Potent antitumor activity after systemic delivery of a doubly fusogenic oncolytic herpes simplex virus against metastatic prostate cancer

Genetic Modifications That Expand Oncolytic Virus Potency

Oncolytic viruses (OVs) are a promising type of cancer therapy since they selectively replicate in tumor cells without damaging healthy cells. Many oncolytic viruses have progressed to human clinical trials, however, their performance as monotherapy has not been as successful as expected. Importantly, recent literature suggests that the oncolytic potential of these viruses can be further increased by genetically modifying the viruses. In this review, we describe genetic modifications to OVs that improve their ability to kill tumor cells directly, to dismantle the tumor microenvironment, or to alter tumor cell signaling and enhance anti-tumor immunity. These advances are particularly important to increase virus spread and reduce metastasis, as demonstrated in animal models. Since metastasis is the principal cause of mortality in cancer patients, having OVs designed to target metastases could transform cancer therapy. The genetic alterations reported to date are only the beginning of all possible improvements to OVs. Modifications described here could be combined together, targeting multiple processes, or with other non-viral therapies with potential to provide a strong and lasting anti-tumor response in cancer patients.

Co-delivery of novel bispecific and trispecific engagers by an amplicon vector augments the therapeutic effect of an HSV-based oncolytic virotherapy

BACKGROUND

Although oncolytic virotherapy has shown substantial promises as a new treatment modality for many malignancies, further improvement on its therapeutic efficacy will likely bring more clinical benefits. One plausible way of enhancing the therapeutic effect of virotherapy is to enable it with the ability to concurrently engage the infiltrating immune cells to provide additional antitumor mechanisms. Here, we report the construction and evaluation of two novel chimeric molecules (bispecific chimeric engager proteins, BiCEP and trispecific chimeric engager protein, TriCEP) that can engage both natural killer (NK) and T cells with tumor cells for enhanced antitumor activities.

METHODS

BiCEP was constructed by linking orthopoxvirus major histocompatibility complex class I-like protein, which can selectively bind to NKG2D with a high affinity to a mutant form of epidermal growth factor (EGF) that can strongly bind to EGF receptor. TriCEP is similarly constructed except that it also contains a modified form of interleukin-2 that can only function as a tethered form. As NKG2D is expressed on both NK and CD8⁺ T cells, both of which can thus be engaged by BiCEP and TriCEP.

RESULTS

Both BiCEP and TriCEP showed the ability to engage NK and T cells to kill tumor cells in vitro. Coadministration of BiCEP and TriCEP with an oncolytic herpes simplex virus enhanced the overall antitumor effect. Furthermore, single-cell RNA sequencing analysis revealed that TriCEP not only engaged NK and T cells to kill tumor cells, it also promotes the infiltration and activation of these important immune cells.

CONCLUSIONS

These novel chimeric molecules exploit the ability of the oncolytic virotherapy in altering the tumor microenvironment with increased infiltration of important immune cells such as NK and T cells for cancer immunotherapy. The ability of BiCEP and TriCEP to engage both NK and T cells makes them an ideal choice for arming an oncolytic virotherapy.

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.

Oncolytic Herpes Simplex Virus and PI3K Inhibitor BKM120 Synergize to Promote Killing of Prostate Cancer Stem-like Cells

Novel therapies to override chemo-radiation resistance in prostate cancer (PCa) are needed. Prostate cancer sphere-forming cells (PCSCs) (also termed prostate cancer stem-like cells) likely participate in tumor progression and recurrence, and they are important therapeutic targets. We established PCSC-enriched spheres by culturing human (DU145) and murine (TRAMP-C2) PCa cells in growth factor-defined serum-free medium, and we characterized stem-like properties of clonogenicity and tumorigenicity. The efficacy of two different oncolytic herpes simplex viruses (oHSVs) (G47Δ and MG18L) in PCSCs was tested alone and in combination with radiation; chemotherapy; and inhibitors of phosphoinositide 3-kinase (PI3K), Wnt, and NOTCH in vitro; and, G47Δ was tested with the PI3K inhibitor BKM120 in a PCSC-derived tumor model in vivo. PCSCs were more tumorigenic than serum-cultured parental cells. Human and murine PCSCs were sensitive to oHSV and BKM120 killing in vitro, while the combination was synergistic. oHSV combined with radiation, docetaxel, Wnt, or NOTCH inhibitors was not. In athymic mice bearing DU145 PCSC-derived tumors, the combination of intra-tumoral G47Δ and systemic BKM120 induced complete regression of tumors in 2 of 7 animals, and it exhibited superior anti-tumor activity compared to either monotherapy alone, with no detectable toxicity. oHSV synergizes with BKM120 in killing PCSCs in vitro, and the combination markedly inhibits tumor growth, even inducing regression in vivo.

Genetically coating oncolytic herpes simplex virus with CD47 allows efficient systemic delivery and prolongs virus persistence at tumor site

Current oncolytic virotherapy is primarily administered by intratumoral injection. However, systemic delivery is desirable for treating patients, particularly for those who have developed metastatic diseases. Several components are impeding the systemic delivery efficiency of oncolytic viruses. Chief among them is the rapid clearance of viral particles by the host’s mononuclear phagocyte system (MPS). We explored the possibility of genetically engrafting CD47, a “don’t eat me” signal molecule, to the membrane envelop of an oncolytic herpes simplex virus (HSV) to enable it to escape from the MPS for systemic delivery. Our results show that this modification indeed allows the virus to be more efficiently delivered to local tumors by the systemic route. Moreover, this modification also prolongs the virus persistence in local tumors after it arrives there. Consequently, systemic delivery of the modified virus produced a measurable antitumor effect against a murine tumor model that is otherwise resistant to the parental virus delivered by the same route. Our data thus suggest that engrafting enveloped oncolytic viruses such as those derived from HSV with CD47 molecule represents a conceivable strategy to enhance the efficiency of systemic delivery.

Oncolytic activity of the rhabdovirus VSV-GP against prostate cancer

Oncolytic viruses, including the oncolytic rhabdovirus VSV-GP tested here, selectively infect and kill cancer cells and are a promising new therapeutic modality. Our aim was to study the efficacy of VSV-GP, a vesicular stomatitis virus carrying the glycoprotein of lymphocytic choriomeningitis virus, against prostate cancer, for which current treatment options still fail to cure metastatic disease. VSV-GP was found to infect 6 of 7 prostate cancer cell lines with great efficacy. However, susceptibility was reduced in one cell line with low virus receptor expression and in 3 cell lines after interferon alpha treatment. Four cell lines had developed resistance to interferon type I at different levels of the interferon signaling pathway, resulting in a deficient antiviral response. In prostate cancer mouse models, long-term remission was achieved upon intratumoral and, remarkably, also upon intravenous treatment of subcutaneous tumors and bone metastases. These promising efficacy data demonstrate that treatment of prostate cancer with VSV-GP is feasible and safe in preclinical models and encourage further preclinical and clinical development of VSV-GP for systemic treatment of metastatic prostate cancer.

Fusogenic Viruses in Oncolytic Immunotherapy

Oncolytic viruses are under intense development and have earned their place among the novel class of cancer immunotherapeutics that are changing the face of cancer therapy. Their ability to specifically infect and efficiently kill tumor cells, while breaking immune tolerance and mediating immune responses directed against the tumor, make oncolytic viruses highly attractive candidates for immunotherapy. Increasing evidence indicates that a subclass of oncolytic viruses, which encodes for fusion proteins, could outperform non-fusogenic viruses, both in their direct oncolytic potential, as well as their immune-stimulatory properties. Tumor cell infection with these viruses leads to characteristic syncytia formation and cell death due to fusion, as infected cells become fused with neighboring cells, which promotes intratumoral spread of the infection and releases additional immunogenic signals. In this review, we discuss the potential of fusogenic oncolytic viruses as optimal candidates to enhance immunotherapy and initiate broad antitumor responses. We provide an overview of the cytopathic mechanism of syncytia formation through viral-mediated expression of fusion proteins, either endogenous or engineered, and their benefits for cancer therapy. Growing evidence indicates that fusogenicity could be an important feature to consider in the design of optimal oncolytic virus platforms for combinatorial oncolytic immunotherapy.

Comparison of infectivity and spread between HSV-1 and HSV-2 based oncolytic viruses on tumor cells with different receptor expression profiles

Herpes simplex virus (HSV) is one of the many viruses that have been modified or adapted for oncolytic purposes. There are two serotypes of HSV, HSV-1 and HSV-2. The majority of oncolytic HSVs, including T-VEC which has recently been approved by the US Food and Drug Administration (FDA) for clinical use in treating late stage melanoma patients, are derived from HSV-1. Recently, we and others have developed several HSV-2 based oncolytic viruses. During our in vitro characterization of oncolytic viruses developed from both serotypes (Baco-1 from HSV-1 and FusOn-H2 from HSV-2), we noticed there is a subpopulation of cancer cells in which both viruses could infect but only FusOn-H2 could spread from cell to cell on monolayers. This observation prompted us to investigate the virus receptor expression profiles in these and other tumor cells. Our data show the following: 1) This subpopulation of tumor cells only express nectin-2, not the other two major receptors (HVEM or nectin-1). 2) Baco-1 grows to a higher titer than FusOn-H2 in this subpopulation of tumor cells, but the latter kills these tumor cells more efficiently than the former. 3) FusOn-H2 is effective at treating tumors formed from these tumor cells while Baco-1 is completely ineffective. Our results suggest that this subpopulation of tumor cells may be intrinsically resistant to the therapeutic effect of a HSV-1 based oncolytic virus but they remain sensitive to a HSV-2 based virotherapy.

Progresses towards safe and efficient gene therapy vectors

The emergence of genetic engineering at the beginning of the 1970′s opened the era of biomedical technologies, which aims to improve human health using genetic manipulation techniques in a clinical context. Gene therapy represents an innovating and appealing strategy for treatment of human diseases, which utilizes vehicles or vectors for delivering therapeutic genes into the patients' body. However, a few past unsuccessful events that negatively marked the beginning of gene therapy resulted in the need for further studies regarding the design and biology of gene therapy vectors, so that this innovating treatment approach can successfully move from bench to bedside. In this paper, we review the major gene delivery vectors and recent improvements made in their design meant to overcome the issues that commonly arise with the use of gene therapy vectors. At the end of the manuscript, we summarized the main advantages and disadvantages of common gene therapy vectors and we discuss possible future directions for potential therapeutic vectors.

Pediatric cancer gone viral. Part I: strategies for utilizing oncolytic herpes simplex virus-1 in children

Progress for improving outcomes in pediatric patients with solid tumors remains slow. In addition, currently available therapies are fraught with numerous side effects, often causing significant life-long morbidity for long-term survivors. The use of viruses to kill tumor cells based on their increased vulnerability to infection is gaining traction, with several viruses moving through early and advanced phase clinical testing. The prospect of increased efficacy and decreased toxicity with these agents is thus attractive for pediatric cancer. In part I of this two-part review, we focus on strategies for utilizing oncolytic engineered herpes simplex virus (HSV) to target pediatric malignancies. We discuss mechanisms of action, routes of delivery, and the role of preexisting immunity on antitumor efficacy. Challenges to maximizing oncolytic HSV in children are examined, and we highlight how these may be overcome through various arming strategies. We review the preclinical and clinical evidence demonstrating safety of a variety of oncolytic HSVs. In Part II, we focus on the antitumor efficacy of oncolytic HSV in pediatric tumor types, pediatric clinical advances made to date, and future prospects for utilizing HSV in pediatric patients with solid tumors.

Therapeutic Effect on Bladder Cancer with a Conditionally Replicating Oncolytic Virus Derived from Type II Herpes Simplex Virus

Purpose:

Despite recent improvements, resistance to traditional immunotherapy or chemotherapy is still common in patients with bladder cancer. We constructed an oncolytic virus from herpes simplex virus type II (HSV-2), which selectively targets tumor cells with an activated Ras signaling pathway. We evaluated the antitumor effect of this oncolytic HSV-2 (FusOn-H2) against bladder cancer, and compared with that of a first generation oncolytic virus derived from HSV-1 (Baco-1).

Materials and methods:

We established bladder tumor at the orthotopic site in C3H/He mice using the MBT-2 cells. Baco-1 or FusOn-H2 was instilled into the bladder through the urethra respectively. Tumor volume and weight were recorded by the end of the experiment. Animal spleens were also collected to determine if any anti-tumor immunity was elicited during virotherapy in this syngeneic bladder cancer model.

Results:

Two instillations of the oncolytic HSVs into bladder of tumor-bearing mice almost completely eradicated the tumor in majority of tumor bearing mice. The results of tumor-specific cytotoxic T lymphocyte activity assay showed that tumor destruction by oncolytic viruses in vivo, especially by the FusOn-H2, induced potent anti-tumor immune responses.

Conclusion:

Oncolytic virus derived from HSV-2 has potent anti-tumor activity against bladder cancer. Oncolytic effect of this virus in vivo induces tumor specific cellular immunity that further enhances the overall anti-tumor activity. Translating this novel virotherapy into the clinic could present an alternative intravesical therapy strategy for patients with bladder cancer.

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.

An armed oncolytic herpes simplex virus expressing thrombospondin-1 has an enhanced in vivo antitumor effect against human gastric cancer

Advanced gastric cancer is a common disease, but the conventional treatments are unsatisfactory because of the high recurrence rate. One of the promising new therapies is oncolytic virotherapy, using oncolytic herpes simplex viruses (HSVs). Thrombospondin-1 (TSP-1) suppresses tumor progression via multiple mechanisms including antiangiogenesis. Our approach to enhance the effects of oncolytic HSVs is to generate an armed oncolytic HSV that combines the direct viral oncolysis with TSP-1-mediated function for gastric cancer treatment. Using the bacterial artificial chromosome (BAC) system, a 3rd generation oncolytic HSV (T-TSP-1) expressing human TSP-1 was constructed for human gastric cancer treatment. The enhanced efficacy of T-TSP-1 was determined in both human gastric cancer cell lines in vitro and subcutaneous tumor xenografts of human gastric cancer cells in vivo. In addition, we examined the apoptotic effect of T-TSP-1 in vitro, and the antiangiogenic effect of T-TSP-1 in vivo compared with a non-armed 3rd generation oncolytic HSV, T-01. No apparent apoptotic induction by T-TSP-1 was observed for human gastric cancer cell lines TMK-1 cells but for MKN1 cells in vitro. Arming the viruses with TSP-1 slightly inhibited their replication in some gastric cancer cell lines, but the viral cytotoxicity was not attenuated. In addition, T-TSP-1 exhibited enhanced therapeutic efficacy and inhibition of angiogenesis compared with T-01 in vivo. In this study, we established a novel armed oncolytic HSV, T-TSP-1, which enhanced the antitumor efficacy by providing a combination of direct viral oncolysis with antiangiogenesis. Arming oncolytic HSVs may be a useful therapeutic strategy for gastric cancer therapy.

Incorporation of the B18R gene of vaccinia virus into an oncolytic herpes simplex virus improves antitumor activity

Interferon (IFN) antiviral defense mechanism plays a critical role in controlling virus infection. It thus represents a formidable hurdle for virotherapy. Despite the reported ability of herpes simplex virus (HSV) to counteract this defense, the duration and extent of HSV infection in vivo is still largely dictated by host's IFN activity status. Because the HSV genes that have been reported to block IFN activity mainly act intracellularly, we hypothesized that their inhibitory effect could be enhanced by exploiting a gene whose product acts extracellularly. The B18R gene from vaccinia virus encodes a secreted decoy receptor with a broad antagonizing effect against type I IFNs. We therefore cloned B18R into an HSV-1-based oncolytic virus to generate Synco-B18R. In the presence of increased IFN levels in vitro, Synco-B18R largely retained its oncolytic effect, whereas the tumor-killing ability of the parental virus, Synco-2D, was severely compromised. When injected intratumorally in vivo, Synco-B18R showed significantly greater oncolytic activity than Synco-2D. Our results suggest that incorporation of the vaccinia virus B18R gene can safely potentiate the antitumor effect of an oncolytic HSV, and that similar strategies may be useful with other types of oncolytic viruses.

Rapamycin enhances the activity of oncolytic herpes simplex virus against tumor cells that are resistant to virus replication

Oncolytic herpes simplex virus (HSV) is currently in phase III clinical trials for development as a novel therapeutic agent against a broad range of human tumors. Although results have been promising, clinical outcome is likely to be compromised by intrinsic and acquired resistance to HSV replication, leading us to test agents that may overcome this obstacle. We found that, despite showing no effect on HSV replication in tumor cells fully permissive to the virus growth, the mTOR inhibitor rapamycin markedly increased the yield and dissemination of oncolytic HSVs in semipermissive tumor cells. Similar results were obtained in tumor-bearing mice. Co-administration of rapamycin with an HSV-derived oncolytic virus either blocked or reversed the growth of tumor xenografts established from semipermissive human tumor cells, while use of either agent alone produced only transient inhibitory effect. Together, our results suggest that rapamycin could be used to potentiate the activity of oncolytic HSVs against difficult-to-treat human tumors or perhaps to prevent the emergence of resistant tumor cells during virotherapy.

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.

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.

VEGF blockade decreases the tumor uptake of systemic oncolytic herpes virus but enhances therapeutic efficacy when given after virotherapy

Effective therapies for metastatic sarcomas remain elusive. Oncolytic viruses have shown promise as anticancer agents, but their access to metastatic sites following systemic delivery is low. As systemic delivery of small-molecule chemotherapy is enhanced by previous treatment with antiangiogenic agents because of changes in intravascular-to-tumor interstitial pressure, we sought to determine whether antiangiogenic pretreatment increases the antitumor efficacy of systemic virotherapy by increasing virus uptake into tumor. Virus biodistribution and antitumor effects were monitored in tumor-bearing mice given antihuman vascular endothelial growth factor (VEGF) or antimouse VEGFR2 before or after an intravenous (i.v.) injection of virus. Without pretreatment, the average virus titers in the tumor samples amplified 1700-fold over 48 h but were undetectable in other organs. After antiangiogenic treatment, average virus titers in the tumor samples were unchanged or in some cases decreased up to 100-fold. Thus, antiangiogenic pretreatment failed to improve the tumor uptake of systemic oncolytic herpes simplex virus (oHSV), in contrast to previously reported enhanced uptake of small molecules. Superior tumor control because of the combined effects of virus and anti-VEGF was seen most dramatically when anti-VEGF was given after virus. Our data suggest that i.v. oHSV can treat distant sites of disease and can be enhanced by antiangiogenic therapy, but only when given in the proper sequence.

Oncolytic virus therapy for prostate cancer

The use of replication-competent viruses that can selectively replicate in and destroy neoplastic cells is an attractive strategy for treating cancer. Various oncolytic viruses have been taken to clinical trials since a recombinant virus was first applied to cancer patients a decade ago. The concept of the therapy is simple: infectious virus kills the host cancer cells in the course of viral replication. It is important, however, that the virus does not harm the surrounding normal tissue. Oncolytic viruses can be classified largely into two groups: DNA viruses genetically engineered to achieve cancer specificity (e.g. adenovirus, herpes simplex virus and vaccinia) and RNA viruses of which human is not the natural host (e.g. Newcastle disease virus and reovirus). Prostate cancer has always been one of the major targets of oncolytic virus therapy development. The result of six clinical trials for prostate cancer has been published and several trials are now going on. Forty-eight of 83 (58%) patients evaluated in the phase I studies demonstrated a >25% decrease in serum prostate-specific antigen level without evidence of severe toxicities. The result shows the oncolytic virus therapy is promising toward clinical application. Here, we review the recent advances in the field and summarize the results from clinical trials.

Eradication of solid human breast tumors in nude mice with an intravenously injected light-emitting oncolytic vaccinia virus

Previously, we reported that a recombinant vaccinia virus (VACV) carrying a light-emitting fusion gene enters, replicates in, and reveals the locations of tumors in mice. A new recombinant VACV, GLV-1h68, as a simultaneous diagnostic and therapeutic agent, was constructed by inserting three expression cassettes (encoding Renilla luciferase-Aequorea green fluorescent protein fusion, beta-galactosidase, and beta-glucuronidase) into the F14.5L, J2R (encoding thymidine kinase) and A56R (encoding hemagglutinin) loci of the viral genome, respectively. I.v. injections of GLV-1h68 (1x10(7) plaque-forming unit per mouse) into nude mice with established (approximately 300-500 mm3) s.c. GI-101A human breast tumors were used to evaluate its toxicity, tumor targeting specificity, and oncolytic efficacy. GLV-1h68 showed an enhanced tumor targeting specificity and much reduced toxicity compared with its parental LIVP strains. The tumors colonized by GLV-1h68 exhibited growth, inhibition, and regression phases followed by tumor eradication within 130 days in 95% of the mice tested. Tumor regression in live animals was monitored in real time based on decreasing light emission, hence demonstrating the concept of a combined oncolytic virus-mediated tumor diagnosis and therapy system. Transcriptional profiling of regressing tumors based on a mouse-specific platform revealed gene expression signatures consistent with immune defense activation, inclusive of IFN-stimulated genes (STAT-1 and IRF-7), cytokines, chemokines, and innate immune effector function. These findings suggest that immune activation may combine with viral oncolysis to induce tumor eradication in this model, providing a novel perspective for the design of oncolytic viral therapies for human cancers.

Fusogenic vesicular stomatitis virus for the treatment of head and neck squamous carcinomas

OBJECTIVES

This study investigates the efficacy of recombinant fusogenic VSV [rVSV-NDV/F(L289A) or rVSV-F] in the treatment of head and neck squamous cell carcinoma (HNSCC).

STUDY DESIGN AND SETTING

The in vitro replication and cytotoxicity of rVSV-F were studied in two human SCC cell lines, in one murine SCC cell line, and in human keratinocytes. The effects on tumor size and animal survival were investigated following in vivo rVSV-F treatment of floor-of-mouth tumor model C3H/HeJ mice.

RESULTS

Recombinant VSV-F preferentially induced rapid syncytia formation, and replicated in (P < 0.04) and killed (P < 1 x 10(-13)) all three SCC lines tested. The virus had no observable effect on human keratinocytes. Tumor size was smaller (P < 0.03) and overall survival was better (P < 0.001) for treated animals than for control animals.

CONCLUSION/SIGNIFICANCE

Recombinant VSV-F confers a modest survival benefit for HNSCC in this orthotopic murine model. This oncolytic virus holds promise as a novel cancer treatment for recurrent HNSCC.

Virotherapy with a type 2 herpes simplex virus-derived oncolytic virus induces potent antitumor immunity against neuroblastoma

PURPOSE

We recently constructed an oncolytic virus from type 2 herpes simplex virus (HSV-2) that selectively targets and kills tumor cells with an activated Ras signaling pathway. Designated FusOn-H2, this virus has shown several discrete killing mechanisms. Here, we evaluated the antitumor immune responses after FusOn-H2-mediated virotherapy in a syngeneic murine neuroblastoma model.

EXPERIMENTAL DESIGN

We directly injected FusOn-H2 into established tumors and then measured its antitumor effect and the accompanying tumor-specific immune responses. Several oncolytic HSVs constructed from HSV-1 were included in the same experiments for comparisons.

RESULTS

Our data show that tumor destruction by FusOn-H2 in vivo induces potent antitumor immune responses in this syngeneic neuroblastoma model. The elicited cellular immunity not only eradicated neuroblastoma cells in vitro but also inhibited the growth of tumors at sites distant from the virus injection site. Moreover, adoptive transfer of splenocytes from mice receiving virotherapy to naïve mice resulted in a measurable antitumor effect.

CONCLUSION

We conclude that the ability of FusOn-H2 to induce tumor-specific cellular immunity expands the oncolytic repertoire of this virus and increases the likelihood that its use in patients would produce significant therapeutic benefits.

Malignant peripheral nerve sheath tumors with high and low Ras-GTP are permissive for oncolytic herpes simplex virus mutants

BACKGROUND

Malignant peripheral nerve sheath tumors (MPNSTs) occur most frequently in patients with neurofibromatosis type 1 and are often fatal. Current therapy relies upon radical surgical resection, which often fails to completely remove the tumor. To address the need for novel treatment approaches for this disease, we sought to determine if human MPNST-derived cell lines are sensitive to oncolytic Herpes simplex virus (oHSV) infection. Activation of the Ras pathway and its inhibitory effects on protein kinase R (PKR) activation have been shown to dictate cellular permissivity to oHSV mutants. Because NF-1-associated MPNSTs possess inherent hyperactive Ras, we hypothesized these tumors would be ideal therapeutic targets for oHSVs.

PROCEDURE

Human MPNST-derived cell lines were examined for sensitivity to oHSV-mediated gene transduction, virus replication, cytotoxicity, and apoptosis. These parameters were correlated with PKR activation following oHSV infection and compared with normal human Schwann cells (NHSCs) without hyperactive Ras.

RESULTS

MPNST-derived cell lines were efficiently transduced, supported virus replication and were killed by the oncolytic HSV mutants, including sporadic MPNSTs without hyperactive Ras. In contrast to the highly sensitive MPNST cell lines, NHSCs did not support mutant virus replication.

CONCLUSIONS

MPNSTs are susceptible to lysis by oncolytic HSV mutants, regardless of Ras status. Tumor-selective virus replication in MPNST cells appears to be mediated by both cellular expression of ribonucleotide reductase and prevention of eIF2alpha phosphorylation. Virus-induced cytotoxicity of MPNST cell lines was caused by both direct lysis and apoptosis. Our data suggest the use of oncolytic HSV mutants may represent a novel treatment approach for patients with MPNSTs.

A mutant type 2 herpes simplex virus deleted for the protein kinase domain of the ICP10 gene is a potent oncolytic virus

Replication-selective oncolytic herpes simplex virus (HSV) has shown considerable promise as an antitumor agent. Although the current oncolytic HSVs were exclusively constructed from HSV-1, HSV-2 has several unique features that could be exploited to convert the virus to an oncolytic agent. The N-terminus of the HSV-2 ICP10 gene product contains a well-defined serine/threonine protein kinase (PK) domain, which can activate the Ras/MEK/MAPK mitogenic pathway and thus facilitate efficient HSV-2 replication. Because the Ras signaling pathway is a key regulator of normal cell growth and malignant transformation, it is aberrantly activated in many human tumors. Here we report that a mutant HSV-2 (FusOn-H2), constructed by replacing the PK domain of ICP10 with the gene encoding the green fluorescent protein, can selectively replicate in and thus lyse tumor cells. Moreover, infection of FusOn-H2 led to syncytia formation in tumor cells, providing an additional tumor-destroying mechanism. A single moderate-dose injection of FusOn-H2 into established breast cancer xenografts completely eradicated the tumors in more than 80% of the animals, leading to their long-term survival. We conclude that this HSV-2 mutant is a safe and potent oncolytic agent useful for the treatment of malignant solid tumors such as breast cancer.

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.

Gene delivery and gene therapy of prostate cancer

Surgery, radiation or hormonal therapy are not adequate to control prostate cancer. Clearly, other novel treatment approaches, such as gene therapy, for advanced/recurrent disease are desperately needed to achieve long-term local control and particularly to develop effective systemic therapy for metastatic prostate cancer. In the last decade, significant progress in gene therapy for the treatment of localised prostate cancer has been demonstrated. A broad range of different gene therapy approaches, including cytolytic, immunological and corrective gene therapy, have been successfully applied for prostate cancer treatment in animal models, with translation into early clinical trials. In addition, a wide variety of viral and nonbiological gene delivery systems are available for basic and clinical research. Gene therapy approaches that have been developed for the treatment of prostate cancer are summarised.