Engineering oncolytic viruses to exploit tumor specific defects in innate immune signaling pathways

Neoadjuvant systemic oncolytic vesicular stomatitis virus is safe and may enhance long-term survivorship in dogs with naturally occurring osteosarcoma

Osteosarcoma is a devastating bone cancer that disproportionally afflicts children, adolescents, and young adults. Standard therapy includes surgical tumor resection combined with multiagent chemotherapy, but many patients still suffer from metastatic disease progression. Neoadjuvant systemic oncolytic virus (OV) therapy has the potential to improve clinical outcomes by targeting primary and metastatic tumor sites and inducing durable antitumor immune responses. Here we describe the first evaluation of neoadjuvant systemic therapy with a clinical-stage recombinant oncolytic vesicular stomatitis virus (VSV), VSV-IFNβ-NIS, in naturally occurring cancer, specifically appendicular osteosarcoma in companion dogs. Canine osteosarcoma has a similar natural disease history as its human counterpart. VSV-IFNβ-NIS was administered prior to standard of care surgical resection, permitting microscopic and genomic analysis of tumors. Treatment was well-tolerated and a "tail" of long-term survivors (∼35%) was apparent in the VSV-treated group, a greater proportion than observed in two contemporary control cohorts. An increase in tumor inflammation was observed in VSV-treated tumors and RNA-seq analysis showed that all the long-term responders had increased expression of a T cell anchored immune gene cluster. We conclude that neoadjuvant VSV-IFNβ-NIS is safe and may increase long-term survivorship in dogs with naturally occurring osteosarcoma, particularly those that exhibit pre-existing antitumor immunity.

Anti-tumor activity of a recombinant measles virus against canine lung cancer cells

Canine primary lung cancer with metastasis has a poor prognosis with no effective treatment. We previously generated a recombinant measles virus (MV) that lost binding affinity to a principal receptor, SLAM, to eliminate its virulence as a new cancer treatment strategy. The virus, rMV-SLAMblind, targets nectin-4, recently listed as a tumor marker, and exerts antitumor activity against nectin-4-positive canine mammary cancer and urinary bladder transitional cell carcinoma cells. However, the effectivity of rMV-SLAMblind for other types of canine cancers is still unknown. Here we evaluated the antitumor effect of rMV-SLAMblind to canine lung cancer. Nectin-4 is expressed on three canine lung cancer cell lines (CLAC, AZACL1, AZACL2) and rMV-SLAMblind was able to infect these cell lines. CLAC cells showed reduced cell viability after virus infection. In the CLAC xenograft nude mouse model, intratumoral administration of rMV-SLAMblind significantly suppressed tumor growth. In rMV-SLAMblind-treated mice, natural killer cells were activated, and Cxcl10 and Il12a levels were significantly increased in comparison with levels in the control group. In addition, the depletion of NK cells reduced the anti-tumor effect. To understand difference in efficacy among canine lung cancer cell lines, we compared virus growth and gene expression pattern after virus treatment in the three canine lung cancer cell lines; virus growth was highest in CLAC cells compared with the other cell lines and the induction of interferon (IFN)-beta and IFN-stimulated genes was at lower levels in CLAC cells. These results suggested that rMV-SLAMblind exhibits oncolytic effect against some canine lung cancer cells and the cellular response after the virus infection may influence its efficacy.

Retroviral Replicating Vectors Mediated Prodrug Activator Gene Therapy in a Gastric Cancer Model

Retroviral replicating vectors (RRVs) selectively replicate and can specifically introduce prodrug-activating genes into tumor cells, whereby subsequent prodrug administration induces the death of the infected tumor cells. We assessed the ability of two distinct RRVs generated from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV), which infect cells via type-III sodium-dependent phosphate transporters, PiT-2 and PiT-1, respectively, to infect human gastric cancer (GC) cells. A quantitative RT-PCR showed that all tested GC cell lines had higher expression levels of PiT-2 than PiT-1. Accordingly, AMLV, encoding a green fluorescent protein gene, infected and replicated more efficiently than GALV in most GC cell lines, whereas both RRVs had a low infection rate in human fibroblasts. RRV encoding a cytosine deaminase prodrug activator gene, which converts the prodrug 5-flucytosine (5-FC) to the active drug 5-fluorouracil, showed that AMLV promoted superior 5-FC-induced cytotoxicity compared with GALV, which correlated with the viral receptor expression level and viral spread. In MKN-74 subcutaneous xenograft models, AMLV had significant antitumor effects compared with GALV. Furthermore, in the MKN-74 recurrent tumor model in which 5-FC was discontinued, the resumption of 5-FC administration reduced the tumor volume. Thus, RRV-mediated prodrug activator gene therapy might be beneficial for treating human GC.

Modelling the spatial dynamics of oncolytic virotherapy in the presence of virus-resistant tumour cells

Oncolytic virotherapy is a promising form of cancer treatment that uses native or genetically engineered viruses to target, infect and kill cancer cells. Unfortunately, this form of therapy is not effective in a substantial proportion of cancer patients, partly due to the occurrence of infection-resistant tumour cells. To shed new light on the mechanisms underlying therapeutic failure and to discover strategies that improve therapeutic efficacy we designed a cell-based model of viral infection. The model allows us to investigate the dynamics of infection-sensitive and infection-resistant cells in tumour tissue in presence of the virus. To reflect the importance of the spatial configuration of the tumour on the efficacy of virotherapy, we compare three variants of the model: two 2D models of a monolayer of tumour cells and a 3D model. In all model variants, we systematically investigate how the therapeutic outcome is affected by the properties of the virus (e.g. the rate of viral spread), the tumour (e.g. production rate of resistant cells, cost of resistance), the healthy stromal cells (e.g. degree of resistance to the virus) and the timing of treatment. We find that various therapeutic outcomes are possible when resistant cancer cells arise at low frequency in the tumour. These outcomes depend in an intricate but predictable way on the death rate of infected cells, where faster death leads to rapid virus clearance and cancer persistence. Our simulations reveal three different causes of therapy failure: rapid clearance of the virus, rapid selection of resistant cancer cells, and a low rate of viral spread due to the presence of infection-resistant healthy cells. Our models suggest that improved therapeutic efficacy can be achieved by sensitizing healthy stromal cells to infection, although this remedy has to be weighed against the toxicity induced in the healthy tissue.

Discovery Proteomics Analysis Determines That Driver Oncogenes Suppress Antiviral Defense Pathways Through Reduction in Interferon-β Autocrine Stimulation

Since the discovery of oncogenes, there has been tremendous interest to understand their mechanistic basis and to develop broadly actionable therapeutics. Some of the most frequently activated oncogenes driving diverse cancers are c-MYC, EGFR, HER2, AKT, KRAS, BRAF, and MEK. Using a reductionist approach, we explored how cellular proteomes are remodeled in isogenic cell lines engineered with or without these driver oncogenes. The most striking discovery for all oncogenic models was the systematic downregulation of scores of antiviral proteins regulated by type 1 interferon. These findings extended to cancer cell lines and patient-derived xenograft models of highly refractory pancreatic cancer and osteosarcoma driven by KRAS and MYC oncogenes. The oncogenes reduced basal expression of and autocrine stimulation by type 1 interferon causing remarkable convergence on common phenotypic and functional profiles. In particular, there was dramatically lower expression of dsRNA sensors including DDX58 (RIG-I) and OAS proteins, which resulted in attenuated functional responses when the oncogenic cells were treated with the dsRNA mimetic, polyI:C, and increased susceptibility to infection with an RNA virus shown using SARS-CoV-2. Our reductionist approach provides molecular and functional insights connected to immune evasion hallmarks in cancers and suggests therapeutic opportunities.

Perspectives for Combining Viral Oncolysis With Additional Immunotherapies for the Treatment of Melanoma

Melanoma is the deadliest type of skin cancer with steadily increasing incidence worldwide during the last few decades. In addition to its tumor associated antigens (TAAs), melanoma has a high mutation rate compared to other tumors, which promotes the appearance of tumor specific antigens (TSAs) as well as increased lymphocytic infiltration, inviting the use of therapeutic tools that evoke new or restore pre-existing immune responses. Innovative therapeutic proposals, such as immune checkpoint inhibitors (ICIs), have emerged as effective options for melanoma. However, a significant portion of these patients relapse and become refractory to treatment. Likewise, strategies using viral vectors, replicative or not, have garnered confidence and approval by different regulatory agencies around the world. It is possible that further success of immune therapies against melanoma will come from synergistic combinations of different approaches. In this review we outline molecular features inherent to melanoma and how this supports the use of viral oncolysis and immunotherapies when used as monotherapies or in combination.

Novel insight into pancreatic adenocarcinoma pathogenesis using liquid association analysis

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy associated with a poor prognosis. High-throughput disease-related-gene expression data provide valuable information on gene interaction, which consequently lead to deeper insight about pathogenesis. The co-expression analysis is a common approach that is used to investigate gene interaction. However, such an approach solely is inadequate to reveal the complexity of the gene interaction. The three-way interaction model is known as a novel approach applied to decode the complex relationship between genes.

METHODS

In the current study, the liquid association method was used to capture the statistically significant triplets involved in the PDAC pathogenesis. Subsequently, gene set enrichment and gene regulatory network analyses were performed to trace the biological relevance of the statistically significant triplets.

RESULTS

The results of the current study suggest that "response to estradiol" and "Regulation of T-cell proliferation" are two critical biological processes that may be associated with the PDAC pathogenesis. Additionally, we introduced six switch genes, namely Lamc2, Klk1, Nqo1, Aox1, Tspan1, and Cxcl12, which might be involved in PDAC triggering.

CONCLUSION

In the current study, for the first time, the critical genes and pathways involved in the PDAC pathogenesis were investigated using the three-way interaction approach. As a result, two critical biological processes, as well as six potential biomarkers, were suggested that might be involved in the PDAC triggering. Surprisingly, strong evidence for the biological relevance of our results can be found in the literature.

Tumor-Associated Macrophages/Microglia in Glioblastoma Oncolytic Virotherapy: A Double-Edged Sword

Oncolytic virotherapy is a rapidly progressing field that uses oncolytic viruses (OVs) to selectively infect malignant cells and cause an antitumor response through direct oncolysis and stimulation of the immune system. Despite demonstrated pre-clinical efficacy of OVs in many cancer types and some favorable clinical results in glioblastoma (GBM) trials, durable increases in overall survival have remained elusive. Recent evidence has emerged that tumor-associated macrophage/microglia (TAM) involvement is likely an important factor contributing to OV treatment failure. It is prudent to note that the relationship between TAMs and OV therapy failures is complex. Canonically activated TAMs (i.e., M1) drive an antitumor response while also inhibiting OV replication and spread. Meanwhile, M2 activated TAMs facilitate an immunosuppressive microenvironment thereby indirectly promoting tumor growth. In this focused review, we discuss the complicated interplay between TAMs and OV therapies in GBM. We review past studies that aimed to maximize effectiveness through immune system modulation-both immunostimulatory and immunosuppressant-and suggest future directions to maximize OV efficacy.

Multi-Omics Analysis of Glioblastoma Cells' Sensitivity to Oncolytic Viruses

Simple Summary

This study aims to uncover the contribution of interferon-dependent antiviral mechanisms preserved in tumor cells to the resistance of glioblastoma multiforme cells to oncolytic viruses. To characterize the functionality of interferon signaling, we used omics profiling and titration-based measurements of cell sensitivity to a panel of viruses of diverse oncolytic potential. This study shows why patient-derived glioblastoma cultures can acquire increased resistance to oncolytic viruses in the presence of interferons and suggests an approach to ranking glioblastoma cells by the acquired resistance. Our findings are important for monitoring the oncolytic potential of viruses to overcome IFN-induced resistance of tumor cells and contribute to successful therapy.

Abstract

Oncolytic viruses have gained momentum in the last decades as a promising tool for cancer treatment. Despite the progress, only a fraction of patients show a positive response to viral therapy. One of the key variable factors contributing to therapy outcomes is interferon-dependent antiviral mechanisms in tumor cells. Here, we evaluated this factor using patient-derived glioblastoma multiforme (GBM) cultures. Cell response to the type I interferons’ (IFNs) stimulation was characterized at mRNA and protein levels. Omics analysis revealed that GBM cells overexpress interferon-stimulated genes (ISGs) and upregulate their proteins, similar to the normal cells. A conserved molecular pattern unambiguously differentiates between the preserved and defective responses. Comparing ISGs’ portraits with titration-based measurements of cell sensitivity to a panel of viruses, the “strength” of IFN-induced resistance acquired by GBM cells was ranked. The study demonstrates that suppressing a single ISG and encoding an essential antiviral protein, does not necessarily increase sensitivity to viruses. Conversely, silencing IFIT3 and PLSCR1 genes in tumor cells can negatively affect the internalization of vesicular stomatitis and Newcastle disease viruses. We present evidence of a complex relationship between the interferon response genes and other factors affecting the sensitivity of tumor cells to viruses.

Clinical development of retroviral replicating vector Toca 511 for gene therapy of cancer

INTRODUCTION

The use of tumor-selectively replicating viruses is a rapidly expanding field that is showing considerable promise for cancer treatment. Retroviral replicating vectors (RRV) are unique among the various replication-competent viruses currently being investigated for potential clinical utility, because they permanently integrate into the cancer cell genome and are capable of long-term persistence within tumors. RRV can mediate efficient tumor-specific delivery of prodrug activator genes, and subsequent prodrug treatment leads to synchronized cell killing of infected cancer cells, as well as activation of antitumor immune responses.

AREAS COVERED

Here we review preclinical studies supporting bench-to-bedside translation of Toca 511, an optimized RRV for prodrug activator gene therapy, the results from Phase I through III clinical trials to date, and potential future directions for this therapy as well as other clinical candidate RRV.

EXPERT OPINION

Toca 511 has shown highly promising results in early-stage clinical trials. This vector progressed to a registrational Phase III trial, but the results announced in late 2019 appeared negative overall. However, the median prodrug dosing schedule was not optimal, and promising possible efficacy was observed in some prespecified subgroups. Further clinical investigation, as well as development of RRV with other transgene payloads, is merited.

Strategies to Develop Potent Oncolytic Viruses and Enhance Their Therapeutic Efficacy

Despite advancements in cancer therapy that have occurred over the past several decades, successful treatment of advanced malignancies remains elusive. Substantial resources and significant efforts have been directed toward the development of novel therapeutic modalities to improve patient outcomes. Oncolytic viruses (OVs) are emerging tools with unique characteristics that have attracted great interest in developing effective anticancer treatment. The original attraction was directed toward selective replication and cell-specific toxicity, two unique features that are either inherent to the virus or could be conferred by genetic engineering. However, recent advancements in the knowledge and understanding of OVs are shifting the therapeutic paradigm toward a greater focus on their immunomodulatory role. Nonetheless, there are still significant obstacles that remain to be overcome to enhance the efficiency of OVs as effective therapeutic modalities and potentially establish them as part of standard treatment regimens. In this review, we discuss advances in the design of OVs, strategies to enhance their therapeutic efficacy, functional translation into the clinical settings, and various obstacles that are still encountered in the efforts to establish them as effective anticancer treatments.

microRNA-induced translational control of antiviral immunity by the cap-binding protein 4EHP

Type I interferons (IFNs) are critical cytokines in the host defense against invading pathogens. Sustained production of IFNs, however, is detrimental to the host, as it provokes autoimmune diseases. Thus, the expression of IFNs is tightly controlled. We report that the mRNA 5' cap-binding protein 4EHP plays a key role in regulating type I IFN concomitant with controlling virus replication, both in vitro and in vivo. Mechanistically, 4EHP suppresses IFN-β production by effecting the miR-34a-induced translational silencing of Ifnb1 mRNA. miR-34a is upregulated by both RNA virus infection and IFN-β induction, prompting a negative feedback regulatory mechanism that represses IFN-β expression via 4EHP. These findings demonstrate the direct involvement of 4EHP in virus-induced host response, underscoring a critical translational silencing mechanism mediated by 4EHP and miR-34a to impede sustained IFN production. This study highlights an intrinsic regulatory function for miRNA and the translation machinery in maintaining host homeostasis.

Virus infections in tumors pave the way for tumor-directed DC-vaccines

Effective treatment of solid cancers by tumor-directed DC-vaccines still remains a challenge in clinical oncology. For therapeutic success, knock-down of tumor-specific tolerance appears mandatory before a potent tumor-specific cytotoxic T-cell response can be triggered by DC-vaccinations. Evidence is emerging that lytic virus infection in tumors can provide valuable help.

A Single Amino Acid Substitution in the Matrix Protein (M51R) of Vesicular Stomatitis New Jersey Virus Impairs Replication in Cultured Porcine Macrophages and Results in Significant Attenuation in Pigs

In this study, we explore the virulence of vesicular stomatitis New Jersey virus (VSNJV) in pigs and its potential relationship with the virus’s ability to modulate innate responses. For this purpose, we developed a mutant of the highly virulent strain NJ0612NME6, containing a single amino acid substitution in the matrix protein (M51R). The M51R mutant of NJ0612NME6 was unable to suppress the transcription of genes associated with the innate immune response both in primary fetal porcine kidney cells and porcine primary macrophage cultures. Impaired viral growth was observed only in porcine macrophage cultures, indicating that the M51 residue is required for efficient replication of VSNJV in these cells. Furthermore, when inoculated in pigs by intradermal scarification of the snout, M51R infection was characterized by decreased clinical signs including reduced fever and development of less and smaller secondary vesicular lesions. Pigs infected with M51R had decreased levels of viral shedding and absence of RNAemia compared to the parental virus. The ability of the mutant virus to infect pigs by direct contact remained intact, indicating that the M51R mutation resulted in a partially attenuated phenotype capable of causing primary lesions and transmitting to sentinel pigs. Collectively, our results show a positive correlation between the ability of VSNJV to counteract the innate immune response in swine macrophage cultures and the level of virulence in pigs, a natural host of this virus. More studies are encouraged to evaluate the interaction of VSNJV with macrophages and other components of the immune response in pigs.

Efficient Prodrug Activator Gene Therapy by Retroviral Replicating Vectors Prolongs Survival in an Immune-Competent Intracerebral Glioma Model

Prodrug activator gene therapy mediated by murine leukemia virus (MLV)-based retroviral replicating vectors (RRV) was previously shown to be highly effective in killing glioma cells both in culture and in vivo. To avoid receptor interference and enable dual vector co-infection with MLV-RRV, we have developed another RRV based on gibbon ape leukemia virus (GALV) that also shows robust replicative spread in a wide variety of tumor cells. We evaluated the potential of GALV-based RRV as a cancer therapeutic agent by incorporating yeast cytosine deaminase (CD) and E. coli nitroreductase (NTR) prodrug activator genes into the vector. The expression of CD and NTR genes from GALV-RRV achieved highly efficient delivery of these prodrug activator genes to RG-2 glioma cells, resulting in enhanced cytotoxicity after administering their respective prodrugs 5-fluorocytosine and CB1954 in vitro. In an immune-competent intracerebral RG-2 glioma model, GALV-mediated CD and NTR gene therapy both significantly suppressed tumor growth with CB1954 administration after a single injection of vector supernatant. However, NTR showed greater potency than CD, with control animals receiving GALV-NTR vector alone (i.e., without CB1954 prodrug) showing extensive tumor growth with a median survival time of 17.5 days, while animals receiving GALV-NTR and CB1954 showed significantly prolonged survival with a median survival time of 30 days. In conclusion, GALV-RRV enabled high-efficiency gene transfer and persistent expression of NTR, resulting in efficient cell killing, suppression of tumor growth, and prolonged survival upon CB1954 administration. This validates the use of therapeutic strategies employing this prodrug activator gene to arm GALV-RRV, and opens the door to the possibility of future combination gene therapy with CD-armed MLV-RRV, as the latter vector is currently being evaluated in clinical trials.

Hepatitis B Virus-Hepatocyte Interactions and Innate Immune Responses: Experimental Models and Molecular Mechanisms

Chronic hepatitis B virus (HBV) infection is a major cause of liver disease and cancer worldwide. While current therapeutic approaches can efficiently control viral infection, efficient curative antivirals are absent. The understanding of virus-hepatocyte interactions and sensing of viral infection is an important prerequisite for the development of novel antiviral therapies for cure. Hepatocyte intrinsic innate immunity provides a rapid first line of defense to combat viral infection through the upregulation of antiviral and inflammatory genes. However, the functional relevance of many of these antiviral signaling pathways in the liver and their role in HBV pathogenesis is still only partially understood. The recent identification of intracellular RNA and DNA sensing pathways and their involvement in disease biology, including viral pathogenesis and carcinogenesis, is currently transforming our understanding of virus-host interactions. Here the authors review the current knowledge on intrinsic antiviral innate immune responses including the role of viral nucleic acid sensing pathways in the liver. Since HBV has been designated as a "stealth virus," the study of the impact of HBV on signaling pathways in the hepatocyte is of significant interest to understand viral pathogenesis. Characterizing the mechanism underlying these HBV-host interactions and targeting related pathways to enhance antiviral innate responses may open new strategies to trigger noncytopathic clearance of covalently closed circular DNA to ultimately cure patients with chronic HBV infection.

Clinical Trials with Oncolytic Measles Virus: Current Status and Future Prospects

Attenuated Edmonston lineage measles virus (MV-Edm) vaccine strains can preferentially infect and lyse a wide variety of cancer cells. Oncolytic MV-Edm derivatives are genetically engineered to express the human carcinoembryonic antigen (MV-CEA virus) or the human sodium iodide symporter (MV-NIS virus) and are currently being tested in clinical trials against ovarian cancer, glioblastoma multiforme, multiple myeloma, mesothelioma, head and neck cancer, breast cancer and malignant peripheral nerve sheath tumors. This review describes the basic and preclinical data that facilitated the clinical translation of MV-Edm strains, and summarizes the clinical results of this oncolytic platform to date. Furthermore, we discuss the latest clinically relevant MV-Edm vector developments and creative strategies for future translational steps.

Early clinical trials of Toca 511 and Toca FC show a promising novel treatment for recurrent malignant glioma

INTRODUCTION

Glioblastoma and anaplastic astrocytoma are two of the most aggressive and common glioma malignancies in adults. These high-grade gliomas (HGG) universally recur despite aggressive treatment modalities and have a median overall survival (mOS) of approximately 14 months from initial diagnosis. Upon recurrence, there is no standard of care and these patients have a dismal prognosis of around 9 months at time of recurrence. Areas covered: In this article, we assess the newly published phase I data of Toca 511 and Toca FC, a two-drug combination therapy for recurrent HGG (rHGG) tumors, for effectiveness and safety. Expert opinion: These early studies provide very encouraging results for Toca 511 and Toca FC in rHGG. This therapy had a response rate of 11.3% and a mOS of 11.9 months in 56 patients, an improvement compared to historical controls. Furthermore, all responders were complete responses after extended follow-up. The drug is well tolerated for most patients. Responders tended to be young and have high-performance scores prior to beginning therapy, but more studies are necessary to understand the patient profile that receives the most benefit. Randomized-controlled trials are warranted for Toca 511 and Toca FC to confirm drug efficacy.

Combination of Oncolytic Measles Virus Armed With BNiP3, a Pro-apoptotic Gene and Paclitaxel Induces Breast Cancer Cell Death

Breast cancer is one of the major causes of cancer related mortality in women worldwide. Limitations of conventional anti-cancer therapies such as severe systemic side effects, narrow therapeutic index, non-specificity, and non-availability of drugs for all types of cancers has resulted in the development of various novel and targeted approaches. The use of viruses as oncolytic agents has gained momentum for the development of an efficient therapeutic platform. In this study, we have developed recombinant measles virus armed with BNiP3, a pro-apoptotic gene of human origin, as an oncolytic agent, and have demonstrated its ability to induce apoptosis in breast cancer cells in vitro. Studies have demonstrated the potential of using oncolytic viruses in combination with conventional therapies as an efficient anti-cancer regimen. We also have explored the synergistic potential of this virus in combination with paclitaxel, and a hydrazone derivative, H2 compound as an anti-cancer agent. MCF-7 and MDA-MB-231, human breast cancer cell lines were used for in vitro studies to evaluate toxic effects of armed virus, rMV-BNiP3 both as a standalone therapy and in combination with paclitaxel or H2 compound, a hydrazone derivative. Generation of armed virus was confirmed by detecting the viral transcript and protein expression, while its oncolytic potential by cell viability assays. Induction of apoptosis was demonstrated by fluorescence based caspase 3 activity and flow cytometry based Annexin V/PI staining. In the current study we have demonstrated the successful generation of an oncolytic measles virus armed with BNiP3 (rMV-BNiP3) and the induction of toxic effects in rMV-BNiP3 infected cells with a curious bias toward MDA-MB-231 cells as compared to MCF-7. Infection of breast cancer cells with rMV-BNiP3 caused induction of cell death, but the combination of rMV-BNiP3 with sub-lethal doses of both paclitaxel and H2 lowered the overall viability of cancer cells. As triple negative breast tumors are highly aggressive and resistant subtype of breast cancer with poor prognosis, comparative sensitivity of MDA-MB-231 cells toward this virus may potentially be used to develop a targeted therapy against triple negative breast cancer.

Validation of a site-specific recombination cloning technique for the rapid development of a full-length cDNA clone of a virulent field strain of vesicular stomatitis New Jersey virus

This study reports the use of a site-specific recombination cloning technique for rapid development of a full-length cDNA clone that can produce infectious vesicular stomatitis New Jersey virus (VSNJV). The full-length genome of the epidemic VSNJV NJ0612NME6 strain was amplified in four overlapping cDNA fragments which were linked together and cloned into a vector plasmid by site-specific recombination. Furthermore, to derive infectious virus, three supporting plasmid vectors containing either the nucleoprotein (N), phosphoprotein (P) or polymerase (L) genes were constructed using the same cloning methodology. Recovery of recombinant VSNJV was achieved after transfecting all four vectors on into BSR-T7/5 cells, a BHK-derived cell line stably expressing T7 RNA polymerase (PMID: 9847328). In vitro characterization of recombinant and parental viruses revealed similar growth kinetics and plaque morphologies. Furthermore, experimental infection of pigs with the recombinant virus resulted in severe vesicular stomatitis with clinical signs similar to those previously reported for the parental field strain. These results validate the use of site-directed specific recombination cloning as a useful alternative method for rapid construction of stable full-length cDNA clones from vesicular stomatitis field strains. The approach reported herein contributes to the improvement of previously published methodologies for the development of full-length cDNA clones of this relevant virus.

A single mutation in the mammalian orthoreovirus S1 gene is responsible for increased interferon sensitivity in a virus mutant selected in Vero cells

In a previous study, a mammalian orthoreovirus mutant was isolated based on its increased ability to infect interferon-defective Vero cells and was referred to as Vero-cells-adapted virus (VeroAV). This virus exhibits reduced ability to resist the antiviral effect of interferon. In the present study, the complete genome sequence of VeroAV was first determined. Reverse genetics was then used to identify a unique mutation on the S1 gene, overlapping the σ1 and σ1 s reading frame, resulting in increased sensitivity to interferon. A virus lacking σ1 s expression consecutive to mutation of its initiation codon was then shown to exhibit a further increase in sensitivity to interferon, supporting the idea that σ1 s is the viral protein responsible. This identification of a new determinant of reovirus sensitivity to interferon gives credentials to the idea that multiple reovirus genes are responsible for the level of interferon induction and susceptibility to the interferon-induced antiviral activities.

Oral poliovirus vaccine-induced programmed cell death involves both intrinsic and extrinsic pathways in human colorectal cancer cells

PURPOSE

Colorectal cancer (CRC) is one of the most common causes of cancer death throughout the world. Replication-competent viruses, which are naturally able to infect and lyse tumor cells, seem to be promising in this field. The aim of this study was to evaluate the potential of oral poliovirus vaccine (OPV) on human CRC cells and elucidate the mechanism of apoptosis induction.

MATERIALS AND METHODS

Protein and gene expression of poliovirus (PV) receptor (CD155) on four human CRC cell lines including HCT116, SW480, HT-29, and Caco-2 and normal fetal human colon (FHC) cell line as a control were examined by flow cytometry and SYBR Green Real-Time PCR, respectively. Cytotoxicity of OPV on indicated cell lines was tested using MTT assay. The ability of OPV on apoptosis induction for both intrinsic and extrinsic pathways was examined using caspase-8 and caspase-9 colorimetric assay kits. The PV propagation in mentioned cell lines was investigated, and the quantity of viral yields (cells associated and extracellular) was determined using TaqMan PCR.

RESULTS

CD155 mRNA and protein were expressed significantly higher in studied CRC cell lines rather than the normal cell line (P=0). OPV induced cell death in a time- and dose-dependent manner in human CRC cells. Apoptosis through both extrinsic and intrinsic pathways was detected in CRC cells with the minimum level found in FHC. PV viral load was significantly correlated with apoptosis via extrinsic (R=0.945, P=0.0001) and intrinsic (R=0.756, P=0.001) pathways.

CONCLUSION

This study suggests that OPV has potential for clinical treatment of CRC. However further studies in animal models (tumor xenografts) are needed to be certain that it is qualified enough for treatment of CRC.

Trial Watch: Oncolytic viro-immunotherapy of hematologic and solid tumors

Oncolytic viruses selectively target and kill cancer cells in an immunogenic fashion, thus supporting the establishment of therapeutically relevant tumor-specific immune responses. In 2015, the US Food and Drug Administration (FDA) approved the oncolytic herpes simplex virus T-VEC for use in advanced melanoma patients. Since then, a plethora of trials has been initiated to assess the safety and efficacy of multiple oncolytic viruses in patients affected with various malignancies. Here, we summarize recent preclinical and clinical progress in the field of oncolytic virotherapy.

Immune Checkpoint Inhibition for Pancreatic Ductal Adenocarcinoma: Current Limitations and Future Options

Pancreatic ductal adenocarcinoma (PDAC), as the most frequent form of pancreatic malignancy, still is associated with a dismal prognosis. Due to its late detection, most patients are ineligible for surgery, and chemotherapeutic options are limited. Tumor heterogeneity and a characteristic structure with crosstalk between the cancer/malignant cells and an abundant tumor microenvironment (TME) make PDAC a very challenging puzzle to solve. Thus far, targeted therapies have failed to substantially improve the overall survival of PDAC patients. Immune checkpoint inhibition, as an emerging therapeutic option in cancer treatment, shows promising results in different solid tumor types and hematological malignancies. However, PDAC does not respond well to immune checkpoint inhibitors anti-programmed cell death protein 1 (PD-1) or anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) alone or in combination. PDAC with its immune-privileged nature, starting from the early pre-neoplastic state, appears to escape from the antitumor immune response unlike other neoplastic entities. Different mechanisms how cancer cells achieve immune-privileged status have been hypothesized. Among them are decreased antigenicity and impaired immunogenicity via both cancer cell-intrinsic mechanisms and an augmented immunosuppressive TME. Here, we seek to shed light on the recent advances in both bench and bedside investigation of immunotherapeutic options for PDAC. Furthermore, we aim to compile recent data about how PDAC adopts immune escape mechanisms, and how these mechanisms might be exploited therapeutically in combination with immune checkpoint inhibitors, such as PD-1 or CTLA-4 antibodies.

Increased Virulence of an Epidemic Strain of Vesicular Stomatitis Virus Is Associated With Interference of the Innate Response in Pigs

Vesicular stomatitis virus (VSV) causes sporadic outbreaks of vesicular disease in the southwestern United States. The intrinsic characteristics of epidemic strains associated with these outbreaks are poorly understood. In this study, we report the distinctive genomic and biological characteristics of an epidemic (NJ0612NME6) strain of VSV compared with an endemic (NJ0806VCB) strain. Genomic comparisons between the two strains revealed a total of 111 nucleotide differences (23 non-synonymous) with potentially relevant replacements located in the P, G, and L proteins. When tested in experimentally infected pigs, a natural host of VSV, the epidemic strain caused higher fever and an increased number of vesicular lesions compared to pigs infected with the endemic strain. Pigs infected with the epidemic strain showed decreased systemic antiviral activity (type I - IFN), lower antibody levels, higher levels of interleukin 6, and lower levels of tumor necrosis factor during the acute phase of disease compared to pigs infected with the endemic strain. Furthermore, we document the existence of an RNAemia phase in pigs experimentally infected with VSV and explored the cause for the lack of recovery of infectious virus from blood. Finally, the epidemic strain was shown to be more efficient in down-regulating transcription of IRF-7 in primary porcine macrophages. Collectively, the data shows that the epidemic strain of VSV we tested has an enhanced ability to modulate the innate immune response of the vertebrate host. Further studies are needed to examine other epidemic strains and what contributions a phenotype of increased virulence might have on the transmission of VSV during epizootics.

Retroviral replicating vector-mediated gene therapy achieves long-term control of tumor recurrence and leads to durable anticancer immunity

Background

Prodrug-activator gene therapy with Toca 511, a tumor-selective retroviral replicating vector (RRV) encoding yeast cytosine deaminase, is being evaluated in recurrent high-grade glioma patients. Nonlytic retroviral infection leads to permanent integration of RRV into the cancer cell genome, converting infected cancer cell and progeny into stable vector producer cells, enabling ongoing transduction and viral persistence within tumors. Cytosine deaminase in infected tumor cells converts the antifungal prodrug 5-fluorocytosine into the anticancer drug 5-fluorouracil, mediating local tumor destruction without significant systemic adverse effects.

Methods

Here we investigated mechanisms underlying the therapeutic efficacy of this approach in orthotopic brain tumor models, employing both human glioma xenografts in immunodeficient hosts and syngeneic murine gliomas in immunocompetent hosts.

Results

In both models, a single injection of replicating vector followed by prodrug administration achieved long-term survival benefit. In the immunodeficient model, tumors recurred repeatedly, but bioluminescence imaging of tumors enabled tailored scheduling of multicycle prodrug administration, continued control of disease burden, and long-term survival. In the immunocompetent model, complete loss of tumor signal was observed after only 1-2 cycles of prodrug, followed by long-term survival without recurrence for >300 days despite discontinuation of prodrug. Long-term survivors rejected challenge with uninfected glioma cells, indicating immunological responses against native tumor antigens, and immune cell depletion showed a critical role for CD4+ T cells.

Conclusion

These results support dual mechanisms of action contributing to the efficacy of RRV-mediated prodrug-activator gene therapy: long-term tumor control by prodrug conversion-mediated cytoreduction, and induction of antitumor immunity.

Interferon alpha antagonizes the anti-hepatoma activity of the oncolytic virus M1 by stimulating anti-viral immunity

Alpha virus M1 is an oncolytic virus that targets zinc-finger antiviral protein (ZAP)-defective cancer cells, and may be useful for treatment of hepatocellular carcinoma (HCC). Most of HCC patients have hepatitis and need long-term antiviral medication. Thus, it is necessary to clarify whether anti-virus medicines influence oncolytic effect of M1. We examined the effect of drugs used to treat hepatitis B/C on M1-mediated oncolysis in vitro and in vivo. Interferon (IFN)-α induces expression of antiviral IFN-stimulated genes (ISGs) in HCC cells with moderate sensitivity to M1 virus. This leads to reduced replication of M1, and blocking of M1-mediated apoptosis. The antagonistic effect of IFN-α is positively related with the expressive level of ISGs. We also examined a population of 147 HCC patients. A total of 107 patients (73%) had low ZAP expression in liver tissues relative to adjacent tissues. Among these 107 patients, 77% were positive for hepatitis B and 2% were positive for hepatitis C. A combination of M1 virus and IFN should be avoided in those patients with HBV or HCV infection, of who ZAP expression is low but ISGs expression is moderate. In conclusion, this study provides a basis for anti-viral regimens for HCC patients with hepatitis B or C who are given oncolytic virus M1.

Multiple proteins differing between laboratory stocks of mammalian orthoreoviruses affect both virus sensitivity to interferon and induction of interferon production during infection

In the course of previous works, it was observed that the virus laboratory stock (T3D^S) differs in sequence from the virus encoded by the ten plasmids currently in use in many laboratories (T3D^K), and derived from a different original virus stock. Seven proteins are affected by these sequence differences. In the present study, replication of T3D^K was shown to be more sensitive to the antiviral effect of interferon. Infection by the T3D^K virus was also shown to induce the production of higher amount of β and α-interferons compared to T3D^S. Two proteins, the μ2 and λ2 proteins, were found to be responsible for increased sensitivity to interferon while both μ2 and λ1 are responsible for increased interferon secretion. Altogether this supports the idea that multiple reovirus proteins are involved in the control of induction of interferon and virus sensitivity to the interferon-induced response. While interrelated, interferon induction and sensitivity can be separated by defined gene combinations. While both μ2 and λ2 were previously suspected of a role in the control of the interferon response, other proteins are also likely involved, as first shown here for λ1. This also further stresses that due caution should be exerted when comparing different virus isolates with different genetic background.

Oncolytic virotherapy as an immunotherapeutic strategy for multiple myeloma

Multiple Myeloma (MM), a clonal malignancy of antibody-producing plasma cells, is the second most common hematologic malignancy and results in significant patient morbidity and mortality. The high degree of immune dysregulation in MM, including T cell imbalances and up-regulation of immunosuppressive checkpoint proteins and myeloid derived suppressor cells, allows this malignancy to escape from host immune control. Despite advances in the therapeutic landscape of MM over the last decade, including the introduction of immunomodulatory drugs, the prognosis for this disease is poor, with less than 50% of patients surviving 5 years. Thus, novel treatment strategies are required. Oncolytic viruses (OV) are a promising new class of therapeutics that rely on tumour specific oncolysis and the generation of a potent adaptive anti-tumour immune response for efficacy. To date, a number of OV have shown efficacy in pre-clinical studies of MM with three reaching early phase clinical trials. OVs represent a rational therapeutic strategy for MM based on (1) their tumour tropism, (2) their ability to potentiate anti-tumour immunity and (3) their ability to be rationally combined with other immunotherapeutic agents to achieve a more robust clinical response.

Comparative Oncology Evaluation of Intravenous Recombinant Oncolytic Vesicular Stomatitis Virus Therapy in Spontaneous Canine Cancer

Clinical translation of intravenous therapies to treat disseminated or metastatic cancer is imperative. Comparative oncology, the evaluation of novel cancer therapies in animals with spontaneous cancer, can be utilized to inform and accelerate clinical translation. Preclinical murine studies demonstrate that single-shot systemic therapy with a vesicular stomatitis virus (VSV)-IFNβ-NIS, a novel recombinant oncolytic VSV, can induce curative remission in tumor-bearing mice. Clinical translation of VSV-IFNβ-NIS therapy is dependent on comprehensive assessment of clinical toxicities, virus shedding, pharmacokinetics, and efficacy in clinically relevant models. Dogs spontaneously develop cancer with comparable etiology, clinical progression, and response to therapy as human malignancies. A comparative oncology study was carried out to investigate feasibility and tolerability of intravenous oncolytic VSV-IFNβ-NIS therapy in pet dogs with spontaneous cancer. Nine dogs with various malignancies were treated with a single intravenous dose of VSV-IFNβ-NIS. Two dogs with high-grade peripheral T-cell lymphoma had rapid but transient remission of disseminated disease and transient hepatotoxicity that resolved spontaneously. There was no shedding of infectious virus. Correlative pharmacokinetic studies revealed elevated levels of VSV RNA in blood in dogs with measurable disease remission. This is the first evaluation of intravenous oncolytic virus therapy for spontaneous canine cancer, demonstrating that VSV-IFNβ-NIS is well-tolerated and safe in dogs with advanced or metastatic disease. This approach has informed clinical translation, including dose and target indication selection, leading to a clinical investigation of intravenous VSV-IFNβ-NIS therapy, and provided preliminary evidence of clinical efficacy and potential biomarkers that correlate with therapeutic response. Mol Cancer Ther; 17(1); 316-26. ©2017 AACR.

Oncolytic Recombinant Vesicular Stomatitis Virus (VSV) Is Nonpathogenic and Nontransmissible in Pigs, a Natural Host of VSV

Vesicular stomatitis virus (VSV) is a negative-stranded RNA virus that naturally causes disease in livestock including horses, cattle and pigs. The two main identified VSV serotypes are New Jersey (VSNJV) and Indiana (VSIV). VSV is a rapidly replicating, potently immunogenic virus that has been engineered to develop novel oncolytic therapies for cancer treatment. Swine are a natural host for VSV and provide a relevant and well-established model, amenable to biological sampling to monitor virus shedding and neutralizing antibodies. Previous reports have documented the pathogenicity and transmissibility of wild-type isolates and recombinant strains of VSIV and VSNJV using the swine model. Oncolytic VSV engineered to express interferon-beta (IFNβ) and the sodium iodide symporter (NIS), VSV-IFNβ-NIS, has been shown to be a potent new therapeutic agent inducing rapid and durable tumor remission following systemic therapy in preclinical mouse models. VSV-IFNβ-NIS is currently undergoing clinical evaluation for the treatment of advanced cancer in human and canine patients. To support clinical studies and comprehensively assess the risk of transmission to susceptible species, we tested the pathogenicity and transmissibility of oncolytic VSV-IFNβ-NIS using the swine model. Following previously established protocols to evaluate VSV pathogenicity, intradermal inoculation with 10⁷ TCID₅₀ VSV-IFNβ-NIS caused no observable symptoms in pigs. There was no detectable shedding of infectious virus in VSV-IFNβ-NIS in biological excreta of inoculated pigs or exposed naive pigs kept in direct contact throughout the experiment. VSV-IFNβ-NIS inoculated pigs became seropositive for VSV antibodies, while contact pigs displayed no symptoms of VSV infection, and importantly did not seroconvert. These data indicate that oncolytic VSV is both nonpathogenic and not transmissible in pigs, a natural host. These findings support further clinical development of oncolytic VSV-IFNβ-NIS as a safe therapeutic for human and canine cancer.

The Sodium/Iodide Symporter (NIS): Molecular Physiology and Preclinical and Clinical Applications

Active iodide (I^-) transport in both the thyroid and some extrathyroidal tissues is mediated by the Na⁺/I^- symporter (NIS). In the thyroid, NIS-mediated I^- uptake plays a pivotal role in thyroid hormone (TH) biosynthesis. THs are key during embryonic and postembryonic development and critical for cell metabolism at all stages of life. The molecular characterization of NIS in 1996 and the use of radioactive I^- isotopes have led to significant advances in the diagnosis and treatment of thyroid cancer and provide the molecular basis for studies aimed at extending the use of radioiodide treatment in extrathyroidal malignancies. This review focuses on the most recent findings on I^- homeostasis and I^- transport deficiency-causing NIS mutations, as well as current knowledge of the structure/function properties of NIS and NIS regulatory mechanisms. We also discuss employing NIS as a reporter gene using viral vectors and stem cells in imaging, diagnostic, and therapeutic procedures.

Systemic virotherapy for multiple myeloma

INTRODUCTION

The multiple myeloma (MM) treatment scenario has changed considerably over the past few years. Several novel targeted therapies are currently under consideration including oncolytic virotherapy. Areas covered: This review provides an analysis of the mechanisms of action of virotherapy, and summarizes the preclinical and clinical studies of systemic virotherapy developed for the treatment of MM. Different types of viruses have been identified, including: adenovirus, vaccinia virus, herpes simplex virus 1, myxoma virus, reovirus, measles virus, vesicular stomatitis virus and coxsackievirus A21. Expert opinion: The above-mentioned viruses can do more than simply infect and kill malignant plasma cells alone or in combination with chemo and/or radiotherapy. In fact, some of them can also be used to purge myeloma cells from an autologous bone marrow (BM) transplant. Further investigations are required to better explore the best therapeutic combinations for MM and to also overcome antiviral response immunity that can limit the efficacy of this therapeutic strategy.

Cap-dependent translational control of oncolytic measles virus infection in malignant mesothelioma

Malignant mesothelioma has a poor prognosis for which there remains an urgent need for successful treatment approaches. Infection with the Edmonston vaccine strain (MV-Edm) derivative of measles virus results in lysis of cancer cells and has been tested in clinical trials for numerous tumor types including mesothelioma. Many factors play a role in MV-Edm tumor cell selectivity and cytopathic activity while also sparing non-cancerous cells. The MV-Edm receptor CD46 (cluster of differentiation 46) was demonstrated to be significantly higher in mesothelioma cells than in control cells. In contrast, mesothelioma cells are not reliant upon the alternative MV-Edm receptor nectin-4 for entry. MV-Edm treatment of mesothelioma reduced cell viability and also invoked apoptotic cell death. Forced expression of eIF4E or translation stimulation following IGF-I (insulin-like growth factor 1) exposure strengthened the potency of measles virus oncolytic activity. It was also shown that repression of cap-dependent translation by treatment with agents [4EASO, 4EGI-1] that suppress host cell translation or by forcing cells to produce an activated repressor protein diminishes the strength of oncolytic viral efficacy.

Paramyxoviruses activation by host proteases in cultures of normal and cancer cells

Multiplication of paramyxovirus Sendai and Newcastle disease virus (NDV) was studied in cultures of normal and tumor cells. Production of noninfectious virus with uncleaved F0 was observed in canine kidney cell line MDCK (line H) and its derivatives carrying tetracycline-regulated expression of transmembrane protease HAT or TMPRSS2 with trypsin-like cleavage specificity. Under tetracycline induction, a cleavage F0 (65 kD)>F1 (50 kD)+F2(15 kD) and production of infectious virus were observed in these cell cultures. Under tetracycline induction, the additional subunit 38K (m.w. 38 kDa) of the F protein was detected both in infected MDCK-HAT cells and in newly synthesized Sendai virus in addition to F0, F1 and F2, indicating thereby a second HAT-sensitive proteolytic site in the F0 molecule. Highly infectious virus containing cleaved F1+F2 was produced in cultures of cancer cells Caco-2 and H1299. Virus Sendai synthesized in H1299 cells contained 38 K subunit indicating a cleavage of the F0 at a second site by H1299 host cell proteases. Levels of cleaved F1+F2 and infectious virions were higher at the late stage of infection in cancer cells, suggesting thus the induction of virus-activating proteases in Caco-2 and H1299 cells under infection with paramyxoviruses. NDV virus was found to induce more rapid death of cancer cells Caco-2 than Sendai virus. Cooperatively, the obtained data show that cancer cells in distinction to nonmalignant cells can synthesize protease(s) activating infectivity of paramyxoviruses. Thus, they are more vulnerable to paramyxovirus infection than normal cells.

Oncolytic Virotherapy: A Contest between Apples and Oranges

Viruses can be engineered or adapted for selective propagation in neoplastic tissues and further modified for therapeutic transgene expression to enhance their antitumor potency and druggability. Oncolytic viruses (OVs) can be administered locally or intravenously and spread to a variable degree at sites of tumor growth. OV-infected tumor cells die in situ, releasing viral and tumor antigens that are phagocytosed by macrophages, transported to regional lymph nodes, and presented to antigen-reactive T cells, which proliferate before dispersing to kill uninfected tumor cells at distant sites. Several OVs are showing clinical promise, and one of them, talimogene laherparepvec (T-VEC), was recently granted marketing approval for intratumoral therapy of nonresectable metastatic melanoma. T-VEC also appears to substantially enhance clinical responsiveness to checkpoint inhibitor antibody therapy. Here, we examine the T-VEC paradigm and review some of the approaches currently being pursued to develop the next generation of OVs for both local and systemic administration, as well as for use in combination with other immunomodulatory agents.

Retroviral Replicating Vector Delivery of miR-PDL1 Inhibits Immune Checkpoint PDL1 and Enhances Immune Responses In Vitro

Tumor cells express a number of immunosuppressive molecules that can suppress anti-tumor immune responses. Efficient delivery of small interfering RNAs to treat a wide range of diseases including cancers remains a challenge. Retroviral replicating vectors (RRV) can be used to stably and selectively introduce genetic material into cancer cells. Here, we designed RRV to express shRNA (RRV-shPDL1) or microRNA30-derived shRNA (RRV-miRPDL1) using Pol II or Pol III promoters to downregulate PDL1 in human cancer cells. We also designed RRV expressing cytosine deaminase (yCD2) and miRPDL1 for potential combinatorial therapy. Among various configurations tested, we showed that RRV-miRPDL1 vectors with Pol II or Pol III promoter replicated efficiently and exhibited sustained downregulation of PDL1 protein expression by more than 75% in human cancer cell lines with high expression of PDL1. Immunologic effects of RRV-miRPDL1 were assessed by a trans-suppression lymphocyte assay. In vitro data showed downregulation of PDL1⁺ tumor cells restored activation of CD8⁺ T cells and bio-equivalency compared to anti-PDL1 antibody treatment. These results suggest RRV-miRPDL1 may be an alternative therapeutic approach to enhance anti-tumor immunity by overcoming PDL1-induced immune suppression from within cancer cells and this approach may also be applicable to other cancer targets.

Measles to the Rescue: A Review of Oncolytic Measles Virus

Oncolytic virotherapeutic agents are likely to become serious contenders in cancer treatment. The vaccine strain of measles virus is an agent with an impressive range of oncolytic activity in pre-clinical trials with increasing evidence of safety and efficacy in early clinical trials. This paramyxovirus vaccine has a proven safety record and is amenable to careful genetic modification in the laboratory. Overexpression of the measles virus (MV) receptor CD46 in many tumour cells may direct the virus to preferentially enter transformed cells and there is increasing awareness of the importance of nectin-4 and signaling lymphocytic activation molecule (SLAM) in oncolysis. Successful attempts to retarget MV by inserting genes for tumour-specific ligands to antigens such as carcinoembryonic antigen (CEA), CD20, CD38, and by engineering the virus to express synthetic microRNA targeting sequences, and "blinding" the virus to the natural viral receptors are exciting measures to increase viral specificity and enhance the oncolytic effect. Sodium iodine symporter (NIS) can also be expressed by MV, which enables in vivo tracking of MV infection. Radiovirotherapy using MV-NIS, chemo-virotherapy to convert prodrugs to their toxic metabolites, and immune-virotherapy including incorporating antibodies against immune checkpoint inhibitors can also increase the oncolytic potential. Anti-viral host immune responses are a recognized barrier to the success of MV, and approaches such as transporting MV to the tumour sites by carrier cells, are showing promise. MV Clinical trials are producing encouraging preliminary results in ovarian cancer, myeloma and cutaneous non-Hodgkin lymphoma, and the outcome of currently open trials in glioblastoma multiforme, mesothelioma and squamous cell carcinoma are eagerly anticipated.

From Benchtop to Bedside: A Review of Oncolytic Virotherapy

Oncolytic viruses (OVs) demonstrate the ability to replicate selectively in cancer cells, resulting in antitumor effects by a variety of mechanisms, including direct cell lysis and indirect cell death through immune-mediate host responses. Although the mechanisms of action of OVs are still not fully understood, major advances have been made in our understanding of how OVs function and interact with the host immune system, resulting in the recent FDA approval of the first OV for cancer therapy in the USA. This review provides an overview of the history of OVs, their selectivity for cancer cells, and their multifaceted mechanism of antitumor action, as well as strategies employed to augment selectivity and efficacy of OVs. OVs in combination with standard cancer therapies are also discussed, as well as a review of ongoing human clinical trials.

Experimental models of hepatitis B and C - new insights and progress

Viral hepatitis is a major cause of morbidity and mortality, affecting hundreds of millions of people worldwide. Hepatitis-causing viruses initiate disease by establishing both acute and chronic infections, and several of these viruses are specifically associated with the development of hepatocellular carcinoma. Consequently, intense research efforts have been focusing on increasing our understanding of hepatitis virus biology and on improving antiviral therapy and vaccination strategies. Although valuable information on viral hepatitis emerged from careful epidemiological studies on sporadic outbreaks in humans, experimental models using cell culture, rodent and non-human primates were essential in advancing the field. Through the use of these experimental models, improvement in both the treatment and prevention of viral hepatitis has progressed rapidly; however, agents of viral hepatitis are still among the most common pathogens infecting humans. In this Review, we describe the important part that these experimental models have played in the study of viral hepatitis and led to monumental advances in our understanding and treatment of these pathogens. Ongoing developments in experimental models are also described.

Pancreatic cancer from bench to bedside: molecular pathways and treatment options

In the last forty years the pancreatic cancer treatment has made advances, however; still novel drugs are needed. It is known that the five year survival rate remains around 5%. The best treatment option still remains surgery, if patients are diagnosed early. In the last decade the biology of pancreatic cancer has been vastly explored and novel agents such as; tyrosine kinase agents, or vaccines have been added as a treatment perspective. The big challenge is now to translate this knowledge in better outcomes for patients. In this current review we will present information from pancreatic cancer diagnosis to molecular pathways and treatment options; current and future.

Perfusion Pressure Is a Critical Determinant of the Intratumoral Extravasation of Oncolytic Viruses

Antitumor efficacy of oncolytic virotherapy is determined by the density and distribution of infectious centers within the tumor, which may be heavily influenced by the permeability and blood flow in tumor microvessels. Here, we investigated whether systemic perfusion pressure, a key driver of tumor blood flow, could influence the intratumoral extravasation of systemically administered oncolytic vesicular stomatitis virus (VSV) in myeloma tumor-bearing mice. Exercise was used to increase mean arterial pressure, and general anesthesia to decrease it. A recombinant VSV expressing the sodium iodide symporter (NIS), which concentrates radiotracers at sites of infection, was administered intravenously to exercising or anesthetized mice, and nuclear NIS reporter gene imaging was used to noninvasively track the density and spatial distribution of intratumoral infectious centers. Anesthesia resulted in decreased intratumoral infection density, while exercise increased the density and uniformity of infectious centers. Perfusion state also had a significant impact on the antitumor efficacy of the VSV therapy. In conclusion, quantitative dynamic radiohistologic imaging was used to noninvasively interrogate delivery of oncolytic virotherapy, highlighting the critical importance of perfusion pressure as a driver of intratumoral delivery and efficacy of oncolytic viruses.

Viro-immune therapy: A new strategy for treatment of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an almost uniformly lethal disease with less than 5% survival at five years. This is largely due to metastatic disease, which is already present in the majority of patients when diagnosed. Even when the primary cancer can be removed by radical surgery, local recurrence occurs within one year in 50%-80% of cases. Therefore, it is imperative to develop new approaches for the treatment of advanced cancer and the prevention of recurrence after surgery. Tumour-targeted oncolytic viruses (TOVs) have become an attractive therapeutic agent as TOVs can kill cancer cells through multiple mechanisms of action, especially via virus-induced engagement of the immune response specifically against tumour cells. To attack tumour cells effectively, tumour-specific T cells need to overcome negative regulatory signals that suppress their activation or that induce tolerance programmes such as anergy or exhaustion in the tumour microenvironment. In this regard, the recent breakthrough in immunotherapy achieved with immune checkpoint blockade agents, such as anti-cytotoxic T-lymphocyte-associate protein 4, programmed death 1 (PD-1) or PD-L1 antibodies, has demonstrated the possibility of relieving immune suppression in PDAC. Therefore, the combination of oncolytic virotherapy and immune checkpoint blockade agents may synergistically function to enhance the antitumour response, lending the opportunity to be the future for treatment of pancreatic cancer.

Combination of the oral histone deacetylase inhibitor resminostat with oncolytic measles vaccine virus as a new option for epi-virotherapeutic treatment of hepatocellular carcinoma

Epigenetic therapies such as histone deacetylase inhibitors (HDACi) not only have the capability to decrease tumor cell proliferation and to induce tumor cell death but also to silence antiviral response genes. Here, we investigated whether the combination of an oncolytic measles vaccine virus (MeV) with the novel oral HDACi resminostat (Res), being in clinical testing in patients with hepatocellular carcinoma (HCC), results in an enhanced efficacy of this epi-virotherapeutic approach compared to any of the two corresponding monotherapies. When testing a panel of human hepatoma cell lines, we found (i) a significantly improved rate of primary infections when using oncolytic MeV under concurrent treatment with resminostat, (ii) a boosted cytotoxic effect of the epi-virotherapeutic combination (Res + MeV) with enhanced induction of apoptosis, and, quite importantly, (iii) an absence of any resminostat-induced impairment of MeV replication and spread. Beyond that, we could also show that (iv) resminostat, after hepatoma cell stimulation with exogenous human interferon (IFN)-β, is able to prevent the induction of IFN-stimulated genes, such as IFIT-1. This finding outlines the possible impact of resminostat on cellular innate immunity, being instrumental in overcoming resistances to MeV-mediated viral oncolysis. Thus, our results support the onset of epi-virotherapeutic clinical trials in patients exhibiting advanced stages of HCC.

Breaking resistance of pancreatic cancer cells to an attenuated vesicular stomatitis virus through a novel activity of IKK inhibitor TPCA-1

Vesicular stomatitis virus (VSV) is an effective oncolytic virus against most human pancreatic ductal adenocarcinoma (PDAC) cell lines. However, some PDAC cell lines are highly resistant to oncolytic VSV-ΔM51 infection. To better understand the mechanism of resistance, we tested a panel of 16 small molecule inhibitors of different cellular signaling pathways, and identified TPCA-1 (IKK-β inhibitor) and ruxolitinib (JAK1/2 inhibitor), as strong enhancers of VSV-ΔM51 replication and virus-mediated oncolysis in all VSV-resistant PDAC cell lines. Both TPCA-1 and ruxolitinib similarly inhibited STAT1 and STAT2 phosphorylation and decreased expression of antiviral genes MxA and OAS. Moreover, an in situ kinase assay provided biochemical evidence that TPCA-1 directly inhibits JAK1 kinase activity. Together, our data demonstrate that TPCA-1 is a unique dual inhibitor of IKK-β and JAK1 kinase, and provide a new evidence that upregulated type I interferon signaling plays a major role in resistance of pancreatic cancer cells to oncolytic viruses.

Interferon Beta and Interferon Alpha 2a Differentially Protect Head and Neck Cancer Cells from Vesicular Stomatitis Virus-Induced Oncolysis

Oncolytic viruses (OV) preferentially kill cancer cells due in part to defects in their antiviral responses upon exposure to type I interferons (IFNs). However, IFN responsiveness of some tumor cells confers resistance to OV treatment. The human type I IFNs include one IFN-β and multiple IFN-α subtypes that share the same receptor but are capable of differentially inducing biological responses. The role of individual IFN subtypes in promoting tumor cell resistance to OV is addressed here. Two human IFNs which have been produced for clinical use, IFN-α2a and IFN-β, were compared for activity in protecting human head and neck squamous cell carcinoma (HNSCC) lines from oncolysis by vesicular stomatitis virus (VSV). Susceptibility of HNSCC lines to killing by VSV varied. VSV infection induced increased production of IFN-β in resistant HNSCC cells. When added exogenously, IFN-β was significantly more effective at protecting HNSCC cells from VSV oncolysis than was IFN-α2a. In contrast, normal keratinocytes and endothelial cells were protected equivalently by both IFN subtypes. Differential responsiveness of tumor cells to IFN-α and -β was further supported by the finding that autocrine IFN-β but not IFN-α promoted survival of HNSCC cells during persistent VSV infection. Therefore, IFN-α and -β differentially affect VSV oncolysis, justifying the evaluation and comparison of IFN subtypes for use in combination with VSV therapy. Pairing VSV with IFN-α2a may enhance selectivity of oncolytic VSV therapy for HNSCC by inhibiting VSV replication in normal cells without a corresponding inhibition in cancer cells.

IMPORTANCE

There has been a great deal of progress in the development of oncolytic viruses. However, a major problem is that individual cancers vary in their sensitivity to oncolytic viruses. In many cases this is due to differences in their production and response to interferons (IFNs). The experiments described here compared the responses of head and neck squamous cell carcinoma cell lines to two IFN subtypes, IFN-α2a and IFN-β, in protection from oncolytic vesicular stomatitis virus. We found that IFN-α2a was significantly less protective for cancer cells than was IFN-β, whereas normal cells were equivalently protected by both IFNs. These results suggest that from a therapeutic standpoint, selectivity for cancer versus normal cells may be enhanced by pairing VSV with IFN-α2a.

Overcoming tumor resistance by heterologous adeno-poxvirus combination therapy

Successful cancer control relies on overcoming resistance to cell death and on activation of host antitumor immunity. Oncolytic viruses are particularly attractive in this regard, as they lyse infected tumor cells and trigger robust immune responses during the infection. However, repeated injections of the same virus promote antiviral rather than antitumor immunity and tumors may mount innate antiviral defenses to restrict oncolytic virus replication. In this article, we have explored if alternating the therapy virus could circumvent these problems. We demonstrate in two virus-resistant animal models a substantial delay in antiviral immune- and innate cellular response induction by alternating injections of two immunologically distinct oncolytic viruses, adenovirus, and vaccinia virus. Our results are in support of clinical development of heterologous adeno-/vaccinia virus therapy of cancer.