Effect of the XIAP inhibitor Embelin on TRAIL-induced apoptosis of pancreatic cancer cells

Nicotine promotes epithelial to mesenchymal transition and gemcitabine resistance via hENT1/RRM1 signalling in pancreatic cancer and chemosensitizing effects of Embelin-a naturally occurring benzoquinone

Pancreatic cancer is lethal due to poor prognosis with 5-year survival rate lesser than 5 %. Gemcitabine is currently used to treat pancreatic cancer and development of chemoresistance is a major obstacle to overcome pancreatic cancer. Nicotine is a known inducer of drug resistance in pancreatic tumor micro-environment. Present study evaluates chemoresistance triggered by nicotine while treating with gemcitabine and chemosensitization using Embelin. Embelin is a naturally occurring benzoquinone from Embelia ribes possessing therapeutic potency. To develop nicotine-induced chemo-resistance, pancreatic cancer cells PANC-1 and MIA PaCa-2 were continuously treated with nicotine followed by exposure to gemcitabine. Gemcitabine sensitivity assay and immunoblotting was performed to assess the chemo-resistance. Antiproliferative assays such as migration assay, clonogenic assay, Mitochondrial Membrane Potential (MMP) assay, dual staining assay, comet assay, Reactive Oxygen Species (ROS) assay, cell cycle analysis and immunoblotting assays were performed to witness the protein expression involved in chemoresistance and chemosensitization. Epithelial to mesenchymal transition was observed in nicotine induced chemoresistant cells. Gemcitabine sensitivity assay revealed that relative resistance was increased to 6.26 (p < 0.0001) and 6.45 (p < 0.0001) folds in resistant PANC-1 and MIA PaCa-2 compared to parental cells. Protein expression studies confirmed resistance markers like hENT1 and dCK were downregulated with subsequent increase in RRM1 expression in resistant cells. Embelin considerably decreased the cell viability with an IC50 value of 4.03 ± 0.08 μM in resistant PANC-1 and 2.11 ± 0.04 μM in resistant MIA PaCa-2. Cell cycle analysis showed Embelin treatment caused cell cycle arrest at S phase in resistant PANC-1 cells; in resistant MIA PaCa-2 cells there was an escalation in the Sub G1. Embelin upregulated Bax, γH2AX, p53, ERK1/2 and hENT1 expression with concomitant down regulation of Bcl-2 and RRM1. Bioactive molecule embelin, its combination with gemcitabine could provide new vistas to overcome chemo resistance in pancreatic cancer.

Embelin: A novel XIAP inhibitor for the prevention and treatment of chronic diseases

Chronic diseases are a serious health concern worldwide, especially in the elderly population. Most chronic diseases like cancer, cardiovascular ailments, neurodegenerative disorders, and autoimmune diseases are caused due to the abnormal functioning of multiple signaling pathways that give rise to critical anomalies in the body. Although a lot of advanced therapies are available, these have failed to entirely cure the disease due to their less efficacy. Apart from this, they have been shown to manifest disturbing side effects which hamper the patient's quality of life to the extreme. Since the last few decades, extensive studies have been done on natural herbs due to their excellent medicinal benefits. Components present in natural herbs target multiple signaling pathways involved in diseases and therefore hold high potential in the prevention and treatment of various chronic diseases. Embelin, a benzoquinone, is one such agent isolated from Embelia ribes, which has shown excellent biological activities toward several chronic ailments by upregulating a number of antioxidant enzymes (e.g., SOD, CAT, GSH, etc.), inhibiting anti-apoptotic genes (e.g., TRAIL, XIAP, survivin, etc.), modulating transcription factors (e.g., NF-κB, STAT3, etc.) blocking inflammatory biomarkers (e.g., NO, IL-1β, IL-6, TNF-α, etc.), monitoring cell cycle synchronizing genes (e.g., p53, cyclins, CDKs, etc.), and so forth. Several preclinical studies have confirmed its excellent therapeutic activities against malicious diseases like cancer, obesity, heart diseases, Alzheimer's, and so forth. This review presents an overview of embelin, its therapeutic prospective, and the molecular targets in different chronic diseases.

Luteolin-7-O-glucoside inhibits cell proliferation and modulates apoptosis through the AKT signaling pathway in human nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an unnoticeable malignant tumor with a high potential of lymphatic metastasis, and its prevalence is high in Asia. Ionizing radiation is the mainstay of treatment for patients with NPC without metastasis. However, patients with metastatic lesions require advanced treatments such as chemotherapy. The present study investigated the apoptotic effect of luteolin-7-O-glucoside on NPC cells and elucidated its underlying signaling mechanisms. The results revealed that luteolin-7-O-glucoside significantly reduced the proliferation of NPC cell lines (NPC-039 and NPC-BM). Flow cytometry and morphological analysis results demonstrated that luteolin-7-O-glucoside treatment induced S and G₂ /M cell cycle arrest, chromatin condensation, and apoptosis. In addition, mitochondrial membrane potential was observed to be depolarized with an increasing concentration of luteolin-7-O-glucoside. Proteins involved in the extrinsic and intrinsic pathways of apoptosis, such as death receptor, caspase-3, caspase-8, caspase-9, and Bcl-2 family proteins (Bax, t-Bid, Bcl-2, and Bcl-xL), were downregulated and upregulated after treatment with luteolin-7-O-glucoside, respectively. Moreover, the addition of a PI3K/AKT inhibitor enhanced the activation of poly-ADP-ribose-polymerase (PARP) and attenuated cell viability, indicating that luteolin-7-O-glucoside induced apoptosis in NPC cells through the AKT signaling pathway. These results indicated that the apoptosis of NPC cells modulated by luteolin-7-O-glucoside may be preceded by mitochondrial depolarization, cell cycle arrest, extrinsic and intrinsic apoptosis pathway activation, and AKT signaling modulation. Thus, luteolin-7-O-glucoside can be a promising anticancer agent against human NPC.

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.

Embelin downregulated cFLIP in breast cancer cell lines facilitate anti-tumor effect of IL-1β-stimulated human umbilical cord mesenchymal stem cells

Breast cancer is the leading cause of cancer-related death for women. In breast cancer treatment, targeted therapy would be more effective and less harmful than radiotherapy or systemic chemotherapy. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce apoptosis in cancer cells but not in normal cells. Mesenchymal stem cells have shown great therapeutic potential in cancer therapy owing to their ability of homing to tumor sites and secreting many kinds of anti-tumor proteins including TRAIL. In this study, we found that IL-1β-stimulated human umbilical cord-derived mesenchymal stem cells (hUCMSCs) enhance the expression of membrane-bound and soluble TRAIL. Cellular FADD-like IL-1β-converting enzyme inhibitory protein (cFLIP) is an important regulator in TRAIL-mediated apoptosis and relates to TRAIL resistance in cancer cells. Previous studies have shown that embelin, which is extracted from Embelia ribes, can increase the TRAIL sensitivity of cancer cells by reducing cFLIP expression. Here we have demonstrated that cFLIP_L is correlated with TRAIL-resistance and that embelin effectively downregulates cFLIP_L in breast cancer cells. Moreover, co-culture of IL-1β-stimulated hUCMSCs with embelin-treated breast cancer cells could effectively induce apoptosis in breast cancer cells. The combined effects of embelin and IL-1β-stimulated hUCMSCs may provide a new therapeutic strategy for breast cancer therapy.

YM155 and BIRC5 downregulation induce genomic instability via autophagy-mediated ROS production and inhibition in DNA repair

Activation of autophagy plays a critical role in DNA repair, especially for the process of homologous recombination. Despite upregulation of autophagy promotes both the survival and the death of cells, the pathways that govern the pro-cell death effects of autophagy are still incompletely understood. YM155 is originally developed as an expression suppressant of BIRC5 (an anti-apoptotic molecule) and it has reached Phase I/II clinical trials for the treatment of variety types of cancer. However, the target-specificity of YM155 has recently been challenged as several studies reported that YM155 exhibits direct DNA damaging effects. Recently, we discovered that BIRC5 is an autophagy negative-modulator. Using function-comparative analysis, we found in the current study that YM155 and BIRC5 siRNA both induced early "autophagy-dependent ROS production-mediated" DNA damage/strand breaks and concurrently downregulated the expression of RAD54L, RAD51, and MRE11, which are molecules known for their important roles in homologous recombination, in human cancer (MCF7, MDA-MB-231, and SK-BR-3) and mouse embryonic fibroblast (MEF) cells. Similar to the effects of YM155 and BIRC5 siRNA, downregulation of RAD54L and RAD51 by siRNA induced autophagy and DNA damage/strand breaks in cells, suggesting YM155/BIRC5 siRNA might also induce autophagy partly through RAD54L and RAD51 downregulations. We further observed that prolonged YM155 and BIRC5 siRNA treatment induced autophagic vesicle formation proximal to the nucleus and triggered DNA leakage. In conclusion, our findings reveal a novel mechanism of action of YM155 (i.e. induces autophagy-dependent ROS production-mediated DNA damage) in cancer cells and show the functional complexity of BIRC5 and autophagy involving the modulation of genome stability, highlighting that upregulation of autophagy is not always beneficial to the DNA repair process. Our findings can aid the development of a variety of BIRC5-directly/indirectly targeted anticancer therapies that are currently under pre-clinical and clinical investigations.

Embelin Promotes Oncolytic Vaccinia Virus-Mediated Antitumor Immunity Through Disruption of IL-6/STAT3 Signaling in Lymphoma

Objective

Oncolytic virotherapy is a promising alternative to conventional treatment, yet limited viral replication and immune-negative feedback are the major hurdles to effective viro-immunotherapy.

Methods

In this study, we found that use of an adjuvant of embelin, a small molecular inhibitor of XIAP, increased the replication of oncolytic vaccinia virus (OVV) by mitigating antiviral innate immunity. Moreover, embelin suppresses constitutive STAT3 phosphorylation and mitigates OVV-induced activation of STAT3 in lymphoma. In the subcutaneous lymphoma model, embelin significantly enhanced the therapeutic efficacy of OVV and prolonged the survival. In addition, embelin significantly increased the OVV-induced infiltration of T cells and NK cells and decreased the number of OVV-induced myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment.

Results

Our results explored the ability of OVV and embelin in combination to enhance lymphoma cell lysis, revealing a beneficial combinatorial effect wherein both lymphoma cell lysis and OVV replication were enhanced both in vitro and in an in vivo murine model system.

Conclusion

Our findings indicate the utility of embelin as an adjuvant for oncolytic viro-immunotherapy.

The role of XIAP in resistance to TNF-related apoptosis-inducing ligand (TRAIL) in Leukemia

The treatment for leukemic malignancies remains a challenge despite the wide use of conventional chemotherapies. Therefore, new therapeutic approaches are highly demanded. TNF-related apoptosis-inducing ligand (TRAIL) represents a targeted therapy against cancer because it induces apoptosis only in tumor cells. TRAIL is currently under investigation for the treatment of leukemia. Preclinical studies evaluated the potential therapeutic efficacy of TRAIL on cell lines and clinical samples and showed promising results. However, like most anti-cancer drugs, resistance to TRAIL-induced apoptosis may limit its clinical efficacy. It is critical to understand the molecular mechanisms of TRAIL. Therefore, rational therapeutic drug combinations for clinical trials of TRAIL-based therapies might be achieved. In a variety of leukemic cells, overexpression of X-linked inhibitor of apoptosis protein (XIAP), a negative regulator of apoptosis pathway, has been discovered. Implication of XIAP in the ineffective induction of cell death by TRAIL in leukemia has been explored in several resistant cell lines. XIAP inhibitors restored TRAIL sensitivity in resistant cells and primary leukemic blasts. Moreover, TRAIL resistance in leukemic cells could be overcome by the effects of several anti-leukemic agents via the mechanisms of XIAP downregulation. Here, we discuss targeting XIAP, a strategy to restore TRAIL sensitivity in leukemia to acquire more insights into the mechanisms of TRAIL resistance. The concluding remarks may lead to identify putative ways to resensitize tumors.

Activation of the Immune-Metabolic Receptor GPR84 Enhances Inflammation and Phagocytosis in Macrophages

GPR84 is a member of the metabolic G protein-coupled receptor family, and its expression has been described predominantly in immune cells. GPR84 activation is involved in the inflammatory response, but the mechanisms by which it modulates inflammation have been incompletely described. In this study, we investigated GPR84 expression, activation, and function in macrophages to establish the role of the receptor during the inflammatory response. We observed that GPR84 expression in murine tissues is increased by endotoxemia, hyperglycemia, and hypercholesterolemia. Ex vivo studies revealed that GPR84 mRNA expression is increased by LPS and other pro-inflammatory molecules in different murine and human macrophage populations. Likewise, high glucose concentrations and the presence of oxidized LDL increased GPR84 expression in macrophages. Activation of the GPR84 receptor with a selective agonist, 6-(octylamino) pyrimidine-2,4(1H,3H)-dione (6-n-octylaminouracil, 6-OAU), enhanced the expression of phosphorylated Akt, p-ERK, and p65 nuclear translocation under inflammatory conditions and elevated the expression levels of the inflammatory mediators TNFα, IL-6, IL-12B, CCL2, CCL5, and CXCL1. In addition, GPR84 activation triggered increased bacterial adhesion and phagocytosis in macrophages. The enhanced inflammatory response mediated by 6-OAU was not observed in GPR84-/- cells nor in macrophages treated with a selective GPR84 antagonist. Collectively, our results reveal that GPR84 functions as an enhancer of inflammatory signaling in macrophages once inflammation is established. Therefore, molecules that antagonize the GPR84 receptor may be potential therapeutic tools in inflammatory and metabolic diseases.

Embelin: a benzoquinone possesses therapeutic potential for the treatment of human cancer

Natural products have been gaining recognition and are becoming a significant part of research in the area of drug development and discovery. Phytochemicals derived from these sources have been comprehensively studied and have displayed a wide range of activities against many fatal diseases including cancer. One such product that has gained recognition from its pharmacological properties and nontoxic nature is embelin, obtained from Embelia ribes. Amid all the vivid pharmacological activities, embelin has gained its prominence in the area of cancer research. Embelin binds to the BIR3 domain of XIAP, preventing the association of XIAP and caspase-9 resulting in the suppression of cell growth, proliferation and migration of various types of cancer cells. Furthermore, embelin modulates anti-apoptotic pathways by suppressing the activity of NF-κB, PI3-kinase/AKT, JAK/STAT pathway - among others. The present review summarizes the various reported effects of embelin on different types of cancer cells and highlights the cellular mechanisms of action.

Anti-inflammatory effects of embelin in A549 cells and human asthmatic airway epithelial tissues

OBJECTIVE

Allergic asthma is the most common type in asthma, which is defined as a chronic inflammatory disease of the lung. In this study, we investigated whether embelin (Emb), the major component of Ardisia japonica BL. (AJB), exhibits anti-inflammatory effects on allergic asthma via inhibition of NF-κB activity using A549 cells and asthmatic airway epithelial tissues.

METHODS

Inflammation was induced in A549 cells, a human airway epithelial cell line, by IL-1β (10 ng/ml) treatment for 4 h. The effects of Emb on NF-κB activity and COX-2 protein expression in inflamed airway epithelial cells and human asthmatic airway epithelial tissues were analyzed via western blot. The secretion levels of NF-κB-mediated cytokines/chemokines, including IL-4, 6, 9, 13, TNF-α and eotaxin, were measured by a multiplex assay.

RESULTS

Emb significantly blocked NF-κB activity in IL-1β-treated A549 cells and human asthmatic airway epithelial tissues. COX-2 expression was also reduced in both IL-1β-treated A549 cells and asthmatic tissues Emb application. Emb significantly reduced the secretion of IL-4, IL-6 and eotaxin in human asthmatic airway epithelial tissues by inhibiting activity of NF-κB.

CONCLUSIONS

The results of this study suggest that Emb may be used as an anti-inflammatory agent via inhibition of NF-κB and related cytokines.

LPS promotes resistance to TRAIL-induced apoptosis in pancreatic cancer

Background

Though TRAIL has been hailed as a promising drug for tumour treatment, it has been observed that many tumour cells have developed escape mechanisms against TRAIL-induced apoptosis. As a receptor of LPS, TLR 4, which is expressed on a variety of cancer cells, can be associated with TRAIL-resistance of tumour cells and tumour progression as well as with the generation of an anti-tumour immune response.

Methods

In this study, the sensitivity to TRAIL-induced apoptosis as well as the influence of LPS-co-stimulation on the cell viability of the pancreatic cancer cell lines PANC-1, BxPC-3 and COLO 357 was examined by FACS analyses and a cell viability assay. Subsequently, the expression of TRAIL-receptors was detected via FACS analyses. Levels of osteoprotegerin (OPG) were also determined using an enzyme-linked immunosorbent assay.

Results

PANC-1 cells were shown to be resistant to TRAIL-induced apoptosis. This was accompanied by significantly increased osteoprotegerin levels and a significantly decreased expression of DR4.

In contrast, TRAIL significantly induced apoptosis in COLO 357 cells and to a lesser degree in BxPC-3 cells. Co-stimulation of COLO 357 as well as BxPC-3 cells combining TRAIL and LPS resulted in a significant decrease in TRAIL-induced apoptosis. In COLO 357 cells TRAIL-stimulation decreased the levels of OPG thereby not altering the expression of the TRAIL-receptors 1–4 resulting in a high susceptibility to TRAIL-induced apoptosis. Co-stimulation with LPS and TRAIL completely reversed the effect of TRAIL on OPG levels reaching a 2-fold increase beyond the level of non-stimulated cells resulting in a lower susceptibility to apoptosis.

In BxPC-3, TRAIL stimulation decreased the expression of DR4 and significantly increased the decoy receptors TRAIL-R3 and TRAIL-R4 leading to a decrease in TRAIL-induced apoptosis. OPG levels remained unchanged. Co-stimulation with TRAIL and LPS further enhanced the changes in TRAIL-receptor-expression promoting apoptosis resistance.

Conclusions

Here it has been shown that TRAIL-resistance in pancreatic cancer cells can be mediated by the inflammatory molecule LPS as well as by different expression patterns of functional and non-functional TRAIL-receptors.

Embelin prevents LMP1-induced TRAIL resistance via inhibition of XIAP in nasopharyngeal carcinoma cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in the majority of tumor cells, whilst sparing normal cells. However, the potential use of TRAIL in the treatment of cancer is limited by the inevitable emergence of drug resistance. The present study reports the upregulation of latent membrane protein 1 (LMP1)-induced TRAIL resistance via the enhanced expression of X-linked inhibitor of apoptosis protein (XIAP) in nasopharyngeal carcinoma (NPC) cells. LMP1-positive NPC cells were indicated to be more sensitive to TRAIL compared with LMP1-negative NPC cells in three NPC cell lines. CNE-1 is a LMP1-negative NPC cell line that was transfected with pGL6-LMP1; following which, sensitivity to TRAIL decreased. LMP1-induced TRAIL resistance was associated with the decreased cleavage of caspase-8,-3 and -9, BH3 interacting domain death agonist (Bid) and mitochondrial depolarization, without any effects on the expression of the death receptors, B-cell lymphoma (Bcl)-2 and Bcl-extra long. Knockdown of XIAP with small interfering RNA increased caspase-3 and -9 and Bid cleavage, and prevented LMP1-induced TRAIL resistance. Furthermore, embelin, the inhibitor of XIAP, prevented LMP1-induced TRAIL resistance in the Epstein-Barr virus (EBV)-positive CNE-1-LMP1 and C666-1 NPC cell lines. However, embelin did not enhance TRAIL-induced apoptosis in NP-69, which was used as a benign nasopharyngeal epithelial cell line. These data show that LMP1 inhibits TRAIL-mediated apoptosis by upregulation of XIAP. Embelin may be used in an efficacious and safe manner to prevent LMP1-induced TRAIL resistance. The present study may have implications for the development and validation of novel strategies to prevent TRAIL resistance in EBV-positive NPC.

TRAIL Promotes Tumor Growth in a Syngeneic Murine Orthotopic Pancreatic Cancer Model and Affects the Host Immune Response

OBJECTIVES

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is currently being evaluated as a possible biological agent for cancer treatment. However, many tumor cells are resistant to TRAIL-induced apoptosis. In these cases, TRAIL may activate different pathways promoting tumor growth as well as showing different interactions with the immunological tumor microenvironment. In this study, the impact of TRAIL on tumor growth and survival in a syngeneic model of TRAIL-resistant pancreatic cancer cells was investigated.

METHODS

Murine 6606PDA pancreatic cancer cells were injected into the pancreatic heads of TRAIL mice and their littermates. To examine a direct effect of TRAIL on tumor cells, cultures of 6606PDA were TRAIL stimulated.

RESULTS

The TRAIL mice displayed significantly decreased tumor volumes and an enhanced overall survival in pancreatic cancer. The decreased tumor growth in TRAIL mice was accompanied by a decrease of regulatory CD4 cells within tumors. Concordantly, TRAIL treatment of wild-type mice enhanced tumor growth and increased the fraction of regulatory CD4 cells. Yet, a direct effect of TRAIL on 6606PDA cells was not detected.

CONCLUSIONS

Thus, TRAIL can promote tumor growth in TRAIL-resistant tumor cells. This may restrict possible future clinical applications of TRAIL in pancreatic cancer.

Targeting Mortalin by Embelin Causes Activation of Tumor Suppressor p53 and Deactivation of Metastatic Signaling in Human Breast Cancer Cells

Embelin, a natural quinone found in the fruits of Embelia ribes, is commonly used in Ayurvedic home medicine for a variety of therapeutic potentials including anti-inflammation, anti-fever, anti-bacteria and anti-cancer. Molecular mechanisms of these activities and cellular targets have not been clarified to-date. We demonstrate that the embelin inhibits mortalin-p53 interactions, and activates p53 protein in tumor cells. We provide bioinformatics, molecular docking and experimental evidence to the binding affinity of embelin with mortalin and p53. Binding of embelin with mortalin/p53 abrogates their complex resulted in nuclear translocation and transcriptional activation function of p53 causing growth arrest in cancer cells. Furthermore, analyses of growth factors and metastatic signaling using antibody membrane array revealed their downregulation in embelin-treated cells. We also found that the embelin causes transcriptional attenuation of mortalin and several other proteins involved in metastatic signaling in cancer cells. Based on these molecular dynamics and experimental data, it is concluded that the anticancer activity of embelin involves targeting of mortalin, activation of p53 and inactivation of metastatic signaling.

[Involvement of oxidative stress in embelin-induced cell death in leukemia HL-60 cells]

OBJECTIVE

To evaluate the effects of Embelin on HL-60 cells by the impact of oxidative stress on DNA double-strain breaks (DSBs).

METHODS

HL-60 cells were treated with Embelin in different concentration (3, 10, 30, 100, and 300 μg/ml) for 24 h, and inhibitory effects was examined by CCK-8 assay. Reactive oxygen species (ROS) levels were evaluated by flow cytometry using DCFH-DA. Comet assay was used to detect the extent of DSBs.

RESULTS

Embelin inhibited proliferation of HL-60 cells in a dose-dependent manner. At the concentration of 10, 30, 100, and 300 μg/ml, the inhibition rate was (12.74 ± 2.27)%, (23.49 ± 1.96)%, (30.30±1.89)%, and (57.55 ± 3.59)% (P<0.05). Embelin also lead to high level of intracellular ROS and deterioration of DNA damage (P<0.05). When HL-60 cells were pretreated with ROS scavenger N-acetyl-l-cysteine (NAC) for 2 h and then treated with 300 μg/ml Embelin for 24 h, the intracellular ROS level declined and DSBs relieved (P<0.05). Meanwhile, embelin-induced cell viability significantly declined to (32.75 ± 2.70)% (P<0.05).

CONCLUSION

Embelin induced the death of HL-60 cells by increasing the generation of intracellular oxidation and the oxidative stress, which drived the damage of DNA double-strand.

The XIAP inhibitor Embelin enhances TRAIL-induced apoptosis in human leukemia cells by DR4 and DR5 upregulation

The present study was designed to explore the effects of low-toxicity Embelin on TRAIL-induced apoptosis and its possible mechanism in human leukemia cells. Our study showed that low-toxicity Embelin enhanced TRAIL-induced apoptosis through DR4 and DR5 upregulation and caspase activation in HL-60 cells. Pan-caspase inhibitor Z-VAD-FMK inhibited cell apoptosis induced by TRAIL alone or combined with low-toxicity Embelin, which indicated the cytotoxic effect is mediated by caspase-dependent apoptosis. Although Embelin is an X chromosome-linked inhibitor-of-apoptosis protein (XIAP) inhibitor, an XIAP independent effect on cell death was detected in HL-60 cells exposed to low-toxicity Embelin and TRAIL. Low-toxicity Embelin upregulated DR4 and DR5 expression to enhance TRAIL-induced apoptosis. The sensitizing effects of Embelin on TRAIL-induced apoptosis were markedly attenuated when DR4/DR5 was knocked down. These data suggested that low-toxicity Embelin enhanced TRAIL-induced cell apoptosis through DR4 and DR5 upregulation, indicating that combination of low-toxicity Embelin and TRAIL may become as a potential antileukemia strategy.

Embelin inhibits pancreatic cancer progression by directly inducing cancer cell apoptosis and indirectly restricting IL-6 associated inflammatory and immune suppressive cells

Pancreatic cancer is an aggressive malignancy and unresponsive to conventional chemotherapies. Here, the anti-inflammatory and anti-tumor effects of embelin on pancreatic cancer were investigated. Embelin significantly attenuated cells invasion, proliferation and induced apoptosis through inhibition of STAT3 and activation of p53 signaling pathways. Embelin substantially reduced the tumorigenicity of pancreatic cancer cells in vivo, which was associated with reduced inflammatory cells and immune suppressive cells, IL-17A(+) Th17, GM-CSF(+) Th, MDSCs and Treg, through inhibition of IL-6 secretion. Moreover, embelin decrease IL-6-induced STAT3 phosphorylation. In summary, embelin represents a novel therapeutic drug candidate for the clinical treatment of pancreatic cancer.

Effect of Embelin on TRAIL receptor 2 mAb-induced apoptosis of TRAIL-resistant A549 non-small cell lung cancer cells

INTRODUCTION

Some non-small cell lung cancer (NSCLC) tumor cells are insensitive to tumor necrosis factor- related apoptosis-inducing ligand (TRAIL) -based therapy. This study was conducted to examine the effect of embelin on the sensitivity of the A549 NSCLC cell line to TRAIL receptor2 (TRAILR2) monoclonal antibodies and to investigate the potential mechanisms.

MATERIALS AND METHODS

A549 cells were treated with embelin, TRAILR2 mAb or a combination of both. Cell viability was measured using ATPlite assay and apoptosis rates were determined by flow cytometry with AnnexinV-FITC and propidium iodide staining, with the expression levels of proteins analyzed by Western blotting.

RESULTS

The cell survival rate of separate treatments with 100 ng/ml TRAILR2 antibody or 25 uM embelin were 81.5±1.57% and 61.7±2.84%, respectively. Their combined use markedly decreased cell viability in A549 cells to 28.1±1.97% (P<0.05). The general caspase inhibitor Z-VAD- FMK could inhibit the embelin-enhanced sensitivity of A549 cells to TRAILR2 mAb (75.97±3.17%)(P<0.05). Both flow cytometry and cell morphological analysis showed that embelin was able to increase TRAIL-induced apoptosis in A549 cells. Combined treatment with embelin and TRAILR2 mAb augmented the activation of initiator caspases and effector caspase. In addition, A549 cells showed increasing levels of TRAILR2 protein and decreasing levels of Bcl-2, survivin and c-FLIP following the treatment with embelin+TRAILR2 mAb.

CONCLUSIONS

Embelin could enhance TRAIL-induced apoptosis in A549 cells. The synergistic effect of the combination treatment might be due to modulation of multiple components in the TRAIL receptor-mediated apoptotic signaling pathway, including TRAILR2, XIAP, survivin, Bcl-2 and c-FLIP.

Polymeric micelles: nanocarriers for cancer-targeted drug delivery

Polymeric micelles represent an effective delivery system for poorly water-soluble anticancer drugs. With small size (10-100 nm) and hydrophilic shell of PEG, polymeric micelles exhibit prolonged circulation time in the blood and enhanced tumor accumulation. In this review, the importance of rational design was highlighted by summarizing the recent progress on the development of micellar formulations. Emphasis is placed on the new strategies to enhance the drug/carrier interaction for improved drug-loading capacity. In addition, the micelle-forming drug-polymer conjugates are also discussed which have both drug-loading function and antitumor activity.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Molecular pathways: targeting death receptors and smac mimetics

Inhibitor of apoptosis (IAP) proteins are overexpressed in multiple human malignancies, an event that is associated with poor prognosis and treatment resistance. Therefore, IAP proteins represent relevant targets for therapeutic intervention. Second mitochondrial activator of caspases (Smac) is a mitochondrial protein that is released into the cytosol upon the induction of programmed cell death and promotes apoptosis by neutralizing IAP proteins. On the basis of this property, a variety of small-molecule inhibitors have been developed that mimic the binding domain of the native Smac protein to IAP proteins. Evaluation of these Smac mimetics in preclinical studies revealed that they particularly synergize together with agents that trigger the death receptor pathway of apoptosis. Such combinations might therefore be of special interest for being included in the ongoing evaluation of Smac mimetics in early clinical trials.

Poor antibody validation is a challenge in biomedical research: a case study for detection of c-FLIP

Successful translation of findings derived from preclinical studies into effective therapies is critical in biomedical research. Lack of robustness and reproducibility of the preclinical data, due to insufficient number of repeats, inadequate cell-based and mouse models contribute to the poor success rate. Antibodies are widely used in preclinical research, notably to determine the expression of potential therapeutic targets in tissues of interest, including tumors, but also to identify disease and/or treatment response biomarkers. We sought to determine whether the current antibody characterization standards in preclinical research are sufficient to ensure reliability of the data found in peer-reviewed publications. To address this issue, we used detection of the protein c-FLIP, a major factor of resistance to apoptosis, as a proof of concept. Accurate detection of endogenous c-FLIP levels in the preclinical settings is imperative since it is considered as a potential theranostic biomarker. Several sources of c-FLIP antibodies validated by their manufacturer and recommended for western blotting were therefore rigorously tested. We found a wide divergence in immune recognition properties. While these antibodies have been used in many publications, our results show that several of them failed to detect endogenous c-FLIP protein by Western blotting. Our results suggest that antibody validation standards are inadequate, and that systematic use of genetic knockdowns and/or knockouts to establish proof of specificity is critical, even for antibodies previously used in the scientific literature. Because antibodies are fundamental tools in both preclinical and clinical research, ensuring their specificity is crucial.

XIAP antagonist embelin inhibited proliferation of cholangiocarcinoma cells

Cholangiocarcinoma cells are dependent on antiapoptotic signaling for survival and resistance to death stimuli. Recent mechanistic studies have revealed that increased cellular expression of the E3 ubiquitin-protein ligase X-linked inhibitor of apoptosis (XIAP) impairs TRAIL- and chemotherapy-induced cytotoxicity, promoting survival of cholangiocarcinoma cells. This study was undertaken to determine if pharmacologic antagonism of XIAP protein was sufficient to sensitize cholangiocarcinoma cells to cell death. We employed malignant cholangiocarcinoma cell lines and used embelin to antagonize XIAP protein. Embelin treatment resulted in decreased XIAP protein levels by 8 hours of treatment with maximal effect at 16 hours in KMCH and Mz-ChA-1 cells. Assessment of nuclear morphology demonstrated a concentration-dependent increase in nuclear staining. Interestingly, embelin induced nuclear morphology changes as a single agent, independent of the addition of TNF-related apoptosis inducing ligand (TRAIL). However, caspase activity assays revealed that increasing embelin concentrations resulted in slight inhibition of caspase activity, not activation. In addition, the use of a pan-caspase inhibitor did not prevent nuclear morphology changes. Finally, embelin treatment of cholangiocarcinoma cells did not induce DNA fragmentation or PARP cleavage. Apoptosis does not appear to contribute to the effects of embelin on cholangiocarcinoma cells. Instead, embelin caused inhibition of cell proliferation and cell cycle analysis indicated that embelin increased the number of cells in S and G2/M phase. Our results demonstrate that embelin decreased proliferation in cholangiocarcinoma cell lines. Embelin treatment resulted in decreased XIAP protein expression, but did not induce or enhance apoptosis. Thus, in cholangiocarcinoma cells the mechanism of action of embelin may not be dependent on apoptosis.

Nanomicellar carriers for targeted delivery of anticancer agents

Clinical application of anticancer drugs is limited by problems such as low water solubility, lack of tissue-specificity and toxicity. Formulation development represents an important approach to these problems. Among the many delivery systems studied, polymeric micelles have gained considerable attention owing to ease in preparation, small sizes (10-100 nm), and ability to solubilize water-insoluble anticancer drugs and accumulate specifically at the tumors. This article provides a brief review of several promising micellar systems and their applications in tumor therapy. The emphasis is placed on the discussion of the authors' recent work on several nanomicellar systems that have both a delivery function and antitumor activity, named dual-function drug carriers.

Reduction of decoy receptor 3 enhances TRAIL-mediated apoptosis in pancreatic cancer

Most human pancreatic cancer cells are resistant to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. However, the mechanisms by which pancreatic cancer cells utilize their extracellular molecules to counteract the proapoptotic signaling mediated by the TNF family are largely unknown. In this study, we demonstrate for the first time that DcR3, a secreted decoy receptor that malignant pancreatic cancer cells express at a high level, acts as an extracellular antiapoptotic molecule by binding to TRAIL and counteracting its death-promoting function. The reduction of DcR3 with siRNA unmasked TRAIL and greatly enhanced TRAIL-induced apoptosis. Gemcitabine, a first-line drug for pancreatic cancer, also reduced the level of DcR3. The addition of DcR3 siRNA further enhanced gemcitabine-induced apoptosis. Notably, our in vivo study demonstrated that the therapeutic effect of gemcitabine could be enhanced via further reduction of DcR3, suggesting that downregulation of DcR3 in tumor cells could tip the balance of pancreatic cells towards apoptosis and potentially serve as a new strategy for pancreatic cancer therapy.

Anti-tumor activity of the X-linked inhibitor of apoptosis (XIAP) inhibitor embelin in gastric cancer cells

This study investigated the anticancer effects of embelin in human gastric cancer cells and the underlying molecular mechanisms. Gastric cancer cells were treated with embelin and 5-FU for methyl-thiazolyl-tetrazolium bromide cell viability assay and flow cytometric detection of cell viability and apoptosis. Protein pathway array (PPA) and Western blot were used to investigate differentially expressed proteins in embelin-treated gastric cancer cells. Embelin reduced gastric cancer cell viability, induced apoptosis, and enhanced 5-FU antitumor activity in gastric cancer cells. Mechanistically, embelin induced cell cycle arrest at the S and G2/M phases. Molecularly, embelin downregulated expression of X-linked inhibitor of apoptosis and cell cycle-regulatory proteins, such as CDK1, CDC25B, CDC25C, cyclinB1, and CDK2. PPA analysis showed that embelin modulated several pathways that are associated with cell growth and apoptosis, such as PI3K/AKT, JAK/STAT, p38 MAPK, and p53. The data from the current study implied that reduction of gastric cancer cell viability after treatment with embelin was through cell cycle arrest at the S and G2/M phases and apoptosis.

Embelin-induced brain glioma cell apoptosis and cell cycle arrest via the mitochondrial pathway

Brain glioma is the most common malignant intracranial tumor and has become the focus of research on diseases of the central nervous system due to its high incidence and poor prognosis. As a small‑molecule inhibitor of X-linked inhibitor of apoptosis protein (XIAP), embelin has the ability to specifically inhibit XIAP to control and regulate the apoptosis of various types of tumor cells. However, to date, the mechanism of action for this effect is not well understood. The aim of this study was to investigate the role that the mitochondrial pathway plays in embelin-induced brain glioma cell apoptosis and the effect of embelin on the cell cycle. Brain glioma cells were treated with different doses of embelin. The MTT method was used to determine cell proliferation, and flow cytometry was used to determine apoptosis, as well as changes in the cell cycle and cell mitochondrial membrane potential. Western blot analysis was performed to determine the expression levels of apoptosis‑associated proteins, Bcl-2, Bcl-xL, Bax and Bak as well as cytochrome c. We found that embelin induced a time‑ and dose‑dependent apoptosis of brain glioma cells, and that it could arrest the cell cycle in the G0/G1 phase. Embelin also caused changes in brain glioma cell mitochondrial membrane potential. Additionally, embelin regulated the shifting of Bax and Bcl-2 to promote the mitochondrial release of cytochrome c, thus activating the caspase proteins to cause apoptosis. Thus, embelin induces apoptosis in brain glioma cells which is closely associated with the mitochondrial pathway.

Embelin inhibits growth and induces apoptosis through the suppression of Akt/mTOR/S6K1 signaling cascades

BACKGROUND

Akt/mTOR/S6K1 signaling cascades play an important role both in the survival and proliferation of tumor cells.

METHODS

In the present study, we investigated the effects of embelin (EB), identified primarily from the Embelia ribes plant, on the Akt/mTOR/S6K1 activation, associated gene products, cellular proliferation, and apoptosis in human prostate cancer cells.

RESULTS

EB exerted significant cytotoxic and suppressive effects on Akt and mTOR activation against androgen-independent PC-3 cells as compared to androgen-dependent LNCaP cells. Moreover, EB suppressed the constitutive activation of Akt/mTOR/S6K1 signaling cascade, which correlated with the induction of apoptosis as characterized by accumulation of cells in subG1 phase, positive Annexin V binding, down-regulation of anti-apoptotic (Bcl-2, Bcl-xL, survivin, IAP-1, and IAP-2) and proliferative (cyclin D1) proteins, activation of caspase-3, and cleavage of PARP. We also observed that EB can significantly enhance the apoptotic effects of a specific pharmacological Akt inhibitor when used in combination and also caused broad inhibition of all the three kinases in Akt/mTOR/S6K1 signaling axis in PC-3 cells.

CONCLUSIONS

EB inhibits multiple signaling cascades involved in tumorigenesis and can be used as a potential therapeutic candidate for both the prevention and treatment of prostate cancer.

Embelin-induced MCF-7 breast cancer cell apoptosis and blockade of MCF-7 cells in the G2/M phase via the mitochondrial pathway

Embelin is a small molecular inhibitor extracted from Myrsinaceae plants that specifically inhibits XIAP, affecting the proliferation and apoptosis of various types of tumor cells. In our previous studies, we have demonstrated that embelin is able to induce the apoptosis of MCF-7 breast cancer cells in a dose-dependent manner. However, its mechanism of action is not yet clear. The purpose of this study was to investigate the involvement of the mitochondrial pathway in embelin-induced apoptosis and the effect of embelin on the cell cycle. Different doses of embelin were added to MCF-7 breast cancer cells and it was found that embelin was able to induce apoptosis of MCF-7 breast cancer cells in a dose- and time-dependent manner. Flow cytometry analysis revealed that embelin caused changes in the MCF-7 cell mitochondrial membrane potential and blocked the cell cycle of MCF-7 cells in the G2/M phase. Moreover, embelin was demonstrated to promote mitochondrial release of cytochrome C via regulation of Bax and Bcl-2, resulting in the activation of caspase-3 and -9, while no significant changes in the level of caspase-8 were observed. The results have demonstrated that embelin-induced apoptosis of MCF-7 breast cancer cells involves the mitochondrial pathway.

The flavonolignan silibinin potentiates TRAIL-induced apoptosis in human colon adenocarcinoma and in derived TRAIL-resistant metastatic cells

Silibinin, a flavonolignan, is the major active component of the milk thistle plant (Silybum marianum) and has been shown to possess anti-neoplastic properties. TNF-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent which selectively induces apoptosis in cancer cells. However, resistance to TRAIL-induced apoptosis is an important and frequent problem in cancer treatment. In this study, we investigated the effect of silibinin and TRAIL in an in vitro model of human colon cancer progression, consisting of primary colon tumor cells (SW480) and their derived TRAIL-resistant metastatic cells (SW620). We showed by flow cytometry that silibinin and TRAIL synergistically induced cell death in the two cell lines. Up-regulation of death receptor 4 (DR4) and DR5 by silibinin was shown by RT-PCR and by flow cytometry. Human recombinant DR5/Fc chimera protein that has a dominant-negative effect by competing with the endogenous receptors abrogated cell death induced by silibinin and TRAIL, demonstrating the activation of the death receptor pathway. Synergistic activation of caspase-3, -8, and -9 by silibinin and TRAIL was shown by colorimetric assays. When caspase inhibitors were used, cell death was blocked. Furthermore, silibinin and TRAIL potentiated activation of the mitochondrial apoptotic pathway and down-regulated the anti-apoptotic proteins Mcl-1 and XIAP. The involvement of XIAP in sensitization of the two cell lines to TRAIL was demonstrated using the XIAP inhibitor embelin. These findings demonstrate the synergistic action of silibinin and TRAIL, suggesting chemopreventive and therapeutic potential which should be further explored.

Embelin-induced apoptosis of HepG2 human hepatocellular carcinoma cells and blockade of HepG2 cells in the G2/M phase via the mitochondrial pathway

Embelin is a small-molecule inhibitor extracted from plants of the Myrsinaceae family demonstrating specific inhibition of the X-linked inhibitor of apoptosis protein (XIAP) to affect the proliferation and apoptosis of various types of tumor cells. However, the mechanism of action for this effect remains unclear. The purpose of the present study was to investigate the role of the mitochondrial pathway in embelin-induced HepG2 human hepatocellular carcinoma cell apoptosis and the effect of embelin on the cell cycle. HepG2 human hepatocellular carcinoma cells were treated with different doses of embelin. The MTT method was used to determine cell viability, and flow cytometry was used to assess the rate of apoptosis and the changes in mitochondrial membrane potential; the cell cycle was also analyzed. Western blot analysis was performed to determine the expression levels of the apoptosis-associated proteins Bax, Bcl-2 and the caspase family. The results revealed that embelin induced the apoptosis of the HepG2 cells in a dose- and time-dependent manner. In addition, embelin caused changes in mitochondrial membrane potential. Flow cytometric analysis demonstrated that embelin caused blockade of the HepG2 cells in the G2/M phase of the cell cycle.

Inhibition of UVB-induced oxidative damage and apoptotic biochemical changes in human lymphocytes by 2,5-dihydroxy-3-undecyl-1,4-benzoquinone (embelin)

PURPOSE

The present study investigates the inhibition of Ultraviolet B (UVB, 290-320 nm) radiation-induced oxidative damage in peripheral blood human lymphocytes by embelin extracted from Embelia ribes.

MATERIALS AND METHODS

Embelin was extracted, purified and characterized. Prior to inhibitory assessment, a maximum concentration of embelin that was non-toxic was determined. Six experimental groups, including respective controls were made to assess the inhibitory effect of embelin for the selected concentrations of 10 and 20 μg/ml. For the experimental groups; lymphocytes (1 × 10(6) cells) were pre-treated with the chosen concentration of embelin for a period of 60 min and then exposed to UVB for 30 min. UVB radiation inhibitory effect of embelin assessed by measuring antioxidant and lipid peroxidation levels, deoxyribonucleic acid (DNA) damage, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) at scheduled time points after irradiation.

RESULTS

Pre-treatment of lymphocytes with embelin prevents UVB-induced oxidative damage. An increase in antioxidant levels in irradiated cells in the presence of embelin and UV absorbance of embelin could be the reason for the decrease in lipid peroxidation level and prevention of DNA damage by UVB radiation.

CONCLUSION

Embelin prevents oxidative stress induced by UVB irradiation via its antioxidant property.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Methyl jasmonate down-regulates survivin expression and sensitizes colon carcinoma cells towards TRAIL-induced cytotoxicity

BACKGROUND AND PURPOSE

Methyl jasmonate (MJ) is a plant stress hormone with selective cytotoxic anti-cancer activities. The TNF-related apoptosis-inducing ligand (TRAIL) death pathway is an attractive target for cancer therapy. Although TRAIL receptors are specifically expressed in primary cancer cells and cancer cell lines, many types of cancer cells remain resistant to TRAIL-induced cytotoxicity. Here we have assessed a possible synergy between MJ and TRAIL cytotoxicity in colorectal cancer (CRC) cell lines.

EXPERIMENTAL APPROACH

CRC cell lines were pre-incubated with sub-cytotoxic concentrations of MJ followed by TRAIL administration. Cell death was determined by XTT assay and microscopy. Cytochrome c release, caspase cleavage, TRAIL-associated factors, X-linked inhibitor of apoptosis (XIAP) and survivin protein levels were detected by immunoblotting. Survivin transcription was examined by RT-PCR.

KEY RESULTS

Pre-treatment with MJ resulted in increased TRAIL-induced apoptotic cell death, increased cytochrome c release and caspase cleavage. TNFRSF10A, TNFRSF10B, TNFRSF10D, Fas-associated death domain and cellular FLICE-like inhibitory protein remained unchanged during MJ-induced TRAIL sensitization, whereas MJ induced a significant decrease in survivin protein levels. Overexpression of survivin prevented MJ-induced TRAIL cytotoxicity, implying a role for survivin in MJ-induced TRAIL sensitization. MJ decreased survivin mRNA indicating that MJ may affect survivin transcription. In a β-catenin/transcription factor (TCF)-dependent luciferase activity assay, MJ decreased TCF-dependent transcriptional activity.

CONCLUSION AND IMPLICATIONS

MJ, at sub-cytotoxic levels, sensitized CRC cells to TRAIL-induced apoptosis. Thus, combinations of MJ and TRAIL, both selective anti-cancer agents, have potential as novel treatments for CRC.

HDAC modulation and cell death in the clinic

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two opposing classes of enzymes, which finely regulate the balance of histone acetylation affecting chromatin packaging and gene expression. Imbalanced acetylation has been associated with carcinogenesis and cancer progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. This implies that epigenetic alterations are amenable to pharmacological interventions. Accordingly, some epigenetic-based drugs (epidrugs) have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment. Here, we focus on the biological features of HDAC inhibitors (HDACis), analyzing the mechanism(s) of action and their current use in clinical practice.

Targeting IAP proteins for therapeutic intervention in cancer

Evasion of apoptosis is one of the crucial acquired capabilities used by cancer cells to fend off anticancer therapies. Inhibitor of apoptosis (IAP) proteins exert a range of biological activities that promote cancer cell survival and proliferation. X chromosome-linked IAP is a direct inhibitor of caspases - pro-apoptotic executioner proteases - whereas cellular IAP proteins block the assembly of pro-apoptotic protein signalling complexes and mediate the expression of anti-apoptotic molecules. Furthermore, mutations, amplifications and chromosomal translocations of IAP genes are associated with various malignancies. Among the therapeutic strategies that have been designed to target IAP proteins, the most widely used approach is based on mimicking the IAP-binding motif of second mitochondria-derived activator of caspase (SMAC), which functions as an endogenous IAP antagonist. Alternative strategies include transcriptional repression and the use of antisense oligonucleotides. This Review provides an update on IAP protein biology as well as current and future perspectives on targeting IAP proteins for therapeutic intervention in human malignancies.

Smac: Its role in apoptosis induction and use in lung cancer diagnosis and treatment

Apoptosis is a conserved and regulated cell suicide process, the malfunction of which is closely linked with carcinogenesis. Caspases control the induction of apoptosis through an enzymatic cascade that can be activated by both the mitochondrial and death receptor pathways. Smac is a mitochondrial protein that interacts with Inhibitor of Apoptosis Proteins (IAPs) and, upon apoptotic stimuli, is released into the cytoplasm to inhibit the capase-binding activity of IAPs. Smac plays key roles in both the diagnosis and treatment of cancer, especially lung cancer. Our review will focus on the roles of Smac in lung carcinogenesis and cancer progression and its relevance in lung cancer treatment.

Sensitization of human bladder tumor cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis with a small molecule IAP antagonist

Urothelial carcinoma of the bladder accounts for approximately 5% of all cancer deaths in humans. The large majority of bladder tumors are non-muscle invasive at diagnosis, but even after local surgical therapy there is a high rate of local tumor recurrence and progression. Current treatments extend time to recurrence but do not significantly alter disease survival. The objective of the present study was to investigate the tumoricidal potential of combining the apoptosis-inducing protein TNF-related apoptosis-inducing ligand (TRAIL) with a small molecule inhibitor of apoptosis proteins (IAP) antagonist to interfere with intracellular regulators of apoptosis in human bladder tumor cells. Our results demonstrate that the IAP antagonist Compound A exhibits high binding affinity to the XIAP BIR3 domain. When Compound A was used at nontoxic concentrations in combination with TRAIL, there was a significant increase in the sensitivity of TRAIL-sensitive and TRAIL-resistant bladder tumor lines to TRAIL-mediated apoptosis. In addition, modulation of TRAIL sensitivity in the TRAIL-resistant bladder tumor cell line T24 with Compound A was reciprocated by XIAP small interfering RNA-mediated suppression of XIAP expression, suggesting the importance of XIAP-mediated resistance to TRAIL in these cells. These results suggest the potential of combining Compound A with TRAIL as an alternative therapy for bladder cancer.

Embelin suppresses STAT3 signaling, proliferation, and survival of multiple myeloma via the protein tyrosine phosphatase PTEN

Even though embelin, an inhibitor of the XIAP, is known to exhibit anti-inflammatory and anti-cancer activities, very little is known about its mechanism of action. Here, we investigated whether embelin mediates its effect through interference with the signal transducer and activator of transcription 3 (STAT3) pathway. We found that embelin inhibited constitutive STAT3 activation in a variety of human cancer cell lines such as U266, DU-145, and SCC4 cells. The suppression of STAT3 was mediated through inhibition of the activation of JAK2 and c-Src. Pervanadate treatment also reversed the embelin-induced down-regulation of STAT3, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that embelin-induced the expression of the tyrosine phosphatase PTEN and deletion of the PTEN gene by small interfering RNA abolished the ability of embelin to inhibit STAT3 activation. Besides, embelin failed to suppress STAT3 activation in PTEN-null PC3 cells, thus indicating that the inhibitory effect of embelin on STAT3 is PTEN-dependent. Embelin down-regulated the expression of STAT3-regulated gene products; this correlated with the suppression of cell proliferation and invasion, and the induction of apoptosis through the activation of caspase-3. Overall, our results indicate that the anti-inflammatory and anti-cancer activities previously assigned to embelin may be mediated in part through the suppression of the STAT3 pathway.

Targeting apoptosis signaling in pancreatic cancer

The ability to escape apoptosis or programmed cell death is a hallmark of human cancers, for example pancreatic cancer. This can promote tumorigenesis, since too little cell death by apoptosis disturbs tissue homeostasis. Additionally, defective apoptosis signaling is the underlying cause of failure to respond to current treatment approaches, since therapy-mediated antitumor activity requires the intactness of apoptosis signaling pathways in cancer cells. Thus, the elucidation of defects in the regulation of apoptosis in pancreatic carcinoma can result in the identification of novel targets for therapeutic interference and for exploitation for cancer drug discovery.

Targeting apoptosis pathways in pancreatic cancer

Pancreatic cancer - here in particular pancreatic ductal adenocarcinoma (PDAC) - is still a highly therapy refractory disease. Amongst the mechanisms by which PDAC cells could escape any non-surgical therapy, anti-apoptotic protection seems to be the most relevant one. PDAC cells have acquired resistance to apoptotic stimuli such as death ligands (FasL, TRAIL) or anti-cancer drugs (gemcitabine) by a great number of molecular alterations either disrupting an apoptosis inducing signal or counteracting the execution of apoptosis. Thus, PDAC cells exhibit alterations in the EGFR/MAPK/Ras/raf1-, PI3K/Akt-, TRAIL/TRAF2-, or IKK/NF-κB pathway accompanied by deregulations in the expression of apoptosis regulators such as cIAP, Bcl2, XIAP or survivin. Along with protection against apoptosis, PDAC cells also overexpress histone deacetylases (HDACs) giving rise to epigenetic patterns of chemoresistance and to acetylation of other regulatory proteins, as well. With respect to the multitude of anti-apoptotic pathways, a great number of molecular targets might be of high potential in novel therapy strategies. Thus, natural compounds as well as novel synthetic drugs are considered to be used in single or combined therapy of PDAC. A number of proteasome and HDAC inhibitors or selective inhibitors of IKK, EGFR, Akt and mTOR have been widely explored in preclinical settings and clinical studies. Even though these early studies encouraged an application in a clinical setting, most of the trials have been rather disappointing yet. Thus, new molecular targets and novel concepts of combination therapies need to get access into clinical trials - either in neoadjuvant/adjuvant or in palliative treatments.