Targeting TRAIL Death Receptors in Triple-Negative Breast Cancers: Challenges and Strategies for Cancer Therapy

The tumor necrosis factor (TNF) superfamily member TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis in cancer cells via death receptor (DR) activation with little toxicity to normal cells or tissues. The selectivity for activating apoptosis in cancer cells confers an ideal therapeutic characteristic to TRAIL, which has led to the development and clinical testing of many DR agonists. However, TRAIL/DR targeting therapies have been widely ineffective in clinical trials of various malignancies for reasons that remain poorly understood. Triple negative breast cancer (TNBC) has the worst prognosis among breast cancers. Targeting the TRAIL DR pathway has shown notable efficacy in a subset of TNBC in preclinical models but again has not shown appreciable activity in clinical trials. In this review, we will discuss the signaling components and mechanisms governing TRAIL pathway activation and clinical trial findings discussed with a focus on TNBC. Challenges and potential solutions for using DR agonists in the clinic are also discussed, including consideration of the pharmacokinetic and pharmacodynamic properties of DR agonists, patient selection by predictive biomarkers, and potential combination therapies. Moreover, recent findings on the impact of TRAIL treatment on the immune response, as well as novel strategies to address those challenges, are discussed.

Tumour Microenvironment Stress Promotes the Development of Drug Resistance

Multi-drug resistance (MDR) is a leading cause of cancer-related death, and it continues to be a major barrier to cancer treatment. The tumour microenvironment (TME) has proven to play an essential role in not only cancer progression and metastasis, but also the development of resistance to chemotherapy. Despite the significant advances in the efficacy of anti-cancer therapies, the development of drug resistance remains a major impediment to therapeutic success. This review highlights the interplay between various factors within the TME that collectively initiate or propagate MDR. The key TME-mediated mechanisms of MDR regulation that will be discussed herein include (1) altered metabolic processing and the reactive oxygen species (ROS)-hypoxia inducible factor (HIF) axis; (2) changes in stromal cells; (3) increased cancer cell survival via autophagy and failure of apoptosis; (4) altered drug delivery, uptake, or efflux and (5) the induction of a cancer stem cell (CSC) phenotype. The review also discusses thought-provoking ideas that may assist in overcoming the TME-induced MDR. We conclude that stressors from the TME and exposure to chemotherapeutic agents are strongly linked to the development of MDR in cancer cells. Therefore, there remains a vast area for potential research to further elicit the interplay between factors existing both within and outside the TME. Elucidating the mechanisms within this network is essential for developing new therapeutic strategies that are less prone to failure due to the development of resistance in cancer cells.

An Overview of Novel Agents for Cervical Cancer Treatment by Inducing Apoptosis: Emerging Drugs Ongoing Clinical Trials and Preclinical Studies

As the leading cause of cancer death, cervical cancer ranks fourth for both incidence and mortality. Cervical cancer incidence and mortality rates have reportedly decreased over the last decades thanks to extensive screening and widespread vaccination against human papilloma virus. However, there have been no major improvements concerning platinum-based chemotherapy on the survival of advanced cervical cancer. Thus, novel agents are urgently needed for the improvement of therapeutic effect. With the development of molecular biology and genomics, targeted therapy research has achieved a breakthrough development, including anti-angiogenesis, immune checkpoint inhibitors, and other treatments that are efficient for treatment of cervical cancer. Apoptosis is a crucial process for tumor progression. Drugs directed at inducing tumor-cell apoptosis are regarded as important treatment modalities. Besides, a number of novel compounds synthesized or derived from plants or microorganisms exhibited prominent anti-cancer activity by changing the apoptotic balance in cervical cancer. In this review, we summarized new target therapy drugs ongoing clinical trials that are used for treatment of cervical cancer. Further, we classified novel agents with a focus on improvement of therapeutic effect pre-clinically. To summarize, we also discussed application prospects of the new uses of old drugs and drug combinations, to provide researchers with new ideas for cervical cancer treatment.

Therapeutics Targeting the Core Apoptotic Machinery

Simple Summary

Cancer develops when the balance between cell death and cell division in tissues is dysregulated. A key focus of cancer drug discovery is identifying therapeutic agents which will selectively kill and eliminate cancer cells from the body. A number of proteins can prevent the death of cancer cells and developing inhibitors against these proteins to promote cancer cell death is a focus of recent drug discovery efforts. This review aims to summarize the key targets being explored, the drug development approaches being adopted, and the success or limitations of agents currently approved or in clinical development.

Abstract

Therapeutic targeting of the apoptotic pathways for the treatment of cancer is emerging as a valid and exciting approach in anti-cancer therapeutics. Accumulating evidence demonstrates that cancer cells are typically “addicted” to a small number of anti-apoptotic proteins for their survival, and direct targeting of these proteins could provide valuable approaches for directly killing cancer cells. Several approaches and agents are in clinical development targeting either the intrinsic mitochondrial apoptotic pathway or the extrinsic death receptor mediated pathways. In this review, we discuss the main apoptosis pathways and the key molecular targets which are the subject of several drug development approaches, the clinical development of these agents and the emerging resistance factors and combinatorial treatment approaches for this class of agents with existing and emerging novel targeted anti-cancer therapeutics.

The Antitumor Effect of Gene-Engineered Exosomes in the Treatment of Brain Metastasis of Breast Cancer

Strategies for treating brain metastases of breast cancer have demonstrated limited efficacy due to the blood–brain barrier (BBB). Gene therapy could improve the efficacy of chemotherapeutic drugs. Exosomes derived from the mesenchymal stem cells (MSCs) are small membrane-based gene vectors that can pass through the BBB. CXCR4 is the most commonly found chemokine receptor in human cancer cells. Furthermore, the SDF-1/CXCR4 axis plays an important role in the homing of MSCs for tumor cell diffusion and metastasis. TRAIL can selectively induce apoptosis in transformed cells without significant toxic side effects in normal tissues. In this study, exosomes were isolated from MSC^CXCR4+TRAIL transduced with CXCR4 and TRAIL using a lentiviral vector. Synergistic antitumor study showed that exosome^CXCR4+TRAIL exerted significant activity as a cooperative agent with carboplatin in an MDA-MB-231Br SCID mouse model, potentially engendering a novel strategy for advancing the treatment of brain metastases of breast cancer. Based on this study, further investigation of the effect of the vector on BBB and inducing apoptosis of brain tumors is warranted. In addition, the safety of the vector in animals during the treatment needs to be evaluated.

Hispidulin Enhances TRAIL-Mediated Apoptosis via CaMKK/AMPK/USP51 Axis-Mediated Bim Stabilization

Hispidulin, a natural compound present in herbs, has anti-cancer effects. Here, we investigated whether hispidulin sensitizes human carcinoma cells to apoptosis induced by TRAIL. Sub-lethal dosages of TRAIL alone and hispidulin alone does not increase apoptosis, but hispidulin increases sensitivity to TRAIL, resulting in induction of apoptosis in hispidulin plus TRAIL-treated cancer cells. In addition, combined treatment with hispidulin and TRAIL also reduced tumor growth and increased apoptosis in xenograft models. However, hispidulin did not alter cell viability in human renal normal mesangial cells and human skin fibroblast. Hispidulin markedly increased the BH3-only proteins Bim at the post-translational levels. Depletion of Bim with siRNA significantly blocked hispidulin plus TRAIL-induced apoptosis. Furthermore, we found that activation of AMPK by hispidulin has a crucial role in Bim proteins stability through up-regulation of USP51 expression. Our findings suggest that USP51-dependent stabilization of Bim by AMPK activation plays a critical role in hispidulin-mediated sensitization of cancer cells to apoptosis induced by TRAIL.

The TRAIL to cancer therapy: Hindrances and potential solutions

Apoptosis is an ordered and orchestrated cellular process that occurs in physiological and pathological conditions. Resistance to apoptosis is a hallmark of virtually all malignancies. Despite being a cause of pathological conditions, apoptosis could be a promising target in cancer treatment. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of TNF cytokine superfamily. It is a potent anti-cancer agent owing to its specific targeting towards cancerous cells, while sparing normal cells, to induce apoptosis. However, resistance occurs either intrinsically or after multiple treatments which may explain why cancer therapy fails. This review summarizes the apoptotic mechanisms via extrinsic and intrinsic apoptotic pathways, as well as the apoptotic resistance mechanisms. It also reviews the current clinically tested recombinant human TRAIL (rhTRAIL) and TRAIL receptor agonists (TRAs) against TRAIL-Receptors, TRAIL-R1 and TRAIL-R2, in which the outcomes of the clinical trials have not been satisfactory. Finally, this review discusses the current strategies in overcoming resistance to TRAIL-induced apoptosis in pre-clinical and clinical settings.

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.

Developing TRAIL/TRAIL death receptor-based cancer therapies

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can initiate the apoptosis pathway by binding to its associated death receptors DR4 and DR5. The activation of the TRAIL pathway in inducing tumor-selective apoptosis leads to the development of TRAIL-based cancer therapies, which include recombinant forms of TRAIL, TRAIL receptor agonists, and other therapeutic agents. Importantly, TRAIL, DR4, and DR5 can all be induced by synthetic and natural agents that activate the TRAIL apoptosis pathway in cancer cells. Thus, understanding the regulation of the TRAIL apoptosis pathway can aid in the development of TRAIL-based therapies for the treatment of human cancer.

Downregulation of SKP2 in Papillary Thyroid Cancer Acts Synergistically With TRAIL on Inducing Apoptosis via ROS

CONTEXT AND OBJECTIVE

S-phase kinase protein 2 (SKP2) is an F-box protein with proteasomal properties and has been found to be overexpressed in a variety of cancers. However, its role in papillary thyroid cancer (PTC) has not been fully elucidated.

EXPERIMENTAL DESIGN

SKP2 expression was assessed by immunohistochemistry in a tissue microarray format on a cohort of >1000 PTC samples. In vitro and in vivo studies were performed using proteasome inhibitor bortezomib and proapoptopic death ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) either alone or in combination on PTC cell lines.

RESULTS

SKP2 was overexpressed in 45.5% of PTC cases and was significantly associated with extrathyroidal extension (P = 0.0451), distant metastasis (P = 0.0435), and tall cell variant (P = 0.0271). SKP2 overexpression was also directly associated with X-linked inhibitor of apoptosis protein overexpression (P < 0.0001) and Bcl-xL overexpression (P = 0.0005) and inversely associated with death receptor 5 (P < 0.0001). The cotreatment of bortezomib and TRAIL synergistically induced apoptosis via mitochondrial apoptotic pathway in PTC cell lines. Furthermore, bortezomib and TRAIL synergistically induced reactive oxygen species (ROS) generation and caused death receptor 5 upregulation through activation of the extracellular signal-regulated kinase-C/EBP homologous protein signaling cascade. Finally, bortezomib treatment augmented the TRAIL-mediated anticancer effect on PTC xenograft tumor growth in nude mice.

CONCLUSION

These data suggest that SKP2 is a potential therapeutic target in PTC and that a combination of bortezomib and TRAIL might be a viable therapeutic option for the treatment of patients with aggressive PTC.

Activation of autophagic flux by epigallocatechin gallate mitigates TRAIL-induced tumor cell apoptosis via down-regulation of death receptors

Epigallocatechin gallate (EGCG) is a major polyphenol in green tea. Recent studies have reported that EGCG can inhibit TRAIL-induced apoptosis and activate autophagic flux in cancer cells. However, the mechanism behind these processes is unclear. The present study found that EGCG prevents tumor cell death by antagonizing the TRAIL pathway and activating autophagy flux. Our results indicate that EGCG dose-dependently inhibits TRAIL-induced apoptosis and decreases the binding of death receptor 4 and 5 (DR4 and 5) to TRAIL. In addition, EGCG activates autophagy flux, which is involved in the inhibition of TRAIL cell death. We confirmed that the protective effect of EGCG can be reversed using genetic and pharmacological tools through re-sensitization to TRAIL. The inhibition of autophagy flux affects not only the re-sensitization of tumor cells to TRAIL, but also the restoration of death receptor proteins. This study demonstrates that EGCG inhibits TRAIL-induced apoptosis through the manipulation of autophagic flux and subsequent decrease in number of death receptors. On the basis of these results, we suggest further consideration of the use of autophagy activators such as EGCG in combination anti-tumor therapy with TRAIL.

Identification of miRNA-7 by genome-wide analysis as a critical sensitizer for TRAIL-induced apoptosis in glioblastoma cells

Glioblastoma (GBM) is still one of the most lethal forms of brain tumor despite of the improvements in treatments. TRAIL (TNF-related apoptosis-inducing ligand) is a promising anticancer agent that can be potentially used as an alternative or complementary therapy because of its specific antitumor activity. To define the novel pathways that regulate susceptibility to TRAIL in GBM cells, we performed a genome-wide expression profiling of microRNAs in GBM cell lines with the distinct sensitivity to TRAIL-induced apoptosis. We found that the expression pattern of miR-7 is closely correlated with sensitivity of GBM cells to TRAIL. Furthermore, our gain and loss of function experiments showed that miR-7 is a potential sensitizer for TRAIL-induced apoptosis in GBM cells. In the mechanistic study, we identified XIAP is a direct downstream gene of miR-7. Additionally, this regulatory axis could also exert in other types of tumor cells like hepatocellular carcinoma cells. More importantly, in the xenograft model, enforced expression of miR-7 in TRAIL-overexpressed mesenchymal stem cells increased apoptosis and suppressed tumor growth in an exosome dependent manner. In conclusion, we identify that miR-7 is a critical sensitizer for TRAIL-induced apoptosis, thus making it as a promising therapeutic candidate for TRAIL resistance in GBM cells.

Metformin sensitizes triple-negative breast cancer to proapoptotic TRAIL receptor agonists by suppressing XIAP expression

PURPOSE

Despite robust antitumor activity in diverse preclinical models, TNF-related apoptosis-inducing ligand (TRAIL) receptor agonists have not demonstrated efficacy in clinical trials, underscoring the need to identify agents that enhance their activity. We postulated that the metabolic stress induced by the diabetes drug metformin would sensitize breast cancer cells to TRAIL receptor agonists.

METHODS

Human triple (estrogen receptor, progesterone receptor, and HER2)-negative breast cancer (TNBC) cell lines were treated with TRAIL receptor agonists (monoclonal antibodies or TRAIL peptide), metformin, or the combination. The effects on cell survival, caspase activation, and expression of TRAIL receptors and the antiapoptotic protein XIAP were determined. In addition, XIAP was silenced by RNAi in TNBC cells and the effects on sensitivity to TRAIL were determined. The antitumor effects of metformin, TRAIL, or the combination were evaluated in an orthotopic model of metastatic TNBC.

RESULTS

Metformin sensitized diverse TNBC cells to TRAIL receptor agonists. Metformin selectively enhanced the sensitivity of transformed breast epithelial cells to TRAIL receptor agonist-induced caspase activation and apoptosis with little effect on untransformed breast epithelial cells. These effects of metformin were accompanied by robust reductions in the protein levels of XIAP, a negative regulator of TRAIL-induced apoptosis. Silencing XIAP in TNBC cells mimicked the TRAIL-sensitizing effects of metformin. Metformin also enhanced the antitumor effects of TRAIL in a metastatic murine TNBC model.

CONCLUSIONS

Our findings indicate that metformin enhances the activity of TRAIL receptor agonists, thereby supporting the rationale for additional translational studies combining these agents.

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.

Niacin alleviates TRAIL-mediated colon cancer cell death via autophagy flux activation

Niacin, also known as vitamin B₃ or nicotinamide is a water-soluble vitamin that is present in black beans and rice among other foods. Niacin is well known as an inhibitor of metastasis in human breast carcinoma cells but the effect of niacin treatment on TRAIL-mediated apoptosis is unknown. Here, we show that niacin plays an important role in the regulation of autophagic flux and protects tumor cells against TRAIL-mediated apoptosis. Our results indicated that niacin activated autophagic flux in human colon cancer cells and the autophagic flux activation protected tumor cells from TRAIL-induced dysfunction of mitochondrial membrane potential and tumor cell death. We also demonstrated that ATG5 siRNA and autophagy inhibitor blocked the niacin-mediated inhibition of TRAIL-induced apoptosis. Taken together, our study is the first report demonstrating that niacin inhibits TRAIL-induced apoptosis through activation of autophagic flux in human colon cancer cells. And our results also suggest that autophagy inhibitors including genetic and pharmacological tools may be a successful therapeutics during anticancer therapy using TRAIL.

Targeting miRNAs associated with surface expression of death receptors to modulate TRAIL resistance in breast cancer

Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) is capable of inducing apoptosis upon engagement of its death receptors (DRs) 4 and 5. TRAIL therapy has garnered intense interest as one of the most promising agents for cancer therapy, for its selective induction of tumor-cell apoptosis while low toxicity to most normal cells. However, a variety of breast cancer cell lines could be resistant to TRAIL-induced apoptosis. Absence of DR4 and DR5 on the breast cancer cell surface has been proposed to be critically involved in resistance to TRAIL and its agonistic antibodies. Moreover, endocytosis and autophagy in breast cancer cells could induce TRAIL resistance through downregulation of surface DR4/5. MicroRNAs (miRNAs), as endogenously expressed small non-coding RNAs, function as regulators of gene expression and involve tremendous biological processes including drug resistance. In this review, we highlight recent advances in the functional role of miRNAs in endocytosis and autophagy pathways. This review aims to present that, through regulation of critical molecules involved in autophagy and endocytosis, miRNAs could lead to mislocalization of DR4/5 in breast cancer cells and therefore play an important role in TRAIL-mediated apoptosis and TRAIL resistance.

Genome-Wide Meta-Analyses of Breast, Ovarian, and Prostate Cancer Association Studies Identify Multiple New Susceptibility Loci Shared by at Least Two Cancer Types

Breast, ovarian, and prostate cancers are hormone-related and may have a shared genetic basis, but this has not been investigated systematically by genome-wide association (GWA) studies. Meta-analyses combining the largest GWA meta-analysis data sets for these cancers totaling 112,349 cases and 116,421 controls of European ancestry, all together and in pairs, identified at P < 10(-8) seven new cross-cancer loci: three associated with susceptibility to all three cancers (rs17041869/2q13/BCL2L11; rs7937840/11q12/INCENP; rs1469713/19p13/GATAD2A), two breast and ovarian cancer risk loci (rs200182588/9q31/SMC2; rs8037137/15q26/RCCD1), and two breast and prostate cancer risk loci (rs5013329/1p34/NSUN4; rs9375701/6q23/L3MBTL3). Index variants in five additional regions previously associated with only one cancer also showed clear association with a second cancer type. Cell-type-specific expression quantitative trait locus and enhancer-gene interaction annotations suggested target genes with potential cross-cancer roles at the new loci. Pathway analysis revealed significant enrichment of death receptor signaling genes near loci with P < 10(-5) in the three-cancer meta-analysis.

SIGNIFICANCE

We demonstrate that combining large-scale GWA meta-analysis findings across cancer types can identify completely new risk loci common to breast, ovarian, and prostate cancers. We show that the identification of such cross-cancer risk loci has the potential to shed new light on the shared biology underlying these hormone-related cancers. Cancer Discov; 6(9); 1052-67. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 932.

Novel targets for paclitaxel nano formulations: Hopes and hypes in triple negative breast cancer

Triple negative breast cancer is defined as one of the utmost prevailing breast cancers worldwide, possessing an inadequate prognosis and treatment option limited to chemotherapy and radiotherapy, creating a challenge for researchers as far as developing a specific targeted therapy is concerned. The past research era has shown several promising outcomes for TNBC such as nano-formulations of the chemotherapeutic agents already used for the management of the malignant tumor. Taking a glance at paclitaxel nano formulations, it has been proven beneficial in several researches in the past decade; nevertheless its solubility is often a challenge to scientists in achieving success. We have henceforth discussed the basic heterogeneity of triple negative breast cancer along with the current management options as well as a brief outlook on pros and cons of paclitaxel, known as the most widely used chemotherapeutic agent for the treatment of the disease. We further analyzed the need of nanotechnology pertaining to the problems encountered with the current paclitaxel formulations available discussing the strategic progress in various nano-formulations till date taking into account the basic research strategies required in terms of solubility, permeability, physicochemical properties, active and passive targeting. A thorough review in recent advances in active targeting for TNBC was carried out whereby the various ligands which are at present finding its way into TNBC research such as hyaluronic acid, folic acid, transferrin, etc. were discussed. These ligands have specific receptor affinity to TNBC tumor cells hence can be beneficial for novel drug targeting approaches. Conversely, there are currently several novel strategies in the research pipeline whose targeting ligands have not yet been studied. Therefore, we reviewed upon the numerous novel receptor targets along with the respective nano-formulation aspects which have not yet been fully researched upon and could be exemplified as outstanding target strategies for TNBC which is currently an urgent requirement.

Folate receptor-targeted aminoglycoside-derived polymers for transgene expression in cancer cells

Targeted delivery of anticancer therapeutics can potentially overcome the limitations associated with current chemotherapeutic regimens. Folate receptors are overexpressed in several cancers, including ovarian, triple-negative breast and bladder cancers, making them attractive for targeted delivery of nucleic acid therapeutics to these tumors. This work describes the synthesis, characterization and evaluation of folic acid-conjugated, aminoglycoside-derived polymers for targeted delivery of transgenes to breast and bladder cancer cell lines. Transgene expression was significantly higher with FA-conjugated aminoglycoside-derived polymers than with Lipofectamine, and these polymers demonstrated minimal cytotoxicty. Competitive inhibition using free folic acid significantly reduced transgene expression efficacy of folate-targeted polymers, suggesting a role for folate receptor-mediated uptake. High efficacy FA-targeted polymers were employed to deliver a plasmid expressing the TRAIL protein, which induced death in cancer cells. These results indicate that FA-conjugated aminoglycoside-derived polymers are promising for targeted delivery of nucleic acids to cancer cells that overexpress folate receptors.

The pyrrolo-1,5-benzoxazepine, PBOX-15, enhances TRAIL‑induced apoptosis by upregulation of DR5 and downregulation of core cell survival proteins in acute lymphoblastic leukaemia cells

Apoptotic defects are frequently associated with poor outcome in pediatric acute lymphoblastic leukaemia (ALL) hence there is an ongoing demand for novel strategies that counteract apoptotic resistance. The death ligand TRAIL (tumour necrosis factor-related apoptosis-inducing ligand) and its selective tumour receptor system has attracted exceptional clinical interest. However, many malignancies including ALL are resistant to TRAIL monotherapy. Tumour resistance can be overcome by drug combination therapy. TRAIL and its agonist antibodies are currently undergoing phase II clinical trials with established chemotherapeutics. Herein, we present promising therapeutic benefits in combining TRAIL with the selective anti-leukaemic agents, the pyrrolo-1,5-benzoxazepines (PBOXs) for the treatment of ALL. PBOX-15 synergistically enhanced apoptosis induced by TRAIL and a DR5-selective TRAIL variant in ALL-derived cells. PBOX-15 enhanced TRAIL-induced apoptosis by dual activation of extrinsic and intrinsic apoptotic pathways. The specific caspase-8 inhibitor, Z-IETD-FMK, identified the extrinsic pathway as the principal mode of apoptosis. We demonstrate that PBOX-15 can enhance TRAIL-induced apoptosis by upregulation of DR5, reduction of cellular mitochondrial potential, activation of the caspase cascade and downregulation of PI3K/Akt, c-FLIP, Mcl-1 and IAP survival pathways. Of note, the PI3K pathway inhibitor LY-294002 significantly enhanced the apoptotic potential of TRAIL and PBOX-15 validating the importance of Akt downregulation in the TRAIL/PBOX-15 synergistic combination. Considering the lack of cytotoxicity to normal cells and ability to downregulate several survival pathways, PBOX-15 may represent an effective agent for use in combination with TRAIL for the treatment of ALL.

Novel Water-Borne Polyurethane Nanomicelles for Cancer Chemotherapy: Higher Efficiency of Folate Receptors Than TRAIL Receptors in a Cancerous Balb/C Mouse Model

PURPOSE

Since the introduction of nanocarriers, the delivery of chemotherapeutic agents for treatment of patients with cancer has been possible with better effectiveness. The latest findings are also support that further enhancement in therapeutic effectiveness of these nanocarriers can be attained, if surface decoration with proper targeting agents is considered.

METHODS

This study aimed at treating a variety of 4T1 murine breast cancer cell line, mainly demonstrating high folate and TRAIL receptor expression of cancerous cells. The therapeutic efficacy of paclitaxel loaded Cremophore EL (Taxol®), paclitaxel loaded waterborne polyurethane nanomicelles (PTX-PU) and paclitaxel loaded waterborne polyurethane nanomicelles conjugated with folate (PTX-PU-FA) and TRAIL (PTX-PU-TRAIL) on treating 4T1 cell was also compared.

RESULTS

The findings that worth noting are: PTX-PU outperformed Taxol® in a Balb/C mouse model, furthermore, tumor growth was adequately curbed by folate and TRAIL-decorated nanomicelles rather than the unconjugated formulation. Tumors of mice treated with PTX-PU-FA and PTX-PU-TRAIL shrank substantially compared to those treated with Taxol®, PTX-PU and PTX-PU-TRAIL (average 573 mm(3) versus 2640, 846, 717 mm(3) respectively), 45 days subsequent to tumor inoculation. The microscopic study of hematoxylin-eosin stained tumors tissue and apoptotic cell fraction substantiated that the most successful therapeutic effects have been observed for the mice treated with PTX-PU-FA (about 90% in PTX-PU-FA versus 75%, 60%, 15% in PTX-PU-TRAIL, PTX-PU, and Taxol® group respectively).

CONCLUSIONS

Using folate-targeted nanocarriers to treat cancers characterized by a high level of folate ligand expression is well substantiated by the findings of this study.

A randomized, double-blind, placebo-controlled phase II study to assess the efficacy and safety of mapatumumab with sorafenib in patients with advanced hepatocellular carcinoma

BACKGROUND

This randomized, double-blind, placebo-controlled, phase II study evaluated the efficacy and safety of mapatumumab (a human agonistic monoclonal antibody against tumor necrosis factor-related apoptosis-inducing ligand receptor 1) in combination with sorafenib in patients with advanced hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

Patients with advanced HCC (stratified by Barcelona Clinic Liver Cancer stage and Eastern Cooperative Oncology Group performance status) were randomized 1:1 to receive sorafenib (400 mg, twice daily per 21-day cycle) and either placebo (placebo-sorafenib arm) or mapatumumab (30 mg/kg on day 1 per 21-day cycle; mapatumumab-sorafenib arm). The primary end point was time to (radiologic) progression (TTP), assessed by blinded independent central review. Key secondary end points included progression-free survival, overall survival, and objective response.

RESULTS

In total, 101 patients were randomized (placebo-sorafenib arm: N = 51; mapatumumab-sorafenib arm: N = 50). There was no significant difference in median TTP between both arms [5.6 versus 4.1 months, respectively; adjusted hazard ratio (one-sided 90% confidence interval) 1.192 (0-1.737)]. No mapatumumab-related benefit was identified when TTP was evaluated in the stratified subgroups. The addition of mapatumumab to sorafenib did not demonstrate improvement in the secondary efficacy end points. The reported frequency of adverse events (AEs) and serious AEs was comparable in both treatment arms.

CONCLUSIONS

The addition of mapatumumab to sorafenib did not improve TTP or other efficacy end points, nor did it substantially change the toxicity profile of sorafenib in patients with advanced HCC. Based on these results, further development of the combination of mapatumumab and sorafenib in HCC is not planned.

TRAIL-based therapy in pediatric bone tumors: how to overcome resistance

Osteosarcoma and Ewing's sarcoma, the two most frequent malignant primary tumors preferentially arise in children and young adults, and have a poor prognosis. TRAIL represents a promising therapeutic approach for most cancers but in the case of primary bone tumors, osteosarcoma cell lines are highly resistant to this pro-apoptotic cytokine. In addition, another signaling pathway mediating cell proliferation and migration may be even activated in this subset of resistant cells leading to protumoral effect. Therapeutic perspectives are linked to possibility to overcome TRAIL resistance by combining other drugs with TRAIL or death receptors agonistic antibodies. We hypothesized that the bone microenvironment may provide a favorable niche for TRAIL resistance that might be targeted by new resensitizing agents.

Delivery of tumor-homing TRAIL sensitizer with long-acting TRAIL as a therapy for TRAIL-resistant tumors

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) has attracted great interest as a cancer therapy because it selectively induces death receptor (DR)-mediated apoptosis in cancer cells while sparing normal tissue. However, recombinant human TRAIL demonstrates limited therapeutic efficacy in clinical trials, possibly due to TRAIL-resistance of primary cancers and its inherent short half-life. Here we introduce drug delivery approaches to maximize in vivo potency of TRAIL in TRAIL-resistant tumor xenografts by (1) extending the half-life of the ligand with PEGylated TRAIL (TRAILPEG) and (2) concentrating a TRAIL sensitizer, selected from in vitro screening, in tumors via tumor-homing nanoparticles. Antitumor efficacy of TRAILPEG with tumor-homing sensitizer was evaluated in HCT116 and HT-29 colon xenografts. Western blot, real-time PCR, immunohistochemistry and cell viability assays were employed to investigate mechanisms of action and antitumor efficacy of the combination. We discovered that doxorubicin (DOX) sensitizes TRAIL-resistant HT-29 colon cancer cells to TRAIL by upregulating mRNA expression of DR5 by 60% in vitro. Intravenously administered free DOX does not effectively upregulate DR5 in tumor tissues nor demonstrate synergy with TRAILPEG in HT-29 xenografts, but rather introduces significant systemic toxicity. Alternatively, when DOX was encapsulated in hyaluronic acid-based nanoparticles (HAC/DOX) and intravenously administered with TRAILPEG, DR-mediated apoptosis was potentiated in HT-29 tumors by upregulating DR5 protein expression by 70% and initiating both extrinsic and intrinsic apoptotic pathways with reduced systemic toxicity compared to HAC/DOX or free DOX combined with TRAILPEG (80% vs. 40% survival rate; 75% vs. 34% tumor growth inhibition). This study demonstrates a unique approach to overcome TRAIL-based therapy drawbacks using sequential administration of a tumor-homing TRAIL sensitizer and long-acting TRAILPEG.

The role of Cullin3-mediated ubiquitination of the catalytic subunit of PP2A in TRAIL signaling

Protein phosphatase 2A (PP2A) is the major serine-threonine phosphatase that regulates a number of cell signaling pathways. PP2A activity is controlled partially through protein degradation; however, the underlying mechanism is not fully understood. Here we show that PP2A/C, a catalytic subunit of PP2A, is degraded by the Cullin3 (Cul3) ligase-mediated ubiquitin-proteasome pathway. In response to death receptor signaling by tumor-necrosis factor-related apoptosis-inducing ligand (TRAIL), PP2A/C, caspase-8 and Cul3, a subunit of the cullin family of E3 ligases, are recruited into the death-inducing signaling complex (DISC) where the Cul3 ligase targets PP2A/C for ubiquitination and subsequent degradation. Functionally, knockdown of PP2A/C expression by siRNA or pharmacological inhibition of PP2A activity increases TRAIL-induced apoptosis. In cancer cells that have developed acquired TRAIL resistance, PP2A phosphatase activity is increased, and PP2A/C protein is resistant to TRAIL-induced degradation. Thus, this work identifies a new mechanism by which PP2A/C is regulated by Cul3 ligase-mediated degradation in response to death receptor signaling and suggests that inhibition of PP2A/C degradation may contribute to resistance of cancer cells to death receptor-induced apoptosis.

Therapeutic applications of TRAIL receptor agonists in cancer and beyond

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

H-Ras regulation of TRAIL death receptor mediated apoptosis

TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis through the death receptors (DRs) 4 and/or 5 expressed on the cell surface. Multiple clinical trials are underway to evaluate the antitumor activity of recombinant human TRAIL and agonistic antibodies to DR4 or DR5. However, their therapeutic potential is limited by the high frequency of cancer resistance. Here we provide evidence demonstrating the role of H-Ras in TRAIL receptor mediated apoptosis. By analyzing the genome wide mRNA expression data of the NCI60 cancer cell lines, we found that H-Ras expression was consistently upregulated in TRAIL-resistant cell lines. By contrast, no correlation was found between TRAIL sensitivity and K-Ras expression levels or their mutational profiles. Notably, H-Ras upregulation associated with a surface deficiency of TRAIL death receptors. Selective inhibition of H-Ras activity in TRAIL-resistant cells restored the surface expression of both DR4 and DR5 without changing their total protein levels. The resulting cells became highly susceptible to both TRAIL and agonistic DR5 antibody, whereas K-Ras inhibition had little or no effect on TRAIL-induced apoptosis, indicating H-Ras plays a distinct role in the regulation of TRAIL death receptors. Further studies are warranted to determine the therapeutic potential of H-Ras-specific inhibitors in combination with TRAIL receptor agonists.

Identification of TRAIL-inducing compounds highlights small molecule ONC201/TIC10 as a unique anti-cancer agent that activates the TRAIL pathway

Background

We previously reported the identification of ONC201/TIC10, a novel small molecule inducer of the human TRAIL gene that improves efficacy-limiting properties of recombinant TRAIL and is in clinical trials in advanced cancers based on its promising safety and antitumor efficacy in several preclinical models.

Methods

We performed a high throughput luciferase reporter screen using the NCI Diversity Set II to identify TRAIL-inducing compounds.

Results

Small molecule-mediated induction of TRAIL reporter activity was relatively modest and the majority of the hit compounds induced low levels of TRAIL upregulation. Among the candidate TRAIL-inducing compounds, TIC9 and ONC201/TIC10 induced sustained TRAIL upregulation and apoptosis in tumor cells in vitro and in vivo. However, ONC201/TIC10 potentiated tumor cell death while sparing normal cells, unlike TIC9, and lacked genotoxicity in normal fibroblasts. Investigating the effects of TRAIL-inducing compounds on cell signaling pathways revealed that TIC9 and ONC201/TIC10, which are the most potent inducers of cell death, exclusively activate Foxo3a through inactivation of Akt/ERK to upregulate TRAIL and its pro-apoptotic death receptor DR5.

Conclusion

These studies reveal the selective activity of ONC201/TIC10 that led to its selection as a lead compound for this novel class of antitumor agents and suggest that ONC201/TIC10 is a unique inducer of the TRAIL pathway through its concomitant regulation of the TRAIL ligand and its death receptor DR5.

Targeting TNF-related apoptosis-inducing ligand (TRAIL) receptor by natural products as a potential therapeutic approach for cancer therapy

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to selectively induce apoptotic cell death in various tumor cells by engaging its death-inducing receptors (TRAIL-R1 and TRAIL-R2). This property has led to the development of a number of TRAIL-receptor agonists such as the soluble recombinant TRAIL and agonistic antibodies, which have shown promising anticancer activity in preclinical studies. However, besides activating caspase-dependent apoptosis in several cancer cells, TRAIL may also activate nonapoptotic signal transduction pathways such as nuclear factor-kappa B, mitogen-activated protein kinases, AKT, and signal transducers and activators of transcription 3, which may contribute to TRAIL resistance that is being now frequently encountered in various cancers. TRAIL resistance can be overcome by the application of efficient TRAIL-sensitizing pharmacological agents. Natural compounds have shown a great potential in sensitizing cells to TRAIL treatment through suppression of distinct survival pathways. In this review, we have summarized both apoptotic and nonapoptotic pathways activated by TRAIL, as well as recent advances in developing TRAIL-receptor agonists for cancer therapy. We also briefly discuss combination therapies that have shown great potential in overcoming TRAIL resistance in various tumors.

Spatial dynamics of TRAIL death receptors in cancer cells

TNF-related apoptosis inducing ligand (TRAIL) selectively induces apoptosis in cancer cells without harming most normal cells. Currently, multiple clinical trials are underway to evaluate the antitumor activity of recombinant human TRAIL (rhTRAIL) and agonistic antibodies that target death receptors (DRs) 4 or 5. It is encouraging that these products have shown a tolerated safety profile in early phase studies. However, their therapeutic potential is likely limited by the emergence of tumor drug resistance phenomena. Increasing evidence indicates that TRAIL DRs are deficient on the plasma membrane of some cancer cells despite their total protein expression. Notably, the lack of surface DR4/DR5 is sufficient to render cancers resistant to TRAIL-induced apoptosis, regardless of the status of other apoptosis signaling components. The current review highlights recent findings on the dynamic expression of TRAIL death receptors, including the regulatory roles of endocytosis, autophagy, and Ras GTPase-mediated signaling events. This information could aid in the identification of novel predictive biomarkers of tumor response as well as the development of combinational drugs to overcome or bypass tumor drug resistance to TRAIL receptor-targeted therapies.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Accumulation of autophagosomes in breast cancer cells induces TRAIL resistance through downregulation of surface expression of death receptors 4 and 5

TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis through death receptors (DRs) 4 and/or 5 expressed on the surface of target cells. We have previously shown that deficiency of DR4 and DR5 on the surface membrane is a critical mechanism of cancer cell resistance to the recombinant human TRAIL and its receptor agonistic antibodies, which are being evaluated clinically for treating cancers. In certain cancer cells, DR4 and DR5 were found to be mislocalized in intracellular compartments yet to be characterized. Here, we report a novel role of autophagy in the regulation of dynamics of TRAIL death receptors. We first assessed basal levels of autophagosomes in a panel of 11 breast cancer cell lines using complementary approaches (LC3 immunoblotting, RFP-LC3 fluorescence microscopy, and electron microscopy). We found high levels of basal autophagosomes in TRAIL resistant breast cancer cell lines (e.g. BT474 and AU565) and relevant mouse xenograft models under nutrition-rich conditions. Notably, DR4 and DR5 co-localized with LC3-II in the autophagosomes of TRAIL-resistant cells. Disruption of basal autophagosomes successfully restored the surface expression of the death receptors which was accompanied by sensitization of TRAIL-resistant cells to TRAIL induced apoptosis. By contrast, TRAIL-sensitive cell lines (MDA-MB-231) are characterized by high levels of surface DR4/DR5 and an absence of basal autophagosomes. Inhibition of lysosomal activity induced an accumulation of autophagosomes and a decrease in surface DR4 and DR5, and the cells became less sensitive to TRAIL-induced apoptosis. These findings demonstrate a novel role for the basal autophagosomes in the regulation of TRAIL death receptors. Further studies are warranted to explore the possibility of using autophagosome markers such as LC3-II/LC3-I ratios for prediction of tumor resistance to TRAIL related therapies. The results also provide a rationale for future non-clinical and clinical studies testing TRAIL agonists in combination with agents that directly inhibit autophagosome assembly.

Getting TRAIL back on track for cancer therapy

Unlike other members of the TNF superfamily, the TNF-related apoptosis-inducing ligand (TRAIL, also known as Apo2L) possesses the unique capacity to induce apoptosis selectively in cancer cells in vitro and in vivo. This exciting discovery provided the basis for the development of TRAIL-receptor agonists (TRAs), which have demonstrated robust anticancer activity in a number of preclinical studies. Subsequently initiated clinical trials testing TRAs demonstrated, on the one hand, broad tolerability but revealed, on the other, that therapeutic benefit was rather limited. Several factors that are likely to account for TRAs' sobering clinical performance have since been identified. First, because of initial concerns over potential hepatotoxicity, TRAs with relatively weak agonistic activity were selected to enter clinical trials. Second, although TRAIL can induce apoptosis in several cancer cell lines, it has now emerged that many others, and importantly, most primary cancer cells are resistant to TRAIL monotherapy. Third, so far patients enrolled in TRA-employing clinical trials were not selected for likelihood of benefitting from a TRA-comprising therapy on the basis of a valid(ated) biomarker. This review summarizes and discusses the results achieved so far in TRA-employing clinical trials in the light of these three shortcomings. By integrating recent insight on apoptotic and non-apoptotic TRAIL signaling in cancer cells, we propose approaches to introduce novel, revised TRAIL-based therapeutic concepts into the cancer clinic. These include (i) the use of recently developed highly active TRAs, (ii) the addition of efficient, but cancer-cell-selective TRAIL-sensitizing agents to overcome TRAIL resistance and (iii) employing proteomic profiling to uncover resistance mechanisms. We envisage that this shall enable the design of effective TRA-comprising therapeutic concepts for individual cancer patients in the future.

Dual inactivation of Akt and ERK by TIC10 signals Foxo3a nuclear translocation, TRAIL gene induction, and potent antitumor effects

Recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an antitumor protein that is in clinical trials as a potential anticancer therapy but suffers from drug properties that may limit efficacy such as short serum half-life, stability, cost, and biodistribution, particularly with respect to the brain. To overcome such limitations, we identified TRAIL-inducing compound 10 (TIC10), a potent, orally active, and stable small molecule that transcriptionally induces TRAIL in a p53-independent manner and crosses the blood-brain barrier. TIC10 induces a sustained up-regulation of TRAIL in tumors and normal cells that may contribute to the demonstrable antitumor activity of TIC10. TIC10 inactivates kinases Akt and extracellular signal-regulated kinase (ERK), leading to the translocation of Foxo3a into the nucleus, where it binds to the TRAIL promoter to up-regulate gene transcription. TIC10 is an efficacious antitumor therapeutic agent that acts on tumor cells and their microenvironment to enhance the concentrations of the endogenous tumor suppressor TRAIL.

Tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL)

The concept to exploit death receptors for cancer therapy is very attractive, since these cell surface receptors have a direct connection to the intracellular cell death machinery. Among the death receptor superfamily, the tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL) receptor/ligand system is of special interest. TRAIL receptor agonists have recently entered the stage of clinical evaluation for the treatment of human cancers. Further insights into the regulatory mechanisms of TRAIL signaling will help to better understand the determinants of TRAIL sensitivity versus resistance of human cancers.

Phase II trial of mapatumumab, a fully human agonist monoclonal antibody to tumor necrosis factor-related apoptosis-inducing ligand receptor 1 (TRAIL-R1), in combination with paclitaxel and carboplatin in patients with advanced non-small-cell lung cancer

BACKGROUND

This phase II study examined the efficacy of mapatumumab in combination with paclitaxel and carboplatin in patients with non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with stage IIIB or stage IV advanced primary NSCLC were randomly assigned (1:1:1) to receive up to 6 courses of standard-dose paclitaxel and carboplatin or a combination of paclitaxel, carboplatin, and mapatumumab (10 mg/kg or 30 mg/kg). Primary efficacy end points were overall response rate and median progression-free survival (PFS). Secondary efficacy end points included disease control rate, overall survival (OS), time to response, and duration of response. Exploratory studies included evaluation of historical biopsy materials for TRAIL-R1 expression by immunohistochemical analysis and serum levels of M30, a marker of apoptosis, before and after the first 2 doses of mapatumumab. Safety parameters, including adverse events (AEs), laboratory tests, and immunogenicity, were assessed.

RESULTS

The majority of patients had stage IV disease (79%) and an Eastern Cooperative Oncology Group (ECOG) performance status of 0 (58%); baseline characteristics were similar across treatment arms. No improvements in response or disease control rates, PFS, or OS were gained from the addition of mapatumumab. Adverse events in the mapatumumab arms were generally consistent with toxicities seen in the carboplatin and paclitaxel control arm. Levels of M30 were highly variable, and consistent patterns were not seen across treatment arms.

CONCLUSION

This study showed no clinical benefit from adding mapatumumab to carboplatin and paclitaxel in unselected patients with NSCLC. The combination was generally well tolerated. The possibility of subgroups sensitive to mapatumumab is discussed.

Death receptor agonist therapies for cancer, which is the right TRAIL?

The activation of cell-surface death receptors represents an attractive therapeutic strategy to promote apoptosis of tumor cells. Several investigational therapeutics that target this extrinsic pathway, including recombinant human Apo2L/TRAIL and monoclonal agonist antibodies directed against death receptors-4 (DR4) or -5 (DR5), have been evaluated in the clinic. Although Phase 1/1b studies provided encouraging preliminary results, findings from randomized Phase 2 studies failed to demonstrate significant clinical benefit. This has raised multiple questions as to why pre-clinical data were not predictive of clinical response. Results from clinical studies and insight into why current agents have failed to yield robust responses are discussed. In addition, new strategies for the development of next generation death receptor agonists are reviewed.

Regulation of the Src-PP2A interaction in tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis

TNF-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in transformed and tumor cells but not in normal cells, making it a promising agent for cancer therapy. However, many cancer cells are resistant to TRAIL, and the underlying mechanisms are not fully understood. Here, we show that the regulation of the PP2A and Src interaction plays a critical role in TRAIL resistance. Specifically, we show that TRAIL treatment activates the tyrosine kinase Src, which subsequently phosphorylates caspase-8 at tyrosine 380, leading to the inhibition of caspase-8 activation. We also show that upon TRAIL treatment, Src, caspase-8, and PP2A/C (a catalytic subunit of the PP2A phosphatase) are redistributed into lipid rafts, a microdomain of the plasma membrane enriched with cholesterol, where PP2A dephosphorylates Src at tyrosine 418 and in turn inhibits caspase-8 phosphorylation. Furthermore, we find that TRAIL treatment causes PP2A/C degradation. These data suggest that the balance between Src-mediated caspase-8 phosphorylation and the inactivation of Src-mediated caspase-8 phosphorylation by PP2A determines the outcome of TRAIL treatment in breast cancer cells. Therefore, this work identifies a novel mechanism by which the interaction between PP2A and Src in the context of caspase-8 activation modulates TRAIL sensitivity in cancer cells.

TRAIL receptor agonist conatumumab with modified FOLFOX6 plus bevacizumab for first-line treatment of metastatic colorectal cancer: A randomized phase 1b/2 trial

BACKGROUND

In patients with previously untreated metastatic colorectal cancer (mCRC), we conducted a phase 1b/randomized phase 2 trial to define the safety, tolerability, and efficacy of mFOLFOX6 plus bevacizumab (mFOLFOX6/bev) with conatumumab, an investigational, fully human monoclonal IgG1 antibody that specifically activates death receptor 5 (DR5).

METHODS

Twelve patients were enrolled in a phase 1b open-label dose-escalation trial of conatumumab with mFOLFOX6/bev; thereafter, 190 patients were randomized 1:1:1 to receive mFOLFOX6/bev in combination with 2 mg/kg conatumumab, 10 mg/kg conatumumab, or placebo. Therapy cycles were repeated every 2 weeks until disease progression or the occurrence of unacceptable toxicity.

RESULTS

In phase 1b, conatumumab with mFOLFOX6/bev was tolerated without apparent added toxicity over mFOLFOX6/bev alone. In phase 2, conatumumab with mFOLFOX6/bev did not confer a benefit in progression-free survival when compared with placebo with mFOLFOX6/bev. Toxicity was similar in all treatment arms. Following treatment, similar increases in circulating caspase-3 levels were observed in all arms.

CONCLUSIONS

Conatumumab with mFOLFOX6/bev did not offer improved efficacy over the same chemotherapy with placebo in first-line treatment of patients with mCRC. These data do not support further development of conatumumab in advanced CRC.

A novel inhibitor of proteasome deubiquitinating activity renders tumor cells sensitive to TRAIL-mediated apoptosis by natural killer cells and T cells

The proteasome inhibitor bortezomib simultaneously renders tumor cells sensitive to killing by natural killer (NK) cells and resistant to killing by tumor-specific T cells. Here, we show that b-AP15, a novel inhibitor of proteasome deubiquitinating activity, sensitizes tumors to both NK and T cell-mediated killing. Exposure to b-AP15 significantly increased the susceptibility of tumor cell lines of various origins to NK (p < 0.0002) and T cell (p = 0.02)-mediated cytotoxicity. Treatment with b-AP15 resulted in increased tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor-2 expression (p = 0.03) and decreased cFLIP expression in tumor cells in vitro. In tumor-bearing SCID/Beige mice, treatment with b-AP15 followed by infusion of either human NK cells or tumor-specific T cells resulted in a significantly delayed tumor progression compared with mice treated with NK cells (p = 0.006), T cells (p < 0.0001) or b-AP15 alone (p = 0.003). Combined infusion of NK and T cells in tumor-bearing BALB/c mice following treatment with b-AP15 resulted in a significantly prolonged long-term survival compared with mice treated with b-AP15 and NK or T cells (p ≤ 0.01). Our findings show that b-AP15-induced sensitization to TRAIL-mediated apoptosis could be used as a novel strategy to augment the anticancer effects of adoptively infused NK and T cells in patients with cancer.

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.

A randomized, placebo-controlled phase 2 study of ganitumab or conatumumab in combination with FOLFIRI for second-line treatment of mutant KRAS metastatic colorectal cancer

BACKGROUND

Targeted agents presently available for mutant KRAS metastatic colorectal cancer (mCRC) are bevacizumab and aflibercept. We evaluated the efficacy and safety of conatumumab (an agonistic monoclonal antibody against human death receptor 5) and ganitumab (a monoclonal antibody against the type 1 insulin-like growth factor receptor) combined with standard FOLFIRI chemotherapy as a second-line treatment in patients with mutant KRAS mCRC.

PATIENTS AND METHODS

Patients with mutant KRAS metastatic adenocarcinoma of the colon or rectum refractory to fluoropyrimidine- and oxaliplatin-based chemotherapy were randomized 1 : 1 : 1 to receive intravenous FOLFIRI plus conatumumab 10 mg/kg (Arm A), ganitumab 12 mg/kg (Arm B), or placebo (Arm C) Q2W. The primary end point was progression-free survival (PFS).

RESULTS

In total, 155 patients were randomized. Median PFS in Arms A, B, and C was 6.5 months (HR, 0.69; P = 0.147), 4.5 months (HR, 1.01; P = 0.998), and 4.6 months, respectively; median overall survival was 12.3 months (HR, 0.89; P = 0.650), 12.4 months (HR, 1.27; P = 0.357), and 12.0 months; and objective response rate was 14%, 8%, and 2%. The most common grade ≥3 adverse events in Arms A/B/C included neutropenia (30%/25%/18%) and diarrhea (18%/2%/10%).

CONCLUSIONS

Conatumumab, but not ganitumab, plus FOLFIRI was associated with a trend toward improved PFS. Both combinations had acceptable toxicity.

Pre-activation of the p53 pathway through Nutlin-3a sensitises sarcomas to drozitumab therapy

The present study evaluated the efficacy of drozitumab, a human monoclonal agonistic antibody directed against death receptor 5 (DR5), as a new therapeutic avenue for the targeted treatment of bone and soft-tissue sarcomas. The antitumour activity of drozitumab as a monotherapy or in combination with Nutlin-3a was evaluated in a panel of sarcoma cell lines in vitro and human sarcoma patient samples ex vivo. Knockdown experiments were used to investigate the central role of p53 as a regulator of drozitumab cytotoxicity. Pre-activation of the p53 pathway through Nutlin-3a upregulated DR5, subsequently sensitising sarcoma cell lines and human sarcoma specimens to the pro-apoptotic effects of drozitumab. Silencing of p53 strongly decreased DR5 mRNA expression resulting in abrogation of drozitumab-induced apoptosis. Our study provides the first pre-clinical evaluation of combination therapy using p53-activating agents with drozitumab to further sensitise sarcomas to the cytotoxic effects of DR5 antibody therapy.

Induction of death receptor 5 expression in tumor vasculature by perifosine restores the vascular disruption activity of TRAIL-expressing CD34(+) cells

The proapoptotic death receptor 5 (DR5) expressed by tumor associated endothelial cells (TECs) mediates vascular disrupting effects of human CD34(+) cells engineered to express membrane-bound tumor necrosis factor-related apoptosis-inducing ligand (CD34-TRAIL (+) cells) in mice. Indeed, lack of DR5 on TECs causes resistance to CD34-TRAIL (+) cells. By xenografting in nonobese diabetic/severe combined immunodeficient mice the TRAIL-resistant lymphoma cell line SU-DHL-4V, which generates tumors lacking endothelial DR5 expression, here we demonstrate for the first time that the Akt inhibitor perifosine induces in vivo DR5 expression on TECs, thereby overcoming tumor resistance to the vascular disruption activity of CD34-TRAIL (+) cells. In fact, CD34-TRAIL (+) cells combined with perifosine, but not CD34-TRAIL (+) cells alone, exerted marked antivascular effects and caused a threefold increase of hemorrhagic necrosis in SU-DHL-4V tumors. Consistent with lack of DR5 expression, CD34-TRAIL (+) cells failed to affect the growth of SU-DHL-4V tumors, but CD34-TRAIL (+) cells plus perifosine reduced tumor volumes by 60 % compared with controls. In view of future clinical studies using membrane-bound TRAIL, our results highlight a strategy to rescue patients with primary or acquired resistance due to the lack of DR5 expression in tumor vasculature.

Safety, pharmacokinetics, and pharmacodynamics of the DR5 antibody LBY135 alone and in combination with capecitabine in patients with advanced solid tumors

PURPOSE

We evaluated the safety, maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, biologic activity, and antitumor efficacy of the DR5 antibody, LBY135 ± capecitabine.

EXPERIMENTAL DESIGN

Escalating LBY135 was administered every 21 days, alone (Arm1) or with capecitabine (Arm2), to patients with advanced solid tumors.

RESULTS

In Arm1 (n = 40), LBY135 (0.3-40 mg/kg) resulted in no dose-limiting toxicities (DLTs); adverse events (AEs) included fatigue, hypotension, abdominal pain, dyspnea, and nausea. Stable disease (SD) was observed in 21/38 (55.3 %) patients. In Arm2 (n = 33), LBY135 (1-40 mg/kg) plus capecitabine resulted in 3 DLTs (each grade 3): dehydration and mucosal inflammation (1 mg/kg), colitis (20 mg/kg), and diarrhea (40 mg/kg). AEs included fatigue, nausea, dyspnea, and vomiting. Partial response was observed in 2 patients (rectal and breast cancer) and SD in 12/27 (44.4 %) patients. Mean elimination half-life of LBY135 ± capecitabine at saturation of clearance (≥10 mg/kg) ranged between 146 h and 492 h. Immunogenicity was detected in 16/73 (22 %) patients, of which 6 patients experienced reduced LBY135 exposure with repeat dosing. M30/M65 levels were not predictive for LBY135 response. FDG-PET responses were not consistently associated with RECIST responses.

CONCLUSIONS

LBY135 was well tolerated up to 40 mg/kg, the maximal dose administered; no MTD for LBY135 ± capecitabine was defined. Clearance was saturated at doses ≥10 mg/kg.

Doxorubicin sensitizes human tumor cells to NK cell- and T-cell-mediated killing by augmented TRAIL receptor signaling

Doxorubicin (DOX) is an anthracycline antibiotic that is widely used to treat different types of malignancy. In this study, it was studied whether DOX could be used to render tumor cells susceptible to apoptosis by NK and T cells. Pretreatment with subapoptotic doses of DOX sensitized tumor cell lines of various histotypes to both NK and T cells resulting in a 3.7 to 32.7% increase in lysis (2.5 mean fold increase, p < 0.0001) and a 2.9 to 14.2% increase in lysis (3.0 mean-fold increase, p < 0.05), respectively. The sensitizing effect of the drug was primarily dependent on the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/TRAIL-receptor signaling, but not on Fas-ligand, perforin, NKG2D or DNAM-1. The central role of the TRAIL signaling pathway was further supported by an increased expression of TRAIL-R2 on DOX-treated tumor cells and by downregulation of cellular FLICE inhibitory protein, the inhibitors of death receptor-mediated apoptosis. Compared to untreated cells, pretreatment of tumor cells with DOX showed increased processing and activation of caspase-8 on coculture with NK or T cells. The significance of this treatment strategy was confirmed using a xenogeneic tumor-bearing mouse model. Tumor progression was delayed in mice that received either NK cells (p < 0.05) or T cells (p < 0.0001) following DOX treatment compared to mice receiving either cell type alone. Moreover, combined infusion of both NK and T cells following DOX treatment not only delayed tumor progression but also significantly improved the long-term survival (p < 0.01). Based on these findings, it was proposed that DOX can be used to improve the efficacy of adoptive cell therapy in patients with cancer.