Comparison of genetically engineered herpes simplex viruses for the treatment of brain tumors in a scid mouse model of human malignant glioma

Efficacy of Systemically Administered Retargeted Oncolytic Herpes Simplex Viruses-Clearance and Biodistribution in Naïve and HSV-Preimmune Mice

We investigated the anticancer efficacy, blood clearance, and tissue biodistribution of systemically administered retargeted oncolytic herpes simplex viruses (ReHVs) in HSV-naïve and HSV-preimmunized (HSV-IMM) mice. Efficacy was tested against lung tumors formed upon intravenous administration of cancer cells, a model of metastatic disease, and against subcutaneous distant tumors. In naïve mice, HER2- and hPSMA-retargeted viruses, both armed with mIL-12, were highly effective, even when administered to mice with well-developed tumors. Efficacy was higher for combination regimens with immune checkpoint inhibitors. A significant amount of infectious virus persisted in the blood for at least 1 h. Viral genomes, or fragments thereof, persisted in the blood and tissues for days. Remarkably, the only sites of viral replication were the lungs of tumor-positive mice and the subcutaneous tumors. No replication was detected in other tissues, strengthening the evidence of the high cancer specificity of ReHVs, a property that renders ReHVs suitable for systemic administration. In HSV-IMM mice, ReHVs administered at late times failed to exert anticancer efficacy, and the circulating virus was rapidly inactivated. Serum stability and in vivo whole blood stability assays highlighted neutralizing antibodies as the main factor in virus inactivation. Efforts to deplete mice of the neutralizing antibodies are ongoing.

Innovative retargeted oncolytic herpesvirus against nectin4-positive cancers

Nectin4 is a recently discovered tumor associated antigen expressed in cancers that constitute relevant unmet clinical needs, including the undruggable triple negative breast cancer, pancreatic ductal carcinoma, bladder/urothelial cancer, cervical cancer, lung carcinoma and melanoma. So far, only one nectin4-specific drug-Enfortumab Vedotin-has been approved and the clinical trials that test novel therapeutics are only five. Here we engineered R-421, an innovative retargeted onco-immunotherapeutic herpesvirus highly specific for nectin4 and unable to infect through the natural herpes receptors, nectin1 or herpesvirus entry mediator. In vitro, R-421 infected and killed human nectin4-positive malignant cells and spared normal cells, e.g., human fibroblasts. Importantly from a safety viewpoint, R-421 failed to infect malignant cells that do not harbor nectin4 gene amplification/overexpression, whose expression level was moderate-to-low. In essence, there was a net threshold value below which cells were spared from infection, irrespective of whether they were malignant or normal; the only cells that R-421 targeted were the malignant overexpressing ones. In vivo, R-421 decreased or abolished the growth of murine tumors made transgenic for human nectin4 and conferred sensitivity to immune checkpoint inhibitors in combination therapies. Its efficacy was augmented by the cyclophosphamide immunomodulator and decreased by depletion of CD8-positive lymphocytes, arguing that it was in part T cell-mediated. R-421 elicited in-situ vaccination that protected from distant challenge tumors. This study provides proof-of-principle specificity and efficacy data justifying nectin4-retargeted onco-immunotherapeutic herpesvirus as an innovative approach against a number of difficult-to-drug clinical indications.

Targeting carcinoembryonic antigen-expressing tumors using a novel transcriptional and translational dual-regulated oncolytic herpes simplex virus type 1

VG2025 is a recombinant oncolytic herpes simplex virus type 1 (HSV-1) that uses transcriptional and translational dual regulation (TTDR) of critical viral genes to enhance virus safety and promote tumor-specific virus replication without reducing virulence. The TTDR platform is based on transcriptional control of the essential HSV-1 immediate-early protein ICP27 using a tumor-specific carcinoembryonic antigen (CEA) promoter, coupled with translational control of the neurovirulence factor ICP34.5 using multiple microRNA (miR)-binding sites. VG2025 further incorporates IL-12 and the IL-15/IL-15 receptor alpha subunit complex to enhance the antitumor and immune stimulatory properties of oncolytic HSVs. The TTDR strategy was verified in vitro and shown to be highly selective. Strong in vivo antitumor efficacy was observed following both intratumoral and intravenous administration. Clear abscopal and immune memory effects were also evident, indicating a robust antitumor immune response. Gene expression profiling of treated tumors revealed increased immune cell infiltration and activation of multiple immune-signaling pathways when compared with the backbone virus. Absence of neurotoxicity was verified in mice and in rhesus monkeys. Taken together, the enhanced tumor clearance, excellent safety profile, and positive correlation between CEA levels and viral replication efficiency may provide an opportunity for using biomarker-based precision medicine in oncolytic virotherapy.

In Situ Cancer Vaccination and Immunovirotherapy Using Oncolytic HSV

Herpes simplex virus (HSV) can be genetically altered to acquire oncolytic properties so that oncolytic HSV (oHSV) preferentially replicates in and kills cancer cells, while sparing normal cells, and inducing anti-tumor immune responses. Over the last three decades, a better understanding of HSV genes and functions, and improved genetic-engineering techniques led to the development of oHSV as a novel immunovirotherapy. The concept of in situ cancer vaccination (ISCV) was first introduced when oHSV was found to induce a specific systemic anti-tumor immune response with an abscopal effect on non-injected tumors, in the process of directly killing tumor cells. Thus, the use of oHSV for tumor vaccination in situ is antigen-agnostic. The research and development of oHSVs have moved rapidly, with the field of oncolytic viruses invigorated by the FDA/EMA approval of oHSV talimogene laherparepvec in 2015 for the treatment of advanced melanoma. Immunovirotherapy can be enhanced by arming oHSV with immunomodulatory transgenes and/or using them in combination with other chemotherapeutic and immunotherapeutic agents. This review offers an overview of the development of oHSV as an agent for ISCV against solid tumors, describing the multitude of different oHSVs and their efficacy in immunocompetent mouse models and in clinical trials.

Immunotherapeutic Efficacy of Retargeted oHSVs Designed for Propagation in an Ad Hoc Cell Line

Our laboratory has pursued the generation of cancer-specific oncolytic herpes simplex viruses (oHSVs) which ensure high efficacy while maintaining a high safety profile. Their blueprint included retargeting to a Tumor-Associated Antigen, e.g., HER2, coupled to detargeting from natural receptors to avoid off-target and off-tumor infections and preservation of the full complement of unmodified viral genes. These oHSVs are "fully virulent in their target cancer cells". The 3rd generation retargeted oHSVs carry two distinct retargeting moieties, which enable infection of a producer cell line and of the target cancer cells, respectively. They can be propagated in an ad hoc Vero cell derivative at about tenfold higher yields than 1st generation recombinants, and more effectively replicate in human cancer cell lines. The R-335 and R-337 prototypes were armed with murine IL-12. Intratumorally-administered R-337 conferred almost complete protection from LLC-1-HER2 primary tumors, unleashed the tumor microenvironment immunosuppression, synergized with the checkpoint blockade and conferred long-term vaccination against distant challenge tumors. In summary, the problem intrinsic to the propagation of retargeted oHSVs-which strictly require cells positive for targeted receptors-was solved in 3rd generation viruses. They are effective as immunotherapeutic agents against primary tumors and as antigen-agnostic vaccines.

oHSV Genome Editing by Means of galK Recombineering

Since the cloning of the herpes simplex virus (HSV) genome as BAC (bacterial artificial chromosome), the genetic engineering of the viral genome has become readily feasible. The advantage is that the modification of the animal virus genome is carried out in bacteria, with no replication or production of viral progeny, and is separated from the reconstitution or regeneration of the recombinant virus in mammalian cells. This allows an easy engineering of essential genes, as well. Many technologies have been developed for herpesvirus BAC engineering. In our hands the most powerful is galK recombineering that exploits a single marker (galK) for positive and negative selection and PCR amplicons for seamless modification in the desired genome locus. Here we describe the engineering of the HSV recombinant BAC 115 by the insertion of a heterologous cassette for the expression of murine interleukin 12 (mIL12) in the intergenic sequence between US1 and US2 ORFs.

Antitumor Efficacy of Oncolytic Herpes Virus Type 1 Armed with GM-CSF in Murine Uveal Melanoma Xenografts

Background

Uveal melanoma (UM) is the most common primary intraocular tumor in adults with a high incidence of metastasis. Standard care therapies for UM include enucleation and radiation, which are minimally effective in prolonging patient survival. Oncolytic virus treatment has become a new trend in cancer field. Of which, oncolytic herpes simplex virus type 1 (HSV-1) therapy is one of the most effective antitumor treatments. Here, we established an oncolytic HSV-1 encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), tested its efficacy in UM therapy, and investigated the innate immune response induced by this virus.

Methods

Oncolytic HSV-1 expressing GM-CSF (HSV-GM-CSF) was constructed, then verified using qPCR and Western blot assays. Cell viability assays and transmission electron microscopy were conducted on three UM cell lines, MUM2B, 92.1, and MP41, to assess the cell-killing ability and virus infection of this virus. For in vivo experiments, BALB/c-nude mice in situ UM xenografts were established to testify the efficacy of the oncolytic virus, oncolytic HSV-1, and HSV-GM-CSF groups, respectively. IVIS images, ocular volumes, mice weights, and survivals were tracked to see the efficacy of the virus. Hematoxylin and eosin staining, immunohistochemistry, and flow cytometry analyses were conducted to demonstrate the immune activity after virus treatment.

Results

All three tested UM cell lines were sensitive to infection by HSV-GM-CSF. In vivo xenograft experiments revealed that oncolytic virus HSV-1 reduced UM tumor volume and that oncolytic virus HSV-1 armed with GM-CSF enhanced the antitumor effect compared with unmodified HSV-1. The bodyweights of untreated control group mice were significantly lower than those of mice in either virus-treated group (HSV-1 or HSV-GM-CSF). Follow-up survivals were prolonged in the virus-treated groups compared with the control group and were prolonged to a greater extent in the HSV-GM-CSF group than in the HSV-1 group. Macrophage stimulation was observed following HSV-GM-CSF treatment.

Conclusion

Our results indicate that the recombinant oncolytic virus HSV-GM-CSF is a potential therapeutic treatment for UM.

Antitumor efficacy of oncolytic HSV-1 expressing cytosine deaminase is synergistically enhanced by DPD down-regulation and EMT inhibition in uveal melanoma xenograft

Uveal melanoma (UM) is the most common intraocular tumor in adults and has a high incidence of metastases. Possible treatments remain limited in UM with enucleation and radiation, leading to poor prognosis in this chemo-resistant carcinoma. Thus, urging demand for novel treatment is needed. We examined the antitumor efficacy of a new recombinant oncolytic herpes simplex virus type 1 (oHSV-1) armed with E.coli cytosine deaminase (CD). We determined the efficacy of the oncolytic virus in UM cell lines. In vivo experiments showed that oHSV-CD/5-fluorocytosine (5-FC) treatment reduce tumor volume and prolonged survival. We further demonstrated the molecular mechanisms of oHSV-CD/5-FC treatment. The oncolytic virus down-regulated IL-6 expression and thereby reversed the epithelial-mesenchymal transition (EMT) phenotype. Dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in 5-fluorouracil (5-FU) metabolism, was also down-regulated. Therefore, the efficacy of oHSV-CD/5-FC was synergistically enhanced by DPD down-regulation and EMT inhibition. This study provides solid evidence for the antitumor efficacy of oHSV-CD/5-FC treatment in vitro and in vivo. The molecular mechanisms of this treatment may bring a new therapeutic approach for future treatment of UM.

The One Health Consortium: Design of a Phase I Clinical Trial to Evaluate M032, a Genetically Engineered HSV-1 Expressing IL-12, in Combination With a Checkpoint Inhibitor in Canine Patients With Sporadic High Grade Gliomas

As the most common and deadly of primary brain tumors, malignant gliomas have earned their place within one of the most multifaceted and heavily-funded realms of medical research. Numerous avenues of pre-clinical investigation continue to provide valuable insight, but modeling the complex evolution and behavior of these tumors within a host under simulated circumstances may pose challenges to extrapolation of data. Remarkably, certain breeds of pet dogs spontaneously and sporadically develop high grade gliomas that follow similar incidence, treatment, and outcome patterns as their human glioma counterparts. The most malignant of these tumors have been refractory to limited treatment options despite aggressive treatment; outcomes are dismal with median survivals of just over 1 year in humans and 2 months in dogs. Novel treatments are greatly needed and combination therapies appear to hold promise. This clinical protocol, a dose-escalating phase I study in dogs with sporadic malignant glioma, represents a first in comparative oncology and combination immunotherapy. The trial will evaluate M032, an Interleukin-12 expressing Herpes Simplex virus, alone and combined with a checkpoint inhibitor, Indoximod. Extensive pre-clinical work has demonstrated safety of intracranial M032 administration in mice and non-human primates. M032 is currently being tested in humans with high-grade malignant gliomas. Thus, in a novel fashion, both canine and human trials will proceed concurrently allowing a direct “head-to-head” comparison of safety and efficacy. We expect this viral oncolytic therapy to be as safe as it is in human patients and M032 to (a) infect and kill glioma cells, producing a virus and tumor cell antigen-rich debris field; (b) provide an adjuvant effect due to liberation of viral DNA, which is rich in unmethylated CpG sequences that “toggle” TLR-9 receptors; and (c) express IL-12 locally, stimulating induction of TH1 lymphocytes. The resultant immune-mediated anti-viral responses should, through cross-epitope spreading, translate into a strong response to tumor antigens. The ability to compare human and dog responses in real time affords the most stringent test of suitability of the dog as an informative model of human brain tumors. Subsequent studies will allow canine trials to properly inform the design of human trials.

Immunotherapeutic Challenges for Pediatric Cancers

Solid tumors contain a mixture of malignant cells and non-malignant infiltrating cells that often create a chronic inflammatory and immunosuppressive microenvironment that restricts immunotherapeutic approaches. Although childhood and adult cancers share some similarities related to microenvironmental changes, pediatric cancers are unique, and adult cancer practices may not be wholly applicable to our pediatric patients. This review highlights the differences in tumorigenesis, viral infection, and immunologic response between children and adults that need to be considered when trying to apply experiences from experimental therapies in adult cancer patients to pediatric cancers.

Selective Editing of Herpes Simplex Virus 1 Enables Interferon Induction and Viral Replication That Destroy Malignant Cells

Oncolytic herpes simplex virus 1 (HSV-1), devoid of the γ₁34.5 gene, exerts antitumor activities. However, the oncolytic effects differ, ranging from pronounced to little responses. Although viral and host factors are involved, much remains to be deciphered. Here we report that engineered HSV-1 ΔN146, bearing amino acids 147 to 263 of γ₁34.5, replicates competently in and lyses malignant cells refractory to the γ₁34.5 null mutant. Upon infection, ΔN146 precludes phosphorylation of translation initiation factor eIF2α (α subunit of eukaryotic initiation factor 2), ensuring viral protein synthesis. On the other hand, ΔN146 activates interferon (IFN) regulatory factor 3 (IRF3) and IFN expression, known to prime immunity against virus and tumor. Nevertheless, ΔN146 exhibits sustained replication even exposed to exogenous IFN-α. In a 4T1 tumor model, ΔN146 markedly reduces tumor growth and metastasis formation. This coincides with viral replication or T cell infiltration in primary tumors. ΔN146 is undetectable in normal tissues in vivo Targeted HSV-1 editing results in a unique antineoplastic agent that enables inflammation without major interference of viral growth within tumor cells.IMPORTANCE Oncolytic herpes simplex virus 1 is a promising agent for cancer immunotherapy. Due to a complex virus-host interaction, less is clear about what viral signature(s) constitutes a potent oncolytic backbone. Through molecular or genetic dissection, we showed that selective editing of the γ₁34.5 gene enables viral replication in malignant cells, activation of transcription factor IRF3, and subsequent induction of type I IFN. This translates into profoundly reduced primary tumor growth and metastasis burden in an aggressive breast carcinoma model in vivo Our work reveals a distinct oncolytic platform that is amendable for further development.

IL-12 Expressing oncolytic herpes simplex virus promotes anti-tumor activity and immunologic control of metastatic ovarian cancer in mice

Background

Despite advances in surgical aggressiveness and conventional chemotherapy, ovarian cancer remains the most lethal cause of gynecologic cancer mortality; consequently there is a need for new therapeutic agents and innovative treatment paradigms for the treatment of ovarian cancer. Several studies have demonstrated that ovarian cancer is an immunogenic disease and immunotherapy represents a promising and novel approach that has not been completely evaluated in ovarian cancer. Our objective was to evaluate the anti-tumor activity of an oncolytic herpes simplex virus “armed” with murine interleukin-12 and its ability to elicit tumor-specific immune responses. We evaluated the ability of interleukin−12-expressing and control oncolytic herpes simplex virus to kill murine and human ovarian cancer cell lines in vitro. We also administered interleukin−12-expressing oncolytic herpes simplex virus to the peritoneal cavity of mice that had developed spontaneous, metastatic ovarian cancer and determined overall survival and tumor burden at 95 days. We used flow cytometry to quantify the tumor antigen-specific CD8⁺ T cell response in the omentum and peritoneal cavity.

Results

All ovarian cancer cell lines demonstrated susceptibility to oncolytic herpes simplex virus in vitro. Compared to controls, mice treated with interleukin−12-expressing oncolytic herpes simplex virus demonstrated a more robust tumor antigen-specific CD8⁺ T-cell immune response in the omentum (471.6 cells vs 33.1 cells; p = 0.02) and peritoneal cavity (962.3 cells vs 179.5 cells; p = 0.05). Compared to controls, mice treated with interleukin−12-expressing oncolytic herpes simplex virus were more likely to control ovarian cancer metastases (81.2 % vs 18.2 %; p = 0.008) and had a significantly longer overall survival (p = 0.02). Finally, five of 6 mice treated with interleukin−12-expressing oHSV had no evidence of metastatic tumor when euthanized at 6 months, compared to two of 4 mice treated with sterile phosphate buffer solution.

Conclusion

Our pilot study demonstrates that an interleukin−12-expressing oncolytic herpes simplex virus effectively kills both murine and human ovarian cancer cell lines and promotes tumor antigen-specific CD8⁺ T-cell responses in the peritoneal cavity and omentum, leading to reduced peritoneal metastasis and improved survival in a mouse model.

Immune Suppression during Oncolytic Virotherapy for High-Grade Glioma; Yes or No?

Oncolytic viruses have been seriously considered for glioma therapy over the last 20 years. The oncolytic activity of several oncolytic strains has been demonstrated against human glioma cell lines and in in vivo xenotransplant models. So far, four of these stains have additionally completed the first phase I/II trials in relapsed glioma patients. Though safety and feasibility have been demonstrated, therapeutic efficacy in these initial trials, when described, was only minor. The role of the immune system in oncolytic virotherapy for glioma remained much less studied until recent years. When investigated, the immune system, adept at controlling viral infections, is often hypothesized to be a strong hurdle to successful oncolytic virotherapy. Several preclinical studies have therefore aimed to improve oncolytic virotherapy efficacy by combining it with immune suppression or evasion strategies. More recently however, a new paradigm has developed in the oncolytic virotherapy field stating that oncolytic virus-mediated tumor cell death can be accompanied by elicitation of potent activation of innate and adaptive anti-tumor immunity that greatly improves the efficacy of certain oncolytic strains. Therefore, it seems the three-way interaction between oncolytic virus, tumor and immune system is critical to the outcome of antitumor therapy. In this review we discuss the studies which have investigated how the immune system and oncolytic viruses interact in models of glioma. The novel insights generated here hold important implications for future research and should be incorporated into the design of novel clinical trials.

Evaluation of the safety and biodistribution of M032, an attenuated herpes simplex virus type 1 expressing hIL-12, after intracerebral administration to aotus nonhuman primates

Herpes simplex virus type 1 (HSV-1) mutants lacking the γ(1)34.5 neurovirulence loci are promising agents for treating malignant glioma. Arming oncolytic HSV-1 to express immunostimulatory genes may potentiate therapeutic efficacy. We have previously demonstrated improved preclinical efficacy, biodistribution, and safety of M002, a γ(1)34.5-deleted HSV-1 engineered to express murine IL-12. Herein, we describe the safety and biodistribution of M032, a γ(1)34.5-deleted HSV-1 virus that expresses human IL-12 after intracerebral administration to nonhuman primates, Aotus nancymae. Cohorts were administered vehicle, 10(6), or 10(8) pfu of M032 on day 1 and subjected to detailed clinical observations performed serially over a 92-day trial. Animals were sacrificed on days 3, 31, and 91 for detailed histopathologic assessments of all organs and to isolate and quantify virus in all organs. With the possible exception of one animal euthanized on day 16, neither adverse clinical signs nor sex- or dose-related differences were attributed to M032. Elevated white blood cell and neutrophil counts were observed in virus-injected groups on day 3, but no other significant changes were noted in clinical chemistry or coagulation parameters. Minimal to mild inflammation and fibrosis detected, primarily in meningeal tissues, in M032-injected animals on days 3 and 31 had mostly resolved by day 91. The highest viral DNA levels were detected at the injection site and motor cortex on day 3 but decreased in central nervous system tissues over time. These data demonstrate the requisite safety of intracerebral M032 administration for consideration as a therapeutic for treating malignant brain tumors.

Treatment of human hepatocellular carcinoma by the oncolytic herpes simplex virus G47delta

Background

Oncolytic herpes simplex virus (HSV) can replicate in and kill cancer cells while sparing the adjacent normal tissue. Hepatocellular carcinoma (HCC) is amongst the most common and lethal cancers, especially in Third World countries. In this study, the cytotoxicity of a third-generation oncolytic HSV, G47Δ, was investigated in different human HCC cell lines and in an immortalized human hepatic cell line. Additionally, subcutaneous models of HCC were established to evaluate the in vivo anti-tumor efficacy of G47Δ.

Methods

The HepG2, HepB, SMMC-7721, BEL-7404, and BEL-7405 human HCC cell lines and the HL-7702 human hepatic immortalized cell lines were infected with G47Δ at different multiplicities of infection (MOIs). The viability of infected cells was determined, and the G47Δ replication was identified by X-gal staining for LacZ expression. Two subcutaneous (s.c.) HCC tumor models of HCC were also established in Balb/c nude mice, which were intratumorally(i.t.) treated with either G47Δ or mock virus. Tumor volume and mouse survival times were documented.

Results

More than 95% of the HepG2, Hep3B,and SMMC-7721 HCC cells were killed on by day 5 after infection with a MOI’s of 0.01. For the HL-7702 human hepatic immortalized cells, 100% of the cells were killed on by day 5 after infection with a MOI’s of 0.01. The BEL-7404 HCC cell line was less susceptible with about 70% cells were killed by day 5 after infection with a MOI’s of 0.01. Whereas the BEL-7405 HCC cells were the least susceptible, with only 30% of the cells were killed. Both the SMMC-7721 and BEL-7404 cells form aggressive sc tumor models. G47Δ replicates in the tumors, such that most of the tumors regressed after the G47Δ-treatment, and treated tumor-bearing mice survived much longer than the control animals.

Conclusions

G47Δ effectively kills human HCC cells and an immortalized hepatic cell line at low MOI. Intra-tumor injection of G47Δ can induce a therapeutic effect and prolong the survival of treated mice bearing SMMC-7721 and BEL-7404 subcutaneously (s.c.) tumors. Thus, G47Δ may be useful as a novel therapeutic agent for HCC.

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.

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.

Glioblastoma multiforme: State of the art and future therapeutics

BACKGROUND

Glioblastoma multiforme (GBM) is the most common and lethal primary malignancy of the central nervous system (CNS). Despite the proven benefit of surgical resection and aggressive treatment with chemo- and radiotherapy, the prognosis remains very poor. Recent advances of our understanding of the biology and pathophysiology of GBM have allowed the development of a wide array of novel therapeutic approaches, which have been developed. These novel approaches include molecularly targeted therapies, immunotherapies, and gene therapy.

METHODS

We offer a brief review of the current standard of care, and a survey of novel therapeutic approaches for treatment of GBM.

RESULTS

Despite promising results in preclinical trials, many of these therapies have demonstrated limited therapeutic efficacy in human clinical trials. Thus, although survival of patients with GBM continues to slowly improve, treatment of GBM remains extremely challenging.

CONCLUSION

Continued research and development of targeted therapies, based on a detailed understanding of molecular pathogenesis can reasonably be expected to yield improved outcomes for patients with GBM.

Production of bioactive soluble interleukin-15 in complex with interleukin-15 receptor alpha from a conditionally-replicating oncolytic HSV-1

Oncolytic type-1 herpes simplex viruses (oHSVs) lacking the γ134.5 neurovirulence gene are being evaluated for treatment of a variety of malignancies. oHSVs replicate within and directly kill permissive cancer cells. To augment their anti-tumor activity, oHSVs have been engineered to express immunostimulatory molecules, including cytokines, to elicit tumor-specific immune responses. Interleukin-15 (IL-15) holds potential as an immunotherapeutic cytokine because it has been demonstrated to promote both natural killer (NK) cell-mediated and CD8(+) T cell-mediated cytotoxicity against cancer cells. The purpose of these studies was to engineer an oHSV producing bioactive IL-15. Two oHSVs were constructed encoding murine (m)IL-15 alone (J100) or with the mIL-15 receptor α (mIL-15Rα, J100D) to determine whether co-expression of these proteins is required for production of bioactive mIL-15 from oHSV. The following were demonstrated: i) both oHSVs retain replication competence and cytotoxicity in permissive tumor cell lines. ii) Enhanced production of mIL-15 was detected in cell lysates of neuro-2a cells following J100D infection as compared to J100 infection, suggesting that mIL-15Rα improved mIL-15 production. iii) Soluble mIL-15 in complex with mIL-15Rα was detected in supernates from J100D-infected, but not J100-infected, neuro-2a, GL261, and CT-2A cells. These cell lines vary in permissiveness to oHSV replication and cytotoxicity, demonstrating soluble mIL-15/IL-15Rα complex production from J100D was independent of direct oHSV effects. iv) The soluble mIL-15/IL-15Rα complex produced by J100D was bioactive, stimulating NK cells to proliferate and reduce the viability of syngeneic GL261 and CT-2A cells. v) J100 and J100D were aneurovirulent inasmuch as no neuropathologic effects were documented following direct inoculation into brains of CBA/J mice at up to 1x10(7) plaque forming units. The production of mIL-15/mIL-15Rα from multiple tumor lines, as well as the lack of neurovirulence, renders J100D suitable for investigating the combined effects of oHSV and mIL-15/IL-15Rα in various cancer models.

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.

Preclinical evaluation of oncolytic δγ(1)34.5 herpes simplex virus expressing interleukin-12 for therapy of breast cancer brain metastases

The metastasis of breast cancer to the brain and central nervous system (CNS) is a problem of increasing importance. As improving treatments continue to extend patient survival, the incidence of CNS metastases from breast cancer is on the rise. New treatments are needed, as current treatments are limited by deleterious side effects and are generally palliative. We have previously described an oncolytic herpes simplex virus (HSV), designated M002, which lacks both copies of the γ₁34.5 neurovirulence gene and carries a murine interleukin 12 (IL-12) expression cassette, and have validated its antitumor efficacy in a variety of preclinical models of primary brain tumors. However, M002 has not been yet evaluated for use against metastatic brain tumors. Here, we demonstrate the following: both human breast cancer and murine mammary carcinoma cells support viral replication and IL-12 expression from M002; M002 replicates in and destroys breast cancer cells from a variety of histological subtypes, including “triple-negative” and HER2 overexpressing; M002 improves survival in an immunocompetent model more effectively than does a non-cytokine control virus. Thus, we conclude from this proof-of-principle study that a γ₁34.5-deleted IL-12 expressing oncolytic HSV may be a potential new therapy for breast cancer brain metastases.

Novel delivery strategies for glioblastoma

Brain tumors--particularly glioblastoma multiforme--pose an important public health problem in the United States. Despite surgical and medical advances, the prognosis for patients with malignant gliomas remains grim: current therapy is insufficient with nearly universal recurrence. A major reason for this failure is the difficulty of delivering therapeutic agents to the brain: better delivery approaches are needed to improve treatment. In this article, we summarize recent progress in drug delivery to the brain, with an emphasis on convection-enhanced delivery of nanocarriers. We examine the potential of new delivery methods to permit novel drug- and gene-based therapies that target brain cancer stem cells and discuss the use of nanomaterials for imaging of tumors and drug delivery.

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.

Novel therapies in glioblastoma

Conventional treatment of glioblastoma has advanced only incrementally in the last 30 years and still yields poor outcomes. The current strategy of surgery, radiation, and chemotherapy has increased median survival to approximately 15 months. With the advent of molecular biology and consequent improved understanding of basic tumor biology, targeted therapies have become cornerstones for cancer treatment. Many pathways (RTKs, PI3K/AKT/mTOR, angiogenesis, etc.) have been identified in GBM as playing major roles in tumorigenesis, treatment resistance, or natural history of disease. Despite the growing understanding of the complex networks regulating GBM tumors, many targeted therapies have fallen short of expectations. In this paper, we will discuss novel therapies and the successes and failures that have occurred. One clear message is that monotherapies yield minor results, likely due to functionally redundant pathways. A better understanding of underlying tumor biology may yield insights into optimal targeting strategies which could improve the overall therapeutic ratio of conventional treatments.

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.

Clinical development directions in oncolytic viral therapy

Oncolytic virotherapy is an emerging experimental treatment platform for cancer therapy. Oncolytic viruses are replicative-competent viruses that are engineered to replicate selectively in cancer cells with specified oncogenic phenotypes. Multiple DNA and RNA viruses have been clinically tested in a variety of tumors. This review will provide a brief description of these novel anticancer biologics and will summarize the results of clinical investigation. To date oncolytic virotherapy has shown to be safe, and has generated clinical responses in tumors that are resistant to chemotherapy or radiotherapy. The major challenge for researchers is to maximize the efficacy of these viral therapeutics, and to establish stable systemic delivery mechanisms.

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.

HSV as a vector in vaccine development and gene therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), major human pathogen whose lifestyle is based on a long-term dual interaction with the infected host characterized by the existence of lytic and latent infections, has allowed the development of potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous system, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases and targeted infection of specific tissues or organs. Three different classes of vectors can be derived from HSV-1: replication-competent attenuated vectors, replication-incompetent recombinant vectors and defective helper-dependent vectors known as amplicons. This chapter highlights the current knowledge concerning design, construction and recent applications, as well as the potential and current limitations of the three different classes of HSV-1-based vectors.

Hyperthermia potentiates oncolytic herpes viral killing of pancreatic cancer through a heat shock protein pathway

BACKGROUND

Oncolytic herpes simplex virus-1 (HSV-1) is designed to specifically infect, replicate in, and lyse cancer cells. This study investigates a novel therapeutic regimen, combining the effects of NV1066 (a recombinant HSV-1) and hyperthermia in the treatment of pancreatic cancer.

METHODS

NV1066 is an attenuated HSV-1 that replicates in cells resistant to apoptosis. Heat shock protein 72 (Hsp72) is a member of a family of proteins that is upregulated after hyperthermic insult, lending cellular protection by inhibiting apoptosis. In these experiments, we test the hypothesis that increased Hsp72 expression in response to hyperthermia enhances anti-apoptotic mechanisms, thereby increasing viral replication and tumor cell kill. Hs 700T pancreatic cancer cells were treated with hyperthermia alone (42 degrees C), NV1066 alone, and combination therapy. Cell survival and viral growth were measured. The effect of siRNA-directed Hsp72 knockdown was also measured.

RESULTS

Combining hyperthermia and viral treatment produced a synergistic effect on cell kill. Viral growth increased greater than 6-fold in the presence of hyperthermia (P < .05). Hyperthermia alone showed minimal cytotoxic activity against Hs 700T cells, while NV1066 infection resulted in approximately 50% cell kill. The combination of hyperthermia and viral infection significantly increased cell kill to approximately 80% (P < .01). Hsp72 knockdown attenuated this synergistic effect.

CONCLUSION

Hyperthermia enhances NV1066 replication, thereby potentiating the viral oncolytic response against pancreatic cancer cells. This finding has potential clinical application in the use of heated perfusion or permissive hyperthermia for delivery of oncolytic viral therapies.

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.

Development of a regulatable oncolytic herpes simplex virus type 1 recombinant virus for tumor therapy

Oncolytic viruses are genetically modified viruses that preferentially replicate in host cancer cells, leading to the production of new viruses and, ultimately, cell death. Currently, no oncolytic viruses that are able to kill only tumor cells while leaving normal cells intact are available. Using T-REx (Invitrogen, Carlsbad, CA) gene switch technology and a self-cleaving ribozyme, we have constructed a novel oncolytic HSV-1 recombinant, KTR27, whose replication can be tightly controlled and regulated by tetracycline in a dose-dependent manner. Infection of normal replicating cells as well as multiple human cancer cell types with KTR27 in the presence of tetracycline led to 1,000- to 250,000-fold-higher progeny virus production than in the absence of tetracycline, while little viral replication and virus-associated cytotoxicity was observed in infected growth-arrested normal human cells. We show that intratumoral inoculation with KTR27 markedly inhibits tumor growth in a xenograft model of human non-small-cell lung cancer in nude mice. It is shown further that replication of KTR27 in the inoculated tumors can be efficiently controlled by local codelivery of tetracycline to the target tumors at the time of KTR27 inoculation. Collectively, KTR27 possesses a unique pharmacological feature that can limit its replication to the targeted tumor microenvironment with localized tetracycline delivery, thus minimizing unwanted viral replication in distant tissues following local virotherapy. This regulatory mechanism would also allow the replication of the virus to be quickly shut down should adverse effects be detected.

Design and application of oncolytic HSV vectors for glioblastoma therapy

Glioblastoma multiforme is one of the most common human brain tumors. The tumor is generally highly infiltrative, making it extremely difficult to treat by surgical resection or radiotherapy. This feature contributes to recurrence and a very poor prognosis. Few anticancer drugs have been shown to alter rapid tumor growth and none are ultimately effective. Oncolytic vectors have been employed as a treatment alternative based on the ability to tailor virus replication to tumor cells. The human neurotropic herpes simplex virus (HSV) is especially attractive for development of oncolytic vectors (oHSV) because this virus is highly infectious, replicates rapidly and can be readily modified to achieve vector attenuation in normal brain tissue. Tumor specificity can be achieved by deleting viral genes that are only required for virus replication in normal cells and permit mutant virus replication selectively in tumor cells. The anti-tumor activity of oHSV can be enhanced by arming the vector with genes that either activate chemotherapeutic drugs within the tumor tissue or promote anti-tumor immunity. In this review, we describe current designs of oHSV and the experience thus far with their potential utility for glioblastoma therapy. In addition, we discuss the impediments to vector effectiveness and describe our view of future developments in vector improvement.

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.

An HSV-2-based oncolytic virus deleted in the PK domain of the ICP10 gene is a potent inducer of apoptotic death in tumor cells

The N-terminus of the ICP10 gene of type 2 herpes simplex virus (HSV-2) encodes a serine/threonine protein kinase (PK) domain that facilitates HSV-2 replication by activating the Ras/MEK/MAPK mitogenic pathway and suppressing apoptosis. We recently demonstrated that deletion of this oncogenic PK domain converts it to a potent oncolytic agent. This mutant, which we have designated FusOn-H2, preferentially replicates in and thus lyses tumor cells in which the Ras signaling pathway is constitutively activated. Here we show that FusOn-H2 exerts strong ability in inducing apoptosis in different lines of human tumor cells and in esophageal tumors growing in mice. The apoptotic effect produced by FusOn-H2 was not restricted to infected cells but extended to uninfected bystander cells, thereby increasing the lethality of the virus. These results add a novel killing mechanism to those previously assigned to FusOn-H2, rendering it an attractive candidate for clinical trials.

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.

ReVOLT: radiation-enhanced viral oncolytic therapy

Viral oncolytic therapy has been pursued with renewed interest as the molecular basis of carcinogenesis and viral replication has been elucidated. Genetically engineered, attenuated viruses have been rationally constructed to achieve a therapeutic index in tumor cells compared with surrounding normal tissue. Many of these attenuated mutant viruses have entered clinical trials. Here we review the preclinical literature demonstrating the interaction of oncolytic viruses with ionizing radiation and provides a basis for future clinical trials.

Engineered herpes simplex virus expressing bacterial cytosine deaminase for experimental therapy of brain tumors

Lack of effective therapy of primary brain tumors has promoted the development of novel experimental approaches utilizing oncolytic viruses combined with gene therapy. Towards this end, we have assessed a conditionally replication-competent, gamma(1)34.5-deleted herpes simplex virus type 1 (HSV-1) expressing cytosine deaminase (CD) for treatment of malignant brain tumors. Our results are summarized as follows: (i) a recombinant HSV (M012) was constructed in which both copies of the gamma(1)34.5 gene were replaced with the bacterial CD gene, under the control of the cellular promoter Egr-1; (ii) M012-infected cells in vitro efficiently convert 5-fluorocytosine (5-FC) to 5-fluorouracil, thereby enhancing cytotoxicity of neighboring, uninfected cells; (iii) both direct and bystander cytotoxicity of murine neuroblastoma and human glioma cell lines after infection with M012 were demonstrated; (iv) direct intracerebral inoculation of A/J mice demonstrated lack of neurotoxicity at doses similar to G207, a gamma(1)34.5-deleted HSV with demonstrated safety in human patient trials and (v) intratumoral injection of M012 into Neuro-2a flank tumors in combination with 5-FC administration significantly reduced tumor growth versus tumors treated with R3659 combined with 5-FC, or treated with M012 alone. Thus, M012 is a promising new oncolytic HSV vector with an enhanced prodrug-mediated, antineoplastic effect that is safe for intracranial administration.

Real-time intraoperative detection of breast cancer axillary lymph node metastases using a green fluorescent protein-expressing herpes virus

OBJECTIVE

To investigate the use of a green fluorescent protein (GFP)-expressing oncolytic herpes virus to enable real-time intraoperative detection of breast cancer lymph node metastases.

SUMMARY BACKGROUND DATA

Axillary lymph node status is the most important factor determining treatment, recurrence, and overall survival for women with breast cancer. The current methods of determining nodal status, however, have limitations. NV1066 is a novel oncolytic herpes viral strain that specifically infects cancer cells and expresses GFP.

METHODS

Seven human breast cancer cell lines were infected in vitro with NV1066 and assessed for GFP expression, viral replication, and cytotoxicity. An in vivo model of breast cancer lymphatic metastasis was established in mice. Tumor-bearing mice were treated with NV1066 via injection into the primary tumor. Axillary lymph nodes were analyzed using an in vivo fluorescent imaging system. Histologic and molecular assessment of lymph nodes were performed using immunohistochemistry and reverse transcriptase PCR and operating characteristics were determined.

RESULTS

NV1066 infected, expressed GFP, replicated within, and killed all human breast cancer cell lines in vitro. Injection of NV1066 into primary breast tumors resulted in viral transit to axillary lymph nodes, infection of lymphatic metastases, and GFP expression that was visualized with in vivo fluorescent imaging. Histologic and molecular confirmation demonstrated favorable operating characteristics of this method (sensitivity 80%; specificity 96%).

CONCLUSIONS

We introduce a novel, sensitive, and specific method of lymphatic mapping that utilizes NV1066-guided cancer cell-specific viral production of GFP to enable real-time intraoperative detection of lymphatic metastases.

Enhanced therapeutic efficacy of G207 for the treatment of glioma through Musashi1 promoter retargeting of gamma34.5-mediated virulence

G207 is a conditionally replicating derivative of herpes simplex virus type1 (HSV-1) engineered with deletions of both ICP34.5 loci and a lacZ insertion disabling the ICP6 gene. G207 exhibits an efficient oncolytic activity in vitro and in vivo, yet minimal toxicity in normal tissue, and is now in clinical trial for malignant glioma. According to the results of clinical trials, however, although G207 was proved to be safe, the efficacy was not so impressive. Deletion of the ICP34.5 gene coding for virulence made G207 extremely safe, but it markedly reduced the cytotoxicity mediated by HSV-1. To enhance the therapeutic efficacy of G207 without diminishing its safety, we used a defective vector containing Musashi1 promoter/ICP34.5, with G207 as helper virus. P/musashi1 was functional selectively in human glioma cell lines (U87MG, U251, T98G) in this study and dvM345 showed a much higher therapeutic efficacy both in culture and in the in vivo glioma model, than G207 alone, without diminishing its favorable toxicity profile. These results suggest that transcriptional regulation of ICP34.5 by P/musashi1 can be used to target HSV-1 virulence toward gliomas while maintaining the desirable neuroattenuated phenotype.

Herpes simplex virus 1 (HSV-1) for cancer treatment

Cancer remains a serious threat to human health, causing over 500 000 deaths each year in US alone, exceeded only by heart diseases. Many new technologies are being developed to fight cancer, among which are gene therapies and oncolytic virotherapies. Herpes simplex virus type 1 (HSV-1) is a neurotropic DNA virus with many favorable properties both as a delivery vector for cancer therapeutic genes and as a backbone for oncolytic viruses. Herpes simplex virus type 1 is highly infectious, so HSV-1 vectors are efficient vehicles for the delivery of exogenous genetic materials to cells. The inherent cytotoxicity of this virus, if harnessed and made to be selective by genetic manipulations, makes this virus a good candidate for developing viral oncolytic approach. Furthermore, its large genome size, ability to infect cells with a high degree of efficiency, and the presence of an inherent replication controlling mechanism, the thymidine kinase gene, add to its potential capabilities. This review briefly summarizes the biology of HSV-1, examines various strategies that have been used to genetically modify the virus, and discusses preclinical as well as clinical results of the HSV-1-derived vectors in cancer treatment.

Highly efficient regulation of gene expression by tetracycline in a replication-defective herpes simplex viral vector

Employing the tetracycline repressor tetR and the wild-type hCMV major immediate-early promoter, we have developed a highly sensitive tetracycline-inducible transcription switch in mammalian cells (T-REx; Invitrogen, Carlsbad, CA, USA). In view of the previous difficulty in achieving regulatable gene expression in recombinant HSV vector systems, we constructed a T-REx-encoding replication-defective HSV-1 recombinant, QR9TO-lacZ, that encodes two copies of the tetR gene controlled by the HSV-1 immediate-early ICP0 promoter and a reporter, the LacZ gene, under the control of the tetO-bearing hCMV major immediate-early promoter. Infection of cells, such as Vero, PC12, and NGF-differentiated PC12 cells, with QR9TO-lacZ led to 300- to 1000-fold tetracycline-regulated gene expression. Moreover, the expression of the LacZ gene by QR9TO-lacZ can be finely controlled by tetracycline in a dose-dependent fashion. Efficiently regulated gene expression can also be achieved in vivo following intracerebral and footpad inoculations in mice. The demonstrated capability of T-REx for achieving high levels of sensitively regulated gene expression in the context of the HSV-1 genome will significantly expand the utility of HSV-based vector systems for studying gene function in the nervous system and delivering regulated gene expression in therapeutic applications, particularly in the treatment of CNS diseases.

Activated MEK suppresses activation of PKR and enables efficient replication and in vivo oncolysis by Deltagamma(1)34.5 mutants of herpes simplex virus 1

Herpes simplex virus mutants lacking the gamma(1)34.5 gene are not destructive to normal tissues but are potent cytolytic agents in human tumor cells in which the activation of double-stranded RNA-dependent protein kinase (PKR) is suppressed. Thus, replication of a Deltagamma(1)34.5 mutant (R3616) in 12 genetically defined cancer cell lines correlates with suppression of PKR but not with the genotype of RAS. Extensive analyses of two cell lines transduced with either dominant negative MEK (dnMEK) or constitutively active MEK (caMEK) indicated that in R3616 mutant-infected cells dnMEK enabled PKR activation and decreased virus yields, whereas caMEK suppressed PKR and enabled better viral replication and cell destruction in transduced cells in vitro or in mouse xenografts. The results indicate that activated MEK mediates the suppression of PKR and that the status of MEK predicts the ability of Deltagamma(1)34.5 mutant viruses to replicate in and destroy tumor cells.

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.

Treatment of Schwannomas with an Oncolytic Recombinant Herpes Simplex Virus in Murine Models of Neurofibromatosis Type 2

Gene therapy for schwannomas was evaluated in two mouse models of neurofibromatosis type 2 (NF2): (1) a transgenic model in which mice express a dominant mutant form of merlin and spontaneously develop schwannomas, and (2) a xenograft model in which human schwannoma tissue is implanted subcutaneously into immune- compromised mice. In both models, schwannoma volumes were monitored by magnetic resonance imaging (MRI) and showed strong gadolinium enhancement typical of these tumors in humans. Both types of tumor were positive for the Schwann cell marker S100, and highly infectable with herpes simplex virus (HSV) vectors. Schwannomas were injected with an oncolytic HSV-1 recombinant virus vector, G47Delta, which has deletions in genes for ribonucleotide reductase (ICP6), gamma34.5, and ICP47. In the NF2 transgenic model, schwannomas were reduced by more than half their original size by 10 days after infection. In the case of subcutaneous schwannoma xenografts, reduction in size after infection occurred more slowly, with a mean reduction of onethird by 42 days after treatment. Schwannomas injected with control vehicles continued to grow slowly over time in both schwannoma models. These studies demonstrate the ability of an oncolytic recombinant HSV vector to reduce the volume of schwannoma tumors in NF2 tumor models in mice and extend the possible therapeutic applications of oncolytic vectors for benign tumors to reduce mass while minimizing nerve damage.

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.

The role of ICP0-Null HSV-1 and interferon signaling defects in the effective treatment of breast adenocarcinoma

Oncolytic viruses that selectively replicate in cancer cells have been described for over 50 years. Despite the observation by several groups that multimutated herpes simplex type 1 vectors are oncolytic in a variety of murine tumor models, the oncolytic potential of ICP0 null mutants has not been described. This study characterizes a novel second-generation oncolytic herpes simplex type 1 vector null for the ICP0 gene. We tested three mutant viruses and found that all were selectively cytotoxic in a variety of human and murine tumor cells in vitro. Furthermore, we provide evidence of a mechanistic link between ICP0's function in interferon signaling pathways and the observed oncolytic capacity of ICP0 mutants. Using an immunocompetent murine model of breast adenocarcinoma we demonstrate that the ICP0 mutant KM100 completely eradicates tumors in approximately 80% of treated animals and significantly increases survival. Our data suggest that active viral replication is necessary for effective tumor regression. In addition, we characterized the potential of KM100 as an anti-tumor vaccine since cured mice were found to elicit a robust anti-tumor immune response and were refractory to subsequent tumor growth upon rechallenge.