Cytolytic virus activation therapy and treatment monitoring for Epstein-Barr virus associated nasopharyngeal carcinoma in a mouse tumor model

A new compound, phomaherbarine A, induces cytolytic reactivation in epstein-barr virus-positive B cell lines

Epstein-Barr virus (EBV), the first virus found to induce cancer in humans, has been frequently detected in various types of B cell lymphomas. During its latent phase, EBV expresses a limited set of proteins crucial for its persistence. Induction of the lytic phase of EBV has shown promise in the treatment of EBV-associated malignancies. The present study assessed the ability of phomaherbarine A, a novel compound derived from the endophytic fungus Phoma herbarum DBE-M1, to stimulate lytic replication of EBV in B95-8 cells. Phomaherbarine A was found to efficiently initiate the expression of both early and late EBV lytic genes in B95-8 cells, with this initiation being further heightened by the addition of phorbol myristate acetate and sodium butyrate. Moreover, phomaherbarine A demonstrated notable cytotoxicity against the EBV-associated B cell lymphoma cell lines B95-8 and Raji. Mechanistically, phomaherbarine A induces apoptosis in these cells through the activation of caspase-3/7. When combined with ganciclovir, phomaherbarine A does not interfere with the reduction of viral replication by ganciclovir and sustains its apoptosis induction. In conclusion, these findings indicate that phomaherbarine A may be a promising candidate for therapeutic intervention in patients with EBV-associated B cell lymphomas.

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.

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.

The role of Epstein-Barr virus in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a metastasis-prone malignancy closely associated with the Epstein-Barr virus (EBV). Despite ubiquitous infection of EBV worldwide, NPC incidences displayed predominance in certain ethnic groups and endemic regions. The majority of NPC patients are diagnosed with advanced-stage disease, as a result of anatomical isolation and non-specific clinical manifestation. Over the decades, researchers have gained insights into the molecular mechanisms underlying NPC pathogenesis as a result of the interplay of EBV infection with several environmental and genetic factors. EBV-associated biomarkers were also used for mass population screening for the early detection of NPC. EBV and its encoded products also serve as potential targets for the development of therapeutic strategies and tumour-specific drug delivery. This review will discuss the pathogenic role of EBV in NPC and efforts in exploiting the potential of EBV-associated molecules as biomarkers and therapeutic targets. The current knowledge on the role of EBV and its associated products in NPC tumorigenesis, development and progression will offer a new outlook and potential intervention strategy against this EBV-associated malignancy.

Nonsense-mediated decay controls the reactivation of the oncogenic herpesviruses EBV and KSHV

The oncogenic human herpesviruses Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) are the causative agents of multiple malignancies. A hallmark of herpesviruses is their biphasic life cycle consisting of latent and lytic infection. In this study, we identified that cellular nonsense-mediated decay (NMD), an evolutionarily conserved RNA degradation pathway, critically regulates the latent-to-lytic switch of EBV and KSHV infection. The NMD machinery suppresses EBV and KSHV Rta transactivator expression and promotes maintenance of viral latency by targeting the viral polycistronic transactivator transcripts for degradation through the recognition of features in their 3' UTRs. Treatment with a small-molecule NMD inhibitor potently induced reactivation in a variety of EBV- and KSHV-infected cell types. In conclusion, our results identify NMD as an important host process that controls oncogenic herpesvirus reactivation, which may be targeted for the therapeutic induction of lytic reactivation and the eradication of tumor cells.

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.

Pharmacologic Activation of Lytic Epstein-Barr Virus Gene Expression without Virion Production

Several therapeutic strategies targeting Epstein-Barr virus (EBV)-associated tumors involve upregulation of viral lytic gene expression. Evidence has been presented that the unfolded protein response (UPR) leads to EBV lytic gene expression. Clofoctol, an antibacterial antibiotic, has been reported to upregulate the UPR in prostate cancer cell lines and to slow their growth. We investigated the effects of clofoctol on an EBV-positive Burkitt lymphoma cell line and confirmed the upregulation of all three branches of the UPR and activation of EBV lytic gene expression. While immediate early, early, and late EBV RNAs were all upregulated, immediate early and early viral proteins but not late viral proteins were expressed. Furthermore, infectious virions were not produced. The use of clofoctol in combination with a protein kinase R-like endoplasmic reticulum kinase inhibitor led to expression of late viral proteins. The effects of clofoctol on EBV lytic protein upregulation were not limited to lymphoid tumor cell lines but also occurred in naturally infected epithelial gastric cancer and nasopharyngeal cancer cell lines. An agent that upregulates lytic viral protein expression but that does not lead to the production of infectious virions may have particular value for lytic induction strategies in the clinical setting.IMPORTANCE Epstein-Barr virus is associated with many different cancers. In these cancers the viral genome is predominantly latent; i.e., most viral genes are not expressed, most viral proteins are not synthesized, and new virions are not produced. Some strategies for treating these cancers involve activation of lytic viral gene expression. We identify an antibacterial antibiotic, clofoctol, that is an activator of EBV lytic RNA and protein expression but that does not lead to virion production.

Translational genomics of nasopharyngeal cancer

Nasopharyngeal carcinoma (NPC), also named the Cantonese cancer, is a unique cancer with strong etiological association with infection of the Epstein-Barr virus (EBV). With particularly high prevalence in Southeast Asia, the involvement of EBV and genetic aberrations contributive to NPC tumorigenesis have remained unclear for decades. Recently, genomic analysis of NPC has defined it as a genetically homogeneous cancer, driven largely by NF-κB signaling caused by either somatic aberrations of NF-κB negative regulators or by overexpression of the latent membrane protein 1 (LMP1), an EBV viral oncoprotein. This represents a landmark finding of the NPC genome. Exome and RNA sequencing data from new EBV-positive NPC models also highlight the importance of PI3K pathway aberrations in NPC. We also realize for the first time that NPC mutational burden, mutational signatures, MAPK/PI3K aberrations, and MHC Class I gene aberrations, are prognostic for patient outcome. Together, these multiple genomic discoveries begin to shape the focus of NPC therapy development. Given the challenge of NF-κB targeting in human cancers, more innovative drug discovery approaches should be explored to target the unique atypical NF-κB activation feature of NPC. Our next decade of NPC research should focus on further identification of the -omic landscapes of recurrent and metastatic NPC, development of gene-based precision medicines, as well as large-scale drug screening with the newly developed and well-characterized EBV-positive NPC models. Focused preclinical and clinical investigations on these major directions may identify new and effective targeting strategies to further improve survival of NPC patients.

Constructing TC-1-GLUC-LMP2 Model Tumor Cells to Evaluate the Anti-Tumor Effects of LMP2-Related Vaccines

Epstein-Barr virus (EBV) is related to a variety of malignant tumors, and its encoded protein, latent membrane protein 2 (LMP2), is an effective target antigen that is widely used to construct vector vaccines. However, the model cells carrying LMP2 have still not been established to assess the oncolytic effect of LMP2-related vaccines at present. In this study, TC-1-GLUC-LMP2 tumor cells were constructed as target cells to evaluate the anti-tumor effects of LMP2-assosiated vaccines. The results showed that both LMP2 and Gaussia luciferase (GLuc) genes could be detected by polymerase chain reaction (PCR) and reverse transcription-polymerase chain reaction (RT-PCR) in TC-1-GLUC-LMP2 cells. Western blot results showed that the LMP2 and Gaussia luciferase proteins were stably expressed in tumor cells for at least 30 generations. We mixed 5 × 10⁴ LMP2-specific mouse splenic lymphocytes with 5 × 10³ TC-1-GLUC-LMP2 target cells and found that the target cells were killed as the specific killing effect was obviously enhanced by the increased quantities of LMP2-peptide stimulated spleens. Furthermore, the tumor cells could not be observed in the mice inoculated TC-1-GLUC-LMP2 cells after being immunized with vaccine-LMP2, while the vaccine-NULL immunized mice showed that tumor volume gradually grew with increased inoculation time. These results indicated that the TC-1-GLUC-LMP2 cells stably expressing LMP2 and GLuc produced tumors in mice, and that the LMP2-specific cytotoxic T lymphocyte (CTL) effectively killed the cells in vitro and in vivo, suggesting that TC-1-GLUC-LMP2 cells can be used as model cells to assess the immune and antitumor effects of LMP2-related vaccines.

Cytolytic virus activation therapy and treatment monitoring for Epstein-Barr virus associated nasopharyngeal carcinoma in a mouse tumor model

Undifferentiated nasopharyngeal carcinoma (NPC) is 100% associated with Epstein‐Barr virus (EBV). Expression of viral proteins in the tumor cells is highly restricted. EBV reactivation by CytoLytic Virus Activation (CLVA) therapy triggers de novo expression of early viral kinases (PK and TK) and uses antiviral treatment to kill activated cells. The mechanism of tumor elimination by CLVA was analyzed in NPC mouse model using C666.1 cells. Valproic acid (VPA) was combined with gemcitabine (GCb) to stimulate EBV reactivation, followed by antiviral treatment with ganciclovir (GCV). A single cycle of CLVA treatment resulted in specific tumor cell killing as indicated by reduced tumor volume, loss of EBV‐positive cells in situ, and paralleled by decreased EBV DNA levels in circulation, which was more pronounced than treatment with GCb alone. In vivo reactivation was confirmed by presence of lytic gene transcripts and proteins in tumors 6 days after GCb/VPA treatment. Virus reactivation was visualized by [¹²⁴I]‐FIAU accumulation in tumors using PET‐scan. This studied showed that CLVA therapy is a potent EBV‐specific targeting approach for killing tumor cells. The [¹²⁴I]‐FIAU appears valuable as PET tracer for studies on CLVA drug dosage and kinetics in vivo, and may find clinical application in treatment monitoring.