Herpes simplex virus type 1 deletion variants 1714 and 1716 pinpoint neurovirulence-related sequences in Glasgow strain 17+ between immediate early gene 1 and the 'a' sequence

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.

p32 is a novel target for viral protein ICP34.5 of herpes simplex virus type 1 and facilitates viral nuclear egress

As a large double-stranded DNA virus, herpes simplex virus type 1 (HSV-1) assembles capsids in the nucleus where the viral particles exit by budding through the inner nuclear membrane. Although a number of viral and host proteins are involved, the machinery of viral egress is not well understood. In a search for host interacting proteins of ICP34.5, which is a virulence factor of HSV-1, we identified a cellular protein, p32 (gC1qR/HABP1), by mass spectrophotometer analysis. When expressed, ICP34.5 associated with p32 in mammalian cells. Upon HSV-1 infection, p32 was recruited to the inner nuclear membrane by ICP34.5, which paralleled the phosphorylation and rearrangement of nuclear lamina. Knockdown of p32 in HSV-1-infected cells significantly reduced the production of cell-free viruses, suggesting that p32 is a mediator of HSV-1 nuclear egress. These observations suggest that the interaction between HSV-1 ICP34.5 and p32 leads to the disintegration of nuclear lamina and facilitates the nuclear egress of HSV-1 particles.

Role of the virion host shutoff protein in neurovirulence of monkey B virus (Macacine herpesvirus 1)

Monkey B virus (Macacine herpesvirus 1; BV) is noted for its extreme neurovirulence in humans. Since the vhs protein encoded by the UL41 gene has been shown to be a neurovirulence factor in the related human herpes simplex viruses, the role of the UL41 gene in BV neurovirulence was investigated. BV mutants were constructed that lacked the entire UL41 ORF (Δ41) or had the RNase active site mutated (Δ41A). Neither mutant shut off host protein synthesis, degraded β-actin mRNA, or prevented an IFN-β response, indicating that the vhs protein and its RNase activity are both necessary for these activities. Replication of both mutants in primary mouse cells was impaired and they exhibited a prolonged disease course in mice. Whereas Δ41 infected mice were euthanized for symptoms related to central nervous system (CNS) infection, Δ41A infected mice were euthanized primarily for symptoms of autonomic nervous system dysfunction. While neuroinvasiveness was not affected, lesions in the CNS were more limited in size, anatomical distribution, and severity than for wild-type virus. These results indicate that the vhs protein affects the general replicative efficiency of BV in vivo rather than being a specific neurovirulence factor critical for invasion of or preferential replication in the CNS.

Oncolytic viruses in head and neck cancer: a new ray of hope in the management protocol

This paper intends to highlight the different types of oncolytic viruses (OVs), mechanism of tumor specificity, its safety, and various obstacles in the design of treatment and combination therapy utilizing oncotherapy. Search was conducted using the internet-based search engines and scholarly bibliographic databases with key words such as OVs, head and neck cancer, viruses, oral squamous cell carcinoma, and gene therapy. Revolutionary technologies in the field of cancer treatment have gone through a series changes leading to the development of innovative therapeutic strategies. Oncolytic virotherapy is one such therapeutic approach that has awaited phase III clinical trial validation. OVs are self-replicating, tumor selective and lyse cancer cells following viral infection. By modifying the viral genome, it is possible to direct their toxicity toward cancer cells. Viruses that are used for treatment of head and neck cancer are either naturally occurring or genetically modified. OVs are tumor selective and potential anticancer agents. Virotherapy may become the standard of care and part of combination therapy in the management of head and neck cancer in the future.

Up to four distinct polypeptides are produced from the γ34.5 open reading frame of herpes simplex virus 2

The herpes simplex virus 1 (HSV-1) ICP34.5 protein strongly influences neurovirulence and regulates several cellular antiviral responses. Despite the clinical importance of HSV-2, relatively little is known about its ICP34.5 ortholog. We found that HSV-2 produces up to four distinct forms of ICP34.5 in infected cells: a full-length protein, one shorter form sharing the N terminus, and two shorter forms sharing the C terminus. These forms appeared with similar kinetics and accumulated in cells over much of the replication cycle. We confirmed that the N-terminal form is translated from the primary unspliced transcript to a stop codon within the intron unique to HSV-2 γ34.5. We found that the N-terminal form was produced in a variety of cell types and by 9 of 10 clinical isolates. ICP27 influenced but was not required for expression of the N-terminal form. Western blotting and reverse transcription-PCR indicated the C-terminal forms did not contain the N terminus and were not products of alternative splicing or internal transcript initiation. Expression plasmids encoding methionine at amino acids 56 and 70 generated products that comigrated in SDS-PAGE with the C1 and C2 forms, respectively, and mutation of these sites abolished C1 and C2. Using a recombinant HSV-2 encoding hemagglutinin (HA)-tagged ICP34.5, we demonstrated that the C-terminal forms were also produced during infection of many human and mouse cell types but were not detectable in mouse primary neurons. The protein diversity generated from the HSV-2 γ34.5 open reading frame implies additional layers of cellular regulation through potential independent activities associated with the various forms of ICP34.5.

IMPORTANCE

The herpes simplex virus 1 (HSV-1) protein ICP34.5, encoded by the γ34.5 gene, interferes with several host defense mechanisms by binding cellular proteins that would otherwise stimulate the cell's autophagic, translational-arrest, and type I interferon responses to virus infection. ICP34.5 also plays a crucial role in determining the severity of nervous system infections with HSV-1 and HSV-2. The HSV-2 γ34.5 gene contains an intron not present in HSV-1 γ34.5. A shorter N-terminal form of HSV-2 ICP34.5 can be translated from the unspliced γ34.5 mRNA. Here, we show that two additional forms consisting of the C-terminal portion of ICP34.5 are generated in infected cells. Production of these N- and C-terminal forms is highly conserved among HSV-2 strains, including many clinical isolates, and they are broadly expressed in several cell types, but not mouse primary neurons. Multiple ICP34.5 polypeptides add additional complexity to potential functional interactions influencing HSV-2 neurovirulence.

Gene therapy for malignant glioma

Glioblastoma multiforme (GBM) is the most frequent and devastating primary brain tumor in adults. Despite current treatment modalities, such as surgical resection followed by chemotherapy and radiotherapy, only modest improvements in median survival have been achieved. Frequent recurrence and invasiveness of GBM are likely due to the resistance of glioma stem cells to conventional treatments; therefore, novel alternative treatment strategies are desperately needed. Recent advancements in molecular biology and gene technology have provided attractive novel treatment possibilities for patients with GBM. Gene therapy is defined as a technology that aims to modify the genetic complement of cells to obtain therapeutic benefit. To date, gene therapy for the treatment of GBM has demonstrated anti-tumor efficacy in pre-clinical studies and promising safety profiles in clinical studies. However, while this approach is obviously promising, concerns still exist regarding issues associated with transduction efficiency, viral delivery, the pathologic response of the brain, and treatment efficacy. Tumor development and progression involve alterations in a wide spectrum of genes, therefore a variety of gene therapy approaches for GBM have been proposed. Improved viral vectors are being evaluated, and the potential use of gene therapy alone or in synergy with other treatments against GBM are being studied. In this review, we will discuss the most commonly studied gene therapy approaches for the treatment of GBM in preclinical and clinical studies including: prodrug/suicide gene therapy; oncolytic gene therapy; cytokine mediated gene therapy; and tumor suppressor gene therapy. In addition, we review the principles and mechanisms of current gene therapy strategies as well as advantages and disadvantages of each.

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.

Oncolytic virus therapies

Oncolytic virus (OV) therapy currently represents one of the most promising approaches to cancer treatment for their dual anticancer mechanisms: direct lysis of cancer cells (oncolytic feature) and activation of the immunosystem (cancer vaccine aspect). The latter demonstrates the advantage of a multi-target approach against multiple tumor-associated antigens. Since the 2005 SFDA (the Chinese FDA) approval for the clinical use of Oncorine™, the first human OV-based cancer treatment, more than 200 patents have been filed worldwide and several Phase I/II studies have been conducted. This patent review analyzes patents and clinical studies of the most promising OV products to highlight the pros and cons of this innovative anticancer approach, which is currently being tested in several cancers (i.e., hepatocellular carcinoma, melanoma and glioblastoma) by systemic as well as intratumoral injection. Clinical results, although effective only for a limited period of time, are encouraging. Combined treatments with radio or chemotherapeutic protocols are also in progress.

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.

Pediatric glioma stem cells: biologic strategies for oncolytic HSV virotherapy

While glioblastoma multiforme (GBM) is the most common adult malignant brain tumor, GBMs in childhood represent less than 10% of pediatric malignant brain tumors and are phenotypically and molecularly distinct from adult GBMs. Similar to adult patients, outcomes for children with high-grade gliomas (HGGs) remain poor. Furthermore, the significant morbidity and mortality yielded by pediatric GBM is compounded by neurotoxicity for the developing brain caused by current therapies. Poor outcomes have been attributed to a subpopulation of chemotherapy and radiotherapy resistant cells, termed “glioma stem cells” (GSCs), “glioma progenitor cells,” or “glioma-initiating cells,” which have the ability to initiate and maintain the tumor and to repopulate the recurring tumor after conventional therapy. Future innovative therapies for pediatric HGG must be able to eradicate these therapy-resistant GSCs. Oncolytic herpes simplex viruses (oHSV), genetically engineered to be safe for normal cells and to express diverse foreign anti-tumor therapeutic genes, have been demonstrated in preclinical studies to infect and kill GSCs and tumor cells equally while sparing normal brain cells. In this review, we discuss the unique aspects of pediatric GSCs, including markers to identify them, the microenvironment they reside in, signaling pathways that regulate them, mechanisms of cellular resistance, and approaches to target GSCs, with a focus on the promising therapeutic, genetically engineered oHSV.

Oncolytic virotherapy for ovarian cancer

In the past two decades, more than 20 viruses with selective tropism for tumor cells have been developed as oncolytic viruses (OVs) for treatments of a variety of malignancies. Of these viruses, eleven have been tested in human ovarian cancer models in preclinical studies. So far, nine phase I or II clinical trials have been conducted or initiated using four different types of OVs in patients with recurrent ovarian cancers. In this article, we summarize the different OVs that are being assessed as therapeutics for ovarian cancer. We also present an overview of recent advances in identification of key genetic or immune-response pathways involved in tumorigenesis of ovarian cancer, which provides a better understanding of the tumor specificities and oncolytic properties of OVs. In addition, we discuss how next-generation OVs could be genetically modified or integrated into multimodality regimens to improve clinical outcomes based on recent advances in ovarian cancer biology.

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.

Oncolytic virus therapy for glioblastoma multiforme: concepts and candidates

Twenty years of oncolytic virus development have created a field that is driven by the potential promise of lasting impact on our cancer treatment repertoire. With the field constantly expanding-more than 20 viruses have been recognized as potential oncolytic viruses-new virus candidates continue to emerge even as established viruses reach clinical trials. They all share the defining commonalities of selective replication in tumors, subsequent tumor cell lysis, and dispersion within the tumor. Members from diverse virus classes with distinctly different biologies and host species have been identified. Of these viruses, 15 have been tested on human glioblastoma multiforme. So far, 20 clinical trials have been conducted or initiated using attenuated strains of 7 different oncolytic viruses against glioblastoma multiforme. In this review, we present an overview of viruses that have been developed or considered for glioblastoma multiforme treatment. We outline the principles of tumor targeting and selective viral replication, which include mechanisms of tumor-selective binding, and molecular elements usurping cellular biosynthetic machinery in transformed cells. Results from clinical trials have clearly established the proof of concept and have confirmed the general safety of oncolytic virus application in the brain. The moderate clinical efficacy has not yet matched the promising preclinical lab results; next-generation oncolytic viruses that are either "armed" with therapeutic genes or embedded in a multimodality treatment regimen should enhance the clinical results.

In vivo evaluation of a cancer therapy strategy combining HSV1716-mediated oncolysis with gene transfer and targeted radiotherapy

Oncolytic herpes viruses show promise for cancer treatment. However, it is unlikely that they will fulfill their therapeutic potential when used as monotherapies. An alternative strategy is to use these viruses not only as oncolytic agents but also as a delivery mechanism of therapeutic transgenes to enhance tumor cell killing. The herpes simplex virus 1 deletion mutant HSV1716 is a conditionally replicating oncolytic virus that selectively replicates in and lyses dividing tumor cells. It has a proven safety profile in clinical trials and has demonstrated efficacy as a gene-delivery vehicle. To enhance its therapeutic potential, we have engineered HSV1716 to convey the noradrenaline transporter (NAT) gene (HSV1716/NAT), whose expression endows infected cells with the capacity to accumulate the noradrenaline analog metaiodobenzylguanidine (MIBG). Thus, the NAT gene-infected cells are susceptible to targeted radiotherapy using radiolabeled (131)I-MIBG, a strategy that has already shown promise for combined targeted radiotherapy-gene therapy in cancer cells after plasmid-mediated transfection.

METHODS

We used HSV1716/NAT as a dual cell lysis-gene delivery vehicle for targeting the NAT transgene to human tumor xenografts in vivo.

RESULTS

In tumor xenografts that did not express NAT, intratumoral or intravenous injection of HSV1716/NAT induced the capacity for active uptake of (131)I-MIBG. Administration of HSV1716/NAT and (131)I-MIBG resulted in decreased tumor growth and enhanced survival relative to injection of either agent alone. Efficacy was dependent on the scheduling of delivery of the 2 agents.

CONCLUSION

These findings support a role for combination radiotherapy-gene therapy for cancer using HSV1716 expressing the NAT transgene and targeted radionuclide therapy.

Preclinical evaluation of a genetically engineered herpes simplex virus expressing interleukin-12

Herpes simplex virus 1 (HSV-1) mutants that lack the γ(1)34.5 gene are unable to replicate in the central nervous system but maintain replication competence in dividing cell populations, such as those found in brain tumors. We have previously demonstrated that a γ(1)34.5-deleted HSV-1 expressing murine interleukin-12 (IL-12; M002) prolonged survival of immunocompetent mice in intracranial models of brain tumors. We hypothesized that M002 would be suitable for use in clinical trials for patients with malignant glioma. To test this hypothesis, we (i) compared the efficacy of M002 to three other HSV-1 mutants, R3659, R8306, and G207, in murine models of brain tumors, (ii) examined the safety and biodistribution of M002 in the HSV-1-sensitive primate Aotus nancymae following intracerebral inoculation, and (iii) determined whether murine IL-12 produced by M002 was capable of activating primate lymphocytes. Results are summarized as follows: (i) M002 demonstrated superior antitumor activity in two different murine brain tumor models compared to three other genetically engineered HSV-1 mutants; (ii) no significant clinical or magnetic resonance imaging evidence of toxicity was observed following direct inoculation of M002 into the right frontal lobes of A. nancymae; (iii) there was no histopathologic evidence of disease in A. nancymae 1 month or 5.5 years following direct inoculation; and (iv) murine IL-12 produced by M002 activates A. nancymae lymphocytes in vitro. We conclude that the safety and preclinical efficacy of M002 warrants the advancement of a Δγ(1)34.5 virus expressing IL-12 to phase I clinical trials for patients with recurrent malignant glioma.

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.

Combination of a fusogenic glycoprotein, pro-drug activation and oncolytic HSV as an intravesical therapy for superficial bladder cancer

Background:

There are still no effective treatments for superficial bladder cancer (SBC)/non-muscle invasive bladder cancer. Following treatment, 20% of patients still develop metastatic disease. Superficial bladder cancer is often multifocal, has high recurrences after surgical resection and recurs after intravesical live Bacillus Calmette–Guérin. Oncovex^GALV/CD, an oncolytic herpes simplex virus-1, has shown enhanced local tumour control by combining oncolysis with the expression of a highly potent pro-drug activating gene and the fusogenic glycoprotein.

Methods:

In vitro fusion/prodrug/apoptotic cell-based assays. In vivo orthotopic bladder tumour model, visualised by computed microtomography.

Results:

Treatment of seven human bladder carcinoma cell lines with the virus resulted in tumour cell killing through oncolysis, pro-drug activation and glycoprotein fusion. Oncovex^GALV/CD and mitomycin C showed a synergistic effect, whereas the co-administration with cisplatin or gemcitabine showed an antagonistic effect in vitro. Transitional cell cancer (TCC) cells follow an apoptotic cell death pathway after infection with Oncovex^GALV/CD with or without 5-FC. In vivo results showed that intravesical treatment with Oncovex^GALV/CD + prodrug (5-FC) reduced the average tumour volume by over 95% compared with controls.

Discussion:

Our in vitro and in vivo results indicate that Oncovex^GALV/CD can improve local tumour control within the bladder, and potentially alter its natural history.

Inhibition of TANK binding kinase 1 by herpes simplex virus 1 facilitates productive infection

The γ(1)34.5 protein of herpes simplex viruses (HSV) is essential for viral pathogenesis, where it precludes translational arrest mediated by double-stranded-RNA-dependent protein kinase (PKR). Paradoxically, inhibition of PKR alone is not sufficient for HSV to exhibit viral virulence. Here we report that γ(1)34.5 inhibits TANK binding kinase 1 (TBK1) through its amino-terminal sequences, which facilitates viral replication and neuroinvasion. Compared to wild-type virus, the γ(1)34.5 mutant lacking the amino terminus induces stronger antiviral immunity. This parallels a defect of γ(1)34.5 for interacting with TBK1 and reducing phosphorylation of interferon (IFN) regulatory factor 3. This activity is independent of PKR. Although resistant to IFN treatment, the γ(1)34.5 amino-terminal deletion mutant replicates at an intermediate level between replication of wild-type virus and that of the γ(1)34.5 null mutant in TBK1(+/+) cells. However, such impaired viral growth is not observed in TBK1(-/-) cells, indicating that the interaction of γ(1)34.5 with TBK1 dictates HSV infection. Upon corneal infection, this mutant replicates transiently but barely invades the trigeminal ganglia or brain, which is a difference from wild-type virus and the γ(1)34.5 null mutant. Therefore, in addition to PKR, γ(1)34.5 negatively regulates TBK1, which contributes viral replication and spread in vivo.

Activation of NF-κB in CD8+ dendritic cells Ex Vivo by the γ134.5 null mutant correlates with immunity against herpes simplex virus 1

The γ(1)34.5 protein of herpes simplex viruses (HSV) is essential for virulence. Accordingly, an HSV mutant lacking γ(1)34.5 is attenuated in vivo. Despite its vaccine potential, the mechanism by which the γ(1)34.5 null mutant triggers protective immunity is unknown. In this report we show that vaccination with the γ(1)34.5 null mutant protects against lethal challenge from wild-type virus via IκB kinase in dendritic cells (DCs), which sense virus-associated molecular patterns. Unlike mock-treated DCs, DCs primed with the γ(1)34.5 null mutant ex vivo mediate resistance to wild-type HSV after adoptive transfer into naïve mice. Furthermore, the γ(1)34.5 null mutant activates IκB kinase, which facilitates p65/RelA phosphorylation and nuclear translocation, resulting in DC maturation. While unable to produce infectious virus in DCs, this mutant virus expresses early and late genes. In its abortive infection, the γ(1)34.5 null mutant induces protective immunity more effectively in CD8(+) DCs than in CD8(-) DCs. This is mirrored by a higher level of interleukin-6 (IL-6) and IL-12 secretion by CD8(+) DCs than CD8(-) DCs. Remarkably, inhibition of p65/RelA phosphorylation or nuclear translocation in CD8(+) DCs disrupts protective immunity. These results suggest that engagement of the γ(1)34.5 null mutant with CD8(+) DCs elicits innate immunity to activate NF-κB, which translates into protective immunity.

Rethinking herpes simplex virus: the way to oncolytic agents

Oncolytic viruses infect, replicate in and kill cancer cells. HSV has emerged as a most promising candidate because it exerts a generally moderate pathogenicity in humans; it is amenable to attenuation and tropism retargeting; the ample genome provides space for heterologous genes; specific antiviral therapy is available in a worst case scenario. The first strategy to convert HSV into an oncolytic agent consisted in deletion of the γ(1) 34.5 gene which counteracts the protein kinase R (PKR) response, and of the UL39 gene which encodes the large ribonucleotide reductase subunit. Tumor specificity resided in low PKR activity, and high deoxyribonucleotides content of cancer cells. These highly attenuated viruses have been and presently are in clinical trials with encouraging results. The preferred route of administration has been intratumor or in tissues adjacent to resected tumors. Although the general population has a high seroprevalence of antibodies to HSV, studies in animals and humans demonstrate that prior immunity is not an obstacle to systemic routes of administration, and that oncolytic HSV (o-HSVs) do populate tumors. As the attenuated viruses undergo clinical experimentation, the research pipeline is developing novel, more potent and highly tumor-specific o-HSVs. These include viruses which overcome tumor heterogeneity in PKR level by insertion of anti-PKR genes, viruses which reinforce the host tumor clearance capacity by encoding immune cytokines (IL-12 or granulocyte-macrophage colony-stimulating factor), and non-attenuated viruses fully retargeted to tumor specific receptors. A strategy to generate o-HSVs fully retargeted to human epidermal growth factor receptor-2 (HER-2) or other cancer-specific surface receptors is detailed.

Engineered herpes simplex virus vectors for antitumor therapy and vaccine delivery

Genetically modified herpes simplex viruses (HSVs) have been exploited for both antitumor therapy and vaccine delivery. These mutant viruses retain their ability to replicate and lyse permissive cells, including many tumor types, and are referred to as oncolytic HSVs. In addition, deletion of nonessential genes permits the introduction of foreign genes to augment the antitumor effect by either immune stimulation, targeting for select tumors, or expression of tumor or vaccine antigens. This article reviews the development of oncolytic HSVs as an anticancer therapy, as well as the application of HSV-1 vectors for delivery of targeted antigens or as vaccine adjuvants. The impact of these novel vectors with respect to enhanced antitumor activity and development of antitumor vaccination strategies is discussed.

Structure and sequence of the saimiriine herpesvirus 1 genome

We report here the complete genome sequence of the squirrel monkey α-herpesvirus saimiriine herpesvirus 1 (HVS1). Unlike the simplexviruses of other primate species, only the unique short region of the HVS1 genome is bounded by inverted repeats. While all Old World simian simplexviruses characterized to date lack the herpes simplex virus RL1 (γ34.5) gene, HVS1 has an RL1 gene. HVS1 lacks several genes that are present in other primate simplexviruses (US8.5, US10-12, UL43/43.5 and UL49A). Although the overall genome structure appears more like that of varicelloviruses, the encoded HVS1 proteins are most closely related to homologous proteins of the primate simplexviruses. Phylogenetic analyses confirm that HVS1 is a simplexvirus. Limited comparison of two HVS1 strains revealed a very low degree of sequence variation more typical of varicelloviruses. HVS1 is thus unique among the primate α-herpesviruses in that its genome has properties of both simplexviruses and varicelloviruses.

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.

Experimental approaches for the treatment of malignant gliomas

Malignant gliomas, which include glioblastomas and anaplastic astrocytomas, are the most common primary tumors of the brain. Over the past 30 years, the standard treatment for these tumors has evolved to include maximal safe surgical resection, radiation therapy and temozolomide chemotherapy. While the median survival of patients with glioblastomas has improved from 6 months to 14.6 months, these tumors continue to be lethal for the vast majority of patients. There has, however, been recent substantial progress in our mechanistic understanding of tumor development and growth. The translation of these genetic, epigenetic and biochemical findings into therapies that have been tested in clinical trials is the subject of this review.

Expression of RNA interference triggers from an oncolytic herpes simplex virus results in specific silencing in tumour cells in vitro and tumours in vivo

Background

Delivery of small interfering RNA (siRNA) to tumours remains a major obstacle for the development of RNA interference (RNAi)-based therapeutics. Following the promising pre-clinical and clinical results with the oncolytic herpes simplex virus (HSV) OncoVEX^GM-CSF, we aimed to express RNAi triggers from oncolytic HSV, which although has the potential to improve treatment by silencing tumour-related genes, was not considered possible due to the highly oncolytic properties of HSV.

Methods

To evaluate RNAi-mediated silencing from an oncolytic HSV backbone, we developed novel replicating HSV vectors expressing short-hairpin RNA (shRNA) or artificial microRNA (miRNA) against the reporter genes green fluorescent protein (eGFP) and β-galactosidase (lacZ). These vectors were tested in non-tumour cell lines in vitro and tumour cells that are moderately susceptible to HSV infection both in vitro and in mice xenografts in vivo. Silencing was assessed at the protein level by fluorescent microscopy, x-gal staining, enzyme activity assay, and western blotting.

Results

Our results demonstrate that it is possible to express shRNA and artificial miRNA from an oncolytic HSV backbone, which had not been previously investigated. Furthermore, oncolytic HSV-mediated delivery of RNAi triggers resulted in effective and specific silencing of targeted genes in tumour cells in vitro and tumours in vivo, with the viruses expressing artificial miRNA being comprehensibly more effective.

Conclusions

This preliminary data provide the first demonstration of oncolytic HSV-mediated expression of shRNA or artificial miRNA and silencing of targeted genes in tumour cells in vitro and in vivo. The vectors developed in this study are being adapted to silence tumour-related genes in an ongoing study that aims to improve the effectiveness of oncolytic HSV treatment in tumours that are moderately susceptible to HSV infection and thus, potentially improve response rates seen in human clinical trials.

Oncolytic herpes simplex virus vectors and chemotherapy: are combinatorial strategies more effective for cancer?

Despite aggressive treatments, including chemotherapy and radiotherapy, cancers often recur owing to resistance to conventional therapies. Oncolytic viruses such as oncolytic herpes simplex virus (oHSV) represent an exciting biological approach to cancer therapy. A range of viral mutations has been engineered into HSV to engender oncolytic activity. While oHSV as a single agent has been tested in a number of cancer clinical trials, preclinical studies have demonstrated enhanced efficacy when it is combined with cytotoxic anticancer drugs. Among the strategies that will be discussed in this article are combinations with standard-of-care chemotherapeutics, expression of prodrug-activating enzymes to enhance chemotherapy and small-molecule inhibitors. The combination of oHSV and chemotherapy can achieve much more efficient cancer cell killing than either single agent alone, often through synergistic interactions. This can be clinically important not just for improving efficacy but also for permitting lower and less toxic chemotherapeutic doses. The viral mutations in an oHSV vector often determine the favorability of its interactions with chemotherapy, just as different cancer cells, due to genetic alterations, vary in their response to chemotherapy. As chemotherapeutics are often the standard of care, combining them with an investigational new drug, such as oHSV, is clinically easier than combining multiple novel agents. As has become clear for most cancer therapies, multimodal treatments are usually more effective. In this article, we will discuss the recent progress of these combinatorial strategies between virotherapy and chemotherapy and future directions.

Ultrastructural analysis of ICP34.5- herpes simplex virus 1 replication in mouse brain cells in vivo

Replication-competent forms of herpes simplex virus 1 (HSV-1) defective in the viral neurovirulence factor infected cell protein 34.5 (ICP34.5) are under investigation for use in the therapeutic treatment of cancer. In mouse models, intratumoral injection of ICP34.5-defective oncolytic HSVs (oHSVs) has resulted in the infection and lysis of tumor cells, an associated decrease in tumor size, and increased survival times. The ability of these oHSVs to infect and lyse cells is frequently characterized as exclusive to or selective for tumor cells. However, the extent to which ICP34.5-deficient HSV-1 replicates in and may be neurotoxic to normal brain cell types in vivo is poorly understood. Here we report that HSV-1 defective in ICP34.5 expression is capable of establishing a productive infection in at least one normal mouse brain cell type. We show that γ34.5 deletion viruses replicate productively in and induce cellular damage in infected ependymal cells. Further evaluation of the effects of oHSVs on normal brain cells in animal models is needed to enhance our understanding of the risks associated with the use of current and future oHSVs in the brains of clinical trial subjects and to provide information that can be used to create improved oHSVs for future use.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

Dephosphorylation of eIF2alpha mediated by the gamma134.5 protein of herpes simplex virus 1 facilitates viral neuroinvasion

The gamma(1)34.5 protein, a virulence factor of herpes simplex viruses, redirects protein phosphatase 1 to dephosphorylate the alpha subunit of translation initiation factor 2 (eIF2alpha). Additionally, it inhibits the induction of antiviral genes by TANK-binding kinase 1. Nevertheless, its precise role in vivo remains to be established. Here we show that eIF2alpha dephosphorylation by gamma(1)34.5 is crucial for viral neuroinvasion. V(193)E and F(195)L substitutions in gamma(1)34.5 abrogate viral replication in the eye and spread to the trigeminal ganglia and brain. Intriguingly, inhibition of antiviral gene induction by gamma(1)34.5 is not sufficient to exhibit viral virulence.

Oncolytic viral therapy of malignant glioma

Novel approaches to treatment of malignant glioma, the most frequently occurring primary brain tumor, have included the use of a wide range of oncolytic viral vectors. These vectors, either naturally tumor-selective, or engineered as such, have shown promise in the handful of phase I and phase II clinical trials conducted in recent years. The strategies developed for each of the different viruses currently being studied and the history of their development are summarized here. In addition, the results of clinical trials in patients and their implication for future trials are also discussed.

Herpes simplex virus oncolytic therapy for pediatric malignancies

Despite improving survival rates for children with cancer, a subset of patients exist with disease resistant to traditional therapies such as surgery, chemotherapy, and radiation. These patients require newer, targeted treatments used alone or in combination with more traditional approaches. Oncolytic herpes simplex virus (HSV) is one of these newer therapies that offer promise for several difficult to treat pediatric malignancies. The potential benefit of HSV therapy in pediatric solid tumors including brain tumors, neuroblastomas, and sarcomas is reviewed along with the many challenges that need to be addressed prior to moving oncolytic HSV therapy from the laboratory to the beside in the pediatric population.

Targeted genetic and viral therapy for advanced head and neck cancers

Head and neck cancers usually present with advanced disease and novel therapies are urgently needed. Genetic therapy aims at restoring malfunctioned tumor suppressor gene(s) or introducing proapoptotic genes. Oncolytic virotherapeutics induce multiple cycles of cancer-specific virus replication, followed by oncolysis, virus spreading and infection of adjacent cancer cells. Oncolytic viruses can also be armed to express therapeutic transgene(s). Recent advances in preclinical and clinical studies are revealing the potential of both therapeutic classes for advanced head and neck cancers, including the approval of two products (Gendicine and H101) by a governmental agency. This review summarizes the available clinical data to date and discusses the challenges and future directions.

The effects of trichostatin A on the oncolytic ability of herpes simplex virus for oral squamous cell carcinoma cells

Combining the use of a chemotherapeutic agent with oncolytic virotherapy is a useful way to increase the efficiency of the treatment of cancer. The effect of the histone diacetylase (HDAC) inhibitor trichostatin A (TSA) on the antitumor activity of a herpes simplex virus type-1 (HSV-1) mutant was examined in oral squamous cell carcinoma (SCC) cells. Immunoblotting analysis and immunoflourescence staining revealed that a cytoplasmic nuclear factor-kappaB (NF-kappaB) component, p65, translocated into the nucleus after infection with gamma(1)34.5 gene-deficient HSV-1 R849, indicating that R849 activated NF-kappaB. TSA induced acetylation of p65 and increased the amount of p65 in the nucleus of oral SCC cells. Treatment of R849-infected cells with TSA also increased the amount of nuclear p65 and binding of NF-kappaB to its DNA-binding site and an NF-kappaB inhibitor SN50 diminished the increase in nuclear p65. In the presence of TSA, the production of virus and the expression of LacZ integrated into R849 and glycoprotein D, but not ICP0, ICP6 and thymidine kinase, were increased. The viability of cells treated with a combination of R849 and TSA was lower than that of those treated with R849 only. After treatment with TSA, expression of the cell cycle kinase inhibitor p21 was upregulated and the cell cycle was arrested at G1. These results indicate that TSA enhanced the replication of the HSV-1 mutant through the activation of NF-kappaB and induced cell cycle arrest at G1 to inhibit cell growth. TSA can be used as an enhancing agent for oncolytic virotherapy for oral SCC with gamma(1)34.5 gene-deficient HSV-1.

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.

Diversity of the a sequence of herpes simplex virus type 1 developed during evolution

Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen. The a sequence of HSV-1 is the cis-acting site required for the cleavage and encapsidation of unit-length HSV-1 DNA from concatemeric forms. The consensus a sequence consists of (i) DR1 (direct repeat 1), (ii) Ub, (iii) a DR2 array [a repeat of various copy numbers of DR2 elements (11 or 12 bp)], (iv) a DR4 stretch and (v) Uc. In the present study, the nucleotide sequences of the a sequences of 26 HSV-1 isolates were determined and the DR4 stretches were classified into three groups. The state of a set of 20 DNA polymorphisms in the genomes of these HSV-1 isolates was determined previously. A correct classification rate of 100 % was achieved when discriminant analysis was performed between the DR4 stretch (criterion variable) and the set of 20 DNA polymorphisms (predictor variables), suggesting a close association of the DR4 stretch with HSV-1 diversification. DR2 elements of 9, 13 and 14 bp were detected in addition to those of 11 and 12 bp, and a correct classification rate of 93 % was achieved when discriminant analysis was performed between the DR2 array and the set of 20 DNA polymorphisms. Some DR2 elements of one HSV-1 isolate had the same nucleotide sequences as part of the adjacent DR4 stretch, and these variations were adequately explained by postulating recombination involving DR2 elements; hence, the DR2 array was deduced to be prone to recombination.

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.

Enhanced antiglioma activity of chimeric HCMV/HSV-1 oncolytic viruses

Oncolytic herpes simplex virus (HSV)-1 gamma(1)34.5-deletion mutants (Deltagamma(1)34.5 HSV) are promising agents for tumor therapy. The attenuating mutation renders the virus aneurovirulent but also limits late viral protein synthesis and efficient replication in many tumors. We tested whether one function of gamma(1)34.5 gene, which mediates late viral protein synthesis through host protein kinase R (PKR) antiviral response evasion, could be restored, without restoring the neurovirulence. We have previously reported the construction of two chimeric Deltagamma(1)34.5 HSV vectors (chimeric HSV), C130 and C134, which express the human cytomegalovirus (HCMV) PKR-evasion genes TRS1 and IRS1, respectively. We now demonstrate the following. The HCMV/HSV-1 chimeric viruses (i) maintain late viral protein synthesis in the human malignant glioma cells tested (D54-MG, U87-MG and U251-MG); (ii) replicate to higher titers than Deltagamma(1)34.5 HSV in malignant glioma cells in vitro and in vivo; (iii) are aneurovirulent; and (iv) are superior to other Deltagamma(1)34.5 HSV with both improved reduction of tumor volumes in vivo, and improved survival in two experimental murine brain tumor models. These findings demonstrate that transfer of HCMV IRS1 or TRS1 gene into Deltagamma(1)34.5 HSV significantly improves replication in malignant gliomas without restoring wild-type neurovirulence, resulting in enhanced tumor reduction and prolonged survival.

Impact of protein kinase PKR in cell biology: from antiviral to antiproliferative action

The double-stranded RNA-dependent protein kinase PKR is a critical mediator of the antiproliferative and antiviral effects exerted by interferons. Not only is PKR an effector molecule on the cellular response to double-stranded RNA, but it also integrates signals in response to Toll-like receptor activation, growth factors, and diverse cellular stresses. In this review, we provide a detailed picture on how signaling downstream of PKR unfolds and what are the ultimate consequences for the cell fate. PKR activation affects both transcription and translation. PKR phosphorylation of the alpha subunit of eukaryotic initiation factor 2 results in a blockade on translation initiation. However, PKR cannot avoid the translation of some cellular and viral mRNAs bearing special features in their 5' untranslated regions. In addition, PKR affects diverse transcriptional factors such as interferon regulatory factor 1, STATs, p53, activating transcription factor 3, and NF-kappaB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IkappaB and NF-kappaB nuclear translocation has been intensively studied. At the cellular and organism levels PKR exerts antiproliferative effects, and it is a key antiviral agent. A point of convergence in both effects is that PKR activation results in apoptosis induction. The extent and strength of the antiviral action of PKR are clearly understood by the findings that unrelated viral proteins of animal viruses have evolved to inhibit PKR action by using diverse strategies. The case for the pathological consequences of the antiproliferative action of PKR is less understood, but therapeutic strategies aimed at targeting PKR are beginning to offer promising results.

A phase I study of OncoVEXGM-CSF, a second-generation oncolytic herpes simplex virus expressing granulocyte macrophage colony-stimulating factor

PURPOSE

To conduct a phase I clinical trial with a second-generation oncolytic herpes simplex virus (HSV) expressing granulocyte macrophage colony-stimulating factor (Onco VEXGM-CSF) to determine the safety profile of the virus, look for evidence of biological activity, and identify a dosing schedule for later studies.

EXPERIMENTAL DESIGN

The virus was administered by intratumoral injection in patients with cutaneous or s.c. deposits of breast, head and neck and gastrointestinal cancers, and malignant melanoma who had failed prior therapy. Thirteen patients were in a single-dose group, where doses of 10(6), 10(7), and 10(8) plaque-forming units (pfu)/mL were tested, and 17 patients were in a multidose group testing a number of dose regimens.

RESULTS

The virus was generally well tolerated with local inflammation, erythema, and febrile responses being the main side effects. The local reaction to injection was dose limiting in HSV-seronegative patients at 10(7) pfu/mL. The multidosing phase thus tested seroconverting HSV-seronegative patients with 10(6) pfu/mL followed by multiple higher doses (up to 10(8) pfu/mL), which was well tolerated by all patients. Biological activity (virus replication, local reactions, granulocyte macrophage colony-stimulating factor expression, and HSV antigen-associated tumor necrosis), was observed. The duration of local reactions and virus replication suggested that dosing every 2 to 3 weeks was appropriate. Nineteen of 26 patient posttreatment biopsies contained residual tumor of which 14 showed tumor necrosis, which in some cases was extensive, or apoptosis. In all cases, areas of necrosis also strongly stained for HSV. The overall responses to treatment were that three patients had stable disease, six patients had tumors flattened (injected and/or uninjected lesions), and four patients showed inflammation of uninjected as well as the injected tumor, which, in nearly all cases, became inflamed.

CONCLUSIONS

Onco VEXGM-CSF is well tolerated and can be safely administered using the multidosing protocol described. Evidence of an antitumor effect was seen.

Combination of a fusogenic glycoprotein, prodrug activation, and oncolytic herpes simplex virus for enhanced local tumor control

We have previously developed an oncolytic herpes simplex virus-1 based on a clinical virus isolate, which was deleted for ICP34.5 to provide tumor selected replication and ICP47 to increase antigen presentation as well as tumor selective virus replication. A phase I/II clinical trial using a version of this virus expressing granulocyte macrophage colony-stimulating factor has shown promising results. The work reported here aimed to develop a version of this virus in which local tumor control was further increased through the combined expression of a highly potent prodrug activating gene [yeast cytosine deaminase/uracil phospho-ribosyltransferase fusion (Fcy::Fur)] and the fusogenic glycoprotein from gibbon ape leukemia virus (GALV), which it was hoped would aid the spread of the activated prodrug through the tumor. Viruses expressing the two genes individually or in combination were constructed and tested, showing (a) GALV and/or Fcy::Fur expression did not affect virus growth; (b) GALV expression causes cell fusion and increases the tumor cell killing at least 30-fold in vitro and tumor shrinkage 5- to 10-fold in vivo; (c) additional expression of Fcy::Fur combined with 5-fluorocytosine administration improves tumor shrinkage further. These results indicate, therefore, that the combined expression of the GALV protein and Fcy::Fur provides a highly potent oncolytic virus with improved capabilities for local tumor control. It is intended to enter the GALV/Fcy::Fur expressing virus into clinical development for the treatment of tumor types, such as pancreatic or lung cancer, where local control would be anticipated to be clinically advantageous.

Enhancement of antitumor activity of herpes simplex virus gamma(1)34.5-deficient mutant for oral squamous cell carcinoma cells by hexamethylene bisacetamide

Current oncolytic viruses exert only limited antitumor activity on their own. There is a need to increase their oncolytic capability. We evaluated the effect of a differentiating reagent, hexamethylene bisacetamide (HMBA), on the antitumor activity of a gamma(1)34.5-deficient herpes simplex virus type 1 (HSV-1) R849 for human oral squamous cell carcinoma (SCC) cells. Hexamethylene bisacetamide increased the viral yield, especially at a low input multiplicity of infection (MOI), and the transcription of immediate early genes of HSV-1. Hexamethylene bisacetamide treatment promoted the cytopathic effect of R849 and increased the proportion of dead cells. Hexamethylene bisacetamide produced more apoptotic cells in R849-infected cells as compared with parental HSV-1(F)-infected cells. The growth of oral SCC xenografts in nude mice was markedly suppressed by treatment with R849 in combination with HMBA, and the survival of the co-treated animals was significantly prolonged as compared with that of animals treated with R849 only. Herpes simplex virus type 1 mRNA was expressed in tumors and trigeminal neurons, but not in brain, lung, liver, and kidney. These results indicate that HMBA enhances the antitumor activity of R849 through the expression of immediate early genes without increasing its toxicity. Hexamethylene bisacetamide can be used as an enhancing agent for oncolytic therapy with HSV-1 mutants.

Oncolytic viruses derived from the gamma34.5-deleted herpes simplex virus recombinant R3616 encode a truncated UL3 protein

Replication-competent herpes simplex virus (HSV-1) mutants are used in clinical trials in the experimental treatment of cancer. Mutants G207, HSV1716, NV1020, and Oncovex GM-CSF share in common a defect in one or both copies of the gene encoding the neurovirulence factor, ICP34.5, and are thus neuroattenuated. These viruses are acknowledged to differ from one another (a) in the specific types of mutations intentionally introduced during their derivation and (b) in the inherent genetic differences retained from the different parent strains used in their construction. Unintended mutations are expected to emerge at some low frequency during the selection for and passage of mutant viruses. Here we demonstrate that during the construction of the oncolytic virus R3616, a nonsense mutation arose in an untargeted region of the HSV-1 genome that resulted in a substantial truncation of the viral protein known as UL3. This report is the first published documentation that oncolytic herpesviruses developed and used in clinical trials contain adventitious mutations. The implications of these findings for the characterization and development of vectors proposed for use in clinical trials are discussed.

Replication-competent herpes simplex vectors: design and applications

Replication-competent vectors are derived from attenuated viruses whose genes, that are nonessential for replication in cultured cells in vitro, are either mutated or deleted. The removal of one or more nonessential genes may reduce pathogenicity without requiring a cell line to complement growth. Herpes simplex viruses (HSV) are potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. This review highlights the progress in creating attenuated genetically engineered HSV vectors.

To replicate or not to replicate: achieving selective oncolytic virus replication in cancer cells through translational control

To ensure that their mRNAs are translated and that the viral proteins necessary for assembling the next generation of infectious progeny are produced, viruses must effectively seize control of the translational machinery within their host cells. In many cases, the ability to productively engage host translational components can determine if a given cell type can support viral replication, illustrating the critical importance of this task in the viral life cycle. Failure to interface properly with the host translational apparatus can compromise the productive growth cycle, resulting in an abortive infection and radically restricting viral replication. Not only have viruses become facile at commandeering this machinery, they are also particularly adept at manipulating cellular translation control pathways for their own ends. In this review, the mechanisms by which numerous viruses manipulate host translational control circuits are discussed. Furthermore, particular attention is devoted to understanding how interfering with the ability of a virus to properly regulate translation in its host can be exploited to generate oncolytic strains that selectively replicate in cancer cells.

Stable Levels of Long-Term Transgene Expression Driven by the Latency-Associated Transcript Promoter in a Herpes Simplex Virus Type 1 Vector

Previous gene transfer studies of the herpes simplex virus type 1 (HSV-1) using the latency-associated transcript (LAT) promoter have reported a decrease in transgene expression in the brain over time, but the extent of this decrease has not been measured and it is unknown if expression eventually stabilizes. We examined LAT promoter-mediated transgene expression in the mouse brain for 1 year following intracranial injection with a HSV-1 vector expressing human beta-glucuronidase (GUSB). The vector genome copy number remained stable from 2 to 52 weeks. Quantitative reverse transcriptase PCR detected a peak of LAT intron expression at 2 weeks (corresponding to the end of the acute phase of viral infection), followed by stable expression during latency (13-52 weeks). The number of GUSB-positive cells also had a peak in the acute phase and then was stable during latency (13-52 weeks). GUSB enzymatic activity was maintained at 11% of normal at 6 and 12 months, indicating that the LAT promoter is capable of driving stable transgene expression in the brain.

Phosphorylation and dephosphorylation events that regulate viral mRNA translation

As they are completely dependent upon the protein synthesis machinery resident in the cells of their host to translate their mRNAs, it is imperative that viruses are able to effectively manipulate the elaborate cellular regulatory network that controls translation. Indeed, this exquisite dependence on host functions has made viral models attractive systems to explore translational regulatory mechanisms operative in eukaryotic cells. Central among these are an intricate array of phosphorylation and dephosphorylation events that have far reaching consequences on the activity of cellular translation factors. Not only do these modulate the activity of a given factor, but they can also determine if the translation of host proteins persists in infected cells, the efficiency with which viral mRNAs are translated and the outcome of a systemic host anti-viral response. In this review, we discuss how various viruses manipulate the phosphorylation state of key cellular translation factors, illustrating the critical nature these interactions play in virus replication, pathogenesis and innate host defense.

Oncolytic HSV exerts direct antiangiogenic activity in ovarian carcinoma

In the present study, we investigated the ability of replication-restricted herpes simplex virus (HSV) 1716 lacking ICP34.5 to infect endothelium and disrupt tumor vasculature. HSV-1716 efficiently infected and killed mouse endothelial cell lines H5V and MS1 cells, as well as human umbilical vein endothelial cells in vitro. Capillary tube formation by endothelial cells was inhibited by HSV-1716 in vitro and in vivo. Following intratumoral administration of oncolytic HSV-1716, HSV-glycoproteins could be detected in CD31-positive tumor vascular endothelium by immunostaining. Viral DNA was recovered from highly purified microdissected tumor vascular endothelium. Furthermore, endothelium of tumors treated with HSV-1716 exhibited expression of tissue factor, a marker of endothelial damage. Importantly, HSV antigen and DNA were also detected in endothelium distant from foci of active tumor infection. After intravascular inoculation of HSV-1716, viral glycoproteins were detected in association to tumor endothelium, but not vascular endothelium of different organs. Purified tumor endothelial cells showed high proliferative capability and were susceptible to HSV-1716 infection and killing ex vivo while endothelium from normal organs was not. We conclude that oncolytic HSV-1716 exerts direct antiangiogenic effects, which may contribute to the overall therapeutic efficacy of the virus.

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.