapies lack specificity for malignant glioma cells and have few to no reliable biomarkers of efficacy. Recent discoveries have revealed that epigenetic disruption by highly conserved mutations in DNA-packaging histone proteins in pHGG, especially DIPG, contribute to the aggressive nature of these cancers. In this review we pose unanswered questions and address unexplored mechanisms in pre-clinical models and clinical trial data from pHGG patients. Particular focus will be paid towards therapeutics targeting chromatin modifiers and other epigenetic vulnerabilities that can be exploited for pHGG therapy. Further delineation of rational therapeutic combinations has strong potential to drive development of safe and efficacious treatments for pHGG patients.

Antidiabetic Biguanides Radiosensitize Hypoxic Colorectal Cancer Cells Through a Decrease in Oxygen Consumption

Background and Purpose: The anti-diabetic biguanide drugs metformin and phenformin exhibit antitumor activity in various models. However, their radiomodulatory effect under hypoxic conditions, particularly for phenformin, is largely unknown. This study therefore examines whether metformin and phenformin as mitochondrial complex I blockades could overcome hypoxic radioresistance through inhibition of oxygen consumption.

Materials and Methods: A panel of colorectal cancer cells (HCT116, DLD-1, HT29, SW480, and CT26) was exposed to metformin or phenformin for 16 h at indicated concentrations. Afterward, cell viability was measured by MTT and colony formation assays. Apoptosis and reactive oxygen species (ROS) were detected by flow cytometry. Phosphorylation of AMP-activated protein kinase (AMPK) was examined by western blot. Mitochondria complexes activity and oxygen consumption rate (OCR) were measured by seahorse analyzer. The radiosensitivity of tumor cells was assessed by colony formation assay under aerobic and hypoxic conditions. The in vitro findings were further validated in colorectal CT26 tumor model.

Results: Metformin and phenformin inhibited mitochondrial complex I activity and subsequently reduced OCR in a dose-dependent manner starting at 3 mM and 30 μM, respectively. As a result, the hypoxic radioresistance of tumor cells was counteracted by metformin and phenformin with an enhancement ratio about 2 at 9 mM and 100 μM, respectively. Regarding intrinsic radioresistance, both of them did not exhibit any effect although there was an increase of phosphorylation of AMPK and ROS production. In tumor-bearing mice, metformin or phenformin alone did not show any anti-tumor effect. While in combination with radiation, both of them substantially delayed tumor growth and enhanced radioresponse, respectively, by 1.3 and 1.5-fold.

Conclusion: Our results demonstrate that metformin and phenformin overcome hypoxic radioresistance through inhibition of mitochondrial respiration, and provide a rationale to explore metformin and phenformin as hypoxic radiosensitizers.

Quantitative Proteomics Implicates Rictor/mTORC2 in Cell Adhesion

The mammalian target of rapamycin complex 2 (mTORC2) plays critical roles in various biological processes. To better understand the functions of mTORC2 and the underlying molecular mechanisms, we established a stable cell line with reduced Rictor, a specific component in mTORC2, and investigated the quantitative changes of the cellular proteome. As a result, we observed that 101 proteins were down-regulated and 50 proteins were up-regulated in Rictor knockdown cells. A protein-protein interaction network regulated by Rictor/mTORC2 was established, showing that Rictor/mTORC2 was involved in various cellular processes. Intriguingly, gene ontology analysis indicated that the proteome regulated by Rictor/mTORC2 was significantly involved with cell adhesion. Rictor knockdown affected the expressions of multiple cell adhesion associated molecules, e.g. integrin α-5 (ITGA5), transforming growth factor beta-1-induced transcript 1 protein (TGFB1I1), lysyl oxidase homologue 2 (LOXL2), etc. Further study suggested that Rictor/mTORC2 may regulate cell adhesion and invasion by modulating the expressions of these cell adhesion molecules through AKT. Taken together, this study maps the proteome regulated by Rictor/mTORC2 and reveals its role in promoting renal cancer cell invasion through modulating cell adhesion and migration.

MGMT Expression Contributes to Temozolomide Resistance in H3K27M-Mutant Diffuse Midline Gliomas and MGMT Silencing to Temozolomide Sensitivity in IDH-Mutant Gliomas

Histone H3 mutations are frequently found in diffuse midline gliomas (DMGs), which include diffuse intrinsic pontine gliomas and thalamic gliomas. These tumors have dismal prognoses. Recent evidence suggests that one reason for the poor prognoses is that O⁶-methylguanine-DNA methyltransferase (MGMT) promoter frequently lacks methylation in DMGs. This review compares the epigenetic changes brought about by histone mutations to those by isocitrate dehydrogenase-mutant gliomas, which frequently have methylated MGMT promoters and are known to be sensitive to temozolomide.

The Role of the Mammalian Target of Rapamycin (mTOR) in Pulmonary Fibrosis

The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR)-dependent pathway is one of the most integral pathways linked to cell metabolism, proliferation, differentiation, and survival. This pathway is dysregulated in a variety of diseases, including neoplasia, immune-mediated diseases, and fibroproliferative diseases such as pulmonary fibrosis. The mTOR kinase is frequently referred to as the master regulator of this pathway. Alterations in mTOR signaling are closely associated with dysregulation of autophagy, inflammation, and cell growth and survival, leading to the development of lung fibrosis. Inhibitors of mTOR have been widely studied in cancer therapy, as they may sensitize cancer cells to radiation therapy. Studies also suggest that mTOR inhibitors are promising modulators of fibroproliferative diseases such as idiopathic pulmonary fibrosis (IPF) and radiation-induced pulmonary fibrosis (RIPF). Therefore, mTOR represents an attractive and unique therapeutic target in pulmonary fibrosis. In this review, we discuss the pathological role of mTOR kinase in pulmonary fibrosis and examine how mTOR inhibitors may mitigate fibrotic progression.

REST upregulates gremlin to modulate diffuse intrinsic pontine glioma vasculature

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive glial tumor that occurs in children. The extremely poor median and 5-year survival in children afflicted with DIPG highlights the need for novel biology-driven therapeutics. Here, we have implicated the chromatin remodeler and regulator of brain development called RE1 Silencing Transcription Factor (REST), in DIPG pathology. We show that REST protein is aberrantly elevated in at least 21% of DIPG tumors compared to normal controls. Its knockdown in DIPG cell lines diminished cell growth and decreased their tumorigenicity in mouse intracranial models. DIPGs are vascularized tumors and interestingly, REST loss in DIPG cells also caused a substantial decline in tumor vasculature as measured by a decrease in CD31 and VEGFR2 staining. These observations were validated in vitro, where a significant decline in tube formation by human umbilical vein endothelial cells (HUVEC) was seen following REST-loss in DIPG cells. Mechanistically, REST controlled the secretion of a pro-angiogenic molecule and ligand for VEGFR2 called Gremlin-1 (GREM-1), and was associated with enhanced AKT activation. Importantly, the decline in tube formation caused by REST loss could be rescued by addition of recombinant GREM-1, which also caused AKT activation in HUVECs and human brain microvascular endothelial cells (HBMECs). In summary, our study is the first to demonstrate autocrine and paracrine functions for REST in DIPG development. It also provides the foundation for future investigations on anti-angiogenic therapies targeting GREM-1 in combination with drugs that target REST-associated chromatin remodeling activities.

Dual targeting of mitochondrial function and mTOR pathway as a therapeutic strategy for diffuse intrinsic pontine glioma

Diffuse Intrinsic Pontine Gliomas (DIPG) are the most devastating of all pediatric brain tumors. They mostly affect young children and, as there are no effective treatments, almost all patients with DIPG will die of their tumor within 12 months of diagnosis. A key feature of this devastating tumor is its intrinsic resistance to all clinically available therapies. It has been shown that glioma development is associated with metabolic reprogramming, redox state disruption and resistance to apoptotic pathways. The mitochondrion is an attractive target as a key organelle that facilitates these critical processes. PENAO is a novel anti-cancer compound that targets mitochondrial function by inhibiting adenine nucleotide translocase (ANT). Here we found that DIPG neurosphere cultures express high levels of ANT2 protein and are sensitive to the mitochondrial inhibitor PENAO through oxidative stress, while its apoptotic effects were found to be further enhanced upon co-treatment with mTOR inhibitor temsirolimus. This combination therapy was found to act through inhibition of PI3K/AKT/mTOR pathway, HSP90 and activation of AMPK. In vivo experiments employing an orthotopic model of DIPG showed a marginal anti-tumour effect likely due to poor penetration of the inhibitors into the brain. Further testing of this anti-DIPG strategy with compounds that penetrate the BBB is warranted.

Preclinical analysis of MTOR complex 1/2 inhibition in diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is an incurable childhood brain tumor. The mechanistic target of rapamycin (MTOR), a key oncogene, functions as two distinct signaling complexes, MTORC1 and MTORC2. We set out to determine the preclinical efficacy and mechanism of action of MTOR inhibitors in DIPG. We evaluated the MTORC1 inhibitor everolimus and the MTORC1/2 inhibitor AZD2014 in three patient-derived DIPG cell lines using cell culture models. We created dose-response curves for both compounds. We measured phenotypic effects on cell self-renewal, apoptosis, cell cycle, differentiation, senescence, and autophagy. We assessed the effects of each compound on the AKT pathway. Finally, we measured the efficacy of AZD2014 in combination with radiation therapy (RT) and a panel of FDA-approved chemotherapy drugs. While everolimus showed minimal antitumor efficacy, AZD2014 revealed IC₅₀ levels of 410–552 nM and IC₉₀ levels of 1.30–8.86 µM in the three cell lines. AZD2014 demonstrated increased inhibition of cell self-renewal compared to everolimus. AZD2014 decreased expression of phospho-AKT, while no such effect was noted with everolimus. Direct AKT inhibition showed similar efficacy to AZD2014, and induction of constitutive AKT activity rescued DIPG cells from the effects of AZD2014. AZD2014 exhibited synergistic relationships with both RT and various chemotherapy agents across classes, including the multikinase inhibitor ponatinib. MTORC1/2 inhibition shows antitumor activity in cell culture models of DIPG due to the effect of MTORC2 inhibition on AKT. This strategy should be further assessed for potential incorporation into combinatorial approaches to the treatment of DIPG.

Multi-focal sequencing of a diffuse intrinsic pontine glioma establishes PTEN loss as an early event

Improved molecular understanding is needed for rational treatment of diffuse intrinsic pontine gliomas (DIPG). Here, using multi-focal paired tumor and germline exome DNA and RNA sequencing, we uncovered phosphatase and tensin homolog (PTEN) loss as a clonal mutation in the case of a 6-year-old boy with a diffuse intrinsic pontine glioma, and incorporated copy number alteration analyses to provide a more detailed understanding of clonal evolution in diffuse intrinsic pontine gliomas. As well, using the PedcBioPortal, we found alterations in PTEN in 16 of 326 (4.9%) cases of pediatric high-grade glioma (3 of 154 (1.9%) brainstem) for which full sequencing data was available. Our data strengthens the association with PTEN loss in diffuse intrinsic pontine gliomas and provides further argument for the inclusion of PTEN in future targeted sequencing panels for pediatric diffuse intrinsic pontine gliomas and for the development and optimization of mTOR/PI3K inhibitors with optimal central nervous system penetration.