Combination of oncolytic herpes simplex viruses armed with angiostatin and IL-12 enhances antitumor efficacy in human glioblastoma models

Interleukin-12 Delivery Strategies and Advances in Tumor Immunotherapy

Interleukin-12 (IL-12) is considered to be a promising cytokine for enhancing an antitumor immune response; however, recombinant IL-12 has shown significant toxicity and limited efficacy in early clinical trials. Recently, many strategies for delivering IL-12 to tumor tissues have been developed, such as modifying IL-12, utilizing viral vectors, non-viral vectors, and cellular vectors. Previous studies have found that the fusion of IL-12 with extracellular matrix proteins, collagen, and immune factors is a way to enhance its therapeutic potential. In addition, studies have demonstrated that viral vectors are a good platform, and a variety of viruses such as oncolytic viruses, adenoviruses, and poxviruses have been used to deliver IL-12-with testing previously conducted in various cancer models. The local expression of IL-12 in tumors based on viral delivery avoids systemic toxicity while inducing effective antitumor immunity and acting synergistically with other therapies without compromising safety. In addition, lipid nanoparticles are currently considered to be the most mature drug delivery system. Moreover, cells are also considered to be drug carriers because they can effectively deliver therapeutic substances to tumors. In this article, we will systematically discuss the anti-tumor effects of IL-12 on its own or in combination with other therapies based on different delivery strategies.

Interleukin-12 in multimodal tumor therapies for induction of anti-tumor immunity

Interleukin-12 (IL-12) can be used as an immunomodulator in cancer immunotherapy. And it has demonstrated enormous potential in inhibiting tumor growth and improving the tumor microenvironment (TME) by several preclinical models. However, some disappointing results have showed in the early clinical trials when IL-12 used as a single agent for systemic cancer therapy. Combination therapy is an effective way to significantly fulfill the great potential of IL-12 as an immunomodulator. Here, we discuss the effects of IL-12 combined with traditional methods (chemotherapy, radiotherapy and surgery), targeted therapy or immunotherapy in the preclinical and clinical studies. Moreover, we summarized the potential mechanism underlying the anti-tumor effect of IL-12 in the combination strategies. And we also discussed the delivery methods and tumor-targeted modification of IL-12 and outlines future prospects for IL-12 as an immunomodulator.

Nanosphere pharmacodynamics improves safety of immunostimulatory cytokine therapy

Systemic administration of interleukin (IL)-12 induces potent anti-tumor immune responses in preclinical cancer models through the systemic activation of effector immune cells and release of proinflammatory cytokines. IL-12-loaded PLGA nanospheres (IL12ns) are hypothesized to improve therapeutic efficacy and thwart unwanted side effects observed in previous human clinical trials. Through the investigation of peripheral blood and local tissue immune responses in healthy BALB/c mice, the immune-protective pharmacodynamics of IL12ns were suggested. Nanospheres increased pro-inflammatory plasma cytokines/chemokines (IFN-γ, IL-6, TNF-α, and CXCL10) without inducing maladaptive transcriptomic signatures in circulating peripheral immune cells. Gene expression profiling revealed activation of pro-inflammatory signaling pathways in systemic tissues, the likely source of these effector cytokines. These data support that nanosphere pharmacodynamics, including shielding IL-12 from circulating immune cells, depositing peripherally in systemic immune tissues, and then slowly eluting bioactive cytokine, thereafter, are essential to safe immunostimulatory therapy.

Oncolytic herpes simplex viruses for the treatment of glioma and targeting glioblastoma stem-like cells

Glioblastoma (GBM) is one of the most lethal cancers, having a poor prognosis and a median survival of only about 15 months with standard treatment (surgery, radiation, and chemotherapy), which has not been significantly extended in decades. GBM demonstrates remarkable cellular heterogeneity, with glioblastoma stem-like cells (GSCs) at the apex. GSCs are a subpopulation of GBM cells that possess the ability to self-renew, differentiate, initiate tumor formation, and manipulate the tumor microenvironment (TME). GSCs are no longer considered a static population of cells with specific markers but are quite flexible phenotypically and in driving tumor heterogeneity and therapeutic resistance. In light of these features, they are a critical target for successful GBM therapy. Oncolytic viruses, in particular oncolytic herpes simplex viruses (oHSVs), have many attributes for therapy and are promising agents to target GSCs. oHSVs are genetically-engineered to selectively replicate in and kill cancer cells, including GSCs, but not normal cells. Moreover, oHSV can induce anti-tumor immune responses and synergize with other therapies, such as chemotherapy, DNA repair inhibitors, and immune checkpoint inhibitors, to potentiate treatment effects and reduce GSC populations that are partly responsible for chemo- and radio-resistance. Herein, we present an overview of GSCs, activity of different oHSVs, clinical trial results, and combination strategies to enhance efficacy, including therapeutic arming of oHSV. Throughout, the therapeutic focus will be on GSCs and studies specifically targeting these cells. Recent clinical trials and approval of oHSV G47Δ in Japan for patients with recurrent glioma demonstrate the efficacy and promise of oHSV therapy.

Fusion peptide is superior to co-expressing subunits for arming oncolytic herpes virus with interleukin 12

BACKGROUND

G47∆ is a triple-mutated oncolytic herpes simplex virus type 1 (HSV-1) recently approved as a new drug for malignant glioma in Japan. As the next-generation, we develop armed oncolytic HSV-1 using G47∆ as the backbone. Because oncolytic HSV-1 elicits specific antitumor immunity, interleukin 12 (IL-12) can function as an effective payload to enhance the efficacy.

METHODS

We evaluate the optimal methods for expressing IL-12 as a payload for G47∆-based oncolytic HSV-1. Two new armed viruses are generated for evaluation by employing different methods to express IL-12: T-mfIL12 expresses murine IL-12 as a fusion peptide, with the genes of two subunits (p35 and p40) linked by bovine elastin motifs, and T-mIL12-IRES co-expresses the subunits, with the two genes separated by an internal ribosome entry site (IRES) sequence.

RESULTS

T-mfIL12 is significantly more efficient in producing IL-12 than T-mIL12-IRES in all cell lines tested, whereas the expression methods do not affect the replication capabilities and cytopathic effects. In two syngeneic mouse subcutaneous tumor models of Neuro2a and TRAMP-C2, T-mfIL12 exhibits a significantly higher efficacy than T-mIL12-IRES when inoculated intratumorally. Furthermore, T-mfIL12 shows a significantly higher intratumoral expression of functional IL-12, causing stronger stimulation of specific antitumor immune responses than T-mIL12-IRES.

CONCLUSIONS

The results implicate that a fusion-type expression of IL-12 is a method superior to co-expression of separate subunits, due to higher production of functional IL-12 molecules. This study led to the creation of triple-mutated oncolytic HSV-1 armed with human IL-12 currently used in phase 1/2 trial for malignant melanoma.

Cross-talk between cancer stem cells and immune cells: potential therapeutic targets in the tumor immune microenvironment

Ongoing research has revealed that the existence of cancer stem cells (CSCs) is one of the biggest obstacles in the current cancer therapy. CSCs make an influential function in tumor progression, recurrence and chemoresistance due to their typical stemness characteristics. CSCs are preferentially distributed in niches, and those niche sites exhibit characteristics typical of the tumor microenvironment (TME). The complex interactions between CSCs and TME illustrate these synergistic effects. The phenotypic heterogeneity within CSCs and the spatial interactions with the surrounding tumor microenvironment led to increased therapeutic challenges. CSCs interact with immune cells to protect themselves against immune clearance by exploiting the immunosuppressive function of multiple immune checkpoint molecules. CSCs also can protect themselves against immune surveillance by excreting extracellular vesicles (EVs), growth factors, metabolites and cytokines into the TME, thereby modulating the composition of the TME. Therefore, these interactions are also being considered for the therapeutic development of anti-tumor agents. We discuss here the immune molecular mechanisms of CSCs and comprehensively review the interplay between CSCs and the immune system. Thus, studies on this topic seem to provide novel ideas for reinvigorating therapeutic approaches to cancer.

Exploring the Past, Present, and Future of Anti-Angiogenic Therapy in Glioblastoma

Glioblastoma, a WHO grade IV astrocytoma, constitutes approximately half of malignant tumors of the central nervous system. Despite technological advancements and aggressive multimodal treatment, prognosis remains dismal. The highly vascularized nature of glioblastoma enables the tumor cells to grow and invade the surrounding tissue, and vascular endothelial growth factor-A (VEGF-A) is a critical mediator of this process. Therefore, over the past decade, angiogenesis, and more specifically, the VEGF signaling pathway, has emerged as a therapeutic target for glioblastoma therapy. This led to the FDA approval of bevacizumab, a monoclonal antibody designed against VEGF-A, for treatment of recurrent glioblastoma. Despite the promising preclinical data and its theoretical effectiveness, bevacizumab has failed to improve patients' overall survival. Furthermore, several other anti-angiogenic agents that target the VEGF signaling pathway have also not demonstrated survival improvement. This suggests the presence of other compensatory angiogenic signaling pathways that surpass the anti-angiogenic effects of these agents and facilitate vascularization despite ongoing VEGF signaling inhibition. Herein, we review the current state of anti-angiogenic agents, discuss potential mechanisms of anti-angiogenic resistance, and suggest potential avenues to increase the efficacy of this therapeutic approach.

Glioblastoma microenvironment and its reprogramming by oncolytic virotherapy

Glioblastoma (GBM), a highly aggressive form of brain tumor, responds poorly to current conventional therapies, including surgery, radiation therapy, and systemic chemotherapy. The reason is that the delicate location of the primary tumor and the existence of the blood-brain barrier limit the effectiveness of traditional local and systemic therapies. The immunosuppressive status and multiple carcinogenic pathways in the complex GBM microenvironment also pose challenges for immunotherapy and single-targeted therapy. With an improving understanding of the GBM microenvironment, it has become possible to consider the immunosuppressive and highly angiogenic GBM microenvironment as an excellent opportunity to improve the existing therapeutic efficacy. Oncolytic virus therapy can exert antitumor effects on various components of the GBM microenvironment. In this review, we have focused on the current status of oncolytic virus therapy for GBM and the related literature on antitumor mechanisms. Moreover, the limitations of oncolytic virus therapy as a monotherapy and future directions that may enhance the field have also been discussed.

Teserpaturev/G47Δ: First Approval

Teserpaturev/G47Δ (Delytact^®) is a third-generation (triple-mutated) recombinant oncolytic herpes simplex virus type 1 being developed by Daiichi Sankyo Co., Ltd. for the treatment of certain solid cancers. Teserpaturev/G47Δ has been approved for the treatment of malignant glioma in Japan and is currently in clinical development for the treatment of prostate cancer (phase II), malignant pleural mesothelioma (phase I) and recurrent olfactory neuroblastoma (phase I). This article summarizes the milestones in the development of teserpaturev/G47Δ leading to this first approval for the treatment of malignant glioma.

Immunology Meets Bioengineering: Improving the Effectiveness of Glioblastoma Immunotherapy

Glioblastoma (GBM) therapy has seen little change over the past two decades. Surgical excision followed by radiation and chemotherapy is the current gold standard treatment. Immunotherapy techniques have recently transformed many cancer treatments, and GBM is now at the forefront of immunotherapy research. GBM immunotherapy prospects are reviewed here, with an emphasis on immune checkpoint inhibitors and oncolytic viruses. Various forms of nanomaterials to enhance immunotherapy effectiveness are also discussed. For GBM treatment and immunotherapy, we outline the specific properties of nanomaterials. In addition, we provide a short overview of several 3D (bio)printing techniques and their applications in stimulating the GBM microenvironment. Lastly, the susceptibility of GBM cancer cells to the various immunotherapy methods will be addressed.

Engineering interferons and interleukins for cancer immunotherapy

Cytokines are a class of potent immunoregulatory proteins that are secreted in response to various stimuli and act locally to regulate many aspects of human physiology and disease. Cytokines play important roles in cancer initiation, progression, and elimination, and thus, there is a long clinical history associated with the use of recombinant cytokines to treat cancer. However, the use of cytokines as therapeutics has been limited by cytokine pleiotropy, complex biology, poor drug-like properties, and severe dose-limiting toxicities. Nevertheless, cytokines are crucial mediators of innate and adaptive antitumor immunity and have the potential to enhance immunotherapeutic approaches to treat cancer. Development of immune checkpoint inhibitors and combination immunotherapies has reinvigorated interest in cytokines as therapeutics, and a variety of engineering approaches are emerging to improve the safety and effectiveness of cytokine immunotherapy. In this review we highlight recent advances in cytokine biology and engineering for cancer immunotherapy.

The War Is on: The Immune System against Glioblastoma—How Can NK Cells Drive This Battle?

Natural killer (NK) cells are innate lymphocytes that play an important role in immunosurveillance, acting alongside other immune cells in the response against various types of malignant tumors and the prevention of metastasis. Since their discovery in the 1970s, they have been thoroughly studied for their capacity to kill neoplastic cells without the need for previous sensitization, executing rapid and robust cytotoxic activity, but also helper functions. In agreement with this, NK cells are being exploited in many ways to treat cancer. The broad arsenal of NK-based therapies includes adoptive transfer of in vitro expanded and activated cells, genetically engineered cells to contain chimeric antigen receptors (CAR-NKs), in vivo stimulation of NK cells (by cytokine therapy, checkpoint blockade therapies, etc.), and tumor-specific antibody-guided NK cells, among others. In this article, we review pivotal aspects of NK cells’ biology and their contribution to immune responses against tumors, as well as providing a wide perspective on the many antineoplastic strategies using NK cells. Finally, we also discuss those approaches that have the potential to control glioblastoma—a disease that, currently, causes inevitable death, usually in a short time after diagnosis.

Oncolytic Viruses for Malignant Glioma: On the Verge of Success?

Glioblastoma is one of the most difficult tumor types to treat with conventional therapy options like tumor debulking and chemo- and radiotherapy. Immunotherapeutic agents like oncolytic viruses, immune checkpoint inhibitors, and chimeric antigen receptor T cells have revolutionized cancer therapy, but their success in glioblastoma remains limited and further optimization of immunotherapies is needed. Several oncolytic viruses have demonstrated the ability to infect tumors and trigger anti-tumor immune responses in malignant glioma patients. Leading the pack, oncolytic herpesvirus, first in its class, awaits an approval for treating malignant glioma from MHLW, the federal authority of Japan. Nevertheless, some major hurdles like the blood–brain barrier, the immunosuppressive tumor microenvironment, and tumor heterogeneity can engender suboptimal efficacy in malignant glioma. In this review, we discuss the current status of malignant glioma therapies with a focus on oncolytic viruses in clinical trials. Furthermore, we discuss the obstacles faced by oncolytic viruses in malignant glioma patients and strategies that are being used to overcome these limitations to (1) optimize delivery of oncolytic viruses beyond the blood–brain barrier; (2) trigger inflammatory immune responses in and around tumors; and (3) use multimodal therapies in combination to tackle tumor heterogeneity, with an end goal of optimizing the therapeutic outcome of oncolytic virotherapy.

Multiple strategies to improve the therapeutic efficacy of oncolytic herpes simplex virus in the treatment of glioblastoma

Oncolytic viruses have attracted widespread attention as biological anticancer agents that can selectively kill tumor cells without affecting normal cells. Although progress has been made in therapeutic strategies, the prognosis of patients with glioblastoma (GBM) remains poor and no ideal treatment approach has been developed. Recently, oncolytic herpes simplex virus (oHSV) has been considered a promising novel treatment approach for GBM. However, the therapeutic efficacy of oHSV in GBM, with its intricate pathophysiology, remains unsatisfactory due to several obstacles, such as limited replication and attenuated potency of oHSV owing to deletions or mutations in virulence genes, and ineffective delivery of the therapeutic virus. Multiple strategies have attempted to identify the optimal strategy for the successful clinical application of oHSV. Several preclinical trials have demonstrated that engineering novel oHSVs, developing combination therapies and improving methods for delivering oHSV to tumor cells seem to hold promise for improving the efficacy of this virotherapy.

The Current State of Oncolytic Herpes Simplex Virus for Glioblastoma Treatment

Glioblastoma (GBM) is a lethal primary malignant brain tumor with no current effective treatments. The recent emergence of immuno-virotherapy and FDA approval of T-VEC have generated a great expectation towards oncolytic herpes simplex viruses (oHSVs) as a promising treatment option for GBM. Since the generation and testing of the first genetically engineered oHSV in glioma in the early 1990s, oHSV-based therapies have shown a long way of great progress in terms of anti-GBM efficacy and safety, both preclinically and clinically. Here, we revisit the literature to understand the recent advancement of oHSV in the treatment of GBM. In addition, we discuss current obstacles to oHSV-based therapies and possible strategies to overcome these pitfalls.

Immunovirotherapy for the treatment of glioblastoma

We have recently described a new murine model of glioblastoma, generated by the implantation of syngeneic glioblastoma stem cells into immunocompetent mice, that recapitulates the salient histopathological and immunological features of the human disease. We employed this model to demonstrate the multifaceted activity of an oncolytic herpes simplex virus genetically modified to express interleukin-12, G47∆-IL12.

Revisiting gene delivery to the brain: silencing and editing

Neurodegenerative disorders, ischemic brain diseases, and brain tumors are debilitating diseases that severely impact a person's life and could possibly lead to their demise if left untreated. Many of these diseases do not respond to small molecule therapeutics and have no effective long-term therapy. Gene therapy offers the promise of treatment or even a cure for both genetic and acquired brain diseases, mediated by either silencing or editing disease-specific genes. Indeed, in the last 5 years, significant progress has been made in the delivery of non-coding RNAs as well as gene-editing formulations to the brain. Unfortunately, the delivery is a major limiting factor for the success of gene therapies. Both viral and non-viral vectors have been used to deliver genetic information into a target cell, but they have limitations. Viral vectors provide excellent transduction efficiency but are associated with toxic effects and have limited packaging capacity; however, non-viral vectors are less toxic and show a high packaging capacity at the price of low transfection efficiency. Herein, we review the progress made in the field of brain gene therapy, particularly in the design of non-toxic and trackable non-viral vectors, capable of controlled release of genes in response to internal/external triggers, and in the delivery of formulations for gene editing. The application of these systems in the context of various brain diseases in pre-clinical and clinical tests will be discussed. Such promising approaches could potentially pave the way for clinical realization of brain gene therapies.

Cytokines in oncolytic virotherapy

Tumors represent a hostile environment for the effector cells of cancer immunosurveillance. Immunosuppressive receptors and soluble or membrane-bound ligands are abundantly exposed and released by malignant entities and their stromal accomplices. As a consequence, executioners of antitumor immunity inefficiently navigate across cancer tissues and fail to eliminate malignant targets. By inducing immunogenic cancer cell death, oncolytic viruses profoundly reshape the tumor microenvironment. They trigger the local spread of danger signals and tumor-associated (as well as viral) antigens, thus attracting antigen-presenting cells, promoting the activation and expansion of lymphocytic populations, facilitating their infiltration in the tumor bed, and reinvigorating cytotoxic immune activity. The present review recapitulates key chemokines, growth factors and other cytokines that orchestrate this ballet of antitumoral leukocytes upon oncolytic virotherapy.

Different T-cell subsets in glioblastoma multiforme and targeted immunotherapy

Glioblastoma multiforme (GBM) is a brain tumor with a high mortality rate. Surgical resection combined with radiotherapy and chemotherapy is the standard treatment for GBM patients, but the 5-year survival rate of patients despite this treatment is low. Immunotherapy has attracted increasing attention in recent years. As the pioneer and the main effector cells of immunotherapy, T cells play a key role in tumor immunotherapy. However, the T cells in GBM microenvironment are inhibited by the highly immunosuppressive environment of GBM, posing huge challenges to T cell-based GBM immunotherapy. This review summarizes the effects of the GBM microenvironment on the infiltration and function of different T-cell subsets and the possible strategies to overcome immunosuppression, and thus enhance the effectiveness of GBM immunotherapy.

The different role of YKL-40 in glioblastoma is a function of MGMT promoter methylation status

Inter- and intratumoral heterogeneity is a hallmark of glioblastoma (GBM) that facilitates recurrence, treatment resistance, and worse prognosis. O⁶-methylguanine-DNA methyltransferase (MGMT) promoter methylation is a significant prognostic marker for Temozolomide (TMZ) resistance in GBM patients. YKL-40 is a molecular marker for the mesenchymal subtype of GBMs and is responsible for TMZ resistance. However, underlying mechanisms by which MGMT epigenetics impacts patient outcomes and the function of YKL-40 are not fully determined. Herein, we performed in vitro and in vivo experiments, six human IDH1/2 wild-type glioblastoma stem-like cells (GSCs) were established and studied to further determine a potential interaction of YKL-40 and MGMT promoter methylation. We demonstrated that YKL-40 functioned differently in human IDH1/2 wild-type GSCs. In MGMT promoter-methylated (MGMT-m) GSCs, it acted as a tumor suppressor gene. On the other hand, in MGMT promoter-unmethylated (MGMT-um) GSCs, it promoted tumorigenesis. Notably, the reason that YKL-40 played different roles in GSCs could not be interpreted by the molecular classification of each GSCs, but is a function of MGMT promoter methylation status and involves the RAS–MEK–ERK pathway. YKL-40 mediated TMZ sensitivity by activating DNA damage responses (DDRs) in MGMT-m GSCs, and it mediated resistance to TMZ by inhibiting DDRs in MGMT-um GSCs. Our report demonstrated that MGMT promoter methylation status might influence a gene’s function in human cancer. Moreover, our data also highlight the point that gene function should be investigated not only according to the molecular tumor classification, but also the epigenetic signature.

Advances and potential pitfalls of oncolytic viruses expressing immunomodulatory transgene therapy for malignant gliomas

Glioblastoma (GBM) is an immunosuppressive, lethal brain tumor. Despite advances in molecular understanding and therapies, the clinical benefits have remained limited, and the life expectancy of patients with GBM has only been extended to ~15 months. Currently, genetically modified oncolytic viruses (OV) that express immunomodulatory transgenes constitute a research hot spot in the field of glioma treatment. An oncolytic virus is designed to selectively target, infect, and replicate in tumor cells while sparing normal tissues. Moreover, many studies have shown therapeutic advantages, and recent clinical trials have demonstrated the safety and efficacy of their usage. However, the therapeutic efficacy of oncolytic viruses alone is limited, while oncolytic viruses expressing immunomodulatory transgenes are more potent inducers of immunity and enhance immune cell-mediated antitumor immune responses in GBM. An increasing number of basic studies on oncolytic viruses encoding immunomodulatory transgene therapy for malignant gliomas have yielded beneficial outcomes. Oncolytic viruses that are armed with immunomodulatory transgenes remain promising as a therapy against malignant gliomas and will undoubtedly provide new insights into possible clinical uses or strategies. In this review, we summarize the research advances related to oncolytic viruses that express immunomodulatory transgenes, as well as potential treatment pitfalls in patients with malignant gliomas.

Oncolytic Virus Encoding a Master Pro-Inflammatory Cytokine Interleukin 12 in Cancer Immunotherapy

Oncolytic viruses (OVs) are genetically modified or naturally occurring viruses, which preferentially replicate in and kill cancer cells while sparing healthy cells, and induce anti-tumor immunity. OV-induced tumor immunity can be enhanced through viral expression of anti-tumor cytokines such as interleukin 12 (IL-12). IL-12 is a potent anti-cancer agent that promotes T-helper 1 (Th1) differentiation, facilitates T-cell-mediated killing of cancer cells, and inhibits tumor angiogenesis. Despite success in preclinical models, systemic IL-12 therapy is associated with significant toxicity in humans. Therefore, to utilize the therapeutic potential of IL-12 in OV-based cancer therapy, 25 different IL-12 expressing OVs (OV-IL12s) have been genetically engineered for local IL-12 production and tested preclinically in various cancer models. Among OV-IL12s, oncolytic herpes simplex virus encoding IL-12 (OHSV-IL12) is the furthest along in the clinic. IL-12 expression locally in the tumors avoids systemic toxicity while inducing an efficient anti-tumor immunity and synergizes with anti-angiogenic drugs or immunomodulators without compromising safety. Despite the rapidly rising interest, there are no current reviews on OV-IL12s that exploit their potential efficacy and safety to translate into human subjects. In this article, we will discuss safety, tumor-specificity, and anti-tumor immune/anti-angiogenic effects of OHSV-IL12 as mono- and combination-therapies. In addition to OHSV-IL12 viruses, we will also review other IL-12-expressing OVs and their application in cancer therapy.

Oncolytic virus therapy in Japan: progress in clinical trials and future perspectives

Oncolytic virus therapy is a promising new option for cancer. It utilizes genetically engineered or naturally occurring viruses that selectively replicate in and kill cancer cells without harming normal cells. T-VEC (talimogene laherparepvec), a second-generation oncolytic herpes simplex virus type 1, was approved by the US Food and Drug Administration for the treatment of inoperable melanoma in 2015 and subsequently approved in Europe in 2016. Other oncolytic viruses using different parental viruses have also been tested in Phase III clinical trials and are ready for drug approval: Pexa-Vec (pexastimogene devacirepvec), an oncolytic vaccinia virus, CG0070, an oncolytic adenovirus, and REOLYSIN (pelareorep), an oncolytic reovirus. In Japan, as of May 2018, several oncolytic viruses have been developed, and some have already proceeded to clinical trials. In this review, we summarize clinical trials assessing oncolytic virus therapy that were conducted or are currently ongoing in Japan, specifically, T-VEC, the abovementioned oncolytic herpes simplex virus type 1, G47Δ, a third-generation oncolytic herpes simplex virus type 1, HF10, a naturally attenuated oncolytic herpes simplex virus type 1, Telomelysin, an oncolytic adenovirus, Surv.m-CRA, another oncolytic adenovirus, and Sendai virus particle. In the near future, oncolytic virus therapy may become an important and major treatment option for cancer in Japan.

Synergistic combination of oncolytic virotherapy with CAR T-cell therapy

For patients with advanced hematological malignancies the therapeutic landscape has been transformed by the emergence of adoptive cell transfer utilizing autologous chimeric antigen receptor (CAR)-redirected T-cells. However, solid tumors have proved far more resistant to this approach. Here, we summarize the numerous challenges faced by CAR T-cells designed to target solid tumors, highlighting, in particular, issues related to impaired trafficking, expansion, and persistence. In parallel, we draw attention to exciting developments in the burgeoning field of oncolytic virotherapy and posit strategies for the synergistic combination of oncolytic viruses with CAR T-cells to improve outcomes for patients with advanced solid tumors.

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.

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.

Immunomodulation of the Tumor Microenvironment: Turn Foe Into Friend

Immunotherapy, where the patient's own immune system is exploited to eliminate tumor cells, has become one of the most prominent new cancer treatment options in the last decade. The main hurdle for classical cancer vaccines is the need to identify tumor- and patient specific antigens to include in the vaccine. Therefore, in situ vaccination represents an alternative and promising approach. This type of immunotherapy involves the direct intratumoral administration of different immunomodulatory agents and uses the tumor itself as the source of antigen. The ultimate aim is to convert an immunodormant tumor microenvironment into an immunostimulatory one, enabling the immune system to eradicate all tumor lesions in the body. In this review we will give an overview of different strategies, which can be exploited for the immunomodulation of the tumor microenvironment and their emerging role in the treatment of cancer patients.

HSV as A Platform for the Generation of Retargeted, Armed, and Reporter-Expressing Oncolytic Viruses

Previously, we engineered oncolytic herpes simplex viruses (o-HSVs) retargeted to the HER2 (epidermal growth factor receptor 2) tumor cell specific receptor by the insertion of a single chain antibody (scFv) to HER2 in gD, gH, or gB. Here, the insertion of scFvs to three additional cancer targets—EGFR (epidermal growth factor receptor), EGFRvIII, and PSMA (prostate specific membrane antigen)—in gD Δ6–38 enabled the generation of specifically retargeted o-HSVs. Viable recombinants resulted from the insertion of an scFv in place of aa 6–38, but not in place of aa 61–218. Hence, only the gD N-terminus accepted all tested scFv inserts. Additionally, the insertion of mIL12 in the US1-US2 intergenic region of the HER2- or EGFRvIII-retargeted o-HSVs, and the further insertion of Gaussia Luciferase, gave rise to viable recombinants capable of secreting the cytokine and the reporter. Lastly, we engineered two known mutations in gB; they increased the ability of an HER2-retargeted recombinant to spread among murine cells. Altogether, current data show that the o-HSV carrying the aa 6–38 deletion in gD serves as a platform for the specific retargeting of o-HSV tropism to a number of human cancer targets, and the retargeted o-HSVs serve as simultaneous vectors for two molecules.

Antitumor effect of the Newcastle disease viral hemagglutinin-neuraminidase gene is expressed through an oncolytic adenovirus effect in osteosarcoma cells

Newcastle disease virus (NDV) can specifically kill cancer cells and has less toxicity to normal cells. The hemagglutinin-neuraminidase (HN) protein is an important structural protein in NDV pathogenesis and has been postulated as a promising candidate for antitumor therapy. The aim of this study was to investigate the anticancer potential of recombinant adenovirus Ad-HN-PEG3p-E1a. An MTS assay was performed to determine viral proliferation after viral infection, the data showed that the proliferation ability of osteosarcoma cells decreased, whereas there was no significant change in normal hepatic cells. DAPI and Annexin V experiments showed that osteosarcoma cells were killed because of apoptosis, active oxygen content, and augmented mitochondrial membrane potential loss. Caspase Activity Assay Kits were used to detect the caspase-3 activities of the treated OS-732 for increased expression. Western blot analysis showed that cytochrome C increased significantly and apoptosis of the virus was confirmed in tumor cells. In-vivo experiments show that NDV has an inhibitory effect on tumor growth. The recombinant adenovirus, which is composed of a HN protein and progressive increment promoter PEG3p, could inhibit the growth of OS-732 and promote the apoptosis of tumor cells. However, there was no clear relationship with normal cell (L02) apoptosis.

Prolonged survival in secondary glioblastoma following local injection of targeted alpha therapy with 213Bi-substance P analogue

Background

Glioblastoma multiforme (GBM), the most common malignant brain tumor, mainly manifests as a primary de novo and less frequently as a secondary glial neoplasm. GBM has been demonstrated to overexpress the NK-1 receptor and substance P can be used as a ligand for targeted therapy. Alpha emitters, e.g. ²¹³Bi, that deposit their high energy within a short range allow the selective irradiation of tumor cells while sparing adjacent neuronal structures.

Material and methods

Among 50 glioma patients of different subtypes that have to date been treated with targeted alpha therapy at the Medical University Warsaw, we report here the data on nine patients with secondary GBM. Following surgery, chemo- and radiotherapy, recurrent GBM was treated by intracavitary injection of 1–6 doses of 0.9–2.3 GBq ²¹³Bi- DOTA-[Thi⁸,Met(O₂)¹¹]-substance P (²¹³Bi-DOTA-SP) in 2-month intervals. ⁶⁸Ga-DOTA-[Thi⁸,Met(O₂)¹¹]-substance P (⁶⁸Ga-DOTA-SP) was co-injected with the therapeutic doses to assess biodistribution using PET/CT. Therapeutic response was monitored with MRI.

Results

Treatment with activities ranging from 1.4 to 9.7 (median 5.8) GBq ²¹³Bi- DOTA-SP was well tolerated with only mild transient adverse reactions, mainly headaches due to a transient perfocal edema reaction. The median progression free survival and overall survival time following the initiation of alpha therapy was 5.8 and 16.4 months, respectively. The median overall survival time from the first diagnosis was 52.3 months. Two out of nine patients are still alive 39 and 51 months, respectively, after the initiation of the therapy.

Conclusions

Targeted alpha therapy of secondary GBM with ²¹³Bi-DOTA-SP is safe and well tolerated and may evolve as a promising novel therapeutic option for secondary GBM.

Combinatorial Effects of VEGFR Kinase Inhibitor Axitinib and Oncolytic Virotherapy in Mouse and Human Glioblastoma Stem-Like Cell Models

Purpose: Glioblastoma (GBM), a fatal brain cancer, contains a subpopulation of GBM stem-like cells (GSCs) that contribute to resistance to current therapy. Angiogenesis also plays a key role in GBM progression. Therefore, we developed a strategy to target the complex GBM microenvironment, including GSCs and tumor vasculature.Experimental Design: We evaluated the cytotoxic effects of VEFGR tyrosine kinase inhibitor (TKI) axitinib in vitro and then tested antitumor efficacy of axitinib in combination with oncolytic herpes simplex virus (oHSV) expressing antiangiogenic cytokine murine IL12 (G47Δ-mIL12) in two orthotopic GSC-derived GBM models: patient-derived recurrent MGG123 GSCs, forming vascular xenografts in immunodeficient mice; and mouse 005 GSCs, forming syngeneic tumors in immunocompetent mice.Results: GSCs form endothelial-like tubes and were sensitive to axitinib. G47Δ-mIL12 significantly improved survival, as did axitinib, while dual combinations further extended survival significantly compared with single therapies alone in both models. In MGG123 tumors, axitinib was effective only at high doses (50 mg/kg), alone and in combination with G47Δ-mIL12, and this was associated with greatly decreased vascularity, increased macrophage infiltration, extensive tumor necrosis, and PDGFR/ERK pathway inhibition. In the mouse 005 model, antiglioma activity, after single and combination therapy, was only observed in immunocompetent mice and not the T-cell-deficient athymic mice. Interestingly, immune checkpoint inhibition did not improve efficacy.Conclusions: Systemic TKI (axitinib) beneficially combines with G47Δ-mIL12 to enhance antitumor efficacy in both immunodeficient and immunocompetent orthotopic GBM models. Our results support further investigation of TKIs in combination with oHSV for GBM treatment. Clin Cancer Res; 24(14); 3409-22. ©2018 AACR.

A novel oncolytic herpes simplex virus armed with the carboxyl-terminus of murine MyD116 has enhanced anti-tumour efficacy against human breast cancer cells

Oncolytic herpes simplex virus-1 (oHSV-1) vectors are promising therapeutic agents for cancer. The deletion of the γ34.5 gene eliminates the neurovirulence but attenuates virus replication at the same time. The carboxyl-terminus of protein phosphatase 1 regulatory subunit 15A (also known as MyD116/GADD34) is homologous to that of γ34.5; hence, it may substitute for γ34.5 to enhance the replication and cytotoxicity of the virus. To investigate whether the C-terminus of MyD116 can enhance the anti-tumour efficacy of G47Δ on human breast cancer cells, a GD116 mutant was constructed by inserting a γ34.5-MyD116 chimaera into the G47Δ genome using a bacterial artificial chromosome and two recombinase systems (Cre/loxP and FLPE/FRT). A GD-empty mutant containing only the cytomegalovirus sequence was also created as a control using the same method. Next, the replication and cytotoxicity of these two virus vectors were evaluated in breast cancer cells. Compared with the GD-empty vector, GD116 possessed an enhanced replication capability and oncolytic activity in MCF-7 and MDA-MB-231 cells. On the fifth day after infection with GD116 at MOIs of 0.01 and 0.1, 49.2 and 82.8% of MCF-7 cells, respectively, were killed, with 35.0 and 50.2% of MDA-MB-231 cells, respectively, killed by GD116 at MOIs of 0.1 and 0.3. Additionally, the insertion of the γ34.5-MyD116 chimaera promoted virus replication in MDA-MB-468 at 48 h after infection, although no increased cytotoxic effect was observed. The findings of the present study indicate that the C terminus of the MyD116 gene can be substituted for the corresponding domain of the γ34.5 gene of oHSV-1 to promote the replication of the virus in infected cells. Furthermore, the novel virus mutant GD116 armed with a γ34.5-MyD116 chimaera has enhanced anti-tumour efficacy against human breast cancer cells in vitro.

Therapeutic targeting of chemoresistant and recurrent glioblastoma stem cells with a proapoptotic variant of oncolytic herpes simplex virus

Temozolomide (TMZ) chemotherapy, in combination with maximal safe resection and radiotherapy, is the current standard of care for patients with glioblastoma (GBM). Despite this multimodal approach, GBM inevitably relapses primarily due to resistance to chemo-radiotherapy, and effective treatment is not available for recurrent disease. In this study we identified TMZ resistant patient-derived primary and previously treated recurrent GBM stem cells (GSC), and investigated the therapeutic activity of a pro-apoptotic variant of oHSV (oHSV-TRAIL) in vitro and in vivo. We show that oHSV-TRAIL modulates cell survival and MAP Kinase proliferation signaling pathways as well as DNA damage response pathways in both primary and recurrent TMZ-resistant GSC. Utilizing real time in vivo imaging and correlative immunohistochemistry, we show that oHSV-TRAIL potently inhibits tumor growth and extends survival of mice bearing TMZ-insensitive recurrent intracerebral GSC tumors via robust and selective induction of apoptosis-mediated death in tumor cells, resulting in cures in 40% of the treated mice. In comparison, the anti-tumor effects in a primary chemoresistant GSC GBM model exhibiting a highly invasive phenotype were significant but less prominent. This work thus demonstrates the ability of oHSV-TRAIL to overcome the therapeutic resistance and recurrence of GBM, and provides a basis for its testing in a GBM clinical trial.

Blockade of transforming growth factor-β signaling enhances oncolytic herpes simplex virus efficacy in patient-derived recurrent glioblastoma models

Despite the current standard of multimodal management, glioblastoma (GBM) inevitably recurs and effective therapy is not available for recurrent disease. A subset of tumor cells with stem-like properties, termed GBM stem-like cells (GSCs), are considered to play a role in tumor relapse. Although oncolytic herpes simplex virus (oHSV) is a promising therapeutic for GBM, its efficacy against recurrent GBM is incompletely characterized. Transforming growth factor beta (TGF-β) plays vital roles in maintaining GSC stemness and GBM pathogenesis. We hypothesized that oHSV and TGF-β inhibitors would synergistically exert antitumor effects for recurrent GBM. Here we established a panel of patient-derived recurrent tumor models from GBMs that relapsed after postsurgical radiation and chemotherapy, based on GSC-enriched tumor sphere cultures. These GSCs are resistant to the standard-of-care temozolomide but susceptible to oHSVs G47Δ and MG18L. Inhibition of TGF-β receptor kinase with selective targeted small molecules reduced clonogenic sphere formation in all tested recurrent GSCs. The combination of oHSV and TGF-βR inhibitor was synergistic in killing recurrent GSCs through, in part, an inhibitor-induced JNK-MAPK blockade and increase in oHSV replication. In vivo, systemic treatment with TGF-βR inhibitor greatly enhanced the antitumor effects of single intratumoral oHSV injections, resulting in cures in 60% of mice bearing orthotopic recurrent GBM. These results reveal a novel synergistic interaction of oHSV therapy and TGF-β signaling blockade, and warrant further investigations aimed at clinical translation of this combination strategy for GBM patients.

Evaluation of JC and Cytomegalo Viruses in Glioblastoma Tissue

Glioblastoma multiforme (GBM) is the most aggressive of the gliomas, a collection of tumors arising from glia in the central nervous system. Possible associations between the human cytomegalovirus (HCMV) and the JC virus with GBM are now attracting interest. Our present aim was to investigate the prevalence of the two viruses in Iranian patients from Kerman’s cities in the south of Iran. In addition, the expression rates of pp65, large T antigen and p53 proteins were assessed and their relation with GBM evaluated using reverse transcription real time PCR (rReal Time PCR) . A total of 199 patients with GBM cancer were enrolled, with mean±SD ages of 50.0±19.5 and 50.7±19.6 years for males and females, respectively. The P53 rate was dramatically low suggesting an aetiological role,. Large T antigen expression was found in JC positive samples, while the PP65 antigen was observed in patients positive for CMV and JC . HCMV products and JC virus with oncogenic potential may induce the development of various tumors including glioblastomas. The JC virus produces an early gene product, T-antigen, which has the ability to associate with and functionally inactivate well-studied tumor suppressor proteins including p53 and pRB .

Surface biotinylation of cytotoxic T lymphocytes for in vivo tracking of tumor immunotherapy in murine models

Currently, there is no stable and flexible method to label and track cytotoxic T lymphocytes (CTLs) in vivo in CTL immunotherapy. We aimed to evaluate whether the sulfo-hydroxysuccinimide (NHS)-biotin-streptavidin (SA) platform could chemically modify the cell surface of CTLs for in vivo tracking. CD8+ T lymphocytes were labeled with sulfo-NHS-biotin under different conditions and then incubated with SA-Alexa647. Labeling efficiency was proportional to sulfo-NHS-biotin concentration. CD8+ T lymphocytes could be labeled with higher efficiency with sulfo-NHS-biotin in DPBS than in RPMI (P < 0.05). Incubation temperature was not a key factor. CTLs maintained sufficient labeling for at least 72 h (P < 0.05), without altering cell viability. After co-culturing labeled CTLs with mouse glioma stem cells (GSCs) engineered to present biotin on their surface, targeting CTLs could specifically target biotin-presenting GSCs and inhibited cell proliferation (P < 0.01) and tumor spheres formation. In a biotin-presenting GSC brain tumor model, targeting CTLs could be detected in biotin-presenting gliomas in mouse brains but not in the non-tumor-bearing contralateral hemispheres (P < 0.05). In vivo fluorescent molecular tomography imaging in a subcutaneous U87 mouse model confirmed that targeting CTLs homed in on the biotin-presenting U87 tumors but not the control U87 tumors. PET imaging with ⁸⁹Zr-deferoxamine-biotin and SA showed a rapid clearance of the PET signal over 24 h in the control tumor, while only minimally decreased in the targeted tumor. Thus, sulfo-NHS-biotin-SA labeling is an efficient method to noninvasively track the migration of adoptive transferred CTLs and does not alter CTL viability or interfere with CTL-mediated cytotoxic activity.

Unlocking the promise of oncolytic virotherapy in glioma: combination with chemotherapy to enhance efficacy

Malignant glioma is a relentless burden to both patients and clinicians, and calls for innovation to overcome the limitations in current management. Glioma therapy using viruses has been investigated to accentuate the nature of a virus, killing a host tumor cell during its replication. As virus mediated approaches progress with promising therapeutic advantages, combination therapy with chemotherapy and oncolytic viruses has emerged as a more synergistic and possibly efficacious therapy. Here, we will review malignant glioma as well as prior experience with oncolytic viruses, chemotherapy and combination of the two, examining how the combination can be optimized in the future.

In situ vaccination for the treatment of cancer

Vaccination has had a tremendous impact on human health by harnessing the immune system to prevent and eradicate infectious diseases and this same approach might be used in cancer therapy. Cancer vaccine development has been slowed hindered by the paucity of universal tumor-associated antigens and the difficulty in isolating and preparing individualized vaccines ex vivo. Another approach has been to initiate or stimulate an immune response in situ (at the tumor site) and thus exploit the potentially numerous tumor-associated antigens there. Here, we review the many approaches that have attempted to accomplish effective in situ vaccination, using intratumoral administration of immunomodulators to increase the numbers or activation state of either antigen present cells or T cells within the tumor.

To Infection and Beyond: The Multi-Pronged Anti-Cancer Mechanisms of Oncolytic Viruses

Over the past 1–2 decades we have witnessed a resurgence of efforts to therapeutically exploit the attributes of lytic viruses to infect and kill tumor cells while sparing normal cells. We now appreciate that the utility of viruses for treating cancer extends far beyond lytic cell death. Viruses are also capable of eliciting humoral and cellular innate and adaptive immune responses that may be directed not only at virus-infected cells but also at uninfected cancer cells. Here we review our current understanding of this bystander effect, and divide the mechanisms into lytic, cytokine, innate cellular, and adaptive phases. Knowing the key pathways and molecular players during virus infection in the context of the cancer microenvironment will be critical to devise strategies to maximize the therapeutic effects of oncolytic viroimmunotherapy.

Trial Watch-Oncolytic viruses and cancer therapy

Oncolytic virotherapy relies on the administration of non-pathogenic viral strains that selectively infect and kill malignant cells while favoring the elicitation of a therapeutically relevant tumor-targeting immune response. During the past few years, great efforts have been dedicated to the development of oncolytic viruses with improved specificity and potency. Such an intense wave of investigation has culminated this year in the regulatory approval by the US Food and Drug Administration (FDA) of a genetically engineered oncolytic viral strain for use in melanoma patients. Here, we summarize recent preclinical and clinical advances in oncolytic virotherapy.

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.

Treatment strategies for combining immunostimulatory oncolytic virus therapeutics with dendritic cell injections

Oncolytic viruses (OVs) are used to treat cancer, as they selectively replicate inside of and lyse tumor cells. The efficacy of this process is limited and new OVs are being designed to mediate tumor cell release of cytokines and co-stimulatory molecules, which attract cytotoxic T cells to target tumor cells, thus increasing the tumor-killing effects of OVs. To further promote treatment efficacy, OVs can be combined with other treatments, such as was done by Huang et al., who showed that combining OV injections with dendritic cell (DC) injections was a more effective treatment than either treatment alone. To further investigate this combination, we built a mathematical model consisting of a system of ordinary differential equations and fit the model to the hierarchical data provided from Huang et al. We used the model to determine the effect of varying doses of OV and DC injections and to test alternative treatment strategies. We found that the DC dose given in Huang et al. was near a bifurcation point and that a slightly larger dose could cause complete eradication of the tumor. Further, the model results suggest that it is more effective to treat a tumor with immunostimulatory oncolytic viruses first and then follow-up with a sequence of DCs than to alternate OV and DC injections. This protocol, which was not considered in the experiments of Huang et al., allows the infection to initially thrive before the immune response is enhanced. Taken together, our work shows how the ordering, temporal spacing, and dosage of OV and DC can be chosen to maximize efficacy and to potentially eliminate tumors altogether.

In situ vaccination: Cancer immunotherapy both personalized and off-the-shelf

As cancer immunotherapy continues to benefit from novel approaches which cut immune 'brake pedals' (e.g. anti-PD1 and anti-CTLA4 antibodies) and push immune cell gas pedals (e.g. IL2, and IFNα) there will be increasing need to develop immune 'steering wheels' such as vaccines to guide the immune system specifically toward tumor associated antigens. Two primary hurdles in cancer vaccines have been: identification of universal antigens to be used in 'off-the-shelf' vaccines for common cancers, and 2) logistical hurdles of ex vivo production of individualized whole tumor cell vaccines. Here we summarize approaches using 'in situ vaccination' in which intratumoral administration of off-the-shelf immunomodulators have been developed to specifically induce (or amplify) T cell responses to each patient's individual tumor. Clinical studies have confirmed the induction of systemic immune and clinical responses to such approaches and preclinical models have suggested ways to further potentiate the translation of in situ vaccine trials for our patients.

Sui generis: gene therapy and delivery systems for the treatment of glioblastoma

Gene therapy offers a multidimensional set of approaches intended to treat and cure glioblastoma (GBM), in combination with the existing standard-of-care treatment (surgery and chemoradiotherapy), by capitalizing on the ability to deliver genes directly to the site of neoplasia to yield antitumoral effects. Four types of gene therapy are currently being investigated for their potential use in treating GBM: (i) suicide gene therapy, which induces the localized generation of cytotoxic compounds; (ii) immunomodulatory gene therapy, which induces or augments an enhanced antitumoral immune response; (iii) tumor-suppressor gene therapy, which induces apoptosis in cancer cells; and (iv) oncolytic virotherapy, which causes the lysis of tumor cells. The delivery of genes to the tumor site is made possible by means of viral and nonviral vectors for direct delivery of therapeutic gene(s), tumor-tropic cell carriers expressing therapeutic gene(s), and "intelligent" carriers designed to increase delivery, specificity, and tumoral toxicity against GBM. These vehicles are used to carry genetic material to the site of pathology, with the expectation that they can provide specific tropism to the desired site while limiting interaction with noncancerous tissue. Encouraging preclinical results using gene therapies for GBM have led to a series of human clinical trials. Although there is limited evidence of a therapeutic benefit to date, a number of clinical trials have convincingly established that different types of gene therapies delivered by various methods appear to be safe. Due to the flexibility of specialized carriers and genetic material, the technology for generating new and more effective therapies already exists.

Targeting tumor vasculature through oncolytic virotherapy: recent advances

The oncolytic virotherapy field has made significant advances in the last decade, with a rapidly increasing number of early- and late-stage clinical trials, some of them showing safety and promising therapeutic efficacy. Targeting tumor vasculature by oncolytic viruses (OVs) is an attractive strategy that offers several advantages over nontargeted viruses, including improved tumor viral entry, direct antivascular effects, and enhanced antitumor efficacy. Current understanding of the biological mechanisms of tumor neovascularization, novel vascular targets, and mechanisms of resistance has allowed the development of oncolytic viral vectors designed to target tumor neovessels. While some OVs (such as vaccinia and vesicular stomatitis virus) can intrinsically target tumor vasculature and induce vascular disruption, the majority of reported vascular-targeted viruses are the result of genetic manipulation of their viral genomes. Such strategies include transcriptional or transductional endothelial targeting, "armed" viruses able to downregulate angiogenic factors, or to express antiangiogenic molecules. The above strategies have shown preclinical safety and improved antitumor efficacy, either alone, or in combination with standard or targeted agents. This review focuses on the recent efforts toward the development of vascular-targeted OVs for cancer treatment and provides a translational/clinical perspective into the future development of new generation biological agents for human cancers.

Quantitative impact of immunomodulation versus oncolysis with cytokine-expressing virus therapeutics

The past century's description of oncolytic virotherapy as a cancer treatment involving specially-engineered viruses that exploit immune deficiencies to selectively lyse cancer cells is no longer adequate. Some of the most promising therapeutic candidates are now being engineered to produce immunostimulatory factors, such as cytokines and co-stimulatory molecules, which, in addition to viral oncolysis, initiate a cytotoxic immune attack against the tumor. This study addresses the combined effects of viral oncolysis and T-cell-mediated oncolysis. We employ a mathematical model of virotherapy that induces release of cytokine IL-12 and co-stimulatory molecule 4-1BB ligand. We found that the model closely matches previously published data, and while viral oncolysis is fundamental in reducing tumor burden, increased stimulation of cytotoxic T cells leads to a short-term reduction in tumor size, but a faster relapse. In addition, we found that combinations of specialist viruses that express either IL-12 or 4-1BBL might initially act more potently against tumors than a generalist virus that simultaneously expresses both, but the advantage is likely not large enough to replace treatment using the generalist virus. Finally, according to our model and its current assumptions, virotherapy appears to be optimizable through targeted design and treatment combinations to substantially improve therapeutic outcomes.