Recent advances in oncolytic virus design

Recent progress in the immunotherapy of hepatocellular carcinoma: Non-coding RNA-based immunotherapy may improve the outcome

Hepatocellular carcinoma (HCC) is the second most lethal cancer and a leading cause of cancer-related mortality worldwide. Immune checkpoint inhibitors (ICIs) significantly improved the prognosis of HCC; however, the therapeutic response remains unsatisfactory in a substantial proportion of patients or needs to be further improved in responders. Herein, other methods of immunotherapy, including vaccine-based immunotherapy, adoptive cell therapy, cytokine delivery, kynurenine pathway inhibition, and gene delivery, have been adopted in clinical trials. Although the results were not encouraging enough to expedite their marketing. A major proportion of human genome is transcribed into non-coding RNAs (ncRNAs). Preclinical studies have extensively investigated the roles of ncRNAs in different aspects of HCC biology. HCC cells reprogram the expression pattern of numerous ncRNAs to decrease the immunogenicity of HCC, exhaust the cytotoxic and anti-cancer function of CD8 + T cells, natural killer (NK) cells, dendritic cells (DCs), and M1 macrophages, and promote the immunosuppressive function of T Reg cells, M2 macrophages, and myeloid-derived suppressor cells (MDSCs). Mechanistically, cancer cells recruit ncRNAs to interact with immune cells, thereby regulating the expression of immune checkpoints, functional receptors of immune cells, cytotoxic enzymes, and inflammatory and anti-inflammatory cytokines. Interestingly, prediction models based on the tissue expression or even serum levels of ncRNAs could predict response to immunotherapy in HCC. Moreover, ncRNAs markedly potentiated the efficacy of ICIs in murine models of HCC. This review article first discusses recent advances in the immunotherapy of HCC, then dissects the involvement and potential application of ncRNAs in the immunotherapy of HCC.

Application of oncolytic virus in tumor therapy

Oncolytic viruses (OVs) can selectively kill tumor cells without affecting normal cells, as well as activate the innate and adaptive immune systems in patients. Thus, they have been considered as a promising measure for safe and effective cancer treatment. Recently, a few genetically engineered OVs have been developed to further improve the effect of tumor elimination by expressing specific immune regulatory factors and thus enhance the body's antitumor immunity. In addition, the combined therapies of OVs and other immunotherapies have been applied in clinical. Although there are many studies on this hot topic, a comprehensive review is missing on illustrating the mechanisms of tumor clearance by OVs and how to modify engineered OVs to further enhance their antitumor effects. In this study, we provided a review on the mechanisms of immune regulatory factors in OVs. In addition, we reviewed the combined therapies of OVs with other therapies including radiotherapy and CAR-T or TCR-T cell therapy. The review is useful in further generalize the usage of OV in cancer treatment.

Immunotherapy for advanced hepatocellular carcinoma: From clinical trials to real-world data and future advances

Hepatocellular carcinoma (HCC) is a leading cause of cancer-associated mortality worldwide. HCC is an inflammation-associated immunogenic cancer that frequently arises in chronically inflamed livers. Advanced HCC is managed with systemic therapies; the tyrosine kinase inhibitor (TKI) sorafenib has been used in 1^st-line setting since 2007. Immunotherapies have emerged as promising treatments across solid tumors including HCC for which immune checkpoint inhibitors (ICIs) are licensed in 1^st- and 2^nd-line treatment setting. The treatment field of advanced HCC is continuously evolving. Several clinical trials are investigating novel ICI candidates as well as new ICI regimens in combination with other therapeutic modalities including systemic agents, such as other ICIs, TKIs, and anti-angiogenics. Novel immunotherapies including adoptive cell transfer, vaccine-based approaches, and virotherapy are also being brought to the fore. Yet, despite advances, several challenges persist. Lack of real-world data on the use of immunotherapy for advanced HCC in patients outside of clinical trials constitutes a main limitation hindering the breadth of application and generalizability of data to this larger and more diverse patient cohort. Consequently, issues encountered in real-world practice include patient ineligibly for immunotherapy because of contraindications, comorbidities, or poor performance status; lack of response, efficacy, and safety data; and cost-effectiveness. Further real-world data from high-quality large prospective cohort studies of immunotherapy in patients with advanced HCC is mandated to aid evidence-based clinical decision-making. This review provides a critical and comprehensive overview of clinical trials and real-world data of immunotherapy for HCC, with a focus on ICIs, as well as novel immunotherapy strategies underway.

Translation of cancer immunotherapy from the bench to the bedside

The tremendous success of immune checkpoint blockades has revolutionized cancer management. Our increased understanding of the cell types that compose the tumor microenvironment (TME), including those of the innate and adaptive immune system, has helped to shape additional immune modulatory strategies in cancer care. Pre-clinical and clinical investigations targeting novel checkpoint interactions and key pathways that regulate cancer immunity continue to increase rapidly. Various combinatorial drug regimens are being tested in attempt to achieve durable response and survival rates of patients with cancer. This review provides an overview of specific components of the TME, an introduction to novel immune checkpoints, followed by a survey of present day and future combination immune modulatory therapies. The idea that the immune system can recognize and destroy tumor cells was first described in the cancer immunosurveillance hypothesis of Burnet and Thomas. However, early experimental evidence failed to support the concept. It was not until the late 1990s when seminal papers clearly showed the existence of cancer immunosurveillance, leading to the cancer immunoediting hypothesis. In this century, progress in the understanding of negative regulators of the immune response led to the discovery that inhibition of these regulators in patients with cancer could lead to dramatic and durable remissions. Drs. Tasuku Honjo and James P. Allison were awarded the Nobel Prize in 2018 for their pioneering work in this field. We now see rapid advances in cancer immunology and emerging effective therapies revolutionizing cancer care across tumor types in the clinic, while pre-clinical research is moving from a focus on the malignant cells themselves to dissect the highly heterogenic and complex multi-cellular tumor microenvironment (TME).

Combination therapy for cancer with oncolytic virus and checkpoint inhibitor: A mathematical model

Oncolytic virus (OV) is a replication competent virus that selectively invades cancer cells; as these cells die under the viral burden, the released virus particles proceed to infect other cancer cells. Oncolytic viruses are designed to also be able to stimulate the anticancer immune response. Thus, one may represent an OV by two parameters: its replication potential and its immunogenicity. In this paper we consider a combination therapy with OV and a checkpoint inhibitor, anti-PD-1. We evaluate the efficacy of the combination therapy in terms of the tumor volume at some later time, for example, 6 months from initial treatment. Since T cells kill not only virus-free cancer cells but also virus-infected cancer cells, the following question arises: Does increasing the amount of the checkpoint inhibitor always improve the efficacy? We address this question, by a mathematical model consisting of a system of partial differential equations. We use the model to construct, by simulations, an efficacy map in terms of the doses of the checkpoint inhibitor and the OV injection. We show that there are regions in the map where an increase in the checkpoint inhibitor actually decreases the efficacy of the treatment. We also construct efficacy maps with checkpoint inhibitor vs. the replication potential of the virus that show the same antagonism, namely, an increase in the checkpoint inhibitor may actually decrease the efficacy. These results have implications for clinical trials.

Immunological landscape and immunotherapy of hepatocellular carcinoma

Advanced hepatocellular carcinoma (HCC) is a serious therapeutic challenge and targeted therapies only provide a modest benefit in terms of overall survival. Novel approaches are urgently needed for the treatment of this prevalent malignancy. Evidence demonstrating the antigenicity of tumour cells, the discovery that immune checkpoint molecules have an essential role in immune evasion of tumour cells, and the impressive clinical results achieved by blocking these inhibitory receptors, are revolutionizing cancer immunotherapy. Here, we review the data on HCC immunogenicity, the mechanisms for HCC immune subversion and the different immunotherapies that have been tested to treat HCC. Taking into account the multiplicity of hyperadditive immunosuppressive forces acting within the HCC microenvironment, a combinatorial approach is advised. Strategies include combinations of systemic immunomodulation and gene therapy, cell therapy or virotherapy.

Enhanced therapeutic efficacy of an adenovirus-PEI-bile-acid complex in tumors with low coxsackie and adenovirus receptor expression

Adenovirus (Ad) is a potential vehicle for cancer gene therapy. However, cells that express low levels of the coxsackie and adenovirus receptor (CAR) demonstrate poor Ad infection efficiency. We developed a bile acid-conjugated poly(ethyleneimine) (DA3)-coated Ad complex (Ad/DA3) to enhance Ad transduction efficiency. The size distribution and zeta potential of Ad/DA3 increased to 324 ± 3.08 nm and 10.13 ± 0.21 mV, respectively, compared with those of naked Ad (108 ± 2.26 nm and -17.7 ± 1.5 mV). The transduction efficiency of Ad/DA3 increased in a DA3 polymer concentration-dependent manner. Enhanced gene transfer by Ad/DA3 was more evident in CAR-moderate and CAR-negative cancer cells. Competition assays with a CAR-specific antibody revealed that internalization of Ad/DA3 was not mediated primarily by CAR but involved clathrin-, caveolae-, and macropinocytosis-mediated endocytosis. Cancer cell death was significantly increased when oncolytic Ad and DA3 were complexed (RdB-KOX/DA3) compared to that of naked oncolytic Ad and was inversely proportional to CAR levels. Importantly, RdB-KOX/DA3 significantly enhanced apoptosis, reduced angiogenesis, reduced proliferation, and increased active viral replication in human tumor xenografts compared to that of naked Ad. These results demonstrate that a hybrid vector system can increase the efficacy of oncolytic Ad virotherapy, particularly in CAR-limited tumors.

STAT3 activation promotes oncolytic HSV1 replication in glioma cells

Recent studies report that STAT3 signaling is a master regulator of mesenchymal transformation of gliomas and that STAT3 modulated genes are highly expressed in the mesenchymal transcriptome of gliomas. A currently studied experimental treatment for gliomas consists of intratumoral injection of oncolytic viruses (OV), such as oncolytic herpes simplex virus type 1 (oHSV). We have described one particular oHSV (rQNestin34.5) that exhibits potent anti-glioma activity in animal models. Here, we hypothesized that alterations in STAT3 signaling in glioma cells may affect the replicative ability of rQNestin34.5. In fact, human U251 glioma cells engineered to either over-express STAT3 or with genetic down-regulation of STAT3 supported oHSV replication to a significantly higher or lesser degree, respectively, when compared to controls. Administration of pharmacologic agents that increase STAT3 phosphorylation/activation (Valproic Acid) or increase STAT3 levels (Interleukin 6) also significantly enhanced oHSV replication. Instead, administration of inhibitors of STAT3 phosphorylation/activation (LLL12) significantly reduced oHSV replication. STAT3 led to a reduction in interferon signaling in oHSV infected cells and inhibition of interferon signaling abolished the effect of STAT3 on oHSV replication. These data thus indicate that STAT3 signaling in malignant gliomas enhances oHSV replication, likely by inhibiting the interferon response in infected glioma cells, thus suggesting avenues for possible potentiation of oncolytic virotherapy.

Non-replicating rhabdovirus-derived particles (NRRPs) eradicate acute leukemia by direct cytolysis and induction of antitumor immunity

Rhabdoviruses (RVs) are currently being pursued as anticancer therapeutics for various tumor types, notably leukemia. However, modest virion production and limited spread between noncontiguous circulating leukemic cells requires high-dose administration of RVs, which exceeds the maximum tolerable dose of the live virus. Furthermore, in severely immunosuppressed leukemic patients, the potential for uncontrolled live virus spread may compromise the safety of a live virus approach. We hypothesized that the barriers to oncolytic virotherapy in liquid tumors may be overcome by administration of high-dose non-replicating RVs. We have developed a method to produce unique high-titer bioactive yet non-replicating rhabdovirus-derived particles (NRRPs). This novel biopharmaceutical is multimodal possessing direct cytolytic and immunomodulatory activity against acute leukemia. We demonstrate that NRRP resistance in normal cells is mediated by intact antiviral defences including interferon (IFN). This data was substantiated using murine models of blast crisis. The translational promise of NRRPs was demonstrated in clinical samples obtained from patients with high-burden multidrug-resistant acute myeloid leukemia. This is the first successful attempt to eradicate disseminated cancer using a non-replicating virus-derived agent, representing a paradigm shift in our understanding of oncolytic virus-based therapies and their application toward the treatment of acute leukemia.

Replication-competent infectious hepatitis B virus vectors carrying substantially sized transgenes by redesigned viral polymerase translation

Viral vectors are engineered virus variants able to deliver nonviral genetic information into cells, usually by the same routes as the parental viruses. For several virus families, replication-competent vectors carrying reporter genes have become invaluable tools for easy and quantitative monitoring of replication and infection, and thus also for identifying antivirals and virus susceptible cells. For hepatitis B virus (HBV), a small enveloped DNA virus causing B-type hepatitis, such vectors are not available because insertions into its tiny 3.2 kb genome almost inevitably affect essential replication elements. HBV replicates by reverse transcription of the pregenomic (pg) RNA which is also required as bicistronic mRNA for the capsid (core) protein and the reverse transcriptase (Pol); their open reading frames (ORFs) overlap by some 150 basepairs. Translation of the downstream Pol ORF does not involve a conventional internal ribosome entry site (IRES). We reasoned that duplicating the overlap region and providing artificial IRES control for translation of both Pol and an in-between inserted transgene might yield a functional tricistronic pgRNA, without interfering with envelope protein expression. As IRESs we used a 22 nucleotide element termed Rbm3 IRES to minimize genome size increase. Model plasmids confirmed its activity even in tricistronic arrangements. Analogous plasmids for complete HBV genomes carrying 399 bp and 720 bp transgenes for blasticidin resistance (BsdR) and humanized Renilla green fluorescent protein (hrGFP) produced core and envelope proteins like wild-type HBV; while the hrGFP vector replicated poorly, the BsdR vector generated around 40% as much replicative DNA as wild-type HBV. Both vectors, however, formed enveloped virions which were infectious for HBV-susceptible HepaRG cells. Because numerous reporter and effector genes with sizes of around 500 bp or less are available, the new HBV vectors should become highly useful tools to better understand, and combat, this important pathogen.

Chapter three--Syrian hamster as an animal model to study oncolytic adenoviruses and to evaluate the efficacy of antiviral compounds

The Syrian (golden) hamster (Mesocricetus auratus) has served as a useful model for different aspects of biology for at least 50 years, and its use has been expanding recently. In earlier years, among other things, it was a model for cancer development. More recently, it has become a model for many different infectious diseases. It has also become an alternative model for the study of oncolytic adenovirus vectors for cancer gene therapy. Among several other human pathogens, the hamster is permissive for the replication of human species C adenoviruses, which are the parental virus for the majority of adenovirus vectors in use today. These vectors replicate in some of the established hamster tumor cell lines that can be used to generate tumors in vivo, that is, one can study oncolytic (replication competent) adenoviruses in a permissive, immunocompetent model. This has afforded the opportunity to study the effect of the host immune system on the vector-infected tumor and has allowed the use of a more relevant animal model to determine the safety and biodistribution of replication-competent adenoviruses. The hamster has also been used to evaluate antiviral compounds and vaccines against many viruses, including adenoviruses, flaviviruses, alphaviruses, arenaviruses, bunyaviruses, and paramyxoviruses.

The Oncolytic Effect of Respiratory Syncytial Virus (RSV) in Human Skin Cancer Cell Line, A431

Background

Oncolytic viruses have become of noticeable interest as a novel biological approach for selectively infecting cancer cells and triggering apoptosis in a number of malignant cells. Many researches are devoted to characterize more viruses with oncolytic properties.

Objectives

Evidences on the oncolytic feature of respiratory syncytial virus (RSV) are conflicting; therefore, this study was designed to elucidate the possible role of RSV on the modulation of cell growth and apoptosis in the skin cancer cells.

Materials and Methods

Plaque assay was used to determine RSV titers. The cytotoxic effect of RSV in A431 (skin carcinoma cell line) was determined using MTT assay. The detection of apoptosis was performed via Annexin-V-FITC staining method and analyzed with flow cytometry.

Results

The results indicated that A431 cell growth was inhibited following infection by RSV in a dose- and time-dependent manner. The most growth inhibitory effect of RSV was occurred at the MOI of 3, and 48 hour after infection. The inhibitory effect of RSV on the cell growth was accompanied by the induction of apoptosis in the skin cancer cells. The percentages of early and late apoptotic cells were increased following exposure to RSV in a concentration- and time-dependent manner.

Conclusions

This study delineated the beneficial role of RSV for growth regulation of skin cancer cells and highlighted the involvement of RSV in the induction of apoptosis in A431 cells. These findings might conduct evidence into the oncolytic properties of RSV in the skin cancer. Further studies are required to indicate intracellular targets for RSV-induced apoptosis in skin cancer cells.

Correlates between host and viral transcriptional program associated with different oncolytic vaccinia virus isolates

Vaccinia virus (VACV) has emerged as an attractive tool in oncolytic virotherapy. VACV replication efficiency plays a crucial role in the therapeutic outcome. However, little is known about the influence of host factors on viral replication efficiency and permissiveness of a host cell line to infection and oncolysis. In this study, replication of the attenuated VACV GLV-1h68 strain and three wild-type VACV isolates was determined in two autologous human melanoma cell lines (888-MEL and 1936-MEL). Host gene expression and viral gene expression in infected cells were evaluated via respective expression array platforms. Microarray analyses followed by sequential statistical approaches characterized human genes that change specifically due to virus infection. Viral gene transcription correlated with viral replication in a time-dependent manner. A set of human genes revealed strong correlations with the respective viral gene expression. Finally we identified a set of human genes with possible predictive value for viral replication in an independent dataset. The results demonstrate a probable correlation between viral replication, early gene expression, and the respective host response, and thus a possible involvement of human host factors in viral early replication. The characterization of human target genes that influence viral replication could help answer the question of host cell permissiveness to oncolytic virotherapy and provide important information for the development of novel recombinant vaccinia viruses with improved features to enhance replication rate and hence trigger therapeutic outcome.

Recombinant viral vaccines for cancer

Cancer arises from 'self' in a series of steps that are all subject to immunoediting. Therefore, therapeutic cancer vaccines must stimulate an immune response against tumour antigens that have already evaded the body's immune defences. Vaccines presenting a tumour antigen in the context of obvious danger signals seem more likely to stimulate a response. This approach can be facilitated by genetic engineering using recombinant viral vectors expressing tumour antigens, cytokines, or both, from an immunogenic virus particle. We overview clinical attempts to use these agents for systemic immunisation and contrast the results with strategies employing direct intratumoural administration. We focus on the challenge of producing an effective response within the immune-suppressive tumour microenvironment, and discuss how the technology can overcome these obstacles.

The use of oncolytic viruses to overcome lung cancer drug resistance

Intrinsic and acquired drug resistance remains a fundamental obstacle to successful applications of anticancer therapies for lung cancer. Combining conventional therapies with immunotherapeutic approaches is a promising strategy to circumvent lung cancer drug resistance. Genetically modified oncolytic viruses (OVs) kill tumor cells via completely unique mechanisms compared to small molecule chemotherapeutics typically used in lung cancer treatment and can also be used to deliver specific toxic, therapeutic or immunomodulatory genes to tumor cells. Recent pre-clinical and clinical studies with oncolytic vaccine approaches have revealed promising combination strategies that enhance oncolysis of tumor cells and circumvent tumor resistance mechanisms. As clinical trials with oncolytic vaccines progress, and as the knowledge acquired from these studies builds a foundation demonstrating OVs safety and efficacy, novel combination approaches could soon have a major impact on the clinical management of patients diagnosed with lung cancer.

Altering adenoviral tropism via click modification with ErbB specific ligands

Methods for targeting oncolytic viruses can increase efficacy and accelerate development. Genetic engineering, the predominant method for changing vector tropism, is limited in scope and often represents the bottleneck for vector development. Metabolic incorporation of an unnatural azido sugar, O-GlcNAz, at a specific site on the adenoviral surface allows chemoselective attachment of affibodies for Her2 or EGF receptors. Modification with these high-affinity, high-selectivity proteins is straightforward and readily generalizable, demonstrates minimal impact on virus physiology, and affords significant increases in gene delivery to cancer cells. As a result, this method has significant potential to increase the efficacy of next-generation viral vectors.

Gene therapy of liver diseases: a 2011 perspective

Liver diseases including inherited metabolic disorders, chronic viral hepatitis, liver cirrhosis and primary and metastatic liver cancer constitute a formidable health problem because of their high prevalence and the important limitations of current therapies. Gene therapy, a procedure based on the transfer of therapeutic genes to tissues, has been used since the 1990s as a new approach to treating a number of incurable conditions. After a period of lights and shades recent success in treating several devastating diseases like inherited immune deficiency disorders, beta-thalassemia, or inherited blindness appear to herald a new era where gene therapy can be listed among standard therapy options for a wide variety of human conditions. In this review, we provide information illustrating the potentiality of gene therapy in the management of liver diseases lacking other effective therapies.