Chikungunya-vesicular stomatitis chimeric virus targets and eliminates brain tumors

Oncolytic Therapy of Solid Tumors by Modified Vesicular Stomatitis Virus

Vesicular stomatitis virus (VSV) is a promising oncolytic virus for treating solid tumors. We recently engineered a replicating VSV that specifically targets and destroys Her2/neu-expressing cancer cells. This virus was created by eliminating its natural binding site and adding a coding sequence for a single chain antibody to the Her2/neu receptor into its genome. Such an approach can be tailored to target various cellular surface molecules. This mini review will discuss genomic modifications of VSVs and their role in oncolytic therapy and discuss some challenges for moving VSVs to clinical applications.

RVG Peptide-Functionalized Favipiravir Nanoparticle Delivery System Facilitates Antiviral Therapy of Neurotropic Virus Infection in a Mouse Model

Neurotropic viruses severely damage the central nervous system (CNS) and human health. Common neurotropic viruses include rabies virus (RABV), Zika virus, and poliovirus. When treating neurotropic virus infection, obstruction of the blood-brain barrier (BBB) reduces the efficiency of drug delivery to the CNS. An efficient intracerebral delivery system can significantly increase intracerebral delivery efficiency and facilitate antiviral therapy. In this study, a rabies virus glycopeptide (RVG) functionalized mesoporous silica nanoparticle (MSN) packaging favipiravir (T-705) was developed to generate T-705@MSN-RVG. It was further evaluated for drug delivery and antiviral treatment in a VSV-infected mouse model. The RVG, a polypeptide consisting of 29 amino acids, was conjugated on the nanoparticle to enhance CNS delivery. The T-705@MSN-RVG caused a significant decrease in virus titers and virus proliferation without inducing substantial cell damage in vitro. By releasing T-705, the nanoparticle promoted viral inhibition in the brain during infection. At 21 days post-infection (dpi), a significantly enhanced survival ratio (77%) was observed in the group inoculated with nanoparticle compared with the non-treated group (23%). The viral RNA levels were also decreased in the therapy group at 4 and 6 dpi compared with that of the control group. The T-705@MSN-RVG could be considered a promising system for CNS delivery for treating neurotropic virus infection.

Recent Developments in Glioblastoma Therapy: Oncolytic Viruses and Emerging Future Strategies

Glioblastoma is the most aggressive form of malignant brain tumor. Standard treatment protocols and traditional immunotherapy are poorly effective as they do not significantly increase the long-term survival of glioblastoma patients. Oncolytic viruses (OVs) may be an effective alternative approach. Combining OVs with some modern treatment options may also provide significant benefits for glioblastoma patients. Here we review virotherapy for glioblastomas and describe several OVs and their combination with other therapies. The personalized use of OVs and their combination with other treatment options would become a significant area of research aiming to develop the most effective treatment regimens for glioblastomas.

Applications of self-replicating RNA

Self-replicating RNA viral vectors have been engineered for both prophylactic and therapeutic applications. Mainly the areas of infectious diseases and cancer have been targeted. Both positive and negative strand RNA viruses have been utilized including alphaviruses, flaviviruses, measles viruses and rhabdoviruses. The high-level of RNA amplification has provided efficient expression of viral surface proteins and tumor antigens. Immunization studies in animal models have elicit robust neutralizing antibody responses. In the context of infectious diseases, immunization with self-replicating RNA viral vectors has provided protection against challenges with lethal doses of pathogens in animal models. Similarly, immunization with vectors expressing tumor antigens has resulted in tumor regression and eradication and protection against tumor challenges in animal models. The transient nature and non-integration of viral RNA into the host genome are ideal features for vaccine development. Moreover, self-replicating RNA viral vectors show great flexibility as they can be applied as recombinant viral particles, RNA replicons or DNA replicon plasmids. Several clinical trials have been conducted especially in the area of cancer immunotherapy.

Application of mRNA Technology in Cancer Therapeutics

mRNA-based therapeutics pose as promising treatment strategies for cancer immunotherapy. Improvements in materials and technology of delivery systems have helped to overcome major obstacles in generating a sufficient immune response required to fight a specific type of cancer. Several in vivo models and early clinical studies have suggested that various mRNA treatment platforms can induce cancer-specific cytolytic activity, leading to numerous clinical trials to determine the optimal method of combinations and sequencing with already established agents in cancer treatment. Nevertheless, further research is required to optimize RNA stabilization, delivery platforms, and improve clinical efficacy by interacting with the tumor microenvironment to induce a long-term antitumor response. This review provides a comprehensive summary of the available evidence on the recent advances and efforts to overcome existing challenges of mRNA-based treatment strategies, and how these efforts play key roles in offering perceptive insights into future considerations for clinical application.

Self-replicating vehicles based on negative strand RNA viruses

Self-replicating RNA viruses have been engineered as efficient expression vectors for vaccine development for infectious diseases and cancers. Moreover, self-replicating RNA viral vectors, particularly oncolytic viruses, have been applied for cancer therapy and immunotherapy. Among negative strand RNA viruses, measles viruses and rhabdoviruses have been frequently applied for vaccine development against viruses such as Chikungunya virus, Lassa virus, Ebola virus, influenza virus, HIV, Zika virus, and coronaviruses. Immunization of rodents and primates has elicited strong neutralizing antibody responses and provided protection against lethal challenges with pathogenic viruses. Several clinical trials have been conducted. Ervebo, a vaccine based on a vesicular stomatitis virus (VSV) vector has been approved for immunization of humans against Ebola virus. Different types of cancers such as brain, breast, cervical, lung, leukemia/lymphoma, ovarian, prostate, pancreatic, and melanoma, have been the targets for cancer vaccine development, cancer gene therapy, and cancer immunotherapy. Administration of measles virus and VSV vectors have demonstrated immune responses, tumor regression, and tumor eradication in various animal models. A limited number of clinical trials have shown well-tolerated treatment, good safety profiles, and dose-dependent activity in cancer patients.

Oncolytic Viro-Immunotherapy: An Emerging Option in the Treatment of Gliomas

The prognosis of malignant gliomas remains poor, with median survival fewer than 20 months and a 5-year survival rate merely 5%. Their primary location in the central nervous system (CNS) and its immunosuppressive environment with little T cell infiltration has rendered cancer therapies mostly ineffective, and breakthrough therapies such as immune checkpoint inhibitors (ICIs) have shown limited benefit. However, tumor immunotherapy is developing rapidly and can help overcome these obstacles. But for now, malignant gliomas remain fatal with short survival and limited therapeutic options. Oncolytic virotherapy (OVT) is a unique antitumor immunotherapy wherein viruses selectively or preferentially kill tumor cells, replicate and spread through tumors while inducing antitumor immune responses. OVTs can also recondition the tumor microenvironment and improve the efficacy of other immunotherapies by escalating the infiltration of immune cells into tumors. Some OVTs can penetrate the blood-brain barrier (BBB) and possess tropism for the CNS, enabling intravenous delivery. Despite the therapeutic potential displayed by oncolytic viruses (OVs), optimizing OVT has proved challenging in clinical development, and marketing approvals for OVTs have been rare. In June 2021 however, as a genetically engineered OV based on herpes simplex virus-1 (G47Δ), teserpaturev got conditional and time-limited approval for the treatment of malignant gliomas in Japan. In this review, we summarize the current state of OVT, the synergistic effect of OVT in combination with other immunotherapies as well as the hurdles to successful clinical use. We also provide some suggestions to overcome the challenges in treating of gliomas.

Self-Replicating RNA Viruses for Vaccine Development against Infectious Diseases and Cancer

Alphaviruses, flaviviruses, measles viruses and rhabdoviruses are enveloped single-stranded RNA viruses, which have been engineered for recombinant protein expression and vaccine development. Due to the presence of RNA-dependent RNA polymerase activity, subgenomic RNA can replicate close to 106 copies per cell for translation in the cytoplasm providing extreme transgene expression levels, which is why they are named self-replicating RNA viruses. Expression of surface proteins of pathogens causing infectious disease and tumor antigens provide the basis for vaccine development against infectious diseases and cancer. Self-replicating RNA viral vectors can be administered as replicon RNA at significantly lower doses than conventional mRNA, recombinant particles, or DNA plasmids. Self-replicating RNA viral vectors have been applied for vaccine development against influenza virus, HIV, hepatitis B virus, human papilloma virus, Ebola virus, etc., showing robust immune response and protection in animal models. Recently, paramyxovirus and rhabdovirus vector-based SARS-CoV-2 vaccines as well as RNA vaccines based on self-amplifying alphaviruses have been evaluated in clinical settings. Vaccines against various cancers such as brain, breast, lung, ovarian, prostate cancer and melanoma have also been developed. Clinical trials have shown good safety and target-specific immune responses. Ervebo, the VSV-based vaccine against Ebola virus disease has been approved for human use.

Diversity in responses to oncolytic Lassa-vesicular stomatitis virus in patient-derived glioblastoma cells

The difficulty of glioblastoma treatment makes it a good candidate for novel therapies, such as oncolytic viruses. Vesicular stomatitis virus expressing Lassa virus glycoprotein (Lassa-VSV) showed significant promise in animal models using established glioblastoma cell lines. These experiments were to determine the susceptibility of low-passage, patient-derived cell lines to Lassa-VSV oncolysis. Four patient-derived glioblastoma cell lines were infected with Lassa-VSV that expresses green fluorescent protein (GFP) and analyzed by fluorescence microscopy, flow cytometry, and cell viability assays. Cells were also analyzed as tumorspheres containing primarily glioma stem-like cells. Three low-passage, patient-derived cells were further analyzed with RNA sequencing (RNA-seq). Individual cell lines varied somewhat in their levels of viral gene expression and time course of Lassa-VSV-induced cell death, but each was susceptible to Lassa-VSV. Brain Tumor Center of Excellence (BTCOE) 4765 cells had the highest level of expression of interferon-stimulated genes but were most susceptible to Lassa-VSV-induced cell death, indicating that more susceptible cells do not necessarily have lower interferon pathway activation. Cells cultured as tumorspheres and infected with Lassa-VSV also showed variable susceptibility to Lassa-VSV, but BTCOE 4765 cells were least susceptible. Thus, patient-derived brain tumor cells show variable responses to Lassa-VSV infection, but each of the lines was susceptible to VSV oncolysis.

Immunovirotherapy for the Treatment of Glioblastoma and Other Malignant Gliomas

Glioblastoma multiforme (GBM) represents one of the most challenging malignancies due to many factors including invasiveness, heterogeneity, and an immunosuppressive microenvironment. Current treatment modalities have resulted in only modest effect on outcomes. The development of viral vectors for oncolytic immunovirotherapy and targeted drug delivery represents a promising therapeutic prospect for GBM and other brain tumors. A host of genetically engineered viruses, herpes simplex virus, poliovirus, measles, and others, have been described and are at various stages of clinical development. Herein we provide a review of the advances and current state of oncolytic virotherapy for the targeted treatment of GBM and malignant gliomas.

Application of Viral Vectors for Vaccine Development with a Special Emphasis on COVID-19

Viral vectors can generate high levels of recombinant protein expression providing the basis for modern vaccine development. A large number of different viral vector expression systems have been utilized for targeting viral surface proteins and tumor-associated antigens. Immunization studies in preclinical animal models have evaluated the elicited humoral and cellular responses and the possible protection against challenges with lethal doses of infectious pathogens or tumor cells. Several vaccine candidates for both infectious diseases and various cancers have been subjected to a number of clinical trials. Human immunization trials have confirmed safe application of viral vectors, generation of neutralizing antibodies and protection against challenges with lethal doses. A special emphasis is placed on COVID-19 vaccines based on viral vectors. Likewise, the flexibility and advantages of applying viral particles, RNA replicons and DNA replicon vectors of self-replicating RNA viruses for vaccine development are presented.

Oncolytic Viruses as a Platform for the Treatment of Malignant Brain Tumors

Malignant brain tumors remain incurable diseases. Although much effort has been devoted to improving patient outcome, multiple factors such as the high tumor heterogeneity, the strong tumor-induced immunosuppressive microenvironment, and the low mutational burden make the treatment of these tumors especially challenging. Thus, novel therapeutic strategies are urgent. Oncolytic viruses (OVs) are biotherapeutics that have been selected or engineered to infect and selectively kill cancer cells. Increasingly, preclinical and clinical studies demonstrate the ability of OVs to recruit T cells and induce durable immune responses against both virus and tumor, transforming a “cold” tumor microenvironment into a “hot” environment. Besides promising clinical results as a monotherapy, OVs can be powerfully combined with other cancer therapies, helping to overcome critical barriers through the creation of synergistic effects in the fight against brain cancer. Although many questions remain to be answered to fully exploit the therapeutic potential of OVs, oncolytic virotherapy will clearly be part of future treatments for patients with malignant brain tumors.

Self-Amplifying RNA Viruses as RNA Vaccines

Single-stranded RNA viruses such as alphaviruses, flaviviruses, measles viruses and rhabdoviruses are characterized by their capacity of highly efficient self-amplification of RNA in host cells, which make them attractive vehicles for vaccine development. Particularly, alphaviruses and flaviviruses can be administered as recombinant particles, layered DNA/RNA plasmid vectors carrying the RNA replicon and even RNA replicon molecules. Self-amplifying RNA viral vectors have been used for high level expression of viral and tumor antigens, which in immunization studies have elicited strong cellular and humoral immune responses in animal models. Vaccination has provided protection against challenges with lethal doses of viral pathogens and tumor cells. Moreover, clinical trials have demonstrated safe application of RNA viral vectors and even promising results in rhabdovirus-based phase III trials on an Ebola virus vaccine. Preclinical and clinical applications of self-amplifying RNA viral vectors have proven efficient for vaccine development and due to the presence of RNA replicons, amplification of RNA in host cells will generate superior immune responses with significantly reduced amounts of RNA delivered. The need for novel and efficient vaccines has become even more evident due to the global COVID-19 pandemic, which has further highlighted the urgency in challenging emerging diseases.

Plant Viruses in Plant Molecular Pharming: Toward the Use of Enveloped Viruses

Plant molecular pharming has emerged as a reliable platform for recombinant protein expression providing a safe and low-cost alternative to bacterial and mammalian cells-based systems. Simultaneously, plant viruses have evolved from pathogens to molecular tools for recombinant protein expression, chimaeric viral vaccine production, and lately, as nanoagents for drug delivery. This review summarizes the genesis of viral vectors and agroinfection, the development of non-enveloped viruses for various biotechnological applications, and the on-going research on enveloped plant viruses.