Analysis of FasL and TRAIL induced apoptosis pathways in glioma cells

Interrelation between Programmed Cell Death and Immunogenic Cell Death: Take Antitumor Nanodrug as an Example

Programmed cell death (PCD, mainly including apoptosis, necrosis, ferroptosis, pyroptosis, and autophagy) and immunogenic cell death (ICD), as important cell death mechanisms, are widely reported in cancer therapy, and understanding the relationship between the two is significant for clinical tumor treatments. Considering that vast nanodrugs are developed to induce tumor PCD and ICD simultaneously, in this review, the interrelationship between PCD and ICD is described using nanomedicines as examples. First, an overview of PCD patterns and focus on the morphological differences and interconnections among them are provided. Then the interrelationship between apoptosis and ICD in terms of endoplasmic reticulum stress is described by introducing various cancer treatments and the recent developments of nanomedicines with inducible immunogenicity. Next, the crosstalk between non-apoptotic (including necrosis, ferroptosis, pyroptosis, and autophagy) signaling pathways and ICD is introduced and their relationship through various nanomedicines as examples is further illustrated. Finally, the relationship between PCD and ICD and its application prospects in the development of new ICD nanomaterials are summarized. This review is believed to deepen the understanding of the relationship between PCD and ICD, extend the biomedical applications of various nanodrugs, and promote the progress of clinical tumor therapy.

Critical View of Novel Treatment Strategies for Glioblastoma: Failure and Success of Resistance Mechanisms by Glioblastoma Cells

According to the invasive nature of glioblastoma, which is the most common form of malignant brain tumor, the standard care by surgery, chemo- and radiotherapy is particularly challenging. The presence of glioblastoma stem cells (GSCs) and the surrounding tumor microenvironment protects glioblastoma from recognition by the immune system. Conventional therapy concepts have failed to completely remove glioblastoma cells, which is one major drawback in clinical management of the disease. The use of small molecule inhibitors, immunomodulators, immunotherapy, including peptide and mRNA vaccines, and virotherapy came into focus for the treatment of glioblastoma. Although novel strategies underline the benefit for anti-tumor effectiveness, serious challenges need to be overcome to successfully manage tumorigenesis, indicating the significance of developing new strategies. Therefore, we provide insights into the application of different medications in combination to boost the host immune system to interfere with immune evasion of glioblastoma cells which are promising prerequisites for therapeutic approaches to treat glioblastoma patients.

Overcoming TRAIL Resistance for Glioblastoma Treatment

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) shows a promising therapeutic potential in cancer treatment as it exclusively causes apoptosis in a broad spectrum of cancer cells through triggering the extrinsic apoptosis pathway via binding to cognate death receptors, with negligible toxicity in normal cells. However, most cancers, including glioblastoma multiforme (GBM), display TRAIL resistance, hindering its application in clinical practice. Recent studies have unraveled novel mechanisms in regulating TRAIL-induced apoptosis in GBM and sought effective combinatorial modalities to sensitize GBM to TRAIL treatment, establishing pre-clinical foundations and the reasonable expectation that the TRAIL/TRAIL death receptor axis could be harnessed to treat GBM. In this review, we will revisit the status quo of the mechanisms of TRAIL resistance and emerging strategies for sensitizing GBM to TRAIL-induced apoptosis and also discuss opportunities of TRAIL-based combinatorial therapies in future clinical use for GBM treatment.

Apoptotic mechanisms of gastric cancer cells induced by isolated erinacine S through epigenetic histone H3 methylation of FasL and TRAIL

Erinacine S, the new bioactive diterpenoid compound isolated from the ethanol extract of the mycelia of Hericium erinaceus, displays great health-promoting properties. However, the effects of erinacine S on inductive apoptosis in cancer cells such as gastric cancer and its molecular mechanisms remain unclear. Our results demonstrated that erinacine S treatment significantly induces cell apoptosis with increased ROS production in gastric cancer cells, but not in normal cells. Significantly, erinacine S also showed its inhibitory effects on tumor growth in an in vivo xenograft mouse model. Furthermore, immunohistochemical analyses revealed that erinacine S treatment significantly increases the FasL and TRAIL protein, whereas it decreases the levels of PCNA and cyclin D1 in the gastric cancer xenograft mice. Consistently, in AGS cells, erinacine S treatment not only triggers the activation of extrinsic apoptosis pathways (TRAIL, Fas-L and caspase-8, -9, -3), but it also suppresses the expression of the anti-apoptotic molecules Bcl-2 and Bcl-XL in a time-dependent manner. In addition, erinacine S also causes cell cycle G1 arrest by the inactivation of CDKs/cyclins. Moreover, our data revealed that activation of the ROS-derived and AKT/FAK/PAK1 pathways is involved in the erinacine S-mediated transcriptional activation of Fas-L and TRAIL through H3K4 trimethylation on their promoters. Together, this study sheds light on the anticancer effects of erinacine S on gastric cancer and its molecular mechanism in vitro and in vivo.

Novel regulator role of CIL-102 in the epigenetic modification of TNFR1/TRAIL to induce cell apoptosis in human gastric cancer

CIL-102 (1-[4-(furo [2,3-b]quinolin-4-ylamino)phenyl]ethanone) is a major active agent and an alkaloid derivative of Camptotheca acuminata, which has valuable biological properties, including anti-tumorigenic activity. However, the molecular mechanisms of CIL-102 related to inductive apoptosis in human gastric cancer remain unclear. By using diphenyltetrazolium bromide (MTT), annexin-V-fluorescein-isothiocyanate (FITC)/propidium iodide staining and a 2',7' -dichlorofluorescin diacetate (DCFDA), a Fluo-3 fluorescence staining assay, the cell death and cell viability in gastric cancer cells and an in vivo xenograft mouse model, with or without the addition of CIL-102, were measured, respectively. Furthermore, signaling pathways and apoptotic molecules were also detected by western blots and an immunohistochemical assay. Our results demonstrated that CIL-102 treatment significantly induced the cell apoptosis of gastric cancer cells, along with increased ROS production and increased intracellular Ca2+ levels. In addition, through the inactivation of CDK1/cyclin B1, CIL-102 treatment induced the cell cycle G2/M arrest of gastric cancer cells. Moreover, our data revealed that multiple signaling pathways were involved in the H3K4 trimethylation of TNFR1 and TRAIL proteins by CIL-102, including ROS-derived and JNK/mTOR/p300 pathways in gastric cancer AGS cells. The CIL-102 treatment also consistently inhibited tumor growth and increased tumor apoptosis, as measured by TUNEL assay in an in vivo xenograft mouse model. An immunohistochemical analysis revealed that the upregulation of the TNFR1 and TRAIL proteins and the downregulation of PCNA and CDK1 proteins were found in the CIL-102-treated gastric cancer xenograft mouse model, compared to that of the saline control. Together, this study sheds light on the novel mechanism associated with CIL-102 for inducing gastric cancer apoptosis.

Defective Regulation of Membrane TNFα Expression in Dendritic Cells of Glioblastoma Patients Leads to the Impairment of Cytotoxic Activity against Autologous Tumor Cells

Besides an antigen-presenting function and ability to induce antitumor immune responses, dendritic cells (DCs) possess a direct tumoricidal activity. We previously reported that monocyte-derived IFNα-induced DCs (IFN-DCs) of glioblastoma multiforme patients express low levels of membrane TNFα molecule (mTNFα) and have impaired TNFα/TNF-R1-mediated cytotoxicity against immortalized tumor cell line HEp-2. However, whether the observed defect could affect killer activity of glioma patient DCs against autologous tumor cells remained unclear. Here, we show that donor IFN-DCs possess cytotoxic activity against glioblastoma cell lines derived from a primary tumor culture. Granule-mediated and TNFα/TNF-R1-dependent pathways were established as the main mechanisms underlying cytotoxic activity of IFN-DCs. Glioblastoma patient IFN-DCs showed lower cytotoxicity against autologous glioblastoma cells sensitive to TNFα/TNFR1-mediated lysis, which was associated with low TNFα mRNA expression and high TACE/ADAM-17 enzyme activity. Recombinant IL-2 (rIL-2) and human double-stranded DNA (dsDNA) increased 1.5-fold cytotoxic activity of patient IFN-DCs against autologous glioblastoma cells. dsDNA, but not rIL-2, enhanced the expression of TNFα mRNA and decreased expression and activity of TACE/ADAM-17 enzyme. In addition, dsDNA and rIL-2 stimulated the expression of perforin and granzyme B (in the presence of dsDNA), suggesting the possibility of enhancing DC cytotoxicity against autologous glioblastoma cells via various mechanisms.

Loss of 5'-Methylthioadenosine Phosphorylase (MTAP) is Frequent in High-Grade Gliomas; Nevertheless, it is Not Associated with Higher Tumor Aggressiveness

The 5’-methylthioadenosine phosphorylase (MTAP) gene is located in the chromosomal region 9p21. MTAP deletion is a frequent event in a wide variety of human cancers; however, its biological role in tumorigenesis remains unclear. The purpose of this study was to characterize the MTAP expression profile in a series of gliomas and to associate it with patients’ clinicopathological features. Moreover, we sought to evaluate, through glioma gene-edited cell lines, the biological impact of MTAP in gliomas. MTAP expression was evaluated in 507 glioma patients by immunohistochemistry (IHC), and the expression levels were associated with patients’ clinicopathological features. Furthermore, an in silico study was undertaken using genomic databases totalizing 350 samples. In glioma cell lines, MTAP was edited, and following MTAP overexpression and knockout (KO), a transcriptome analysis was performed by NanoString Pan-Cancer Pathways panel. Moreover, MTAP’s role in glioma cell proliferation, migration, and invasion was evaluated. Homozygous deletion of 9p21 locus was associated with a reduction of MTAP mRNA expression in the TCGA (The Cancer Genome Atlas) - glioblastoma dataset (p < 0.01). In addition, the loss of MTAP expression was markedly high in high-grade gliomas (46.6% of cases) determined by IHC and Western blotting (40% of evaluated cell lines). Reduced MTAP expression was associated with a better prognostic in the adult glioblastoma dataset (p < 0.001). Nine genes associated with five pathways were differentially expressed in MTAP-knockout (KO) cells, with six upregulated and three downregulated in MTAP. Analysis of cell proliferation, migration, and invasion did not show any significant differences between MTAP gene-edited and control cells. Our results integrating data from patients as well as in silico and in vitro models provide evidence towards the lack of strong biological importance of MTAP in gliomas. Despite the frequent loss of MTAP, it seems not to have a clinical impact in survival and does not act as a canonic tumor suppressor gene in gliomas.

The fungal metabolite chaetocin is a sensitizer for pro-apoptotic therapies in glioblastoma

Glioblastoma Multiforme (GBM) is the most common and aggressive primary brain tumor. Despite recent developments in surgery, chemo- and radio-therapy, a currently poor prognosis of GBM patients highlights an urgent need for novel treatment strategies. TRAIL (TNF Related Apoptosis Inducing Ligand) is a potent anti-cancer agent that can induce apoptosis selectively in cancer cells. GBM cells frequently develop resistance to TRAIL which renders clinical application of TRAIL therapeutics inefficient. In this study, we undertook a chemical screening approach using a library of epigenetic modifier drugs to identify compounds that could augment TRAIL response. We identified the fungal metabolite chaetocin, an inhibitor of histone methyl transferase SUV39H1, as a novel TRAIL sensitizer. Combining low subtoxic doses of chaetocin and TRAIL resulted in very potent and rapid apoptosis of GBM cells. Chaetocin also effectively sensitized GBM cells to further pro-apoptotic agents, such as FasL and BH3 mimetics. Chaetocin mediated apoptosis sensitization was achieved through ROS generation and consequent DNA damage induction that involved P53 activity. Chaetocin induced transcriptomic changes showed induction of antioxidant defense mechanisms and DNA damage response pathways. Heme Oxygenase 1 (HMOX1) was among the top upregulated genes, whose induction was ROS-dependent and HMOX1 depletion enhanced chaetocin mediated TRAIL sensitization. Finally, chaetocin and TRAIL combination treatment revealed efficacy in vivo. Taken together, our results provide a novel role for chaetocin as an apoptosis priming agent and its combination with pro-apoptotic therapies might offer new therapeutic approaches for GBMs.

TNF Family Cytokines Induce Distinct Cell Death Modalities in the A549 Human Lung Epithelial Cell Line when Administered in Combination with Ricin Toxin

Ricin is a member of the ribosome-inactivating protein (RIP) family of toxins and is classified as a biothreat agent by the Centers for Disease Control and Prevention (CDC). Inhalation, the most potent route of toxicity, triggers an acute respiratory distress-like syndrome that coincides with near complete destruction of the lung epithelium. We previously demonstrated that the TNF-related apoptosis-inducing ligand (TRAIL; CD253) sensitizes human lung epithelial cells to ricin-induced death. Here, we report that ricin/TRAIL-mediated cell death occurs via apoptosis and involves caspases -3, -7, -8, and -9, but not caspase-6. In addition, we show that two other TNF family members, TNF-α and Fas ligand (FasL), also sensitize human lung epithelial cells to ricin-induced death. While ricin/TNF-α- and ricin/FasL-mediated killing of A549 cells was inhibited by the pan-caspase inhibitor, zVAD-fmk, evidence suggests that these pathways were not caspase-dependent apoptosis. We also ruled out necroptosis and pyroptosis. Rather, the combination of ricin plus TNF-α or FasL induced cathepsin-dependent cell death, as evidenced by the use of several pharmacologic inhibitors. We postulate that the effects of zVAD-fmk were due to the molecule’s known off-target effects on cathepsin activity. This work demonstrates that ricin-induced lung epithelial cell killing occurs by distinct cell death pathways dependent on the presence of different sensitizing cytokines, TRAIL, TNF-α, or FasL.

Autophagic and Apoptotic Pathways as Targets for Chemotherapy in Glioblastoma

Glioblastoma multiforme is the most malignant and aggressive type of brain tumor, with a mean life expectancy of less than 15 months. This is due in part to the high resistance to apoptosis and moderate resistant to autophagic cell death in glioblastoma cells, and to the poor therapeutic response to conventional therapies. Autophagic cell death represents an alternative mechanism to overcome the resistance of glioblastoma to pro-apoptosis-related therapies. Nevertheless, apoptosis induction plays a major conceptual role in several experimental studies to develop novel therapies against brain tumors. In this review, we outline the different components of the apoptotic and autophagic pathways and explore the mechanisms of resistance to these cell death pathways in glioblastoma cells. Finally, we discuss drugs with clinical and preclinical use that interfere with the mechanisms of survival, proliferation, angiogenesis, migration, invasion, and cell death of malignant cells, favoring the induction of apoptosis and autophagy, or the inhibition of the latter leading to cell death, as well as their therapeutic potential in glioma, and examine new perspectives in this promising research field.

Polylysine-modified polyethylenimine polymer can generate genetically engineered mesenchymal stem cells for combinational suicidal gene therapy in glioblastoma

Glioblastoma remains the most resistant malignant brain tumor owing to the lack of an efficient delivery system for therapeutic genes or drugs, especially in outgrowing tumor islands. Cell-based delivery systems such as mesenchymal stem cells (MSCs) are a potential candidate in this regard. Conventionally, MSCs have been genetically modified for cancer therapy by using viral vectors that can illicit oncogenicity and limit their use in clinical trials. In this study, we have used nonviral agents such as the polylysine-modified polyethylenimine (PEI-PLL) copolymer to generate genetically engineered MSCs with suicidal genes, namely, HSV-TK and TRAIL. Our results demonstrated that an intratumoral injection of polymer-double-transfected MSCs along with prodrug ganciclovir injections can induce a significant synergistic therapeutic response both in vitro and in vivo compared to single plasmid transfections or untransfected MSCs. The proliferation marker Ki67 and the angiogenesis marker VEGF were also significantly reduced in treatment groups, whereas the TUNEL assay demonstrated that apoptosis is significantly increased after treatment. Our findings suggest that the PEI-PLL copolymer can successfully modify MSCs with therapeutic genes and can produce a pronounced impact during glioblastoma therapy. This study proposes a potential nonviral approach to develop a cell-based therapy for the treatment of glioma. STATEMENT OF SIGNIFICANCE: In this study, we have used a polylysine-modified polyethylenimine polymer (PEI-PLL) copolymer, a non viral transfection agent, for gene delivery in mesenchymal stem cells. These PEI-PLL-transfected mesenchymal stem cells with HSV-TK and TRAIL genes have the potential to treat glioma both in vitro and in vivo. This combinational therapy through PEI-PLL-transfected mesenchymal stem cells can provide cost-effective, low immunogenic, and tumor-targeted delivery of suicideal genes (HSV-TK and TRAIL) for promising glioblastoma treatment.

Predicting the cell death responsiveness and sensitization of glioma cells to TRAIL and temozolomide

Genotoxic chemotherapy with temozolomide (TMZ) is a mainstay of treatment for glioblastoma (GBM); however, at best, TMZ provides only modest survival benefit to a subset of patients. Recent insight into the heterogeneous nature of GBM suggests a more personalized approach to treatment may be necessary to overcome cancer drug resistance and improve patient care. These include novel therapies that can be used both alone and with TMZ to selectively reactivate apoptosis within malignant cells. For this approach to work, reliable molecular signatures that can accurately predict treatment responsiveness need to be identified first. Here, we describe the first proof-of-principle study that merges quantitative protein-based analysis of apoptosis signaling networks with data- and knowledge-driven mathematical systems modeling to predict treatment responsiveness of GBM cell lines to various apoptosis-inducing stimuli. These include monotherapies with TMZ and TRAIL, which activate the intrinsic and extrinsic apoptosis pathways, respectively, as well as combination therapies of TMZ+TRAIL. We also successfully employed this approach to predict whether individual GBM cell lines could be sensitized to TMZ or TRAIL via the selective targeting of Bcl-2/Bcl-xL proteins with ABT-737. Our findings suggest that systems biology-based approaches could assist in personalizing treatment decisions in GBM to optimize cell death induction.

miR-133a Promotes TRAIL Resistance in Glioblastoma via Suppressing Death Receptor 5 and Activating NF-κB Signaling

Recombinant tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), as a novel cancer therapeutic, is being tested in phase II and III clinical trials; however, TRAIL resistance remains a big obstacle preventing its clinical application. Considering that TRAIL-induced apoptosis through death receptors DR4 and DR5, their activation may be an alternative pathway to suppress TRAIL resistance. In this study, a negative correlation between DR5 expression and TRAIL resistance was observed, and miR-133a was predicted to be the most promising candidate to suppress DR5 expression. Further investigation demonstrated that miR-133a knockdown dramatically suppressed TRAIL resistance in glioblastoma in vitro and in vivo. An NF-κB family member, phosphorylated IκBα (P-IκBα), was shown to be stimulated by miR-133a, leading to the activation of this signaling. Finally, miR-133a was found to be inversely correlated with DR5 expression in human clinical specimens. In conclusion, our data demonstrate that miR-133a promotes TRAIL resistance in glioblastoma by suppressing DR5 expression and activating NF-κB signaling.

Inhibition of Notch1 signaling overcomes resistance to the death ligand Trail by specificity protein 1-dependent upregulation of death receptor 5

The Notch1 signaling pathway contributes to tumorigenesis by influencing differentiation, proliferation and apoptosis. Here, we demonstrate that inhibition of the Notch1 signaling pathway sensitizes glioblastoma cell lines and glioblastoma initiating cells to apoptosis induced by the death ligand TRAIL. This sensitization occurs through transcriptional upregulation of the death receptor 5 (DR5, TRAIL-R2). The increase in DR5 expression is abrogated by concomitant repression of the transcription factor Sp1, which directly binds to the DR5 promoter in the absence of Notch1 as revealed by chromatin immunoprecipitation. Consistent with these findings, Notch1 inhibition resulted in increased DR5 promoter activity, which was impaired by mutation of one out of two Sp1-binding sites within the proximal DR5 promoter. Moreover, we demonstrate that JNK signaling contributes to the regulation of DR5 expression by Notch1. Taken together, our results identify Notch1 as key driver for TRAIL resistance and suggest Notch1 as a promising target for anti-glioblastoma therapy.

The ER stress inducer DMC enhances TRAIL-induced apoptosis in glioblastoma

Glioblastoma multiforme (GBM) is the most aggressive malignant brain tumour in humans and is highly resistant to current treatment modalities. We have explored the combined treatment of the endoplasmic reticulum (ER) stress-inducing agent 2,5-dimethyl-celecoxib (DMC) and TNF-related apoptosis-inducing ligand (TRAIL WT) or the DR5-specific TRAIL D269H/E195R variant as a potential new strategy to eradicate GBM cells using TRAIL-resistant and -sensitive GBM cells. GBM cell lines were investigated for their sensitivity to TRAIL, DMC and combination of both agents. Cell viability was measured by MTS assay and apoptosis was assessed by Annexin V/PI and acridine orange staining. Caspase activation and protein expression levels were analysed with Western blotting. Death Receptor (DR) cell surface expression levels were quantified by flow cytometry. DR5 expression was increased in U87 cells by ectopic expression using a retroviral plasmid and survivin expression was silenced using specific siRNAs. We demonstrate that A172 expresses mainly DR5 on the cell surface and that these cells show increased sensitivity for the DR5-specific rhTRAIL D269H/E195R variant. In contrast, U87 cells show low DR cell surface levels and is insensitive via both DR4 and DR5. We determined that DMC treatment displays a dose-dependent reduction in cell viability against a number of GBM cells, associated with ER stress induction, as shown by the up-regulation of glucose-regulated protein 78 (GRP78) and CCAAT/-enhancer-binding protein homologous protein (CHOP) in A172 and U87 cells. The dramatic decrease in cell viability is not accompanied by a correspondent increase in Annexin V/PI or caspase activation typically seen in apoptotic or/and necrotic cells within 24h of treatment. Although DMC did not affect DR5 expression in the GBM cells, it increased TRAIL-induced caspase-8 activation in both TRAIL-sensitive and -resistant cells, indicating that DMC potentiates initiator caspase activation in these cells. In A172 cells, sub-toxic concentrations of DMC greatly potentiated TRAIL-induced apoptosis. Furthermore, DMC strongly reduced survivin expression in A172 and U87 cells and silencing of this anti-apoptotic protein partially sensitized cells to TRAIL-induced apoptosis. Our findings corroborate that DMC is a promising agent against GBM, and uncovers a potential synergistic cooperation with TRAIL in this highly malignant cancer.

MicroRNA-30b functions as a tumour suppressor in human colorectal cancer by targeting KRAS, PIK3CD and BCL2

Colorectal cancer (CRC) is the third most common cancer in the USA. MicroRNAs play important roles in the pathogenesis of CRC. In this study, we investigated the role of miR-30b in CRC and found that its expression was significantly lower in CRC tissues than that in normal tissues. We showed that a low expression level of miR-30b was closely related to poor differentiation, advanced TNM stage and poor prognosis of CRC. Further experiments showed that over-expression of miR-30b suppressed CRC cell proliferation in vitro and tumour growth in vivo. Specifically, miR-30b promoted G1 arrest and induced apoptosis. Moreover, KRAS, PIK3CD and BCL2 were identified as direct and functional targets of miR-30b. MiR-30b directly targeted the 3'-untranslated regions of their mRNAs and repressed their expression. This study revealed functional and mechanistic links between miRNA-30b and oncogene KRAS, PIK3CD and BCL2 in the pathogenesis of CRC. MiR-30b not only plays important roles in the regulation of cell proliferation and tumour growth in CRC, but is also a potential prognostic marker or therapeutic target for CRC. Restoration of miR-30b expression may represent a promising therapeutic approach for targeting malignant CRC.

Critical physiological and pathological functions of Forkhead Box O tumor suppressors

The Forkhead box, subclass O (FOXO) proteins are critical transcription factors, ubiquitously expressed in the human body. These proteins are characterized by a remarkable functional diversity, being involved in cell cycle arrest, apoptosis, oxidative detoxification, DNA damage repair, stem cell maintenance, cell differentiation, cell metabolism, angiogenesis, cardiac development, aging and others. In addition, FOXO have critical implications in both normal and cancer stem cell biology. New strategies to modulate FOXO expression and activity may now be developed since the discovery of novel FOXO regulators and non-coding RNAs (such as microRNAs) targeting FOXO transcription factors. This review focuses on physiological and pathological functions of FOXO proteins and on their action as fine regulators of cell fate and context-dependent cell decisions. A better understanding of the structure and critical functions of FOXO transcription factors and tumor suppressors may contribute to the development of novel therapies for cancer and other diseases.

Combination treatment for glioblastoma cells with tumor necrosis factor-related apoptosis-inducing ligand and oncolytic adenovirus delta-24

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits cancer-selective killing activity representing a promising anticancer therapeutic strategy. Adenovirus Delta-24 is another interested anticancer agent selectively killing cells with a defective p16/Rb/E2F pathway. However, many types of cancer, including gliomas, could develop resistance to Delta-24 or TRAIL-induced apoptosis. In this study, we investigated whether TRAIL, in combination with adenovirus Delta-24, could result in an enhanced antiglioma effect in vitro in a panel of glioblastoma cell lines (U87MG, U251MG, D54, and T98G). The treatment of glioblastoma cell lines with TRAIL and Delta-24 adenovirus in combination showed markedly enhanced effect, compared to each agent alone.

Identification of death receptors DR4 and DR5 in HTB-12 astrocytoma cell lines and determination of TRAIL sensitivity

Astrocytomas are tumors which arise from astrocytes, cells that form the blood-brain barrier. There are very few drugs that successfully treat brain tumors. In this study, the cytotoxic effects on the HTB-12 astrocytoma cell line by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) were studied. The presence of the TRAIL receptors, Death receptor 4 (DR4) and Death receptor 5 (DR5), were detected in HTB-12 cells by Enzyme-Linked Immunosorbent Assay (ELISA). Cytotoxicity assay by Trypan Blue Exclusion Method showed effective cell killing by TRAIL treatment. Thus, the presence of death receptors and TRAIL efficacy raises the therapeutic potential for this type of brain tumor.

Neobavaisoflavone sensitizes apoptosis via the inhibition of metastasis in TRAIL-resistant human glioma U373MG cells

AIMS

Neobavaisoflavone (NBIF), an isoflavone isolated from Psoralea corylifolia (Leguminosae), has striking anti-inflammatory and anti-cancer effects. NBIF inhibits the proliferation of prostate cancer in vitro and in vivo.

MAIN METHODS

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a key endogenous molecule that selectively induces apoptosis in cancer cells with little or no toxicity in normal cells. However, some cancer cells, including U373MG cells, are resistant to TRAIL-mediated apoptosis. We demonstrated that the cell viability, migration and invasion assay were used in U373MG glioma cells.

KEY FINDINGS

In this study, we found that NBIF sensitizes human U373MG glioma cells to TRAIL-mediated apoptosis. Co-treatment of TRAIL and NBIF effectively induced Bid cleavage and activated caspases 3, 8, and 9. Importantly, DR5 expression was upregulated by NBIF. We also observed that the combination NBIF and TRAIL increased expression of BAX. We further demonstrate that NBIF induced TRAIL-mediated apoptosis in human glioma cells by suppressing migration and invasion, and by inhibiting anoikis resistance.

SIGNIFICANCE

Taken together, our results suggest that NBIF reduces the resistance of cancer cells to TRAIL and that the combination of NBIF and TRAIL may be a new therapeutic strategy for treating TRAIL-resistant glioma cells.

Immunomodulatory effects of interferons in malignancies

Investigation of the antitumor and immunomodulatory activities of interferon (IFN) began shortly after the cytokine was discovered in 1957. Early work showed a direct correlation between administration of IFN and inhibition of symptoms associated with virally induced leukemia in mice as well as an increase in their survival time. Subsequent studies with purified IFNs confirmed the direct and indirect stimulation of immune cells, resulting in antitumor activities of IFN. Clinically, IFN-alphas (αs) have been shown to have activity against a variety of tumors. Initially, the U.S. Food and Drug Administration licensed 2 recombinant IFN-αs for the treatment of hairy-cell leukemia and then later for several other cancers. The success rate seen with IFNs and certain tumors has been varied. Unfortunately, some neoplasms show no response to IFN. Monocytes/macrophages play an important role in cancer progression. Monocytes in combination with IFN may be an important therapy for several cancers. This article focuses on the role of IFN and monocytes alone or in combination in affecting malignancies.

Evaluating the effect of therapeutic stem cells on TRAIL resistant and sensitive medulloblastomas

Mesenchymal stem cells (MSC) are emerging as novel cell-based delivery agents; however, a thorough investigation addressing their therapeutic potential in medulloblastomas (MB) has not been explored to date. In this study, we engineered human MSC to express a potent and secretable variant of a tumor specific agent, tumor necrosis factor-apoptosis-inducing ligand (S-TRAIL) and assessed the ability of MSC-S-TRAIL mediated MB killing alone or in combination with a small molecule inhibitor of histone-deacetylase, MS-275, in TRAIL-sensitive and -resistant MB in vitro and in vivo. We show that TRAIL sensitivity/resistance correlates with the expression of its cognate death receptor (DR)5 and MSC-S-TRAIL induces caspase-3 mediated apoptosis in TRAIL-sensitive MB lines. In TRAIL-resistant MB, we show upregulation of DR4/5 levels when pre-treated with MS-275 and a subsequent sensitization to MSC-S-TRAIL mediated apoptosis. Using intracranially implanted MB and MSC lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that MSC-S-TRAIL has significant anti-tumor effects in mice bearing TRAIL-sensitive and MS-275 pre-treated TRAIL-resistant MBs. To our knowledge, this is the first study that explores the use of human MSC as MB-targeting therapeutic-vehicles in vivo in TRAIL-sensitive and resistant tumors, and has implications for developing effective therapies for patients with medulloblastomas.

Genetics of glioblastoma: a window into its imaging and histopathologic variability

Glioblastoma is a highly malignant brain tumor that relentlessly defies therapy. Efforts over the past decade have begun to tease out the biochemical details that lead to its aggressive behavior and poor prognosis. There is hope that this new understanding will lead to improved treatment strategies for patients with glioblastoma, in the form of targeted, molecularly based therapies that are individualized to specific changes in individual tumors. However, these new therapies have the potential to fundamentally alter the biologic behavior of glioblastoma and, as a result, its imaging appearance. Knowledge about common genetic alterations and the resultant cellular and tissue changes (ie, induced angiogenesis and abnormal cell survival, proliferation, and invasion) in glioblastomas is important as a basis for understanding imaging findings before treatment. It is equally critical that radiologists understand which genetic pathway is targeted by each specific therapeutic agent or class of agents in order to accurately interpret changes in the imaging appearances of treated tumors.

Heterogeneity of primary glioblastoma cells in the expression of caspase-8 and the response to TRAIL-induced apoptosis

Recent studies suggest that cancer stem cells (CSCs) are responsible for cancer resistance to therapies. We therefore investigated how glioblastoma-derived CSCs respond to the treatment of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Neurospheres were generated from glioblastomas, characterized for CSC properties including self-renewal, cell differentiation and xenograft formation capacity, and analyzed for TRAIL-induced apoptosis, CASP8 genomic status, and caspase-8 protein expression. The neurosphere NSC326 was sensitive to TRAIL-induced apoptosis as evidenced by cell death and caspase-8, -3, and -7 enzymatic activities. In contrast, however, the neurosphere NSC189 was TRAIL-resistant. G-banding analysis identified five chromosomally distinguishable cell populations in the neurospheres. Fluorescence in situ hybridization revealed the variation of chromosome 2 copy number in these populations and the loss of CASP8 locus in 2q33-34 region in a small set of cell populations in the neurosphere. Immunohistochemistry of NSC189 cell blocks revealed the lack of caspase-8 protein in a subset of neurosphere cells. Western blotting and immunohistochemistry of human glioblastoma tumors demonstrated the expression of caspase-8 protein in the vast majority of the tumors as compared to normal human brain tissues that lack the caspase-8 expression. This study shows heterogeneity of glioblastomas and derived CSCs in the genomic status of CASP8, expression of caspase-8, and thus responsiveness to TRAIL-induced apoptosis. Clinic trials may consider genomic analysis of the cancer tissue to identify the genomic loss of CASP8 and use it as a genomic marker to predict the resistance of glioblastomas to TRAIL apoptosis pathway-targeted therapies.

Cisplatin restores TRAIL apoptotic pathway in glioblastoma-derived stem cells through up-regulation of DR5 and down-regulation of c-FLIP

Glioblastoma-derived stem cells (GSCs) are responsible for the cancer resistance to therapies. We show here that GSC-enriched neurospheres are resistant to the treatment of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) due to the insufficient expression of the death receptor DR4 and DR5 and the overexpression of cellular Fas-associated death domain-like interleukin-1β-converting enzyme-inhibitory protein (c-FLIP). However, treatment with cisplatin leads to the upregulation of DR5 and downregulation of c-FLIP and restores TRAIL apoptotic pathway in the neurospheres. This study suggests that the combined treatment of TRAIL and cisplatin can induce apoptosis in GSCs and thus provide an effective treatment of glioblastomas.

High cell surface death receptor expression determines type I versus type II signaling

Previous studies have suggested that there are two signaling pathways leading from ligation of the Fas receptor to induction of apoptosis. Type I signaling involves Fas ligand-induced recruitment of large amounts of FADD (FAS-associated death domain protein) and procaspase 8, leading to direct activation of caspase 3, whereas type II signaling involves Bid-mediated mitochondrial perturbation to amplify a more modest death receptor-initiated signal. The biochemical basis for this dichotomy has previously been unclear. Here we show that type I cells have a longer half-life for Fas message and express higher amounts of cell surface Fas, explaining the increased recruitment of FADD and subsequent signaling. Moreover, we demonstrate that cells with type II Fas signaling (Jurkat or HCT-15) can signal through a type I pathway upon forced receptor overexpression and that shRNA-mediated Fas down-regulation converts cells with type I signaling (A498) to type II signaling. Importantly, the same cells can exhibit type I signaling for Fas and type II signaling for TRAIL (TNF-α-related apoptosis-inducing ligand), indicating that the choice of signaling pathway is related to the specific receptor, not some other cellular feature. Additional experiments revealed that up-regulation of cell surface death receptor 5 levels by treatment with 7-ethyl-10-hydroxy-camptothecin converted TRAIL signaling in HCT116 cells from type II to type I. Collectively, these results suggest that the type I/type II dichotomy reflects differences in cell surface death receptor expression.

Amiodarone sensitizes human glioma cells but not astrocytes to TRAIL-induced apoptosis via CHOP-mediated DR5 upregulation

Amiodarone is a widely used anti-arrhythmic drug that inhibits diverse ion channels, including the Na(+)/Ca(2+) exchanger (NCX), L-type Ca(2+) channels, and Na(+) channels. Here, we report that subtoxic doses of amiodarone and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) synergistically induced apoptosis of various glioma cells. Treatment of U251MG glioma cells with amiodarone increased intracellular Ca(2+) levels and enhanced the expression of the endoplasmic reticulum (ER) stress-inducible transcription factor C/EBP homologous protein (CHOP). This upregulation of CHOP was followed by marked upregulation of the TRAIL receptor, DR5. Suppression of DR5 expression by small interfering (si) RNAs almost completely blocked amiodarone/TRAIL-induced apoptosis in U251MG glioma cells, demonstrating that DR5 is critical to this cell death. siRNA-mediated CHOP suppression reduced amiodarone-induced DR5 upregulation and attenuated the cell death induced by amiodarone plus TRAIL. In addition, omitting Ca(2+) from the external medium using ethylene glycol tetraacetic acid markedly inhibited this cell death, reducing the protein levels of CHOP and DR5. These results suggest that amiodarone-induced influx of Ca(2+) plays an important role in sensitizing U251MG cells to TRAIL-mediated apoptosis through CHOP-mediated DR5 upregulation. Furthermore, subtoxic doses of bepridil and cibenzoline, two other anti-arrhythmic drugs with NCX-inhibitor activity, also sensitized glioma cells to TRAIL-mediated apoptosis, via the upregulation of both CHOP and DR5. Notably, amiodarone/TRAIL cotreatment did not induce cell death in astrocytes, nor did it affect the expression of CHOP or DR5 in these cells. These results collectively suggest that a combined regimen of amiodarone plus TRAIL may offer an effective therapeutic strategy for safely and selectively treating resistant gliomas.

Survival signalling and apoptosis resistance in glioblastomas: opportunities for targeted therapeutics

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults and one of the most aggressive cancers in man. Despite technological advances in surgical management, combined regimens of radiotherapy with new generation chemotherapy, the median survival for these patients is 14.6 months. This is largely due to a highly deregulated tumour genome with opportunistic deletion of tumour suppressor genes, amplification and/or mutational hyper-activation of receptor tyrosine kinase receptors. The net result of these genetic changes is augmented survival pathways and systematic defects in the apoptosis signalling machinery. The only randomised, controlled phase II trial conducted targeting the epidermal growth factor receptor (EGFR) signalling with the small molecule inhibitor, erlotinib, has showed no therapeutic benefit. Survival signalling and apoptosis resistance in GBMs can be viewed as two sides of the same coin. Targeting increased survival is unlikely to be efficacious without at the same time targeting apoptosis resistance. We have critically reviewed the literature regarding survival and apoptosis signalling in GBM, and highlighted experimental, preclinical and recent clinical trials attempting to target these pathways. Combined therapies simultaneously targeting apoptosis and survival signalling defects might shift the balance from tumour growth stasis to cytotoxic therapeutic responses that might be associated with greater therapeutic benefits.

Review: on TRAIL for malignant glioma therapy?

Glioblastoma (GBM) is a devastating cancer with a median survival of around 15 months. Significant advances in treatment have not been achieved yet, even with a host of new therapeutics under investigation. Therefore, the quest for a cure for GBM remains as intense as ever. Of particular interest for GBM therapy is the selective induction of apoptosis using the pro-apoptotic tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). TRAIL signals apoptosis via its two agonistic receptors TRAIL-R1 and TRAIL-R2. TRAIL is normally present as homotrimeric transmembrane protein, but can also be processed into a soluble trimeric form (sTRAIL). Recombinant sTRAIL has strong tumouricidal activity towards GBM cells, with no or minimal toxicity towards normal human cells. Unfortunately, GBM is a very heterogeneous tumour, with multiple genetically aberrant clones within one tumour. Consequently, any single agent therapy is likely to be not effective enough. However, the anti-GBM activity of TRAIL can be synergistically enhanced by a variety of conventional and novel targeted therapies, making TRAIL an ideal candidate for combinatorial strategies. Here we will, after briefly detailing the biology of TRAIL/TRAIL receptor signalling, focus on the promises and pitfalls of recombinant TRAIL as a therapeutic agent alone and in combinatorial therapeutic approaches for GBM.

Capsaicin sensitizes malignant glioma cells to TRAIL-mediated apoptosis via DR5 upregulation and survivin downregulation

Capsaicin, a pungent ingredient of red chili peppers, has been reported to possess antitumor activities. Here, we show that subtoxic doses of capsaicin effectively sensitize multiple malignant glioma cell lines to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Although TRAIL alone mediated partial proteolytic processing of procaspase-3 in glioma cells, cotreatment with capsaicin and TRAIL efficiently restored complete activation of caspases. We found that treatment of various gliomas with capsaicin significantly upregulated DR5, a death receptor of TRAIL, and downregulated the caspase inhibitor survivin. The induction of DR5 was mediated by CHOP/GADD153. The reduction in survivin protein level was associated with downregulation of cyclin B and Cdc2 expression, suggesting that inhibition of Cdc2 activity might contribute to capsaicin-induced survivin downregulation. Taken together, these results indicate that the activity of capsaicin toward DR5 and survivin contributes to the amplification of caspase cascades, thereby restoring TRAIL sensitivity in malignant glioma cells. Interestingly, normal astrocytes were resistant to combined treatment with capsaicin and TRAIL. Neither capsaicin-induced DR5 upregulation/survivin downregulation nor the partial processing of procaspase-3 by TRAIL was induced in astrocytes. Thus, a combined regimen using capsaicin and TRAIL may provide a safe and effective strategy for treating malignant gliomas.

Dual-targeted antitumor effects against brainstem glioma by intravenous delivery of tumor necrosis factor-related, apoptosis-inducing, ligand-engineered human mesenchymal stem cells

OBJECTIVE

We sought to explore the dual-targeted antitumor effects of membrane-spanned, tumor necrosis factor-related, apoptosis-inducing ligand (TRAIL)-engineered human mesenchymal stem cells (hMSCs) against brainstem gliomas.

METHODS

The migration capacity of hMSCs toward gliomas was studied by the Transwell system in vitro and by intravenous injection of hMSCs in glioma-bearing mice in vivo. MSCs were engineered with native full-length human TRAIL (hTRAIL) by a recombinant adeno-associated virus (rAAV) vector (rAAV-hTRAIL). The targeted antiglioma effect was analyzed by coculture of hTRAIL-engineered MSCs with glioma in vitro and by systematic delivery of hTRAIL-engineered MSCs to established human brainstem glioma xenografts.

RESULTS

We demonstrated systematically that transplanted MSCs migrated to a brainstem glioma with a high specificity. MSCs penetrated the vessels surrounding the tumor, then streamed in a chain pattern toward the glioma, eventually surrounding the tumor. Membrane-spanned, TRAIL-engineered MSCs not only expressed full-length TRAIL in MSC surface, but secreted some soluble TRAIL in medium. After being infected with rAAV-hTRAIL, hMSCs showed no increase in apoptosis. After coculture of hTRAIL-engineered MSCs and U87MG cells, the apoptosis of U87MG cells significantly increased more than soluble TRAIL-treated U87MG cells. Systematic delivery of hTRAIL-engineered MSCs to established human brainstem glioma xenografts resulted in the potent induction of apoptosis in gliomas, but not in normal brain and prolonged survival to 38.0 +/- 10.46 days compared with phosphate-buffered saline (16.0 +/- 0.66 days), soluble TRAIL (19.0 +/- 1.65 days), and hMSC-LacZ (14.0 +/- 0.59 days) treated groups.

CONCLUSION

Systematically transplanted MSCs migrated to gliomas with a high specificity. Systematic delivery of MSC-hTRAIL can prolong the survival of brainstem glioma-bearing mice, presumably through a dual-targeted effect of membrane-spanned, TRAIL-engineered MSCs in the tumor microenvironment. MSCs may be an effective vehicle for the targeted delivery of therapeutic agents to brainstem gliomas.

Epigenetic silencing of death receptor 4 mediates tumor necrosis factor-related apoptosis-inducing ligand resistance in gliomas

PURPOSE

To identify and characterize epigenetically regulated genes able to predict sensitivity or resistance to currently tested chemotherapeutic agents in glioma therapy.

EXPERIMENTAL DESIGN

We used methylation-sensitive BeadArray technology to identify novel epigenetically regulated genes associated with apoptosis and with potential therapeutic targets in glioma therapy. To elucidate the functional consequences of promoter methylation in the identified target death receptor 4 (DR4), we investigated tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated and anti-DR4-mediated apoptosis in glioma cell lines (U373 and A172) with loss of DR4 and one glioma cell line (LN18) with robust DR4 expression.

RESULTS

In human astrocytic tumors, we detected DR4 promoter hypermethylation in 60% (n = 5) of diffuse astrocytomas WHO grade 2, in 75% (n = 8) of anaplastic astrocytomas WHO grade 3, and in 70% of glioblastomas WHO grade 4 (n = 33). DR4 is a cell surface protein restricted to glioma cells and is targeted by TRAIL. Glioma cell lines U373 and A172 harbored heavily methylated DR4 promoters, and 5-aza-2-deoxycytidine-mediated demethylation reconstituted DR4 expression in these cell lines. Functional knockdown of DR4 by DR4-specific small interfering RNA in TRAIL-sensitive glioma cell line LN18 significantly mitigated apoptosis induced by an agonistic anti-DR4 antibody. 5-Aza-2-deoxycytidine-mediated demethylation resulted in a functional reconstitution of DR4 on the cell surface of TRAIL-resistant glioma cell line U373 and sensitized U373 to TRAIL-mediated apoptosis. Suppression of DR4 by small interfering RNA in demethylated U373 successfully reestablished the TRAIL-resistant phenotype of U373.

CONCLUSIONS

DR4 promoter methylation is frequent in human astrocytic gliomas, and epigenetic silencing of DR4 mediates resistance to TRAIL/DR4-based glioma therapies.

FAPP2 gene downregulation increases tumor cell sensitivity to Fas-induced apoptosis

The gene for phosphatidylinositol-4-phosphate adaptor-2 (FAPP2) encodes a cytoplasmic lipid transferase with a plekstrin homology domain that has been implicated in vesicle maturation and transport from trans-Golgi to the plasma membrane. The introduction of ribozymes targeting the FAPP2 gene in colon carcinoma cells induced their apoptosis in the presence of Fas agonistic antibody. Furthermore, by quantitative PCR we showed that a siRNA specific to FAPP2, but not a randomized siRNA control, reduced FAPP2 gene expression in tumor cells. Transfection of FAPP2 siRNA into human tumor cells then incubated with FasL resulted in reduction of viable cell numbers. Also, FAPP2 siRNA transfected glioma and breast tumor cells showed significant increases in apoptosis upon incubation with soluble FasL, but the apoptosis did not necessarily correlate with increased Fas expression. These data demonstrate a previously unknown role for FAPP2 in conferring resistance to apoptosis and indicate that FAPP2 may be a target for cancer therapy.

The flavonoid kaempferol sensitizes human glioma cells to TRAIL-mediated apoptosis by proteasomal degradation of survivin

Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) limits its potential as a drug for cancer therapy. Here, we report that kaempferol, a bioactive plant flavonoid, sensitizes U251 and U87 glioma cells to TRAIL-mediated apoptosis. In contrast, U373 cells are not affected by kaempferol treatment. Treatment of kaempferol alone for 24 h did not induce apoptosis in the cell lines. We provide evidence that TRAIL-induced apoptosis is partially driven by kaempferol-mediated reduction of survivin protein levels. On kaempferol treatment, proteasomal degradation of survivin was observed. Inhibition of proteasomal degradation with MG132 in kaempferol-treated cells restored survivin protein levels in both glial cell lines. Consequently, overexpression of survivin attenuated TRAIL-kaempferol-induced apoptosis. In addition, we show that kaempferol mediates down-regulation of phosphorylated Akt, thereby further reducing survivin protein level. Furthermore, the blockage of the serine/threonine kinase Akt activity by kaempferol is important for inhibition of survivin because active phosphorylated Akt enhances the stability of survivin. However, we also show that the combined treatment of TRAIL and kaempferol induces cleavage (activation) of caspase-8, thereby exerting a proapoptotic effect independent of survivin known not to inhibit caspase-8 activation. Other effects induced by kaempferol were suppression of X-linked inhibitor of apoptosis proteins as the antiapoptotic members of the Bcl-2 family, Bcl-2, Bcl-xL, and Mcl-1 in a concentration-dependent manner. In summary, we showed that suppression of survivin is an essential mechanism in TRAIL-kaempferol-mediated apoptosis.

Quercetin promotes degradation of survivin and thereby enhances death-receptor-mediated apoptosis in glioma cells

The flavonoid quercetin has been reported to inhibit the proliferation of cancer cells, whereas it has no effect on nonneoplastic cells. U87-MG, U251, A172, LN229, and U373 malignant glioma cells were treated with quercetin (50-200 microM). Quercetin did not cause cytotoxicity 24 h after treatment. Combining quercetin with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) strongly augmented TRAIL-mediated apoptosis in U87-MG, U251, A172, and LN229 glioma cells; U373 cells could not be sensitized by quercetin to TRAIL-mediated apoptosis. TRAIL-induced apoptosis was enhanced by quercetin-induced reduction of survivin protein levels. Upon treatment with quercetin, the protein level of survivin was strongly suppressed in U87-MG, U251, and A172 but not in U373 glioma cells. Quercetin exposure resulted in proteasomal degradation of survivin. TRAIL-quercetin-induced apoptosis was markedly reduced by overexpression of survivin. In addition, upon treatment with quercetin, downregulation of survivin was also regulated by the Akt pathway. Taken together, the results of the present study suggest that quercetin sensitizes glioma cells to death-receptor-mediated apoptosis by suppression of inhibitor of the apoptosis protein survivin.

In vitro sensitivity testing of minimally passaged and uncultured gliomas with TRAIL and/or chemotherapy drugs

TRAIL/Apo-2L has shown promise as an anti-glioma drug, based on investigations of TRAIL sensitivity in established glioma cell lines, but it is not known how accurately TRAIL signalling pathways of glioma cells in vivo are reproduced in these cell lines in vitro. To replicate as closely as possible the in vivo behaviour of malignant glioma cells, 17 early passage glioma cell lines and 5 freshly resected gliomas were exposed to TRAIL-based agents and/or chemotherapeutic drugs. Normal human hepatocytes and astrocytes and established glioma cell lines were also tested. Cross-linked TRAIL, but not soluble TRAIL, killed both normal cell types and cells from three tumours. Cells from only one glioma were killed by soluble TRAIL, although only inefficiently. High concentrations of cisplatin were lethal to glioma cells, hepatocytes and astrocytes. Isolated combinations of TRAIL and chemotherapy drugs were more toxic to particular gliomas than normal cells, but no combination was generally selective for glioma cells. This study highlights the widespread resistance of glioma cells to TRAIL-based agents, but suggests that a minority of high-grade glioma patients may benefit from particular combinations of TRAIL and chemotherapy drugs. In vitro sensitivity assays may help identify effective drug combinations for individual glioma patients.

Identification of a novel switch in the dominant forms of cell adhesion-mediated drug resistance in glioblastoma cells

The failure of malignant cells to undergo apoptosis is a major obstacle in cancer therapy, and thus identifying the underlining molecules involved therein is imperative for improving patient survival. An important mechanism of drug resistance is cell adhesion-mediated drug resistance (CAM-DR). In this study we identify a novel switch by which glioblastoma multiforme (GBM) cells alter the mode of CAM-DR. In the absence of a microenvironmental cue provided by components of the extracellular matrix (ECM), GBM cells are able to employ an alternative, but equally effective, mode of CAM-DR by forming spheres via cell-cell interactions. Intriguingly, when inhibiting cell-cell interactions in the absence of ECM components, either by low cell density or by inhibition of gap junctions (intercellular connexin tunnels) through chemical inhibition with carbenoxyolone or co-incubation with the connexin-mimicking Gap 27 Cx37,43 peptide, GBM cells were sensitized to tumor necrosis factor-related apoptosis-inducing ligand- and CD95-induced apoptosis. By demonstrating that GBM cells can alternate from one form of CAM-DR (cell-substrate tethering) to another (homocellular cell-cell adhesion) and that inhibition of both forms is necessary for apoptosis sensitization, our findings not only have important implications for novel approaches to restore defective apoptosis programs, but also reveal a novel role of gap junctions in GBM.

Independent activation of Akt and NF-kappaB pathways and their role in resistance to TNF-alpha mediated cytotoxicity in gliomas

Tumor associated macrophages (TAMs) constitute a substantial mass in gliomas. The activated macrophages secrete various cytokines that affect diverse functions of tumors. The aim of this study was to elucidate the role of Akt and NF-kappaB pathways in resistance to TNF-alpha mediated cell death in human gliomas using monolayers and multicellular spheroids (MCS) as in vitro models. Akt and NF-kappaB are constitutively expressed and intimately involved in progression of gliomas. The activation of these pathways also renders the tumors resistant to conventional treatments including chemotherapy. While PI3K/Akt is shown to regulate the NF-kappaB activation in diverse systems, other studies place NF-kappaB upstream of Akt activation. Using a stable IkappaBalpha mutant LN-18 cell line and pharmacological inhibitors to PI3K/Akt (LY294002) and Akt (Akt2), we provide evidence that Akt and NF-kappaB are activated independently on stimulation with TNF-alpha and both the pathways contribute towards resistance to TNF-alpha mediated cell death. TNF-alpha-induced NF-kappaB activation independent of PI3K/Akt pathway was also confirmed in human glioma cell lines-LN-229 and U373MG. We also show that NF-kappaB and Akt are activated during spheroidogenesis and their expression is further enhanced on stimulation with TNF-alpha implicating their involvement in resistance to cell death. The findings thus underscore the relevance of spheroids as appropriate in vitro models for studying the signaling pathways in drug induced resistance.

Mitoparan and target-selective chimeric analogues: membrane translocation and intracellular redistribution induces mitochondrial apoptosis

Mastoparan, and structurally-related amphipathic peptides, may induce cell death by augmentation of necrotic and/or apoptotic pathways. To more precisely delineate cytotoxic mechanisms, we determined that [Lys(5,8)Aib(10)]mastoparan (mitoparan) specifically induces apoptosis of U373MG and ECV304 cells, as demonstrated by endonuclease and caspase-3 activation and phosphatidylserine translocation. Live cell imaging confirmed that, following translocation of the plasma membrane, mitoparan specifically co-localizes with mitochondria. Complementary studies indicated that mitoparan induces swelling and permeabilization of isolated mitochondria, through cooperation with a protein of the permeability transition pore complex VDAC, leading to the release of the apoptogenic factor, cytochrome c. N-terminal acylation of mitoparan facilitated the synthesis of chimeric peptides that incorporated target-specific address motifs including an integrin-specific RGD sequence and a Fas ligand mimetic. Significantly, these sychnologically-organised peptides demonstrated further enhanced cytotoxic potencies. We conclude that the cell penetrant, mitochondriotoxic and apoptogenic properties of mitoparan, and its chimeric analogues, offer new insights to the study and therapeutic induction of apoptosis.

Decoy receptor 3 expressed in rheumatoid synovial fibroblasts protects the cells against Fas-induced apoptosis

OBJECTIVE

Decoy receptor 3 (DcR3), a newly identified member of the tumor necrosis factor receptor (TNFR) superfamily, is a soluble receptor that binds to members of the TNF family, including FasL, LIGHT, and TNF-like molecule 1A. DcR3 is mostly expressed in tumor cells, and it competitively inhibits binding of TNF to TNFRs. The present study was undertaken to investigate DcR3 expression in fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and osteoarthritis (OA), and to analyze the effects of DcR3 on Fas-induced apoptosis in RA FLS.

METHODS

Expression of DcR3 in FLS was measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. FLS were incubated with DcR3-Fc chimera protein or transfected with DcR3 small interfering RNA (siRNA) using the lipofection method, before induction of apoptosis. Apoptosis induced by Fas in FLS was detected with TUNEL staining and Western blotting of caspase 8 and poly(ADP-ribose) polymerase. Finally, FLS were incubated with TNFalpha prior to Fas-induced apoptosis, expression of DcR3 was analyzed by quantitative RT-PCR, and apoptosis was measured.

RESULTS

DcR3 was expressed in both RA FLS and OA FLS. DcR3-Fc protein inhibited Fas-induced apoptosis in FLS. Down-regulation of DcR3 in FLS by siRNA increased Fas-induced apoptosis. TNFalpha increased DcR3 expression and inhibited Fas-induced apoptosis in RA FLS, but not in OA FLS.

CONCLUSION

DcR3 expressed in RA FLS is increased by TNFalpha and protects the cells against Fas-induced apoptosis. These findings indicate that DcR3 may be a possible therapeutic target in RA.

Enhanced proapoptotic effects of tumor necrosis factor-related apoptosis-inducing ligand on temozolomide-resistant glioma cells

OBJECT

Death receptor targeting is an attractive approach in experimental treatment for tumors such as malignant gliomas, which are resistant to radiation and chemotherapy. Among the family of cytokines referred to as death li gands, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted clinical interest. The aim of this study was to assess whether TRAIL can be used as an adjuvant to temozolomide (TMZ) for apoptosis induction in malignant glioma cell lines.

METHODS

Six human malignant glioma cell lines (A172, U87, U251, T98, U343, and U373) were exposed to human (h)TRAIL, TMZ, or an hTRAIL/TMZ combined treatment. Cell viability was assayed using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide and phase-contrast microscopy. Cell apoptosis was detected using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling technique and quantified using flow cytometric analysis. The apoptosis signaling cascade was studied with Western blotting. The additive effects of hTRAIL and TMZ resulted in a significant decrease in cell viability and an increased apoptotic rate. Expression of the death receptors DR5 and DR4 in two cell lines (A172 and U251) upregulated significantly when they were used in combination hTRAIL/TMZ treatment (p < 0.05 compared with baseline control), leading to activation of caspase-8 and caspase-3 (p < 0.05 compared with baseline control) and confirming an extrinsic apoptotic pathway. A cell intrinsic pathway through mitochondrial cytochrome c was not activated.

CONCLUSIONS

Based on this work, one may infer that hTRAIL should be considered as an adjuvant treatment for TMZ-resistant human malignant gliomas.

Interferon regulatory factor-1-induced apoptosis mediated by a ligand-independent fas-associated death domain pathway in breast cancer cells

Interferon (IFN) regulatory factor-1 (IRF-1) is a transcription factor that has apoptotic anti-tumor activity. In breast cancer cell types, IRF-1 is implicated in mediating apoptosis by both novel and established anti-tumor agents, including the anti-estrogens tamoxifen and faslodex. Here we demonstrate that in MDA468 breast cancer cells, apoptosis by IFN-gamma is mediated by IRF-1 and IFN-gamma, and IRF-1-induced apoptosis is caspase-mediated. IRF-1 induction results in cleavage of caspase-8, -3 and -7, and application of caspase inhibitors attenuate activated cleavage products. IRF-1-induced apoptosis involves caspase-8 since apoptosis is significantly decreased by the caspase-8-specific inhibitor IETD, c-FLIP expression and in caspase-8-deficient cancer cells. Furthermore, we demonstrate that IRF-1-induced apoptosis requires fas-associated death domain (FADD) since dominant-negative FADD expressing cells resist IRF-1-induced apoptosis and activated downstream products. Immunofluorescent studies demonstrate perinuclear colocalization of FADD and caspase-8. Despite the known role of FADD in mediating death-ligand induced apoptosis, neutralizing antibodies against classical death receptors do not inhibit IRF-1 induced apoptosis, and no secreted ligand appears to be involved since MDA468 coincubated with IRF-1 transfected cells do not apoptose. Therefore, we demonstrate that IRF-1 induces a ligand-independent FADD/caspase-8-mediated apoptosis in breast cancer cells.

Synthetic triterpenoids inhibit growth and induce apoptosis in human glioblastoma and neuroblastoma cells through inhibition of prosurvival Akt, NF-kappaB and Notch1 signaling

Glioblastomas are high-risk primary brain tumors that are generally unresponsive or only weakly responsive to the currently available antineoplastic agents. Thus novel therapeutic strategies and agents are urgently needed to treat these incurable cancers. Oleanolic acid and ursolic acid are naturally occurring triterpenoids that have been used in traditional Asian medicine as anti-inflammatory and anti-cancer agents. Recently, synthetic oleanolic acid triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) and its C-28 methyl ester (CDDO-Me) and C-28 imidazole (CDDO-Im) derivatives have been shown to exhibit potent antitumor activity against diverse types of tumor cell lines, including leukemia, multiple myeloma, osteosarcoma, breast, lung, and pancreatic cancer cell lines; however, the anticancer activity of these agents for brain tumors has not been reported. In the present study, we investigated the apoptosis-inducing activity of CDDOs in glioblastoma (U87MG, U251MG) and neuroblastoma (SK-N-MC) cell lines. Cell growth/viability (MTS) and cytotoxicity (LDH release) assays demonstrated that glioblastoma cell lines are least sensitive to CDDO, but are highly sensitive to CDDO-Me and CDDO-Im at concentrations of 2.5-10 muM. CDDO-Im and CDDO-Me were equipotenent in their growth inhibitory activity. The primary mode of tumor cell destruction was apoptosis as demonstrated by significant increase in the number of hypo-diploid (sub-G0) cells and annexin V-FITC binding. Induction of apoptosis was associated with the activation of procaspases-3, -8, and -9, mitochondrial depolarization and the release of cytochrome c from mitochondria. Furthermore, CDDO-Me inhibited the levels of anti-apoptotic and prosurvival p-Akt, NF-kappaB (p65) and Notch1 signaling molecules. These studies provide rationale for clinical evaluation of these novel agents for the management of lethal brain neoplasms.

ERK1/2 activation attenuates TRAIL-induced apoptosis through the regulation of mitochondria-dependent pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) functions as an extracellular signal, which triggers apoptosis in tumor cells. In order to characterize the molecular events involved in TRAIL cytotoxic signaling, we attempted to determine the role of extracellular signal-regulated kinase 1/2 (ERK1/2), as well as its downstream targets in TRAIL-treated HeLa cells. Here we demonstrate that TRAIL exposure resulted in the activation of ERK1/2, and the elevation of anti-apoptotic Bcl-2 protein levels. ERK1/2 inhibition with PD98059 promoted cell death via the down-regulation of Bcl-2 protein levels, together with increasing mitochondrial damage, including the collapse of mitochondrial membrane potential, the release of cytochrome c from mitochondria to cytoplasm and caspase activity. These results suggest that the ERK1/2 activation is a kind of survival mechanism to struggle against TRAIL-induced stress condition in early stage, via activating cellular defense mechanisms like as the up-regulation of the Bcl-2/Bax ratio, as well as several mitochondrial events.