Role of endoplasmic reticulum stress in alpha-TEA mediated TRAIL/DR5 death receptor dependent apoptosis

An Update on Tamoxifen and the Chemo-Preventive Potential of Vitamin E in Breast Cancer Management

Breast cancer (BC) is the most common female cancer in terms of incidence and mortality worldwide. Tamoxifen (Nolvadex) is a widely prescribed, oral anti-estrogen drug for the hormonal treatment of estrogen-receptor-positive BC, which represents 70% of all BC subtypes. This review assesses the current knowledge on the molecular pharmacology of tamoxifen in terms of its anticancer and chemo-preventive actions. Due to the importance of vitamin E compounds, which are widely taken as a supplementary dietary component, the review focuses only on the potential importance of vitamin E in BC chemo-prevention. The chemo-preventive and onco-protective effects of tamoxifen combined with the potential effects of vitamin E can alter the anticancer actions of tamoxifen. Therefore, methods involving an individually designed, nutritional intervention for patients with BC warrant further consideration. These data are of great importance for tamoxifen chemo-prevention strategies in future epidemiological studies.

Molecular Mechanism of Tocotrienol-Mediated Anticancer Properties: A Systematic Review of the Involvement of Endoplasmic Reticulum Stress and Unfolded Protein Response

BACKGROUND

Tocotrienol, a type of vitamin E, is well known for its anti-cancer and other biological activities. This systematic review aims to summarize the involvement of endoplasmic reticulum stress (ERS) and subsequent unfolded protein response (UPR) as the underlying molecular mechanisms for the anticancer properties of tocotrienol.

METHOD

A comprehensive literature search was performed in March 2023 using the PubMed, Scopus, Web of Science, and EMBASE databases. In vitro, in vivo, and human studies were considered.

RESULT

A total of 840 articles were retrieved during the initial search, and 11 articles that fit the selection criteria were included for qualitative analysis. The current mechanistic findings are based solely on in vitro studies. Tocotrienol induces cancer cell growth arrest, autophagy, and cell death primarily through apoptosis but also through paraptosis-like cell death. Tocotrienol-rich fractions, including α-, γ- and δ-tocotrienols, induce ERS, as evidenced by upregulation of UPR markers and/or ERS-related apoptosis markers. Early endoplasmic reticulum calcium ion release, increased ceramide level, proteasomal inhibition, and upregulation of microRNA-190b were suggested to be essential in modulating tocotrienol-mediated ERS/UPR transduction. Nevertheless, the upstream molecular mechanism of tocotrienol-induced ERS is largely unknown.

CONCLUSION

ERS and UPR are essential in modulating tocotrienol-mediated anti-cancer effects. Further investigation is needed to elucidate the upstream molecular mechanism of tocotrienol-mediated ERS.

How vitamin E and its derivatives regulate tumour cells via the MAPK signalling pathway?'

In tumour cells, vitamin E and its derivatives play a critical role in the regulation of multiple signalling pathways through their oxidative and nonoxidative functions. To date, there are 8 known natural vitamin E forms and many kinds of derivatives, among which VES and α-TEA have excellent anticancer activities. The MAPK pathway consists of a complex cascade of proteins that control the proliferation, differentiation and apoptosis of tumour cells. The MAPK pathway includes four subfamilies, ERK1/2, JNK1/2, p38 MAPK, and ERK5. Most of the proteins in these subfamilies interact with each other in a complex manner. The anticancer function of vitamin E and its derivatives is closely related to the MAPK cascade. Studies have shown that in tumour cells, α-T/γ-T/γ-T3/δ-T3/VES/α-TEA regulated ERK1/2, prevent tumorigenesis, inhibit tumour cell growth and metastasis and induce cell differentiation, apoptosis, and cell cycle arrest; γ-T3/δ-T3/VES/α-TEA regulates JNK1/2, induce apoptosis, reduce ceramide synthesis and inhibit proliferation; and γ-T3/δ-T3/VES regulate p38 MAPK and induce apoptosis. This paper reviews the role of vitamin E and its derivatives in the MAPK cascade, and tumour cells are used as a model in an attempt to explore the mechanism of their interactions.

The recombinant Newcastle disease virus Anhinga strain expressing human TRAIL exhibit antitumor effects on a glioma nude mice model

Oncolytic virus therapy is perhaps the next major breakthrough in cancer treatment following the success in immunotherapy using immune checkpoint inhibitors. However, the potential oncolytic ability of the recombinant newcastle disease virus (NDV) Anhinga strain carried with tumor necrosis factor-related apoptosis inducing ligand (TRAIL) has not been fully explored at present. In the present study, the recombinant NDV/Anh-TRAIL that secretes soluble TRAIL was constructed and the experiment results suggested NDV/Anh-TRAIL as a promising candidate for glioma therapy. Growth kinetic and TRAIL secreted quantity of recombinant NDV/Anh-TRAIL virus were measured. Cytotoxic and cell apoptosis were analyzed for its anti-glioma therapy in vitro. Nude mice were used for the in vivo evaluation. Both tumor volume and mice behavior after injection were observed. The recombinant virus replicated with the same kinetics as the parental virus and the highest expression of TRAIL (77.8 ng/L) was found at 48 hours. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole and flow cytometry data revealed that the recombinant NDV/Anh-TRAIL (56.1 ± 8.2%) virus could induce a more severe apoptosis rate, when compared with the NDV wild type (37.2 ± 7.0%) and mock (7.0 ± 1.8%) groups (P < .01), in U251 cells. Furthermore, in the present animal study, the average tumor volume was smaller in the NDV/Anh-TRAIL group (97.21 mm3 ), when compared with the NDV wild type (205.03 mm3 , P < .05) and PBS (310.30 mm3 , P < .01) groups.

Lian Hua Qing Wen Capsules, a Potent Epithelial Protector in Acute Lung Injury Model, Block Proapoptotic Communication Between Macrophages, and Alveolar Epithelial Cells

Besides pathogen evading, Acute Lung Injury (ALI), featuring the systematic inflammation and severe epithelial damages, is widely believed to be the central non-infectious factor controlling the progression of infectious diseases. ALI is partly caused by host immune responses. Under the inspiration of unsuccessful treatment in COVID-19, recent insights into pathogen–host interactions are leading to identification and development of a wide range of host-directed therapies with different mechanisms of action. The interaction unit consisting of macrophages and the alveolar epithelial cells has recently revealed as the therapeutic basis targeting ALI. Lian Hua Qing Wen capsule is the most effective and commonly-used clinical formula in treating respiratory infection for thousands of years in China. However, little is known about its relevance with ALI, especially its protective role against ALI-induced alveolar tissue damages. Aiming to evaluate its contribution in antibiotics-integrating therapies, this study pharmacologically verified whether LHQW could alleviate lipopolysaccharide (LPS)-induced ALI and explore its potential mechanisms in maintaining the physiology of macrophage-epithelial unit. In ALI mouse model, the pathological parameters, including the anal temperature, inflammation condition, lung edema, histopathological structures, have all been systematically analyzed. Results consistently supported the effectiveness of the combined strategy for LHQW and low-dose antibiotics. Furthermore, we established the macrophages-alveolar epithelial cells co-culture model and firstly proved that LHQW inhibited LPS-induced ER stress and TRAIL secretion in macrophages, thereby efficiently protected epithelial cells against TRAIL-induced apoptosis. Mechanistically, results showed that LHQW significantly deactivated NF-κB and reversed the SOCS3 expression in inflammatory macrophages. Furthermore, we proved that the therapeutic effects of LHQW were highly dependent on JNK-AP1 regulation. In conclusion, our data proved that LHQW is an epithelial protector in ALI, implying its promising potential in antibiotic alternative therapy.

Epigallocatechin-3-Gallate Induces Apoptosis as a TRAIL Sensitizer via Activation of Caspase 8 and Death Receptor 5 in Human Colon Cancer Cells

Though epigallocatechin-3-gallate (EGCG), a major compound of green tea, has anti-diabetes, anti-obesity, anti-inflammatory, and antitumor effects, the underlying antitumor molecular mechanism of EGCG was not fully understood so far. Here the sensitizing effect of EGCG to tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL) was examined in colorectal cancers. Cotreatment of EGCG and TRAIL synergistically enhanced cytotoxicity and sub G1 accumulation, increased the number of terminal deoxynucleotidyl transferase-dT-mediated dUTP nick end labelling (TUNEL)-positive cells in SW480 and HCT116 cells. Furthermore, this cotreatment promoted the cleavages of poly (adenosine diphosphate-ribose) polymerase (PARP) and induced caspase 8 activation compared to TRAIL or EGCG alone in SW480 and HCT116 cells. Of note, cotreatment of EGCG and TRAIL increased the expression of death receptor 5 (DR5) at protein and mRNA levels and also DR5 cell surface level in colon cancer cells. Conversely, depletion of DR5 reduced the apoptotic activity of cotreatment of EGCG and TRAIL to increase cytotoxicity, sub-G1 population and PARP cleavages in colon cancer cells. Overall, our findings provide evidence that EGCG can be a sensitizer of TRAIL via DR5 and caspase 8 mediated apoptosis in colorectal cancer cells.

Disulfide bond-disrupting agents activate the tumor necrosis family-related apoptosis-inducing ligand/death receptor 5 pathway

Disulfide bond-disrupting agents (DDAs) are a new chemical class of agents recently shown to have activity against breast tumors in animal models. Blockade of tumor growth is associated with downregulation of EGFR, HER2, and HER3 and reduced Akt phosphorylation, as well as the induction of endoplasmic reticulum stress. However, it is not known how DDAs trigger cancer cell death without affecting nontransformed cells. As demonstrated here, DDAs are the first compounds identified that upregulate the TRAIL receptor DR5 through transcriptional and post-transcriptional mechanisms to activate the extrinsic cell death pathway. At the protein level, DDAs alter DR5 disulfide bonding to increase steady-state DR5 levels and oligomerization, leading to downstream caspase 8 and 3 activation. DDAs and TRAIL synergize to kill cancer cells and are cytotoxic to HER2+ cancer cells with acquired resistance to the EGFR/HER2 tyrosine kinase inhibitor Lapatinib. Investigation of the mechanisms responsible for DDA selectivity for cancer cells reveals that DDA-induced upregulation of DR5 is enhanced in the context of EGFR overexpression. DDA-induced cytotoxicity is strongly amplified by MYC overexpression. This is consistent with the known potentiation of TRAIL-mediated cell death by MYC. Together, the results demonstrate selective DDA lethality against oncogene-transformed cells, DDA-mediated DR5 upregulation, and protein stabilization, and that DDAs have activity against drug-resistant cancer cells. Our results indicate that DDAs are unique in causing DR5 accumulation and oligomerization and inducing downstream caspase activation and cancer cell death through mechanisms involving altered DR5 disulfide bonding. DDAs thus represent a new therapeutic approach to cancer therapy.

Ixazomib promotes CHOP-dependent DR5 induction and apoptosis in colorectal cancer cells

BACKGROUND

Ixazomib (Ninlaro), a novel proteasome inhibitor, has been developed for the treatment of many cancers and has demonstrated anti-tumor efficacy against various malignancies. However, the mechanism of the anti-tumor effect of ixazomib in colorectal cancer (CRC) cells remains unclear.

METHODS

MTS and flow cytometry were performed to determine the effect of ixazomib on CRC cells. Western blotting and real-time RT-PCR were performed to detect ixazomib-induced DR5 upregulation. ChIP was performed to detect CHOP binding to DR5 promoter. Finally, xenograft experiments were carried out to measure the antitumor effect of ixazomib in vivo.

RESULTS

In this study, we revealed the mechanism by which ixazomib inhibits the growth of CRC cells. Our findings indicated that ixazomib treatment induces CHOP-dependent DR5 induction, irrespective of p53 status. Furthermore, DR5 is necessary for ixazomib-mediated apoptosis. Ixazomib also synergized with TRAIL to induce marked apoptosis via DR5 in CRC cells.

CONCLUSIONS

Our findings further suggested that ixazomib sensitizes TRAIL/death receptor signaling pathway-targeted CRC and suggested that DR5 induction could be a valuable indicator of ixazomib sensitivity.

FLIP as a therapeutic target in cancer

One of the classic hallmarks of cancer is disruption of cell death signalling. Inhibition of cell death promotes tumour growth and metastasis, causes resistance to chemo- and radiotherapies as well as targeted agents, and is frequently due to overexpression of antiapoptotic proteins rather than loss of pro-apoptotic effectors. FLIP is a major apoptosis-regulatory protein frequently overexpressed in solid and haematological cancers, in which its high expression is often correlated with poor prognosis. FLIP, which is expressed as long (FLIP(L)) and short (FLIP(S)) splice forms, achieves its cell death regulatory functions by binding to FADD, a critical adaptor protein which links FLIP to the apical caspase in the extrinsic apoptotic pathway, caspase-8, in a number of cell death regulating complexes, such as the death-inducing signalling complexes (DISCs) formed by death receptors. FLIP also plays a key role (together with caspase-8) in regulating another form of cell death termed programmed necrosis or 'necroptosis', as well as in other key cellular processes that impact cell survival, including autophagy. In addition, FLIP impacts activation of the intrinsic mitochondrial-mediated apoptotic pathway by regulating caspase-8-mediated activation of the pro-apoptotic Bcl-2 family member Bid. It has been demonstrated that FLIP can not only inhibit death receptor-mediated apoptosis, but also cell death induced by a range of clinically relevant chemotherapeutic and targeted agents as well as ionizing radiation. More recently, key roles for FLIP in promoting the survival of immunosuppressive tumour-promoting immune cells have been discovered. Thus, FLIP is of significant interest as an anticancer therapeutic target. In this article, we review FLIP's biology and potential ways of targeting this important tumour and immune cell death regulator.

Discovery and clinical introduction of first-in-class imipridone ONC201

ONC201 is the founding member of a novel class of anti-cancer compounds called imipridones that is currently in Phase II clinical trials in multiple advanced cancers. Since the discovery of ONC201 as a p53-independent inducer of TRAIL gene transcription, preclinical studies have determined that ONC201 has anti-proliferative and pro-apoptotic effects against a broad range of tumor cells but not normal cells. The mechanism of action of ONC201 involves engagement of PERK-independent activation of the integrated stress response, leading to tumor upregulation of DR5 and dual Akt/ERK inactivation, and consequent Foxo3a activation leading to upregulation of the death ligand TRAIL. ONC201 is orally active with infrequent dosing in animals models, causes sustained pharmacodynamic effects, and is not genotoxic. The first-in-human clinical trial of ONC201 in advanced aggressive refractory solid tumors confirmed that ONC201 is exceptionally well-tolerated and established the recommended phase II dose of 625 mg administered orally every three weeks defined by drug exposure comparable to efficacious levels in preclinical models. Clinical trials are evaluating the single agent efficacy of ONC201 in multiple solid tumors and hematological malignancies and exploring alternative dosing regimens. In addition, chemical analogs that have shown promise in other oncology indications are in pre-clinical development. In summary, the imipridone family that comprises ONC201 and its chemical analogs represent a new class of anti-cancer therapy with a unique mechanism of action being translated in ongoing clinical trials.

Discovery and characterization of Isofistularin-3, a marine brominated alkaloid, as a new DNA demethylating agent inducing cell cycle arrest and sensitization to TRAIL in cancer cells

We characterized the brominated alkaloid Isofistularin-3 (Iso-3), from the marine sponge Aplysina aerophoba, as a new DNA methyltransferase (DNMT)1 inhibitor. Docking analysis confirmed our in vitro DNMT inhibition data and revealed binding of Iso-3 within the DNA binding site of DNMT1. Subsequent increased expression of tumor suppressor gene aryl hydrocarbon receptor (AHR) could be correlated to decreased methylation of CpG sites within the essential Sp1 regulatory region of its promoter. Iso-3 induced growth arrest of cancer cells in G0/G1 concomitant with increased p21 and p27 expression and reduced cyclin E1, PCNA and c-myc levels. Reduced proliferation was accompanied by morphological changes typical of autophagy revealed by fluorescent and transmission electron microscopy and validated by LC3I-II conversion. Furthermore, Iso-3 strongly synergized with tumor-necrosis-factor related apoptosis inducing ligand (TRAIL) in RAJI [combination index (CI) = 0.22] and U-937 cells (CI = 0.21) and increased TRAIL-induced apoptosis via a mechanism involving reduction of survivin expression but not of Bcl-2 family proteins nor X-linked inhibitor of apoptosis protein (XIAP). Iso-3 treatment decreased FLIP_L expression and triggered activation of endoplasmatic reticulum (ER) stress with increased GRP78 expression, eventually inducing TRAIL receptor death receptor (DR)5 surface expression. Importantly, as a potential candidate for further anticancer drug development, Iso-3 reduced the viability, colony and in vivo tumor forming potential without affecting the viability of PBMCs from healthy donors or zebrafish development.

PLCγ2 promotes apoptosis while inhibits proliferation in rat hepatocytes through PKCD/JNK MAPK and PKCD/p38 MAPK signalling

OBJECTIVES

The PLCG2 (PLCγ2) gene is a member of PLC gene family encoding transmembrane signalling enzymes involved in various biological processes including cell proliferation and apoptosis. Our earlier study indicated that PLCγ2 may be involved in the termination of regeneration of the liver which is mainly composed of hepatocytes, but its exact biological function and molecular mechanism in liver regeneration termination remains unclear. This study aims to examine the role of PLCγ2 in the growth of hepatocytes.

MATERIALS AND METHODS

A recombinant adenovirus expressing PLCγ2 was used to infect primary rat hepatocytes. PLCγ2 mRNA and protein levels were detected by qRT-PCR and Western blot. The subcellular location of PLCγ2 protein was tested by an immunofluorescence assay. The proliferation of hepatocytes was measured by MTT assay. The cell cycle and apoptosis were analysed by flow cytometry. Caspase-3, -8 and -9 activities were measured by a spectrophotometry method. Phosphorylation levels of PKCD, JNK and p38 in the infected cells were detected by Western blot. The possible mechanism underlying the role of PLCγ2 in hepatocyte growth was also explored by adding a signalling pathway inhibitor.

RESULTS

Hepatocyte proliferation was dramatically reduced, while cell apoptosis was remarkably increased. The results demonstrated that PLCγ2 increased the phosphorylation of PKCD, p38 and JNK in rat hepatocytes. After PKCD activity was inhibited by the inhibitor Go 6983, the levels of both p-p38 and p-JNK MAPKs significantly decreased, and PLCγ2-induced cell proliferation inhibition and cell apoptosis were obviously reversed.

CONCLUSIONS

This study showed that PLCγ2 regulates hepatocyte growth through PKCD-dependently activating p38 MAPK and JNK MAPK pathways; this result was experimentally based on the further exploration of the effect of PLCγ2 on hepatocyte growth in vivo.

PLEKHN1 promotes apoptosis by enhancing Bax-Bak hetro-oligomerization through interaction with Bid in human colon cancer

The anti-apoptotic nature of cancer cells often impedes the effects of anti-cancer therapeutic agents. Multiple death signals influence mitochondria during apoptosis, and though many studies have attempted to elucidate these complicated pathways, Bax oligomerization, an important step in the process, remains controversial. Here we demonstrate that pleckstrin-homology N1 (PLEKHN1), also known as cardiolipin phosphatidic acid binding protein, plays pro-apoptotic roles during reactive oxygen species (ROS)-induced apoptosis. Human PLEKHN1 was expressed in several cancer cell lines of differing origin. Its expression was regulated by hypoxia, and it existed in the mitochondrial fraction. Genome editing of hPLEKHN1 in human colon cancer HT-29 cells revealed enhanced survival of knockout cells compared with that of parental cells in vitro and in vivo. Thapsigargin or hydrogen peroxide treatment activated multiple death signals including JNK, Bcl-2 family members, and caspases. PLEKHN1 was bound to Bid, a pro-apoptotic protein, and not to Bax, and PLEKHN1 could remove Bid from transient Bid-Bax complexes. Fluorescent time-lapse imaging revealed that PLEKHN1 aggregated with Bid during thapsigargin- or hydrogen peroxide-induced apoptosis prior to Bax aggregation. Inhibition of PLEKHN1 led to attenuation of Bax-Bak hetero-oligomerization and Bid translocation. The immunohistochemistry of cancer patient specimens showed that PLEKHN1 expression was absent from cancer region at the transition area of normal/cancer tissues. Collectively, the silencing of PLEKHN1 may be the key that cancer cells acquire the drug resistance.

Silibinin sensitizes TRAIL-mediated apoptosis by upregulating DR5 through ROS-induced endoplasmic reticulum stress-Ca2+-CaMKII-Sp1 pathway

In this study, we addressed how silibinin enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in various cancer cells. Combined treatment with silibinin and TRAIL (silibinin/TRAIL) induced apoptosis accompanied by the activation of caspase-3, caspase-8, caspase-9, and Bax, and cytosolic accumulation of cytochrome c. Anti-apoptotic proteins such as Bcl-2, IAP-1, and IAP-2 were inhibited as well. Silibinin also triggered TRAIL-induced apoptosis in A549 cells through upregulation of death receptor 5 (DR5). Pretreatment with DR5/Fc chimeric protein and DR5-targeted small interfering RNA (siRNA) significantly blocked silibinin/TRAIL-mediated apoptosis in A549 cells. Furthermore, silibinin increased the production of reactive oxygen species (ROS), which led to the induction of TRAIL-mediated apoptosis through DR5 upregulation. Antioxidants such as N-acetyl-L-cysteine and glutathione reversed the apoptosis-inducing effects of TRAIL. Silibinin further induced endoplasmic reticulum (ER) stress as was indicated by the increase in ER marker proteins such as PERK, eIF2α, and ATF-4, which stimulate the expression of CCAAT/enhancer binding protein homologous protein (CHOP). CHOP-targeted siRNA eliminated the induction of DR5 and resulted in a significant decrease in silibinin/TRAIL-mediated apoptosis. We also found that silibinin/TRAIL-induced apoptosis was accompanied with intracellular influx of Ca²⁺, which was stimulated by ER stress and the Ca²⁺ chelator, ethylene glycol tetraacetic acid (EGTA). Ca²⁺/calmodulin-dependent protein kinase (CaMKII) inhibitor, K252a, blocked silibinin/TRAIL-induced DR5 expression along with TRAIL-mediated apoptosis. Accordingly, we showed that ROS/ER stress-induced CaMKII activated Sp1, which is an important transcription factor for DR5 expression. Our results showed that silibinin enhanced TRAIL-induced apoptosis by upregulating DR5 expression through the ROS-ER stress-CaMKII-Sp1 axis.

TRAIL, Wnt, Sonic Hedgehog, TGFβ, and miRNA Signalings Are Potential Targets for Oral Cancer Therapy

Clinical studies and cancer cell models emphasize the importance of targeting therapies for oral cancer. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is highly expressed in cancer, and is a selective killing ligand for oral cancer. Signaling proteins in the wingless-type mouse mammary tumor virus (MMTV) integration site family (Wnt), Sonic hedgehog (SHH), and transforming growth factor β (TGFβ) pathways may regulate cell proliferation, migration, and apoptosis. Accordingly, the genes encoding these signaling proteins are potential targets for oral cancer therapy. In this review, we focus on recent advances in targeting therapies for oral cancer and discuss the gene targets within TRAIL, Wnt, SHH, and TGFβ signaling for oral cancer therapies. Oncogenic microRNAs (miRNAs) and tumor suppressor miRNAs targeting the genes encoding these signaling proteins are summarized, and the interactions between Wnt, SHH, TGFβ, and miRNAs are interpreted. With suitable combination treatments, synergistic effects are expected to improve targeting therapies for oral cancer.

Antiproliferative and apoptosis induction of α-mangostin in T47D breast cancer cells

α-Mangostin extracted from mangosteen, Garcinia mangostana Linn. is known as 'queen of fruits'. The anticancer activity of α-mangostin through apoptosis induction and related signaling pathways in human breast cancer T47D cells was investigated. Human epidermal growth factor receptor 2 (HER2) and mitogen-activated protein kinase (MAPK) signaling have been shown to play important roles in apoptosis. The results showed that α-mangostin induced cell proliferation inhibition, DNA fragmentation, nuclear condensation, increased cleaved caspase-3 and cleaved caspase-9, but decreased Bcl-2 and Mcl-1 expression. Mitochondrial dysfunction and cytochrome c release were also detected. In addition, phosphorylation of ERα, HER2, PI3K, Akt and ERK1/2 were downregulated whereas p-JNK1/2 and p-p38 were upregulated. These results indicated that α-mangostin induced apoptosis associated with HER2/PI3K/Akt and MAPK signaling pathways suggesting that α-mangostin may be used as food supplement or a potential therapeutic compound for breast cancer.

Apoptosis-Inducing Activity of Marine Sponge Haliclona sp. Extracts Collected from Kosrae in Nonsmall Cell Lung Cancer A549 Cells

Although various anticancer drugs have been developed for the treatment of nonsmall cell lung cancer, chemotherapeutic efficacy is still limited. Natural products such as phytochemicals have been screened as novel alternative materials, but alternative funds such as marine bioresources remain largely untapped. Of these resources, marine sponges have undergone the most scrutiny for their biological activities, including antiinflammatory, antiviral, and anticancer properties. However, the biological mechanisms of the activities of these marine sponges are still unclear. We investigated the anticancer activity of marine sponges collected from Kosrae in Micronesia and examined their mechanisms of action using nonsmall cell lung cancer A549 cells as a model system. Of 20 specimens, the Haliclona sp. (KO1304-328) showed both dose- and time-dependent cytotoxicity. Further, methanol extracts of Haliclona sp. significantly inhibited cell proliferation and cell viability. A549 cells treated with Haliclona sp. demonstrated induced expression of c-Jun N-terminal kinase (JNK), p53, p21, caspase-8, and caspase-3. The percentage of apoptotic cells significantly increased in A549 cultures treated with Haliclona sp. These results indicate that Haliclona sp. induces apoptosis via the JNK-p53 pathway and caspase-8, suggesting that this marine sponge is a good resource for the development of drugs for treatment of nonsmall cell lung cancer.

Drug Delivery Innovations for Enhancing the Anticancer Potential of Vitamin E Isoforms and Their Derivatives

Vitamin E isoforms have been extensively studied for their anticancer properties. Novel drug delivery systems (DDS) that include liposomes, nanoparticles, and micelles are actively being developed to improve Vitamin E delivery. Furthermore, several drug delivery systems that incorporate Vitamin E isoforms have been synthesized in order to increase the bioavailability of chemotherapeutic agents or to provide a synergistic effect. D-alpha-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) is a synthetic derivative of natural alpha-tocopherol which is gaining increasing interest in the development of drug delivery systems and has also shown promising anticancer effect as a single agent. This review provides a summary of the properties and anticancer effects of the most potent Vitamin E isoforms and an overview of the various formulations developed to improve their efficacy, with an emphasis on the use of TPGS in drug delivery approaches.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Adenovirus-mediated co-expression of the TRAIL and HN genes inhibits growth and induces apoptosis in Marek's disease tumor cell line MSB-1

Background

The objective of this study was to determine the in vitro tumor-inhibitory effect of a recombinant adenovirus expressing a fusion protein of tumor necrosis factor (TNF) related apoptosis inducing ligand (TRAIL) and hemagglutinin-neuraminidase (HN) genes on the MSB-1 Marek’s disease tumor cell line.

Methods

TRAIL and HN genes were amplified from lymphocytes in the peripheral blood of chickens and the LaSota strain of Newcastle disease virus (NDV), respectively, using RT-PCR. The two genes were connected with a 2A connecting peptide by site-directed mutagenesis and gene splicing by overlap extension (SOE). The target gene TRAIL-2A-HN was cloned into the shuttle vector pShuttle-CMV. Homologous recombination was carried out with the vector pAdeasy-1 in the bacterium BJ5183 to construct the recombinant adenovirus plasmid pAd-TRAIL-2A-HN. After linearization, the plasmid was transfected into AD293 cells and packaged. Real-time quantitative PCR (RT-PCR) and fluorescence microscopy confirmed the introduction of the recombinant adenovirus into AD293 cells. The TCID₅₀ method (50% tissue culture infectious dose) was employed to determine viral titers for the exprimental and control viruses, which met criteria for use. The Marek’s disease tumor cell line MSB-1 was transfected with the constructed recombinant adenovirus. The infectivity of the recombinant adenovirus and the expression levels of exogenous genes were detected with RT-PCR and western blotting. The effects of the recombinant adenovirus on the growth of MSB-1 cells and cellular apoptosis were determined using flow cytometry.

Results

The recombinant adenovirus infected the cultured cells in vitro, and replicated and expressed exogenous genes in the cells. The recombinant adenovirus Ad-TRAIL-2A-HN inhibited the growth of MSB-1 cells and induced apoptosis by expressing exogenous genes. The rate of induced MSB-1 cell apoptosis reached 11.61%, which indicated that TRAIL and HN produced synergistic tumor-inhibiting effects.

Conclusion

The constructed TRAIL-2A-HN fusion gene combined the apoptosis-inducing function of TRAIL and the adsorptive capacity of HN from NDV for tumor cells, and the capacity of the recombinant adenovirus expressing this fusion gene to induce tumor cell apoptosis was reported. These results provide a basis for future in vivo tumor suppression studies using recombinant adenoviruses.

Antitumor effects of a sirtuin inhibitor, tenovin-6, against gastric cancer cells via death receptor 5 up-regulation

Up-regulated sirtuin 1 (SIRT1), an NAD⁺-dependent class III histone deacetylase, deacetylates p53 and inhibits its transcriptional activity, leading to cell survival. SIRT1 overexpression has been reported to predict poor survival in some malignancies, including gastric cancer. However, the antitumor effect of SIRT1 inhibition remains elusive in gastric cancer. Here, we investigated the antitumor mechanisms of a sirtuin inhibitor, tenovin-6, in seven human gastric cancer cell lines (four cell lines with wild-type TP53, two with mutant-type TP53, and one with null TP53). Interestingly, tenovin-6 induced apoptosis in all cell lines, not only those with wild-type TP53, but also mutant-type and null versions, accompanied by up-regulation of death receptor 5 (DR5). In the KatoIII cell line (TP53-null), DR5 silencing markedly attenuated tenovin-6-induced apoptosis, suggesting that the pivotal mechanism behind its antitumor effects is based on activation of the death receptor signal pathway. Although endoplasmic reticulum stress caused by sirtuin inhibitors was reported to induce DR5 up-regulation in other cancer cell lines, we could not find marked activation of its related molecules, such as ATF6, PERK, and CHOP, in gastric cancer cells treated with tenovin-6. Tenovin-6 in combination with docetaxel or SN-38 exerted a slight to moderate synergistic cytotoxicity against gastric cancer cells. In conclusion, tenovin-6 has potent antitumor activity against human gastric cancer cells via DR5 up-regulation. Our results should be helpful for the future clinical development of sirtuin inhibitors.

Induction of cell cycle arrest and apoptosis in caspase-3 deficient MCF-7 cells by Dillenia suffruticosa root extract via multiple signalling pathways

BACKGROUND

Dillenia suffruticosa root dichloromethane extract (DCM-DS) has been reported to exhibit strong cytotoxicity towards breast cancer cells. The present study was designed to investigate the cell cycle profile, mode of cell death and signalling pathways of DCM-DS-treated human caspase-3 deficient MCF-7 breast cancer cells.

METHODS

Dillenia suffruticosa root was extracted by sequential solvent extraction. The anti-proliferative activity of DCM-DS was determined by using MTT assay. The mode of cell death was evaluated by using inverted light microscope and Annexin-V/PI-flow cytometry analysis. Cell cycle analysis and measurement of intracellular reactive oxygen species (ROS) were performed by using flow cytometry. MCF-7 cells were co-treated with antioxidants α-tocopherol and ascorbic acid to evaluate whether the cell death was mainly due to oxidative stress. GeXP-based multiplex system was employed to investigate the expression of apoptotic, growth and survival genes in MCF-7 cells. Western blot analysis was performed to confirm the expression of the genes.

RESULTS

DCM-DS was cytotoxic to the MCF-7 cells in a time-and dose-dependent manner. The IC50 values of DCM-DS at 24, 48 and 72 hours were 20.3 ± 2.8, 17.8 ± 1.5 and 15.5 ± 0.5 μg/mL, respectively. Cell cycle analysis revealed that DCM-DS induced G0/G1 and G2/M phase cell cycle arrest in MCF-7 cells at low concentration (12.5 and 25 μg/mL) and high concentration (50 μg/mL), respectively. Although Annexin-V/PI-flow cytometry analysis has confirmed that DCM-DS induced apoptosis in MCF-7 cells, the distinct characteristics of apoptosis such as membrane blebbing, chromatin condensation, nuclear fragmentation and formation of apoptotic bodies were not observed under microscope. DCM-DS induced formation of ROS in MCF-7 cells. Nevertheless, co-treatment with antioxidants did not attenuate the cell death at low concentration of DCM-DS. The pro-apoptotic gene JNK was up-regulated whereby anti-apoptotic genes AKT1 and ERK1/2 were down-regulated in a dose-dependent manner. Western blot analysis has confirmed that DCM-DS significantly up-regulated the expression of pro-apoptotic JNK1, pJNK and down-regulated anti-apoptotic AKT1, ERK1 in MCF-7 cells.

CONCLUSION

DCM-DS induced cell cycle arrest and apoptosis in MCF-7 cells via multiple signalling pathways. It shows the potential of DCM-DS to be developed to target the cancer cells with mutant caspase-3.

ER stress regulates myeloid-derived suppressor cell fate through TRAIL-R-mediated apoptosis

Myeloid-derived suppressor cells (MDSCs) dampen the immune response thorough inhibition of T cell activation and proliferation and often are expanded in pathological conditions. Here, we studied the fate of MDSCs in cancer. Unexpectedly, MDSCs had lower viability and a shorter half-life in tumor-bearing mice compared with neutrophils and monocytes. The reduction of MDSC viability was due to increased apoptosis, which was mediated by increased expression of TNF-related apoptosis-induced ligand receptors (TRAIL-Rs) in these cells. Targeting TRAIL-Rs in naive mice did not affect myeloid cell populations, but it dramatically reduced the presence of MDSCs and improved immune responses in tumor-bearing mice. Treatment of myeloid cells with proinflammatory cytokines did not affect TRAIL-R expression; however, induction of ER stress in myeloid cells recapitulated changes in TRAIL-R expression observed in tumor-bearing hosts. The ER stress response was detected in MDSCs isolated from cancer patients and tumor-bearing mice, but not in control neutrophils or monocytes, and blockade of ER stress abrogated tumor-associated changes in TRAIL-Rs. Together, these data indicate that MDSC pathophysiology is linked to ER stress, which shortens the lifespan of these cells in the periphery and promotes expansion in BM. Furthermore, TRAIL-Rs can be considered as potential targets for selectively inhibiting MDSCs.

Targeting the Anti-Apoptotic Protein c-FLIP for Cancer Therapy

Cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) is a major resistance factor and critical anti-apoptotic regulator that inhibits tumor necrosis factor-alpha (TNF-alpha), Fas-L, and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis as well as chemotherapy-triggered apoptosis in malignant cells. c-FLIP is expressed as long (c-FLIP(L)), short (c-FLIP(S)), and c-FLIP(R) splice variants in human cells. c-FLIP binds to FADD and/or caspase-8 or -10 in a ligand-dependent and-independent fashion, which in turn prevents death-inducing signaling complex (DISC) formation and subsequent activation of the caspase cascade. Moreover, c-FLIP(L) and c-FLIP(S) are known to have multifunctional roles in various signaling pathways, as well as activating and/or upregulating several cytoprotective signaling molecules. Upregulation of c-FLIP has been found in various tumor types, and its downregulation has been shown to restore apoptosis triggered by cytokines and various chemotherapeutic agents. Hence, c-FLIP is an important target for cancer therapy. For example, small interfering RNAs (siRNAs) that specifically knockdown the expression of c-FLIP(L) in diverse human cancer cell lines augmented TRAIL-induced DISC recruitment and increased the efficacy of chemotherapeutic agents, thereby enhancing effector caspase stimulation and apoptosis. Moreover, small molecules causing degradation of c-FLIP as well as decreasing mRNA and protein levels of c-FLIP(L) and c-FLIP(S) splice variants have been found, and efforts are underway to develop other c-FLIP-targeted cancer therapies. This review focuses on (1) the functional role of c-FLIP splice variants in preventing apoptosis and inducing cytokine and drug resistance; (2) the molecular mechanisms that regulate c-FLIP expression; and (3) strategies to inhibit c-FLIP expression and function.

B19, a novel monocarbonyl analogue of curcumin, induces human ovarian cancer cell apoptosis via activation of endoplasmic reticulum stress and the autophagy signaling pathway

BACKGROUND

The unfolded protein response, autophagy and endoplasmic reticulum (ER) stress-induced apoptosis regulate tumor cell fate and have become novel signaling targets for the development of cancer therapeutic drugs. Curcumin has been used to treat several different cancers, including ovarian cancer, in clinical trials and research; however, the role of ER stress and autophagy in the therapeutic effects of curcumin and new curcumin analogues remains unclear.

METHODS

Cell viability was determined using the MTT assay. Apoptosis was detected using flow cytometry with PI/Annexin V-FITC staining. The expression levels of ER stress- and autophagy-related proteins were analyzed by western blotting. The activation of autophagy was detected using immunofluorescence staining.

RESULTS

We demonstrated that B19 induced HO8910 cell apoptosis in a dose-responsive manner. We also determined and that this effect was associated with corresponding increases in a series of key components in the UPR and ER stress-mediated apoptosis pathways, followed by caspase 3 cleavage and activation. We also observed that B19 treatment induced autophagy in HO8910 cells. The inhibition of autophagy using 3-methyladenine (3-MA) increased levels of intracellular misfolded proteins, which enhanced ovarian cancer apoptosis.

CONCLUSIONS

Our data indicate that ER stress and autophagy may play a role in the apoptosis that is induced by the curcumin analogue B19 in an epithelial ovarian cancer cell line and that autophagy inhibition can increase curcumin analogue-induced apoptosis by inducing severe ER stress.

The endoplasmic reticulum stress inhibitor salubrinal inhibits the activation of autophagy and neuroprotection induced by brain ischemic preconditioning

AIM

To investigate whether endoplasmic reticulum (ER) stress participates in the neuroprotective effects of ischemic preconditioning (IPC)-induced neuroprotection and autophagy activation in rat brains.

METHODS

The right middle cerebral artery in SD rats was occluded for 10 min to induce focal cerebral IPC, and was occluded permanently 24 h later to induce permanent focal ischemia (PFI). ER stress inhibitor salubrinal (SAL) was injected via intracerebral ventricle infusion 10 min before the onset of IPC. Infarct volume and motor behavior deficits were examined after the ischemic insult. The protein levels of LC3, p62, HSP70, glucose-regulated protein 78 (GRP 78), p-eIF2α and caspase-12 in the ipsilateral cortex were analyzed using immunoblotting. LC3 expression pattern in the sections of ipsilateral cortex was observed with immunofluorescence.

RESULTS

Pretreatment with SAL (150 pmol) abolished the neuroprotective effects of IPC, as evidenced by the significant increases in mortality, infarct volume and motor deficits after PFI. At the molecular levels, pretreatment with SAL (150 pmol) significantly increased p-eIF2α level, and decreased GRP78 level after PFI, suggesting that SAL effectively inhibited ER stress in the cortex. Furthermore, the pretreatment with SAL blocked the IPC-induced upregulation of LC3-II and downregulation of p62 in the cortex, thus inhibiting the activation of autophagy. Moreover,SAL blocked the upregulation of HSP70, but significantly increased the cleaved caspase-12 level, thus promoting ER stress-dependent apoptotic signaling in the cortex.

CONCLUSION

ER stress-induced autophagy might contribute to the neuroprotective effect of brain ischemic preconditioning.

Novel phosphorylation and ubiquitination sites regulate reactive oxygen species-dependent degradation of anti-apoptotic c-FLIP protein

The cytosolic protein c-FLIP (cellular Fas-associated death domain-like interleukin 1β-converting enzyme inhibitory protein) is an inhibitor of death receptor-mediated apoptosis that is up-regulated in a variety of cancers, contributing to apoptosis resistance. Several compounds found to restore sensitivity of cancer cells to TRAIL, a TNF family death ligand with promising therapeutic potential, act by targeting c-FLIP ubiquitination and degradation by the proteasome. The generation of reactive oxygen species (ROS) has been implicated in c-FLIP protein degradation. However, the mechanism by which ROS post-transcriptionally regulate c-FLIP protein levels is not well understood. We show here that treatment of prostate cancer PPC-1 cells with the superoxide generators menadione, paraquat, or buthionine sulfoximine down-regulates c-FLIP long (c-FLIP(L)) protein levels, which is prevented by the proteasome inhibitor MG132. Furthermore, pretreatment of PPC-1 cells with a ROS scavenger prevented ubiquitination and loss of c-FLIP(L) protein induced by menadione or paraquat. We identified lysine 167 as a novel ubiquitination site of c-FLIP(L) important for ROS-dependent degradation. We also identified threonine 166 as a novel phosphorylation site and demonstrate that Thr-166 phosphorylation is required for ROS-induced Lys-167 ubiquitination. The mutation of either Thr-166 or Lys-167 was sufficient to stabilize c-FLIP protein levels in PPC-1, HEK293T, and HeLa cancer cells treated with menadione or paraquat. Accordingly, expression of c-FLIP T166A or K167R mutants protected cells from ROS-mediated sensitization to TRAIL-induced cell death. Our findings reveal novel ROS-dependent post-translational modifications of the c-FLIP protein that regulate its stability, thus impacting sensitivity of cancer cells to TRAIL.

Salermide up-regulates death receptor 5 expression through the ATF4-ATF3-CHOP axis and leads to apoptosis in human cancer cells

Sirtuins (a class III histone deacetylase) have emerged as novel targets for cancer therapy. Salermide, a reverse amide compound that inhibits Sirtuin 1 (Sirt1) and Sirtuin 2 (Sirt2), has been shown to induce apoptosis in human cancer cells. The mechanism underlying cellular apoptotic signalling by salermide remains unclear. In this study, we show that salermide up-regulates the expression of death receptor 5 (DR5) in human non-small cell lung cancer (NSCLC) cells. Blocking DR5 expression by gene silencing technology results in a decrease in activated forms of several pro-apoptotic proteins (caspase-8, caspase-9, caspase-3, PARP). Increasing DR5 protein expression correlates with salermide-induced apoptosis in human NSCLC cells. We discovered that IRE-1α, Bip, activating transcription factor 3 (ATF4), activating transcription factor 3 (ATF3) and C/EBP homologous protein (CHOP) are induced by salermide, which suggests that DR5-dependent apoptosis is induced by endoplasmic reticulum stress. Moreover, knockdown of Sirt1 and Sirt2 expression resulted in up-regulation of ATF4, CHOP and DR5. Transfected NSCLC cells with ATF4, ATF3 or CHOP siRNA results in a decline in pro-apoptotic proteins (such as caspase-8, caspase-9, caspase-3 and PARP) despite salermide treatment. We demonstrate that salermide induces expression of ATF4, and ATF4 up-regulates ATF3 and subsequently modulates CHOP. This suggests that DR5 is modulated by the ATF4-ATF3-CHOP axis in NSCLC after Sirt1/2 inhibition or salermide treatment. This study highlights the importance of DR5 up-regulation in apoptosis induced by Sirt1/2 inhibition and elucidates the underlying mechanism in human NSCLC cells.

Involvement of de novo ceramide synthesis in gamma-tocopherol and gamma-tocotrienol-induced apoptosis in human breast cancer cells

SCOPE

This study further examines mechanisms involved in the pro-apoptotic action of gamma-tocopherol (γT) and gamma-tocotrienol (γT3) in human breast cancer cell lines.

METHODS AND RESULTS

γT upregulates phospho-JNK (pJNK), CCAAT/enhancer-binding protein homologous protein (CHOP), and death receptor-5 (DR5) protein expression as detected by Western blot assays. siRNA knockdown of JNK, CHOP, or DR5 shows that γT-induced apoptosis is JNK/CHOP/DR5 signaling dependent, which is similar to γT3-mediated apoptotic signaling. Furthermore, both γT and γT3 induce increased levels of cellular ceramides and dihydroceramides as determined by LC-MS/MS analyses. Inhibition of de novo ceramide synthesis using chemical inhibitors blocked the ability of γT and γT3 to induce apoptosis as detected by Annexin V-FITC/PI assay and to activate JNK/CHOP/DR5 pro-apoptotic signaling thereby demonstrating the involvement of de novo ceramide synthesis in γT- and γT3-induced apoptosis.

CONCLUSION

Taken together, data show that both γT and γT3 induce apoptosis via de novo ceramide synthesis dependent activation of JNK/CHOP/DR5 pro-apoptotic signaling.

ER stress sensitizes cells to TRAIL through down-regulation of FLIP and Mcl-1 and PERK-dependent up-regulation of TRAIL-R2

Despite recent evidences suggesting that agents inducing endoplasmic reticulum (ER) stress could be exploited as potential antitumor drugs in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), the mechanisms of this anticancer action are not fully understood. Moreover, the effects of ER stress and TRAIL in nontransformed cells remain to be investigated. In this study we report that ER stress-inducing agents sensitizes both transformed and nontransformed cells to TRAIL-induced apoptosis. In addition, glucose-regulated protein of 78 kDa (GRP78) knockdown by RNA interference induces ER stress and facilitates apoptosis by TRAIL. We demonstrate that TRAIL death-inducing signaling complex (DISC) formation and early signaling are enhanced in ER stressed cells. ER stress alters the cellular levels of different apoptosis-related proteins including a decline in the levels of FLIP and Mcl-1 and the up-regulation of TRAIL-R2. Up-regulation of TRAIL-R2 following ER stress is dependent on the expression of PKR-like ER kinase (PERK) and independent of CAAT/enhancer binding protein homologous protein (CHOP) and Ire1α. Silencing of TRAIL-R2 expression by siRNA blocks the ER stress-mediated sensitization to TRAIL-induced apoptosis. Furthermore, simultaneous silencing of cFLIP and Mcl-1 expression by RNA interference results in a marked sensitization to TRAIL-induced apoptosis. Finally, in FLIP-overexpressing cells ER stress-induced sensitization to TRAIL-activated apoptosis is markedly reduced. In summary, our data reveal a pleiotropic mechanism involving both apoptotic and anti-apoptotic proteins for the sensitizing effect of ER stress on the regulation of TRAIL receptor-mediated apoptosis in both transformed and nontransformed cells.

Utilization of the cellular stress response to sensitize cancer cells to TRAIL-mediated apoptosis

INTRODUCTION

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is a promising death ligand who has received significant attention due to its specific anti-cancer activity. Recently, a number of clinical trials involving either recombinant soluble TRAIL or agonistic death receptor (DR) antibodies have even been initiated. One major caveat in TRAIL-based anti-cancer therapies is that a considerable number of cancer cells are notorious resistant to apoptosis induction by TRAIL. Overcoming this primary or secondary evolved resistance is an utmost important goal of present cancer research. The current literature suggests that TRAIL resistance is mediated by a number of endogenous factors.

AREAS COVERED

According to recent research, stress-related transcription factors have acquired a pivotal role in the sensitization of highly resistant cancer cells, for example, pancreatic cancer and glioblastoma cells, to TRAIL-mediated cell death. Out of this transcription factor family, C/EBP-homologous protein (CHOP) is linked to the control of DR-mediated apoptosis by modulation of several apoptotic and anti-apoptotic factors. Stress responses in certain organelles, such as endoplasmic reticulum (ER) and mitochondria, are potent inductors of CHOP expression. This report focuses on the influence of stress responses on endogenous or acquired resistance to extrinsic apoptosis in tumor cells and summarizes recent findings and results. The Medline and ClinicalTrials database with key words were used for this review.

EXPERT OPINION

A potential novel treatment strategy for highly treatment-resistant tumors is the induction of a cellular stress response in cancer cells. The induction of an organelle-related stress response, such as nuclear, ER and mitochondrial stress, leads to a dramatic sensitization of a broad variety of cancer cells of different tumor entities to the apoptotic ligand, TRAIL. Importantly, non-neoplastic cells are not sensitized to TRAIL-mediated cell death through the unfolded protein response in most instances, suggesting that this treatment is not only of high efficacy, but even more less of unwanted toxicity in patients.

TRAIL and vitamins: opting for keys to castle of cancer proteome instead of open sesame

Cancer is a multifaceted molecular disorder that is modulated by a combination of genetic, metabolic and signal transduction aberrations, which severely impair the normal homeostasis of cell growth and death. Accumulating findings highlight the fact that different genetic alterations, such as mutations in tumor suppressor genes, might be related to distinct and differential sensitivity to targeted therapies. It is becoming increasingly apparent that a multipronged approach that addresses genetic milieu (alterations in upstream and/or parallel pathways) eventually determines the response of individual tumors to therapy. Cancerous cells often acquire the ability to evade death by attenuating cell death pathways that normally function to eliminate damaged and harmful cells. Therefore impaired cell death nanomachinery and withdrawal of death receptors from cell surface are some of major determinants for the development of chemotherapeutic resistance encountered during treatment. It is therefore essential to emphasize underlying factors which predispose cells to refractoriness against TRAIL mediated cell death pathway and the relevant regulatory components involved. We bring to limelight the strategies to re-sensitize TRAIL resistant cells via vitamins to induce apoptosis.

Endoplasmic reticulum stress mediating downregulated StAR and 3-beta-HSD and low plasma testosterone caused by hypoxia is attenuated by CPU86017-RS and nifedipine

Background

Hypoxia exposure initiates low serum testosterone levels that could be attributed to downregulated androgen biosynthesizing genes such as StAR (steroidogenic acute regulatory protein) and 3-beta-HSD (3-beta-hydroxysteroid dehydrogenase) in the testis. It was hypothesized that these abnormalities in the testis by hypoxia are associated with oxidative stress and an increase in chaperones of endoplasmic reticulum stress (ER stress) and ER stress could be modulated by a reduction in calcium influx. Therefore, we verify that if an application of CPU86017-RS (simplified as RS, a derivative to berberine) could alleviate the ER stress and depressed gene expressions of StAR and 3-beta-HSD, and low plasma testosterone in hypoxic rats, these were compared with those of nifedipine.

Methods

Adult male Sprague-Dawley rats were randomly divided into control, hypoxia for 28 days, and hypoxia treated (mg/kg, p.o.) during the last 14 days with nifedipine (Nif, 10) and three doses of RS (20, 40, 80), and normal rats treated with RS isomer (80). Serum testosterone (T) and luteinizing hormone (LH) were measured. The testicular expressions of biomarkers including StAR, 3-beta-HSD, immunoglobulin heavy chain binding protein (Bip), double-strand RNA-activated protein kinase-like ER kinase (PERK) and pro-apoptotic transcription factor C/EBP homologous protein (CHOP) were measured.

Results

In hypoxic rats, serum testosterone levels decreased and mRNA and protein expressions of the testosterone biosynthesis related genes, StAR and 3-beta-HSD were downregulated. These changes were linked to an increase in oxidants and upregulated ER stress chaperones: Bip, PERK, CHOP and distorted histological structure of the seminiferous tubules in the testis. These abnormalities were attenuated significantly by CPU86017-RS and nifedipine.

Conclusion

Downregulated StAR and 3-beta-HSD significantly contribute to low testosterone in hypoxic rats and is associated with ER stress which mediates testis damage caused by oxygen deprivation. CPU86017-RS is potential in ameliorating hypoxia-induced testicular injuries, possibly by its calcium antagonist effects on the testis.

Induction of DNA damage and caspase-independent programmed cell death by vitamin E

Vitamin E comprises 8 functionally unique isoforms and may be a suitable candidate for the adjuvant treatment of prostate cancer. In this study, we examined the ability of 2 vitamin E isoforms [α-tocotrienol (γ-TT) and δ-tocotrienol (δ-TT)] and 4 synthetic derivatives [γ- and δ-tocotrienol succinate (γ-TS, δ-TS), α-tocopheryl polyethylene glycol succinate (TPGS), and α-tocopheryl polyethylene glycol ether (TPGS-e)] of vitamin E to induce cell death in AR- (DU145 and PC-3) and AR+ (LNCaP) prostate cancer cell lines. Our results show that δ-TT and TPGS-e are the most effective isoform and synthetic derivative, respectively, of all compounds examined. Overall, the results of our study suggest that isoforms and synthetic derivatives of vitamin E have the potency to trigger both caspase-dependent and -independent DNA damage and dominant caspase-independent programmed cell death. The capacity of vitamin E to trigger caspase-independent programmed cell death suggests that it may be useful in the chemotherapy of prostate cancer since it may prevent the tumor resistance commonly associated with the use of classical chemotherapeutic agents that trigger caspase-dependent programmed cell death.

Targeting cholesterol-rich microdomains to circumvent tamoxifen-resistant breast cancer

INTRODUCTION

Adjuvant treatment with tamoxifen substantially improves survival of women with estrogen-receptor positive (ER+) tumors. Tamoxifen resistance (TAMR) limits clinical benefit. RRR-α-tocopherol ether-linked acetic acid analogue (α-TEA) is a small bioactive lipid with potent anticancer activity. We evaluated the ability of α-TEA in the presence of tamoxifen to circumvent TAMR in human breast cancer cell lines.

METHODS

Two genotypically matched sets of TAM-sensitive (TAMS) and TAM-resistant (TAMR) human breast cancer cell lines were assessed for signal-transduction events with Western blotting, apoptosis induction with Annexin V-FITC/PI assays, and characterization of cholesterol-rich microdomains with fluorescence staining. Critical involvement of selected mediators was determined by using RNA interference and chemical inhibitors.

RESULTS

Growth-factor receptors (total and phosphorylated forms of HER-1 and HER-2), their downstream prosurvival mediators pAkt, pmTOR, and pERK1/2, phosphorylated form of estrogen receptor-α (pER-α at Ser-167 and Ser-118, and cholesterol-rich lipid microdomains were highly amplified in TAMR cell lines and enhanced by treatment with TAM. α-TEA disrupted cholesterol-rich microdomains, acted cooperatively with TAM to reduce prosurvival mediators, and induced DR5-mediated mitochondria-dependent apoptosis via an endoplasmic reticulum stress-triggered pro-death pJNK/CHOP/DR5 amplification loop. Furthermore, methyl-β-cyclodextrin (MβCD), a chemical disruptor of cholesterol rich microdomains, acted cooperatively with TAM to reduce prosurvival mediators and to induce apoptosis.

CONCLUSIONS

Data for the first time document that targeting cholesterol-rich lipid microdomains is a potential strategy to circumvent TAMR, and the combination of α-TEA + TAM can circumvent TAMR by suppression of prosurvival signaling via disruption of cholesterol-rich lipid microdomains and activation of apoptotic pathways via induction of endoplasmic reticulum stress.

Death receptor 5 signaling promotes hepatocyte lipoapoptosis

Nonalcoholic steatohepatitis is characterized by hepatic steatosis, elevated levels of circulating free fatty acids (FFA), endoplasmic reticulum (ER) stress, and hepatocyte lipoapoptosis. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor 5 (DR5) is significantly elevated in patients with nonalcoholic steatohepatitis, and steatotic hepatocytes demonstrate increased sensitivity to TRAIL-mediated cell death. Nonetheless, a role for TRAIL and/or DR5 in mediating lipoapoptotic pathways is unexplored. Here, we examined the contribution of DR5 death signaling to lipoapoptosis by free fatty acids. The toxic saturated free fatty acid palmitate induces an increase in DR5 mRNA and protein expression in Huh-7 human hepatoma cells leading to DR5 localization into lipid rafts, cell surface receptor clustering with subsequent recruitment of the initiator caspase-8, and ultimately cellular demise. Lipoapoptosis by palmitate was not inhibited by a soluble human recombinant DR5-Fc chimera protein suggesting that DR5 cytotoxic signaling is ligand-independent. Hepatocytes from murine TRAIL receptor knock-out mice (DR(-/-)) displayed reduced palmitate-mediated lipotoxicity. Likewise, knockdown of DR5 or caspase-8 expression by shRNA technology attenuated palmitate-induced Bax activation and apoptosis in Huh-7 cells, without altering induction of ER stress markers. Similar observations were verified in other cell models. Finally, knockdown of CHOP, an ER stress-mediated transcription factor, reduced DR5 up-regulation and DR5-mediated caspase-8 activation upon palmitate treatment. Collectively, these results suggest that ER stress-induced CHOP activation by palmitate transcriptionally up-regulates DR5, likely resulting in ligand-independent cytotoxic signaling by this death receptor.

5, 7-Dimethoxyflavone sensitizes TRAIL-induced apoptosis through DR5 upregulation in hepatocellular carcinoma cells

PURPOSE

5, 7-dimethoxyflavone (DMF) has been reported to induce apoptosis in various cancer cells. The aim of this study was to examine whether DMF sensitizes human hepatocellular carcinoma (HCC) cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis and its mechanism.

METHODS

Human hepatocellular carcinoma cell lines Hep3B, Huh-7, and Hep G2 and human embryo liver L-02 cells were cultured in vitro. The cytotoxic activities were determined using MTT assay. The apoptotic cell death was examined using Flow cytometry using PI staining and DNA agarose gel electrophoresis. The activities of caspase-3, caspase-8, and caspase-9 were measured using ELISA. Intracellular ROS was measured by FCM using the fluorescent probe DCHF-DA, and the expression of DR4, DR5, CHOP, GPR78, and ATF4 proteins was analyzed using Western blot.

RESULTS

Our results demonstrated subtoxic concentrations of DMF sensitize HCC cells to TRAIL-induced apoptosis and induce the death receptor 5 (DR5) expression level, accompanying the generation of reactive oxygen species (ROS) and the upregulation of CHOP, GPR78, and ATF4 protein expression. Pretreatment with N-acetylcysteine (NAC) inhibited DMF-induced upregulation of DR5, CHOP, GPR78, and ATF4 protein expression and blocked the cotreatment-induced apoptosis. Furthermore, DMF-mediated sensitization of HCC cells to TRAIL was reduced by administration of a blocking antibody or small interfering RNAs for DR5, salubrinal, an inhibitor of ER stress, and the small interfering RNAs for CHOP. However, DMF could not induce the upregulation of DR5 expression, generation of ROS, and sensitization of TRAIL-induced apoptotic cell death in human embryo liver L-02 cells or normal human peripheral blood mononuclear cells (PBMCs).

CONCLUSION

The present study demonstrates that DMF selectively enhances TRAIL-induced apoptosis by ROS-stimulated ER-stress triggering CHOP-mediated DR5 upregulation in HCC.

Paxilline enhances TRAIL-mediated apoptosis of glioma cells via modulation of c-FLIP, survivin and DR5

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) induces apoptosis selectively in cancer cells while sparing normal cells. However, many cancer cells are resistant to TRAIL-induced cell death. Here, we report that paxilline, an indole alkaloid from Penicillium paxilli, can sensitize various glioma cells to TRAIL-mediated apoptosis. While treatment with TRAIL alone caused partial processing of caspase-3 to its p20 intermediate in TRAIL-resistant glioma cell lines, co-treatment with TRAIL and subtoxic doses of paxilline caused complete processing of caspase-3 into its active subunits. Paxilline treatment markedly upregulated DR5, a receptor of TRAIL, through a CHOP/GADD153-mediated process. In addition, paxilline treatment markedly downregulated the protein levels of the short form of the cellular FLICE-inhibitory protein (c-FLIPs) and the caspase inhibitor, survivin, through proteasome-mediated degradation. Taken together, these results show that paxilline effectively sensitizes glioma cells to TRAIL-mediated apoptosis by modulating multiple components of the death receptor-mediated apoptotic pathway. Interestingly, paxilline/TRAIL co-treatment did not induce apoptosis in normal astrocytes, nor did it affect the protein levels of CHOP, DR5 or survivin in these cells. Thus, combined treatment regimens involving paxilline and TRAIL may offer an attractive strategy for safely treating resistant gliomas.

A novel monocarbonyl analogue of curcumin, (1E,4E)-1,5-bis(2,3-dimethoxyphenyl)penta-1,4-dien-3-one, induced cancer cell H460 apoptosis via activation of endoplasmic reticulum stress signaling pathway

Endoplasmic reticulum (ER) stress-induced cancer cell apoptosis has become a novel signaling target for development of cancer therapeutic drugs. Curcumin exhibits growth-suppressive activity against a variety of cancer cells. We previously synthesized a series of monocarbonyl analogues of curcumin with strong cytotoxicity against tumor cells. In this study, we found that only compound 19 [(1E,4E)-1,5-bis(2,3-dimethoxyphenyl)penta-1,4-dien-3-one] can induce C/EBP-homologous protein (CHOP) expression in human lung cancer H460 cells. Treatment with 19 induced H460 cell apoptosis in a dose-responsive manner, and this effect was associated with corresponding increases in a series of key components in ER stress-mediated apoptosis pathway, followed by caspase cleavage and activation. However, curcumin at the same concentrations does not display such properties. CHOP knockdown by specific siRNA attenuated 19-induced cell apoptosis, further indicating that the apoptotic pathway is ER stress-dependent. In vivo, 19 showed a dramatic 53.5% reduction in H460 xenograft tumor size after 22 days of treatment. Taken together, these mechanistic insights on the novel compound 19, with nontoxicity, may provide us with a novel anticancer candidate.

α-TEA cooperates with chemotherapeutic agents to induce apoptosis of p53 mutant, triple-negative human breast cancer cells via activating p73

Introduction

Successful treatment of p53 mutant, triple-negative breast cancers (TNBC) remains a daunting challenge. Doxorubicin (DOXO) and cisplatin (CDDP) are standard-of-care treatments for TNBC, but eventually fail due to acquired drug resistance and toxicity. New treatments for overcoming drug resistance and toxicity in p53 mutant, TNBC are therefore badly needed. Unlike p53, p73 - a member of the p53 family - is usually not mutated in cancers and has been shown to regulate p53-mediated apoptotic signaling in p53-deficient cancers. Therefore, identification of anticancer agents that can activate p73 in p53-deficient cancers may provide a chemotherapeutic approach for treatment of p53 mutant cancers. Here we report on the reconstitution of the p53 tumor suppressor pathway in a p53-independent manner via p73 with combination treatments of α-TEA, a small bioactive lipid, plus DOXO or CDDP.

Methods

p53 mutant, TNBC cell lines MDA-MB-231, BT-20 and MDA-MB-468 were used to evaluate the anticancer effect of chemotherapeutic drugs and α-TEA using annexin V (FITC)/PI staining, western blot analyses, RT-PCR and siRNA knockdown techniques.

Results

Combination treatments of α-TEA plus DOXO or CDDP act cooperatively to induce apoptosis, caspase-8 and caspase-9 cleavage, p73, phospho-c-Ab1 and phospho-JNK protein expression, and increase expression of p53 downstream mediators; namely, death receptor-5, CD95/APO-1 (Fas), Bax and Noxa, as well as Yap nuclear translocation - plus reduce expression of Bcl-2. Knockdown of p73, c-Abl, JNK or Yap using siRNAs shows that p73 plays a critical role in combination treatment-enhanced apoptosis and the expression of pro-apoptotic and anti-apoptotic mediators, and that c-Abl, JNK and Yap are upstream mediators of p73 in combination treatment responses.

Conclusions

Data show that α-TEA in combination with DOXO or CDDP synergistically enhances apoptosis in TNBC via targeting p53-mediated genes in a p73-dependent manner, and that p73 responses are downstream of c-Abl, JNK and Yap.

α-TEA cooperates with MEK or mTOR inhibitors to induce apoptosis via targeting IRS/PI3K pathways

Background:

α-Tocopherol ether-linked acetic acid (α-TEA) is a promising agent for cancer prevention/therapy based on its antitumour actions in a variety of cancers.

Methods:

Human breast cancer cells, MCF-7 and HCC-1954, were used to study the effect of α-TEA using Annexin V/PI staining, western blot analyses, and siRNA knockdown techniques.

Results:

α-Tocopherol ether-linked acetic acid suppressed constitutively active basal levels of pAKT, pERK, pmTOR, and their downstream targets, as well as induced both cell types to undergo apoptosis. Phosphoinositide 3-kinase (PI3K) inhibitor wortmannin suppressed pAKT, pERK, pmTOR, and their downstream targets, indicating PI3K to be a common upstream mediator. In addition, α-TEA induced increased levels of pIRS-1 (Ser-307), a phosphorylation site correlated with insulin receptor substrate-1 (IRS-1) inactivation, and decreased levels of total IRS-1. Small interfering RNA (siRNA) knockdown of JNK blocked the impact of α-TEA on pIRS-1 and total IRS-1 and impeded its ability to downregulate the phosphorylated status of AKT, ERK, and mTOR. Combinations of α-TEA+MEK or mTOR inhibitor acted cooperatively to induce apoptosis and reduce basal levels of pERK and pmTOR. Importantly, inhibition of MEK and mTOR resulted in increased levels of pAKT and IRS-1, and α-TEA blocked them.

Conclusions:

Downregulation of IRS-1/PI3K pathways via JNK are critical for α-TEA and α-TEA+MEK or mTOR inhibitor-induced apoptosis in human MCF-7 and HCC-1954 breast cancer cells.

α-TEA-induced death receptor dependent apoptosis involves activation of acid sphingomyelinase and elevated ceramide-enriched cell surface membranes

BACKGROUND

Alpha-tocopherol ether-linked acetic acid (α-TEA), an analog of vitamin E (RRR-alpha-tocopherol), is a potent and selective apoptosis-inducing agent for human cancer cells in vivo and in vitro. α-TEA induces apoptosis via activation of extrinsic death receptors Fas (CD95) and DR5, JNK/p73/Noxa pathways, and suppression of anti-apoptotic mediators Akt, ERK, c-FLIP and survivin in breast, ovarian and prostate cancer cells.

RESULTS

In this study, we demonstrate that α-TEA induces the accumulation of cell surface membrane ceramide, leading to co-localization with Fas, DR5, and FADD, followed by activation of caspases-8 and -9 and apoptosis in human MDA-MB-231 breast cancer cells. α-TEA treatment leads to increased acid sphingomyelinase (ASMase) activity by 30 min, peaking at 4 hrs, which is correlated with ASMase translocation from cytosol to the cell surface membrane. Functional knockdown of ASMase with either the chemical inhibitor, desipramine, or siRNA markedly reduces α-TEA-induced cell surface membrane accumulation of ceramide and its co-localization with Fas, DR5, and FADD, cleavage of caspases-8 and -9 and apoptosis, suggesting an early and critical role for ASMase in α-TEA-induced apoptosis. Consistent with cell culture data, immunohistochemical analyses of tumor tissues taken from α-TEA treated nude mice bearing MDA-MB-231 xenografts show increased levels of cell surface membrane ceramide in comparison to tumor tissues from control animals.

CONCLUSION

Taken together, these studies demonstrate that ASMase activation and membrane ceramide accumulation are early events contributing to α-TEA-induced apoptosis in vitro and perhaps in vivo.