15-deoxy-Δ12,14-prostaglandin J2 up-regulates death receptor 5 gene expression in HCT116 cells: involvement of reactive oxygen species and C/EBP homologous transcription factor gene transcription

Oxidative Stress Inducers in Cancer Therapy: Preclinical and Clinical Evidence

Reactive oxygen species (ROS) are metabolic byproducts that regulate various cellular processes. However, at high levels, ROS induce oxidative stress, which in turn can trigger cell death. Cancer cells alter the redox homeostasis to facilitate protumorigenic processes; however, this leaves them vulnerable to further increases in ROS levels. This paradox has been exploited as a cancer therapeutic strategy with the use of pro-oxidative drugs. Many chemotherapeutic drugs presently in clinical use, such as cisplatin and doxorubicin, induce ROS as one of their mechanisms of action. Further, various drugs, including phytochemicals and small molecules, that are presently being investigated in preclinical and clinical studies attribute their anticancer activity to ROS induction. Consistently, this review aims to highlight selected pro-oxidative drugs whose anticancer potential has been characterized with specific focus on phytochemicals, mechanisms of ROS induction, and anticancer effects downstream of ROS induction.

Alternol Sensitizes Renal Carcinoma Cells to TRAIL-Induced Apoptosis

Purpose: Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), a member of the TNF family, can selectively induce cancer cell death while sparing normal cells. However, the application of TRAIL-based antitumor therapies has been hindered due to drug resistance. Alternol is a new compound isolated from microbial fermentation that possesses antitumor activity in different tumors. In our research, we discovered that alternol can sensitize TRAIL-induced apoptosis in renal carcinoma cells (RCCs).

Materials and Methods: Cytotoxic activity was measured by MTT assay. Apoptosis was probed using the PI/annexin V method. Real-time PCR and western blot were used to test the levels of mRNA and protein, respectively. Luciferase assay was used to investigate whether CHOP regulated the expression of death receptor (DR) 5 through transcription. A xenogeneic tumor transplantation model was used to evaluate the anticancer effects of alternol/TRAIL in vivo.

Results: When the mechanisms were investigated, we discovered that alternol increased DR5 expression. DR5 knockdown by siRNA eliminated the enhanced effect of alternol on TRAIL-mediated apoptosis. Alternol reduced the expression of antiapoptotic proteins and increased the levels of proapoptotic proteins. Moreover, alternol increased the level of CHOP, which is necessary for the enhancing effect of alternol on TRAIL-induced apoptosis, given that downregulation of CHOP abrogated the synergistic effect. DR5 upregulation induced by alternol required the production of reactive oxygen species (ROS). Removing ROS inhibited the induction of DR5 and blocked the antiapoptotic proteins induced by alternol.

Conclusion: Taken together, our research suggested that alternol increased TRAIL-mediated apoptosis via inhibiting antiapoptotic proteins and upregulating DR5 levels via ROS generation and the CHOP pathway.

The Role of Oxidative Stress and Its Counteractive Utility in Colorectal Cancer (CRC)

An altered redox status accompanied by an elevated generation of reactive oxygen/nitrogen species (ROS/RNS) has been implicated in a number of diseases including colorectal cancer (CRC). CRC, being one of the most common cancers worldwide, has been reported to be associated with multiple environmental and lifestyle factors (e.g., dietary habits, obesity, and physical inactivity) and harboring heightened oxidative stress that results in genomic instability. Although under normal condition ROS regulate many signal transduction pathways including cell proliferation and survival, overwhelming of the antioxidant capacity due to metabolic abnormalities and oncogenic signaling leads to a redox adaptation response that imparts drug resistance. Nevertheless, excessive reliance on elevated production of ROS makes the tumor cells increasingly vulnerable to further ROS insults, and the abolition of such drug resistance through redox perturbation could be instrumental to preferentially eliminate them. The goal of this review is to demonstrate the evidence that links redox stress to the development of CRC and assimilate the most up-to-date information that would facilitate future investigation on CRC-associated redox biology. Concomitantly, we argue that the exploitation of this distinct biochemical property of CRC cells might offer a fresh avenue to effectively eradicate these cells.

Non-Thermal Plasma Couples Oxidative Stress to TRAIL Sensitization through DR5 Upregulation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various tumor cells without affecting most normal cells. Despite being in clinical testing, novel strategies to induce TRAIL-mediated apoptosis are in need to overcome cancer cell unresponsiveness and resistance. Plasma-activated medium (PAM) markedly stimulates reactive oxygen/nitrogen species (ROS/RNS)-dependent apoptosis in cancer cells. We investigate the capability of PAM and TRAIL (PAM/TRAIL) combination therapy to overcome TRAIL resistance and improve the anticancer efficacy of TRAIL. The combinatorial treatment of PAM and TRAIL shows synergistic effects on growth inhibition in TRAIL-resistant cancer cells via augmented apoptosis by two attributes. DR5 (TRAIL-R2) transcription by CHOP is upregulated in a PAM-generated ROS/RNS-dependent manner, and PAM itself upregulates PTEN expression mediated by suppression of miR-425 which is involved in Akt inactivation, leading to increased apoptosis induction. Treatment of cancer cell lines with the antioxidant N-acetylcysteine reduces the extent of membrane dysfunction and the expression of both CHOP-DR5 and miR-425-PTEN axes, attenuating PAM/TRAIL-induced cancer cell apoptosis. These data suggest that PAM/TRAIL treatment is a novel approach to sensitizing cancer cells to TRAIL-induced apoptosis and overcoming TRAIL resistance. PAM is a promising candidate for further investigations as a chemotherapeutic sensitizer in the treatment of cancer.

Molecular pathobiology of scleritis and its therapeutic implications

Scleritis and other autoimmune diseases are characterized by an imbalance in the levels of pro-inflammatory and anti-inflammatory molecules with the balance tilted more towards the former due to the failure of recognition of self. The triggering of inflammatory process could be ascribed to the presence of cytoplasmic DNA/chromatin that leads to activation of cytosolic DNA-sensing cGAS-STING (cyclic GMP-AMP synthase linked to stimulator of interferon genes) pathway and enhanced expression of NF-κB that results in an increase in the production of pro-inflammatory bioactive lipids. Bioactive lipids gamma-linolenic acid (GLA), dihomo-GLA (DGLA), prostaglandin E1 (PGE1), prostacyclin (PGI2) and lipoxin A4, resolvins, protectins and maresins have anti-inflammatory actions, bind to DNA to render it non-antigenic and are decreased in autoimmune diseases. These results suggest that efforts designed to enhance the production of anti-inflammatory bioactive lipids may form a new approach to autoimmune diseases. Local injection or infusion of lipoxins, resolvins, protectins and maresins or their precursors such as arachidonic acid may be exploited in the prevention and management of autoimmune diseases including scleritis, uveitis and lupus/rheumatoid arthritis.

Benzoquinones from Cyperus spp. trigger IRE1α-independent and PERK-dependent ER stress in human stomach cancer cells and are novel proteasome inhibitors

BACKGROUND

The roots and tubers of several species of the Cyperus genus are used in several parts of the world as foodstuffs and beverages. The genus is rich in several classes of quinones, however their biological properties have not been studied before.

PURPOSE

We evaluated the anticancer effect of several benzoquinones isolated from the genus and described their mechanism of action towards cancer cells.

METHODS

The most potent molecules were selected according to their effect upon cell viability. The mechanism of cell death was studied by using pharmacological inhibitors of caspases, caspase-3/4/9 activity assays, annexin-V/7-AAD by flow cytometry and intracellular reactive oxygen species and calcium levels through fluorescence spectroscopy. Elucidation of the involvement of distinct branches of the ER stress pathway was pursued by RT-PCR and WB for mRNA and protein expression levels, respectively, as well as pharmacological inhibitors. Proteasome inhibitory activity was assessed by using purified 20S catalytic subunit with the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-AMC.

RESULTS

Cytotoxicity studies against cancer cell lines showed that the human gastric cancer cell line AGS was the most susceptible, the most potent molecule, hydroxycyperaquinone, exhibiting an IC₅₀ close to 1 µM. Morphological and biochemical traits suggested that a process of regulated cell death was taking place, which was shown to be intrinsic pathway-independent. Results indicated that benzoquinones exert their toxicity by triggering ER stress, as shown by increased expression of CHOP (mRNA and protein levels), intracellular reactive oxygen species, changes in calcium dynamics and caspase-4 activation. Proteasome inhibition by these molecules is described for the first time.

CONCLUSION

Hydroxycyperaquinone is a novel sub-micromolar inhibitor of the 20S catalytic core of the 26S proteasome, causing cell death via IRE1α-independent/PERK-dependent pathways in stomach cancer cells. Its presence in products consumed orally may be of relevance for gastric tumors.

15-Deoxy-∆-12,14-Prostaglandin J2 (15d-PGJ2), an Endogenous Ligand of PPAR-γ: Function and Mechanism

15-Deoxy-∆-^12,14-prostaglandin J2 (15d-PGJ2), a natural peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, has been explored in some detail over the last 20 years. By triggering the PPAR-γ signalling pathway, it plays many roles and exerts antitumour, anti-inflammatory, antioxidation, antifibrosis, and antiangiogenesis effects. Although many synthetic PPAR-γ receptor agonists have been developed, as an endogenous product of PPAR-γ receptors, 15d-PGJ2 has beneficial characteristics including rapid expression and the ability to contribute to a natural defence mechanism. In this review, we discuss the latest advances in our knowledge of the biological role of 15d-PGJ2 mediated through PPAR-γ. It is important to understand its structure, synthesis, and functional mechanisms to develop preventive agents and limit the progression of associated diseases.

Dihydroartemisinin Induces Endoplasmic Reticulum Stress-Mediated Apoptosis in HepG2 Human Hepatoma Cells

Aims and Background

Previous studies showed that dihydroartemisinin (DHA) possessed antitumor activity in many human tumor cells through the induction of apoptosis. The aim of this study was to investigate the effects of DHA on apoptosis in the human hepatocellular carcinoma cell line HepG2 and the possible molecular mechanisms involved.

Methods

The inhibitory effect of DHA on HepG2 cells was measured by MTT assay. The percentage of apoptotic cells was detected by flow cytometry with double staining of fluorescein isothiocyanate-annexin V/propidium iodide. The intracellular production of reactive oxygen species (ROS) and intracellular Ca2+ concentration ([Ca2+]i) were detected by fluorescence spectrophotometry. Protein expression of GADD153, Bcl-2 and Bax in HepG2 cells was examined by Western blot and immunocytochemistry.

Results

DHA significantly inhibited proliferation of HepG2 cells in a dose- and time-dependent manner. The apoptosis rates in HepG2 cells treated with 0, 50, 100 and 200 mol/L DHA for 24 hours were 2.53 ± 0.88%, 24.85 ± 3.63%, 35.27 ± 5.92% and 48.53 ± 7.76%, respectively. Compared with the control group, DHA significantly increased ROS generation and [Ca2+]i level (P <0.05), with the generation of ROS preceding the increase in [Ca2+]i. An increase in GADD153 and Bax expression and a decrease in Bcl-2 were observed in DHA-treated cells. Pretreatment with the antioxidant N-acetylcysteine could attenuate the effects of DHA in the experiments.

Conclusion

DHA could inhibit proliferation and induce apoptosis in HepG2 cell lines through increasing the intracellular production of ROS and [Ca2+]i. Endoplasmic reticulum stress-induced apoptosis may contribute to this effect by regulating the expression of GADD153, proapoptotic Bax, and antiapoptotic Bcl-2.

Reactive oxygen species and colorectal cancer

Colorectal cancer (CRC) has become the fourth leading cause of cancer-related death in the worldwide. It is urgent to find more effective therapeutic strategies for it. Reactive oxygen species (ROS) play multiple roles in normal cellular physiology processes. Thus, a certain level of ROS is essential to keep normal cellular function. However, the accumulation of ROS shows dual roles for cells, which is mainly dependent on the concentration of ROS, the origin of the cancer cell and the activated signaling pathways during tumor progression. In general, moderate level of ROS leads to cell damage, DNA mutation and inflammation, which promotes the initiation and development of cancer. Excessive high level of ROS induces cancer cell death, showing an anti-cancer role. ROS are commonly higher in CRC cells than their normal counterpart cells. Therefore, it is possible that ROS induce cell death in cancer cells while not affecting the normal cells, demonstrating lower side effects. Besides, ROS also play a role in tumor microenvironment and drug resistance. These multiple roles of ROS make them a promising therapeutic target for cancer. To explore potential ROS-target therapies against CRC, it is worth to comprehensively understanding the role of ROS in CRC and therapy. In this review, we mainly discuss the strategies of ROS in CRC therapy, including direct CRC cell target and indirect tumor environment target. In addition, the influences of ROS in drug resistance will also been discussed.

A new brominated chalcone derivative suppresses the growth of gastric cancer cells in vitro and in vivo involving ROS mediated up-regulation of DR5 and 4 expression and apoptosis

A new series of 20 brominated chalcone derivatives were designed, synthesized, and investigated for their effects against the growth of four cancer cell lines (EC109, SKNSH, HepG2, MGC803). Among them, compound 19 which given chemical name of H72, was the most potent one on gastric cancer cell lines (i.e. MGC803, HGC27, SGC7901) with IC50s ranged from 3.57 to 5.61μM. H72 exhibited less cytotoxicity to non-malignant gastric epithelial cells GES-1. H72 treatment of MGC803 and HGC27 induced generation of reactive oxygen species (ROS) leading to activation of caspase 9/3 cascade and mitochondria mediated apoptosis. H72 also up-regulated the expression of DR5, DR4 and BimEL, and down-regulated the expression of Bid, Bcl-xL, and XIAP. N-acetyl cysteine (NAC), a ROS scavenger completely blocked these effects of H72 in MGC803 cells. Intraperitoneal administration of H72 significantly inhibited the growth of MGC803 cells in vivo in a xenograft mouse model without observed toxicity. These results indicated that H72 is a lead brominated chalcone derivate and deserves further investigation for prevention and treatment of gastric cancer.

Prostaglandin J2: a potential target for halting inflammation-induced neurodegeneration

Prostaglandins (PGs) are produced via cyclooxygenases, which are enzymes that play a major role in neuroinflammation. Epidemiological studies show that chronic treatment with low levels of cyclooxygenase inhibitors (nonsteroidal anti-inflammatory drugs (NSAIDs)) lowers the risk for Alzheimer's disease (AD) and Parkinson's disease (PD) by as much as 50%. Unfortunately, inhibiting cyclooxygenases with NSAIDs blocks the synthesis of downstream neuroprotective and neurotoxic PGs, thus producing adverse side effects. We focus on prostaglandin J2 (PGJ2) because it is highly neurotoxic compared to PGA1, D2, and E2. Unlike other PGs, PGJ2 and its metabolites have a cyclopentenone ring with reactive α,β-unsaturated carbonyl groups that form covalent Michael adducts with key cysteines in proteins and GSH. Cysteine-binding electrophiles such as PGJ2 are considered to play an important role in determining whether neurons will live or die. We discuss in vitro and in vivo studies showing that PGJ2 induces pathological processes relevant to neurodegenerative disorders such as AD and PD. Further, we discuss our work showing that increasing intracellular cAMP with the lipophilic peptide PACAP27 counteracts some of the PGJ2-induced detrimental effects. New therapeutic strategies that neutralize the effects of specific neurotoxic PGs downstream from cyclooxygenases could have a significant impact on the treatment of chronic neurodegenerative disorders with fewer adverse side effects.

Anandamide-induced endoplasmic reticulum stress and apoptosis are mediated by oxidative stress in non-melanoma skin cancer: Receptor-independent endocannabinoid signaling

Endocannabinoids are neuromodulatory lipids that regulate central and peripheral physiological functions. Endocannabinoids have emerged as effective antitumor drugs due to their ability to induce apoptosis in various cancer studies. The G-protein coupled cannabinoid receptors (CB1 and CB2) and the TRPV1 ion channel were reported to mediate the antiproliferative activity of endocannabinoids. However, receptor-independent effects also account for their activity. Our previous studies showed that the antiproliferative activity of anandamide (AEA) was regulated by cyclooxygenase-2 (COX-2) via induction of endoplasmic reticulum (ER) stress. We also determined that AEA induced oxidative stress. However, the role of oxidative stress, the cannabinoid receptors, and TRPV1 in AEA-induced ER stress-apoptosis was unclear. Therefore, the current study examines the role of oxidative stress in ER stress-apoptosis and investigates whether this effect is modulated by CB1, CB2, or TRPV1. In non-melanoma skin cancer (NMSC) cells, AEA reduced the total intracellular level of glutathione and induced oxidative stress. To evaluate the importance of oxidative stress in AEA-induced cell death, the antioxidants, N-acetylcysteine (NAC) and Trolox, were utilized. Each antioxidant ameliorated the antiproliferative effect of AEA. Furthermore, Trolox inhibited AEA-induced CHOP10 expression and caspase 3 activity, indicating that oxidative stress was required for AEA-induced ER stress-apoptosis. On the other hand, selective blockade of CB1, CB2, and TRPV1 did not inhibit AEA-induced oxidative stress or ER stress-apoptosis. These findings suggest that AEA-induced ER stress-apoptosis in NMSC cells is mediated by oxidative stress through a receptor-independent mechanism. Hence, receptor-independent AEA signaling pathways may be targeted to eliminate NMSC. © 2015 Wiley Periodicals, Inc.

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.

Neuroinflammation and J2 prostaglandins: linking impairment of the ubiquitin-proteasome pathway and mitochondria to neurodegeneration

The immune response of the CNS is a defense mechanism activated upon injury to initiate repair mechanisms while chronic over-activation of the CNS immune system (termed neuroinflammation) may exacerbate injury. The latter is implicated in a variety of neurological and neurodegenerative disorders such as Alzheimer and Parkinson diseases, amyotrophic lateral sclerosis, multiple sclerosis, traumatic brain injury, HIV dementia, and prion diseases. Cyclooxygenases (COX-1 and COX-2), which are key enzymes in the conversion of arachidonic acid into bioactive prostanoids, play a central role in the inflammatory cascade. J2 prostaglandins are endogenous toxic products of cyclooxygenases, and because their levels are significantly increased upon brain injury, they are actively involved in neuronal dysfunction induced by pro-inflammatory stimuli. In this review, we highlight the mechanisms by which J2 prostaglandins (1) exert their actions, (2) potentially contribute to the transition from acute to chronic inflammation and to the spreading of neuropathology, (3) disturb the ubiquitin-proteasome pathway and mitochondrial function, and (4) contribute to neurodegenerative disorders such as Alzheimer and Parkinson diseases, and amyotrophic lateral sclerosis, as well as stroke, traumatic brain injury (TBI), and demyelination in Krabbe disease. We conclude by discussing the therapeutic potential of targeting the J2 prostaglandin pathway to prevent/delay neurodegeneration associated with neuroinflammation. In this context, we suggest a shift from the traditional view that cyclooxygenases are the most appropriate targets to treat neuroinflammation, to the notion that J2 prostaglandin pathways and other neurotoxic prostaglandins downstream from cyclooxygenases, would offer significant benefits as more effective therapeutic targets to treat chronic neurodegenerative diseases, while minimizing adverse side effects.

Arachidonoyl-ethanolamide activates endoplasmic reticulum stress-apoptosis in tumorigenic keratinocytes: Role of cyclooxygenase-2 and novel J-series prostamides

Non-melanoma skin cancer and other epithelial tumors overexpress cyclooxygenase-2 (COX-2), differentiating them from normal cells. COX-2 metabolizes arachidonic acid to prostaglandins including, the J-series prostaglandins, which induce apoptosis by mechanisms including endoplasmic reticulum (ER) stress. Arachidonoyl-ethanolamide (AEA) is a cannabinoid that causes apoptosis in diverse tumor types. Previous studies from our group demonstrated that AEA was metabolized by COX-2 to J-series prostaglandins. Thus, the current study examines the role of COX-2, J-series prostaglandins, and ER stress in AEA-induced apoptosis. In tumorigenic keratinocytes that overexpress COX-2, AEA activated the PKR-like ER kinase (PERK), inositol requiring kinase-1 (IRE1), and activating transcription factor-6 (ATF6) ER stress pathways and the ER stress apoptosis-associated proteins, C/EBP homologous protein-10 (CHOP10), caspase-12, and caspase-3. Using an ER stress inhibitor, it was determined that ER stress was required for AEA-induced apoptosis. To evaluate the role of COX-2 in ER stress-apoptosis, HaCaT keratinocytes with low endogenous COX-2 expression were transfected with COX-2 cDNA or an empty vector and AEA-induced ER stress-apoptosis occurred only in the presence of COX-2. Moreover, LC-MS analysis showed that the novel prostaglandins, 15-deoxyΔ(12,14) PGJ2 -EA and Δ(12) PGJ2 /PGJ2-EA, were synthesized from AEA. These findings suggest that AEA will be selectively toxic in tumor cells that overexpress COX-2 due to the metabolism of AEA by COX-2 to J-series prostaglandin-ethanolamides (prostamides). Hence, AEA may be an ideal topical agent for the elimination of malignancies that overexpress COX-2.

Piperlongumine induces cell death through ROS-mediated CHOP activation and potentiates TRAIL-induced cell death in breast cancer cells

PURPOSE

Piperlongumine (PL) has been shown to selectively induce apoptotic cell death in cancer cells via reactive oxygen species (ROS) accumulation. In this study, we characterized a molecular mechanism for PL-induced cell death.

METHODS

Cell viability and cell death were assessed by MTT assay and Annexin V-FITC/PI staining, respectively. ROS generation was measured using the H2DCFDA. Small interfering RNA (siRNA) was used for suppressing gene expression. The mRNA and protein expression were analyzed by RT-PCR and Western blot analysis, respectively.

RESULTS

We found that PL promotes C/EBP homologous protein (CHOP) induction, which leads to the up-regulation of its targets Bim and DR5. Pretreatment with the ROS scavenger N-acetyl-cysteine abolishes the PL-induced up-regulation of CHOP and its target genes, suggesting an essential role for ROS in PL-induced CHOP activation. The down-regulation of CHOP or Bim with siRNA efficiently attenuates PL-induced cell death, suggesting a critical role for CHOP in this cell death. Furthermore, PL potentiates TRAIL-induced cytotoxicity in breast cancer cells by upregulating DR5, as DR5 knockdown abolished the sensitizing effect of PL on TRAIL responses.

CONCLUSIONS

Overall, our data suggest a new mechanism for the PL-induced cell death in which ROS mediates CHOP activation, and combination treatment with PL and TRAIL could be a potential strategy for breast cancer therapy.

Molecular targets of TRAIL-sensitizing agents in colorectal cancer

Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily, interacts with its functional death receptors (DRs) and induces apoptosis in a wide range of cancer cell types. Therefore, TRAIL has been considered as an attractive agent for cancer therapy. However, many cancers are resistant to TRAIL-based therapies mainly due to the reduced expression of DRs and/or up-regulation of TRAIL pathway-related anti-apoptotic proteins. Compounds that revert such defects restore the sensitivity of cancer cells to TRAIL, suggesting that combined therapies could help manage neoplastic patients. In this article, we will focus on the TRAIL-sensitizing effects of natural products and synthetic compounds in colorectal cancer (CRC) cells and discuss the molecular mechanisms by which such agents enhance the response of CRC cells to TRAIL.

Cardamonin sensitizes tumour cells to TRAIL through ROS- and CHOP-mediated up-regulation of death receptors and down-regulation of survival proteins

BACKGROUND AND PURPOSE

TNF-related apoptosis-inducing ligand (TRAIL) is currently in clinical trials as a treatment for cancer, but development of resistance is a major drawback. Thus agents that can overcome resistance to TRAIL are urgently needed. Cardamonin (2',4'-dihydroxy-6'-methoxychalcone) has been shown to affect cell growth by modulating various cell signalling pathways. Hence, we investigated the effect of cardamonin on the actions of TRAIL.

EXPERIMENTAL APPROACH

The effect of cardamonin on TRAIL was measured by plasma membrane integrity, phosphatidylserine exposure, mitochondrial activity, and activation of caspase-8, caspase-9, and caspase-3 in human colon cancer cells.

KEY RESULTS

Cardamonin potentiated TRAIL-induced apoptosis and this correlated with up-regulation of both the TRAIL death receptor (DR) 4, 5 at mRNA and protein levels. TRAIL-decoy receptor DcR1 was down-regulated by cardamonin. Induction of DRs by cardamonin occurred in a variety of cell types. Gene silencing of the DRs by small interfering RNA (siRNA) abolished the effect of cardamonin on TRAIL-induced apoptosis, suggesting that sensitization was mediated through the DR. Induction of the DR by cardamonin was p53-independent but required CCAAT/enhancer binding protein homologous protein (CHOP); cardamonin induced CHOP, and its silencing by siRNA eliminated the induction of DR5. Cardamonin increased the production of reactive oxygen species (ROS) and quenching ROS abolished its induction of receptors and enhancement of TRAIL-induced apoptosis. Cardamonin also decreased the expression of various cell survival proteins.

CONCLUSIONS AND IMPLICATIONS

Cardamonin potentiates TRAIL-induced apoptosis through ROS-CHOP-mediated up-regulation of DRs, decreased expression of decoy receptor and cell survival proteins. Thus, cardamonin has the potential to make TRAIL more effective as an anticancer therapy.

Eicosanoid signalling pathways in the development and progression of colorectal cancer: novel approaches for prevention/intervention

Arachidonic acid metabolism through cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P-450 epoxygenase (EPOX) pathways leads to the generation of biologically active eicosanoids, including prostanoids, leukotrienes, hydroxyeicosatetraenoic acid, epoxyeicosatrienoic acid and hydroperoxyeicosatetraenoic acids. Eicosanoid expression levels vary during tumor development and progression of a range of malignancies, including colorectal cancer. The actions of these autocoids are also directly influenced by diet, as demonstrated by recent evidence for omega-3 fatty acids in colorectal cancer (CRC) prevention and/or treatment. Eicosanoids regulate CRC development and progression, while inhibition of these pathways has generally been shown to inhibit tumor growth/progression. A progressive sequence of colorectal cancer development has been identified, ranging from normal colon, to colitis, dysplasia, and carcinoma. While both COX and LOX inhibition are both promising candidates for colorectal cancer prevention and/or treatment, there is an urgent need to understand the mechanisms through which these signalling pathways mediate their effects on tumorigenesis. This will allow identification of safer, more effective strategies for colorectal cancer prevention and/or treatment. In particular, binding to/signalling through prostanoid receptors have recently been the subject of considerable interest in this area. In this review, we discuss the role of the eicosanoid signalling pathways in the development and progression of colorectal cancer. We discuss the effects of the eicosanoids on tumor cell proliferation, their roles in cell death induction, effects on angiogenesis, migration, invasion and their regulation of the immune response. Signal transduction pathways involved in these processes are also discussed. Finally, novel approaches targeting these arachidonic acid-derived eicosanoids (using pharmacological or natural agents) for chemoprevention and/or treatment of colorectal cancer are outlined.

Targeting p53 as a therapeutic strategy in sensitizing TRAIL-induced apoptosis in cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been intensively studied as a cancer therapeutic agent due to its unique ability to induce apoptosis in malignant cells but not in normal cells. However, as more human cancer cells are reported to be resistant to TRAIL treatment, it is important to develop new therapeutic strategies to overcome this resistance. p53 is an important tumor suppressor that is widely involved in cellular responses to various stresses. In this mini-review, we aim to provide an overview of the intricate relationship between p53 and the TRAIL-mediated apoptosis pathway, and to summarize the current approaches of targeting p53 as a therapeutic strategy to sensitize TRAIL-induced apoptosis in human cancer cells. Although in some cases TRAIL kills cancer cells in a p53-independent manner, it is believed that in cancers with wild-type and functional p53, targeting p53 may be an important strategy for overcoming TRAIL-resistance in cancer therapy.

COX-derived prostanoid pathways in gastrointestinal cancer development and progression: novel targets for prevention and intervention

Arachidonic acid metabolism through cyclooxygenase (COX) pathways leads to the generation of biologically active eicosanoids. Eicosanoid expression levels vary during development and progression of gastrointestinal (GI) malignancies. COX-2 is the major COX-isoform responsible for G.I. cancer development/progression. COX-2 expression increases during progression from a normal to cancerous state. Evidence from observational studies has demonstrated that chronic NSAID use reduces the risk of cancer development, while both incidence and risk of death due to G.I. cancers were significantly reduced by daily aspirin intake. A number of randomized controlled trials (APC trial, Prevention of Sporadic Adenomatous Polyps trial, APPROVe trial) have also shown a significant protective effect in patients receiving selective COX-2 inhibitors. However, chronic use of selective COX-2 inhibitors at high doses was associated with increased cardiovascular risk, while NSAIDs have also been associated with increased risk. More recently, downstream effectors of COX-signaling have been investigated in cancer development/progression. PGE(2), which binds to both EP and PPAR receptors, is the major prostanoid implicated in the carcinogenesis of G.I. cancers. The role of TXA(2) in G.I. cancers has also been examined, although further studies are required to uncover its role in carcinogenesis. Other prostanoids investigated include PGD(2) and its metabolite 15d-PGJ2, PGF(1α) and PGI(2). Targeting these prostanoids in G.I. cancers has the promise of avoiding cardiovascular toxicity associated with chronic selective COX-2 inhibition, while maintaining anti-tumor reactivity. A progressive sequence from normal to pre-malignant to a malignant state has been identified in G.I. cancers. In this review, we will discuss the role of the COX-derived prostanoids in G.I. cancer development and progression. Targeting these downstream prostanoids for chemoprevention and/or treatment of G.I. cancers will also be discussed. Finally, we will highlight the latest pre-clinical technologies as well as avenues for future investigation in this highly topical research field.

UBC and YWHAZ as suitable reference genes for accurate normalisation of gene expression using MCF7, HCT116 and HepG2 cell lines

Relative quantification of in vitro gene expression using real-time PCR requires stably expressed reference gene for normalisation. In this study, total RNA from MCF7, HCT116 and HepG2 cells were extracted and converted to cDNA using commercially available kit, and real-time PCR was then performed to analyse the expression levels of twelve reference genes to select the most ideal reference gene for accurate normalisation in gene expression study. geNorm and NormFinder software were used to analyse the stabilities of the reference genes, which showed a wide range of C(t) values. The geNorm analysis showed the following ranking for stability of genes: UBC, YWHAZ > RPLP > TBP > ACTB > HPRT1 > PPIA > GAPDH > GUSB > B2M > TUBB > RRN18S. A similar ranking of reference genes was obtained by NormFinder, and the four most stable reference genes were identical using both approaches. UBC and YWHAZ were proposed to be the two most suitable reference genes based on the above analyses. To further assess the stabilities of the UBC and YWHAZ in a formal experiment, MCF7, HCT116 and HepG2 cell lines were subjected to treatments with 5-aza-dC and TSA. Both UBC and YWHAZ exhibited stable expression levels across control and treatment groups. Therefore, we propose that UBC and YWHAZ are the two most suitable reference genes for our gene expression studies using MCF7, HCT116 and HepG2 cell lines.

Attenuating the endoplasmic reticulum stress response improves functional recovery after spinal cord injury

Activation of the unfolded protein response (UPR) is involved in the pathogenesis of numerous CNS myelin abnormalities; yet, its direct role in traumatic spinal cord injury (SCI)-induced demyelination is not known. The UPR is an evolutionarily conserved cell defense mechanism initiated to restore endoplasmic reticulum homeostasis in response to various cellular stresses including infection, trauma, and oxidative damage. However, if uncompensated, the UPR triggers apoptotic cell death. We demonstrate that the three signaling branches of UPR including the PERK, ATF6, and IRE1α are rapidly initiated in a mouse model of contusive SCI specifically at the injury epicenter. Immunohistochemical analyses of the various UPR markers revealed that in neurons, the UPR appeared at 6 and 24-h post-SCI. In contrast, in oligodendrocytes and astroglia, UPR persisted at least for up to 3 days post-SCI. The UPR-associated proapoptotic transcriptional regulator CHOP was among the UPR markers upregulated in neurons and oligodendrocytes, but not in astrocytes, of traumatized mouse spinal cords. To directly analyze its role in SCI, WT and CHOP null mice received a moderate T9 contusive injury. Deletion of CHOP led to an overall attenuation of the UPR after contusive SCI. Furthermore, analyses of hindlimb locomotion demonstrated a significant functional recovery that correlated with an increase in white-matter sparing, transcript levels of myelin basic protein, and Claudin 11 and decreased oligodendrocyte apoptosis in CHOP null mice in contrast to WT animals. Thus, our study provides evidence that the UPR contributes to oligodendrocyte loss after traumatic SCI.

TRAIL-induced keratinocyte differentiation requires caspase activation and p63 expression

Cornification, the terminal differentiation of keratinocytes, is a special form of programmed cell death in the skin. In this article, we report that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce the expression of the keratinocyte differentiation markers involucrin and type 1 transglutaminase in normal human epidermal keratinocytes. The induction of differentiation occurs mainly under the activation of caspases 3 and 8, and apoptosis can also be triggered. Inhibition of these apoptotic caspases attenuates both apoptosis and differentiation of keratinocytes caused by TRAIL but barely affects the induction of differentiation caused by calcium and phorbol 12-myristate 13-acetate. Differential regulation of extracellular signal-regulated kinase and p38 activation by TRAIL is also observed. Moreover, the degradation of p63 is induced by TRAIL-elicited caspase activation. However, the existence of p63 is essential for the initiation of keratinocyte differentiation by TRAIL because knockdown of ΔNp63 decreases TRAIL-induced differentiation. Taken together, our results suggest that TRAIL can be an inducer of both differentiation and apoptosis in human keratinocytes, and that caspases critically mediate these processes. This study identifies a new role of apoptotic caspases for terminal differentiation of keratinocytes and further elucidates the molecular pathways involved in this unique model of cell death.

ROS and CHOP are critical for dibenzylideneacetone to sensitize tumor cells to TRAIL through induction of death receptors and downregulation of cell survival proteins

Because tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) selectively kills tumor cells, it is being tested in cancer patients. Unfortunately, patients develop resistance to the cytokine, therefore, agents that can sensitize cells to TRAIL are urgently needed. In this study, we investigated whether dibenzylideneacetone (DBA) can sensitize cancer cells to TRAIL and potentiates TRAIL-induced apoptosis. As indicated by accumulation of the membrane phospholipid phosphatidylserine, DNA breaks, intracellular esterase activity, and activation of caspase-8, -9, and -3, we concluded that DBA potentiated TRAIL-induced apoptosis in colon cancer cells. DBA also converted TRAIL resistant-cells to TRAIL-sensitive. When examined for the mechanism, we found that DBA decreased the expression of antiapoptotic proteins and decoy receptor-2 and increased proapoptotic proteins. DBA also induced both death receptor (DR)-5 and DR4. Knockdown of DR5 and DR4 by small interfering RNA (SiRNA) reduced the sensitizing effect of DBA on TRAIL-induced apoptosis. In addition, DBA increased the expression of CHOP proteins. Knockdown of CHOP by siRNA decreased the induction of DBA-induced DR5 expression and apoptosis. Induction of receptors by DBA, however, was p53-independent, as deletion of p53 had no effect on receptor induction. We observed that DBA-induced induction of DR5 and DR4 was mediated through generation of reactive oxygen species (ROS), as N-acetylcysteine blocked the induction of death receptors and suppression of cell survival proteins by DBA. Overall, our results show that DBA potentiates TRAIL-induced apoptosis through downregulation of cell survival proteins and upregulation of death receptors via activation of ROS and CHOP mediated pathways.

2-Tellurium-bridged β-cyclodextrin, a thioredoxin reductase inhibitor, sensitizes human breast cancer cells to TRAIL-induced apoptosis through DR5 induction and NF-κB suppression

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumor activity via membrane receptors on cancer cells without deleterious side effects for normal tissue. Unfortunately, breast cancer cells, as many other cancer types, develop resistance to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. 2-Tellurium-bridged β-cyclodextrin (2-TeCD) is a synthetic organotellurium compound, with both glutathione peroxidase-like catalytic ability and thioredoxin reductase inhibitor activity. In the present study, we reported that 2-TeCD sensitized TRAIL-resistant human breast cancer cells and xenograft tumors to undergo apoptosis. In vitro, 2-TeCD efficiently sensitized MDA-MB-468 and T47D cells, but not untransformed human mammary epithelial cells, to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly (adenosine diphosphate-ribose) polymerase cleavage. From a mechanistic standpoint, we showed that 2-TeCD treatment of breast cancer cells significantly upregulated the messenger RNA and protein levels of TRAIL receptor, death receptor (DR) 5, in a transcription factor Sp1-dependent manner. 2-TeCD treatment also suppressed TRAIL-induced nuclear factor-κB (NF-κB) prosurvival pathways by preventing cytosolic IκBα degradation, as well as p65 nuclear translocation. Consequently, the combined administration suppressed anti-apoptotic molecules that are transcriptionally regulated by NF-κB. In vivo, 2-TeCD and TRAIL were well tolerated in mice and their combination significantly inhibited growth of MDA-MB-468 xenografts and promoted apoptosis. Upregulation of DR5 and downregulation of NF-κB by the dual treatment were also observed in tumor tissues. Overall, 2-TeCD sensitizes resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.

Fenretinide-dependent upregulation of death receptors through ASK1 and p38α enhances death receptor ligand-induced cell death in Ewing's sarcoma family of tumours

Background:

Sustained p38^MAPK phosphorylation upregulates p75 neurotrophin (p75^NTR) and induces apoptosis in Ewing's sarcoma family of tumours (ESFT). As fenretinide induces ESFT death through sustained p38^MAPK phosphorylation, we hypothesised that this may be effected through upregulation of death receptors (DRs) and that treatment of fenretinide plus DR ligands may enhance apoptosis.

Methods:

DR expression was determined by flow cytometry. Trypan blue exclusion assays, caspase-8 flow cytometry and immunoblotting for Bid were used to measure cell death.

Results:

Fenretinide upregulated cell surface expression of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors, FAS and p75^NTR, in an ASK1- and p38α-dependent manner. Cotreatment with fenretinide and DR ligands resulted in synergistic death compared with either agent alone; caspase-8 and Bid were cleaved in a time-dependent manner. Fenretinide did not increase DR expression in non-malignant cells. Furthermore, fenretinide, TRAIL or a combination of both agents was non-cytotoxic to non-malignant cells. Etoposide and actinomycin D increased expression of all DRs examined, whereas vincristine increased FAS alone. Only actinomycin D and TRAIL, and etoposide with TRAIL or FasL, enhanced death compared with either agent alone.

Conclusion:

The synergistic death observed with fenretinide and DR ligands suggests that this combination may be an attractive strategy for the treatment of ESFT.

Signaling through C/EBP homologous protein and death receptor 5 and calpain activation differentially regulate THP-1 cell maturation-dependent apoptosis induced by Shiga toxin type 1

Shiga toxins (Stxs) induce apoptosis via activation of the intrinsic and extrinsic pathways in many cell types. Toxin-mediated activation of the endoplasmic reticulum (ER) stress response was shown to be instrumental in initiating apoptosis in THP-1 myeloid leukemia cells. THP-1 cells responded to Shiga toxin type 1 (Stx1) in a cell maturation-dependent manner, undergoing rapid apoptosis in the undifferentiated state but reduced and delayed apoptosis in differentiated cells. The onset of apoptosis was associated with calpain activation and changes in expression of C/EBP homologous protein (CHOP), Bcl-2 family members, and death receptor 5 (DR5). Ligation of DR5 by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) activates the extrinsic pathway of apoptosis. We show here that expression of TRAIL and DR5 is increased by Stx1 treatment. Addition of exogenous TRAIL enhances, and anti-TRAIL antibodies inhibit, Stx1-induced apoptosis of THP-1 cells. Silencing of CHOP or DR5 expression selectively prevented caspase activation, loss of mitochondrial membrane potential, and Stx1-induced apoptosis of macrophage-like THP-1 cells. In contrast, the rapid kinetics of apoptosis induction in monocytic THP-1 cells correlated with rates of calpain cleavage. The results suggest that CHOP-DR5 signaling and calpain activation differentially contribute to cell maturation-dependent Stx1-induced apoptosis. Inhibition of these signaling pathways may protect cells from Stx cytotoxicity.

Histone deacetylase inhibitors and 15-deoxy-Delta12,14-prostaglandin J2 synergistically induce apoptosis

PURPOSE

The clinically relevant histone deacetylase inhibitors (HDI) valproic acid (VPA) and suberoylanilide hydroxamic acid exert variable antitumor activities but increase therapeutic efficacy when combined with other agents. The natural endogenous ligand of peroxisome proliferator-activated receptor gamma 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is a potent antineoplastic agent. Therefore, we investigated whether these HDIs in combination with 15d-PGJ(2) could show synergistic antitumor activity in colon cancer DLD-1 cells.

EXPERIMENTAL DESIGN

Cell viability was determined using a Cell Counting Kit-8 assay. Apoptosis and reactive oxygen species (ROS) generation were determined using flow cytometry analysis. Western blotting and real-time reverse transcription-PCR analysis were carried out to investigate the expression of apoptosis-related molecules. Mice bearing DLD-1 xenograft were divided into four groups (n = 5) and injected everyday (i.p.) with diluent, VPA (100 mg/kg), 15d-PGJ(2) (5 mg/kg), or a combination for 25 days.

RESULTS

HDI/15d-PGJ(2) cotreatments synergistically induced cell death through caspase-dependent apoptosis in DLD-1 cells. Moreover, HDIs/15d-PGJ(2) caused histone deacetylase inhibition, leading to subsequent ROS generation and endoplasmic reticulum stress to decrease the expression of antiapoptotic molecules Bcl-X(L) and XIAP and to increase that of proapoptotic molecules CAAT/enhancer binding protein homologous protein and death receptor 5. Additionally, VPA/15d-PGJ(2) cotreatment induced ROS-dependent apoptosis in other malignant tumor cells and was more effective than a VPA or 15d-PGJ(2) monotherapy in vivo.

CONCLUSIONS

Cotreatments with the clinically relevant HDIs and the endogenous peroxisome proliferator-activated receptor gamma ligand 15d-PGJ(2) are promising for the treatment of a broad spectrum of malignant tumors.

TRAILing death in cancer

The observation that certain types of cancer express death receptors on their cell surface has triggered heightened interest in exploring the potential of receptor ligation as a novel anti-cancer modality, and since the expression is somewhat restricted to cancer cells the therapeutic implications are very promising. One such death receptor ligand belonging to the tumor necrosis receptor (TNF) superfamily, TNF-related apoptosis-inducing ligand (TRAIL), has been in the limelight as a tumor selective molecule that transmits death signal via ligation to its receptors (TRAIL-R1 and TRAIL-R2 or death receptors 4 and 5; DR4 and DR5). Interestingly, TRAIL-induced apoptosis exhibits hallmarks of extrinsic as well as intrinsic death pathways, and, therefore, is subject to regulation both at the cell surface receptor level as well as more downstream at the post-mitochondrial level. Despite the remarkable selectivity of DR expression on cancer cell surface, development of resistance to TRAIL-induced apoptosis remains a major challenge. Therefore, unraveling the cellular and molecular mechanisms of TRAIL resistance as well as identifying strategies to overcome this problem for an effective therapeutic response remains the cornerstone of many research endeavors. This review aims at presenting an overview of the biology, function and translational relevance of TRAIL with a specific view to discussing the various regulatory mechanisms and the current trends in reverting TRAIL resistance of cancer cells with the obvious implication of an improved clinical outcome.

Zerumbone enhances TRAIL-induced apoptosis through the induction of death receptors in human colon cancer cells: Evidence for an essential role of reactive oxygen species

Identification of the active component and mechanisms of action of traditional medicines is highly desirable. We investigated whether zerumbone, a sesquiterpene from tropical ginger, can enhance the anticancer effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). We found that zerumbone potentiated TRAIL-induced apoptosis in human HCT116 colon cancer cells and that this correlated with the up-regulation of TRAIL death receptor (DR) 4 and DR5. Induction of DRs occurred at the transcriptional level, and this induction was not cell-type specific, as its expression was also up-regulated in prostate, kidney, breast, and pancreatic cancer cell lines. Deletion of DR5 or DR4 by small interfering RNA significantly reduced the apoptosis induced by TRAIL and zerumbone. In addition to up-regulating DRs, zerumbone also significantly down-regulated the expression of cFLIP but not that of other antiapoptotic proteins. The induction of both DRs by zerumbone was abolished by glutathione and N-acetylcysteine (NAC), and this correlated with decreased TRAIL-induced apoptosis, suggesting a critical role of reactive oxygen species. Inhibition of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase but not of Jun NH(2)-terminal kinase abolished the effect of zerumbone on DR induction. Zerumbone also induced the p53 tumor suppressor gene but was found to be optional for DR induction or for enhancement of TRAIL-induced apoptosis. Both bax and p21, however, were required for zerumbone to stimulate TRAIL-induced apoptosis. Overall, our results show that zerumbone can potentiate TRAIL-induced apoptosis through the reactive oxygen species-mediated activation of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase leading to DR4 and DR5 induction and resulting in enhancement of the anticancer effects of TRAIL.

Guardian of corpulence: a hypothesis on p53 signaling in the fat cell

Adipocytes provide an organism with fuel in times of caloric deficit, and are an important type of endocrine cell in the maintenance of metabolic homeostasis. In addition, as a lipid-sink, adipocytes serve an equally important role in the protection of organs from the damaging effects of ectopic lipid deposition. For the organism, it is of vital importance to maintain adipocyte viability, yet the fat depot is a demanding extracellular environment with high levels of interstitial free fatty acids and associated lipotoxic effects. These surroundings are less than beneficial for the overall health of any resident cell, adipocyte and preadipocyte alike. In this review, we discuss the process of adipogenesis and the potential involvement of the p53 tumor-suppressor protein in alleviating some of the cellular stress experienced by these cells. In particular, we discuss p53-mediated mechanisms that prevent damage caused by reactive oxygen species and the effects of lipotoxicity. We also suggest the potential for two p53 target genes, START domain-containing protein 4 (StARD4) and oxysterol-binding protein (OSBP), with the concomitant synthesis of the signaling molecule oxysterol, to participate in adipogenesis.