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

Comprehensive characterization of tumor immune landscape following oncolytic virotherapy by single-cell RNA sequencing

An important mechanism of oncolytic virotherapy in ameliorating cancer immunotherapy is by inducing significant changes in the immune landscape in the tumor microenvironment (TME). Despite this notion and the potential therapeutic implications, a comprehensive analysis of the immune changes in carcinomas induced by virotherapy has not yet been elucidated. We conducted single-cell RNA sequencing analysis on carcinomas treated with an HSV-2-based oncolytic virus to characterize the immunogenic changes in the TME. We specifically analyzed and compared the immune cell composition between viral treated and untreated tumors. We also applied CellChat to analyze the complex interactions among the infiltrated immune cells. Our data revealed significant infiltration of B cells in addition to other important immune cells, including CD4+, CD8+, and NK cells following virotherapy. Further analysis identified distinct subset compositions of the infiltrated immune cells and their activation status upon virotherapy. The intensive interactions among the infiltrated immune cells as revealed by CellChat analysis may further shape the immune landscape in favor of generating antitumor immunity. Our findings will facilitate the design of new strategies in incorporating immunotherapy into virotherapy for clinical translation. Moreover, the significant infiltration of B cells makes it suitable for combining virotherapy with immune checkpoint inhibitors.

A novel cocktail therapy based on quintuplet combination of oncolytic herpes simplex virus-2 vectors armed with interleukin-12, interleukin-15, GM-CSF, PD1v, and IL-7 × CCL19 results in enhanced antitumor efficacy

BACKGROUND

Selectively replicating herpes simplex virus-2 (HSV-2) vector is a promising treatment for cancer therapy. The insertion of multiple transgenes into the viral genome has been performed to improve its oncolytic activity.

METHODS

Herein, we simultaneously constructed five "armed" oncolytic viruses (OVs), designated oHSV2-IL12, -IL15, GM-CSF, -PD1v, and IL7 × CCL19. These OVs delete the ICP34.5 and ICP47 genes with the insertion of transgenes into the deleted ICP34.5 locus. The anti-tumor efficacy in vivo was tested in the syngeneic 4T1 and CT26 tumor-bearing mice model.

RESULTS

The OVs showed comparable oncolytic capability in vitro. The combination therapy of oHSV2-IL12, -IL15, GM-CSF, -PD1v, and IL7 × CCL19 exhibited the highest tumor inhibition efficacy compared with the treatment of single OV or two OVs combination.

CONCLUSIONS

The OVs armed with different transgenes combination therapy also named 5-valent oHSV2 (also called cocktail therapy) might be an effective therapeutic strategy for solid tumors.

Progress of oncolytic virotherapy for neuroblastoma

As a neuroendocrine tumor derived from the neural crest, neuroblastoma (NB) is the most common extracranial solid tumor in children. The prognosis in patients with low- and intermediate-risk NB is favorable while that in high-risk patients is often detrimental. However, the management of the considerably large proportion of high-risk patients remains challenging in clinical practice. Among various new approaches, oncolytic virus (OV) therapy offers great advantages in tumor treatment, especially for high-risk NB. Genetic modified OVs can target NB specifically without affecting normal tissue and avoid the widespread drug resistance issue in anticancer monotherapy. Meanwhile, its safety profile provides great potential in combination therapy with chemo-, radio-, and immunotherapy. The therapeutic efficacy of OV for NB is impressive from bench to bedside. The effectiveness and safety of OVs have been demonstrated and reported in studies on children with NB. Furthermore, clinical trials on some OVs (Celyvir, Pexa-Vec (JX-594) and Seneca Valley Virus (NTX-010)) have reported great results. This review summarizes the latest evidence in the therapeutic application of OVs in NB, including those generated in cell lines, animal models and clinical trials.

Single-cell RNA sequencing reveals a strong connection between Gadd45g upregulation and oncolytic HSV infection in tumor tissue

The oncolytic effect of virotherapy derives from the intrinsic capability of the applied virus in selectively infecting and killing tumor cells. Although oncolytic viruses of various constructions have been shown to efficiently infect and kill tumor cells in vitro, the efficiency of these viruses to exert the same effect on tumor cells within tumor tissues in vivo has not been extensively investigated. Here we report our studies using single-cell RNA sequencing to comprehensively analyze the gene expression profile of tumor tissues following herpes simplex virus 2-based oncolytic virotherapy. Our data revealed the extent and cell types within the tumor microenvironment that could be infected by the virus. Moreover, we observed changes in the expression of cellular genes, including antiviral genes, in response to viral infection. One notable gene found to be upregulated significantly in oncolytic virus-infected tumor cells was Gadd45g, which is desirable for optimal virus replication. These results not only help reveal the precise infection status of the oncolytic virus in vivo but also provide insight that may lead to the development of new strategies to further enhance the therapeutic efficacy of oncolytic virotherapy.

A chimeric virus-based probe unambiguously detects live circulating tumor cells with high specificity and sensitivity

The current methods for detecting circulating tumor cells (CTCs) suffer from several drawbacks. We report a novel method that is based on a chimeric virus probe and can detect CTCs with extremely high specificity and sensitivity. Moreover, it exclusively detects live CTCs, and its detection efficacy is not impacted by the variation of epithelial cell adhesion molecule (EpCAM) expression. The chimeric virus probe is composed of a capsid from human papillomavirus that provides the detection with high specificity and an SV40-based genome that can amplify extensively inside CTCs and, hence, endows the detection with high sensitivity. Furthermore, different marker genes can be incorporated into the probe to provide detection with versatility. These unique capabilities will likely improve the validity and utility of this CTC detection in several clinical applications, which is one of the drawbacks suffered by many of the current CTC detection methods.

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.

Oncolytic Herpes Simplex Virus-Based Therapies for Cancer

With the increased worldwide burden of cancer, including aggressive and resistant cancers, oncolytic virotherapy has emerged as a viable therapeutic option. Oncolytic herpes simplex virus (oHSV) can be genetically engineered to target cancer cells while sparing normal cells. This leads to the direct killing of cancer cells and the activation of the host immunity to recognize and attack the tumor. Different variants of oHSV have been developed to optimize its antitumor effects. In this review, we discuss the development of oHSV, its antitumor mechanism of action and the clinical trials that have employed oHSV variants to treat different types of tumor.

Oncolytic Herpes Simplex Virus Type 2 Can Effectively Inhibit Colorectal Cancer Liver Metastasis by Modulating the Immune Status in the Tumor Microenvironment and Inducing Specific Antitumor Immunity

Although colorectal cancer is the leading cause of death in patients with liver metastases, there are no efficient treatments available. Oncolytic virus therapy, a new type of tumor therapy, has become a potential solution. With the goal of improving the treatment of advanced colorectal cancer, we applied oncolytic herpes simplex virus type 2 (oHSV2) in a mouse model of colorectal cancer with liver metastasis. Compared with the control, oHSV2 effectively inhibited the growth of subcutaneous primary tumors, significantly reduced the number and size of liver metastases, and prolonged the median survival time of the mice. In addition, neutrophils, natural killer (NK) cells, T cells, B cells, and cytokines in the tumor microenvironment and the body were all activated, and their frequencies increased significantly. Moreover, the proportion of immunosuppressive myeloid-derived suppressor cells decreased. oHSV2 treatment, which establishes an effective long-term antitumor immune response, is strongly resistant to rechallenge by the same tumor. Our data show that oHSV2 can effectively kill the primary tumor and attack distal and metastatic tumors by inducing immune responses, resulting in lasting antitumor efficacy and preventing tumor recurrence. It is believed that oHSV2 has good clinical application prospects.

The construction of a new oncolytic herpes simplex virus expressing murine interleukin-15 with gene-editing technology

The treatment of tumors with oncolytic viruses is an important cancer immunotherapy strategy. Interleukin-15 (IL-15) can enhance the antitumor effect of natural killer cells and T cells. An oncolytic herpes simplex type II virus (oHSV2-mIL-15CherryFP) expressing mouse IL-15 was constructed using the CRISPR/Cas9 system, and its antitumor activity in vitro and in vivo was evaluated. In vitro, the mouse interleukin-15 (mIL-15) present in the culture supernatant expressed by oHSV2-mIL-15CherryFP was able to enhance the killing of CT26-GFP tumor cells by T cells. In addition, the intratumoral injection of oHSV2-mIL-15CherryFP inhibited tumor growth in the CT26-iRFP and BGC823-iRFP model. These results indicate that the use of oncolytic herpes simplex virus expressing IL-15 may be a potential therapeutic strategy in tumor immunotherapy.

New viral vectors for infectious diseases and cancer

Since the discovery in 1796 by Edward Jenner of vaccinia virus as a way to prevent and finally eradicate smallpox, the concept of using a virus to fight another virus has evolved into the current approaches of viral vectored genetic vaccines. In recent years, key improvements to the vaccinia virus leading to a safer version (Modified Vaccinia Ankara, MVA) and the discovery that some viruses can be used as carriers of heterologous genes encoding for pathological antigens of other infectious agents (the concept of 'viral vectors') has spurred a new wave of clinical research potentially providing for a solution for the long sought after vaccines against major diseases such as HIV, TB, RSV and Malaria, or emerging infectious diseases including those caused by filoviruses and coronaviruses. The unique ability of some of these viral vectors to stimulate the cellular arm of the immune response and, most importantly, T lymphocytes with cell killing activity, has also reawakened the interest toward developing therapeutic vaccines against chronic infectious diseases and cancer. To this end, existing vectors such as those based on Adenoviruses have been improved in immunogenicity and efficacy. Along the same line, new vectors that exploit viruses such as Vesicular Stomatitis Virus (VSV), Measles Virus (MV), Lymphocytic choriomeningitis virus (LCMV), cytomegalovirus (CMV), and Herpes Simplex Virus (HSV), have emerged. Furthermore, technological progress toward modifying their genome to render some of these vectors incompetent for replication has increased confidence toward their use in infant and elderly populations. Lastly, their production process being the same for every product has made viral vectored vaccines the technology of choice for rapid development of vaccines against emerging diseases and for 'personalised' cancer vaccines where there is an absolute need to reduce time to the patient from months to weeks or days. Here we review the recent developments in viral vector technologies, focusing on novel vectors based on primate derived Adenoviruses and Poxviruses, Rhabdoviruses, Paramixoviruses, Arenaviruses and Herpesviruses. We describe the rationale for, immunologic mechanisms involved in, and design of viral vectored gene vaccines under development and discuss the potential utility of these novel genetic vaccine approaches in eliciting protection against infectious diseases and cancer.

Arming HSV-Based Oncolytic Viruses with the Ability to Redirect the Host's Innate Antiviral Immunity to Attack Tumor Cells

One of the major hurdles for cancer immunotherapy is the host's innate antiviral defense mechanisms. They include innate immune cells, such as natural killer (NK) cells and macrophages, which can be recruited within hours to the site of injection to clear the introduced oncolytic viruses. Here, we report a strategy to redirect these infiltrating innate immune cells to attack tumor cells instead by arming herpes simplex virus (HSV)-derived oncolytic viruses with secreted chimeric molecules that can engage these innate immune cells with tumor cells to kill the latter. These chimeric molecules have, at their N terminus, a custom-binding moiety for a tumor-associated antigen (TAA) and at their C terminus, protein L (PL) that binds to immunoglobulins (Igs). The binding of PL to Igs exposes the Fc to the Fc receptors on the surface of the innate immune cells, trigging them to attack the engaged tumor cells. In vitro and in vivo evaluation in a murine tumor model with limited permissiveness to oncolytic HSVs showed that arming the viruses with these chimeric molecules significantly boosts the killing effect and therapeutic activity. Moreover, our data also showed that the combined killing effect from the engaged innate immune cells and the oncolytic virus resulted in a more efficient stimulation of neoantigen-specific antitumor immunity than the virotherapy alone. Our data suggest that arming an oncolytic virus with this strategy represents a unique and pragmatic way of potentiating the oncolytic and immunotherapeutic effect of virotherapy.

Oncolytic virotherapy in hepato-bilio-pancreatic cancer: The key to breaking the log jam?

Traditional therapies have limited efficacy in hepatocellular carcinoma, pancreatic cancer, and biliary tract cancer, especially for advanced and refractory cancers. Through a deeper understanding of antitumor immunity and the tumor microenvironment, novel immunotherapies are becoming available for cancer treatment. Oncolytic virus (OV) therapy is an emerging type of immunotherapy that has demonstrated effective antitumor efficacy in many preclinical studies and clinical studies. Thus, it may represent a potential feasible treatment for hard to treat gastrointestinal (GI) tumors. Here, we summarize the research progress of OV therapy for the treatment of hepato-bilio-pancreatic cancers. In general, most OV therapies exhibits potent, specific oncolysis both in cell lines in vitro and the animal models in vivo. Currently, several clinical trials have suggested that OV therapy may also be effective in patients with refractory hepato-bilio-pancreatic cancer. Multiple strategies such as introducing immunostimulatory genes, modifying virus capsid and combining various other therapeutic modalities have been shown enhanced specific oncolysis and synergistic anti-cancer immune stimulation. Combining OV with other antitumor therapies may become a more effective strategy than using virus alone. Nevertheless, more studies are needed to better understand the mechanisms underlying the therapeutic effects of OV, and to design appropriate dosing and combination strategies.

Inhibition of colorectal cancer liver metastasis in BALB/c mice following intratumoral injection of oncolytic herpes simplex virus type 2 for the induction of specific antitumor immunity

Liver metastasis represents the most prominent metastasis of colorectal cancer (CRC) and is the leading cause of CRC mortality, making the early prevention of this event very important. While current CRC therapies include surgery, radiotherapy and chemotherapy, no effective treatment option for CRC liver metastasis (CRLM) exists. Furthermore, the effects of currently available metastatic CRC drugs are frequently limited by their toxicity and side effects. Oncolytic herpes simplex virus type 2 (oHSV2) selectively infects tumor cells and also induces an antitumor immune response. The present study investigated the cytopathic effects of oHSV2 on CT-26 cells in vitro and tested its inhibitory effect on CRLM. In vitro experimental data demonstrated that oHSV2 effectively inhibited the growth of CT-26 cells. In vivo study data demonstrated that treatment with oHSV2 alone slowed the growth of subcutaneous xenograft tumors without inducing weight loss and also inhibited CRLM by increasing the numbers of cluster of differentiation (CD)4⁺ T, CD8+ T and natural killer cells. In summary, oHSV2 shows potential as a safe and effective therapeutic agent for inhibiting the metastasis of CT-26 CRC cells to the liver.

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.

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.

Targeting Nucleotide Biosynthesis: A Strategy for Improving the Oncolytic Potential of DNA Viruses

The rapid growth of tumors depends upon elevated levels of dNTPs, and while dNTP concentrations are tightly regulated in normal cells, this control is often lost in transformed cells. This feature of cancer cells has been used to advantage to develop oncolytic DNA viruses. DNA viruses employ many different mechanisms to increase dNTP levels in infected cells, because the low concentration of dNTPs found in non-cycling cells can inhibit virus replication. By disrupting the virus-encoded gene(s) that normally promote dNTP biosynthesis, one can assemble oncolytic versions of these agents that replicate selectively in cancer cells. This review covers the pathways involved in dNTP production, how they are dysregulated in cancer cells, and the various approaches that have been used to exploit this biology to improve the tumor specificity of oncolytic viruses. In particular, we compare and contrast the ways that the different types of oncolytic virus candidates can directly modulate these processes. We limit our review to the large DNA viruses that naturally encode homologs of the cellular enzymes that catalyze dNTP biogenesis. Lastly, we consider how this knowledge might guide future development of oncolytic viruses.

Oncolytic Viruses-Interaction of Virus and Tumor Cells in the Battle to Eliminate Cancer

Oncolytic viruses (OVs) are an emerging treatment option for many cancer types and have recently been the focus of extensive research aiming to develop their therapeutic potential. The ultimate aim is to design a virus which can effectively replicate within the host, specifically target and lyse tumor cells and induce robust, long lasting tumor-specific immunity. There are a number of viruses which are either naturally tumor-selective or can be modified to specifically target and eliminate tumor cells. This means they are able to infect only tumor cells and healthy tissue remains unharmed. This specificity is imperative in order to reduce the side effects of oncolytic virotherapy. These viruses can also be modified by various methods including insertion and deletion of specific genes with the aim of improving their efficacy and safety profiles. In this review, we have provided an overview of the various virus species currently being investigated for their oncolytic potential and the positive and negative effects of a multitude of modifications used to increase their infectivity, anti-tumor immunity, and treatment safety, in particular focusing on the interaction of tumor cells and OVs.

Antitumor effects of oncolytic herpes simplex virus type 2 against colorectal cancer in vitro and in vivo

Background

The incidence of colorectal cancer (CRC) is on the rise. Furthermore, late-stage diagnoses and limited efficacious treatment options make CRC a complex clinical challenge. Therefore, a new therapeutic regimen with a completely novel therapeutic mechanism is necessary for CRC. In the present study, the therapeutic efficacy of oncolytic herpes simplex virus type 2 (oHSV2) in CRC was assessed in vitro and in vivo. oHSV2 is an oncolytic agent derived from herpes simplex virus type 2 that encodes granulocyte-macrophage colony-stimulating factor.

Materials and methods

We investigated the cytopathic effects of oHSV2 in CRC cell lines using the MTT assay. Then, cell cycle progression and apoptosis of oHSV2 were examined by flow cytometry. We generated a model of CRC with mouse CRC cell CT26 in BALB/c mice. The antitumor effects and adaptive immune response of oHSV2 were assessed in tumor-bearing mice. The therapeutic efficacy of oHSV2 was compared with the traditional chemotherapeutic agent, 5-fluorouracil.

Results

The in vitro data showed that oHSV2 infected the CRC cell lines successfully and that the tumor cells formed a significant number of syncytiae postinfection. The oHSV2 killed cancer cells independent of the cell cycle and mainly caused tumor cells necrosis. The in vivo results showed that oHSV2 significantly inhibited tumor growth and prolonged survival of tumor-bearing mice without weight loss. With virus replication, oHSV2 not only resulted in a reduction of myeloid-derived suppressor cells and regulatory T cells in the spleen, but also increased the number of mature dendritic cells in tumor-draining lymph nodes and the effective CD4⁺T and CD8⁺T-cells in the tumor microenvironment.

Conclusion

Our study provides the first evidence that oHSV2 induces cell death in CRC in vitro and in vivo. These findings indicate that oHSV2 is an effective therapeutic cancer candidate that causes an oncolytic effect and recruits adaptive immune responses for an enhanced therapeutic impact, thus providing a potential therapeutic tool for treatment of CRC.

An HSV-2 based oncolytic virus can function as an attractant to guide migration of adoptively transferred T cells to tumor sites

Adoptive T-cell therapy has shown promises for cancer treatment. However, for treating solid tumors, there is a need for improving the ability of the adoptively transferred T cells to home to tumor sites. We explored the possibility of using an oncolytic virus derived from HSV-2, which can actively pull T effector cells to the site of infection, as a local attractant for migration of adoptively transferred T cells. Our data show that intratumoral administration of this virus can indeed attract active migration of the adoptively transferred T cells to the treated tumor. Moreover, once attracted to the tumor site by the virus, T cells persisted in there significantly longer than in mock-treated tumor. Chemokine profiling identified significant elevation of CXCL9 and CXCL10, as well as several other chemokines belonging to the inflammatory chemokine family in the virus-treated tumors. These chemokines initially guided the T-cell migration to and then maintained their persistence in the tumor site, leading to a significantly enhanced therapeutic effect. Our data suggests that this virotherapy may be combined with adoptive T-cell therapy to potentiate its therapeutic effect against solid tumors that are otherwise difficult to manage with the treatment alone.

Designing Herpes Viruses as Oncolytics

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

Promising oncolytic agents for metastatic breast cancer treatment

New therapies for metastatic breast cancer patients are urgently needed. The long-term survival rates remain unacceptably low for patients with recurrent disease or disseminated metastases. In addition, existing therapies often cause a variety of debilitating side effects that severely impact quality of life. Oncolytic viruses constitute a developing therapeutic modality in which interest continues to build due to their ability to spare normal tissue while selectively destroying tumor cells. A number of different viruses have been used to develop oncolytic agents for breast cancer, including herpes simplex virus, adenovirus, vaccinia virus, measles virus, reovirus, and others. In general, clinical trials for several cancers have demonstrated excellent safety records and evidence of efficacy. However, the impressive tumor responses often observed in preclinical studies have yet to be realized in the clinic. In order for the promise of oncolytic virotherapy to be fully realized for breast cancer patients, effectiveness must be demonstrated in metastatic disease. This review provides a summary of oncolytic virotherapy strategies being developed to target metastatic breast cancer.

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.

Enhancing the bystander killing effect of an oncolytic HSV by arming it with a secretable apoptosis activator

Although oncolytic viruses have shown great promise as cancer therapeutics, results from a recent phase III clinical trial indicate that their potency may need further improvement for a clear clinical benefit. Here, we report a novel strategy to increase the bystander effect of virotherapy by arming an oncolytic virus with a secreted form of a Her2 single chain antibody linked to a self-multimerizing Fas ligand extracellular domain (Her2-COL-sFasL). The rationale is that, due to its much smaller size, this apoptosis activator can overcome obstacles such as the dense collagen in the tumor tissues to spread more freely than the viral particles. When measured in vitro, Her2-COL-sFasL was found to efficiently induce caspase cleavage, resulting in an 80% reduction in cell viability. Once incorporated into the genome of an oncolytic type 2 herpes simplex virus, FusOn-H3, Her2-COL-sFasL potentiates the therapeutic efficacy of the virus in an aggressive syngeneic mammary tumor model. Our data suggest that arming an oncolytic virus with a secretable and self-multimerizing apoptosis inducer is a feasible strategy to improve the potency of virotherapy.

A novel oncolytic herpes simplex virus type 2 has potent anti-tumor activity

Oncolytic viruses are promising treatments for many kinds of solid tumors. In this study, we constructed a novel oncolytic herpes simplex virus type 2: oHSV2. We investigated the cytopathic effects of oHSV2 in vitro and tested its antitumor efficacy in a 4T1 breast cancer model. We compared its effect on the cell cycle and its immunologic impact with the traditional chemotherapeutic agent doxorubicin. In vitro data showed that oHSV2 infected most of the human and murine tumor cell lines and was highly oncolytic. oHSV2 infected and killed 4T1 tumor cells independent of their cell cycle phase, whereas doxorubicin mainly blocked cells that were in S and G2/M phase. In vivo study showed that both oHSV2 and doxorubicin had an antitumor effect, though the former was less toxic. oHSV2 treatment alone not only slowed down the growth of tumors without causing weight loss but also induced an elevation of NK cells and mild decrease of Tregs in spleen. In addition, combination therapy of doxorubicin followed by oHSV2 increased survival with weight loss than oHSV2 alone. The data showed that the oncolytic activity of oHSV2 was similar to oHSV1 in cell lines examined and in vivo. Therefore, we concluded that our virus is a safe and effective therapeutic agent for 4T1 breast cancer and that the sequential use of doxorubicin followed by oHSV2 could improve antitumor activity without enhancing doxorubicin’s toxicity.

From scourge to cure: tumour-selective viral pathogenesis as a new strategy against cancer

Tumour mutations corrupt cellular pathways, and accumulate to disrupt, dysregulate, and ultimately avoid mechanisms of cellular control. Yet the very changes that tumour cells undergo to secure their own growth success also render them susceptible to viral infection. Enhanced availability of surface receptors, disruption of antiviral sensing, elevated metabolic activity, disengagement of cell cycle controls, hyperactivation of mitogenic pathways, and apoptotic avoidance all render the malignant cell environment highly supportive to viral replication. The therapeutic use of oncolytic viruses (OVs) with a natural tropism for infecting and subsequently lysing tumour cells is a rapidly progressing area of cancer research. While many OVs exhibit an inherent degree of tropism for transformed cells, this can be further promoted through pharmacological interventions and/or the introduction of viral mutations that generate recombinant oncolytic viruses adapted to successfully replicate only in a malignant cellular environment. Such adaptations that augment OV tumour selectivity are already improving the therapeutic outlook for cancer, and there remains tremendous untapped potential for further innovation.

Enhancement of systemic tumor immunity for squamous cell carcinoma cells by an oncolytic herpes simplex virus

RH2 is a neurovirulent γ134.5 gene-deficient herpes simplex virus type 1 (HSV-1) with a lytic ability in human squamous cell carcinoma (SCC) cells; it is related to spontaneously occurring HSV-1 mutant HF10. The effect of RH2 on SCC was examined using a syngeneic C3H mouse model. After infection of mouse SCCVII cells with RH2, cell viability was decreased at first, but recovered by prolonged culture, indicating the limited replication of RH2. The antitumor ability of RH2 was examined using a bilateral SCCVII tumor model. The growth of the RH2-injected tumors was suppressed compared with that of phosphate-buffered saline-injected tumors. Moreover, the growth of contralateral tumor of RH2-treated mice was also suppressed significantly. The splenocytes of C3H mice treated with RH2 lysed more SCCVII cells than NFSaY83 cells and YAC-1 cells. The cytotoxicity of the splenocytes on SCCVII cells was significantly greater than that of splenocytes from tumor-bearing mice. Removal of CD8(+) T cells from splenocytes decreased their cell killing activity remarkably. The antitumor effect of RH2 on SCCVII xenografts in nude mice was not demonstrated. These results indicate that RH2 exhibited a suppressive effect on mouse SCC, even if the replication of RH2 was limited. This is ascribed to the ability of RH2 to enhance existing tumor-specific cytotoxic T lymphocyte activity.

Advance in herpes simplex viruses for cancer therapy

Oncolytic virotherapy is an attractive approach that uses live viruses to selectively kill cancer cells. Oncolytic viruses can be genetically engineered to induce cell lyses through virus replication and cytotoxic protein expression. Herpes simplex virus (HSV) has become one of the most widely clinically used oncolytic agent. Various types of HSV have been studied in basic or clinical research. Combining oncolytic virotherapy with chemotherapy or radiotherapy generally produces synergic action with unclear molecular mechanisms. Arming HSV with therapeutic transgenes is a promising strategy and can be used to complement conventional therapies. As an efficient gene delivery system, HSV has been successfully used to deliver various immunomodulatory molecules. Arming HSV with therapeutic genes merits further investigation for potential clinical application.

Virotherapy induces massive infiltration of neutrophils in a subset of tumors defined by a strong endogenous interferon response activity

Oncolytic virotherapy has shown substantial promises as an alternative therapeutic modality for solid tumors in both preclinical studies and clinical trials. The main therapeutic activity of virotherapy derives from the direct lytic effect associated with virus replication and the induction of host immune responses to the infected tumor cells. Here we show that some human and murine tumor cell lines are highly resistant to the lytic effect of a type II herpes simplex virus-derived oncolytic virus, FusOn-H2, which was constructed by deleting the N-terminal region of the ICP10 gene. However, these tumor cells still respond exceptionally well to FusOn-H2 virotherapy in vivo. Histological examination of the treated tumors revealed that, in contrast to tumors supporting FusOn-H2 replication, implants of these highly resistant lines showed massive infiltration of neutrophils after virotherapy. Further analysis showed that there is a correlation between an intrinsically strong interferon response activity and the recruitment of neutrophils in these tumors. These results suggest that an innate immune response mainly represented by neutrophils may be part of the virotherapy-mediated antitumor mechanism in these tumors.

A short polypeptide from the herpes simplex virus type 2 ICP10 gene can induce antigen aggregation and autophagosomal degradation for enhanced immune presentation

It has been reported that certain polypeptides derived from aggregation-prone cellular proteins can turn soluble green fluorescent protein (GFP) into aggregates. Here we report our finding that a short peptide derived from a viral gene, ICP10 of herpes simplex virus (HSV)-2, also possesses such a property. A sequence as short as 13 amino acids from the middle region of the gene can convert GFP into an aggregation-prone toxic protein once it is fused to the C terminus. Moreover, this short peptide can direct a surrogate tumor antigen into the autophagosome/lysosome degradation pathway, drastically increasing both MHC class I and class II antigen presentation. The simultaneous induction of both arms of the T cell immune response to the tumor antigen effectively protects the immunized animals from tumor challenge. Designated VIPA (i.e., viral inducer of protein aggregation), this unique viral sequence may represent an attractive candidate as a molecular adjuvant for cancer immunotherapy and for other immunologically preventable diseases.

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 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.

Herpesviruses: hijacking the Ras signaling pathway

Cancer is the final result of the accumulation of several genetic alterations occurring in a cell. Several herpesviruses and especially gamma-herpesviruses have played an important role in Cancer Biology, contributing significantly to our comprehension of cell signaling and growth control pathways which lead to malignancy. Unlike other infectious agents, herpesviruses persist in the host by establishing a latent infection, so that they can reactivate periodically. Interestingly, some herpesviruses are able to either deliver or induce the expression of cellular oncogenes. Such alterations can result in the derailment of the normal cell cycle and ultimately shift the balance between continuous proliferation and programmed cell death. Herpesvirus infection employs key molecules of cellular signaling cascades mostly to enhance viral replication. However, most of these molecules are also involved in essential cellular functions, such as proliferation, cellular differentiation and migration, as well as in DNA repair mechanisms. Ras proteins are key molecules that regulate a wide range of cellular functions, including differentiation, proliferation and cell survival. A broad field of medical research is currently focused on elucidating the role of ras oncogenes in human tumor initiation as well as tumor progression and metastasis. Upon activation, Ras proteins employ several downstream effector molecules such as phosphatidylinositol 3-kinase (PI3-K) and Raf and Ral guanine nucleotide-dissociation stimulators (RALGDS) to regulate a cascade of events ranging from cell proliferation and survival to apoptosis and cellular death. In this review, we give an overview of the impact that herpesvirus infection has on the host-cell Ras signaling pathway, providing an outline of their interactions with the key cascade molecules with which they associate. Several of these interactions of viral proteins with member of the Ras signaling pathway may be crucial in determining herpesviruses' oncogenic potential or their oncomodulatory behavior. The questions that emerge concern the potential role of these molecules as therapeutic targets both for viral infections and cancer. Understanding the means by which viruses may cause oncogenesis would therefore provide a deeper knowledge of the overall oncogenic process.

Oncolytic HSV as a vector in cancer immunotherapy

It is well documented that immunotherapy has a great potential for cancer treatment. The ideal cancer immunotherapeutic strategies should be relatively simple, but able to trick the host's immune system to elicit a robust immune response to the tumor target. Herpes Simplex Virus (HSV) has been engineered for the purpose of oncolysis. These so-called oncolytic HSVs can selectively replicate within tumor cells, resulting in their destruction and in the production of progeny virions that can spread to adjacent tumor cells. In addition to their direct oncolytic effect, tumor lysis by oncolytic viruses releases tumor antigens in their native form and configuration in an individualized way. Immune responses thus generated would be more likely to recognize the original tumor than would tumor vaccines produced by other methods, most of which require extensive in vitro modification and manipulation. Several recently published studies have shown that HSV-elicited antitumor immune responses are an essential part of the overall antitumor effect produced by oncolytic HSVs, not only for controlling primary tumor growth, but also for preventing long distance metastases. In this chapter several key methods will be illustrated to monitor the immune response elicited by oncolytic HSVs.

The HSV-2 mutant DeltaPK induces melanoma oncolysis through nonredundant death programs and associated with autophagy and pyroptosis proteins

Malignant melanoma is a highly aggressive and drug-resistant cancer. Virotherapy is a novel therapeutic strategy based on cancer cell lysis through selective virus replication. However, its clinical efficacy is modest, apparently related to poor virus replication within the tumors. We report that the growth compromised herpes simplex virus type 2 (HSV-2) mutant, DeltaPK, has strong oncolytic activity for melanoma largely caused by a mechanism other than replication-induced cell lysis. The ratio of dead cells (determined by trypan blue or ethidium homodimer staining) to cells that stain with antibody to the major capsid protein VP5 (indicative of productive infection) was 1.8-4.1 for different melanoma cultures at 24-72 h post-infection. Cell death was due to activation of calpain as well as caspases-7 and -3 and it was abolished by the combination of calpain (PD150606) and pancaspase (benzyloxycarbonyl-Val-Ala-Asp-fluormethyl ketone, z-VAD-fmk) inhibitors. Upregulation of the autopahgy protein Beclin-1 and the pro-apoptotic protein H11/HspB8 accompanied DeltaPK-induced melanoma oncolysis. Intratumoral DeltaPK injection (10(6)-10(7) plaque-forming unit (pfu)) significantly reduced melanoma tumor burden associated with calpain and caspases-7 and -3 activation, Beclin-1 and H11/HspB8 upregulation and activation of caspase-1-related inflammation. Complete remission was seen for 87.5% of the LM melanoma xenografts at 5 months after treatment termination. The data indicate that DeltaPK is a promising virotherapy for melanoma that functions through virus-induced programmed cell death pathways.

Herpes simplex virus type-1(HSV-1) oncolytic and highly fusogenic mutants carrying the NV1020 genomic deletion effectively inhibit primary and metastatic tumors in mice

Background

The NV1020 oncolytic herpes simplex virus type-1 has shown significant promise for the treatment of many different types of tumors in experimental animal models and human trials. Previously, we described the construction and use of the NV1020-like virus OncSyn to treat human breast tumors implanted in nude mice. The syncytial mutation gKsyn1 (Ala-to-Val at position 40) was introduced into the OncSyn viral genome cloned into a bacterial artificial chromosome using double-red mutagenesis in E. coli to produce the OncdSyn virus carrying syncytial mutations in both gB(syn3) and gK(syn1).

Results

The OncdSyn virus caused extensive virus-induced cell fusion in cell culture. The oncolytic potential of the OncSyn and OncdSyn viruses was tested in the highly metastatic syngeneic mouse model system, which utilizes 4T1 murine mammary cancer cells implanted within the interscapular region of Balb/c mice. Mice were given three consecutive intratumor injections of OncSyn, OncdSyn, or phosphate buffered saline four days apart. Both OncSyn and OncdSyn virus injections resulted in significant reduction of tumor sizes (p < 0.05) compared to control tumors. Virus treated mice but not controls showed a marked reduction of metastatic foci in lungs and internal organs. Mouse weights were not significantly impacted by any treatment during the course of the entire study (p = 0.296).

Conclusion

These results show that the attenuated, but highly fusogenic OncSyn and OncdSyn viruses can effectively reduce primary and metastatic breast tumors in immuncompetent mice. The available bac-cloned OncSyn and OncdSyn viral genomes can be rapidly modified to express a number of different anti-tumor and immunomodulatory genes that can further enhance their anti-tumor potency.

Oncolytic herpes virus with defective ICP6 specifically replicates in quiescent cells with homozygous genetic mutations in p16

Oncolytic herpes simplex viruses (HSVs), in clinical trials for the treatment of malignant gliomas, are assumed to be selective for tumor cells because their replication is strongly attenuated in quiescent cells, but not in cycling cells. Oncolytic selectivity is thought to occur because mutations in viral ICP6 (encoding a viral ribonucleotide reductase function) and/or γ34.5 function are respectively complemented by mammalian ribonucleotide reductase and GADD34, whose genes are expressed in cycling cells. However, it is estimated that only 5–15% of malignant glioma cells are in mitosis at any one time. Therefore, effective replication of HSV oncolytic viruses might be limited to a subpopulation of tumor cells, since at any one time the majority of tumor cells would not be cycling. However, we report that an HSV with defective ICP6 function replicates in quiescent cultured murine embryonic fibroblasts obtained from mice with homozygous p16 deletions. Furthermore, intracranial inoculation of this virus into the brains of p16−/− mice provides evidence of viral replication that does not occur when the virus is injected into the brains of wild-type mice. These approaches provide in vitro and in vivo evidence that ICP6-negative HSVs are ‘molecularly targeted,’ because they replicate in quiescent tumor cells carrying specific oncogene deletions, independent of cell cycle status.

Oncolytic virotherapy: molecular targets in tumor-selective replication and carrier cell-mediated delivery of oncolytic viruses

Tremendous advances have been made in developing oncolytic viruses (OVs) in the last few years. By taking advantage of current knowledge in cancer biology and virology, specific OVs have been genetically engineered to target specific molecules or signal transduction pathways in cancer cells in order to achieve efficient and selective replication. The viral infection and amplification eventually induce cancer cells into cell death pathways and elicit host antitumor immune responses to further help eliminate cancer cells. Specifically targeted molecules or signaling pathways (such as RB/E2F/p16, p53, IFN, PKR, EGFR, Ras, Wnt, anti-apoptosis or hypoxia) in cancer cells or tumor microenvironment have been studied and dissected with a variety of OVs such as adenovirus, herpes simplex virus, poxvirus, vesicular stomatitis virus, measles virus, Newcastle disease virus, influenza virus and reovirus, setting the molecular basis for further improvements in the near future. Another exciting new area of research has been the harnessing of naturally tumor-homing cells as carrier cells (or cellular vehicles) to deliver OVs to tumors. The trafficking of these tumor-homing cells (stem cells, immune cells and cancer cells), which support proliferation of the viruses, is mediated by specific chemokines and cell adhesion molecules and we are just beginning to understand the roles of these molecules. Finally, we will highlight some avenues deserving further study in order to achieve the ultimate goals of utilizing various OVs for effective cancer treatment.

Coadministration of a Herpes Simplex Virus-2–Based Oncolytic Virus and Cyclophosphamide Produces a Synergistic Antitumor Effect and Enhances Tumor-Specific Immune Responses

Despite their unique property of selective replication and propagation in tumor tissues, oncolytic viruses have had only limited antitumor effects in cancer patients. One of the major reasons is probably the host's immune defense mechanisms, which can restrict the ability of the virus to replicate and spread within tumors. The innate immune system, which can be rapidly activated during virus infection, likely plays a more pivotal antiviral role than does acquired immunity, as the antitumor effect of an oncolytic virus is mainly generated during the acute phase of virus replication. To exploit the potential of cyclophosphamide, a cancer chemotherapeutic drug that also inhibits innate immune responses, to enhance the activity of oncolytic viruses, we evaluated the effect of coadministration of this drug with a herpes simplex virus-2-based oncolytic virus (FusOn-H2) against Lewis lung carcinoma, which is only semipermissive to infection with FusOn-H2. This strategy synergistically enhanced the antitumor effect against lung carcinoma growing in mice. It also potentiated the ability of FusOn-H2 to induce tumor-specific immune responses. Together, our results suggest that coadministration of FusOn-H2 with cyclophosphamide would be a feasible way to enhance the antitumor effects of this oncolytic virus in future clinical trials.

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.

Induction of strong antitumor immunity by an HSV-2-based oncolytic virus in a murine mammary tumor model

Oncolytic viruses have shown considerable promise for the treatment of solid tumors. In previous studies, we demonstrated that a novel oncolytic virus (FusOn-H2), constructed by replacing the serine/threonine protein kinase (PK) domain of the ICP10 gene of type 2 herpes simplex virus (HSV-2) with the gene encoding the green fluorescent protein, can selectively replicate in and thus lyse tumor cells. 4T1 tumor cells are weakly immunogenic and the mammary tumors derived from them aggressively metastasize to different parts of body, thus providing an attractive model for evaluating anticancer agents. We thus tested the antitumor effect of FusOn-H2 in this tumor model, in comparisons with several other oncolytic HSVs derived from HSV-1, including a nonfusogenic HSV-1 (Baco-1) and a doubly fusogenic virus (Synco-2D). Our results show that FusOn-H2 and Synco-2D have greater oncolytic activity in vitro than Baco-1. Moreover, FusOn-H2 induced strong T cell responses against primary and metastatic mammary tumors in vivo, and splenocytes adoptively transferred from FusOn-H2-treated mice effectively prevented metastasis in naïve mice bearing implanted mammary tumors. We conclude that the HSV-2-based FusOn-H2 oncolytic virus may be an effective agent for the treatment of both primary and metastatic breast cancer.

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.

Oncolytic viruses in cancer therapy

Oncolytic virotherapy is a promising form of gene therapy for cancer, employing nature’s own agents to find and destroy malignant cells. The purpose of this review is to provide an introduction to this very topical field of research and to point out some of the current observations, insights and ideas circulating in the literature. We have strived to acknowledge as many different oncolytic viruses as possible to give a broader picture of targeting cancer using viruses. Some of the newest additions to the panel of oncolytic viruses include the avian adenovirus, foamy virus, myxoma virus, yaba-like disease virus, echovirus type 1, bovine herpesvirus 4, Saimiri virus, feline panleukopenia virus, Sendai virus and the non-human coronaviruses. Although promising, virotherapy still faces many obstacles that need to be addressed, including the emergence of virus-resistant tumor cells.

An oncolytic virus derived from type 2 herpes simplex virus has potent therapeutic effect against metastatic ovarian cancer

Oncolytic viruses derived from herpes simplex virus (HSV) have shown considerable promise as antitumor agents against solid tumors including ovarian cancer. The current group of oncolytic HSVs was constructed exclusively from type 1 HSV. To exploit further the therapeutic potential of replication-selective viruses, we constructed an oncolytic virus from type 2 HSV by deleting the protein kinase domain of the viral ICP10 gene, which targets the activated Ras signaling pathway in tumor cells. In the study reported here, we administered this HSV-2-derived virus intraperitoneally (i.p.) to nude mice bearing metastatic human ovarian tumor xenografts, evaluated its oncolytic activity, and compared with to that of a virus constructed from HSV-1. Two injections of the HSV-2-derived virus (3 x 10(6) pfu per dose) led to complete eradication of disseminated tumors in the peritoneal cavity in more than 87% of the mice, whereas the HSV-1-based oncolytic virus, administered at the same dose and on the same schedule, eradicated tumor nodules in only 12% of mice (P<0.01). We conclude that i.p. administration of this HSV-2-based oncolytic virus may provide effective treatment for metastatic human ovarian cancer.

Effective treatment of pancreatic cancer xenografts with a conditionally replicating virus derived from type 2 herpes simplex virus

PURPOSE

Pancreatic cancer is a devastating disease that is almost universally fatal because of the lack of effective treatments. We recently constructed a novel oncolytic virus (FusOn-H2) from the type 2 herpes simplex virus. Because the replication potential of FusOn-H2 depends on the activation of the Ras signaling pathway, we evaluated its antitumor effect against pancreatic cancer, which often harbors K-ras gene mutations.

EXPERIMENTAL DESIGN

Human pancreatic cancer xenografts were established in nude mice either s.c. or orthotopically (n = 8/group). FusOn-H2 was injected either directly (s.c. tumors) or by the i.v. or i.p. route (orthotopic tumors). Tumor volume, weight, and survival time were recorded for each animal. Statistical analyses were done by Student's t test.

RESULTS

A single intratumor injection of FusOn-H2 completely eradicated s.c. pancreatic cancers in all animals. Systemic injection of the oncolytic virus produced clear antitumor effects but did not abolish tumors in any animal. The most striking antitumor effect was seen when the virus was given i.p. Delivery of FusOn-H2 by this route completely eradicated established orthotopic tumors in 75% of the animals and completely prevented local metastases.

CONCLUSIONS

FusOn-H2 has potent activity against human pancreatic cancer xenografts and may be a promising candidate for investigative virotherapy of this malignancy.