The effect of hypoxia on the uptake, replication and lytic potential of group B adenovirus type 3 (Ad3) and type 11p (Ad11p)

Tumor-targeted delivery of copper-manganese biomineralized oncolytic adenovirus for colorectal cancer immunotherapy

Oncolytic viral therapy (OVT) is a novel anti-tumor immunotherapy approach, specifically replicating within tumor cells. Currently, oncolytic viruses are mainly administered by intratumoral injection. However, achieving good results for distant metastatic tumors is challenging. In this study, a multifunctional oncolytic adenovirus, OA@CuMnCs, was developed using bimetallic ions copper and manganese. These metal cations form a biomineralized coating on the virus's surface, reducing immune clearance. It is known that viruses upregulate the expression of PD-L1. Copper ions in OA@CuMnCs can decrease the PD-L1 expression of tumor cells, thereby promoting immune cell-related factor release. This process involves antigen presentation and the combination of immature dendritic cells, transforming them into mature dendritic cells. It changes "cold" tumors into "hot" tumors, further inducing immunogenic cell death. While oncolytic virus replication requires oxygen, manganese ions in OA@CuMnCs can react with endogenous hydrogen peroxide. This reaction produces oxygen, enhancing the virus's replication ability and the tumor lysis effect. Thus, this multifunctionally coated OA@CuMnCs demonstrates potent amplification in immunotherapy efficacy, and shows great potential for further clinical OVT. STATEMENT OF SIGNIFICANCE: Oncolytic virus therapy (OVs) is a new anti-tumor immunotherapy method that can specifically replicate in tumor cells. Although the oncolytic virus can achieve a therapeutic effect on some non-metastatic tumors through direct intratumoral injection, there are still three major defects in the treatment of metastatic tumors: immune response, hypoxia effect, and administration route. Various studies have shown that the immune response in vivo can be overcome by modifying or wrapping the surface protein of the oncolytic virus. In this paper, a multifunctional coating of copper and manganese was prepared by combining the advantages of copper and manganese ions. The coating has a simple preparation method and mild conditions, and can effectively enhance tumor immunotherapy.

Hypoxia effects on oncolytic virotherapy in Cancer: Friend or Foe?

Researchers have tried to find novel strategies for cancer treatment in the past decades. Among the utilized methods, administering oncolytic viruses (OVs) alone or combined with other anticancer therapeutic approaches has had promising outcomes, especially in solid tumors. Infecting the tumor cells by these viruses can lead to direct lysis or induction of immune responses. However, the immunosuppressive tumor microenvironment (TME) is considered a significant challenge for oncolytic virotherapy in treating cancer. Based on OV type, hypoxic conditions in the TME can accelerate or repress virus replication. Therefore, genetic manipulation of OVs or other molecular modifications to reduce hypoxia can induce antitumor responses. Moreover, using OVs with tumor lysis capability in the hypoxic TME may be an attractive strategy to overcome the limitations of the therapy. This review summarizes the latest information available in the field of cancer virotherapy and discusses the dual effect of hypoxia on different types of OVs to optimize available related therapeutic methods.

Mesenchymal stem cell-released oncolytic virus: an innovative strategy for cancer treatment

Oncolytic viruses (OVs) infect, multiply, and finally remove tumor cells selectively, causing no damage to normal cells in the process. Because of their specific features, such as, the ability to induce immunogenic cell death and to contain curative transgenes in their genomes, OVs have attracted attention as candidates to be utilized in cooperation with immunotherapies for cancer treatment. This treatment takes advantage of most tumor cells' inherent tendency to be infected by certain OVs and both innate and adaptive immune responses are elicited by OV infection and oncolysis. OVs can also modulate tumor microenvironment and boost anti-tumor immune responses. Mesenchymal stem cells (MSC) are gathering interest as promising anti-cancer treatments with the ability to address a wide range of cancers. MSCs exhibit tumor-trophic migration characteristics, allowing them to be used as delivery vehicles for successful, targeted treatment of isolated tumors and metastatic malignancies. Preclinical and clinical research were reviewed in this study to discuss using MSC-released OVs as a novel method for the treatment of cancer. Video Abstract.

Combining of Oncolytic Virotherapy and Other Immunotherapeutic Approaches in Cancer: A Powerful Functionalization Tactic

Oncolytic viruses have found a good place in the treatment of cancer. Administering oncolytic viruses directly or by applying genetic changes can be effective in cancer treatment through the lysis of tumor cells and, in some cases, by inducing immune system responses. Moreover, oncolytic viruses induce antitumor immune responses via releasing tumor antigens in the tumor microenvironment (TME) and affect tumor cell growth and metabolism. Despite the success of virotherapy in cancer therapies, there are several challenges and limitations, such as immunosuppressive TME, lack of effective penetration into tumor tissue, low efficiency in hypoxia, antiviral immune responses, and off-targeting. Evidence suggests that oncolytic viruses combined with cancer immunotherapy-based methods such as immune checkpoint inhibitors and adoptive cell therapies can effectively overcome these challenges. This review summarizes the latest data on the use of oncolytic viruses for the treatment of cancer and the challenges of this method. Additionally, the effectiveness of mono, dual, and triple therapies using oncolytic viruses and other anticancer agents has been discussed based on the latest findings.

Remodeling the tumor microenvironment by oncolytic viruses: beyond oncolysis of tumor cells for cancer treatment

Tumor cells manipulate the local environment in which they grow, creating a tumor microenvironment (TME) that promotes tumor survival and metastasis. The TME is an extremely complex environment rich in immunosuppressive cells and cytokines. Various methods to therapeutically target the complicated TME are emerging as a potential approach for cancer treatment. Oncolytic viruses (OVs) are one of the most promising methods for remodeling the TME into an antitumor environment and can be used alone or in combination with other immunotherapy options. OVs replicate specifically in tumor cells and can be genetically engineered to target multiple elements of the TME simultaneously, thus representing a therapeutic with the potential to modify the TME to promote activation of antitumor immune cells and overcome tumor therapeutic resistance and recurrence. In this review, we analyze the tropism of OVs towards tumor cells and explore the interaction between OVs and immune cells, tumor stroma, vasculature and the metabolic environment in detail to help understand how OVs may be one of our most promising prospects for long-term curative therapies. We also discuss some of the challenges associated with TME therapies, and future perspectives in this evolving field.

Oncolytic Virotherapy in Peritoneal Metastasis Gastric Cancer: The Challenges and Achievements

Gastric cancer (GC) is the fourth most common cancer and the second leading cause of cancer death globally. Although the mortality rate in some parts of the world, such as East Asia, is still high, new treatments and lifestyle changes have effectively reduced deaths from this type of cancer. One of the main challenges of this type of cancer is its late diagnosis and poor prognosis. GC patients are usually diagnosed in the advanced stages of the disease, which is often associated with peritoneal metastasis (PM) and significantly reduces survival. This type of metastasis in patients with GC poses a serious challenge due to limitations in common therapies such as surgery and tumor resection, as well as failure to respond to systemic chemotherapy. To solve this problem, researchers have used virotherapy such as reovirus-based anticancer therapy in patients with GC along with PM who are resistant to current chemotherapies because this therapeutic approach is able to overcome immune suppression by activating dendritic cells (DCs) and eventually lead to the intrinsic activity of antitumor effector T cells. This review summarizes the immunopathogenesis of peritoneal metastasis of gastric cancer (PMGC) and the details for using virotherapy as an effective anticancer treatment approach, as well as its challenges and opportunities.

Hypoxia and viral infectious diseases

Oxygen-sensing mechanisms allow cells to adapt and respond to changes in cellular oxygen tension, including hypoxic conditions. Hypoxia-inducible factor (HIF) is a central mediator in this fundamental adaptive response, and has critical functions in normal and disease physiology. Viruses have been shown to manipulate HIFs during their life cycle to facilitate replication and invasion. Conversely, HIFs are also implicated in the development of the host immune system and response to viral infections. Here, we highlight the recent revelations of host-pathogen interactions that involve the hypoxic response pathway and the role of HIF in emerging viral infectious diseases, as well as discussing potential antiviral therapeutic strategies targeting the HIF signaling axis.

Hypoxia-Inducible Factor 1α (HIF1α) Suppresses Virus Replication in Human Cytomegalovirus Infection by Limiting Kynurenine Synthesis

Viruses, including human cytomegalovirus (HCMV), reprogram cellular metabolism using host metabolic regulators to support virus replication. Alternatively, in response to infection, the host can use metabolism to limit virus replication.

Human cytomegalovirus (HCMV) replication depends on the activities of several host regulators of metabolism. Hypoxia-inducible factor 1α (HIF1α) was previously proposed to support virus replication through its metabolic regulatory function. HIF1α protein levels rise in response to HCMV infection in nonhypoxic conditions, but its effect on HCMV replication was not investigated. We addressed the role of HIF1α in HCMV replication by generating primary human cells with HIF1α knocked out using CRISPR/Cas9. When HIF1α was absent, we found that HCMV replication was enhanced, showing that HIF1α suppresses viral replication. We used untargeted metabolomics to determine if HIF1α regulates metabolite concentrations in HCMV-infected cells. We discovered that in HCMV-infected cells, HIF1α suppresses intracellular and extracellular concentrations of kynurenine. HIF1α also suppressed the expression of indoleamine 2,3-dioxygenase 1 (IDO1), the rate-limiting enzyme in kynurenine synthesis. In addition to its role in tryptophan metabolism, kynurenine acts as a signaling messenger by activating aryl hydrocarbon receptor (AhR). Inhibiting AhR reduces HCMV replication, while activating AhR with an exogenous ligand increases virus replication. Moreover, we found that feeding kynurenine to cells promotes HCMV replication. Overall, our findings indicate that HIF1α reduces HCMV replication by regulating metabolism and metabolite signaling.

Hypoxic microenvironment shapes HIV-1 replication and latency

Viral replication is defined by the cellular microenvironment and one key factor is local oxygen tension, where hypoxia inducible factors (HIFs) regulate the cellular response to oxygen. Human immunodeficiency virus (HIV) infected cells within secondary lymphoid tissues exist in a low-oxygen or hypoxic environment in vivo. However, the majority of studies on HIV replication and latency are performed under laboratory conditions where HIFs are inactive. We show a role for HIF-2α in restricting HIV transcription via direct binding to the viral promoter. Hypoxia reduced tumor necrosis factor or histone deacetylase inhibitor, Romidepsin, mediated reactivation of HIV and inhibiting HIF signaling-pathways reversed this phenotype. Our data support a model where the low-oxygen environment of the lymph node may suppress HIV replication and promote latency. We identify a mechanism that may contribute to the limited efficacy of latency reversing agents in reactivating HIV and suggest new strategies to control latent HIV-1.

Attenuation of the Hypoxia Inducible Factor Pathway after Oncolytic Adenovirus Infection Coincides with Decreased Vessel Perfusion

The interplay between oncolytic virus infection and tumour hypoxia is particularly unexplored in vivo, although hypoxia is present in virtually all solid carcinomas. In this study, oncolytic adenovirus infection foci were found within pimonidazole-reactive, oxygen-poor areas in a colorectal xenograft tumour, where the expression of VEGF, a target gene of the hypoxia-inducible factor (HIF), was attenuated. We hypothesised that adenovirus infection interferes with the HIF-signalling axis in the hypoxic tumour niche, possibly modifying the local vascular supply. In vitro, enadenotucirev (EnAd), adenovirus 11p and adenovirus 5 decreased the protein expression of HIF-1α only during the late phase of the viral life cycle by transcriptional down-regulation and not post-translational regulation. The decreasing HIF levels resulted in the down-regulation of angiogenic factors such as VEGF, coinciding with reduced endothelial tube formation but also increased T-cell activation in conditioned media transfer experiments. Using intravital microscopy, a decreased perfused vessel volume was observed in infected tumour nodules upon systemic delivery of EnAd, encoding the oxygen-independent fluorescent reporter UnaG to a tumour xenograft grown under an abdominal window chamber. We conclude that the attenuation of the HIF pathway upon adenoviral infection may contribute to anti-vascular and immunostimulatory effects in the periphery of established infection foci in vivo.

Oncolytic viral therapy for pancreatic cancer

Outcomes of pancreatic adenocarcinoma (PDA) remain dismal despite extensive clinical investigation. Combination chemotherapy provides modest improvements in survival above best supportive care, and immunotherapy has thus far not proven effective. Nevertheless, growing insight into antitumor immunity and the tumor microenvironment has inspired the discovery of novel agents targeting PDA. Oncolytic viruses represent an emerging class of immunotherapeutic agents that have undergone extensive preclinical investigation and warrant further investigation in well-designed clinical trials.

Talimogene Laherparepvec (T-VEC) and Other Oncolytic Viruses for the Treatment of Melanoma

Many mammalian viruses have properties that can be commandeered for the treatment of cancer. These characteristics include preferential infection and replication in tumor cells, the initiation of tumor cell lysis, and the induction of innate and adaptive anti-tumor immunity. Furthermore, viruses can be genetically engineered to reduce pathogenicity and increase immunogenicity resulting in minimally toxic therapeutic agents. Talimogene laherparepvec (T-VEC; Imlygic™), is a genetically modified herpes simplex virus, type 1, and is the first oncolytic virus therapy to be approved for the treatment of advanced melanoma by the US FDA. T-VEC is attenuated by the deletion of the herpes neurovirulence viral genes and enhanced for immunogenicity by the deletion of the viral ICP47 gene. Immunogenicity is further supported by expression of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) gene, which helps promote the priming of T cell responses. T-VEC demonstrated significant improvement in durable response rate, objective response rate, and progression-free survival in a randomized phase III clinical trial for patients with advanced melanoma. This review will discuss the optimal selection of patients for such treatment and describe how therapy is optimally delivered. We will also discuss future directions for oncolytic virus immunotherapy, which will likely include combination T-VEC clinical trials, expansion of T-VEC to other types of non-melanoma skin cancers, and renewed efforts at oncolytic virus drug development with other viruses.

Actin-resistant DNAse I Expression From Oncolytic Adenovirus Enadenotucirev Enhances Its Intratumoral Spread and Reduces Tumor Growth

Spread of oncolytic viruses through tumor tissue is essential to effective virotherapy. Interstitial matrix is thought to be a significant barrier to virus particle convection between "islands" of tumor cells. One way to address this is to encode matrix-degrading enzymes within oncolytic viruses, for secretion from infected cells. To test the hypothesis that extracellular DNA provides an important barrier, we assessed the ability of DNase to promote virus spread. Nonreplicating Ad5 vectors expressing actin-resistant DNase (aDNAse I), proteinase K (PK), hyaluronidase (rhPH20), and chondroitinase ABC (CABC) were injected into established DLD human colorectal adenocarcinoma xenografts, transcomplemented with a replicating Ad5 virus. Each enzyme improved oncolysis by the replicating adenovirus, with no evidence of tumor cells being shed into the bloodstream. aDNAse I and rhPH20 hyaluronidase were then cloned into conditionally-replicating group B adenovirus, Enadenotucirev (EnAd). EnAd encoding each enzyme showed significantly better antitumor efficacy than the parental virus, with the aDNAse I-expressing virus showing improved spread. Both DNase and hyaluronidase activity was still measurable 32 days postinfection. This is the first time that extracellular DNA has been implicated as a barrier for interstitial virus spread, and suggests that oncolytic viruses expressing aDNAse I may be promising candidates for clinical translation.

Improved in vitro human tumor models for cancer gene therapy

Developing effective anticancer treatments is a particular challenge, as agents must contend with not only the target cellular biology, but also with the complex tumor microenvironment. Here we discuss various in vitro strategies that have sought to address this issue, with a particular focus on new methodologies that utilize clinical samples in basic research and their application in gene therapy and virotherapy.

Lister strain vaccinia virus with thymidine kinase gene deletion is a tractable platform for development of a new generation of oncolytic virus

Vaccinia virus (VV) has many attractive characteristics as a potential cancer therapeutic. There are several strains of VV. The nonvaccine strain Western Reserve VV with deletion of both the thymidine kinase and the viral growth factor genes (known as WRDD) has been reported as the most potent tumor-targeted oncolytic VV. Other strains, such as the European vaccine Lister strain, are largely untested. This study evaluated the antitumor potency and biodistribution of different VV strains using in vitro and in vivo models of cancer. Lister strain virus with thymidine kinase gene deletion (VVΔTK) demonstrated superior antitumor potency and cancer-selective replication in vitro and in vivo, compared with WRDD, especially in human cancer cell lines and immune-competent hosts. Further investigation of functional mechanisms revealed that Lister VVΔTK presented favorable viral biodistribution within the tumors, with lower levels of proinflammatory cytokines compared with WRDD, suggesting that Lister strain may induce a diminished host inflammatory response. This study indicates that the Lister strain VVΔTK may be a particularly promising VV strain for the development of the next generation of tumor-targeted oncolytic therapeutics.

Role of cellular iron and oxygen in the regulation of HIV-1 infection

Despite efficient antiretroviral therapy, eradication of HIV-1 infection is challenging and requires novel biological insights and therapeutic strategies. Among other physiological and environmental factors, intracellular iron greatly affects HIV-1 replication. Higher iron stores were shown to be associated with faster progression of HIV-1 infection and to inversely correlate with the survival of HIV-1 infected patients. Iron is required for several steps in the HIV-1 life cycle, including reverse transcription, HIV-1 gene expression and capsid assembly. Here, the authors present a comprehensive review of the molecular mechanisms involved in iron- and oxygen-mediated regulation of HIV-1 replication. We also propose key intracellular pathways that may be involved in regulating HIV-1 replication, via protein kinase complexes, CDK9/cyclin T1 and CDK 2/cyclin E, protein phosphatase-1 and other host factors.

Vascular endothelial growth factor A promotes vaccinia virus entry into host cells via activation of the Akt pathway

Vaccinia virus (VV) is an enveloped DNA virus from the poxvirus family and has played a crucial role in the eradication of smallpox. It continues to be used in immunotherapy for the prevention of infectious diseases and treatment of cancer. However, the mechanisms of poxvirus entry, the host factors that affect viral virulence, and the reasons for its natural tropism for tumor cells are incompletely understood. By studying the effect of hypoxia on VV infection, we found that vascular endothelial growth factor A (VEGF-A) augments oncolytic VV cytotoxicity. VEGF derived from tumor cells acts to increase VV internalization, resulting in increased replication and cytotoxicity in an AKT-dependent manner in both tumor cells and normal respiratory epithelial cells. Overexpression of VEGF also enhances VV infection within tumor tissue in vivo after systemic delivery. These results highlight the importance of VEGF expression in VV infection and have potential implications for the design of new strategies to prevent poxvirus infection and the development of future generations of oncolytic VV in combination with conventional or biological therapies.

Hypoxia induces the gene expression and extracellular transmission of persistent lymphocytic choriomeningitis virus

The physiological context of virus-infected cells can markedly affect multiplication and spread of the virus progeny. During persistent infection, the virus exploits the host cell without disturbing its vital functions. However, microenvironmental hypoxia can uncouple this intimate relationship and escalate virus pathogenesis. Accumulating evidence suggests that hypoxia-inducible factor (HIF) modulates gene expression of the viruses that pass through a DNA stage, contain hypoxia-responsive promoter elements, and replicate in the nucleus. Here we show that hypoxia can influence the gene expression and transmission of the cytoplasmic RNA virus lymphocytic choriomeningitis virus (LCMV), which is a neglected human pathogen and teratogen. The MX strain of LCMV, which we used as a model, replicates in a persistent mode in human HeLa cells, fails to produce mature envelope glycoproteins, and spreads through cell-cell contacts in the absence of extracellular infectious virions. Both exposure of MX-infected HeLa cells to chronic hypoxia and gene transfer approaches led to increased virus RNA transcription and higher levels of the viral proteins via a HIF-dependent mechanism. Moreover, hypoxia enhanced the formation of infectious virions capable of transmitting LCMV by cell-free medium. This LCMV "reactivation" might have health-compromising consequences in hypoxia-associated situations, such as fetal development and ischemia-related pathologies.

Oncolytic adenovirus based on serotype 3

Oncolytic adenoviruses have been safe in clinical trials but the efficacy has been mostly limited. All published trials have been performed with serotype 5 based viruses. The expression level of the Ad5 receptor CAR may be variable in advanced tumors. In contrast, the Ad3 receptor remains unclear, but is known to be abundantly expressed in most tumors. Therefore, we hypothesized that a fully serotype 3 oncolytic adenovirus might be useful for treating cancer. Patients exposed to adenoviruses develop high titers of serotype-specific neutralizing antibodies, which might compromise re-administration. Thus, having different serotype oncolytic viruses available might facilitate repeated dosing in humans. Ad3-hTERT-E1A is a fully serotype 3 oncolytic adenovirus controlled by the promoter of the catalytic domain of human telomerase. It was effective in vitro on cell lines representing seven major cancer types, although low toxicity was seen in non-malignant cells. In vivo, the virus had anti-tumor efficacy in three different animal models. Although in vitro oncolysis mediated by Ad3-hTERT-E1A and wild-type Ad3 occurred more slowly than with Ad5 or Ad5/3 (Ad3 fiber knob in Ad5) based viruses, in vivo the virus was at least as potent as controls. Anti-tumor efficacy was retained in presence of neutralizing anti-Ad5 antibodies whereas Ad5 based controls were blocked. In summary, we report generation of a non-Ad5 based oncolytic adenovirus, which might be useful for testing in cancer patients, especially in the context of high anti-Ad5 neutralizing antibodies.

Impact of tumor microenvironment on oncolytic viral therapy

Interactions between tumor cells and their microenvironment have been shown to play a very significant role in the initiation, progression, and invasiveness of cancer. These tumor-stromal interactions are capable of altering the delivery and effectiveness of therapeutics into the tumor and are also known to influence future resistance and re-growth after treatment. Here we review recent advances in the understanding of the tumor microenvironment and its response to oncolytic viral therapy. The multifaceted environmental response to viral therapy can influence viral infection, replication, and propagation within the tumor. Recent studies have unveiled the complicated temporal changes in the tumor vasculature post-oncolytic virus (OV) treatment, and their impact on tumor biology. Similarly, the secreted extracellular matrix in solid tumors can affect both infection and spread of the therapeutic virus. Together, these complex changes in the tumor microenvironment also modulate the activation of the innate antiviral host immune response, leading to quick and efficient viral clearance. In order to combat these detrimental responses, viruses have been combined with pharmacological adjuvants and "armed" with therapeutic genes in order to suppress the pernicious environmental conditions following therapy. In this review we will discuss the impact of the tumor environment on viral therapy and examine some of the recent literature investigating methods of modulating this environment to enhance oncolysis.

Oncolytic (replication-competent) adenoviruses as anticancer agents

IMPORTANCE OF THE FIELD

Whilst therapies for neoplasies have advanced tremendously in the last few decades, there is still a need for new anti-cancer treatments. One option is genetically-engineered oncolytic adenovirus (Ad) 'vectors'. These kill cancer cells via the viral replication cycle, and amplify the anti-tumor effect by producing progeny virions able to infect neighboring tumor cells.

AREAS COVERED IN THIS REVIEW

We provide a description of basic Ad biology and summarize the literature for oncolytic Ads from 1996 to the present.

WHAT THE READER WILL GAIN

An overall view of oncolytic Ads, the merits and drawbacks of the various features of these vectors, and obstacles to further development and future directions for research.

TAKE HOME MESSAGE

Ads are attractive for gene therapy because they are relatively innocuous, easy to produce in large quantities, genetically stable, and easy to manipulate. A variety of have been constructed and tested, in pre-clinical and clinical experiments. Oncolytic Ads proved to be remarkably safe; no dose-limiting toxicity was observed in any clinical trial, and the maximum tolerated dose was not reached. At present, the major challenge for researchers is to increase the efficacy of the vectors, and to incorporate oncolytic virotherapy into existing treatment protocols.

Oncolytic Viruses for Cancer Therapy: Overcoming the Obstacles

Targeted therapy of cancer using oncolytic viruses has generated much interest over the past few years in the light of the limited efficacy and side effects of standard cancer therapeutics for advanced disease. In 2006, the world witnessed the first government-approved oncolytic virus for the treatment of head and neck cancer. It has been known for many years that viruses have the ability to replicate in and lyse cancer cells. Although encouraging results have been demonstrated in vitro and in animal models, most oncolytic viruses have failed to impress in the clinical setting. The explanation is multifactorial, determined by the complex interactions between the tumor and its microenvironment, the virus, and the host immune response. This review focuses on discussion of the obstacles that oncolytic virotherapy faces and recent advances made to overcome them, with particular reference to adenoviruses.

Lister strain vaccinia virus, a potential therapeutic vector targeting hypoxic tumours

Hypoxia contributes to the aggressive and treatment-resistant phenotype of pancreatic ductal adenocarcinoma (PDAC). Oncolytic vaccinia virus has potential as an anti-tumour agent but the ability to lyse hypoxic tumour cells is vital for clinical efficacy. We hypothesised that unique aspects of the poxvirus lifecycle would protect it from attenuation in hypoxic conditions. We characterised and compared the viral protein production, viral replication, cytotoxicity and transgene expression of Lister strain vaccinia virus in a panel of pancreatic cancer cell lines after exposure to normoxic or hypoxic conditions. Viral protein production was not affected by hypoxia, and high viral titres were produced in both normoxic and hypoxic conditions. Interestingly there was a five-fold (P<0.001) and 10-fold (P<0.0001) increase in viral cytotoxicity for CFPac1 and MiaPaca2 cell lines respectively in hypoxic conditions. Cytotoxicity was equivalent in the remaining cell lines. Levels of transgene expression (luciferase reporter gene) from the vaccinia viral vector were comparable regardless of the ambient oxygen concentration. The present study suggests that vaccinia virus is a promising vector for targeting pancreatic cancer and potentially other hypoxic tumour types.

Regulation of HIV-1 transcription at 3% versus 21% oxygen concentration

HIV transcription is induced by the HIV-1 Tat protein, in concert with cellular co-factors including CDK9, CDK2, NF-kappaB, and others. The cells of most of the body's organs are exposed to approximately 3-6% oxygen, but most in vitro studies of HIV replication are conducted at 21% oxygen. We hypothesized that activities of host cell factors involved in HIV-1 replication may differ at 3% versus 21% O(2), and that such differences may affect HIV-1 replication. Here we show that Tat-induced HIV-1 transcription was reduced at 3% O(2) compared to 21% O(2). HIV-1 replication was also reduced in acutely or chronically infected cells cultured at 3% O(2) compared to 21% O(2). This reduction was not due the decreased cell growth or increased cellular toxicity and also not due to the induction of hypoxic response. At 3% O(2), the activity of CDK9/cyclin T1 was inhibited and Sp1 activity was reduced, whereas the activity of other host cell factors such as CDK2 or NF-kappaB was not affected. CDK9-specific inhibitor ARC was much less efficient at 3% compared to 21% O(2) and also expression of CDK9/cyclin T1-dependent IkappaB inhibitor alpha was repressed. Our results suggest that lower HIV-1 transcription at 3% O(2) compared to 21% O(2) may be mediated by lower activity of CDK9/cyclin T1 and Sp1 at 3% O(2) and that additional host cell factors such as CDK2 and NF-kappaB might be major regulators of HIV-1 transcription at low O(2) concentrations.

Cancer gene therapy with targeted adenoviruses

BACKGROUND

Clinical experience with adenovirus vectors has highlighted the need for improved delivery and targeting.

OBJECTIVE

This manuscript aims to provide an overview of the techniques currently under development for improving adenovirus delivery to malignant cells in vivo.

METHODS

Primary research articles reporting improvements in adenoviral gene delivery are described. Strategies include genetic modification of viral coat proteins, non-genetic modifications including polymer encapsulation approaches and pharmacological interventions.

RESULTS/CONCLUSION

Reprogramming adenovirus tropism in vitro has been convincingly demonstrated using a range of genetic and physical strategies. These studies have provided new insights into our understanding of virology and the field is progressing. However, there are still some limitations that need special consideration before adenovirus-targeted cancer gene therapy emerges as a routine treatment in the clinical setting.

Gene therapy progress and prospects cancer: oncolytic viruses

The past 2 years have seen several major advances in oncolytic virotherapy. Studies on the interaction between viruses, immune responses and tumor microenvironment have provided important insight, while clinical trials have shown promise. This review summarizes key findings in this field over the past 2 years, and provides directions for future success.

Human mesenchymal stem cells lack tumor tropism but enhance the antitumor activity of oncolytic adenoviruses in orthotopic lung and breast tumors

Systemic adenoviral delivery into tumors is inefficient because of liver sequestration of intravenously administered virus. One potential solution for improving bioavailability is the use of carrier cells such as human mesenchymal stem cells (MSCs), which have been suggested to have inherent tumor tropism. Here we investigated the capacity of capsid-modified adenoviruses to infect and replicate in MSCs. Further, biodistribution and tumor-killing efficacy of MSCs loaded with oncolytic adenoviruses were evaluated in orthotopic murine models of lung and breast cancer. In vitro, heparan sulfate proteoglycan- and alpha(v)beta integrin-targeted viruses enhanced gene delivery to bone marrow- and adipose tissue-derived MSCs up to 11,000-fold over adenovirus serotype 5 (Ad5). Infectivity-enhanced oncolytic adenoviruses showed notably higher rates of cytolysis of in vitro-passaged MSCs in comparison with wild-type virus. In vivo, intravenously injected MSCs homed primarily to the lungs, and virus was released into advanced orthotopic breast and lung tumors for therapeutic efficacy and increased survival. When the same dose of virus was injected intravenously without MSCs, only transduction of the liver was seen. These results suggest that MSCs loaded with oncolytic adenoviruses might be a useful approach for improving the bioavailability of systemically administered oncolytic adenoviruses.

Targeted inflammation during oncolytic virus therapy severely compromises tumor blood flow

Oncolytic viruses (OVs) are selected or designed to eliminate malignancies by direct infection and lysis of cancer cells. In contrast to this concept of direct tumor lysis by viral infection, we observed that a significant portion of the in vivo tumor killing activity of two OVs, vesicular stomatitis virus (VSV) and vaccinia virus is caused by indirect killing of uninfected tumor cells. Shortly after administering the oncolytic virus we observed limited virus infection, coincident with a loss of blood flow to the interior of the tumor that correlated with induction of apoptosis in tumor cells. Transcript profiling of tumors showed that virus infection resulted in a dramatic transcriptional activation of pro-inflammatory genes including the neutrophil chemoattractants CXCL1 and CXCL5. Immunohistochemical examination of infected tumors revealed infiltration by neutrophils correlating with chemokine induction. Depletion of neutrophils in animals prior to VSV administration eliminated uninfected tumor cell apoptosis and permitted more extensive replication and spreading of the virus throughout the tumor. Taken all together, these results indicate that targeted recruitment of neutrophils to infected tumor beds enhances the killing of malignant cells. We propose that activation of inflammatory cells can be used for enhancing the effectiveness of oncolytic virus therapeutics, and that this approach should influence the planning of therapeutic doses.