Ionizing Radiation Activates Late Herpes Simplex Virus 1 Promoters via the p38 Pathway in Tumors Treated with Oncolytic Viruses

Clinical Applications of Immunotherapy for Recurrent Glioblastoma in Adults

Glioblastoma (GBM) is the most common malignant primary brain tumor in adults. Despite standard therapies, including resection and chemoradiation, recurrence is virtually inevitable. Current treatment for recurrent glioblastoma (rGBM) is rapidly evolving, and emerging therapies aimed at targeting primary GBM are often first tested in rGBM to demonstrate safety and feasibility, which, in recent years, has primarily been in the form of immunotherapy. The purpose of this review is to highlight progress in clinical trials of immunotherapy for rGBM, including immune checkpoint blockade, oncolytic virotherapy, chimeric antigen receptor (CAR) T-cell therapy, cancer vaccine and immunotoxins. Three independent reviewers covered literature, published between the years 2000 and 2022, in various online databases. In general, the efficacy of immunotherapy in rGBM remains uncertain, and is limited to subsets/small cohorts of patients, despite demonstrating feasibility in early-stage clinical trials. However, considerable progress has been made in understanding the mechanisms that may preclude rGBM patients from responding to immunotherapy, as well as in developing new approaches/combination strategies that may inspire optimism for the utility of immunotherapy in this devastating disease. Continued trials are necessary to further assess the best therapeutic avenues and ascertain which treatments might benefit each patient individually.

Glioblastoma microenvironment and its reprogramming by oncolytic virotherapy

Glioblastoma (GBM), a highly aggressive form of brain tumor, responds poorly to current conventional therapies, including surgery, radiation therapy, and systemic chemotherapy. The reason is that the delicate location of the primary tumor and the existence of the blood-brain barrier limit the effectiveness of traditional local and systemic therapies. The immunosuppressive status and multiple carcinogenic pathways in the complex GBM microenvironment also pose challenges for immunotherapy and single-targeted therapy. With an improving understanding of the GBM microenvironment, it has become possible to consider the immunosuppressive and highly angiogenic GBM microenvironment as an excellent opportunity to improve the existing therapeutic efficacy. Oncolytic virus therapy can exert antitumor effects on various components of the GBM microenvironment. In this review, we have focused on the current status of oncolytic virus therapy for GBM and the related literature on antitumor mechanisms. Moreover, the limitations of oncolytic virus therapy as a monotherapy and future directions that may enhance the field have also been discussed.

Current clinical landscape of oncolytic viruses as novel cancer immunotherapeutic and recent preclinical advancements

Oncolytic viruses (OVs) have been gaining attention in the pharmaceutical industry as a novel immunotherapeutic and therapeutic adjuvant due to their ability to induce and boost antitumor immunity through multiple mechanisms. First, intrinsic mechanisms of OVs that enable exploitation of the host immune system (e.g., evading immune detection) can nullify the immune escape mechanism of tumors. Second, many types of OVs have been shown to cause direct lysis of tumor cells, resulting in an induction of tumor-specific T cell response mediated by release of tumor-associated antigens and danger signal molecules. Third, armed OV-expressing immune stimulatory therapeutic genes could be highly expressed in tumor tissues to further improve antitumor immunity. Last, these OVs can inflame cold tumors and their microenvironment to be more immunologically favorable for other immunotherapeutics. Due to these unique characteristics, OVs have been tested as an adjuvant of choice in a variety of therapeutics. In light of these promising attributes of OVs in the immune-oncology field, the present review will examine OVs in clinical development and discuss various strategies that are being explored in preclinical stages for the next generation of OVs that are optimized for immunotherapy applications.

Clinical advances in oncolytic virotherapy for pediatric brain tumors

Malignant brain tumors constitute nearly one-third of cancer diagnoses in children and have recently surpassed hematologic malignancies as the most lethal neoplasm in the pediatric population. Outcomes for children with brain tumors are unacceptably poor and current standards of care-surgical resection, chemotherapy, and radiation-are associated with significant long-term morbidity. Oncolytic virotherapy has emerged as a promising immunotherapy for the treatment of brain tumors. While the majority of brain tumor clinical trials utilizing oncolytic virotherapy have been in adults, five viruses are being tested in pediatric brain tumor clinical trials: herpes simplex virus (G207), reovirus (pelareorep/Reolysin), measles virus (MV-NIS), poliovirus (PVSRIPO), and adenovirus (DNX-2401, AloCELYVIR). Herein, we review past and current pediatric immunovirotherapy brain tumor trials including the relevant preclinical and clinical research that contributed to their development. We describe mechanisms by which the viruses may overcome barriers in treating pediatric brain tumors, examine challenges associated with achieving effective, durable responses, highlight unique aspects and successes of the trials, and discuss future directions of immunovirotherapy research for the treatment of pediatric brain tumors.

Replication and Spread of Oncolytic Herpes Simplex Virus in Solid Tumors

Oncolytic herpes simplex virus (oHSV) is a highly promising treatment for solid tumors. Intense research and development efforts have led to first-in-class approval for an oHSV for melanoma, but barriers to this promising therapy still exist that limit efficacy. The process of infection, replication and transmission of oHSV in solid tumors is key to obtaining a good lytic destruction of infected cancer cells to kill tumor cells and release tumor antigens that can prime anti-tumor efficacy. Intracellular tumor cell signaling and tumor stromal cells present multiple barriers that resist oHSV activity. Here, we provide a review focused on oncolytic HSV and the essential viral genes that allow for virus replication and spread in order to gain insight into how manipulation of these pathways can be exploited to potentiate oHSV infection and replication among tumor cells.

[Prospects for using low-dose radiation in the complex therapy for COVID-19]

This review presents the literature data of new approaches for the treatment of COVID-19 with low doses of radiation (LDR). In addition, data on the use of LDR for the treatment of various disorders, in particular pneumonia, a number of inflammatory processes of various etiology, as well as Alzheimer's disease are discussed. The mechanisms of LDR action are briefly described, associated with the activation of the immune system and antiinflammatory response due to the effect on the processes of oxidative stress, which is reflected in an increase in the activity of cytokines (interleukin- (IL-) 6), changes in the expression of a number of genes (such as P53 and NF-κB (p65)) and long non-coding RNAs (ncRNAs) (the authors' own data are presented). Based on the analysis of the material presented, it can be assumed that further clinical trials of the effect of MDR (5-10 cGy) on patients with COVID-19, who are at different stages of the disease, will reveal the optimal conditions for the development and use of an effective treatment regimen.

Low-dose radiation therapy for coronavirus disease-2019 pneumonia: Is it time to look beyond apprehensions?

Coronavirus disease-2019 (COVID-19) has become a global health crisis. Mortality associated with COVID-19 is characterized mainly by acute respiratory distress syndrome (ARDS), sepsis, pneumonia, and respiratory failure. The pathogenesis of the disease is known to be associated with pro-inflammatory processes after virus infection. Hence, various therapeutic strategies are being developed to control the inflammation and cytokine storm in COVID-19 patients. Recently, low-dose radiation therapy (LDRT) has been suggested for the treatment of pneumonia/ADRS in COVID-19 patients through irradiation of lungs by gamma/X-ray. In this direction, a few clinical trials have also been initiated. However, a few recent publications have raised some concerns regarding LDRT, especially about possibilities of activation/aggressiveness of virus (severe acute respiratory syndrome coronavirus 2 in case of COVID-19), lung injury and risk of second cancer after low-dose therapy. The present manuscript is an attempt to analyze these apprehensions based on cited references and other available literature, including some from our laboratory. At this point, LDRT may be not the first line of therapy. However, based on existing anti-inflammatory evidence of LDRT, it needs encouragement as an adjuvant therapy and for more multi-centric clinical trials. In addition, it would be worth combining LDRT with other anti-inflammatory therapies, which would open avenues for multi-modal therapy of pneumonia/ARDS in COVID-19 patients. The mode of irradiation (local lung irradiation or whole-body irradiation) and the window period after infection of the virus, need to be optimized using suitable animal studies for effective clinical outcomes of LDRT. However, considering ample evidence, it is time to look beyond the apprehensions if a low dose of radiation could be exploited for better management of COVID-19 patients.

The Oncolytic Virus in Cancer Diagnosis and Treatment

Cancer has always been an enormous threat to human health and survival. Surgery, radiotherapy, and chemotherapy could improve the survival of cancer patients, but most patients with advanced cancer usually have a poor survival or could not afford the high cost of chemotherapy. The emergence of oncolytic viruses provided a new strategy for us to alleviate or even cure malignant tumors. An oncolytic virus can be described as a genetically engineered or naturally existing virus that can selectively replicate in cancer cells and then kill them without damaging the healthy cells. There have been many kinds of oncolytic viruses, such as herpes simplex virus, adenovirus, and Coxsackievirus. Moreover, they have different clinical applications in cancer treatment. This review focused on the clinical application of oncolytic virus and predicted the prospect by analyzing the advantages and disadvantages of oncolytic virotherapy.

Infection Load and Prevalence of Novel Viruses Identified from the Bank Vole Do Not Associate with Exposure to Environmental Radioactivity

Bank voles (Myodes glareolus) are host to many zoonotic viruses. As bank voles inhabiting areas contaminated by radionuclides show signs of immunosuppression, resistance to apoptosis, and elevated DNA repair activity, we predicted an association between virome composition and exposure to radionuclides. To test this hypothesis, we studied the bank vole virome in samples of plasma derived from animals inhabiting areas of Ukraine (contaminated areas surrounding the former nuclear power plant at Chernobyl, and uncontaminated areas close to Kyiv) that differed in level of environmental radiation contamination. We discovered four strains of hepacivirus and four new virus sequences: two adeno-associated viruses, an arterivirus, and a mosavirus. However, viral prevalence and viral load, and the ability to cause a systemic infection, was not dependent on the level of environmental radiation.

Rationale and Design of a Phase 1 Clinical Trial to Evaluate HSV G207 Alone or with a Single Radiation Dose in Children with Progressive or Recurrent Malignant Supratentorial Brain Tumors

Primary central nervous system tumors are the most common solid neoplasm of childhood and the leading cause of cancer-related death in pediatric patients. Survival rates for children with malignant supratentorial brain tumors are poor despite aggressive treatment with combinations of surgery, radiation, and chemotherapy, and survivors often suffer from damaging lifelong sequelae from current therapies. Novel innovative treatments are greatly needed. One promising new approach is the use of a genetically engineered, conditionally replicating herpes simplex virus (HSV) that has shown tumor-specific tropism and potential efficacy in the treatment of malignant brain tumors. G207 is a genetically engineered HSV-1 lacking genes essential for replication in normal brain cells. Safety has been established in preclinical investigations involving intracranial inoculation in the highly HSV-sensitive owl monkey (Aotus nancymai), and in three adult phase 1 trials in recurrent/progressive high-grade gliomas. No dose-limiting toxicities were seen in the adult studies and a maximum tolerated dose was not reached. Approximately half of the 35 treated adults had radiographic or neuropathologic evidence of response at a minimum of one time point. Preclinical studies in pediatric brain tumor models indicate that a variety of pediatric tumor types are highly sensitive to killing by G207. This clinical protocol outlines a first in human children study of intratumoral inoculation of an oncolytic virus via catheters placed directly into recurrent or progressive supratentorial malignant tumors.

Genetically Engineered Vaccinia Viruses As Agents for Cancer Treatment, Imaging, and Transgene Delivery

Despite advances in technology, the formidable challenge of treating cancer, especially if advanced, still remains with no significant improvement in survival rates, even with the most common forms of cancer. Oncolytic viral therapies have shown great promise for the treatment of various cancers, with the possible advantages of stronger treatment efficacy compared to conventional therapy due to higher tumor selectivity, and less toxicity. They are able to preferentially and selectively propagate in cancer cells, consequently destroying tumor tissue mainly via cell lysis, while leaving non-cancerous tissues unharmed. Several wild-type and genetically engineered vaccinia virus (VACV) strains have been tested in both preclinical and clinical trials with promising results. Greater understanding and advancements in molecular biology have enabled the generation of genetically engineered oncolytic viruses for safer and more efficacious treatment, including arming VACVs with cytokines and immunostimulatory molecules, anti-angiogenic agents, and enzyme prodrug therapy, in addition to combining VACVs with conventional external and systemic radiotherapy, chemotherapy, immunotherapy, and other virus strains. Furthermore, novel oncolytic vaccinia virus strains have been generated that express reporter genes for the tracking and imaging of viral therapy and monitoring of therapeutic response. Further study is needed to unlock VACVs’ full potential as part of the future of cancer therapy.

Deciphering fact from artifact when using reporter assays to investigate the roles of host factors on L1 retrotransposition

BACKGROUND

The Long INterspersed Element-1 (L1, LINE-1) is the only autonomous mobile DNA element in humans and has generated as much as half of the genome. Due to increasing clinical interest in the roles of L1 in cancer, embryogenesis and neuronal development, it has become a priority to understand L1-host interactions and identify host factors required for its activity. Apropos to this, we recently reported that L1 retrotransposition in HeLa cells requires phosphorylation of the L1 protein ORF1p at motifs targeted by host cell proline-directed protein kinases (PDPKs), which include the family of mitogen-activated protein kinases (MAPKs). Using two engineered L1 reporter assays, we continued our investigation into the roles of MAPKs in L1 activity.

RESULTS

We found that the MAPK p38δ phosphorylated ORF1p on three of its four PDPK motifs required for L1 activity. In addition, we found that a constitutively active p38δ mutant appeared to promote L1 retrotransposition in HeLa cells. However, despite the consistency of these findings with our earlier work, we identified some technical concerns regarding the experimental methodology. Specifically, we found that exogenous expression of p38δ appeared to affect at least one heterologous promoter in an engineered L1 reporter, as well as generate opposing effects on two different reporters. We also show that two commercially available non-targeting control (NTC) siRNAs elicit drastically different effects on the apparent retrotransposition reported by both L1 assays, which raises concerns about the use of NTCs as normalizing controls.

CONCLUSIONS

Engineered L1 reporter assays have been invaluable for determining the functions and critical residues of L1 open reading frames, as well as elucidating many aspects of L1 replication. However, our results suggest that caution is required when interpreting data obtained from L1 reporters used in conjunction with exogenous gene expression or siRNA.

Effect of Repeat Dosing of Engineered Oncolytic Herpes Simplex Virus on Preclinical Models of Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), a tumor of skeletal muscle origin, is the most common sarcoma of childhood. Despite multidrug chemotherapy regimens, surgical intervention, and radiation treatment, outcomes remain poor, especially in advanced disease, and novel therapies are needed for the treatment of these aggressive malignancies. Genetically engineered oncolytic viruses, such as herpes simplex virus-1 (HSV), are currently being explored as treatments for pediatric tumors. M002, an oncolytic HSV, has both copies of the γ₁34.5 gene deleted, enabling replication in tumor cells but thwarting infection of normal, postmitotic cells. We hypothesized that M002 would infect human RMS tumor cells and lead to decreased tumor cell survival in vitro and impede tumor growth in vivo. In the current study, we demonstrated that M002 could infect, replicate in, and decrease cell survival in both embryonal (ERMS) and alveolar rhabdomyosarcoma (ARMS) cells. Additionally, M002 reduced xenograft tumor growth and increased animal survival in both ARMS and ERMS. Most importantly, we showed for the first time that repeated dosing of oncolytic virus coupled with low-dose radiation provided improved tumor response in RMS. These findings provide support for the clinical investigation of oncolytic HSV in pediatric RMS.

Radiation-Guided Gene Therapy of Cancer

Gene therapy has been proposed as a means to combat cancer. However, systemic toxicity observed in preclinical trials suggested the importance of selectively targeted delivery and inducible gene expression in tumor tissues. Discovery of radiation-inducible promoter sequences provides one way to minimize inadvertent toxicity from gene therapy in normal tissues. Radiation is administered to selectively induce cytotoxic gene expression in the targeted tumor tissues. With promising results from phase II clinical trials using TNF-expressing adenovirus, it is possible to have radiation-guided gene therapy regimes once the tumor-targeted delivery has been achieved. Tumor endothelium is an attractive biological target for gene therapy, because it has the advantage of stability, accessibility, and bioavailability for therapeutic agents. Technological development of DNA microarray, proteomic profiling, and phage-displayed libraries accelerates the identification of tumor-specific endothelial biomarkers and discovery of its relevant affinity reagents for targeted delivery. The application of radiation-guided gene delivery, its amplification, as well as expression of gene therapy presents great opportunities to be employed as an alternative cancer treatment.

Therapeutic potential of antiviral drugs targeting chemorefractory colorectal adenocarcinoma cells overexpressing endogenous retroviral elements

Background

Endoretroviruses account for circa 8 % of all transposable elements found in the genome of humans and other animals. They represent a genetic footprint of ancestral germ-cell infections of exoviruses that is transmittable to the progeny by Mendelian segregation. Traces of human endogenous retroviruses are physiologically expressed in ovarial, testicular and placental tissues as well as in stem cells. In addition, a number of these fossil viral elements have also been related to carcinogenesis. However, a relation between endoretroviruses expression and chemoresistance has not been reported yet.

Methods

Twenty colorectal carcinoma patient samples were scrutinized for HERV-W_E1 and HERV-FRD₁ endoretroviruses using immunohistochemical approaches. In order to search for differential expression of these elements in chemotherapy refractory cells, a resistant HCT8 colon carcinoma subline was developed by serial etoposide exposure. Endoretroviral elements were detected by immunocytochemical staining, qPCR and ELISA. IC₅₀-values of antiviral and cytostatic drugs in HCT8 cells were determined by MTT proliferation assay. The antivirals-cytostatics interaction was evaluated by the isobologram method.

Results

In this work, we show for the first time that HERV-W_E1, HERV-FRD₁, HERV-3₁, and HERV-V₁ are a) simultaneously expressed in treatment-naïve colon carcinoma cells and b) upregulated after cytostatic exposure, suggesting that these retroviral elements are intimately related to chemotherapy resistance. We found a number of antiviral drugs to have cytotoxic activity and the ability to force the downregulation of HERV proteins in vitro. We also demonstrate that the use of different antiviral compounds alone or in combination with anticancer agents results in a synergistic antiproliferative effect and downregulation of different endoretroviral elements in highly chemotherapy-resistant colorectal tumor cells.

Conclusions

Enhanced HERV-expression is associated with chemoresistance in colon carcinomas which can be overcome by antiviral drugs alone or in combination with anticancer drugs. Therefore, the introduction of antiviral compounds to the current chemotherapy regimens potentially improves patient outcomes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0199-5) contains supplementary material, which is available to authorized users.

γ₁34.5-deleted HSV-1-expressing human cytomegalovirus IRS1 gene kills human glioblastoma cells as efficiently as wild-type HSV-1 in normoxia or hypoxia

Pathophysiological hypoxia, which fosters the glioma stem-like cell (GSC) phenotype, is present in high-grade gliomas and has been linked to tumor development, invasiveness and resistance to chemotherapy and radiation. Oncolytic virotherapy with engineered herpes simplex virus-1 (HSV-1) is a promising therapy for glioblastoma; however, the efficacy of γ(1)34.5-deleted HSVs, which have been used in clinical trials, was diminished in hypoxia. We investigated the ability of a chimeric human cytolomegalovirus (HCMV)/HSV-1 virus, which expresses the human CMV protein kinase R evasion gene IRS1 and is in preparation for clinical trials, to infect and kill adult and pediatric patient-derived glioblastoma xenografts in hypoxia and normoxia. Infectivity, cytotoxicity and viral recovery were significantly greater with the chimeric virus compared with the γ(1)34.5-deleted virus, regardless of oxygen tension. The chimeric virus infected and killed CD133+ GSCs similarly to wild-type HSV-1. Increased activation of mitogen-activated protein kinase p38 and its substrate heat-shock protein 27 (Hsp27) was seen after viral infection in normoxia compared with hypoxia. Hsp27 knockdown or p38 inhibition reduced virus recovery, indicating that the p38 pathway has a role in the reduced efficacy of the γ(1)34.5-deleted virus in hypoxia. Taken together, these findings demonstrate that chimeric HCMV/HSV-1 efficiently targets both CD133+ GSCs and glioma cells in hypoxia.

Combinatorial strategies for oncolytic herpes simplex virus therapy of brain tumors

Oncolytic viruses, such as the oncolytic herpes simplex virus (oHSV), are an exciting new therapeutic strategy for cancer as they are replication competent in tumor cells but not normal cells. In order to engender herpes simplex virus with oncolytic activity and make it safe for clinical application, mutations are engineered into the virus. Glioblastoma multiforme (GBM) is the most common and deadly primary brain tumor in adults. Despite many advances in therapy, overall survival has not been substantially improved over the last several decades. A number of different oHSVs have been tested as monotherapy in early-phase clinical trials for GBM and have demonstrated safety and anecdotal evidence of efficacy. However, strategies to improve efficacy are likely to be necessary to successfully treat GBM. Cancer treatment usually involves multimodal approaches, so the standard of care for GBM includes surgery, radiotherapy and chemotherapy. In preclinical GBM models, combinations of oHSV with other types of therapy have exhibited markedly improved activity over individual treatments alone. In this review, we will discuss the various combination strategies that have been employed with oHSV, including chemotherapy, small-molecule inhibitors, antiangiogenic agents, radiotherapy and expression of therapeutic transgenes. Effective combinations, especially synergistic ones, are clinically important not just for improved efficacy but also to permit lower and less-toxic doses and potentially overcome resistance.

Tumor radiosensitization by monomethyl auristatin E: mechanism of action and targeted delivery

Intrinsic tumor resistance to radiotherapy limits the efficacy of ionizing radiation (IR). Sensitizing cancer cells specifically to IR would improve tumor control and decrease normal tissue toxicity. The development of tumor-targeting technologies allows for developing potent radiosensitizing drugs. We hypothesized that the anti-tubulin agent monomethyl auristatin E (MMAE), a component of a clinically approved antibody-directed conjugate, could function as a potent radiosensitizer and be selectively delivered to tumors using an activatable cell-penetrating peptide targeting matrix metalloproteinases and RGD-binding integrins (ACPP-cRGD-MMAE). We evaluated the ability of MMAE to radiosensitize both established cancer cells and a low-passage cultured human pancreatic tumor cell line using clonogenic and DNA damage assays. MMAE sensitized colorectal and pancreatic cancer cells to IR in a schedule- and dose-dependent manner, correlating with mitotic arrest. Radiosensitization was evidenced by decreased clonogenic survival and increased DNA double-strand breaks in irradiated cells treated with MMAE. MMAE in combination with IR resulted in increased DNA damage signaling and activation of CHK1. To test a therapeutic strategy of MMAE and IR, PANC-1 or HCT-116 murine tumor xenografts were treated with nontargeted free MMAE or tumor-targeted MMAE (ACPP-cRGD-MMAE). While free MMAE in combination with IR resulted in tumor growth delay, tumor-targeted ACPP-cRGD-MMAE with IR produced a more robust and significantly prolonged tumor regression in xenograft models. Our studies identify MMAE as a potent radiosensitizer. Importantly, MMAE radiosensitization can be localized to tumors by targeted activatable cell-penetrating peptides.

Molecular imaging of oncolytic viral therapy

Oncolytic viruses have made their mark on the cancer world as a potential therapeutic option, with the possible advantages of reduced side effects and strengthened treatment efficacy due to higher tumor selectivity. Results have been so promising, that oncolytic viral treatments have now been approved for clinical trials in several countries. However, clinical studies may benefit from the ability to noninvasively and serially identify sites of viral targeting via molecular imaging in order to provide safety, efficacy, and toxicity information. Furthermore, molecular imaging of oncolytic viral therapy may provide a more sensitive and specific diagnostic technique to detect tumor origin and, more importantly, presence of metastases. Several strategies have been investigated for molecular imaging of viral replication broadly categorized into optical and deep tissue imaging, utilizing several reporter genes encoding for fluorescence proteins, conditional enzymes, and membrane protein and transporters. Various imaging methods facilitate molecular imaging, including computer tomography, magnetic resonance imaging, positron emission tomography, single photon emission CT, gamma-scintigraphy, and photoacoustic imaging. In addition, several molecular probes are used for medical imaging, which act as targeting moieties or signaling agents. This review will explore the preclinical and clinical use of in vivo molecular imaging of replication-competent oncolytic viral therapy.

Preclinical evaluation of engineered oncolytic herpes simplex virus for the treatment of pediatric solid tumors

Recently, investigators showed that mice with syngeneic murine gliomas that were treated with a neuroattenuated oncolytic herpes simplex virus-1 (oHSV), M002, had a significant increase in survival. M002 has deletions in both copies of the γ134.5 gene, enabling replication in tumor cells but precluding infection of normal cells. Previous studies have shown antitumor effects of other oHSV against a number of adult tumors including hepatocellular carcinoma and renal cell carcinoma. The purpose of the current study was to investigate the oncolytic potential of M002 against difficult to treat pediatric liver and kidney tumors. We showed that the oHSV, M002, infected, replicated, and decreased cell survival in hepatoblastoma, malignant rhabdoid kidney tumor, and renal sarcoma cell lines. In addition, we showed that in murine xenografts, treatment with M002 significantly increased survival and decreased tumor growth. Finally, these studies showed that the primary entry protein for oHSV, CD111 (nectin-1) was present in human hepatoblastoma and malignant rhabdoid kidney tumor specimens. We concluded that M002 effectively targeted these rare aggressive tumor types and that M002 may have potential for use in children with unresponsive or relapsed pediatric solid tumors.

Preclinical evaluation of engineered oncolytic herpes simplex virus for the treatment of neuroblastoma

Despite intensive research efforts and therapeutic advances over the last few decades, the pediatric neural crest tumor, neuroblastoma, continues to be responsible for over 15% of pediatric cancer deaths. Novel therapeutic options are needed for this tumor. Recently, investigators have shown that mice with syngeneic murine gliomas treated with an engineered, neuroattenuated oncolytic herpes simplex virus-1 (oHSV), M002, had a significant increase in survival. M002 has deletions in both copies of the γ₁34.5 gene, enabling replication in tumor cells but precluding infection of normal neural cells. We hypothesized that M002 would also be effective in the neural crest tumor, neuroblastoma. We showed that M002 infected, replicated, and decreased survival in neuroblastoma cell lines. In addition, we showed that in murine xenografts, treatment with M002 significantly decreased tumor growth, and that this effect was augmented with the addition of ionizing radiation. Importantly, survival could be increased by subsequent doses of radiation without re-dosing of the virus. Finally, these studies showed that the primary entry protein for oHSV, CD111 was expressed by numerous neuroblastoma cell lines and was also present in human neuroblastoma specimens. We concluded that M002 effectively targeted neuroblastoma and that this oHSV may have potential for use in children with unresponsive or relapsed neuroblastoma.

Pediatric glioma stem cells: biologic strategies for oncolytic HSV virotherapy

While glioblastoma multiforme (GBM) is the most common adult malignant brain tumor, GBMs in childhood represent less than 10% of pediatric malignant brain tumors and are phenotypically and molecularly distinct from adult GBMs. Similar to adult patients, outcomes for children with high-grade gliomas (HGGs) remain poor. Furthermore, the significant morbidity and mortality yielded by pediatric GBM is compounded by neurotoxicity for the developing brain caused by current therapies. Poor outcomes have been attributed to a subpopulation of chemotherapy and radiotherapy resistant cells, termed “glioma stem cells” (GSCs), “glioma progenitor cells,” or “glioma-initiating cells,” which have the ability to initiate and maintain the tumor and to repopulate the recurring tumor after conventional therapy. Future innovative therapies for pediatric HGG must be able to eradicate these therapy-resistant GSCs. Oncolytic herpes simplex viruses (oHSV), genetically engineered to be safe for normal cells and to express diverse foreign anti-tumor therapeutic genes, have been demonstrated in preclinical studies to infect and kill GSCs and tumor cells equally while sparing normal brain cells. In this review, we discuss the unique aspects of pediatric GSCs, including markers to identify them, the microenvironment they reside in, signaling pathways that regulate them, mechanisms of cellular resistance, and approaches to target GSCs, with a focus on the promising therapeutic, genetically engineered oHSV.

The roles of viruses in brain tumor initiation and oncomodulation

While some avian retroviruses have been shown to induce gliomas in animal models, human herpesviruses, specifically, the most extensively studied cytomegalovirus, and the much less studied roseolovirus HHV-6, and Herpes simplex viruses 1 and 2, currently attract more and more attention as possible contributing or initiating factors in the development of human brain tumors. The aim of this review is to summarize and highlight the most provoking findings indicating a potential causative link between brain tumors, specifically malignant gliomas, and viruses in the context of the concepts of viral oncomodulation and the tumor stem cell origin.

Rethinking herpes simplex virus: the way to oncolytic agents

Oncolytic viruses infect, replicate in and kill cancer cells. HSV has emerged as a most promising candidate because it exerts a generally moderate pathogenicity in humans; it is amenable to attenuation and tropism retargeting; the ample genome provides space for heterologous genes; specific antiviral therapy is available in a worst case scenario. The first strategy to convert HSV into an oncolytic agent consisted in deletion of the γ(1) 34.5 gene which counteracts the protein kinase R (PKR) response, and of the UL39 gene which encodes the large ribonucleotide reductase subunit. Tumor specificity resided in low PKR activity, and high deoxyribonucleotides content of cancer cells. These highly attenuated viruses have been and presently are in clinical trials with encouraging results. The preferred route of administration has been intratumor or in tissues adjacent to resected tumors. Although the general population has a high seroprevalence of antibodies to HSV, studies in animals and humans demonstrate that prior immunity is not an obstacle to systemic routes of administration, and that oncolytic HSV (o-HSVs) do populate tumors. As the attenuated viruses undergo clinical experimentation, the research pipeline is developing novel, more potent and highly tumor-specific o-HSVs. These include viruses which overcome tumor heterogeneity in PKR level by insertion of anti-PKR genes, viruses which reinforce the host tumor clearance capacity by encoding immune cytokines (IL-12 or granulocyte-macrophage colony-stimulating factor), and non-attenuated viruses fully retargeted to tumor specific receptors. A strategy to generate o-HSVs fully retargeted to human epidermal growth factor receptor-2 (HER-2) or other cancer-specific surface receptors is detailed.

Increased oncolytic efficacy for high-grade gliomas by optimal integration of ionizing radiation into the replicative cycle of HSV-1

Oncolytic viruses have been combined with standard cancer therapies to increase therapeutic efficacy. Given the sequential activation of herpes viral genes (herpes simplex virus-1, HSV-1) and the temporal cellular changes induced by ionizing radiation, we hypothesized an optimal temporal sequence existed in combining oncolytic HSV-1 with ionizing radiation. Murine U-87 glioma xenografts were injected with luciferase encoding HSV-1, and ionizing radiation (IR) was given at times before or after viral injection. HSV-1 replication and tumor-volume response were followed. Radiation given 6-9 h after HSV-1 injection resulted in maximal viral luciferase expression and infectious viral production in tumor xenografts. The greatest xenograft regression was also seen with radiation given 6 h after viral injection. We then tested if HSV-1 replication had a dose response to ionizing radiation. HSV-1 luciferase expression exhibited a dose response as xenografts were irradiated from 0 to 5 Gy. There was no difference in viral luciferase expression as IR dose increased from 5 Gy up to 20 Gy. These results suggest that the interaction of IR with the HSV-1 lytic cycle can be manipulated for therapeutic gain by delivering IR at a specific time within viral replicative cycle.

Engineered herpes simplex virus vectors for antitumor therapy and vaccine delivery

Genetically modified herpes simplex viruses (HSVs) have been exploited for both antitumor therapy and vaccine delivery. These mutant viruses retain their ability to replicate and lyse permissive cells, including many tumor types, and are referred to as oncolytic HSVs. In addition, deletion of nonessential genes permits the introduction of foreign genes to augment the antitumor effect by either immune stimulation, targeting for select tumors, or expression of tumor or vaccine antigens. This article reviews the development of oncolytic HSVs as an anticancer therapy, as well as the application of HSV-1 vectors for delivery of targeted antigens or as vaccine adjuvants. The impact of these novel vectors with respect to enhanced antitumor activity and development of antitumor vaccination strategies is discussed.

Synergistic action of oncolytic herpes simplex virus and radiotherapy in pancreatic cancer cell lines

BACKGROUND

Despite much research in chemotherapy and radiotherapy, pancreatic adenocarcinoma remains a fatal disease, highly resistant to all treatment modalities. Recent developments in the field of herpes simplex virus (HSV) engineering have allowed the generation of a number of promising virus vectors for treatment of many cancers, including pancreatic tumours. This study examined the use of one such virus, NV1023, in combination with radiation therapy in pancreatic cancer cell lines.

METHODS

HSV therapy in combination with radiotherapy was investigated in pancreatic cancer cell lines Hs766T, Panc-1 and MIA PaCa-2. Multiple therapy effect analysis was performed by computerized simulation. Mechanisms underlying synergy, such as virus replication and apoptosis, were investigated.

RESULTS

The combination of NV1023 and radiation yielded a synergistic oncolytic effect in all tested pancreatic cancer cell lines, with the greatest effect achieved in MIA PaCa-2. This effect was not mediated by an increase in rapid viral replication, but by a substantial increase in apoptosis.

CONCLUSION

The synergistic oncolytic actions of HSV and radiotherapy observed in pancreatic cancer cell lines encourage further testing of this multimodality treatment.

Herpesvirus vectors for therapy of brain tumors

Genetically modified, conditionally-replicating Herpes Simplex Virus Type 1 (HSV-1) vectors for the treatment of malignant glioma have provided encouraging results in the handful of Phase I and Phase II clinical trials conducted to date. In recent years, a number of new strategies have been developed to improve anti-tumor activity of these attenuated vectors, through either introduction of foreign gene inserts to enhance tumor killing through a variety of mechanisms, or through combination with existing treatment regimens, including radiation and/or chemotherapeutics. Another promising new approach has been the engineering of novel oncolytic HSV vectors that retain wildtype replication, but are targeted to tumor cells through a variety of mechanisms. This review summarizes the latest advances in herpesvirus-mediated oncolytic therapies from both preclinical results and clinical trials with oncolytic HSV vectors in patients, and their implication for design of future trials.

Conserved gammaherpesvirus kinase and histone variant H2AX facilitate gammaherpesvirus latency in vivo

Many herpesvirus-encoded protein kinases facilitate viral lytic replication. Importantly, the role of viral kinases in herpesvirus latency is less clear. Mouse gammaherpesvirus-68 (MHV68)-encoded protein kinase orf36 facilitates lytic replication in part through activation of the host DNA damage response (DDR). Here we show that MHV68 latency was attenuated in the absence of orf36 expression. Unexpectedly, our study uncovered enzymatic activity-independent role of orf36 in the establishment of MHV68 latency following intraperitoneal route of infection. H2AX, an important DDR protein, facilitates MHV68 lytic replication and may be directly phosphorylated by orf36 during lytic infection. In this study, H2AX deficiency, whether systemic or limited to infected cells, attenuated the establishment of MHV68 latency in vivo. Thus, our work reveals viral kinase-dependent regulation of gammaherpesvirus latency and illuminates a novel link between H2AX, a component of a tumor suppressor DDR network, and in vivo latency of a cancer-associated gammaherpesvirus.

Herpes simplex virus oncolytic therapy for pediatric malignancies

Despite improving survival rates for children with cancer, a subset of patients exist with disease resistant to traditional therapies such as surgery, chemotherapy, and radiation. These patients require newer, targeted treatments used alone or in combination with more traditional approaches. Oncolytic herpes simplex virus (HSV) is one of these newer therapies that offer promise for several difficult to treat pediatric malignancies. The potential benefit of HSV therapy in pediatric solid tumors including brain tumors, neuroblastomas, and sarcomas is reviewed along with the many challenges that need to be addressed prior to moving oncolytic HSV therapy from the laboratory to the beside in the pediatric population.

Systemic delivery of (gamma1)34.5-deleted herpes simplex virus-1 selectively targets and treats distant human xenograft tumors that express high MEK activity

Deltagamma(1)34.5 mutant herpes simplex type 1 viruses are under active clinical investigation as oncolytic therapy for cancer. Mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) activity has been shown to suppress protein kinase R and thereby confer oncolytic susceptibility to some human tumors by R3616, a virus deleted for both copies of gamma(1)34.5. We report that systemic delivery of R3616 can selectively target and destroy human xenograft tumors that overexpress MEK activity compared with tumors that express lower MEK activity. These results suggest systemic delivery of R3616 may be effective in the treatment of some human tumors.

Tumor genotype determines susceptibility to oncolytic herpes simplex virus mutants: strategies for clinical application

Oncolytic Herpes simplex virus -1 (HSV-1) mutants based on deletion of the γ134.5 gene are promising therapies for cancer. Δγ134.5 mutant replication and cytolysis is tumor cell type specific and severely attenuated in normal tissues. The basis for attenuation lies in the activation of the protein kinase R (PKR)-mediated host cellular defense pathway, which inhibits protein synthesis in infected cells. Tumor cells which overexpress MAPK kinase (MEK) activity support robust replication of Δγ134.5 mutants via MEK-mediated inhibition of PKR, resulting in tumor oncolysis. Systemic delivery of γ134.5 mutants may allow selective targeting and destruction of metastases from a broad range of solid human tumors that overexpress MEK. Barriers to systemic HSV-1 oncolytic therapy include innate immunity, adaptive immunity and hepatic adsorption. Immunomodulating agents may overcome innate immunity to HSV-1-based vectors. Preclinical data combined with the pervasiveness of HSV-1 despite widespread immunity suggest that preexisting immunity may not eliminate oncolytic efficacy. In the future, biopsy-determined tumor MEK status may select patients for Δγ134.5 oncolytic therapy.

Development of a second-generation oncolytic Herpes simplex virus expressing TNFalpha for cancer therapy

BACKGROUND

Tumour necrosis factor alpha (TNFalpha) therapy is a promising anti-cancer treatment when combined with radiotherapy due to its potent radio sensitising effects, but systemic toxicity has limited its clinical use. Previously, non-replicative adenovirus vectors have been used to deliver TNFalpha directly to the tumour, including under the control of a radiation sensitive promoter. Here, we have used an ICP34.5 deleted, oncolytic herpes simplex virus (HSV) for delivery to increase expression levels and spread through the tumour, and the use of the US11 true late HSV promoter to limit expression to where the virus replicates, i.e. selectively in tumour tissue.

METHODS

TNFalpha expression under the CMV or US11 promoter was compared on cell lines CT26, BHK and Fadu. To further compare the activities of the promoters, expression of human TNFalpha was analysed in the presence and absence of acyclovir--an inhibitor of viral DNA replication and on HSV/ICP34.5- non-permissive cell line 3T6. The in vivo efficacy and toxicity of TNFalpha viruses were compared using A20 double flank tumour model in Balb/C mice and Fadu tumour model in nude mice.

RESULTS

The results demonstrated that the US11 promoter significantly reduced and delayed TNFalpha expression as compared to use of the CMV promoter, especially in non-permissive cells or in the presence of acyclovir. Despite the reduced and more selective expression levels, US11 driven TNFalpha showed improved anti-tumour effects compared to CMV driven TNFalpha, and without the toxic side effects.

CONCLUSIONS

This approach is therefore beneficial in increasing localised TNFalpha expression as compared to the use of non-replicative approaches, and combines the effects of TNFalpha with oncolytic virus replication which is expected to further enhance the efficacy of radiotherapy in a combined treatment approach.

ReVOLT: radiation-enhanced viral oncolytic therapy

Viral oncolytic therapy has been pursued with renewed interest as the molecular basis of carcinogenesis and viral replication has been elucidated. Genetically engineered, attenuated viruses have been rationally constructed to achieve a therapeutic index in tumor cells compared with surrounding normal tissue. Many of these attenuated mutant viruses have entered clinical trials. Here we review the preclinical literature demonstrating the interaction of oncolytic viruses with ionizing radiation and provides a basis for future clinical trials.

Radiation-induced cellular DNA damage repair response enhances viral gene therapy efficacy in the treatment of malignant pleural mesothelioma

BACKGROUND

Malignant pleural mesothelioma (MPM) treated with radiotherapy (RT) has incomplete responses as a result of radiation-induced tumoral stress response that repairs DNA damage. Such stress response is beneficial for oncolytic viral therapy. We hypothesized that a combination of RT and NV1066, an oncolytic herpes virus, might exert an additive or synergistic effect in the treatment of MPM.

METHODS

JMN, a MPM cell line, was infected with NV1066 at multiplicities of infection of .05 to .25 in vitro with and without radiation (1 to 5 Gy). Virus replication was determined by plaque assay, cell kill by lactate dehydrogenase assay, and GADD34 (growth arrest and DNA damage repair 34, a DNA damage-repair protein) by real-time reverse transcriptase-polymerase chain reaction and Western blot test. Synergistic cytotoxicity dependence on GADD34 upregulation was confirmed by GADD34 small inhibitory RNA (siRNA).

RESULTS

Synergism was demonstrated between RT and NV1066 across a wide range of doses. As a result of such synergism, a dose-reduction for each agent (up to 5500-fold) can be accomplished over a wide range of therapeutic-effect levels without sacrificing tumor cell kill. This effect is correlated with increased GADD34 expression and inhibited by transfection of siRNA directed against GADD34.

CONCLUSIONS

RT can be combined with oncolytic herpes simplex virus therapy in the treatment of malignant pleural mesothelioma to achieve synergistic efficacy while minimizing dosage and toxicity.

Establishment of a syngeneic model of hepatic colorectal oligometastases

BACKGROUND

Regional and systemic therapies aimed at improving the outcome for patients with colorectal hepatic metastases have met with modest yet tangible success. Currently, liver resection remains the only curative treatment, but only a minority of patients are candidates for surgery. Animal models are an ideal way to study new treatments for patients with metastatic colorectal cancer. We propose a syngeneic animal model of hepatic colorectal metastases that simulates oligometastases, which is a clinical state considered amenable to regional therapeutic strategies.

MATERIALS AND METHODS

BDIX (BD-9) rats underwent intrasplenic injection of DHD/K12/TRb (Prob/K12) cells to create hepatic metastases via the portal system. After injection of 5 x 10(6) cells, rats underwent laparotomy to determine metastatic burden. Histological analysis confirmed the presence of metastases from resected tumors.

RESULTS

Fifty-three animals were prospectively treated and observed for the development of oligometastases defined as between 1 and 10 hepatic lesions. Thirty-six (68%) of the animals developed detectable metastases while 32 (60%) developed oligometastases (average = 4.40 +/- 2.67). Four animals had overwhelming metastatic liver and peritoneal disease. All animals underwent peritoneal examination and thoracotomy to ensure localized disease. Histological analysis of five hepatectomy specimens confirmed the presence of metastatic cancer. Animals with oligometastases were healthy as evidenced by normal feeding and grooming behavior.

CONCLUSIONS

An animal model of oligometastatic colorectal cancer to the liver can reproducibly mimic the stage IV state in humans conducive to regional therapy and can be used reliably to test novel treatments and mechanisms of metastatic colorectal cancer.

Construction and properties of a herpes simplex virus 1 designed to enter cells solely via the IL-13alpha2 receptor

Current design of genetically engineered viruses for selective destruction of cancer cells is based on the observation that attenuated viruses replicate better in tumor cells than in normal cells. The ideal virus, however, is one that can infect only cancer cells by virtue of altered host range. Such a virus can be made more robust than the highly attenuated viruses used in clinical trials. Earlier, we reported the construction of a recombinant herpes simplex virus 1 (R5111) in which the capacity to bind heparan sulfate was disabled and which contained a chimeric IL-13-glycoprotein D that enabled the virus to infect cells expressing the IL-13alpha2 receptor (IL-13Ralpha2) commonly found on the surface of malignant glioblastomas or high-grade astrocytomas. In the earlier report, we showed that the recombinant R5111 was able to enter and infect cells via the interaction of the chimeric glycoprotein D with IL-13Ralpha2 but that the virus retained the capacity to bind and replicate in cells expressing the natural viral receptors HveA or nectin-1. Here, we report the construction of a recombinant virus (R5141) that can only enter and replicate in cells that express the IL-13Ralpha2. The recombinant R5141 does not depend on endocytosis to infect cells. It does not infect cells expressing HveA or nectin-1 receptors or cells expressing IL-13Ralpha2 that had been exposed to soluble IL-13 before infection. The studies described here show that the host range of herpes simplex viruses can be altered by genetic manipulation to specifically target cancer cells.

Activated MEK suppresses activation of PKR and enables efficient replication and in vivo oncolysis by Deltagamma(1)34.5 mutants of herpes simplex virus 1

Herpes simplex virus mutants lacking the gamma(1)34.5 gene are not destructive to normal tissues but are potent cytolytic agents in human tumor cells in which the activation of double-stranded RNA-dependent protein kinase (PKR) is suppressed. Thus, replication of a Deltagamma(1)34.5 mutant (R3616) in 12 genetically defined cancer cell lines correlates with suppression of PKR but not with the genotype of RAS. Extensive analyses of two cell lines transduced with either dominant negative MEK (dnMEK) or constitutively active MEK (caMEK) indicated that in R3616 mutant-infected cells dnMEK enabled PKR activation and decreased virus yields, whereas caMEK suppressed PKR and enabled better viral replication and cell destruction in transduced cells in vitro or in mouse xenografts. The results indicate that activated MEK mediates the suppression of PKR and that the status of MEK predicts the ability of Deltagamma(1)34.5 mutant viruses to replicate in and destroy tumor cells.