STAT1 and NF-κB Inhibitors Diminish Basal Interferon-Stimulated Gene Expression and Improve the Productive Infection of Oncolytic HSV in MPNST Cells

The quest for effective immunotherapies against malignant peripheral nerve sheath tumors: Is there hope?

Immune-based therapies represent a new paradigm in the treatment of multiple cancers, where they have helped achieve durable and safe clinical responses in a growing subset of patients. While a wealth of information is available concerning the use of these agents in treating the more common malignancies, little has been reported about the use of immunotherapies against malignant peripheral nerve sheath tumors (MPNSTs), a rare form of soft tissue sarcoma that arises from the myelin sheaths that protect peripheral nerves. Surgical resection has been the mainstay of therapy in MPNSTs, but the recurrence rate is as high as 65%, and chemotherapy is generally ineffective. The immune contexture of MPNSTs, replete with macrophages and a varying degree of T cell infiltration, presents multiple opportunities to design meaningful therapeutic interventions. While preliminary results with macrophage-targeting strategies and oncolytic viruses are promising, identifying the subset of patients that respond to immune-based strategies will be a milestone. As part of our effort to help advance the use of immunotherapy for MPNSTs, here we describe recent insights regarding the immune contexture of MPNSTs, discuss emerging immune-based strategies, and provide a brief overview of potential biomarkers of response.

Histone Deacetylase Inhibitor Panobinostat Benefits the Therapeutic Efficacy of Oncolytic Herpes Simplex Virus Combined with PD-1/PD-L1 Blocking in Glioma and Squamous Cell Carcinoma Models

BACKGROUND

Combination therapy has been widely explored for oncolytic virus (OV), as it can be met with tumor resistance. The HDAC inhibitor (HDACi) panobinostat is a potent pan-deacetylase inhibitor which blocks multiple cancer-related pathways and reverses epigenetic events in cancer progression.

METHODS

In this study, oncolytic activity in vitro and antitumor therapeutic efficacy in vivo when combined with oHSV and panobinostat were investigated.

RESULTS

(1) Treatment with panobinostat enhanced oHSV propagation and cytotoxicity in human glioma A172 and squamous cell carcinoma SCC9 cells. (2) Combined treatment with oHSV and panobinostat enhanced virus replication mediated by the transcriptional downregulation of IFN-β- and IFN-responsive antiviral genes in human glioma A172 and squamous cell carcinoma SCC9 cells. (3) Panobinostat treatment induced upregulation of PD-L1 expression in both glioma and squamous cell carcinoma cells. (4) A significantly enhanced therapeutic efficacy was shown in vivo for the murine glioma CT-2A and squamous cell carcinoma SCC7 models when treated with a combination of oHSV, including PD-1/PD-L1 blockade and HDAC inhibition.

CONCLUSIONS

Consequently, these data provide some new clues for the clinical development of combination therapy with OVs, epigenetic modifiers, and checkpoint blockades for glioma and squamous cell carcinoma.

Parsing the role of NSP1 in SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) leads to shutoff of protein synthesis, and nsp1, a central shutoff factor in coronaviruses, inhibits cellular mRNA translation. However, the diverse molecular mechanisms employed by nsp1 as well as its functional importance are unresolved. By overexpressing various nsp1 mutants and generating a SARS-CoV-2 mutant, we show that nsp1, through inhibition of translation and induction of mRNA degradation, targets translated cellular mRNA and is the main driver of host shutoff during infection. The propagation of nsp1 mutant virus is inhibited exclusively in cells with intact interferon (IFN) pathway as well as in vivo, in hamsters, and this attenuation is associated with stronger induction of type I IFN response. Therefore, although nsp1's shutoff activity is broad, it plays an essential role, specifically in counteracting the IFN response. Overall, our results reveal the multifaceted approach nsp1 uses to shut off cellular protein synthesis and uncover nsp1's explicit role in blocking the IFN response.

Parsing the role of NSP1 in SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the ongoing coronavirus disease 19 (COVID-19) pandemic. Despite its urgency, we still do not fully understand the molecular basis of SARS-CoV-2 pathogenesis and its ability to antagonize innate immune responses. SARS-CoV-2 leads to shutoff of cellular protein synthesis and over-expression of nsp1, a central shutoff factor in coronaviruses, inhibits cellular gene translation. However, the diverse molecular mechanisms nsp1 employs as well as its functional importance in infection are still unresolved. By overexpressing various nsp1 mutants and generating a SARS-CoV-2 mutant in which nsp1 does not bind ribosomes, we untangle the effects of nsp1. We uncover that nsp1, through inhibition of translation and induction of mRNA degradation, is the main driver of host shutoff during SARS-CoV-2 infection. Furthermore, we find the propagation of nsp1 mutant virus is inhibited specifically in cells with intact interferon (IFN) response as well as in-vivo , in infected hamsters, and this attenuation is associated with stronger induction of type I IFN response. This illustrates that nsp1 shutoff activity has an essential role mainly in counteracting the IFN response. Overall, our results reveal the multifaceted approach nsp1 uses to shut off cellular protein synthesis and uncover the central role it plays in SARS-CoV-2 pathogenesis, explicitly through blockage of the IFN response.

Oncolytic virotherapy as promising immunotherapy against cancer: mechanisms of resistance to oncolytic viruses

Oncolytic virotherapy has currently emerged as a powerful therapeutic approach in cancer treatment. Although the history of using viruses goes back to the early 20th century, the approval of talimogene laherparepvec (T-VEC) in 2015 increased interest in oncolytic viruses (OVs). OVs are multifaceted biotherapeutic agents because they replicate in and kill tumor cells and augment immune responses by releasing immunostimulatory molecules from lysed cells. Despite promising results, some limitations hinder the efficacy of oncolytic virotherapy. The delivery challenges and the upregulation of checkpoints following oncolytic virotherapy also mediate resistance to OVs by diminishing immune responses. Furthermore, the localization of receptors of viruses in the tight junctions, interferon responses, and the aberrant expression of genes involved in the cell cycle of the virus, including their infection and replication, reduce the efficacy of OVs. In this review, we present different mechanisms of resistance to OVs and strategies to overcome them.

Actin Cytoskeleton Dynamics and Type I IFN-Mediated Immune Response: A Dangerous Liaison in Cancer?

Simple Summary

Actin cytoskeleton is a dynamic subcellular component critical for maintaining cell shape and for elaborating response to any stimulus converging on the cell. Cytoskeleton constantly interfaces with diverse cellular components and affects a wide range of processes important in homeostasis and disease. What has been clearly demonstrated to date is that pathogens modify and use host cytoskeleton to their advantage. What is now emerging is that in sterile conditions, when a chronic inflammation occurs as in cancer, the subversion of tissue homeostasis induces an alarm status which mimics infection. This activates cellular players similar to those that solve an infection, but their persistence may pave the way for tumor progression. Understanding molecular mechanisms engaged by cytoskeleton to induce this viral mimicry could improve our knowledge of processes governing tumor progression and resistance to therapy.

Abstract

Chronic viral infection and cancer are closely inter-related and are both characterized by profound alteration of tissue homeostasis. The actin cytoskeleton dynamics highly participate in tissue homeostasis and act as a sensor leading to an immune-mediated anti-cancer and anti-viral response. Herein we highlight the crucial role of actin cytoskeleton dynamics in participating in a viral mimicry activation with profound effect in anti-tumor immune response. This still poorly explored field understands the cytoskeleton dynamics as a platform of complex signaling pathways which may regulate Type I IFN response in cancer. This emerging network needs to be elucidated to identify more effective anti-cancer strategies and to further advance the immuno-oncology field which has revolutionized the cancer treatment. For a progress to occur in this exciting arena we have to shed light on actin cytoskeleton related pathways and immune response. Herein we summarize the major findings, considering the double sword of the immune response and in particular the role of Type I IFN pathways in resistance to anti-cancer treatment.

Enhancing Therapeutic Efficacy of Oncolytic Herpes Simplex Virus with MEK Inhibitor Trametinib in Some BRAF or KRAS-Mutated Colorectal or Lung Carcinoma Models

Oncolytic virus (OV) as a promising therapeutic agent can selectively infect and kill tumor cells with naturally inherited or engineered properties. Considering the limitations of OVs monotherapy, combination therapy has been widely explored. MEK inhibitor (MEKi) Trametinib is an FDA-approved kinase inhibitor indicated for the treatment of tumors with BRAF V600E or V600K mutations. In this study, the oncolytic activity in vitro and anti-tumor therapeutic efficacy in vivo when combined with oHSV and MEKi Trametinib were investigated. We found: (1) Treatment with MEKi Trametinib augmented oHSV oncolytic activity in BRAF V600E-mutated tumor cells. (2) Combination treatment with oHSV and MEKi Trametinib enhanced virus replication mediated by down-regulation of STAT1 and PKR expression or phosphorylation in BRAF V600E-mutated tumor cells as well as BRAF wt/KRAS-mutated tumor cells. (3) A remarkably synergistic therapeutic efficacy was shown in vivo for BRAF wt/KRAS-mutated tumor models, when a combination of oHSV including PD-1 blockade and MEK inhibition. Collectively, these data provide some new insights for clinical development of combination therapy with oncolytic virus, MEK inhibition, and checkpoint blockade for BRAF or KRAS-mutated tumors.

Statins act as transient type I interferon inhibitors to enable the antitumor activity of modified vaccinia Ankara viral vectors

BACKGROUND

Modified vaccinia virus Ankara (MVA) are genetically engineered non-replicating viral vectors. Intratumoral administration of MVA induces a cyclic GMP-AMP synthase-mediated type I interferon (IFN) response and the production of high levels of the transgenes engineered into the viral genome such as tumor antigens to construct cancer vaccines. Although type I IFNs are essential for establishing CD8-mediated antitumor responses, this cytokine family may also give rise to immunosuppressive mechanisms.

METHODS

In vitro assays were performed to evaluate the activity of simvastatin and atorvastatin on type I IFN signaling and on antigen presentation. Surface levels of IFN α/β receptor 1, endocytosis of bovine serum albumin-fluorescein 5 (6)-isothiocyanate, signal transducer and activator of transcription (STAT) phosphorylation, and real-time PCR of IFN-stimulated genes were assessed in the murine fibroblast cell line L929. In vivo experiments were performed to characterize the effect of simvastatin on the MVA-induced innate immune response and on the antitumor effect of MVA-based antitumor vaccines in B16 melanoma expressing ovalbumin (OVA) and Lewis lung carcinoma (LLC)-OVA tumor models. RNAseq analysis, depleting monoclonal antibodies, and flow cytometry were used to evaluate the MVA-mediated immune response.

RESULTS

In this work, we identified commonly prescribed statins as potent IFNα pharmacological inhibitors due to their ability to reduce surface expression levels of IFN-α/β receptor 1 and to reduce clathrin-mediated endocytosis. Simvastatin and atorvastatin efficiently abrogated for 8 hours the transcriptomic response to IFNα and enhanced the number of dendritic cells presenting an OVA-derived peptide bound to major histocompatibility complex (MHC) class I. In vivo, intraperitoneal or intramuscular administration of simvastatin reduced the inflammatory response mediated by peritumoral administration of MVA and enhanced the antitumor activity of MVA encoding tumor-associated antigens. The synergistic antitumor effects critically depend on CD8⁺ cells, whereas they were markedly improved by depletion of CD4⁺ lymphocytes, T regulatory cells, or NK cells. Either MVA-OVA alone or combined with simvastatin augmented B cells, CD4⁺ lymphocytes, CD8⁺ lymphocytes, and tumor-specific CD8⁺ in the tumor-draining lymph nodes. However, only the treatment combination increased the numbers of these lymphocyte populations in the tumor microenvironment and in the spleen.

CONCLUSION

In conclusion, blockade of IFNα functions by simvastatin markedly enhances lymphocyte infiltration and the antitumor activity of MVA, prompting a feasible drug repurposing.

Combining Oncolytic Viruses and Small Molecule Therapeutics: Mutual Benefits

The focus of treating cancer with oncolytic viruses (OVs) has increasingly shifted towards achieving efficacy through the induction and augmentation of an antitumor immune response. However, innate antiviral responses can limit the activity of many OVs within the tumor and several immunosuppressive factors can hamper any subsequent antitumor immune responses. In recent decades, numerous small molecule compounds that either inhibit the immunosuppressive features of tumor cells or antagonize antiviral immunity have been developed and tested for. Here we comprehensively review small molecule compounds that can achieve therapeutic synergy with OVs. We also elaborate on the mechanisms by which these treatments elicit anti-tumor effects as monotherapies and how these complement OV treatment.

Human Metapneumovirus Induces IRF1 via TANK-Binding Kinase 1 and Type I IFN

The innate immune and host-protective responses to viruses, such as the airway pathogen human metapneumovirus (HMPV), depend on interferons (IFNs) that is induced through TANK-binding kinase 1 (TBK1) and IFN regulatory factors (IRFs). The transcription factor IRF1 is important for host resistance against several viruses and has a key role in induction of IFN-λ at mucosal surfaces. In most cell types IRF1 is expressed at very low levels, but its mRNA is rapidly induced when the demand for IRF1 activity arises. Despite general recognition of the importance of IRF1 to antiviral responses, the molecular mechanisms by which IRF1 is regulated during viral infections are not well understood. Here we identify the serine/threonine kinase TBK1 and IFN-β as critical regulators of IRF1 mRNA and protein levels in human monocyte-derived macrophages. We find that inhibition of TBK1 activity either by the semi-selective TBK1/IKKε inhibitor BX795 or by siRNA-mediated knockdown abrogates HMPV-induced expression of IRF1. Moreover, we show that canonical NF-κB signaling is involved in IRF1 induction and that the TBK1/IKKε inhibitor BX795, but not siTBK1 treatment, impairs HMPV-induced phosphorylation of the NF-κB subunit p65. At later time-points of the infection, IRF1 expression depended heavily on IFN-β-mediated signaling via the IFNAR-STAT1 pathway. Hence, our results suggest that TBK1 activation and TBK1/IKKε-mediated phosphorylation of the NF-κB subunit p65 control transcription of IRF1. Our study identifies a novel mechanism for IRF1 induction in response to viral infection of human macrophages that could be relevant not only to defense against HMPV, but also to other viral, bacterial and fungal pathogens.

Oncolytic Virotherapy in Solid Tumors: The Challenges and Achievements

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

Regorafenib combined with PD1 blockade increases CD8 T-cell infiltration by inducing CXCL10 expression in hepatocellular carcinoma

BACKGROUND AND PURPOSE

Combining inhibitors of vascular endothelial growth factor and the programmed cell death protein 1 (PD1) pathway has shown efficacy in multiple cancers, but the disease-specific and agent-specific mechanisms of benefit remain unclear. We examined the efficacy and defined the mechanisms of benefit when combining regorafenib (a multikinase antivascular endothelial growth factor receptor inhibitor) with PD1 blockade in murine hepatocellular carcinoma (HCC) models.

BASIC PROCEDURES

We used orthotopic models of HCC in mice with liver damage to test the effects of regorafenib-dosed orally at 5, 10 or 20 mg/kg daily-combined with anti-PD1 antibodies (10 mg/kg intraperitoneally thrice weekly). We evaluated the effects of therapy on tumor vasculature and immune microenvironment using immunofluorescence, flow cytometry, RNA-sequencing, ELISA and pharmacokinetic/pharmacodynamic studies in mice and in tissue and blood samples from patients with cancer.

MAIN FINDINGS

Regorafenib/anti-PD1 combination therapy increased survival compared with regofarenib or anti-PD1 alone in a regorafenib dose-dependent manner. Combination therapy increased regorafenib uptake into the tumor tissues by normalizing the HCC vasculature and increasing CD8 T-cell infiltration and activation at an intermediate regorafenib dose. The efficacy of regorafenib/anti-PD1 therapy was compromised in mice lacking functional T cells (Rag1-deficient mice). Regorafenib treatment increased the transcription and protein expression of CXCL10-a ligand for CXCR3 expressed on tumor-infiltrating lymphocytes-in murine HCC and in blood of patients with HCC. Using Cxcr3-deficient mice, we demonstrate that CXCR3 mediated the increased intratumoral CD8 T-cell infiltration and the added survival benefit when regorafenib was combined with anti-PD1 therapy.

PRINCIPAL CONCLUSIONS

Judicious regorafenib/anti-PD1 combination therapy can inhibit tumor growth and increase survival by normalizing tumor vasculature and increasing intratumoral CXCR3+CD8 T-cell infiltration through elevated CXCL10 expression in HCC cells.

Improving antitumor efficacy via combinatorial regimens of oncolytic virotherapy

As a promising therapeutic strategy, oncolytic virotherapy has shown potent anticancer efficacy in numerous pre-clinical and clinical trials. Oncolytic viruses have the capacity for conditional-replication within carcinoma cells leading to cell death via multiple mechanisms, including direct lysis of neoplasms, induction of immunogenic cell death, and elicitation of innate and adaptive immunity. In addition, these viruses can be engineered to express cytokines or chemokines to alter tumor microenvironments. Combination of oncolytic virotherapy with other antitumor therapeutic modalities, such as chemotherapy and radiation therapy as well as cancer immunotherapy can be used to target a wider range of tumors and promote therapeutic efficacy. In this review, we outline the basic biological characteristics of oncolytic viruses and the underlying mechanisms that support their use as promising antitumor drugs. We also describe the enhanced efficacy attributed to virotherapy combined with other drugs for the treatment of cancer.

Diagnosis and management of malignant peripheral nerve sheath tumors: Current practice and future perspectives

One of the most common malignancies affecting adults with the neurofibromatosis type 1 (NF1) cancer predisposition syndrome is the malignant peripheral nerve sheath tumor (MPNST), a highly aggressive sarcoma that typically develops from benign plexiform neurofibromas. Approximately 8-13% of individuals with NF1 will develop MPNST during young adulthood. There are few therapeutic options, and the vast majority of people with these cancers will die within 5 years of diagnosis. Despite efforts to understand the pathogenesis of these aggressive tumors, the overall prognosis remains dismal. This manuscript will review the current understanding of the cellular and molecular progression of MPNST, diagnostic workup of patients with these tumors, current treatment paradigms, and investigational treatment options. Additionally, we highlight novel areas of preclinical research, which may lead to future clinical trials. In summary, MPNST remains a diagnostic and therapeutic challenge, and future work is needed to develop novel and rational combinational therapy for these tumors.

New Model Systems and the Development of Targeted Therapies for the Treatment of Neurofibromatosis Type 1-Associated Malignant Peripheral Nerve Sheath Tumors

Neurofibromatosis Type 1 (NF1) is a common genetic disorder and cancer predisposition syndrome (1:3000 births) caused by mutations in the tumor suppressor gene NF1. NF1 encodes neurofibromin, a negative regulator of the Ras signaling pathway. Individuals with NF1 often develop benign tumors of the peripheral nervous system (neurofibromas), originating from the Schwann cell linage, some of which progress further to malignant peripheral nerve sheath tumors (MPNSTs). Treatment options for neurofibromas and MPNSTs are extremely limited, relying largely on surgical resection and cytotoxic chemotherapy. Identification of novel therapeutic targets in both benign neurofibromas and MPNSTs is critical for improved patient outcomes and quality of life. Recent clinical trials conducted in patients with NF1 for the treatment of symptomatic plexiform neurofibromas using inhibitors of the mitogen-activated protein kinase (MEK) have shown very promising results. However, MEK inhibitors do not work in all patients and have significant side effects. In addition, preliminary evidence suggests single agent use of MEK inhibitors for MPNST treatment will fail. Here, we describe the preclinical efforts that led to the identification of MEK inhibitors as promising therapeutics for the treatment of NF1-related neoplasia and possible reasons they lack single agent efficacy in the treatment of MPNSTs. In addition, we describe work to find targets other than MEK for treatment of MPNST. These have come from studies of RAS biochemistry, in vitro drug screening, forward genetic screens for Schwann cell tumors, and synthetic lethal screens in cells with oncogenic RAS gene mutations. Lastly, we discuss new approaches to exploit drug screening and synthetic lethality with NF1 loss of function mutations in human Schwann cells using CRISPR/Cas9 technology.

Oncolytic Viruses and the Immune System: The Dynamic Duo

Oncolytic viruses (OVs) constitute a new and promising immunotherapeutic approach toward cancer treatment. This therapy takes advantage of the natural propensity of most tumor cells to be infected by specific OVs. Besides the direct killing potential (oncolysis), what makes OV administration attractive for the present cancer immunotherapeutic scenario is the capacity to induce two new overlapping, but distinct, immunities: anti-tumoral and anti-viral. OV infection and oncolysis naturally elicit both innate and adaptive immune responses (required for long-term anti-tumoral immunity); at the same time, the viral infection prompts an anti-viral response. In this review, we discuss the dynamic interaction between OVs and the triggered responses of the immune system. The anti-OV immunological events that lead to viral clearance and the strategies to deal with such potential loss of the therapeutic virus are discussed. Additionally, we review the immune stimulatory actions induced by OVs through different inherent strategies, such as modulation of the tumor microenvironment, the role of immunogenic cell death, and the consequences of genetically modifying OVs by arming them with therapeutic transgenes. An understanding of the balance between the OV-induced anti-tumoral versus anti-viral immunities will provide insight when choosing the appropriate virotherapy for any specific cancer.

STING Restricts oHSV Replication and Spread in Resistant MPNSTs but Is Dispensable for Basal IFN-Stimulated Gene Upregulation

Malignant peripheral nerve sheath tumors (MPNSTs) are an aggressive soft-tissue sarcoma amenable only to surgical resection. Oncolytic herpes simplex viruses (oHSVs) are a promising experimental therapy. We previously showed that basal interferon (IFN) and nuclear factor κB (NFκB) signaling upregulate IFN-stimulated gene (ISG) expression and restrict efficient viral infection and cell-to-cell spread in ∼50% of tested MPNSTs. Stimulator of Interferon Genes (STING) integrates DNA sensor activity and mediates downstream IFN signaling in infected cells. We sought to identify STING’s role in oHSV resistance and contribution to basal ISG upregulation in MPNSTs. We show that the level of STING activity in human MPNST cell lines is predictive of oHSV sensitivity and that resistant cell lines have intact mechanisms for detection of cytosolic double-stranded DNA (dsDNA). Furthermore, we show that STING downregulation renders MPNSTs more permissive to oHSV infection and cell-to-cell spread. While next-generation viruses can exploit this loss of STING activity, first-generation viruses remain restricted. Finally, STING is not integral to the previously-observed basal ISG upregulation, indicating that other pathways contribute to basal IFN signaling in resistant MPNSTs. These data broaden our understanding of the intrinsic pathways in MPNSTs and their role in oHSV resistance and offer potential targets to potentiate oncolytic virus activity.

Immunotherapeutic Challenges for Pediatric Cancers

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

NF-κB Signaling in Targeting Tumor Cells by Oncolytic Viruses-Therapeutic Perspectives

In recent years, oncolytic virotherapy became a promising therapeutic approach, leading to the introduction of a novel generation of anticancer drugs. However, despite evoking an antitumor response, introducing an oncolytic virus (OV) to the patient is still inefficient to overcome both tumor protective mechanisms and the limitation of viral replication by the host. In cancer treatment, nuclear factor (NF)-κB has been extensively studied among important therapeutic targets. The pleiotropic nature of NF-κB transcription factor includes its involvement in immunity and tumorigenesis. Therefore, in many types of cancer, aberrant activation of NF-κB can be observed. At the same time, the activity of NF-κB can be modified by OVs, which trigger an immune response and modulate NF-κB signaling. Due to the limitation of a monotherapy exploiting OVs only, the antitumor effect can be enhanced by combining OV with NF-κB-modulating drugs. This review describes the influence of OVs on NF-κB activation in tumor cells showing NF-κB signaling as an important aspect, which should be taken into consideration when targeting tumor cells by OVs.

Combination Therapy Using Ruxolitinib and Oncolytic HSV Renders Resistant MPNSTs Susceptible to Virotherapy

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft-tissue sarcomas resistant to most cancer treatments. Surgical resection remains the primary treatment, but this is often incomplete, ultimately resulting in high mortality and morbidity rates. There has been a resurgence of interest in oncolytic virotherapy because of encouraging preclinical and clinical trial results. Oncolytic herpes simplex virus (oHSV) selectively replicates in cancer cells, lysing the cell and inducing antitumor immunity. We previously showed that basal interferon (IFN) signaling increases interferon-stimulated gene (ISG) expression, restricting viral replication in almost 50% of MPNSTs. The FDA-approved drug ruxolitinib (RUX) temporarily resets this constitutively active STAT signaling and renders the tumor cells susceptible to oHSV infection in cell culture. In the studies described here, we translated our in vitro results into a syngeneic MPNST tumor model. Consistent with our previous results, murine MPNSTs exhibit a similar IFN- and ISG-mediated oHSV-resistance mechanism, and virotherapy alone provides no antitumor benefit in vivo However, pretreatment of mice with ruxolitinib reduced ISG expression, making the tumors susceptible to oHSV infection. Ruxolitinib pretreatment improved viral replication and altered the oHSV-induced immune-mediated response. Our results showed that this combination therapy increased CD8⁺ T-cell activation in the tumor microenvironment and that this population was indispensable for the antitumor benefit that follows from the combination of RUX and oHSV. These data suggest that JAK inhibition prior to oncolytic virus treatment augments both oHSV replication and the immunotherapeutic efficacy of oncolytic herpes virotherapy.

Oncolytic Viruses on Drugs: Achieving Higher Therapeutic Efficacy

Over the past 20 years there has been a dramatic expansion in the testing of oncolytic viruses (OVs) for the treatment of cancer. OVs are unique biotherapeutics that induce multimodal responses toward tumors, from direct cytopathic effects on cancer cells, to tumor associated blood vessel disruption, and ultimately potent stimulation of anti-tumor immune activation. These agents are highly targeted and can be efficacious as cancer treatments resulting in some patients experiencing complete tumor regression and even cures from OV monotherapy. However, most patients have limited responses with viral replication in tumors often found to be modest and transient. To augment OV replication, increase bystander killing of cancer cells, and/or stimulate stronger targeted anti-cancer immune responses, drug combination approaches have taken center stage for translation to the clinic. Here we comprehensively review drugs that have been combined with OVs to increase therapeutic efficacy, examining the proposed mechanisms of action, and we discuss trends in pharmaco-viral immunotherapeutic approaches currently being investigated.

Engineered Oncolytic Poliovirus PVSRIPO Subverts MDA5-Dependent Innate Immune Responses in Cancer Cells

We are pursuing cancer immunotherapy with a neuro-attenuated recombinant poliovirus, PVSRIPO. PVSRIPO is the live attenuated type 1 (Sabin) poliovirus vaccine carrying a heterologous internal ribosomal entry site (IRES) of human rhinovirus type 2 (HRV2). Intratumoral infusion of PVSRIPO is showing promise in the therapy of recurrent WHO grade IV malignant glioma (glioblastoma), a notoriously treatment-refractory cancer with dismal prognosis. PVSRIPO exhibits profound cytotoxicity in infected neoplastic cells expressing the poliovirus receptor CD155. In addition, it elicits intriguing persistent translation and replication, giving rise to sustained type I interferon (IFN)-dominant proinflammatory stimulation of antigen-presenting cells. A key determinant of the inflammatory footprint generated by neoplastic cell infection and its role in shaping the adaptive response after PVSRIPO tumor infection is the virus's inherent relationship to the host's innate antiviral response. In this report, we define subversion of innate host immunity by PVSRIPO, enabling productive viral translation and cytopathogenicity with extremely low multiplicities of infection in the presence of an active innate antiviral IFN response.IMPORTANCE Engaging innate antiviral responses is considered key for instigating tumor-antigen-specific antitumor immunity with cancer immunotherapy approaches. However, they are a double-edged sword for attempts to enlist viruses in such approaches. In addition to their role in the transition from innate to adaptive immunity, innate antiviral IFN responses may intercept the viral life cycle in cancerous cells, prevent viral cytopathogenicity, and restrict viral spread. This has been shown to reduce overall antitumor efficacy of several proposed oncolytic virus prototypes, presumably by limiting direct cell killing and the ensuing inflammatory profile within the infected tumor. In this report, we outline how an unusual recalcitrance of polioviruses toward innate antiviral responses permits viral cytotoxicity and propagation in neoplastic cells, combined with engaging active innate antiviral IFN responses.

Plasticity of Type I Interferon-Mediated Responses in Cancer Therapy: From Anti-tumor Immunity to Resistance

The efficacy of several therapeutic strategies against cancer, including cytotoxic drugs, radiotherapy, targeted immunotherapies and oncolytic viruses, depend on intact type I interferon (IFN) signaling for the promotion of both direct (tumor cell inhibition) and indirect (anti-tumor immune responses) effects. Malfunctions of this pathway in tumor cells or in immune cells may be responsible for the lack of response or resistance. Although type I IFN signaling is required to trigger anti-tumor immunity, emerging evidence indicates that chronic activation of type I IFN pathway may be involved in mediating resistance to different cancer treatments. The plastic and dynamic features of type I IFN responses should be carefully considered to fully exploit the therapeutic potential of strategies targeting IFN signaling. Here, we review available evidence supporting the involvement of type I IFN signaling in mediating resistance to various cancer therapies and highlight the most promising modalities that are being tested to overcome resistance.

Restriction of Replication of Oncolytic Herpes Simplex Virus with a Deletion of γ34.5 in Glioblastoma Stem-Like Cells

Oncolytic viruses, including herpes simplex viruses (HSVs), are a new class of cancer therapeutic engineered to infect and kill cancer cells while sparing normal tissue. To ensure that oncolytic HSV (oHSV) is safe in the brain, all oHSVs in clinical trial for glioma lack the γ34.5 genes responsible for neurovirulence. However, loss of γ34.5 attenuates growth in cancer cells. Glioblastoma (GBM) is a lethal brain tumor that is heterogeneous and contains a subpopulation of cancer stem cells, termed GBM stem-like cells (GSCs), that likely promote tumor progression and recurrence. GSCs and matched serum-cultured GBM cells (ScGCs), representative of bulk or differentiated tumor cells, were isolated from the same patient tumor specimens. ScGCs are permissive to replication and cell killing by oHSV with deletion of the γ34.5 genes (γ34.5- oHSV), while patient-matched GSCs were not, implying an underlying biological difference between stem and bulk cancer cells. GSCs specifically restrict the synthesis of HSV-1 true late (TL) proteins, without affecting viral DNA replication or transcription of TL genes. A global shutoff of cellular protein synthesis also occurs late after γ34.5- oHSV infection of GSCs but does not affect the synthesis of early and leaky late viral proteins. Levels of phosphorylated eIF2α and eIF4E do not correlate with cell permissivity. Expression of Us11 in GSCs rescues replication of γ34.5- oHSV. The difference in degrees of permissivity between GSCs and ScGCs to γ34.5- oHSV illustrates a selective translational regulatory pathway in GSCs that may be operative in other stem-like cells and has implications for creating oHSVs.IMPORTANCE Herpes simplex virus (HSV) can be genetically engineered to endow cancer-selective replication and oncolytic activity. γ34.5, a key neurovirulence gene, has been deleted in all oncolytic HSVs in clinical trial for glioma. Glioblastoma stem-like cells (GSCs) are a subpopulation of tumor cells thought to drive tumor heterogeneity and therapeutic resistance. GSCs are nonpermissive for γ34.5- HSV, while non-stem-like cancer cells from the same patient tumors are permissive. GSCs restrict true late protein synthesis, despite normal viral DNA replication and transcription of all kinetic classes. This is specific for true late translation as early and leaky late transcripts are translated late in infection, notwithstanding shutoff of cellular protein synthesis. Expression of Us11 in GSCs rescues the replication of γ34.5- HSV. We have identified a cell type-specific innate response to HSV-1 that limits oncolytic activity in glioblastoma.

Constitutive Interferon Maintains GBP Expression Required for Release of Bacterial Components Upstream of Pyroptosis and Anti-DNA Responses

Legionella pneumophila elicits caspase-11-driven macrophage pyroptosis through guanylate-binding proteins (GBPs) encoded on chromosome 3. It has been proposed that microbe-driven IFN upregulates GBPs to facilitate pathogen vacuole rupture and bacteriolysis preceding caspase-11 activation. We show here that macrophage death occurred independently of microbial-induced IFN signaling and that GBPs are dispensable for pathogen vacuole rupture. Instead, the host-intrinsic IFN status sustained sufficient GBP expression levels to drive caspase-1 and caspase-11 activation in response to cytosol-exposed bacteria. In addition, endogenous GBP levels were sufficient for the release of DNA from cytosol-exposed bacteria, preceding the cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) pathway for Ifnb induction. Mice deficient for chromosome 3 GBPs were unable to mount a rapid IL-1/chemokine (C-X-C motif) ligand 1 (CXCL1) response during Legionella-induced pneumonia, with defective bacterial clearance. Our results show that rapid GBP activity is controlled by host-intrinsic cytokine signaling and that GBP activities precede immune amplification responses, including IFN induction, inflammasome activation, and cell death.

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.

Chimeric HCMV/HSV-1 and Δγ134.5 oncolytic herpes simplex virus elicit immune mediated antigliomal effect and antitumor memory

Malignant gliomas are the most common primary brain tumor and are characterized by rapid and highly invasive growth. Because of their poor prognosis, new therapeutic strategies are needed. Oncolytic virotherapy (OV) is a promising strategy for treating cancer that incorporates both direct viral replication mediated and immune mediated mechanisms to kill tumor cells. C134 is a next generation Δγ₁34.5 oHSV-1 with improved intratumoral viral replication. It remains safe in the CNS environment by inducing early IFN signaling which restricts its replication in non-malignant cells. We sought to identify how C134 performed in an immunocompetent tumor model that restricts its replication advantage over first generation viruses. To achieve this we identified tumors that have intact IFN signaling responses that restrict C134 and first generation virus replication similarly. Our results show that both viruses elicit a T cell mediated anti-tumor effect and improved animal survival but that subtle difference exist between the viruses effect on median survival despite equivalent in vivo viral replication. To further investigate this we examined the anti-tumor activity in immunodeficient mice and in syngeneic models with re-challenge. These studies show that the T cell response is integral to C134 replication independent anti-tumor response and that OV therapy elicits a durable and circulating anti-tumor memory. The studies also show that repeated intratumoral administration can extend both OV anti-tumor effects and induce durable anti-tumor memory that is superior to tumor antigen exposure alone.

Aurora A kinase inhibition enhances oncolytic herpes virotherapy through cytotoxic synergy and innate cellular immune modulation

Malignant peripheral nerve sheath tumor (MPNST) and neuroblastoma models respond to the investigational small molecule Aurora A kinase inhibitor, alisertib. We previously reported that MPNST and neuroblastomas are also susceptible to oncolytic herpes virus (oHSV) therapy. Herein, we show that combination of alisertib and HSV1716, a virus derived from HSV-1 and attenuated by deletion of RL1, exhibits significantly increased antitumor efficacy compared to either monotherapy. Alisertib and HSV1716 reduced tumor growth and increased survival in two xenograft models of MPNST and neuroblastoma. We found the enhanced antitumor effect was due to multiple mechanisms that likely each contribute to the combination effect. First, oncolytic herpes virus increased the sensitivity of uninfected cells to alisertib cytotoxicity, a process we term virus-induced therapeutic adjuvant (VITA). Second, alisertib increased peak virus production and slowed virus clearance from tumors, both likely a consequence of it preventing virus-mediated increase of intratumoral NK cells. We also found that alisertib inhibited virus-induced accumulation of intratumoral myeloid derived suppressor cells, which normally are protumorigenic. Our data suggest that clinical trials of the combination of oHSV and alisertib are warranted in patients with neuroblastoma or MPNST.

Pre-clinical Assessment of C134, a Chimeric Oncolytic Herpes Simplex Virus, in Mice and Non-human Primates

Oncolytic herpes simplex virus (oHSV) type I constructs are investigational anti-neoplastic agents for a variety of malignancies, including malignant glioma. Clinical trials to date have supported the safety of these agents even when directly administered in the CNS. Traditional pre-clinical US Food and Drug Administration (FDA) toxicity studies for these agents have included the use of two species, generally including murine and primate studies. Recently, the FDA has decreased its requirement of non-human primates as an animal model for ethical reasons, especially for established viral systems where there are good alternative model systems. Here we present data demonstrating the safety of C134, a chimeric oHSV construct, in CBA mice as well as in a limited number of the HSV-sensitive non-human primate Aotus nancymaae as a proposed agent for clinical trials. These data, along with the previously conducted clinical trials of oHSV constructs, support the use of the CBA mouse model as sufficient for the pre-clinical toxicity studies of this agent. We summarize our experience with different HSV recombinants and differences between them using multiple assays to assess neurovirulence, as well as our experience with C134 in a limited number of A. nancymaae.

Oncolytic herpes simplex virus interactions with the host immune system

Oncolytic viruses (OVs), like oncolytic herpes simplex virus (oHSV), are genetically engineered to selectively replicate in and kill cancer cells, while sparing normal cells. Initial OV infection, cell death, and subsequent OV propagation within the tumor microenvironment leads to a cascade of host responses (innate and adaptive), reflective of natural anti-viral immune responses. These host-virus interactions are critical to the balance between OV activities, anti-viral immune responses limiting OV, and induction of anti-tumor immunity. The host response against oHSV is complex, multifaceted, and modulated by the tumor microenvironment and immunosuppression. As a successful pathogen, HSV has multiple mechanisms to evade such host responses. In this review, we will discuss these mechanisms and HSV evasion, and how they impact oHSV therapy.