The histone deacetylase inhibitor valproic acid enhances equine herpesvirus type 1 (EHV-1)-mediated oncolysis of human glioma cells

Synergistic efficacy of telomerase-specific oncolytic adenoviral therapy and histone deacetylase inhibition in human hepatocellular carcinoma

The telomerase-specific oncolytic adenovirus Telomelysin and the histone deacetylase inhibitor AR42 have demonstrated anticancer effects in preclinical models of human hepatocellular carcinoma (HCC). However, the clinical development of Telomelysin may be hindered by human antiviral immunity and tumor resistance. Combining oncolytic and epigenetic therapies is a viable approach for treating various cancers. This study investigated the potential synergism of Telomelysin and AR42 and the relevant underlying mechanisms. Telomelysin and AR42 exhibited synergistic antiproliferative effects in human HCC models in vitro and in vivo. Apoptosis induced by Telomelysin was significantly enhanced by AR42 in both PLC5 and Hep3B HCC cells. AR42 treatment unexpectedly attenuated the expression of the coxsackievirus and adenovirus receptor and the mRNA levels of human telomerase reverse transcriptase, which may be positively associated with the cytotoxicity of Telomelysin. Meanwhile, the cellular antiviral interferon response was not altered by AR42 treatment. Further, we found that Telomelysin enhanced Akt phosphorylation in HCC cells. AR42 reduced Telomelysin-induced phospho-Akt activation and enhanced Telomelysin-induced apoptosis. The correlation of Akt phosphorylation with drug-induced apoptosis was validated in HCC cells with upregulated or downregulated Akt signaling. Combination therapy with Telomelysin and AR42 demonstrated synergistic anti-HCC efficacy. Clinical trials investigating this new combination regimen are warranted.

Equid Alphaherpesvirus 1 Modulates Actin Cytoskeleton and Inhibits Migration of Glioblastoma Multiforme Cell Line A172

Equid alphaherpesvirus 1 (EHV-1) causes respiratory diseases, abortion, and neurological disorders in horses. Recently, the oncolytic potential of this virus and its possible use in anticancer therapy has been reported, but its influence on cytoskeleton was not evaluated yet. In the following study, we have examined disruptions in actin cytoskeleton of glioblastoma multiforme in vitro model—A172 cell line, caused by EHV-1 infection. We used three EHV-1 strains: two non-neuropathogenic (Jan-E and Rac-H) and one neuropathogenic (EHV-1 26). Immunofluorescent labelling, confocal microscopy, real-time cell growth analysis and Oris^TM cell migration assay revealed disturbed migration of A172 cells infected with the EHV-1, probably due to rearrangement of actin cytoskeleton and the absence of cell projections. All tested strains caused disruption of the actin network and general depolymerization of microfilaments. The qPCR results confirmed the effective replication of EHV-1. Thus, we have demonstrated, for the first time, that EHV-1 infection leads to inhibition of proliferation and migration in A172 cells, which might be promising for new immunotherapy treatment.

Valproic Acid: A Promising Therapeutic Agent in Glioma Treatment

Glioma, characterized by infiltrative growth and treatment resistance, is regarded as the most prevalent intracranial malignant tumor. Due to its poor prognosis, accumulating investigation has been performed for improvement of overall survival (OS) and progression-free survival (PFS) in glioma patients. Valproic acid (VPA), one of the most common histone deacetylase inhibitors (HDACIs), has been detected to directly or synergistically exert inhibitory effects on glioma in vitro and in vivo. In this review, we generalize the latest advances of VPA in treating glioma and its underlying mechanisms and clinical implications, providing a clearer profile for clinical application of VPA as a therapeutic agent for glioma.

Evolving Role of Oncolytic Virotherapy: Challenges and Prospects in Clinical Practice

Selective oncotropism and cytolytic activity against tumors have made certain viruses subject to investigation as novel treatment modalities. However, monotherapy with oncolytic viruses (OVs) has shown limited success and modest clinical benefit. The capacity to genetically engineer OVs makes them a desirable platform to design complementary treatment modalities to overcome the existing treatment options' shortcomings. In recent years, our knowledge of interactions of the tumors with the immune system has expanded profoundly. There is a growing body of literature supporting immunomodulatory roles for OVs. The concept of bioengineering these platforms to induce the desired immune response and complement the current immunotherapeutic modalities to make immune-resistant tumors responsive to immunotherapy is under investigation in preclinical and early clinical trials. This review provides an overview of attempts to optimize oncolytic virotherapy as essential components of the multimodality anticancer therapeutic approach and discusses the challenges in translation to clinical practice.

Inhibition of herpes virus infection in oligodendrocyte cultured cells by valproic acid

Valproic acid (VPA) is a small fatty acid used for treatment of different neurologic diseases such as epilepsy, migraines or bipolar disorders. VPA modulates different processes of cell metabolism that can lead to alterations in susceptibility of several cell types to the infection of Human Immunodeficiency Virus (HIV), Epstein-Barr virus (EBV), as well as to exert an inhibitory effect on the replication of different enveloped viruses in cultured cells. Taken these data into account and the fact that HSV-1 has been involved in some neuropathies, we have characterized the effect of VPA on this herpesvirus infection of the differentiation/maturation-inducible human oligodendrocyte cell line HOG, which resulted more susceptible to VPA inhibition of virus growth after cell differentiation. In these cells, the role of VPA in virus entry was tackled. Incubation with VPA induced a slight but reproducible inhibition in the virus particles uptake mainly observed when the drug was added in the adsorption or early upon infection. In addition, transcription and expression of viral proteins were significantly downregulated in the presence of VPA. Remarkably, when the infective viral production was assessed, VPA dramatically blocked the detection of infectious HSV-1 particles. Herein, our results indicate that VPA treatment of HOG cells significantly reduces the effect of HSV-1 infection, virus entry and productivity without affecting cellular viability.

Overcoming Barriers in Oncolytic Virotherapy with HDAC Inhibitors and Immune Checkpoint Blockade

Oncolytic viruses (OVs) target and destroy cancer cells while sparing their normal counterparts. These viruses have been evaluated in numerous studies at both pre-clinical and clinical levels and the recent Food and Drug Administration (FDA) approval of an oncolytic herpesvirus-based treatment raises optimism that OVs will become a therapeutic option for cancer patients. However, to improve clinical outcome, there is a need to increase OV efficacy. In addition to killing cancer cells directly through lysis, OVs can stimulate the induction of anti-tumour immune responses. The host immune system thus represents a "double-edged sword" for oncolytic virotherapy: on the one hand, a robust anti-viral response will limit OV replication and spread; on the other hand, the immune-mediated component of OV therapy may be its most important anti-cancer mechanism. Although the relative contribution of direct viral oncolysis and indirect, immune-mediated oncosuppression to overall OV efficacy is unclear, it is likely that an initial period of vigorous OV multiplication and lytic activity will most optimally set the stage for subsequent adaptive anti-tumour immunity. In this review, we consider the use of histone deacetylase (HDAC) inhibitors as a means of boosting virus replication and lessening the negative impact of innate immunity on the direct oncolytic effect. We also discuss an alternative approach, aimed at potentiating OV-elicited anti-tumour immunity through the blockade of immune checkpoints. We conclude by proposing a two-phase combinatorial strategy in which initial OV replication and spread is maximised through transient HDAC inhibition, with anti-tumour immune responses subsequently enhanced by immune checkpoint blockade.

Histone deacetylase 6 inhibition enhances oncolytic viral replication in glioma

Oncolytic viral (OV) therapy, which uses genetically engineered tumor-targeting viruses, is being increasingly used in cancer clinical trials due to the direct cytolytic effects of this treatment that appear to provoke a robust immune response against the tumor. As OVs enter tumor cells, intrinsic host defenses have the potential to hinder viral replication and spread within the tumor mass. In this report, we show that histone deacetylase 6 (HDAC6) in tumor cells appears to alter the trafficking of post-entry OVs from the nucleus toward lysosomes. In glioma cell lines and glioma-stem-like cells, HDAC6 inhibition (HDAC6i) by either pharmacologic or genetic means substantially increased replication of oncolytic herpes simplex virus type 1 (oHSV). Moreover, HDAC6i increased shuttling of post-entry oHSV to the nucleus. In addition, electron microscopic analysis revealed that post-entry oHSVs are preferentially taken up into glioma cells through the endosomal pathway rather than via fusion at the cell surface. Together, these findings illustrate a mechanism of glioma cell defense against an incoming infection by oHSV and identify possible approaches to enhance oHSV replication and subsequent lysis of tumor cells.

Evolution of oncolytic viruses: novel strategies for cancer treatment

Many viruses have documented oncolytic activity, with the first evidence observed clinically over a decade ago. In recent years, there has been a resurgence of interest in the field of oncolytic viruses. Viruses may be innately oncotropic, lacking the ability to cause disease in people or they may require engineering to allow selective tumor targeting and attenuation of pathogenicity. Following infection of a neoplastic cell, several events may occur, including direct viral oncolysis, apoptosis, necrotic cell death and autophagic cellular demise. Of late, a large body of work has recognized the ability of oncolytic viruses (OVs) to activate the innate and adaptive immune system, as well as directly killing tumors. The production of viruses expressing transgenes encoding for cytokines, colony-stimulating factors, costimulatory molecules and tumor-associated antigens has been able to further incite immune responses against target tumors. Multiple OVs are now in the advanced stages of clinical trials, with several individual viruses having completed their respective trials with positive results. This review introduces the multiple mechanisms by which OVs are able to act as an antineoplastic therapy, either on their own or in combination with other more traditional treatment modalities. The full benefit and the place where OVs will be integrated into standard-of-care therapies will be determined with ongoing studies ranging from the laboratory to the patient. With various different viruses now in the clinic this therapeutic option is beginning to prove its worth, and the versatility of these agents means further innovative and novel applications will continue to be developed.