Recent advances in the use of PI3K inhibitors for glioblastoma multiforme: current preclinical and clinical development

An update on the emerging approaches for histone deacetylase (HDAC) inhibitor drug discovery and future perspectives

INTRODUCTION

HDACs catalyze the removal of acetyl groups from the ε-N-acetylated lysine residues of various protein substrates including both histone and nonhistone proteins. Different HDACs have distinct biological functions and are recruited to specific regions of the genome. HDAC inhibitors have attracted much attention in recent decades; indeed, there have been more than thirty HDAC inhibitors investigated in clinic trials with five approvals being achieved.

AREAS COVERED

This review covers the emerging approaches for HDAC inhibitor drug discovery from the past five years and includes discussion of structure-based rational design, isoform selectivity, and dual mechanism/multi-targeting. Chemical structures in addition to the in vitro and in vivo inhibiting activity of these compounds have also been discussed.

EXPERT OPINION

The exact role and biological functions of HDACs is still under investigation with a variety of HDAC inhibitors having been designed and evaluated. HDAC inhibitors have shown promise in treating cancer, AD, metabolic disease, viral infection, and multiple sclerosis, but there is still a lot of room for clinical improvement. In the future, more efforts should be put into (i) HDAC isoform identification (ii) the optimization of selectivity, activity, and pharmacokinetics; and (iii) unconventional approaches for discovering different effective scaffolds and pharmacophores.

The interplay of ROS and the PI3K/Akt pathway in autophagy regulation

Autophagy causes the breakdown of damaged proteins and organelles to their constituent components. The phosphatidylinositol 3-kinase (PI3K) pathway played an important role in regulating the autophagic response of cells in response to changing reactive oxygen species (ROS) levels. The PI3K α catalytic subunit inhibits autophagy, while its β catalytic subunit promotes autophagy in response to changes in ROS levels. The downstream Akt protein acts against autophagy initiation in response to increases in ROS levels under nutrient-rich conditions. Akt acts by activating a mechanistic target of the rapamycin complex 1 (mTORC1) and by arresting autophagic gene expression. The AMP-activated protein kinase (AMPK) protein counteracts the Akt actions. mTORC1 and mTORC2 inhibit autophagy under moderate ROS levels, but under high ROS levels, mTORC2 can promote cellular senescence via autophagy. Phosphatase and tensin homolog (PTEN) protein are the negative regulators of the PI3K pathway, and it has proautophagic activities. Studies conducted on cells treated with flavonoids and ionizing radiation showed that the moderate increase in ROS levels in the flavonoid-treated groups corresponded with higher PTEN levels and lowered Akt levels leading to a higher occurrence of autophagy. In contrast, higher ROS levels evoked by ionizing radiation caused a lowering of the incidence of autophagy.

Updated Insights on EGFR Signaling Pathways in Glioma

Nowadays, due to recent advances in molecular biology, the pathogenesis of glioblastoma is better understood. For the newly diagnosed, the current standard of care is represented by resection followed by radiotherapy and temozolomide administration, but because median overall survival remains poor, new diagnosis and treatment strategies are needed. Due to the quick progression, even with aggressive multimodal treatment, glioblastoma remains almost incurable. It is known that epidermal growth factor receptor (EGFR) amplification is a characteristic of the classical subtype of glioma. However, targeted therapies against this type of receptor have not yet shown a clear clinical benefit. Many factors contribute to resistance, such as ineffective blood-brain barrier penetration, heterogeneity, mutations, as well as compensatory signaling pathways. A better understanding of the EGFR signaling network, and its interrelations with other pathways, are essential to clarify the mechanisms of resistance and create better therapeutic agents.

Synergism between the phosphatidylinositol 3-kinase p110β isoform inhibitor AZD6482 and the mixed lineage kinase 3 inhibitor URMC-099 on the blockade of glioblastoma cell motility and focal adhesion formation

Background

Glioblastoma multiforme, the most aggressive and malignant primary brain tumor, is characterized by rapid growth and extensive infiltration to neighboring normal brain parenchyma. Our previous studies delineated a crosstalk between PI3K/Akt and JNK signaling pathways, and a moderate anti-glioblastoma synergism caused by the combined inhibition of PI3K p110β (PI3Kβ) isoform and JNK. However, this combination strategy is not potent enough. MLK3, an upstream regulator of ERK and JNK, may replace JNK to exert stronger synergism with PI3Kβ.

Methods

To develop a new combination strategy with stronger synergism, the expression pattern and roles of MLK3 in glioblastoma patient’s specimens and cell lines were firstly investigated. Then glioblastoma cells and xenografts in nude mice were treated with the PI3Kβ inhibitor AZD6482 and the MLK3 inhibitor URMC-099 alone or in combination to evaluate their combination effects on tumor cell growth and motility. The combination effects on cytoskeletal structures such as lamellipodia and focal adhesions were also evaluated.

Results

MLK3 protein was overexpressed in both newly diagnosed and relapsing glioblastoma patients’ specimens. Silencing of MLK3 using siRNA duplexes significantly suppressed migration and invasion, but promoted attachment of glioblastoma cells. Combined inhibition of PI3Kβ and MLK3 exhibited synergistic inhibitory effects on glioblastoma cell proliferation, migration and invasion, as well as the formation of lamellipodia and focal adhesions. Furthermore, combination of AZD6482 and URMC-099 effectively decreased glioblastoma xenograft growth in nude mice. Glioblastoma cells treated with this drug combination showed reduced phosphorylation of Akt and ERK, and decreased protein expression of ROCK2 and Zyxin.

Conclusion

Taken together, combination of AZD6482 and URMC-099 showed strong synergistic anti-tumor effects on glioblastoma in vitro and in vivo. Our findings suggest that combined inhibition of PI3Kβ and MLK3 may serve as an attractive therapeutic approach for glioblastoma multiforme.

A Computational Framework to Identify Biomarkers for Glioma Recurrence and Potential Drugs Targeting Them

Background: Recurrence is still a major obstacle to the successful treatment of gliomas. Understanding the underlying mechanisms of recurrence may help for developing new drugs to combat gliomas recurrence. This study provides a strategy to discover new drugs for recurrent gliomas based on drug perturbation induced gene expression changes. Methods: The RNA-seq data of 511 low grade gliomas primary tumor samples (LGG-P), 18 low grade gliomas recurrent tumor samples (LGG-R), 155 glioblastoma multiforme primary tumor samples (GBM-P), and 13 glioblastoma multiforme recurrent tumor samples (GBM-R) were downloaded from TCGA database. DESeq2, key driver analysis and weighted gene correlation network analysis (WGCNA) were conducted to identify differentially expressed genes (DEGs), key driver genes and coexpression networks between LGG-P vs LGG-R, GBM-P vs GBM-R pairs. Then, the CREEDS database was used to find potential drugs that could reverse the DEGs and key drivers. Results: We identified 75 upregulated and 130 downregulated genes between LGG-P and LGG-R samples, which were mainly enriched in human papillomavirus (HPV) infection, PI3K-Akt signaling pathway, Wnt signaling pathway, and ECM-receptor interaction. A total of 262 key driver genes were obtained with frizzled class receptor 8 (FZD8), guanine nucleotide-binding protein subunit gamma-12 (GNG12), and G protein subunit β2 (GNB2) as the top hub genes. By screening the CREEDS database, we got 4 drugs (Paclitaxel, 6-benzyladenine, Erlotinib, Cidofovir) that could downregulate the expression of up-regulated genes and 5 drugs (Fenofibrate, Oxaliplatin, Bilirubin, Nutlins, Valproic acid) that could upregulate the expression of down-regulated genes. These drugs may have a potential in combating recurrence of gliomas. Conclusion: We proposed a time-saving strategy based on drug perturbation induced gene expression changes to find new drugs that may have a potential to treat recurrent gliomas.

Amalgamation of PI3K and EZH2 blockade synergistically regulates invasion and angiogenesis: combination therapy for glioblastoma multiforme

Glioblastoma multiforme is known as the primary malignant and most devastating form of tumor in central nervous system of adult population. Amongst all CNS cancers, Glioblastoma multiforme GBM is a rare grade IV astrocytoma and it has the worst prognosis initiated by metastasis to supra-tentorial region of the brain. Current options for the treatment include surgery, radiation therapy and chemotherapy. Substantial information of its pathology and molecular signaling exposed new avenues for generating innovative therapies. In our study, we have undertaken a novel combination approach for GBM treatment. PI3K signaling participates in cancer progression and plays a significant role in metastasis. Here, we are targeting PI3K signaling pathways in glioblastoma along with EZH2, a known transcriptional regulator. We found that targeting transcriptional regulator EZH2 and PI3K affect cellular migration and morphological changes. These changes in signatory activities of cancerous cells led to inhibit its progression in vitro. With further analysis we confirmed the angiogenic inhibition and reduction in stem-ness potential of GBM. Later, cytokine proteome array analysis revealed several participants of metastasis and tumor induced angiogenesis using combination regime. This study provides a significant reduction in GBM progression investigated using Glioblastoma Multiforme U-87 cells with effective combination of pharmacological inhibitors PI-103 and EPZ-6438. This strategy will be further used to combat GBM more innovatively along with the existing therapies.

Nanodelivery Systems Targeting Epidermal Growth Factor Receptors for Glioma Management

A paradigm shift in treating the most aggressive and malignant form of glioma is continuously evolving; however, these strategies do not provide a better life and survival index. Currently, neurosurgical debulking, radiotherapy, and chemotherapy are the treatment options available for glioma, but these are non-specific in action. Patients invariably develop resistance to these therapies, leading to recurrence and death. Receptor Tyrosine Kinases (RTKs) are among the most common cell surface proteins in glioma and play a significant role in malignant progression; thus, these are currently being explored as therapeutic targets. RTKs belong to the family of cell surface receptors that are activated by ligands which in turn activates two major downstream signaling pathways via Rapidly Accelerating Sarcoma/mitogen activated protein kinase/extracellular-signal-regulated kinase (Ras/MAPK/ERK) and phosphatidylinositol 3-kinase/a serine/threonine protein kinase/mammalian target of rapamycin (PI3K/AKT/mTOR). These pathways are critically involved in regulating cell proliferation, invasion, metabolism, autophagy, and apoptosis. Dysregulation in these pathways results in uncontrolled glioma cell proliferation, invasion, angiogenesis, and cancer progression. Thus, RTK pathways are considered a potential target in glioma management. This review summarizes the possible risk factors involved in the growth of glioblastoma (GBM). The role of RTKs inhibitors (TKIs) and the intracellular signaling pathways involved, small molecules under clinical trials, and the updates were discussed. We have also compiled information on the outcomes from the various endothelial growth factor receptor (EGFR)-TKIs-based nanoformulations from the preclinical and clinical points of view. Aided by an extensive literature search, we propose the challenges and potential opportunities for future research on EGFR-TKIs-based nanodelivery systems.

Discovery of Potent and Selective 7-Azaindole Isoindolinone-Based PI3Kγ Inhibitors

The successful application of immunotherapy in the treatment of cancer relies on effective engagement of immune cells in the tumor microenvironment. Phosphoinositide 3-kinase γ (PI3Kγ) is highly expressed in tumor-associated macrophages, and its expression levels are associated with tumor immunosuppression and growth. Selective inhibition of PI3Kγ offers a promising strategy in immuno-oncology, which has led to the development of numerous potent PI3Kγ inhibitors with variable selectivity profiles. To facilitate further investigation of the therapeutic potential of PI3Kγ inhibition, we required a potent and PI3Kγ-selective tool compound with sufficient metabolic stability for use in future in vivo studies. Herein, we describe some of our efforts to realize this goal through the systematic study of SARs within a series of 7-azaindole-based PI3Kγ inhibitors. The large volume of data generated from this study helped guide our subsequent lead optimization efforts and will inform further development of PI3Kγ-selective inhibitors for use in immunomodulation.

The therapeutic value of XL388 in human glioma cells

XL388 is a highly efficient and orally-available ATP-competitive PI3K-mTOR dual inhibitor. Its activity against glioma cells was studied here. In established and primary human glioma cells, XL388 potently inhibited cell survival and proliferation as well as cell migration, invasion and cell cycle progression. The dual inhibitor induced significant apoptosis activation in glioma cells. In A172 cells and primary human glioma cells, XL388 inhibited Akt-mTORC1/2 activation by blocking phosphorylation of Akt and S6K1. XL388-induced glioma cell death was only partially attenuated by a constitutively-active mutant Akt1. Furthermore, it was cytotoxic against Akt1-knockout A172 glioma cells. XL388 downregulated MAF bZIP transcription factor G (MAFG) and inhibited Nrf2 signaling, causing oxidative injury in glioma cells. Conversely, antioxidants, n-acetylcysteine, pyrrolidine dithiocarbamate and AGI-106, alleviated XL388-induced cytotoxicity and apoptosis in glioma cells. Oral administration of XL388 inhibited subcutaneous A172 xenograft growth in severe combined immunodeficient mice. Akt-S6K1 inhibition and MAFG downregulation were detected in XL388-treated A172 xenograft tissues. Collectively, XL388 efficiently inhibits human glioma cell growth, through Akt-mTOR-dependent and -independent mechanisms.

KIF3C Promotes Proliferation, Migration, and Invasion of Glioma Cells by Activating the PI3K/AKT Pathway and Inducing EMT

Kinesin superfamily protein 3C (KIF3C), a motor protein of the kinesin superfamily, is expressed in the central nervous system (CNS). Recently, several studies have suggested that KIF3C may act as a potential therapeutic target in solid tumors. However, the exact function and possible mechanism of the motor protein KIF3C in glioma remain unclear. In this study, a variety of tests including CCK-8, migration, invasion, and flow cytometry assays, and western blot were conducted to explore the role of KIF3C in glioma cell lines (U87 and U251). We found that overexpression of KIF3C in glioma cell lines promoted cell proliferation, migration, and invasion and suppressed apoptosis, while silencing of KIF3C reversed these effects. Ectopic KIF3C also increased the expression of N-cadherin, vimentin, snail, and slug to promote the epithelial-mesenchymal transition (EMT). Mechanistically, overexpression of KIF3C increased the levels of phosphatidylinositol 3-kinase (PI3K) and phosphorylated protein kinase B (p-AKT). These responses were reversed by KIF3C downregulation or AKT inhibition. Our results indicate that KIF3C promotes proliferation, migration, and invasion and inhibits apoptosis in glioma cells, possibly by activating the PI3K/AKT pathway in vitro. KIF3C might act as a potential biomarker or therapeutic target for further basic research or clinical management of glioma.

Identification of Prognostic Model and Biomarkers for Cancer Stem Cell Characteristics in Glioblastoma by Network Analysis of Multi-Omics Data and Stemness Indices

The progression of most human cancers mainly involves the gradual accumulation of the loss of differentiated phenotypes and the sequential acquisition of progenitor and stem cell-like features. Glioblastoma multiforme (GBM) stem cells (GSCs), characterized by self-renewal and therapeutic resistance, play vital roles in GBM. However, a comprehensive understanding of GBM stemness remains elusive. Two stemness indices, mRNAsi and EREG-mRNAsi, were employed to comprehensively analyze GBM stemness. We observed that mRNAsi was significantly related to multi-omics parameters (such as mutant status, sample type, transcriptomics, and molecular subtype). Moreover, potential mechanisms and candidate compounds targeting the GBM stemness signature were illuminated. By combining weighted gene co-expression network analysis with differential analysis, we obtained 18 stemness-related genes, 10 of which were significantly related to survival. Moreover, we obtained a prediction model from both two independent cancer databases that was not only an independent clinical outcome predictor but could also accurately predict the clinical parameters of GBM. Survival analysis and experimental data confirmed that the five hub genes (CHI3L2, FSTL3, RPA3, RRM2, and YTHDF2) could be used as markers for poor prognosis of GBM. Mechanistically, the effect of inhibiting the proliferation of GSCs was attributed to the reduction of the ratio of CD133 and the suppression of the invasiveness of GSCs. The results based on an in vivo xenograft model are consistent with the finding that knockdown of the hub gene inhibits the growth of GSCs in vitro. Our approach could be applied to facilitate the development of objective diagnostic and targeted treatment tools to quantify cancer stemness in clinical tumors, and perhaps lead considerable benefits that could predict tumor prognosis, identify new stemness-related targets and targeted therapies, or improve targeted therapy sensitivity. The five genes identified in this study are expected to be the targets of GBM stem cell therapy.

IRF-1 Inhibits Angiogenic Activity of HPV16 E6 Oncoprotein in Cervical Cancer

HPV16 E6 oncoprotein is a member of the human papillomavirus (HPV) family that contributes to enhanced cellular proliferation and risk of cervical cancer progression via viral infection. In this study, interferon regulatory factor-1 (IRF-1) regulates cell growth inhibition and transcription factors in immune response, and acts as an HPV16 E6-binding cellular molecule. Over-expression of HPV16 E6 elevated cell growth by attenuating IRF-1-induced apoptosis and repressing p21 and p53 expression, but activating cyclin D1 and nuclear factor kappa B (NF-κB) expression. The promoter activities of p21 and p53 were suppressed, whereas NF-κB activities were increased by HPV16 E6. Additionally, the cell viability of HPV16 E6 was diminished by IRF-1 in a dose-dependent manner. We found that HPV16 E6 activated vascular endothelial growth factor (VEGF)-induced endothelial cell migration and proliferation as well as phosphorylation of VEGFR-2 via direct interaction in vitro. HPV16 E6 exhibited potent pro-angiogenic activity and clearly enhanced the levels of hypoxia-inducible factor-1α (HIF-1α). By contrast, the loss of function of HPV16 E6 by siRNA-mediated knockdown inhibited the cellular events. These data provide direct evidence that HPV16 E6 facilitates tumour growth and angiogenesis. HPV16 E6 also activates the PI3K/mTOR signalling cascades, and IRF-1 suppresses HPV16 E6-induced tumourigenesis and angiogenesis. Collectively, these findings suggest a biological mechanism underlying the HPV16 E6-related activity in cervical tumourigenesis.

A Novel Orthotopic Patient-Derived Xenograft Model of Radiation-Induced Glioma Following Medulloblastoma

Radiation-induced glioma (RIG) is a highly aggressive brain cancer arising as a consequence of radiation therapy. We report a case of RIG that arose in the brain stem following treatment for paediatric medulloblastoma, and the development and characterisation of a matched orthotopic patient-derived xenograft (PDX) model (TK-RIG915). Patient and PDX tumours were analysed using DNA methylation profiling, whole genome sequencing (WGS) and RNA sequencing. While initially thought to be a diffuse intrinsic pontine glioma (DIPG) based on disease location, results from methylation profiling and WGS were not consistent with this diagnosis. Furthermore, clustering analyses based on RNA expression suggested the tumours were distinct from primary DIPG. Additional gene expression analysis demonstrated concordance with a published RIG expression profile. Multiple genetic alterations that enhance PI3K/AKT and Ras/Raf/MEK/ERK signalling were discovered in TK-RIG915 including an activating mutation in PIK3CA, upregulation of PDGFRA and AKT2, inactivating mutations in NF1, and a gain-of-function mutation in PTPN11. Additionally, deletion of CDKN2A/B, increased IDH1 expression, and decreased ARID1A expression were observed. Detection of phosphorylated S6, 4EBP1 and ERK via immunohistochemistry confirmed PI3K pathway and ERK activation. Here, we report one of the first PDX models for RIG, which recapitulates the patient disease and is molecularly distinct from primary brain stem glioma. Genetic interrogation of this model has enabled the identification of potential therapeutic vulnerabilities in this currently incurable disease.

SMAGP knockdown inhibits the malignant phenotypes of glioblastoma cells by inactivating the PI3K/Akt pathway

Small trans-membrane and glycosylated protein (SMAGP), a novel small trans-membrane glycoprotein, is reported to be upregulated in multiple cancers and involved in tumor development. However, little is known about its role in the development of glioblastoma (GBM). GEPIA database was used to analyze SMAGP expression and evaluate the prognostic value of SMAGP in GBM. GO and KEGG pathway enrichment analyses were used to predict the biological functions and pathways of SMAGP and 948 SMAGP-correlated genes using DAVID database. Cell viability, colony formation ability, apoptosis, and invasion were evaluated by MTT, colony formation assay, flow cytometry analysis, and Transwell invasion assay, respectively. Western blot was applied to detect the expression of SMAGP, matrix metalloproteinase (MMP)-2, and MMP-9 and analyze the changes of phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling. Results showed that SMAGP was upregulated and correlated with poor prognosis in GBM. Functional annotation analysis revealed that SMAGP and 948 SMAGP-correlated genes were primarily associated with cell adhesion and PI3K/Akt pathway. SMAGP interference inhibited cell viability and colony formation ability and promoted apoptosis in GBM cells. Moreover, SMAGP interference inhibited GBM cell invasion and suppressed MMP-2 and MMP-9 expression. Additionally, SMAGP silencing inhibited the PI3K/Akt pathway in GBM cells. Overexpression of Akt abolished the effects of SMAGP knockdown on the malignant phenotypes of GBM cells. In conclusion, SMAGP silencing inhibited the malignant phenotypes of GBM cells by inactivating the PI3K/Akt pathway.

Cell-to-cell communication mediates glioblastoma progression in Drosophila

Glioblastoma (GB) is the most aggressive and lethal tumour of the central nervous system (CNS). GB cells grow rapidly and display a network of projections, ultra-long tumour microtubes (TMs), that mediate cell to cell communication. GB-TMs infiltrate throughout the brain, enwrap neurons and facilitate the depletion of the signalling molecule wingless (Wg)/WNT from the neighbouring healthy neurons. GB cells establish a positive feedback loop including Wg signalling upregulation that activates cJun N-terminal kinase (JNK) pathway and matrix metalloproteases (MMPs) production, which in turn promote further TMs infiltration, GB progression and neurodegeneration. Thus, cellular and molecular signals other than primary mutations emerge as central players of GB. Using a Drosophila model of GB, we describe the temporal organisation of the main cellular events that occur in GB, including cell-to-cell interactions, neurodegeneration and TM expansion. We define the progressive activation of JNK pathway signalling in GB mediated by the receptor Grindelwald (Grnd) and activated by the ligand Eiger (Egr)/TNFα produced by surrounding healthy brain tissue. We propose that cellular interactions of GB with the healthy brain tissue precede TM expansion and conclude that non-autonomous signals facilitate GB progression. These results contribute to deciphering the complexity and versatility of these incurable tumours.

Transcriptomics predicts compound synergy in drug and natural product treated glioblastoma cells

Pathway analysis is an informative method for comparing and contrasting drug-induced gene expression in cellular systems. Here, we define the effects of the marine natural product fucoxanthin, separately and in combination with the prototypic phosphatidylinositol 3-kinase (PI3K) inhibitor LY-294002, on gene expression in a well-established human glioblastoma cell system, U87MG. Under conditions which inhibit cell proliferation, LY-294002 and fucoxanthin modulate many pathways in common, including the retinoblastoma, DNA damage, DNA replication and cell cycle pathways. In sharp contrast, we see profound differences in the expression of genes characteristic of pathways such as apoptosis and lipid metabolism, contributing to the development of a differentiated and distinctive drug-induced gene expression signature for each compound. Furthermore, in combination, fucoxanthin synergizes with LY-294002 in inhibiting the growth of U87MG cells, suggesting complementarity in their molecular modes of action and pointing to further treatment combinations. The synergy we observe between the dietary nutraceutical fucoxanthin and the synthetic chemical LY-294002 in producing growth arrest in glioblastoma, illustrates the potential of nutri-pharmaceutical combinations in targeting this challenging disease.

The Botanical Drug PBI-05204, a Supercritical CO2 Extract of Nerium Oleander, Inhibits Growth of Human Glioblastoma, Reduces Akt/mTOR Activities, and Modulates GSC Cell-Renewal Properties

Glioblastoma multiform (GBM) is the most common primary glial tumor resulting in very low patient survival despite current extensive therapeutic efforts. Emerging evidence suggests that more effective treatments are required to overcome tumor heterogeneity, drug resistance and a complex tumor-supporting microenvironment. PBI-05204 is a specifically formulated botanical drug consisting of a modified supercritical C0₂ extract of Nerium oleander that has undergone both phase I and phase II clinical trials in the United States for treatment of patients with a variety of advanced cancers. The present study was designed to investigate the antitumor efficacy of this botanical drug against glioblastoma using both in vitro and in vivo cancer models as well as exploring efficacy against glioblastoma stem cells. All three human GBM cell lines, U87MG, U251, and T98G, were inhibited by PBI-05204 in a concentration dependent manner that was characterized by induction of apoptosis as evidenced by increased ANNEXIN V staining and caspase activities. The expression of proteins associated with both Akt and mTOR pathway was suppressed by PBI-05240 in all treated human GBM cell lines. PBI-05204 significantly suppressed U87 spheroid formation and the expression of important stem cell markers such as SOX2, CD44, and CXCR4. Oral administration of PBI-05204 resulted in a dose-dependent inhibition of U87MG, U251, and T98G xenograft growth. Additionally, PBI-05204–treated mice carrying U87-Luc cells as an orthotropic model exhibited significantly delayed onset of tumor proliferation and significantly increased overall survival. Immunohistochemical staining of xenograft derived tumor sections revealed dose-dependent declines in expression of Ki67 and CD31 positive stained cells but increased TUNEL staining. PBI-05204 represents a novel therapeutic botanical drug approach for treatment of glioblastoma as demonstrated by significant responses with in vivo tumor models. Both in vitro cell culture and immunohistochemical studies of tumor tissue suggest drug induction of tumor cell apoptosis and inhibition of PI3k/mTOR pathways as well as cancer stemness. Given the fact that PBI-05204 has already been examined in phase I and II clinical trials for cancer patients, its efficacy when combined with standard of care chemotherapy and radiotherapy should be explored in future clinical trials of this difficult to treat brain cancer.

Anticancer effects of novel NSAIDs derivatives on cultured human glioblastoma cells

Several epidemiologic, clinical and experimental reports indicate that nonsteroidal anti-inflammatory drugs (NSAIDs) could have a potential as anticancer agents. The aim of this study was the evaluation of cytotoxic potential in human glioblastoma cells of novel synthesized NSAID derivatives, obtained by linking, through a spacer, α-lipoic acid (ALA) to anti-inflammatory drugs, such as naproxen (AL-3, 11 and 17), flurbiprofen (AL-6, 13 and 19) and ibuprofen (AL-9, 15 and 21). The effects on the level of gene expression were also determined using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. According to our results, NSAID derivatives exhibited concentration dependent cytotoxic effects on U87-MG cell line when compared with the control group. Moreover, treatment of the most active compounds (AL-3, AL-6 and AL-9) caused upregulation of tumor suppressor gene PTEN and downregulation of some oncogenes such as AKT1, RAF1 and EGFR. In conclusion, our results revealed that AL-3, AL-6 and AL-9 could be suitable candidates for further investigation to develop new pharmacological strategies for the prevention of cancer.

Integrated regulatory models for inference of subtype-specific susceptibilities in glioblastoma

Glioblastoma multiforme (GBM) is a highly malignant form of cancer that lacks effective treatment options or well-defined strategies for personalized cancer therapy. The disease has been stratified into distinct molecular subtypes; however, the underlying regulatory circuitry that gives rise to such heterogeneity and its implications for therapy remain unclear. We developed a modular computational pipeline, Integrative Modeling of Transcription Regulatory Interactions for Systematic Inference of Susceptibility in Cancer (inTRINSiC), to dissect subtype-specific regulatory programs and predict genetic dependencies in individual patient tumors. Using a multilayer network consisting of 518 transcription factors (TFs), 10,733 target genes, and a signaling layer of 3,132 proteins, we were able to accurately identify differential regulatory activity of TFs that shape subtype-specific expression landscapes. Our models also allowed inference of mechanisms for altered TF behavior in different GBM subtypes. Most importantly, we were able to use the multilayer models to perform an in silico perturbation analysis to infer differential genetic vulnerabilities across GBM subtypes and pinpoint the MYB family member MYBL2 as a drug target specific for the Proneural subtype.

Decreased Expression of ZNF554 in Gliomas is Associated with the Activation of Tumor Pathways and Shorter Patient Survival

Zinc finger protein 554 (ZNF554), a member of the Krüppel-associated box domain zinc finger protein subfamily, is predominantly expressed in the brain and placenta in humans. Recently, we unveiled that ZNF554 regulates trophoblast invasion during placentation and its decreased expression leads to the early pathogenesis of preeclampsia. Since ZNF proteins are immensely implicated in the development of several tumors including malignant tumors of the brain, here we explored the pathological role of ZNF554 in gliomas. We examined the expression of ZNF554 at mRNA and protein levels in normal brain and gliomas, and then we searched for genome-wide transcriptomic changes in U87 glioblastoma cells transiently overexpressing ZNF554. Immunohistochemistry of brain tissues in our cohort (n = 62) and analysis of large TCGA RNA-Seq data (n = 687) of control, oligodendroglioma, and astrocytoma tissues both revealed decreased expression of ZNF554 towards higher glioma grades. Furthermore, low ZNF554 expression was associated with shorter survival of grade III and IV astrocytoma patients. Overexpression of ZNF554 in U87 cells resulted in differential expression, mostly downregulation of 899 genes. The "PI3K-Akt signaling pathway", known to be activated during glioma development, was the most impacted among 116 dysregulated pathways. Most affected pathways were cancer-related and/or immune-related. Congruently, cell proliferation was decreased and cell cycle was arrested in ZNF554-transfected glioma cells. These data collectively suggest that ZNF554 is a potential tumor suppressor and its decreased expression may lead to the loss of oncogene suppression, activation of tumor pathways, and shorter survival of patients with malignant glioma.

Microglia promote glioblastoma via mTOR-mediated immunosuppression of the tumour microenvironment

Tumour-associated microglia/macrophages (TAM) are the most numerous non-neoplastic populations in the tumour microenvironment in glioblastoma multiforme (GBM), the most common malignant brain tumour in adulthood. The mTOR pathway, an important regulator of cell survival/proliferation, is upregulated in GBM, but little is known about the potential role of this pathway in TAM. Here, we show that GBM-initiating cells induce mTOR signalling in the microglia but not bone marrow-derived macrophages in both in vitro and in vivo GBM mouse models. mTOR-dependent regulation of STAT3 and NF-κB activity promotes an immunosuppressive microglial phenotype. This hinders effector T-cell infiltration, proliferation and immune reactivity, thereby contributing to tumour immune evasion and promoting tumour growth in mouse models. The translational value of our results is demonstrated in whole transcriptome datasets of human GBM and in a novel in vitro model, whereby expanded-potential stem cells (EPSC)-derived microglia-like cells are conditioned by syngeneic patient-derived GBM-initiating cells. These results raise the possibility that microglia could be the primary target of mTOR inhibition, rather than the intrinsic tumour cells in GBM.

Neuregulin 1 enhances cell adhesion molecule L1 like expression levels and promotes malignancy in human glioma

Neural cell adhesion molecular L1-like protein (CHL1) is a member of the cell adhesion molecule L1 family and serves an important role in the development and progression of tumors. The cytokine neuregulin 1 (NRG1) has been indicated in the tumorigenesis and promotion of metastasis through the modulation of L1. However, the roles of NRG1 in regulating CHL1 in glioma have not been elucidated. The present study investigated the protein expression levels and roles of CHL1 and the possible correlation between NRG1 and CHL1 protein expression levels in human gliomas, both in vivo and in vitro. Using immunohistochemistry coupled with a human glioma tissue microarray, it was demonstrated that the percentage of CHL1-positive areas was the highest in grade II glioma tissues. Using immunofluorescence staining, a positive correlation was identified between the expression levels of CHL1 and proliferating cell nuclear antigen. In addition, CHL1 downregulation also resulted in increased senescence of U-87 MG human glioblastoma cells. In vitro, administration of NRG1α induced a significant increase in CHL1 protein expression levels in human glioma SHG-44 and U251 cells and in human glioblastoma U-87 MG cells, whereas NRG1β failed to increase CHL1 expression levels in U251 cells. These findings were further confirmed by the downregulation of NRG1 expression levels using small interfering RNA treatment, which resulted in the reduction of CHL1 protein expression levels in U-87 MG cells. These data indicate that NRG1 can regulate CHL1 protein expression levels in gliomas, that it is correlated with malignancy, and that NRG1 may contribute to malignancy by upregulating CHL1 protein expression levels in glioma/glioblastoma cells.

Role of PI3K/AKT pathway in cancer: the framework of malignant behavior

Given that the PI3K/AKT pathway has manifested its compelling influence on multiple cellular process, we further review the roles of hyperactivation of PI3K/AKT pathway in various human cancers. We state the abnormalities of PI3K/AKT pathway in different cancers, which are closely related with tumorigenesis, proliferation, growth, apoptosis, invasion, metastasis, epithelial-mesenchymal transition, stem-like phenotype, immune microenvironment and drug resistance of cancer cells. In addition, we investigated the current clinical trials of inhibitors against PI3K/AKT pathway in cancers and found that the clinical efficacy of these inhibitors as monotherapy has so far been limited despite of the promising preclinical activity, which means combinations of targeted therapy may achieve better efficacies in cancers. In short, we hope to feature PI3K/AKT pathway in cancers to the clinic and bring the new promising to patients for targeted therapies.

Long non-coding RNA GAS5, by up-regulating PRC2 and targeting the promoter methylation of miR-424, suppresses multiple malignant phenotypes of glioma

PURPOSE

Malignant gliomas remain significant challenges in clinic and pose dismal prognosis on patients. In this study, we focused on growth arrest-specific 5 (GAS5), a tumor suppressive long non-coding RNA in glioma, explored its crosstalk with miR-424, and examined their biological functions in glioma.

METHODS

Expressions of GAS5 and miR-424 were measured using qRT-PCR. The regulation of GAS5 on miR-424 expression was examined in GAS5-overexpressing glioma cells by combining methylation-specific PCR, western blotting, and RNA immunoprecipitation. Functional significance of GAS5 and miR-424 on in vitro cell proliferation, apoptosis, migration, invasion, and in vivo tumor growth was examined using colony formation, flow cytometry, wound healing, transwell assay, and the xenograft model, respectively. The potential targeting of AKT3 by miR-424 was investigated using luciferase reporter assay.

RESULTS

GAS5 and miR-424 were significantly down-regulated in glioma cells. GAS5 directly interacted with enhancer of zeste homolog 2 (EZH2), stimulated the formation of polycomb repressive complex 2 (PRC2), reduced the levels of DNA methyltransferases (Dnmts), alleviated promoter methylation of miR-424, and promoted miR-424 expression. Functionally, GAS5, by up-regulating miR-424, inhibited cell proliferation, migration, and invasion, while increased apoptosis of glioma cells in vitro, and suppressed xenograft growth in vivo. miR-424 directly inhibited AKT3 and altered the expressions of AKT3 targets, cyclinD1, c-Myc, Bax, and Bcl-2, which might contribute to its tumor suppressive activities.

CONCLUSIONS

GAS5, by inhibiting methylation and boosting expression of miR-424, inhibits AKT3 signaling and suppresses multiple malignant phenotypes. Therefore, stimulating GAS5/miR-424 signaling may benefit the treatment of glioma.

LncRNA SAMMSON Knockdown Inhibits the Malignancy of Glioblastoma Cells by Inactivation of the PI3K/Akt Pathway

Dysregulated lncRNAs are proposed to be tightly associated with the progression of various tumors including glioblastoma (GBM). LncRNA Survival Associated Mitochondrial Melanoma-Specific Oncogenic Non-Coding RNA (SAMMSON) has been reported to be an oncogenic lncRNA in several tumors. Nevertheless, the specific role and molecular mechanism of SAMMSON in GBM progression remain unknown. Expression of SAMMSON in GBM tissues and cells was detected by qRT-PCR. CCK-8 and LDH release assays were applied to evaluate cellular viability. Invasion effect was assessed by Transwell invasion assay and western blot analysis of E-cadherin and N-cadherin expression. Apoptosis was detected using flow cytometry analysis and caspase-3 activity assay. The protein levels of phosphatidylinositol-3-kinase (PI3K), phosphorylated (p)-PI3K, protein kinase B (Akt) and p-Akt were estimated by western blot. We found that SAMMSON was highly expressed in GBM tissues and cells. SAMMSON knockdown suppressed cell viability and increased LDH release in GBM cells. Moreover, SAMMSON silencing impeded the invasive ability of GBM cells by regulating epithelial-to-mesenchymal transition (EMT). Furthermore, SAMMSON downregulation increased the apoptotic rate and caspase-3 activity in GBM cells. Additionally, it was demonstrated that the PI3K/Akt pathway was inhibited following SAMMSON silencing in GBM cells. Rescue assays revealed that activation of the PI3K/Akt pathway by 740Y-P abolished SAMMSON knockdown-induced viability reduction, invasion suppression and apoptosis in GBM cells. Taken together, lncRNA SAMMSON knockdown inhibited the malignancy of GBM cells by inactivation of the PI3K/Akt pathway.

Feasibility of Targeting Glioblastoma Stem Cells: From Concept to Clinical Trials

OBJECTIVE

Glioblastoma is a highly aggressive and invasive brain and Central Nervous System (CNS) tumor. Current treatment options do not prolong overall survival significantly because the disease is highly prone to relapse. Therefore, research to find new therapies is of paramount importance. It has been discovered that glioblastomas contain a population of cells with stem-like properties and that these cells are may be responsible for tumor recurrence.

METHODS

A review of relevant papers and clinical trials in the field was conducted. A PubMed search with related keywords was used to gather the data. For example, "glioblastoma stem cells AND WNT signaling" is an example used to find information on clinical trials using the database ClinicalTrials.gov.

RESULTS

Cancer stem cell research has several fundamental issues and uncertainties that should be taken into consideration. Theoretically, a number of treatment options that target glioblastoma stem cells are available for patients. However, only a few of them have obtained promising results in clinical trials. Several strategies are still under investigation.

CONCLUSION

The majority of treatments to target cancer stem cells have failed during clinical trials. Taking into account a number of biases in the field and the number of unsuccessful investigations, the application of the cancer stem cells concept is questionable in clinical settings, at least with respect to glioblastoma.

Deep graph embedding for prioritizing synergistic anticancer drug combinations

Drug combinations are frequently used for the treatment of cancer patients in order to increase efficacy, decrease adverse side effects, or overcome drug resistance. Given the enormous number of drug combinations, it is cost- and time-consuming to screen all possible drug pairs experimentally. Currently, it has not been fully explored to integrate multiple networks to predict synergistic drug combinations using recently developed deep learning technologies. In this study, we proposed a Graph Convolutional Network (GCN) model to predict synergistic drug combinations in particular cancer cell lines. Specifically, the GCN method used a convolutional neural network model to do heterogeneous graph embedding, and thus solved a link prediction task. The graph in this study was a multimodal graph, which was constructed by integrating the drug-drug combination, drug-protein interaction, and protein-protein interaction networks. We found that the GCN model was able to correctly predict cell line-specific synergistic drug combinations from a large heterogonous network. The majority (30) of the 39 cell line-specific models show an area under the receiver operational characteristic curve (AUC) larger than 0.80, resulting in a mean AUC of 0.84. Moreover, we conducted an in-depth literature survey to investigate the top predicted drug combinations in specific cancer cell lines and found that many of them have been found to show synergistic antitumor activity against the same or other cancers in vitro or in vivo. Taken together, the results indicate that our study provides a promising way to better predict and optimize synergistic drug pairs in silico.

Long Non-Coding RNA PART1 Exerts Tumor Suppressive Functions in Glioma via Sponging miR-190a-3p and Inactivation of PTEN/AKT Pathway

Background

Glioma is the most commonly diagnosed primary brain tumor. Dysregulation of long non-coding RNA (lncRNA) is associated with initiation and development of various cancer types including glioma.

Methods

The relative expression of lncRNA was analyzed by real time-quantitative polymerase chain reaction (RT-qPCR). Cell counting kit (CCK-8) and flow cytometry analysis were applied to explore the role of prostate androgen-regulated transcript 1 (PART1) in glioma cell lines. Luciferase reporter assay, Western blotting and RT-qPCR were used to investigate the association between PART1, miR-190a-3p and phosphatase and tensin homolog deleted on chromosome ten (PTEN) in glioma cell lines.

Results

In the present study, we elucidated a pivotal role and molecular mechanism of lncRNA PART1 in glioma cell lines. It was found that PART1 was significantly downregulated in glioma tissues compared to normal tissues according to TCGA data and our RT-qPCR results. The cell-based assays showed that PART1 suppressed cell proliferation and triggered cell apoptosis in glioma cell lines. PART1 inactivated PI3K/AKT cascade in glioma cell lines. Transfection of constitutively activated AKT (Myr-AKT) reversed PART1 induced cell apoptosis and cell growth arrest. The bioinformatic analysis suggested that miR-190a-3p might bind to PART1. In the dual luciferase reporter assay, we validated that PART1 directly bound to miR-190a-3p in glioma cell lines. Furthermore, there was a reciprocal repression between PART1 and miR-190-3p. In addition, PART1 upregulated PTEN and inactivated PI3K/AKT pathway in glioma cell lines. Moreover, silencing of PTEN reversed PART1 overexpression induced cell growth arrest and apoptosis. In glioma tissues, the Pearson Correlation analysis showed that there was a strong-positive correlation between PART1 level and PTEN mRNA level.

Conclusion

Taken together, the current study revealed a PART1/miR-190a-3p/PTEN/PI3K/AKT axis in glioma and provided novel insights for understanding the complex lncRNA-miRNA network in glioma.

Repression of PCGF1 Decreases the Proliferation of Glioblastoma Cells in Association with Inactivation of c-Myc Signaling Pathway

Purpose

Glioblastoma (GBM) is the most common primary brain tumor with a poor therapeutic outcome. Polycomb group factor 1 (PCGF1), a member of the PcG (Polycomb group) family, is highly expressed in the developing nervous system of mice. However, the function and the mechanism of PCGF1 in GBM proliferation still remain unclear.

Methods

Knockdown of PCGF1 was performed in U87 GBM cell by shRNA strategy via lentivirus vector. MTT assay, colony formation assays, and flow cytometry were used to measure the properties of cell proliferation and cell cycle distribution, respectively. GeneChip analysis was performed to identify the downstream effector molecules. Rescue assay was constructed to verify the screening results.

Results

We first found that knockdown of PCGF1 led to the inhibition of U87 cells proliferation and decreased colony formation ability. The data from GeneChip expression profiling and Ingenuity Pathway Analysis (IPA) indicated that many of the altered gene cells are associated with the cell proliferation control pathways. We have further confirmed the suppression of AKT/GSK3β/c-Myc/cyclinD1 expressions by Western blotting analysis. The over-expression of c-Myc could partly restore the attenuated proliferation ability caused by knockdown of PCGF1.

Conclusion

All the above evidences suggested that PCGF1 might be closely associated with tumorigenesis and progression of glioblastoma (GBM), in which process the oncoprotein c-Myc may participate. PCGF1 could thus be a potential therapeutic target for the treatment of glioblastoma (GBM).

Mitochondrial dysfunction contributes to Rapamycin-induced apoptosis of Human Glioblastoma Cells - A synergistic effect with Temozolomide

Mammalian target of rapamycin (mTOR) is upregulated in a high percentage of glioblastomas. While a well-known mTOR inhibitor, rapamycin, has been shown to reduce glioblastoma survival, the role of mitochondria in achieving this therapeutic effect is less well known. Here, we examined mitochondrial dysfunction mechanisms that occur with the suppression of mTOR signaling. We found that, along with increased apoptosis, and a reduction in transformative potential, rapamycin treatment significantly affected mitochondrial health. Specifically, increased production of reactive oxygen species (ROS), depolarization of the mitochondrial membrane potential (MMP), and altered mitochondrial dynamics were observed. Furthermore, we verified the therapeutic potential of rapamycin-induced mitochondrial dysfunction through co-treatment with temzolomide (TMZ), the current standard of care for glioblastoma. Together these results demonstrate that the mitochondria remain a promising target for therapeutic intervention against human glioblastoma and that TMZ and rapamycin have a synergistic effect in suppressing glioblastoma viability, enhancing ROS production, and depolarizing MMP.

Upregulation of contactin-1 expression promotes prostate cancer progression

Contactin-1 (CNTN-1) has been reported to serve an oncogenic role in several cancer types. However, detailed mechanisms describing the influence of CNTN-1 in prostate cancer progression have not yet been elucidated. The present study aimed to determine the clinical significance of CNTN-1 expression in prostate cancer progression, and also to investigate the regulatory role of CNTN-1 in the proliferation, migration and invasive ability of prostate cancer cells. The results of the present study indicated that expression levels of CNTN-1 were significantly higher in prostate cancer tissues compared with adjacent normal tissues. Moreover, a high expression level of CNTN-1 was positively correlated with tumor size, stage and metastasis, as well as a poorer prognosis in patients with prostate cancer. Furthermore, CNTN-1-knockdown in prostate cancer cells (using short hairpin RNA) resulted in the significant inhibition of cancer cell proliferation, colony formation, migration and invasiveness. Silencing of CNTN-1 expression also suppressed epithelial-mesenchymal transition in prostate cancer cells via the upregulation of E-cadherin, and the downregulation of N-cadherin and vimentin expression. Inhibition of CNTN-1 expression also reduced the activity of the PI3K/AKT signaling pathway in prostate cancer cells. Thus, it was demonstrated that CNTN-1 expression is upregulated, and plays an oncogenic role, in prostate cancer cells. The results of the current study suggest that CNTN-1 may represent a promising therapeutic target, potentially improving the treatment of patients with prostate cancer.

Involvement of Phosphatase and Tensin Homolog in Cyclin-Dependent Kinase 4/6 Inhibitor-Induced Blockade of Glioblastoma

Dysregulation of retinoblastoma (Rb) signaling pathway have been established as a requirement for glioblastoma (GBM) initiation and progression, which suggests that blockade of CDK4/6-Rb signaling axis for GBM treatment. Palbociclib, a selective inhibitor of the cyclin-dependent kinases CDK4/6, has been applied for breast cancer treatment. However, its efficacy against glioblastoma has not been well clarified. Here, effects of CDK4/6 inhibitors on various kinds of GBM cell lines are investigated and the functional mechanisms are identified. Data showed that cells with diverse PTEN status respond to palbociclib differently. Gain-of-function and loss-of-function studies indicated that PTEN enhanced the sensitivity of GBM cells to palbociclib in vitro and in vivo, which was associated with suppressions of Akt and ERK signaling and independent of Rb signaling inhibition. Hence, our findings support that palbociclib selectively

PI3K/mTOR Pathway Inhibition: Opportunities in Oncology and Rare Genetic Diseases

The phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway has been implicated as a cancer target. Big pharma players and small companies have been developing small molecule inhibitors of PI3K and/or mTOR since the 1990s. Although four inhibitors have been approved, many open questions regarding tolerability, patient selection, sensitivity markers, development of resistances, and toxicological challenges still need to be addressed. Besides clear oncological indications, PI3K and mTOR inhibitors have been suggested for treating a plethora of different diseases. In particular, genetically induced PI3K/mTOR pathway activation causes rare disorders, known as overgrowth syndromes, like PTEN (phosphatase and tensin homolog) hamartomas, tuberous sclerosis complex (TSC), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA)-related overgrowth spectrum (PROS), and activated PI3-Kinase delta syndrome (PI3KCD, APDS). Some of those disorders likeTSC or hemimegalencephaly, which are one of the PROS disorders, also belong to a group of diseases called mTORopathies. This group of syndromes presents with additional neurological manifestations associated with epilepsy and other neuropsychiatric symptoms induced by neuronal mTOR pathway hyperactivation. While PI3K and mTOR inhibitors have been and still are intensively tested in oncology indications, their use in genetically defined syndromes and mTORopathies appear to be promising avenues for a pharmacological intervention.

Inhibition of phosphatidylinositol 3-kinase by PX-866 suppresses temozolomide-induced autophagy and promotes apoptosis in glioblastoma cells

Background

Temozolomide (TMZ) is the most commonly used chemotherapeutic agent used to treat glioblastoma (GBM), which causes significant DNA damage to highly proliferative cells. Our observations have added to accumulating evidence that TMZ induces stress-responsive cellular programs known to promote cell survival, including autophagy. As such, targeting these survival pathways may represent new vulnerabilities of GBM after treatment with TMZ.

Methods

Using the T98G human glioma cell line, we assessed the molecular signaling associated with TMZ treatment, the cellular consequences of using the pan-PI3K inhibitor PX-866, and performed clonogenic assays to determine the effect sequential treatment of TMZ and PX-866 had on colony formation. Additionally, we also use subcutaneous GBM patient derived xenograft (PDX) tumors to show relative LC3 protein expression and correlations between survival pathways and molecular markers which dictate clinical responsiveness to TMZ.

Results

Here, we report that TMZ can induce autophagic flux in T98G glioma cells. GBM patient-derived xenograft (PDX) tumors treated with TMZ also display an increase in the autophagosome marker LC3 II. Additionally, O⁶-methylguanine-DNA-methyltransferase (MGMT) expression correlates with PI3K/AKT activity, suggesting that patients with inherent resistance to TMZ (MGMT-high) would benefit from PI3K/AKT inhibitors in addition to TMZ. Accordingly, we have identified that the blood-brain barrier (BBB) penetrant pan-PI3K inhibitor, PX-866, is an early-stage inhibitor of autophagic flux, while maintaining its ability to inhibit PI3K/AKT signaling in glioma cells. Lastly, due to the induction of autophagic flux by TMZ, we provide evidence for sequential treatment of TMZ followed by PX-866, rather than combined co-treatment, as a means to shut down autophagy-induced survival in GBM cells and to enhance apoptosis.

Conclusions

The understanding of how TMZ induces survival pathways, such as autophagy, may offer new therapeutic vulnerabilities and opportunities to use sequential inhibition of alternate pro-survival pathways that regulate autophagy. As such, identification of additional ways to inhibit TMZ-induced autophagy could enhance the efficacy of TMZ.

A phase I study of vistusertib (dual mTORC1/2 inhibitor) in patients with previously treated glioblastoma multiforme: a CCTG study

The PI3K/AKT/mTOR pathway activation plays a central role in glioblastoma multiforme (GBM) development and progression, and in resistance to anti-cancer therapies. Inhibition of the PI3K pathway has been shown to sensitize cultured glioma cells and tumor xenografts to the effects of temozolomide (TMZ) and radiation. Vistusertib is an oral inhibitor of mTORC1/2 complexes. The primary objective of this Canadian Cancer Trials Group phase I study was to determine the recommended phase II dose (RP2D) of vistusertib in patients with GBM receiving TMZ at first progression following primary treatment. Vistusertib was administered at a starting dose of 100 mg bid 2 days on/5 days off weekly with TMZ 150 mg/m² daily for 5 days/28-days cycle. Dose escalation was according to a 3 + 3 design. Secondary objectives included assessment of vistusertib safety and toxicity profile, and preliminary efficacy. 15 patients were enrolled in the study (median age 66 (range 51-77), females 8). Vistusertib 125 mg BID in combination with TMZ 150 mg/m² daily for 5 days was well tolerated. Vistusertib treatment-related adverse events were generally grade 1-2, with the most frequently reported being fatigue, gastrointestinal symptoms, and rash. Of 13 response evaluable patients, 1 patient (8%) had a partial response ongoing at 7.6 months of follow-up, and 5 patients had stable disease (38%) as best response (median duration 9.6 months, range 3.7-not yet reached). Six-month progression-free survival (PFS) rate was 26.6%. Combination of vistusertib with TMZ in GBM patients at first recurrence demonstrated a favorable safety profile at the tested dose levels.

Tissues Harvested Using an Automated Surgical Approach Confirm Molecular Heterogeneity of Glioblastoma and Enhance Specimen's Translational Research Value

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults. Designing effective individualized therapies for GBM requires quality fresh tissue specimens, and a comprehensive molecular profile of this highly heterogenous neoplasm. Novel neuro-surgical approaches, such as the automated resection NICO Myriad™ system, are increasingly used by neurosurgeons to better reach the invasive front of tumors. However, no information exists on how harvesting GBM tissue using this approach may impact the translational research value of the sample. Here, we set out to characterize matched specimens from 15 patients, where one tissue sample was obtained using traditional tumor de-bulking (herein referred to as “en bloc” sample), and the other sample was obtained using the Myriad^TM System (herein referred to as “Myriad” sample). We investigated the fidelity of patient derived xenografts (PDXs) for each sample type to the corresponding human tissues and evaluated the added value of sequencing both samples for each patient. Matched en bloc and Myriad samples processed in parallel, were subjected to the following assays: cell viability, self-renewal, in vivo tumorigenicity using an orthotopic model of glioma, genomic sequencing, and pharmacological testing using PI3K-MTOR pathway inhibitors. Our results demonstrate that primary GBM cultures derived from matched specimens grew at similar rates (correlation coefficient R = 0.72), generated equivalent number of neurospheres, and had equivalent tumorigenic potential in vivo (mouse survival correlation coefficient R = 0.93). DNA Sequencing using the Illumina tumor panel amplicons revealed over 70% concordance in non-synonymous mutations between matched human GBM specimens. PDX genomic profiles were also highly concordant with the corresponding patient tissues (>70%). RNA sequencing of paired GBM samples revealed unique genomic variants and differential gene expression between the en bloc and Myriad specimens, with the former molecularly resembling the “tumor core” and the latter resembling the “invasive tumor front” signature. Functionally, we show that primary-derived GBM cells—obtained after fresh specimen's dissociation—are more effectively growth-inhibited by co-targeting non-overlapping mutations enriched in each sample type, suggesting that profiling both specimens more adequately capture the molecular heterogeneity of GBM and may enhance the design accuracy and efficacy of individualized therapies.

The Brain Penetrating and Dual TORC1/TORC2 Inhibitor, RES529, Elicits Anti-Glioma Activity and Enhances the Therapeutic Effects of Anti-Angiogenetic Compounds in Preclinical Murine Models

Background. Glioblastoma multiforme (GBM) is a devastating disease showing a very poor prognosis. New therapeutic approaches are needed to improve survival and quality of life. GBM is a highly vascularized tumor and as such, chemotherapy and anti-angiogenic drugs have been combined for treatment. However, as treatment-induced resistance often develops, our goal was to identify and treat pathways involved in resistance to treatment to optimize the treatment strategies. Anti-angiogenetic compounds tested in preclinical and clinical settings demonstrated recurrence associated to secondary activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway. Aims. Here, we determined the sensitizing effects of the small molecule and oral available dual TORC1/TORC2 dissociative inhibitor, RES529, alone or in combination with the anti-VEGF blocking antibody, bevacizumab, or the tyrosine kinase inhibitor, sunitinib, in human GBM models. Results. We observed that RES529 effectively inhibited dose-dependently the growth of GBM cells in vitro counteracting the insurgence of recurrence after bevacizumab or sunitinib administration in vivo. Combination strategies were associated with reduced tumor progression as indicated by the analysis of Time to Tumor Progression (TTP) and disease-free survival (DSF) as well as increased overall survival (OS) of tumor bearing mice. RES529 was able to reduce the in vitro migration of tumor cells and tubule formation from both brain-derived endothelial cells (angiogenesis) and tumor cells (vasculogenic mimicry). Conclusions. In summary, RES529, the first dual TORC1/TORC2 dissociative inhibitor, lacking affinity for ABCB1/ABCG2 and having good brain penetration, was active in GBM preclinical/murine models giving credence to its use in clinical trial for patients with GBM treated in association with anti-angiogenetic compounds.

Glioblastoma Multiforme: An Overview of Emerging Therapeutic Targets

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumour in humans and has a very poor prognosis. The existing treatments have had limited success in increasing overall survival. Thus, identifying and understanding the key molecule(s) responsible for the malignant phenotype of GBM will yield new potential therapeutic targets. The treatment of brain tumours faces unique challenges, including the presence of the blood brain barrier (BBB), which limits the concentration of drugs that can reach the site of the tumour. Nevertheless, several promising treatments have been shown to cross the BBB and have shown promising pre-clinical results. This review will outline the status of several of these promising targeted therapies.

Delivery luteolin with folacin-modified nanoparticle for glioma therapy

Background

Glioblastoma mutliforme is the most common and has the poorest prognosis of any malignant tumor of the central nervous system. Luteolin, the most abundant xanthone extracted from vegetables and medicinal plants, has been shown to have treatment effects in various cancer cell types. Luteolin is however, hydrophobic and has poor biocompatibility, which leads to low bioavailability.

Patients and methods

In this study, folic acid modifiedpoly(ethylene glycol)-poly(e-caprolactone) (Fa-PEG-PCL) nano-micelles was used to encapsulate the luteolin, creating luteolin loaded PEG-PCL (Lut/Fa-PEG-PCL) micelles to treat glioma both in vitro and in vivo.

Results

When compared with the free luteolin and Lut/MPEG-PCL, Lut/Fa-PEG-PCL induced a significant cell growth inhibition and more apoptosis of GL261 cells both in vitro and in vivo. The safety assessment also showed no obvious side effects were observed in mice which were administrated with free luteolin or Lut/MPEG-PCL and Lut/Fa-PEG-PCL.

Conclusion

These results suggested Lut/Fa-PEG-PCL may be used as an excellent intravenously injectable formulation for the treatment and chemoprevention.

Temozolomide and Other Alkylating Agents in Glioblastoma Therapy

The alkylating agent temozolomide (TMZ) together with maximal safe bulk resection and focal radiotherapy comprises the standard treatment for glioblastoma (GB), a particularly aggressive and lethal primary brain tumor. GB affects 3.2 in 100,000 people who have an average survival time of around 14 months after presentation. Several key aspects make GB a difficult to treat disease, primarily including the high resistance of tumor cells to cell death-inducing substances or radiation and the combination of the highly invasive nature of the malignancy, i.e., treatment must affect the whole brain, and the protection from drugs of the tumor bulk—or at least of the invading cells—by the blood brain barrier (BBB). TMZ crosses the BBB, but—unlike classic chemotherapeutics—does not induce DNA damage or misalignment of segregating chromosomes directly. It has been described as a DNA alkylating agent, which leads to base mismatches that initiate futile DNA repair cycles; eventually, DNA strand breaks, which in turn induces cell death. However, while much is assumed about the function of TMZ and its mode of action, primary data are actually scarce and often contradictory. To improve GB treatment further, we need to fully understand what TMZ does to the tumor cells and their microenvironment. This is of particular importance, as novel therapeutic approaches are almost always clinically assessed in the presence of standard treatment, i.e., in the presence of TMZ. Therefore, potential pharmacological interactions between TMZ and novel drugs might occur with unforeseeable consequences.

A novel tumor suppressor protein encoded by circular AKT3 RNA inhibits glioblastoma tumorigenicity by competing with active phosphoinositide-dependent Kinase-1

Background

The RTK/PI3K/AKT pathway plays key roles in the development and progression of many cancers, including GBM. As a regulatory molecule and a potential drug target, the oncogenic role of AKT has been substantially studied. Three isoforms of AKT have been identified, including AKT1, AKT2 and AKT3, but their individual functions in GBM remain controversial. Moreover, it is not known if there are more AKT alternative splicing variants.

Methods

High-throughput RNA sequencing and quantitative reverse transcription-PCR were used to identify the differentially expressed circRNAs in GBM samples and in paired normal tissues. High throughput RNA sequencing was used to identify circ-AKT3 regulated signaling pathways. Mass spectrometry, western blotting and immunofluorescence staining analyses were used to validate AKT3-174aa expression. The tumor suppressive role of AKT3-174aa was validated in vitro and in vivo. The competing interaction between AKT3-174aa and p-PDK1 was investigated by mass spectrometry and immunoprecipitation analyses.

Results

Circ-AKT3 is a previously uncharacterized AKT transcript variant. Circ-AKT3 is expressed at low levels in GBM tissues compared with the expression in paired adjacent normal brain tissues. Circ-AKT3 encodes a 174 amino acid (aa) novel protein, which we named AKT3-174aa, by utilizing overlapping start-stop codons. AKT3-174aa overexpression decreased the cell proliferation, radiation resistance and in vivo tumorigenicity of GBM cells, while the knockdown of circ-AKT3 enhanced the malignant phenotypes of astrocytoma cells. AKT3-174aa competitively interacts with phosphorylated PDK1, reduces AKT-thr308 phosphorylation, and plays a negative regulatory role in modulating the PI3K/AKT signal intensity.

Conclusions

Our data indicate that the impaired circRNA expression of the AKT3 gene contributes to GBM tumorigenesis, and our data corroborate the hypothesis that restoring AKT3-174aa while inhibiting activated AKT may provide more benefits for certain GBM patients.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1056-5) contains supplementary material, which is available to authorized users.

Bromodomain inhibitor jq1 induces cell cycle arrest and apoptosis of glioma stem cells through the VEGF/PI3K/AKT signaling pathway

Bromodomain and extraterminal domain proteins, especially bromodomain-containing protein 4 (Brd4), have recently emerged as therapeutic targets for several cancers, although the role and mechanism of Brd4 in glioblastoma multiforme (GBM) are unclear. In this study, we aimed to explore the underlying mechanisms of the anti-tumor effects of Brd4 and the bromodomain inhibitor JQ1 on glioma stem cells (GSCs). In vitro, JQ1 and small interfering RNAs targeting Brd4 (siBrd4) inhibited the proliferation and self-renewal of GSCs. In vivo, JQ1 significantly inhibited the growth of xenograft GSCs tumors. The RNA-seq analysis revealed that the PI3K-AKT pathway played an important role in GBM. Vascular endothelial growth factor (VEGF) and VEGF receptor 2 phosphorylation was downregulated by exposure to JQ1 in GSCs, thereby reducing PI3K and AKT activity. In addition, treatment with JQ1 inhibited MMP expression, thereby inhibiting degradation of the extracellular matrix by MMP and angiogenesis in GBM tumors. Suppression of AKT phosphorylation inhibited the expression of the retinoblastoma/E2F1 complex, resulting in cell cycle arrest. In addition, treatment with siBrd4 or JQ1 induced apoptosis by activating AKT downstream target genes involved in apoptosis. In conclusion, these results suggest that Brd4 has great potential as a therapeutic target, and JQ1 has notable anti-tumor effects against GBM which may be mediated via the VEGF/PI3K/AKT signaling pathway.

For Better or Worse: The Potential for Dose Limiting the On-Target Toxicity of PI 3-Kinase Inhibitors

The hyper-activation of the phosphoinositide (PI) 3-kinase signaling pathway is a hallmark of many cancers and overgrowth syndromes, and as a result, there has been intense interest in the development of drugs that target the various isoforms of PI 3-kinase. Given the key role PI 3-kinases play in many normal cell functions, there is significant potential for the disruption of essential cellular functions by PI 3-kinase inhibitors in normal tissues; so-called on-target drug toxicity. It is, therefore, no surprise that progress within the clinical development of PI 3-kinase inhibitors as single-agent anti-cancer therapies has been slowed by the difficulty of identifying a therapeutic window. The aim of this review is to place the cellular, tissue and whole-body effects of PI 3-kinase inhibition in the context of understanding the potential for dose limiting on-target toxicities and to introduce possible strategies to overcome these.

The Autophagy Status of Cancer Stem Cells in Gliobastoma Multiforme: From Cancer Promotion to Therapeutic Strategies

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor featuring rapid cell proliferation, treatment resistance, and tumor relapse. This is largely due to the coexistence of heterogeneous tumor cell populations with different grades of differentiation, and in particular, to a small subset of tumor cells displaying stem cell-like properties. This is the case of glioma stem cells (GSCs), which possess a powerful self-renewal capacity, low differentiation, along with radio- and chemo-resistance. Molecular pathways that contribute to GBM stemness of GSCs include mTOR, Notch, Hedgehog, and Wnt/β-catenin. Remarkably, among the common biochemical effects that arise from alterations in these pathways, autophagy suppression may be key in promoting GSCs self-renewal, proliferation, and pluripotency maintenance. In fact, besides being a well-known downstream event of mTOR hyper-activation, autophagy downregulation is also bound to the effects of aberrantly activated Notch, Hedgehog, and Wnt/β-catenin pathways in GBM. As a major orchestrator of protein degradation and turnover, autophagy modulates proliferation and differentiation of normal neuronal stem cells (NSCs) as well as NSCs niche maintenance, while its failure may contribute to GSCs expansion and maintenance. Thus, in the present review we discuss the role of autophagy in GSCs metabolism and phenotype in relationship with dysregulations of a variety of NSCs controlling pathways, which may provide novel insights into GBM neurobiology.