Oncolytic targeting of androgen-sensitive prostate tumor by the respiratory syncytial virus (RSV): consequences of deficient interferon-dependent antiviral defense

Identification of an anaplastic subtype of prostate cancer amenable to therapies targeting SP1 or translation elongation

Histopathological heterogeneity is a hallmark of prostate cancer (PCa). Using spatial and parallel single-nucleus transcriptomics, we report an androgen receptor (AR)-positive but neuroendocrine-null primary PCa subtype with morphologic and molecular characteristics of small cell carcinoma. Such small cell-like PCa (SCLPC) is clinically aggressive with low AR, but high stemness and proliferation, activity. Molecular characterization prioritizes protein translation, represented by up-regulation of many ribosomal protein genes, and SP1, a transcriptional factor that drives SCLPC phenotype and overexpresses in castration-resistant PCa (CRPC), as two potential therapeutic targets in AR-indifferent CRPC. An SP1-specific inhibitor, plicamycin, effectively suppresses CRPC growth in vivo. Homoharringtonine, a Food And Drug Administration-approved translation elongation inhibitor, impedes CRPC progression in preclinical models and patients with CRPC. We construct an SCLPC-specific signature capable of stratifying patients for drug selectivity. Our studies reveal the existence of SCLPC in admixed PCa pathology, which may mediate tumor relapse, and establish SP1 and translation elongation as actionable therapeutic targets for CRPC.

Personalizing Oncolytic Immunovirotherapy Approaches

Development of successful cancer therapeutics requires exploration of the differences in genetics, metabolism, and interactions with the immune system among malignant and normal cells. The clinical observation of spontaneous tumor regression following natural infection with microorganism has created the premise of their use as cancer therapeutics. Oncolytic viruses (OVs) originate from viruses with attenuated virulence in humans, well-characterized vaccine strains of known human pathogens, or engineered replication-deficient viral vectors. Their selectivity is based on receptor expression level and post entry restriction factors that favor replication in the tumor, while keeping the normal cells unharmed. Clinical trials have demonstrated a wide range of patient responses to virotherapy, with subgroups of patients significantly benefiting from OV administration. Tumor-specific gene signatures, including antiviral interferon-stimulated gene (ISG) expression profile, have demonstrated a strong correlation with tumor permissiveness to infection. Furthermore, the combination of OVs with immunotherapeutics, including anticancer vaccines and immune checkpoint inhibitors [ICIs, such as anti-PD-1/PD-L1 or anti-CTLA-4 and chimeric antigen receptor (CAR)-T or CAR-NK cells], could synergistically improve the therapeutic outcome. Creating response prediction algorithms represents an important step for the transition to individualized immunovirotherapy approaches in the clinic. Integrative predictors could include tumor mutational burden (TMB), inflammatory gene signature, phenotype of tumor-infiltrating lymphocytes, tumor microenvironment (TME), and immune checkpoint receptor expression on both immune and target cells. Additionally, the gut microbiota has recently been recognized as a systemic immunomodulatory factor and could further be used in the optimization of individualized immunovirotherapy algorithms.

The antitumor effect of oncolytic respiratory syncytial virus via the tumor necrosis factor-alpha induction and ROS-bax-mediated mechanisms

BACKGROUND

Cervical cancer represents one of the most prevalent cancers among women worldwide, particularly in low- and middle-income nations. Oncolytic viruses (OVs) can infect cancer cells selectively and lethally without harming normal cells. Respiratory syncytial virus (RSV) is an oncolytic virus for anticancer therapy because of its propensity to multiply within tumor cells. This research aimed to assess the in vitro antitumor activities and molecular basis processes of the oncolytic RSV-A2 on the TC-1 cancer cells as a model for HPV‑related cervical cancers.

METHODS

Cellular proliferation (MTT) and lactate dehydrogenase (LDH) release assays were used to investigate the catalytic impacts of RSV-A2 by the ELISA method. Real-time PCR and flow cytometry assays were utilized to assess apoptosis, autophagy, intracellular concentrations of reactive oxygen species (ROS), and cell cycle inhibition.

RESULTS

Our MTT and LDH results demonstrated that TC-1 cell viability after oncolytic RSV-A2 treatment was MOI-dependently and altered significantly with increasing RSV-A2 virus multiplicity of infection (MOI). Other findings showed that the RSV-A2 potentially resulted in apoptosis and autophagy induction, caspase-3 activation, ROS generation, and cell cycle inhibition in the TC-1 cell line. Real-time PCR assay revealed that RSV-A2 infection significantly elevated the Bax and decreased the Bcl2 expression.

CONCLUSIONS

The results indicated that oncolytic RSV-A2 has cytotoxic and inhibiting effects on HPV-associated cervical cancer cells. Our findings revealed that RSV-A2 is a promising treatment candidate for cervical cancer.

Prostate cancer addiction to oxidative stress defines sensitivity to anti-tumor neutrophils

Bone metastatic prostate cancer (BM-PCa) remains one of the most difficult cancers to treat due to the complex interactions of cancer and stromal cells. We previously showed that bone marrow neutrophils elicit an anti-tumor immune response against BM-PCa. Further, we demonstrated that BM-PCa induces neutrophil oxidative burst, which has previously been identified to promote primary tumor growth of other cancers, and a goal of this study was to define the importance of neutrophil oxidative burst in BM-PCa. To do this, we first examined the impact of depletion of reactive oxygen species (ROS), via systemic deletion of the main source of ROS in phagocytes, NADPH oxidase (Nox)2, which we found to suppress prostate tumor growth in bone. Further, using pharmacologic ROS inhibitors and Nox2-null neutrophils, we found that ROS depletion specifically suppresses growth of androgen-insensitive prostate cancer cells. Upon closer examination using bulk RNA sequencing analysis, we identified that metastatic prostate cancer induces neutrophil transcriptomic changes that activates pathways associated with response to oxidative stress. In tandem, prostate cancer cells resist neutrophil anti-tumor response via extracellular (i.e., regulation of neutrophils) and intracellular alterations of glutathione synthesis, the most potent cellular antioxidant. These findings demonstrate that BM-PCa thrive under oxidative stress conditions and such that regulation of ROS and glutathione programming could be leveraged for targeting of BM-PCa progression.

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.

Host Sex Steroids Interact With Virus Infection: New Insights Into Sex Disparity in Infectious Diseases

Sex hormones are steroid hormones synthesized from the gonads of animals and tissues such as the placenta and adrenocortical reticular zone. The physiological functions of sex hormones are complex. Sex hormones are not only pathologically correlated with many diseases of the reproductive system, but are etiological factors in some viral infectious diseases, including disease caused by infections of coronaviruses, herpesviruses, hepatitis viruses, and other kinds of human viruses, which either exhibit a male propensity in clinical practice, or crosstalk with androgen receptor (AR)-related pathways in viral pathogenesis. Due to the global pandemic of coronavirus disease 2019 (COVID-19), the role of androgen/AR in viral infectious disease is highlighted again, majorly representing by the recent advances of AR-responsive gene of transmembrane protease/serine subfamily member 2 (TMPRSS2), which proteolytically activates the receptor-mediated virus entry by many coronaviruses and influenza virus, along with the role of androgen-mediated signaling for the transcription of hepatitis B virus (HBV), and the role of sex hormone responsive genes during Zika virus (ZIKV) pathogenesis, et al. Collectively, we propose to provide a comprehensive overview of the role of male sex hormones during multiple phases in the life cycle of different human viruses, which may be partly responsible for the sex-specific prevalence, severity and mortality of some diseases, therefore, may provide clues to develop more efficient prevention and treatment strategies for high-risk populations.

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.

Defects in interferon pathways as potential biomarkers of sensitivity to oncolytic viruses

Increased sensitivity of cancer cells to viruses is a prerequisite for the success of oncolytic virotherapy. One of the major causes of such a phenotype is the disruption of innate antiviral defenses associated with dysfunction of type 1 interferons (IFNs) that permits unlimited replication of viruses in cancer cells. Defects in IFN pathways help cancer progression by providing additional advantages to tumor cells. However, while these defects promote the survival and accelerated proliferation of malignant cells, they facilitate viral replication and thus enhance the efficiency of viral oncolysis. This review describes a broad spectrum of defects in genes that participate in IFN induction and IFN response pathways. Expression levels and/or functional activities of these genes are frequently low or absent in cancer cells, making them sensitive to virus infection. Therefore, certain specific defects in IFN signaling cascades might serve as potential biomarkers to help in identifying individual cancer patients who are likely to benefit from oncolytic virotherapy.

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.

Interleukin-6 and Interferon-α Signaling via JAK1-STAT Differentially Regulate Oncolytic versus Cytoprotective Antiviral States

Malignancy-induced alterations to cytokine signaling in tumor cells differentially regulate their interactions with the immune system and oncolytic viruses. The abundance of inflammatory cytokines in the tumor microenvironment suggests that such signaling plays key roles in tumor development and therapy efficacy. The JAK-STAT axis transduces signals of interleukin-6 (IL-6) and interferons (IFNs), mediates antiviral responses, and is frequently altered in prostate cancer (PCa) cells. However, how activation of JAK-STAT signaling with different cytokines regulates interactions between oncolytic viruses and PCa cells is not known. Here, we employ LNCaP PCa cells, expressing (or not) JAK1, activated (or not) with IFNs (α or γ) or IL-6, and infected with RNA viruses of different oncolytic potential (EHDV-TAU, hMPV-GFP, or HIV-GFP) to address this matter. We show that in JAK1-expressing cells, IL-6 sensitized PCa cells to viral cell death in the presence or absence of productive infection, with dependence on virus employed. Contrastingly, IFNα induced a cytoprotective antiviral state. Biochemical and genetic (knockout) analyses revealed dependency of antiviral state or cytoprotection on STAT1 or STAT2 activation, respectively. In IL-6-treated cells, STAT3 expression was required for anti-proliferative signaling. Quantitative proteomics (SILAC) revealed a core repertoire of antiviral IFN-stimulated genes, induced by IL-6 or IFNs. Oncolysis in the absence of productive infection, induced by IL-6, correlated with reduction in regulators of cell cycle and metabolism. These results call for matching the viral features of the oncolytic agent, the malignancy-induced genetic-epigenetic alterations to JAK/STAT signaling and the cytokine composition of the tumor microenvironment for efficient oncolytic virotherapy.

Exome-Wide Association Study Identifies Low-Frequency Coding Variants in 2p23.2 and 7p11.2 Associated with Survival of Non-Small Cell Lung Cancer Patients

INTRODUCTION

A growing body of evidence has suggested that low-frequency or rare coding variants might have strong effects on the development and prognosis of cancer. Here, we aim to assess the role of low-frequency and rare coding variants in the survival of NSCLC in Chinese populations.

METHODS

We performed an exome-wide scan of 247,870 variants in 1008 patients with NSCLC and replicated the promising variants by using imputed genotype data of The Cancer Genome Atlas (TCGA) with a Cox regression model. Gene-based and pathway-based analysis were also performed for nonsynonymous or splice site variants. Additionally, analysis of gene expression data in the TCGA was used to increase the reliability of candidate loci and genes.

RESULTS

A low-frequency missense variant in chaperonin containing TCP1 subunit 6A gene (CCT6A) (rs33922584: adjusted hazard ratio [HR_adjusted] = 1.75, p = 6.06 × 10^-4) was significantly related to the survival of patients with NSCLC, which was further replicated by the TCGA samples (HR_adjusted = 4.19, p = 0.015). Interestingly, the G allele of rs33922584 was significantly associated with high expression of CCT6A (p = 0.019) that might induce the worse survival in the TCGA samples (HR_adjusted = 1.15, p = 0.047). Besides, rs117512489 in gene phospholipase B1 gene (PLB1) (HR = 2.02, p = 7.28 × 10^-4) was also associated with survival of the patients with NSCLC in our samples, but it was supported only by gene expression analysis in the TCGA (HR_adjusted = 1.15, p = 0.023). Gene-based and pathway-based analysis revealed a total of 32 genes, including CCT6A and 34 potential pathways might account for the survival of NSCLC, respectively.

CONCLUSION

These results provided more evidence for the important role of low-frequency or rare variants in the survival of patients with NSCLC.

Effect of respiratory syncytial virus on the growth of hepatocellular carcinoma cell-lines

In several reports, the respiratory syncytial virus (RSV) was identified as an oncolytic virus in cancer cells (e.g., lung and prostate cancer). However, the effects of RSV in hepatocellular carcinoma (HCC) cells have not yet been investigated. Here, we observed the inhibitory effects of RSV infection in HCC cell-lines. Cell growth was significantly decreased by RSV infection in BNL-HCC, Hep3B, Huh-7 and SNU-739 cells. After RSV infection, plaque formation and syncytial formation were observed in affected Hep3B and Huh-7 cells. RSV protein-expression was also detected in Hep3B and Huh-7 cells; however, only Huh-7 cells showed apoptosis after RSV infection. Furthermore, inhibition of cell migration by RSV infection was observed in BNL-HCC, Hep3B, Huh-7 and SNU-739 cells. Therefore, further investigation is required to clarify the molecular mechanism of RSV-mediated inhibition of HCC cell growth, and to develop potential RSV oncolytic viro-therapeutics. [BMB Reports 2015; 48(10): 565-570]

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

Interferon-stimulated genes (ISG) encode diverse proteins that mediate intrinsic antiviral resistance in infected cells. Here it was hypothesized that malignant peripheral nerve sheath tumor (MPNST) cells resist the productive infection of oncolytic herpes simplex virus (oHSV) through activation of the JAK/STAT1 pathway and resultant upregulation of ISGs. Multiple human and mouse MPNST cells were used to explore the relationship between STAT1 activation and the productive infection of Δγ134.5 oHSVs. STAT1 activation in response to oHSV infection was found to associate with diminished Δγ134.5 oHSVs replication and spread. Multiday pretreatment, but not cotreatment, with a JAK inhibitor significantly improved viral titer and spread. ISG expression was found to be elevated prior to infection and downregulated when treated with the inhibitor, suggesting that the JAK/STAT1 pathway is active prior to infection. Conversely, upregulation of ISG expression in normally permissive cells significantly decreased oHSV productivity. Finally, a possible link between NF-κB pathway activation and ISG expression was established through the expression of inhibitor of kB (IκB) which decreased basal STAT1 transcription and ISG expression. These results demonstrate that basal ISG expression prior to infection contributes to the resistance of Δγ134.5 oHSVs in MPNST cells.

IMPLICATIONS

Although cancer-associated ISG expression has been previously reported to impart resistance to chemotherapy and radiotherapy, these data show that basal ISG expression also contributes to oncolytic HSV resistance. Mol Cancer Res; 14(5); 482-92. ©2016 AACR.

To Infection and Beyond: The Multi-Pronged Anti-Cancer Mechanisms of Oncolytic Viruses

Over the past 1–2 decades we have witnessed a resurgence of efforts to therapeutically exploit the attributes of lytic viruses to infect and kill tumor cells while sparing normal cells. We now appreciate that the utility of viruses for treating cancer extends far beyond lytic cell death. Viruses are also capable of eliciting humoral and cellular innate and adaptive immune responses that may be directed not only at virus-infected cells but also at uninfected cancer cells. Here we review our current understanding of this bystander effect, and divide the mechanisms into lytic, cytokine, innate cellular, and adaptive phases. Knowing the key pathways and molecular players during virus infection in the context of the cancer microenvironment will be critical to devise strategies to maximize the therapeutic effects of oncolytic viroimmunotherapy.

DAMP molecule S100A9 acts as a molecular pattern to enhance inflammation during influenza A virus infection: role of DDX21-TRIF-TLR4-MyD88 pathway

Pathogen-associated molecular patterns (PAMPs) trigger host immune response by activating pattern recognition receptors like toll-like receptors (TLRs). However, the mechanism whereby several pathogens, including viruses, activate TLRs via a non-PAMP mechanism is unclear. Endogenous “inflammatory mediators” called damage-associated molecular patterns (DAMPs) have been implicated in regulating immune response and inflammation. However, the role of DAMPs in inflammation/immunity during virus infection has not been studied. We have identified a DAMP molecule, S100A9 (also known as Calgranulin B or MRP-14), as an endogenous non-PAMP activator of TLR signaling during influenza A virus (IAV) infection. S100A9 was released from undamaged IAV-infected cells and extracellular S100A9 acted as a critical host-derived molecular pattern to regulate inflammatory response outcome and disease during infection by exaggerating pro-inflammatory response, cell-death and virus pathogenesis. Genetic studies showed that the DDX21-TRIF signaling pathway is required for S100A9 gene expression/production during infection. Furthermore, the inflammatory activity of extracellular S100A9 was mediated by activation of the TLR4-MyD88 pathway. Our studies have thus, underscored the role of a DAMP molecule (i.e. extracellular S100A9) in regulating virus-associated inflammation and uncovered a previously unknown function of the DDX21-TRIF-S100A9-TLR4-MyD88 signaling network in regulating inflammation during infection.

The lung disease severity following influenza A virus (IAV) infection is dependent on the extent of inflammation in the respiratory tract. Severe inflammation in the lung manifests in development of pneumonia. Therefore, it is very critical to identify cellular factors and dissect the molecular/cellular mechanism controlling inflammation in the respiratory tract during IAV infection. Knowledge derived from these studies will be instrumental in development of therapeutics to combat the lung disease associated with IAV infection. Towards that end, in the current study we have identified a cellular factor S100A9 which is responsible for enhanced inflammation during IAV infection. In addition, we have characterized a signal transduction pathway involving various cellular receptors and signaling adaptors that are involved in mediating S100A9-dependent inflammatory response. Thus, our studies have illuminated a cellular/molecular mechanism that can be intervened by therapeutics to reduce and control IAV-associated lung inflammatory disease like pneumonia.

Suppression of antiviral innate immunity by sunitinib enhances oncolytic virotherapy

The use of lytic viruses to preferentially infect and eliminate cancer cells while sparing normal cells is a promising experimental therapeutic approach for treating cancer. However, the efficacy of oncolytic virotherapy is often limited by two innate immunity pathways, the protein kinase PKR and the 2'-5'-oligoadenylate (OAS)/RNase L systems, which are widely present in many but not all tumor cell types. Previously, we reported that the anticancer drug, sunitinib, an inhibitor of VEGF-R and PDGF-R, has off-target effects against both PKR and RNase L. Here we show that combining sunitinib treatments with infection by an oncolytic virus, vesicular stomatitis virus (VSV), led to the elimination of prostate, breast, and kidney malignant tumors in mice. In contrast, either virus or sunitinib alone slowed tumor progression but did not eliminate tumors. In prostate tumors excised from treated mice, sunitinib decreased levels of the phosphorylated form of translation initiation factor, eIF2-α, a substrate of PKR, by 10-fold while increasing median viral titers by 23-fold. The sunitinib/VSV regimen caused complete and sustained tumor regression in both immunodeficient and immunocompetent animals. Results indicate that transient inhibition of innate immunity with sunitinib enhances oncolytic virotherapy allowing the recovery of tumor-bearing animals.

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

Background

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

Objectives

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

Materials and Methods

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

Results

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

Conclusions

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

Optimization and preclinical design of genetically engineered viruses for human oncolytic therapy

INTRODUCTION

Oncolytic viruses (OVs) occupy a strategic niche in the dynamic era of biological and gene therapy of human cancers. However, the use of OVs is the subject of close scrutiny due to impediments such as the insufficiency of patient generalizations posed by heterogeneous tumor responses to treatment, inherent or potentially lethal viral pathogenicities, unanticipated host- or immune-related adverse effects, and the emergence of virus-resistant cancer cells. These challenges can be overcome by the design and development of more definitive (optimized, targeted, and individualized) cancer virotherapeutics.

AREAS COVERED

The translation of current knowledge and recent innovations into rational treatment prospects hinges on an iterative loop of variables pertaining to genetically engineered viral oncolytic efficacy and safety profiles, mechanism-of-action data, potencies of synergistic oncolytic viral combinations with conventional tumor, immuno-, chemo-, and radiation treatment modalities, optimization of the probabilities of treatment successes in heterogeneous (virus-sensitive and -resistant) tumor cell populations by mathematical modeling, and lessons learned from preclinical studies and human clinical trials.

EXPERT OPINION

In recent years, it has become increasingly clear that proof-of-principle is critical for the preclinical optimization of oncolytic viruses to target heterogeneous forms of cancer and to prioritize current concerns related to the efficacy and safety of oncolytic virotherapy.

Transactivation of inducible nitric oxide synthase gene by Kruppel-like factor 6 regulates apoptosis during influenza A virus infection

Influenza A virus (flu) is a respiratory tract pathogen causing high morbidity and mortality among the human population. NO is a cellular mediator involved in tissue damage through its apoptosis of target cells and resulting enhancement of local inflammation. Inducible NO synthase (iNOS) is involved in the production of NO following infection. Although NO is a key player in the development of exaggerated lung disease during flu infection, the underlying mechanism, including the role of NO in apoptosis during infection, has not been reported. Similarly, the mechanism of iNOS gene induction during flu infection is not well defined in terms of the host transactivator(s) required for iNOS gene expression. In the current study, we identified Kruppel-like factor 6 (KLF6) as a critical transcription factor essential for iNOS gene expression during flu infection. We also underscored the requirement for iNOS in inducing apoptosis during infection. KLF6 gene silencing in human lung epithelial cells resulted in the drastic loss of NO production, iNOS promoter-specific luciferase activity, and expression of iNOS mRNA following flu infection. Chromatin immunoprecipitation assay revealed a direct interaction of KLF6 with iNOS promoter during in vitro and in vivo flu infection of human lung cells and mouse respiratory tract, respectively. A significant reduction in flu-mediated apoptosis was noted in KLF6-silenced cells, cells treated with iNOS inhibitor, and primary murine macrophages derived from iNOS knockout mice. A similar reduction in apoptosis was noted in the lungs following intratracheal flu infection of iNOS knockout mice.

Vesicular stomatitis virus as an oncolytic agent against pancreatic ductal adenocarcinoma

Vesicular stomatitis virus (VSV) is a promising oncolytic agent against a variety of cancers. However, it has never been tested in any pancreatic cancer model. Pancreatic ductal adenocarcinoma (PDA) is the most common and aggressive form of pancreatic cancer. In this study, the oncolytic potentials of several VSV variants were analyzed in a panel of 13 clinically relevant human PDA cell lines and compared to conditionally replicative adenoviruses (CRAds), Sendai virus and respiratory syncytial virus. VSV variants showed oncolytic abilities superior to those of other viruses, and some cell lines that exhibited resistance to other viruses were successfully killed by VSV. However, PDA cells were highly heterogeneous in their susceptibility to virus-induced oncolysis, and several cell lines were resistant to all tested viruses. Resistant cells showed low levels of very early VSV RNA synthesis, indicating possible defects at initial stages of infection. In addition, unlike permissive PDA cell lines, most of the resistant cell lines were able to both produce and respond to interferon, suggesting that intact type I interferon responses contributed to their resistance phenotype. Four cell lines that varied in their permissiveness to VSV-ΔM51 and CRAd dl1520 were tested in mice, and the in vivo results closely mimicked those in vitro. While our results demonstrate that VSV is a promising oncolytic agent against PDA, further studies are needed to better understand the molecular mechanisms of resistance of some PDAs to oncolytic virotherapy.