Bovine herpesvirus type 1 as a novel oncolytic virus

Targeting the nucleic acid oxidative damage repair enzyme MTH1: a promising therapeutic option

The accumulation of reactive oxygen species (ROS) plays a pivotal role in the development of various diseases, including cancer. Elevated ROS levels cause oxidative stress, resulting in detrimental effects on organisms and enabling tumors to develop adaptive responses. Targeting these enhanced oxidative stress protection mechanisms could offer therapeutic benefits with high specificity, as normal cells exhibit lower dependency on these pathways. MTH1 (mutT homolog 1), a homolog of Escherichia coli's MutT, is crucial in this context. It sanitizes the nucleotide pool, preventing incorporation of oxidized nucleotides, thus safeguarding DNA integrity. This study explores MTH1's potential as a therapeutic target, particularly in cancer treatment, providing insights into its structure, function, and role in disease progression.

Carnitine palmitoyl-transferase 1A is potentially involved in bovine herpesvirus 1 productive infection

Bovine herpesvirus 1(BoHV-1) is an important bovine pathogen that causes great economic loss to cattle farms worldwide. The virus-productive infection in bovine kidney (MDBK) cells results in ATP depletion. The mechanisms are not well understood. Mitochondrial fatty acid β-oxidation (FAO) is an important energy source in many tissues with high energy demand. Since carnitine palmitoyl-transferase 1 A (CPT1A) is the rate-limiting enzyme of FAO, we investigated the interactions between virus-productive infection and CPT1A signaling. Here, we found that virus-productive infection at the later stage significantly decreased CPT1A protein levels in all the detected cells, including MDBK, A549, and Neuro-2A cells, differentially altered the accumulation of CPT1A proteins in the nucleus and cytosol, and re-localized the protein in the nucleus. Etomoxir (ETO), an irreversible inhibitor of CPT1A, inhibited viral replication and partially interfered with the ability of BoHV-1 to alter CPT1A accumulation in the nucleus but not in the cytosol. Furthermore, ETO consistently reduced RNA levels of two viral regulatory proteins (bICP0 and bICP22) and protein expression of virion-associated proteins during productive infection, further supporting the important roles of CPT1A signaling in BoHV-1 productive infection. These data, for the first time, suggest that CPT1A is potentially involved in BoHV-1 productive infection.

GARP and EARP are required for efficient BoHV-1 replication as identified by a genome wide CRISPR knockout screen

The advances in gene editing bring unprecedented opportunities in high throughput functional genomics to animal research. Here we describe a genome wide CRISPR knockout library, btCRISPRko.v1, targeting all protein coding genes in the cattle genome. Using it, we conducted genome wide screens during Bovine Herpes Virus type 1 (BoHV-1) replication and compiled a list of pro-viral and anti-viral candidates. These candidates might influence multiple aspects of BoHV-1 biology such as viral entry, genome replication and transcription, viral protein trafficking and virion maturation in the cytoplasm. Some of the most intriguing examples are VPS51, VPS52 and VPS53 that code for subunits of two membrane tethering complexes, the endosome-associated recycling protein (EARP) complex and the Golgi-associated retrograde protein (GARP) complex. These complexes mediate endosomal recycling and retrograde trafficking to the trans Golgi Network (TGN). Simultaneous loss of both complexes in MDBKs resulted in greatly reduced production of infectious BoHV-1 virions. We also found that viruses released by these deficient cells severely lack VP8, the most abundant tegument protein of BoHV-1 that are crucial for its virulence. In combination with previous reports, our data suggest vital roles GARP and EARP play during viral protein packaging and capsid re-envelopment in the cytoplasm. It also contributes to evidence that both the TGN and the recycling endosomes are recruited in this process, mediated by these complexes. The btCRISPRko.v1 library generated here has been controlled for quality and shown to be effective in host gene discovery. We hope it will facilitate efforts in the study of other pathogens and various aspects of cell biology in cattle.

Oncolytic BHV-1 Is Sufficient to Induce Immunogenic Cell Death and Synergizes with Low-Dose Chemotherapy to Dampen Immunosuppressive T Regulatory Cells

Immunogenic cell death (ICD) can switch immunologically "cold" tumors "hot", making them sensitive to immune checkpoint inhibitor (ICI) therapy. Many therapeutic platforms combine multiple modalities such as oncolytic viruses (OVs) and low-dose chemotherapy to induce ICD and improve prognostic outcomes. We previously detailed many unique properties of oncolytic bovine herpesvirus type 1 (oBHV) that suggest widespread clinical utility. Here, we show for the first time, the ability of oBHV monotherapy to induce bona fide ICD and tumor-specific activation of circulating CD8⁺ T cells in a syngeneic murine model of melanoma. The addition of low-dose mitomycin C (MMC) was necessary to fully synergize with ICI through early recruitment of CD8⁺ T cells and reduced infiltration of highly suppressive PD-1⁺ Tregs. Cytokine and gene expression analyses within treated tumors suggest that the addition of MMC to oBHV therapy shifts the immune response from predominantly anti-viral, as evidenced by a high level of interferon-stimulated genes, to one that stimulates myeloid cells, antigen presentation and adaptive processes. Collectively, these data provide mechanistic insights into how oBHV-mediated therapy modalities overcome immune suppressive tumor microenvironments to enable the efficacy of ICI therapy.

DNA Damage Response Differentially Affects BoHV-1 Gene Transcription in Cell Type-Dependent Manners

Bovine herpesvirus 1 (BoHV-1), an important pathogen of cattle, is also a promising oncolytic virus. Recent studies have demonstrated that the virus infection induces DNA damage and DNA damage response (DDR), potentially accounting for virus infection-induced cell death and oncolytic effects. However, whether the global DDR network affects BoHV-1 productive infection remains to be elucidated. In this study, we show that global DDR induced by ultraviolet (UV) irradiation prior to BoHV-1 infection differentially affected transcription of immediate early (IE) genes, such as infected cell protein 0 (bICP0) and bICP22, in a cell-type-dependent manner. In addition, UV-induced DDR may affect the stabilization of viral protein levels, such as glycoprotein C (gC) and gD, because the variation in mRNA levels of gC and gD as a consequence of UV treatment were not in line with the variation in individual protein levels. The virus productive infection also affects UV-primed DDR signaling, as demonstrated by the alteration of phosphorylated histone H2AX (γH2AX) protein levels and γH2AX formation following virus infection. Taken together, for the first time, we evidenced the interplay between UV-primed global DDR and BoHV-1 productive infection. UV-primed global DDR differentially modulates the transcription of virus genes and stabilization of virus protein. Vice versa, the virus infection may affect UV-primed DDR signaling.

β-Catenin-Specific Inhibitor, iCRT14, Promotes BoHV-1 Infection-Induced DNA Damage in Human A549 Lung Adenocarcinoma Cells by Enhancing Viral Protein Expression

Oncolytic bovine herpesvirus type 1 (BoHV-1) infection induces DNA damage in human lung adenocarcinoma cell line A549. However, the underlying mechanisms are not fully understood. We found that BoHV-1 infection decreased the steady-state protein levels of p53-binding protein 1 (53BP1), which plays a central role in dictating DNA damage repair and maintaining genomic stability. Furthermore, BoHV-1 impaired the formation of 53BP1 foci, suggesting that BoHV-1 inhibits 53BP1-mediated DNA damage repair. Interestingly, BoHV-1 infection redistributed intracellular β-catenin, and iCRT14 (5-[[2,5-Dimethyl-1-(3-pyridinyl)-1H-pyrrol-3-yl]methylene]-3-phenyl-2,4-thiazolidinedione), a β-catenin-specific inhibitor, enhanced certain viral protein expression, such as the envelope glycoproteins gC and gD, and enhanced virus infection-induced DNA damage. Therefore, for the first time, we provide evidence showing that BoHV-1 infection disrupts 53BP1-mediated DNA damage repair and suggest β-catenin as a potential host factor restricting both virus replication and DNA damage in A549 cells.

Potential Approaches Versus Approved or Developing Chronic Myeloid Leukemia Therapy

Tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of patients with chronic myeloid leukemia (CML). However, continued use of these inhibitors has contributed to the increase in clinical resistance and the persistence of resistant leukemic stem cells (LSCs). So, there is an urgent need to introduce additional targeted and selective therapies to eradicate quiescent LSCs, and to avoid the relapse and disease progression. Here, we focused on emerging BCR-ABL targeted and non-BCR-ABL targeted drugs employed in clinical trials and on alternative CML treatments, including antioxidants, oncolytic virus, engineered exosomes, and natural products obtained from marine organisms that could pave the way for new therapeutic approaches for CML patients.

The Oncolytic Caprine Herpesvirus 1 (CpHV-1) Induces Apoptosis and Synergizes with Cisplatin in Mesothelioma Cell Lines: A New Potential Virotherapy Approach

Malignant mesothelioma (MM) is an aggressive asbestos-related cancer, against which no curative modalities exist. Oncolytic virotherapy is a promising therapeutic approach, for which MM is an ideal candidate; indeed, the pleural location provides direct access for the intra-tumoral injection of oncolytic viruses (OVs). Some non-human OVs offer advantages over human OVs, including the non-pathogenicity in humans and the absence of pre-existing immunity. We previously showed that caprine herpesvirus 1 (CpHV-1), a non-pathogenic virus for humans, can kill different human cancer cell lines. Here, we assessed CpHV-1 effects on MM (NCI-H28, MSTO, NCI-H2052) and non-tumor mesothelial (MET-5A) cells. We found that CpHV-1 reduced cell viability and clonogenic potential in all MM cell lines without affecting non-tumor cells, in which, indeed, we did not detect intracellular viral DNA after treatment. In particular, CpHV-1 induced MM cell apoptosis and accumulation in G0/G1 or S cell cycle phases. Moreover, CpHV-1 strongly synergized with cisplatin, the drug currently used in MM chemotherapy, and this agent combination did not affect normal mesothelial cells. Although further studies are required to elucidate the mechanisms underlying the selective CpHV-1 action on MM cells, our data suggest that the CpHV-1-cisplatin combination could be a feasible strategy against MM.

The contribution of bovines to human health against viral infections

In the last 40 years, novel viruses have evolved at a much faster pace than other pathogens. Viral diseases pose a significant threat to public health around the world. Bovines have a longstanding history of significant contributions to human nutrition, agricultural, industrial purposes, medical research, drug and vaccine development, and livelihood. The life cycle, genomic structures, viral proteins, and pathophysiology of bovine viruses studied in vitro paved the way for understanding the human counterparts. Calf model has been used for testing vaccines against RSV, papillomavirus vaccines and anti-HCV agents were principally developed after using the BPV and BVDV model, respectively. Some bovine viruses-based vaccines (BPIV-3 and bovine rotaviruses) were successfully developed, clinically tried, and commercially produced. Cows, immunized with HIV envelope glycoprotein, produced effective broadly neutralizing antibodies in their serum and colostrum against HIV. Here, we have summarized a few examples of human viral infections for which the use of bovines has contributed to the acquisition of new knowledge to improve human health against viral infections covering the convergence between some human and bovine viruses and using bovines as disease models. Additionally, the production of vaccines and drugs, bovine-based products were covered, and the precautions in dealing with bovines and bovine-based materials.

Oncolytic Bovine Herpesvirus 1 Inhibits Human Lung Adenocarcinoma A549 Cell Proliferation and Tumor Growth by Inducing DNA Damage

Bovine herpesvirus 1 (BoHV-1) is a promising oncolytic virus with broad antitumor spectrum; however, its oncolytic effects on human lung adenocarcinoma in vivo have not been reported. In this study, we report that BoHV-1 can be used as an oncolytic virus for human lung adenocarcinoma, and elucidate the underlying mechanism of how BoHV-1 suppresses tumor cell proliferation and growth. First, we examined the oncolytic activities of BoHV-1 in human lung adenocarcinoma A549 cells. BoHV-1 infection reduced the protein levels of histone deacetylases (HDACs), including HDAC1-4 that are promising anti-tumor drug targets. Furthermore, the HDAC inhibitor Trichostatin A (TSA) promoted BoHV-1 infection and exacerbated DNA damage and cytopathology, suggesting a synergy between BoHV-1 and TSA. In the A549 tumor xenograft mouse model, we, for the first time, showed that BoHV-1 can infect tumor and suppressed tumor growth with a similar high efficacy as the treatment of TSA, and HDACs have potential effects on the virus replication. Taken together, our study demonstrates that BoHV-1 has oncolytic effects against human lung adenocarcinoma in vivo.

Oncolytic Viruses in Combination Therapeutic Approaches with Epigenetic Modulators: Past, Present, and Future Perspectives

Simple Summary

Cancer rates have been accelerating significantly in recent years. Despite notable advances having been made in cancer therapy, and numerous studies being currently conducted in clinical trials, research is always looking for new treatment. Novel and promising anticancer therapies comprise combinations of oncolytic viruses and epigenetic modulators, including chromatin modifiers, such as DNA methyltransferase and histone deacetylases, and microRNA. Combinatorial treatments have several advantages: they enhance viral entry, replication, and spread between proximal cells and, moreover, they strengthen the immune response. In this review we summarize the main combination of therapeutic approaches, giving an insight into past, present, and future perspectives.

Abstract

According to the World Cancer Report, cancer rates have been increased by 50% with 15 million new cases in the year 2020. Hepatocellular carcinoma (HCC) is the only one of the most common tumors to cause a huge increase in mortality with a survival rate between 40% and 70% at 5 years, due to the high relapse and limitations associated with current therapies. Despite great progress in medicine, oncological research is always looking for new therapies: different technologies have been evaluated in clinical trials and others have been already used in clinics. Among them, oncolytic virotherapy represents a therapeutic option with a widespread possibility of approaches and applications. Oncolytic viruses are naturally occurring, or are engineered, viruses characterized by the unique features of preferentially infecting, replicating, and lysing malignant tumor cells, as well as activating the immune response. The combination of oncolytic virotherapy and chemical drugs are arousing great interest in the tumor treatment. In this scenario, novel and promising anticancer therapies comprise combinations of oncolytic viruses and epigenetic modulators or inhibitors of the signalling pathways. Combination treatments are required to improve the immune response and allow viral entry, replication, and diffusion between proximal cells. In this review, we summarize all combination therapies associated with virotherapy, including co-administered inhibitors of chromatin modifiers (combination strategies) and inserted target sites for miRNAs (recombination or arming strategies).

The Role of Epidermal Growth Factor Receptor Signaling Pathway during Bovine Herpesvirus 1 Productive Infection in Cell Culture

Accumulating studies have shown that the epidermal growth factor receptor (EGFR) signaling pathway plays an essential role in mediating cellular entry of numerous viruses. In this study, we report that bovine herpesvirus 1 (BoHV-1) productive infection in both the human lung carcinoma cell line A549 and bovine kidney (MDBK) cells leads to activation of EGFR, as demonstrated by the increased phosphorylation of EGFR at Tyr1068 (Y1068), which in turn plays important roles in virus infection. A time-of-addition assay supported that virus replication at post-entry stages was affected by the EGFR specific inhibitor Gefitinib. Interestingly, both phospholipase C-γ1 (PLC-γ1) and Akt, canonical downstream effectors of EGFR, were activated following virus infection in A549 cells, while Gefitinib could inhibit the activation of PLC-γ1 but not Akt. In addition, virus titers in A549 cells was inhibited by chemical inhibition of PLC-γ1, but not by the inhibition of Akt. However, the Akt specific inhibitor Ly294002 could significantly reduce the virus titer in MDBK cells. Taken together, our data suggest that PLC-γ1 is stimulated in part through EGFR for efficient replication in A549 cells, whereas Akt can be stimulated by virus infection independent of EGFR, and is not essential for virus productive infection, indicating that Akt modulates BoHV-1 replication in a cell type-dependent manner. This study provides novel insights on how BoHV-1 infection activates EGFR signaling transduction to facilitate virus replication.

Bovine herpesvirus-1 infection in mouse neuroblastoma (Neuro-2A) cells

Bovine herpesvirus 1 (BoHV-1) is an important cattle pathogen, that may cause rhinotracheitis, abortions and shipping fever. Virus establishes latency in sensory neurons, but periodically could reactivate. Recent studies identified mouse neuroblastoma (Neuro-2A) cells as a novel cell culture model to study factors that regulate BoHV-1 productive infection in neuronal cells. Herein, following BoHV-1 infection in Neuro-2A, a reduced cell viability occurred. Membrane damage and death morphological alterations, features of apoptosis and necrosis, were distinguished in infected cells. In addition, biochemical signs of apoptosis (caspase 3 activation and PARP cleavage) were observed. These results were accompanied by incomplete autophagy due to enhanced amounts of autophagic markers (LC3-II, ATG5 and Beclin 1), in the presence of increased levels of p62. Interestingly, protein expression of viral infected cell protein 0 (bICP0) was detected in Neuro-2A cells, although BoHV-1 inefficiently replicates in these cells, because just low levels of viral yield were found. Taken together, our results suggest that BoHV-1 may exert its potential neurotoxicity through a combined mechanism of necrosis and apoptosis. Moreover, incomplete autophagy occurred during BoHV-1 replication in Neuro-2A cells, which were favourable for viral persistence.

Crystal structure of bovine herpesvirus 1 glycoprotein D bound to nectin-1 reveals the basis for its low-affinity binding to the receptor

Bovine herpesvirus 1 (BHV-1) has received increasing attention for its potential oncolytic applications. BHV-1 recognizes nectin-1 for cell entry via viral glycoprotein D (gD) but represents a low-affinity nectin-1 binding virus. The molecular basis underlying this low receptor-binding affinity, however, remains unknown. Here, the crystal structures of BHV-1 gD in the free and nectin-1-bound forms are presented. While showing an overall resembled nectin-1 binding mode to other alphaherpesvirus gDs, BHV-1 gD has a unique G-strand/α2-helix interloop that disturbs gD/nectin-1 interactions. Residue R188 residing in this loop is observed to otherwise cause strong steric hindrance with the bound receptor, making a large conformational change of the loop a prerequisite for nectin-1 engagement. Subsequently, substitution of R188 with glycine markedly enhances the affinity of the BHV-1-gD/nectin-1 interaction (by about fivefold). These structural and functional data delineate the receptor-recognition basis for BHV-1, which might facilitate BHV-1-based oncolytic design in the future.

Caprine herpesvirus 1 (CpHV-1) as a potential candidate for oncolytic virotherapy

Caprine Herpesvirus type 1 (CpHV-1) is a species-specific herpes virus able to induce apoptosis in several biological systems. In the present study we aimed to investigate the ability of CpHV-1 to reduce cells viability, to replicate and to cause cell death also in human cancer cell lines. We tested the CpHV-1 effects on HEL-299, Vero, MDA-MB-468, HeLa, U2OS, PC3, A549 and K562 neoplastic cell lines and on MDBK cells. Firstly, we evaluated the effect of CpHV-1 infection on cell viability by MTT assay and our data showed that CpHV-1 can induce a marked cytopathic effect (CPE) in most of cell lines tested, except for HEL-299, Vero and K562 cells. The reduction of cell viability was associated with a significant increase of viral production. We next investigated if CpHV-1 was able to induce cell death and so through western blotting analysis we evaluated cleaved caspase 3, LC3II and p62 protein levels after infection. Caspase 3 activation was detected in MDBK cells and, even if at different times p.i., also in MDA-MB-468, U2OS, and PC3 cell lines, while LC3II increase and concomitant p62 protein reduction were observed only in U2OS, and A549 cells, no significant alteration of these proteins was observed in the other cell lines tested. Finally, to confirm virus ability to trigger apoptosis we performed an Annexin-V apoptosis test after 24 h p.i. Although we need to further explore mechanisms underlying CpHV-1 treatment, this study could serve as the basis for the development of new treatment options aiming to fight several cancer types.

Induction of Oxidative DNA Damage in Bovine Herpesvirus 1 Infected Bovine Kidney Cells (MDBK Cells) and Human Tumor Cells (A549 Cells and U2OS Cells)

Bovine herpesvirus 1 (BoHV-1) is an important pathogen of cattle that causes lesions in mucosal surfaces, genital tracts and nervous systems. As a novel oncolytic virus, BoHV-1 infects and kills numerous human tumor cells. However, the mechanisms underlying the virus-induced cell damages are not fully understood. In this study, we demonstrated that virus infection of MDBK cells induced high levels of DNA damage, because the percentage of comet tail DNA (tailDNA%) determined by comet assay, a direct indicator of DNA damage, and the levels of 8-hydroxyguanine (8-oxoG) production, an oxidative DNA damage marker, consistently increased following the virus infection. The expression of 8-oxoguanine DNA glycosylase (OGG-1), an enzyme responsible for the excision of 8-oxoG, was significantly decreased due to the virus infection, which corroborated with the finding that BoHV-1 infection stimulated 8-oxoG production. Furthermore, the virus replication in human tumor cells such as in A549 cells and U2OS cells also induced DNA damage. Chemical inhibition of reactive oxidative species (ROS) production by either ROS scavenger N-Acetyl-l-cysteine or NOX inhibitor diphenylene iodonium (DPI) significantly decreased the levels of tailDNA%, suggesting the involvement of ROS in the virus induced DNA lesions. Collectively, these results indicated that BoHV-1 infection of these cells elicits oxidative DNA damages, providing a perspective in understanding the mechanisms by which the virus induces cell death in both native host cells and human tumor cells.

Designing Herpes Viruses as Oncolytics

Oncolytic herpes simplex virus (oHSV) was one of the first genetically-engineered oncolytic viruses. Because herpes simplex virus (HSV) is a natural human pathogen that can cause serious disease, it is incumbent that it be genetically-engineered or significantly attenuated for safety. Here we present a detailed explanation of the functions of HSV-1 genes frequently mutated to endow oncolytic activity. These genes are non-essential for growth in tissue culture cells but are important for growth in post-mitotic cells, interfering with intrinsic antiviral and innate immune responses or causing pathology, functions dispensable for replication in cancer cells. Understanding the function of these genes leads to informed creation of new oHSVs with better therapeutic efficacy. Virus infection and replication can also be directed to cancer cells through tumor-selective receptor binding and transcriptional- or post-transcriptional miRNA-targeting, respectively. In addition to the direct effects of oHSV on infected cancer cells and tumors, oHSV can be 'armed' with transgenes that are: reporters, to track virus replication and spread; cytotoxic, to kill uninfected tumor cells; immune modulatory, to stimulate anti-tumor immunity; or tumor microenvironment altering, to enhance virus spread or to inhibit tumor growth. In addition to HSV-1, other alphaherpesviruses are also discussed for their oncolytic activity.

Oncolytic bovine herpesvirus type 1 as a broad spectrum cancer therapeutic

Oncolytic viruses selectively replicate in tumor cells and elicit antitumor effects in vivo by both direct and indirect methods. They are attractive avenues of cancer therapy due to the absence of toxic side effects often seen in current treatment modalities. Bovine herpesvirus type 1 (BHV-1) holds promise as a broad-spectrum oncolytic vector that is able to infect and kill human tumor cells from a variety of histological origins, including cancer-initiating cells. In the majority of cases, BHV-1 elicits tumor cell death in the absence of a productive infection. In vivo, BHV-1 affects the incidence of secondary lesions in cotton rats bearing subcutaneous breast adenocarcinomas. These recent studies contribute to the characterization of BHV-1 as an oncolytic virus.

Enhanced efficacy with azacytidine and oncolytic BHV-1 in a tolerized cotton rat model of breast adenocarcinoma

Oncolytic viruses selectively replicate in cancer cells by exploiting biochemical differences between normal and tumor cells. Treatment with epigenetic modifiers such as 5-Azacytidine, a DNA methyltransferase inhibitor, increases the replication and cytotoxicity of oncolytic viruses in vivo and in vitro. The cotton rat is an attractive animal to study oncolytic viruses, as syngeneic models of breast adenocarcinoma and osteosarcoma are well established, and many features of primary and secondary tumor growth recapitulate human disease. Treatment of LCRT breast cancer cells with 5-Azacytidine increases bovine herpesvirus type 1 (BHV-1)-mediated cytotoxicity in vitro, with Chou-Talalay analysis indicating a very strong synergy. In vivo, BHV-1 monotherapy delayed tumor growth but did not improve survival of cotton rats with subcutaneous breast adenocarcinomas. However, combination therapy significantly decreased the incidence of secondary lesions, with enhanced tumor cell clearance and evidence of immune cell infiltration compared to BHV-1 monotherapy. Together, these results warrant further investigation of BHV-1 combination therapy with epigenetic modifiers for the treatment of breast cancer, particularly in the context of the prevention and treatment of secondary lesions.

Permissiveness of human cancer cells to oncolytic bovine herpesvirus 1 is mediated in part by KRAS activity

Oncolytic viruses (OVs) are attractive avenues of cancer therapy due to the absence of toxic side effects often seen with current treatment modalities. Bovine herpesvirus 1 (BHV-1) is a species-specific virus that does not induce cytotoxicity in normal primary human cells but can infect and kill various human immortalized and transformed cell lines. To gain a better understanding of the oncolytic breadth of BHV-1, the NCI panel of established human tumor cell lines was screened for sensitivity to the virus. Overall, 72% of the panel is permissive to BHV-1 infection, with corresponding decreases in cellular viability. This sensitivity is in comparison to a sensitivity of only 32% for a herpes simplex virus 1 (HSV-1)-based oncolytic vector. Strikingly, while 35% of the panel supports minimal or no BHV-1 replication, significant decreases in cellular viability still occur. These data suggest that BHV-1 is an OV with tropism for multiple tumor types and is able to induce cytotoxicity independent of significant virus replication. In contrast to other species-specific OVs, cellular sensitivity to BHV-1 does not correlate with type I interferon (IFN) signaling; however, mutations in KRAS were found to correlate with high levels of virus replication. The knockdown or overexpression of KRAS in human tumor cell lines yields modest changes in viral titers; however, overexpression of KRAS in normal primary cells elicits permissivity to BHV-1 infection. Together, these data suggest that BHV-1 is a broad-spectrum OV with a distinct mechanism of tumor targeting.

IMPORTANCE

Cancer remains a significant health issue, and novel treatments are required, particularly for tumors that are refractory to conventional therapies. Oncolytic viruses are a novel platform given their ability to specifically target tumor cells while leaving healthy cells intact. For this strategy to be successful, a fundamental understanding of virus-host interactions is required. We previously identified bovine herpesvirus 1 as a novel oncolytic virus with many unique and clinically relevant features. Here, we show that BHV-1 can target a wide range of human cancer types, most potently lung cancer. In addition, we show that enhanced KRAS activity, a hallmark of many cancers, is one of the factors that increases BHV-1 oncolytic capacity. These findings hold potential for future treatments, particularly in the context of lung cancer, where KRAS mutations are a negative predictor of treatment efficacy.

Cellular transcription factors induced in trigeminal ganglia during dexamethasone-induced reactivation from latency stimulate bovine herpesvirus 1 productive infection and certain viral promoters

Bovine herpesvirus 1 (BHV-1), an alphaherpesvirinae subfamily member, establishes latency in sensory neurons. Elevated corticosteroid levels, due to stress, reproducibly triggers reactivation from latency in the field. A single intravenous injection of the synthetic corticosteroid dexamethasone (DEX) to latently infected calves consistently induces reactivation from latency. Lytic cycle viral gene expression is detected in sensory neurons within 6 h after DEX treatment of latently infected calves. These observations suggested that DEX stimulated expression of cellular genes leads to lytic cycle viral gene expression and productive infection. In this study, a commercially available assay-Bovine Gene Chip-was used to compare cellular gene expression in the trigeminal ganglia (TG) of calves latently infected with BHV-1 versus DEX-treated animals. Relative to TG prepared from latently infected calves, 11 cellular genes were induced more than 10-fold 3 h after DEX treatment. Pentraxin three, a regulator of innate immunity and neurodegeneration, was stimulated 35- to 63-fold after 3 or 6 h of DEX treatment. Two transcription factors, promyelocytic leukemia zinc finger (PLZF) and Slug were induced more than 15-fold 3 h after DEX treatment. PLZF or Slug stimulated productive infection 20- or 5-fold, respectively, and Slug stimulated the late glycoprotein C promoter more than 10-fold. Additional DEX-induced transcription factors also stimulated productive infection and certain viral promoters. These studies suggest that DEX-inducible cellular transcription factors and/or signaling pathways stimulate lytic cycle viral gene expression, which subsequently leads to successful reactivation from latency in a small subset of latently infected neurons.

Non-human viruses developed as therapeutic agent for use in humans

Viruses usually infect a restricted set of host species, and only in rare cases does productive infection occur outside the natural host range. Infection of a new host species can manifest as a distinct disease. In this respect, the use of non‐human viruses in clinical therapy may be a cause for concern. It could provide the opportunity for the viruses to adapt to the new host and be transferred to the recipient's relatives or medical caretakers, or even to the normal host species. Such environmental impact is evidently undesirable. To forecast future clinical use of non‐human viruses, a literature study was performed to identify the viruses that are being considered for application as therapeutic agents for use in humans. Twenty‐seven non‐human virus species were identified that are in (pre)clinical development, mainly as oncolytic agents. For risk management, it is essential that the potential environmental consequences are assessed before initiating clinical use, even if the virus is not formally classified as a genetically modified organism. To aid such assessment, each of these viruses was classified in one of five relative environmental risk categories, ranging from “Negligible” to “Very High”. Canary pox virus and the Autographa californica baculovirus were assigned a “Negligible” classification, and Seneca Valley virus, murine leukemia virus, and Maraba virus to the “High” category. A complicating factor in the classification is the scarcity of publicly available information on key aspects of virus biology in some species. In such cases the relative environmental risk score was increased as a precaution. Copyright © 2011 John Wiley & Sons, Ltd.