Cysteine 230 is essential for the structure and activity of the cytotoxic ligand TRAIL

The Role of TRAIL in Apoptosis and Immunosurveillance in Cancer

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that selectively induces apoptosis in tumor cells without harming normal cells, making it an attractive agent for cancer therapy. TRAIL induces apoptosis by binding to and activating its death receptors DR4 and DR5. Several TRAIL-based treatments have been developed, including recombinant forms of TRAIL and its death receptor agonist antibodies, but the efficacy of TRAIL-based therapies in clinical trials is modest. In addition to inducing cancer cell apoptosis, TRAIL is expressed in immune cells and plays a critical role in tumor surveillance. Emerging evidence indicates that the TRAIL pathway may interact with immune checkpoint proteins, including programmed death-ligand 1 (PD-L1), to modulate PD-L1-based tumor immunotherapies. Therefore, understanding the interaction between TRAIL and the immune checkpoint PD-L1 will lead to the development of new strategies to improve TRAIL- and PD-L1-based therapies. This review discusses recent findings on TRAIL-based therapy, resistance, and its involvement in tumor immunosurveillance.

Harnessing TRAIL-induced cell death for cancer therapy: a long walk with thrilling discoveries

Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) can induce apoptosis in a wide variety of cancer cells, both in vitro and in vivo, importantly without killing any essential normal cells. These findings formed the basis for the development of TRAIL-receptor agonists (TRAs) for cancer therapy. However, clinical trials conducted with different types of TRAs have, thus far, afforded only limited therapeutic benefit, as either the respectively chosen agonist showed insufficient anticancer activity or signs of toxicity, or the right TRAIL-comprising combination therapy was not employed. Therefore, in this review we will discuss molecular determinants of TRAIL resistance, the most promising TRAIL-sensitizing agents discovered to date and, importantly, whether any of these could also prove therapeutically efficacious upon cancer relapse following conventional first-line therapies. We will also discuss the more recent progress made with regards to the clinical development of highly active non-immunogenic next generation TRAs. Based thereupon, we next propose how TRAIL resistance might be successfully overcome, leading to the possible future development of highly potent, cancer-selective combination therapies that are based on our current understanding of biology TRAIL-induced cell death. It is possible that such therapies may offer the opportunity to tackle one of the major current obstacles to effective cancer therapy, namely overcoming chemo- and/or targeted-therapy resistance. Even if this were achievable only for certain types of therapy resistance and only for particular types of cancer, this would be a significant and meaningful achievement.

Carboxyl Esterase-TRAIL Expressing Human Adipose Stem Cells Inhibit Tumor Growth in Castration-Resistant Prostate Cancer-Bearing Mice with Less Toxicity

It has been proposed that CRPC treatment with reduced systemic toxicity can be achieved by employing genes that express enzymes that activate pharmacological agents. In this paper, we report our study that used human adipose-derived stem cells (ADSC), rabbit CE, and human TRAIL with reduced toxicity to explore how tumor development can be suppressed in CRPC-bearing mouse models. In vitro and in vivo directional migration of ADSC.CE.sTRAIL cells toward PC3 cells was significantly stimulated.ADSC.CE.sTRAIL showed higher suicide effects than did ADSC, ADSC.CE, or ADSC.sTRAIL under CPT-11 treatment. PC3 cells co-cultured with ADSC.CE.TRAIL showed higher cytotoxicity than did CPT-11 monotherapy, ADSC.CE, or ADSC.sTRAIL under CPT-11 treatment. ADSC.CE.sTRAIL showed higher apoptosis than did CPT-11 monotherapy, ADSC.CE, or ADSC.sTRAIL under CPT-11 treatment. In the in vivo study, ADSC.CE.sTRAIL inhibited tumor growth more than did CPT-11 monotherapy, ADSC.CE, or ADSC.sTRAIL under CPT-11 treatment. The evidence suggests that patients' own ADSC could be used in clinical trials for CRPC treatment based on therapeutic stem cells that express CE and TRAIL complex genes.

Functional characterization of a putative tumor necrosis factor superfamily member 10 in blood clam (Tegillarca granosa)

Tumor necrosis factor superfamily member 10 (TNFSF10), also known as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or Apo-2L, is one of the important members of the TNF superfamily. It is well demonstrated that TNFSF10 preferentially induces a variety of tumor cell apoptosis, and therefore exerts an important role in tumor immune surveillance. However, the function of TNFSF10 in pathogen defense is poorly understood, especially in invertebrates. The blood clam (Tegillarca granosa), an important commercial marine bivalve, plays an important ecological role in the marine ecosystem. The identification of immune genes will provide new perspective for disease control in the blood clam (T. granosa) farming. To better understand the biological function of TNFSF10 protein, the full-length cDNA of TNFSF10 homologous gene of T. granosa (TgTNFSF10) was cloned and identified for the first time, which was found to contain 1239 base pairs and encode 254 amino acids with a molecular weight of 29.5 kDa and a conserved TNF domain in the C-terminal. Quantitative RT-PCR analysis showed that TgTNFSF10 gene was constitutively expressed in all tested tissues, with the highest expression in hemocytes. LPS, Vibrio alginolyticus and Vibrio parahaemolyticus stimulations dramatically increased the expression of TgTNFSF10 in T. granosa (11.47-fold, 3.71-fold and 8.29-fold compared with the control respectively). In vitro experiments showed that recombinant TgTNFSF10 protein strongly inhibited the proliferation of HepG2 cells. Further confocal microscopy and flow cytometry analysis showed that obvious apoptosis occurred in TgTNFSF10-treated hemocytes and HepG2 cells. To sum up, our study demonstrated that TgTNFSF10 had strong apoptosis-inducing activity, which may participate in the innate immune response of T. granosa to pathogen invasion.

Apoptosis-Inducing TNF Superfamily Ligands for Cancer Therapy

Cancer is a complex disease with apoptosis evasion as one of its hallmarks; therefore, apoptosis induction in transformed cells seems a promising approach as a cancer treatment. TNF apoptosis-inducing ligands, which are naturally present in the body and possess tumoricidal activity, are attractive candidates. The most studied proteins are TNF-α, FasL, and TNF-related apoptosis-inducing ligand (TRAIL). Over the years, different recombinant TNF family-derived apoptosis-inducing ligands and agonists have been designed. Their stability, specificity, and half-life have been improved because most of the TNF ligands have the disadvantages of having a short half-life and affinity to more than one receptor. Here, we review the outlook on apoptosis-inducing ligands as cancer treatments in diverse preclinical and clinical stages and summarize strategies of overcoming their natural limitations to improve their effectiveness.

Human Cancers Express TRAILshort, a Dominant Negative TRAIL Splice Variant, Which Impairs Immune Effector Cell Killing of Tumor Cells

PURPOSE

TNF-related apoptosis inducing ligand (TRAIL) expression by immune cells contributes to antitumor immunity. A naturally occurring splice variant of TRAIL, called TRAILshort, antagonizes TRAIL-dependent cell killing. It is unknown whether tumor cells express TRAILshort and if it impacts antitumor immunity.

EXPERIMENTAL DESIGN

We used an unbiased informatics approach to identify TRAILshort expression in primary human cancers, and validated those results with IHC and ISH. TRAILshort-specific mAbs were used to determine the effect of TRAILshort on tumor cell sensitivity to TRAIL, and to immune effector cell dependent killing of autologous primary tumors.

RESULTS

As many as 40% of primary human tumors express TRAILshort by both RNA sequencing and IHC analysis. By ISH, TRAILshort expression is present in tumor cells and not bystander cells. TRAILshort inhibition enhances cancer cell lines sensitivity to TRAIL-dependent killing both in vitro and in immunodeficient xenograft mouse models. Immune effector cells isolated from patients with B-cell malignancies killed more autologous tumor cells in the presence compared with the absence of TRAILshort antibody (P < 0.05).

CONCLUSIONS

These results identify TRAILshort in primary human malignancies, and suggest that TRAILshort blockade can augment the effector function of autologous immune effector cells.See related commentary by de Miguel and Pardo, p. 5546.

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.

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.

Molecular Mode of Action of TRAIL Receptor Agonists-Common Principles and Their Translational Exploitation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its death receptors TRAILR1/death receptor 4 (DR4) and TRAILR2/DR5 trigger cell death in many cancer cells but rarely exert cytotoxic activity on non-transformed cells. Against this background, a variety of recombinant TRAIL variants and anti-TRAIL death receptor antibodies have been developed and tested in preclinical and clinical studies. Despite promising results from mice tumor models, TRAIL death receptor targeting has failed so far in clinical studies to show satisfying anti-tumor efficacy. These disappointing results can largely be explained by two issues: First, tumor cells can acquire TRAIL resistance by several mechanisms defining a need for combination therapies with appropriate sensitizing drugs. Second, there is now growing preclinical evidence that soluble TRAIL variants but also bivalent anti-TRAIL death receptor antibodies typically require oligomerization or plasma membrane anchoring to achieve maximum activity. This review discusses the need for oligomerization and plasma membrane attachment for the activity of TRAIL death receptor agonists in view of what is known about the molecular mechanisms of how TRAIL death receptors trigger intracellular cell death signaling. In particular, it will be highlighted which consequences this has for the development of next generation TRAIL death receptor agonists and their potential clinical application.

TRAIL-expressing recombinant Lactococcus lactis induces apoptosis in human colon adenocarcinoma SW480 and HCT116 cells

AIMS

We investigated the ability of Lactococcus lactis, a species generally regarded as safe, to express tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) protein. The expressed protein was either cell wall anchored or secreted, and it was assessed whether this could induce apoptosis in human colon adenocarcinoma cell lines SW480 and HCT116.

METHODS AND RESULTS

Constructs were designed to produce either secreted or cell wall-anchored forms of human TRAIL cloned into pNZ7021 expression vector. The expression by L. lactis was confirmed by Western blotting and immunofluorescence. Induction of cell death was evaluated by coculturing transformants producing either form of TRAIL protein with the two cell lines followed by MTT assay. Gene expression of apoptosis genes, Bax and Bcl2, was assessed by qPCR. The viability of SW480 and HCT116 cells treated with recombinant L. lactis was significantly reduced. A significant change was observed in the ratio of Bax/Bcl2 expression in HCT116 cells only following treatment with the supernatant of recombinant L. lactis containing secreted TRAIL.

CONCLUSION

Recombinant L. lactis producing TRAIL protein can induce apoptosis in human colon adenocarcinoma cell lines SW480 and HCT116.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of recombinant probiotics that produce anticancer compounds is a promising option for combating cancer cells.

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.

Construction and characterization of a new TRAIL soluble form, active at picomolar concentrations

Apoptosis induction has emerged as a treatment option for anticancer therapy. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a type II transmembrane protein, is a potent and specific pro-apoptotic protein ligand, which activates the extrinsic apoptosis pathway of the cell death receptors. Here we describe the construction and characterization of a new soluble TRAIL, sfTRAIL, stabilized with the trimerization Foldon domain from the Fibritin protein of the bacteriophage T4. Supernatants of 0.22 μM-filtered supernatants were produced in Vero-transduced cells with HSV1-derived viral amplicon vectors. Experiments were undertaken in two known TRAIL-sensitive (U373 and MDA.MB.231) and two TRAIL-resistant (MCF7 and A549) cell lines, to determine (i) whether the sfTRAIL protein is synthetized and, (ii) whether sfTRAIL could induce receptor-mediated apoptosis. Our results showed that sfTRAIL was able to induce apoptosis at concentrations as low as 1899.29 pg/mL (27.71 pM), independently of caspase-9 activation, and reduction in cell viability at 998.73 fM.

Both HIV-Infected and Uninfected Cells Express TRAILshort, Which Confers TRAIL Resistance upon Bystander Cells within the Microenvironment

TNF-related apoptosis-inducing ligand (TRAIL) was initially described to induce apoptosis of tumor cells and/or virally infected cells, although sparing normal cells, and has been implicated in the pathogenesis of HIV disease. We previously identified TRAILshort, a TRAIL splice variant, in HIV-infected patients and characterized it as being a dominant negative ligand to subvert TRAIL-mediated killing. Herein, using single-cell genomics we demonstrate that TRAILshort is produced by HIV-infected cells, as well as by uninfected bystander cells, and that the dominant stimulus which induces TRAILshort production are type I IFNs and TLR7, TLR8, and TLR9 agonists. TRAILshort has a short t1/2 by virtue of containing a PEST domain, which targets the protein toward the ubiquitin proteasome pathway for degradation. Further we show that TRAILshort binds preferentially to TRAIL receptors 1 and 2 with significantly reduced interaction with the decoy TRAIL receptors 3 and 4. Recombinant TRAILshort is sufficient to protect cells against TRAIL-induced killing, whereas immunodepletion of TRAILshort with a specific Ab restores TRAIL sensitivity. Importantly we show that TRAILshort is shed in microvesicles into the cellular microenvironment and therefore confers TRAIL resistance not only on the cell which produces it, but also upon neighboring bystander cells. These results establish a novel paradigm for understanding and overcoming TRAIL resistance, in particular how HIV-infected cells escape immune elimination by the TRAIL:TRAILshort receptor axis.

Structural principles of tumor necrosis factor superfamily signaling

The tumor necrosis factor (TNF) ligand and receptor superfamilies play an important role in cell proliferation, survival, and death. Stimulating or inhibiting TNF superfamily signaling pathways is expected to have therapeutic benefit for patients with various diseases, including cancer, autoimmunity, and infectious diseases. We review our current understanding of the structure and geometry of TNF superfamily ligands, receptors, and their interactions. A trimeric ligand and three receptors, each binding at the interface of two ligand monomers, form the basic unit of signaling. Clustering of multiple receptor subunits is necessary for efficient signaling. Current reports suggest that the receptors are prearranged on the cell surface in a "nonsignaling," resting state in a large hexagonal structure of antiparallel dimers. Receptor activation requires ligand binding, and cross-linking antibodies can stabilize the receptors, thereby maintaining the active, signaling state. On the other hand, an antagonist antibody that locks receptor arrangement in antiparallel dimers effectively blocks signaling. This model may aid the design of more effective TNF signaling-targeted therapies.

Antibodies and Derivatives Targeting DR4 and DR5 for Cancer Therapy

Developing therapeutics that induce apoptosis in cancer cells has become an increasingly attractive approach for the past 30 years. The discovery of tumor necrosis factor (TNF) superfamily members and more specifically TNF-related apoptosis-inducing ligand (TRAIL), the only cytokine of the family capable of eradicating selectively cancer cells, led to the development of numerous TRAIL derivatives targeting death receptor 4 (DR4) and death receptor 5 (DR5) for cancer therapy. With a few exceptions, preliminary attempts to use recombinant TRAIL, agonistic antibodies, or derivatives to target TRAIL agonist receptors in the clinic have been fairly disappointing. Nonetheless, a tremendous effort, worldwide, is being put into the development of novel strategic options to target TRAIL receptors. Antibodies and derivatives allow for the design of novel and efficient agonists. We summarize and discuss here the advantages and drawbacks of the soar of TRAIL therapeutics, from the first developments to the next generation of agonistic products, with a particular insight on new concepts.

Journey of TRAIL from Bench to Bedside and its Potential Role in Immuno-Oncology

Induction of apoptosis in cancer cells has increasingly been the focus of many therapeutic approaches in oncology field. Since its identification as a TNF family member, TRAIL (TNF-related apoptosis-inducing ligand) paved a new path in apoptosis inducing cancer therapies. Its selective ability to activate extrinsic and intrinsic cell death pathways in cancer cells only, independently from p53 mutations responsible for conventional therapeutics resistance, spotted TRAIL as a potent cancer apoptotic agent. Many recombinant preparations of TRAIL and death receptor targeting monoclonal antibodies have been developed and being tested pre-clinically and clinically both as a single agent and in combinations. Of note, the monoclonal antibodies were not the only type of antibodies developed to target TRAIL receptors. Recent technology has brought forth several single chain variable domains (scFv) designs fused recombinantly to TRAIL as well. Also, it is becoming progressively more understandable that field of nanotechnology has revolutionized cancer diagnosis and therapy. The recent breakthroughs in materials science and protein engineering have helped considerably in strategically loading drugs into nanoparticles or conjugating drugs to their surface. In this review we aim to comprehensively highlight the molecular knowledge of TRAIL in the context of its pathway, receptors and resistance factors. We also aim to review the clinical trials that have been done using TRAIL based therapies and to review various scFv designs, the arsenal of nano-carriers and molecules available to selectively target tumor cells with TRAIL.

Identification, characterization and bioactivity of tumor necrosis factor (TNF)-related apoptosis-inducing ligand from Equus caballus

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily and plays multifunctional roles in the immune system. In the present study, a homolog of TRAIL from the Mongolian horse (named ecTRAIL) was identified and characterized. The 870-bp open reading frame encodes a polypeptide of 289 amino acid residues with a predicted molecular weight of 33.47 kDa and pI of 8.47. The genomic structure of ecTRAIL shares a five-exon/six-intron arrangement similar to its orthologs. Multiple alignments show that ecTRAIL is a type II transmembrane protein with a typical transmembrane region, three conserved cysteine residues (Cys56, Cys77, Cys238) and a TNF family signature sequence ([LV]-x-[LIVM]-x(3)-G-[LIVMF]-Y-[LIVMFY](2)-x(2)-[QEKHL]-[LIVMGT]-x-[LIVMFY]). Three-dimensional structure prediction based on the same template revealed that the positional arrangement of the key amino acid residues, Cys238 and Cys230 in ecTRAIL and human TRAIL, respectively, is significantly conserved. Evolutionary analysis suggests that ecTRAIL is most closely related to its ortholog from pigs, with an identity of 83.99%. The solubilizing small ubiquitin-related modifier (SUMO) tag fused recombinant protein SUMO-ecsTRAIL was successfully expressed in E. coli and exhibited binding activity and cytotoxicity to HeLa cells in a cross-species manner in vitro. These results provide a better understanding of TRAILs in mammals and indicate that ecTRAIL may play an important role in the immune response in horses.

Engineered adenovirus fiber shaft fusion homotrimer of soluble TRAIL with enhanced stability and antitumor activity

Successful cancer therapies aim to induce selective apoptosis in neoplastic cells. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is considered an attractive anticancer agent due to its tumor cell-specific cytotoxicity. However, earlier studies with recombinant TRAIL revealed many shortcomings, including a short half-life, off-target toxicity and existence of TRAIL-resistant tumor cells. In this study, we developed a novel engineering strategy for recombinant soluble TRAIL by redesigning its structure with the adenovirus knobless fiber motif to form a stable homotrimer with improved antitumor activity. The result is a highly stable fiber-TRAIL fusion protein that could form homotrimers similar to natural TRAIL. The recombinant fusion TRAIL developed here displayed high specific activity in both cell-based assays in vitro and animal tests in vivo. This construct will serve as a foundation for a new generation of recombinant proteins suitable for use in preclinical and clinical studies and for effective combination therapies to overcome tumor resistance to TRAIL.

Membrane-proximal TRAIL species are incapable of inducing short circuit apoptosis signaling: Implications for drug development and basic cytokine biology

TRAIL continues to garner substantial interest as a recombinant cancer therapeutic while the native cytokine itself serves important tumor surveillance functions when expressed in membrane-anchored form on activated immune effector cells. We have recently developed the genetically stabilized TRAIL platform TR3 in efforts to improve the limitations associated with currently available drug variants. While in the process of characterizing mesothelin-targeted TR3 variants using a single chain antibody (scFv) delivery format (SS-TR3), we discovered that the membrane-tethered cytokine had a substantially increased activity profile compared to non-targeted TR3. However, cell death proceeded exclusively via a bystander mechanism and protected the mesothelin-positive targets from apoptosis rather than leading to their elimination. Incorporation of a spacer-into the mesothelin surface antigen or the cancer drug itself-converted SS-TR3 into a cis-acting phenotype. Further experiments with membrane-anchored TR3 variants and the native cytokine confirmed our hypothesis that membrane-proximal TRAIL species lack the capacity to physically engage their cognate receptors coexpressed on the same cell membrane. Our findings not only provide an explanation for the “peaceful” coexistence of ligand and receptor of a representative member of the TNF superfamily but give us vital clues for the design of activity-enhanced TR3-based cancer therapeutics.

Hetero-modification of TRAIL trimer for improved drug delivery and in vivo antitumor activities

Poor pharmacokinetics and resistance within some tumor cell lines have been the major obstacles during the preclinical or clinical application of TRAIL (tumor-necrosis-factor (TNF)-related apoptosis-inducing ligand). The half-life of TRAIL_114-281 (114 to 281 amino acids) was revealed to be no more than 30 minutes across species. Therefore maleimido activated PEG (polyethylene glycol) and MMAE (Monomethyl Auristatin E) were applied to site-specifically conjugate with the mutated cysteines from different monomers of TRAIL successively, taking advantage of steric effects involved within TRAIL mutant conjugations. As a result, TRAIL trimer was hetero-modified for different purposes. And the resulting PEG-TRAIL-vcMMAE conjugate exhibited dramatically improved half-life (11.54 h), favourable in vivo targeting capability and antitumor activities while no sign of toxicity in xenograft models, suggesting it’s a viable therapeutic and drug delivery strategy.

Expression, purification and characterization of heterotrimeric forms of sTRAIL using a polycistronic expression vector

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is capable of selectively inducing apoptosis of cancer cells, is a potential targeted drug for cancer therapy. The TRAIL protein induces apoptosis only in trimeric form. However, the recombinant soluble TRAIL (sTRAIL) trimer has low stability and a short half-life, which is a major obstacle for its advancement into clinical trials. Moreover, a percentage of engineered sTRAIL proteins are produced as dimers which may be toxic to normal human hepatocytes. In this study, we inserted three copies of the same subunit fragment of sTRAIL with a His tag into a polycistronic expression vector (pST39) to explore whether it would increase the proportion of trimers. We also constructed a heterozygous vector containing three subunit fragments of sTRAIL each with a different tag (His, HA, and Cmyc). Hybrid sTRAIL proteins (P-dTags) mainly as heterologous trimers were obtained by elution with a low concentration of imidazole based on different binding affinities of His with a nickel column. Functional analysis demonstrated that heterotrimeric forms of sTRAIL showed more stable activity compared to the P-3H at 4°C but not at 37°C without alteration in the native killing capacity. In addition, the heterologous trimers showed decreased toxicity to hepatocytes. These results suggest that the polycistronic expression system may be useful for expression of recombinant sTRAIL and improving its potential in cancer therapeutic applications.

In situ facile-forming PEG cross-linked albumin hydrogels loaded with an apoptotic TRAIL protein

The key to making a practicable hydrogel for pharmaceutical or medical purposes is to endow it with relevant properties, i.e., facile fabrication, gelation time-controllability, and in situ injectability given a firm basis for safety/biocompatibility. Here, the authors describe an in situ gelling, injectable, albumin-cross-linked polyethylene glycol (PEG) hydrogel that was produced using a thiol-maleimide reaction. This hydrogel consists of two biocompatible components, namely, thiolated human serum albumin and 4-arm PEG20k-maleimide, and can be easily fabricated and gelled in situ within 60s by simply mixing its two components. In addition, the gelation time of this system is controllable in the range 15s to 5min. This hydrogel hardly interacted with an apoptotic TRAIL protein, ensuring suitable release profiles that maximize therapeutic efficacy. Specifically, tumors (volume: 278.8mm(3)) in Mia Paca-2 cell-xenografted BALB/c nu/nu mice treated with the TRAIL-loaded HSA-PEG hydrogel were markedly smaller than mice treated with the hydrogel prepared via an amine-N-hydroxysuccinimide reaction or non-treated mice (1275.5mm(3) and 1816.5mm(3), respectively). We believe that this hydrogel would be a new prototype of locally injectable sustained-release type anti-cancer agents, and furthermore offers practical convenience for a doctor and universal applicability for a variety of therapeutic proteins.

TRAIL-Based High Throughput Screening Reveals a Link between TRAIL-Mediated Apoptosis and Glutathione Reductase, a Key Component of Oxidative Stress Response

A high throughput screen for compounds that induce TRAIL-mediated apoptosis identified ML100 as an active chemical probe, which potentiated TRAIL activity in prostate carcinoma PPC-1 and melanoma MDA-MB-435 cells. Follow-up in silico modeling and profiling in cell-based assays allowed us to identify NSC130362, pharmacophore analog of ML100 that induced 65-95% cytotoxicity in cancer cells and did not affect the viability of human primary hepatocytes. In agreement with the activation of the apoptotic pathway, both ML100 and NSC130362 synergistically with TRAIL induced caspase-3/7 activity in MDA-MB-435 cells. Subsequent affinity chromatography and inhibition studies convincingly demonstrated that glutathione reductase (GSR), a key component of the oxidative stress response, is a target of NSC130362. In accordance with the role of GSR in the TRAIL pathway, GSR gene silencing potentiated TRAIL activity in MDA-MB-435 cells but not in human hepatocytes. Inhibition of GSR activity resulted in the induction of oxidative stress, as was evidenced by an increase in intracellular reactive oxygen species (ROS) and peroxidation of mitochondrial membrane after NSC130362 treatment in MDA-MB-435 cells but not in human hepatocytes. The antioxidant reduced glutathione (GSH) fully protected MDA-MB-435 cells from cell lysis induced by NSC130362 and TRAIL, thereby further confirming the interplay between GSR and TRAIL. As a consequence of activation of oxidative stress, combined treatment of different oxidative stress inducers and NSC130362 promoted cell death in a variety of cancer cells but not in hepatocytes in cell-based assays and in in vivo, in a mouse tumor xenograft model.

A humanized leucine zipper-TRAIL hybrid induces apoptosis of tumors both in vitro and in vivo

Evidence suggests that stimulating apoptosis in malignant cells without inflicting collateral damage to the host's normal tissues is a promising cancer therapy. Chemo- and radiation therapies that, especially if combined, induce apoptosis in tumor cells have been used for treating cancer patients for decades. These treatments, however, are limited in their ability to discriminate between malignant and non-malignant cells and, therefore, produce substantial healthy tissue damage and subsequent toxic side-effects. In addition, as a result of these therapies, many tumor types acquire an apoptosis-resistant phenotype and become more aggressive and metastatic. Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL) has been considered a promising and reliable selective inducer of apoptosis in cancerous cells. TRAIL, however, is not uniformly effective in cancer and multiple cancer cell types are considered resistant to natural TRAIL. To overcome this deficiency of TRAIL, we have earlier constructed a yeast-human hybrid leucine zipper-TRAIL in which the yeast GCN4-pII leucine zipper was fused to human TRAIL (GCN4-TRAIL). This construct exhibited a significantly improved anti-tumor apoptotic activity and safety, but is potentially immunogenic in humans. Here, we report a novel, potent, and fully human ATF7 leucine zipper-TRAIL (ATF7-TRAIL) fusion construct that is expected to have substantially lower immunogenicity. In solution, ATF7-TRAIL exists solely as a trimer with a Tm of 80°C and is active against cancer cells both in vitro and in vivo, in a mouse tumor xenograft model. Our data suggest that our re-engineered TRAIL is a promising candidate for further evaluation as an antitumor agent.

GMP production and characterization of leucine zipper-tagged tumor necrosis factor-related apoptosis-inducing ligand (LZ-TRAIL) for phase I clinical trial

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumor activity in a wide range of cancers without deleterious side effects on normal tissues. Several TRAIL derivatives have been developed to improve its pharmacokinetics and therapeutic effects through strategies such as adding a leucine zipper to increase the circulation half-life. To obtain clinical grade LZ-TRAIL for phase I clinical trial, a single batch of 30 L bioreactor culture was performed using the Escherichia coli BL21 (DE3) strain expressing the recombinant LZ-TRAIL. A robust LZ-TRAIL production fermentation process was developed, which could be scaled up from 5L to 50 L, and had a titer of approximately 1.4 g/l. A four-step purification strategy was carried out to obtain a final product with over 95% purity and 45% yield. The final material was filter sterilized, aseptically vialed, and stored at 4°C, and comprehensively characterized using multiple assays (vialed product was sterile, purity was 95%, aggregates were <5%, potency revealed IC50 of 9 nM on MDA-MB-231 cells, and the endotoxin level was <0.25 U/mg). The purity, composition, and functional activities of the molecule were confirmed. in vivo investigations indicated that LZ-TRAIL has better antitumor potency in three Xenograft tumor models compared to TRAIL (95-281). LZ-TRAIL also showed improved pharmacokinetic and safety profiles in cynomolgus monkeys without abnormalities associated with drug exposure. In conclusion, the scalable synthesis of LZ-TRAIL is useful for production of phase I clinical trial material. These preclinical investigations warrant further clinical development of this product for cancer therapy.

Improvement in the stability and functionality of Nicotiana tabacum produced recombinant TRAIL through employment of endoplasmic reticulum expression and ascorbate buffer mediated extraction strategies

Introduction: In order to employ Nicotiana tabacum cells as a profitable natural bioreactor for production of bio-functional "Soluble human TRAIL" (ShTRAIL), endoplasmic reticulum (ER) targeted expression and innovative extraction procedures were exploited.

Methods: At first, the ShTRAIL encoding gene was sub-cloned into designed H2 helper vector to equip it with potent TMV omega leader sequences, ER sorting signal peptide, poly-histidine tag and ER retention signal peptide (KDEL). Then, the ER targeted ShTRAIL cassette was sequentially sub-cloned into "CaMV-35S" helper and "pGreen-0179" final expression vectors. Afterward, Agrobacterium mediated transformation method was adopted to express the ShTRAIL in the ER of N. tabacum . Next, the ShTRAIL protein was extracted through both phosphate and innovative ascorbate extraction buffers. Subsequently, oligomerization state of the ShTRAIL was evaluated through cross-linking assay and western blot analysis. Then, semi-quantitative western blot analysis was performed to estimate the ShTRAIL production. Finally, biological activity of the ShTRAIL was evaluated through MTT assay.

Results: The phosphate buffer extracted ShTRAIL was produced in dimmer form, whereas the ShTRAIL extracted with ascorbate buffer generated trimer form. The ER targeted ShTRAIL strategy increased the ShTRAIL’s production level up to about 20 μg/g of fresh weight of N. tabacum . MTT assay indicated that ascorbate buffer extracted ShTRAIL could prohibit proliferation of A549 cell line.

Conclusion: Endoplasmic reticulum expression and reductive ascorbate buffer extraction procedure can be employed to enhance the stability and overall production level of bio-functional recombinant ShTRAIL from transgenic N. tabacum cells.

Novel treatment option for MUC16-positive malignancies with the targeted TRAIL-based fusion protein Meso-TR3

Background

The targeted delivery of cancer therapeutics represents an ongoing challenge in the field of drug development. TRAIL is a promising cancer drug but its activity profile could benefit from a cancer-selective delivery mechanism, which would reduce potential side effects and increase treatment efficiencies. We recently developed the novel TRAIL-based drug platform TR3, a genetically fused trimer with the capacity for further molecular modifications such as the addition of tumor-directed targeting moieties. MUC16 (CA125) is a well characterized biomarker in several human malignancies including ovarian, pancreatic and breast cancer. Mesothelin is known to interact with MUC16 with high affinity. In order to deliver TR3 selectively to MUC16-expressing cancers, we investigated the possibility of targeted TR3 delivery employing the high affinity mesothelin/MUC16 ligand/receptor interaction.

Methods

Using genetic engineering, we designed the novel cancer drug Meso-TR3, a fusion protein between native mesothelin and TR3. The recombinant proteins were produced with mammalian HEK293T cells. Meso-TR3 was characterized for binding selectivity and killing efficacy against MUC16-positive cancer cells and controls that lack MUC16 expression. Drug efficacy experiments were performed in vitro and in vivo employing an intraperitoneal xenograft mouse model of ovarian cancer.

Results

Similar to soluble mesothelin itself, the strong MUC16 binding property was retained in the Meso-TR3 fusion protein. The high affinity ligand/receptor interaction was associated with a selective accumulation of the cancer drug on MUC16-expressing cancer targets and directly correlated with increased killing activity in vitro and in a xenograft mouse model of ovarian cancer. The relevance of the mesothelin/MUC16 interaction for attaching Meso-TR3 to the cancer cells was verified by competitive blocking experiments using soluble mesothelin. Mechanistic studies using soluble DR5-Fc and caspase blocking assays confirmed engagement of the extrinsic death receptor pathway. Compared to non-targeted TR3, Meso-TR3 displayed a much reduced killing potency on cells that lack MUC16.

Conclusions

Soluble Meso-TR3 targets the cancer biomarker MUC16 in vitro and in vivo. Following attachment to the tumor via surface bound MUC16, Meso-TR3 acquires full activation with superior killing profiles compared to non-targeted TR3, while its bioactivity is substantially reduced on cells that lack the tumor marker. This prodrug phenomenon represents a highly desirable property because it has the potential to enhance cancer killing with fewer side-effects than non-targeted TRAIL-based therapeutics. Thus, further exploration of this novel fusion protein is warranted as a possible therapeutic for patients with MUC16-positive malignancies.

Novel conjugation of tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL) with monomethyl auristatin E for efficient antitumor drug delivery

Monomethyl auristatin E (MMAE) is conjugated with TNF-related apoptosis-inducing ligand (TRAIL) via a linker that is stable in extracellular fluid, while it is cleaved by cathepsin once the conjugate has entered a tumor cell, thus activating the antimitotic mechanism of MMAE. The TRAIL-MMAE conjugate is a conceptually viable therapeutic strategy with improved in vitro antitumor activity, cell circle arrest and specific accumulation in tumor to treat TRAIL-resistant tumors.

Site-specific PEGylation of a mutated-cysteine residue and its effect on tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a promising antitumor agent that specifically induces apoptosis in broad-spectrum tumor cell lines, meanwhile leaving normal cells unaffected. Unfortunately, the clinical development of TRAIL was hampered, and could be attributed to its instability, bioavailability or poor delivery. Although N-terminal specific PEGylation provides a means to improve the pharmacokinetic and stability of TRAIL, it took a bit longer time to accomplish the PEGylation process than expected. We therefore designed another PEGylation approach, mutated Cys-SH site-specific PEGylation, to conjugate methoxypoly(ethylene glycol) maleimide (mPEG-MAL) with TRAIL (95-281) mutant N109C. Asn-109 was chosen as the PEGylated site for it is a potential N-linked glycosylation site. It was shown that ~90% TRAIL mutant N109C could be PEGylated by mPEG-MAL within 40 min. And mPEG(MAL)-N109C was revealed to possess superior in vitro stability and antitumor activity than N-terminal specifically PEGylated TRAIL (114-281) (mPEG(ALD)-TRAIL(114-281)). What's more, mPEG(MAL)-N109C exhibited more therapeutic potentials than mPEG(ALD)-TRAIL(114-281) in tumor xenograft model, benefitting from better drug delivery and bioavailability. These results have demonstrated mutated Cys-SH specific PEGylation is an alternative to site-specifically PEGylate TRAIL efficiently and effectively other than N-terminal specific PEGylation.

Death receptors as targets in cancer

Anti-tumour therapies based on the use pro-apoptotic receptor agonists, including TNF-related apoptosis-inducing ligand (TRAIL) or monoclonal antibodies targeting TRAIL-R1 or TRAIL-R2, have been disappointing so far, despite clear evidence of clinical activity and lack of adverse events for the vast majority of these compounds, whether combined or not with conventional or targeted anti-cancer therapies. This brief review aims at discussing the possible reasons for the lack of apparent success of these therapeutic approaches and at providing hints in order to rationally design optimal protocols based on our current understanding of TRAIL signalling regulation or resistance for future clinical trials.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Engineering and refolding of a novel trimeric fusion protein TRAIL-collagen XVIII NC1

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is considered to be a promising anticancer agent because its active form TRAIL trimer is able to induce apoptosis in different tumor cell lines while sparing normal cells. However, TRAIL trimer possesses a short half-life and low stability, which turns out to be a major obstacle for the development of clinical trials. In our present study, we constructed a recombined TRAIL trimer by genetic fusion of non-collagenous domain (NC1) of human collagen XVIII or its trimerization domain (TD) to C-terminus of TRAIL via a flexible linker, and then refolded the fusion proteins using a two-step refolding approach, namely a combination of dilution and gel filtration chromatography. As a result, both recombinant proteins, TRAIL-NC1 and TRAIL-TD, were expressed in Escherichia coli as inclusion bodies, and they exhibited difficultly to refold efficiently by conventional methods. Thereby, we applied a modified two-step refolding approach to refold fusion proteins. More than 55 % of TRAIL-NC1 and 90 % of TRAIL-TD protein activity was recovered during the two-step refolding approach, and their stability was also increased significantly. Also, size exclusion chromatography showed refolded TRAIL-NC1 was a trimer while TRAIL-TD, hexamer. However, both of them exerted good apoptosis activity on NCI-H460 cells.

Construction and expression of sTRAIL-melittin combining enhanced anticancer activity with antibacterial activity in Escherichia coli

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), as an anticancer protein with tumor-selective apoptotic activity, has been examined for use in clinical application. Melittin, an antibacterial peptide isolated from the bee Apis mellifera, has shown strong cytotoxicity to both tumor and normal cells. To ameliorate the cytotoxicity of melittin on cells and enhance the activity of TRAIL on cancer cells, we constructed a novel fusion protein, sTRAIL-melittin, containing a small ubiquitin-related modifier (SUMO) tag and expressed this fusion protein in Escherichia coli. Data showed that expression of the soluble fusion protein with the SUMO tag was approximately 85% of total target protein which was much higher than that without the SUMO tag (approximately 10%); sTRAIL-melittin was easily purified using Ni-NTA affinity chromatography and the tag was removed easily using SUMO-specific protease. To assay anticancer activity and side effects, methyl thiazolyl tetrazolium, hemolytic, and apoptosis assays were employed. Results demonstrated that sTRAIL-melittin had cytotoxic and apoptotic activity in K562 leukemia cells and HepG2 liver carcinoma cells, while it had only a minimal effect on erythrocytes and normal HEK293 cells. This indicates that the cytotoxicity of sTRAIL-melittin in normal cells was low and the anticancer activity of the fusion protein in tumor cells was significantly enhanced compared with sTRAIL (P<0.01). Furthermore, we found that sTRAIL-melittin also showed antibacterial activity to Staphylococcus aureus due to the presence of the melittin domain. Therefore, TRAIL fused with an antibacterial peptide may be a promising novel TRAIL-based anticancer treatment strategy.

The adaptor protein FADD and the initiator caspase-8 mediate activation of NF-κB by TRAIL

Besides inducing apoptosis, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates NF-κB. The apoptosis signaling pathway of TRAIL is well characterized involving TRAIL receptors, Fas-associated protein with death domain (FADD) and caspase-8. In contrast, the molecular mechanism of TRAIL signaling to NF-κB remains controversial. Here, we characterized the receptor–proximal mediators of NF-κB activation by TRAIL. Deletion of the DD of TRAIL receptors 1 and 2 revealed that it is essential in NF-κB signaling. Because FADD interacts with the TRAIL receptor DD, FADD was tested. RNAi-mediated knockdown of FADD or FADD deficiency in JURKAT T-cell leukemia cells decreased or disabled NF-κB signaling by TRAIL. In contrast, TRAIL-induced activation of NF-κB was maintained upon loss of receptor interacting protein 1 (RIP1) or knockdown of FLICE-like inhibitory protein (FLIP). Exogenous expression of FADD rescued TRAIL-induced NF-κB signaling. Loss-of-function mutations of FADD within the RHDLL motif of the death effector domain, which is required for TRAIL-induced apoptosis, abrogated FADD's ability to recruit caspase-8 and mediate NF-κB activation. Accordingly, deficiency of caspase-8 inhibited TRAIL-induced activation of NF-κB, which was rescued by wild-type caspase-8, but not by a catalytically inactive caspase-8 mutant. These data establish the mechanism of TRAIL-induced NF-κB activation involving the TRAIL receptor DD, FADD and caspase-8, but not RIP1 or FLIP. Our results show that signaling of TRAIL-induced apoptosis and NF-κB bifurcates downstream of caspase-8.

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.

TRAIL signaling and synergy mechanisms used in TRAIL-based combination therapies

TRAIL and agonistic antibodies raised against TRAIL death receptors are highly promising new anticancer agents. In this brief review, we describe the recent advances in the molecular understanding of TRAIL signaling and the progress made in using TRAIL or agonistic antibodies clinically in mono- and combination therapies. Synergies have been reported in various scenarios of TRAIL-based multidrug treatments, and these can be used to potentiate the efficacy of therapies targeting TRAIL death receptors. We pay particular attention to structure the current knowledge on the diverse molecular mechanisms that are thought to give rise to these synergies and describe how different signaling features evoking synergies can be associated with distinct classes of drugs used in TRAIL-based combination treatments.

Preclinical toxicity of DATR, a recombinant soluble human TRAIL mutant, in rats and cynomolgus monkeys

The recombinant soluble human TRAIL mutant (DATR), derived from tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), is a promising agent for cancer therapy. The present study evaluated the toxicity of DATR in rats and monkeys. Based on the results, the safety and toxic doses of DATR intravenously injected to rats for 50 days were 60 and 180 mg/kg, respectively, and when delivered intravenously guttae to monkeys for 50 days, these levels were 10 and 30 mg/kg, respectively. The main toxic effects in rats were red blood cell count and haemoglobin decreases; blood urea nitrogen and creatinine increases. The main toxic effects in monkeys included red blood cell count and haemoglobin decreases; alanine aminotransferase and aspartate aminotransferase increases; high proliferation of karyocytes of the erythrocyte series; and regional hydropic degeneration of hepatic parenchymal cells. The TUNEL assay showed both 90 mg/kg DATR- and TRAIL-induced apoptosis of the liver in monkeys, which confirmed the hepatotoxicity of DATR. These findings indicated that the target toxic organs of DATR might be the haematological system. Furthermore, kidney in rats and liver in monkeys are also likely target toxic organs. The toxicity was reversible and did not differ from that associated with TRAIL administered at the same dosage.

5-allyl-7-gen-difluoromethoxychrysin enhances TRAIL-induced apoptosis in human lung carcinoma A549 cells

Background

5-allyl-7-gen-difluoromethoxychrysin (AFMC) is a novel synthetic analogue of chrysin that has been reported to inhibit proliferation in various cancer cell lines. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent.

Methods

The cytotoxicity of A549 and WI-38 cells were determined using colorimetry. Apoptosis was detected by flow cytometry (FCM) after propidium iodide (PI) fluorescence staining and agarose gel electrophoresis. Caspase activities were evaluated using enzyme-linked immunosorbent assay (ELISA).The expressions of DR4 and DR5 were analyzed using FCM and western blot.

Results

Subtoxic concentrations of AFMC sensitize human non-small cell lung cancer (NSCLC) A549 cells to TRAIL-mediated apoptosis. Combined treatment of A549 cells with AFMC and TRAIL significantly activated caspase-3, -8 and -9. The caspase-3 inhibitor zDEVD-fmk and the caspase-8 inhibitor zIETD-fmk blocked the apoptosis of A549 cells induced by co-treatment with AFMC and TRAIL. In addition, we found that treatment of A549 cells with AFMC significantly induced the expression of death receptor 5 (DR5). AFMC-mediated sensitization of A549 cells to TRAIL was efficiently reduced by administration of a blocking antibody or small interfering RNAs against DR5. AFMC also caused increase of the Sub-G1 cells by TRAIL treatment and increased the expression levels of DR5 in other NSCLC H460 and H157 cell lines. In contrast, AFMC-mediated induction of DR5 expression was not observed in human embryo lung WI-38 cells, and AFMC did not sensitize WI-38 cells to TRAIL-induced apoptosis.

Conclusions

AFMC synergistically enhances TRAIL-mediated apoptosis in NSCLC cells through up-regulating DR5 expression.

Hepatocyte death: a clear and present danger

The hepatocyte is especially vulnerable to injury due to its central role in xenobiotic metabolism including drugs and alcohol, participation in lipid and fatty acid metabolism, its unique role in the enterohepatic circulation of bile acids, the widespread prevalence of hepatotropic viruses, and its existence within a milieu of innate immune responding cells. Apoptosis and necrosis are the most widely recognized forms of hepatocyte cell death. The hepatocyte displays many unique features regarding cell death by apoptosis. It is quite susceptible to death receptor-mediated injury, and its death receptor signaling pathways involve the mitochondrial pathway for efficient cell killing. Also, death receptors can trigger lysosomal disruption in hepatocytes which further promote cell and tissue injury. Interestingly, hepatocytes are protected from cell death by only two anti-apoptotic proteins, Bcl-x(L) and Mcl-1, which have nonredundant functions. Endoplasmic reticulum stress or the unfolded protein response contributes to hepatocyte cell death during alterations of lipid and fatty acid metabolism. Finally, the current information implicating RIP kinases in necrosis provides an approach to more fully address this mode of cell death in hepatocyte injury. All of these processes contributing to hepatocyte injury are discussed in the context of potential therapeutic strategies.

A genetically encoded multifunctional TRAIL trimer facilitates cell-specific targeting and tumor cell killing

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL, Apo2L) has been shown to exhibit potent and specific apoptotic activity against tumor cells. Several TRAIL constructs have been tried in patients, and the molecule remains under active clinical investigation. Native and recombinant TRAIL must form a homotrimer to become biologically active. However, noncovalently associated TRAIL displays a high degree of sensitivity to degradation, which limits its therapeutic potential. To enforce trimerization of the recombinant protein, we developed a covalently linked TRAIL trimer (TR3) by genetic fusion. This molecular drug design conferred improved stability without altering the native killing ability of TRAIL. Target specificity was shown by blocking TR3 activity with soluble death receptor 5 (DR5-Fc). In addition, we have shown that TR3 is amenable to further, genetic modifications. The incorporation of additional functional domains to TR3, such as antibody fragments (scFvs) that allow for a more cell-specific delivery of the agent, is stoichiometrically controlled and inconsequential with regard to the bioactivity of TRAIL. As proof of this concept, TR3 activity was targeted to the mouse RBC membrane. TR3-decorated RBCs were effectively capable of target cell killing in a model of pancreatic cancer. TR3 represents a generally applicable platform tool to study basic mechanisms along the death receptor pathway. More importantly, the ability to target TR3 to a cell surface presents the opportunity to create a cancer-selective drug with fewer off-target toxicities and enhanced killing capacities.

New insights into apoptosis signaling by Apo2L/TRAIL

Apoptosis ligand 2 tumor necrosis factor (TNF)-related apoptosis-inducing ligand (Apo2L/TRAIL) belongs to a small subset of proapoptotic protein ligands in the TNF superfamily. This subset, which also includes Fas ligand and TNF-alpha, can activate the extrinsic apoptotic cell death pathway on binding to cognate death receptors at the cell surface. Over the past 10 years, Apo2L/TRAIL has emerged as a promising candidate for cancer therapy, on the basis of its unique ability to trigger apoptosis in various types of cancer cells without significant toxicity toward normal cells. Herein, we review key advances in understanding the molecular events that control apoptosis signaling by Apo2L/TRAIL, which may aid in the development of cancer therapies based on the extrinsic apoptotic pathway.

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.

A novel gene of tumor necrosis factor ligand superfamily from kuruma shrimp, Marsupenaeus japonicus

A tumor necrosis factor (TNF) gene has been isolated and characterized in kuruma shrimp, Marsupenaeus japonicus, providing the first conclusive evidence for the existence of the TNF ligand in shrimp. The kuruma shrimp TNF (MjTNF) cDNA was composed of 1868 bp with a 262 bp 5'-untranslated region (UTR) and a 220 bp 3'-UTR, which was translated into a protein of 462 amino acid residues that included a predicted transmembrane domain of 23 amino acid residues (Trp20-Val42) and the TNF family signature (Pro321-Leu448). Homology analysis of MjTNF showed 30.7% and 26.7% identities with fruit fly (Drosophila melanogaster) Eiger and human (Homo sapiens) ectodysplasin A, respectively. The MjTNF gene was constitutively expressed in unstimulated organs of shrimp such as the muscle, stomach, brain and gill. In lymphoid organ cells, an enhanced expression of the MjTNF gene was observed following stimulation with peptidoglycan and polycytidylic acid. A high expression level of MjTNF was observed in vivo 2 h and 4 h after stimulation with lipopolysaccharide and Vibrio penaeicida, respectively. These observations suggest that MjTNF plays a role in the innate immune defense in kuruma shrimp. The discovery of shrimp TNF will allow a more complete and concrete understanding of shrimp inflammatory responses.

Acute toxicity of a single dose DATR, recombinant soluble human TRAIL mutant, in rodents and crab-eating macaques

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been reported to possess activity of inducing apoptosis in variety of tumor cells in preclinical models. Several mutational versions of TRAIL have been studied as promising agents for cancer therapy and the recombinant soluble human TRAIL mutant (DATR) is one of them. The objective of the present study was to provide possible toxic target organs and proposal non-toxic dose level of DATR for clinical usage. Rodents and crab-eating macaques were used to estimate potential adverse effects of DATR following a single dose administration. The median lethal dose (LD(50)) of intravenous injection to rats and mice was determined as 262.0 and 1018.0 mg/kg b.w., respectively. The LD(50) of intraperitoneal administration to mice was found to be 1432.1 mg/kg b.w. The main changes in macaques were found in the following aspects. Hematology analysis revealed an obvious decrease of red blood cell count (RBC), hemoglobin (HB) and hematocrit (HCT) after injection. Serum biochemical analysis showed an apparent increase of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), blood urea nitrogen (BUN) and creatinine (Crea). Furthermore, inflammatory cell infiltrate in liver and kidney was found by microscope. All the disorders suggested that liver, renal and hematological systems might be the target effectors of toxic effect induced by DATR. Based on the results of this study, the no observed-adverse-effect level (NOAEL) and the lowest observed-adverse-effect level of DATR in macaques are 90.0 and 135.0 mg/kg b.w., respectively.