Engineering and combining oncolytic measles virus for cancer therapy

Cancer immunotherapy using tumor-selective, oncolytic viruses is an emerging therapeutic option for solid and hematologic malignancies. A considerable variety of viruses ranging from small picornaviruses to large poxviruses are currently being investigated as potential candidates. In the early days of virotherapy, non-engineered wild-type or vaccine-strain viruses were employed. However, these viruses often did not fully satisfy the major criteria of safety and efficacy. Since the advent of reverse genetics systems for manipulating various classes of viruses, the field has shifted to developing genetically engineered viruses with an improved therapeutic index. In this review, we will summarize the concepts and strategies of multi-level genetic engineering of oncolytic measles virus, a prime candidate for cancer immunovirotherapy. Furthermore, we will provide a brief overview of measles virus-based multimodal combination therapies for improved tumor control and clinical efficacy.     

Oncolytic virotherapy

Oncolytic virotherapy is an emerging treatment modality that uses replication-competent viruses to destroy cancers. Recent advances include preclinical proof of feasibility for a single-shot virotherapy cure, identification of drugs that accelerate intratumoral virus propagation, strategies to maximize the immunotherapeutic action of oncolytic viruses and clinical confirmation of a critical viremic threshold for vascular delivery and intratumoral virus replication. The primary clinical milestone has been completion of accrual in a phase 3 trial of intratumoral herpes simplex virus therapy using talimogene laherparepvec for metastatic melanoma. Key challenges for the field are to select 'winners' from a burgeoning number of oncolytic platforms and engineered derivatives, to transiently suppress but then unleash the power of the immune system to maximize both virus spread and anticancer immunity, to develop more meaningful preclinical virotherapy models and to manufacture viruses with orders-of-magnitude higher yields than is currently possible.     

Advance in herpes simplex viruses for cancer therapy

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

Lung cancer and oncolytic virotherapy——enemy's enemy

Lung cancer is one of the malignant tumors that seriously threaten human health worldwide, while the covid-19 virus has become people's nightmare after the coronavirus pandemic. There are too many similarities between cancer cells and viruses, one of the most significant is that both of them are our enemies. The strategy to take the advantage of the virus to beat cancer cells is called Oncolytic virotherapy. When immunotherapy represented by immune checkpoint inhibitors has made remarkable breakthroughs in the clinical practice of lung cancer, the induction of antitumor immunity from immune cells gradually becomes a rapidly developing and promising strategy of cancer therapy. Oncolytic virotherapy is based on the same mechanisms that selectively kill tumor cells and induce systemic anti-tumor immunity, but still has a long way to go before it becomes a standard treatment for lung cancer. This article provides a comprehensive review of the latest progress in oncolytic virotherapy for lung cancer, including the specific mechanism of oncolytic virus therapy and the main types of oncolytic viruses, and the combination of oncolytic virotherapy and existing standard treatments. It aims to provide new insights and ideas on oncolytic virotherapy for lung cancer.     

Optimization of Virotherapy for Cancer

Several viruses preferentially infect and replicate in cancer cells by usurping pathways that are defective in the tumor cell population. Such viruses have a potential as oncolytic agents. The aim of tumor virotherapy is that after injection of the replicating virus, it propagates in the tumor cell population with amplification. As a result, the oncolytic virus spreads to eradicate the tumor. The outcome of tumor virotherapy is determined by population dynamics and different from standard cancer therapy. Several models have been developed that provided considerable insights on the potential therapeutic scenarios. However, virotherapy is potentially risky since large amounts of a replicating virus are injected in the host with a risk of adverse effects. Therefore, the optimal dose, number of doses, and timing are expected to play an important role on the outcome both for the tumor and the host. In the current work, we combine a model of the dynamics of tumor virotherapy that was validated with experimental data with optimization theory to illustrate how we can improve the outcome of tumor therapy. In this first report, we demonstrate that (i) in most circumstances, anything more than two administrations of a vector is not helpful, (ii) correctly timed delivery of the virus provides superior results compared to regularly scheduled therapy or continuous infusion, (iii) a second dose of virus that is not properly timed leads to a worse outcome compared to a single dose of virus, and (iv) it is less costly to treat larger tumors.     

Current landscape and perspective of oncolytic viruses and their combination therapies

Oncolytic virotherapy has become an important strategy in cancer immunotherapy. Oncolytic virus (OV) can reshape the tumor microenvironment (TME) through its replication-mediated oncolysis and transgene-produced anticancer effect, inducing an antitumor immune response and creating favorable conditions for the combination of other therapeutic measures. Extensive preclinical and clinical data have suggested that OV-based combination therapy has definite efficacy and promising prospects. Recently, several clinical trials of oncolytic virotherapy combined with immunotherapy have made breakthroughs. This review comprehensively elaborates the OV types and their targeting mechanisms, the selection of anticancer genes armed in OVs, and the therapeutic modes of action and strategies of OVs to provide a theoretical basis for the better design and construction of OVs and the optimization of OV-based therapeutic strategies.     

Clinical trials with oncolytic reovirus: Moving beyond phase I into combinations with standard therapeutics

It is time for those working on oncolytic viruses to take stock of the status of the field. We now have at our disposal an array of potential therapeutic agents, and are beginning to conduct early-phase clinical trials in patients with relapsed/metastatic cancers. By drawing on lessons learned during the development of other biological therapies, such as monoclonal antibodies and targeted small molecule inhibitors, we are now in a position to chart the course of the next wave of trials that will go beyond the phase I studies of safety and feasibility. In this article we review our approach to the development of oncolytic viruses as cancer therapeutics. In doing so, we emphasise the fact that this process is modular and involves multiple iterative steps between the laboratory and the clinic. Ultimately, at least in the medium term, the future of oncolytic virotherapy lies in combination regimens with standard anti-cancer agents such as radiation and chemotherapy.     

溶瘤病毒的免疫学机制及临床研究进展

溶瘤病毒（oncolytic virus,OVs）历经百年发展,应用于当前最具潜力的肿瘤免疫疗法。它主要是天然的或基因修饰的DNA病毒和RNA病毒。近年来随着基因工程技术的飞跃发展,经基因改造的溶瘤病毒在肿瘤治疗领域取得很大进展,很多不同类型的病毒（包括单纯疱疹病毒、腺病毒、痘病毒、麻疹病毒和呼肠孤病毒等）正处于临床前研究、临床试验阶段或已批准上市,显示了良好的安全性和临床疗效。普遍认为溶瘤病毒靶向杀伤肿瘤细胞是通过选择性在肿瘤细胞内自我复制,最终裂解肿瘤细胞,同时可激发机体的免疫应答反应,进而增强抗肿瘤免疫效果,靶向杀伤肿瘤细胞而对正常细胞无明显影响。运用基因重组技术将溶瘤病毒与免疫检查点相结合以及肿瘤免疫联合疗法的兴起和不断进步,使溶瘤病毒的应用更加广泛,但仍存在病毒靶向性、安全性、给药途径等瓶颈问题。本文综述了溶瘤病毒的发展史、病毒分类、不同类型溶瘤病毒产品的临床研究进展、溶瘤病毒靶向杀伤肿瘤的免疫学机制及未来发展面临的挑战与展望等。     

Non-invasive in vivo monitoring of trackable viruses expressing soluble marker peptides

Noninvasive methods are needed to study the kinetic properties of viruses in living organisms. Oncolytic viruses are used increasingly for cancer therapy but there is currently no satisfactory way to measure efficiency of tumor transduction, changing levels of viral gene expression or the timing of virus elimination. We therefore generated trackable oncolytic measles viruses expressing inert (nonimmunogenic, nonfunctional and accurately measurable) soluble marker peptides. The marker peptides did not compromise virus replication. Ex vivo and in vivo kinetics of the trackable viruses could be easily followed by measuring the concentrations of virally encoded marker peptides in culture supernatant or in serum. When mice bearing human tumor xenografts were challenged with the trackable viruses, distinct kinetic profiles of marker-gene expression could be correlated with distinct therapeutic outcomes. Oncolytic viruses expressing inert soluble marker polypeptides should greatly facilitate the rational development of effective, individually tailored cancer virotherapy.     

The emergence of combinatorial strategies in the development of RNA oncolytic virus therapies

Oncolytic viruses (OVs) represent an exciting new biological approach to cancer therapy. In particular, RNA viruses have emerged as potent agents for oncolytic virotherapy because of their capacity to specifically target and destroy tumour cells while sparing normal cells and tissues. Several barriers remain in the development of OV therapy, including poor penetration into the tumour mass, inefficient virus replication in primary cancers, and tumour-specific resistance to OV-mediated killing. The combination of OVs with cytotoxic agents, such as small molecule inhibitors of signalling or immunomodulators, as well as stealth delivery of therapeutic viruses have shown promise as novel experimental strategies to overcome resistance to viral oncolysis. These agents complement OV therapy by unblocking host pathways, delivering viruses with greater efficiency and/or increasing virus proliferation at the tumour site. In this review, we summarize recent development of these concepts, the potential obstacles, and future prospects for the clinical utilization of RNA OVs in cancer therapy.     

Kinase inhibitors with viral oncolysis: Unmasking pharmacoviral approaches for cancer therapy

There are more than 500 kinases in the human genome, many of which are oncogenic once constitutively activated. Fortunately, numerous hyperactive kinases are druggable, and several targeted small molecule kinase inhibitors have demonstrated impressive clinical benefits in cancer treatment. However, their often cytostatic rather than cytotoxic effect on cancer cells, and the development of resistance mechanisms, remain significant limitations to these targeted therapies. Oncolytic viruses are an emerging class of immunotherapeutic agents with a specific oncotropic nature and excellent safety profile, highlighting them as a promising alternative to conventional therapeutic modalities. Nonetheless, the clinical efficacy of oncolytic virotherapy is challenged by immunological and physical barriers that limit viral delivery, replication, and spread within tumours. Several of these barriers are often associated with oncogenic kinase activity and, in some cases, worsened by the action of oncolytic viruses on kinase signaling during infection. What if inhibiting these kinases could potentiate the cancer-lytic and anti-tumour immune stimulating properties of oncolytic virotherapies? This could represent a paradigm shift in the use of specific kinase inhibitors in the clinic and provide a novel therapeutic approach to the treatment of cancers. A phase III clinical trial combining the oncolytic Vaccinia virus Pexa-Vec with the kinase inhibitor Sorafenib was initiated. While this trial failed to show any benefits over Sorafenib monotherapy in patients with advanced liver cancer, several pre-clinical studies demonstrate that targeting kinases combined with oncolytic viruses have synergistic effects highlighting this strategy as a unique avenue to cancer therapy. Herein, we review the combinations of oncolytic viruses with kinase inhibitors reported in the literature and discuss the clinical opportunities that represent these pharmacoviral approaches.     

Posttranslational modification of vesicular stomatitis virus glycoprotein, but not JNK inhibition, is the antiviral mechanism of SP600125

Vesicular stomatitis virus (VSV), a negative-sense single-stranded-RNA rhabdovirus, is an extremely promising oncolytic agent for cancer treatment. Since oncolytic virotherapy is moving closer to clinical application, potentially synergistic combinations of oncolytic viruses and molecularly targeted antitumor agents are becoming a meaningful strategy for cancer treatment. Mitogen-activated protein kinase (MAPK) inhibitors have been shown to impair liver cell proliferation and tumor development, suggesting their potential use as therapeutic agents for hepatocellular carcinoma (HCC). In this work, we show that the impairment of MAPK in vitro did not interfere with the oncolytic properties of VSV in HCC cell lines. Moreover, the administration of MAPK inhibitors did not restore the responsiveness of HCC cells to alpha/beta interferon (IFN-α/β). In contrast to previous reports, we show that JNK inhibition by the inhibitor SP600125 is not responsible for VSV attenuation in HCC cells and that this compound acts by causing a posttranslational modification of the viral glycoprotein.     

Cancer selective adenoviruses

Ten years ago Frank McCormick proposed dl1520 as an oncolytic adenovirus. Although great as an inspiration for better oncolytic viruses it was far from a good product. As Onyx-015, it underwent a wish-fulfilling clinical development program seizing the opportunity left by its p53-targeted non-replicative counterpart Ad-p53. Now, facing a skeptical environment, more selective and potent oncolytic adenoviruses await their clinical opportunity. However, advance in key issues remains elusive, such as, selectivity or retargeting at the level of cell receptors to improve pharmacokinetics. Preclinical models and a few clinical data on biodistribution show that only a minimal proportion of the injected dose reaches the tumors after systemic administration. Once in the tumor, the virus must overcome barriers to efficient spread imposed by stroma and immune responses. Arming the oncolytic virus with transgenes is a natural combination of virotherapy and gene therapy strategies. Transgenes that increase virus production or cellular spread may help to overcome these barriers. Cytotoxic transgenes can help to eliminate tumor cells but need to be compatible with efficient virus replication. These challenges require a careful approach to clinical development and a great deal of collaboration to launch clinical tests with a virus backbone that contains intellectual property from multiple sources.     

The two-faces of NK cells in oncolytic virotherapy

Oncolytic viruses (OVs) are immunotherapeutics capable of directly killing cancer cells and with potent immunostimulatory properties. OVs exert their antitumor effect, at least partially, by activating the antitumor immune response, of which NK cells are an important component. However, if on the one hand increasing evidence revealed that NK cells are important mediators of oncolytic virotherapy, on the other hand, NK cells have evolved to fight viral infections, and therefore they can have a detrimental effect for the efficacy of OVs. In this review, we will discuss the dichotomy between the antitumor and antiviral functions of NK cells related to oncolytic virotherapy. We will also review NK cell-based and OV-based therapies, engineered OVs aimed at enhancing immune stimulation, and combination therapies involving OVs and NK cells currently used in cancer immunotherapy.     

The role of cancer metabolism in defining the success of oncolytic viro-immunotherapy

Oncolytic viruses infect, replicate in, and kill cancer cells selectively without harming normal cells. The rapidly expanding clinical development of oncolytic virotherapy is an exciting interdisciplinary field that provides insights into virology, oncology, and immunotherapy. Recent years have seen greater focus on rational design of cancer-selective viruses together with strategies to exploit their immunostimulatory capabilities, ultimately to develop powerful oncolytic cancer vaccines. However, despite great interest in the field, many important experiments are still conducted under optimum conditions in vitro, with many nutrients present in excess and with cellular stress kept to a minimum. Whilst this provides a convenient platform for cell culture, it bears little relation to the typical conditions found within a tumour in vivo, where cells are often subject to a range of metabolic and environmental stresses. Viral infection and cancer will both lead to production of metabolites that are also not present in media in vitro. Understanding how oncolytic viruses interact with cells exposed to more representative metabolic conditions in vitro represents an under-explored area of study that could provide valuable insight into the intelligent design of superior oncolytic viruses and help bridge the gap between bench and bedside. This review summarises the major metabolic pathways altered in cancer cells, during viral infection and highlights possible targets for future studies.     

Oncolytic virotherapy for cancer treatment: challenges and solutions

Advances in gene modification and viral therapy have led to the development of a variety of vectors in several viral families that are capable of replication specifically in tumor cells. Because of the nature of viral delivery, infection, and replication, this technology, oncolytic virotherapy, may prove valuable for treating cancer patients, especially those with inoperable tumors. Current limitations exist, however, for oncolytic virotherapy. They include the body's B and T cell responses, innate inflammatory reactions, host range, safety risks involved in using modified viruses as treatments, and the requirement that most currently available oncolytic viruses require local administration. Another important constraint is that genetically enhanced vectors may or may not adhere to their replication restrictions in long-term applications. Several solutions and strategies already exist, however, to minimize or circumvent many of these limitations, supporting viral oncolytic therapy as a viable option and powerful tool in the fight against cancer.     

溶瘤单纯疱疹病毒治疗技术及其进展

溶瘤病毒治疗是当前肿瘤治疗技术的研究热点,溶瘤单纯疱疹病毒是目前研究最多的,也是抗肿瘤作用最好的溶瘤病毒之一,本文就主要介绍溶瘤单纯疱疹病毒的优势、遗传操作、发展策略、研究进展及靶向性策略等。     

Oncolytic virotherapy for pancreatic ductal adenocarcinoma: A glimmer of hope after years of disappointment?

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and highly lethal malignancies. Existing therapeutic interventions have so far been unsuccessful in improving prognosis, and survival remains very poor. Oncolytic virotherapy represents a promising, yet not fully explored, alternative strategy for the treatment of PDAC. Oncolytic viruses (OVs) infect, replicate within and lyse tumor cells specifically and stimulate antitumor immune responses. Multiple challenges have hampered the efficacy of oncolytic virotherapy for PDAC, the most significant being the desmoplastic and immunosuppressive pancreatic tumor microenvironment (TME). The TME limits the access of therapeutic drugs and the infiltration of effector T cells and natural killer (NK) cells into the tumor mass. Additionally, cancer cells promote the secretion of immunosuppressive factors and develop mechanisms to evade the host immune system. Because of their oncolytic and immune-stimulating properties, OVs are the ideal candidates for counteracting the pancreatic immunosuppressive TME and for designing combination therapies that can be clinically exploited in clinical trials that seek to improve the prognosis of PDAC.     

Oncolytic adenovirus: A tool for cancer therapy in combination with other therapeutic approaches

Cancer therapy using oncolytic viruses is an emerging area, in which viruses are engineered to selectively propagate in tumor tissues without affecting healthy cells. Because of the advantages that adenoviruses (Ads) have over other viruses, they are more considered. To achieve tumor selectivity, two main modifications on Ads genome have been applied: small deletions and insertion of tissue- or tumor-specific promoters. Despite oncolytic adenoviruses ability in tumor cell lysis and immune responses stimulation, to further increase their antitumor effects, genomic modifications have been carried out including insertion of checkpoint inhibitors and antigenic or immunostimulatory molecules into the adenovirus genome and combination with dendritic cells and chemotherapeutic agents. This study reviews oncolytic adenoviruses structures, their antitumor efficacy in combination with other therapeutic strategies, and finally challenges around this treatment approach.