Silibinin sensitizes human glioma cells to TRAIL-mediated apoptosis via DR5 up-regulation and down-regulation of c-FLIP and survivin

The importance of integrated therapies on cancer: Silibinin, an old and new molecule

In the landscape of cancer treatments, the efficacy of coadjuvant molecules remains a focus of attention for clinical research with the aim of reducing toxicity and achieving better outcomes. Most of the pathogenetic processes causing tumour development, neoplastic progression, ageing, and increased toxicity involve inflammation. Inflammatory mechanisms can progress through a variety of molecular patterns. As is well known, the ageing process is determined by pathological pathways very similar and often parallel to those that cause cancer development. Among these complex mechanisms, inflammation is currently much studied and is often referred to in the geriatric field as 'inflammaging'. In this context, treatments active in the management of inflammatory mechanisms could play a role as adjuvants to standard therapies. Among these emerging molecules, Silibinin has demonstrated its anti-inflammatory properties in different neoplastic types, also in combination with chemotherapeutic agents. Moreover, this molecule could represent a breakthrough in the management of age-related processes. Thus, Silibinin could be a valuable adjuvant to reduce drug-related toxicity and increase therapeutic potential. For this reason, the main aim of this review is to collect and analyse data presented in the literature on the use of Silibinin, to better understand the mechanisms of the functioning of this molecule and its possible therapeutic role.

Amyloid Beta Oligomers Activate Death Receptors and Mitochondria-Mediated Apoptotic Pathways in Cerebral Vascular Smooth Muscle Cells; Protective Effects of Carbonic Anhydrase Inhibitors

Amyloid beta (Aβ) deposition within the brain vasculature is an early hallmark of Alzheimer's disease (AD), which triggers loss of brain vascular smooth muscle cells (BVSMCs) in cerebral arteries, via poorly understood mechanisms, altering cerebral blood flow, brain waste clearance, and promoting cognitive impairment. We have previously shown that, in brain endothelial cells (ECs), vasculotropic Aβ species induce apoptosis through death receptors (DRs) DR4 and DR5 and mitochondria-mediated mechanisms, while FDA-approved carbonic anhydrase inhibitors (CAIs) prevent mitochondria-mediated EC apoptosis in vitro and in vivo. In this study, we analyzed Aβ-induced extrinsic and intrinsic (DR- and mitochondria-mediated) apoptotic pathways in BVSMC, aiming to unveil new therapeutic targets to prevent BVSMC stress and death. We show that both apoptotic pathways are activated in BVSMCs by oligomeric Aβ42 and Aβ40-Q22 (AβQ22) and mitochondrial respiration is severely impaired. Importantly, the CAIs methazolamide (MTZ) and acetazolamide (ATZ) prevent the pro-apoptotic effects in BVSMCs, while reducing caspase 3 activation and Aβ deposition in the arterial walls of TgSwDI animals, a murine model of cerebral amyloid angiopathy (CAA). This study reveals new molecular targets and a promising therapeutic strategy against BVSMC dysfunction in AD, CAA, and ARIA (amyloid-related imaging abnormalities) complications of recently FDA-approved anti-Aβ antibodies.

Current approaches in enhancing TRAIL therapies in glioblastoma

Glioblastoma (GBM) is the most prevalent, aggressive, primary brain cancer in adults and continues to pose major medical challenges due in part to its high rate of recurrence. Extensive research is underway to discover new therapies that target GBM cells and prevent the inevitable recurrence in patients. The pro-apoptotic protein tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted attention as an ideal anticancer agent due to its ability to selectively kill cancer cells with minimal toxicity in normal cells. Although initial clinical evaluations of TRAIL therapies in several cancers were promising, later stages of clinical trial results indicated that TRAIL and TRAIL-based therapies failed to demonstrate robust efficacies due to poor pharmacokinetics, resulting in insufficient concentrations of TRAIL at the therapeutic site. However, recent studies have developed novel ways to prolong TRAIL bioavailability at the tumor site and efficiently deliver TRAIL and TRAIL-based therapies using cellular and nanoparticle vehicles as drug loading cargos. Additionally, novel techniques have been developed to address monotherapy resistance, including modulating biomarkers associated with TRAIL resistance in GBM cells. This review highlights the promising work to overcome the challenges of TRAIL-based therapies with the aim to facilitate improved TRAIL efficacy against GBM.

Neuroimmunomodulatory Properties of Flavonoids and Derivates: A Potential Action as Adjuvants for the Treatment of Glioblastoma

Glioblastomas (GBMs) are tumors that have a high ability to migrate, invade and proliferate in the healthy tissue, what greatly impairs their treatment. These characteristics are associated with the complex microenvironment, formed by the perivascular niche, which is also composed of several stromal cells including astrocytes, microglia, fibroblasts, pericytes and endothelial cells, supporting tumor progression. Further microglia and macrophages associated with GBMs infiltrate the tumor. These innate immune cells are meant to participate in tumor surveillance and eradication, but they become compromised by GBM cells and exploited in the process. In this review we discuss the context of the GBM microenvironment together with the actions of flavonoids, which have attracted scientific attention due to their pharmacological properties as possible anti-tumor agents. Flavonoids act on a variety of signaling pathways, counteracting the invasion process. Luteolin and rutin inhibit NFκB activation, reducing IL-6 production. Fisetin promotes tumor apoptosis, while inhibiting ADAM expression, reducing invasion. Naringenin reduces tumor invasion by down-regulating metalloproteinases expression. Apigenin and rutin induce apoptosis in C6 cells increasing TNFα, while decreasing IL-10 production, denoting a shift from the immunosuppressive Th2 to the Th1 profile. Overall, flavonoids should be further exploited for glioma therapy.

Role of Silymarin in Cancer Treatment: Facts, Hypotheses, and Questions

The flavonoid silymarin extracted from the seeds of Sylibum marianum is a mixture of 6 flavolignan isomers. The 3 more important isomers are silybin (or silibinin), silydianin, and silychristin. Silybin is functionally the most active of these compounds. This group of flavonoids has been extensively studied and they have been used as hepato-protective substances for the mushroom Amanita phalloides intoxication and mainly chronic liver diseases such as alcoholic cirrhosis and nonalcoholic fatty liver. Hepatitis C progression is not, or slightly, modified by silymarin. Recently, it has also been proposed for SARS COVID-19 infection therapy. The biochemical and molecular mechanisms of action of these substances in cancer are subjects of ongoing research. Paradoxically, many of its identified actions such as antioxidant, promoter of ribosomal synthesis, and mitochondrial membrane stabilization, may seem protumoral at first sight, however, silymarin compounds have clear anticancer effects. Some of them are: decreasing migration through multiple targeting, decreasing hypoxia inducible factor-1α expression, inducing apoptosis in some malignant cells, and inhibiting promitotic signaling among others. Interestingly, the antitumoral activity of silymarin compounds is limited to malignant cells while the nonmalignant cells seem not to be affected. Furthermore, there is a long history of silymarin use in human diseases without toxicity after prolonged administration. The ample distribution and easy accessibility to milk thistle-the source of silymarin compounds, its over the counter availability, the fact that it is a weed, some controversial issues regarding bioavailability, and being a nutraceutical rather than a drug, has somehow led medical professionals to view its anticancer effects with skepticism. This is a fundamental reason why it never achieved bedside status in cancer treatment. However, in spite of all the antitumoral effects, silymarin actually has dual effects and in some cases such as pancreatic cancer it can promote stemness. This review deals with recent investigations to elucidate the molecular actions of this flavonoid in cancer, and to consider the possibility of repurposing it. Particular attention is dedicated to silymarin's dual role in cancer and to some controversies of its real effectiveness.

The multifaceted NF-kB: are there still prospects of its inhibition for clinical intervention in pediatric central nervous system tumors?

Despite advances in the understanding of the molecular mechanisms underlying the basic biology and pathogenesis of pediatric central nervous system (CNS) malignancies, patients still have an extremely unfavorable prognosis. Over the years, a plethora of natural and synthetic compounds has emerged for the pharmacologic intervention of the NF-kB pathway, one of the most frequently dysregulated signaling cascades in human cancer with key roles in cell growth, survival, and therapy resistance. Here, we provide a review about the state-of-the-art concerning the dysregulation of this hub transcription factor in the most prevalent pediatric CNS tumors: glioma, medulloblastoma, and ependymoma. Moreover, we compile the available literature on the anti-proliferative effects of varied NF-kB inhibitors acting alone or in combination with other therapies in vitro, in vivo, and clinical trials. As the wealth of basic research data continues to accumulate, recognizing NF-kB as a therapeutic target may provide important insights to treat these diseases, hopefully contributing to increase cure rates and lower side effects related to therapy.

Bioactive Heterocyclic Compounds as Potential Therapeutics in the Treatment of Gliomas: A Review

Cancer is one of the most alarming diseases, with an estimation of 9.6 million deaths in 2018. Glioma occurs in glial cells surrounding nerve cells. The majority of the patients with gliomas have a terminal prognosis, and the ailment has significant sway on patients and their families, be it physical, psychological, or economic wellbeing. As Glioma exhibits, both intra and inter tumour heterogeneity with multidrug resistance and current therapies are ineffective. So the development of safer anti gliomas agents is the need of hour. Bioactive heterocyclic compounds, eithernatural or synthetic,are of potential interest since they have been active against different targets with a wide range of biological activities, including anticancer activities. In addition, they can cross the biological barriers and thus interfere with various signalling pathways to induce cancer cell death. All these advantages make bioactive natural compounds prospective candidates in the management of glioma. In this review, we assessed various bioactive heterocyclic compounds, such as jaceosidin, hispudlin, luteolin, silibinin, cannabidiol, tetrahydrocannabinol, didemnin B, thymoquinone, paclitaxel, doxorubicin, and cucurbitacins for their potential anti-glioma activity. Also, different kinds of chemical reactions to obtain various heterocyclic derivatives, e.g. indole, indazole, benzimidazole, benzoquinone, quinoline, quinazoline, pyrimidine, and triazine, are listed.

Harnessing TRAIL-Induced Apoptosis Pathway for Cancer Immunotherapy and Associated Challenges

The immune cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted rapidly evolving attention as a cancer treatment modality because of its competence to selectively eliminate tumor cells without instigating toxicity in vivo. TRAIL has revealed encouraging promise in preclinical reports in animal models as a cancer treatment option; however, the foremost constraint of the TRAIL therapy is the advancement of TRAIL resistance through a myriad of mechanisms in tumor cells. Investigations have documented that improvement of the expression of anti-apoptotic proteins and survival or proliferation involved signaling pathways concurrently suppressing the expression of pro-apoptotic proteins along with down-regulation of expression of TRAILR1 and TRAILR2, also known as death receptor 4 and 5 (DR4/5) are reliable for tumor cells resistance to TRAIL. Therefore, it seems that the development of a therapeutic approach for overcoming TRAIL resistance is of paramount importance. Studies currently have shown that combined treatment with anti-tumor agents, ranging from synthetic agents to natural products, and TRAIL could result in induction of apoptosis in TRAIL-resistant cells. Also, human mesenchymal stem/stromal cells (MSCs) engineered to generate and deliver TRAIL can provide both targeted and continued delivery of this apoptosis-inducing cytokine. Similarly, nanoparticle (NPs)-based TRAIL delivery offers novel platforms to defeat barricades to TRAIL therapeutic delivery. In the current review, we will focus on underlying mechanisms contributed to inducing resistance to TRAIL in tumor cells, and also discuss recent findings concerning the therapeutic efficacy of combined treatment of TRAIL with other antitumor compounds, and also TRAIL-delivery using human MSCs and NPs to overcome tumor cells resistance to TRAIL.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

Combination treatment with VPA and MSCs‑TRAIL could increase anti‑tumor effects against intracranial glioma

Human bone marrow-derived mesenchymal stem cells secreting tumor necrosis factor-related apoptosis-inducing ligand (MSCs-TRAIL) have demonstrated effective anti-tumor activity against various tumors including lung, pancreatic and prostate tumors, although several tumor types are not responsive. In such case, other reagents may decrease tumor growth via TRAIL-mediated cell death. The present study aimed to examine the effectiveness of valproic acid (VPA) in enhancing the efficacy of TRAIL, which was delivered using MSCs. Moreover, the present study examined the induced tumor tropism of MSCs via cell viability and migration assays. Combination treatment with VPA and MSCs-TRAIL enhanced the glioma therapeutic effect by increasing death receptor 5 and caspase activation. Migration assays identified increased MSC migration in VPA and MSCs-TRAIL-treated glioma cells and in the tumor site in glioma-bearing mice compared with VPA or MSC-TRAIL treatment alone. In vivo experiments demonstrated that MSC-based TRAIL gene delivery to VPA-treated tumors had greater therapeutic efficacy compared with treatment with each agent alone. These findings suggested that VPA treatment increased the therapeutic efficacy of MSC-TRAIL via TRAIL-induced apoptosis and enhanced tropism of MSCs, which may offer a useful strategy for tumor gene therapy.

Path of Silibinin from diet to medicine: A dietary polyphenolic flavonoid having potential anti-cancer therapeutic significance

In the last few decades, targeting cancer by the use of dietary phytochemicals has gained enormous attention. The plausible reason and believe or mind set behind this fact is attributed to either lesser or no side effects of natural compounds as compared to the modern chemotherapeutics, or due to their conventional use as dietary components by mankind for thousands of years. Silibinin is a naturally derived polyphenol (a flavonolignans), possess following biochemical features; molecular formula C₂₅H₂₂O₁₀, Molar mass: 482.44 g/mol, Boiling point 793 °C, with strikingly high antioxidant and anti-tumorigenic properties. The anti-cancer properties of Silibinin are determined by a variety of cellular pathways which include induction of apoptosis, cell cycle arrest, inhibition of angiogenesis and metastasis. In addition, Silibinin controls modulation of the expression of aberrant miRNAs, inflammatory response, and synergism with existing anti-cancer drugs. Therefore, modulation of a vast array of cellular responses and homeostatic aspects makes Silibinin an attractive chemotherapeutic agent. However, like other polyphenols, the major hurdle to declare Silibinin a translational chemotherapeutic agent, is its lesser bioavailability. After summarizing the chemistry and metabolic aspects of Silibinin, this extensive review focuses on functional aspects governed by Silibinin in chemoprevention with an ultimate goal of summarizing the evidence supporting the chemopreventive potential of Silibinin and clinical trials that are currently ongoing, at a single platform.

RALB GTPase: a critical regulator of DR5 expression and TRAIL sensitivity in KRAS mutant colorectal cancer

RAS mutant (MT) metastatic colorectal cancer (mCRC) is resistant to MEK1/2 inhibition and remains a difficult-to-treat group. Therefore, there is an unmet need for novel treatment options for RASMT mCRC. RALA and RALB GTPases function downstream of RAS and have been found to be key regulators of several cell functions implicated in KRAS-driven tumorigenesis. However, their role as regulators of the apoptotic machinery remains to be elucidated. Here, we found that inhibition of RALB expression, but not RALA, resulted in Caspase-8-dependent cell death in KRASMT CRC cells, which was not further increased following MEK1/2 inhibition. Proteomic analysis and mechanistic studies revealed that RALB depletion induced a marked upregulation of the pro-apoptotic cell surface TRAIL Death Receptor 5 (DR5) (also known as TRAIL-R2), primarily through modulating DR5 protein lysosomal degradation. Moreover, DR5 knockdown or knockout attenuated siRALB-induced apoptosis, confirming the role of the extrinsic apoptotic pathway as a regulator of siRALB-induced cell death. Importantly, TRAIL treatment resulted in the association of RALB with the death-inducing signalling complex (DISC) and targeting RALB using pharmacologic inhibition or RNAi approaches triggered a potent increase in TRAIL-induced cell death in KRASMT CRC cells. Significantly, high RALB mRNA levels were found in the poor prognostic Colorectal Cancer Intrinsic Subtypes (CRIS)-B CRC subgroup. Collectively, this study provides to our knowledge the first evidence for a role for RALB in apoptotic priming and suggests that RALB inhibition may be a promising strategy to improve response to TRAIL treatment in poor prognostic RASMT CRIS-B CRC.

An Update on the Role of Dietary Phytochemicals in Human Skin Cancer: New Insights into Molecular Mechanisms

Human skin is continuously subjected to environmental stresses, as well as extrinsic and intrinsic noxious agents. Although skin adopts various molecular mechanisms to maintain homeostasis, excessive and repeated stresses can overwhelm these systems, leading to serious cutaneous damage, including both melanoma and non-melanoma skin cancers. Phytochemicals present in the diet possess the desirable effects of protecting the skin from damaging free radicals as well as other benefits. Dietary phytochemicals appear to be effective in preventing skin cancer and are inexpensive, widely available, and well tolerated. Multiple in vitro and in vivo studies have demonstrated the significant anti-inflammatory, antioxidant, and anti-angiogenic characteristics of dietary phytochemicals against skin malignancy. Moreover, dietary phytochemicals affect multiple important cellular processes including cell cycle, angiogenesis, and metastasis to control skin cancer progression. Herein, we discuss the advantages of key dietary phytochemicals in whole fruits and vegetables, their bioavailability, and underlying molecular mechanisms for preventing skin cancer. Current challenges and future prospects for research are also reviewed. To date, most of the chemoprevention investigations have been conducted preclinically, and additional clinical trials are required to conform and validate the preclinical results in humans.

Myricanol 5-fluorobenzyloxy ether regulation of survivin pathway inhibits human lung adenocarcinoma A549 cells growth in vitro

Background

This study aimed to explore the growth inhibitory effect of myricanol 5-fluorobenzyloxy ether (5FEM) and its underlying mechanisms in human lung adenocarcinoma A549 cells in vitro.

Methods

5FEM was obtained by the chemical modification of myricanol with fluorobenzyloxy ether at the OH(5) position. The cytotoxicity, cell apoptosis, cell cycle, mitochondrial membrane potential (ΔΨm), scratch test, colony formation, and the expression levels of the key survivin pathway-related genes in A549 were evaluated.

Results

5FEM could significantly inhibit A549 cell growth; induce cell apoptosis; increase G0/G1 population; reduce ΔΨm; inhibit cell migration and colony formation; upregulate caspase-9, P21, and Bax expression levels; and downregulate PARP, survivin, and Bcl-2 expression level.

Conclusion

These results enhanced our understanding of 5FEM and aid the discovery of novel myricanol derivatives as potential antitumor agents.

Autophagy activated by silibinin contributes to glioma cell death via induction of oxidative stress-mediated BNIP3-dependent nuclear translocation of AIF

Induction of lethal autophagy has become a strategy to eliminate glioma cells, but it remains elusive whether autophagy contributes to cell death via causing mitochondria damage and nuclear translocation of apoptosis inducing factor (AIF). In this study, we find that silibinin induces AIF translocation from mitochondria to nuclei in glioma cells in vitro and in vivo, which is accompanied with autophagy activation. In vitro studies reveal that blocking autophagy with 3MA, bafilomycin A1 or by knocking down ATG5 with SiRNA inhibits silibinin-induced mitochondrial accumulation of superoxide, AIF translocation from mitochondria to nuclei and glioma cell death. Mechanistically, silibinin activates autophagy through depleting ATP by suppressing glycolysis. Then, autophagy improves intracellular H2O2 via promoting p53-mediated depletion of GSH and cysteine and downregulation of xCT. The increased H2O2 promotes silibinin-induced BNIP3 upregulation and translocation to mitochondria. Knockdown of BNIP3 with SiRNA inhibits silibinin-induced mitochondrial depolarization, accumulation of mitochondrial superoxide, and AIF translocation from mitochondria to nuclei, as well as prevents glioma cell death. Furthermore, we find that the improved H2O2 reinforces silibinin-induced glycolysis dysfunction. Collectively, autophagy contributes to silibinin-induced glioma cell death via promotion of oxidative stress-mediated BNIP3-dependent nuclear translocation of AIF.

Silymarin and Cancer: A Dual Strategy in Both in Chemoprevention and Chemosensitivity

Silymarin extracted from milk thistle consisting of flavonolignan silybin has shown chemopreventive and chemosensitizing activity against various cancers. The present review summarizes the current knowledge on the potential targets of silymarin against various cancers. Silymarin may play on the system of xenobiotics, metabolizing enzymes (phase I and phase II) to protect normal cells against various toxic molecules or to protect against deleterious effects of chemotherapeutic agents on normal cells. Furthermore, silymarin and its main bioactive compounds inhibit organic anion transporters (OAT) and ATP-binding cassettes (ABC) transporters, thus contributing to counteracting potential chemoresistance. Silymarin and its derivatives play a double role, namely, limiting the progression of cancer cells through different phases of the cycle-thus forcing them to evolve towards a process of cell death-and accumulating cancer cells in a phase of the cell cycle-thus making it possible to target a greater number of tumor cells with a specific anticancer agent. Silymarin exerts a chemopreventive effect by inducing intrinsic and extrinsic pathways and reactivating cell death pathways by modulation of the ratio of proapoptotic/antiapoptotic proteins and synergizing with agonists of death domains receptors. In summary, we highlight how silymarin may act as a chemopreventive agent and a chemosensitizer through multiple pathways.

Vitamin E δ-tocotrienol sensitizes human pancreatic cancer cells to TRAIL-induced apoptosis through proteasome-mediated down-regulation of c-FLIPs

BACKGROUND

Vitamin E δ-tocotrienol (VEDT), a vitamin E compound isolated from sources such as palm fruit and annatto beans, has been reported to have cancer chemopreventive and therapeutic effects.

METHODS

We report a novel function of VEDT in augmenting tumor necrosis factor-related apoptosis-inducing ligand- (TRAIL-) induced apoptosis in pancreatic cancer cells. The effects of VEDT were shown by its ability to trigger caspase-8-dependent apoptosis in pancreatic cancer cells.

RESULTS

When combined with TRAIL, VEDT significantly augmented TRAIL-induced apoptosis of pancreatic cancer cells. VEDT decreased cellular FLICE inhibitory protein (c-FLIP) levels without consistently modulating the expression of decoy death receptors 1, 2, 3 or death receptors 4 and 5. Enforced expression of c-FLIP substantially attenuated VEDT/TRAIL-induced apoptosis. Thus, c-FLIP reduction plays an important part in mediating VEDT/TRAIL-induced apoptosis. Moreover, VEDT increased c-FLIP ubiquitination and degradation but did not affect its transcription, suggesting that VEDT decreases c-FLIP levels through promoting its degradation. Of note, degradation of c-FLIP and enhanced TRAIL-induced apoptosis in pancreatic cancer cells were observed only with the anticancer bioactive vitamin E compounds δ-, γ-, and β-tocotrienol but not with the anticancer inactive vitamin E compounds α-tocotrienol and α-, β-, γ-, and δ-tocopherol.

CONCLUSIONS

c-FLIP degradation is a key event for death receptor-induced apoptosis by anticancer bioactive vitamin E compounds in pancreatic cancer cells. Moreover, VEDT augmented TRAIL inhibition of pancreatic tumor growth and induction of apoptosis in vivo. Combination therapy with TRAIL agonists and bioactive vitamin E compounds may offer a novel strategy for pancreatic cancer intervention.

Artonin E sensitizes TRAIL-induced apoptosis by DR5 upregulation and cFLIP downregulation in TRAIL-refractory colorectal cancer LoVo cells

Background

The TRAIL treatment is an ideal strategy for colorectal cancer (CRC) therapy because of minimal collateral damage to normal cells. Unfortunately, some CRC is TRAIL-refractory cancer, such as LoVo cells. In an effort to overcome TRAIL-refractory cancer, we investigated the effect of artonin E in regulating death receptor 5 (DR5) and cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein (cFLIP), two major mediators regulate TRAIL-induced apoptosis, in LoVo cells as a model of TRAIL refractory CRC.

Methods

TRAIL-refractory cancer (LoVo cells) was treated with artonin E and TRAIL. Cell viability was determined by MTT assay. Apoptotic chromatin condensation was observed by fluorescent Hoechst33342 staining. The mRNA and protein expression of DR5 and FLIP was determined by quantitative PCR and Western blotting analysis, respectively.

Results

The combination treatment of artonin E and TRAIL enhanced cytotoxicity and apoptotic chromatin condensation in LoVo cells significantly, while treatment of artonin E or TRAIL alone was not. Artonin E enhanced both mRNA and protein expression of DR5. Interestingly, this is the first report showing that artonin E decreased protein expression of cFLIP. All together we showed that artonin E enhanced TRAIL-induced apoptosis in LoVo cells through DR5 upregulation and cFLIP downregulation.

Conclusions

Artonin E was able to increase DR5 expression and decrease cFLIP expression in LoVo cells. These results showed that LoVo cells sensitized TRAIL-induced apoptosis in combined treatment with artonin E and TRAIL. Therefore, the combination treatment of artonin E and TRAIL is one of the potential strategies used for TRAIL-refractory CRC therapy in the future.

Targeting KPNB1 overcomes TRAIL resistance by regulating DR5, Mcl-1 and FLIP in glioblastoma cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine with potential anticancer effect, but innate and adaptive TRAIL resistance in majority of cancers limit its clinical application. Karyopherin β1 (KPNB1) inhibition in cancer cells has been reported to abrogate the nuclear import of TRAIL receptor DR5 and facilitate its localization on the cell surface ready for TRAIL stimulation. However, our study reveals a more complicated mechanism. Genetic or pharmacological inhibition of KPNB1 potentiated TRAIL-induced apoptosis selectively in glioblastoma cells mainly by unfolded protein response (UPR). First, it augmented ATF4-mediated DR5 expression and promoted the assembly of death-inducing signaling complex (DISC). Second, it freed Bax and Bak from Mcl-1. Third, it downregulated FLIP_L and FLIP_S, inhibitors of caspase-8 cleavage, partly through upregulating ATF4–induced 4E-BP1 expression and disrupting the cap-dependent translation initiation. Meanwhile, KPNB1 inhibition-induced undesirable autophagy and accelerated cleaved caspase-8 clearance. Inhibition of autophagic flux maintained cleaved caspase-8 and aggravated apoptosis induced by KPNB1 inhibitor plus TRAIL, which were abolished by caspase-8 inhibitor. These results unveil new molecular mechanism for optimizing TRAIL-directed therapeutic efficacy against cancer.

C-27-carboxylated oleanane triterpenoids up-regulate TRAIL DISC assembly via p38 MAPK and CHOP-mediated DR5 expression in human glioblastoma cells

Despite recent tremendous progress, targeting of TNF-related apoptosis-inducing ligand (TRAIL) as a cancer therapy has limited success in many clinical trials, in part due to inactivation of death inducing signaling complex (DISC)-mediated caspase-8 signaling cascade in highly malignant tumors such as glioblastoma. In this study, screening of constituents derived from Astilbe rivularis for TRAIL-sensitizing activity identified C-27-carboxylated oleanolic acid derivatives (C27OAs) including 3β-hydroxyolean-12-en-27-oic acid (C27OA-1), 3β,6β,7α-trihydroxyolean-12-en-27-oic acid (C27OA-2), and 3β-trans-p-coumaroyloxy-olean-12-en-27-oic acid (C27OA-3) as novel TRAIL sensitizers. Interestingly, these C27OAs did not affect apoptotic cell death induced by either ligation of other death receptor (DR) types, such as TNF and Fas or DNA damaging agents, which suggests that C27OAs effectively and selectively sensitize TRAIL-mediated caspase-8 activation. Mechanistically, C27OAs upregulate the expression of cell surface DR5 and DISC formation without affecting downstream intracellular apoptosis-related proteins. The upregulation of DR5 expression by C27OAs strictly depends on transactivation of C/EBP homology protein, which is regulated through the p38 MAPK pathway, rather than p53 and intracellular reactive oxygen species status. Taken together, our results identify the novel C27OAs as TRAIL sensitizers targeting the upstream DISC assembly of DR5, and provide a rationale for further development of C27OAs for facilitating TRAIL-based chemotherapy in glioblastoma patients.

Phytochemicals in Skin Cancer Prevention and Treatment: An Updated Review

Skin is the largest human organ, our protection against various environmental assaults and noxious agents. Accumulation of these stress events may lead to the formation of skin cancers, including both melanoma and non-melanoma skin cancers. Although modern targeted therapies have ameliorated the management of cutaneous malignancies, a safer, more affordable, and more effective strategy for chemoprevention and treatment is clearly needed for the improvement of skin cancer care. Phytochemicals are biologically active compounds derived from plants and herbal products. These agents appear to be beneficial in the battle against cancer as they exert anti-carcinogenic effects and are widely available, highly tolerated, and cost-effective. Evidence has indicated that the anti-carcinogenic properties of phytochemicals are due to their anti-oxidative, anti-inflammatory, anti-proliferative, and anti-angiogenic effects. In this review, we discuss the preventive potential, therapeutic effects, bioavailability, and structure–activity relationship of these selected phytochemicals for the management of skin cancers. The knowledge compiled here will provide clues for future investigations on novel oncostatic phytochemicals and additional anti-skin cancer mechanisms.

A hypoxia- and telomerase-responsive oncolytic adenovirus expressing secretable trimeric TRAIL triggers tumour-specific apoptosis and promotes viral dispersion in TRAIL-resistant glioblastoma

Glioblastoma is a highly aggressive and malignant type of cancer that is apoptosis resistant and difficult to cure by conventional cancer therapies. In this regard, an oncolytic adenovirus that selectively targets the tumour tissue and induces tumour cell lysis is a promising treatment option. We designed and constructed a hypoxia-responsive and cancer-specific modified human telomerase reverse transcriptase (H5CmTERT) promoter to drive replication of an oncolytic adenovirus (H5CmTERT-Ad). To enhance the anti-tumour efficacy of H5CmTERT-Ad against malignant glioblastoma, we also generated an H5CmTERT-Ad expressing secretable trimeric tumour necrosis factor-related apoptosis-inducing ligand (H5CmTERT-Ad/TRAIL). H5CmTERT promoter-regulated oncolytic adenoviruses showed cancer-specific and superior cell-killing effect in contrast to a cognate control oncolytic adenovirus replicating under the control of the endogenous adenovirus promoter. The cancer cell-killing effects of H5CmTERT-Ad and H5CmTERT-Ad/TRAIL were markedly higher during hypoxia than normoxia owing to hypoxia responsiveness of the promoter. H5CmTERT-Ad/TRAIL showed more potent anti-tumour efficacy than H5CmTERT-Ad did in a xenograft model of TRAIL-resistant subcutaneous and orthotopic glioblastoma through superior induction of apoptosis and more extensive virus distribution in the tumour tissue. Altogether, our findings show that H5CmTERT-Ad/TRAIL can promote dispersion of an oncolytic adenovirus through robust induction of apoptosis in a highly TRAIL-resistant glioblastoma.

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.

Silibinin Inhibits Platelet-Derived Growth Factor-Driven Cell Proliferation via Downregulation of N-Glycosylation in Human Tenon's Fibroblasts in a Proteasome-Dependent Manner

The objective of this study was to evaluate the effects of silibinin on cell proliferation in platelet-derived growth factor (PDGF)-treated human Tenon's fibroblasts (HTFs). The effect of silibinin on cell proliferation in PDGF-treated HTFs was determined by examining the expression of proliferating cell nuclear antigen (PCNA) and performing WST-1 assays. Cell cycle progression was evaluated using flow cytometry. The related cyclins and cyclin-dependent kinases (CDKs) were also analyzed using western blot. A modified rat trabeculectomy model was established to evaluate the effect of silibinin on cell proliferation in vivo. Western blot analysis was carried out to determine the effect of silibinin on the expression of PDGF receptor and on the downstream signaling pathways regulated by PDGF receptor. PDGF elevated the expression of PCNA in HTFs, and this elevation was inhibited by silibinin. The inhibitory effect of silibinin on cell proliferation was also confirmed via WST-1 assay. PDGF-stimulated cell cycle in HTFs was delayed by silibinin, and the related cyclin D1 and CDK4 were also suppressed by silibinin. In the rat model of trabeculectomy, silibinin reduced the expression of PCNA at the site of blebs in vivo. The effects of silibinin on PDGF-stimulated HTFs were mediated via the downregulation of PDGF receptor-regulated signaling pathways, such as ERKs and STATs, which may be partially caused by the downregulation of N-glycosylation of PDGF receptor beta (PDGFRβ). The effect of silibinin on modulation of N-glycosylation of PDGFRβ was mediated in a proteasome-dependent manner. Silibinin inhibited cell proliferation and delayed cell cycle progression in PDGF-treated HTFs in vitro. PDGF also modulated the process of N-glycosylation of the PDGFRβ in a proteasome-dependent manner. Our findings suggest that silibinin has potential therapeutic applications in glaucoma filtering surgery.

Ellagic acid inhibits human glioblastoma growth in vitro and in vivo

Ellagic acid (EA) is present in various fruits and plants and has recently been found to possess anticarcinogenic effects. The objective of this study was to investigate the anti‑glioblastoma effect of EA and its mechanisms in vitro and in vivo. We first studied the anticancer activity of EA in U87 and U118 human glioblastoma cell lines. The cell viability and cell proliferation were examined by Cell Counting Kit-8 (CCK-8) assay and 5-ethynyl-2'-deoxyuridine staining respectively. The cell cycle was detected with propidium iodide staining method by flow cytometry and the DNA damage of the cells caused by EA exposure was evaluated by detection of γ-H2AX foci. Then we examined the effect of EA on tumor growth in glioblastoma xenografted mice, and expression of Akt and Notch signaling and their target gene products were detected by immunohistochemistry and western blot analysis. As a result, we found that the cell viability and proliferation of glioblastoma cells treated with EA were significantly suppressed compared with the control; EA significantly increased the proportion of cells in the S phase accompanied by a decrease in the population in the G1 and G2/M phase in both cell lines. Meanwhile, the level of DNA damage in the EA-treated group was significantly higher than that of the control. Treatment of glioblastoma in xenografted mice by EA led to a significant suppression in tumor growth. EA upregulated the expression of E-cadherin and inhibited the expression of Snail, matrix metalloproteinase (MMP)-2 and MMP-9. EA also inhibited the expression of Bcl-2, cyclin D1, cyclin-dependent kinase (CDK)2 and CDK6 in U87 xenograft tissues. In addition, significant suppression of Akt and Notch was found in the xenografts of the tumor-bearing mice treated with EA. These data indicate that EA can suppress glioblastoma proliferation and invasion by inhibiting the Akt and Notch signaling pathways, which suggests that EA may be beneficial for the treatment of glioblastoma.

Epigallocatechin-3-gallate Sensitizes Human 786-O Renal Cell Carcinoma Cells to TRAIL-Induced Apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent. Epigallocatechin-3-gallate (EGCG) is a polyphenolic constituent of green tea. In this study, potentiating effect of EGCG on TRAIL-induced apoptosis human renal carcinoma cell line 786-O which is relatively resistant to TRAIL was examined, and the possible mechanism was investigated. Here, we show that co-treatment with EGCG and TRAIL induced significantly more profound apoptosis in 786-O cells. Treatment of 786-O cells with EGCG and TRAIL downregulated c-FLIP, Mcl-1, and Bcl-2 proteins in a caspase-dependent pathway. Moreover, we found that pretreatment with NAC markedly inhibited the expression levels of c-FLIP, Mcl-1, and Bcl-2 downregulated by the combinatory treatment, suggesting that the regulating effect of EGCG on these above apoptosis-relevant molecules was partially mediated by generation of ROS. Taken together, the present study demonstrates that EGCG sensitizes human 786-O renal cell carcinoma cells to TRAIL-induced apoptosis by downregulation of c-FLIP, Mcl-1, and Bcl-2.

Ibulocydine sensitizes human hepatocellular carcinoma cells to TRAIL-induced apoptosis via calpain-mediated Bax cleavage

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) induces apoptosis selectively in cancer cells without affecting the majority of normal human cells. However, hepatocellular carcinoma (HCC) cells often display resistance to TRAIL-induced apoptosis. Ibulocydine (IB) is an isobutyrate ester pro-drug of a novel synthetic Cdk inhibitor that targets Cdk7 and Cdk9. In this study, we show that treatment with subtoxic doses of IB in combination with TRAIL displays potent cytotoxicity in TRAIL-resistant human HCC cells. Combination of IB and TRAIL was found to synergistically induce apoptosis through activation of caspases, which was blocked by a pan-caspase inhibitor (zVAD). Although the expression of Mcl-1 and survivin were reduced by IB plus TRAIL, overexpression of Mcl-1 and survivin did not block the cell death induced by co-treatment. Moreover, overexpression of Bcl-xL did not significantly interfere with the cell death induced by co-treatment of IB and TRAIL. Interestingly, the combination treatment induced cleavage of Bax, which was translocated to mitochondria upon induction of apoptosis. Furthermore, down-regulation of Bax by small interfering RNA effectively reduced the cell death and loss of mitochondrial membrane potential (MMP) caused by co-treatment with IB and TRAIL. Finally, pre-treatment of HCC cells with a calpain inhibitor effectively blocked IB plus TRAIL-induced cleavage of Bax and apoptosis. Collectively, our results demonstrate that IB increases the sensitivity of human HCC cells to TRAIL via mitochondria signaling pathway mediated by calpain-induced cleavage of Bax, suggesting that combined treatment with IB and TRAIL may offer an effective therapeutic strategy for human HCC.

Ellagic acid inhibits proliferation and induces apoptosis in human glioblastoma cells

PURPOSE

To investigate the anticancer activity of ellagic acid (EA) in U251 human glioblastoma cells and its possible molecular mechanism.

METHODS

The cells were treated with EA at various concentrations for different time periods. Cell viability and cell proliferation were detected by cell counting kit-8(CCK-8) assay and live/dead assay respectively. Cell apoptosis were measured with Annexin V-FITC/PI double staining method by flow cytometry and Mitochondrial membrane potential assay separately. Cell cycle was measured with PI staining method by flow cytometry. The expressions of Bcl-2, Survivin, XIAP, Caspase-3, Bax, JNK, p-JNK, ERK1/2, p-ERK1/2, p38, p-p38, DR4, DR5, CHOP and GRP78-related proteins were detected by western blot after EA treatment.

RESULTS

Cell viability and proliferation of glioblastoma cells treated with EA were significantly lower than the control group. EA caused robust apoptosis of the glioblastoma cells compared to the control group. EA significantly decreased the proportion at G0/G1 phases of cell cycling accompanied by increased populations at S phase in U251 cell lines. And the expressions of anti-apoptotic proteins were dramatically down-regulated.

CONCLUSION

Ellagic acid potentially up-regulated DR4, DR5 and MAP kinases (JNK, ERK1/2 and p38). EA also caused significant increase in the expressions of CHOP and GRP78. Our findings suggest that EA would be beneficial for the treatment of glioblastoma.

Evolving lessons on nanomaterial-coated viral vectors for local and systemic gene therapy

Viral vectors are promising gene carriers for cancer therapy. However, virus-mediated gene therapies have demonstrated insufficient therapeutic efficacy in clinical trials due to rapid dissemination to nontarget tissues and to the immunogenicity of viral vectors, resulting in poor retention at the disease locus and induction of adverse inflammatory responses in patients. Further, the limited tropism of viral vectors prevents efficient gene delivery to target tissues. In this regard, modification of the viral surface with nanomaterials is a promising strategy to augment vector accumulation at the target tissue, circumvent the host immune response, and avoid nonspecific interactions with the reticuloendothelial system or serum complement. In the present review, we discuss various chemical modification strategies to enhance the therapeutic efficacy of viral vectors delivered either locally or systemically. We conclude by highlighting the salient features of various nanomaterial-coated viral vectors and their prospects and directions for future research.

Adenovirus expressing dual c-Met-specific shRNA exhibits potent antitumor effect through autophagic cell death accompanied by senescence-like phenotypes in glioblastoma cells

c-Met, a cognate receptor tyrosine kinase of hepatocyte growth factor, is overexpressed and/or mutated in number of tumors. Therefore, abrogation of c-Met signaling may serve as potential therapeutic targets. In this study, we generated Ads expressing single shRNA specific to c-Met (shMet) (dl/shMet4 and dl/shMet5) or dual shRNAs specific to c-Met (dl/shMet4+5); and examined the therapeutic potential of these newly engineered Ads in targeting c-Met, and delineated their mechanism of action in vitro and in vivo. Ads expressing shMet induced knock-down in c-Met, and phenotypically resulted in autophagy-like features including appearance of membranousvacuoles, formation of acidic vesicular organelles, and cleavage and recruitment of microtubule-associated protein1 light chain 3 to autophagosomes. Ads expressing shMet also suppressed Akt phosphorylation and increased number of senescence-related gene products including SM22, TGase II, and PAI-1. These changes resulted in inhibition of cell proliferation and G₂/M arrest of U343 cells. In vivo, intratumoral injection with dl/shMet4+5 resulted in a significant reduction of tumor growth with corresponding increasing overall survival. Histopathological analysis of these treated tumors revealed that Atg5 was highly up-regulated, indicating the therapeutic induction of autophagy. In sum, these results reveal that autophagic cell death induced by shMet-expressing Ads provide a novel strategy for targeting c-Met-expressing tumors through non-apoptotic mechanism of cell death.

Marine Drugs Regulating Apoptosis Induced by Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)

Marine biomass diversity is a tremendous source of potential anticancer compounds. Several natural marine products have been described to restore tumor cell sensitivity to TNF-related apoptosis inducing ligand (TRAIL)-induced cell death. TRAIL is involved during tumor immune surveillance. Its selectivity for cancer cells has attracted much attention in oncology. This review aims at discussing the main mechanisms by which TRAIL signaling is regulated and presenting how marine bioactive compounds have been found, so far, to overcome TRAIL resistance in tumor cells.

Silibinin-induced glioma cell apoptosis by PI3K-mediated but Akt-independent downregulation of FoxM1 expression

The oncogenic transcription factor Forkhead box M1 (FoxM1) is overexpressed in many human tumors, including glioma. As a critical regulator of the cell cycle and apoptosis-related genes, FoxM1 is a potential therapeutic target against human malignant glioma. Silibinin, a flavonoid isolated from Silybum marianum, dose-dependently reduced glioma cell proliferation, promoted apoptosis, and downregulated FoxM1 expression. Knockdown of FoxM1 by small hairpin RNA (shRNA) transfection also promoted glioma cell apoptosis and augmented the antiproliferative and pro-apoptotic properties of silibinin. Moreover, silibinin increased caspase-3 activation, upregulated pro-apoptotic Bax, and suppressed anti-apoptotic Bcl-2 expression, effects enhanced by FoxM1 knockdown. Silibinin treatment suppressed U87 cell PI3K phospho-activation, and simultaneous silibinin exposure, FoxM1 knockdown, and PI3K inhibition additively increased U87 cell apoptosis. Furthermore, PI3K inhibition reduced FoxM1 expression. Akt activity was also suppressed by FoxM1 downregulation but Akt inhibition did not alter FoxM1 expression. Thus, silibinin likely inhibited glioma cell proliferation and induced apoptosis through inactivation of PI3K and FoxM1, leading to activation of the mitochondrial apoptotic pathway. FoxM1 may be a novel target for chemotherapy against human glioma.

A novel adenoviral vector carrying an all-in-one Tet-On system with an autoregulatory loop for tight, inducible transgene expression

Background

One of the most commonly used vectors for gene therapy is the adenoviral vector; its ability to tightly regulate transgene expression is critical for optimizing therapeutic outcomes. The tetracycline-regulated system (especially the Tet-On system) for gene expression is one of the most valuable tools for controlling gene expression. The major problem of an adenoviral vector carrying a Tet-On system is suboptimal regulation of transgene expression.

Results

We constructed a single adenoviral vector carrying in its E1 region a novel “all-in-one” Tet-On system with an autoregulatory loop. This system had improved Dox-inducible gene expression in terms of low basal expression, high induced expression and high responsiveness to Dox. To our knowledge, this is the first reported adenovirus-based, all-in-one Tet-On system with an autoregulatory loop inserted into a single region of adenoviral genome. This system was further tested by inducible expression of soluble tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL). The adenovirus that expressed soluble TRAIL under the control of this novel Tet-On system showed tumor-derived cells inhibitory activity in SW480 cells only under induced conditions.

Conclusions

Our novel, single adenoviral vector carrying in its E1 region an all-in-one Tet-On system with an autoregulatory loop displayed tight regulation of transgene expression in vitro. This system has great potential for a variety of applications, including gene therapy and the study of gene function.

The role of selected flavonols in tumor necrosis factor-related apoptosis-inducing ligand receptor-1 (TRAIL-R1) expression on activated RAW 264.7 macrophages

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand Receptors (TRAIL-R) are an important factor of apoptosis in cancer cells. There are no data about the effect of flavonols on the receptor expression on a surface of macrophage like cells. In this study, the expression level of TRAIL-R1 on murine RAW264.7 macrophages in the presence of selected flavonols: galangin, kaempferol, kaempferide and quercetin, which differ from their phenyl ring substituents, were studied. The expression of TRAIL-R1 death receptors on non-stimulated and lipopolysaccharide (LPS)-stimulated macrophages was determined using flow cytometry. The results suggested that compounds being tested can modulate TRAIL-R1 expression and can enhance TRAIL-mediated apoptosis.

The Histone Deacetylase Inhibitor Trichostatin A Sensitizes Human Renal Carcinoma Cells to TRAIL-Induced Apoptosis through Down-Regulation of c-FLIPL

Histone acetylation plays a critical role in the regulation of transcription by altering the structure of chromatin, and it may influence the resistance of some tumor cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) by regulating the gene expression of components of the TRAIL signaling pathway. In this study, we investigated the effects and molecular mechanisms of trichostatin A (TSA), a histone deacetylase inhibitor, in sensitizing TRAIL-induced apoptosis in Caki human renal carcinoma cells. Our results indicate that nontoxic concentrations of TSA substantially enhance TRAIL-induced apoptosis compared with treatment with either agent alone. Cotreatment with TSA and TRAIL effectively induced cleavage of Bid and loss of mitochondrial membrane potential (MMP), which was associated with the activation of caspases (-3, -8, and -9) and degradation of poly (ADP-ribose) polymerase (PARP), contributing toward the sensitization to TRAIL. Combined treatment with TSA and TRAIL significantly reduced the levels of the cellular Fas-associated death domain (FADD)-like interleukin-1β-converting enzyme (FLICE) inhibitory protein (c-FLIP), whereas those of death receptor (DR) 4, DR5, and FADD remained unchanged. The synergistic effect of TAS and TRAIL was perfectly attenuated in c-FLIP_L-overexpressing Caki cells. Taken together, the present study demonstrates that down-regulation of c-FLIP contributes to TSA-facilitated TRAIL-induced apoptosis, amplifying the death receptor, as well as mitochondria-mediated apoptotic signaling pathways.

Targeting death receptors for TRAIL by agents designed by Mother Nature

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

Chrysin, apigenin and acacetin inhibit tumor necrosis factor-related apoptosis-inducing ligand receptor-1 (TRAIL-R1) on activated RAW264.7 macrophages

Expression level of Tumor Necrosis Factor—related apoptosis—inducing ligand (TRAIL) receptors is one of the most important factors of TRAIL-mediated apoptosis in cancer cells. We here report for the first time data concerning TRAIL-R1 and TRAIL-R2 receptor expression on RAW264.7 macrophages. Three substances belonging to flavones: chrysin, apigenin and acacetin which differ from their substituents at the 4' position in the phenyl ring were used in assays because of the variety of biological activities (e.g., anticancer activity) of the polyphenol compounds. The expression of TRAIL-R1 and TRAIL-R2 death receptors on non-stimulated and LPS (lipopolysaccharide)-stimulated macrophages was determined using flow cytometry. We demonstrate that RAW264.7 macrophages exhibit TRAIL-R1 surface expression and that the tested compounds: chrysin, apigenin and acacetin can inhibit TRAIL-R1 death receptor expression level on macrophages.

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.

Death receptors as targets in cancer

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

LINKED ARTICLES

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