Induction of macrophagic prostaglandin E2 synthesis by glioma cells

Synthesis and Significance of Arachidonic Acid, a Substrate for Cyclooxygenases, Lipoxygenases, and Cytochrome P450 Pathways in the Tumorigenesis of Glioblastoma Multiforme, Including a Pan-Cancer Comparative Analysis

Glioblastoma multiforme (GBM) is one of the most aggressive gliomas. New and more effective therapeutic approaches are being sought based on studies of the various mechanisms of GBM tumorigenesis, including the synthesis and metabolism of arachidonic acid (ARA), an omega-6 polyunsaturated fatty acid (PUFA). PubMed, GEPIA, and the transcriptomics analysis carried out by Seifert et al. were used in writing this paper. In this paper, we discuss in detail the biosynthesis of this acid in GBM tumors, with a special focus on certain enzymes: fatty acid desaturase (FADS)1, FADS2, and elongation of long-chain fatty acids family member 5 (ELOVL5). We also discuss ARA metabolism, particularly its release from cell membrane phospholipids by phospholipase A₂ (cPLA₂, iPLA₂, and sPLA₂) and its processing by cyclooxygenases (COX-1 and COX-2), lipoxygenases (5-LOX, 12-LOX, 15-LOX-1, and 15-LOX-2), and cytochrome P450. Next, we discuss the significance of lipid mediators synthesized from ARA in GBM cancer processes, including prostaglandins (PGE₂, PGD₂, and 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂)), thromboxane A₂ (TxA₂), oxo-eicosatetraenoic acids, leukotrienes (LTB₄, LTC₄, LTD₄, and LTE₄), lipoxins, and many others. These lipid mediators can increase the proliferation of GBM cancer cells, cause angiogenesis, inhibit the anti-tumor response of the immune system, and be responsible for resistance to treatment.

Ferroptosis in Glioma Immune Microenvironment: Opportunity and Challenge

Glioma is the most common intracranial malignant tumor in adults and the 5-year survival rate of glioma patients is extremely poor, even in patients who received Stupp treatment after diagnosis and this forces us to explore more efficient clinical strategies. At this time, immunotherapy shows great potential in a variety of tumor clinical treatments, however, its clinical effect in glioma is limited because of tumor immune privilege which was induced by the glioma immunosuppressive microenvironment, so remodeling the immunosuppressive microenvironment is a practical way to eliminate glioma immunotherapy resistance. Recently, increasing studies have confirmed that ferroptosis, a new form of cell death, plays an important role in tumor progression and immune microenvironment and the crosstalk between ferroptosis and tumor immune microenvironment attracts much attention. This work summarizes the progress studies of ferroptosis in the glioma immune microenvironment.

Prospects of immune checkpoint blockade and vaccine-based immunotherapy for glioblastoma

Glioblastoma multiforme (GBM) is the most prevalent primary brain tumor endowed with a dismal prognosis. Nowadays, immunotherapy in a particular immune checkpoint blockade and therapeutic vaccines are being extensively pursued. Yet, several characteristics of GBM may impact such immunotherapeutic approaches. This includes tumor heterogeneity, the relatively low mutational load of primary GBM, insufficient delivery of antibodies to tumor parenchyma and the unique immunosuppressive microenvironment of GBM. Moreover, standard treatment of GBM, comprising temozolomide chemotherapy, radiotherapy and in most instances the application of glucocorticoids for management of brain edema, results in a further increased immunosuppression. This review will provide a brief introduction to the principles of vaccine-based immunotherapy and give an overview of the current clinical studies, which employed immune checkpoint inhibitors, oncolytic viruses-based vaccination, cell-based and peptide-based vaccines. Recent experiences as well as the latest developments are reviewed. Overcoming obstacles, which limit the induction and long-term immune response against GBM when using vaccination approaches, are necessary for the implementation of effective immunotherapy of GBM.

Mechanisms of intimate and long-distance cross-talk between glioma and myeloid cells: how to break a vicious cycle

Glioma-associated microglia and macrophages (GAMs) and myeloid-derived suppressor cells (MDSCs) condition the glioma microenvironment to generate an immunosuppressed niche for tumour expansion. This immunosuppressive microenvironment is considered to be shaped through a complex multi-step interactive process between glioma cells, GAMs and MDSCs. Glioma cells recruit GAMs and MDSCs to the tumour site and block their maturation. Glioma cell-derived factors subsequently skew these cells towards an immunosuppressive, tumour-promoting phenotype. Finally, GAMs and MDSCs enhance immune suppression in the glioma microenvironment and promote glioma growth, invasiveness, and neovascularization. The local and distant cross-talk between glioma cells and GAMs and MDSCs is regulated by a plethora of soluble proteins and cell surface-bound factors, and possibly via extracellular vesicles and platelets. Importantly, GAMs and MDSCs have been reported to impair the efficacy of glioma therapy, in particular immunotherapeutic approaches. Therefore, advancing our understanding of the function of GAMs and MDSCs in brain tumours and targeted intervention of their immunosuppressive function may benefit the treatment of glioma.

Cellular immunotherapy for pediatric solid tumors

Substantial progress has been made in the treatment of pediatric solid tumors over the past 4 decades. However, children with metastatic and or recurrent disease continue to do poorly despite the aggressive multi-modality conventional therapies. The increasing understanding of the tumor biology and the interaction between the tumor and the immune system over the recent years have led to the development of novel immune-based therapies as alternative options for some of these high-risk malignancies. The safety and anti-tumor efficacy of various tumor vaccines and tumor-antigen specific immune cells are currently being investigated for various solid tumors. In early clinical trials, most of these cellular therapies have been well tolerated and have shown promising clinical responses. Although substantial work is being done in this field, the available knowledge for pediatric tumors remains limited. We review the contemporary early phase cell-based immunotherapy efforts for pediatric solid tumors and discuss the rationale and the challenges thereof.

The multi-faceted roles of prostaglandin E2 in cancer-infiltrating mononuclear phagocyte biology

Extensive research in the last two decades implemented that the inflammatory cell infiltrate, especially in solid tumors, is a major determinant for patient prognosis. Mononuclear phagocytes, i.e. monocytes/macrophages, dendritic cells and myeloid-derived suppressor cells, constitute the majority of tumor-associated immune cells. Instead of inducing anti-tumor immunity, mononuclear phagocytes are functionally subverted by tumor microenvironmental factors to support each stage of oncogenesis. Although mechanisms how tumors program their inflammatory infiltrate to support tumor development are ill-defined, few master regulators are beginning to emerge. One of them is the inflammatory eicosanoid prostaglandin E(2) (PGE(2)), produced by tumor cells or the infiltrating immune cells. In this review we summarize the impact of PGE(2) on mononuclear phagocytes in inflammation and cancer and discuss potential implications for cancer therapy.

Medulloblasoma: challenges for effective immunotherapy

For medulloblastoma patients, the current therapeutic paradigm of surgery followed by radiation and chemotherapy can lead to long-term remission. However, the sequelae of treatment can be very debilitating, particularly in young children. Immunotherapy is an attractive treatment approach to optimize the targeting of tumor cells while sparing the vulnerable surrounding brain that is still developing in children. Understanding the relationship between medulloblastoma and the immune system is critical to develop effective immunologic-based treatment strategies for these patients. This review focuses on current knowledge of tumor immunology and the factors that contribute to the lack of immune system recognition of these tumors. The specificity of tumor antigens present in medulloblastoma is also discussed along with a summary of early clinical immunotherapy results.

A novel composition for in vitro and in vivo regeneration of skin and connective tissues

The particular combination of polydeoxyribonucleotides, l-carnitine, calcium ions, proteolytic enzyme and other ingredients acts in a synergetic way in the regeneration of skin and connective tissues. This new formulation of active principles was tested in vitro as a cell and tissue culture medium and in vivo for various preparations in support of tissue regeneration. In vitro, the new blend allowed the maintenance of skin biopsies for more than 1 year in eutrophic conditions. Immunocytochemical analyses of fibroblasts isolated from these biopsies confirmed a significant increase of the epidermal and connective wound-healing markers such as collagen type I, collagen type IV, cytokeratin 1 (CK1), CK5, CK10 and CK14 versus controls. To examine the effects of the new compound in vivo, we studied impaired wound healing in genetically diabetic db/db mice. At day 18, diabetic mice treated with the new composition showed 100% closure of wounds and faster healing than mice treated with the other solutions. This complex of vital continuity factors or life-keeping factors could be used as a tissue-preserving solution or a cosmetic/drug/medical device to accelerate wound healing in the treatment of patients with deficient wound repair to promote the regeneration of cutaneous and connective tissues (injuries-wound, dermatitis) and prevent the recurrent relapses.

Molecular alterations in glioblastoma: potential targets for immunotherapy

Glioblastoma is the most common and deadly brain tumor, possibly arising from genetic and epigenetic alterations in normal astroglial cells. Multiple cytogenetic, chromosomal, and genetic alterations have been identified in glioblastoma, with distinct expression of antigens (Ags) and biomarkers that may alter therapeutic potential of this aggressive cancer. Current therapy consists of surgical resection, followed by radiation therapy and chemotherapy. In spite of these treatments, the prognosis for glioblastoma patients is poor. Although recent studies have focused on the development of novel immunotherapeutics against glioblastoma, little is known about glioblastoma-specific immune responses. A better understanding of the molecular interactions among glioblastoma tumors, host immune cells, and the tumor microenvironment may give rise to novel integrated approaches for the simultaneous control of tumor escape pathways and the activation of antitumor immune responses. This review provides a detailed overview concerning genetic alterations in glioblastoma, their effects on Ag and biomarker expression, and the future design of chemoimmunotherapeutics against glioblastoma.

mRNA levels of enzymes and receptors implicated in arachidonic acid metabolism in gliomas

BACKGROUND

Gliomas are tumors of the central nervous system derived from glial cells. They show cellular heterogeneity and lack specific diagnostic markers. Although a possible role for the eicosanoid cascade has been suggested in glioma tumorigenesis, the relationship between enzymes and receptors implicated in arachidonic acid metabolism, with histological tumor type has not yet been determined.

DESIGN AND METHODS

Quantitative real-time reverse transcription-polymerase chain reaction was performed to measure and compare transcript levels of enzymes and receptors implicated in both lipoxygenase and cyclooxygenase pathways between oligodendrogliomas, astrocytomas, glioblastomas and mixed oligoastrocytomas.

RESULTS

Arachidonic acid metabolism-related enzymes and receptor transcripts (i) were underexpressed in classical oligodendrogliomas compared to astrocytomas and/or glioblastomas, (ii) differed between astrocytomas and glioblastomas and (iii) had an intermediate expression in mixed oligoastrocytomas.

CONCLUSIONS

mRNA levels of enzymes and receptors implicated both in lipoxygenase and cyclooxygenase pathways differed significantly in gliomas according to the histological type.

Enhanced expression of the high affinity glutamate transporter GLT-1 in C6 glioma cells delays tumour progression in rat

High grade gliomas are known to release excitotoxic concentrations of glutamate, a process thought to contribute to their malignant phenotype through enhanced autocrine stimulation of their proliferation and destruction of the surrounding nervous tissue. A model of C6 glioma cells in which expression of the high affinity glutamate transporter GLT-1 can be manipulated both in vivo and in vitro was used in order to investigate the consequences of increasing glutamate clearance on tumour progression. These cells were grafted in the striatum of Wistar rats and doxycycline was administered after validation of tumour development by magnetic resonance imaging. Both GLT-1 expression examined by immunohistochemistry and glutamate transport activity measured on synaptosomes appeared robustly increased in samples from doxycycline-treated animals. Moreover, these rats showed extended survival times as compared to vehicle-treated animals, an effect that was consistent with volumetric data revealing delayed tumour growth. As constitutive deficiency in glutamate clearance at the vicinity of brain tumours is well established, these data illustrate the potential benefit that could be obtained by enhancing glutamate transport by glioma cells in order to reduce their invasive behaviour.

A safety and efficacy study of local delivery of interleukin-12 transgene by PPC polymer in a model of experimental glioma

Interleukin-12 (IL-12) triggers an antitumoral immune response and an antiangiogenic effect against cancer. In this study, we tested a novel polymeric vehicle for IL-12 gene therapy along with adjuvant local biodegradable carmustine (BCNU) chemotherapy for the treatment of malignant glioma. Highly concentrated DNA/PPC (polyethylenimine covalently modified with methoxypolyethyleneglycol and cholesterol) complexes were used to deliver a murine plasmid encoding IL-12 (pmIL-12). For toxicity assessment, mice received intracranial injections with different volumes of pmIL-12/PPC. For efficacy, mice with intracranial GL261 glioma were treated with local delivery of pmIL-12/PPC and/or BCNU-containing polymers. Intracranial injections of 5-10 microl of pmIL-12/PPC were well tolerated and led to IL-12 expression in the brains of treated animals. Treatment with pmIL-12/PPC led to a significant increase in survival compared with untreated mice (median survival 57 days; 25% long-term survival >95 vs. 45 days for control; P<0.05). Treatment with BCNU led to a significant increase in survival compared with untreated mice, with 75% of treated mice having a long-term survival >95 days, (P<0.05). Most importantly, the combination of BCNU and pmIL-12/PPC led to a survival of 100% of the mice for 95 days after treatment (P<0.0001). This novel strategy is safe and effective for the treatment of malignant glioma. The synergy resultant from the combination of locally administered pmIL-12/PPC and BCNU suggests a role for this approach in the treatment of malignant brain tumors.

Targeting epidermal growth factor receptor variant III: a novel strategy for the therapy of malignant glioma

Immunotherapy represents an exciting approach for the treatment of glioblastoma multiforme. The success of this approach depends on the identification of tumor-specific antigens that can then be exploited to target the tumor. One such antigen, the epidermal growth factor receptor variant III (EGFRvIII) is found in up to 50% of malignant gliomas. This molecule is an interesting vaccine candidate since its expression is tumor specific. Recent preclinical, as well as clinical, studies of EGFRvIII-based vaccines suggest a promising role for immunotherapy of malignant gliomas. This review focuses on vaccines that target EGFRvIII. We review preclinical and clinical data and emphasize the immunological mechanisms involved in its therapeutic effect.

Induction of prostaglandin E2 synthesis and microsomal prostaglandin E synthase–1 expression in murine microglia by glioma-derived soluble factors

Object

Microglia are one of the members of monocyte/macrophage lineage in the central nervous system (CNS) and exist as ramified microglia in a normal resting state, but they are activated by various stimuli, such as tumors. Activated microglia induce immune responses in the CNS, but the precise functions of microglia in glioma microenvironments are not clear. It has been reported that glioma cells produce prostaglandin (PG)E2, which promotes the growth of tumor cells and possesses immunosuppressive activity. The authors previously reported that PGE2 production by peritoneal macrophages was enhanced by glioma-derived soluble factors, which induce an immunosuppressive state. In this study, they investigated PGE2 production by microglia treated with glioma cells and assessed the role of microglia in glioma microenvironments in the mouse.

Methods

Microglia and peritoneal macrophages were cultured in vitro with or without lipopolysaccharide, and tumor necrosis factor (TNF) and PGE2 in the culture supernatant were measured using L929 bioassay and enzyme immunoassay. The expression of mRNA was measured using reverse transcriptase polymerase chain reaction, and the protein expression was assayed with Western blotting. In some experiments glioma cells and conditioned glioma medium were added to the microglia cultures.

Results

Glioma cells studied in this report did not produce a significant amount of PGE2. However, the coculture of microglia with glioma cells or conditioned glioma medium led to the production of a large amount of PGE2. The enhancement of PGE2 production by microglia was more significant than that by peritoneal macrophages. The expression of cyclooxygenase (COX)–2 and particularly the expression of microsomal PGE synthase (mPGES)–1 (a terminal enzyme of the arachidonate cascade) in microglia were enhanced by conditioned glioma medium. The enhancement of mPGES-1 expression in microglia was more significant than that in peritoneal macrophages. The production of TNF was suppressed when culturing microglia with conditioned glioma medium, but this suppression was abrogated by the addition of a COX inhibitor (NS-398) and a PGE2 receptor (EP4) antagonist. Furthermore, TNF production was not suppressed in microglia from mPGES-1–deficient mice.

Conclusions

These results indicate that PGE2 production by microglia is enhanced by conditioned glioma medium, which induces an immunosuppressive state in the CNS. Therefore, the manipulation of microglia, from the standpoint of PGE2, provides investigators with an important strategy to induce an effective antiglioma immune response.

Dynamic cross-talk between tumor and immune cells in orchestrating the immunosuppressive network at the tumor microenvironment

Accumulating evidence indicates that a dynamic cross-talk between tumors and the immune system can regulate tumor growth and metastasis. Increased understanding of the biochemical nature of tumor antigens and the molecular mechanisms responsible for innate and adaptive immune cell activation has revolutionized the fields of tumor immunology and immunotherapy. Both the protective effects of the immune system against tumor cells (immunosurveillance) and the evasion of tumor cells from immune attack (tumor-immune escape) have led to the concept of cancer immunoediting, a proposal which infers that a bidirectional interaction between tumor and inflammatory/regulatory cells is ultimately responsible for orchestrating the immunosuppressive network at the tumor site. In this context, a major challenge is the potentiation or redirection of tumor antigen-specific immune responses. The success in reaching this goal is highly dependent on an improved understanding of the interactions and mechanisms operating during the different phases of the cancer immunoediting process. In this review, we discuss the multiple defense and counterattack strategies that tumors have devised in order to evade immune attack and to thwart the effectiveness of several immunotherapeutic approaches.