Malignant gliomas

Thioredoxin, Glutathione and Related Molecules in Tumors of the Nervous System

BACKGROUND

Central Nervous System (CNS) tumors have a poor survival prognosis due to their invasive and heterogeneous nature, in addition to the resistance to multiple treatments.

OBJECTIVE

In this paper, the main aspects of brain tumor biology and pathogenesis are reviewed both for primary tumors of the brain, (i.e., gliomas) and for metastasis from other malignant tumors, namely lung cancer, breast cancer and malignant melanoma which account for a high percentage of overall malignant brain tumors. We review the role of antioxidant systems, namely the thioredoxin and glutathione systems, in the genesis and/or progression of brain tumors.

METHODS

Although overexpression of Thioredoxin Reductase (TrxR) and Thioredoxin (Trx) is often linked to increased malignancy rate of brain tumors, and higher expression of Glutathione (GSH) and Glutathione S-Transferases (GST) are associated to resistance to therapy, several knowledge gaps still exist regarding for example, the role of Peroxiredoxins (Prx), and Glutaredoxins (Grx).

CONCLUSION

Due to their central role in redox homeostasis and ROS scavenging, redox systems are potential targets for new antitumorals and examples of innovative therapeutics aiming at improving success rates in brain tumor treatment are discussed.

U87MG glioma cells overexpressing IL-17 acclerate early-stage growth in vivo and cause a higher level of CD31 mRNA expression in tumor tissues

Immunological alterations have been reported to be involved in glioma, the most common malignant disease of the adult brain. Our recent study identified higher levels of IL-17 in glioma specimens. The present study investigated the role and possible mechanisms of IL-17 in glioma tumorigenesis. Human IL-17 cDNA was cloned and inserted into the eukaryotic pEGFP-N1 expression vector, which was used to transfect the glioma U87MG cell line, resulting in a high level of IL-17 expression in these cells. The cells were then transfected with IL-17 (pEGFP-N1-IL-17-U87MG) or mock (pEGFP-N1-U87MG) vector or left untransfected (U87MG) and subcutaneously inoculated into the right flank of nude mice. The results revealed that the pEGFP-N1-IL-17-U87MG cells grew more rapidly in the early stages (P<0.05, determined on day 32 post-inoculation compared with the other two groups). Quantitative (q)PCR detected higher mouse (m)CD31 mRNA levels in the IL-17-transfected group (P<0.01) compared with the mock-transfected and untransfected groups. IL-17 transfection altered the mRNA expression of a panel of molecules that are associated with immunity and inflammation in U87MG cells in vitro. An effect of the vector was identified, whereby the mock transfection strongly inhibited cell growth in vivo and dramatically altered the mRNA levels of multiple molecules in the cell culture in vitro compared with the untransfected cells. The present study confirmed that IL-17 overexpression may enhance glioma cell growth in vivo, which may be associated with accelerated angiogenesis. IL-17 overexpression may also alter the cellular mRNA expression of immune-related molecules.

Autotaxin and LPA receptors represent potential molecular targets for the radiosensitization of murine glioma through effects on tumor vasculature

Despite wide margins and high dose irradiation, unresectable malignant glioma (MG) is less responsive to radiation and is uniformly fatal. We previously found that cytosolic phospholipase A2 (cPLA₂) is a molecular target for radiosensitizing cancer through the vascular endothelium. Autotaxin (ATX) and lysophosphatidic acid (LPA) receptors are downstream from cPLA₂ and highly expressed in MG. Using the ATX and LPA receptor inhibitor, α-bromomethylene phosphonate LPA (BrP-LPA), we studied ATX and LPA receptors as potential molecular targets for the radiosensitization of tumor vasculature in MG. Treatment of Human Umbilical Endothelial cells (HUVEC) and mouse brain microvascular cells bEND.3 with 5 µmol/L BrP-LPA and 3 Gy irradiation showed decreased clonogenic survival, tubule formation, and migration. Exogenous addition of LPA showed radioprotection that was abrogated in the presence of BrP-LPA. In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells. Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation. However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect. Using heterotopic tumor models of GL-261, mice treated with BrP-LPA and irradiation showed a tumor growth delay of 6.8 days compared to mice treated with irradiation alone indicating that inhibition of ATX and LPA receptors may significantly improve malignant glioma response to radiation therapy. These findings identify ATX and LPA receptors as molecular targets for the development of radiosensitizers for MG.

Emerging strategies for EphA2 receptor targeting for cancer therapeutics

IMPORTANCE OF THE FIELD

High mortality rates with cancers warrant further development of earlier diagnostics and better treatment strategies. Membrane-bound erythropoietin-producing hepatocellular receptor tyrosine kinase class A2 (EphA2) is overexpressed in breast, prostate, urinary bladder, skin, lung, ovary and brain cancers.

AREAS COVERED IN THIS REVIEW

EphA2 overexpression in cancers, its signaling mechanisms and strategies to target its deregulation.

WHAT THE READER WILL GAIN

High EphA2 expression in cancer cells is correlated with a poor prognosis associated with recurrence due to enhanced metastasis. Interaction of the EphA2 receptor with its ligand (e.g., ephrinA1) triggers events that are deregulated and implicated in carcinogenesis. EphrinA1-independent oncogenic activity and ephrinA1-dependent tumor suppressor roles for EphA2 are described. Molecular interactions of EphA2 with signaling proteins are associated with the modulation of cytoskeleton dynamics, cell adhesion, proliferation, differentiation and metastasis. The deregulated signaling by EphA2 and its involvement in oncogenesis provide multiple avenues for the rational design of intervention approaches.

TAKE HOME MESSAGE

EphA2 has been tested as a drug target using multiple approaches such as agonist antibodies, RNA interference, immunotherapy, virus vector-mediated gene transfer, small-molecule inhibitors and nanoparticles. With over a decade of research, encouraging results with targeting of EphA2 expression in various pre-clinical cancer models necessitate further studies.

Use of dentritic cells pulsed with HLA-A2-restricted MAGE-A1 peptide to generate cytotoxic T lymphocytes against malignant glioma

This study developed a novel approach of targeting malignant glioma with pMAGE-A1(278-286)-specific cytotoxic T lymphocytes (CTLs) induced from the peripheral blood mononuclear cells of healthy donors by multiple stimulations with human leukocyte antigen (HLA)-A2-restricted pMAGE-A1(278-286) peptide-pulsed dentritic cells. Cytotoxic assays were performed by the colorimetric CytoTox 96 assay to analyze cytotoxic activity of the induced CTLs against various target cells. The induced CTLs showed approximately 45% specific lysis against T2pMAGE-A1(278-286) (pMAGE-A1(278-286) peptide pulsed T2 cells) and U251 (HLA-A2(+), MAGE-A1(+)) at an effector:target ratio of 40:1, and approximately 5% cytolysis against T2pHIV, A172 (HLA-A2(-), MAGE-A1(+)), K562 and T2 cells without being pulsed with peptide at any effector:target ratio. The specific killing activity of the induced CTLs against T2pMAGE-A1(278-286) and U251 was much more obvious than in any other control group (P<0.05). The cytotoxic activity against the T2pMAGE-A1(278-286) and U251 was significantly eliminated by anti-HLA class I mAb W6/32. These results suggest that pMAGE-A1(278-286) epitope may serve as a surrogate tumor antigen target of specific immunotherapy for treating HLA-A2 patients with malignant glioma.

Vaccine therapy with dendritic cells transfected with Il13ra2 mRNA for glioma in mice

OBJECT

The Il13ra2 gene is often overexpressed in brain tumors, making Il13ra2 one of the vaccine targets for immunotherapy of glioma. In this study, using a mouse glioma model, the authors tested the hypothesis that vaccination using dendritic cells transfected with Il13ra2 mRNA induces strong immunological antitumor effects.

METHODS

A plasmid was constructed for transduction of the mRNAs transcribed in vitro into dendritic cells. This was done to transport the intracellular protein efficiently into major histocompatibility complex class II compartments by adding a late endosomal/lysosomal sorting signal to the Il13ra2 gene. The dendritic cells transfected with this Il13ra2 mRNA were injected intraperitoneally into the mouse glioma model at 3 and 10 days after tumor cell implantation. The antitumor effects were estimated based on the survival rate, results of histological analysis, and immunohistochemical findings for immune cells.

RESULTS

The group treated by vaccination therapy with dendritic cells transfected with Il13ra2 mRNA survived significantly longer than did the control groups. Immunohistochemical analysis revealed that greater numbers of T lymphocytes containing CD4+ and CD8+ T cells were found in the group vaccinated with dendritic cells transfected with Il13ra2 mRNA.

CONCLUSIONS

These results demonstrate the therapeutic potential of vaccination with dendritic cells transfected with Il13ra2 mRNA for the treatment of malignant glioma.

Molecularly targeted therapies for malignant glioma: rationale for combinatorial strategies

Median survival of patients with malignant glioma (MG) from time of diagnosis is approximately 1 year, despite surgery, irradiation and conventional chemotherapy. Improving patient outcome relies on our ability to develop more effective therapies that are directed against the unique molecular aberrations within a patient's tumor. Such molecularly targeted therapies may provide novel treatments that are more effective than conventional chemotherapeutics. Recently developed therapeutic strategies have focused on targeting several core glioma signaling pathways, including pathways mediated by growth-factors, PI3K/Akt/PTEN/mTOR, Ras/Raf/MEK/MAPK and other vital pathways. However, given the molecular diversity, heterogeneity and diverging and converging signaling pathways associated with MG, it is unlikely that any single agent will have efficacy in more than a subset of tumors. Overcoming these therapeutic barriers will require multiple agents that can simultaneously inhibit these processes, providing a rationale for combination therapies. This review summarizes the currently implemented single-agent and combination molecularly targeted therapies for MG.

cDNA clone, prokaryotic expression and purification of human interleukin-13 receptor [alpha]2 chain

Despite advances in surgical technology and radiation therapy, the prognosis in the patients with malignant glioma remains poor. Recent studies show that interleukin-13 receptor [alpha]2 chain (IL-13Ra2), a brain tumor-associated receptor for IL-13, may play a role in immunotherapy for glioblastoma. We thus amplified human IL-13Ra2 gene from the human glioblastoma cell line using RT-PCR and cloned the target gene into the pET-28a, a prokaryotic expressing plasmid. After transformation, the recombinant plasmid expressed a soluble protein induced by IPTG. The purified recombinant protein was shown to be a single band on the SDS-PAGE with a predicated molecular weight of human IL-13Ra2 gene, suggesting that the recombinant protein of human IL-13Ra2 was successfully expressed. Recombinant IL-13Ra2 protein can be used as an anti-tumor vaccine, which may provide a promising new strategy for the treatment of brain malignant gliomas.

Immunotherapeutic approaches for glioma

The development of effective immunotherapy strategies for glioma requires adequate understanding of the unique immunological microenvironment in the central nervous system (CNS) and CNS tumors. Although the CNS is often considered to be an immunologically privileged site and poses unique challenges for the delivery of effector cells and molecules, recent advances in technology and discoveries in CNS immunology suggest novel mechanisms that may significantly improve the efficacy of immunotherapy against gliomas. In this review, we first summarize recent advances in the CNS and CNS tumor immunology. We address factors that may promote immune escape of gliomas. We also review advances in passive and active immunotherapy strategies for glioma, with an emphasis on lessons learned from recent early-phase clinical trials. We also discuss novel immunotherapy strategies that have been recently tested in non-CNS tumors and show great potential for application to gliomas. Finally, we discuss how each of these promising strategies can be combined to achieve clinical benefit for patients with gliomas.

Induction of protective and therapeutic antitumor immunity by a DNA vaccine with a glioma antigen, SOX6

We previously reported identifying SOX6 as a glioma antigen by serological screening using a testis cDNA library. Its preferential expression and frequent IgG responses in glioma patients indicate that SOX6 may be a useful target for immunotherapy. To examine whether cytotoxic T-lymphocyte (CTL) responses specific for SOX6 to destroy glioma can be generated in vivo, we treated glioma-bearing mice by vaccination with a plasmid DNA encoding murine full-length SOX6 protein. Following SOX6-DNA vaccination, CTLs specific for SOX6-expressing glioma cells were induced, while normal autologous-cells that had restrictedly expressed SOX6 during embryogenesis were not destroyed. Furthermore, DNA vaccination with SOX6 exerted protective and therapeutic antitumor responses in the glioma-bearing mice. This antitumor activity was abrogated by the depletion of CD4 positive T cells and/or CD8 positive T cells. These results suggest that the SOX6 protein has multiple CTL and helper epitopes to induce antitumor activity and the effectiveness of SOX6-DNA vaccine for the prevention and treatment of glioma.

Inhibition of STAT3 promotes the efficacy of adoptive transfer therapy using type-1 CTLs by modulation of the immunological microenvironment in a murine intracranial glioma

A variety of cancers, including malignant gliomas, show aberrant activation of STAT3, which plays a pivotal role in negative regulation of antitumor immunity. We hypothesized that inhibition of STAT3 signals would improve the efficacy of T cell adoptive transfer therapy by reversal of STAT3-induced immunosuppression in a murine GL261 intracranial glioma model. In vitro treatment of GL261 cells with JSI-124, a STAT3 inhibitor, reversed highly phosphorylated status of STAT3. Systemic i.p. administration of JSI-124 in glioma-bearing immunocompetent mice, but not athymic mice, resulted in prolonged survival, suggesting a role of adaptive immunity in the antitumor effect. Furthermore, JSI-124 promoted maturation of tumor-infiltrating CD11c(+) dendritic cells and activation of tumor-conditioned cytotoxic T cells, enhanced dendritic cells and GL261 production of CXCL-10, a critical chemokine for attraction of Tc1 cells. When i.p. JSI-124 administration was combined with i.v. transfer of Pmel-I mouse-derived type-1 CTLs (Tc1), glioma-bearing mice exhibited prolonged survival compared with i.p. JSI-124 or i.v. Tc1 therapy alone. Flow cytometric analyses of brain infiltrating lymphocytes revealed that JSI-124-treatment enhanced the tumor-homing of i.v. transferred Tc1 cells in a CXCL-10-dependent fashion. Systemic JSI-124 administration also up-regulated serum IL-15 levels, and promoted the persistence of transferred Tc1 in the host. These data suggest that systemic inhibition of STAT3 signaling can reverse the suppressive immunological environment of intracranial tumor bearing mice both systemically and locally, thereby promoting the efficacy of adoptive transfer therapy with Tc1.

Autologous glioma cell vaccine admixed with interleukin-4 gene transfected fibroblasts in the treatment of patients with malignant gliomas

Background

The prognosis for malignant gliomas remains dismal. We addressed the safety, feasibility and preliminary clinical activity of the vaccinations using autologous glioma cells and interleukin (IL)-4 gene transfected fibroblasts.

Methods

In University of Pittsburgh Cancer Institute (UPCI) protocol 95-033, adult participants with recurrent glioblastoma multiforme (GBM) or anaplastic astrocytoma (AA) received gross total resection (GTR) of the recurrent tumors, followed by two vaccinations with autologous fibroblasts retrovirally transfected with TFG-IL4-Neo-TK vector admixed with irradiated autologous glioma cells. In UPCI 99-111, adult participants with newly diagnosed GBM or AA, following GTR and radiation therapy, received two intradermal vaccinations with the TFG-IL4-Neo-TK-transfected fibroblasts admixed with type-1 dendritic cells (DC) loaded with autologous tumor lysate. The participants were evaluated for occurrence of adverse events, immune response, and clinical response by radiological imaging.

Results and Discussion

In UPCI 95-033, only 2 of 6 participants received the vaccinations. Four other participants were withdrawn from the trial because of tumor progression prior to production of the cellular vaccine. However, both participants who received two vaccinations demonstrated encouraging immunological and clinical responses. Biopsies from the local vaccine sites from one participant displayed IL-4 dose-dependent infiltration of CD4⁺ as well as CD8⁺ T cells. Interferon (IFN)-γ Enzyme-Linked Immuno-SPOT (ELISPOT) assay in another human leukocyte antigen (HLA)-A2⁺ participant demonstrated systemic T-cell responses against an HLA-A2-restricted glioma-associated antigen (GAA) epitope EphA2_883–891. Moreover, both participants demonstrated clinical and radiological improvement with no evidence of allergic encephalitis, although both participants eventually succumbed with the tumor recurrence. In 99-111, 5 of 6 enrolled participants received scheduled vaccinations with no incidence of major adverse events. Monocyte-derived DCs produced high levels of IL-12 p70. Treatment was well tolerated; however, we were unable to observe detectable IFN-γ post-vaccine responses or prolonged progression-free survival in these participants.

Conclusion

Feasibility challenges inherent in the generation of a patient-specific gene transfection-based vaccine strongly suggests the need for more practical formulations that would allow for the timely administration of vaccines. Nevertheless, successful generation of type-1 DCs and preliminary safety in the current study provide a strong rationale for further efforts to develop novel glioma vaccines.

HLA Tetramer Based Artificial Antigen-Presenting Cells Efficiently Stimulate CTLs Specific for Malignant Glioma

PURPOSE

The interleukin-13 receptor alpha 2 (IL-13R alpha 2) is a glioma-restricted cell-surface epitope not otherwise detected within the central nervous system. Here, we report a novel approach for targeting malignant glioma with IL-13R alpha 2-specific CTLs.

EXPERIMENTAL DESIGN

Artificial antigen-presenting cells (aAPC) were made by coating human leukocyte antigen (HLA)-A2/pIL-13R alpha 2(345-354) tetrameric complexes, anti-CD28 antibody, and CD83 molecules to cell-sized latex beads, and used to stimulate IL-13R alpha 2-specific CTLs from the peripheral blood mononuclear cells of HLA-A2+ healthy donors. After multiple stimulations, the induced CTLs were analyzed for tetramer staining, IFN-gamma production, and CTL reactivity.

RESULTS

Tetramer staining assay showed that the induced CTLs specifically bound HLA-A2/pIL-13R alpha 2(345-354) tetramers. The CTLs specifically produced IFN-gamma in response to the HLA-A2/pIL-13R alpha 2(345-354)-aAPCs and exhibited specific lysis against T2 cells pulsed with the peptide pIL-13R alpha 2(345-354) and HLA-A2+ glioma cells expressing IL-13R alpha 2(345-354), whereas HLA-A2(-) glioma cell lines that express IL-13R alpha 2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-HLA class I monoclonal antibody.

CONCLUSION

The induced CTLs specific for IL-13R alpha 2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2+ patients with malignant glioma.

Induction of cytotoxic T-lymphocytes specific for malignant glioma by HLA dimer-based artificial antigen-presenting cells

AIM

The aim of this study was to investigate the novel approach for targeting malignant glioma.

METHODS

Interleukin-13 receptor alpha2 (IL-13Ralpha2)-specific cytotoxic T-cells (CTLs) were induced from the peripheral blood lymphocytes (PBLs) of human leukocyte antigen (HLA)-A2 positive healthy donors by multiple stimulations with artificial antigen-presenting cells (aAPCs) made by coating HLA-A2-Ig/pIL-13Ralpha2(345-354) dimeric complexes, anti-CD28 antibody, and CD83 molecules to cell-sized latex beads.

RESULTS

The induced CTLs exhibited a specific lysis against T2 cells pulsed with the peptide pIL-13Ralpha2(345-354) and HLA-A2(+) glioma cells expressing IL-13Ralpha2(345-354), while HLA-A2(-) glioma cell lines that express IL-13Ralpha2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by the anti-HLA class I monoclonal antibody.

CONCLUSIONS

The induced CTLs specific for the IL-13Ralpha2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2(+) patients with malignant glioma.

Generation of allo-restricted cytotoxic T lymphocytes against malignant glioma by artificial antigen-presenting cells

The interleukin (IL) 13 receptor alpha2 (IL-13Ralpha2) is a glioma-restricted cell-surface epitope not otherwise detected within the central nervous system. This study reported a novel approach for targeting malignant glioma with IL-13Ralpha2-specific allo-restricted cytotoxic T cells (CTLs) induced from the peripheral blood lymphocytes (PBLs) of HLA-A2-negative healthy donors by multiple stimulations with artificial antigen-presenting cells (aAPCs) made by coating HLA-A2/pIL-13Ralpha2(345-354) tetrameric complexes, anti-CD28 antibody and CD83 molecules to cell-sized latex beads. The induced allo-restricted CTLs exhibited specific lysis against T2 cells pulsed with the peptide pIL-13Ralpha2(345-354) and HLA-A2+ glioma cells expressing IL-13Ralpha2(345-354), while HLA-A2- glioma cell lines that express IL-13Ralpha2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-HLA class I monoclonal antibody. These results suggested the induced allo-restricted CTLs specific for IL-13Ralpha2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2+ patients with malignant glioma.

New chemotherapy options for the treatment of malignant gliomas

This review focuses on the recent advances in chemotherapy of malignant gliomas, with special emphasis on the most common primary brain tumor in adults, glioblastoma. The demonstration of the superiority of concomitant and adjuvant temozolomide with standard radiotherapy over radiotherapy alone in patients with newly diagnosed glioblastomas by means of phase III international trial has been the major advance in the care of these patients so far. Moreover, patients whose tumors display the hypermethylation of the promoter of the gene for the repairing enzyme O-methylguanine-DMA methyltransferase are most likely to benefit from the combination regimen. The advantage of a postsurgical local administration of carmustine by slow-release polymers ('gliadel wafers') is more modest, and the efficacy and safety of a sequence of carmustine wafers followed by temozolomide combined with radiotherapy remain to be defined. Different DNA repair modulation strategies are being investigated to further improve the results: dose-dense regimens of temozolomide, combination of temozolomide with specific inhibitors of O-methylguanine-DMA methyltransferase and combination of temozolomide with specific inhibitors of base excision repair [poly(ADP-ribose) polymerase inhibitors]. Other developments include the combination of cytotoxic, cytostatic and targeted therapies. Multitargeted compounds that simultaneously affect multiple signaling pathways, such as those involving epidermal growth factor receptor, platelet-derived growth factor receptor and vascular endothelial growth factor receptor, are increasingly employed. In the future, innovative trial designs (factorial and adaptative designs), pretreatment molecular profiling of individual tumors and the adoption of biological end-points (changes in serum tumor markers, measures of target inhibition), in addition to the traditional clinical and radiographic end-points, will be needed to achieve further advances.

On the potential of thioredoxin reductase inhibitors for cancer therapy

Thioredoxin reductase (TrxR)-as part of a major thiol regulating system-allows redox metabolism to adjust to cellular requirements. Therefore, changes at the redox level reflect as a pars pro toto changes concerning the entire cell. Three different TrxR isoenzymes, TrxR1 as cytosolic, TrxR2 as mitochondrial, and TrxR3 as testis-specific thiol regulator are known. All three enzymes contain a reactive and solvent accessible selenocysteine residue which is located on a flexible C-terminal arm of the protein. This selenocysteine is essentially involved in the catalytic cycle of TrxR and thus represents an attractive binding site for inhibitors. Many tumor cells have elevated TrxR levels and TrxR has been shown to play a major role in drug resistance. Inhibition of TrxR and its related redox reactions may thus contribute to a successful single, combinatory or adjuvant cancer therapy. A great number of effective natural and synthetic TrxR inhibitors are now available possessing antitumor potential ranging from induction of oxidative stress to cell cycle arrest and apoptosis. This article summarizes the present knowledge on the potential of TrxR inhibitors and TrxR as anticancer drug target.

Identification of interleukin-13 receptor alpha2 peptide analogues capable of inducing improved antiglioma CTL responses

Restricted and high-level expression of interleukin-13 receptor alpha2 (IL-13Ralpha2) in a majority of human malignant gliomas makes this protein an attractive vaccine target. We have previously described the identification of the IL-13Ralpha2(345-353) peptide as a human leukocyte antigen-A2 (HLA-A2)-restricted CTL epitope. However, as it remains unclear how efficiently peptide-based vaccines can induce specific CTLs in patients with malignant gliomas, we have examined whether analogue epitopes could elicit heteroclitic antitumor T-cell responses versus wild-type peptides. We have created three IL-13Ralpha2 analogue peptides by substitutions of the COOH-terminal isoleucine (I) for valine (V) and the NH(2)-terminal tryptophan (W) for either alanine (A), glutamic acid (E), or nonsubstituted (W; designated as 1A9V, 1E9V, and 9V, respectively). In comparison with the native IL-13Ralpha2 epitope, the analogue peptides 9V and 1A9V displayed higher levels of binding affinity and stability in HLA-A2 complexes and yielded an improved stimulatory index for patient-derived, specific CTLs against the native epitope expressed by HLA-A2(+) glioma cells. In HLA-A2-transgenic HHD mice, immunization with the peptides 9V and 1A9V induced enhanced levels of CTL reactivity and protective immunity against an intracranial challenge with IL13Ralpha2-expressing syngeneic tumors when compared with vaccines containing the native IL-13Ralpha2 epitope. These findings indicate highly immunogenic IL-13Ralpha2 peptide analogues may be useful for the development of vaccines capable of effectively expanding IL-13Ralpha2-specific, tumor-reactive CTLs in glioma patients.

Targeted molecular therapy of malignant gliomas

Malignant gliomas are the most common form of primary brain tumors in adults. Despite advances in diagnosis and standard therapies such as surgery, radiation, and chemotherapy, the prognosis remains poor. Recent scientific advances have enhanced our understanding of the biology of gliomas and the role of tyrosine kinase receptors and signal transduction pathways in tumor initiation and maintenance, such as the epidermal growth factor receptors, platelet-derived growth factor receptors, vascular endothelial growth factor receptors, and the Ras/Raf/mitogen-activated protein (MAP)-kinase and phosphatidylinositol-3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathways. Novel targeted drugs such as small molecular inhibitors of these receptors and signaling pathways are showing some activity in initial studies. As we learn more about these drugs and how to optimize their use as single agents and in combination with radiation, chemotherapy, and other targeted molecular agents, they will likely play an increasing role in the management of this devastating disease. This review summarizes the current results with targeted molecular agents in malignant gliomas and strategies under evaluation to increase their effectiveness.

EphA2 as a glioma-associated antigen: a novel target for glioma vaccines

EphA2 is a receptor tyrosine kinase and is frequently overexpressed in a wide array of advanced cancers. We demonstrate in the current study that the EphA2 protein is restrictedly expressed in primary glioblastoma multiforme and anaplastic astrocytoma tissues in comparison to normal brain tissues. To evaluate the possibility of targeting EphA2 in glioma vaccine strategies, we stimulated human leukocyte antigen (HLA) A2+ peripheral blood mononuclear cells (PBMCs) obtained from healthy donors and glioma patients with autologous dendritic cells (DCs) loaded with synthetic EphA2883-891 peptide (TLADFDPRV), which has previously been reported to induce interferon-gamma in HLA-A2+ PBMCs. Stimulated PBMCs demonstrated antigen-specific cytotoxic T lymphocyte (CTL) responses as detected by specific lysis of T2 cells loaded with the EphA2883 peptide as well as HLA-A2+ glioma cells, SNB19 and U251, that express EphA2. Furthermore, in vivo immunization of HLA-A2 transgenic HHD mice with the EphA2883-891 peptide resulted in the development of an epitope-specific CTL response in splenocytes, despite the fact that EphA2883-891 is an autoantigen in these mice. Taken together, these data suggest that EphA2883-891 may be an attractive antigen epitope for molecularly targeted glioma vaccines.

Signal transduction mechanisms involved in the proliferation of C6 glioma cells induced by lysophosphatidic acid

We studied pathways involved in the proliferation of rat C6 glioma cells induced by lysophosphatidic acid (LPA), a phospholipid with diverse biological functions. LPA induced a dose-responsive proliferation of C6 cells after 48 h. Proliferation was blocked by inhibitors of the sodium/proton exchanger type 1 (NHE1), Rho-associated kinase, the phosphatidylinositol 3-kinase/Akt pathway (PI3K/Akt), protein kinase C (PKC) and extracellular signal regulated kinase kinase (MEK). Phospho-specific antibodies were used to investigate the pathways involved. LPA induced transient (10 min) phosphorylations of ERK 1/2, Akt and the transcription factor CREB. The LPA-induced phosphorylation of ERK 1/2 and CREB was blocked by inhibition of PI3K, PKC and MEK, but that of Akt was only inhibited by wortmannin, the PI3K inhibitor. Inhibition of Rho kinase or NHE1 did not reduce the LPA-induced phosphorylation of ERK, Akt or CREB. The results were compared with the effects of LPA on transduction pathways in other cell types.

Targeted molecular therapy of malignant gliomas

Malignant gliomas are the most common form of primary brain tumors in adults. Despite advances in diagnosis and standard therapies such as surgery, radiation, and chemotherapy, the prognosis remains poor. Recent scientific advances have enhanced our understanding of the biology of gliomas and the role of tyrosine kinase receptors and signal transduction pathways in tumor initiation and maintenance, such as the epidermal growth factor receptors, platelet-derived growth factor receptors, vascular endothelial growth factor receptors, and the Ras/Raf/mitogen-activated protein (MAP)-kinase and phosphatidylinositol-3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathways. Novel targeted drugs such as small molecular inhibitors of these receptors and signaling pathways are showing some activity in initial studies. As we learn more about these drugs and how to optimize their use as single agents and in combination with radiation, chemotherapy, and other targeted molecular agents, they will likely play an increasing role in the management of this devastating disease. This review summarizes the current results with targeted molecular agents in malignant gliomas and strategies under evaluation to increase their effectiveness.

Cytokine gene therapy for malignant glioma

Despite advances in surgical and adjuvant therapy, the prognosis for malignant gliomas remains dismal. Malignant gliomas, like other malignancies, are able to overcome host immune defences through a variety of mechanisms that have become increasingly well-characterised over the past decade. However, this 'immunologically privileged' status of the brain is not absolute. Systemic immunisation with brain-specific antigens can induce immune responses that are manifested in the CNS, such as experimental allergic encephalomyelitis. The efficacy of peripheral immunisation against brain tumours has also been demonstrated in preclinical models. Based on these observations, clinical trials of peripheral immunisations with brain tumour-derived antigens have been initiated. A limitation of this approach is that the immunological environment within brain tumours is suboptimal for functions of antitumour immune effector cells. As a means to overcome this issue, delivery of cytokine genes to the tumour site may reverse the inhibitory immunological environment of the brain tumours and enhance the efficacy of peripheral vaccine-induced immune effector cells. The brain tumour environment may also be rendered more immunologically favourable by the delivery of additional antigen-presenting cells that can provide infiltrating effector cells with secondary activation signals. Indeed, the authors' recent data indicate that the injection of intracranial tumours with dendritic cells secreting interferon-alpha enhances the efficacy of peripheral vaccinations with tumour-specific antigens by cross-priming tumour antigen-specific T cells in the cervical lymph nodes. This review highlights the recent literature on cytokine gene therapy for brain tumours, and proposes the effective use of cytokine gene delivery both at the site of vaccines (i.e., the site of antigen presentation) and within the target brain tumours (i.e., the site where the effector cells exert their antitumour immunity). Successful immunogene therapy for brain tumours requires detailed understanding of cytokine functions and the use of them at the appropriate stages/sites of the immunological milieu.

Non-cytotoxic drugs as potential treatments for gliomas

PURPOSE OF REVIEW

Despite advances in surgery, radiation therapy, and chemotherapy, malignant gliomas continue to be associated with a poor prognosis. Even the most intensive combinations of radiotherapy and chemotherapy are not curative. In recent years our understanding of how tumor cells overcome cell cycle control, evade programmed cell death, induce blood vessel formation, and escape immune regulation has increased substantially. Significant efforts are directed towards the development of novel experimental therapies to target these molecular and biological mechanisms that lead to the development and growth of brain tumors. This review summarizes the most recent developments in non-cytotoxic therapy for malignant gliomas, such as targeted molecular drugs, inhibitors of angiogenesis and intratumoral therapy.

RECENT FINDINGS

The first generation of studies using these novel therapies is nearing completion. In general, most of these treatments are well tolerated, but single-agent activity is modest. There is significant interest in combining these therapies with each other and with conventional cytotoxic therapies such as radiation therapy and chemotherapy.

SUMMARY

These new therapeutic approaches for malignant gliomas are showing modest activity. As we learn to use these agents more effectively, and as an increasing number of new and potentially promising agents are developed, it is likely that therapies for malignant gliomas will improve over the next few years.