Development of a rapid method to generate multiple oncolytic HSV vectors and their in vivo evaluation using syngeneic mouse tumor models

Targeting NKG2D ligands in glioblastoma with a bispecific T-cell engager is augmented with conventional therapy and enhances oncolytic virotherapy of glioma stem-like cells

BACKGROUND

Glioblastoma (GBM) almost invariably becomes resistant towards conventional treatment of radiotherapy and temozolomide (TMZ) chemotherapy, partly due to subpopulations of intrinsically resistant glioma stem-like cells (GSC). The oncolytic herpes simplex virus-1 G207 is a promising approach for GBM virotherapy although its efficacy in patients with GBM is often limited. Natural killer group 2 member D ligands (NKG2DLs) are minimally expressed by healthy cells but are upregulated by the DNA damage response (DDR) and in malignant cells with chronic DDR signaling, resulting in innate immune activation.

METHODS

We have designed a bispecific T-cell engager (BiTE) capable of cross-linking CD3 on T cells with NKG2DL-expressing GBM cells. We then engineered the G207 virus to express the NKG2D BiTE and secrete it from infected cells. The efficacy of the free BiTE and BiTE delivered by G207 was evaluated in combination with conventional therapies in GBM cells and against patient-derived GSCs in the context of T-cell activation and target cell viability.

RESULTS

NKG2D BiTE-mediated cross-linking of GBM cells and T cells causes antigen-independent T-cell activation, pro-inflammatory cytokine release, and tumor cell death, thereby combining direct viral oncolysis with BiTE-mediated cytotoxicity. Surface NKG2DL expression was further elevated on GBM cells following pretreatment with sublethal doses of TMZ and radiation to induce the DDR, increasing sensitivity towards G207-NKG2D BiTE and achieving synergistic cytotoxicity. We also demonstrate a novel strategy for targeting GSCs that are non-permissive to G207 infection but remain sensitive to NKG2D BiTE.

CONCLUSIONS

We propose a potential model for targeting GSCs in heterogeneous tumors, whereby differentiated GBM cells infected with G207-NKG2D BiTE produce NKG2D BiTE locally, directing T-cell cytotoxicity towards the GSC subpopulations in the tumor microenvironment.

Molecular Circuits of Immune Sensing and Response to Oncolytic Virotherapy

Oncolytic virotherapy is a promising immunotherapy approach for cancer treatment that utilizes viruses to preferentially infect and eliminate cancer cells while stimulating the immune response. In this review, we synthesize the current literature on the molecular circuits of immune sensing and response to oncolytic virotherapy, focusing on viral DNA or RNA sensing by infected cells, cytokine and danger-associated-signal sensing by neighboring cells, and the subsequent downstream activation of immune pathways. These sequential sense-and-response mechanisms involve the triggering of molecular sensors by viruses or infected cells to activate transcription factors and related genes for a breadth of immune responses. We describe how the molecular signals induced in the tumor upon virotherapy can trigger diverse immune signaling pathways, activating both antigen-presenting-cell-based innate and T cell-based adaptive immune responses. Insights into these complex mechanisms provide valuable knowledge for enhancing oncolytic virotherapy strategies.

An oncolytic herpes simplex virus type 1 strain expressing a single-chain variable region antibody fragment against PD-1 and a PI3K inhibitor synergize to elicit antitumor immunity in ovarian cancer

Due to recurrence and resistance to chemotherapy, the current standard therapeutics are not fully effective against ovarian cancer. Therefore, we aimed to find an effective approach to improve the prognosis and therapy of ovarian cancer. NG34ScFvPD-1 is a modified oncolytic herpes simplex virus NG34 strain that expresses a single-chain antibody against programmed cell death protein 1 (PD-1) (ScFvPD-1). We assessed its efficacy and its regulatory mechanism in a mouse model of ovarian cancer. Enzyme-linked immunosorbent assay and western blot techniques were used to measure protein expression. Oncolysis caused by NG34ScFvPD-1 was examined using cytotoxicity and replication assays. The mechanism by which NG34ScFvPD-1 regulates apoptosis of ovarian cancer cells in vitro was also evaluated. We assessed the antitumor immunity and therapeutic potency of NG34ScFvPD-1 in combination with a phosphoinositide 3-kinase (PI3K) inhibitor. We found that NG34ScFvPD-1-infected ovarian cancer cells expressed and secreted ScFvPD-1, which bound mouse PD-1. The insertion of the ScFvPD-1 sequence did not inhibit the oncolytic activity of NG34ScFvPD-1, which induced apoptosis of ovarian cancer cells via the caspase-dependent pathway in vitro and activated the PI3K/AKT signaling pathway. Synergy was observed between NG34ScFvPD-1 and a PI3K inhibitor, and the combination was able to suppress tumor development, to prolong survival, and to elicit potent antitumor immunity. Thus, inhibition of PI3K enhanced the potent antitumor immunity induced by NG34ScFvPD-1 against ovarian cancer.

esRAGE-expressing oHSV enhances anti-tumor efficacy by inhibition of endothelial cell activation

High-mobility group box 1 (HMGB1) is a damage-associated molecular pattern (DAMP) molecule that plays an important role in inflammation and tumorigenesis. Receptor for advanced glycation end products (RAGE) is one of the major receptors to which extracellular HMGB1 binds to mediate its activity. RAGE is highly expressed on the endothelial cells (ECs) and regulates endothelial permeability during inflammation. Here, we introduced the endogenous secretory form of RAGE (esRAGE) as a decoy receptor for RAGE ligands into an oncolytic herpes simplex virus 1 (oHSV) (OVesRAGE), which, upon release, can function to block RAGE signaling. OVesRAGE significantly decreased phosphorylation of MEK1/2 and Erk and increased cleaved PARP in glioblastoma (GBM) cells in vitro and in vivo. oHSV-infected GBM cells co-cultured with ECs were used to test OVesRAGE effect on EC activation, vessel leakiness, virus replication, and tumor cell killing. OVesRAGE could effectively secrete esRAGE and rescue virus-induced EC migration and activation. Reduced EC activation facilitated virus replication in tumor cells when co-cultured with ECs. Finally, OVesRAGE significantly enhanced therapeutic efficacy in GBM-bearing mice. Collectively, our data demonstrate that HMGB1-RAGE signaling could be a promising target and that its inhibition is a feasible approach to improve the efficacy of oHSV therapy.

Specific targeting of glioblastoma with an oncolytic virus expressing a cetuximab-CCL5 fusion protein via innate and adaptive immunity

Chemokines such as C-C motif ligand 5 (CCL5) regulate immune cell trafficking in the tumor microenvironment (TME) and govern tumor development, making them promising targets for cancer therapy. However, short half-lives and toxic off-target effects limit their application. Oncolytic viruses (OVs) have become attractive therapeutic agents. Here, we generate an oncolytic herpes simplex virus type 1 (oHSV) expressing a secretable single-chain variable fragment of the epidermal growth factor receptor (EGFR) antibody cetuximab linked to CCL5 by an Fc knob-into-hole strategy that produces heterodimers (OV-Cmab-CCL5). OV-Cmab-CCL5 permits continuous production of CCL5 in the TME, as it is redirected to EGFR+ glioblastoma (GBM) tumor cells. OV-Cmab-CCL5 infection of GBM significantly enhances the migration and activation of natural killer cells, macrophages and T cells; inhibits tumor EGFR signaling; reduces tumor size; and prolongs survival of GBM-bearing mice. Collectively, our data demonstrate that OV-Cmab-CCL5 offers a promising approach to improve OV therapy for solid tumors.

Emerging immune-based technologies for high-grade gliomas

INTRODUCTION

The selection of a tailored and successful strategy for high-grade gliomas (HGGs) treatment is still a concern. The abundance of aberrant mutations within the heterogenic genetic landscape of glioblastoma strongly influences cell expansion, proliferation, and therapeutic resistance. Identification of immune evasion pathways opens the way to novel immune-based strategies. This review intends to explore the emerging immunotherapies for HGGs. The immunosuppressive mechanisms related to the tumor microenvironment and future perspectives to overcome glioma immunity barriers are also debated.

AREAS COVERED

An extensive literature review was performed on the PubMed/Medline and ClinicalTrials.gov databases. Only highly relevant articles in English and published in the last 20 years were selected. Data about immunotherapies coming from preclinical and clinical trials were summarized.

EXPERT OPINION

The overall level of evidence about the efficacy and safety of immunotherapies for HGGs is noteworthy. Monoclonal antibodies have been approved as second-line treatment, while peptide vaccines, viral gene strategies, and adoptive technologies proved to boost a vivid antitumor immunization. Malignant brain tumor-treating fields are ever-changing in the upcoming years. Constant refinements and development of new routes of drug administration will permit to design of novel immune-based treatment algorithms thus improving the overall survival.

Genetically modified cancer vaccines: Current status and future prospects

Vaccines can stimulate the immune system to protect individuals from infectious diseases. Moreover, vaccines have also been applied to the prevention and treatment of cancers. Due to advances in genetic engineering technology, cancer vaccines could be genetically modified to increase antitumor efficacy. Various genes could be inserted into cells to boost the immune response, such as cytokines, T cell costimulatory molecules, tumor-associated antigens, and tumor-specific antigens. Genetically modified cancer vaccines utilize innate and adaptive immune responses to induce durable antineoplastic capacity and prevent the recurrence. This review will discuss the major approaches used to develop genetically modified cancer vaccines and explore recent advances to increase the understanding of engineered cancer vaccines.

CD40L-armed oncolytic herpes simplex virus suppresses pancreatic ductal adenocarcinoma by facilitating the tumor microenvironment favorable to cytotoxic T cell response in the syngeneic mouse model

Background

Pancreatic ductal adenocarcinoma (PDAC) is one of the most malignant cancers worldwide. Despite the promising outcome of immune checkpoint inhibitors and agonist antibody therapies in different malignancies, PDAC exhibits high resistance due to its immunosuppressive tumor microenvironment (TME). Ameliorating the TME is thus a rational strategy for PDAC therapy. The intratumoral application of oncolytic herpes simplex virus-1 (oHSV) upregulates pro-inflammatory macrophages and lymphocytes in TME, and enhances the responsiveness of PDAC to immunotherapy. However, the antitumor activity of oHSV remains to be maximized. The aim of this study is to investigate the effect of the CD40L armed oHSV on the tumor immune microenvironment, and ultimately prolong the survival of the PDAC mouse model.

Methods

The membrane-bound form of murine CD40L was engineered into oHSV by CRISPR/Cas9-based gene editing. oHSV-CD40L induced cytopathic effect and immunogenic cell death were determined by microscopy and flow cytometry. The expression and function of oHSV-CD40L was assessed by reporter cell assay. The oHSV-CD40L was administrated intratumorally to the immune competent syngeneic PDAC mouse model, and the leukocytes in TME and tumor-draining lymph node were analyzed by multicolor flow cytometry. Intratumoral cytokines were determined by ELISA.

Results

Intratumoral application of oHSV-CD40L efficiently restrained the tumor growth and prolonged the survival of the PDAC mouse model. In TME, oHSV-CD40L-treated tumor accommodated more maturated dendritic cells (DCs), which in turn activated T helper 1 and cytotoxic CD8⁺ T cells in an interferon-γ-dependent and interleukin-12-dependent manner. In contrast, the regulatory T cells were significantly reduced in TME by oHSV-CD40L treatment. Repeated dosing and combinational therapy extended the lifespan of PDAC mice.

Conclusion

CD40L-armed oncolytic therapy endues TME with increased DCs maturation and DC-dependent activation of cytotoxic T cells, and significantly prolongs the survival of the model mice. This study may lead to the understanding and development of oHSV-CD40L as a therapy for PDAC in synergy with immune checkpoint blockade.

Targeting Fc receptor-mediated effects and the "don't eat me" signal with an oncolytic virus expressing an anti-CD47 antibody to treat metastatic ovarian cancer

Purpose: Monoclonal antibodies (mAbs) blocking immune checkpoints have emerged as important cancer therapeutics, as exemplified by systemic administration of the IgG1 anti-CD47 mAb that blocks the "don't eat me" pathway. However, this strategy is associated with severe toxicity. Experimental Design: To improve therapeutic efficacy while reducing toxicities for ovarian cancer, we engineered an oncolytic herpesvirus (oHSV) to express a full-length, soluble anti-CD47 mAb with a human IgG1 scaffold (OV-αCD47-G1) or IgG4 scaffold (OV-αCD47-G1). Results: Both IgG1 and IgG4 anti-CD47 mAbs secreted by oHSV-infected tumor cells blocked the CD47-SIRPα signal pathway, enhancing macrophage phagocytosis against ovarian tumor cells. OV-αCD47-G1, but not OV-αCD47-G4, activated human NK cell cytotoxicity and macrophage phagocytosis by binding to the Fc receptors of these cells. In vivo, these multifaceted functions of OV-αCD47-G1 improved mouse survival in xenograft and immunocompetent mouse models of ovarian cancer when compared to OV-αCD47-G4 and a parental oHSV. The murine counterpart of OV-αCD47-G1, OV-αmCD47-G2b, also enhanced mouse NK cell cytotoxicity and macrophage phagocytosis and prolonged survival of mice bearing ovarian tumors compared to OV-αmCD47-G3. OV-αmCD47-G2b was also superior to αmCD47-G2b and showed a significantly better effect when combined with an antibody against PD-L1 that was upregulated by oHSV infection. Conclusion: Our data demonstrate that an oHSV encoding a full-length human IgG1 anti-CD47 mAb, when used as a single agent or combined with another agent, is a promising approach for improving ovarian cancer treatment via enhancing innate immunity, as well as performing its known oncolytic function and modulation of immune cells.

An oncolytic virus expressing a full-length antibody enhances antitumor innate immune response to glioblastoma

Oncolytic herpes simplex virus-1 is capable of lysing tumor cells while alerting the immune system. CD47, in collaboration with SIRPα, represents an important immune checkpoint to inhibit phagocytosis by innate immune cells. Here we show locoregional control of glioblastoma by an oncolytic herpes virus expressing a full-length anti(α)-human CD47 IgG1 or IgG4 antibody. The antibodies secreted by the virus-infected glioblastoma cells block the CD47 'don't eat me' signal irrespective of the subclass; however, αCD47-IgG1 has a stronger tumor killing effect than αCD47-IgG4 due to additional antibody-dependent cellular phagocytosis by macrophages and antibody-dependent cellular cytotoxicity by NK cells. Intracranially injected αCD47-IgG1-producing virus continuously releases the respective antibody in the tumor microenvironment but not into systemic circulation; additionally, αCD47-IgG1-producing virus also improves the survival of tumor-bearing mice better than control oncolytic herpes virus combined with topical αCD47-IgG1. Results from immunocompetent mouse tumor models further confirm that macrophages, and to a lesser extent NK cells, mediate the anti-tumor cytotoxicity of antibody-producing oncolytic herpesviruses. Collectively, oncolytic herpes simplex virus-1 encoding full-length antibodies could improve immune-virotherapy for glioblastoma.

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.

Against the Resilience of High-Grade Gliomas: Gene Therapies (Part II)

Introduction: High-grade gliomas (HGGs) still have a high rate of recurrence and lethality. Gene therapies were projected to overcome the therapeutic resilience of HGGs, due to the intrinsic genetic heterogenicity and immune evasion pathways. The present literature review strives to provide an updated overview of the novel gene therapies for HGGs treatment, highlighting evidence from clinical trials, molecular mechanisms, and future perspectives. Methods: An extensive literature review was conducted through PubMed/Medline and ClinicalTrials.gov databases, using the keywords “high-grade glioma,” “glioblastoma,” and “malignant brain tumor”, combined with “gene therapy,” “oncolytic viruses,” “suicide gene therapies,” “tumor suppressor genes,” “immunomodulatory genes,” and “gene target therapies”. Only articles in English and published in the last 15 years were chosen, further screened based on best relevance. Data were analyzed and described according to the PRISMA guidelines. Results: Viruses were the most vehicles employed for their feasibility and transduction efficiency. Apart from liposomes, other viral vehicles remain largely still experimental. Oncolytic viruses and suicide gene therapies proved great results in phase I, II preclinical, and clinical trials. Tumor suppressor, immunomodulatory, and target genes were widely tested, showing encouraging results especially for recurrent HGGs. Conclusions: Oncolytic virotherapy and suicide genes strategies are valuable second-line treatment options for relapsing HGGs. Immunomodulatory approaches, tumor suppressor, and target genes therapies may implement and upgrade standard chemoradiotherapy. Future research aims to improve safety profile and prolonging therapeutic effectiveness. Further clinical trials are needed to assess the efficacy of gene-based therapies.

The Effect of Herpes Simplex Virus-Type-1 (HSV-1) Oncolytic Immunotherapy on the Tumor Microenvironment

The development of cancer causes disruption of anti-tumor immunity required for surveillance and elimination of tumor cells. Immunotherapeutic strategies aim for the restoration or establishment of these anti-tumor immune responses. Cancer immunotherapies include immune checkpoint inhibitors (ICIs), adoptive cellular therapy (ACT), cancer vaccines, and oncolytic virotherapy (OVT). The clinical success of some of these immunotherapeutic modalities, including herpes simplex virus type-1 derived OVT, resulted in Food and Drug Administration (FDA) approval for use in treatment of human cancers. However, a significant proportion of patients do not respond or benefit equally from these immunotherapies. The creation of an immunosuppressive tumor microenvironment (TME) represents an important barrier preventing success of many immunotherapeutic approaches. Mechanisms of immunosuppression in the TME are a major area of current research. In this review, we discuss how oncolytic HSV affects the tumor microenvironment to promote anti-tumor immune responses. Where possible we focus on oncolytic HSV strains for which clinical data is available, and discuss how these viruses alter the vasculature, extracellular matrix and immune responses in the tumor microenvironment.

Dual roles of a novel oncolytic viral vector-based SARS-CoV-2 vaccine: preventing COVID-19 and treating tumor progression

The ongoing coronavirus disease 2019 (COVID-19) pandemic is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Cancer patients are usually immunocompromised and thus are particularly susceptible to SARS-CoV-2 infection resulting in COVID-19. Although many vaccines against COVID-19 are being preclinically or clinically tested or approved, none have yet been specifically developed for cancer patients or reported as having potential dual functions to prevent COVID-19 and treat cancer. Here, we confirmed that COVID-19 patients with cancer have low levels of antibodies against the spike (S) protein, a viral surface protein mediating the entry of SARS-CoV-2 into host cells, compared with COVID-19 patients without cancer. We developed an oncolytic herpes simplex virus-1 vector-based vaccine named oncolytic virus (OV)-spike. OV-spike induced abundant anti-S protein neutralization antibodies in both tumor-free and tumor-bearing mice, which inhibit infection of VSV-SARS-CoV-2 and wild-type (WT) live SARS-CoV-2 as well as the B.1.1.7 variant in vitro. In the tumor-bearing mice, OV-spike also inhibited tumor growth, leading to better survival in multiple preclinical tumor models than the untreated control. Furthermore, OV-spike induced anti-tumor immune response and SARS-CoV-2-specific T cell response without causing serious adverse events. Thus, OV-spike is a promising vaccine candidate for both preventing COVID-19 and enhancing the anti-tumor response.

One Sentence Summary

A herpes oncolytic viral vector-based vaccine is a promising vaccine with dual roles in preventing COVID-19 and treating tumor progression.

Oncolytic herpesvirus expressing PD-L1 BiTE for cancer therapy: exploiting tumor immune suppression as an opportunity for targeted immunotherapy

BACKGROUND

Programmed death-ligand 1 (PD-L1) is an important immune checkpoint protein that can be regarded as a pan-cancer antigen expressed by multiple different cell types within the tumor. While antagonizing PD-L1 is well known to relieve PD-1/PD-L1-mediated T cell suppression, here we have combined this approach with an immunotherapy strategy to target T cell cytotoxicity directly toward PD-L1-expressing cells. We developed a bi-specific T cell engager (BiTE) crosslinking PD-L1 and CD3ε and demonstrated targeted cytotoxicity using a clinically relevant patient-derived ascites model. This approach represents an immunological 'volte-face' whereby a tumor immunological defense mechanism can be instantly transformed into an Achilles' heel for targeted immunotherapy.

METHODS

The PD-L1 targeting BiTE comprises an anti-PD-L1 single-chain variable fragment (scFv) or nanobody (NB) domain and an anti-CD3 scFv domain in a tandem repeat. The ability to activate T cell cytotoxicity toward PD-L1-expressing cells was established using human carcinoma cells and PD-L1-expressing human ('M2') macrophages in the presence of autologous T cells. Furthermore, we armed oncolytic herpes simplex virus-1 (oHSV-1) with PD-L1 BiTE and demonstrated successful delivery and targeted cytotoxicity in unpurified cultures of malignant ascites derived from different cancer patients.

RESULTS

PD-L1 BiTE crosslinks PD-L1-positive cells and CD3ε on T cells in a 'pseudo-synapse' and triggers T cell activation and release of proinflammatory cytokines such as interferon-gamma (IFN-γ), interferon gamma-induced protein 10 (IP-10) and tumour necrosis factor-α (TNF-α). Activation of endogenous T cells within ascites samples led to significant lysis of tumor cells and M2-like macrophages (CD11b+CD64+ and CD206+/CD163+). The survival of CD3+ T cells (which can also express PD-L1) was unaffected. Intriguingly, ascites fluid that appeared particularly immunosuppressive led to higher expression of PD-L1 on tumor cells, resulting in improved BiTE-mediated T cell activation.

CONCLUSIONS

The study reveals that PD-L1 BiTE is an effective immunotherapeutic approach to kill PD-L1-positive tumor cells and macrophages while leaving T cells unharmed. This approach activates endogenous T cells within malignant ascites, generates a proinflammatory response and eliminates cells promoting tumor progression. Using an oncolytic virus for local expression of PD-L1 BiTE also prevents 'on-target off-tumor' systemic toxicities and harnesses immunosuppressive protumor conditions to augment immunotherapy in immunologically 'cold' clinical cancers.

Herpes Simplex Virus Oncolytic Immunovirotherapy: The Blossoming Branch of Multimodal Therapy

Oncolytic viruses are smart therapeutics against cancer due to their potential to replicate and produce the needed therapeutic dose in the tumor, and to their ability to self-exhaust upon tumor clearance. Oncolytic virotherapy strategies based on the herpes simplex virus are reaching their thirties, and a wide variety of approaches has been envisioned and tested in many different models, and on a range of tumor targets. This huge effort has culminated in the primacy of an oncolytic HSV (oHSV) being the first oncolytic virus to be approved by the FDA and EMA for clinical use, for the treatment of advanced melanoma. The path has just been opened; many more cancer types with poor prognosis await effective and innovative therapies, and oHSVs could provide a promising solution, especially as combination therapies and immunovirotherapies. In this review, we analyze the most recent advances in this field, and try to envision the future ahead of oHSVs.

Enhancing Antitumor Efficacy of Heavily Vascularized Tumors by RAMBO Virus through Decreased Tumor Endothelial Cell Activation

Vascularization is a common pathology for many solid tumors, and therefore anti-angiogenic strategies are being investigated as a therapeutic target for treatment. Numerous studies are also being conducted regarding the effects of oncolytic viruses, including Imlygic^TM, an FDA approved oncolytic herpes simplex virus-1 (oHSV) for the treatment of highly vascularized tumors such as Kaposi sarcoma (NCT04065152), and brain tumors. To our knowledge, the effects of combining oncolytic HSV with angiogenesis inhibition on endothelial cell activation has not been previously described. Here, we tested the effects of Rapid Antiangiogenesis Mediated By Oncolytic Virus (RAMBO), an oHSV which expresses a potent anti-angiogenic gene Vasculostatin on endothelial cell activation in heavily vascularized solid tumors. oHSV treatment induces endothelial cell activation, which inhibits virus propagation and oncolysis in adjacent tumor cells in vitro. Consistently, this was also observed in intravital imaging of intracranial tumor-bearing mice in vivo where infected tumor endothelial cells could efficiently clear the virus without cell lysis. Quantitative real-time PCR (Q-PCR), leukocyte adhesion assay, and fluorescent microscopy imaging data, however, revealed that RAMBO virus significantly decreased expression of endothelial cell activation markers and leukocyte adhesion, which in turn increased virus replication and cytotoxicity in endothelial cells. In vivo RAMBO treatment of subcutaneously implanted sarcoma tumors significantly reduced tumor growth in mice bearing sarcoma compared to rHSVQ. In addition, histological analysis of RAMBO-treated tumor tissues revealed large areas of necrosis and a statistically significant reduction in microvessel density (MVD). This study provides strong preclinical evidence of the therapeutic benefit for the use of RAMBO virus as a treatment option for highly vascularized tumors.

Local and Systemic Immune Dysregulation Alters Glioma Growth in Hyperglycemic Mice

PURPOSE

Unlike most cancers, no clear epidemiological correlation between diabetes (Db) and malignant glioma progression exists. Because hyperglycemia activates proinflammatory pathways through the receptor for advanced glycation endproducts (RAGE), we hypothesized that Db can also promote malignant glioma progression.

EXPERIMENTAL DESIGN

We compared the growth of two phenotypically diverse syngeneic glioma models in control and diabetic mice. Tumor growth and antitumor immune responses were evaluated in orthotopic and heterotopic models and correlated to RAGE and RAGE ligand expression.

RESULTS

Irrespective of tumor implantation site, growth of a "classical" glioma model, GL261, increased in hyperglycemic mice and was mediated by upregulation of RAGE and its ligand, HMGB1. However, growth of a "mesenchymal" glioma subtype, K-Luc, depended on tumor implantation site. Whereas heterotopic K-Luc tumors progressed rapidly in Db mice, intracranial K-Luc tumors grew slower. We further showed that hyperglycemia inhibited the innate antitumor inflammatory responses in both models. Although this contributed to the accelerated growth of heterotopic tumors, suppression of tumor inflammatory responses dampened the growth of orthotopic K-Luc gliomas.

CONCLUSIONS

Hyperglycemia may enhance glioma growth through promotion of RAGE expression and suppression of antitumor immune responses. However, abrogation of the proinflammatory milieu in tumors may also dampen the growth of inflammatory glioma subtypes in the brains of diabetic mice. This dichotomy in glioma growth response to hyperglycemia may partly explain why conflicting epidemiological studies show both an increased risk and a protective effect of Db in patients with malignant gliomas.

Generation and validation of recombinant herpes simplex type 1 viruses (HSV-1) using CRISPR/Cas9 genetic disruption

Herpes simplex virus type 1 (HSV-1) is a large DNA virus that has been popular for oncolytic virus development in pre-clinical research and clinical trials. An oncolytic HSV-1 encoding granulocyte-macrophage colony stimulating factor (GM-CSF), designated talimogene laherparepvec (T-VEC) was approved for the treatment of patients with advanced melanoma in 2015. There are numerous advantages of HSV-1 for oncolytic development, including the ease of recombinant engineering, presence of non-essential genes allowing attenuation of pathogenicity and space for foreign transgene expression. In addition, most recombinants retain sensitivity to acyclovir providing an additional safety feature. In this chapter, we will focus on the key methods for the development of oncolytic HSV-1 vectors and some of the commonly utilized laboratory protocols used to characterize and assess the structure and oncolytic activity of recombinant HSV-1 viruses.

Oncolytic HSV therapy increases trametinib access to brain tumors and sensitizes them in vivo

BACKGROUND

Hyperactivation of the RAS-RAF-MEK-ERK signaling pathway is exploited by glioma cells to promote their growth and evade apoptosis. MEK activation in tumor cells can increase replication of ICP34.5-deleted herpes simplex virus type 1 (HSV-1), but paradoxically its activation in tumor-associated macrophages promotes a pro-inflammatory signaling that can inhibit virus replication and propagation. Here we investigated the effect of blocking MEK signaling in conjunction with oncolytic HSV-1 (oHSV) for brain tumors.

METHODS

Infected glioma cells co-cultured with microglia or macrophages treated with or without trametinib were used to test trametinib effect on macrophages/microglia. Enzyme-linked immunosorbent assay, western blotting, and flow cytometry were utilized to evaluate the effect of the combination therapy. Pharmacokinetic (PK) analysis of mouse plasma and brain tissue was used to evaluate trametinib delivery to the CNS. Intracranial human and mouse glioma-bearing immune deficient and immune competent mice were used to evaluate the antitumor efficacy.

RESULT

Oncolytic HSV treatment rescued trametinib-mediated feedback reactivation of the mitogen-activated protein kinase signaling pathway in glioma. In vivo, PK analysis revealed enhanced blood-brain barrier penetration of trametinib after oHSV treatment. Treatment by trametinib, a MEK kinase inhibitor, led to a significant reduction in microglia- and macrophage-derived tumor necrosis factor alpha (TNFα) secretion in response to oHSV treatment and increased survival of glioma-bearing mice. Despite the reduced TNFα production observed in vivo, the combination treatment activated CD8+ T-cell mediated immunity and increased survival in a glioma-bearing immune-competent mouse model.

CONCLUSION

This study provides a rationale for combining oHSV with trametinib for the treatment of brain tumors.

Oncolytic Herpes Virus Armed with Vasculostatin in Combination with Bevacizumab Abrogates Glioma Invasion via the CCN1 and AKT Signaling Pathways

Anti-VEGF treatments such as bevacizumab have demonstrated convincing therapeutic advantage in patients with glioblastoma. However, bevacizumab has also been reported to induce invasiveness of glioma. In this study, we examined the effects of rapid antiangiogenesis mediated by oncolytic virus (RAMBO), an oncolytic herpes simplex virus-1 expressing vasculostatin, on bevacizumab-induced glioma invasion. The effect of the combination of RAMBO and bevacizumab in vitro was assessed by cytotoxicity, migration, and invasion assays. For in vivo experiments, glioma cells were stereotactically inoculated into the brain of mice. RAMBO was intratumorally injected 7 days after tumor inoculation, and bevacizumab was administered intraperitoneally twice a week. RAMBO significantly decreased both the migration and invasion of glioma cells treated with bevacizumab. In mice treated with bevacizumab and RAMBO combination, the survival time was significantly longer and the depth of tumor invasion was significantly smaller than those treated with bevacizumab monotherapy. Interestingly, RAMBO decreased the expression of cysteine-rich protein 61 and phosphorylation of AKT, which were increased by bevacizumab. These results suggest that RAMBO suppresses bevacizumab-induced glioma invasion, which could be a promising approach to glioma therapy.

Oncolytic herpes simplex virus therapy for malignant glioma: current approaches to successful clinical application

INTRODUCTION

With the approval of talimogene laherparepvec (T-VEC) for advanced malignant melanoma, virotherapy using oncolytic herpes simplex virus (oHSV) is now emerging as a viable therapeutic option for cancer patients, including malignant gliomas.

AREAS COVERED

This review summarizes the most recent literature to provide cutting-edge knowledge about preclinical and clinical development of oHSV therapy for malignant gliomas, presenting current approaches to overcome obstacles to successful clinical application of oHSV in neuro-oncology.

EXPERT OPINION

Current strategies to improve the efficacy of oHSV therapy include engineering new viruses, modulation of innate and adaptive immune responses, combination with other treatments, and developing new oHSV delivery. All of these could rapidly be translated into clinical investigations, following several clinical trials that are currently ongoing.

Enhancing Therapeutic Efficacy of Oncolytic Herpes Simplex Virus-1 with Integrin β1 Blocking Antibody OS2966

Integrin β1 receptor, expressed on the surface of tumor cells and macrophages in the tumor microenvironment (TME), has been implicated in both tumor progression and resistance to multiple modalities of therapy. OS2966 is the first clinical-ready humanized monoclonal antibody to block integrin β1 and was recently orphan designated by the FDA Office of Orphan Products Development. Here, we tested therapeutic potential of OS2966-mediated integrin β1 blockade to enhance the efficacy of oncolytic herpes simplex virus-1 (oHSV) through evaluation of virus replication, tumor cell killing efficiency, effect on the antiviral signaling pathway, co-culture assays of oHSV-infected cells with macrophages, and in vivo bioluminescence imaging on mammary fat pad triple-negative breast cancer xenograft and subcutaneous and intracranial glioma xenografts. OS2966 treatment decreased interferon signaling and proinflammatory cytokine induction in oHSV-treated tumor cells and inhibited migration of macrophages, resulting in enhanced oHSV replication and cytotoxicity. OS2966 treatment also significantly enhanced oHSV replication and oHSV-mediated antitumor efficacy in orthotopic xenograft models, including triple-negative breast cancer and glioblastoma. The results demonstrated the synergistic potential of the combinatory treatment approach with OS2966 to improve antitumor efficacy of conventional oHSV therapy.

Construction of Oncolytic Herpes Simplex Virus with Therapeutic Genes of Interest

Herpes simplex virus (HSV) is one of the most extensively studied oncolytic virus platforms. The recent FDA approval of talimogene laherparepvec (T-VEC) has been accelerating translational research of oncolytic HSV (oHSV) as a promising therapeutic for refractory cancers such as glioblastoma, the deadliest primary malignancy in the brain. The large genome size of HSV readily allows arming of oHSV by incorporating therapeutic transgenes within the virus, as exemplified by T-VEC carrying GM-CSF, thereby enhancing the anticancer activity of oHSV. Here we describe a bacterial artificial chromosome-based method for construction of an oHSV expressing a transgene, which we routinely use in the laboratory to create a number of different recombinant oHSV bearing either therapeutic or reporter genes.

PTEN expression by an oncolytic herpesvirus directs T-cell mediated tumor clearance

Engineered oncolytic viruses are used clinically to destroy cancer cells and have the ability to boost anticancer immunity. Phosphatase and tensin homolog deleted on chromosome 10 loss is common across a broad range of malignancies, and is implicated in immune escape. The N-terminally extended isoform, phosphatase and tensin homolog deleted on chromosome 10 alpha (PTENα), regulates cellular functions including protein kinase B signaling and mitochondrial adenosine triphosphate production. Here we constructed HSV-P10, a replicating, PTENα expressing oncolytic herpesvirus, and demonstrate that it inhibits PI3K/AKT signaling, increases cellular adenosine triphosphate secretion, and reduces programmed death-ligand 1 expression in infected tumor cells, thus priming an adaptive immune response and overcoming tumor immune escape. A single dose of HSV-P10 resulted in long term survivors in mice bearing intracranial tumors, priming anticancer T-cell immunity leading to tumor rejection. This implicates HSV-P10 as an oncolytic and immune stimulating therapeutic for anticancer therapy.

Oncolytic viruses are a promising therapeutic approach for cancer treatment. The authors demonstrate the efficacy of an engineered HSV-1 expressing PTENα as an oncolytic and immune stimulating therapy against brain cancer metastases.

An oncolytic herpesvirus expressing E-cadherin improves survival in mouse models of glioblastoma

The efficacy of oncolytic herpes simplex virus (oHSV) is limited by rapid viral clearance by innate immune effector cells and poor intratumoral viral spread. We combine two approaches to overcome these barriers: inhibition of natural killer (NK) cells and enhancement of intratumoral viral spread. We engineered an oHSV to express CDH1, encoding E-cadherin, an adherent molecule and a ligand for KLRG1, an inhibitory receptor expressed on NK cells. In vitro, infection with this engineered virus, named OV-CDH1, induced high surface E-cadherin expression on infected glioblastoma (GBM) cells, which typically lack endogenous E-cadherin. Ectopically expressed E-cadherin enhanced the spread of OV-CDH1 by facilitating cell-to-cell infection and viral entry and reduced viral clearance by selectively protecting OV-CDH1-infected cells from KLRG1+ NK cell killing. In vivo, OV-CDH1 treatment substantially prolonged the survival in GBM-bearing mouse models, primarily because of improved viral spread rather than inhibition of NK cell activity. Thus, virus-induced overexpression of E-cadherin may be a generalizable strategy for improving cancer virotherapy.

Arming an Oncolytic Herpes Simplex Virus Type 1 with a Single-chain Fragment Variable Antibody against PD-1 for Experimental Glioblastoma Therapy

PURPOSE

Glioblastoma (GBM) is resistant to standard of care. Immune checkpoints inhibitors (such as anti-PD-1 mAbs) efficiently restore antitumor T-cell activity. We engineered a new oncolytic herpes simplex virus (oHSV) expressing a single-chain antibody against PD-1 (scFvPD-1) to evaluate its efficacy in mouse models of GBM.

EXPERIMENTAL DESIGN

NG34scFvPD-1 expresses the human GADD34 gene transcriptionally controlled by the Nestin promoter to allow replication in GBM cells and a scFvPD-1 cDNA transcriptionally controlled by the CMV promoter. ELISA assays were performed to detect binding of scFvPD-1 to mouse and human PD-1. In vitro cytotoxicity and replication assays were performed to measure NG34scFvPD-1 oncolysis, and scFvPD-1 expression and secretion were determined. In vivo survival studies using orthotopic mouse GBM models were performed to evaluate the therapeutic potency of NG34scFvPD-1.

RESULTS

NG34scFvPD-1-infected GBM cells express and secrete scFvPD-1 that binds mouse PD-1. The introduction of the scFvPD-1 sequence in the viral backbone does not alter the oncolytic properties of NG34scFvPD-1. In situ NG34scFvPD-1 treatment improved the survival with a tail of durable survivorship in 2 syngeneic immunocompetent mouse models of GBM. Mice that survived the first GBM challenge rejected the second challenge of GBM when implanted in the contralateral hemisphere. However, this was not true when athymic mice were employed as the recipients of the second challenge, consistent with the need for an intact immune system to obtain a memory response.

CONCLUSIONS

NG34scFvPD-1 treatment induces a durable antitumor response in 2 preclinical mouse models of GBM with evidence for antitumor memory.

S100B suppression alters polarization of infiltrating myeloid-derived cells in gliomas and inhibits tumor growth

S100B, a member of the multigene family of Ca²⁺-binding proteins, is overexpressed by most malignant gliomas but its biological role in gliomagenesis is unclear. Recently, we demonstrated that low concentrations of S100B attenuated microglia activation through the induction of STAT3. Furthermore, S100B downregulation in a murine glioma model inhibited macrophage trafficking and tumor growth. Based on these observations, we hypothesized that S100B inhibitors may have antiglioma properties through modulation of tumor microenvironment.

To discover novel S100B inhibitors, we developed a high-throughput screening cell-based S100B promoter-driven luciferase reporter assay. Initial screening of 768 compounds in the NIH library identified 36 hits with >85% S100B inhibitory activity. Duloxetine (Dul, an SNRI) was selected for the initial proof-of-concept studies. At low concentrations (1–5 μM) Dul inhibited S100B and CCL2 production in mouse GL261 glioma cells, but had minimal cytotoxic activity in vitro. In vivo, however, Dul (30 mg/kg/14 days) inhibited S100B production, altered the polarization and trafficking of tumor-associated myeloid-derived cells, and inhibited the growth of intracranial GL261 gliomas. Dul therapeutic efficacy, however, was not observed in the K-Luc glioma model that expresses low levels of S100B. These findings affirm the role of S100B in gliomagenesis and justify the development of more potent S100B inhibitors for glioma therapy.

Immunostimulatory CpG on Carbon Nanotubes Selectively Inhibits Migration of Brain Tumor Cells

Even when treated with aggressive current therapies, patients with glioblastoma usually survive less than two years and exhibit a high rate of recurrence. CpG is an oligonucleotide that activates the innate immune system via Toll-like receptor 9 (TLR9) activation. Injection of CpG into glioblastoma tumors showed promise as an immunotherapy in mouse models but proved disappointing in human trials. One aspect of glioma that is not addressed by CpG therapy alone is the highly invasive nature of glioma cells, which is associated with resistance to radiation and chemotherapy. Here, we demonstrate that single-walled carbon nanotubes noncovalently functionalized with CpG (SWNT/CpG), which retain the immunostimulatory property of the CpG, selectively inhibit the migration of glioma cells and not macrophages without affecting cell viability or proliferation. SWNT/CpG also selectively decreased NF-κB activation in glioma cells, while activating macrophages by induction of the TLR9/NF-κB pathway, as we have previously reported. The migration inhibition of glioma cells was correlated with selective reduction of intracellular levels of reactive oxygen species (ROS), suggesting that an antioxidant-based mechanism mediates the observed effects. To the best of our knowledge, SWNT/CpG is the first nanomaterial that inhibits the migration of cancer cells while stimulating the immune system.

Toxicity and Efficacy of a Novel GADD34-expressing Oncolytic HSV-1 for the Treatment of Experimental Glioblastoma

Purpose: Glioblastoma (GBM) is the most common primary central nervous system cancer in adults. Oncolytic HSV-1 (oHSV) is the first FDA-approved gene therapy approach for the treatment of malignant melanoma. For GBM, oHSVs need to be engineered to replicate within and be toxic to the glial tumor but not to normal brain parenchymal cells. We have thus engineered a novel oHSV to achieve these objectives.Experimental Design: NG34 is an attenuated HSV-1 with deletions in the genes encoding viral ICP6 and ICP34.5. These mutations suppress virus replication in nondividing brain neurons. NG34 expresses the human GADD34 gene under transcriptional control of a cellular Nestin gene promoter/enhancer element, whose expression occurs selectively in GBM. In vitro cytotoxicity assay and survival studies with mouse models were performed to evaluate therapeutic potency of NG34 against glioblastoma. In vivo neurotoxicity evaluation of NG34 was tested by intracerebral inoculation.Results: NG34 replicates in GBM cells in vitro with similar kinetics as those exhibited by an oHSV that is currently in clinical trials (rQNestin34.5). Dose-response cytotoxicity of NG34 in human GBM panels was equivalent to or improved compared with rQNestin34.5. The in vivo efficacy of NG34 against two human orthotopic GBM models in athymic mice was similar to that of rQNestin34.5, whereas intracerebral injection of NG34 in the brains of immunocompetent and athymic mice showed significantly better tolerability. NG34 was also effective in a syngeneic mouse glioblastoma model.Conclusions: A novel oHSV encoding GADD34 is efficacious and relatively nontoxic in mouse models of GBM. Clin Cancer Res; 24(11); 2574-84. ©2018 AACR.

Construction of Various γ34.5 Deleted Fluorescent-Expressing Oncolytic herpes Simplex type 1 (oHSV) for Generation and Isolation of HSV-Based Vectors

Background

Oncolytic herpes simplex virus (oHSV)-based vectors lacking γ34.5 gene, are considered as ideal templates to construct efficient vectors for (targeted) cancer gene therapy. Herein, we reported the construction of three single/dually-flourescence labeled and γ34.5-deleted, recombinant HSV-1 vectors for rapid generation and easy selection/isolation of different HSV-Based vectors.

Methods

Generation of recombinant viruses was performed with conventional homologous recombination methods using green fluorescent protein (GFP) and BleCherry harboring shuttle vectors. Viruses were isolated by direct fluorescence observation and standard plaque purifying methods and confirmed by PCR and sequencing and flow cytometry. XTT and plaque assay titration were performed on Vero, U87MG, and T98 GBM cell lines.

Results

We generated three recombinant viruses, HSV-GFP, HSV-GR (Green-Red), and HSV-Red. The HSV-GFP showed two log higher titer (1010 PFU) than wild type (108 PFU). In contrast, HSV-GR and HSV-Red showed one log lower titer (107 PFU) than parental HSV. Cytotoxicity analysis showed that HSV-GR and HSV-Red can lyse target tumor cells at multiplicity of infection of 10 and 1 (P<0.001). Moreover, HSV-GFP showed higher infection potency (98%) in comparison with HSV-GR (82%).

Conclusion

Our oHSVs provide a simple and an efficient platform for construction and rapid isolation of 2nd and 3rd generation oHSVs by replacing the inserted dyes with transgenes and also for rapid identification via fluorescence activated cell sorting. These vectors can also be used for tracing the efficacy of therapeutic agents on target cells, imaging of neural or tumoral cells in vitro/in vivo and as oncolytic agents in cancer therapy.

Characterization of Arginase Expression in Glioma-Associated Microglia and Macrophages

Microglia (MG) and macrophages (MPs) represent a significant component of the inflammatory response to gliomas. When activated, MG/MP release a variety of pro-inflammatory cytokines, however, they also secrete anti-inflammatory factors that limit their cytotoxic function. The balance between pro and anti-inflammatory functions dictates their antitumor activity. To evaluate potential variations in MG and MP function in gliomas, we isolated these cells (and other Gr1⁺ cells) from intracranial GL261 murine gliomas by FACS and evaluated their gene expression profiles by microarray analysis. As expected, arginase 1 (Arg1, M2 marker) was highly expressed by tumor-associated Gr1⁺, MG and MP. However, in contrast to MP and Gr1⁺ cells that expressed Arg1 shortly after tumor trafficking, Arg1 expression in MG was delayed and occurred in larger tumors. Interestingly, depletion of MPs in tumors did not prevent MG polarization, suggesting direct influence of tumor-specific factors on MG Arg1 upregulation. Finally, Arg1 expression was confirmed in human GBM samples, but most Arg1⁺ cells were neutrophils and not MPs. These findings confirm variations in tumor MG and MP polarization states and its dependency on tumor microenvironmental factors.

BAI1 Orchestrates Macrophage Inflammatory Response to HSV Infection-Implications for Oncolytic Viral Therapy

Purpose: Brain angiogenesis inhibitor (BAI1) facilitates phagocytosis and bacterial pathogen clearance by macrophages; however, its role in viral infections is unknown. Here, we examined the role of BAI1, and its N-terminal cleavage fragment (Vstat120) in antiviral macrophage responses to oncolytic herpes simplex virus (oHSV).Experimental Design: Changes in infiltration and activation of monocytic and microglial cells after treatment of glioma-bearing mice brains with a control (rHSVQ1) or Vstat120-expressing (RAMBO) oHSV was analyzed using flow cytometry. Co-culture of infected glioma cells with macrophages or microglia was used to examine antiviral signaling. Cytokine array gene expression and Ingenuity Pathway Analysis (IPA) helped evaluate changes in macrophage signaling in response to viral infection. TNFα-blocking antibodies and macrophages derived from Bai1^-/- mice were used.Results: RAMBO treatment of mice reduced recruitment and activation of macrophages/microglia in mice with brain tumors, and showed increased virus replication compared with rHSVQ1. Cytokine gene expression array revealed that RAMBO significantly altered the macrophage inflammatory response to infected glioma cells via altered secretion of TNFα. Furthermore, we showed that BAI1 mediated macrophage TNFα induction in response to oHSV therapy. Intracranial inoculation of wild-type/RAMBO virus in Bai1^-/- or wild-type non-tumor-bearing mice revealed the safety of this approach.Conclusions: We have uncovered a new role for BAI1 in facilitating macrophage anti-viral responses. We show that arming oHSV with antiangiogenic Vstat120 also shields them from inflammatory macrophage antiviral response, without reducing safety. Clin Cancer Res; 23(7); 1809-19. ©2016 AACR.

Increasing the Efficiency of CRISPR/Cas9-mediated Precise Genome Editing of HSV-1 Virus in Human Cells

Genetically modified HSV-1 viruses serve as promising vectors for tumour therapy and vaccine development. The CRISPR/Cas9 system is one of the most powerful tools for precise gene editing of the genomes of organisms. However, whether the CRISPR/Cas9 system can precisely and efficiently make gene replacements in the genome of HSV-1 remains essentially unknown. Here, we reported CRISPR/Cas9-mediated editing of the HSV-1 genome in human cells, including the knockout and replacement of large genes. In established cells stably expressing CRISPR/Cas9, gRNA in coordination with Cas9 could direct a precise cleavage within a pre-defined target region, and foreign genes were successfully used to replace the target gene seamlessly by HDR-mediated gene replacement. Introducing the NHEJ inhibitor SCR7 to the CRISPR/Cas9 system greatly facilitated HDR-mediated gene replacement in the HSV-1 genome. We provided the first genetic evidence that two copies of the ICP0 gene in different locations on the same HSV-1 genome could be simultaneously modified with high efficiency and with no off-target modifications. We also developed a revolutionized isolation platform for desired recombinant viruses using single-cell sorting. Together, our work provides a significantly improved method for targeted editing of DNA viruses, which will facilitate the development of anti-cancer oncolytic viruses and vaccines.

Oncolytic viruses-immunotherapeutics on the rise

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

Metronomic Doses of Temozolomide Enhance the Efficacy of Carbon Nanotube CpG Immunotherapy in an Invasive Glioma Model

Even when treated with aggressive current therapies, most patients with glioblastoma survive less than two years. Rapid tumor growth, an invasive nature, and the blood-brain barrier, which limits the penetration of large molecules into the brain, all contribute to the poor tumor response associated with conventional therapies. Immunotherapy has emerged as a therapeutic approach that may overcome these challenges. We recently reported that single-walled carbon nanotubes (SWCNTs) can be used to dramatically increase the immunotherapeutic efficacy of CpG oligonucleotides in a mouse model of glioma. Following implantation in the mouse brain, the tumor cell line used in these previous studies (GL261) tends to form a spherical tumor with limited invasion into healthy brain. In order to evaluate SWCNT/CpG therapy under more clinically-relevant conditions, here we report the treatment of a more invasive mouse glioma model (K-Luc) that better recapitulates human disease. In addition, a CpG sequence previously tested in humans was used to formulate the SWCNT/CpG which was combined with temozolomide, the standard of care chemotherapy for glioblastoma patients. We found that, following two intracranial administrations, SWCNT/CpG is well-tolerated and improves the survival of mice bearing invasive gliomas. Interestingly, the efficacy of SWCNT/CpG was enhanced when combined with temozolomide. This enhanced anti-tumor efficacy was correlated to an increase of tumor-specific cytotoxic activity in splenocytes. These results reinforce the emerging understanding that immunotherapy can be enhanced by combining it with chemotherapy and support the continued development of SWCNT/CpG.

Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

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.

ATN-224 enhances antitumor efficacy of oncolytic herpes virus against both local and metastatic head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most frequent cancer worldwide, and the 5-year survival rates are among the worst of the major cancers. Oncolytic herpes simplex viruses (oHSV) have the potential to make a significant impact in the targeted treatment of these patients. Here, we tested antitumor efficacy of RAMBO, an oHSV armed with the antiangiogenic Vstat120, alone and in conjunction with ATN-224, a copper chelator against HNSCC in vitro and in vivo animal models. We found that all tested HNSCC cells responded well to virus treatment and were sensitive to RAMBO-mediated oncolytic destruction. In vivo, RAMBO had a significant antiangiogenic and antitumorigenic effect. Physiologic levels of copper inhibited viral replication and HNSCC cell killing. Chelation of copper using ATN-224 treatment significantly improved serum stability of RAMBO and permitted systemic delivery in HNSCC tumor xenografts models. Furthermore, our results show that the combination of ATN-224 and RAMBO strongly inhibits lung metastases in a mouse model of HNSCC. These findings suggest that combining ATN-224 with RAMBO has potential for clinical trials in both early and advanced HNSCC patients.

Arming oncolytic viruses to leverage antitumor immunity

INTRODUCTION

Over the past decade, the cytolytic capabilities of oncolytic viruses (OVs), exploited to selectively eliminate neoplastic cells, have become secondary to their use to elicit a tumor-directed immune response.

AREAS COVERED

Here, based on an NCBI-PubMed literature survey, we review the efforts undertaken to arm OVs in order to improve therapeutic antitumor responses upon administration of these agents. Specifically, we explore the different options to modulate immune suppression in the tumor microenvironment (TME) and to facilitate the generation of effective antitumor responses that have been investigated in conjunction with OVs in recent years.

EXPERT OPINION

Their induction of immunogenic tumor cell death and association with pro-inflammatory signals make OVs attractive immunotherapeutic modalities. The first promising clinical results with immunologically armed OVs warrant their further optimization and development. OVs should be modified to avoid detrimental effects of pre-existent anti-OV immunity as well as for increased tumor targeting and selectivity, so as to ultimately allow for systemic administration while achieving local immune potentiation and tumor elimination in the TME. In particular, a combination of trans-genes encoding bispecific T-cell engagers, immune checkpoint blockers and antigen-presenting cell enhancers will remove suppressive hurdles in the TME and allow for optimal antitumor efficacy of armed OVs.

Combinatorial strategies for oncolytic herpes simplex virus therapy of brain tumors

Oncolytic viruses, such as the oncolytic herpes simplex virus (oHSV), are an exciting new therapeutic strategy for cancer as they are replication competent in tumor cells but not normal cells. In order to engender herpes simplex virus with oncolytic activity and make it safe for clinical application, mutations are engineered into the virus. Glioblastoma multiforme (GBM) is the most common and deadly primary brain tumor in adults. Despite many advances in therapy, overall survival has not been substantially improved over the last several decades. A number of different oHSVs have been tested as monotherapy in early-phase clinical trials for GBM and have demonstrated safety and anecdotal evidence of efficacy. However, strategies to improve efficacy are likely to be necessary to successfully treat GBM. Cancer treatment usually involves multimodal approaches, so the standard of care for GBM includes surgery, radiotherapy and chemotherapy. In preclinical GBM models, combinations of oHSV with other types of therapy have exhibited markedly improved activity over individual treatments alone. In this review, we will discuss the various combination strategies that have been employed with oHSV, including chemotherapy, small-molecule inhibitors, antiangiogenic agents, radiotherapy and expression of therapeutic transgenes. Effective combinations, especially synergistic ones, are clinically important not just for improved efficacy but also to permit lower and less-toxic doses and potentially overcome resistance.

The ex vivo purge of cancer cells using oncolytic viruses: recent advances and clinical implications

Hematological malignancies are treated with intensive high-dose chemotherapy, with or without radiation. This is followed by hematopoietic stem cell (HSC) transplantation (HSCT) to rescue or reconstitute hematopoiesis damaged by the anticancer therapy. Autologous HSC grafts may contain cancer cells and purging could further improve treatment outcomes. Similarly, allogeneic HSCT may be improved by selectively purging alloreactive effector cells from the graft rather than wholesale immune cell depletion. Viral agents that selectively replicate in specific cell populations are being studied in experimental models of cancer and immunological diseases and have potential applications in the context of HSC graft engineering. This review describes preclinical studies involving oncolytic virus strains of adenovirus, herpes simplex virus type 1, myxoma virus, and reovirus as ex vivo purging agents for HSC grafts, as well as in vitro and in vivo experimental studies using oncolytic coxsackievirus, measles virus, parvovirus, vaccinia virus, and vesicular stomatitis virus to eradicate hematopoietic malignancies. Alternative ex vivo oncolytic virus strategies are also outlined that aim to reduce the risk of relapse following autologous HSCT and mitigate morbidity and mortality due to graft-versus-host disease in allogeneic HSCT.

RAGE expression in tumor-associated macrophages promotes angiogenesis in glioma

Interaction of RAGE (the receptor for advanced glycation endproducts) with its ligands can promote tumor progression, invasion, and angiogenesis. Although blocking RAGE signaling has been proposed as a potential anticancer strategy, functional contributions of RAGE expression in the tumor microenvironment (TME) have not been investigated in detail. Here, we evaluated the effect of genetic depletion of RAGE in TME on the growth of gliomas. In both invasive and noninvasive glioma models, animal survival was prolonged in RAGE knockout (Ager(-/-)) mice. However, the improvement in survival in Ager(-/-) mice was not due to changes in tumor growth rate but rather to a reduction in tumor-associated inflammation. Furthermore, RAGE ablation in the TME abrogated angiogenesis by downregulating the expression of proangiogenic factors, which prevented normal vessel formation, thereby generating a leaky vasculature. These alterations were most prominent in noninvasive gliomas, in which the expression of VEGF and proinflammatory cytokines were also lower in tumor-associated macrophages (TAM) in Ager(-/-) mice. Interestingly, reconstitution of Ager(-/-) TAM with wild-type microglia or macrophages normalized tumor vascularity. Our results establish that RAGE signaling in glioma-associated microglia and TAM drives angiogenesis, underscoring the complex role of RAGE and its ligands in gliomagenesis.

Doxorubicin synergizes with 34.5ENVE to enhance antitumor efficacy against metastatic ovarian cancer

PURPOSE

Novel therapeutic regimens are needed to improve dismal outcomes associated with late-stage ovarian cancer. Oncolytic viruses are currently being tested in patients with ovarian cancer. Here, we tested the therapeutic efficacy of combining doxorubicin with 34.5ENVE, an oncolytic herpes simplex virus transcriptionally driven by a modified stem cell-specific nestin promoter, and encoding for antiangiogenic Vasculostatin-120 (VStat120) for use against progressive ovarian cancer.

EXPERIMENTAL DESIGN

Antitumor efficacy of 34.5ENVE was assessed in ovarian cancer cell lines, mouse ascites-derived tumor cells, and primary patient ascites-derived tumor cells by standard MTT assay. The ability of conditioned medium derived from 34.5ENVE-infected ovarian cancer cells to inhibit endothelial cell migration was measured by a Transwell chamber assay. Scope of cytotoxic interactions between 34.5ENVE and doxorubicin were evaluated using Chou-Talalay synergy analysis. Viral replication, herpes simplex virus receptor expression, and apoptosis were evaluated. Efficacy of oncolytic viral therapy in combination with doxorubicin was evaluated in vivo in the murine xenograft model of human ovarian cancer.

RESULTS

Treatment with 34.5ENVE reduced cell viability of ovarian cancer cell lines, and mouse ascites-derived and patient ascites-derived ovarian tumor cells. Conditioned media from tumor cells infected with 34.5ENVE reduced endothelial cell migration. When combined with doxorubicin, 34.5ENVE killed synergistically with a significant increase in caspase-3/7 activation, and an increase in sub-G1 population of cells. The combination of doxorubicin and 34.5ENVE significantly prolonged survival in nude mice bearing intraperitoneal ovarian cancer tumors.

CONCLUSIONS

This study indicates significant antitumor efficacy of 34.5ENVE alone, and in combination with doxorubicin against disseminated peritoneal ovarian cancer.

Going viral with cancer immunotherapy

Recent clinical data have emphatically shown the capacity of our immune systems to eradicate even advanced cancers. Although oncolytic viruses (OVs) were originally designed to function as tumour-lysing therapeutics, they have now been clinically shown to initiate systemic antitumour immune responses. Cell signalling pathways that are activated and promote the growth of tumour cells also favour the growth and replication of viruses within the cancer. The ability to engineer OVs that express immune-stimulating 'cargo', the induction of immunogenic tumour cell death by OVs and the selective targeting of OVs to tumour beds suggests that they are the ideal reagents to enhance antitumour immune responses. Coupling of OV therapy with tumour antigen vaccination, immune checkpoint inhibitors and adoptive cell therapy seems to be ready to converge towards a new generation of multimodal therapeutics to improve outcomes for cancer patients.

Role of cysteine-rich 61 protein (CCN1) in macrophage-mediated oncolytic herpes simplex virus clearance

Glioblastoma is a devastating disease, and there is an urgent need to develop novel therapies, such as oncolytic HSV1 (OV) to effectively target tumor cells. OV therapy depends on tumor-specific replication leading to destruction of neoplastic tissues. Host responses that curtail virus replication limit its efficacy in vivo. We have previously shown that cysteine-rich 61 protein (CCN1) activates a type 1 IFN antiviral defense response in glioblastoma cells. Incorporating TCGA data, we found CCN1 expression to be a negative prognostic factor for glioblastoma patients. Based on this, we used neutralizing antibodies against CCN1 to investigate its effect on OV therapy. Use of an anti-CCN1 antibody in mice bearing glioblastomas treated with OV led to enhanced virus expression along with reduced immune cell infiltration. OV-induced CCN1 increases macrophage migration toward infected glioblastoma cells by directly binding macrophages and also by enhancing the proinflammatory activation of macrophages inducing MCP-1 expression in glioblastoma cells. Activation of macrophages by CCN1 also increases viral clearance. Neutralization of integrin αMβ2 reversed CCN1-induced macrophage activation and migration, and reduced MCP-1 expression by glioblastoma cells. Our findings reveal that CCN1 plays a novel role in pathogen clearance; increasing macrophage infiltration and activation resulting in increased virus clearance in tumors.

Glioblastoma multiforme: State of the art and future therapeutics

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

The potential application of a transcriptionally regulated oncolytic herpes simplex virus for human cancer therapy

BACKGROUND

Emerging studies have shown the potential benefit of arming oncolytic viruses with therapeutic genes. However, most of these therapeutic genes are placed under the regulation of ubiquitous viral promoters. Our goal is to generate a safer yet potent oncolytic herpes simplex virus type-1 (HSV-1) for cancer therapy.

METHODS

Using bacterial artificial chromosome (BAC) recombineering, a cell cycle-regulatable luciferase transgene cassette was replaced with the infected cell protein 6 (ICP6) coding region (encoded for UL39 or large subunit of ribonucleotide reductase) of the HSV-1 genome. These recombinant viruses, YE-PC8, were further tested for its proliferation-dependent luciferase gene expression.

RESULTS

The ability of YE-PC8 to confer proliferation-dependent transgene expression was demonstrated by injecting similar amount of viruses into the tumour-bearing region of the brain and the contralateral normal brain parenchyma of the same mouse. The results showed enhanced levels of luciferase activities in the tumour region but not in the normal brain parenchyma. Similar findings were observed in YE-PC8-infected short-term human brain patient-derived glioma cells compared with normal human astrocytes. intratumoural injection of YE-PC8 viruses resulted in 77% and 80% of tumour regression in human glioma and human hepatocellular carcinoma xenografts, respectively.

CONCLUSION

YE-PC8 viruses confer tumour selectivity in proliferating cells and may be developed further as a feasible approach to treat human cancers.

Cytomegalovirus contributes to glioblastoma in the context of tumor suppressor mutations

To study the controversial role of cytomegalovirus (CMV) in glioblastoma, we assessed the effects of murine CMV (MCMV) perinatal infection in a GFAP-cre; Nf1(loxP/+); Trp53(-/+) genetic mouse model of glioma (Mut3 mice). Early on after infection, MCMV antigen was predominantly localized in CD45+ lymphocytes in the brain with active viral replication and local areas of inflammation, but, by 7 weeks, there was a generalized loss of MCMV in brain, confirmed by bioluminescent imaging. MCMV-infected Mut3 mice exhibited a shorter survival time from their gliomas than control Mut3 mice perinatally infected with mock or with a different neurotropic virus. Animal survival was also significantly shortened when orthotopic gliomas were implanted in mice perinatally infected with MCMV versus controls. MCMV infection increased phosphorylated STAT3 (p-STAT3) levels in neural stem cells (NSC) harvested from Mut3 mice subventricular zone, and, in vivo, there was increased p-STAT3 in NSCs in MCMV-infected compared with control mice. Of relevance, human CMV (HCMV) also increased p-STAT3 and proliferation of patient-derived glioblastoma neurospheres, whereas a STAT3 inhibitor reversed this effect in vitro and in vivo. These findings thus associate CMV infection to a STAT3-dependent modulatory role in glioma formation/progression in the context of tumor suppressor mutations in mice and possibly in humans.

Modification of HSV-1 to an oncolytic virus

Cancer-permissive viruses or oncolytic viruses consist of either genetically engineered or naturally occurring strains that possess relatively selective replicative and/or infection abilities for cancer vs. normal cells (Chiocca, Nat Rev Cancer 2: 938-950, 2002). They can also be armed with additional anticancer cDNAs (e.g., cytokines, prodrug-activating, anti-angiogenesis genes, and others) to extend therapeutic effects (Kaur et al., Curr Gene Ther 9: 341-355, 2009). Herpes simplex virus type 1 (HSV-1) possesses several advantages as an oncolytic virus such as a rapid lytic cycle and a large capacity for insertion of heterologous DNA sequences (Wade-Martins et al., Nat Biotechnol, 19: 1067-1070, 2001). However, the technical nuances of genetic manipulation of the HSV-1 genome may still be relatively challenging. Here, we describe a system that has been durable and consistent in providing the ability to generate multiple recombinant HSV-1. The HsvQuik technology utilizes an HSV-1 genome cloned in a bacterial artificial chromosome to recombine heterologous cDNAs in a relatively rapid and reliable manner (Terada et al., Gene Ther 13: 705-714, 2006).