The receptor for the cytotoxic ligand TRAIL

The multifaceted role of TRAIL signaling in cancer and immunity

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can lead to the induction of apoptosis in tumor or infected cells. However, activation of TRAIL signaling may also trigger nonapoptotic pathways in cancer and in nontransformed cells, that is, immune cells. Here, we review the current knowledge on noncanonical TRAIL signaling. The biological outcomes of TRAIL signaling in immune and malignant cells are presented and explained, with a focus on the role of TRAIL for natural killer (NK) cell function. Furthermore, we highlight the technical difficulties in dissecting the precise molecular mechanisms involved in the switch between apoptotic and nonapoptotic TRAIL signaling. Finally, we discuss the consequences thereof for a therapeutic manipulation of TRAIL in cancer and possible approaches to bypass these difficulties.

Encorafenib enhances TRAIL-induced apoptosis of colorectal cancer cells dependent on p53/PUMA signaling

TRAIL has been demonstrated to play a critical role in the apoptosis of colorectal cancer (CRC) cells, but drug resistance markedly restricts its therapeutic effects. Objectives: This study aims to investigate whether encorafenib can enhance TRAIL-induced apoptosis of colorectal cancer cells and the underlying mechanism. TRAIL was first used to induce CRC cells. CCK-8 assays were conducted for detecting cell viability of TRAIL-induced CRC cells with encorafenib treatment. Flow cytometry was used to detect the cell apoptosis of CRC cells and western blot was used to measure the expressions of apoptosis-related proteins. The expressions of DR4, DR5, p53, and PUMA were then evaluated by qPCR and western blot. After transfecting the interference plasmid of p53 into CRC cells, the expressions of PUMA and DR5 were further explored. TRAIL reduced the cell viability of CRC cells, and the inhibition was further reinforced under co-treatment of TRAIL and encorafenib. Encorafenib also triggered the promotion of CRC cell apoptosis induced by TRAIL. It was also found that encorafenib exerted its promoting effects on cell apoptosis of CRC cells via the elevation of DR5. Besides, encorafenib administration promoted the expression levels of p53 and PUMA in TRAIL-induced CRC cells. Furthermore, p53 knockdown attenuated the expression of PUMA and DR5 in TRAIL-induced CRC cells treated with encorafenib. This study indicates that encorafenib stimulates TRAIL-induced apoptosis of CRC cells dependent on p53/PUMA signaling, which may provide instructions for the treatment of CRC.

Cucurbitacin mediated regulation of deregulated oncogenic signaling cascades and non-coding RNAs in different cancers: Spotlight on JAK/STAT, Wnt/β-catenin, mTOR, TRAIL-mediated pathways

Research over decades has enabled us in developing a better understanding of the multifaceted and heterogeneous nature of cancer. High-throughput technologies have helped the researchers in unraveling of the underlying mechanisms which centrally regulate cancer onset, metastasis and drug resistance. Our rapidly expanding knowledge about signal transduction cascade has added another layer of complexity to already complicated nature of cancer. Deregulation of cell signaling pathways played a linchpin role in carcinogenesis and metastasis. Cucurbitacins have gained tremendous attention because of their remarkable pharmacological properties and considerable ability to mechanistically modulate myriad of cell signaling pathways in different cancers. In this review, we have attempted to provide a mechanistic and comprehensive analysis of regulation of oncogenic pathways by cucurbitacins in different cancers. We have partitioned this review into separate sections for exclusive analysis of each signaling pathway and critical assessment of the knowledge gaps. In this review, we will summarize most recent and landmark developments related to regulation of Wnt/β-catenin, JAK/STAT, mTOR, VEGFR, EGFR and Hippo pathway by cucurbitacins. Moreover, we will also address how cucurbitacins regulate DNA damage repair pathway and TRAIL-driven signaling in various cancers. However, there are still outstanding questions related to regulation of SHH/GLI, TGF/SMAD and Notch-driven pathway by cucurbitacins in different cancers. Future studies must converge on the analysis of full-fledge potential of cucurbitacins by in-depth analysis of these pathways and how these pathways can be therapeutically targeted by cucurbitacins.

Doxorubicin hydrochloride enhanced antitumour effect of CEA-regulated oncolytic virotherapy in live cancer cells and a mouse model

Oncolytic adenovirus (OA) has attracted increasing attention due to their specific proliferation in tumour cells and resulting in lysis of tumour cells. To further improve the antitumour effect of OA, in this study, we combined CD55-TRAIL-IETD-MnSOD (CD55-TMn), a CEA-controlled OA constructed previously, and chemotherapy to investigate their synergistic effect and possible mechanisms. MTT assay was performed to detect antitumour effects. Hoechst 33 342 and flow cytometric analysis were used to examine cell apoptosis. Western blotting was performed to examine cell pyroptosis and apoptosis mechanism. Animal experiment was used to detect antitumour effect of doxorubicin hydrochloride (Dox) combined with CD55-TMn in vivo. We firstly found that Dox promotes gene expression mediated by CEA-regulated OA and virus progeny replication by activating phosphorylation of Smad3, and Dox can enhance antitumour effect of CEA-regulated CD55-TMn by promoting cell apotopsis and cell pyroptosis. Thus, our results provide an experimental and theoretical basis on tumour therapy by combination treatment of the oncolytic virotherapy and chemotherapy and it is expected to become a novel strategy for liver cancer therapy.

TRAIL receptor agonists convert the response of breast cancer cells to ONC201 from anti-proliferative to apoptotic

ONC201 was initially identified as an inducer of cell death through the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway. The compound is currently being tested in patients with hematological malignancies and solid tumors, including those of the breast. We investigated strategies to convert the response of breast cancers to ONC201 from anti-proliferative to apoptotic. ONC201 treatment upregulates TRAIL and primes TRAIL-resistant non-triple negative breast cancer (TNBC) cells to undergo cell death through the extrinsic pathway. Remarkably, the addition of exogenous recombinant human TRAIL (rhTRAIL) converts the response of TRAIL-resistant non-TNBC cells to ONC201 from anti-proliferative to apoptotic in a death receptor 5 (DR5)-dependent manner in vitro. Importantly, normal fibroblasts do not undergo apoptosis following rhTRAIL plus ONC201. In vivo, MDA-MB-361 tumor growth rate is significantly reduced following treatment with a combination of ONC201 and rhTRAIL as compared to control tumors. Natural killer (NK) cells which use TRAIL to kill DR5-expressing cancer cells, exhibit greater cytotoxicity against ONC201-treated breast cancer cells compared to controls. rhTRAIL also converts the response of cells from other tumor types to ONC201 from anti-proliferative to apoptotic. A monoclonal DR5-agonistic antibody converts the response of non-TNBC cells to ONC201 from anti-proliferative to apoptotic. Our findings describe a novel therapeutic strategy that potently converts the response of a cancer cell to ONC201 from anti-proliferative to apoptotic. This approach may be clinically relevant and has potential to induce tumor regression of patient tumors with relative resistance to ONC201 monotherapy.

Noncompetitive Allosteric Antagonism of Death Receptor 5 by a Synthetic Affibody Ligand

Fatty acid-induced upregulation of death receptor 5 (DR5) and its cognate ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), promotes hepatocyte lipoapoptosis, which is a key mechanism in the progression of fatty liver disease. Accordingly, inhibition of DR5 signaling represents an attractive strategy for treating fatty liver disease. Ligand competition strategies are prevalent in tumor necrosis factor receptor antagonism, but recent studies have suggested that noncompetitive inhibition through perturbation of the receptor conformation may be a compelling alternative. To this end, we used yeast display and a designed combinatorial library to identify a synthetic 58-amino acid affibody ligand that specifically binds DR5. Biophysical and biochemical studies show that the affibody neither blocks TRAIL binding nor prevents the receptor-receptor interaction. Live-cell fluorescence lifetime measurements indicate that the affibody induces a conformational change in transmembrane dimers of DR5 and favors an inactive state of the receptor. The affibody inhibits apoptosis in TRAIL-treated Huh-7 cells, an in vitro model of fatty liver disease. Thus, this lead affibody serves as a potential drug candidate, with a unique mechanism of action, for fatty liver disease.

Insulin-like growth factor binding protein 3 chemosensitizes pancreatic ductal adenocarcinoma through its death receptor

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human malignancies. Gemcitabine and doxorubicin are commonly used as the chemotherapy agents, but most of PDAC tumors eventually acquired resistance to chemotherapy. Accumulating evidence indicates that Insulin-like growth factor binding protein 3 (IGFBP-3) plays a key role against tumor growth but its expression has commonly suppressed. The present study was designed to evaluate IGFBP-3 effects in chemotherapy sensitization of PDAC cells. Here, we report that the re-sensitization of chemoresistant PDAC cells was occurred by IGFBP-3 through recruitment of its death receptor (IGFBP-3R). Using gemcitabine, doxorubicin-resistant PDAC cell lines, we found that IGFBP-3 sensitized chemoresistant cells by activating apoptosis (as evaluated by Bax up-regulation, Bcl-2 down-regulation as well as Caspase-3 and Caspase 8 activation). IGFBP-3R was also found to have higher expression level in resistant AsPc-1 and MIA PaCa-2 cells in comparison to parental cells. IGFBP-3R was also highly expressed in PDAC tumor which exposed to chemotherapy in comparison to un-treated PDAC tumors. In addition, we confirmed our finding by using specific siRNA to knocking down of IGFBP-3R which prevents IGFBP-3 Chemosensitization. Taken together, the present study for the first time indicates the clinical relevance for combining IGFBP-3 with chemotherapy to reduce chemoresistance in PDAC.

Death Receptors and Their Ligands in Inflammatory Disease and Cancer

On binding to their cognate ligands, death receptors can initiate a cascade of events that can result in two distinct outcomes: gene expression and cell death. The study of three different death receptor-ligand systems, the tumor necrosis factor (TNF)-TNF receptor 1 (TNFR1), the CD95L-CD95, and the TNF-related apoptosis-inducing ligand (TRAIL)-TRAIL-R1/2 system, has drawn the attention of generations of scientists over the past 50 years. This scientific journey, as often happens in science, has been anything but a straight line to success and discoveries in this field were often made by serendipity, catching the scientists by surprise. However, as Louis Pasteur pointed out, luck prefers the prepared mind. It is therefore not surprising that the most impactful discovery of the field to date, the fact that TNF inhibition serves as an effective treatment for several inflammatory and autoimmune diseases, has been like this. Luckily, the scientists who made this discovery were prepared and, most importantly, determined to harness their discovery for therapeutic benefit. Today's research on these death receptor-ligand systems has led to the discovery of a causal link between cell death induced by a variety of these systems and inflammation. In this review, we explain why we predict that therapeutic exploitation of this discovery may profoundly impact the future treatment of inflammatory disease and cancer.

Hantavirus Inhibits TRAIL-Mediated Killing of Infected Cells by Downregulating Death Receptor 5

Cytotoxic lymphocytes normally kill virus-infected cells by apoptosis induction. Cytotoxic granule-dependent apoptosis induction engages the intrinsic apoptosis pathway, whereas death receptor (DR)-dependent apoptosis triggers the extrinsic apoptosis pathway. Hantaviruses, single-stranded RNA viruses of the order Bunyavirales, induce strong cytotoxic lymphocyte responses in infected humans. Cytotoxic lymphocytes, however, are largely incapable of eradicating hantavirus-infected cells. Here, we show that the prototypic hantavirus, Hantaan virus (HTNV), induces TRAIL production but strongly inhibits TRAIL-mediated extrinsic apoptosis induction in infected cells by downregulating DR5 cell surface expression. Mechanistic analyses revealed that HTNV triggers both 26S proteasome-dependent degradation of DR5 through direct ubiquitination of DR5 and hampers DR5 transport to the cell surface. These results corroborate earlier findings, demonstrating that hantavirus also inhibits cytotoxic cell granule-dependent apoptosis induction. Together, these findings show that HTNV counteracts intrinsic and extrinsic apoptosis induction pathways, providing a defense mechanism utilized by hantaviruses to inhibit cytotoxic cell-mediated eradication of infected cells.

Osteoclast-associated receptor blockade prevents articular cartilage destruction via chondrocyte apoptosis regulation

Osteoarthritis (OA), primarily characterized by articular cartilage destruction, is the most common form of age-related degenerative whole-joint disease. No disease-modifying treatments for OA are currently available. Although OA is primarily characterized by cartilage destruction, our understanding of the processes controlling OA progression is poor. Here, we report the association of OA with increased levels of osteoclast-associated receptor (OSCAR), an immunoglobulin-like collagen-recognition receptor. In mice, OSCAR deletion abrogates OA manifestations, such as articular cartilage destruction, subchondral bone sclerosis, and hyaline cartilage loss. These effects are a result of decreased chondrocyte apoptosis, which is caused by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in induced OA. Treatments with human OSCAR-Fc fusion protein attenuates OA pathogenesis caused by experimental OA. Thus, this work highlights the function of OSCAR as a catabolic regulator of OA pathogenesis, indicating that OSCAR blockade is a potential therapy for OA.

Osteoarthritis (OA) is associated with cartilage disruption, but the underlying mechanisms remain unclear. Here, the authors show that expression of osteoclast-associated receptor (OSCAR) is associated with OA, that its genetic ablation or targeting with OSCAR-Fc fusion protein ameliorates OA in mice by decreasing chondrocyte apoptosis.

Insight into the divergent role of TRAIL in non-neoplastic neurological diseases

Tumour necrosis factor–related apoptosis‐inducing ligand (TRAIL) is a member of the tumour necrosis factor (TNF) superfamily which mainly induces apoptosis of tumour cells and transformed cell lines with no systemic toxicity, whereas they share high sequence homology with TNF and CD95L. These unique effects of TRAIL have made it an important molecule in oncology research. However, the research on TRAIL‐related antineoplastic agents has lagged behind and has been limited by the extensive drug resistance in cancer cells. Given the several findings showing that TRAIL is involved in immune regulation and other pleiotropic biological effects in non‐malignant cells, TRAIL and its receptors have attracted widespread attention from researchers. In the central nervous system (CNS), TRAIL is highly correlated with malignant tumours such as glioma and other non‐neoplastic disorders such as acute brain injury, CNS infection and neurodegenerative disease. Many clinical and animal studies have revealed the dual roles of TRAIL in which it causes damage by inducing cell apoptosis, and confers protection by enhancing both pro‐ and non‐apoptosis effects in different neurological disorders and at different sites or stages. Its pro‐apoptotic effect produces a pro‐survival effect that cannot be underestimated. This review extensively covers in vitro and in vivo experiments and clinical studies investigating TRAIL. It also provides a summary of the current knowledge on the TRAIL signalling pathway and its involvement in pathogenesis, diagnosis and therapeutics of CNS disorders as a basis for future research.

IL13Rα1 protects against rheumatoid arthritis by combating the apoptotic resistance of fibroblast-like synoviocytes

Background

Endoplasmic reticulum (ER) stress is closely related with the pathological progression of rheumatoid arthritis (RA), and fibroblast-like synoviocytes (FLSs) are known as its resistance against ER stress-induced apoptosis. Studies on overcoming such resistance would provide a novel treatment strategy for RA in a clinical setting.

Methods

IL13Rα1 expression was assessed in the synovial tissue by RT-qPCR, immunohistology, and Western blot. Gain or loss of functional analysis was applied to evaluate the biological roles of IL13Rα1 in RA FLSs. Cell viability and apoptosis were assessed by MTS, Western blot, and flow cytometry. The therapeutic effects of IL13Rα1 on the severity of type II collagen-induced arthritis (CIA) in DBA-/1 mouse model were evaluated by scoring synovitis, hyperplasia, cartilage degradation, and bone destruction.

Results

IL13Rα1 expression was selectively downregulated when RA FLSs were stimulated by ER stress inducers. Functionally, IL13Rα1 overexpression could inhibit the viability, but induce the apoptosis of RA FLSs in the presence of ER stress inducers. Mechanistically, IL13Rα1 promotes cell apoptosis via transcriptionally activating trail expression. Besides, IL13Rα1 could interact and stabilize DR5 protein, thus forming a positive loop involving trail and DR5 to render RA FLSs more susceptible to apoptosis. Additionally, intraarticular injection of IL13Rα1 conferred therapeutic effects in CIA models and showed a limited degree of synovial proliferation and joint destruction.

Conclusions

Together, our data establishes a regulatory role for IL13Rα1 to combat the apoptotic resistance of RA FLSs against ER stress. The inhibitory effects of IL13Rα1 on arthritis progression suggest the therapeutic potential in RA.

Tumor cellular membrane camouflaged liposomes as a non-invasive vehicle for genes: specific targeting toward homologous gliomas and traversing the blood-brain barrier

Gene therapy aimed at malignant gliomas has shown limited success to date due in part to the inability of conventional gene vectors to achieve widespread and specific gene transfer throughout the highly disseminated tumor zone within the brain. Herein, cationic micelles assembled from vitamin E succinate-grafted ε-polylysine (VES-g-PL) polymers were first exploited to condense TRAIL plasmids (pDNA). Thereafter, the condensed pDNA was further encapsulated into liposomes camouflaged with tumor cellular membrane. The condensed pDNA was successfully encapsulated into the inner aqueous compartments of the liposomes instead of the surface, which was proved based on the TEM morphology and decreased cytotoxicity toward HUVEC and PC-12 cells. Moreover, glioma cell membrane (CM) was easily inlaid into the lipid layer of the pDNA-loaded liposomes to form T@VP-MCL, as shown via TEM, AFM, and SDS-PAGE analysis. T@VP-MCL exhibited good particle size stability at strong ion strength and effectively protected pDNA from DNase I induced degradation. Owing to the CM-associated proteins, T@VP-MCL specifically targeted not only ICAM-1 overexpressed in glioma RBMECs but also homogenous glioma cells. Moreover, in vivo imaging showed that T@VP-MCL was effectively located in orthotopic gliomas of rats after intravenous administration, resulting in effective tumor growth inhibition, prolonging the lives of the rats. The mechanism of T@VP-MCL traversing the BBB was highly associated with the down-regulation of the tight junction-associated proteins ZO-1 and claudin-5. Conclusively, T@VP-MCL designed herein may be a potential carrier for therapeutic genes.

Targeting apoptosis in cancer therapy

For over three decades, a mainstay and goal of clinical oncology has been the development of therapies promoting the effective elimination of cancer cells by apoptosis. This programmed cell death process is mediated by several signalling pathways (referred to as intrinsic and extrinsic) triggered by multiple factors, including cellular stress, DNA damage and immune surveillance. The interaction of apoptosis pathways with other signalling mechanisms can also affect cell death. The clinical translation of effective pro-apoptotic agents involves drug discovery studies (addressing the bioavailability, stability, tumour penetration, toxicity profile in non-malignant tissues, drug interactions and off-target effects) as well as an understanding of tumour biology (including heterogeneity and evolution of resistant clones). While tumour cell death can result in response to therapy, the selection, growth and dissemination of resistant cells can ultimately be fatal. In this Review, we present the main apoptosis pathways and other signalling pathways that interact with them, and discuss actionable molecular targets, therapeutic agents in clinical translation and known mechanisms of resistance to these agents.

TRAIL signals, extracellular matrix and vessel remodelling

The extracellular matrix (ECM) is an essential part of the vasculature, not only providing structural support to the blood vessel wall, but also in its ability to interact with cells to regulate cell phenotype and function including proliferation, migration, differentiation and death – processes important in vascular remodelling. Increasing evidence implicates TNF-related apoptosis-inducing ligand (TRAIL) signalling in the modulation of vascular cell function and remodelling under normal and pathological conditions such as in atherosclerosis. TRAIL can also stimulate synthesis of multiple ECM components within blood vessels. This review explores the relationship between TRAIL signals, the ECM, and its implications in vessel remodelling in cardiovascular disease.

On the TRAIL of Better Therapies: Understanding TNFRSF Structure-Function

Tumor necrosis factor (TNF) superfamily ligands show diverse biological functions, such as the induction of apoptotic cell death or cell survival and proliferation, making them excellent therapeutic targets for cancer and autoimmunity. We review the latest literature on TNF receptor superfamily signaling with a focus on structure-function. Using combinatorics, we argue that receptors that cluster on the cell surface and are activated by membrane-bound ligands need to arrange in a highly ordered manner, as the probability of random ligand and receptor arrangements matching up for receptor activation is very low. A growing body of evidence indicates that antiparallel receptor dimers that sequester the ligand binding site cluster on the cell surface, forming a hexagonal lattice. Upon ligand binding, this arrangement puts the activated receptors at the right distance to accommodate the downstream signaling partners. The data also suggest that the same geometry is utilized regardless of receptor type. The unified model provides important clues about TNF receptor signaling and should aid the design of better therapies for cancer and various immune mediated diseases.

Mechanism of cargo recognition by retromer-linked SNX-BAR proteins

Endocytic recycling of internalized transmembrane proteins is essential for many important physiological processes. Recent studies have revealed that retromer-related Sorting Nexin family (SNX)–Bin/Amphiphysin/Rvs (BAR) proteins can directly recognize cargoes like cation-independent mannose 6-phosphate receptor (CI-MPR) and Insulin-like growth factor 1 receptor (IGF1R); however, it remains poorly understood how SNX-BARs select specific cargo proteins and whether they recognize additional ligands. Here, we discovered that the binding between SNX-BARs and CI-MPR or IGF1R is mediated by the phox-homology (PX) domain of SNX5 or SNX6 and a bipartite motif, termed SNX-BAR-binding motif (SBM), in the cargoes. Using this motif, we identified over 70 putative SNX-BAR ligands, many of which play critical roles in apoptosis, cell adhesion, signal transduction, or metabolite homeostasis. Remarkably, SNX-BARs could cooperate with both SNX27 and retromer in the recycling of ligands encompassing the SBM, PDZ-binding motif, or both motifs. Overall, our studies establish that SNX-BARs function as a direct cargo-selecting module for a large set of transmembrane proteins transiting the endosome, in addition to their roles in phospholipid recognition and biogenesis of tubular structures.

Internalized transmembrane proteins can be recognized by specific protein complexes and diverted away from the degradation process. This study identifies a new sorting motif recognized by retromer-linked SNX-BAR proteins and reveals a large repertoire of potential cargoes recycled by the SNX-BAR proteins.

TRAIL receptor signaling: From the basics of canonical signal transduction toward its entanglement with ER stress and the unfolded protein response

The cytokine tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the large TNF superfamily that can trigger apoptosis in transformed or infected cells by binding and activating two receptors, TRAIL receptor 1 (TRAILR1) and TRAIL receptor 2 (TRAILR2). Compared to other death ligands of the same family, TRAIL induces apoptosis preferentially in malignant cells while sparing normal tissue and has therefore been extensively investigated for its suitability as an anti-cancer agent. Recently, it was noticed that TRAIL receptor signaling is also linked to endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The role of TRAIL receptors in regulating cellular apoptosis susceptibility therefore is broader than previously thought. Here, we provide an overview of TRAIL-induced signaling, covering the core signal transduction during extrinsic apoptosis as well as its link to alternative outcomes, such as necroptosis or NF-κB activation. We discuss how environmental factors, transcriptional regulators, and genetic or epigenetic alterations regulate TRAIL receptors and thus alter cellular TRAIL susceptibility. Finally, we provide insight into the role of TRAIL receptors in signaling scenarios that engage the unfolded protein response and discuss how these findings might be translated into new combination therapies for cancer treatment.

Targeting apoptotic caspases in cancer

Members of the caspase family of proteases play essential roles in the initiation and execution of apoptosis. These caspases are divided into two groups: the initiator caspases (caspase-2, -8, -9 and -10), which are the first to be activated in response to a signal, and the executioner caspases (caspase-3, -6, and -7) that carry out the demolition phase of apoptosis. Many conventional cancer therapies induce apoptosis to remove the cancer cell by engaging these caspases indirectly. Newer therapeutic applications have been designed, including those that specifically activate individual caspases using gene therapy approaches and small molecules that repress natural inhibitors of caspases already present in the cell. For such approaches to have maximal clinical efficacy, emerging insights into non-apoptotic roles of these caspases need to be considered. This review will discuss the roles of caspases as safeguards against cancer in the context of the advantages and potential limitations of targeting apoptotic caspases for the treatment of cancer.

Targeting PP2A inhibits the growth of triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) does not respond to widely used targeted/endocrine therapies because of the absence of progesterone and estrogen receptors and HER2 amplification. It has been shown that the majority of TNBC cells are highly sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, but the development of TRAIL resistance limits its efficacy. We previously found that protein phosphatase 2A (PP2A) plays an important role in TRAIL resistance. In this study, we evaluated the effects of PP2A inhibition on cell death in TRAIL-resistant TNBC cells. We found that the PP2A inhibitor LB-100 effectively inhibits the growth of a panel of TNBC cell lines including lines that are intrinsically resistant to TRAIL. Using two TRAIL-resistant cell lines generated from TRAIL-sensitive parental cells (MDA231 and SUM159), we found that both TRAIL-sensitive and -resistant cell lines are equally sensitive to LB-100. We also found that LB-100 sensitizes TNBC cells to clinically used chemotherapeutical agents, including paclitaxel and cisplatin. Importantly, we found that LB-100 effectively inhibits the growth of MDA468 tumors in mice in vivo without apparent toxicity. Collectively, these data suggest that pharmacological inhibition of PP2A activity could be a novel therapeutic strategy for treating patients with TNBC in a clinical setting.

Therapeutic Mesenchymal Stromal Cells for Immunotherapy and for Gene and Drug Delivery

Mesenchymal stromal cells (MSCs) possess several fairly unique properties that, when combined, make them ideally suited for cellular-based immunotherapy and as vehicles for gene and drug delivery for a wide range of diseases and disorders. Key among these are: (1) their relative ease of isolation from a variety of tissues; (2) the ability to be expanded in culture without a loss of functionality, a property that varies to some degree with tissue source; (3) they are relatively immune-inert, perhaps obviating the need for precise donor/recipient matching; (4) they possess potent immunomodulatory functions that can be tailored by so-called licensing in vitro and in vivo; (5) the efficiency with which they can be modified with viral-based vectors; and (6) their almost uncanny ability to selectively home to damaged tissues, tumors, and metastases following systemic administration. In this review, we summarize the latest research in the immunological properties of MSCs, their use as immunomodulatory/anti-inflammatory agents, methods for licensing MSCs to customize their immunological profile, and their use as vehicles for transferring both therapeutic genes in genetic disease and drugs and genes designed to destroy tumor cells.

Targeted IgMs agonize ocular targets with extended vitreal exposure

Treatment of ocular disease is hindered by the presence of the blood-retinal barrier, which restricts access of systemic drugs to the eye. Intravitreal injections bypass this barrier, delivering high concentrations of drug to the targeted tissue. However, the recommended dosing interval for approved biologics is typically 6-12 weeks, and frequent travel to the physician's office poses a substantial burden for elderly patients with poor vision. Real-world data suggest that many patients are under-treated. Here, we investigate IgMs as a novel platform for treating ocular disease. We show that IgMs are well-suited to ocular administration due to moderate viscosity, long ocular exposure, and rapid systemic clearance. The complement-dependent cytotoxicity of IgMs can be readily removed with a P436G mutation, reducing safety liabilities. Furthermore, dodecavalent binding of IgM hexamers can potently activate pathways implicated in the treatment of progressive blindness, including the Tie2 receptor tyrosine kinase signaling pathway for the treatment of diabetic macular edema, or the death receptor 4 tumor necrosis family receptor pathway for the treatment of wet age-related macular degeneration. Collectively, these data demonstrate the promise of IgMs as therapeutic agonists for treating progressive blindness.

Combination of the natural compound Periplocin and TRAIL induce esophageal squamous cell carcinoma apoptosis in vitro and in vivo: Implication in anticancer therapy

BACKGROUND

Esophageal cancer is one of the most common malignant tumors in the world. With currently available therapies, only 20% ~ 30% patients can survive this disease for more than 5 years. TRAIL, a natural ligand for death receptors that can induce the apoptosis of cancer cells, has been explored as a therapeutic agent for cancers, but it has been reported that many cancer cells are resistant to TRAIL, limiting the potential clinical use of TRAIL as a cancer therapy. Meanwhile, Periplocin (CPP), a natural compound from dry root of Periploca sepium Bge, has been studied for its anti-cancer activity in a variety of cancers. It is not clear whether CPP and TRAIL can have activity on esophageal squamous cell carcinoma (ESCC) cells, or whether the combination of these two agents can have synergistic activity.

METHODS

We used MTS assay, flow cytometry and TUNEL assay to detect the effects of CPP alone or in combination with TRAIL on ESCC cells. The mechanism of CPP enhances the activity of TRAIL was analyzed by western blot, dual luciferase reporter gene assay and chromatin immunoprecipitation (ChIP) assay. The anti-tumor effects and the potential toxic side effects of CPP alone or in combination with TRAIL were also evaluated in vivo.

RESULTS

In our studies, we found that CPP alone or in combination with TRAIL could inhibit the proliferation of ESCC cells and induce apoptosis, and we certificated that combination of two agents exert synergized functions. For the first time, we identified FoxP3 as a key transcriptional repressor for both DR4 and DR5. By down-regulating FoxP3, CPP increases the expression of DR4/DR5 and renders ESCC cells much more sensitive to TRAIL. We also showed that CPP reduced the expression of Survivin by inhibiting the activity of Wnt/β-catenin pathway. All these contributed to synergistic activity of CPP and TRAIL on ESCC cells in vitro and in vivo.

CONCLUSION

Our data suggest that CPP and TRAIL could be further explored as potential therapeutic approach for esophageal cancer.

TRAIL-based gene delivery and therapeutic strategies

TRAIL (tumor necrosis factor-related apoptosis-inducing ligand), also known as APO2L, belongs to the tumor necrosis factor family. By binding to the death receptor 4 (DR4) or DR5, TRAIL induces apoptosis of tumor cells without causing side toxicity in normal tissues. In recent years TRAIL-based therapy has attracted great attention for its promise of serving as a cancer drug candidate. However, the treatment efficacy of TRAIL protein was under expectation in the clinical trials because of the short half-life and the resistance of cancer cells. TRAIL gene transfection can produce a "bystander effect" of tumor cell killing and provide a potential solution to TRAIL-based cancer therapy. In this review we focus on TRAIL gene therapy and various design strategies of TRAIL DNA delivery including non-viral vectors and cell-based TRAIL therapy. In order to sensitize the tumor cells to TRAIL-induced apoptosis, combination therapy of TRAIL DNA with other drugs by the codelivery methods for yielding a synergistic antitumor efficacy is summarized. The opportunities and challenges of TRAIL-based gene delivery and therapy are discussed.

Delivery of TRAIL-expressing plasmid DNA to cancer cells in vitro and in vivo using aminoglycoside-derived polymers

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a death ligand that can preferentially induce apoptosis in cancer cells over normal cells. The transmembrane form of TRAIL has been shown to elicit much stronger activity than its soluble counterpart but delivery is a potential challenge. Here, we investigated the potential of aminoglycoside-derived polymers to enhance delivery of a plasmid (pEF-TRAIL) that expresses the transmembrane form of TRAIL in order to determine the effect on cell death in vitro and tumor growth in vivo. Transgene delivery efficacy and toxicity of aminoglycoside-derived polymers was first evaluated using a GFP-expressing plasmid (pEF-GFP) at different plasmid amounts and plasmid : polymer ratios in UMUC3 bladder cancer and HeLa cervical cancer cells. Delivery of the TRAIL plasmid using aminoglycoside-derived polymers resulted in up to 60% cell death in UMUC3 and HeLa cells; TRAIL protein expression was confirmed using Western blots. TRAIL plasmid delivery resulted in a decrease in cellular procaspase-8 and an increase in TRAIL receptor DR5 levels, suggesting a role for the death receptor and caspase cascade in TRAIL-mediated apoptosis. The TRAIL plasmid did not cause cell death in normal human or mouse fibroblasts. The in vivo delivery of the TRAIL plasmid using a paromomycin-derived polymer resulted in significant reduction in tumor burden and increased survival in tumor-bearing live mice.

Trimer form of tumor necrosis factor-related apoptosis inducing ligand induces apoptosis in canine cell lines derived from mammary tumors

We evaluated the cytotoxic effect of isoleucine-zipper tumor necrosis factor-related apoptosis inducing ligand (izTRAIL) against cell lines, B101592, Cha, and C090115, derived from canine mammary gland tumors. These cells were derived from three dogs diagnosed with mammary adenoma or carcinoma. All three cells were positive for vimentin, while B101592 and C090115 were positive for cytokeratin (CK) AE1/AE3 and CK CAM5.2. Treatment with izTRAIL decreased the viability of the three cell lines. The proportion of annexin V+/propidium iodide- cells increased in all three cell lines after treatment with izTRAIL. Additionally, cell cycle analysis revealed that izTRAIL treatment increased the number of cells in sub-G1 phase. Moreover, izTRAIL treatment activated caspase-8 and caspase-3 and enhanced the levels of cleaved poly (ADP-ribose) polymerase. The cytotoxic effect of izTRAIL was mitigated upon co-treatment with caspase-8 or caspase-3 inhibitor. These results indicated that izTRAIL induces apoptosis in cell lines derived from canine mammary tumor, which was also previously reported in canine hemangiosarcoma cell lines. This suggested that canine tumor cells have conserved TRAIL receptors. This study will provide the basis for further studies on TRAIL receptors and TRAIL-related molecules.

Circulating Dkk1 and TRAIL Are Associated With Cognitive Decline in Community-Dwelling, Older Adults With Cognitive Concerns

Background

Osteoporosis and Alzheimer's disease are common diseases of aging that would seem to be unrelated, but may be linked through the influence of bone-derived signals on brain function. The aim of the current study is to investigate the relationship between circulating levels of bone-related biomarkers and cognition.

Methods

The population included 103 community-dwelling older individuals with memory concerns but without cognitive impairment. A global cognition summary measure was collected at baseline and 6, 12, and 18 months post-enrollment by converting raw scores from 19 cognitive function tests to z-scores and averaging. Baseline plasma concentrations of bone-related biomarkers, including undercarboxylated, carboxylated, and total osteocalcin, parathyroid hormone, C-terminal telopeptide of collagen 1 (CTX-1), procollagen type 1 amino-terminal propeptide, osteoprotegrin, osteopontin, Dickkopf WNT signaling pathway inhibitor 1 (Dkk1), sclerostin, and amyloid β peptides (Aβ40 and Aβ42), were measured.

Results

Using sex, age, and education-adjusted mixed-effects models, we found that baseline levels of TNF-related apoptosis-inducing ligand (TRAIL; p < .001), Dkk1 (p = .014), and CTX-1 (p = .046) were related to the annual rate of change of global cognition over the 18 month follow-up. In cognitive domain-specific analysis, baseline TRAIL was found to be positively related to the annual rate of change in episodic (p < .001) and working memory (p = .016), and baseline Dkk1 was positively related to semantic memory (p = .027) and negatively related to working memory (p = .016).

Conclusions

These results further confirm the link between bone and brain health and suggest that circulating levels of bone-related biomarkers may have diagnostic potential to predict worsening cognition.

HIV elite control is associated with reduced TRAILshort expression

OBJECTIVE

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) dependent apoptosis has been implicated in CD4 T-cell death and immunologic control of HIV-1 infection. We have described a splice variant called TRAILshort, which is a dominant negative ligand that antagonizes TRAIL-induced cell death in the context of HIV-1 infection. HIV-1 elite controllers naturally control viral replication for largely unknown reasons. Since enhanced death of infected cells might be responsible, as might occur in situations of low (or inhibited) TRAILshort, we tested whether there was an association between elite controller status and reduced levels of TRAILshort expression.

DESIGN

Cohort study comparing TRAILshort and full length TRAIL expression between HIV-1 elite controllers and viremic progressors from two independent populations.

METHODS

TRAILshort and TRAIL gene expression in peripheral blood mononuclear cells (PBMCs) was determined by RNA-seq. TRAILshort and TRAIL protein expression in plasma was determined by antibody bead array and proximity extension assay respectively.

RESULTS

HIV-1 elite controllers expressed less TRAILshort transcripts in PBMCs (P = 0.002) and less TRAILshort protein in plasma (P < 0.001) than viremic progressors.

CONCLUSION

Reduced TRAILshort expression in PBMCs and plasma is associated with HIV-1 elite controller status.

TRAIL Induces Nuclear Translocation and Chromatin Localization of TRAIL Death Receptors

Binding of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to the plasma membrane TRAIL-R1/-R2 selectively kills tumor cells. This discovery led to evaluation of TRAIL-R1/-R2 as targets for anti-cancer therapy, yet the corresponding clinical trials were disappointing. Meanwhile, it emerged that many cancer cells are TRAIL-resistant and that TRAIL-R1/-R2-triggering may lead to tumor-promoting effects. Intriguingly, recent studies uncovered specific functions of long ignored intracellular TRAIL-R1/-R2, with tumor-promoting functions of nuclear (n)TRAIL-R2 as the regulator of let-7-maturation. As nuclear trafficking of TRAIL-Rs is not well understood, we addressed this issue in our present study. Cell surface biotinylation and tracking of biotinylated proteins in intracellular compartments revealed that nTRAIL-Rs originate from the plasma membrane. Nuclear TRAIL-Rs-trafficking is a fast process, requiring clathrin-dependent endocytosis and it is TRAIL-dependent. Immunoprecipitation and immunofluorescence approaches revealed an interaction of nTRAIL-R2 with the nucleo-cytoplasmic shuttle protein Exportin-1/CRM-1. Mutation of a putative nuclear export sequence (NES) in TRAIL-R2 or the inhibition of CRM-1 by Leptomycin-B resulted in the nuclear accumulation of TRAIL-R2. In addition, TRAIL-R1 and TRAIL-R2 constitutively localize to chromatin, which is strongly enhanced by TRAIL-treatment. Our data highlight the novel role for surface-activated TRAIL-Rs by direct trafficking and signaling into the nucleus, a previously unknown signaling principle for cell surface receptors that belong to the TNF-superfamily.

Interactions of Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) with the Immune System: Implications for Inflammation and Cancer

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily. TRAIL has historically been distinct from the Fas ligand and TNFα in terms of selective apoptosis induction in tumor cells and has a nearly non-existent systemic toxicity. Consequently, in the search for an ideal drug for tumor therapy, TRAIL rapidly drew interest, promising effective tumor control with minimal side effects. However, euphoria gave way to disillusionment as it turned out that carcinoma cells possess or can acquire resistance to TRAIL-induced apoptosis. Additionally, studies on models of inflammation and autoimmunity revealed that TRAIL can influence immune cells in many different ways. While TRAIL was initially found to be an important player in tumor defense by natural killer cells or cytotoxic T cells, additional effects of TRAIL on regulatory T cells and effector T cells, as well as on neutrophilic granulocytes and antigen-presenting cells, became focuses of interest. The tumor-promoting effects of these interactions become particularly important for consideration in cases where tumors are resistant to TRAIL-induced apoptosis. Consequently, murine models have shown that TRAIL can impair the tumor microenvironment toward a more immunosuppressive type, thereby promoting tumor growth. This review summarizes the current state of knowledge on TRAIL’s interactions with the immune system in the context of cancer.

TRAILshort Protects against CD4 T Cell Death during Acute HIV Infection

CD4 T cells from HIV-1 infected patients die at excessive rates compared to those from uninfected patients, causing immunodeficiency. We previously identified a dominant negative ligand that antagonizes the TRAIL-dependent pathway of cell death, which we called TRAILshort. Because the TRAIL pathway has been implicated in CD4 T cell death occurring during HIV-1 infection, we used short hairpin RNA knockdown, CRISPR deletion, or Abs specific for TRAILshort to determine the effect of inhibiting TRAILshort on the outcome of experimental acute HIV infection in vitro. Strikingly, all three approaches to TRAILshort deletion/inhibition enhanced HIV-induced death of both infected and uninfected human CD4 T cells. Thus, TRAILshort impacts T cell dynamics during HIV infection, and inhibiting TRAILshort causes more HIV-infected and uninfected bystander cells to die. TRAILshort is, therefore, a host-derived, host-adaptive mechanism to limit the effects of TRAIL-induced cell death. Further studies on the effects of TRAILshort in other disease states are warranted.

Novel Apoptosis-Inducing Agents for the Treatment of Cancer, a New Arsenal in the Toolbox

Evasion from apoptosis is an important hallmark of cancer cells. Alterations of apoptosis pathways are especially critical as they confer resistance to conventional anti-cancer therapeutics, e.g., chemotherapy, radiotherapy, and targeted therapeutics. Thus, successful induction of apoptosis using novel therapeutics may be a key strategy for preventing recurrence and metastasis. Inhibitors of anti-apoptotic molecules and enhancers of pro-apoptotic molecules are being actively developed for hematologic malignancies and solid tumors in particular over the last decade. However, due to the complicated apoptosis process caused by a multifaceted connection with cross-talk pathways, protein–protein interaction, and diverse resistance mechanisms, drug development within the category has been extremely challenging. Careful design and development of clinical trials incorporating predictive biomarkers along with novel apoptosis-inducing agents based on rational combination strategies are needed to ensure the successful development of these molecules. Here, we review the landscape of currently available direct apoptosis-targeting agents in clinical development for cancer treatment and update the related biomarker advancement to detect and validate the efficacy of apoptosis-targeted therapies, along with strategies to combine them with other agents.

A New Efficient Method for Production of Recombinant Antitumor Cytokine TRAIL and Its Receptor-Selective Variant DR5-B

The cytokine TRAIL induces apoptosis in tumor cells of various origin without affecting normal cells. Clinical trials of TRAIL-receptor (DR4 and DR5) agonists (recombinant TRAIL or death receptors antibodies) have largely failed because most human tumors were resistant to them. Currently, a second generation of agents targeted at TRAIL-R with increased efficiency has been developed. To this end, we have developed DR5-B, a variant of TRAIL selectively interacting with DR5. We have developed a new efficient method for production of TRAIL and DR5-B using expression of these proteins in Escherichia coli strain SHuffle B. The proteins were isolated from the cytoplasmic fraction of cells and purified to a high degree of homogeneity using metal-affinity and ion-exchange chromatography. The protein yield was 211 and 173 mg from one liter of cell culture for DR5-B and TRAIL, respectively, which significantly exceeded the results obtained by other methods. DR5-B killed tumor cells of different origin more efficiently and rapidly compared with TRAIL. The resulting preparations can be used for the study of TRAIL signaling pathways and in preclinical and clinical trials as antitumor agents.

A novel anti-DR5 antibody-drug conjugate possesses a high-potential therapeutic efficacy for leukemia and solid tumors

It is well known that tumor necrosis factor-related apoptosis inducing ligand receptor 1 or 2 (DR4/DR5) is specifically expressed in various tumor cells, but less or no expression in most normal cells. Many first generations of TRAIL agonists including recombinant preparations of TRAIL, agonistic antibodies against DR4/DR5 have been developed in phase I/II clinical trials for cancer therapy. However, the outcomes of clinical trials by using DR4/DR5 agonist mono-therapy were disappointed even though the safety profile was well tolerance. In the present study, we report an anti-DR5 antibody-drug conjugate (ADC, named as Zapadcine-1) possesses a higher potential for the therapy of lymphocyte leukemia and solid cancers. Methods: Zapadcine-1 was made by a fully humanized DR5-specific monoclonal antibody (Zaptuzumab) coupled via a cleavable linker to a highly toxic inhibitor of tubulin, monomethyl auristatin D (MMAD), by using ThioBridge technology. Cytotoxicity of the ADC in various tumor cells was identified by luminescent cell viability assay and the efficacy in vivo was determined in cells derived xenografts (CDX) of Jurkat E6-1, BALL-1, Reh, and patient derived xenografts (PDX) of human acute leukemia. Preliminary safety evaluation was carried out in rat and monkey. Results: Zapadcine-1 possesses a similar binding ability to the death receptor DR5 as the naked monoclonal antibody Zaptuzumab, and can be rapidly endocytosed into the lysosome of cancer cells. Zapadcine-1 specifically kills human lymphocyte leukemia cells and solid tumor cells, but not normal cells tested. More importantly, Zapadcine-1 drastically eliminates the xenografts in both CDX and PDX models of human acute leukemia. The excellent and comparable therapeutic efficacy is also observed in lung cancer NCI-H1975 CDX mouse model. The maximum-tolerated dose (MTD) of single injected Zapadcine-1 in rat and cynomolgus monkey shows an acceptable safety profile. Conclusion: These data demonstrate a promising anti-cancer activity, meriting further exploration of its potential as a novel cancer therapeutic agent, especially for the acute lymphocyte leukemia.

Trained Macrophage Bioreactor for Penetrating Delivery of Fused Antitumor Protein

Macromolecular protein drugs are promising anti-neoplastic agents based on their precise tumor affinity and innocuousness to normal tissues. Although direct delivery of protein drugs remains impractical due to its short half-life in circulation, inefficiency in tumor accumulation, and poor penetrability in intratumoral distribution. Recently, biogenetic cell-based drug vectors have been widely reported for antitumor drug delivery. Macrophage is naturally independent with endogenous proteolysis, elimination of reticuloendothelial system, and immune surveillance. Meanwhile, its innate recruitment behaviors responsive to chronic inflammation signals make it a potential cellular vector for tumor targeting drug delivery. In this study, we develop a trained macrophage bioreactor for tumor homing and an in situ expression of fused antitumor protein. The recombinant tumor necrosis factor related apoptosis-inducing ligand is coded on a plasmid vector with penetrating domain on the C terminus, which improves the intratumoral distribution by facilitating protein dispersion in tumor tissue after in situ secretion. The combination of tumor-infiltrating macrophage bioreactor and multifunctional fused protein drug embodies a new effective tumor homing system for antitumor protein delivery.

The first cloned sea cucumber FADD from Holothuria leucospilota: Molecular characterization, inducible expression and involvement of apoptosis

In this study, a sea cucumber Fas-associated death domain (FADD) named HLFADD was first cloned from Holothuria leucospilota. The full-length cDNA of HLFADD is 2137 bp in size, containing a 116-bp 5'-untranslated region (UTR), a 1334-bp 3'-UTR and a 687-bp open reading frame (ORF) encoding a protein of 228 amino acids with a deduced molecular weight of 26.42 kDa. HLFADD protein contains a conserved death effector domain at its N-terminal and a conserved death domain at its C-terminal, structurally similar to its counterparts in vertebrates. The over-expressed HLFADD protein could induce apoptosis in HEK293 cells, suggesting a possible death receptor-mediated apoptosis pathway in echinoderms adapted with FADD. Moreover, HLFADD mRNA is ubiquitously expressed in all examined tissues, with the highest transcript level in the coelomocytes, followed by intestine. In vitro experiments performed in the H. leucospilota coelomocytes, the expression of HLFADD mRNA was significantly up-regulated by lipopolysaccharides (LPS) or polyriboinosinic-polyribocytidylic acid [poly (I:C)] challenge, suggesting that HLFADD might play important roles in the innate immune defense of sea cucumber against the invasion of bacteria and viruses.

Salmonella Effectors SseK1 and SseK3 Target Death Domain Proteins in the TNF and TRAIL Signaling Pathways

Strains of Salmonella utilize two distinct type three secretion systems to deliver effector proteins directly into host cells. The Salmonella effectors SseK1 and SseK3 are arginine glycosyltransferases that modify mammalian death domain containing proteins with N-acetyl glucosamine (GlcNAc) when overexpressed ectopically or as recombinant protein fusions. Here, we combined Arg-GlcNAc glycopeptide immunoprecipitation and mass spectrometry to identify host proteins GlcNAcylated by endogenous levels of SseK1 and SseK3 during Salmonella infection. We observed that SseK1 modified the mammalian signaling protein TRADD, but not FADD as previously reported. Overexpression of SseK1 greatly broadened substrate specificity, whereas ectopic co-expression of SseK1 and TRADD increased the range of modified arginine residues within the death domain of TRADD. In contrast, endogenous levels of SseK3 resulted in modification of the death domains of receptors of the mammalian TNF superfamily, TNFR1 and TRAILR, at residues Arg376 and Arg293 respectively. Structural studies on SseK3 showed that the enzyme displays a classic GT-A glycosyltransferase fold and binds UDP-GlcNAc in a narrow and deep cleft with the GlcNAc facing the surface. Together our data suggest that salmonellae carrying sseK1 and sseK3 employ the glycosyltransferase effectors to antagonise different components of death receptor signaling.

Small molecule ONC201 inhibits HIV-1 replication in macrophages via FOXO3a and TRAIL

Despite the success of antiretroviral therapy (ART), eradication of HIV-1 from brain reservoirs remains elusive. HIV-1 brain reservoirs include perivascular macrophages that are behind the blood-brain barrier and difficult to access by ART. Macrophages express transcription factor FOXO3a and the TNF superfamily cytokine TRAIL, which are known to target HIV-1-infected macrophages for viral inhibition. ONC201 is a novel and potent FOXO3a activator capable of inducing TRAIL. It can cross the blood-brain barrier, and has shown antitumor effects in clinical trials. We hypothesized that activation of FOXO3a/TRAIL by ONC201 will inhibit HIV-1 replication in macrophages. Using primary human monocyte-derived macrophages, we demonstrated that ONC201 dose-dependently decreased replication levels of both HIV-1 laboratory strain and primary strains as determined by HIV-1 reverse transcriptase activity assay. Consistent with data on HIV-1 replication, ONC201 also reduced intracellular and extracellular p24, viral RNA, and integrated HIV-1 DNA in infected macrophages. Blocking TRAIL or knockdown of FOXO3a with siRNA reversed ONC201-mediated HIV-1 suppression, suggesting that ONC201 inhibits HIV-1 through FOXO3a and TRAIL. The anti-HIV-1 effect of ONC201 was further validated in vivo in NOD/scid-IL-2Rgcnull mice. After intracranial injection of HIV-1-infected macrophages into the basal ganglia, we treated the mice daily with ONC201 through intraperitoneal injection for six days. ONC201 significantly decreased p24 levels in both the macrophages and the brain tissues, suggesting that ONC201 suppresses HIV-1 in vivo. Therefore, ONC201 can be a promising drug candidate to combat persistent HIV-1 infection in the brain.

The Hepatic Microenvironment and TRAIL-R2 Impact Outgrowth of Liver Metastases in Pancreatic Cancer after Surgical Resection

Most patients with pancreatic ductal adenocarcinoma (PDAC) undergoing curative resection relapse within months, often with liver metastases. The hepatic microenvironment determines induction and reversal of dormancy during metastasis. Both tumor growth and metastasis depend on the Tumor necrosis factor (TNF)-related apoptosis-inducing ligand-receptor 2 (TRAIL-R2). This study investigated the interplay of TRAIL-R2 and the hepatic microenvironment in liver metastases formation and the impact of surgical resection. Although TRAIL-R2-knockdown (PancTu-I shTR2) decreased local relapses and number of macroscopic liver metastases after primary tumor resection in an orthotopic PDAC model, the number of micrometastases was increased. Moreover, abdominal surgery induced liver inflammation involving activation of hepatic stellate cells (HSCs) into hepatic myofibroblasts (HMFs). In coculture with HSCs, proliferation of PancTu-I shTR2 cells was significantly lower compared to PancTu-I shCtrl cells, an effect still observed after switching coculture from HSC to HMF, mimicking surgery-mediated liver inflammation and enhancing cell proliferation. CXCL-8/IL-8 blockade diminished HSC-mediated growth inhibition in PancTu-I shTR2 cells, while Vascular Endothelial Growth Factor (VEGF) neutralization decreased HMF-mediated proliferation. Overall, this study points to an important role of TRAIL-R2 in PDAC cells in the interplay with the hepatic microenvironment during metastasis. Resection of primary PDAC seems to induce liver inflammation, which might contribute to outgrowth of liver metastases.

TRAIL, OPG, and TWEAK in kidney disease: biomarkers or therapeutic targets?

Ligands and receptors of the tumor necrosis factor (TNF) superfamily regulate immune responses and homeostatic functions with potential diagnostic and therapeutic implications. Kidney disease represents a global public health problem, whose prevalence is rising worldwide, due to the aging of the population and the increasing prevalence of diabetes, hypertension, obesity, and immune disorders. In addition, chronic kidney disease is an independent risk factor for the development of cardiovascular disease, which further increases kidney-related morbidity and mortality. Recently, it has been shown that some TNF superfamily members are actively implicated in renal pathophysiology. These members include TNF-related apoptosis-inducing ligand (TRAIL), its decoy receptor osteoprotegerin (OPG), and TNF-like weaker inducer of apoptosis (TWEAK). All of them have shown the ability to activate crucial pathways involved in kidney disease development and progression (e.g. canonical and non-canonical pathways of the transcription factor nuclear factor-kappa B), as well as the ability to regulate cell proliferation, differentiation, apoptosis, necrosis, inflammation, angiogenesis, and fibrosis with double-edged effects depending on the type and stage of kidney injury. Here we will review the actions of TRAIL, OPG, and TWEAK on diabetic and non-diabetic kidney disease, in order to provide insights into their full clinical potential as biomarkers and/or therapeutic options against kidney disease.

Apoptosis of tumor-infiltrating T lymphocytes: a new immune checkpoint mechanism

Immunotherapy based on checkpoint inhibitors is providing substantial clinical benefit, but only to a minority of cancer patients. The current priority is to understand why the majority of patients fail to respond. Besides T-cell dysfunction, T-cell apoptosis was reported in several recent studies as a relevant mechanism of tumoral immune resistance. Several death receptors (Fas, DR3, DR4, DR5, TNFR1) can trigger apoptosis when activated by their respective ligands. In this review, we discuss the immunomodulatory role of the main death receptors and how these are shaping the tumor microenvironment, with a focus on Fas and its ligand. Fas-mediated apoptosis of T cells has long been known as a mechanism allowing the contraction of T-cell responses to prevent immunopathology, a phenomenon known as activation-induced cell death, which is triggered by induction of Fas ligand (FasL) expression on T cells themselves and qualifies as an immune checkpoint mechanism. Recent evidence indicates that other cells in the tumor microenvironment can express FasL and trigger apoptosis of tumor-infiltrating lymphocytes (TIL), including endothelial cells and myeloid-derived suppressor cells. The resulting disappearance of TIL prevents anti-tumor immunity and may in fact contribute to the absence of TIL that is typical of "cold" tumors that fail to respond to immunotherapy. Interfering with the Fas-FasL pathway in the tumor microenvironment has the potential to increase the efficacy of cancer immunotherapy.

TRAILblazing Strategies for Cancer Treatment

In the late 1990s, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF-family, started receiving much attention for its potential in cancer therapy, due to its capacity to induce apoptosis selectively in tumour cells in vivo. TRAIL binds to its membrane-bound death receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5) inducing the formation of a death-inducing signalling complex (DISC) thereby activating the apoptotic cascade. The ability of TRAIL to also induce apoptosis independently of p53 makes TRAIL a promising anticancer agent, especially in p53-mutated tumour entities. Thus, several so-called TRAIL receptor agonists (TRAs) were developed. Unfortunately, clinical testing of these TRAs did not reveal any significant anticancer activity, presumably due to inherent or acquired TRAIL resistance of most primary tumour cells. Since the potential power of TRAIL-based therapies still lies in TRAIL's explicit cancer cell-selectivity, a desirable approach going forward for TRAIL-based cancer therapy is the identification of substances that sensitise tumour cells for TRAIL-induced apoptosis while sparing normal cells. Numerous of such TRAIL-sensitising strategies have been identified within the last decades. However, many of these approaches have not been verified in animal models, and therefore potential toxicity of these approaches has not been taken into consideration. Here, we critically summarise and discuss the status quo of TRAIL signalling in cancer cells and strategies to force tumour cells into undergoing apoptosis triggered by TRAIL as a cancer therapeutic approach. Moreover, we provide an overview and outlook on innovative and promising future TRAIL-based therapeutic strategies.

Importance of TRAIL Molecular Anatomy in Receptor Oligomerization and Signaling. Implications for Cancer Therapy

(TNF)-related apoptosis-inducing ligand (TRAIL) is able to activate the extrinsic apoptotic pathway upon binding to DR4/TRAIL-R1 and/or DR5/TRAIL-R2 receptors. Structural data indicate that TRAIL functions as a trimer that can engage three receptor molecules simultaneously, resulting in receptor trimerization and leading to conformational changes in TRAIL receptors. However, receptor conformational changes induced by the binding of TRAIL depend on the molecular form of this death ligand, and not always properly trigger the apoptotic cascade. In fact, TRAIL exhibits a much stronger pro-apoptotic activity when is found as a transmembrane protein than when it occurs as a soluble form and this enhanced biological activity is directly linked to its ability to cluster TRAIL receptors in supra-molecular structures. In this regard, cells involved in tumor immunosurveillance, such as activated human T cells, secrete endogenous TRAIL as a transmembrane protein associated with lipid microvesicles called exosomes upon T-cell reactivation. Consequently, it seems clear that a proper oligomerization of TRAIL receptors, which leads to a strong apoptotic signaling, is crucial for inducing apoptosis in cancer cells upon TRAIL treatment. In this review, the current knowledge of oligomerization status of TRAIL receptors is discussed as well as the implications for cancer treatment when using TRAIL-based therapies.

Ex-vivo perfusion as a successful strategy for reduction of ischemia-reperfusion injury in prolonged muscle flap preservation - A gene expression study

INTRODUCTION

With the introduction of vascularized composite allotransplantation (VCA) as new surgical technique, the need arose for strategies that could safely prolong graft preservation. Ex-vivo machine perfusion is a promising technique and is currently applied in solid organ transplantation. There is still limited evidence in the field of VCA and free flap transplantation. This gene expression study aimed to assess the degree of ischemia-reperfusion (IR) injury after preservation and replantation of free muscle flaps in a porcine model.

MATERIALS AND METHODS

A microarray analysis was first conducted on muscle flaps preserved by ex-vivo perfusion versus cold storage, to select genes of interest for further investigation. The expression of these selected genes was then examined in a muscle flap replantation model after 18 hour ex-vivo perfusion (n = 14) using qRT-PCR. Two preservation solutions were compared to static cold storage: University of Wisconsin-mp (n = 5) and Histidine-Tryptophan-Ketoglutarate solution (n = 5).

RESULTS

A selection of 8 genes was made based on micro-array results: Tumor necrosis factor receptor superfamily member 10-A like, Regulator of G-protein signaling 2, Nuclear factor kappa beta inhibitor zeta, Interleukin-1 beta, Fibroblast growth factor 6 and DNA damage-inducible transcript 4, Hypoxia-inducible factor 1-alpha and Caspase-3. The muscle flap replantation experiment compared their expression patterns before and after preservation and replantation and showed overall comparable gene expression between the preservation groups.

CONCLUSIONS

The expression of genes related to ischemia, apoptosis and inflammation was comparable between the ex-vivo perfusion and static cold storage groups. These results suggest that ex-vivo perfusion might be a promising technique for 18 hour muscle preservation in terms of decreasing ischemia-reperfusion injury.

TBX1 Functions as a Tumor Suppressor in Thyroid Cancer Through Inhibiting the Activities of the PI3K/AKT and MAPK/ERK Pathways

BACKGROUND

TBX1 is a member of the T-box family of transcription factors characterized by a conserved DNA binding domain termed T-box. TBX1 has been reported to be downregulated in mouse skin tumors and is considered a negative regulator of tumor cell growth in mice. However, its role and exact mechanism in human cancers, including thyroid cancer, remain totally unknown.

METHODS

Quantitative reverse transcription polymerase chain reaction and Western blot assays were performed to evaluate the expression of investigated genes. Methylation-specific polymerase chain reaction and pyrosequencing were used to analyze TBX1 promoter methylation. The biological functions of TBX1 in thyroid cancer cells were determined by a series of in vitro and in vivo experiments. Chromatin immunoprecipitation sequencing and dual-luciferase reporter assays were used to identify its downstream targets.

RESULTS

This study demonstrates that TBX1 is frequently downregulated by promoter methylation in both papillary thyroid cancers and thyroid cancer cell lines. Ectopic expression of TBX1 in thyroid cancer cells dramatically inhibits cell viability, colony formation, and tumorigenic potential in nude mice, and induces cell-cycle arrest and apoptosis through modulating a panel of cell-cycle and apoptosis-related genes. In addition, ectopic expression of TBX1 significantly decreases the migration and invasion potential of thyroid cancer cells through inhibiting the process of epithelial-mesenchymal transition and the expression of matrix metalloproteinases. On the other hand, TBX1 knockdown markedly promotes thyroid cancer cell viability and invasiveness. Mechanistically, TBX1 exerts its tumor suppressor function in thyroid cancer cells through inhibiting phosphorylation of AKT at Ser473 and ERK via regulating its downstream targets such as RNF41, PARK2, and PHLPP2.

CONCLUSIONS

The data show that TBX1 is frequently inactivated by promoter methylation and functions as a potential tumor suppressor in thyroid cancer through inhibiting the activities of the PI3K/AKT and MAPK/ERK signaling pathways.

Development of Novel Anticancer Agents with a Scaffold of Tetrahydropyrido[4,3-d]pyrimidine-2,4-dione

ONC201 is a small molecular anticancer agent currently in multiple Phase II clinical trials. Based on the pharmacophore of ONC201, a series of small molecular compounds with a core structure of tetrahydropyrido[4,3-d]pyrimidine-2,4-dione were designed and synthesized. Preliminary mechanism studies of these compounds indicated that they can inhibit the phosphorylation of AKT and ERK, induce the dephosphorylation of Foxo3a, and promote the expression of TRAIL and the enhancement of activating transcription factor 4 (ATF4) in PC-3 cells. Structure-activity relationship (SAR) studies indicated that modifications of the substituted groups on the core structure can significantly improve the cellular activities of these compounds. The most potent compounds are over 100 times more potent than ONC201 in inhibition of cell growth in a panel of different types of human cancer cell lines.