Suberoylanilide hydroxamic acid induces viral lytic cycle in Epstein-Barr virus-positive epithelial malignancies and mediates enhanced cell death

Exploring the anti-EBV potential of suberoylanilide hydroxamic acid: Induction of apoptosis in infected cells through suppressing BART gene expression and inducing lytic infection

Epstein-Barr virus (EBV) is linked to lymphoma and epithelioma but lacks drugs specifically targeting EBV-positive tumors. BamHI A Rightward Transcript (BART) miRNAs are expressed in all EBV-positive tumors, suppressing both lytic infection and host cell apoptosis. We identified suberoylanilide hydroxamic acid (SAHA), an inhibitor of histone deacetylase enzymes, as an agent that suppresses BART promoter activity and transcription of BART miRNAs. SAHA treatment demonstrated a more pronounced inhibition of cell proliferation in EBV-positive cells compared to EBV-negative cells, affecting both p53 wild-type and mutant gastric epithelial cells. SAHA treatment enhanced lytic infection in wild-type EBV-infected cells, while also enhancing cell death in BZLF1-deficient EBV-infected cells. It reduced BART gene expression by 85% and increased the expression of proapoptotic factors targeted by BART miRNAs. These findings suggest that SAHA not only induces lytic infection but also leads to cell death by suppressing BART miRNA transcription and promoting the apoptotic program.

Treatment of Epstein-Barr Virus infection in immunocompromised patients

Epstein-Barr Virus (EBV), is a ubiquitous γ-Herpesvirus that infects over 95% of the human population and can establish a life-long infection without causing any clinical symptoms in healthy individuals by residing in memory B-cells. Primary infection occurs in childhood and is mostly asymptomatic, however in some young adults it can result in infectious mononucleosis (IM). In immunocompromised individuals however, EBV infection has been associated with many different malignancies. Since EBV can infect both epithelial and B-cells and very rarely NK cells and T-cells, it is associated with both epithelial cancers like nasopharyngeal carcinoma (NPC) and gastric carcinoma (GC), with lymphomas including Burkitt Lymphoma (BL) or Post-transplant Lymphoproliferative Disorder (PTLD) and rarely with NK/T-cell lymphomas. Currently there are no approved antivirals active in PTLD nor in any other malignancy. Moreover, lytic phase disease almost never requires antiviral treatment. Although many novel therapies against EBV have been described, the management and/or prevention of EBV primary infections or reactivations remains difficult. In this review, we discuss EBV infection, therapies targeting EBV in both lytic and latent state with novel therapeutics developed that show anti-EBV activity as well as EBV-associated malignancies both, epithelial and lymphoproliferative malignancies and emerging therapies targeting the EBV-infected cells.

Chidamide Induces Epstein-Barr Virus (EBV) Lytic Infection and Acts Synergistically with Tenofovir to Eliminate EBV-Positive Burkitt Lymphoma

Epstein-Barr virus (EBV) is a type of human γ-herpesvirus, and its reactivation plays an important role in the development of EBV-driven Burkitt lymphoma (BL). Despite intensive chemotherapy, the prognosis of relapsed/refractory BL patients remains unfavorable, and a definitive method to completely eliminate latent EBV infection is lacking. Previous studies have demonstrated that histone deacetylase (HDAC) inhibitors can induce the transition of EBV from latency to the lytic phase. The lytic activation of EBV can be inhibited by tenofovir, a potent inhibitor of DNA replication. Herein, we explored the antitumor effect and EBV clearance potential of a novel HDAC inhibitor called chidamide, combined with tenofovir, in the treatment of EBV-positive BL. In the study, chidamide exhibited inhibitory activity against HDAC. Moreover, chidamide inhibited BL cell proliferation, arrested cell cycle progression, and induced BL cell apoptosis primarily by regulating the MAPK pathways. Additionally, chidamide promoted the transcription of lytic genes, including BZLF1, BMRF1, and BMLF1 Compared with chidamide alone, the addition of tenofovir further induced growth arrest and apoptosis in EBV-positive BL cells and inhibited the transcriptions of EBV lytic genes induced by chidamide alone. Furthermore, our in vivo data demonstrated that the combination of chidamide and tenofovir had superior tumor-suppressive effects in a mouse model of BL cell tumors. The aforementioned findings confirm the synergistic effect of chidamide combined with tenofovir in inducing growth inhibition and apoptosis in EBV-positive BL cells and provide an effective strategy for eliminating EBV and EBV-associated malignancies. SIGNIFICANCE STATEMENT: High levels of Epstein-Barr virus (EBV)-DNA have consistently been associated with unfavorable progression-free survival and overall survival in EBV-associated lymphomas. Therefore, identifying novel strategies to effectively eradicate tumor cells and eliminate EBV is crucial for lymphoma patients. This study confirmed, for the first time, the synergistic effect of chidamide combined with tenofovir in the treatment of Burkitt lymphoma and the eradication of EBV virus.

Histone Deacetylase Functions in Gastric Cancer: Therapeutic Target?

Gastric cancer (GC) is one of the most aggressive cancers. Therapeutic treatments are based on surgery combined with chemotherapy using a combination of platinum-based agents. However, at metastatic stages of the disease, survival is extremely low due to late diagnosis and resistance mechanisms to chemotherapies. The development of new classifications has not yet identified new prognostic markers for clinical use. The studies of epigenetic processes highlighted the implication of histone acetylation status, regulated by histone acetyltransferases (HATs) and by histone deacetylases (HDACs), in cancer development. In this way, inhibitors of HDACs (HDACis) have been developed and some of them have already been clinically approved to treat T-cell lymphoma and multiple myeloma. In this review, we summarize the regulations and functions of eighteen HDACs in GC, describing their known targets, involved cellular processes, associated clinicopathological features, and impact on survival of patients. Additionally, we resume the in vitro, pre-clinical, and clinical trials of four HDACis approved by Food and Drug Administration (FDA) in cancers in the context of GC.

Integration Profiling Between Plasma Lipidomics, Epstein–Barr Virus and Clinical Phenomes in Nasopharyngeal Carcinoma Patients

Plasma lipidomics has been commonly used for biomarker discovery. Studies in cancer have suggested a significant alteration of circulating metabolite profiles which is correlated with cancer characteristics and treatment outcome. However, the lipidomics characteristics of nasopharyngeal carcinoma (NPC) have rarely been studied. We previously described the phenomenon of lipid droplet accumulation in NPC cells and showed that such accumulation could be regulated by latent infection of Epstein–Barr virus (EBV). Here, we compared the plasma lipidome of NPC patients to that of healthy controls by liquid chromatography-tandem mass spectrometry (LC–MS/MS). We found 19 lipids (e.g., phosphatidylinositols 18:0/20:4 and 18:0/18:2 and free fatty acid 22:6) to be remarkably decreased, whereas 2 lipids (i.e., diacylglycerols 16:0/16:1 and 16:0/20:3) to be increased, in the plasma of NPC patients, compared with controls. Different lipid profiles were also observed between patients with different titers of EBV antibodies (e.g., EA-IgA and VCA-IgA) as well as between patients with and without lymph node or distant organ metastasis. In conclusion, plasma lipidomics might help to differentiate NPC cases from controls, whereas EBV infection might influence the risk and prognosis of NPC through modulating lipid metabolism in both tumor cells and peripheral blood.

Treatment Advances in EBV Related Lymphoproliferative Diseases

Epstein Barr virus (EBV) can affect 90% of the human population. It can invade B lymphocytes, T lymphocytes and natural killer cells of the host and remain in the host for life. The long latency and reactivation of EBV can cause malignant transformation, leading to various lymphoproliferative diseases (LPDs), including EBV-related B-cell lymphoproliferative diseases (EBV-B-LPDs) (for example, Burkitt lymphoma (BL), classic Hodgkin's lymphoma (cHL), and posttransplantation and HIV-related lymphoproliferative diseases) and EBV-related T-cell lymphoproliferative diseases (EBV-T/NK-LPDs) (for example, extranodal nasal type natural killer/T-cell lymphoma (ENKTCL), aggressive NK cell leukaemia (ANKL), and peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS). EBV-LPDs are heterogeneous with different clinical features and prognoses. The treatment of EBV-LPDs is usually similar to that of EBV-negative lymphoma with the same histology and can include chemotherapy, radiotherapy, and hematopoietic stem cell transplant (HSCT). However, problems such as serious toxicity and drug resistance worsen the survival prognosis of patients. EBV expresses a variety of viral and lytic proteins that regulate cell cycle and death processes and promote the survival of tumour cells. Based on these characteristics, a series of treatment strategies for EBV in related malignant tumours have been developed, such as monoclonal antibodies, immune checkpoint inhibitors, cytotoxic T lymphocytes (CTLs) and epigenetic therapy. These new individualized therapies can produce highly specific killing effects on tumour cells, and nontumour cells can be protected from toxicity. This paper will focus on the latest progress in the treatment of EBV-LPDs based on pathological mechanisms.

EBV-associated diseases: Current therapeutics and emerging technologies

EBV is a prevalent virus, infecting >90% of the world's population. This is an oncogenic virus that causes ~200,000 cancer-related deaths annually. It is, in addition, a significant contributor to the burden of autoimmune diseases. Thus, EBV represents a significant public health burden. Upon infection, EBV remains dormant in host cells for long periods of time. However, the presence or episodic reactivation of the virus increases the risk of transforming healthy cells to malignant cells that routinely escape host immune surveillance or of producing pathogenic autoantibodies. Cancers caused by EBV display distinct molecular behaviors compared to those of the same tissue type that are not caused by EBV, presenting opportunities for targeted treatments. Despite some encouraging results from exploration of vaccines, antiviral agents and immune- and cell-based treatments, the efficacy and safety of most therapeutics remain unclear. Here, we provide an up-to-date review focusing on underlying immune and environmental mechanisms, current therapeutics and vaccines, animal models and emerging technologies to study EBV-associated diseases that may help provide insights for the development of novel effective treatments.

Advances in pathogenesis and precision medicine for nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a squamous carcinoma with apparent geographical and racial distribution, mostly prevalent in East and Southeast Asia, particularly concentrated in southern China. The epidemiological trend over the past decades has suggested a substantial reduction in the incidence rate and mortality rate due to NPC. These results may reflect changes in lifestyle and environment, and more importantly, a deeper comprehension of the pathogenic mechanism of NPC, leading to much progress in the preventing, screening, and treating for this cancer. Herein, we present the recent advances on the key signal pathways involved in pathogenesis of NPC, the mechanism of Epstein‐Barr virus (EBV) entry into the cell, and the progress of EBV vaccine and screening biomarkers. We will also discuss in depth the development of various therapeutic approaches including radiotherapy, chemotherapy, surgery, targeted therapy, and immunotherapy. These research advancements have led to a new era of precision medicine in NPC.

SNHG8 Promotes the Progression of Epstein-Barr Virus-Associated Gastric Cancer via Sponging miR-512-5p and Targeting TRIM28

SNHG8, a family member of small nucleolar RNA host genes (SNHG), has been reported to act as an oncogene in gastric carcinoma (GC). However, its biological function in Epstein–Barr virus (EBV)-associated gastric cancer (EBVaGC) remains unclear. This study investigated the role of SNHG8 in EBVaGC. Sixty-one cases of EBVaGC, 20 cases of non-EBV-infected gastric cancer (EBVnGC), and relative cell lines were studied for the expression of SNHG8 and BHRF1 (BCL2 homolog reading frame 1) encoded by EBV with Western blot and qRT-PCR assays. The relationship between the expression levels of SNHG8 and the clinical outcome in 61 EBVaGC cases was analyzed. Effects of overexpression or knockdown of BHRF1, SNHG8, or TRIM28 on cell proliferation, migration, invasion, and cell cycle and the related molecules were determined by several assays, including cell proliferation, colony assay, wound healing assay, transwell invasion assay, cell circle with flow cytometry, qRT-PCR, and Western blot for expression levels. The interactions among SNHG8, miR-512-5p, and TRIM28 were determined with Luciferase reporter assay, RNA immunoprecipitation (RIP), pull-down assays, and Western blot assay. The in vivo activity of SNHG8 was assessed with SNHG8 knockdown tumor xenografts in zebrafish. Results demonstrated that the following. (1) BHRF1 and SNHG8 were overexpressed in EBV-encoded RNA 1-positive EBVaGC tissues and cell lines. BHRF1 upregulated the expressions of SNHG8 and TRIM28 in AGS. (2) SNHG8 overexpression had a significant correlation with tumor size and vascular tumor thrombus. Patients with high SNHG8 expression had poorer overall survival (OS) compared to those with low SNHG8 expression. (3) SNHG8 overexpression promoted EBVaGC cell proliferation, migration, and invasion in vitro and in vivo, cell cycle arrested at the G2/M phase via the activation of BCL-2, CCND1, PCNA, PARP1, CDH1, CDH2 VIM, and Snail. (4) Results of dual-luciferase reporter assay, RNA immunoprecipitation, and pull-down assays indicated that SNHG8 sponged miR-512-5p, which targeted on TRIM28 and promoted cancer malignant behaviors of EBVaGC cells. Our data suggest that BHRF1 triggered the expression of SNHG8, which sponged miR-512-5p and upregulated TRIM28 and a set of effectors (such as BCL-2, CCND1, CDH1, CDH2 Snail, and VIM) to promote EBVaGC tumorigenesis and invasion. SNHG8 could be an independent prognostic factor for EBVaGC and sever as target for EBVaGC therapy.

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.

Epstein-Barr Virus Promotes B Cell Lymphomas by Manipulating the Host Epigenetic Machinery

Simple Summary

Epstein-Barr Virus (EBV)-induced lymphomas have a significant global incidence, given the widespread infection to the human population. EBV adopts several mechanisms to replicate and persist in the host, by hijacking its epigenetic machinery. The main topic of this review details the current insights of EBV interactions with the host epigenetic system, and it will be discussed the potential relationship between the EBV-induced chronic inflammation and the dysregulation of epigenetic modifiers that might lead to tumorigenesis. Promising novel therapies against several types of cancer involve the use of epigenetic modifier inhibitors. To design new therapeutical strategies targeting lymphomas, it is crucial to conduct exhaustive reaserch on the regulation of these enzymes.

Abstract

During the past decade, the rapid development of high-throughput next-generation sequencing technologies has significantly reinforced our understanding of the role of epigenetics in health and disease. Altered functions of epigenetic modifiers lead to the disruption of the host epigenome, ultimately inducing carcinogenesis and disease progression. Epstein–Barr virus (EBV) is an endemic herpesvirus that is associated with several malignant tumours, including B-cell related lymphomas. In EBV-infected cells, the epigenomic landscape is extensively reshaped by viral oncoproteins, which directly interact with epigenetic modifiers and modulate their function. This process is fundamental for the EBV life cycle, particularly for the establishment and maintenance of latency in B cells; however, the alteration of the host epigenetic machinery also contributes to the dysregulated expression of several cellular genes, including tumour suppressor genes, which can drive lymphoma development. This review outlines the molecular mechanisms underlying the epigenetic manipulation induced by EBV that lead to transformed B cells, as well as novel therapeutic interventions to target EBV-associated B-cell lymphomas.

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.

Autophagy-Dependent Reactivation of Epstein-Barr Virus Lytic Cycle and Combinatorial Effects of Autophagy-Dependent and Independent Lytic Inducers in Nasopharyngeal Carcinoma

Autophagy, a conserved cellular mechanism, is manipulated by a number of viruses for different purposes. We previously demonstrated that an iron-chelator-like small compound, C7, reactivates Epstein-Barr virus (EBV) lytic cycle by activating the ERK1/2-autophagy axis in epithelial cancers. Here, we aim to identify the specific stage of autophagy required for EBV lytic reactivation, determine the autophagy dependency of EBV lytic inducers including histone deacetylase inhibitor (HDACi) and C7/iron chelators, for EBV lytic reactivation and measure the combinatorial effects of these types of lytic inducers in nasopharyngeal carcinoma (NPC). Inhibition of autophagy initiation by 3-MA and autolysosome formation by chloroquine demonstrated that only autophagy initiation is required for EBV lytic reactivation. Gene knockdown of various autophagic proteins such as beclin-1, ATG5, ATG12, ATG7, LC3B, ATG10, ATG3 and Rab9, revealed the importance of ATG5 in EBV lytic reactivation. 3-MA could only abrogate lytic cycle induction by C7/iron chelators but not by HDACi, providing evidence for autophagy-dependent and independent mechanisms in EBV lytic reactivation. Finally, the combination of C7 and SAHA at their corresponding reactivation kinetics enhanced EBV lytic reactivation. These findings render new insights in the mechanisms of EBV lytic cycle reactivation and stimulate a rational design of combination drug therapy against EBV-associated cancers.

Epstein-Barr virus (EBV) reactivation and therapeutic inhibitors

Epstein-Barr virus (EBV) is a ubiquitous human virus which infects almost all humans during their lifetime and following the acute phase, persists for the remainder of the life of the individual. EBV infects B lymphocytes leading to their immortalisation, with persistence of the EBV genome as an episome. In the latent phase, EBV is prevented from reactivating through efficient cytotoxic cellular immunity. EBV reactivates (lytic phase) under conditions of psychological stress with consequent weakening of cellular immunity, and EBV reactivation has been shown to occur in a subset of individuals with each of a variety of cancers, autoimmune diseases, the autoimmune-like disease, chronic fatigue syndrome/myalgic encephalitis and under other circumstances such as being an inpatient in an intensive care unit. Chronic EBV reactivation is an important mechanism in the pathogenesis of many such diseases, yet is rarely tested for in immunocompetent individuals. This review summarises the pathogenesis of EBV infection, EBV reactivation and its role in disease, and methods which may be used to detect it. Known inhibitors of EBV reactivation and replication are discussed, including drugs licensed for treatment of other herpesviruses, licensed or experimental drugs for various other indications, compounds at an early stage of drug development and nutritional constituents such as vitamins and dietary supplements.

Lysine-specific post-translational modifications of proteins in the life cycle of viruses

The process of protein post-translational modifications (PTM) is one of the critical mechanisms of regulation of many cellular processes, which makes it an attractive target for various viruses. Since viruses cannot replicate on their own, they have developed unique abilities to alter metabolic and signaling cell pathways, including protein PTMs, to ensure faithful replication of their genomes. This review describes several ways of how lysine-specific PTMs are used by various viruses to ensure its successful invasion and replication. Covalent modifications like acetylation, ubiquitination, and methylation form a complex system of reversible and often competing modifications, which adds an additional level of complexity to the system of regulation of the activity of host proteins involved in viral replication and propagation. In furthering these, we also describe the manner in which PTM pathways can also be accosted by various types of viruses to neutralize the host's cellular mechanisms for anti-viral protection and highlight key areas for future therapeutic targeting and design.

EBV(LMP1)-induced metabolic reprogramming inhibits necroptosis through the hypermethylation of the RIP3 promoter

EBV infection is a recognized epigenetic driver of carcinogenesis. We previously showed that EBV could protect cancer cells from TNF-induced necroptosis. This study aims to explore the epigenetic mechanisms allowing cancer cells with EBV infection to escape from RIP3-dependent necroptosis.

Methods: Data from the TCGA database were used to evaluate the prognostic value of RIP3 promoter methylation and its expression. Western blotting, real-time PCR, and immunochemistry were conducted to investigate the relationship between LMP1 and RIP3 in cell lines and NPC tissues. BSP, MSP and hMeDIP assays were used to examine the methylation level. Induction of necroptosis was detected by cell viability assay, p-MLKL, and Sytox Green staining.

Results: RIP3 promoter hypermethylation is an independent prognostic factor of poorer disease-free and overall survival in HNSCC patients, respectively. RIP3 is down-regulated in NPC (a subtype of HNSCC). EBV(LMP1) suppresses RIP3 expression by hypermethylation of the RIP3 promoter. RIP3 protein expression was inversely correlated with LMP1 expression in NPC tissues. Restoring RIP3 expression in EBV(LMP1)-positive cells inhibits xenograft tumor growth. The accumulation of fumarate and reduction of α-KG in EBV(LMP1)-positive cells led to RIP3 silencing due to the inactivation of TETs. Decreased FH activity caused fumarate accumulation, which might be associated with its acetylation. Incubating cells with fumarate protected NPC cells from TNF-induced necroptosis.

Conclusion: These results demonstrate a pathway by which EBV(LMP1)-associated metabolite changes inhibited necroptosis signaling by DNA methylation, and shed light on the mechanism underlying EBV-related carcinogenesis, which may provide new options for cancer diagnosis and therapy.

Icaritin: A Novel Natural Candidate for Hematological Malignancies Therapy

Hematological malignancies including leukemia and lymphoma can severely impact human health. With the current therapies combined with chemotherapy, stem cell transplantation, radiotherapy, and immunotherapy, the prognosis of hematologic malignancies improved significantly. However, most hematological malignancies are still incurable. Therefore, research for novel treatment options was continuing with the natural product as one source. Icaritin is a compound extracted from a traditional Chinese herb, Epimedium Genus, and demonstrated an antitumor effect in various neoplasms including hematological malignancies such as leukemia, lymphoma, and multiple myeloma. In hematological malignancies, icaritin showed multiple cytotoxic effects to induce apoptosis, arrest the cell cycle, inhibit proliferation, promote differentiation, restrict metastasis and infiltration, and suppress the oncogenic virus. The proved underlying mechanisms of the cytotoxic effects of icaritin are different in various cell types of hematological malignancies but associated with the critical cell signal pathway, including PI3K/Akt, JAK/STAT3, and MAPK/ERK/JNK. Although the primary target of icaritin is still unspecified, the existing evidence indicates that icaritin is a potential novel therapeutic agent for neoplasms as with hematological malignancies. Here, in the field of hematology, we reviewed the reported activity of icaritin in hematologic malignancies and the underlying mechanisms and recognized icaritin as a candidate for therapy of hematological malignancies.

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.

Aspirin Inhibits Natural Killer/T-Cell Lymphoma by Modulation of VEGF Expression and Mitochondrial Function

Extranodal nasal-type natural killer/T-cell lymphoma (NKTCL) is an Epstein-Barr virus (EBV)-associated lymphoma with a strong tendency relapse or be refractory in response to chemotherapy. Development of a new strategy for NKTCL treatment is still quite necessary. In this study, we found that aspirin treatment suppresses VEGF expression in NKTCL SNK-6 cells. Further investigation showed that aspirin treatment increases histone methylation in the range of −100~0 that is proximal to the transcription start site on the VEGF promoter, subsequently decreasing the binding ability of Sp1 to the VEGF promoter with VEGF suppression. Furthermore, aspirin treatment modulates mitochondrial function with increased ROS formation and apoptosis in NKTCL cells. Aspirin treatment alone slightly inhibits NKTCL SNK-6 tumor growth and EBV replication; while in the presence of histone deacetylase inhibitor (HDACi) chidamide (CDM), aspirin significantly suppresses the VEGF signaling pathway with increased ROS overgeneration and EBV inhibition. We also showed that with the addition of chidamide, aspirin significantly suppresses NKTCL tumor growth in both in vitro cell culture and in vivo mouse model with prolonged mouse survival. This is the first time that the potential mechanism for aspirin-mediated VEGF suppression and anti-tumor effect has been discovered, and this study provides a new strategy for anti-tumor drug development for NKTCL treatment based on aspirin-mediated targeting of the VEGF signaling pathway and ROS formation.

Intracellular Iron Chelation by a Novel Compound, C7, Reactivates Epstein⁻Barr Virus (EBV) Lytic Cycle via the ERK-Autophagy Axis in EBV-Positive Epithelial Cancers

Pharmaceutical reactivation of lytic cycle of Epstein–Barr virus (EBV) represents a potential therapeutic strategy against EBV-associated epithelial malignancies, e.g., gastric carcinoma (GC) and nasopharyngeal carcinoma (NPC). A novel lytic-inducing compound, C7, which exhibits structural similarity to Di-2-Pyridyl Ketone 4, 4-Dimethyl-3-Thiosemicarbazone (Dp44mT), a known chelator of intracellular iron, is found to reactivate EBV lytic cycle in GC and NPC. This study aims to investigate the role of intracellular iron chelation by C7 and other iron chelators in lytic reactivation of EBV in GC and NPC. Testing of six structural analogs of C7 revealed only those which have high affinity towards transition metals could induce EBV lytic cycle. Precomplexing C7 and iron chelators to iron prior to treatment of the cells abolished EBV lytic reactivation. Though hypoxia signaling pathway was activated, it was not the only pathway associated with EBV reactivation. Specifically, C7 and iron chelators initiated autophagy by activating extracellular signal-regulated kinase (ERK1/2) to reactivate EBV lytic cycle since autophagy and EBV lytic reactivation were abolished in cells treated with ERK1/2 blockers whilst inhibition of autophagy by 3-Methyladenine (3-MA) and atg5 knockdown significantly abolished EBV lytic reactivation. In summary, we discovered a novel mechanism of reactivation of the EBV lytic cycle through intracellular iron chelation and induction of ERK-autophagy axis in EBV-positive epithelial malignancies, raising the question whether clinically available iron chelators can be incorporated into existing therapeutic regimens to treat these cancers.

Establishment and characterization of new tumor xenografts and cancer cell lines from EBV-positive nasopharyngeal carcinoma

The lack of representative nasopharyngeal carcinoma (NPC) models has seriously hampered research on EBV carcinogenesis and preclinical studies in NPC. Here we report the successful growth of five NPC patient-derived xenografts (PDXs) from fifty-eight attempts of transplantation of NPC specimens into NOD/SCID mice. The take rates for primary and recurrent NPC are 4.9% and 17.6%, respectively. Successful establishment of a new EBV-positive NPC cell line, NPC43, is achieved directly from patient NPC tissues by including Rho-associated coiled-coil containing kinases inhibitor (Y-27632) in culture medium. Spontaneous lytic reactivation of EBV can be observed in NPC43 upon withdrawal of Y-27632. Whole-exome sequencing (WES) reveals a close similarity in mutational profiles of these NPC PDXs with their corresponding patient NPC. Whole-genome sequencing (WGS) further delineates the genomic landscape and sequences of EBV genomes in these newly established NPC models, which supports their potential use in future studies of NPC.

The lack of appropriate models restricts pre-clinical research for nasopharyngeal carcinoma (NPC). Here the authors report the development and characterization of NPC patient-derived xenografts (PDXs), and EBV positive NPC cell line from patient tumor, and suggest their potential use in future NPC research.

Therapies based on targeting Epstein-Barr virus lytic replication for EBV-associated malignancies

In recent years, Epstein‐Barr virus (EBV) lytic infection has been shown to significantly contribute to carcinogenesis. Thus, therapies aimed at targeting the EBV lytic cycle have been developed as novel strategies for treatment of EBV‐associated malignancies. In this review, focusing on the viral lytic proteins, we describe recent advances regarding the involvement of the EBV lytic cycle in carcinogenesis. Moreover, we further discuss 2 distinct EBV lytic cycle‐targeted therapeutic strategies against EBV‐induced malignancies. One of the strategies involves inhibition of the EBV lytic cycle by natural compounds known to have anti‐EBV properties; another is to intentionally induce EBV lytic replication in combination with nucleotide analogues. Recent advances in EBV lytic‐based strategies are beginning to show promise in the treatment and/or prevention of EBV‐related tumors.

Counteracting survival functions of EBNA3C in Epstein-Barr virus (EBV)-driven lymphoproliferative diseases by combination of SAHA and bortezomib

Combination of suberoylanilide hydroxamic acid (SAHA) and bortezomib (SAHA/bortezomib) was shown to synergistically induce killing of lymphoblastoid cell lines (LCL) and Burkitt lymphoma (BL) of type III or Wp-restricted latency, both of which express EBNA3A, -3B and -3C proteins. We hypothesize that SAHA/bortezomib can counteract the survival functions conferred by the EBNA3 proteins. We tested the effect of SAHA/bortezomib on the survival of BL cell lines containing EBNA3A, -3B or -3C knockout EBV with or without the respective revertant EBNA3 genes. Isobologram analysis showed that SAHA/bortezomib induced significantly greater synergistic killing of EBNA3C-revertant cells when compared with EBNA3C-knockout cells. Such differential response was not observed in either EBNA3A or -3B revertant versus their knockout pairs. Interestingly, EBNA3C-knockout cells showed significant G2/M arrest whilst EBNA3C-revertant cells and LCLs escaped G2/M arrest induced by SAHA/bortezomib and became more susceptible to the induction of apoptosis. In parallel, SAHA/bortezomib induced stronger expression of p21^WAF1 but weaker expression of p-cdc25c, an M-phase inducer phosphatase, in EBNA3C-expressing cells when compared with EBNA3C-knockout cells. SAHA/bortezomib also induced greater growth suppression of EBNA3C-expressing xenografts (EBNA3C-revertant and LCL) than that of EBNA3C-knockout xenografts in SCID mice. In conclusion, our data showed that SAHA/bortezomib could synergistically induce killing of BL and LCL through counteracting the survival functions of EBNA3C, providing a strong basis for clinical testing of this drug combination in patients with EBV-associated lymphoproliferative diseases.

Curcuminoids as EBV Lytic Activators for Adjuvant Treatment in EBV-Positive Carcinomas

Epstein-Barr virus (EBV) persists in nasopharyngeal (NPC) and gastric carcinomas (EBVaGC) in a tightly latent form. Cytolytic virus activation (CLVA) therapy employs gemcitabine and valproic acid (GCb+VPA) to reactivate latent EBV into the lytic phase and antiviral valganciclovir to enhance cell death and prevent virus production. CLVA treatment has proven safe in phase-I/II trials with promising clinical responses in patients with recurrent NPC. However, a major challenge is to maximize EBV lytic reactivation by CLVA. Curcumin, a dietary spice used in Asian countries, is known for its antitumor property and therapeutic potential. Novel curcuminoids that were developed to increase efficacy and bioavailability may serve as oral CLVA adjuvants. We investigated the potential of curcumin and its analogs (curcuminoids) to trigger the EBV lytic cycle in EBVaGC and NPC cells. EBV-reactivating effects were measured by immunoblot and immunofluorescence using monoclonal antibodies specific for EBV lytic proteins. Two of the hit compounds (41, EF24) with high lytic inducing activity were further studied for their synergistic or antagonistic effects when combined with GCb+VPA and analyzed by cytotoxicity and mRNA profiling assays to measure the EBV reactivation. Curcuminoid as a single agent significantly induced EBV reactivation in recombinant GC and NPC lines. The drug effects were dose- and time-dependent. Micromolar concentration of curcuminoid EF24 enhanced the CLVA effect in all cell systems except SNU719, a naturally infected EBVaGC cell that carries a more tightly latent viral genome. These findings indicated that EF24 has potential as EBV lytic activator and may serve as an adjuvant in CLVA treatment.

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.

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.

Induction of MAPK- and ROS-dependent autophagy and apoptosis in gastric carcinoma by combination of romidepsin and bortezomib

Proteasome inhibitors and histone deacetylase (HDAC) inhibitors can synergistically induce apoptotic cell death in certain cancer cell types but their combinatorial effect on the induction of autophagy remains unknown. Here, we investigated the combinatorial effects of a proteasome inhibitor, bortezomib, and an HDAC inhibitor, romidepsin, on the induction of apoptotic and autophagic cell death in gastric carcinoma (GC) cells. Isobologram analysis showed that low nanomolar concentrations of bortezomib/romidepsin could synergistically induce killing of GC cells. The synergistic killing was due to the summative effect of caspase-dependent intrinsic apoptosis and caspase-independent autophagy. The autophagic cell death was dependent on the activation of MAPK family members (ERK1/2 and JNK), and generation of reactive oxygen species (ROS), but was independent of Epstein-Barr virus infection. In vivo, bortezomib/romidepsin also significantly induced apoptosis and autophagy in GC xenografts in nude mice. This is the first report demonstrating the potent effect of combination of HDAC and proteasome inhibitors on the induction of MAPK- and ROS-dependent autophagy in addition to caspase-dependent apoptosis in a cancer type.

Trichloromethane fraction of Incarvillea compacta induces lytic cytotoxicity and apoptosis in Epstein-Barr virus-positive gastric cancer AGS cells

Background

Incarvillea compacta Maxim. has been used to treat stomach disease in Tibet for many years. The objectives of this study were to explore the anti-cancer ability of trichloromethane fraction of I. compacta Maxim. roots (IC-TCL, R2) in EBV positive AGS cancer cells and its effects on cell cycle arrest, apoptosis and lytic induction.

Methods

MTT and trypan blue assays were to detect the inhibitory effects of different fraction in different cell lines. Hoechst 33342 staining, Annexin V-PE/7-AAD staining and DIOC₆ staining were used to detect the apoptosis induction effects of R2. Western blot experiments were used to detect the expression of apoptosis related proteins BAX and Bcl-2, EBV lytic related proteins BZLF1 and BMRF1, cell cycle regulation related proteins Cyclin D1 and RB after R2 treatment. Cell cycle arrest was analyzed by flow cytometry.

Results

MTT and trypan blue assays revealed that R2 could significantly reduce cell viability in a dose-dependent manner in EBV positive AGS cells compared with non-EBV infected AGS and other cancer cell lines, whereas n-BuOH and H₂O fractions showed non-inhibitory effects in tested cancer cells. R2 could decrease mitochondrial membrane potential and the expression of Bcl-2, while increase the expression of BAX. R2 could also induce EBV lytic replication by activating mRNA levels of BZLF1, BRLF1 and BMRF1. Protein expressions of BZLF1 and BMRF1 were also increased after R2 treatment. Cell cycle analysis showed that R2 treatment could induce G0/G1 phase arrest. The expression of Cyclin D1 decreased, while Rb increased.

Conclusions

These results demonstrated that R2 could inhibit the proliferation of AGS-EBV cancer cells by inducing EBV lytic replication, apoptosis and G0/G1 arrest, through the regulation of related proteins. Therefore, R2 could be used as a potential treatment in AGS-EBV cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1331-6) contains supplementary material, which is available to authorized users.

Targeted therapy for Epstein-Barr virus-associated gastric carcinoma using low-dose gemcitabine-induced lytic activation

The constant presence of the viral genome in Epstein-Barr virus (EBV)-associated gastric cancers (EBVaGCs) suggests the applicability of novel EBV-targeted therapies. The antiviral nucleoside drug, ganciclovir (GCV), is effective only in the context of the viral lytic cycle in the presence of EBV-encoded thymidine kinase (TK)/protein kinase (PK) expression. In this study, screening of the Johns Hopkins Drug Library identified gemcitabine as a candidate for combination treatment with GCV. Pharmacological induction of EBV-TK or PK in EBVaGC-originated tumor cells were used to study combination treatment with GCV in vitro and in vivo. Gemcitabine was found to be a lytic inducer via activation of the ataxia telangiectasia-mutated (ATM)/p53 genotoxic stress pathway in EBVaGC. Using an EBVaGC mouse model and a [¹²⁵I] fialuridine (FIAU)-based lytic activation imaging system, we evaluated gemcitabine-induced lytic activation in an in vivo system and confirmed the efficacy of gemcitabine-GCV combination treatment. This viral enzyme-targeted anti-tumor strategy may provide a new therapeutic approach for EBVaGCs.

Gastric adenocarcinoma microRNA profiles in fixed tissue and in plasma reveal cancer-associated and Epstein-Barr virus-related expression patterns

MicroRNA expression in formalin-fixed paraffin-embedded tissue (FFPE) or plasma may add value for cancer management. The GastroGenus miR Panel was developed to measure 55 cancer-specific human microRNAs, Epstein-Barr virus (EBV)-encoded microRNAs, and controls. This Q-rtPCR panel was applied to 100 FFPEs enriched for adenocarcinoma or adjacent non-malignant mucosa, and to plasma of 31 patients. In FFPE, microRNAs upregulated in malignant versus adjacent benign gastric mucosa were hsa-miR-21, -155, -196a, -196b, -185, and -let-7i. Hsa-miR-18a, 34a, 187, -200a, -423-3p, -484, and -744 were downregulated. Plasma of cancer versus non-cancer controls had upregulated hsa-miR-23a, -103, and -221 and downregulated hsa-miR-378, -346, -486-5p, -200b, -196a, -141, and -484. EBV-infected versus uninfected cancers expressed multiple EBV-encoded microRNAs, and concomitant dysregulation of four human microRNAs suggests that viral infection may alter cellular biochemical pathways. Human microRNAs were dysregulated between malignant and benign gastric mucosa and between plasma of cancer patients and non-cancer controls. Strong association of EBV microRNA expression with known EBV status underscores the ability of microRNA technology to reflect disease biology. Expression of viral microRNAs in concert with unique human microRNAs provides novel insights into viral oncogenesis and reinforces the potential for microRNA profiles to aid in classifying gastric cancer subtypes. Pilot studies of plasma suggest the potential for a noninvasive addition to cancer diagnostics.

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.

Epstein-Barr virus BZLF1 protein impairs accumulation of host DNA damage proteins at damage sites in response to DNA damage

Epstein-Barr virus (EBV) infection is closely associated with several human malignancies including nasopharyngeal carcinoma (NPC). The EBV immediate-early protein BZLF1 is the key mediator that switches EBV infection from latent to lytic forms. The lytic form of EBV infection has been implicated in human carcinogenesis but its molecular mechanisms remain unclear. BZLF1 has been shown to be a binding partner of several DNA damage response (DDR) proteins. Its functions in host DDR remain unknown. Thus, we explore the effects of BZLF1 on cellular response to DNA damage in NPC cells. We found that expression of BZLF1 impaired the binding between RNF8 and MDC1 (mediator of DNA damage checkpoint 1), which in turn interfered with the localization of RNF8 and 53BP1 to the DNA damage sites. The RNF8-53BP1 pathway is important for repair of DNA double-strand breaks and DNA damage-induced G2/M checkpoint activation. Our results showed that, by impairing DNA damage repair as well as abrogating G2/M checkpoint, BZLF1 induced genomic instability and rendered cells more sensitive to ionizing radiation. Moreover, the blockage of 53BP1 and RNF8 foci formation was recapitulated in EBV-infected cells. Taken together, our study raises the possibility that, by causing mis-localization of important DDR proteins, BZLF1 may function as a link between lytic EBV infection and impaired DNA damage repair, thus contributing to the carcinogenesis of EBV-associated human epithelial malignancies.

Icaritin induces lytic cytotoxicity in extranodal NK/T-cell lymphoma

Background

Extranodal NK/T-cell lymphoma (ENKL) is an aggressive hematological malignancy associated with Epstein–Barr virus (EBV) infection. It is often resistant to conventional chemotherapy and has a poor prognosis. Icaritin, a compound derived from Chinese herbal medicine, Herba Epimedii, has been reported to exert antitumor effects on a variety of cancer cell lines. In the present study, we investigated the cytotoxic effects of Icaritin on the two EBV-positive ENKL cell lines SNK-10 and SNT-8, along with the underlying molecular mechanisms.

Methods

ENKL cell lines SNK-10 and SNT-8 were exposed to different concentrations of Icaritin for the indicated time. Treated cells were analyzed for cell proliferation, cell cycle, and cell apoptosis. Phosphorylation of Stat3 and Akt proteins in signaling pathways and the EBV-encoded LMP1 proteins were measured by Western blot. Expression of EBV genes was assessed by Real-Time PCR.

Results

Our results showed that Icaritin dose-dependently inhibits ENKL cell proliferation and induces apoptosis and cell cycle arrest at G₂/M phase. Additionally, Icaritin upregulates Bax, downregulates Bcl-2 and pBad, and activates caspase-3 and caspase-9. The anti-proliferative and pro-apoptotic effects of Icaritin are likely mediated by inhibition of Stat3 and Akt pathways through LMP1 downregulation. Importantly, Icaritin induces EBV lytic gene expression in ENKL cells, and the combination of Icaritin and the antiviral drug ganciclovir (GCV) is more effective in inducing ENKL cells apoptosis than Icaritin or GCV alone.

Conclusions

These findings indicate that EBV-targeted approaches may have significant therapeutic potential for ENKL treatment.

Anti-tumor effects of suberoylanilide hydroxamic acid on Epstein-Barr virus-associated T cell and natural killer cell lymphoma

The ubiquitous Epstein–Barr virus (EBV) infects not only B cells but also T cells and natural killer (NK) cells and is associated with various lymphoid malignancies. Recent studies have reported that histone deacetylase (HDAC) inhibitors exert anticancer effects against various tumor cells. In the present study, we have evaluated both the in vitro and in vivo effects of suberoylanilide hydroxamic acid (SAHA), an HDAC inhibitor, on EBV-positive and EBV-negative T and NK lymphoma cells. Several EBV-positive and EBV-negative T and NK cell lines were treated with various concentrations of SAHA. SAHA suppressed the proliferation of T and NK cell lines, although no significant difference was observed between EBV-positive and EBV-negative cell lines. SAHA induced apoptosis and/or cell cycle arrest in several T and NK cell lines. In addition, SAHA increased the expression of EBV-lytic genes and decreased the expression of EBV-latent genes. Next, EBV-positive NK cell lymphoma cells were subcutaneously inoculated into severely immunodeficient NOD/Shi-scid/IL-2Rγnull mice, and then SAHA was administered intraperitoneally. SAHA inhibited tumor progression and metastasis in the murine xenograft model. SAHA displayed a marked suppressive effect against EBV-associated T and NK cell lymphomas through either induction of apoptosis or cell cycle arrest, and may represent an alternative treatment option.

EBV-related lymphomas: new approaches to treatment

In the treatment of Epstein-Barr virus (EBV)-related lymphomas, there are few therapies specifically targeted against the latent virus within these tumors; in most cases the treatment approach is not different than the approach to EBV-negative lymphomas. Nonetheless, current and emerging therapies focused on exploiting aspects of EBV biology may offer more targeted strategies for EBV-positive lymphomas in the future. Conceptually, EBV-specific approaches include bolstering the antiviral/antitumor immune response with vaccines or EBV-specific cytotoxic T-lymphocytes, activating lytic viral genes to render the tumor cells susceptible to antiviral therapies, and inhibiting the downstream prosurvival or antiapoptotic pathways that may be activated by latent EBV proteins. EBV-specific cytotoxic T-cell infusions have proven effective in EBV-related posttransplantation lymphoproliferative disorder (EBV-PTLD) and expanding such adoptive immunotherapies to other EBV-related malignancies is an area of active research. However, other EBV-related lymphomas typically have more restricted, less immunogenic arrays of viral antigens to therapeutically target with adoptive immunotherapy compared with EBV-PTLD. Furthermore, the malignant EBV-positive tumor cells of Hodgkin lymphoma are scattered amid a dense infiltrate of regulatory T-cells, macrophages, and other cells that may dampen the antitumor efficacy of adoptive immunotherapy. Strategies to overcome these obstacles are areas of ongoing preclinical and clinical investigations. Some emerging approaches to EBV-related lymphomas include the coupling of agents that induce lytic viral replication with antiherpesvirus agents, or the use of small molecule inhibitors that block signaling pathways that are constitutively activated by EBV. EBV vaccines seem most promising for the treatment or prevention of EBV-related malignancies, rather than the prevention of primary EBV infection. EBV vaccine trials in patients with residual or low-bulk EBV-related malignancies or for the prevention of EBV-PTLD in EBV-seronegative patients awaiting solid organ transplantation are ongoing.

Co-treatment with arsenic trioxide and ganciclovir reduces tumor volume in a murine xenograft model of nasopharyngeal carcinoma

We have previously shown that disruption of promyelocytic leukemia nuclear bodies (PML NBs) is sufficient to activate the EBV lytic cycle thus making infected cells susceptible to ganciclovir (GCV) mediated killing in vitro. Here we show that co-administration of GCV and arsenic trioxide (ATO), a PML NB disruptor, reduces tumor volume in a xenograft model of nasopharyngeal carcinoma utilizing CNE1 cells. When administered at pharmacologic levels, both GCV and ATO reduced tumor growth while co-treatment with GCV + ATO resulted in a diminution of tumor volume. Treatment with GCV or ATO individually resulted in an increased number of apoptotic cells while co-treatment with GCV + ATO synergistically induced apoptosis. Treatment with ATO or co-treatment with GCV + ATO resulted in expression of EBV lytic proteins. These data suggest that co-treatment with GCV + ATO may provide an effective treatment for nasopharyngeal carcinoma patients.

Epstein-barr virus infected gastric adenocarcinoma expresses latent and lytic viral transcripts and has a distinct human gene expression profile

BACKGROUND

EBV DNA is found within the malignant cells of 10% of gastric cancers. Modern molecular technology facilitates identification of virus-related biochemical effects that could assist in early diagnosis and disease management.

METHODS

In this study, RNA expression profiling was performed on 326 macrodissected paraffin-embedded tissues including 204 cancers and, when available, adjacent non-malignant mucosa. Nanostring nCounter probes targeted 96 RNAs (20 viral, 73 human, and 3 spiked RNAs).

RESULTS

In 182 tissues with adequate housekeeper RNAs, distinct profiles were found in infected versus uninfected cancers, and in malignant versus adjacent benign mucosa. EBV-infected gastric cancers expressed nearly all of the 18 latent and lytic EBV RNAs in the test panel. Levels of EBER1 and EBER2 RNA were highest and were proportional to the quantity of EBV genomes as measured by Q-PCR. Among protein coding EBV RNAs, EBNA1 from the Q promoter and BRLF1 were highly expressed while EBNA2 levels were low positive in only 6/14 infected cancers. Concomitant upregulation of cellular factors implies that virus is not an innocent bystander but rather is linked to NFKB signaling (FCER2, TRAF1) and immune response (TNFSF9, CXCL11, IFITM1, FCRL3, MS4A1 and PLUNC), with PPARG expression implicating altered cellular metabolism. Compared to adjacent non-malignant mucosa, gastric cancers consistently expressed INHBA, SPP1, THY1, SERPINH1, CXCL1, FSCN1, PTGS2 (COX2), BBC3, ICAM1, TNFSF9, SULF1, SLC2A1, TYMS, three collagens, the cell proliferation markers MYC and PCNA, and EBV BLLF1 while they lacked CDH1 (E-cadherin), CLDN18, PTEN, SDC1 (CD138), GAST (gastrin) and its downstream effector CHGA (chromogranin). Compared to lymphoepithelioma-like carcinoma of the uterine cervix, gastric cancers expressed CLDN18, EPCAM, REG4, BBC3, OLFM4, PPARG, and CDH17 while they had diminished levels of IFITM1 and HIF1A. The druggable targets ERBB2 (Her2), MET, and the HIF pathway, as well as several other potential pharmacogenetic indicators (including EBV infection itself, as well as SPARC, TYMS, FCGR2B and REG4) were identified in some tumor specimens.

CONCLUSION

This study shows how modern molecular technology applied to archival fixed tissues yields novel insights into viral oncogenesis that could be useful in managing affected patients.

Dynamic chromatin environment of key lytic cycle regulatory regions of the Epstein-Barr virus genome

The ability of Epstein-Barr virus (EBV) to establish latency allows it to evade the immune system and to persist for the lifetime of its host; one distinguishing characteristic is the lack of transcription of the majority of viral genes. Entry into the lytic cycle is coordinated by the viral transcription factor, Zta (BZLF1, ZEBRA, and EB1), and downstream effectors, while viral genome replication requires the concerted action of Zta and six other viral proteins at the origins of lytic replication. We explored the chromatin context at key EBV lytic cycle promoters (BZLF1, BRLF1, BMRF1, and BALF5) and the origins of lytic replication during latency and lytic replication. We show that a repressive heterochromatin-like environment (trimethylation of histone H3 at lysine 9 [H3K9me3] and lysine 27 [H3K27me3]), which blocks the interaction of some transcription factors with DNA, encompasses the key early lytic regulatory regions. Epigenetic silencing of the EBV genome is also imposed by DNA methylation during latency. The chromatin environment changes during the lytic cycle with activation of histones H3, H4, and H2AX occurring at both the origins of replication and at the key lytic regulatory elements. We propose that Zta is able to reverse the effects of latency-associated repressive chromatin at EBV early lytic promoters by interacting with Zta response elements within the H3K9me3-associated chromatin and demonstrate that these interactions occur in vivo. Since the interaction of Zta with DNA is not inhibited by DNA methylation, it is clear that Zta uses two routes to overcome epigenetic silencing of its genome.

Exploiting the interplay between innate and adaptive immunity to improve immunotherapeutic strategies for Epstein-Barr-virus-driven disorders

The recent demonstration that immunotherapeutic approaches may be clinically effective for cancer patients has renewed the interest for this strategy of intervention. In particular, clinical trials using adoptive T-cell therapies disclosed encouraging results, particularly in the context of Epstein-Barr-virus- (EBV-) related tumors. Nevertheless, the rate of complete clinical responses is still limited, thus stimulating the development of more effective therapeutic protocols. Considering the relevance of innate immunity in controlling both infections and cancers, innovative immunotherapeutic approaches should take into account also this compartment to improve clinical efficacy. Evidence accumulated so far indicates that innate immunity effectors, particularly NK cells, can be exploited with therapeutic purposes and new targets have been recently identified. We herein review the complex interactions between EBV and innate immunity and summarize the therapeutic strategies involving both adaptive and innate immune system, in the light of a fruitful integration between these immunotherapeutic modalities for a better control of EBV-driven tumors.

Newly emerging therapies targeting viral-related lymphomas

Gamma-(γ)-herpes virus lymphomas comprise a heterogenous group of B-cell and T-cell neoplasms most commonly associated with Epstein-Barr virus and rarely human herpes virus-8 infection. Adult T-cell leukemia/lymphoma (ATLL) is a unique disease entity caused by the human T-cell lymphotrophic virus, type 1 (HTLV-I), the only retrovirus known to cause cancer in humans. Viral lymphomas behave aggressively and disproportionally affect immunocompromised individuals and those living in underdeveloped regions. These diseases are often difficult to treat with conventional approaches. Despite recent advancements using cytotoxic, lymphoma-specific, and adoptive therapies, the long-term outcome of patients with γ-herpesvirus lymphomas occurring in severely immunocompromised patients and ATLL continues to be poor. Lytic-inducing therapies targeting NF-κB, and viral and tumor cell epigenetic mechanisms afford the advantage of exploiting the intrinsic presence of oncogenic viruses to eradicate infected tumor cells. In this review, viral-related lymphomas and newly emerging clinical approaches targeting viral latency are discussed.

Arsenic mediated disruption of promyelocytic leukemia protein nuclear bodies induces ganciclovir susceptibility in Epstein-Barr positive epithelial cells

Promyelocytic leukemia protein nuclear bodies (PML NBs) have been implicated in host immune response to viral infection. PML NBs are targeted for degradation during reactivation of herpes viruses, suggesting that disruption of PML NB function supports this aspect of the viral life cycle. The Epstein-Barr virus (EBV) Latent Membrane Protein 1 (LMP1) has been shown to suppress EBV reactivation. Our finding that LMP1 induces PML NB immunofluorescence intensity led to the hypothesis that LMP1 may modulate PML NBs as a means of maintaining EBV latency. Increased PML protein and morphometric changes in PML NBs were observed in EBV infected alveolar epithelial cells and nasopharyngeal carcinoma cells. Treatment with low dose arsenic trioxide disrupted PML NBs, induced expression of EBV lytic proteins, and conferred ganciclovir susceptibility. This study introduces an effective modality to induce susceptibility to ganciclovir in epithelial cells with implications for the treatment of EBV associated pathologies.

Valproic acid antagonizes the capacity of other histone deacetylase inhibitors to activate the Epstein-barr virus lytic cycle

Diverse stimuli reactivate the Epstein-Barr virus (EBV) lytic cycle in Burkitt lymphoma (BL) cells. In HH514-16 BL cells, two histone deacetylase (HDAC) inhibitors, sodium butyrate (NaB) and trichostatin A (TSA), and the DNA methyltransferase inhibitor azacytidine (AzaCdR) promote lytic reactivation. Valproic acid (VPA), which, like NaB, belongs to the short-chain fatty acid class of HDAC inhibitors, fails to induce the EBV lytic cycle in these cells. Nonetheless, VPA behaves as an HDAC inhibitor; it causes hyperacetylation of histone H3 (J. K. Countryman, L. Gradoville, and G. Miller, J. Virol. 82:4706-4719, 2008). Here we show that VPA blocked the induction of EBV early lytic proteins ZEBRA and EA-D in response to NaB, TSA, or AzaCdR. The block in lytic activation occurred prior to the accumulation of BZLF1 transcripts. Reactivation of EBV in Akata cells, in response to anti-IgG, and in Raji cells, in response to tetradecanoyl phorbol acetate (TPA), was also inhibited by VPA. MS-275 and apicidin, representing two additional classes of HDAC inhibitors, and suberoylanilide hydroxamic acid (SAHA) reactivated EBV in HH514-16 cells; this activity was also inhibited by VPA. Although VPA potently blocked the expression of viral lytic-cycle transcripts, it did not generally block the transcription of cellular genes and was not toxic. The levels and kinetics of specific cellular transcripts, such as Stat3, Frmd6, Mad1, Sepp1, c-fos, c-jun, and egr1, which were activated by NaB and TSA, were similar in HH514-16 cells treated with VPA. When combined with NaB or TSA, VPA did not inhibit the activation of these cellular genes. Changes in cellular gene expression in response to VPA, NaB, or TSA were globally similar as assessed by human genome arrays; however, VPA selectively stimulated the expression of some cellular genes, such as MEF2D, YY1, and ZEB1, that could repress the EBV lytic cycle. We describe a novel example of functional antagonism between HDAC inhibitors.