Induction of apoptosis in glioma cell lines by TRAIL/Apo-2l

Iron(II)-Polypyridyl Complexes Inhibit the Growth of Glioblastoma Tumor and Enhance TRAIL-Induced Cell Apoptosis

A promising cancer-targeting agent for the induction of apoptosis in tumor necrosis factor (TNF) proteins, the TNF-related apoptosis-inducing ligand (TRAIL) ligand, has found limited applications in the treatment of cancer cells, owing to its resistance by cancer cell lines. Therefore, the rational design of anticancer agents that could sensitize cancer cells towards TRAIL is of great significance. Herein, we report that synthetic iron(II)-polypyridyl complexes are capable of inhibiting the proliferation of glioblastoma cancer cells and efficiently enhancing TRAIL-induced cell apoptosis. Mechanistic studies demonstrated that the synthesized complexes induced cancer-cell apoptosis through triggering the activation of p38 and p53 and inhibiting the activation of ERK. Moreover, uPA and MMP-2/MMP-9, among the most important metastatic regulatory proteins, were also found to be significantly alerted after the treatment. Furthermore, we also found that tumor growth in nude mice was significantly inhibited by iron complex Fe2 through the induction of apoptosis without clear systematic toxicity, as indicated by histological analysis. Taken together, this study provides evidence for the further development of metal-based anticancer agents and chemosensitizers of TRAIL for the treatment of human glioblastoma cancer cells.

TNF-related apoptosis-inducing ligand level in Alzheimer's disease

In the present study, we determined the significance of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in Alzheimer's disease (AD). We characterized the expression of TRAIL protein in the cerebrospinal fluid (CSF) and serum with ELISA and TRAIL mRNA in the peripheral blood mononuclear cells (PBMCs) with real-time PCR in 22 patients with AD and 20 control cases. We could not find TRAIL protein in the CSF samples. The concentration of TRAIL protein in sera from patients with AD was not different from controls. However, there was an inverse correlation between serum TRAIL levels and Mini-Mental State Examination scores in AD patients. Also we did not find significant difference in TRAIL mRNA in the PBMCs of patients with AD when compared with control group. Our data indicate that TRAIL serum level decreases in the late stage of disease.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

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.

Radioresponsive tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene therapy for malignant brain tumors

Patients with malignant gliomas have a very poor prognosis. To explore a novel and more effective approach for the treatment of malignant gliomas, a strategy that combined tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene therapy and radiation treatment (RT) was designed in this study. Plasmid pE4-GFP was constructed by including the radioinducible early growth response gene 1 (Egr-1) promoter, and it yielded the best response with fractionated RT. Plasmid pE4-TRAIL was constructed by including the Egr-1 promoter and evaluated using U251 and U87 glioma cells. In the assay of apoptosis and killing activities, pE4-TRAIL exhibited radioresponse. pE4-TRAIL combined with RT is capable of inducing cell death synergistically. The expression of TRAIL death receptors was evaluated; which may be influenced by RT. Glioma cells with wild-type p53 showed upregulated expression of death receptors, and more synergistic effects on killing activities are expected. pE4-TRAIL was transfected into the subcutaneous U251 glioma cells in nude mice by the in vivo electroporation method. In the mice treated with pE4-TRAIL and RT, apoptotic cells were detected in pathological sections, and a significant difference of tumor volumes was observed when compared with the other groups (P<0.001). Our results indicate that radioresponsive gene therapy may have great potential as a novel therapy because this therapeutic system can be spatially or temporally controlled by exogenous RT and provides specificity and safety.

Immunomodulatory neural stem cells for brain tumour therapy

Advances in the understanding of stem cells have enabled the development of novel therapies for brain tumours. Neural stem cells (NSCs) possess the ability to migrate throughout the CNS. By exploiting the tropism of NSCs to various neural pathologies (e.g., glioma, degeneration, stroke and so on) and the delivery of various immunomodulatory cytokines, new treatments for brain tumours have been investigated. These new strategies offer significantly more specificity than existing treatment regimens, such as surgery, radiation and chemotherapy. As methods in isolating and culturing NSCs are better understood, clinical applications of this therapeutic strategy may inevitably emerge. Here, the preclinical advances and the results supporting the effectiveness of stem cell therapies are reviewed. In addition, the obstacles to clinical development and methods to circumvent these caveats are discussed.

TRAIL-induced apoptosis in U-1242 MG glioma cells

Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) induces apoptosis in U-1242 MG cells. To investigate the molecular events involved in this process, we studied the effects of TRAIL on the localization within membrane fractions of molecules critical to the extrinsic apoptotic pathway. We report here that death receptor-5 (DR5), tumor necrosis factor receptor-1 (TNF-R1), and Fas receptor (FasR) are all located in the caveolin-1-enriched membrane fractions, and TRAIL caused the translocation of DR5, FasR, and TNF-R1 to the caveolar fractions. Caspase-8 is mainly located outside of caveolae, but TRAIL caused it to redistribute to the caveolin-1-enriched fractions where it was cleaved. Within 6 hours, the cleaved caspase-8 appeared in the high-density, noncaveolin fractions. Using confocal microscopy, we found that DR5, caspase-8, and caveolin-1 became progressively concentrated in blebs of plasmalemma as they formed in response to TRAIL. Our results provide the first evidence for the caveolar localization of TNF-R1 and DR5 and the coordinated redistribution among membrane fractions of several death receptors in response to TRAIL. We propose that the coordinated movement of these molecules among membrane compartments is probably an important component of the mechanisms regulating and initiating the extrinsic apoptotic pathway in human glioma cells.

Antitumor activity of TRAIL recombinant adenovirus in human malignant glioma cells

Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL) has been reported to specifically kill malignant cells but to be relatively nontoxic to normal cells. One of disadvantages to previous in vivo protocols was the need for large quantities of TRAIL recombinant protein to suppress tumor growth. To evaluate the antitumor activity and therapeutic value of the TRAIL gene, we constructed adenoviral vectors expressing the human TRAIL gene (Ad.hTRAIL) and transferred them into malignant glioma cells in vitro and tumors in vivo, as an alternative to recombinant soluble TRAIL protein. The results show that TRAIL-sensitive glioma cells infected Ad.hTRAIL undergo apoptosis through the production and expression of TRAIL protein. The in vitro transfer elicited apoptosis, as demonstrated by the quantification of viable or apoptotic cells and by the analysis of cleavage of poly (ADP-ribose) polymerase. Furthermore, in vivo administration of Ad.hTRAIL at the site of tumor implantation suppressed the outgrowth of human glioma xenografts in SCID mice. These results further define Ad.hTRAIL as an anti-tumor therapeutic and demonstrate its potential use as an alternative approach to treatment for malignant glioma.

Caspase 8 is absent or low in many ex vivo gliomas

BACKGROUND

Better treatments are required urgently for patients with malignant glioma, which currently is incurable. Death ligands, such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), may offer promise for the treatment high-grade glioma if such ligands induce apoptotic signaling in vivo in glioma cells. Caspase 8 is required for death ligand signaling, and its levels may influence the sensitivity of glioma cells to death ligands. It also may act as a tumor suppressor protein. The authors analyzed caspase 8 expression levels in ex vivo glioma specimens and explored potential mechanisms of its regulation.

METHODS

Eleven glioblastomas, 5 anaplastic astrocytomas, and 3 low-grade astrocytomas were studied. The levels of caspase 8, caspase 10, cellular FLICE inhibitory protein (c-FLIP), and signal transducer and activator of transcription (STAT)-1 were assayed using quantitative immunoblotting. Caspase 8 mRNA was measured by Northern blot analysis. The methylation status of the caspase 8 gene was determined by bisulfate modification of genomic DNA, cloning, and sequencing. Statistical analyses were performed using nonparametric (Spearman) correlations.

RESULTS

Some ex vivo glioma samples lacked detectable caspase 8, with many expressing barely detectable levels. No tumors expressed significant amounts of caspase 10 or c-FLIP. A strong association was found between caspase 8 mRNA and protein levels. Neither expression of the transcription factor STAT-1 nor caspase 8 gene methylation correlated with caspase 8 levels.

CONCLUSIONS

The absence of caspase 8 protein in many resected glioma samples implied that many patients with glioma may not benefit from death ligand-based treatments, unless caspase 8 (or caspase 10) protein expression can be elevated. Demethylating agents are unlikely to boost caspase 8 levels in glioma cells, but treatments that increase caspase 8 mRNA levels may up-regulate expression of the protein.

Stem cell therapies for malignant glioma

The prognosis for patients with malignant glioma, which is the most common primary intracranial neoplasm, remains dismal despite significant progress in neurooncological therapies and technology. This is largely due to the inability of current treatment strategies to address the highly invasive nature of this disease. Malignant glial cells often disseminate throughout the brain, making it exceedingly difficult to target and treat all intracranial neoplastic foci, with the result that tumor recurrence is inevitable despite aggressive surgery and adjuvant radiotherapy and/or chemotherapy. The use of neural stem cells (NSCs) as delivery vehicles for tumor-toxic molecules represents the first experimental strategy aimed specifically at targeting disseminated tumor pockets. Investigators have demonstrated that NSCs possess robust tropism for infiltrating tumor cells, and that they can be used to deliver therapeutic agents directly to tumor satellites, with significant therapeutic benefit. With the aim of developing these findings into a clinically viable technology that would not be hindered by ethical and tissue rejection-related concerns, the use of adult tissue-derived stem cells has recently been explored. These technologies represent important progress in the development of a treatment strategy that can specifically target disseminated neoplastic pockets within the brain. Despite encouraging results in preclinical models, however, there are significant impediments that must be overcome prior to clinical implementation of this strategy. Key among these are an inadequate understanding of the specific tropic mechanisms that govern NSC migration toward invasive tumor, and the need to refine the processes used to generate tumor-tropic stem cells from adult tissues so that this can be accomplished in a clinically practicable fashion. Despite these limitations, the use of stem cell therapies for brain tumors holds significant promise and may emerge as an important therapeutic modality for patients with malignant glioma.

Novel chemotherapeutic agents for the treatment of glioblastoma multiforme

During the last few decades, the discovery of novel targets for therapeutic intervention led to the development of chemotherapeutic agents that specifically interfere with altered cellular functions of tumour cells. Genetic alterations in glioblastoma affect cell proliferation and cell cycle control, as well as invasive and metastatic growth. Therefore, innovative therapeutic strategies have been based on drugs targeting cellular proliferation, invasion, angiogenesis, metastasis and differentiation of tumour cells. Furthermore, disruption of cell-death pathways also contributes to the pathogenesis of glioblastoma and may result in resistance to chemotherapy and radiation. Therefore, additional treatment strategies that target intracellular survival and/or apoptotic pathways are under current laboratory investigation. The progress in the understanding of glioblastoma tumour biology and the refined diagnosis of individual patients together with the exploration of targeted drugs may allow a risk-adapted, individualised therapeutic strategy and will hopefully improve prognosis of glioblastoma patients in the future.

XIAP inhibits caspase-3 and -7 using two binding sites: evolutionarily conserved mechanism of IAPs

The X-linked inhibitor of apoptosis protein (XIAP) uses its second baculovirus IAP repeat domain (BIR2) to inhibit the apoptotic executioner caspase-3 and -7. Structural studies have demonstrated that it is not the BIR2 domain itself but a segment N-terminal to it that directly targets the activity of these caspases. These studies failed to demonstrate a role of the BIR2 domain in inhibition. We used site-directed mutagenesis of BIR2 and its linker to determine the mechanism of executioner caspase inhibition by XIAP. We show that the BIR2 domain contributes substantially to inhibition of executioner caspases. A surface groove on BIR2, which also binds to Smac/DIABLO, interacts with a neoepitope generated at the N-terminus of the caspase small subunit following activation. Therefore, BIR2 uses a two-site interaction mechanism to achieve high specificity and potency for inhibition. Moreover, for caspase-7, the precise location of the activating cleavage is critical for subsequent inhibition. Since apical caspases utilize this cleavage site differently, we predict that the origin of the death stimulus should dictate the efficiency of inhibition by XIAP.

Hypermethylation of the Death-Associated Protein Kinase Promoter Attenuates the Sensitivity to Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand-Induced Apoptosis in Human Non–Small Cell Lung Cancer Cells

Death-associated protein (DAP) kinase plays an important role in IFN-γ, tumor necrosis factor (TNF)-α, or Fas–ligand induced apoptosis. TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF ligand family and can induce caspase-dependent apoptosis in cancer cells while sparing most of the normal cells. However, some of the cancer cell lines are insensitive to TRAIL, and such resistance cannot be explained by the dysfunction of TRAIL receptors or their known downstream targets. We reported previously that DAP kinase promoter is frequently methylated in non-small cell lung cancer (NSCLC), and such methylation is associated with a poor clinical outcome. To determine whether DAP kinase promoter methylation contributes to TRAIL resistance in NSCLC cells, we measured DAP kinase promoter methylation and its gene expression status in 11 NSCLC cell lines and correlated the methylation/expression status with the sensitivity of cells to TRAIL. Of the 11 cell lines, 1 had a completely methylated DAP kinase promoter and no detectable DAP kinase expression, 4 exhibited partial promoter methylation and substantially decreased gene expression, and the other 6 cell lines showed no methylation in the promoter and normal DAP kinase expression. Therefore, the amount of DAP kinase expression amount was negatively correlated to its promoter methylation (r = −0.77; P = 0.003). Interestingly, the cell lines without the DAP kinase promoter methylation underwent substantial apoptosis even in the low doses of TRAIL, whereas those with DAP kinase promoter methylation were resistant to the treatment. The resistance to TRAIL was reciprocally correlated to DAP kinase expression in 10 of the 11 cell lines at 10 ng/mL concentration (r = 0.91; P = 0.001). We treated cells resistant to TRAIL with 5-aza-2′-deoxycytidine, a demethylating reagent, and found that these cells expressed DAP kinase and became sensitive to TRAIL. These results suggest that DAP kinase is involved in TRAIL-mediated cell apoptosis and that a demethylating agent may have a role in enhancing TRAIL-mediated apoptosis in some NSCLC cells by reactivation of DAP kinase.

Sensitization of human glioblastomas to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by NF-kappaB inhibitors

Glioblastoma is the most malignant form of primary brain tumor in adults, with no effective therapy and a low survival rate. TRAIL is a member of the TNF family, which selectively induces apoptosis in certain neoplastic cells, but not normal cells. In this study, we investigated the sensitivity of 7 human glioblastoma cell lines to TRAIL and the expression in them of TRAIL receptors. TRAIL exhibited significant cytotoxicity in 5 of 7 glioma cell lines. These glioblastoma cell lines expressed TRAIL-R2, but not TRAIL-R1, R3, or R4. However, no correlation was observed between the TRAIL sensitivity and the TRAIL-R2 expression level, suggesting that there is an additional determinant of TRAIL sensitivity. Treatments with NF-kappaB inhibitors, such as LLnL, MG132, and SN50, significantly increased the sensitivity of glioma cells to TRAIL. These results suggested that activation of NF-kappaB is a protective mechanism against TRAIL-induced cell death in some glioma cells, and thus NF-kappaB inhibitors may be useful to improve the clinical treatment of glioblastoma with TRAIL.

Caspase-8 levels affect necessity for mitochondrial amplification in death ligand-induced glioma cell apoptosis

Fifty percent of high-grade glioma patients die within a year of diagnosis and less than two percent survive five years postdiagnosis. Elucidating apoptosis signaling pathways may assist in designing better adjuvant therapies. Preliminary characterizations suggested that glioma cells may either employ mitochondrial-independent or -dependent death receptor-induced apoptotic pathways, characteristic of cells termed type I and type II, respectively. In the present study, we generated panels of clonal transfectants overexpressing various levels of Bcl-2, in two parental glioma cell lines. These cells were used to explore molecular factors determining the necessity for mitochondrial amplification of death receptor signaling. Moderate Bcl-2 expression was sufficient to render one glioma cell line (D270) resistant to apoptosis induced by Fas ligand or TRAIL, consistent with these cells being type II. However, expression of even very high levels of Bcl-2 in a second line (D645) did not affect death ligand sensitivity, indicative of a type I phenotype. D270 cells expressed much less caspase-8 protein than D645 cells. Enforced overexpression of caspase-8 (or cytoplasmic Diablo/Smac) in D270 cells overcame Bcl-2 inhibition of death ligand-induced apoptosis, converting them from type II to type I. This indicates that caspase-8 levels can influence the requirement for mitochondrial involvement in death receptor apoptotic signaling in glioma cells.

p53-Dependent Apoptotic Mechanism of a New Designer Bimetallic Compound Tri-phenyl Tin Benzimidazolethiol Copper Chloride (TPT-CuCl2): In Vivo Studies in Wistar Rats as Well as in Vitro Studies in Human Cervical Cancer Cells

We have studied the effect of tri-phenyl tin benzimadazolethiolcopper chloride (TPT-CuCl(2)), a novel bimetallic compound, on the regulation of apoptosis in HeLa cells, MCF-7 cells, and in vivo Wistar rat model. TPT-CuCl(2) induces significant apoptosis in HeLa cell line characterized by DNA fragmentation and chromosome condensation. Comet assay revealed that TPT-CuCl(2) targets and causes severe damage to the DNA. Treatment of HeLa cells with TPT-CuCl(2) rescues the accumulation of p53 from the suppression of human papilloma virus E6, resulting in a dramatic up-regulation of Bax and Bak and down-regulation of the antiapoptotic factor Survivin. Apoptotic induction by TPT-CuCl(2) was shown to mediate in a p53-depedent manner; loss of p53 impairs the release of cytochrome c and Smac/DIABLO from mitochondria to cytosol. Moreover, we have shown that TPT-CuCl(2) induced-apoptosis was through an intrinsic mitochondrial pathway, which was inhibited by viral oncoprotein E1B19K. Caspase-3 was found to be indispensable in TPT-CuCl(2)-triggered apoptosis signaling pathway, because caspase-3 deficient cell line MCF-7 was resistant to TPT-CuCl(2). Furthermore, in vivo studies using C6 glioblastoma xenograft rat model revealed that TPT-CuCl(2) exhibits significant antiproliferative activity against tumor development with minimal cytotoxicity toward normal physiological function of the experimental rats. These findings imply the attractiveness of TPT-CuCl(2) as a drug candidate for further development.

TRAIL and Malignant Glioma

Encouragingly, some types of cancer can now be considered treatable, with patients reasonably expecting their disease to be cured. Chemotherapy and radiation therapy are effective against these cancers because they activate the so-called intrinsic apoptosis pathways within the cancer cells. Unfortunately currently available treatments are only effective against a subset of tumor types. In contrast, other cancers, such as malignant glioma, typically do not respond to currently available therapies. Some of this resistance can be attributed to these tumor cells failing to undergo apoptosis upon anticancer treatment. Recently, considerable research attention has focused on triggering apoptosis in chemotherapy- and radiation-therapy-resistant cancer cells via an alternative route-the "extrinsic" pathway, as a means of bypassing this block in apoptosis. Binding of members of the tumor necrosis factor-alpha (TNF-alpha) family of death ligands to their receptors on the cell surface triggers this pathway. Death ligands can kill some cancer cells that are resistant to the apoptotic pathway triggered by conventional anticancer treatments. Some death ligands, such as TNF-alpha and FasL, cause unacceptable toxicity to normal cells and are therefore not suitable anticancer agents. However another death ligand, TNF-related apoptosis-inducing ligand (TRAIL)/Apo-2L, and antibodies that emulate its actions, show greater promise as candidate anticancer drugs because they have negligible effects on normal cells. This review will discuss the ability of TRAIL to induce apoptosis in malignant glioma cells and the potential clinical applications of TRAIL-based agents for glioma treatment.

TRAIL/Apo2L ligands induce apoptosis in malignant rhabdoid tumor cell lines

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) is a potent inducer of apoptosis in various cancer cells, whereas normal cells are not sensitive to TRAIL-mediated apoptosis. Four TRAIL/Apo2L receptors (DR4, DR5, DcR1, and DcR2) have been identified. DR4 and DR5 have a death domain, whereas DcR1 and DcR2 are called decoy receptors because of their incomplete or lack of a death domain. Malignant rhabdoid tumor (MRT) is an aggressive neoplasm showing a poor prognosis because of its resistance to chemotherapeutic agents. In this study, we examined whether TRAIL could induce apoptotic cell death in MRT cell lines. We found that although half of the MRT cell lines examined were sensitive to TRAIL/Apo2L, Western blot analysis revealed that the expression of DcR2 was low in TRAIL-sensitive MRT cells. We examined the effect of doxorubicin on the expression levels of TRAIL receptors and its enhancement on the susceptibility of MRT cell lines to TRAIL. Western blot and flow cytometric analyses revealed that doxorubicin significantly increased the expression of DR5, and somewhat up-regulated the expression of DR4 and DcR2. Moreover, doxorubicin, NF-kappaB inhibitor (SN50), and PI3-kinase/Akt inhibitor (wortmannin, LY294002) enhanced the susceptibility of MRT cell lines to TRAIL/Apo2L-induced apoptosis. These results suggest that TRAIL/Apo2L may provide the basis for clinical trials of TRAIL-based treatment to improve the outcome of MRT patients.

Expression of antisense bcl-2 cDNA abolishes tumorigenicity and enhances chemosensitivity of human malignant glioma cells

Bcl-2 is a key antiapoptotic protein, and it confers survival advantages on many types of tumors by inhibiting apoptotic cell death. Malignant gliomas are the most common primary central nervous system tumors, but the role of bcl-2 in these tumors has not been defined. We investigated the impact of bcl-2 on malignant gliomas by suppressing its expression. Antisense human bcl-2 cDNA was transfected into human malignant glioma cells. The effects of bcl-2 protein down-regulation on glioma cell morphology, in vitro tumor growth, and tumorigenicity in nude mice, as well as chemosensitivity to cisplatin, were studied. Expression of antisense bcl-2 cDNA decreased bcl-2 protein by more than sixfold. Antisense bcl-2 stable transfectants (AS-bcl-2) showed profound morphological change and markedly retarded cell growth in vitro. Transplantation of AS-bcl-2 cells resulted in no tumor formation, whereas backbone plasmid transfectant control formed tumors in each mouse transplanted. Expression of antisense bcl-2 in glioma cells resulted in significantly increased cytotoxicity of cisplatin. In conclusion, antisense bcl-2 expression can effectively reduce glioma survival, including retarding in vitro growth, complete loss of tumorigenicity, and significantly enhanced cisplatin cytotoxicity. These results suggest that bcl-2 plays an important role in glioma malignancy and chemoresistance. Development of strategies targeted at bcl-2 has the potential to advance treatment for malignant gliomas.

Trail-induced apoptosis and interaction with cytotoxic agents in soft tissue sarcoma cell lines

Five human soft tissue sarcoma (STS) cell lines (HTB-82 rhabdomyosarcoma, HTB-91 fibrosarcoma, HTB-92 liposarcoma, HTB-93 synovial sarcoma and HTB-94 chondrosarcoma) were analysed for their sensitivity to tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and the function of the TRAIL apoptotic pathway in these cells. TRAIL induced significant apoptosis (>90%) in HTB-92 and HTB-93 cells, whereas no effect was observed in HTB-82, HTB-91 and HTB-94 cells. TRAIL-Receptor 1 (TRAIL-R1) was expressed in TRAIL-sensitive HTB-92 and HTB-93 cell lines, but not in TRAIL-resistant HTB-91 and HTB-94 cells. HTB-82 cells, which expressed the long (c-FLIP(L)) and short (c-FLIP(S)) splice variants of the FLICE-like inhibitory protein (FLIP), were resistant to TRAIL in spite of the presence of TRAIL-R1. TRAIL-R2,-R3,-R4 and osteoprotegerin (OPG) expression did not correlate with TRAIL sensitivity. Coincubation of TRAIL and doxorubicin led to the overexpression of TRAIL-R2 resulting in a synergistic effect of doxorubicin and TRAIL in TRAIL-sensitive cell lines and in the overcoming of TRAIL-resistance in all of the TRAIL-resistant cell lines, except HTB-91, which lacked caspase 8 expression. These data suggest that TRAIL, either as a single agent or in combination with cytotoxic agents, might represent a new treatment option for advanced STS, which constitutes a largely chemotherapy-resistant disease.

Interferon gamma and lipopolysaccharide upregulate TNF-related apoptosis-inducing ligand expression in murine microglia

In this study, it is reported that neonatal murine microglia and N9 murine microglial cell line express tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL). TRAIL protein and mRNA expression in murine microglia greatly upregulate upon stimulation with interferon gamma (IFNgamma) or lipopolysaccharide (LPS) as revealed by immunoprecipitation-immunoblotting, reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry techniques. IFNgamma and LPS act synergistically to induce TRAIL expression on both translational and transcriptional levels. The upregulated microglial TRAIL in inflammatory conditions may involve in the cytotoxic effect of these cells and play a role in neurodegenerative processes.

Tumor necrosis factor-related apoptosis-inducing ligand induces caspase-dependent interleukin-8 expression and apoptosis in human astroglioma cells

Among the tumor necrosis factor (TNF) family of cytokines, FasL and TNF-related apoptosis-inducing ligand (TRAIL) are known to induce cell death via caspase activation. Recently, other biological functions of these death ligands have been postulated in vitro and in vivo. It was previously shown that Fas ligation induces chemokine expression in human glioma cells. In this study, we investigated whether the TRAIL-DR5 system transduces signals similar to those induced by other TNF family ligands and receptors. To address this issue, two human glioma cell lines, CRT-MG and U87-MG, were used, and an agonistic antibody against DR5 (TRA-8) and human recombinant TRAIL were used to ligate DR5. We demonstrate that DR5 ligation by either TRAIL or TRA-8 induces two functional outcomes, apoptosis and expression of the chemokine interleukin-8 (IL-8); the nonspecific caspase inhibitor Boc-D-Fmk blocks both TRAIL-mediated cell death and IL-8 production; the caspase 3-specific inhibitor z-DEVD-Fmk suppresses TRAIL-mediated apoptosis but not IL-8 induction; caspase 1- and 8-specific inhibitors block both TRAIL-mediated cell death and IL-8 production; and DR5 ligation by TRAIL mediates AP-1 and NF-kappaB activation, which can be inhibited by caspase 1- and 8-specific inhibitors. These findings collectively indicate that DR5 ligation on human glioma cells leads to apoptosis and that the activation of AP-1 and NF-kappaB leads to the induction of IL-8 expression; these responses are dependent on caspase activation. Therefore, the TRAIL-DR5 system has a role not only as an inducer of apoptotic cell death but also as a transducer for proinflammatory and angiogenic signals in human brain tumors.

Molecular cross-talk between the TRAIL and interferon signaling pathways

TRAIL/APO-2L induces apoptosis in a variety of transformed cells and has potential as an anti-cancer therapeutic. The physiologic role of TRAIL is presumably more complex than merely activating caspase-mediated cell death. To shed light into TRAIL-mediated signaling, we used DNA microarrays to profile gene expression mediated by TRAIL in breast carcinoma cells. Primary response genes induced by TRAIL included a number of known NF-kappaB-dependent genes such as cIAP2, A20, and E-selectin. Remarkably, global transcriptome analysis revealed that TRAIL also induced a cohort of genes related to the interferon-signaling pathway. Assessing interferon-induced gene expression suggested various points of interaction with the TRAIL signaling pathway. Interestingly, while we observed interferon-mediated up-regulation of TRAIL, we also demonstrated a concomitant TRAIL-mediated induction of interferon-beta. Combining TRAIL and interferon in vitro, synergistically induced apoptosis and caspase activation in breast cancer cells. Together, these data indicate multiple levels of molecular cross-talk between the two diverse cytokines with anti-tumor properties.

Death receptor ligands in tumors

Activation of apoptosis via death receptors is a tightly regulated event, and the death pathway itself is open to interference on the part of soluble or membrane-bound decoy receptors. The aggregation state of the death-inducing ligand is a crucial factor, particularly when these molecules are used as recombinant drugs against tumors. Whether tumors are sensitive to such ligands is determined by both the net abundance of death receptors versus decoy receptors and the balance between intracellular apoptotic and antiapoptotic mechanisms. This means that in vivo elimination of tumor cells by effector arms such as T lymphocytes, natural killer cells, macrophages, and dendritic cells is dependent on both the function of activated lymphoid cells and the genetic properties of tumor cells. Death receptor ligands, however, may be a double-edged sword. When expressed on cytotoxic T lymphocytes, natural killer cells, monocytes, and dendritic cells, they induce the apoptosis of many tumor cells, whereas their expression on tumor cells induces the apoptosis of killer cells. The in vivo result is influenced by the number of infiltrating cells, their state of activation, the cytokine repertoire in the tumor microenvironment, and the ability of the tumor to produce soluble factors inhibiting their cytolytic functions.

Analysis of FasL and TRAIL induced apoptosis pathways in glioma cells

FasL and TNF-related apoptosis-inducing ligand (TRAIL) belong to a subgroup of the TNF superfamily which induce apoptosis by binding to their death domain containing receptors. In the present study we have utilized a panel of seven cell lines derived from human malignant gliomas to characterize molecular pathways through which FasL and TRAIL induce apoptosis in sensitive glioma cells and the mechanisms of resistance in cell lines which survive the death stimuli. Our findings indicate that FADD and Caspase-8 are essential for FasL and TRAIL mediated apoptosis in glioma cells. One sensitive cell line (D270) can be protected from FasL and TRAIL induced death by anti-apoptotic Bcl-2 family members while another (D645) cannot, implying that these lines may represent glioma examples of type II and type I cells respectively. For the first time we demonstrate resistance to FasL but not to TRAIL within the one glioma cell line. Furthermore, we report distinct mechanisms of resistance within different glioma lines, including downregulation of Caspase-8 in U373MG. Cycloheximide sensitized four of the resistant cell lines suggesting the presence of labile inhibitors. None of the known apoptosis inhibitors examined accounted for the observed resistance, suggesting novel inhibitors may exist in glioma cells.

Potential and caveats of TRAIL in cancer therapy

Induction of apoptosis in tumor cells is a major goal for chemotherapy and radiation treatment strategies. However, disordered gene expression often leads to apoptosis resistance rendering tumor cells insensitive to various conventional treatments. TNF-related apoptosis-inducing ligand (TRAIL) is a recently identified cytokine of the TNF superfamily that induces apoptosis in tumor cells upon binding to different receptors. Remarkably, the majority of tumor cell lines are sensitive to TRAIL-induced apoptosis, while most nontransformed cell types are TRAIL-resistant. Furthermore, a combination treatment of TRAIL with ionizing irradiation or chemotherapeutic agents induces apoptosis in a highly synergistic manner, particularly in those cells that are otherwise resistant to a sole treatment. In contrast to other TNF members, TRAIL apparently does not exert overt systemic toxicity in murine and primate models, although unexpected concerns about a potential hepatotoxicity of TRAIL have been recently raised. While the molecular mechanisms of TRAIL sensitivity and resistance are poorly understood, TRAIL seems to be a promising biological agent for combination therapy with chemotherapeutic drugs or irradiation.