A phase I trial and viral clearance study of reovirus (Reolysin) in children with relapsed or refractory extra-cranial solid tumors: a Children's Oncology Group Phase I Consortium report

Translation of oncolytic viruses in sarcoma

Sarcomas are a rare and highly diverse group of malignancies of mesenchymal origin. While sarcomas are generally considered resistant to immunotherapy, recent studies indicate subtype-specific differences in clinical response to checkpoint inhibitors (CPIs) that are associated with distinct immune phenotypes present in sarcoma subtypes. Oncolytic viruses (OVs) are designed to selectively infect and kill tumor cells and induce intratumoral immune infiltration, enhancing immunogenicity and thereby sensitizing tumors to immunotherapy. Herein we review the accumulated clinical data evaluating OVs in sarcoma. Small numbers of patients with sarcoma were enrolled in early-stage OV trials as part of larger solid tumor cohorts demonstrating safety but providing limited insight into the biological effects due to the low patient numbers and lack of histologic grouping. Several recent studies have investigated talimogene laherparepvec (T-VEC), an approved oncolytic herpes simplex virus (HSV-1), in combination therapy regimens in sarcoma patient cohorts. These studies have shown promising responses in heavily pre-treated and immunotherapy-resistant patients associated with increased intratumoral immune infiltration. As new and more potent OVs enter the clinical arena, prospective evaluation in subtype-specific cohorts with correlative studies to define biomarkers of response will be critical to advancing this promising approach for sarcoma therapy.

Oncolytic Viral Therapy in Osteosarcoma

Primary bone malignancies, including osteosarcoma (OS), are rare but aggressive. Current OS treatment, involving surgical resection and chemotherapy, has improved survival for non-metastatic cases but remains ineffective for recurrent or metastatic OS. Oncolytic viral therapy (OVT) is a promising alternative, using naturally occurring or genetically modified viruses to selectively target and lyse cancer cells and induce a robust immune response against remaining OS cells. Various oncolytic viruses (OVs), such as adenovirus, herpes simplex virus, and measles virus, have demonstrated efficacy in preclinical OS models. Combining OVT with other therapeutics, such as chemotherapy or immunotherapy, may further improve outcomes. Despite these advances, challenges in reliability of preclinical models, safety, delivery, and immune response must be addressed to optimize OVT for clinical use. Future research should focus on refining delivery methods, exploring combination treatments, and clinical trials to ensure OVT's efficacy and safety for OS. Overall, OVT represents a novel approach with the potential to drastically improve survival outcomes for patients with OS.

Hypoxia effects on oncolytic virotherapy in Cancer: Friend or Foe?

Researchers have tried to find novel strategies for cancer treatment in the past decades. Among the utilized methods, administering oncolytic viruses (OVs) alone or combined with other anticancer therapeutic approaches has had promising outcomes, especially in solid tumors. Infecting the tumor cells by these viruses can lead to direct lysis or induction of immune responses. However, the immunosuppressive tumor microenvironment (TME) is considered a significant challenge for oncolytic virotherapy in treating cancer. Based on OV type, hypoxic conditions in the TME can accelerate or repress virus replication. Therefore, genetic manipulation of OVs or other molecular modifications to reduce hypoxia can induce antitumor responses. Moreover, using OVs with tumor lysis capability in the hypoxic TME may be an attractive strategy to overcome the limitations of the therapy. This review summarizes the latest information available in the field of cancer virotherapy and discusses the dual effect of hypoxia on different types of OVs to optimize available related therapeutic methods.

Anticancer Activity of Measles-Mumps-Rubella MMR Vaccine Viruses against Glioblastoma

BACKGROUND

Oncolytic viruses (OVs) have been utilized since 1990s for targeted cancer treatment. Our study examined the Measles-Mumps-Rubella (MMR) vaccine's cancer-killing potency against Glioblastoma (GBM), a therapy-resistant, aggressive cancer type.

METHODOLOGY

We used GBM cell lines, primary GBM cells, and normal mice microglial cells, to assess the MMR vaccine's efficacy through cell viability, cell cycle analysis, intracellular viral load via RT-PCR, and Transmission Electron Microscopy (TEM).

RESULTS

After 72 h of MMR treatment, GBM cell lines and primary GBM cells exhibited significant viability reduction compared to untreated cells. Conversely, normal microglial cells showed only minor changes in viability and morphology. Intracellular viral load tests indicated GBM cells' increased sensitivity to MMR viruses compared to normal cells. The cell cycle study also revealed measles and mumps viruses' crucial role in cytopathic effects, with the rubella virus causing cell cycle arrest.

CONCLUSION

Herein the reported results demonstrate the anti-cancer activity of the MMR vaccine against GBM cells. Accordingly, the MMR vaccine warrants further study as a potential new tool for GBM therapy and relapse prevention. Therapeutic potential of the MMR vaccine has been found to be promising in earlier studies as well.

Oncolytic virotherapies for pediatric tumors

INTRODUCTION

Many pediatric patients with malignant tumors continue to suffer poor outcomes. The current standard of care includes maximum safe surgical resection followed by chemotherapy and radiation which may be associated with considerable long-term morbidity. The emergence of oncolytic virotherapy (OVT) may provide an alternative or adjuvant treatment for pediatric oncology patients.

AREAS COVERED

We reviewed seven virus types that have been investigated in past or ongoing pediatric tumor clinical trials: adenovirus (AdV-tk, Celyvir, DNX-2401, VCN-01, Ad-TD-nsIL-12), herpes simplex virus (G207, HSV-1716), vaccinia (JX-594), reovirus (pelareorep), poliovirus (PVSRIPO), measles virus (MV-NIS), and Senecavirus A (SVV-001). For each virus, we discuss the mechanism of tumor-specific replication and cytotoxicity as well as key findings of preclinical and clinical studies.

EXPERT OPINION

Substantial progress has been made in the past 10 years regarding the clinical use of OVT. From our review, OVT has favorable safety profiles compared to chemotherapy and radiation treatment. However, the antitumor effects of OVT remain variable depending on tumor type and viral agent used. Although the widespread adoption of OVT faces many challenges, we are optimistic that OVT will play an important role alongside standard chemotherapy and radiotherapy for the treatment of malignant pediatric solid tumors in the future.

Development and application of oncolytic viruses as the nemesis of tumor cells

Viruses and tumors are two pathologies that negatively impact human health, but what occurs when a virus encounters a tumor? A global consensus among cancer patients suggests that surgical resection, chemotherapy, radiotherapy, and other methods are the primary means to combat cancer. However, with the innovation and development of biomedical technology, tumor biotherapy (immunotherapy, molecular targeted therapy, gene therapy, oncolytic virus therapy, etc.) has emerged as an alternative treatment for malignant tumors. Oncolytic viruses possess numerous anti-tumor properties, such as directly lysing tumor cells, activating anti-tumor immune responses, and improving the tumor microenvironment. Compared to traditional immunotherapy, oncolytic virus therapy offers advantages including high killing efficiency, precise targeting, and minimal side effects. Although oncolytic virus (OV) therapy was introduced as a novel approach to tumor treatment in the 19th century, its efficacy was suboptimal, limiting its widespread application. However, since the U.S. Food and Drug Administration (FDA) approved the first OV therapy drug, T-VEC, in 2015, interest in OV has grown significantly. In recent years, oncolytic virus therapy has shown increasingly promising application prospects and has become a major research focus in the field of cancer treatment. This article reviews the development, classification, and research progress of oncolytic viruses, as well as their mechanisms of action, therapeutic methods, and routes of administration.

Vaccinating against cancer: getting to prime time

Immunotherapies, such as immune checkpoint inhibitors, cellular therapies, and T-cell engagers, have fundamentally changed our approach to treating cancer. However, successes with cancer vaccines have been more difficult to realize. While vaccines against specific viruses have been widely adopted to prevent the development of cancer, only two vaccines can improve survival in advanced disease: sipuleucel-T and talimogene laherparepvec. These represent the two approaches that have the most traction: vaccinating against cognate antigen and priming responses using tumors in situ. Here, we review the challenges and opportunities researchers face in developing therapeutic vaccines for cancer.

Therapeutic avenues for targeting treatment challenges of diffuse midline gliomas

Diffuse midline glioma (DMG) is the leading cause of brain tumor-related deaths in children. DMG typically presents with variable neurologic symptoms between ages 3 and 10. Currently, radiation remains the standard therapy for DMG to halt progression and reduce tumor bulk to minimize symptoms. However, tumors recur in almost 100% of patients and thus, DMG is still considered an incurable cancer with a median survival of 9-12 months. Surgery is generally contraindicated due to the delicate organization of the brainstem, where DMG is located. Despite extensive research efforts, no chemotherapeutic agents, immune therapies, or molecularly targeted therapies have been approved to provide survival benefit. Furthermore, the efficacy of therapies is limited by poor blood-brain barrier penetration and inherent resistance mechanisms of the tumor. However, novel drug delivery approaches, along with recent advances in molecularly targeted therapies and immunotherapies, have advanced to clinical trials and may provide viable future treatment options for DMG patients. This review seeks to evaluate current therapeutics at the preclinical stage and those that have advanced to clinical trials and to discuss the challenges of drug delivery and inherent resistance to these therapies.

A phase 1, first-in-child, multicenter study to evaluate the safety and efficacy of the oncolytic herpes virus talimogene laherparepvec in pediatric patients with advanced solid tumors

Background

The survival rates for pediatric patients with relapsed and refractory tumors are poor. Successful treatment strategies are currently lacking and there remains an unmet need for novel therapies for these patients. We report here the results of a phase 1 study of talimogene laherparepvec (T-VEC) and explore the safety of this oncolytic immunotherapy for the treatment of pediatric patients with advanced non-central nervous system tumors.

Methods

T-VEC was delivered by intralesional injection at 10⁶ plaque-forming units (PFU)/ml on the first day, followed by 10⁸ PFU/ml on the first day of week 4 and every 2 weeks thereafter. The primary objective was to evaluate the safety and tolerability as assessed by the incidence of dose-limiting toxicities (DLTs). Secondary objectives included efficacy indicated by response and survival per modified immune-related response criteria simulating the Response Evaluation Criteria in Solid Tumors (irRC-RECIST).

Results

Fifteen patients were enrolled into two cohorts based on age: cohort A1 (n = 13) 12 to ≤21 years old (soft-tissue sarcoma, n = 7; bone sarcoma, n = 3; neuroblastoma, n = 1; nasopharyngeal carcinoma, n = 1; and melanoma, n = 1) and cohort B1 (n = 2) 2 to <12 years old (melanoma, n = 2). Overall, patients received treatment for a median (range) of 5.1 (0.1, 39.4) weeks. No DLTs were observed during the evaluation period. All patients experienced at least one treatment-emergent adverse event (TEAE), and 53.3% of patients reported grade ≥3 TEAEs. Overall, 86.7% of patients reported treatment-related TEAEs. No complete or partial responses were observed, and three patients (20%) overall exhibited stable disease as the best response.

Conclusions

T-VEC was tolerable as assessed by the observation of no DLTs. The safety data were consistent with the patients' underlying cancer and the known safety profile of T-VEC from studies in the adult population. No objective responses were observed.

Trial Registration

ClinicalTrials.gov: NCT02756845. https://clinicaltrials.gov/ct2/show/NCT02756845.

Oncolytic virotherapy: basic principles, recent advances and future directions

Oncolytic viruses (OVs) have attracted growing awareness in the twenty-first century, as they are generally considered to have direct oncolysis and cancer immune effects. With the progress in genetic engineering technology, OVs have been adopted as versatile platforms for developing novel antitumor strategies, used alone or in combination with other therapies. Recent studies have yielded eye-catching results that delineate the promising clinical outcomes that OVs would bring about in the future. In this review, we summarized the basic principles of OVs in terms of their classifications, as well as the recent advances in OV-modification strategies based on their characteristics, biofunctions, and cancer hallmarks. Candidate OVs are expected to be designed as "qualified soldiers" first by improving target fidelity and safety, and then equipped with "cold weapons" for a proper cytocidal effect, "hot weapons" capable of activating cancer immunotherapy, or "auxiliary weapons" by harnessing tactics such as anti-angiogenesis, reversed metabolic reprogramming and decomposing extracellular matrix around tumors. Combinations with other cancer therapeutic agents have also been elaborated to show encouraging antitumor effects. Robust results from clinical trials using OV as a treatment congruously suggested its significance in future application directions and challenges in developing OVs as novel weapons for tactical decisions in cancer treatment.

Therapy with oncolytic viruses: progress and challenges

Oncolytic viruses (OVs) are an emerging class of cancer therapeutics that offer the benefits of selective replication in tumour cells, delivery of multiple eukaryotic transgene payloads, induction of immunogenic cell death and promotion of antitumour immunity, and a tolerable safety profile that largely does not overlap with that of other cancer therapeutics. To date, four OVs and one non-oncolytic virus have been approved for the treatment of cancer globally although talimogene laherparepvec (T-VEC) remains the only widely approved therapy. T-VEC is indicated for the treatment of patients with recurrent melanoma after initial surgery and was initially approved in 2015. An expanding body of data on the clinical experience of patients receiving T-VEC is now becoming available as are data from clinical trials of various other OVs in a range of other cancers. Despite increasing research interest, a better understanding of the underlying biology and pharmacology of OVs is needed to enable the full therapeutic potential of these agents in patients with cancer. In this Review, we summarize the available data and provide guidance on optimizing the use of OVs in clinical practice, with a focus on the clinical experience with T-VEC. We describe data on selected novel OVs that are currently in clinical development, either as monotherapies or as part of combination regimens. We also discuss some of the preclinical, clinical and regulatory hurdles that have thus far limited the development of OVs.

Current State of Immunotherapy and Mechanisms of Immune Evasion in Ewing Sarcoma and Osteosarcoma

We argue here that in many ways, Ewing sarcoma (EwS) is a unique tumor entity and yet, it shares many commonalities with other immunologically cold solid malignancies. From the historical perspective, EwS, osteosarcoma (OS) and other bone and soft-tissue sarcomas were the first types of tumors treated with the immunotherapy approach: more than 100 years ago American surgeon William B. Coley injected his patients with a mixture of heat-inactivated bacteria, achieving survival rates apparently higher than with surgery alone. In contrast to OS which exhibits recurrent somatic copy-number alterations, EwS possesses one of the lowest mutation rates among cancers, being driven by a single oncogenic fusion protein, most frequently EWS-FLI1. In spite these differences, both EwS and OS are allied with immune tolerance and low immunogenicity. We discuss here the potential mechanisms of immune escape in these tumors, including low representation of tumor-specific antigens, low expression levels of MHC-I antigen-presenting molecules, accumulation of immunosuppressive M2 macrophages and myeloid proinflammatory cells, and release of extracellular vesicles (EVs) which are capable of reprogramming host cells in the tumor microenvironment and systemic circulation. We also discuss the vulnerabilities of EwS and OS and potential novel strategies for their targeting.

Oncolytic viral vectors in the era of diversified cancer therapy: from preclinical to clinical

With the in-depth research and wide application of immunotherapy recently, new therapies based on oncolytic viruses are expected to create new prospects for cancer treatment via eliminating the suppression of the immune system by tumors. Currently, an increasing number of viruses are developed and engineered, and various virus vectors based on effectively stimulating human immune system to kill tumor cells have been approved for clinical treatment. Although the virus can retard the proliferation of tumor cells, the choice of oncolytic viruses in biological cancer therapy is equally critical given their therapeutic efficacy, safety and adverse effects. Moreover, previously known oncolytic viruses have not been systematically classified. Therefore, in this review, we summarized and distinguished the characteristics of several common types of oncolytic viruses: herpes simplex virus, adenovirus, measles virus, Newcastle disease virus, reovirus and respiratory syncytial virus. Subsequently, we outlined that these oncolytic viral vectors have been transformed from preclinical studies in combination with immunotherapy, radiotherapy, chemotherapy, and nanoparticles into clinical therapeutic strategies for various advanced solid malignancies or circulatory system cancers.

Clinical advances in oncolytic virotherapy for pediatric brain tumors

Malignant brain tumors constitute nearly one-third of cancer diagnoses in children and have recently surpassed hematologic malignancies as the most lethal neoplasm in the pediatric population. Outcomes for children with brain tumors are unacceptably poor and current standards of care-surgical resection, chemotherapy, and radiation-are associated with significant long-term morbidity. Oncolytic virotherapy has emerged as a promising immunotherapy for the treatment of brain tumors. While the majority of brain tumor clinical trials utilizing oncolytic virotherapy have been in adults, five viruses are being tested in pediatric brain tumor clinical trials: herpes simplex virus (G207), reovirus (pelareorep/Reolysin), measles virus (MV-NIS), poliovirus (PVSRIPO), and adenovirus (DNX-2401, AloCELYVIR). Herein, we review past and current pediatric immunovirotherapy brain tumor trials including the relevant preclinical and clinical research that contributed to their development. We describe mechanisms by which the viruses may overcome barriers in treating pediatric brain tumors, examine challenges associated with achieving effective, durable responses, highlight unique aspects and successes of the trials, and discuss future directions of immunovirotherapy research for the treatment of pediatric brain tumors.

Immunovirotherapy for Pediatric Solid Tumors: A Promising Treatment That is Becoming a Reality

Immunotherapy has seen tremendous strides in the last decade, acquiring a prominent position at the forefront of cancer treatment since it has been proven to be efficacious for a wide variety of tumors. Nevertheless, while immunotherapy has changed the paradigm of adult tumor treatment, this progress has not yet been translated to the pediatric solid tumor population. For this reason, alternative curative therapies are urgently needed for the most aggressive pediatric tumors. In recent years, oncolytic virotherapy has consolidated as a feasible strategy for cancer treatment, not only for its tumor-specific effects and safety profile but also for its capacity to trigger an antitumor immune response. This review will summarize the current status of immunovirotherapy to treat cancer, focusing on pediatric solid malignancies. We will revisit previous basic, translational, and clinical research and discuss advances in overcoming the existing barriers and limitations to translate this promising therapeutic as an every-day cancer treatment for the pediatric and young adult populations.

Phase I trial of sargramostim/pelareorep therapy in pediatric patients with recurrent or refractory high-grade brain tumors

Background

Brain tumors are the leading cause of cancer death for pediatric patients. Pelareorep, an immunomodulatory oncolytic reovirus, has intravenous efficacy in preclinical glioma models when preconditioned with GM-CSF (sargramostim). We report a phase I trial with the primary goal of evaluating the safety of sargramostim/pelareorep in pediatric patients with recurrent or refractory high-grade brain tumors and a secondary goal of characterizing immunologic responses.

Methods

The trial was open to pediatric patients with recurrent or refractory high-grade brain tumors (3 + 3 cohort design). Each cycle included 3 days of subcutaneous sargramostim followed by 2 days of intravenous pelareorep. Laboratory studies and imaging were acquired upon recruitment and periodically thereafter.

Results

Six patients participated, including three glioblastoma, two diffuse intrinsic pontine glioma, and one medulloblastoma. Two pelareorep dose levels of 3 × 10⁸ and 5 × 10⁸ tissue culture infectious dose 50 (TCID₅₀) were assessed. One patient experienced a dose limiting toxicity of persistent hyponatremia. Common low-grade (1 or 2) adverse events included transient fatigue, hypocalcemia, fever, flu-like symptoms, thrombocytopenia, and leukopenia. High-grade (3 or 4) adverse events included neutropenia, lymphopenia, leukopenia, hypophosphatemia, depressed level of consciousness, and confusion. All patients progressed on therapy after a median of 32.5 days and died a median of 108 days after recruitment. Imaging at progression did not show evidence of pseudoprogression or inflammation. Correlative assays revealed transient but consistent changes in immune cells across patients.

Conclusions

Sargramostim/pelareorep was administered to pediatric patients with recurrent or refractory high-grade brain tumors. Hyponatremia was the only dose limiting toxicity (DLT), though maximum tolerated dose (MTD) was not determined.

A systematic analysis on the clinical safety and efficacy of onco-virotherapy

Several onco-virotherapy candidates have been developed and clinically evaluated for the treatment of cancer, and several are approved for clinical use. In this systematic review we explored the clinical impact of onco-virotherapy compared to other cancer therapies by analyzing factors such as trial design, patient background, therapy design, delivery strategies, and study outcomes. For this purpose, we retrieved clinical studies from three platforms: ClinicalTrials.gov, PubMed, and EMBASE. We found that most studies were performed in patients with advanced and metastatic tumors, using a broad range of genetically engineered vectors and mainly administered intratumorally. Therapeutic safety was the most frequently assessed outcome, while relatively few studies focused on immunological antitumor responses. Moreover, only 59 out of 896 clinical studies were randomized controlled trials reporting comparative data. This systemic review thus reveals the need of more, and better controlled, clinical studies to increase our understanding on the application of onco-virotherapy either as a single treatment or in combination with other cancer immunotherapies.

The Use of Oncolytic Viruses in the Treatment of Multiple Myeloma

Simple Summary

Multiple myeloma is a type of blood cancer caused by the uncontrolled growth of antibody producing B cells (known as plasma cells) that reside in the bone marrow. It is classed as a largely incurable cancer as whilst patients respond well to initial chemotherapy treatments, unfortunately after periods of disease remission, relapse usually occurs with the emergence of chemotherapy resistance. Therefore, there is a need for new approaches that not only reduce tumour load but also prevent tumour relapse. Oncolytic viruses (OVs) (tumour killing viruses) are being explored as a therapy for various cancers, including multiple myeloma. This review discusses the use of OVs in myeloma in preclinical model systems and early phase clinical trials, and discusses some of the hurdles involved in the translation to myeloma patients.

Abstract

Multiple myeloma accounts for 1% of all new cancers worldwide. It is the second most common haematological malignancy and has a low five-year survival rate (53.2%). Myeloma remains an incurable disease and is caused by the growth of malignant plasma cells in the bone marrow. Current anti-myeloma therapies (conventional chemotherapies, immunomodulatory drugs i.e., thalidomide and its’ analogues, proteasome inhibitors, monoclonal antibodies, and radiotherapy) initially substantially debulk tumour burden, but after a period of remission ‘plateau phase’ disease invariably relapses due to tumour recrudescence from foci of minimal residual disease (MRD) and accumulating drug resistance. Therefore, there is a compelling clinical need for the development of novel treatment regimens to target MRD and effectively eliminate all remaining tumour cells. This review will discuss the potential use of oncolytic virus (OV) therapies in the treatment of myeloma. Specifically, it will focus on preclinical studies using DNA viruses (adenovirus (Ad), vaccinia virus (VV), myxoma virus (MYXV), and herpes simplex virus (HSV)), RNA viruses (reovirus (reo), coxsackie virus, measles virus (MV) and bovine viral diarrhoea virus (BVDV), and vesicular stomatitis virus (VSV)), and on four types of viruses (VV, reo, MV-NIS and VSV-IFNβ-NIS) that have been assessed clinically in a small number of myeloma patients.

MSCs loaded with oncolytic reovirus: migration and in vivo virus delivery potential for evaluating anti-cancer effect in tumor-bearing C57BL/6 mice

Background and aims

Several oncolytic viruses applications have been approved in the clinic or in different phases of clinical trials. However, these methods have some rudimentary problems. Therefore, to enhance the delivery and quality of treatment, considering the advantage of cell carrier-based methods such as Mesenchymal Stem Cells (MSC) have been proposed. This study was designed to evaluate the performance and quality of cancer treatment based on MSCs loaded by oncolytic reovirus in the cancerous C57BL/6 mouse model. Also, we evaluated MSCs migration potency in vitro and in vivo following the oncolytic reovirus infection.

Methods

C57BL/6 mice were inoculated with TC-1 cell lines and tumors were established in the right flank. Mice were systemically treated with reovirus, MSCs-loaded with reovirus, MSCs, and PBS as a control in separated groups. Effects of infected AD-MSCs with reovirus on tumor growth and penetration in the tumor site were monitored. All groups of mice were monitored for two months in order to therapeutic and anticancer potential. After treatments, tumor size alteration and apoptosis rate, as well as cytokine release pattern was assessed.

Results

The results of the current study indicated that the effect of reovirus infection on AD-MSCs is not devastating the migration capacity especially in MOI 1 and 5 while intact cells remain. On the other hand, MSCs play an efficient role as a carrier to deliver oncolytic virus into the tumor site in comparison with systemic administration of reovirus alone. Apoptosis intensity relies on viral titration and passing time. Followed by systemic administration, treatment with oncolytic reovirus-infected AD-MSCs and MSCs alone had shown significant inhibition in tumor growth. Also, treatment by reovirus causes an increase in IFN-γ secretion.

Conclusion

The results of in vitro and in vivo study confirmed the tumor-homing properties of infected AD-MSCs and the significant antitumor activity of this platform. Hence, our results showed that the cell carrier strategy using oncolytic reovirus-loaded AD-MSCs enhanced virus delivery, infiltration, and antitumor activity can be effectively applied in most cancers.

Current strategies of virotherapy in clinical trials for cancer treatment

As a novel immune-active agent for cancer treatment, viruses have the ability of infecting and replicating in tumor cells. The safety and efficacy of viruses has been tested and confirmed in preclinical and clinical trials. In the last decade, virotherapy has been adopted as a monotherapy or combined therapy with immunotherapy, chemotherapy, or radiotherapy, showing promising outcomes against cancer. In this review, the current strategies of viruses used in clinical trials are classified and described. Besides this, the challenge and future prospects of virotherapy in the management for cancer patients are discussed in this review.

Mesenchymal stem cell carriers enhance anti-tumor efficacy of oncolytic virotherapy

Oncolytic viruses (OVs) specifically infect, replicate and eventually destroy tumor cells, with no concomitant toxicity to adjacent normal cells. Furthermore, OVs can regulate tumor microenvironments and stimulate anti-tumor immune responses. Mesenchymal stem cells (MSCs) have inherent tumor tropisms and immunosuppressive functions. MSCs carrying OVs not only protect viruses from clearing by the immune system, but they also deliver the virus to tumor lesions. Equally, cytokines released by MSCs enhance anti-tumor immune responses, suggesting that MSCs carrying OVs may be considered as a promising strategy in enhancing the anti-tumor efficacies of virotherapy. In the present review, preclinical and clinical studies were evaluated and discussed, as well as the effectiveness of MSCs carrying OVs for tumor treatment.

Mesenchymal stem cell carriers enhance antitumor efficacy induced by oncolytic reovirus in acute myeloid leukemia

Chemotherapy is the main treatment for acute myeloid leukemia (AML), but the therapeutic efficacy is modest, and most commonly manifests as relapse from remission. Thus, improving long-term AML survival is a crucial clinical challenge. In recent years, oncolytic virotherapy has provided an alternative approach for AML treatment. The use of oncolytic reoviruses has been explored in more than 30 clinical trials for safety and feasibility issues. However, like other oncolytic viruses, neutralizing antibodies (NAbs) reduce therapeutic efficacy. To tackle this problem, human umbilical cord mesenchymal stem cells (hUC-MSCs) were used to deliver reovirus using in vitro and in vivo models. Human UC-MSCs were successfully loaded with reovirus, without impairing biological function.We also observed in vitro protective effects of hUC-MSCs on reovirus in the presence of NAbs. In the immunocompromised AML mouse model, hUC-MSCs effectively carried reoviruses to tumor lesions and significantly prolonged the survival of AML xenografts in mice in the presence of a high titer anti-reovirus antibody (p = 0.001). However, reovirus-induced activation of AKT, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and NF-κB signaling led to the maintenance of intrinsic migratory properties and secretion of pro-inflammatory cytokines from hUC-MSCs, particularly CXCL10. In immuno-competent AML mice, MSCs carrying reovirus triggered immune responses, and eventually inhibited tumor growth. Therefore, these results suggest that MSCs as carriers of oncolytic reoviruses can enhance the antitumor efficacy of virotherapy.

Oncolytic Virotherapy in Solid Tumors: The Challenges and Achievements

Oncolytic virotherapy (OVT) is a promising approach in cancer immunotherapy. Oncolytic viruses (OVs) could be applied in cancer immunotherapy without in-depth knowledge of tumor antigens. The capability of genetic modification makes OVs exciting therapeutic tools with a high potential for manipulation. Improving efficacy, employing immunostimulatory elements, changing the immunosuppressive tumor microenvironment (TME) to inflammatory TME, optimizing their delivery system, and increasing the safety are the main areas of OVs manipulations. Recently, the reciprocal interaction of OVs and TME has become a hot topic for investigators to enhance the efficacy of OVT with less off-target adverse events. Current investigations suggest that the main application of OVT is to provoke the antitumor immune response in the TME, which synergize the effects of other immunotherapies such as immune-checkpoint blockers and adoptive cell therapy. In this review, we focused on the effects of OVs on the TME and antitumor immune responses. Furthermore, OVT challenges, including its moderate efficiency, safety concerns, and delivery strategies, along with recent achievements to overcome challenges, are thoroughly discussed.

Sarcoma treatment in the era of molecular medicine

Sarcomas are heterogeneous and clinically challenging soft tissue and bone cancers. Although constituting only 1% of all human malignancies, sarcomas represent the second most common type of solid tumors in children and adolescents and comprise an important group of secondary malignancies. More than 100 histological subtypes have been characterized to date, and many more are being discovered due to molecular profiling. Owing to their mostly aggressive biological behavior, relative rarity, and occurrence at virtually every anatomical site, many sarcoma subtypes are in particular difficult-to-treat categories. Current multimodal treatment concepts combine surgery, polychemotherapy (with/without local hyperthermia), irradiation, immunotherapy, and/or targeted therapeutics. Recent scientific advancements have enabled a more precise molecular characterization of sarcoma subtypes and revealed novel therapeutic targets and prognostic/predictive biomarkers. This review aims at providing a comprehensive overview of the latest advances in the molecular biology of sarcomas and their effects on clinical oncology; it is meant for a broad readership ranging from novices to experts in the field of sarcoma.

Clinical Application of Oncolytic Viruses: A Systematic Review

Leveraging the immune system to thwart cancer is not a novel strategy and has been explored via cancer vaccines and use of immunomodulators like interferons. However, it was not until the introduction of immune checkpoint inhibitors that we realized the true potential of immunotherapy in combating cancer. Oncolytic viruses are one such immunotherapeutic tool that is currently being explored in cancer therapeutics. We present the most comprehensive systematic review of all oncolytic viruses in Phase 1, 2, and 3 clinical trials published to date. We performed a systematic review of all published clinical trials indexed in PubMed that utilized oncolytic viruses. Trials were reviewed for type of oncolytic virus used, method of administration, study design, disease type, primary outcome, and relevant adverse effects. A total of 120 trials were found; 86 trials were available for our review. Included were 60 phase I trials, five phase I/II combination trials, 19 phase II trials, and two phase III clinical trials. Oncolytic viruses are feverously being evaluated in oncology with over 30 different types of oncolytic viruses being explored either as a single agent or in combination with other antitumor agents. To date, only one oncolytic virus therapy has received an FDA approval but advances in bioengineering techniques and our understanding of immunomodulation to heighten oncolytic virus replication and improve tumor kill raises optimism for its future drug development.

Determinants of the efficacy of viro-immunotherapy: A review

Oncolytic virus immunotherapy is rapidly gaining interest in the field of immunotherapy against cancer. The minimal toxicity upon treatment and the dual activity of direct oncolysis and immune activation make therapy with oncolytic viruses (OVs) an interesting treatment modality. The safety and efficacy of several OVs have been assessed in clinical trials and, so far, the Food and Drug Administration (FDA) has approved one OV. Unfortunately, most treatments with OVs have shown suboptimal responses in clinical trials, while they appeared more promising in preclinical studies, with tumours reducing after immune cell influx. In several clinical trials with OVs, parameters such as virus replication, virus-specific antibodies, systemic immune responses, immune cell influx into tumours and tumour-specific antibodies have been studied as predictors or correlates of therapy efficacy. In this review, these studies are summarized to improve our understanding of the determinants of the efficacy of OV therapies in humans and to provide insights for future developments in the viro-immunotherapy treatment field.

Oncolytic viruses: what to expect from their use in cancer treatment

Oncolytic viruses are biologic agents able to selectively infect and destroy cancer cells while sparing the normal ones. Furthermore, they also stimulate the host immune system to combat the tumor growth and to promote tumor removal. This review thoroughly describes different types of viruses developed for targeting specific cancers, as well as the strategies to improve the efficacy and safety of oncolytic virotherapy. It also explores how their potential as anticancer agents may be enhanced through combination with other traditional therapies, such as chemotherapy or more recent approaches, such as checkpoint inhibitors. There are many oncolytic viruses currently being tested in clinical trials for the treatment of various types of cancer, suggesting that this approach could become the near future of the oncology field.

First-in-Human, First-in-Child Trial of Autologous MSCs Carrying the Oncolytic Virus Icovir-5 in Patients with Advanced Tumors

We present here the results of a first-in-human, first-in-child trial for patients with relapsed/refractory solid tumors using Celyvir, an advanced therapy medicine that combines autologous mesenchymal stem cells (MSCs) carrying an oncolytic adenovirus. Celyvir was manufactured from a bone marrow aspirate and then given intravenously. Patients received weekly infusions for 6 weeks at a dose of 2 × 10⁶ cells/kg (children) or 0.5-1 × 10⁶ cells/kg (adults), 2 × 10⁴ viral particles per cell. Fifteen pediatric and 19 adult patients were recruited, but 18 were screen failures, mainly because rapid disease progression before Celyvir was available. No grade 2-5 toxicities were reported. Adenoviral replication detected by PCR was found in all but 2 pediatric patient and in none of the adult ones. Absolute numbers of circulating leukocytes suffered minor changes along therapy, but some subsets showed differences comparing the pediatric versus the adult cohorts. Two patients with neuroblastoma showed disease stabilization, and one of them continued on treatment for up to 6 additional weeks. Celyvir, the combination of MSCs and oncolytic adenovirus, is safe and warrants further evaluation in a phase 2 setting. The use of MSCs may be a strategy to increase the amount of oncolytic virus administered to patients, minimizing toxicities and avoiding direct tumor injections.

Oncolytic Viruses and Their Potential as a Therapeutic Opportunity in Osteosarcoma

Osteosarcoma remains an unmet medical need. Oncolytic viruses are gaining traction as novel cancer therapeutics. These viruses are either naturally nonpathogenic or engineered to be safe by specific genetic deletions yet retain the ability to infect and kill human cancer cells and elicit anticancer immunity. Some versions are being specifically designed and tested in patients with osteosarcoma, though due to their generalized mechanism of action most are being tested in patients across a broad range of cancer types. The activity of these viruses is impacted not only by the susceptibility of tumor cells to infection but also by the tumor microenvironment (TME) and by tumor immunogenicity. Here we review the field of oncolytic viruses with a particular emphasis on highlighting any available data in preclinical osteosarcoma models or in patients with osteosarcoma. While in general the viruses have been shown safe to administer to patients by a variety of routes, their therapeutic efficacy to date has been limited. Given the low rate of adverse events and the likely absence of long-term side effects, the utility of oncolytic viruses will most likely be realized when used in combination with other agents.

First-in-Human Intravenous Seprehvir in Young Cancer Patients: A Phase 1 Clinical Trial

Seprehvir (HSV1716) is an oncolytic herpes simplex virus-1 (HSV-1) previously demonstrated to be well tolerated in pediatric patients when administered intratumorally. To determine the safety of administering Seprehvir systemically, we conducted the first-in-human phase I trial of intravenous injection in young patients with relapsed or refractory extra-cranial solid cancers. We delivered a single dose of 5 × 10⁴ infectious units (iu)/kg (maximum dose of 2 × 10⁶) or 2.5 × 10⁵ iu/kg (maximum dose of 1 × 10⁷ iu) of Seprehvir via the peripheral vein, monitored adverse events, and measured tumor responses by imaging. We monitored HSV-1 serology as well as viremia and shedding by PCR and culture. We administered a single dose of Seprehvir to seven patients and multiple doses to two patients. We did not observe any dose-limiting toxicities. All five HSV-1 seronegative patients seroconverted by day 28. Four of nine patients had detectable HSV-1 genomes in peripheral blood appearing on day +4 consistent with de novo virus replication. Two patients had stable disease in response to Seprehvir. Intravenous Seprehvir is well tolerated without viral shedding in children and young adults with late-stage cancer. Viremia consistent with virus replication holds promise for future Seprehvir studies at higher doses and/or in combination with other anti-neoplastic therapies.

Immunotherapeutic Challenges for Pediatric Cancers

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

Review: Oncolytic virotherapy, updates and future directions

Oncolytic viruses (OVs) are viral strains that can infect and kill malignant cells while spare their normal counterparts. OVs can access cells through binding to receptors on their surface or through fusion with the plasma membrane and establish a lytic cycle in tumors, while leaving normal tissue essentially unharmed. Multiple viruses have been investigated in humans for the past century. IMLYGIC™ (T-VEC/Talimogene Laherparepvec), a genetically engineered Herpes Simplex Virus, is the first OV approved for use in the United States and the European Union for patients with locally advanced or non-resectable melanoma. Although OVs have a favorable toxicity profile and are impressively active anticancer agents in vitro and in vivo the majority of OVs have limited clinical efficacy as a single agent. While a virus-induced antitumor immune response can enhance oncolysis, when OVs are used systemically, the antiviral immune response can prevent the virus reaching the tumor tissue and having a therapeutic effect. Intratumoral administration can provide direct access to tumor tissue and be beneficial in reducing side effects. Immune checkpoint stimulation in tumor tissue has been noted after OV therapy and can be a natural response to viral-induced oncolysis. Also for immune checkpoint inhibition to be effective in treating cancer, an immune response to tumor neoantigens and an inflamed tumor microenvironment are required, both of which treatment with an OV may provide. Therefore, direct and indirect mechanisms of tumor killing provide rationale for clinical trials investigating the combination of OVs other forms of cancer therapy, including immune checkpoint inhibition.

Preclinical Testing of an Oncolytic Parvovirus: Standard Protoparvovirus H-1PV Efficiently Induces Osteosarcoma Cell Lysis In Vitro

Osteosarcoma is the most frequent malignant disease of the bone. On the basis of early clinical experience in the 1960s with H-1 protoparvovirus (H-1PV) in osteosarcoma patients, this effective oncolytic virus was selected for systematic preclinical testing on various osteosarcoma cell cultures. A panel of five human osteosarcoma cell lines (CAL 72, H-OS, MG-63, SaOS-2, U-2OS) was tested. Virus oncoselectivity was confirmed by infecting non-malignant human neonatal fibroblasts and osteoblasts used as culture models of non-transformed mesenchymal cells. H-1PV was found to enter osteosarcoma cells and to induce viral DNA replication, transcription of viral genes, and translation to viral proteins. After H-1PV infection, release of infectious viral particles from osteosarcoma cells into the supernatant indicated successful viral assembly and egress. Crystal violet staining revealed progressive cytomorphological changes in all osteosarcoma cell lines. Infection of osteosarcoma cell lines with the standard H-1PV caused an arrest of the cell cycle in the G2 phase, and these lines had a limited capacity for standard H-1PV virus replication. The cytotoxicity of wild-type H-1PV virus towards osteosarcoma cells was compared in vitro with that of two variants, Del H-1PV and DM H-1PV, previously described as fitness variants displaying higher infectivity and spreading in human transformed cell lines of different origins. Surprisingly, wild-type H-1PV displayed the strongest cytostatic and cytotoxic effects in this analysis and thus seems the most promising for the next preclinical validation steps in vivo.

NKp46 Recognizes the Sigma1 Protein of Reovirus: Implications for Reovirus-Based Cancer Therapy

The recent approval of oncolytic virus for therapy of melanoma patients has increased the need for precise evaluation of the mechanisms by which oncolytic viruses affect tumor growth. Here we show that the human NK cell-activating receptor NKp46 and the orthologous mouse protein NCR1 recognize the reovirus sigma1 protein in a sialic-acid-dependent manner. We identify sites of NKp46/NCR1 binding to sigma1 and show that sigma1 binding by NKp46/NCR1 leads to NK cell activation in vitro Finally, we demonstrate that NCR1 activation is essential for reovirus-based therapy in vivo Collectively, we have identified sigma1 as a novel ligand for NKp46/NCR1 and demonstrated that NKp46/NCR1 is needed both for clearance of reovirus infection and for reovirus-based tumor therapy.IMPORTANCE Reovirus infects much of the population during childhood, causing mild disease, and hence is considered to be efficiently controlled by the immune system. Reovirus also specifically infects tumor cells, leading to tumor death, and is currently being tested in human clinical trials for cancer therapy. The mechanisms by which our immune system controls reovirus infection and tumor killing are not well understood. We report here that natural killer (NK) cells recognize a viral protein named sigma1 through the NK cell-activating receptor NKp46. Using several mouse tumor models, we demonstrate the importance of NK cells in protection from reovirus infection and in reovirus killing of tumors in vivo Collectively, we identify a new ligand for the NKp46 receptor and provide evidence for the importance of NKp46 in the control of reovirus infections and in reovirus-based cancer therapy.

Opportunities and challenges in the immunological therapy of pediatric malignancy: a concise snapshot

Over the last 50 years, collaborative clinical trials have reduced the number of children dying from pediatric cancer significantly. Unfortunately, certain tumor types have remained resistant to conventional surgical, radiotherapy and chemotherapy combinations, and relapsing and/or refractory disease remains associated with dismal outcomes. Recently, renewed attention has been given to the role for immunotherapies in pediatric oncology. In fact, these combine several attractive features, including (but possibly not limited to) the specificity for cancer cells, potentially in vivo persistence and longevity, and potency against refractory disease. In this narrative review designed for the academic pediatrician, we will concisely review the biological underpinnings behind the immunological therapy of pediatric neoplasms and illustrate the current humoral, cellular approaches, and novel drugs targeting the immune checkpoint, oncolytic viruses, and tumor vaccines. We will also comment on the future directions, challenges, and open questions faced by the field. What is Known: • Cancer immunotherapy drives immune cells and its humoral weaponry to eliminate tumor cells. • This occurs by recognizing antigens ideally expressed only on tumoral, but not normal/healthy, cells. What is New: • Clinical immunotherapy trials have shown responses in children with relapsing/refractory neoplasms. • Novel humoral/cellular immunotherapies, immune checkpoint inhibitors, oncolytic viruses, and tumor vaccines are currently being investigated in pediatric oncology.

Intratumoral Injection of HSV1716, an Oncolytic Herpes Virus, Is Safe and Shows Evidence of Immune Response and Viral Replication in Young Cancer Patients

Purpose: HSV1716 is an oncolytic herpes simplex virus-1 (HSV-1) studied in adults via injection into the brain and superficial tumors. To determine the safety of administering HSV1716 to pediatric patients with cancer, we conducted a phase I trial of image-guided injection in young patients with relapsed or refractory extracranial cancers.Experimental Design: We delivered a single dose of 105 to 107 infectious units of HSV1716 via computed tomography-guided intratumoral injection and measured tumor responses by imaging. Patients were eligible for up to three more doses if they achieved stable disease. We monitored HSV-1 serum titers and shedding by PCR and culture.Results: We administered a single dose of HSV1716 to eight patients and two doses to one patient. We did not observe any dose-limiting toxicities. Adverse events attributed to virus included low-grade fever, chills, and mild cytopenias. Six of eight HSV-1 seronegative patients at baseline showed seroconversion on day 28. Six of nine patients had detectable HSV-1 genomes by PCR in peripheral blood appearing on day +4 consistent with de novo virus replication. Two patients had transient focal increases in metabolic activity on 18fluorine-deoxyglucose PET, consistent with inflammatory reactions. In one case, the same geographic region that flared later appeared necrotic on imaging. No patient had an objective response to HSV1716.Conclusions: Intratumoral HSV1716 is safe and well-tolerated without shedding in children and young adults with late-stage, aggressive cancer. Viremia consistent with virus replication and transient inflammatory reactions hold promise for future HSV1716 studies. Clin Cancer Res; 23(14); 3566-74. ©2017 AACR.

Current Immunotherapeutic Strategies to Enhance Oncolytic Virotherapy

Oncolytic viruses (OV) represent a promising strategy to augment the spectrum of cancer therapeutics. For efficacy, they rely on two general mechanisms: tumor-specific infection/cell-killing, followed by subsequent activation of the host’s adaptive immune response. Numerous OV genera have been utilized in clinical trials, ultimately culminating in the 2015 Food and Drug Administration approval of a genetically engineered herpes virus, Talminogene laherparepvec (T-VEC). It is generally accepted that OV as monotherapy have only modest clinical efficacy. However, due to their ability to elicit specific antitumor immune responses, they are prime candidates to be paired with other immune-modulating strategies in order to optimize therapeutic efficacy. Synergistic strategies to enhance the efficacy of OV include augmenting the host antitumor response through the insertion of therapeutic transgenes such as GM-CSF, utilization of the prime-boost strategy, and combining OV with immune-modulatory drugs such as cyclophosphamide, sunitinib, and immune checkpoint inhibitors. This review provides an overview of these immune-based strategies to improve the clinical efficacy of oncolytic virotherapy.

Shaping the Tumor Stroma and Sparking Immune Activation by CD40 and 4-1BB Signaling Induced by an Armed Oncolytic Virus

Purpose: Pancreatic cancer is a severe indication with short expected survival despite surgery and/or combination chemotherapeutics. Checkpoint blockade antibodies are approved for several cancer indications, but pancreatic cancer has remained refractory. However, there are clinical data suggesting that stimulation of the CD40 pathway may be of interest for these patients. Oncolytic viruses armed with immunostimulatory genes represent an interesting approach. Herein, we present LOAd703, a designed adenovirus armed with trimerized CD40L and 4-1BBL that activates the CD40 and 4-1BB pathways, respectively. As many cells in the tumor stroma, including stellate cells and the infiltrating immune cells, express CD40 and some 4-1BB, we hypothesize that LOAd703 activates immunity and simultaneously modulates the biology of the tumor stroma.Experimental Design: Tumor, stellate, endothelial, and immune cells were infected by LOAd703 and investigated by flow cytometry, proteomics, and functional analyses.Results: LOAd703-infected pancreatic cell lines were killed by oncolysis, and the virus was more effective than standard-of-care gemcitabine. In in vivo xenograft models, LOAd703 efficiently reduced established tumors and could be combined with gemcitabine for additional effect. Infected stellate and tumor cells reduced factors that promote tumor growth (Spp-1, Gal-3, HGF, TGFβ and collagen type I), while chemokines were increased. Molecules involved in lymphocyte migration were upregulated on infected endothelial cells. Dendritic cells were robustly stimulated by LOAd703 to produce costimulators, cytokines and chemokines, and such DCs potently expanded both antigen-specific T cells and NK cells.Conclusions: LOAd703 is a potent immune activator that modulates the stroma to support antitumor responses. Clin Cancer Res; 23(19); 5846-57. ©2017 AACR.

Talimogene Laherparepvec (T-VEC) and Other Oncolytic Viruses for the Treatment of Melanoma

Many mammalian viruses have properties that can be commandeered for the treatment of cancer. These characteristics include preferential infection and replication in tumor cells, the initiation of tumor cell lysis, and the induction of innate and adaptive anti-tumor immunity. Furthermore, viruses can be genetically engineered to reduce pathogenicity and increase immunogenicity resulting in minimally toxic therapeutic agents. Talimogene laherparepvec (T-VEC; Imlygic™), is a genetically modified herpes simplex virus, type 1, and is the first oncolytic virus therapy to be approved for the treatment of advanced melanoma by the US FDA. T-VEC is attenuated by the deletion of the herpes neurovirulence viral genes and enhanced for immunogenicity by the deletion of the viral ICP47 gene. Immunogenicity is further supported by expression of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) gene, which helps promote the priming of T cell responses. T-VEC demonstrated significant improvement in durable response rate, objective response rate, and progression-free survival in a randomized phase III clinical trial for patients with advanced melanoma. This review will discuss the optimal selection of patients for such treatment and describe how therapy is optimally delivered. We will also discuss future directions for oncolytic virus immunotherapy, which will likely include combination T-VEC clinical trials, expansion of T-VEC to other types of non-melanoma skin cancers, and renewed efforts at oncolytic virus drug development with other viruses.

Oncolytic virotherapy for pediatric malignancies: future prospects

Pediatric solid tumors remain a major health concern, with nearly 16,000 children diagnosed each year. Of those, ~2,000 succumb to their disease, and survivors often suffer from lifelong disability secondary to toxic effects of current treatments. Countless multimodality treatment regimens are being explored to make advances against this deadly disease. One targeted treatment approach is oncolytic virotherapy. Conditionally replicating viruses can infect tumor cells while leaving normal cells unharmed. Four viruses have been advanced to pediatric clinical trials, including herpes simplex virus-1, Seneca Valley virus, reovirus, and vaccinia virus. In this review, we discuss the mechanism of action of each virus, pediatric preclinical studies conducted to date, past and ongoing pediatric clinical trials, and potential future direction for these novel viral therapeutics.

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.

Oncolytic virotherapy for urological cancers

Oncolytic virotherapy is a cancer treatment in which replication-competent viruses are used that specifically infect, replicate in and lyse malignant tumour cells, while minimizing harm to normal cells. Anecdotal evidence of the effectiveness of this strategy has existed since the late nineteenth century, but advances and innovations in biotechnological methods in the 1980s and 1990s led to a renewed interest in this type of therapy. Multiple clinical trials investigating the use of agents constructed from a wide range of viruses have since been performed, and several of these enrolled patients with urological malignancies. Data from these clinical trials and from preclinical studies revealed a number of challenges to the effectiveness of oncolytic virotherapy that have prompted the development of further sophisticated strategies. Urological cancers have a range of distinctive features, such as specific genetic mutations and cell surface markers, which enable improving both effectiveness and safety of oncolytic virus treatments. The strategies employed in creating advanced oncolytic agents include alteration of the virus tropism, regulating transcription and translation of viral genes, combination with chemotherapy, radiotherapy or gene therapy, arming viruses with factors that stimulate the immune response against tumour cells and delivery technologies to ensure that the viral agent reaches its target tissue.

Targeted immunotherapy for pediatric solid tumors

Metastatic and refractory pediatric solid tumor malignancies continue to have a poor outcome despite the > 80% cure rates appreciated in many pediatric cancers. Targeted immunotherapy is impacting treatment and survival in these aggressive tumors. We review current promising immunotherapeutic approaches in the pediatric oncology solid tumor setting.

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.

EXPLORING THE ANTITUMOR EFFECT OF VIRUS IN MALIGNANT GLIOMA

Malignant gliomas are the most common type of primary malignant brain tumor with no effective treatments. Current conventional therapies (surgical resection, radiation therapy, temozolomide (TMZ), and bevacizumab administration) typically fail to eradicate the tumors resulting in the recurrence of treatment-resistant tumors. Therefore, novel approaches are needed to improve therapeutic outcomes. Oncolytic viruses (OVs) are excellent candidates as a more effective therapeutic strategy for aggressive cancers like malignant gliomas since OVs have a natural preference or have been genetically engineered to selectively replicate in and kill cancer cells. OVs have been used in numerous preclinical studies in malignant glioma, and a large number of clinical trials using OVs have been completed or are underway that have demonstrated safety, as well as provided indications of effective antiglioma activity. In this review, we will focus on those OVs that have been used in clinical trials for the treatment of malignant gliomas (herpes simplex virus, adenovirus, parvovirus, reovirus, poliovirus, Newcastle disease virus, measles virus, and retrovirus) and OVs examined preclinically (vesicular stomatitis virus and myxoma virus), and describe how these agents are being used.