Polyphenon E(R), a standardized green tea extract, induces endoplasmic reticulum stress, leading to death of immortalized PNT1a cells by anoikis and tumorigenic PC3 by necroptosis

Tumor biomarkers for diagnosis, prognosis and targeted therapy

Tumor biomarkers, the substances which are produced by tumors or the body's responses to tumors during tumorigenesis and progression, have been demonstrated to possess critical and encouraging value in screening and early diagnosis, prognosis prediction, recurrence detection, and therapeutic efficacy monitoring of cancers. Over the past decades, continuous progress has been made in exploring and discovering novel, sensitive, specific, and accurate tumor biomarkers, which has significantly promoted personalized medicine and improved the outcomes of cancer patients, especially advances in molecular biology technologies developed for the detection of tumor biomarkers. Herein, we summarize the discovery and development of tumor biomarkers, including the history of tumor biomarkers, the conventional and innovative technologies used for biomarker discovery and detection, the classification of tumor biomarkers based on tissue origins, and the application of tumor biomarkers in clinical cancer management. In particular, we highlight the recent advancements in biomarker-based anticancer-targeted therapies which are emerging as breakthroughs and promising cancer therapeutic strategies. We also discuss limitations and challenges that need to be addressed and provide insights and perspectives to turn challenges into opportunities in this field. Collectively, the discovery and application of multiple tumor biomarkers emphasized in this review may provide guidance on improved precision medicine, broaden horizons in future research directions, and expedite the clinical classification of cancer patients according to their molecular biomarkers rather than organs of origin.

Potential impacts of bisphenols on prostate cells: An overview of cytotoxicity, proliferation, oxidative stress, apoptosis, and ER-stress response activation

This study aimed to evaluate the toxic effects of Bisphenol A (BPA), Bisphenol F (BPF) and Bisphenol S (BPS) on PNT1A and PC-3 cells, focusing on their effects on endoplasmic reticulum (ER) stress and related pathways. PNT1A and PC-3 were treated with BPA, BPF and BPS at concentrations of 0.1, 1 and 10 μM for 48 h cytotoxicity, BrdU cell proliferation, ROS generation, apoptosis detection, gene expression analysis and Western blot analysis were performed. BPA induced proliferation and late apoptosis in PNT1A cells, whereas it induced both late apoptosis and early apoptosis in PC-3 cells. BPF and BPS induced late apoptosis in PC-3 cells. Increased ROS levels were observed in PNT1A cells exposed to 1-10 μM BPA. BPA, BPF and BPS increased the expression levels of ER stress-related genes in PNT1A cells. Furthermore, exposure to BPA increased the expression of ER stress-related CHOP/DDIT3 protein in PNT1A cells. These findings highlight the potential health risks associated with BPA, BPF and BPS exposure and emphasize the importance of investigating the underlying mechanisms by which these chemicals may affect human health. Further research is required to comprehensively understand the role of ER stress pathways in cellular responses to these substances.

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

Necroptosis Induced by Delta-Tocotrienol Overcomes Docetaxel Chemoresistance in Prostate Cancer Cells

Prostate cancer (PCa) represents the fifth cause of cancer death in men. Currently, chemotherapeutic agents for the treatment of cancers, including PCa, mainly inhibit tumor growth by apoptosis induction. However, defects in apoptotic cellular responses frequently lead to drug resistance, which is the main cause of chemotherapy failure. For this reason, trigger non-apoptotic cell death might represent an alternative approach to prevent drug resistance in cancer. Several agents, including natural compounds, have been shown to induce necroptosis in human cancer cells. In this study we evaluated the involvement of necroptosis in anticancer activity of delta-tocotrienol (δ-TT) in PCa cells (DU145 and PC3). Combination therapy is one tool used to overcome therapeutic resistance and drug toxicity. Evaluating the combined effect of δ-TT and docetaxel (DTX), we found that δ-TT potentiates DTX cytotoxicity in DU145 cells. Moreover, δ-TT induces cell death in DU145 cells that have developed DTX resistance (DU-DXR) activating necroptosis. Taken together, obtained data indicate the ability of δ-TT to induce necroptosis in both DU145, PC3 and DU-DXR cell lines. Furthermore, the ability of δ-TT to induce necroptotic cell death may represent a promising therapeutical approach to overcome DTX chemoresistance in PCa.

The endoplasmic reticulum stress response in prostate cancer

In order to proliferate in unfavourable conditions, cancer cells can take advantage of the naturally occurring endoplasmic reticulum-associated unfolded protein response (UPR) via three highly conserved signalling arms: IRE1α, PERK and ATF6. All three arms of the UPR have key roles in every step of tumour progression: from cancer initiation to tumour growth, invasion, metastasis and resistance to therapy. At present, no cure for metastatic prostate cancer exists, as targeting the androgen receptor eventually results in treatment resistance. New research has uncovered an important role for the UPR in prostate cancer tumorigenesis and crosstalk between the UPR and androgen receptor signalling pathways. With an improved understanding of the mechanisms by which cancer cells exploit the endoplasmic reticulum stress response, targetable points of vulnerability can be uncovered.

New Visions on Natural Products and Cancer Therapy: Autophagy and Related Regulatory Pathways

Macroautophagy (autophagy) has been a highly conserved process throughout evolution and allows cells to degrade aggregated/misfolded proteins, dysfunctional or superfluous organelles and damaged macromolecules, in order to recycle them for biosynthetic and/or energetic purposes to preserve cellular homeostasis and health. Changes in autophagy are indeed correlated with several pathological disorders such as neurodegenerative and cardiovascular diseases, infections, cancer and inflammatory diseases. Conversely, autophagy controls both apoptosis and the unfolded protein response (UPR) in the cells. Therefore, any changes in the autophagy pathway will affect both the UPR and apoptosis. Recent evidence has shown that several natural products can modulate (induce or inhibit) the autophagy pathway. Natural products may target different regulatory components of the autophagy pathway, including specific kinases or phosphatases. In this review, we evaluated ~100 natural compounds and plant species and their impact on different types of cancers via the autophagy pathway. We also discuss the impact of these compounds on the UPR and apoptosis via the autophagy pathway. A multitude of preclinical findings have shown the function of botanicals in regulating cell autophagy and its potential impact on cancer therapy; however, the number of related clinical trials to date remains low. In this regard, further pre-clinical and clinical studies are warranted to better clarify the utility of natural compounds and their modulatory effects on autophagy, as fine-tuning of autophagy could be translated into therapeutic applications for several cancers.

Polyphenon E Effects on Gene Expression in PC-3 Prostate Cancer Cells

Polyphenon E (Poly E) is a standardized, caffeine-free green tea extract with defined polyphenol content. Poly E is reported to confer chemoprotective activity against prostate cancer (PCa) progression in the TRAMP model of human PCa, and has shown limited activity against human PCa in human trials. The molecular mechanisms of the observed Poly E chemopreventive activity against PCa are not fully understood. We hypothesized that Poly E treatment of PCa cells induces gene expression changes, which could underpin the molecular mechanisms of the limited Poly E chemoprevention activity against PCa. PC-3 cells were cultured in complete growth media supplemented with varied Poly E concentrations for 24 h, then RNA was isolated for comparative DNA microarray (0 vs. 200 mg/L Poly E) and subsequent TaqMan qRT-PCR analyses. Microarray data for 54,613 genes were filtered for >2-fold expression level changes, with 8319 genes increased and 6176 genes decreased. Eight genes involved in key signaling or regulatory pathways were selected for qRT-PCR. Two genes increased expression significantly, MXD1 (13.98-fold; p = 0.0003) and RGS4 (21.98-fold; p = 0.0011), by qRT-PCR. MXD1 and RGS4 significantly increased gene expression in Poly E-treated PC-3 cells, and the MXD1 gene expression increases were Poly E dose-dependent.

A comprehensive pan-cancer analysis of necroptosis molecules in four gynecologic cancers

Background

In recent years, it has been proved that necroptosis plays an important role in the occurrence, development, invasion, metastasis and drug resistance of malignant tumors. Hence, further evaluation and targeting of necroptosis may be of clinical benefit for gynecologic cancers (GCs).

Methods

To compare consistency and difference, we explored the expression pattern and prognostic value of necroptosis-related genes (NRGs) in pan-GC analysis through Linear regression and Empirical Bayesian, Univariate Cox analysis, and public databases from TCGA and Genotype-Tissue Expression (GTEx), including CESC, OV, UCEC, and UCS. We explored the copy number variation (CNV), methylation level and enrichment pathways of NRGs in the four GCs. Based on LASSO Cox regression analysis or principal component analysis, we established the prognostic NRG-signature or necroptosis-score for the four GCs. In addition, we predicted and compared functional pathways, tumor mutational burden (TMB), somatic mutation features, immunity status, immunotherapy, chemotherapeutic drug sensitivity of the NRG-signature based on NRGs. We also examined the expression level of several NRGs in OV samples that we collected using Quantitative Real-time PCR.

Results

We confirmed the presence of NRGs in expression, prognosis, CNV, and methylation for four GCs, thus comparing the consistency and difference among the four GCs. The prognosis and independent prognostic value of the risk signatures based on NRGs were determined. Through the results of subclass mapping, we found that GC patients with lower risk score may be more sensitive to PDL1 response and more sensitive to immune checkpoint blockade therapy. Drug susceptibility analysis showed that, 51, 45, 64, and 29 drugs with differences between risk groups were yielded in CESC, OV, UCEC, and UCS respectively. For OV, the expression differences of several NRGs in the tissues we collected were similar to that in TCGA.

Conclusion

Our comprehensive analysis of NRGs and NRG-signature demonstrated their similarity and difference, as well as their potential roles in prognosis and could guide therapeutic strategies, thus improving the outcome of GC patients.

Guanmaitong Granule Attenuates Atherosclerosis by Inhibiting Inflammatory Immune Response in ApoE−/− Mice Fed High-Fat Diet

Background

Atherosclerosis (AS) is the leading cause of cardiovascular diseases, such as myocardial infarction and stroke. Guanmaitong granule (GMTG) is a TCM (Traditional Chinese medicine) prescribed to treat AS. However, its mechanism remains unclear.

Methods

We obtained reliable ingredients and targets of GMTG using the HERB database. AS-related targets were obtained from HERB and GeneCards databases. The target database was constructed by intersecting the ingredients of GMTG with the AS-related targets. STRING and Cytoscape were used to create protein-protein interaction (PPI) network and screen core targets. GO enrichment analysis and KEGG pathway analyses were performed using R. Finally, the ApoE^−/− mice AS model was induced by a high-fat diet (HFD) for in vivo validation of core pathways and targets.

Results

A total of 124 ingredients and 418 potential targets of GMTG for treating AS were obtained. Numerous ingredients and targets were related to Panax notoginseng, Salvia miltiorrhiza, and Astragalus. Most core targets and pathways were involved in the inflammatory immune response. GMTG could decrease serum triglycerides, total cholesterol, low-density lipoprotein-cholesterol, and oxidized low-density lipoprotein level and increase the serum high-density lipoprotein-cholesterol level. Furthermore, GMTG reduced the plaque burden and promoted plaque remodeling by reducing plaque area, lipid deposition, foam cell content, and collagen fiber content in the plaque in the aortic root of ApoE^−/− mice. GMTG inhibited systemic and plaque inflammatory immune response and increased plaque stability by inhibiting the excessive release of the TLR4/MyD88/NF-κB pathway-induced inflammatory cytokines, tumor necrosis factor, interleukin-6, and interleukin-1 beta.

Conclusion

Radix notoginseng, Radix salviae liguliobae, and Radix astragali are the main ingredients of GMTG for treating AS. Further, GMTG could regulate the level of serum lipids and inhibit inflammatory immune response, which resulted in anti-AS effects such as plaque stabilization, reduction of plaque burden, and plaque remodeling. GMTG is a promising multi-target treatment for AS.

Regulated cell death (RCD) in cancer: key pathways and targeted therapies

Regulated cell death (RCD), also well-known as programmed cell death (PCD), refers to the form of cell death that can be regulated by a variety of biomacromolecules, which is distinctive from accidental cell death (ACD). Accumulating evidence has revealed that RCD subroutines are the key features of tumorigenesis, which may ultimately lead to the establishment of different potential therapeutic strategies. Hitherto, targeting the subroutines of RCD with pharmacological small-molecule compounds has been emerging as a promising therapeutic avenue, which has rapidly progressed in many types of human cancers. Thus, in this review, we focus on summarizing not only the key apoptotic and autophagy-dependent cell death signaling pathways, but the crucial pathways of other RCD subroutines, including necroptosis, pyroptosis, ferroptosis, parthanatos, entosis, NETosis and lysosome-dependent cell death (LCD) in cancer. Moreover, we further discuss the current situation of several small-molecule compounds targeting the different RCD subroutines to improve cancer treatment, such as single-target, dual or multiple-target small-molecule compounds, drug combinations, and some new emerging therapeutic strategies that would together shed new light on future directions to attack cancer cell vulnerabilities with small-molecule drugs targeting RCD for therapeutic purposes.

Targeting necroptosis as an alternative strategy in tumor treatment: From drugs to nanoparticles

Over last decades, most antitumor therapeutic strategies have focused on apoptosis, however, apoptosis resistance and immunological silence usually led to treatment failure. In this sense, triggering other programmed cell death such as necroptosis may achieve a better therapeutic efficacy and has gained widespread attentions in tumor therapy. Studies in this field have identified several types of necroptosis modulators and highlighted the therapeutic potential of necroptotic cell death in cancer. Nanoparticles further provide possibilities to improve therapeutic outcomes as an efficient drug delivery system, facilitating tumor targeting and controlled cargo release. Furthermore, some nanoparticles themselves can trigger/promote programmed necrosis through hyperthermia, ultrasound and autophagy blockage. These investigations have entered necroptosis for consideration as a promising strategy for tumor therapy, though numerous challenges remain and clinical applications are still distant. In this review, we would briefly introduce molecular mechanism and characteristics of necroptosis, and then summarize recent progress of programmed necrosis and their inducers in tumor therapy. Furthermore, the antitumor strategies that take advantages of nanoparticles to induce necroptosis are also discussed.

Green Tea Epigallocatechin-3-Gallate Regulates Autophagy in Male and Female Reproductive Cancer

With a rich abundance of natural polyphenols, green tea has become one of the most popular and healthiest nonalcoholic beverages being consumed worldwide. Epigallocatechin-3-gallate (EGCG) is the predominant catechin found in green tea, which has been shown to promote numerous health benefits, including metabolic regulation, antioxidant, anti-inflammatory, and anticancer. Clinical studies have also shown the inhibitory effects of EGCG on cancers of the male and female reproductive system, including ovarian, cervical, endometrial, breast, testicular, and prostate cancers. Autophagy is a natural, self-degradation process that serves important functions in both tumor suppression and tumor cell survival. Naturally derived products have the potential to be an effective and safe alternative in balancing autophagy and maintaining homeostasis during tumor development. Although EGCG has been shown to play a critical role in the suppression of multiple cancers, its role as autophagy modulator in cancers of the male and female reproductive system remains to be fully discussed. Herein, we aim to provide an overview of the current knowledge of EGCG in targeting autophagy and its related signaling mechanism in reproductive cancers. Effects of EGCG on regulating autophagy toward reproductive cancers as a single therapy or cotreatment with other chemotherapies will be reviewed and compared. Additionally, the underlying mechanisms and crosstalk of EGCG between autophagy and other cellular processes, such as reactive oxidative stress, ER stress, angiogenesis, and apoptosis, will be summarized. The present review will help to shed light on the significance of green tea as a potential therapeutic treatment for reproductive cancers through regulating autophagy.

Necroptosis and Prostate Cancer: Molecular Mechanisms and Therapeutic Potential

Necroptosis is a programmed form of necrosis characterized by mitochondrial alterations and plasma membrane permeabilization resulting in the release of cytoplasmic content into extracellular space, and leading to inflammatory reactions. Besides its critical role in viral defense mechanisms and inflammatory diseases, necroptosis plays pivotal functions in the drug response of tumors, including prostate cancer. Necroptosis is mainly governed by kinase enzymes, including RIP1, RIP3, and MLKL, and conversely to apoptosis, is a caspase-independent mechanism of cell death. Numerous compounds induce necroptosis in prostate cancer models, including (i) compounds of natural origin, (ii) synthetic and semisynthetic small molecules, and (iii) selenium and selenium-based nanoparticles. Here, we overview the molecular mechanisms underlying necroptosis and discuss the possible implications of drugs inducing necroptosis for prostate cancer therapy.

Pan-cancer analysis of necroptosis-related gene signature for the identification of prognosis and immune significance

BACKGROUND

Necroptosis is a novel programmed cell death mode independent on caspase. A number of studies have revealed that the induction of necroptosis could act as an alternative therapeutic strategy for drug-resistant tumors as well as affect tumor immune microenvironment.

METHODS

Gene expression profiles and clinical data were downloaded from XENA-UCSC (including The Cancer Genome Atlas and Genotype-Tissue Expression), Gene Expression Omnibus, International Cancer Genome Consortium and Chinese Glioma Genome Atlas. We used non-negative matrix factorization method to conduct tumor classification. The least absolute shrinkage and selection operator regression was applied to establish risk models, whose prognostic effectiveness was examined in both training and testing sets with Kaplan-Meier analysis, time-dependent receiver operating characteristic curves as well as uni- and multi-variate survival analysis. Principal Component Analysis, t-distributed Stochastic Neighbor Embedding and Uniform Manifold Approximation and Projection were conducted to check the risk group distribution. Gene Set Enrichment Analyses, immune infiltration analysis based on CIBERSORT, EPIC, MCPcounter, ssGSEA and ESTIMATE, gene mutation and drug sensitivity between the risk groups were also taken into consideration.

RESULTS

There were eight types of cancer with at least ten differentially expressed necroptosis-related genes which could influence patients' prognosis, namely, adrenocortical carcinoma (ACC), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), acute myeloid leukemia (LAML), brain lower grade glioma (LGG), pancreatic adenocarcinoma (PAAD), liver hepatocellular carcinoma (LIHC), skin cutaneous melanoma (SKCM) and thymoma (THYM). Patients could be divided into different clusters with distinct overall survival in all cancers above except for LIHC. The risk models could efficiently predict prognosis of ACC, LAML, LGG, LIHC, SKCM and THYM patients. LGG patients from high-risk group had a higher infiltration level of M2 macrophages and cancer-associated fibroblasts. There were more CD8+ T cells, Th1 cells and M1 macrophages in low-risk SKCM patients' tumor microenvironment. Gene mutation status and drug sensitivity are also different between low- and high-risk groups in the six cancers.

CONCLUSIONS

Necroptosis-related genes can predict clinical outcomes of ACC, LAML, LGG, LIHC, SKCM and THYM patients and help to distinguish immune infiltration status for LGG and SKCM.

Polyphenol-Mediated Autophagy in Cancer: Evidence of In Vitro and In Vivo Studies

One of the hallmarks of cellular transformation is the altered mechanism of cell death. There are three main types of cell death, characterized by different morphological and biochemical features, namely apoptosis (type I), autophagic cell death (type II) and necrosis (type III). Autophagy, or self-eating, is a tightly regulated process involved in stress responses, and it is a lysosomal degradation process. The role of autophagy in cancer is controversial and has been associated with both the induction and the inhibition of tumor growth. Autophagy can exert tumor suppression through the degradation of oncogenic proteins, suppression of inflammation, chronic tissue damage and ultimately by preventing mutations and genetic instability. On the other hand, tumor cells activate autophagy for survival in cellular stress conditions. Thus, autophagy modulation could represent a promising therapeutic strategy for cancer. Several studies have shown that polyphenols, natural compounds found in foods and beverages of plant origin, can efficiently modulate autophagy in several types of cancer. In this review, we summarize the current knowledge on the effects of polyphenols on autophagy, highlighting the conceptual benefits or drawbacks and subtle cell-specific effects of polyphenols for envisioning future therapies employing polyphenols as chemoadjuvants.

Proteotoxic Stress and Cell Death in Cancer Cells

To maintain proteostasis, cells must integrate information and activities that supervise protein synthesis, protein folding, conformational stability, and also protein degradation. Extrinsic and intrinsic conditions can both impact normal proteostasis, causing the appearance of proteotoxic stress. Initially, proteotoxic stress elicits adaptive responses aimed at restoring proteostasis, allowing cells to survive the stress condition. However, if the proteostasis restoration fails, a permanent and sustained proteotoxic stress can be deleterious, and cell death ensues. Many cancer cells convive with high levels of proteotoxic stress, and this condition could be exploited from a therapeutic perspective. Understanding the cell death pathways engaged by proteotoxic stress is instrumental to better hijack the proliferative fate of cancer cells.

L-Ascorbic Acid Inhibits Breast Cancer Growth by Inducing IRE/JNK/CHOP-Related Endoplasmic Reticulum Stress-Mediated p62/SQSTM1 Accumulation in the Nucleus

Anticancer effects of L-ascorbic acid (Vitamin C, L-AA) have been reported in various types of cancers. L-AA intake reduces breast cancer recurrence and mortality; however, the role of L-AA in the treatment of breast cancer remains poorly understood. In this study, we investigated the effect and mechanism action of L-AA on breast cancer growth. L-AA inhibited the growth of breast cancer cells by inducing apoptotic cell death at the evaluated treatment concentrations without affecting normal cells. Moreover, L-AA induces autophagosome formation via regulation of mammalian target of rapamycin (mTOR), Beclin1, and autophagy-related genes (ATGs) and increased autophagic flux. Notably, we observed that L-AA increased p62/SQSTM1 (sequestosome 1) protein levels. Accumulation of p62 protein in cancer cells in response to stress has been reported, but its role in cancer regulation remains controversial. Here, we demonstrated that L-AA-induced p62 accumulation is related to L-AA-induced breast cancer growth inhibition. Furthermore, L-AA induced endoplasmic reticulum (ER) stress via the IRE–JNK–CHOP (inositol-requiring endonuclease–c-Jun N-terminal kinase–C/EBP homologous protein) signaling pathways, which increased the nuclear levels of p62/SQSTM1. These findings provide evidence that L-AA-induced ER stress could be crucial for p62 accumulation-dependent cell death, and L-AA can be useful in breast cancer treatment.

Flavonoids as Epigenetic Modulators for Prostate Cancer Prevention

Prostate cancer (PCa) is a multifactorial disease with an unclear etiology. Due to its high prevalence, long latency, and slow progression, PCa is an ideal target for chemoprevention strategies. Many research studies have highlighted the positive effects of natural flavonoids on chronic diseases, including PCa. Different classes of dietary flavonoids exhibit anti-oxidative, anti-inflammatory, anti-mutagenic, anti-aging, cardioprotective, anti-viral/bacterial and anti-carcinogenic properties. We overviewed the most recent evidence of the antitumoral effects exerted by dietary flavonoids, with a special focus on their epigenetic action in PCa. Epigenetic alterations have been identified as key initiating events in several kinds of cancer. Many dietary flavonoids have been found to reverse DNA aberrations that promote neoplastic transformation, particularly for PCa. The epigenetic targets of the actions of flavonoids include oncogenes and tumor suppressor genes, indirectly controlled through the regulation of epigenetic enzymes such as DNA methyltransferase (DNMT), histone acetyltransferase (HAT), and histone deacetylase (HDAC). In addition, flavonoids were found capable of restoring miRNA and lncRNA expression that is altered during diseases. The optimization of the use of flavonoids as natural epigenetic modulators for chemoprevention and as a possible treatment of PCa and other kinds of cancers could represent a promising and valid strategy to inhibit carcinogenesis and fight cancer.

Goniothalamin Induces Necroptosis and Anoikis in Human Invasive Breast Cancer MDA-MB-231 Cells

Goniothalamin (GTN) is toxic to several types of cancer cells in vitro. However, its effects on non-apoptotic cell death induction of human cancer cells have been poorly documented. Here, an investigation of the anti-cancer activity of GTN and the molecular signaling pathways of non-apoptotic cell death in the invasive human breast cancer MDA-MB-231 cell line were undertaken. Apoptotic cell death was suppressed by using a pan-caspase inhibitor (Benzyloxycarbonyl-Val-Ala-Asp-[O-methyl]-fluoromethylketone), z-VAD-fmk) as a model to study whether GTN induced caspase-independent cell death. In the anoikis study, MDA-MB-231 cells were cultured on poly-(2-hydroxyethyl methacrylate)- or poly-HEMA- coated plates to mimic anoikis-resistance growth and determine whether GTN induced cell death and the mechanisms involved. GTN and z-VAD-fmk induced human breast cancer MDA-MB-231 cells to undergo necroptosis via endoplasmic reticulum (ER) and oxidative stresses, with increased expressions of necroptotic genes such as rip1, rip3, and mlkl. GTN induced MDA-MB-231 cells to undergo anoikis via reversed epithelial-mesenchymal transition (EMT) protein expressions, inhibited the EGFR/FAK/Src survival signaling pathway, and decreased matrix metalloproteinase secretion.

Redox biology of regulated cell death in cancer: A focus on necroptosis and ferroptosis

Redox changes and generation of reactive oxygen species (ROS) are part of normal cell metabolism. While low ROS levels are implicated in cellular signaling pathways necessary for survival, higher levels play major roles in cancer development as well as cell death signaling and execution. A role for redox changes in apoptosis has been long established; however, several new modalities of regulated cell death have been brought to light, for which the importance of ROS production as well as ROS source and targets are being actively investigated. In this review, we summarize recent findings on the role of ROS and redox changes in the activation and execution of two major forms of regulated cell death, necroptosis and ferroptosis. We also discuss the potential of using modulators of these two forms of cell death to exacerbate ROS as a promising anticancer therapy.

Effects and mechanisms of tea for the prevention and management of cancers: An updated review

Tea is a traditional and popular beverage worldwide, and the consumption of tea has been demonstrated to possess many health benefits, such as cardiovascular protection, anti-obesity, anti-diabetes, and anticancer. Epidemiological studies have shown that the consumption of tea is inversely associated with the risk of several cancers. In addition, experimental studies have revealed that the anticancer actions of tea are mainly attributed to tea polyphenols, such as epigallocatechin-3-gallate and theaflavins. Both in vitro and in vivo studies have demonstrated that the possible anticancer mechanisms are the inhibition on proliferation, anti-angiogenesis, induction of apoptosis, suppression on metastasis, inhibition on cancer stem cells, and modulation on gut microbiota. Its synergetic anticancer effects with drugs or other compounds could promote anticancer therapies. Furthermore, clinical trials have elucidated that intervention of tea phytochemicals is effective in the prevention of several cancers. This paper is an updated review for the prevention and management of cancers by tea based on the findings from epidemiological, experimental and clinical studies, and special attention is paid on the mechanisms of action.

Molecular Mechanisms and Bioavailability of Polyphenols in Prostate Cancer

Prostate cancer is the one of the most frequently diagnosed cancers among men over the age of 50. Several lines of evidence support the observation that polyphenols have preventive and therapeutic effects in prostate cancer. Moreover, prostate cancer is ideal for chemoprevention due to its long latency. We propose here an equilibrated lifestyle with a diet rich in polyphenols as prophylactic attempts to slow down the progression of localized prostate cancer or prevent the occurrence of the disease. In this review, we will first summarize the molecular mechanisms of polyphenols in prostate cancer with a focus on the antioxidant and pro-oxidant effects, androgen receptors (AR), key molecules involved in AR signaling and their transactivation pathways, cell cycle, apoptosis, angiogenesis, metastasis, genetic aspects, and epigenetic mechanisms. The relevance of the molecular mechanisms is discussed in light of current bioavailability data regarding the activity of polyphenols in prostate cancer. We also highlight strategies for improving the bioavailability of polyphenols. We hope that this review will lead to further research regarding the bioavailability and the role of polyphenols in prostate cancer prevention and treatment.

Role of Endoplasmic Reticulum Stress in the Anticancer Activity of Natural Compounds

Cancer represents a serious global health problem, and its incidence and mortality are rapidly growing worldwide. One of the main causes of the failure of an anticancer treatment is the development of drug resistance by cancer cells. Therefore, it is necessary to develop new drugs characterized by better pharmacological and toxicological profiles. Natural compounds can represent an optimal collection of bioactive molecules. Many natural compounds have been proven to possess anticancer effects in different types of tumors, but often the molecular mechanisms associated with their cytotoxicity are not completely understood. The endoplasmic reticulum (ER) is an organelle involved in multiple cellular processes. Alteration of ER homeostasis and its appropriate functioning originates a cascade of signaling events known as ER stress response or unfolded protein response (UPR). The UPR pathways involve three different sensors (protein kinase RNA(PKR)-like ER kinase (PERK), inositol requiring enzyme1α (IRE1) and activating transcription factor 6 (ATF6)) residing on the ER membranes. Although the main purpose of UPR is to restore this organelle's homeostasis, a persistent UPR can trigger cell death pathways such as apoptosis. There is a growing body of evidence showing that ER stress may play a role in the cytotoxicity of many natural compounds. In this review we present an overview of different plant-derived natural compounds, such as curcumin, resveratrol, green tea polyphenols, tocotrienols, and garcinia derivates, that exert their anticancer activity via ER stress modulation in different human cancers.

The Role of the ER-Induced UPR Pathway and the Efficacy of Its Inhibitors and Inducers in the Inhibition of Tumor Progression

Cancer is the second most frequent cause of death worldwide. It is considered to be one of the most dangerous diseases, and there is still no effective treatment for many types of cancer. Since cancerous cells have a high proliferation rate, it is pivotal for their proper functioning to have the well-functioning protein machinery. Correct protein processing and folding are crucial to maintain tumor homeostasis. Endoplasmic reticulum (ER) stress is one of the leading factors that cause disturbances in these processes. It is induced by impaired function of the ER and accumulation of unfolded proteins. Induction of ER stress affects many molecular pathways that cause the unfolded protein response (UPR). This is the way in which cells can adapt to the new conditions, but when ER stress cannot be resolved, the UPR induces cell death. The molecular mechanisms of this double-edged sword process are involved in the transition of the UPR either in a cell protection mechanism or in apoptosis. However, this process remains poorly understood but seems to be crucial in the treatment of many diseases that are related to ER stress. Hence, understanding the ER stress response, especially in the aspect of pathological consequences of UPR, has the potential to allow us to develop novel therapies and new diagnostic and prognostic markers for cancer.

Anti-Cancer Effects of Green Tea Polyphenols Against Prostate Cancer

Prostate cancer is the most common cancer among men. Green tea consumption is reported to play an important role in the prevention of carcinogenesis in many types of malignancies, including prostate cancer; however, epidemiological studies show conflicting results regarding these anti-cancer effects. In recent years, in addition to prevention, many investigators have shown the efficacy and safety of green tea polyphenols and combination therapies with green tea extracts and anti-cancer agents in in vivo and in vitro studies. Furthermore, numerous studies have revealed the molecular mechanisms of the anti-cancer effects of green tea extracts. We believe that improved understanding of the detailed pathological roles at the molecular level is important to evaluate the prevention and treatment of prostate cancer. Therefore, in this review, we present current knowledge regarding the anti-cancer effects of green tea extracts in the prevention and treatment of prostate cancer, with a particular focus on the molecular mechanisms of action, such as influencing tumor growth, apoptosis, androgen receptor signaling, cell cycle, and various malignant behaviors. Finally, the future direction for the use of green tea extracts as treatment strategies in patients with prostate cancer is introduced.

Molecular Targets of Epigallocatechin-Gallate (EGCG): A Special Focus on Signal Transduction and Cancer

Green tea is a beverage that is widely consumed worldwide and is believed to exert effects on different diseases, including cancer. The major components of green tea are catechins, a family of polyphenols. Among them, epigallocatechin-gallate (EGCG) is the most abundant and biologically active. EGCG is widely studied for its anti-cancer properties. However, the cellular and molecular mechanisms explaining its action have not been completely understood, yet. EGCG is effective in vivo at micromolar concentrations, suggesting that its action is mediated by interaction with specific targets that are involved in the regulation of crucial steps of cell proliferation, survival, and metastatic spread. Recently, several proteins have been identified as EGCG direct interactors. Among them, the trans-membrane receptor 67LR has been identified as a high affinity EGCG receptor. 67LR is a master regulator of many pathways affecting cell proliferation or apoptosis, also regulating cancer stem cells (CSCs) activity. EGCG was also found to be interacting directly with Pin1, TGFR-II, and metalloproteinases (MMPs) (mainly MMP2 and MMP9), which respectively regulate EGCG-dependent inhibition of NF-kB, epithelial-mesenchimal transaction (EMT) and cellular invasion. EGCG interacts with DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), which modulates epigenetic changes. The bulk of this novel knowledge provides information about the mechanisms of action of EGCG and may explain its onco-suppressive function. The identification of crucial signalling pathways that are related to cancer onset and progression whose master regulators interacts with EGCG may disclose intriguing pharmacological targets, and eventually lead to novel combined treatments in which EGCG acts synergistically with known drugs.

Anti-Cancer Natural Products and Their Bioactive Compounds Inducing ER Stress-Mediated Apoptosis: A Review

Cancer is the second biggest cause of death worldwide. Despite a number of studies being conducted, the effective mechanism for treating cancer has not yet been fully understood. The tumor-microenvironment such as hypoxia, low nutrients could disturb function of endoplasmic reticulum (ER) to maintain cellular homeostasis, ultimately leading to the accumulation of unfolded proteins in ER, so-called ER stress. The ER stress has a close relation with cancer. ER stress initiates unfolded protein response (UPR) to re-establish ER homeostasis as an adaptive pathway in cancer. However, persistent ER stress triggers the apoptotic pathway. Therefore, blocking the adaptive pathway of ER stress or facilitating the apoptotic pathway could be an anti-cancer strategy. Recently, natural products and their derivatives have been reported to have anti-cancer effects via ER stress. Here, we address mechanisms of ER stress-mediated apoptosis and highlight strategies for cancer therapy by utilizing ER stress. Furthermore, we summarize anti-cancer activity of the natural products via ER stress in six major types of cancers globally (lung, breast, colorectal, gastric, prostate and liver cancer). This review deepens the understanding of ER stress mechanisms in major cancers as well as the suppressive impact of natural products against cancers via ER stress.

Necroptosis in tumorigenesis, activation of anti-tumor immunity, and cancer therapy

While the mechanisms underlying apoptosis and autophagy have been well characterized over recent decades, another regulated cell death event, necroptosis, remains poorly understood. Elucidating the signaling networks involved in the regulation of necroptosis may allow this form of regulated cell death to be exploited for diagnosis and treatment of cancer, and will contribute to the understanding of the complex tumor microenvironment. In this review, we have summarized the mechanisms and regulation of necroptosis, the converging and diverging features of necroptosis in tumorigenesis, activation of anti-tumor immunity, and cancer therapy, as well as attempts to exploit this newly gained knowledge to provide therapeutics for cancer.

Oxidative stress-induced Akt downregulation mediates green tea toxicity towards prostate cancer cells

Green tea consumption has been shown to possess cancer chemopreventive activity. Polyphenol E (PE) is a widely used standardized green tea extract formulation. This study was designed to investigate the impact of PE on prostate cancer cells (PC3), analyze the potential signals involved and elucidate whether anti- or pro-oxidant effects may be implicated. Treatment of PC3 cells with 30 and 100μg/ml PE significantly decreased cell viability and proliferation. At the tested concentrations, PE did not exert any antioxidant activity, eliciting instead a pro-oxidant effect at concentrations 30 and 100μg/ml, which was consistent with the observed PE cytotoxicity. PE-induced cell death was associated with mitochondrial dysfunction and downregulation of Akt activation, thus suggesting their implication in the PE-elicited cell dysfunction. Cell exposure to the ROS scavenger N-Acetyl Cysteine prevented PE-induced ROS increase, pAkt impairment, and cell death, clearly indicating the causative role of ROS in the observed phenomena. Failure of PE to induce PC3 damage in cells overexpressing Akt further confirms its implication in the PE-elicited cell death. Our findings showed an association between the antiproliferative and the pro-oxidant effect elicited by PE on PC3 cells and delineates a molecular signaling pattern potentially implicated in the toxicity of PE towards prostate cancer cells.

Green Tea Catechins for Prostate Cancer Prevention: Present Achievements and Future Challenges

Green tea catechins (GTCs) are a family of chemically related compounds usually classified as antioxidant molecules. Epidemiological evidences, supported by interventional studies, highlighted a more than promising role for GTCs in human prostate cancer (PCa) chemoprevention. In the last decades, many efforts have been made to gain new insights into the mechanism of action of GTCs. Now it is clear that GTCs' anticancer action can no longer be simplistically limited to their direct antioxidant/pro-oxidant properties. Recent contributions to the advancement of knowledge in this field have shown that GTCs specifically interact with cellular targets, including cell surface receptors, lipid rafts, and endoplasmic reticulum, modulate gene expression through direct effect on transcription factors or indirect epigenetic mechanisms, and interfere with intracellular proteostasis at various levels. Many of the effects observed in vitro are dose and cell context dependent and take place at concentrations that cannot be achieved in vivo. Poor intestinal absorption together with an extensive systemic and enteric metabolism influence GTCs' bioavailability through still poorly understood mechanisms. Recent efforts to develop delivery systems that increase GTCs' overall bioavailability, by means of biopolymeric nanoparticles, represent the main way to translate preclinical results in a real clinical scenario for PCa chemoprevention.

Effect of Cold Plasma Treatment on the Functional Properties of Fresh-Cut Apples

Atmospheric double-barrier discharge (DBD) plasma technology is a promising tool in the food industry as an alternative to traditional food preservation methods. However, the effect of the reactive species generated during the treatment on the content of bioactive compounds in food is still little studied, and there are no data concerning potential deleterious effects of DBD-treated foods on human cells. Some functional properties of DBD-treated minimally processed Pink Lady apples were evaluated in comparison with untreated samples through different in vitro and ex vivo tests. Plasma treatment caused only a slight reduction of antioxidant content and antioxidant capacity (up to 10%), mainly limited to the amphiphilic fraction. Noteworthy, treated apple polyphenol extracts did not reduce cell viability and did not suppress the beneficial physiological cell response to oxidative stress in terms of reactive oxygen species production and phase II enzyme activation in human cultured colonocytes.

Prostate cancer and the unfolded protein response

The endoplasmic reticulum (ER) is an essential organelle that contributes to several key cellular functions, including lipogenesis, gluconeogenesis, calcium storage, and organelle biogenesis. The ER also serves as the major site for protein folding and trafficking, especially in specialized secretory cells. Accumulation of misfolded proteins and failure of ER adaptive capacity activates the unfolded protein response (UPR) which has been implicated in several chronic diseases, including cancer. A number of recent studies have implicated UPR in prostate cancer (PCa) and greatly expanded our understanding of this key stress signaling pathway and its regulation in PCa. Here we summarize these developments and discuss their potential therapeutic implications.

Vitamin E δ-tocotrienol triggers endoplasmic reticulum stress-mediated apoptosis in human melanoma cells

Malignant melanoma is the leading cause of death from skin cancer. Drug toxicity and resistance represent a serious challange for melanoma treatments. Evidence demonstrates that natural compounds may play a crucial role in cancer prevention, growth and progression. Vitamin E tocotrienols (TT) were shown to possess antitumor activity. Here, we analyzed the effects of δ-TT on melanoma cell growth and the involvement of the endoplasmic reticulum (ER) stress in this activity. The experiments were performed on human melanoma cell lines, BLM and A375. δ-TT exerted a significant proapoptotic effect on both cell lines, involving the intrinsic apoptosis pathway; importantly, this compound did not affect the viability of normal human melanocytes. In melanoma cells, δ-TT exerted its antitumor effect through activation of the PERK/p-eIF2α/ATF4/CHOP, IRE1α and caspase-4 ER stress-related branches. Salubrinal, an inhibitor of the ER stress, counteracted the cytotoxic activity of δ-TT. In vivo experiments performed in nude mice bearing A375 xenografts evidenced that δ-TT reduces tumor volume and tumor mass; importantly, tumor progression was significantly delayed by δ-TT treatment. In conclusion, δ-TT exerts a proapoptotic activity on melanoma cells, through activation of the ER stress-related pathways. δ-TT might represent an effective option for novel chemopreventive/therapeutic strategies for melanoma.

Cancer and necroptosis: friend or foe?

Regulated cell death is one major factor to ensure homoeostasis in multicellular organisms. For decades, apoptosis was considered as the sole form of regulated cell death, whereas necrosis was believed to be accidental and unregulated. Due to this view, research on necrosis was somewhat neglected, especially in the field of anti-cancer treatment. However, new interest in necrosis has been sparked by the recent discovery of different forms of necrosis that show indeed regulated pathways. More and more studies now address the molecular pathways of regulated necrosis and its connections within the cellular signaling networks. Necroptosis, a subform of regulated necrosis, has so far hardly been focused on with regard to a future treatment of cancer patients and may emerge as a novel and effective approach to eliminate tumor cells. However, and similar to apoptosis, tumor cells can develop resistances against necroptosis to ensure their own survival. In this context, new molecules that enhance necroptosis are currently being identified to overcome such resistances. This review discusses cancer and necroptosis as friends or foes, i.e. the options to exploit necroptosis in anti-cancer therapies ("foes"), but also potential limitations that may block or actually cause necroptosis to act in a protumoral manner ("friends"). The balance between these two possible roles will determine whether necroptosis can indeed be used as a promising tool for early diagnosis of tumors, prevention of metastasis and anti-cancer treatment.

Nupr1/Chop signal axis is involved in mitochondrion-related endothelial cell apoptosis induced by methamphetamine

Methamphetamine (METH) abuse has been a serious global public health problem for decades. Previous studies have shown that METH causes detrimental effects on the nervous and cardiovascular systems. METH-induced cardiovascular toxicity has been, in part, attributed to its destructive effect on vascular endothelial cells. However, the underlying mechanism of METH-caused endothelium disruption has not been investigated systematically. In this study, we identified a novel pathway involved in endothelial cell apoptosis induced by METH. We demonstrated that exposure to METH caused mitochondrial apoptosis in human umbilical vein endothelial cells and rat cardiac microvascular endothelial cells in vitro as well as in rat cardiac endothelial cells in vivo. We found that METH mediated endothelial cell apoptosis through Nupr1–Chop/P53–PUMA/Beclin1 signaling pathway. Specifically, METH exposure increased the expression of Nupr1, Chop, P53 and PUMA. Elevated p53 expression raised up PUMA expression, which initiated mitochondrial apoptosis by downregulating antiapoptotic Bcl-2, followed by upregulation of proapoptotic Bax, resulting in translocation of cytochrome c (cyto c), an apoptogenic factor, from the mitochondria to cytoplasm and activation of caspase-dependent pathways. Interestingly, increased Beclin1, upregulated by Chop, formed a ternary complex with Bcl-2, thereby decreasing the dissociative Bcl-2. As a result, the ratio of dissociative Bcl-2 to Bax was also significantly decreased, which led to translocation of cyto c and initiated more drastic apoptosis. These findings were supported by data showing METH-induced apoptosis was significantly inhibited by silencing Nupr1, Chop or P53, or by PUMA or Beclin1 knockdown. Based on the present data, a novel mechanistic model of METH-induced endothelial cell toxicity is proposed. Collectively, these results highlight that the Nupr1–Chop/P53–PUMA/Beclin1 pathway is essential for mitochondrion-related METH-induced endothelial cell apoptosis and may be a potential therapeutic target for METH-caused cardiovascular toxicity. Future studies using knockout animal models are warranted to substantiate the present findings.

Function of phosphorylation of NF-kB p65 ser536 in prostate cancer oncogenesis

Majority of prostate cancer (PCa) patients carry TMPRSS2/ERG (T/E) fusion genes and there has been tremendous interest in understanding how the T/E fusion may promote progression of PCa. We showed that T/E fusion can activate NF-kB pathway by increasing phosphorylation of NF-kB p65 Ser536 (p536), but the function of p536 has never been studied in PCa. We report here that active p536 can significantly increase cell motility and transform PNT1a cells (an immortalized normal cell line), suggesting p536 plays a critical role in promoting PCa tumorigenesis. We have discovered a set of p536 regulated genes, among which we validated the regulation of CCL2 by p536. Based on all evidence, we favor that T/E fusion, NF-kB p536 and CCL2 form a signaling chain. Finally, PNT1a cells (not tumorigenic) can form tumors in SCID mice when overexpressing of either wild type or active p65 in the presence of activated AKT, demonstrating synergistic activities of NF-kB and AKT signals in promoting PCa tumorigenesis. These findings indicate that combination therapies targeting T/E fusion, NF-kB, CCL2 and/or AKT pathways may have efficacy in T/E fusion gene expressing PCa. If successful, such targeted therapy will benefit more than half of PCa patients who carry T/E fusions.

(-)-Epigallocatechin-3-Gallate Enhances Hepatitis C Virus Double-Stranded RNA Intermediates-Triggered Innate Immune Responses in Hepatocytes

(-)-Epigallocatechin-3-gallate (EGCG), a major polyphenol component of green tea, has recently been identified as an inhibitor of hepatitis C virus (HCV) entry. Here, we examined whether EGCG can enhance hepatocyte-mediated intracellular innate immunity against HCV. HCV dsRNAs (Core, E1-P7, NS-3'NTR and NS5A) induced interferon-λ1 (IFN-λ1) expression in human hepatocytes. These HCV dsRNAs also induced the expression of Toll-like receptor 3 (TLR3), retinoic acid-inducible gene I (RIG-I) and several antiviral IFN-stimulated genes (ISGs) expression. Although EGCG treatment of hepatocytes alone had little effect on TLR3 and RIG-I signaling pathways, EGCG significantly enhanced HCV dsRNAs-induced the expression of IFN-λ1, TLR3, RIG-I and antiviral ISGs in hepatocytes. Furthermore, treatment of HCV-infected hepatocytes with EGCG and HCV dsRNAs inhibited viral replication. Given that EGCG has the ability to enhance HCV dsRNAs-induced intracellular antiviral innate immunity against HCV, suggesting the potential application of EGCG as a new anti-HCV agent for HCV therapy.

Inhibition of Receptor Interacting Protein Kinases Attenuates Cardiomyocyte Hypertrophy Induced by Palmitic Acid

Palmitic acid (PA) is known to cause cardiomyocyte dysfunction. Cardiac hypertrophy is one of the important pathological features of PA-induced lipotoxicity, but the mechanism by which PA induces cardiomyocyte hypertrophy is still unclear. Therefore, our study was to test whether necroptosis, a receptor interacting protein kinase 1 and 3 (RIPK1 and RIPK3-) dependent programmed necrosis, was involved in the PA-induced cardiomyocyte hypertrophy. We used the PA-treated primary neonatal rat cardiac myocytes (NCMs) or H9c2 cells to study lipotoxicity. Our results demonstrated that cardiomyocyte hypertrophy was induced by PA treatment, determined by upregulation of hypertrophic marker genes and cell surface area enlargement. Upon PA treatment, the expression of RIPK1 and RIPK3 was increased. Pretreatment with the RIPK1 inhibitor necrostatin-1 (Nec-1), the PA-induced cardiomyocyte hypertrophy, was attenuated. Knockdown of RIPK1 or RIPK3 by siRNA suppressed the PA-induced myocardial hypertrophy. Moreover, a crosstalk between necroptosis and endoplasmic reticulum (ER) stress was observed in PA-treated cardiomyocytes. Inhibition of RIPK1 with Nec-1, phosphorylation level of AKT (Ser473), and mTOR (Ser2481) was significantly reduced in PA-treated cardiomyocytes. In conclusion, RIPKs-dependent necroptosis might be crucial in PA-induced myocardial hypertrophy. Activation of mTOR may mediate the effect of necroptosis in cardiomyocyte hypertrophy induced by PA.

EGCG antagonizes Bortezomib cytotoxicity in prostate cancer cells by an autophagic mechanism

The proteasome inhibitors Bortezomib (BZM) and MG132 trigger cancer cell death via induction of endoplasmic reticulum (ER) stress and unfolded protein response. Epigallocatechin gallate (EGCG), the most bioactive green tea polyphenol, is known to display strong anticancer properties as it inhibits proteasome activity and induces ER stress. We investigated whether combined delivery of a proteasome inhibitor with EGCG enhances prostate cancer cell death through increased induction of ER stress. Paradoxically, EGCG antagonized BZM cytotoxicity even when used at low concentrations. Conversely, the MG132 dose-response curve was unaffected by co-administration of EGCG. Moreover, apoptosis, proteasome inhibition and ER stress were inhibited in PC3 cells simultaneously treated with BZM and EGCG but not with a combination of MG132 and EGCG; EGCG enhanced autophagy induction in BZM-treated cells only. Autophagy inhibition restored cytotoxicity concomitantly with CHOP and p-eIF2α up-regulation in cells treated with BZM and EGCG. Overall, these findings demonstrate that EGCG antagonizes BZM toxicity by exacerbating the activation of autophagy, which in turn mitigates ER stress and reduces CHOP up-regulation, finally protecting PC3 cells from cell death.

Cancer Microenvironment and Endoplasmic Reticulum Stress Response

Different stressful conditions such as hypoxia, nutrient deprivation, pH changes, or reduced vascularization, potentially able to act as growth-limiting factors for tumor cells, activate the unfolded protein response (UPR). UPR is therefore involved in tumor growth and adaptation to severe environments and is generally cytoprotective in cancer. The present review describes the molecular mechanisms underlying UPR and able to promote survival and proliferation in cancer. The critical role of UPR activation in tumor growth promotion is discussed in detail for a few paradigmatic tumors such as prostate cancer and melanoma.

Roles of autophagy induced by natural compounds in prostate cancer

Autophagy is a homeostatic mechanism through which intracellular organelles and proteins are degraded and recycled in response to increased metabolic demand or stress. Autophagy dysfunction is often associated with many diseases, including cancer. Because of its role in tumorigenesis, autophagy can represent a new therapeutic target for cancer treatment. Prostate cancer (PCa) is one of the most common cancers in aged men. The evidence on alterations of autophagy related genes and/or protein levels in PCa cells suggests a potential implication of autophagy in PCa onset and progression. The use of natural compounds, characterized by low toxicity to normal tissue associated with specific anticancer effects at physiological levels in vivo, is receiving increasing attention for prevention and/or treatment of PCa. Understanding the mechanism of action of these compounds could be crucial for the development of new therapeutic or chemopreventive options. In this review we focus on the current evidence showing the capacity of natural compounds to exert their action through autophagy modulation in PCa cells.

The heat shock protein 90 inhibitor, (-)-epigallocatechin gallate, has anticancer activity in a novel human prostate cancer progression model

(-)-Epigallocatechin gallate (EGCG), a major tea polyphenol, elicits anticancer effects. However, the mechanism of action is not fully understood. Our laboratory previously showed that EGCG inhibits heat shock protein 90 (HSP90). We used nontumorigenic (NT), tumorigenic, and metastatic cancer cells from a novel human prostate cancer progression model to test the hypotheses that certain stages are more or less sensitive to EGCG and that sensitivity is related to HSP90 inhibition. Treatment of cells with EGCG, novobiocin, or 17-AAG resulted in more potent cytotoxic effects on tumorigenic and metastatic cells than NT cells. When tumorigenic or metastatic cells were grown in vivo, mice supplemented with 0.06% EGCG in drinking water developed significantly smaller tumors than untreated mice. Furthermore, EGCG prevented malignant transformation in vivo using the full prostate cancer model. To elucidate the mechanism of EGCG action, we performed binding assays with EGCG-Sepharose, a C-terminal HSP90 antibody, and HSP90 mutants. These experiments revealed that EGCG-Sepharose bound more HSP90 from metastatic cells compared with NT cells and binding occurred through the HSP90 C-terminus. In addition, EGCG bound HSP90 mutants that mimic both complexed and uncomplexed HSP90. Consistent with HSP90 inhibitory activity, EGCG, novobiocin, and 17-AAG induced changes in HSP90-client proteins in NT cells and larger differences in metastatic cells. These data suggest that EGCG may be efficacious for the treatment of prostate cancer because it preferentially targets cancer cells and inhibits a molecular chaperone supportive of the malignant phenotype.

Therapeutic exploitation of necroptosis for cancer therapy

Evasion of programmed cell death represents one of the hallmarks of cancers that contributes to tumor initiation, progression and treatment resistance. This calls for novel therapeutic concepts to reactivate cell death programs in human malignancies. Since necroptosis represents a regulated form of necrosis that is under the control of defined signal transduction pathways, it offers molecular targets for rational therapeutic intervention. Indeed, there is mounting evidence showing that many currently used anticancer agents can engage necroptotic signaling pathways and thereby elicit cell death in malignant cells. A better understanding of the signaling networks regulating necroptosis in cancer cells is expected to speed up the development of anticancer drugs for therapeutic exploitation of necroptosis for cancer therapy.