Reactive oxygen species mediate Epstein-Barr virus reactivation by N-methyl-N'-nitro-N-nitrosoguanidine

Building a Bridge Between the Mechanism of EBV Reactivation and the Treatment of EBV-Associated Cancers

Epstein-Barr virus (EBV) infection is closely associated with the development of various tumors such as lymphomas and epithelial cancers. EBV has a discrete life cycle with latency and lytic phases. In recent years, significant progress has been made in the understanding of the mechanism underlying the transition of EBV from latency to lytic replication. Multiple new lytic activation factors have been emerged and promoted our understanding of this field. In addition, we have comprehensively presented the existing therapeutic strategies and their relationship to the mechanism underlying the transition of EBV from latency to lytic replication in this review, such as lytic induction therapy and drugs to prevent EBV from entering the lytic phase fully utilize the EBV reactivation mechanisms. This year marks the 60th anniversary of the discovery of EBV, and building a bridge between the mechanism of EBV reactivation and the treatment may help us to design new approaches for treating EBV-associated diseases.

Activation of Epstein-Barr Virus' Lytic Cycle in Nasopharyngeal Carcinoma Cells by NEO212, a Conjugate of Perillyl Alcohol and Temozolomide

The Epstein-Barr virus (EBV) is accepted as a primary risk factor for certain nasopharyngeal carcinoma (NPC) subtypes, where the virus persists in a latent stage which is thought to contribute to tumorigenesis. Current treatments are sub-optimal, and recurrence occurs in many cases. An alternative therapeutic concept is aimed at triggering the lytic cycle of EBV selectively in tumor cells as a means to add clinical benefit. While compounds able to stimulate the lytic cascade have been identified, their clinical application so far has been limited. We are developing a novel anticancer molecule, NEO212, that was generated by covalent conjugation of the alkylating agent temozolomide (TMZ) to the naturally occurring monoterpene perillyl alcohol (POH). In the current study, we investigated its potential to trigger the lytic cycle of EBV in NPC cells in vitro and in vivo. We used the established C666.1 cell line and primary patient cells derived from the brain metastasis of a patient with NPC, both of which harbored latent EBV. Upon treatment with NEO212, there was an increase in EBV proteins Zta and Ea-D, key markers of the lytic cycle, along with increased levels of CCAAT/enhancer-binding protein homologous protein (CHOP), a marker of endoplasmic reticulum (ER) stress, followed by the activation of caspases. These effects could also be confirmed in tumor tissue from mice implanted with C666.1 cells. Towards a mechanistic understanding of these events, we used siRNA-mediated knockdown of CHOP and inclusion of anti-oxidant compounds. Both approaches blocked lytic cycle induction by NEO212. Therefore, we established a sequence of events, where NEO212 caused reactive oxygen species (ROS) production, which triggered ER stress and elevated the levels of CHOP, which was required to stimulate the lytic cascade of EBV. Inclusion of the antiviral agent ganciclovir synergistically enhanced the cytotoxic impact of NEO212, pointing to a potential combination treatment for EBV-positive cancers which should be explored further. Overall, our study establishes NEO212 as a novel agent able to stimulate EBV's lytic cycle in NPC tumors, with implications for other virus-associated cancers.

RE.GA.IN.: the Real-world Gastritis Initiative-updating the updates

At the end of the last century, a far-sighted 'working party' held in Sydney, Australia addressed the clinicopathological issues related to gastric inflammatory diseases. A few years later, an international conference held in Houston, Texas, USA critically updated the seminal Sydney classification. In line with these initiatives, Kyoto Global Consensus Report, flanked by the Maastricht-Florence conferences, added new clinical evidence to the gastritis clinicopathological puzzle.The most relevant topics related to the gastric inflammatory diseases have been addressed by the Real-world Gastritis Initiative (RE.GA.IN.), from disease definitions to the clinical diagnosis and prognosis. This paper reports the conclusions of the RE.GA.IN. consensus process, which culminated in Venice in November 2022 after more than 8 months of intense global scientific deliberations. A forum of gastritis scholars from five continents participated in the multidisciplinary RE.GA.IN. consensus. After lively debates on the most controversial aspects of the gastritis spectrum, the RE.GA.IN. Faculty amalgamated complementary knowledge to distil patient-centred, evidence-based statements to assist health professionals in their real-world clinical practice. The sections of this report focus on: the epidemiology of gastritis; Helicobacter pylori as dominant aetiology of environmental gastritis and as the most important determinant of the gastric oncogenetic field; the evolving knowledge on gastric autoimmunity; the clinicopathological relevance of gastric microbiota; the new diagnostic horizons of endoscopy; and the clinical priority of histologically reporting gastritis in terms of staging. The ultimate goal of RE.GA.IN. was and remains the promotion of further improvement in the clinical management of patients with gastritis.

The Application of Emodin Treatment on Nasopharyngeal Carcinoma Therapy

Nasopharyngeal carcinoma (NPC) is a malignancy prevailing in Taiwan, Hong Kong, Southern China, Southeast Asia, and North Africa. Although early-stage NPC responds well to the primary treatment of radio-chemotherapy, the mortality rate of advanced NPC remains high. Therefore, developing new therapies for nasopharyngeal carcinoma is an urgent task. Emodin is an anthraquinone derivative mainly found in Rheum palmatum. Emodin has been found to possess many anti-cancer functions against various types of cancers, but they are less discussed in the treatment of NPC. This review organized the different studies about the anti-NPC activity of emodin and discussed the potential and challenges of emodin treatment in NPC therapy.

Advancing therapeutic strategies for Epstein-Barr virus-associated malignancies through lytic reactivation

Epstein-Barr virus (EBV) is a widespread human herpes virus associated with lymphomas and epithelial cell cancers. It establishes two separate infection phases, latent and lytic, in the host. Upon infection of a new host cell, the virus activates several pathways, to induce the expression of lytic EBV antigens and the production of infectious virus particles. Although the carcinogenic role of latent EBV infection has been established, recent research suggests that lytic reactivation also plays a significant role in carcinogenesis. In this review, we summarize the mechanism of EBV reactivation and recent findings about the role of viral lytic antigens in tumor formation. In addition, we discuss the treatment of EBV-associated tumors with lytic activators and the targets that may be therapeutically effective in the future.

The Dietary Flavonol Kaempferol Inhibits Epstein-Barr Virus Reactivation in Nasopharyngeal Carcinoma Cells

Kaempferol (KP, 3,4',5,7-tetrahydroxyflavone), a dietary flavonol, has anti-cancer, antioxidant, anti-inflammatory, antimicrobial, and antimutagenic functions. However, it is unknown whether kaempferol possesses anti-Epstein-Barr virus (EBV) activity. Previously, we demonstrated that inhibition of EBV reactivation represses nasopharyngeal carcinoma (NPC) tumourigenesis, suggesting the importance of identifying EBV inhibitors. In this study, Western blotting, immunofluorescence staining, and virion detection showed that kaempferol repressed EBV lytic gene protein expression and subsequent virion production. Specifically, kaempferol was found to inhibit the promoter activities of Zta and Rta (Zp and Rp) under various conditions. A survey of the mutated Zp constructs revealed that Sp1 binding regions are critical for kaempferol inhibition. Kaempferol treatment repressed Sp1 expression and decreased the activity of the Sp1 promoter, suggesting that Sp1 expression was inhibited. In conclusion, kaempferol efficiently inhibits EBV reactivation and provides a novel choice for anti-EBV therapy and cancer prevention.

Mitochondrial protein, TBRG4, modulates KSHV and EBV reactivation from latency

Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr (EBV) are gammaherpesviruses associated with multiple human malignancies. KSHV is the etiological agent of Kaposi's Sarcoma, primary effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). EBV is associated with Burkitt's lymphoma (BL), Hodgkin's lymphoma (HL), nasopharyngeal carcinoma (NPC) and gastric carcinoma (GC). KSHV and EBV establish life-long latency in the human host with intermittent periods of lytic reactivation. Here, we identified a cellular factor named transforming growth factor-beta regulator 4 (TBRG4) that plays a role in the gammaherpesvirus lifecycle. We find that TBRG4, a protein that is localized to the mitochondria, can regulate lytic reactivation from latency of both KSHV and EBV. Knockdown of TBRG4 in cells latently infected with KSHV or EBV induced viral lytic gene transcription and replication. TBRG4 deficiency causes mitochondrial stress and increases reactive oxygen species (ROS) production. Treatment with a ROS scavenger decreased viral reactivation from latency in TBRG4-depleted cells. These data suggest that TBRG4 serves as a cellular repressor of KSHV and EBV reactivation through the regulation of ROS production.

The Human Cytomegalovirus β2.7 Long Non-Coding RNA Prevents Induction of Reactive Oxygen Species to Maintain Viral Gene Silencing during Latency

Human cytomegalovirus (HCMV) is a significant source of disease for the immunosuppressed and immunonaive. The treatment of HCMV is made more problematic by viral latency, a lifecycle stage in which the virus reduces its own gene expression and produces no infectious virus. The most highly expressed viral gene during HCMV latency is the viral β2.7 long non-coding RNA. Although we have recently shown that the β2.7 lncRNA lowers levels of reactive oxygen species (ROS) during infection in monocytes, how this impacts latency is unclear. We now show that β2.7 is important for establishing and maintaining HCMV latency by aiding the suppression of viral lytic gene expression and that this is directly related to its ability to quench reactive oxygen species (ROS). Consistent with this, we also find that exogenous inducers of ROS cause reactivation of latent HCMV. These effects can be compensated by treatment with an antioxidant to lower ROS levels. Finally, we show that ROS-mediated reactivation is independent of myeloid differentiation, but instead relies on NF-κB activation. Altogether, these results reveal a novel factor that is central to the complex process that underpins HCMV latency. These findings may be of particular relevance in the transplant setting, in which transplanted tissue/organs are subject to very high ROS levels, and HCMV reactivation poses a significant threat.

Epstein-Barr Virus Infection in Lung Cancer: Insights and Perspectives

Lung cancer (LC) is the leading cause of cancer death worldwide. Tobacco smoke is the most frequent risk factor etiologically associated with LC, although exposures to other environmental factors such as arsenic, radon or asbestos are also involved. Additionally, the involvement of some viral infections such as high-risk human papillomaviruses (HR-HPVs), Merkel cell polyomavirus (MCPyV), Jaagsiekte Sheep Retrovirus (JSRV), John Cunningham Virus (JCV), and Epstein-Barr virus (EBV) has been suggested in LC, though an etiological relationship has not yet been established. EBV is a ubiquitous gamma herpesvirus causing persistent infections and some lymphoid and epithelial tumors. Since EBV is heterogeneously detected in LCs from different parts of the world, in this review we address the epidemiological and experimental evidence of a potential role of EBV. Considering this evidence, we propose mechanisms potentially involved in EBV-associated lung carcinogenesis. Additional studies are warranted to dissect the role of EBV in this very frequent malignancy.

Cell-Type-Specific Profibrotic Scores across Multi-Organ Systems Predict Cancer Prognosis

Simple Summary

Fibrosis is a major player and contributor in the tumor microenvironment. Profibrotic changes precede the early development and establishment of a variety of human diseases, such as fibrosis and cancer. Being able to measure such early signals at the single cell level is critically useful for identifying new mechanisms and potential drug targets for a wide range of diseases. This study was designed to computationally identify profibrotic cell populations using single-cell transcriptomic data and to identify gene signatures that could predict cancer prognosis.

Abstract

Fibrosis is a major cause of mortality. Key profibrotic mechanisms are common pathways involved in tumorigenesis. Characterizing the profibrotic phenotype will help reveal the underlying mechanisms of early development and progression of a variety of human diseases, such as fibrosis and cancer. Fibroblasts have been center stage in response to various stimuli, such as viral infections. However, a comprehensive catalog of cell types involved in this process is currently lacking. Here, we deployed single-cell transcriptomic data across multi-organ systems (i.e., heart, kidney, liver, and lung) to identify novel profibrotic cell populations based on ECM pathway activity at single-cell resolution. In addition to fibroblasts, we also reported that epithelial, endothelial, myeloid, natural killer T, and secretory cells, as well as proximal convoluted tubule cells of the nephron, were significantly actively involved. Cell-type-specific gene signatures were enriched in viral infection pathways, enhanced glycolysis, and carcinogenesis, among others; they were validated using independent datasets in this study. By projecting the signatures into bulk TCGA tumor samples, we could predict prognosis in the patients using profibrotic scores. Our profibrotic cellular phenotype is useful for identifying new mechanisms and potential drug targets at the cell-type level for a wide range of diseases involved in ECM pathway activation.

ΔNp63α promotes Epstein-Barr virus latency in undifferentiated epithelial cells

Epstein-Barr virus (EBV) is a human herpesvirus that causes infectious mononucleosis and contributes to both B-cell and epithelial-cell malignancies. EBV-infected epithelial cell tumors, including nasopharyngeal carcinoma (NPC), are largely composed of latently infected cells, but the mechanism(s) maintaining viral latency are poorly understood. Expression of the EBV BZLF1 (Z) and BRLF1 (R) encoded immediate-early (IE) proteins induces lytic infection, and these IE proteins activate each other's promoters. ΔNp63α (a p53 family member) is required for proliferation and survival of basal epithelial cells and is over-expressed in NPC tumors. Here we show that ΔNp63α promotes EBV latency by inhibiting activation of the BZLF1 IE promoter (Zp). Furthermore, we find that another p63 gene splice variant, TAp63α, which is expressed in some Burkitt and diffuse large B cell lymphomas, also represses EBV lytic reactivation. We demonstrate that ΔNp63α inhibits the Z promoter indirectly by preventing the ability of other transcription factors, including the viral IE R protein and the cellular KLF4 protein, to activate Zp. Mechanistically, we show that ΔNp63α promotes viral latency in undifferentiated epithelial cells both by enhancing expression of a known Zp repressor protein, c-myc, and by decreasing cellular p38 kinase activity. Furthermore, we find that the ability of cis-platinum chemotherapy to degrade ΔNp63α contributes to the lytic-inducing effect of this agent in EBV-infected epithelial cells. Together these findings demonstrate that the loss of ΔNp63α expression, in conjunction with enhanced expression of differentiation-dependent transcription factors such as BLIMP1 and KLF4, induces lytic EBV reactivation during normal epithelial cell differentiation. Conversely, expression of ΔNp63α in undifferentiated nasopharyngeal carcinoma cells and TAp63α in Burkitt lymphoma promotes EBV latency in these malignancies.

Transcriptome-based analysis of blood samples reveals elevation of DNA damage response, neutrophil degranulation, cancer and neurodegenerative pathways in Plasmodium falciparum patients

BACKGROUND

Malaria caused by Plasmodium falciparum results in severe complications including cerebral malaria (CM) especially in children. While the majority of falciparum malaria survivors make a full recovery, there are reports of some patients ending up with neurological sequelae or cognitive deficit.

METHODS

An analysis of pooled transcriptome data of whole blood samples derived from two studies involving various P. falciparum infections, comprising mild malaria (MM), non-cerebral severe malaria (NCM) and CM was performed. Pathways and gene ontologies (GOs) elevated in the distinct P. falciparum infections were determined.

RESULTS

In all, 2876 genes were expressed in common between the 3 forms of falciparum malaria, with CM having the least number of expressed genes. In contrast to other research findings, the analysis from this study showed MM share similar biological processes with cancer and neurodegenerative diseases, NCM is associated with drug resistance and glutathione metabolism and CM is correlated with endocannabinoid signalling and non-alcoholic fatty liver disease (NAFLD). GO revealed the terms biogenesis, DNA damage response and IL-10 production in MM, down-regulation of cytoskeletal organization and amyloid-beta clearance in NCM and aberrant signalling, neutrophil degranulation and gene repression in CM. Differential gene expression analysis between CM and NCM showed the up-regulation of neutrophil activation and response to herbicides, while regulation of axon diameter was down-regulated in CM.

CONCLUSIONS

Results from this study reveal that P. falciparum-mediated inflammatory and cellular stress mechanisms may impair brain function in MM, NCM and CM. However, the neurological deficits predominantly reported in CM cases could be attributed to the down-regulation of various genes involved in cellular function through transcriptional repression, axonal dysfunction, dysregulation of signalling pathways and neurodegeneration. It is anticipated that the data from this study, might form the basis for future hypothesis-driven malaria research.

Reactive oxygen species as potential antiviral targets

Reactive oxygen species (ROS) are by-products of cellular metabolism and can be either beneficial, at low levels, or deleterious, at high levels, to the cell. It is known that several viral infections can increase oxidative stress, which is mainly facilitated by viral-induced imbalances in the antioxidant defence mechanisms of the cell. While the exact role of ROS in certain viral infections (adenovirus and dengue virus) remains unknown, other viruses can use ROS for enhancement of pathogenesis (SARS coronavirus and rabies virus) or replication (rhinovirus, West Nile virus and vesicular stomatitis virus) or both (hepatitis C virus, human immunodeficiency virus and influenza virus). While several viral proteins (mainly for hepatitis C and human immunodeficiency virus) have been identified to play a role in ROS formation, most mediators of viral ROS modulation are yet to be elucidated. Treatment of viral infections, including hepatitis C virus, human immunodeficiency virus and influenza virus, with ROS inhibitors has shown a decrease in both pathogenesis and viral replication both in vitro and in animal models. Clinical studies indicating the potential for targeting ROS-producing pathways as possible broad-spectrum antiviral targets should be evaluated in randomized controlled trials.

Targeting Epstein-Barr virus oncoprotein LMP1-mediated high oxidative stress suppresses EBV lytic reactivation and sensitizes tumors to radiation therapy

Generating oxidative stress is a critical mechanism by which host cells defend against infection by pathogenic microorganisms. Radiation resistance is a critical problem in radiotherapy against cancer. Epstein-Barr virus (EBV) is a cancer-causing virus and its reactivation plays an important role in the development of EBV-related tumors. This study aimed to explore the inner relationship and regulatory mechanism among oxidative stress, EBV reactivation, and radioresistance and to identify new molecular subtyping models and treatment strategies to improve the therapeutic effects of radiotherapy.

Methods: ROS, NADP⁺/NADPH, and GSSG/GSH were detected to evaluate the oxidative stress of cells. 8-OHdG is a reliable oxidative stress marker to evaluate the oxidative stress in patients. Its concentration in serum was detected using an ELISA method and in biopsies was detected using IHC. qPCR array was performed to evaluate the expression of essential oxidative stress genes. qPCR, Western blot, and IHC were used to measure the level of EBV reactivation in vitro and in vivo. A Rta-IgG ELISA kit and EBV DNA detection kit were used to analyze the reactivation of EBV in serum from NPC patients. NPC tumor tissue microarrays was used to investigate the prognostic role of oxidative stress and EBV reactivation. Radiation resistance was evaluated by a colony formation assay. Xenografts were treated with NAC, radiation, or a combination of NAC and radiation. EBV DNA load of tumor tissue was evaluated using an EBV DNA detection kit. Oxidative stress, EBV reactivation, and the apoptosis rate in tumor tissues were detected by using 8-OHdG, EAD, and TUNEL assays, respectively.

Results: We found that EBV can induce high oxidative stress, which promotes its reactivation and thus leads to radioresistance. Basically, EBV caused NPC cells to undergo a process of 'Redox Resetting' to acquire a new redox status with higher levels of ROS accumulation and stronger antioxidant systems by increasing the expression of the ROS-producing enzyme, NOX2, and the cellular master antioxidant regulator, Nrf2. Also, EBV encoded driving protein LMP1 promotes EBV reactivation through production of ROS. Furthermore, high oxidative stress and EBV reactivation were positively associated with poor overall survival of patients following radiation therapy and were significant related to NPC patients' recurrence and clinical stage. By decreasing oxidative stress using an FDA approved antioxidant drug, NAC, sensitivity of tumors to radiation was increased. Additionally, 8-OHdG and EBV DNA could be dual prognostic markers for NPC patients.

Conclusions: Oxidative stress mediates EBV reactivation and leads to radioresistance. Targeting oxidative stress can provide therapeutic benefits to cancer patients with radiation resistance. Clinically, we, for the first time, generated a molecular subtyping model for NPC relying on 8-OHdG and EBV DNA level. These dual markers could identify patients who are at a high risk of poor outcomes but who might benefit from the sequential therapy of reactive oxygen blockade followed by radiation therapy, which provides novel perspectives for the precise treatment of NPC.

Lytic Induction Therapy against Epstein-Barr Virus-Associated Malignancies: Past, Present, and Future

Epstein-Barr virus (EBV) lytic induction therapy is an emerging virus-targeted therapeutic approach that exploits the presence of EBV in tumor cells to confer specific killing effects against EBV-associated malignancies. Efforts have been made in the past years to uncover the mechanisms of EBV latent-lytic switch and discover different classes of chemical compounds that can reactivate the EBV lytic cycle. Despite the growing list of compounds showing potential to be used in the lytic induction therapy, only a few are being tested in clinical trials, with varying degrees of success. This review will summarize the current knowledge on EBV lytic reactivation, the major hurdles of translating the lytic induction therapy into clinical settings, and highlight some potential strategies in the future development of this therapy for EBV-related lymphoid and epithelial malignancies.

Targeting Epstein-Barr Virus in Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is consistently associated with Epstein-Barr virus (EBV) infection in regions in which it is endemic, including Southern China and Southeast Asia. The high mortality rates of NPC patients with advanced and recurrent disease highlight the urgent need for effective treatments. While recent genomic studies have revealed few druggable targets, the unique interaction between the EBV infection and host cells in NPC strongly implies that targeting EBV may be an efficient approach to cure this virus-associated cancer. Key features of EBV-associated NPC are the persistence of an episomal EBV genome and the requirement for multiple viral latent gene products to enable malignant transformation. Many translational studies have been conducted to exploit these unique features to develop pharmaceutical agents and therapeutic strategies that target EBV latent proteins and induce lytic reactivation in NPC. In particular, inhibitors of the EBV latent protein EBNA1 have been intensively explored, because of this protein's essential roles in maintaining EBV latency and viral genome replication in NPC cells. In addition, recent advances in chemical bioengineering are driving the development of therapeutic agents targeting the critical functional regions of EBNA1. Promising therapeutic effects of the resulting EBNA1-specific inhibitors have been shown in EBV-positive NPC tumors. The efficacy of multiple classes of EBV lytic inducers for NPC cytolytic therapy has also been long investigated. However, the lytic-induction efficiency of these compounds varies among different EBV-positive NPC models in a cell-context-dependent manner. In each tumor, NPC cells can evolve and acquire somatic changes to maintain EBV latency during cancer progression. Unfortunately, the poor understanding of the cellular mechanisms regulating EBV latency-to-lytic switching in NPC cells limits the clinical application of EBV cytolytic treatment. In this review, we discuss the potential approaches for improvement of the above-mentioned EBV-targeting strategies.

Total Antioxidant Status (TAS), Superoxide Dismutase (SOD), and Glutathione Peroxidase (GPx) in Oropharyngeal Cancer Associated with EBV Infection

A growing number of studies reveal that oxidative stress is associated with viral infections or cancer development. However, there are few reports assessing the relationships between oxidative stress, viral infection, and carcinogenesis. The present study analyzed the level of total antioxidant status (TAS) as well as the activities of glutathione peroxidase (GPx) and superoxide dismutase (SOD) in patients with oropharyngeal cancer both Epstein-Barr virus (EBV)-positive and EBV-negative in comparison with the control group. The correlations between these parameters and EBV type (wild-type LMP1 (wt-LMP1) or LMP1 with deletion (del-LMP1)), level of antibodies against EBV, the degree of tumor differentiation, and TNM classification were also investigated. Fresh frozen tumor tissue samples collected from 66 patients with oropharyngeal squamous cell carcinoma were tested using nested PCR assay for EBV DNA detection. Spectrophotometric methods were used to measure TAS values as well as SOD and GPx activities in homogenates of tissue, using diagnostic kits produced by Randox Laboratories. Sera from all individuals were investigated using ELISA method to detect the presence of Epstein-Barr virus capsid antigen (EBVCA) IgM and IgG, Epstein-Barr virus nuclear antigen (EBNA) IgG, and early antigen (EA) IgG antibodies. The level of TAS and activities of antioxidant enzymes (GPx and SOD) were significantly decreased in tissues with oropharyngeal cancer, particularly in EBV-positive cases. In 82.3% of patients, wt-LMP1 was detected. Significantly lower TAS, GPx, and SOD values were stated in patients infected with wild-type EBV. The presence of antibodies against early antigen (anti-EA) was detected in over 80% of patients, which suggests reactivation of EBV infection. The correlation between the degree of tumor differentiation and TN classification, especially in EBV-positive patients, was also observed. Determination of these parameters may be useful in evaluating tumor burden in patients with various stages of oropharyngeal cancer and could be an important prognostic factor. Future studies are needed to understand the role of EBV lytic reactivation induced by oxidative stress.

Down-regulation of intracellular reactive oxygen species attenuates P-glycoprotein-associated chemoresistance in Epstein-Barr virus-positive NK/T-cell lymphoma

Epstein-Barr virus (EBV)-positive extranodal NK/T-cell lymphoma is a rare and highly aggressive disease with a poor prognosis and strong resistance to anti-cancer drugs. Reactive oxygen species (ROS) are closely related to tumorigenesis and P-glycoprotein (P-gp) is highly expressed in various cancers. However, the exact relationship between ROS and P-gp in EBV-positive lymphoma remains unclear. In this study, we demonstrated that EBV latent infection induced intracellular ROS production and increased ROS levels triggered elevated P-gp expression, which resulted in strong resistance to existing anti-cancer drugs in EBV-positive lymphoma cell lines and in patients' tissue samples. We also verified that regulation of intracellular ROS reduced P-gp expression and function via inhibition of STAT1 phosphorylation. These results indicate that treatment with a ROS scavenger is a potential therapeutic strategy to overcome resistance to anti-cancer drugs by downregulating the expression of P-gp in EBV-positive NK/T-cell lymphoma.

Viral-Targeted Strategies Against EBV-Associated Lymphoproliferative Diseases

Epstein-Barr virus (EBV) is strongly associated with a spectrum of EBV-associated lymphoproliferative diseases (EBV-LPDs) ranging from post-transplant lymphoproliferative disorder, B cell lymphomas (e.g., endemic Burkitt lymphoma, Hodgkin lymphoma, and diffuse large B cell lymphoma) to NK or T cell lymphoma (e.g., nasal NK/T-cell lymphoma). The virus expresses a number of latent viral proteins which are able to manipulate cell cycle and cell death processes to promote survival of the tumor cells. Several FDA-approved drugs or novel compounds have been shown to induce killing of some of the EBV-LPDs by inhibiting the function of latent viral proteins or activating the viral lytic cycle from latency. Here, we aim to provide an overview on the mechanisms by which EBV employs to drive the pathogenesis of various EBV-LPDs and to maintain the survival of the tumor cells followed by a discussion on the development of viral-targeted strategies based on the understanding of the patho-mechanisms.

Perspective: Contribution of Epstein-Barr virus (EBV) Reactivation to the Carcinogenicity of Nasopharyngeal Cancer Cells

Nasopharyngeal carcinoma (NPC) is a squamous cell carcinoma derived from the epithelium of the post-nasal cavity, with a unique geographic and ethnic distribution. Epstein–Barr virus (EBV) is an etiological agent of NPC, but how it contributes to carcinogenesis is not completely clear. Although it is thought that EBV latency participates in the development of NPC, increasing evidence reveals that the lytic cycle also plays an important role in the carcinogenic process. In this review, we summarize our recent studies on how EBV reactivation causes genomic instability and accelerates tumorigenesis in epithelial cells. The roles of three lytic genes, namely, BRLF1, BGLF5 and BALF3, in this process are also introduced. Moreover, blocking EBV reactivation using natural compounds may help delay the progression of NPC tumorigenesis. These studies provide a new insight into NPC carcinogenesis and raise the possibility that inhibition of EBV reactivation may be a novel approach to prevent the relapse of NPC.

Perspectives of Phage-Eukaryotic Cell Interactions to Control Epstein-Barr Virus Infections

Recently, leading medical journals emphasized the importance of further studies on the potential application of bacterial viruses (phages) for the treatment of antibiotics-resistant infections outlining the present status of the therapy and perspectives for the future. Furthermore, a leading scientific journal pointed to the recent progress in research on phage interactions with eukaryotic cells (especially cells of the immune system) and potential implications of their results for our broader understanding of the role of phages – not only as “bacteria eaters” – but also as an important part of our body defense protecting against external and internal pathogenic invaders (as suggested previously). This illustrates how our understanding of the actual role and potential of phages is expanding and how worldwide interest in their use in medicine is growing. In this article we envision how this advancement of our knowledge about phages could be translated into the progress in combating herpesvirus infections especially those caused by Epstein–Barr virus (EBV).

Rapamycin enhances lytic replication of Epstein-Barr virus in gastric carcinoma cells by increasing the transcriptional activities of immediate-early lytic promoters

Epstein-Barr virus (EBV), a human herpesvirus, is linked to both epithelial and lymphoid malignancies. Induction of EBV reactivation is a potential therapeutic strategy for EBV-associated tumors. In this study, we assessed the effects of rapamycin on EBV reactivation in gastric carcinoma cells. We found that rapamycin upregulated expression of EBV lytic proteins and increased the viral proliferation triggered by the EBV lytic inducer sodium butyrate. Reverse transcription-qPCR, luciferase activity assays, chromatin immunoprecipitation and western blotting were employed to explore the mechanism by which rapamycin promotes EBV reactivation. Our results showed that rapamycin treatment resulted in increased mRNA levels of EBV immediate-early genes. Rapamycin also enhanced the transcriptional activities of the EBV immediate-early lytic promoters Zp and Rp by strengthening Sp1 binding. Repression of the cellular ataxia telangiectasia-mutated/p53 pathway by siRNA-mediated knockdown of the ataxia telangiectasia-mutated gene significantly abrogated virus reactivation by rapamycin/sodium butyrate treatment, indicating that the ataxia telangiectasia-mutated/p53 pathway is involved in rapamycin-promoted EBV reactivation. Taken together, these findings demonstrate that rapamycin might have the potential to enhance the effectiveness of oncolytic viral therapies developed for EBV-associated malignancies.

Glutaredoxin 3 promotes nasopharyngeal carcinoma growth and metastasis via EGFR/Akt pathway and independent of ROS

Glutaredoxin 3 (GLRX3) is antioxidant enzyme, maintaining a low level of ROS, thus contributing to the survival and metastasis of several types of cancer. However, the expression and functions of GLRX3 have not been addressed in nasopharyngeal carcinoma (NPC). In this study, we found that GLRX3 was overexpressed in NPC. Knockdown of GLRX3 in NPC cell lines inhibited proliferation in vitro, tumorignesis in vivo, and colony formation. In addition, GLRX3 knockdown decreased the migration and invasion capacity of NPC cells by reversing the epithelial-mesenchymal transition (EMT). Furthermore, stabilization of GLRX3 was positively related to with epidermal growth factor receptor (EGFR) expression and negatively with ROS generation. Phosphorylation of Akt, a key downstream effector, was induced by EGFR signaling but did not rely on increasing ROS level in NPC cells. GLRX3 might be an oncoprotein in NPC, playing important roles in increasing redox reaction and activating EGFR/ Akt signals, so it may be a therapeutic target for NPC.

Therapeutic Strategies against Epstein-Barr Virus-Associated Cancers Using Proteasome Inhibitors

Epstein-Barr virus (EBV) is closely associated with several lymphomas (endemic Burkitt lymphoma, Hodgkin lymphoma and nasal NK/T-cell lymphoma) and epithelial cancers (nasopharyngeal carcinoma and gastric carcinoma). To maintain its persistence in the host cells, the virus manipulates the ubiquitin-proteasome system to regulate viral lytic reactivation, modify cell cycle checkpoints, prevent apoptosis and evade immune surveillance. In this review, we aim to provide an overview of the mechanisms by which the virus manipulates the ubiquitin-proteasome system in EBV-associated lymphoid and epithelial malignancies, to evaluate the efficacy of proteasome inhibitors on the treatment of these cancers and discuss potential novel viral-targeted treatment strategies against the EBV-associated cancers.

Inactivation of HMGCL promotes proliferation and metastasis of nasopharyngeal carcinoma by suppressing oxidative stress

Altered metabolism is considered as a hallmark of cancer. Here we investigated expression of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) 2 lyase (HMGCL), an essential enzyme in ketogenesis, which produces ketone bodies by the breakdown of fatty acids to supply energy, in nasopharyngeal carcinoma (NPC). The expression of HMGCL was silenced in NPC tissue. Downregulation of HMGCL in NPC was associated with low intracellular β-hydroxybutyrate (β-HB) production, thereby reducing reactive oxygen species (ROS) generation. Ectopic expression of HMGCL restored β-HB level, associated with suppressed proliferation and colony formation of NPC cells in vitro and decreased tumorigenicity in vivo. HMGCL suppressed the migration and invasion of NPC cells in vitro via mesenchymal-epithelial transition. Furthermore, extracellular β-HB supply suppressed the proliferation and migration of NPC cells. Both intra- and extracellular β-HB exerting a suppressive role in NPC depends on ROS generation. Ketogenesis may be impaired in NPC cells due to lack of HMGCL expression, suggesting that it may be a promising target in NPC therapy.

Epstein-Barr Virus Rta-Mediated Accumulation of DNA Methylation Interferes with CTCF Binding in both Host and Viral Genomes

Rta, an Epstein-Barr virus (EBV) immediate-early protein, reactivates viral lytic replication that is closely associated with tumorigenesis. In previous studies, we demonstrated that in epithelial cells Rta efficiently induced cellular senescence, which is an irreversible G₁ arrest likely to provide a favorable environment for productive replications of EBV and Kaposi's sarcoma-associated herpesvirus (KSHV). To restrict progression of the cell cycle, Rta simultaneously upregulates CDK inhibitors and downregulates MYC, CCND1, and JUN, among others. Rta has long been known as a potent transcriptional activator, thus its role in gene repression is unexpected. In silico analysis revealed that the promoter regions of MYC, CCND1, and JUN are common in (i) the presence of CpG islands, (ii) strong chromatin immunoprecipitation (ChIP) signals of CCCTC-binding factor (CTCF), and (iii) having at least one Rta binding site. By combining ChIP assays and DNA methylation analysis, here we provide evidence showing that Rta binding accumulated CpG methylation and decreased CTCF occupancy in the regulatory regions of MYC, CCND1, and JUN, which were associated with downregulated gene expression. Stable residence of CTCF in the viral latency and reactivation control regions is a hallmark of viral latency. Here, we observed that Rta-mediated decreased binding of CTCF in the viral genome is concurrent with virus reactivation. Via interfering with CTCF binding, in the host genome Rta can function as a transcriptional repressor for gene silencing, while in the viral genome Rta acts as an activator for lytic gene loci by removing a topological constraint established by CTCF.IMPORTANCE CTCF is a multifunctional protein that variously participates in gene expression and higher-order chromatin structure of the cellular and viral genomes. In certain loci of the genome, CTCF occupancy and DNA methylation are mutually exclusive. Here, we demonstrate that the Epstein-Barr virus (EBV) immediate-early protein, Rta, known to be a transcriptional activator, can also function as a transcriptional repressor. Via enriching CpG methylation and decreasing CTCF reloading, Rta binding efficiently shut down the expression of MYC, CCND1, and JUN, thus impeding cell cycle progression. Rta-mediated disruption of CTCF binding was also detected in the latency/reactivation control regions of the EBV genome, and this in turn led to viral lytic cycle progression. As emerging evidence indicates that a methylated EBV genome is a preferable substrate for EBV Zta, the other immediate-early protein, our results suggest a mechanistic link in understanding the molecular processes of viral latent-lytic switch.

DNA Oncogenic Virus-Induced Oxidative Stress, Genomic Damage, and Aberrant Epigenetic Alterations

Approximately 20% of human cancers is attributable to DNA oncogenic viruses such as human papillomavirus (HPV), hepatitis B virus (HBV), and Epstein-Barr virus (EBV). Unrepaired DNA damage is the most common and overlapping feature of these DNA oncogenic viruses and a source of genomic instability and tumour development. Sustained DNA damage results from unceasing production of reactive oxygen species and activation of inflammasome cascades that trigger genomic changes and increased propensity of epigenetic alterations. Accumulation of epigenetic alterations may interfere with genome-wide cellular signalling machineries and promote malignant transformation leading to cancer development. Untangling and understanding the underlying mechanisms that promote these detrimental effects remain the major objectives for ongoing research and hope for effective virus-induced cancer therapy. Here, we review current literature with an emphasis on how DNA damage influences HPV, HVB, and EBV replication and epigenetic alterations that are associated with carcinogenesis.

Combination of betulinic acid and chidamide synergistically inhibits Epstein-Barr virus replication through over-generation of reactive oxygen species

Epstein-Barr virus (EBV) has widely infected more than 90% of human populations. Currently, there is no efficient way to remove the virus because the EBV carriers are usually in a latent stage that allows them to escape the immune system and common antiviral drugs. In the effort to develop an efficient strategy for the removal of the EBV virus, we have shown that betulinic acid (BA) slightly suppresses EBV replication through SOD2 suppression with subsequent reactive oxygen species (ROS) generation and DNA damage in EBV-transformed LCL (lymphoblastoid cell line) cells. Chidamide (CDM, CS055), a novel histone deacetylase inhibitor (HDACi), could significantly switch EBV from the latent stage to the lytic stage with increased gene expression of BZLF1 and BMRF1, but has a small effect on EBV replication due to the suppression effect of CDM-mediated ROS generation. Interestingly, a combination of BA and CDM synergistically inhibits EBV replication with ROS over-generation and subsequent DNA damage and apoptosis. Overexpression of SOD2 diminishes this effect, while SOD2 knockdown mimics this effect. An in vivo xenograft tumor development study with the tail vein injection of EBV-transformed LCL cells in nude mice proves that the combination of BA and CDM synergistically increases superoxide anion release in tumor tissues and suppresses EBV replication and tumor growth, and significantly prolongs mouse survival. We conclude that the combination of BA and CDM could be an efficient strategy for clinical EBV removal.

Effect of mitochondrially targeted carboxy proxyl nitroxide on Akt-mediated survival in Daudi cells: Significance of a dual mode of action

Vicious cycles of mutations and reactive oxygen species (ROS) generation contribute to cancer progression. The use of antioxidants to inhibit ROS generation promotes cytostasis by affecting the mutation cycle and ROS-dependent survival signaling. However, cancer cells select mutations to elevate ROS albeit maintaining mitochondrial hyperpolarization (Δψm), even under hypoxia. From this perspective, the use of drugs that disrupt both ROS generation and Δψm is a viable anticancer strategy. Hence, we studied the effects of mitochondrially targeted carboxy proxyl nitroxide (Mito-CP) and a control ten carbon TPP moiety (Dec-TPP⁺) in the human Burkitt lymphoma cell line (Daudi) and normal peripheral blood mononuclear cells under hypoxia and normoxia. We found preferential localization, Δψm and adenosine triphosphate loss, and significant cytotoxicity by Mito-CP in Daudi cells alone. Interestingly, ROS levels were decreased and maintained in hypoxic and normoxic cancer cells, respectively, by Mito-CP but not Dec-TPP⁺, therefore preventing any adaptive signaling. Moreover, dual effects on mitochondrial bioenergetics and ROS by Mito-CP curtailed the cancer survival via Akt inhibition, AMPK-HIF-1α activation and promoted apoptosis via increased BCL2-associated X protein and poly (ADP-ribose) polymerase expression. This dual mode of action by Mito-CP provides a better explanation of the application of antioxidants with specific relevance to cancerous transformation and adaptations in the Daudi cell line.

Roles of reactive oxygen species in cell signaling pathways and immune responses to viral infections

Several biological processes as well as infectious agents, physiological or environmental stress, and perturbed antioxidant response can promote oxidative stress. Oxidative stress usually happens when cells are exposed to more electrically charged reactive oxygen species (ROS) such as H₂O₂ or O₂^-. ROS are well known for being both beneficial and deleterious. Recent studies have indicated that ROS are deleterious to cells, leading to programmed cell death (PCD) at high concentrations. At low concentrations, however, ROS can act as signaling molecules in a variety of cellular processes. In this review, we present an update of our current understanding of the role and regulation of reactive oxygen species in various viral infections, cellular signaling pathways and immune responses. We then discuss how the antioxidant defense system acts as an antiviral effector to limit cell damage.

Epstein-Barr virus lytic reactivation regulation and its pathogenic role in carcinogenesis

Epstein-Barr virus (EBV) has been associated with several types of human cancers. In the host, EBV can establish two alternative modes of life cycle, known as latent or lytic and the switch from latency to the lytic cycle is known as EBV reactivation. Although EBV in cancer cells is found mostly in latency, a small number of lytically-infected cells promote carcinogenesis through the release of growth factors and oncogenic cytokines. This review focuses on the mechanisms by which EBV reactivation is controlled by cellular and viral factors, and discusses how EBV lytic infection contributes to human malignancies.

Anti-Helicobacter pylori Antibody Profiles in Epstein-Barr virus (EBV)-Positive and EBV-Negative Gastric Cancer

BACKGROUND

Helicobacter pylori is the primary cause of gastric cancer, but about 9% of cases harbor Epstein-Barr virus (EBV) in the tumor cells. There is limited evidence on the possible interaction or antagonism between these infectious agents in gastric carcinogenesis.

METHODS

We compared H. pylori serologic profiles of EBV-positive (n = 58) and EBV-negative (n = 111) noncardia gastric cancer patients from the United States National Cancer Institute's International EBV-Gastric Cancer Consortium. EBV positivity of tumors was assessed by in situ hybridization. Serum levels of 15 antibodies to immunogenic proteins of H. pylori (Cad, CagA, Cagδ, CagM, Catalase, GroEL, HcpC, HP0231, HP0305, HpaA, HyuA, NapA, Omp, UreA, VacA) were assessed using bead-based multiplex serology. Logistic regression models were used to adjust odds ratios (OR) for country, age, sex, and year of diagnosis.

RESULTS

Seropositivity to individual proteins ranged up to 90% overall. Antibodies to Catalase were borderline associated with tumor EBV positivity (adjusted OR = 3.15, p = .0024, Bonferroni corrected p = .036). Distributions of other antibodies did not vary by tumor EBV status.

CONCLUSION

Similarity of host-response indicates the essential etiological role of H. pylori in EBV-positive gastric cancer.

Identification of Novel Small Organic Compounds with Diverse Structures for the Induction of Epstein-Barr Virus (EBV) Lytic Cycle in EBV-Positive Epithelial Malignancies

Phorbol esters, which are protein kinase C (PKC) activators, and histone deacetylase (HDAC) inhibitors, which cause enhanced acetylation of cellular proteins, are the main classes of chemical inducers of Epstein-Barr virus (EBV) lytic cycle in latently EBV-infected cells acting through the PKC pathway. Chemical inducers which induce EBV lytic cycle through alternative cellular pathways may aid in defining the mechanisms leading to lytic cycle reactivation and improve cells' responsiveness towards lytic induction. We performed a phenotypic screening on a chemical library of 50,240 novel small organic compounds to identify novel class(es) of strong inducer(s) of EBV lytic cycle in gastric carcinoma (GC) and nasopharyngeal carcinoma (NPC) cells. Five hit compounds were selected after three successive rounds of increasingly stringent screening. All five compounds are structurally diverse from each other and distinct from phorbol esters or HDAC inhibitors. They neither cause hyperacetylation of histone proteins nor significant PKC activation at their working concentrations, suggesting that their biological mode of action are distinct from that of the known chemical inducers. Two of the five compounds with rapid lytic-inducing action were further studied for their mechanisms of induction of EBV lytic cycle. Unlike HDAC inhibitors, lytic induction by both compounds was not inhibited by rottlerin, a specific inhibitor of PKCδ. Interestingly, both compounds could cooperate with HDAC inhibitors to enhance EBV lytic cycle induction in EBV-positive epithelial cancer cells, paving way for the development of strategies to increase cells' responsiveness towards lytic reactivation. One of the two compounds bears structural resemblance to iron chelators and the other strongly activates the MAPK pathways. These structurally diverse novel organic compounds may represent potential new classes of chemicals that can be used to investigate any alternative mechanism(s) leading to EBV lytic cycle reactivation from latency.

Combinative effects of β-Lapachone and APO866 on pancreatic cancer cell death through reactive oxygen species production and PARP-1 activation

Pancreatic cancer (PC) is one of the most lethal human malignancies and a major health problem. Patients diagnosed with PC and treated with conventional approaches have an overall 5-year survival rate of less than 5%. Novel strategies are needed to treat this disease. Herein, we propose a combinatorial strategy that targets two unrelated metabolic enzymes overexpressed in PC cells:

NAD(P)H

quinone oxidoreductase-1 (NQO1) and nicotinamide phosphoribosyl transferase (NAMPT) using β-lapachone (BL) and APO866, respectively. We show that BL tremendously enhances the antitumor activity of APO866 on various PC cell lines without affecting normal cells, in a PARP-1 dependent manner. The chemopotentiation of APO866 with BL was characterized by the following: (i) nicotinamide adenine dinucleotide (NAD) depletion; (ii) catalase (CAT) degradation; (iii) excessive H2O2 production; (iv) dramatic drop of mitochondrial membrane potential (MMP); and finally (v) autophagic-associated cell death. H2O2 production, loss of MMP and cell death (but not NAD depletion) were abrogated by exogenous supplementation with CAT or pharmacological or genetic inhibition of PARP-1. Our data demonstrates that the combination of a non-lethal dose of BL and low dose of APO866 optimizes significantly cell death on various PC lines over both compounds given separately and open new and promising combination in PC therapy.

EGCG inhibits proliferation, invasiveness and tumor growth by up-regulation of adhesion molecules, suppression of gelatinases activity, and induction of apoptosis in nasopharyngeal carcinoma cells

(-)-Epigallocatechin-3-gallate (EGCG), a major green tea polyphenol, has been shown to inhibit the proliferation of a variety of tumor cells. Epidemiological studies have shown that drinking green tea can reduce the incidence of nasopharyngeal carcinoma (NPC), yet the underlying mechanism is not well understood. In this study, the inhibitory effect of EGCG was tested on a set of Epstein Barr virus-negative and -positive NPC cell lines. Treatment with EGCG inhibited the proliferation of NPC cells but did not affect the growth of a non-malignant nasopharyngeal cell line, NP460hTert. Moreover, EGCG treated cells had reduced migration and invasive properties. The expression of the cell adhesion molecules E-cadherin and β-catenin was found to be up-regulated by EGCG treatment, while the down-regulation of matrix metalloproteinases (MMP)-2 and MMP-9 were found to be mediated by suppression of extracellular signal-regulated kinase (ERK) phosphorylation and AP-1 and Sp1 transactivation. Spheroid formation by NPC cells in suspension was significantly inhibited by EGCG. Oral administration of EGCG was capable of suppressing tumor growth in xenografted mice bearing NPC tumors. Treatment with EGCG was found to elevate the expression of p53 and p21, and eventually led to apoptosis of NPC cells via caspase 3 activation. The nuclear translocation of NF-κB and β-catenin was also suppressed by EGCG treatment. These results indicate that EGCG can inhibit the proliferation and invasiveness, and induce apoptosis, of NPC cells, making it a promising agent for chemoprevention or adjuvant therapy of NPC.