TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

Human neutrophils ≠ murine neutrophils: Does it matter?

Human and murine neutrophils differ with respect to representation in blood, receptors, nuclear morphology, signaling pathways, granule proteins, NADPH oxidase regulation, magnitude of oxidant and hypochlorous acid production, and their repertoire of secreted molecules. These differences often matter and can undermine extrapolations from murine studies to clinical care, as illustrated by several failed therapeutic interventions based on mouse models. Likewise, coevolution of host and pathogen undercuts fidelity of murine models of neutrophil-predominant human infections. However, murine systems that accurately model the human condition can yield insights into human biology difficult to obtain otherwise. The challenge for investigators who employ murine systems is to distinguish models from pretenders and to know when the mouse provides biologically accurate insights. Testing with human neutrophils observations made in murine systems would provide a safeguard but is not always possible. At a minimum, studies that use exclusively murine neutrophils should have accurate titles supported by data and restrict conclusions to murine neutrophils and not encompass all neutrophils. For now, the integration of evidence from studies of neutrophil biology performed using valid murine models coupled with testing in vitro of human neutrophils combines the best of both approaches to elucidate the mysteries of human neutrophil biology.

Mathematical model of tumor immunotherapy for bladder carcinoma identifies the limitations of the innate immune response

Treatment for non-muscle invasive carcinoma of the bladder represents one of the few examples of successful tumor immunity. Six weekly intravesical instillations of Bacillus Calmette-Guerin (BCG), often followed by maintenance schedule, result in up to 50-70% clinical response. Current models suggest that the mechanism of action involves the non-specific activation of innate effector cells, which may be capable of acting in the absence of an antigen-specific response. For example, recent evidence suggests that BCG-activated neutrophils possess anti-tumor potential. Moreover, weekly BCG treatment results in a prime-boost pattern with massive influx of innate immune cells (107-108 PMN/ml urine). Calibrating in vivo data, we estimate that the number of neutrophil degranulations per instillation is approximately 106-107, more than sufficient to potentially eliminate ~106 residual tumor cells. Furthermore, neutrophils, as well as other innate effector cells are not selective in their targeting-thus surrounding cells may be influenced by degranulation and / or cytokine production. To establish if these observed conditions could account for clinically effective tumor immunity, we built a mathematical model reflecting the early events and tissue conditioning in patients undergoing BCG therapy. The model incorporates key features of tumor growth, BCG instillations and the observed prime / boost pattern of the innate immune response. Model calibration established that each innate effector cell must kill 90-95 bystander cells for achieving the expected 50-70% clinical response. This prediction was evaluated both empirically and experimentally and found to vastly exceed the capacity of the innate immune system. We therefore conclude that the innate immune system alone is unable to eliminate the tumor cells. We infer that other aspects of the immune response (e.g., antigen-specific lymphocytes) decisively contribute to the success of BCG immunotherapy.

The Role of TRAIL/DRs in the Modulation of Immune Cells and Responses

Expression of TRAIL (tumor necrosis factor–related apoptosis–inducing ligand) by immune cells can lead to the induction of apoptosis in tumor cells. However, it becomes increasingly clear that the interaction of TRAIL and its death receptors (DRs) can also directly impact immune cells and influence immune responses. Here, we review what is known about the role of TRAIL/DRs in immune cells and immune responses in general and in the tumor microenvironment in particular.

Neutrophil Degranulation, Plasticity, and Cancer Metastasis

Neutrophils are the first responders to inflammation and infection. Recently, an elevated neutrophil-to-lymphocyte ratio has generally become a prognostic indicator of poor overall survival in cancer. Accordingly, heterogeneous ill-defined neutrophil-like populations have been increasingly recognized as important players in cancer development. In addition, neutrophil granule proteins released upon cell activation have been associated with tumor progression; this differential granule mobilization may allow neutrophils - and possibly associated cancer cells - to leave the bloodstream and enter inflamed/infected tissues. This review discusses and proposes how granule mobilization may facilitate neutrophil-mediated transport of cancer cells into different tissues as well as leading to different cellular phenotypes that underlie remarkable neutrophil plasticity. This concept might inform novel neutrophil-centered approaches to putative cancer therapies.

Biliary tract instillation of a SMAC mimetic induces TRAIL-dependent acute sclerosing cholangitis-like injury in mice

Primary sclerosing cholangitis (PSC) is a cholestatic liver disease of unknown etiopathogenesis characterized by fibrous cholangiopathy of large and small bile ducts. Systemic administration of a murine TNF-related apoptosis-inducing ligand (TRAIL) receptor agonist induces a sclerosing cholangitis injury in C57BL/6 mice, suggesting endogenous TRAIL may contribute to sclerosing cholangitis syndromes. Cellular inhibitor of apoptosis proteins (cIAP-1 and cIAP-2) are negative regulators of inflammation and TRAIL receptor signaling. We hypothesized that if endogenous TRAIL promotes sclerosing cholangitis, then cIAP depletion should also induce this biliary tract injury. Herein, we show that cIAP protein levels are reduced in the interlobular bile ducts of human PSC livers. Downregulation of cIAPs in normal human cholangiocytes in vitro by use of a SMAC mimetic (SM) induces moderate, ripoptosome-mediated apoptosis and RIP1-independent upregulation of proinflammatory cytokines and chemokines. Cytokine and chemokine expression was mediated by the non-canonical activation of NF-κB. To investigate whether downregulation of cIAPs is linked to generation of a PSC-like phenotype, an SM was directly instilled into the mouse biliary tree. Twelve hours after biliary instillation, TUNEL-positive cholangiocytes were identified; 5 days later, PSC-like changes were observed in the SM-treated mice, including a fibrous cholangiopathy of the interlobular bile ducts, portal inflammation, significant elevation of serum markers of cholestasis and cholangiographic evidence of intrahepatic biliary tract injury. In contrast, TRAIL and TRAIL-receptor deficient mice showed no sign of cholangiopathy following SM intrabiliary injection. We conclude that in vivo antagonism of cIAPs in mouse biliary epithelial cells is sufficient to trigger cholangiocytes apoptosis and a proinflammatory response resulting in a fibrous cholangiopathy resembling human sclerosing cholangitis. Therefore, downregulation of cIAPs in PSC cholangiocytes may contribute to the development of the disease. Our results also indicate that inhibition of TRAIL signaling pathways may be beneficial in the treatment of PSC.

Isoproterenol Enhances Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand-Induced Apoptosis in Human Embryonic Kidney Cells through Death Receptor 5 up-Regulation

BACKGROUND AND OBJECTIVES

Chronic impairment of β-adrenergic receptor signaling increases cardiac apoptosis, hypertrophy and fibrosis. The aim of this study was to investigate whether isoproterenol (ISO), an agonist of the adrenergic receptor, can enhance tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human embryonic kidney (HEK) 293 cells.

MATERIALS AND METHODS

HEK 293 cells were treated with ISO and/or TRAIL for 24 hours. Cell viability was evaluated by microscopy and an established viability assay, and apoptotic cell death was analyzed by staining with fluorescein isothiocynate-annexin-V/propidium iodide (PI) and caspase activation. To confirm the mechanism of cell death induced by co-treatment with ISO and TRAIL, expression of TRAIL receptor 2 (death receptor 5, DR5) was evaluated by immunoblotting.

RESULTS

Although ISO or TRAIL treatment decreased HEK 293 cell viability by 13% and 17%, respectively, co-treatment with ISO and TRAIL resulted in a markedly higher death rate of 35% after 24 hours. Increases were evident in early apoptotic cells (i.e., annexin-V positive/PI negative; 19.4%), late apoptotic cells (i.e., annexin-V positive/PI positive; 6.3%) and dead cells (i.e., annexin-V negative/PI positive; 1.1%) when cells were co-treated with ISO and TRAIL, compared to cells treated with either ISO or TRAIL. In addition, marked increases of cleaved cas-3, cleaved poly (adenosine diphosphate-ribose) polymerase and DR5 were observed in HEK 293 cells co-treated with ISO and TRAIL.

CONCLUSION

Treatments combining ISO with TRAIL may be responsible for death of HEK 293 cells through DR5 up-regulation. Activation of adrenergic receptors is responsible for the synergistic cell death observed with TRAIL.

Therapeutic applications of TRAIL receptor agonists in cancer and beyond

TRAIL/Apo-2L is a member of the TNF superfamily first described as an apoptosis-inducing cytokine in 1995. Similar to TNF and Fas ligand, TRAIL induces apoptosis in caspase-dependent manner following TRAIL death receptor trimerization. Because tumor cells were shown to be particularly sensitive to this cytokine while normal cells/tissues proved to be resistant along with being able to synthesize and release TRAIL, it was rapidly appreciated that TRAIL likely served as one of our major physiologic weapons against cancer. In line with this, a number of research laboratories and pharmaceutical companies have attempted to exploit the ability of TRAIL to kill cancer cells by developing recombinant forms of TRAIL or TRAIL receptor agonists (e.g., receptor-specific mAb) for therapeutic purposes. In this review article we will describe the biochemical pathways used by TRAIL to induce different cell death programs. We will also summarize the clinical trials related to this pathway and discuss possible novel uses of TRAIL-related therapies. In recent years, the physiological importance of TRAIL has expanded beyond being a tumoricidal molecule to one critical for a number of clinical settings - ranging from infectious disease and autoimmunity to cardiovascular anomalies. We will also highlight some of these conditions where modulation of the TRAIL/TRAIL receptor system may be targeted in the future.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

The gene signature in CCAAT-enhancer-binding protein α dysfunctional acute myeloid leukemia predicts responsiveness to histone deacetylase inhibitors

C/EPBα proteins, encoded by the CCAAT-enhancer-binding protein α gene, play a crucial role in granulocytic development, and defects in this transcription factor have been reported in acute myeloid leukemia. Here, we defined the C/EBPα signature characterized by a set of genes up-regulated upon C/EBPα activation. We analyzed expression of the C/EBPα signature in a cohort of 525 patients with acute myeloid leukemia and identified a subset characterized by low expression of this signature. We referred to this group of patients as the C/EBPα dysfunctional subset. Remarkably, a large percentage of samples harboring C/EBPα biallelic mutations clustered within this subset. We hypothesize that re-activation of the C/EBPα signature in the C/EBPα dysfunctional subset could have therapeutic potential. In search for small molecules able to reverse the low expression of the C/EBPα signature we applied the connectivity map. This analysis predicted positive connectivity between the C/EBPα activation signature and histone deacetylase inhibitors. We showed that these inhibitors reactivate expression of the C/EBPα signature and promote granulocytic differentiation of primary samples from the C/EBPα dysfunctional subset harboring biallelic C/EBPα mutations. Altogether, our study identifies histone deacetylase inhibitors as potential candidates for the treatment of certain leukemias characterized by down-regulation of the C/EBPα signature.

On the cytokines produced by human neutrophils in tumors

Although traditionally viewed as short-lived innate immunity cells, only playing a crucial role in host defense toward infections, neutrophils have recently become subject of a new wave of research in diverse areas including in tumors. Indeed, increasing experimental evidence indicate that neutrophils may directly or indirectly influence the tumor fate through the release of a wide array of molecules able to exert either pro-tumor or anti-tumor functions depending on the microenvironment milieu, including cytokines. This review therefore attempts to uncover the role that neutrophils play during the different steps of tumor development (from promotion to progression), as well as in anti-tumor responses, via cytokine production.

PMN and anti-tumor immunity--the case of bladder cancer immunotherapy

Urothelial carcinoma of the bladder accounts for ∼5% of all cancer deaths in humans. The majority of bladder tumors are non-muscle invasive at diagnosis, and there is a high rate of tumor recurrence and progression even after local surgical therapy. Thus, many patients require lifelong follow-up examinations that include additional prophylactic treatments in the event of recurrence. Since its first use in 1976, Mycobacterium bovis bacillus Calmette-Guerin (BCG) has been the treatment of choice for non-muscle invasive bladder cancer. Despite nearly 40 years of clinical use, the mechanism(s) by which intravesical administration of BCG results in elimination of bladder tumors remains undefined. Granulocytes (polymorphonuclear neutrophils (PMN)) are the predominant immune cell (in number) that enters the bladder after BCG installation, and a number of studies have highlighted the importance of PMN in the antitumor activity of BCG. Studies from our laboratory demonstrated presence of intracellular stores of the apoptosis-inducing protein TNF-related apoptosis-inducing ligand (TRAIL) in PMN that are rapidly released after interaction with BCG cell wall components, along with a correlation between increased urinary levels of TRAIL and BCG responsiveness. Mature PMN in circulation are terminally differentiated cells with limited biosynthetic capacity, so the proteins located in the distinct PMN granule populations are compartmentalized concomitant with their synthesis during myelopoiesis. Thus, understanding PMN production, localization, and release of TRAIL is important in the design of future BCG-based bladder tumor immunotherapy protocols.

Regulation of the human TRAIL gene

TRAIL is a member of the TNF superfamily that induces tumor-selective cell death by engaging the pro-apoptotic death receptors DR4 and DR5. The antitumor potential of the TRAIL pathway has been targeted by several therapeutic approaches including recombinant TRAIL and TRAIL-receptor agonist antibodies among others. Interest in sensitizing tumor cells to TRAIL-mediated apoptosis has driven investigations of TRAIL-receptor gene regulation, though regulation of the TRAIL gene has been less studied. Physiologically, TRAIL serves as a pro-apoptotic effector molecule in the immune surveillance of cancer that is conditionally expressed by immune cells upon stimulation via an interferon-response element that was identified in early studies of the TRAIL gene promoter. Here, we map the TRAIL gene promoter and review studies of TRAIL gene regulation that involve several modalities of gene regulation including transcription factors, epigenetics, single-nucleotide polymorphisms and functionally distinct isoforms.

Attenuated, oncolytic, but not wild-type measles virus infection has pleiotropic effects on human neutrophil function

We previously showed that neutrophils play a role in regression of human tumor xenografts in immunodeficient mice following oncolytic vaccine measles virus (MV-Vac) treatment. In this study, we sought, using normal human neutrophils, to identify potential neutrophil-mediated mechanisms for the attenuated MV-Vac induced effects seen in vivo, by comparison with those consequent on wild-type (WT-MV) infection. Both MV-Vac and WT-MV infected and replicated within neutrophils, despite lack of SLAM expression. In both cases, neutrophils survived longer ex vivo postinfection. Furthermore, MV-Vac (but not WT-MV) infection activated neutrophils and stimulated secretion of several specific antitumor cytokines (IL-8, TNF-α, MCP-1, and IFN-α) via induction of de novo RNA and protein synthesis. In addition, MV-Vac (but not WT-MV) infection caused TRAIL secretion in the absence of de novo synthesis by triggering release of prefabricated TRAIL, via a direct effect upon degranulation. The differences between the outcome of infection by MV-Vac and WT-MV were not entirely explained by differential infection and replication of the viruses within neutrophils. To our knowledge, this is the first demonstration of potential mechanisms of oncolytic activity of an attenuated MV as compared with its WT parent. Furthermore, our study suggests that neutrophils have an important role to play in the antitumor effects of oncolytic MV.

TNF-related apoptosis-inducing ligand (TRAIL) regulates inflammatory neutrophil apoptosis and enhances resolution of inflammation

Novel therapeutics targeting neutrophilic inflammation are a major unmet clinical need in acute and chronic inflammation. The timely induction of neutrophil apoptosis is critical for inflammation resolution, and it is thought that acceleration of apoptosis may facilitate resolution at inflammatory sites. We previously demonstrated that a death receptor ligand, TRAIL, accelerates neutrophil apoptosis in vitro. We examined the role of TRAIL in neutrophil-dominant inflammation in WT and TRAIL-deficient mice. TRAIL deficiency did not alter constitutive neutrophil apoptosis, whereas exogenous TRAIL accelerated apoptosis of murine peripheral blood neutrophils. We compared TRAIL-deficient and WT mice in two independent models of neutrophilic inflammation: bacterial LPS-induced acute lung injury and zymosan-induced peritonitis. In both models, TRAIL-deficient mice had an enhanced inflammatory response with increased neutrophil numbers and reduced neutrophil apoptosis. Correction of TRAIL deficiency and supraphysiological TRAIL signaling using exogenous protein enhanced neutrophil apoptosis and reduced neutrophil numbers in both inflammatory models with no evidence of effects on other cell types. These data indicate the potential therapeutic benefit of TRAIL in neutrophilic inflammation.

Advances in Viral Vector-Based TRAIL Gene Therapy for Cancer

Numerous biologic approaches are being investigated as anti-cancer therapies in an attempt to induce tumor regression while circumventing the toxic side effects associated with standard chemo- or radiotherapies. Among these, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has shown particular promise in pre-clinical and early clinical trials, due to its preferential ability to induce apoptotic cell death in cancer cells and its minimal toxicity. One limitation of TRAIL use is the fact that many tumor types display an inherent resistance to TRAIL-induced apoptosis. To circumvent this problem, researchers have explored a number of strategies to optimize TRAIL delivery and to improve its efficacy via co-administration with other anti-cancer agents. In this review, we will focus on TRAIL-based gene therapy approaches for the treatment of malignancies. We will discuss the main viral vectors that are being used for TRAIL gene therapy and the strategies that are currently being attempted to improve the efficacy of TRAIL as an anti-cancer therapeutic.

Identification and functional characterization of a human sTRAIL homolog, CasTRAIL, in an invertebrate oyster Crassostrea ariakensis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) is one of the tumor necrosis factor (TNF) superfamily members, participating in many biological processes including apoptosis and immune responses. In present study, a novel human soluble TRAIL (sTRAIL) homolog, CasTRAIL was identified from the oyster, Crassostrea ariakensis. CasTRAIL has a 99% and 98% similarity to human sTRAIL over the cDNA sequence and the amino acid sequence, respectively. It mostly distributes in tissues of the oyster defense system and was mainly localized at cell membrane, and has no cytotoxicity to normal hemocytes of oyster. The phosphorylation state of MAP kinases revealed that CasTRAIL induced a rapid increase in the phospho-ERK and phospho-p38 levels, which indicated that the MAPK pathway was involved in CasTRAIL-mediated signaling. In addition, CasTRAIL also showed an ability of anti-RLO infection which might be through the p38-MAPK activation pathway. Present studies provide an understanding and insight of the biological functions of CasTRAIL.

Control of death receptor ligand activity by posttranslational modifications

The death receptor ligands are involved in many physiological and pathological processes involving triggering of apoptosis, inflammation, proliferation, and activation. The expression of these molecules is reported to be tightly regulated at the transcriptional level. However, over the last few years, an increasing number of data demonstrated that the control of transcription is only one of the mechanisms that manage the expression of the death receptor ligands. Thus, this review is focused on posttranslational regulation of the three main members of this family, namely FasL, TNF-alpha, and TRAIL. We discuss here the importance of distribution, storage, and degranulation of these molecules, as well as their shedding by proteases on the control of death receptor ligands expression and activity.

TNF-related apoptosis-inducing ligand (TRAIL): a new path to anti-cancer therapies

Since its discovery in 1995, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor super family, has been under intense focus because of its remarkable ability to induce apoptosis in malignant human cells while leaving normal cells unscathed. Consequently, activation of the apoptotic signaling pathway from the death-inducing TRAIL receptors provides an attractive, biologically-targeted approach to cancer therapy. A great deal of research has focused on deciphering the TRAIL receptor signaling cascade and intracellular regulation of this pathway, as many human tumor cells possess mechanisms of resistance to TRAIL-induced apoptosis. This review focuses on the current state of knowledge regarding TRAIL signaling and resistance, the preclinical development of therapies targeted at TRAIL receptors and modulators of the pathway, and the results of clinical trials for cancer treatment that have emerged from this base of knowledge. TRAIL-based approaches to cancer therapy vary from systemic administration of recombinant, soluble TRAIL protein with or without the combination of traditional chemotherapy, radiation or novel anti-cancer agents to agonistic monoclonal antibodies directed against functional TRAIL receptors to TRAIL gene transfer therapy. A better understanding of TRAIL resistance mechanisms may allow for the development of more effective therapies that exploit this cell-mediated pathway to apoptosis.

Neutrophil apoptosis and the resolution of infection

Polymorphonuclear leukocytes (PMNs) are the most abundant white cell in humans and an essential component of the innate immune system. PMNs are typically the first type of leukocyte recruited to sites of infection or areas of inflammation. Ingestion of microorganisms triggers production of reactive oxygen species and fusion of cytoplasmic granules with forming phagosomes, leading to effective killing of ingested microbes. Phagocytosis of bacteria typically accelerates neutrophil apoptosis, which ultimately promotes the resolution of infection. However, some bacterial pathogens alter PMN apoptosis to survive and thereby cause disease. Herein, we review PMN apoptosis and the ability of microorganisms to alter this important process.