The herpes simplex virus virulence factor ICP34.5 and the cellular protein MyD116 complex with proliferating cell nuclear antigen through the 63-amino-acid domain conserved in ICP34.5, MyD116, and GADD34

Triple-Negative Breast Cancer: Basic Biology and Immuno-Oncolytic Viruses

Triple-negative breast cancer (TNBC) is the most lethal subtype of breast cancer. TNBC diagnoses account for approximately one-fifth of all breast cancer cases globally. The lack of receptors for estrogen, progesterone, and human epidermal growth factor 2 (HER-2, CD340) results in a lack of available molecular-based therapeutics. This increases the difficulty of treatment and leaves more traditional as well as toxic therapies as the only available standards of care in many cases. Recurrence is an additional serious problem, contributing substantially to its higher mortality rate as compared to other breast cancers. Tumor heterogeneity also poses a large obstacle to treatment approaches. No driver of tumor development has been identified for TNBC, and large variations in mutational burden between tumors have been described previously. Here, we describe the biology of six different subtypes of TNBC, based on differential gene expression. Subtype differences can have a large impact on metastatic potential and resistance to treatment. Emerging antibody-based therapeutics, such as immune checkpoint inhibitors, have available targets for small subsets of TNBC patients, leading to partial responses and relatively low overall efficacy. Immuno-oncolytic viruses (OVs) have recently become significant in the pursuit of effective treatments for TNBC. OVs generally share the ability to ignore the heterogeneous nature of TNBC cells and allow infection throughout a treated tumor. Recent genetic engineering has allowed for the enhancement of efficacy against certain tumor types while avoiding the most common side effects in non-cancerous tissues. In this review, TNBC is described in order to address the challenges it presents to potential treatments. The OVs currently described preclinically and in various stages of clinical trials are also summarized, as are their strategies to enhance therapeutic potential.

HSV1716 Prevents Myeloma Cell Regrowth When Combined with Bortezomib In Vitro and Significantly Reduces Systemic Tumor Growth in Mouse Models

Multiple myeloma remains largely incurable due to refractory disease; therefore, novel treatment strategies that are safe and well-tolerated are required. Here, we studied the modified herpes simplex virus HSV1716 (SEPREHVIR®), which only replicates in transformed cells. Myeloma cell lines and primary patient cells were infected with HSV1716 and assessed for cell death using propidium iodide (PI) and Annexin-V staining and markers of apoptosis and autophagy by qPCR. Myeloma cell death was associated with dual PI and Annexin-V positivity and increased expression of apoptotic genes, including CASP1, CASP8, CASP9, BAX, BID, and FASL. The combination of HSV1716 and bortezomib treatments prevented myeloma cell regrowth for up to 25 days compared to only transient cell growth suppression with bortezomib treatment. The viral efficacy was tested in a xenograft (JJN-3 cells in NSG mice) and syngeneic (murine 5TGM1 cells in C57BL/KaLwRijHsd mice) systemic models of myeloma. After 6 or 7 days, the post-tumor implantation mice were treated intravenously with the vehicle or HSV1716 (1 × 107 plaque forming units/1 or 2 times per week). Both murine models treated with HSV1716 had significantly lower tumor burden rates compared to the controls. In conclusion, HSV1716 has potent anti-myeloma effects and may represent a novel therapy for multiple myeloma.

Enterovirus 71 Activates GADD34 via Precursor 3CD to Promote IRES-Mediated Viral Translation

Enterovirus 71 (EV71) is the major pathogen of hand, foot, and mouth disease. In severe cases, it can cause life-threatening neurological complications, such as aseptic meningitis and polio-like paralysis. There are no specific antiviral treatments for EV71 infections. In a previous study, the host protein growth arrest and DNA damage-inducible protein 34 (GADD34) expression was upregulated during EV71 infection determined by ribosome profiling and RNA-sequencing. Here, we investigated the interactions of host protein GADD34 and EV71 during infections. Rhabdomyosarcoma (RD) cells were infected with EV71 resulting in a significant increase in expression of GADD34 mRNA and protein. Through screening of EV71 protein we determined that the non-structural precursor protein 3CD is responsible for upregulating GADD34. EV71 3CD increased the RNA and protein levels of GADD34, while the 3CD mutant Y441S could not. 3CD upregulated GADD34 translation via the upstream open reading frame (uORF) of GADD34 5'untranslated regions (UTR). EV71 replication was attenuated by the knockdown of GADD34. The function of GADD34 to dephosphorylate eIF2α was unrelated to the upregulation of EV71 replication, but the PEST 1, 2, and 3 regions of GADD34 were required. GADD34 promoted the EV71 internal ribosome entry site (IRES) activity through the PEST repeats and affected several other viruses. Finally, GADD34 amino acids 563 to 565 interacted with 3CD, assisting GADD34 to target the EV71 IRES. Our research reveals a new mechanism by which GADD34 promotes viral IRES and how the EV71 non-structural precursor protein 3CD regulates host protein expression to support viral replication.

IMPORTANCE Identification of host factors involved in viral replication is an important approach in discovering viral pathogenic mechanisms and identifying potential therapeutic targets. Previously, we screened host proteins that were upregulated by EV71 infection. Here, we report the interaction between the upregulated host protein GADD34 and EV71. EV71 non-structural precursor protein 3CD activates the RNA and protein expression of GADD34. Our study reveals that 3CD regulates the uORF of the 5′-UTR to increase GADD34 translation, providing a new explanation for how viral proteins regulate host protein expression. GADD34 is important for EV71 replication, and the key functional domains of GADD34 that promote EV71 are PEST 1, 2, and 3 regions. We report that GADD34 promotes viral IRES for the first time and this process is independent of its eIF2α phosphatase activity.

Oncolytic virus therapy in cancer: A current review

In view of the advancement in the understanding about the most diverse types of cancer and consequently a relentless search for a cure and increased survival rates of cancer patients, finding a therapy that is able to combat the mechanism of aggression of this disease is extremely important. Thus, oncolytic viruses (OVs) have demonstrated great benefits in the treatment of cancer because it mediates antitumor effects in several ways. Viruses can be used to infect cancer cells, especially over normal cells, to present tumor-associated antigens, to activate "danger signals" that generate a less immune-tolerant tumor microenvironment, and to serve transduction vehicles for expression of inflammatory and immunomodulatory cytokines. The success of therapies using OVs was initially demonstrated by the use of the genetically modified herpes virus, talimogene laherparepvec, for the treatment of melanoma. At this time, several OVs are being studied as a potential treatment for cancer in clinical trials. However, it is necessary to be aware of the safety and possible adverse effects of this therapy; after all, an effective treatment for cancer should promote regression, attack the tumor, and in the meantime induce minimal systemic repercussions. In this manuscript, we will present a current review of the mechanism of action of OVs, main clinical uses, updates, and future perspectives on this treatment.

"Non-Essential" Proteins of HSV-1 with Essential Roles In Vivo: A Comprehensive Review

Viruses encode for structural proteins that participate in virion formation and include capsid and envelope proteins. In addition, viruses encode for an array of non-structural accessory proteins important for replication, spread, and immune evasion in the host and are often linked to virus pathogenesis. Most virus accessory proteins are non-essential for growth in cell culture because of the simplicity of the infection barriers or because they have roles only during a state of the infection that does not exist in cell cultures (i.e., tissue-specific functions), or finally because host factors in cell culture can complement their absence. For these reasons, the study of most nonessential viral factors is more complex and requires development of suitable cell culture systems and in vivo models. Approximately half of the proteins encoded by the herpes simplex virus 1 (HSV-1) genome have been classified as non-essential. These proteins have essential roles in vivo in counteracting antiviral responses, facilitating the spread of the virus from the sites of initial infection to the peripheral nervous system, where it establishes lifelong reservoirs, virus pathogenesis, and other regulatory roles during infection. Understanding the functions of the non-essential proteins of herpesviruses is important to understand mechanisms of viral pathogenesis but also to harness properties of these viruses for therapeutic purposes. Here, we have provided a comprehensive summary of the functions of HSV-1 non-essential proteins.

Herpes Simplex Virus 1 ICP34.5 Alters Mitochondrial Dynamics in Neurons

Expression of viral genes and activation of innate antiviral responses during infection result in an increase in reactive oxygen species (ROS) and toxic by-products of energy metabolism which can lead to cell death. The mitochondrion and its associated proteins are crucial regulators of these responses and related pathways such as autophagy and apoptosis. Through a mass spectrometry approach, we have shown that the herpes simplex virus 1 (HSV-1) neurovirulence- and autophagy-modulating protein ICP34.5 interacts with numerous mitochondrion-associated factors. Specifically, we showed that amino acids 68 to 87 of ICP34.5, the domain that binds beclin1 and controls neurovirulence, are necessary for interactions with PGAM5, KEAP1, and other regulators of the antioxidant response, mitochondrial trafficking, and programmed cell death. We further show that while this domain interacts with multiple cellular stress response factors, it does not alter apoptosis or antioxidant gene expression. That said, the attenuated replication of a recombinant virus lacking residues 68 to 87 (termed Δ68-87) in primary human fibroblasts was restored by addition of ferric nitrate. Furthermore, in primary mouse neurons, the perinuclear localization of mitochondria that follows infection with HSV-1 was notably absent following Δ68-87 infection. Through this 20-amino-acid domain, ICP34.5 significantly reduces mitochondrial motility in axons of neurons. We propose the hypothesis that ICP34.5 promotes perinuclear mitochondrial localization by modulating transport of mitochondria through interaction with PGAM5. These data expand upon previous observations of altered mitochondrial dynamics following alphaherpesvirus infections and identify a key determinant of this activity during HSV-1 infections.IMPORTANCE Herpes simplex virus persists lifelong in neurons and can reactivate to cause recurrent lesions in mucosal tissues. A key determinant of virulence is the viral protein ICP34.5, of which residues 68 to 87 significantly contribute to neurovirulence through an unknown mechanism. Our report provides evidence that residues 68 to 87 of ICP34.5 are required for binding mitochondrion-associated factors. These interactions alter mitochondrial dynamics in neurons, thereby facilitating viral replication and pathogenesis.

The Central Role of Inflammation Associated with Checkpoint Inhibitor Treatments

An important function of the immune system is its ability to differentiate between healthy cells in the organism and "foreign" cells, allowing the latest to be attacked and the first ones to be conserved. The most important molecules in this process are considered to be checkpoint inhibitors. This review is focused on the association between cancer and inflammation, underlying the mechanisms of action of monoclonal antibodies that are targeting checkpoint inhibitors: ipilimumab against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and pembrolizumab and nivolumab against programmed cell death protein 1 (PD-1), their indications for treatment, and side effects. Presence of antibodies against checkpoint inhibitors shows promising results in the clinical trials in patients with types of cancer difficult to treat until now such as melanoma, non-small-cell lung cancer (NSCLC), and renal cell carcinoma, offering an increase in the overall survival rate, response rate, and progression-free rate. Resistance is now observed to emerge in patients treated with this therapy, showing the need for more studies in order to design a biomarker that will predict the type of response to immunotherapy.

Pharmacologic Modulation of Human Immunity in the Era of Immuno-oncology: Something Old, Something New

The concept of exploiting the immune system to treat cancer forms the basis of immuno-oncology. Since its birth in the late 1800s, immuno-oncology, or cancer immunotherapy, has come a long way. With better understanding of the complex relationship between tumor and the immune system, we have been able to explore and develop various modalities of anticancer therapies. In this review, we summarize the main strategies of immunotherapy that are available today: monoclonal antibodies, anticancer vaccines, cytokines, and adoptive T-cell therapy. We also highlight the unique set of adverse effects associated with modern immunotherapy and propose nonsteroidal immunomodulators and anticytokine antibodies as treatment options for toxicities. The future of immuno-oncology is discussed, including combination therapy, drug-antibody conjugates, epigenetic drugs, using nanoparticles for drug delivery, new antigen discovery, and developing biomarkers to assess treatment responses. A data search was conducted using PubMed and included studies published through November 1, 2017. Search terms used include cancer immunotherapy, pembrolizumab, ipilimumab, nivolumab, PD-1 inhibitors, PD-L1 inhibitors, checkpoint inhibitors, anticancer vaccines, TVEC, and adoptive cell therapy.

Overcoming resistance to targeted therapy with immunotherapy and combination therapy for metastatic melanoma

Resistance to targeted therapy is an ongoing problem for the successful treatment of Stage IV metastatic melanoma. For many patients, the use of targeted therapies, such as BRAF kinase inhibitors, were initially promising yet resistance inevitably occurred. Even after combining BRAF kinase inhibitors with MEK pathway inhibitors to offset re-activation of the MAP kinase pathway, resistance is still documented. Similarly, outcomes with immune checkpoint inhibitors as monotherapy were optimistic for some patients without relapse or progression, yet the majority of patients undergoing monotherapy have progressive disease. Will immunotherapy and combination therapy trials overcome resistance in metastatic melanoma? In an effort to treat resistant disease, new clinical trials evaluating the combination of immunotherapy with other therapies, such as kinase inhibitors, adoptive cell therapy, chimeric CD40 ligand to boost costimulation, or a tumor-specific oncolytic virus enhancing granulocyte macrophage colony-stimulating factor (GM-CSF) expression, are currently underway. Updated studies on the mechanisms of resistance, immune escape and options to reinvigorate immune cells support the continued discovery of new and improved forms of therapy.

PPP1R15A-mediated dephosphorylation of eIF2α is unaffected by Sephin1 or Guanabenz

Dephosphorylation of translation initiation factor 2 (eIF2α) terminates signalling in the mammalian integrated stress response (ISR) and has emerged as a promising target for modifying the course of protein misfolding diseases. The [(o-chlorobenzylidene)amino]guanidines (Guanabenz and Sephin1) have been proposed to exert protective effects against misfolding by interfering with eIF2α-P dephosphorylation through selective disruption of a PP1-PPP1R15A holophosphatase complex. Surprisingly, they proved inert in vitro affecting neither stability of the PP1-PPP1R15A complex nor substrate-specific dephosphorylation. Furthermore, eIF2α-P dephosphorylation, assessed by a kinase shut-off experiment, progressed normally in Sephin1-treated cells. Consistent with its role in defending proteostasis, Sephin1 attenuated the IRE1 branch of the endoplasmic reticulum unfolded protein response. However, repression was noted in both wildtype and Ppp1r15a deleted cells and in cells rendered ISR-deficient by CRISPR editing of the Eif2s1 locus to encode a non-phosphorylatable eIF2α (eIF2α^S51A). These findings challenge the view that [(o-chlorobenzylidene)amino]guanidines restore proteostasis by interfering with eIF2α-P dephosphorylation.

Oncolytic viral therapy for pancreatic cancer

Outcomes of pancreatic adenocarcinoma (PDA) remain dismal despite extensive clinical investigation. Combination chemotherapy provides modest improvements in survival above best supportive care, and immunotherapy has thus far not proven effective. Nevertheless, growing insight into antitumor immunity and the tumor microenvironment has inspired the discovery of novel agents targeting PDA. Oncolytic viruses represent an emerging class of immunotherapeutic agents that have undergone extensive preclinical investigation and warrant further investigation in well-designed clinical trials.

Oncolytic viruses-immunotherapeutics on the rise

The oncolytic virus (OV) field has entered an exciting period in its evolution in which our basic understanding of viral biology and anti-cancer potential are being actively translated into viable therapeutic options for aggressive malignancies. OVs are naturally occurring or engineered viruses that are able to exploit cancer-specific changes in cellular signaling to specifically target cancers and their microenvironment. The direct cytolytic effect of OVs on cancer cells is known to release antigens, which can begin a cascade of events that results in the induction of anti-cancer adaptive immunity. This response is now regarded as the most critical mechanism of OV action and harnessing it can lead to the elimination of distant micrometastases as well as provide long-term anti-cancer immune surveillance. In this review, we highlight the development of the OV field, why OVs are gaining an increasingly elevated standing as members of the cancer immunotherapy armamentarium, and finally, ongoing clinical studies that are aimed at translating unique OV therapies into approved therapies for aggressive cancers.

Cancer immunotherapy: the beginning of the end of cancer?

These are exciting times for cancer immunotherapy. After many years of disappointing results, the tide has finally changed and immunotherapy has become a clinically validated treatment for many cancers. Immunotherapeutic strategies include cancer vaccines, oncolytic viruses, adoptive transfer of ex vivo activated T and natural killer cells, and administration of antibodies or recombinant proteins that either costimulate cells or block the so-called immune checkpoint pathways. The recent success of several immunotherapeutic regimes, such as monoclonal antibody blocking of cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD1), has boosted the development of this treatment modality, with the consequence that new therapeutic targets and schemes which combine various immunological agents are now being described at a breathtaking pace. In this review, we outline some of the main strategies in cancer immunotherapy (cancer vaccines, adoptive cellular immunotherapy, immune checkpoint blockade, and oncolytic viruses) and discuss the progress in the synergistic design of immune-targeting combination therapies.

Talimogene Laherparepvec for the Treatment of Advanced Melanoma

Talimogene laherparepvec (T-VEC) is a first-in-class oncolytic virus that mediates local and systemic antitumor activity by direct cancer cell lysis and an "in situ vaccine" effect. Based on an increased durable response rate compared with granulocyte macrophage-colony stimulating factor in a randomized phase III trial, it was approved by the FDA for the treatment of melanoma metastatic to skin or lymph nodes. The drug is currently in clinical trials as monotherapy and in combination with immune-checkpoint inhibitors and radiotherapy in melanoma and other cancers. The mechanism of action, toxicity, and efficacy as well as its role in current clinical practice and potential future applications are reviewed. Clin Cancer Res; 22(13); 3127-31. ©2016 AACR.

Talimogene Laherparepvec Improves Durable Response Rate in Patients With Advanced Melanoma

Purpose

Talimogene laherparepvec (T-VEC) is a herpes simplex virus type 1–derived oncolytic immunotherapy designed to selectively replicate within tumors and produce granulocyte macrophage colony-stimulating factor (GM-CSF) to enhance systemic antitumor immune responses. T-VEC was compared with GM-CSF in patients with unresected stage IIIB to IV melanoma in a randomized open-label phase III trial.

Patients and Methods

Patients with injectable melanoma that was not surgically resectable were randomly assigned at a two-to-one ratio to intralesional T-VEC or subcutaneous GM-CSF. The primary end point was durable response rate (DRR; objective response lasting continuously ≥ 6 months) per independent assessment. Key secondary end points included overall survival (OS) and overall response rate.

Results

Among 436 patients randomly assigned, DRR was significantly higher with T-VEC (16.3%; 95% CI, 12.1% to 20.5%) than GM-CSF (2.1%; 95% CI, 0% to 4.5%]; odds ratio, 8.9; P < .001). Overall response rate was also higher in the T-VEC arm (26.4%; 95% CI, 21.4% to 31.5% v 5.7%; 95% CI, 1.9% to 9.5%). Median OS was 23.3 months (95% CI, 19.5 to 29.6 months) with T-VEC and 18.9 months (95% CI, 16.0 to 23.7 months) with GM-CSF (hazard ratio, 0.79; 95% CI, 0.62 to 1.00; P = .051). T-VEC efficacy was most pronounced in patients with stage IIIB, IIIC, or IVM1a disease and in patients with treatment-naive disease. The most common adverse events (AEs) with T-VEC were fatigue, chills, and pyrexia. The only grade 3 or 4 AE occurring in ≥ 2% of T-VEC–treated patients was cellulitis (2.1%). No fatal treatment-related AEs occurred.

Conclusion

T-VEC is the first oncolytic immunotherapy to demonstrate therapeutic benefit against melanoma in a phase III clinical trial. T-VEC was well tolerated and resulted in a higher DRR (P < .001) and longer median OS (P = .051), particularly in untreated patients or those with stage IIIB, IIIC, or IVM1a disease. T-VEC represents a novel potential therapy for patients with metastatic melanoma.

Oncolytic viruses: a new class of immunotherapy drugs

Oncolytic viruses represent a new class of therapeutic agents that promote anti-tumour responses through a dual mechanism of action that is dependent on selective tumour cell killing and the induction of systemic anti-tumour immunity. The molecular and cellular mechanisms of action are not fully elucidated but are likely to depend on viral replication within transformed cells, induction of primary cell death, interaction with tumour cell antiviral elements and initiation of innate and adaptive anti-tumour immunity. A variety of native and genetically modified viruses have been developed as oncolytic agents, and the approval of the first oncolytic virus by the US Food and Drug Administration (FDA) is anticipated in the near future. This Review provides a comprehensive overview of the basic biology supporting oncolytic viruses as cancer therapeutic agents, describes oncolytic viruses in advanced clinical trials and discusses the unique challenges in the development of oncolytic viruses as a new class of drugs for the treatment of cancer.

Oncolytic herpes simplex virus-based strategies: toward a breakthrough in glioblastoma therapy

Oncolytic viruses (OV) are a class of antitumor agents that selectively kill tumor cells while sparing normal cells. Oncolytic herpes simplex virus (oHSV) has been investigated in clinical trials for patients with the malignant brain tumor glioblastoma for more than a decade. These clinical studies have shown the safety of oHSV administration to the human brain, however, therapeutic efficacy of oHSV as a single treatment remains unsatisfactory. Factors that could hamper the anti-glioblastoma efficacy of oHSV include: attenuated potency of oHSV due to deletion or mutation of viral genes involved in virulence, restricting viral replication and spread within the tumor; suboptimal oHSV delivery associated with intratumoral injection; virus infection-induced inflammatory and cellular immune responses which could inhibit oHSV replication and promote its clearance; lack of effective incorporation of oHSV into standard-of-care, and poor knowledge about the ability of oHSV to target glioblastoma stem cells (GSCs). In an attempt to address these issues, recent research efforts have been directed at: (1) design of new engineered viruses to enhance potency, (2) better understanding of the role of the cellular immunity elicited by oHSV infection of tumors, (3) combinatorial strategies with different antitumor agents with a mechanistic rationale, (4) “armed” viruses expressing therapeutic transgenes, (5) use of GSC-derived models in oHSV evaluation, and (6) combinations of these. In this review, we will describe the current status of oHSV clinical trials for glioblastoma, and discuss recent research advances and future directions toward successful oHSV-based therapy of glioblastoma.

Critical analysis of an oncolytic herpesvirus encoding granulocyte-macrophage colony stimulating factor for the treatment of malignant melanoma

Oncolytic viruses that selectively lyse tumor cells with minimal damage to normal cells are a new area of therapeutic development in oncology. An attenuated herpesvirus encoding the granulocyte-macrophage colony stimulating factor (GM-CSF), known as talimogene laherparepvec (T-VEC), has been identified as an attractive oncolytic virus for cancer therapy based on preclinical tumor studies and results from early-phase clinical trials and a large randomized Phase III study in melanoma. In this review, we discuss the basic biology of T-VEC, describe the role of GM-CSF as an immune adjuvant, summarize the preclinical data, and report the outcomes of published clinical trials using T-VEC. The emerging data suggest that T-VEC is a safe and potentially effective antitumor therapy in malignant melanoma and represents the first oncolytic virus to demonstrate therapeutic activity against human cancer in a randomized, controlled Phase III study.

Herpes simplex virus 2 expresses a novel form of ICP34.5, a major viral neurovirulence factor, through regulated alternative splicing

Herpes simplex virus 1 (HSV-1) and HSV-2, two closely related neurotropic human herpesviruses, achieve neurotropism through ICP34.5, a major viral neurovirulence factor. In this report, in addition to the full-length 38-kDa protein (ICP34.5α), we identified a 28-kDa novel form of ICP34.5 (ICP34.5β) in HSV-2-infected cells. ICP34.5β is translated from unspliced ICP34.5 mRNA, with the retained intron introducing a premature stop codon. Thus, ICP34.5β lacks the C-terminal conserved GADD34 domain but includes 19 additional amino acids encoded by the intron. Although a fraction of both HSV-2 ICP34.5 proteins are detected in the nucleolus, ICP34.5α is predominantly located in cytoplasm, and ICP34.5β is mainly detected more diffusely in the nucleus. ICP34.5β is unable to counteract PKR-mediated eIF2 phosphorylation but does not interfere with ICP34.5α's function in this process. Efficient expression of ICP34.5β in cell culture assays is dependent on viral infection or expression of ICP27, a multifunctional immediate-early gene. The effect of ICP27 on the ICP34.5β protein level is attributed to its selective inhibition of ICP34.5 splicing, which results in increased expression of ICP34.5β but a reduced level of ICP34.5α. The C- terminal KH3 domain but not the RNA binding domain of ICP27 is required for its specific inhibition of ICP34.5 splicing and promotion of ICP34.5β expression. Our results suggest that the expression of ICP34.5α and ICP34.5β is tightly regulated in HSV-2 and likely contributes to viral pathogenesis.

Expression of inhibitor of growth 4 by HSV1716 improves oncolytic potency and enhances efficacy

We have isolated and characterized a novel variant of the replication-competent oncolytic HSV1716 that expresses inhibitor of growth 4 (Ing4) (HSV1716Ing4). We demonstrate that Ing4 expression enhances progeny output during HSV1716 infection of human tumor cells both in vitro and in vivo, thereby significantly augmenting its oncolytic potency. In tissue culture, compared with HSV1716, HSV1716Ing4 produced significantly higher numbers of infectious progeny in human squamous cell carcinoma (SCC), breast, ovarian, prostate and colorectal cancer cell lines. Immediate-early expression of Ing4 was crucial for this effect and an intact Ing4 was required as there was no enhanced progeny production with HSV1716 variants that expressed Ing4 mutants lacking the C-terminal plant homeodomain domain or conserved nuclear localization signals. In mouse xenograft models of SCC, ovarian and breast cancer, HSV1716Ing4 was significantly more efficacious than HSV1716 with at least 1000-fold more infectious virus found in tumors after HSV1716Ing4 treatment compared with tumors from HSV1716 treatment. Using a sensitive herpes simplex virus type 1 (HSV-1) PCR, virus DNA was only detected in tumors and was not detected in the DNA extracted from any organs of the injected mice demonstrating that, like HSV1716, HSV1716Ing4 replication is exclusively restricted to tumor cells. Our results suggest that the potential for enhanced tumor destruction by oncolytic HSV expressing Ing4 merits clinical investigation.

Effect of γ34.5 deletions on oncolytic herpes simplex virus activity in brain tumors

The ICP34.5 protein of herpes simplex virus (HSV) is involved in many aspects of viral pathogenesis; promoting neurovirulence, inhibiting interferon-induced shutoff of protein synthesis, interacting with PCNA and TBK1, inhibiting dendritic cell (DC) maturation, and binding to Beclin 1 to interfere with autophagy. Because of its key role in neuropathogenicity, the γ34.5 gene is deleted in all oncolytic HSVs (oHSVs) currently in clinical trial for treating malignant gliomas. Unfortunately, deletion of γ34.5 attenuates virus replication in cancer cells, especially human glioblastoma stem cells (GSCs). To develop new oHSVs for use in the brain and that replicate in GSCs, we explored the effect of deleting the γ34.5 Beclin 1 binding domain (BBD). To ensure cancer selectivity and safety, we inactivated the ICP6 gene (UL39, large subunit of ribonucleotide reductase), constructing ICP6 mutants with different γ34.5 genotypes: Δ68HR-6, intact γ34.5; Δ68H-6, γ34.5 BBD deleted; and 1716-6, γ34.5 deleted. Multimutated Δ68H-6 exhibited minimal neuropathogenicity in HSV-1-susceptible mice, as opposed to Δ68H and Δ68HR-6. It replicated well in human glioma cell lines and GSCs, effectively killing cells in vitro and prolonging survival of mice bearing orthotopic brain tumors. In contrast, 1716 and 1716-6 barely replicated in GSCs. Infection of glioma cells with Δ68H-6 and 1716-6 induced autophagy and increased phosphorylation of eIF2α, while inhibition of autophagy, by Beclin 1 short hairpin RNA (shRNA) knockdown or pharmacological inhibition, had no effect on virus replication or phosphorylated eIF2α (p-eIF2α) levels. Thus, Δ68H-6 represents a new oHSV vector that is safe and effective against a variety of brain tumor models.

Phosphoproteins in stress-induced disease

The integrated stress response (ISR) is an evolutionarily conserved homeostatic program activated by specific pathological states. These include amino acid deprivation, viral infection, iron deficiency, and the misfolding of proteins within the endoplasmic reticulum (ER), the so-called ER stress. Although apparently disparate, each of these stresses induces phosphorylation of a translation initiation factor, eIF2α, to attenuate new protein translation while simultaneously triggering a transcriptional program. This is achieved by four homologous stress-sensing kinases: GCN2, PKR, HRI, and PERK. In addition to these kinases, mammals possess two specific eIF2α phosphatases, GADD34 and CReP, which play crucial roles in the recovery of protein synthesis following the initial insult. They are not only important in embryonic development but also appear to play important roles in disease, particularly cancer. In this chapter, we discuss each of the eIF2α kinases, in turn, with particular emphasis on their regulation and the new insights provided by recent structural studies. We also discuss the potential for developing novel drug therapies that target the ISR.

Oncolytic virotherapy reaches adolescence

Lytic viruses kill cells as a consequence of their normal replication life cycle. The idea of harnessing viruses to kill cancer cells arose over a century ago, before viruses were even discovered, from medical case reports of infections associated with cancer remissions. Since then, there has been no shortage of hype, hope, or fear regarding the prospect of oncolytic virotherapy for cancer. Early developments in the field included encouraging antitumor efficacy both in animal studies in the 1920s-1940s and in human clinical trials in the 1950s-1970s. Despite its long-standing history, oncolytic virotherapy was an idea ahead of its time. Without needed advances in molecular biology, virology, immunology, and clinical research ethics, early clinical trials resulted in infectious complications and were fraught with controversial research conduct, so that enthusiasm in the medical community waned. Oncolytic virotherapy is now experiencing a major growth spurt, having sustained numerous laboratory advances and undergone multiple encouraging adult clinical trials, and is now witnessing the emergence of pediatric trials. Here we review the history and salient biology of the field, including preclinical and clinical data, with a special emphasis on those agents now being tested in pediatric cancer patients.

OPTIM trial: a Phase III trial of an oncolytic herpes virus encoding GM-CSF for unresectable stage III or IV melanoma

There are few effective treatment options available for patients with advanced melanoma. An oncolytic herpes simplex virus type 1 encoding granulocyte macrophage colony-stimulating factor (GM-CSF; Oncovex(GM-CSF)) for direct injection into accessible melanoma lesions resulted in a 28% objective response rate in a Phase II clinical trial. Responding patients demonstrated regression of both injected and noninjected lesions highlighting the dual mechanism of action of Oncovex(GM-CSF) that includes both a direct oncolytic effect in injected tumors and a secondary immune-mediated anti-tumor effect on noninjected tumors. Based on these preliminary results a prospective, randomized Phase III clinical trial in patients with unresectable Stage IIIb or c and Stage IV melanoma has been initiated. The rationale, study design, end points and future development of the Oncovex(GM-CSF) Pivotal Trial in Melanoma (OPTIM) trial are discussed in this article.

Functional roles of the tegument proteins of herpes simplex virus type 1

Herpes virions consist of four morphologically distinct structures, a DNA core, capsid, tegument, and envelope. Tegument occupies the space between the nucleocapsid (capsid containing DNA core) and the envelope. A combination of genetic, biochemical and proteomic analysis of alphaherpes virions suggest the tegument contains in the order of 20 viral proteins. Historically the tegument has been described as amorphous but increasing evidence suggests there is an ordered addition of tegument during assembly. This review highlights the diverse roles, in addition to structural, that tegument plays during herpes viral replication using as an example herpes simplex virus type 1. Such diverse roles include: capsid transport during entry and egress; targeting of the capsid to the nucleus; regulation of transcription, translation and apoptosis; DNA replication; immune modulation; cytoskeletal assembly; nuclear egress of capsid; and viral assembly and final egress.

Analyses of the spleen proteome of chickens infected with Marek's disease virus

Marek's disease virus (MDV), which causes a lymphoproliferative disease in chickens, is known to induce host responses leading to protection against disease in a manner dependent on genetic background of chickens and virulence of the virus. In the present study, changes in the spleen proteome at 7, 14 and 21 days post-infection in response to MDV infection were studied using two-dimensional polyacrylamide gel electrophoresis. Differentially expressed proteins were identified using one-dimensional liquid chromatography electrospray ionization tandem mass spectrometry (1D LC ESI MS/MS). Comparative analysis of multiple gels revealed that the majority of changes had occurred at early stages of the disease. In total, 61 protein spots representing 48 host proteins were detected as either quantitatively (false discovery rate (FDR)<or=0.05 and fold change>or=2) or qualitatively differentially expressed at least once during different sampling points. Overall, the proteins identified in the present study are involved in a variety of cellular processes such as the antigen processing and presentation, ubiquitin-proteasome protein degradation (UPP), formation of the cytoskeleton, cellular metabolism, signal transduction and regulation of translation. Notably, early stages of the disease were characterized by changes in the UPP, and antigen presentation. Furthermore, changes indicative of active cell proliferation as well as apoptosis together with significant changes in cytoskeletal components that were observed throughout the experimental period suggested the complexity of the pathogenesis. The present findings provide a basis for further studies aimed at elucidation of the role of these proteins in MDV interactions with its host.

Regression of human pancreatic tumor xenografts in mice after a single systemic injection of recombinant vaccinia virus GLV-1h68

Oncolytic virotherapy of tumors has shown promising results in both preclinical and clinical studies. Here, we investigated the therapeutic efficacy of a replication-competent vaccinia virus, GLV-1h68, against human pancreatic carcinomas in cell cultures and in nude mice. We found that GLV-1h68 was able to infect, replicate in, and lyse tumor cells in vitro. Virus-mediated marker gene expressions were readily detected. Moreover, s.c. PANC-1 pancreatic tumor xenografts were effectively treated by a single i.v. dose of GLV-1h68. Cancer killing was achieved with minimal toxicity. Viral titer analyses in homogenized organs and PANC-1 tumors showed that the mutant virus resides almost exclusively in the tumors and not in healthy organs. Except mild spleen enlargements, no histopathology changes were observed in any other organs 2 months after virus injection. Surprisingly, s.c. MIA PaCa-2 pancreatic tumors were treated with similar efficiency as PANC-1 tumors, although they differ significantly in sensitivity to viral lysis in cell cultures. When GLV-1h68 oncolytic viral therapy was used together with cisplatin or gemcitabine to treat PANC-1 tumors, the combination therapy resulted in enhanced and accelerated therapeutic results compared with the virus treatment alone. Profiling of proteins related to immune response revealed a significant proinflammatory immune response and marked activation of innate immunity in virus-colonized tumors. In conclusion, the GLV-1h68 strain showed outstanding therapeutic effects and a documented safety profile in mice, with great promise for future clinical development.

Control of TANK-binding kinase 1-mediated signaling by the gamma(1)34.5 protein of herpes simplex virus 1

TANK-binding kinase 1 (TBK1) is a key component of Toll-like receptor-dependent and -independent signaling pathways. In response to microbial components, TBK1 activates interferon regulatory factor 3 (IRF3) and cytokine expression. Here we show that TBK1 is a novel target of the gamma(1)34.5 protein, a virulence factor whose expression is regulated in a temporal fashion. Remarkably, the gamma(1)34.5 protein is required to inhibit IRF3 phosphorylation, nuclear translocation, and the induction of antiviral genes in infected cells. When expressed in mammalian cells, the gamma(1)34.5 protein forms complexes with TBK1 and disrupts the interaction of TBK1 and IRF3, which prevents the induction of interferon and interferon-stimulated gene promoters. Down-regulation of TBK1 requires the amino-terminal domain. In addition, unlike wild type virus, a herpes simplex virus mutant lacking gamma(1)34.5 replicates efficiently in TBK1(-/-) cells but not in TBK1(+/+) cells. Addition of exogenous interferon restores the antiviral activity in both TBK1(-/-) and TBK(+/+) cells. Hence, control of TBK1-mediated cell signaling by the gamma(1)34.5 protein contributes to herpes simplex virus infection. These results reveal that TBK1 plays a pivotal role in limiting replication of a DNA virus.

Oncolytic Viruses: A New Weapon to Fight Cancer

Remission from cancer after viral infection was first noted in the beginning of the 20th century, and with advances in virotherapy and genetic engineering, the advent of an approved viral therapeutic in North America is fast approaching. Mechanisms of tumour selectivity and killing, along with information obtained from clinical trials are reviewed here. Although oncolytic viruses are generally safe and well tolerated, their overall anti-tumour efficacy has varied. This article outlines strategies to improve the efficacy of the oncolytic platform without compromising its impressive safety profile. It will highlight new methods being developed to quantify the activity of oncolytic viruses in real time. Harnessing the factors that control the tumour microenvironment and the immune system are the key to enhancing the oncolytic activity. The purpose of this article is to introduce and provide an overview of the current state of cancer killing of oncolytic viruses. The reader will acquire knowledge of the basic principles of oncolytic viruses and their use in the clinical setting. This review summarizes articles retrieved from Medline using key words such as "virus," "oncolytic virus," "virotherapy," "cancer," and "clinical trials." Review articles published in the English language from 2005 onward were read and corroborating data and conclusions were summarized. When appropriate, cited references were also reviewed and incorporated. The reader is directed to references we found most concise.

A strategy for systemic delivery of the oncolytic herpes virus HSV1716: redirected tropism by antibody-binding sites incorporated on the virion surface as a glycoprotein D fusion protein

We report on the ability of single-chain variable fragment (scFv) incorporated into the viral envelope to alter the tropism of herpes simplex virus (HSV) 1716. Using recombinant viruses expressing fusion proteins comprising cell-surface antigen-specific scFvs N terminus linked to amino acids 274-393 of gD, we demonstrated that the tropism of these HSV1716 variants was modified such that infection was mediated by the cognate antigen. Thus, an HSV1716 variant that expressed an anti-CD55 scFv targeting moiety linked to these gD residues was able to infect non-permissive Chinese hamster ovary cells expressing CD55 and this infection was specifically blocked by an anti-CD55 monoclonal antibody. Similarly, the infection efficiency of an HSV1716 variant for semi-permissive human leukaemic, CD38-positive cell lines was greatly improved by an anti-CD38 scFv targeting moiety linked to gD residues 274-393, and this enhanced infectivity was abrogated specifically by an anti-CD38 monoclonal antibody. Finally, intravenous/intraperitoneal injection of an HSV1716 variant displaying an anti-epidermal growth factor receptor (EGFR) scFv linked to residues 274-393 of gD enhanced destruction of subcutaneous EGFR-positive tumours in nude mice compared to unmodified HSV1716. Therefore, targeting of HSV1716 oncolysis to specific cell types through the display of entry mediating scFv/gD fusion proteins represents an efficient route for systemic delivery.

Neurovirulent factor ICP34.5 uniquely expressed in the herpes simplex virus type 1 Delta gamma 1 34.5 mutant 1716

The herpes simplex virus type 1 (HSV-1) diploid gene gamma(1)34.5 encodes a neurovirulent factor, infected cell protein 34.5 (ICP34.5). The promoter to gamma(1)34.5 is located within the HSV-1 genome where there are repeated sequences. This region of the genome also contains important overlapping transcripts involved with the virus's ability to establish lytic and latent infections and reactivation. These transcripts include the latency-associated transcripts and regulator proteins ICP0 and ICP4. This study aimed to separate ICP34.5 from these overlapping transcripts and test if its expression from a single gene could restore wild-type HSV-1 strain 17+ virulence. To address these aims, different recombinant viruses were constructed using the Delta gamma(1)34.5 mutant 1716. Immunoblots probed with different ICP34.5 antisera demonstrated that one of the newly generated recombinant viruses, 1622, overexpresses ICP34.5 relative to a panel of wild-type viruses. Interestingly, the overexpression of ICP34.5 does not yield a more virulent virus. The onset of ICP34.5 expression from 1622-infected cells in vitro matched that of 17+, and its expression restored the function of maintaining protein synthesis in human neuroblastoma cells. Replication of 1622, however, was only partially restored to 17+ levels in vivo. Additionally, plaque morphology from 1622-infected cells indicates there is an additional defect. The authors report that the mutant virus 1622 can express ICP34.5 from a single gamma(1)34.5 gene and restore most (but not all) wild-type function. These findings are discussed with respect to the use of the gamma(1)34.5 deleted mutant, 1716, in oncolytic viral vector therapies and future studies for ICP34.5.

Using or abusing: viruses and the cellular DNA damage response

During infection, viruses attempt to hijack the cell while the host responds with various defense systems. Traditional defenses include the interferon response and apoptosis, but recent work suggests that this antiviral arsenal also includes the cellular DNA damage response machinery. The observation of interactions between viruses and cellular DNA repair proteins has not only uncovered new complexities of the virus-host interaction but is also reinforcing the view that viruses can reveal key regulators of cellular pathways through the proteins they target.

Recent clinical progress in virus-based therapies for cancer

As our knowledge of the molecular basis of cancer expands, viral vectors have been increasingly studied as potential antitumour therapeutic agents. With their ability to invade and replicate within target cells, viruses have been utilised as oncolytic agents to directly lyse tumour cells. Viruses can also deliver their genetic payload into infected cells, allowing for the repair of defective tumour suppressor genes, disruption of oncogenic pathways, and production of cytokines that activate the immune system. Finally, viruses encoding tumour-associated antigens can infect dendritic cells, triggering the development of a tumour-specific immune response. The ability to engineer viruses with high levels of tumour specificity and efficient rates of infection has enhanced the safety profile of these agents, allowing for the development of viable therapeutic options that have been examined in the clinic, either alone or in conjunction with more conventional therapies. This review highlights the principles underlying virus-based therapies for cancer, with an emphasis on recent developments from the clinic.

Functional genomic analysis of herpes simplex virus type 1 counteraction of the host innate response

Herpes simplex virus type 1 (HSV-1) mutants lacking the ICP34.5 gene are severely attenuated in mouse models and have a significant growth defect in confluent mouse embryo fibroblasts. Previously, ICP34.5 was demonstrated to have a crucial role in evading the innate immune response to infection by mediating the dephosphorylation of eIF2alpha, a translation initiation factor phosphorylated by PKR during the antiviral response. To further understand the role of ICP34.5 in evasion of the antiviral response, we used transcriptional profiling to examine host cell gene expression in both wild-type and ICP34.5-null virus-infected mouse embryo fibroblasts over a time course of infection. Our study revealed that cells responded to infection within 3 h through PKR-dependent eIF2alpha phosphorylation and that the majority of up-regulated genes at 3 h postinfection were involved in the antiviral response. HSV-1 counters this response through early expression of ICP34.5 and dephosphorylation of eIF2alpha. By 12 h postinfection, the differences between the number and functional classification of genes differentially up- and down-regulated between wild-type and ICP34.5-null virus-infected cells were maximal. Specifically, in wild-type virus-infected cells, the majority of changed genes were involved in metabolic and biosynthetic processes, while in ICP34.5-null virus-infected cells, mostly antiviral genes were up-regulated. Further, ICP34.5-null virus-infected cells produced greater amounts of beta interferon than wild-type virus-infected cells. These results indicate that ICP34.5 expression and function at early times postinfection have a pivotal role in the ability of HSV-1 to gain control of the host cell and maintain an environment for successful viral replication.

Identification of the growth arrest and DNA damage protein GADD34 in the normal human heart and demonstration of alterations in expression following myocardial ischaemia

Growth arrest and DNA damage protein 34 (GADD34) is a multifunctional protein upregulated in response to cellular stress and is believed to mediate DNA repair and restore protein synthesis. In the present study we have examined GADD34 immunoreactivity in human myocardial tissue at defined survival times following cardiac arrest and determined alterations in expression following ischaemia. In the normal human heart, GADD34 immunoreactivity was generally intense and present within most cells. GADD34 immunoreactivity was downregulated in tissue displaying ischaemic damage and remained intense in adjacent non-infarcted tissue. Unlike brain, GADD34 was not found to be upregulated in the peri-infarct zone. Cells displaying apoptotic changes were located in regions displaying reduced GADD34 immunoreactivity. In the brain, it is thought that GADD34 supports re-initiation of protein synthesis following ischaemia. Similarly, GADD34 may perform important functions in cardiac tissue in response to ischaemia.

Identifying cellular genes crucial for the reactivation of Kaposi's sarcoma-associated herpesvirus latency

Kaposi's sarcoma-associated herpesvirus (KSHV) is the latest addition to the long list of human herpesviruses. Reactivation of latent herpesvirus infections is still a mystery. It was demonstrated recently that the phorbol ester TPA was efficient in inducing a reactivation of KSHV infection in the S phase of the cell cycle. In the present study, flow cytometry-sorted, TPA-induced, KSHV-infected haematopoietic cells (BCBL-1) were used to analyse the expression profiles of cancer-related cellular genes in the S phase of the cell cycle compared with the G0/1 phase by using microarrays. Overall, the S phase of the cell cycle seems to provide KSHV with an apt environment for a productive lytic cycle of infection. The apt conditions include cellular signalling that promotes survivability, DNA replication and lipid metabolism, while blocking cell-cycle progression to M phase. Some of the important genes that were overexpressed during the S phase of the cell cycle compared with the G0/1 phase of TPA-induced BCBL-1 cells are v-myb myeloblastosis (MYBL2), protein kinase-membrane associated tyrosine/threonine 1 (PKMYT1), ribonucleotide reductase M1 polypeptide (RRM1) and peroxisome proliferator-activated receptors delta (PPARD). Inhibition of PKMYT1 expression by the use of specific short interfering RNAs significantly lowered the TPA-induced KSHV lytic cycle of infection. The significance of these and other genes in the reactivation of KSHV is discussed in the following report. Taken together, a flow cytometry-microarray-based method to study the cellular conditions critical for the reactivation of KSHV infection is reported here for the first time.

Prediction of functional class of the SARS coronavirus proteins by a statistical learning method

The complete genome of severe acute respiratory syndrome coronavirus (SARS-CoV) reveals the existence of putative proteins unique to SARS-CoV. Identification of their function facilitates a mechanistic understanding of SARS infection and drug development for its treatment. The sequence of the majority of these putative proteins has no significant similarity to those of known proteins, which complicates the task of using sequence analysis tools to probe their function. Support vector machines (SVM), useful for predicting the functional class of distantly related proteins, is employed to ascribe a possible functional class to SARS-CoV proteins. Testing results indicate that SVM is able to predict the functional class of 73% of the known SARS-CoV proteins with available sequences and 67% of 18 other novel viral proteins. A combination of the sequence comparison method BLAST and SVMProt can further improve the prediction accuracy of SMVProt such that the functional class of two additional SARS-CoV proteins is correctly predicted. Our study suggests that the SARS-CoV genome possibly contains a putative voltage-gated ion channel, structural proteins, a carbon-oxygen lyase, oxidoreductases acting on the CH-OH group of donors, and an ATP-binding cassette transporter. A web version of our software, SVMProt, is accessible at http://jing.cz3.nus.edu.sg/cgi-bin/svmprot.cgi .

Oncolytic viral therapies – the clinical experience

It has been 9 years since the beginning of the first clinical trial in which an oncolytic virus was administered to cancer patients. Since then, oncolytic viruses from five different species have been taken to phase I and II clinical trials in over 300 cancer patients. While additional studies will be required to ascertain if the efficacy of any of these agents is high enough to warrant adding them to the existing therapeutic regimen, it has been reassuring that DNA viruses engineered to achieve tumor selectivity and RNA viruses with relative inherent natural tumor selectivity have proven reasonably safe at the wide range of doses that were tested. Here, we review the biology and clinical results of these five species of viruses and discuss lessons learned and challenges for the future.

Characterization of the triplet repeats in the central domain of the gamma134.5 protein of herpes simplex virus 1

The gamma134.5 protein of herpes simplex virus 1 (HSV-1) consists of an amino-terminal domain, a central domain with triplet repeats (Ala-Thr-Pro) and a carboxyl-terminal domain. The triplet repeats are a unique feature of the gamma134.5 protein encoded by HSV-1, but the number of repeats varies among different strains. Notably, the central domain containing the triplet repeats is implicated in neuroinvasion. In this report, it has been shown that partial or full deletion of triplet repeats, i.e. from ten to either three or zero, in the gamma134.5 protein has no effect on the virus response to interferon. The triplet deletion mutants replicate efficiently in CV-1 and mouse 10T1/2 cells. However, in mouse 3T6 cells, these mutants grow with delayed growth kinetics. This decrease in growth, compared with wild-type HSV-1(F), does not result from failure of the virus to suppress the RNA-dependent protein kinase response, but rather from a delay in virus release or egress. Accordingly, these mutant viruses are predominantly present within infected cells. These results indicate that deletions in the central domain of the gamma134.5 protein impair virus egress, but not virus response to interferon.

Evolution of GADD34 expression after focal cerebral ischaemia

GADD34, a stress response protein associated with cell rescue, DNA repair and apoptosis, is expressed in the ischaemic brain. The C-terminal region of GADD34 has homology with the Herpes Simplex Virus protein, ICP34.5, which overcomes the protein synthesis block after viral infection by actively dephosphorylating eukaryotic translation initiation factor 2alpha (eIF2alpha). The carboxy terminus of GADD34 is also capable of dephosphorylating eIF2alpha and therefore has the capacity to restore the protein synthesis shutoff associated with ischaemia. This study examines the distribution and time course of GADD34 expression after focal cerebral ischaemia. Focal ischaemia or sham procedure was carried out on Sprague-Dawley rats with survival times of 4, 12, 24 h, 7 and 30 days. Brains were processed for histology and immunohistochemistry. Ischaemic damage was mapped onto line diagrams and GADD34 positive cells counted in selected regions of cortex and caudate. GADD34 immunopositive cells (mainly neurones), expressed as cells/mm2, were present in ischaemic brains at 4 h (e.g., peri-infarct cortex 20 +/- 5; contralateral cortex 3 +/- 1, P < 0.05). Of the time points examined, numbers of GADD34 positive cells were highest 24 h after ischaemia (peri-infarct cortex 31 +/- 7.3, contralateral cortex 0.1 +/- 0.1, P < 0.05). Immunopositive cells, following a similar time course, were identified within the peri-infarct zone in the caudate nucleus and in ipsilateral cingulate cortex (possibly as a consequence of cortical spreading depression). GADD34 positive cells did not co-localise with a marker of irreversible cell death (TUNEL). Taken together, GADD34 positive cells in key neuroanatomical locations pertinent to the evolving ischaemic lesion, the lack of co-localisation with TUNEL and the protein's known effects on restoring protein synthesis, repairing DNA and involvement in ischaemic pre-conditioning suggests that it has the potential to influence cell survival in ischaemically compromised tissue.

Combination of mutated herpes simplex virus type 1 (G207 virus) with radiation for the treatment of squamous cell carcinoma of the head and neck

G207 is an oncolytic herpes simplex virus (HSV) with deletions at both gamma134.5 loci and a LacZ gene insertion inactivating the HSV ribonucleotide reductase gene. Ionising radiation induces the growth arrest-inducible gene, GADD34, and ribonucleotide reductase. GADD34 is a protein that correlates with apoptosis following radiation and has homology with the G207 gamma134.5 gene. We hypothesised that the combination of radiotherapy with G207 may have a potentiating effect on viral replication and anti-tumour efficacy. The purpose of this study was therefore to evaluate the combination of G207 with radiation therapy to treat head and neck tumours. The cytotoxicity of G207 was tested in six head and neck squamous carcinoma cell lines, in the presence or absence of irradiation. For in vivo experiments, flank tumours in C3H/HeJ mice or in nude mice were treated with direct injections of G207, with or without radiation. All head and neck squamous cancer cell lines tested demonstrated significantly increased antitumour effects with the combination of G207 virus and radiation therapy compared with each individual modality (P<0.01). Furthermore, the combination treatment effect was better than the expected additive effect of the two therapies in combination. Even the radiation-resistant cell lines (SCC25, MSKQLL2, SCCVII) were susceptible. The combination of direct G207 injection with radiation therapy suppressed human and murine squamous cell carcinoma growth significantly (P<0.05 and P<0.001) compared with controls or single modality therapy. G207 enhanced the effectiveness of radiation therapy and low-dose radiation potentiated the effectiveness of G207 viral therapy in head and neck cancer. These findings suggest a potential clinical application for this combined therapy as treatment for radiation-resistant head and neck cancers.

African swine fever virus proteins involved in evading host defence systems

African swine fever virus (ASFV) can cause an acutely fatal haemorrhagic fever in domestic pigs although in its natural hosts, warthogs, bushpigs and the soft tick vector, Ornithodoros moubata, ASFV causes inapparent persistent infections. The virus is a large, cytoplasmic, double-stranded DNA virus which has a tropism for macrophages. As it is the only member of the Asfarviridae family, ASFV encodes many novel genes not encoded by other virus families. The ability of the virus to persist in its natural hosts and in domestic pigs, which recover from infection with less virulent isolates, shows that the virus has effective mechanisms to evade host defence systems. This review focuses on recent progress made in understanding the function of ASFV-encoded proteins, which are involved in modulating the host response to infection. Growing evidence suggests that a major strategy used by the virus is to modulate signalling pathways in infected macrophages, thus interfering with the expression of a large number of immunomodulatory genes. One potent immunomodulatory protein, A238L, inhibits both activation of the host NFkappaB transcription factor and inhibits calcineurin phosphatase activity. Calcineurin-dependent pathways, including activation of the NFAT transcription factor, are therefore inhibited. Another ASFV-encoded protein, CD2v, resembles the host CD2 protein, which is expressed on T cells and NK cells. This virus protein causes the adsorption of red blood cells around virus-infected cells and extracellular virus particles. Expression of the CD2v protein aids virus dissemination in pigs and the protein also has a role in impairing bystander lymphocyte function. This may be mediated either by a direct interaction of CD2v extracellular domain with ligands on lymphocytes or by an indirect mechanism involving interaction of the CD2v cytoplasmic tail with host proteins involved in signalling or trafficking pathways. Two ASFV proteins, an IAP and a Bcl2 homologue, inhibit apoptosis in infected cells and thus facilitate production of progeny virions. The prediction is that half to two-thirds of the approximately 150 genes encoded by ASFV are not essential for replication in cells but have an important role for virus survival and transmission in its hosts. These genes provide an untapped repository, and will be valuable tools for deciphering not only how the virus manipulates the host response to infection to avoid elimination, but also useful for understanding important host anti-viral mechanisms. In addition, they may provide leads for discovery of novel immunomodulatory drugs.

GADD34 induces p53 phosphorylation and p21/WAF1 transcription

Recently, others and we have shown that one of the functions of GADD34 is a recovery from a shutoff of protein synthesis induced by endoplasmic reticulum stress. GADD34 has been shown to induce growth arrest and apoptosis. Main protein of apoptosis is p53, especially phosphorylation of p53. And one of the main proteins of growth arrest is p21/WAF1. Here we analyzed the effects of GADD34 on p53 phosphorylation and p21/WAF1 transcription. Transfected Myc-tagged p53 was dose-dependently phosphorylated at Ser15 by increasing the amount of GADD34. Transfection of GADD34 also induced the endogenous phosphorylation of p53 and enhanced p21 protein expression. Transfection of GADD34 induced p21/WAF1 promoter activity. This activity was dependent on p53, because GADD34 transfection to p53-deficient cells produced only a slight increase of p21/WAF1 promoter activity. The p21/WAF1 promoter activity was greatly enhanced by the transfection of p53. Both GADD34 and p53 transfection induced much higher p21/WAF1 promoter activity. The promoter activity of p21/WAF1 was very low in GADD34 deficient MEF. The transfection of GADD34 increased the p21/WAF1 promoter activity in GADD34 deficient MEF.

Replication of herpes simplex virus 1 depends on the gamma 134.5 functions that facilitate virus response to interferon and egress in the different stages of productive infection

The ability of the gamma(1)34.5 protein to suppress the PKR response plays a crucial role in herpes simplex virus pathogenesis. In this process, the gamma(1)34.5 protein associates with protein phosphatase 1 to form a large complex that dephosphorylates eIF-2alpha and thereby prevents translation shutoff mediated by PKR. Accordingly, gamma(1)34.5 null mutants are virulent in PKR-knockout mice but not in wild-type mice. However, gamma(1)34.5 deletion mutants, with an extragenic compensatory mutation, inhibit PKR activity but remain avirulent, suggesting that the gamma(1)34.5 protein has additional functions. Here, we show that a substitution of the gamma(1)34.5 gene with the NS1 gene from influenza A virus renders viral resistance to interferon involving PKR. The virus replicates as efficiently as wild-type virus in SK-N-SH and CV-1 cells. However, in mouse 3T6 cells, the virus expressing the NS1 protein grows at an intermediate level between the wild-type virus and the gamma(1)34.5 deletion mutant. This decrease in growth, compared to that of the wild-type virus, is due not to an inhibition of viral protein synthesis but rather to a block in virus release or egress. Virus particles are predominantly present in the nucleus and cytoplasm. Notably, deletions in the amino terminus of the gamma(1)34.5 protein lead to a significant decrease in virus growth in mouse 3T6 cells, which is independent of eIF-2alpha dephosphorylation. In correlation, a series of deletions in the amino-terminal domain impair nuclear as well as cytoplasmic egress. These results indicate that efficient viral replication depends on the gamma(1)34.5 functions required to prevent the PKR response and to facilitate virus egress in the different stages during virus infection.

Up-regulation of a growth arrest and DNA damage protein (GADD34) in the ischaemic human brain: implications for protein synthesis regulation and DNA repair

GADD34 is a growth arrest and DNA damage inducible gene up-regulated in response to DNA damage, cell cycle arrest and apoptosis. It is thought that GADD34 may play a crucial role in cell survival in ischaemia. GADD34 expression was assessed immunohistochemically in post-mortem human hippocampal tissue obtained from patients surviving for defined periods (0-24 h; 24 h-7 days) after a cardiac arrest and in age-matched control subjects. In control brain, cytoplasm staining in GADD34 immunopositive cells was faint but present throughout the hippocampus and cortex. There was minimal change in GADD34 expression in the group surviving 0-24 h after cardiac arrest. However GADD34 immunostaining was markedly increased in selectively vulnerable regions in the 24 h-7 day survival group. Increased GADD34 staining was present in ischaemic neurones and in some morphologically normal neurones after cardiac arrest. Extensive ischaemic damage was found to correlate with elevated GADD34 immunostaining in the CA1 layer of the hippocampus (**P < 0.0016). In addition, GADD34 was found to colocalize with proliferating cell nuclear antigen in some neurones. The up-regulation of GADD34 in response to global ischaemia in the human brain plus its influence on protein synthesis and DNA repair suggests that this protein may have the potential to influence cell survival.

Imaging in gene therapy of patients with glioma

Over 10 years ago, the first successful gene therapy paradigms for experimental brain tumors models have been conducted, and they were thought to revolutionize the treatment of patients with gliomas. Application of gene therapy has been quickly forced into clinical trials, the first patients being enrolled in 1994, with overall results being disappointing. However, single patients seemed to benefit from gene therapy showing long-term treatment response, and most of these patients bearing small glioblastomas. Whereas the gene therapy itself has been performed with high sophistication, limited attention has been paid on technologies, which (i) allow an identification of viable target tissue in heterogenous glioma tissue and which (ii) enable an assessment of successful vector administration and vector-mediated gene expression in vivo. However, these measures are a prerequisite for the development of successful gene therapy in the clinical application. As biological treatment strategies such as gene and cell-based therapies hold promise to selectively correct disease pathogenesis, successful clinical implementation of these treatment strategies rely on the establishment of molecular imaging technology allowing the non-invasive assessment of endogenous and exogenous gene expression in vivo. Imaging endogenous gene expression will allow the characterization and identification of target tissue for gene therapy. Imaging exogenously introduced cells and genes will allow the determination of the 'tissue dose' of transduced cell function and vector-mediated gene expression, which in turn can be correlated to the induced therapeutic effect. Only these combined strategies of non-invasive imaging of gene expression in vivo will enable the establishment of safe and efficient vector administration and gene therapy protocols for clinical application. Here, we review some aspects of imaging in gene therapy trials for glioblastoma, and we present a 'proof-of-principle' 2nd-generation gene therapy protocol integrating molecular imaging technology for the establishment of efficient gene therapy in clinical application.

Dephosphorylation of eIF-2alpha mediated by the gamma(1)34.5 protein of herpes simplex virus type 1 is required for viral response to interferon but is not sufficient for efficient viral replication

The gamma(1)34.5 protein of herpes simplex virus type 1 (HSV-1) functions to block the shutoff of protein synthesis involving double-stranded RNA-dependent protein kinase (PKR). In this process, the gamma(1)34.5 protein recruits cellular protein phosphatase 1 (PP1) to form a high-molecular-weight complex that dephosphorylates eIF-2alpha. Here we show that the gamma(1)34.5 protein is capable of mediating eIF-2alpha dephosphorylation without any other viral proteins. While deletion of amino acids 1 to 52 from the gamma(1)34.5 protein has no effect on eIF-2alpha dephosphorylation, further truncations up to amino acid 146 dramatically reduce the activity of the gamma(1)34.5 protein. An additional truncation up to amino acid 188 is deleterious, indicating that the carboxyl-terminal domain alone is not functional. Like wild-type HSV-1, the gamma(1)34.5 mutant with a truncation of amino acids 1 to 52 is resistant to interferon, and resistance to interferon is coupled to eIF-2alpha dephosphorylation. Intriguingly, this mutant exhibits a similar growth defect seen for the gamma(1)34.5 null mutant in infected cells. Restoration of the wild-type gamma(1)34.5 gene in the recombinant completely reverses the phenotype. These results indicate that eIF-2alpha dephosphorylation mediated by the gamma(1)34.5 protein is required for HSV response to interferon but is not sufficient for viral replication. Additional functions or activities of the gamma(1)34.5 protein contribute to efficient viral infection.