Bevacizumab treatment induces metabolic adaptation toward anaerobic metabolism in glioblastomas

The secreted glycolytic enzyme GPI/AMF stimulates glioblastoma cell migration and invasion in an autocrine fashion but can have anti-proliferative effects

Background

Aerobic glycolysis confers several advantages to tumor cells, including shunting of metabolites into anabolic pathways. In glioblastoma cells, hypoxia induces a flux shift from the pentose phosphate pathway toward glycolysis and a switch from proliferation to migration. The mechanistic link between glycolysis and migration is poorly understood. Since glucose-6-phosphate isomerase (GPI) is identical to the secreted cytokine autocrine motility factor (AMF), we investigated whether GPI/AMF regulates glioblastoma cell invasion.

Methods

The expression and hypoxic regulation of GPI/AMF and its receptor AMFR were analyzed in glioblastoma tissue and cell lines. Functional effects were studied in vitro and in xenograft models.

Results

High GPI/AMF expression in glioblastomas was found to be associated with a worse patient prognosis, and levels were highest in hypoxic pseudopalisades. Hypoxia upregulated both GPI/AMF and AMFR expression as well as GPI/AMF secretion in vitro. GPI/AMF stimulated cell migration in an autocrine fashion, and GPI/AMF expression was upregulated in migratory cells but reduced in rapidly proliferating cells. Knockdown or inhibition of GPI/AMF reduced glioblastoma cell migration but in part stimulated proliferation. In a highly invasive orthotopic glioblastoma model, GPI/AMF knockdown reduced tumor cell invasion but did not prolong survival. In a highly proliferative model, knockdown tumors were even larger and more proliferative than controls; however, perivascular invasion, provoked by simultaneous bevacizumab treatment, was reduced.

Conclusions

GPI/AMF is a potent motogen for glioblastoma cells, explaining in part the association between glycolysis and migration. Targeting GPI/AMF is, however, problematic, since beneficial anti-invasive effects may be outweighed by unintended mitogenic effects.

Key Points

1.Increased glycolysis is linked with increased cell migration and invasion in glioblastoma cells. 2.The glycolysis enzyme GPI/AMF may serve as a target for antimetabolic and anti-invasive therapy. 3.Despite reducing tumor invasion, GPI/AMF targeting may have unwanted growth stimulatory effects.

Capture at the single cell level of metabolic modules distinguishing aggressive and indolent glioblastoma cells

Glioblastoma cell ability to adapt their functioning to microenvironment changes is a source of the extensive intra-tumor heterogeneity characteristic of this devastating malignant brain tumor. A systemic view of the metabolic pathways underlying glioblastoma cell functioning states is lacking. We analyzed public single cell RNA-sequencing data from glioblastoma surgical resections, which offer the closest available view of tumor cell heterogeneity as encountered at the time of patients’ diagnosis. Unsupervised analyses revealed that information dispersed throughout the cell transcript repertoires encoded the identity of each tumor and masked information related to cell functioning states. Data reduction based on an experimentally-defined signature of transcription factors overcame this hurdle. It allowed cell grouping according to their tumorigenic potential, regardless of their tumor of origin. The approach relevance was validated using independent datasets of glioblastoma cell and tissue transcriptomes, patient-derived cell lines and orthotopic xenografts. Overexpression of genes coding for amino acid and lipid metabolism enzymes involved in anti-oxidative, energetic and cell membrane processes characterized cells with high tumorigenic potential. Modeling of their expression network highlighted the very long chain polyunsaturated fatty acid synthesis pathway at the core of the network. Expression of its most downstream enzymatic component, ELOVL2, was associated with worsened patient survival, and required for cell tumorigenic properties in vivo. Our results demonstrate the power of signature-driven analyses of single cell transcriptomes to obtain an integrated view of metabolic pathways at play within the heterogeneous cell landscape of patient tumors.

Ellagic Acid Enhances the Antitumor Efficacy of Bevacizumab in an In Vitro Glioblastoma Model

BACKGROUND

The anticarcinogenic effect of ellagic acid (EA), a natural phenol of fruits and vegetables, has been investigated in several types of tumors. The combined effect of EA with bevacizumab (BEV), a common drug used in treatment of recurrent glioma, on glioblastoma has not been reported. This study observed the combined effect of EA with BEV on the expression profile of the C6 glioma cell line.

METHODS

Rat C6 glioma cells were treated with EA at 100 μmol/L concentration in combination with BEV at 100 ng/mL concentration for 24, 48, and 72 hours. Cell proliferation was detected by 5-bromo-2'-deoxyuridine immunohistochemistry, and p53 and caspase-3 protein levels were determined by immunohistochemistry and assessed by the H-Score. Expression profiles for P-glycoprotein (MDR1), O⁶-methylguanine DNA methyltransferase (MGMT), caspase-3, and p53 related proteins were detected by reverse transcriptase polymerase chain reaction after EA treatment with or without BEV.

RESULTS

EA combined with BEV conspicuously reduced the cell viability of C6 glioma cells for all incubation times. EA significantly downregulated expression of MGMT regardless of combination with BEV even in the early hours after treatment. Combined EA and BEV reduced MDR1 expression only at 72 hours. EA affected the apoptotic proteins of p53 and caspase-3 at protein level in a time-dependent manner, but not at gene level.

CONCLUSIONS

This study suggests successful antiproliferative efficacy of EA combined with BEV, probably through inhibition of MGMT expression and time-dependent inhibition of MDR1. EA combined with BEV may be an alternative treatment for drug-resistant gliomas.

Metabolic Abnormalities in Glioblastoma and Metabolic Strategies to Overcome Treatment Resistance

Glioblastoma (GBM) is the most common and aggressive primary brain tumor and is nearly universally fatal. Targeted therapy and immunotherapy have had limited success in GBM, leaving surgery, alkylating chemotherapy and ionizing radiation as the standards of care. Like most cancers, GBMs rewire metabolism to fuel survival, proliferation, and invasion. Emerging evidence suggests that this metabolic reprogramming also mediates resistance to the standard-of-care therapies used to treat GBM. In this review, we discuss the noteworthy metabolic features of GBM, the key pathways that reshape tumor metabolism, and how inhibiting abnormal metabolism may be able to overcome the inherent resistance of GBM to radiation and chemotherapy.

Patterns of bevacizumab use in patients with glioblastoma: an online survey among experts in neuro-oncology

Background

Bevacizumab (BEV) received accelerated FDA approval in 2009 for the treatment of recurrent glioblastoma (rGBM). Unfortunately, prospective randomized controlled phase 3 studies (AVAglio and Radiation Therapy Oncology Group 0825 in newly diagnosed, European Organisation for Research and Treatment of Cancer 26101 in rGBM) failed to show an overall survival benefit with BEV added to standard therapy. In light of these data, we aimed to capture current utilization patterns and perceived value of BEV in the treatment of GBM among experts in the field.

Methods

An online questionnaire comprising 14 multiple choice questions was sent out in spring 2017 to 207 oncologists/neuro-oncologists treating patients with GBM at all National Cancer Institute-designated cancer centers in the United States.

Results

Sixty-two of 207 (30%) invitees responded (by training, 70% neuro-oncologists, 20% medical oncologists, 10% pediatric oncologists/neuro-oncologists). Participants reported use of BEV most frequently in rGBM for control of edema (85% of respondents) and/or when no other treatment options were available (68%). BEV is rarely used in newly diagnosed GBM (<5% of cases by 78% respondents and in 5% to 10% cases by 15% respondents). Sixty-six percent of participants indicated that they thought BEV improved symptoms, 30% that it improved symptoms and survival, 3% that it had no benefit in GBM patients.

Conclusion

In this cross-sectional online survey we found that among neuro-oncology experts in the United States in 2017, BEV is predominantly utilized in select patients with rGBM, and is only rarely used in a small subgroup of patients with newly diagnosed GBM for control of edema. The low response rate may have introduced a nonresponse bias.

Epithelial membrane protein 1 promotes glioblastoma progression through the PI3K/AKT/mTOR signaling pathway

Glioblastoma multiforme (GBM) is the most malignant intracranial tumor. Although the affected patients are usually treated with surgery combined with radiotherapy and chemotherapy, the median survival time for GBM patients is still approximately 12–14 months. Identifying the key molecular mechanisms and targets of GBM development may therefore lead to the development of improved therapies for GBM patients. In the present study, the clinical significance and potential function of epithelial membrane protein 1 (EMP1) in malignant gliomas were investigated. Increased EMP1 expression was associated with increasing tumor grade (P<0.001) and worse prognosis in patients (P<0.001) based on TCGA, Rembrandt and CGGA databases for human gliomas. In vitro, gene silencing of EMP1 in U87MG and P3 GBM (primary glioma) cells significantly inhibited tumor proliferation and invasion. In addition, it was revealed that activation of the PI3K/AKT/mTOR signaling pathway is the driving force of EMP1-promoted glioma progression. Finally, it was demonstrated, using an intracranial GBM animal model, that EMP1 knockdown significantly inhibits tumor growth in vivo and increases overall survival in tumor-bearing animals. Our research provides new insights into the molecular mechanisms underlying EMP1 knockdown-mediated inhibition of GBM cell invasion and raises the possibility that targeting of EMP1 may represent a promising strategy for the treatment of GBM.

Stem cell-associated heterogeneity in Glioblastoma results from intrinsic tumor plasticity shaped by the microenvironment

The identity and unique capacity of cancer stem cells (CSC) to drive tumor growth and resistance have been challenged in brain tumors. Here we report that cells expressing CSC-associated cell membrane markers in Glioblastoma (GBM) do not represent a clonal entity defined by distinct functional properties and transcriptomic profiles, but rather a plastic state that most cancer cells can adopt. We show that phenotypic heterogeneity arises from non-hierarchical, reversible state transitions, instructed by the microenvironment and is predictable by mathematical modeling. Although functional stem cell properties were similar in vitro, accelerated reconstitution of heterogeneity provides a growth advantage in vivo, suggesting that tumorigenic potential is linked to intrinsic plasticity rather than CSC multipotency. The capacity of any given cancer cell to reconstitute tumor heterogeneity cautions against therapies targeting CSC-associated membrane epitopes. Instead inherent cancer cell plasticity emerges as a novel relevant target for treatment.

Cancer stem cells (CSCs) comprise a putative population that can drive growth and resistance. Here, in glioblastoma models the authors show that rather than being a distinct clonal entity, the CSC population represents a plastic state adoptable by most cancer cells via reversible state transitions induced by the microenvironment.

Deciphering the complex role of thrombospondin-1 in glioblastoma development

We undertook a systematic study focused on the matricellular protein Thrombospondin-1 (THBS1) to uncover molecular mechanisms underlying the role of THBS1 in glioblastoma (GBM) development. THBS1 was found to be increased with glioma grades. Mechanistically, we show that the TGFβ canonical pathway transcriptionally regulates THBS1, through SMAD3 binding to the THBS1 gene promoter. THBS1 silencing inhibits tumour cell invasion and growth, alone and in combination with anti-angiogenic therapy. Specific inhibition of the THBS1/CD47 interaction using an antagonist peptide decreases cell invasion. This is confirmed by CD47 knock-down experiments. RNA sequencing of patient-derived xenograft tissue from laser capture micro-dissected peripheral and central tumour areas demonstrates that THBS1 is one of the gene with the highest connectivity at the tumour borders. All in all, these data show that TGFβ1 induces THBS1 expression via Smad3 which contributes to the invasive behaviour during GBM expansion. Furthermore, tumour cell-bound CD47 is implicated in this process.

Thrombospondin-1 (THSB1) is a component of the ECM with a role in regulating cancer development and tumour vasculature. Here, the authors show that TGF-beta-induced THBS1 expression contributes to the invasive behaviour of GBM cells and promotes resistance to antiangiogenic therapy partially through interaction with CD47.

Chemoresistance caused by the microenvironment of glioblastoma and the corresponding solutions

Glioblastoma multiforme (GBM) is the most common and aggressive primary human brain tumor. Although comprehensive therapies combining radiotherapy and chemotherapy after surgery can prolong survival, the prognosis is still poor with a median survival of only 14.6 months. Chemoresistance is one of the major causes of relapse as well as poor survival in glioma patients. Therefore, novel strategies to overcome chemoresistance are desperately needed for improved treatment of human GBM. Recent studies have demonstrated that the tumor microenvironment plays a critical role in the chemoresistance of various tumor types, which makes it a suitable target in anti-cancer therapies, as well as a valuable biomarker for prognostic purposes. This review focuses on chemoresistance in GBM induced by stromal cells, including the endothelium of blood vessels, astrocytes, and myeloid cells, as well as non-cellular factors in the tumor microenvironment. Corresponding therapies are discussed, including progressive strategies involving 3-dimensional models integrating engineering as well as biological advances.

Lack of functional normalisation of tumour vessels following anti-angiogenic therapy in glioblastoma

Neo-angiogenesis represents an important factor for the delivery of oxygen and nutrients to a growing tumour, and is considered to be one of the main pathodiagnostic features of glioblastomas (GBM). Anti-angiogenic therapy by vascular endothelial growth factor (VEGF) blocking agents has been shown to lead to morphological vascular normalisation resulting in a reduction of contrast enhancement as seen by magnetic resonance imaging (MRI). Yet the functional consequences of this normalisation and its potential for improved delivery of cytotoxic agents to the tumour are not known. The presented study aimed at determining the early physiologic changes following bevacizumab treatment. A time series of perfusion MRI and hypoxia positron emission tomography (PET) scans were acquired during the first week of treatment, in two human GBM xenograft models treated with either high or low doses of bevacizumab. We show that vascular morphology was normalised over the time period investigated, but vascular function was not improved, resulting in poor tumoural blood flow and increased hypoxia.

The interplay between metabolic remodeling and immune regulation in glioblastoma

The fields of tumor metabolism and immune oncology have both independently received considerable attention over the last several years. The majority of research in tumor metabolism has largely focused on the Warburg effect and its resulting biologic consequences, including energy and macromolecule production. However, recent investigations have identified elegant, multifaceted strategies by which alterations in tumor metabolism can also contribute to a potent tolerogenic immune environment. One of the most notable is increased tryptophan metabolism through activation of indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO). However, this pathway represents one of numerous metabolic pathways that may modulate the immune system. For example, metabolites associated with aerobic glycolysis, adenosine, arginine, and prostaglandin metabolism have all been implicated in cancer-mediated immune tolerance and represent attractive therapeutic targets. In this review, we will provide an overview of the emerging interface between these 2 timely areas of cancer research and provide an overview of strategies currently being tested to target these next-generation metabolic immune checkpoints.

Induction of reactive oxygen species: an emerging approach for cancer therapy

Reactive oxygen species (ROS), a group of ions and molecules, include hydroxyl radicals (·OH), alkoxyl radicals, superoxide anion (O₂·-), singlet oxygen (¹O₂) and hydrogen peroxide (H₂O₂). Hydroxyl radicals and alkoxyl radicals are extremely and highly reactive species respectively. Endogenous ROS are mainly formed in mitochondrial respiratory chain. Low levels of ROS play important roles in regulating biological functions in mammalian cells. However, excess production of ROS can induce cell death by oxidative damaging effects to intracellular biomacromolecules. Cancer cell death types induced by ROS include apoptotic, autophagic, ferroptotic and necrotic cell death. Since abnormal metabolism in cancer cells, they have higher ROS content compared to normal cells. The higher endogenous ROS levels in cancer cells endow them more susceptible to the ROS-induction treatment. Indeed, some anticancer drugs currently used in clinic, such as molecular targeted drugs and chemotherapeutic agents, effectively kill cancer cells by inducing ROS generation. In addition, photodynamic therapy (PDT) is mainly based on induction of ROS burst to kill cancer cells. The mechanism of cell death induced by radiotherapy using ionizing radiation also refers to ROS production. Moreover, ROS play an important role in tumor immune therapy. Altogether, combining above traditional treatments with ROS-induced agents will be considered as a promising strategy in cancer therapy. In this review, we focus on our current understanding of the anticancer effects of ROS.

In silico gene expression analysis reveals glycolysis and acetate anaplerosis in IDH1 wild-type glioma and lactate and glutamate anaplerosis in IDH1-mutated glioma

Hotspot mutations in isocitrate dehydrogenase 1 (IDH1) initiate low-grade glioma and secondary glioblastoma and induce a neomorphic activity that converts α-ketoglutarate (α-KG) to the oncometabolite D-2-hydroxyglutarate (D-2-HG). It causes metabolic rewiring that is not fully understood. We investigated the effects of IDH1 mutations (IDH1^MUT) on expression of genes that encode for metabolic enzymes by data mining The Cancer Genome Atlas. We analyzed 112 IDH1 wild-type (IDH1^WT) versus 399 IDH1^MUT low-grade glioma and 157 IDH1^WT versus 9 IDH1^MUT glioblastoma samples. In both glioma types, IDH1^WT was associated with high expression levels of genes encoding enzymes that are involved in glycolysis and acetate anaplerosis, whereas IDH1^MUT glioma overexpress genes encoding enzymes that are involved in the oxidative tricarboxylic acid (TCA) cycle. In vitro, we observed that IDH1^MUT cancer cells have a higher basal respiration compared to IDH1^WT cancer cells and inhibition of the IDH1^MUT shifts the metabolism by decreasing oxygen consumption and increasing glycolysis. Our findings indicate that IDH1^WT glioma have a typical Warburg phenotype whereas in IDH1^MUT glioma the TCA cycle, rather than glycolytic lactate production, is the predominant metabolic pathway. Our data further suggest that the TCA in IDH1^MUT glioma is driven by lactate and glutamate anaplerosis to facilitate production of α-KG, and ultimately D-2-HG. This metabolic rewiring may be a basis for novel therapies for IDH1^MUT and IDH1^WT glioma.

The pro-tumorigenic effects of metabolic alterations in glioblastoma including brain tumor initiating cells

De-regulated cellular energetics is an emerging hallmark of cancer with alterations to glycolysis, oxidative phosphorylation, the pentose phosphate pathway, lipid oxidation and synthesis and amino acid metabolism. Understanding and targeting of metabolic reprogramming in cancers may yield new treatment options, but metabolic heterogeneity and plasticity complicate this strategy. One highly heterogeneous cancer for which current treatments ultimately fail is the deadly brain tumor glioblastoma. Therapeutic resistance, within glioblastoma and other solid tumors, is thought to be linked to subsets of tumor initiating cells, also known as cancer stem cells. Recent profiling of glioblastoma and brain tumor initiating cells reveals changes in metabolism, as compiled here, that may be more broadly applicable. We will summarize the profound role for metabolism in tumor progression and therapeutic resistance and discuss current approaches to target glioma metabolism to improve standard of care.

Targeting Oxidatively Induced DNA Damage Response in Cancer: Opportunities for Novel Cancer Therapies

Cancer is a death cause in economically developed countries that results growing also in developing countries. Improved outcome through targeted interventions faces the scarce selectivity of the therapies and the development of resistance to them that compromise the therapeutic effects. Genomic instability is a typical cancer hallmark due to DNA damage by genetic mutations, reactive oxygen and nitrogen species, ionizing radiation, and chemotherapeutic agents. DNA lesions can induce and/or support various diseases, including cancer. The DNA damage response (DDR) is a crucial signaling-transduction network that promotes cell cycle arrest or cell death to repair DNA lesions. DDR dysregulation favors tumor growth as downregulated or defective DDR generates genomic instability, while upregulated DDR may confer treatment resistance. Redox homeostasis deeply and capillary affects DDR as ROS activate/inhibit proteins and enzymes integral to DDR both in healthy and cancer cells, although by different routes. DDR regulation through modulating ROS homeostasis is under investigation as anticancer opportunity, also in combination with other treatments since ROS affect DDR differently in the patients during cancer development and treatment. Here, we highlight ROS-sensitive proteins whose regulation in oxidatively induced DDR might allow for selective strategies against cancer that are better tailored to the patients.

Antitumor Activity of DLX1008, an Anti-VEGFA Antibody Fragment with Low Picomolar Affinity, in Human Glioma Models

Angiogenesis mediated by vascular endothelial growth factor (VEGF) is a hallmark of glioblastoma. Based on the response rate and improved progression-free survival, although not on overall survival, the 149-kDa anti-VEGF-A IgG antibody bevacizumab (Avastin) has been approved in the United States and Japan for recurrent glioblastoma and in Japan for newly diagnosed glioblastoma; however, it is not approved in the EU. Here we characterize the biologic activity of DLX1008, a 26-kDa anti-VEGF-A single-chain antibody fragment that shows 30-fold stronger affinity to human VEGF-A than bevacizumab. The small molecular size of DLX1008 is predicted to result in improved target coverage over bevacizumab. DLX1008 showed superiority to bevacizumab in the inhibition of VEGF-A binding to VEGF receptor (VEGFR) 1 in enzyme-linked immunosorbent assay by a factor of around 10 and comparable efficacy for the inhibition of VEGF-A-stimulated VEGFR2 dimerization. In a tube-formation assay with human cerebral microvascular endothelial cells, DLX1008 was at least as active as bevacizumab. In vivo, DLX1008 delayed growth in a mouse subcutaneous U87 xenograft model (P = 0.0021) and improved survival in a mouse orthotopic U87 xenograft model (P = 0.00026). Given the exceptionally high affinity and small molecular size of DLX1008, these data warrant further clinical development of DLX1008 as an antiangiogenic agent in glioblastoma.

Over-expression of TOP2A as a prognostic biomarker in patients with glioma

Topoisomerase (DNA) II alpha (TOP2A), an enzyme that controls and alters the topologic states of DNA during transcription, is aberrantly expressed in many cancers. However, few studies have investigated expression of TOP2A and its clinical significance in glioma. We retrieved six independent investigations from the Oncomine database and found that TOP2A is highly expressed in glioma tissues compared with corresponding normal controls. Similar results were also found in clinical specimens at the protein level. Immunohistochemical analysis indicated that TOP2A over expression was highly correlated with grade stage, KI67 positive percentage, IDH1 mutation, and age, but other clinical parameters such as sex distribution and tumor size were barely associated with high TOP2A gene expression. Meanwhile we used Prognos can to assess the prognostic value of TOP2A expression in glioma patients, and found that high expression was associated with poor prognosis of patients with glioma. Furthermore, we used the Gene-Cloud of Biotechnology Information (GCBI) bioinformatics platform predict the role of TOP2A in glioma. It was not only involved in DNA replication, chromosome condensation, and responses to DNA damage stimuli, but also promoted cancer cell mitotic cell cycle and apoptosis, and phosphatidylinositol-mediated signaling by regulating gene expression. By these approaches we demonstrate that TOP2A may be a reliable prognostic factor or therapeutic target in glioma.

Large Intergenic Non-coding RNA-RoR Inhibits Aerobic Glycolysis of Glioblastoma Cells via Akt Pathway

Reprogramming energy metabolism is a hallmark of malignant tumors, including glioblastoma (GBM). Aerobic glycolysis is often utilized by tumor cells to maintain survival and proliferation. However, the underlying mechanisms of aerobic glycolysis in GBM remain elusive. Herein, we demonstrated that large intergenic non-coding RNA-RoR (LincRNA-RoR) functioned as a critical suppressor to inhibit the aerobic glycolysis and viability of GBM cells. We found that LincRNA-RoR was markedly reduced in GBM tissues compared with adjacent non-tumor tissues from 10 cases of GBM patients. Consistently, LincRNA-RoR expression in GBM cells was significantly lower than that in normal glial cells. The aerobic glycolysis of GBM cells, as determined by the measurement of glucose uptake and lactate production, was impaired by LincRNA-RoR overexpression. Mechanistically, LincRNA-RoR inhibited the expression of Rictor, the key component of mTORC2 (mammalian target of rapamycin complex 2), to suppress the activity of Akt pathway and impair the expression of glycolytic effectors, including Glut1, HK2, PKM2 and LDHA. Finally, enforced expression of LincRNA-RoR reduced the proliferation of GBM cells in vitro, restrained tumor growth in vivo, and repressed the expression of glycolytic molecules in GBM xenografts. Collectively, our results underscore LincRNA-RoR as a new suppressor of GBM aerobic glycolysis with therapeutic potential.

Developmentally regulated signaling pathways in glioma invasion

Malignant gliomas are the most common, infiltrative, and lethal primary brain tumors affecting the adult population. The grim prognosis for this disease is due to a combination of the presence of highly invasive tumor cells that escape surgical resection and the presence of a population of therapy-resistant cancer stem cells found within these tumors. Several studies suggest that glioma cells have cleverly hijacked the normal developmental program of neural progenitor cells, including their transcriptional programs, to enhance gliomagenesis. In this review, we summarize the role of developmentally regulated signaling pathways that have been found to facilitate glioma growth and invasion. Furthermore, we discuss how the microenvironment and treatment-induced perturbations of these highly interconnected signaling networks can trigger a shift in cellular phenotype and tumor subtype.

Temozolomide, sirolimus and chloroquine is a new therapeutic combination that synergizes to disrupt lysosomal function and cholesterol homeostasis in GBM cells

Glioblastoma (GBM) cells are characterized by high phagocytosis, lipogenesis, exocytosis activities, low autophagy capacity and high lysosomal demand are necessary for survival and invasion. The lysosome stands at the cross roads of lipid biosynthesis, transporting, sorting between exogenous and endogenous cholesterol. We hypothesized that three already approved drugs, the autophagy inducer, sirolimus (rapamycin, Rapa), the autophagy inhibitor, chloroquine (CQ), and DNA alkylating chemotherapy, temozolomide (TMZ) could synergize against GBM. This repurposed triple therapy combination induced GBM apoptosis in vitro and inhibited GBM xenograft growth in vivo. Cytotoxicity is caused by induction of lysosomal membrane permeabilization and release of hydrolases, and may be rescued by cholesterol supplementation. Triple treatment inhibits lysosomal function, prevents cholesterol extraction from low density lipoprotein (LDL), and causes clumping of lysosome associated membrane protein-1 (LAMP-1) and lipid droplets (LD) accumulation. Co-treatment of the cell lines with inhibitor of caspases and cathepsin B only partially reverse of cytotoxicities, while N-acetyl cysteine (NAC) can be more effective. A combination of reactive oxygen species (ROS) generation from cholesterol depletion are the early event of underling mechanism. Cholesterol repletion abolished the ROS production and reversed the cytotoxicity from QRT treatment. The shortage of free cholesterol destabilizes lysosomal membranes converting aborted autophagy to apoptosis through either direct mitochondria damage or cathepsin B release. This promising anti-GBM triple therapy combination severely decreases mitochondrial function, induces lysosome-dependent apoptotic cell death, and is now poised for further clinical testing and validation.

Molecular crosstalk between tumour and brain parenchyma instructs histopathological features in glioblastoma

The histopathological and molecular heterogeneity of glioblastomas represents a major obstacle for effective therapies. Glioblastomas do not develop autonomously, but evolve in a unique environment that adapts to the growing tumour mass and contributes to the malignancy of these neoplasms. Here, we show that patient-derived glioblastoma xenografts generated in the mouse brain from organotypic spheroids reproducibly give rise to three different histological phenotypes: (i) a highly invasive phenotype with an apparent normal brain vasculature, (ii) a highly angiogenic phenotype displaying microvascular proliferation and necrosis and (iii) an intermediate phenotype combining features of invasion and vessel abnormalities. These phenotypic differences were visible during early phases of tumour development suggesting an early instructive role of tumour cells on the brain parenchyma. Conversely, we found that tumour-instructed stromal cells differentially influenced tumour cell proliferation and migration in vitro, indicating a reciprocal crosstalk between neoplastic and non-neoplastic cells. We did not detect any transdifferentiation of tumour cells into endothelial cells. Cell type-specific transcriptomic analysis of tumour and endothelial cells revealed a strong phenotype-specific molecular conversion between the two cell types, suggesting co-evolution of tumour and endothelial cells. Integrative bioinformatic analysis confirmed the reciprocal crosstalk between tumour and microenvironment and suggested a key role for TGFβ1 and extracellular matrix proteins as major interaction modules that shape glioblastoma progression. These data provide novel insight into tumour-host interactions and identify novel stroma-specific targets that may play a role in combinatorial treatment strategies against glioblastoma.

A method for the long-term cultivation of mammalian cells in the absence of oxygen: Characterization of cell replication, hypoxia-inducible factor expression and reactive oxygen species production

The center of tumors, stem cell niches and mucosal surfaces all represent areas of the body that are reported to be anoxic. However, long-term study of anoxic cell physiology is hindered by the lack of a sustainable method permitting cell cultivation in the complete absence of oxygen. A novel methodology was developed that enabled anoxic cell cultivation (17d maximum time tested) and cell passage. In the absence of oxygen, cell morphology is significantly altered. All cells tested exhibited morphologic changes, i.e., a combination of tethered (monolayer-like) and runagate (suspension-like) morphologies. Both morphologies replicated (Vero and HeLa cells tested) and could be passaged anaerobically. In the absence of exogenous oxygen, anoxic cells produced reactive oxygen species (ROS). Anaerobic runagate HeLa and Vero cells increased ROS production from day 3 to day 10 by 2- and 3-fold, respectively. In contrast, anoxic tethered HeLa and Vero cells either showed no significant change in ROS production between days 3 and 10 or exhibited a 3-fold decrease in ROS, respectively. Detection of ROS was inversely related to detection of hypoxia-inducible factor-1α (HIF1) mRNA and HIF-1 protein expression which cycled over a 10-day period. This methodology has broad applications for the study of tumor and stem cell physiology as well as gastrointestinal cell-microbiome interactions. In addition, sustainable anaerobic cell culture may lead to the identification of novel pathways and targets for chemotherapeutic drug development.

Hexokinase 2 (HK2), the tumor promoter in glioma, is downregulated by miR-218/Bmi1 pathway

In cancer, glycolysis driving enzymes and their regulating microRNAs are one of the key focus of oncology research lately. The glycolytic enzyme hexokinase 2 (HK2) is crucial for the Warburg effect in human glioma, the most common malignant brain tumor. In the present study, we studied the tumorigenic role of HK2 in glioma, and clarified the mechanism of miR-218 induced HK2 regulation in glioma development. The HK2 expression in patient derived glioma and non neoplastic brain tissue was quantified. The HK2 silenced U87 and U251 cell lines were assessed for their proliferation, migration and invasive potential in vitro, while the tumor forming potential of U87 cells was evaluated in vivo. The untreated cell lines served as control. The HK2 expression in (a) lentivirus-infected, miR-218 overexpressing and (b) shRNA mediated Bmi1 silenced U87 and U251 glioma cell lines were quantified. Luciferase reporter assay, qRT-PCR analysis and WB were employed as required. The HK2 expression was significantly increased in glioma tissues comparing with the non neoplastic brain tissues and was positively correlated with the glioma grade. Silencing HK2 in glioma cell lines significantly decreased their proliferation, migration, invasion and tumorigenic abilities. Although, overexpression of miR-218 significantly downregulated the HK2 expression, luciferase reporter assay failed to show HK2 as the direct target of miR-218. A direct correlation, however, was observed between HK2 and Bmi-1, the direct target of miR-218. Taken together, our findings confirmed the tumorigenic activity of HK2 in glioma, and the involvement of the miR218/Bmi1 pathway in the regulation of its expression.

Altered metabolic landscape in IDH-mutant gliomas affects phospholipid, energy, and oxidative stress pathways

Heterozygous mutations in NADP-dependent isocitrate dehydrogenases (IDH) define the large majority of diffuse gliomas and are associated with hypermethylation of DNA and chromatin. The metabolic dysregulations imposed by these mutations, whether dependent or not on the oncometabolite D-2-hydroxyglutarate (D2HG), are less well understood. Here, we applied mass spectrometry imaging on intracranial patient-derived xenografts of IDH-mutant versus IDH wild-type glioma to profile the distribution of metabolites at high anatomical resolution in situ This approach was complemented by in vivo tracing of labeled nutrients followed by liquid chromatography-mass spectrometry (LC-MS) analysis. Selected metabolites were verified on clinical specimen. Our data identify remarkable differences in the phospholipid composition of gliomas harboring the IDH1 mutation. Moreover, we show that these tumors are characterized by reduced glucose turnover and a lower energy potential, correlating with their reduced aggressivity. Despite these differences, our data also show that D2HG overproduction does not result in a global aberration of the central carbon metabolism, indicating strong adaptive mechanisms at hand. Intriguingly, D2HG shows no quantitatively important glucose-derived label in IDH-mutant tumors, which suggests that the synthesis of this oncometabolite may rely on alternative carbon sources. Despite a reduction in NADPH, glutathione levels are maintained. We found that genes coding for key enzymes in de novo glutathione synthesis are highly expressed in IDH-mutant gliomas and the expression of cystathionine-β-synthase (CBS) correlates with patient survival in the oligodendroglial subtype. This study provides a detailed and clinically relevant insight into the in vivo metabolism of IDH1-mutant gliomas and points to novel metabolic vulnerabilities in these tumors.

Biological basis and clinical study of glycogen synthase kinase- 3β-targeted therapy by drug repositioning for glioblastoma

Background

Glycogen synthase kinase (GSK)-3β has emerged as an appealing therapeutic target for glioblastoma (GBM). Here, we investigated the therapeutic effect of the current approved drugs against GBM via inhibition of GSK3β activity both, in experimental setting and in a clinical study for recurrent GBM patients by repositioning existent drugs in combination with temozolomide (TMZ).

Materials and Methods

Progression-free and overall survival rates were compared between patients with low or high expression of active GSK3β in the primary tumor. GBM cells and a mouse model were examined for the effects of GSK3β-inhibitory drugs, cimetidine, lithium, olanzapine, and valproate. The safety and efficacy of the cocktail of these drugs (CLOVA cocktail) in combination with TMZ were tested in the mouse model and in a clinical study for recurrent GBM patients.

Results

Activation of GSK3β in the tumor inversely correlated with patient survival as an independent prognostic factor. CLOVA cocktail significantly inhibited cell invasion and proliferation. The patients treated with CLOVA cocktail in combination with TMZ showed increased survival compared to the control group treated with TMZ alone.

Conclusions

Repositioning of the GSK3β-inhibitory drugs improved the prognosis of refractory GBM patients with active GSK3β in tumors. Combination of CLOVA cocktail and TMZ is a promising approach for recurrent GBM.

Metabolic alterations underlying Bevacizumab therapy in glioblastoma cells

Anti-VEGF therapy with Bevacizumab is approved for glioblastoma treatment, however, it is known that tumors acquired resistance and eventually became even more aggressive and infiltrative after treatment. In the present study we aimed to unravel the potential cellular mechanisms of resistance to Bevacizumab in glioblastoma in vitro models.

Using a panel of glioblastoma cell lines we found that Bevacizumab is able to block the secreted VEGF by the tumor cells and be internalized to the cytoplasm, inducing cytotoxicity in vitro. We further found that Bevacizumab increases the expression of hypoxic (HIF-1α and CAIX) and glycolytic markers (GLUT1 and MCT1), leading to higher glucose uptake and lactate production. Furthermore, we showed that part of the consumed glucose by the tumor cells can be stored as glycogen, hampering cell dead following Bevacizumab treatment. Importantly, we found that this change on the glycolytic metabolism occurs independently of hypoxia and before mitochondrial impairment or autophagy induction. Finally, the combination of Bevacizumab with glucose uptake inhibitors decreased in vivo tumor growth and angiogenesis and shift the expression of glycolytic proteins.

In conclusion, we reported that Bevacizumab is able to increase the glucose metabolism on cancer cells by abrogating autocrine VEGF in vitro. Define the effects of anti-angiogenic drugs at the cellular level can allow us to discover ways to revert acquired resistance to this therapeutic approaches in the future.

Mammalian target of rapamycin complex 1 activation sensitizes human glioma cells to hypoxia-induced cell death

Glioblastomas are characterized by fast uncontrolled growth leading to hypoxic areas and necrosis. Signalling from EGFR via mammalian target of rapamycin complex 1 (mTORC1) is a major driver of cell growth and proliferation and one of the most commonly altered signalling pathways in glioblastomas. Therefore, epidermal growth factor receptor and mTORC1 signalling are plausible therapeutic targets and clinical trials with inhibitors are in progress. However, we have previously shown that epidermal growth factor receptor and mTORC1 inhibition triggers metabolic changes leading to adverse effects under the conditions of the tumour microenvironment by protecting from hypoxia-induced cell death. We hypothesized that conversely mTORC1 activation sensitizes glioma cells to hypoxia-induced cell death. As a model for mTORC1 activation we used gene suppression of its physiological inhibitor TSC2 (TSC2sh). TSC2sh glioma cells showed increased sensitivity to hypoxia-induced cell death that was accompanied by an earlier ATP depletion and an increase in reactive oxygen species. There was no difference in extracellular glucose consumption but an altered intracellular metabolic profile with an increase of intermediates of the pentose phosphate pathway. Mechanistically, mTORC1 upregulated the first and rate limiting enzyme of the pentose phosphate pathway, G6PD. Furthermore, an increase in oxygen consumption in TSC2sh cells was detected. This appeared to be due to higher transcription rates of genes involved in mitochondrial respiratory function including PPARGC1A and PPARGC1B (also known as PGC-1α and -β). The finding that mTORC1 activation causes an increase in oxygen consumption and renders malignant glioma cells susceptible to hypoxia and nutrient deprivation could help identify glioblastoma patient cohorts more likely to benefit from hypoxia-inducing therapies such as the VEGFA-targeting antibody bevacizumab in future clinical evaluations.

Targeting Malignant Brain Tumors with Antibodies

Antibodies have been shown to be a potent therapeutic tool. However, their use for targeting brain diseases, including neurodegenerative diseases and brain cancers, has been limited, particularly because the blood–brain barrier (BBB) makes brain tissue hard to access by conventional antibody-targeting strategies. In this review, we summarize new antibody therapeutic approaches to target brain tumors, especially malignant gliomas, as well as their potential drawbacks. Many different brain delivery platforms for antibodies have been studied such as liposomes, nanoparticle-based systems, cell-penetrating peptides (CPPs), and cell-based approaches. We have already shown the successful delivery of single-chain fragment variable (scFv) with CPP as a linker between two variable domains in the brain. Antibodies normally face poor penetration through the BBB, with some variants sufficiently passing the barrier on their own. A “Trojan horse” method allows passage of biomolecules, such as antibodies, through the BBB by receptor-mediated transcytosis (RMT). Such examples of therapeutic antibodies are the bispecific antibodies where one binding specificity recognizes and binds a BBB receptor, enabling RMT and where a second binding specificity recognizes an antigen as a therapeutic target. On the other hand, cell-based systems such as stem cells (SCs) are a promising delivery system because of their tumor tropism and ability to cross the BBB. Genetically engineered SCs can be used in gene therapy, where they express anti-tumor drugs, including antibodies. Different types and sources of SCs have been studied for the delivery of therapeutics to the brain; both mesenchymal stem cells (MSCs) and neural stem cells (NSCs) show great potential. Following the success in treatment of leukemias and lymphomas, the adoptive T-cell therapies, especially the chimeric antigen receptor-T cells (CAR-Ts), are making their way into glioma treatment as another type of cell-based therapy using the antibody to bind to the specific target(s). Finally, the current clinical trials are reviewed, showing the most recent progress of attractive approaches to deliver therapeutic antibodies across the BBB aiming at the specific antigen.

Regulation of hypoxia-induced autophagy in glioblastoma involves ATG9A

BACKGROUND

Hypoxia is negatively associated with glioblastoma (GBM) patient survival and contributes to tumour resistance. Anti-angiogenic therapy in GBM further increases hypoxia and activates survival pathways. The aim of this study was to determine the role of hypoxia-induced autophagy in GBM.

METHODS

Pharmacological inhibition of autophagy was applied in combination with bevacizumab in GBM patient-derived xenografts (PDXs). Sensitivity towards inhibitors was further tested in vitro under normoxia and hypoxia, followed by transcriptomic analysis. Genetic interference was done using ATG9A-depleted cells.

RESULTS

We find that GBM cells activate autophagy as a survival mechanism to hypoxia, although basic autophagy appears active under normoxic conditions. Although single agent chloroquine treatment in vivo significantly increased survival of PDXs, the combination with bevacizumab resulted in a synergistic effect at low non-effective chloroquine dose. ATG9A was consistently induced by hypoxia, and silencing of ATG9A led to decreased proliferation in vitro and delayed tumour growth in vivo. Hypoxia-induced activation of autophagy was compromised upon ATG9A depletion.

CONCLUSIONS

This work shows that inhibition of autophagy is a promising strategy against GBM and identifies ATG9 as a novel target in hypoxia-induced autophagy. Combination with hypoxia-inducing agents may provide benefit by allowing to decrease the effective dose of autophagy inhibitors.

Multifaceted C-X-C Chemokine Receptor 4 (CXCR4) Inhibition Interferes with Anti-Vascular Endothelial Growth Factor Therapy-Induced Glioma Dissemination

Resistance to antiangiogenic therapy in glioblastoma (GBM) patients may involve hypoxia-induced expression of C-X-C motif chemokine receptor 4 (CXCR4) on invading tumor cells, macrophage/microglial cells (MGCs), and glioma stem cells (GSCs). We determined whether antagonizing CXCR4 with POL5551 disrupts anti-vascular endothelial growth factor (VEGF) therapy-induced glioma growth and dissemination. Mice bearing orthotopic CT-2A or GL261 gliomas received POL5551 and/or anti-VEGF antibody B20-4.1.1. Brain tissue was analyzed for tumor volume, invasiveness, hypoxia, vascular density, proliferation, apoptosis, GSCs, and MGCs. Glioma cells were evaluated for CXCR4 expression and polymorphism and POL5551's effects on CXCR4 ligand binding, cell viability, and migration. No CXCR4 mutations were identified. POL5551 inhibited CXCR4 binding to its ligand, stromal cell-derived factor-1α, and reduced hypoxia- and stromal cell-derived factor-1α-mediated migration dose-dependently but minimally affected cell viability. In vivo, B20-4.1.1 increased hypoxic foci and invasiveness, as seen in GBM patients receiving anti-VEGF therapy. Combination of POL5551 and B20-4.1.1 reduced both glioma invasiveness by 16% to 39% and vascular density compared to B20-4.1.1 alone in both glioma models. Reduced populations of GSCs and MGCs were also seen in CT-2A tumors. POL5551 concentrations, evaluated by mass spectrometry, were higher in tumors than in neighboring brain tissues, likely accounting for the results. Inhibition of CXCR4-regulated tumoral, stem cell, and immune mechanisms by adjunctive CXCR4 antagonists may help overcome antiangiogenic therapy resistance, benefiting GBM patients.

In Vivo Assessment of Ovarian Tumor Response to Tyrosine Kinase Inhibitor Pazopanib by Using Hyperpolarized 13C-Pyruvate MR Spectroscopy and 18F-FDG PET/CT Imaging in a Mouse Model

Purpose To assess in a mouse model whether early or late components of glucose metabolism, exemplified by fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) positron emission tomography (PET) and hyperpolarized carbon 13 (¹³C)-pyruvate magnetic resonance (MR) spectroscopy, can serve as indicators of response in ovarian cancer to multityrosine kinase inhibitor pazopanib. Materials and Methods In this Animal Care and Use Committee approved study, 17 days after the injection of 2 × 10⁶ human ovarian SKOV3 tumors cells into 14 female nude mice, treatment with vehicle or pazopanib (2.5 mg per mouse peroral every other day) was initiated. Longitudinal T2-weighted MR imaging, dynamic MR spectroscopy of hyperpolarized pyruvate, and ¹⁸F-FDG PET/computed tomographic (CT) imaging were performed before treatment, 2 days after treatment, and 2 weeks after treatment. Results Pazopanib inhibited ovarian tumor growth compared with control (0.054 g ± 0.041 vs 0.223 g ± 0.112, respectively; six mice were treated with pazopanib and seven were control mice; P < .05). Significantly higher pyruvate-to-lactate conversion (lactate/pyruvate + lactate ratio) was found 2 days after treatment with pazopanib than before treatment (0.46 ± 0.07 vs 0.31 ± 0.14, respectively; P < .05; six tumors after treatment, seven tumors before treatment). This was not observed with the control group or with ¹⁸F-FDG PET/CT imaging. Conclusion The findings suggest that hyperpolarized ¹³C-pyruvate MR spectroscopy may serve as an early indicator of response to tyrosine kinase (angiogenesis) inhibitors such as pazopanib in ovarian cancer even when ¹⁸F-FDG PET/CT does not indicate a response. ^© RSNA, 2017 Online supplemental material is available for this article.

Effects of soluble CPE on glioma cell migration are associated with mTOR activation and enhanced glucose flux

Carboxypeptidase E (CPE) has recently been described as a multifunctional protein that regulates proliferation, migration and survival in several tumor entities. In glioblastoma (GBM), the most malignant primary brain tumor, secreted CPE (sCPE) was shown to modulate tumor cell migration. In our current study, we aimed at clarifying the underlying molecular mechanisms regulating anti-migratory as well as novel metabolic effects of sCPE in GBM. Here we show that sCPE activates mTORC1 signaling in glioma cells detectable by phosphorylation of its downstream target RPS6. Additionally, sCPE diminishes glioma cell migration associated with a negative regulation of Rac1 signaling via RPS6, since both inhibition of mTOR and stimulation of Rac1 results in a reversed effect of sCPE on migration. Knockdown of CPE leads to a decrease of active RPS6 associated with increased GBM cell motility. Apart from this, we show that sCPE enhances glucose flux into the tricarboxylic acid cycle at the expense of lactate production, thereby decreasing aerobic glycolysis, which might as well contribute to a less invasive behavior of tumor cells. Our data contributes to a better understanding of the complexity of GBM cell migration and sheds new light on how tumor cell invasion and metabolic plasticity are interconnected.

Reactive Oxygen Species-Mediated Mechanisms of Action of Targeted Cancer Therapy

Targeted cancer therapies, involving tyrosine kinase inhibitors and monoclonal antibodies, for example, have recently led to substantial prolongation of survival in many metastatic cancers. Compared with traditional chemotherapy and radiotherapy, where reactive oxygen species (ROS) have been directly linked to the mediation of cytotoxic effects and adverse events, the field of oxidative stress regulation is still emerging in targeted cancer therapies. Here, we provide a comprehensive review regarding the current evidence of ROS-mediated effects of antibodies and tyrosine kinase inhibitors, use of which has been indicated in the treatment of solid malignancies and lymphomas. It can be concluded that there is rapidly emerging evidence of ROS-mediated effects of some of these compounds, which is also relevant in the context of drug resistance and how to overcome it.

Reactive Oxygen Species-Mediated Mechanisms of Action of Targeted Cancer Therapy

Targeted cancer therapies, involving tyrosine kinase inhibitors and monoclonal antibodies, for example, have recently led to substantial prolongation of survival in many metastatic cancers. Compared with traditional chemotherapy and radiotherapy, where reactive oxygen species (ROS) have been directly linked to the mediation of cytotoxic effects and adverse events, the field of oxidative stress regulation is still emerging in targeted cancer therapies. Here, we provide a comprehensive review regarding the current evidence of ROS-mediated effects of antibodies and tyrosine kinase inhibitors, use of which has been indicated in the treatment of solid malignancies and lymphomas. It can be concluded that there is rapidly emerging evidence of ROS-mediated effects of some of these compounds, which is also relevant in the context of drug resistance and how to overcome it.

Trimming the Vascular Tree in Tumors: Metabolic and Immune Adaptations

Angiogenesis, the formation of new blood vessels, has become a well-established hallmark of cancer. Its functional importance for the manifestation and progression of tumors has been further validated by the beneficial therapeutic effects of angiogenesis inhibitors, most notably ones targeting the vascular endothelial growth factor (VEGF) signaling pathways. However, with the transient and short-lived nature of the patient response, it has become evident that tumors have the ability to adapt to the pressures of vascular growth restriction. Several escape mechanisms have been described that adapt tumors to therapy-induced low-oxygen tension by either reinstating tumor growth by vascular rebound or by altering tumor behavior without the necessity to reinitiate revascularization. We review here two bypass mechanisms that either instigate angiogenic and immune-suppressive polarization of intratumoral innate immune cells to facilitate VEGF-independent angiogenesis or enable metabolic adaptation and reprogramming of endothelial cells and tumor cells to adapt to low-oxygen tension.

Nucleus accumbens-associated protein-1 promotes glycolysis and survival of hypoxic tumor cells via the HDAC4-HIF-1α axis

Nucleus accumbens-associated protein-1 (NAC1), a nuclear factor of the BTB/POZ gene family, has emerging roles in cancer. In this study, we identified the NAC1-HDAC4-HIF-1α axis as an important pathway in regulating glycolysis and hypoxic adaptation in tumor cells. We show that nuclear NAC1 binds to histone deacetylase type 4 (HDAC4), hindering phosphorylation of HDAC4 at Ser²⁴⁶ and preventing its nuclear export that leads to cytoplasmic degradation of the deacetylase. Accumulation of HDAC4 in the nuclei results in an attenuation of HIF-1α acetylation, enhancing the stabilization and transcriptional activity of HIF-1α and strengthening adaptive response of cells to hypoxia. We also show the role of NAC1 in promoting glycolysis in a mouse xenograft model, and demonstrate that knockdown of NAC1 expression can reinforce the antitumor efficacy of bevacizumab, an inhibitor of angiogenesis. Clinical implication of the NAC1-HDAC4-HIF-1α pathway is suggested by the results showing that expression levels of these proteins are significantly correlative in human tumor specimens and associated with the disease progression. This study not only reveals an important function of NAC1 in regulating glycolysis, but also identifies the NAC1-HDAC4-HIF-1α axis as a novel molecular pathway that promotes survival of hypoxic tumor cells.

Bevacizumab and radiotherapy for the treatment of glioblastoma: brothers in arms or unholy alliance?

Glioblastoma (GBM) represents the most frequent primary brain tumor in adults and carries a dismal prognosis despite aggressive, multimodal treatment regimens involving maximal resection, radiochemotherapy, and maintenance chemotherapy. Histologically, GBMs are characterized by a high degree of VEGF-mediated vascular proliferation. In consequence, new targeted anti-angiogenic therapies, such as the monoclonal anti-VEGF-A antibody bevacizumab, have proven effective in attenuating tumor (neo)angiogenesis and were shown to possess therapeutic activity in several phase II trials. However, the role of bevacizumab in the context of multimodal therapy approaches appears to be rather complex. This review will give insights into current concepts, limitations, and controversies regarding the molecular mechanisms and the clinical benefits of bevacizumab treatment in combination with radio(chemo)therapy - particularly in face of the results of recent phase III trials, which failed to demonstrate convincing improvements in overall survival (OS).

Targeting cancer stem-like cells in glioblastoma and colorectal cancer through metabolic pathways

Cancer stem-like cells (CSCs) are thought to be the main cause of tumor occurrence, progression and therapeutic resistance. Strong research efforts in the last decade have led to the development of several tailored approaches to target CSCs with some very promising clinical trials underway; however, until now no anti-CSC therapy has been approved for clinical use. Given the recent improvement in our understanding of how onco-proteins can manipulate cellular metabolic networks to promote tumorigenesis, cancer metabolism research may well lead to innovative strategies to identify novel regulators and downstream mediators of CSC maintenance. Interfering with distinct stages of CSC-associated metabolics may elucidate novel, more efficient strategies to target this highly malignant cell population. Here recent discoveries regarding the metabolic properties attributed to CSCs in glioblastoma (GBM) and malignant colorectal cancer (CRC) were summarized. The association between stem cell markers, the response to hypoxia and other environmental stresses including therapeutic insults as well as developmentally conserved signaling pathways with alterations in cellular bioenergetic networks were also discussed. The recent developments in metabolic imaging to identify CSCs were also summarized. This summary should comprehensively update basic and clinical scientists on the metabolic traits of CSCs in GBM and malignant CRC.

Metabolism of 4-Hydroxy-7-oxo-5-heptenoic Acid (HOHA) Lactone by Retinal Pigmented Epithelial Cells

4-Hydroxy-7-oxo-5-heptenic acid (HOHA)-lactone is a biologically active oxidative truncation product released (t1/2 = 30 min at 37 °C) by nonenzymatic transesterification/deacylation from docosahexaenoate lipids. We now report that HOHA-lactone readily diffuses into retinal pigmented epithelial (RPE) cells where it is metabolized. A reduced glutathione (GSH) Michael adduct of HOHA-lactone is the most prominent metabolite detected by LC-MS in both the extracellular medium and cell lysates. This molecule appeared inside of ARPE-19 cells within seconds after exposure to HOHA-lactone. The intracellular level reached a maximum concentration at 30 min and then decreased with concomitant increases in its level in the extracellular medium, thus revealing a unidirectional export of the reduced GSH-HOHA-lactone adduct from the cytosol to extracellular medium. This metabolism is likely to modulate the involvement of HOHA-lactone in the pathogenesis of human diseases. HOHA-lactone is biologically active, e.g., low concentrations (0.1-1 μM) induce secretion of vascular endothelial growth factor (VEGF) from ARPE-19 cells. HOHA-lactone is also a precursor of 2-(ω-carboxyethyl)pyrrole (CEP) derivatives of primary amino groups in proteins and ethanolamine phospholipids that have significant pathological and physiological relevance to age-related macular degeneration (AMD), cancer, and wound healing. Both HOHA-lactone and the derived CEP can contribute to the angiogenesis that defines the neovascular "wet" form of AMD and that promotes the growth of tumors. While GSH depletion can increase the lethality of radiotherapy, because it will impair the metabolism of HOHA-lactone, the present study suggests that GSH depletion will also increase levels of HOHA-lactone and CEP that may promote recurrence of tumor growth.

Vascular endothelial growth factor blockade elicits a stable metabolic shift in tumor cells: therapeutic implications

The metabolism of tumors differs remarkably from that of normal tissues, but whether this is a stable feature of tumor cells is largely unknown. Recent findings by independent teams indicate that antiangiogenic drugs cause a metabolic shift in tumor cells that is associated with increased malignancy. These results suggest therapy-driven evolutionary dynamics of tumor metabolism that could be therapeutically targeted.

Limited role for transforming growth factor-β pathway activation-mediated escape from VEGF inhibition in murine glioma models

BACKGROUND

The vascular endothelial growth factor (VEGF) and transforming growth factor (TGF)-β pathways regulate key biological features of glioblastoma. Here we explore whether the TGF-β pathway, which promotes angiogenesis, invasiveness, and immunosuppression, acts as an escape pathway from VEGF inhibition.

METHODS

The role of the TGF-β pathway in escape from VEGF inhibition was assessed in vitro and in vivo and by gene expression profiling in syngeneic mouse glioma models.

RESULTS

We found that TGF-β is an upstream regulator of VEGF, whereas VEGF pathway activity does not alter the TGF-β pathway in vitro. In vivo, single-agent activity was observed for the VEGF antibody B20-4.1.1 in 3 and for the TGF-β receptor 1 antagonist LY2157299 in 2 of 4 models. Reduction of tumor volume and blood vessel density, but not induction of hypoxia, correlated with benefit from B20-4.1.1. Reduction of phosphorylated (p)SMAD2 by LY2157299 was seen in all models but did not predict survival. Resistance to B20 was associated with anti-angiogenesis escape pathway gene expression, whereas resistance to LY2157299 was associated with different immune response gene signatures in SMA-497 and GL-261 on transcriptomic profiling. The combination of B20 with LY2157299 was ineffective in SMA-497 but provided prolongation of survival in GL-261, associated with early suppression of pSMAD2 in tumor and host immune cells, prolonged suppression of angiogenesis, and delayed accumulation of tumor infiltrating microglia/macrophages.

CONCLUSIONS

Our study highlights the biological heterogeneity of murine glioma models and illustrates that cotargeting of the VEGF and TGF-β pathways might lead to improved tumor control only in subsets of glioblastoma.

Emerging Approaches for Targeting Metabolic Vulnerabilities in Malignant Glioma

Malignant gliomas are intractable and among the most lethal human malignancies. Like other cancers, metabolic reprogramming is a key feature of glioma and is thought to accommodate the heightened nutrient requirements for tumor cell proliferation, growth, and survival. This metabolic rewiring, driven by oncogenic signaling and molded by the unique environment of the brain, may impose vulnerabilities that could be exploited therapeutically for increased tumor control. In this review, we discuss the prominent metabolic features of malignant glioma, the key pathways regulating glioma metabolism, and the potential therapeutic opportunities for targeting metabolic processes.

Randomized phase II study of axitinib versus physicians best alternative choice of therapy in patients with recurrent glioblastoma

We conducted a randomized, non-comparative, multi center, phase II clinical trial in order to investigate the efficacy of axitinib, an oral small molecule tyrosine kinase inhibitor with high affinity and specificity for the vascular endothelial growth factor receptors, in patients with recurrent glioblastoma following prior treatment with radiation and temozolomide. Forty-four patients were randomly assigned to receive treatment with axitinib (5 mg BID starting dose; N = 22) or "physicians best alternative choice of therapy" that consisted of bevacizumab (N = 20) or lomustine (N = 2). Six-month progression-free survival served as the primary endpoint. The estimated 6-month progression-free survival rate was 34 % (95 % CI 14-54) for patients treated with axitinib and 28 % (95 % CI 8-48) with best alternative treatment; median overall survival was 29 and 17 weeks, respectively. Objective responses according to RANO criteria were documented in 28 % of patients treated with axitinib and 23 % of patients treated with best alternative therapy. A decrease in maximal uptake of 18F-fluoro-ethyL-tyrosine (18F-FET) by the glioblastoma on PET imaging was documented in 85 % of patients at the time of response on axitinib. Corticosteroid treatment could be stopped in four and tapered in seven out of the 15 patients who were treated with steroids at baseline in the axitinib cohort. Most frequent axitinib related grade ≥3 adverse events consisted of fatigue (9 %), diarrhea (9 %), and oral hyperesthesia (4.5 %). We conclude that axitinib has single-agent clinical activity and a manageable toxicity profile in patients with recurrent glioblastoma.

Glycolysis and the pentose phosphate pathway are differentially associated with the dichotomous regulation of glioblastoma cell migration versus proliferation

BACKGROUND

The dichotomy between glioblastoma cell migration and proliferation is regulated by various parameters including oxygen tension. In glioblastoma stem-like cells, hypoxia induces downregulation of pentose phosphate pathway (PPP) enzymes and a flux shift towards glycolysis. We investigated whether the 2 parallel glucose metabolic pathways are intrinsically linked with cell function and whether these pathways are mechanistically involved in regulating functional programs.

METHODS

Enzyme expression, migration, and proliferation under hypoxia were studied in multiple cell types. Rapidly and slowly dividing or migrating glioblastoma cells were separated, and enzyme profiles were compared. Glucose-6-phosphate dehydrogenase (G6PD) and Aldolase C (ALDOC), the most strongly inversely regulated PPP and glycolysis enzymes, were knocked down by short hairpin RNA.

RESULTS

Hypoxia caused downregulation of PPP enzymes and upregulation of glycolysis enzymes in a broad spectrum of cancer and nonneoplastic cells and consistently stimulated migration while reducing proliferation. PPP enzyme expression was increased in rapidly dividing glioblastoma cells, whereas glycolysis enzymes were decreased. Conversely, glycolysis enzymes were elevated in migrating cells, whereas PPP enzymes were diminished. Knockdown of G6PD reduced glioblastoma cell proliferation, whereas ALDOC knockdown decreased migration. Enzyme inhibitors had similar effects. G6PD knockdown in a highly proliferative but noninvasive glioblastoma cell line resulted in prolonged survival of mice with intracerebral xenografts, whereas ALDOC knockdown shortened survival. In a highly invasive glioblastoma xenograft model, tumor burden was unchanged by either knockdown.

CONCLUSIONS

Cell function and metabolic state are coupled independently of hypoxia, and glucose metabolic pathways are causatively involved in regulating "go or grow" cellular programs.

Radiation treatment monitoring using multimodal functional imaging: PET/CT ((18)F-Fluoromisonidazole & (18)F-Fluorocholine) and DCE-US

Background

This study aims to assess the effect of radiation treatment on the tumour vasculature and its downstream effects on hypoxia and choline metabolism using a multimodal approach in the murine prostate tumour model CWR22. Functional parameters derived from Positron Emission Tomography (PET)/Computer Tomography (CT) with ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) and ¹⁸F-Fluorocholine (¹⁸F-FCH) as well as Dynamic Contrast-Enhanced Ultrasound (DCE-US) were employed to determine the relationship between metabolic parameters and microvascular parameters that reflect the tumour microenvironment. Immunohistochemical analysis was employed for validation.

Methods

PET/CT and DCE-US were acquired pre- and post-treatment, at day 0 and day 3, respectively. At day 1, radiation treatment was delivered as a single fraction of 10 Gy. Two experimental groups were tested for treatment response with ¹⁸F-FMISO and ¹⁸F-FCH.

Results

The maximum Standardized Uptake Values (SUVmax) and the mean SUV (SUVmean) for the ¹⁸F-FMISO group were decreased after treatment, and the SUVmean of the tumour-to-muscle ratio was correlated to microvessel density (MVD) at day 3. The kurtosis of the amplitude of the contrast uptake A was significantly decreased for the control tumours in the ¹⁸F-FCH group. Furthermore, the eliminating rate constant of the contrast agent from the plasma k_el derived from DCE-US was negatively correlated to the SUVmean of tumour-to-muscle ratio, necrosis and MVD.

Conclusions

The present study suggests that the multimodal approach using ¹⁸F-FMISO PET/CT and DCE-US seems reliable in the assessment of both microvasculature and necrosis as validated by histology. Thus, it has valuable diagnostic and prognostic potential for early non-invasive evaluation of radiotherapy.

Engraftment of Human Glioblastoma Cells in Immunocompetent Rats through Acquired Immunosuppression

Transplantation of glioblastoma patient biopsy spheroids to the brain of T cell-compromised Rowett (nude) rats has been established as a representative animal model for human GBMs, with a tumor take rate close to 100%. In immunocompetent littermates however, primary human GBM tissue is invariably rejected. Here we show that after repeated passaging cycles in nude rats, human GBM spheroids are enabled to grow in the brain of immunocompetent rats. In case of engraftment, xenografts in immunocompetent rats grow progressively and host leukocytes fail to enter the tumor bed, similar to what is seen in nude animals. In contrast, rejection is associated with massive infiltration of the tumor bed by leukocytes, predominantly ED1+ microglia/macrophages, CD4+ T helper cells and CD8+ effector cells, and correlates with elevated serum levels of pro-inflammatory cytokines IL-1β, IL-18 and TNF-α. We observed that in nude rat brains, an adaptation to the host occurs after several in vivo passaging cycles, characterized by striking attenuation of microglial infiltration. Furthermore, tumor-derived chemokines that promote leukocyte migration and their entry into the CNS such as CXCL-10 and CXCL-12 are down-regulated, and the levels of TGF-β2 increase. We propose that through serial in vivo passaging in nude rats, human GBM cells learn to avoid and or/ suppress host immunity. Such adapted GBM cells are in turn able to engraft in immunocompetent rats without signs of an inflammatory response.