Oncolytic viral therapy of malignant glioma

Herpes Simplex Oncolytic Viral Therapy for Malignant Glioma and Mechanisms of Delivery

The authors present a comprehensive review on the history and development of oncolytic herpes simplex viral therapies for malignant glioma with a focus on mechanisms of delivery in prior and ongoing clinical trials. This review highlights the advancements made with regard to delivering these therapies to a highly complex immunologic environment in the setting of the blood-brain and blood-tumor barrier in a safe and effective manner.

Non-secreting IL12 expressing oncolytic adenovirus Ad-TD-nsIL12 in recurrent high-grade glioma: a phase I trial

Malignant glioma is a highly fatal central nervous system malignancy with high recurrence rates. Oncolytic viruses offer potential treatment but need improvement in efficacy and safety. Here we describe a phase I, dose-escalating, single arm trial (ChiCTR2000032402) to study the safety of Ad-TD-nsIL12, an oncolytic adenovirus expressing non-secreting interleukin-12, in patients with recurrent high-grade glioma that connects with the ventricular system. Eight patients received intratumoral treatment via stereotaxis or an Ommaya reservoir, with doses ranging from 5 × 109 to 5 × 1010vp. The primary end point was to determine the maximal tolerated dose. Secondary endpoints included toxicity and anti-tumour ability. Minimal adverse events were observed at doses of 5 × 109 and 1 × 1010vp. Grade 3 seizure was observed in two patients from Cohort 3 (5 × 1010vp). Therefore, the maximum tolerated dose was determined to be 1 × 1010vp. Four patients developed hydrocephalus during follow-up. Among them, symptoms in two patients were relieved after placement of a ventriculo-peritoneal shunt, and the other two only showed ventriculomegaly on MRI scan without neurological deterioration. Complete response (according to Response Assessment in Neuro-Oncology Criteria) in one patient, a partial response in one patient and post-treatment infiltrations of CD4+ and CD8 + T cells into the tumour were documented during this trial. In conclusion, Ad-TD-nsIL12 has demonstrated safety and preliminary efficacy in patients with recurrent high-grade glioma.

The Development of Immunotherapy for the Treatment of Recurrent Glioblastoma

Recurrent glioblastoma (rGBM) is a highly aggressive form of brain cancer that poses a significant challenge for treatment in neuro-oncology, and the survival status of patients after relapse usually means rapid deterioration, thus becoming the leading cause of death among patients. In recent years, immunotherapy has emerged as a promising strategy for the treatment of recurrent glioblastoma by stimulating the body's immune system to recognize and attack cancer cells, which could be used in combination with other treatments such as surgery, radiation, and chemotherapy to improve outcomes for patients with recurrent glioblastoma. This therapy combines several key methods such as the use of monoclonal antibodies, chimeric antigen receptor T cell (CAR-T) therapy, checkpoint inhibitors, oncolytic viral therapy cancer vaccines, and combination strategies. In this review, we mainly document the latest immunotherapies for the treatment of glioblastoma and especially focus on rGBM.

Cell-based and cell-free immunotherapies for glioblastoma: current status and future directions

Glioblastoma (GBM) is among the most fatal and recurring malignant solid tumors. It arises from the GBM stem cell population. Conventional neurosurgical resection, temozolomide (TMZ)-dependent chemotherapy and radiotherapy have rendered the prognosis of patients unsatisfactory. Radiotherapy and chemotherapy can frequently induce non-specific damage to healthy brain and other tissues, which can be extremely hazardous. There is therefore a pressing need for a more effective treatment strategy for GBM to complement or replace existing treatment options. Cell-based and cell-free immunotherapies are currently being investigated to develop new treatment modalities against cancer. These treatments have the potential to be both selective and successful in minimizing off-target collateral harm in the normal brain. In this review, several aspects of cell-based and cell-free immunotherapies related to GBM will be discussed.

The recombinant Newcastle disease virus Anhinga strain expressing human TRAIL exhibit antitumor effects on a glioma nude mice model

Oncolytic virus therapy is perhaps the next major breakthrough in cancer treatment following the success in immunotherapy using immune checkpoint inhibitors. However, the potential oncolytic ability of the recombinant newcastle disease virus (NDV) Anhinga strain carried with tumor necrosis factor-related apoptosis inducing ligand (TRAIL) has not been fully explored at present. In the present study, the recombinant NDV/Anh-TRAIL that secretes soluble TRAIL was constructed and the experiment results suggested NDV/Anh-TRAIL as a promising candidate for glioma therapy. Growth kinetic and TRAIL secreted quantity of recombinant NDV/Anh-TRAIL virus were measured. Cytotoxic and cell apoptosis were analyzed for its anti-glioma therapy in vitro. Nude mice were used for the in vivo evaluation. Both tumor volume and mice behavior after injection were observed. The recombinant virus replicated with the same kinetics as the parental virus and the highest expression of TRAIL (77.8 ng/L) was found at 48 hours. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole and flow cytometry data revealed that the recombinant NDV/Anh-TRAIL (56.1 ± 8.2%) virus could induce a more severe apoptosis rate, when compared with the NDV wild type (37.2 ± 7.0%) and mock (7.0 ± 1.8%) groups (P < .01), in U251 cells. Furthermore, in the present animal study, the average tumor volume was smaller in the NDV/Anh-TRAIL group (97.21 mm3 ), when compared with the NDV wild type (205.03 mm3 , P < .05) and PBS (310.30 mm3 , P < .01) groups.

Advances in Anti-Cancer Immunotherapy: Car-T Cell, Checkpoint Inhibitors, Dendritic Cell Vaccines, and Oncolytic Viruses, and Emerging Cellular and Molecular Targets

Unlike traditional cancer therapies, such as surgery, radiation and chemotherapy that are typically non-specific, cancer immunotherapy harnesses the high specificity of a patient’s own immune system to selectively kill cancer cells. The immune system is the body’s main cancer surveillance system, but cancers may evade destruction thanks to various immune-suppressing mechanisms. We therefore need to deploy various immunotherapy-based strategies to help bolster the anti-tumour immune responses. These include engineering T cells to express chimeric antigen receptors (CARs) to specifically recognise tumour neoantigens, inactivating immune checkpoints, oncolytic viruses and dendritic cell (DC) vaccines, which have all shown clinical benefit in certain cancers. However, treatment efficacy remains poor due to drug-induced adverse events and immunosuppressive tendencies of the tumour microenvironment. Recent preclinical studies have unveiled novel therapies such as anti-cathepsin antibodies, galectin-1 blockade and anti-OX40 agonistic antibodies, which may be utilised as adjuvant therapies to modulate the tumour microenvironment and permit more ferocious anti-tumour immune response.

How We Treat Recurrent Glioblastoma Today and Current Evidence

PURPOSE OF REVIEW

Recurrent glioblastoma (rGBM) has no standard treatment. Despite a better molecular knowledge, few therapies have brought changes in clinical practice so far. Here we will review the current data evaluating the re-radiation, re-resection, bevacizumab, and cytotoxic chemotherapy agents in this setting. We will also discuss the advances of immunotherapy and the possible benefit of this treatment for patients with rGBM.

RECENT FINDINGS

Next-generation sequencing is increasingly utilized in the clinical practice of neuro-oncologists, bringing gene mutations as targets for therapies. As in other solid tumors, immunotherapy has been also extensively studied in rGBM, with interesting results in phase I and II trials. The most promising therapies in the horizon are combinations including immune checkpoint inhibitors, virotherapy, vaccines, and monoclonal antibodies. Although re-radiation, re-resection, bevacizumab, and chemotherapy are still the most widely used therapies for treating rGBM, the clinical benefit from these treatments is still not well established. Preliminary results of studies with immune checkpoint inhibitors were disappointing, but virotherapy emerges as more promising immunotherapy in rGBM, especially in combination with other strategies. In addition to the gain in overall survival, the improvement in the quality of life of these patients is also expected.

Viral vector: potential therapeutic for glioblastoma multiforme

Glioblastoma multiforme is a highly malignant primary brain tumour found in adults and is highlighted as the most devastating among all the other grades of glioma. Well-established standard treatment methods, such as chemotherapy, radiation and surgery, have resulted in modest improvement in the survival of patients. Hence, the arduous search for novel treatments backed by advancements in molecular biology still persists. Glioblastoma has many distinctive characteristics, which makes it a potential candidate for gene therapy. Gene therapy involves the delivery of genetic material of therapeutic use into tumour cells, which produces a specific antitumour response. Moreover, viruses stimulate a vigorous cytotoxic effect, they are easily modifiable and the inherent property of horizontal transfer of genetic material makes them valuable tools for genetic engineering. In this review, we have enlisted the various viral vectors employed in gene therapy for glioblastoma.

Oncolytic viro-chemotherapy exhibits antitumor effect in laryngeal squamous cell carcinoma cells and mouse xenografts

Background: Oncolytic virus can specifically replicate in and then lyse tumor cells, but seldom in normal cells. Further studies have shown the significant therapeutic effect of oncolytic virotherapy combining with other strategies, such as chemo-, radio-, and immunotherapy et al. In this study, we investigated the combinational effect of oncolytic virus ZD55-TRAIL and chemotherapy drug doxorubicin (DOX) on human laryngeal squamous cell carcinoma (LSCC).

Methods: The effect of ZD55-TRAIL combined with DOX on cell growth was assessed in LSCC Hep2 cells and normal cells by MTT assay. Hochest 33342 staining was performed to observe cell morphological changes. Western blot was used to detect the expression of apoptotic activation proteins. The in vivo antitumor efficacy of combination treatment was estimated in laryngeal cancer xenograft models.

Results: The combination of ZD55-TRAIL and DOX exhibited enhanced inhibitory effects on laryngocarcinoma cell growth, and had few side effects to normal cells in vitro. Chemotherapy drug increased the inducement of tumor cell apoptosis mediated by oncolytic virus. In vivo experiment confirmed that the combination treatment significantly inhibited Hep2 laryngocarcinoma xenografts growth in mice.

Conclusion: The oncolytic viro-chemotherapy is a potent therapeutic approach for in vitro cytotoxicity evaluation of Hep2 cells and xenograft growth in vivo.

Targeting GD2-positive glioblastoma by chimeric antigen receptor empowered mesenchymal progenitors

Tumor targeting by genetically modified mesenchymal stromal/stem cells (MSCs) carrying anti-cancer molecules represents a promising cell-based strategy. We previously showed that the pro-apoptotic agent tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can be successfully delivered by MSCs to cancer sites. While the interaction between TRAIL and its receptors is clear, more obscure is the way in which MSCs can selectively target tumors and their antigens. Several neuroectoderm-derived neoplasms, including glioblastoma (GBM), sarcomas, and neuroblastoma, express high levels of the tumor-associated antigen GD2. We have already challenged this cell surface disialoganglioside by a chimeric antigen receptor (CAR)-T cell approach against neuroblastoma. With the intent to maximize the therapeutic profile of MSCs delivering TRAIL, we here originally developed a bi-functional strategy where TRAIL is delivered by MSCs that are also gene modified with the truncated form of the anti-GD2 CAR (GD2 tCAR) to mediate an immunoselective recognition of GD2-positive tumors. These bi-functional MSCs expressed high levels of TRAIL and GD2 tCAR associated with a robust anti-tumor activity against GD2-positive GBM cells. Most importantly, the anti-cancer action was reinforced by the enhanced targeting potential of such bi-functional cells. Collectively, our results suggest that a truncated anti-GD2 CAR might be a powerful new tool to redirect MSCs carrying TRAIL against GD2-expressing tumors. This affinity-based dual targeting holds the promise to combine site-specific and prolonged retention of MSCs in GD2-expressing tumors, thereby providing a more effective delivery of TRAIL for still incurable cancers.

Newcastle disease virus enhances the growth-inhibiting and proapoptotic effects of temozolomide on glioblastoma cells in vitro and in vivo

Glioblastoma (GBM) is the most serious and most common brain tumor in humans. Despite recent advances in the diagnosis of GBM and the development of new treatments, the prognosis of patients has not improved. Multidrug resistance, particularly resistance to temozolomide (TMZ), is a challenge in combating glioma, and more effective therapies are needed. Complementary treatment with the LaSota strain of the naturally oncolytic Newcastle disease virus (NDV-LaSota) is an innovation. In our experiments, the combination therapy of NDV-LaSota and temozolomide (TMZ) was more effective than either treatment alone in inducing apoptosis in glioma cells. NDV can function as a tumor cell selective approach to inhibit AKT and activate AMPK. Consequently, mTOR, 4EBP1 and S6K were also suppressed. The combination therapy of NDV and TMZ also significantly extended survival in a rat xenograft tumor model. In conclusion, NDV suppress AKT signaling and enhances antitumor effects of TMZ. Our study provides one of the theoretical basis for the use of a combined therapy of TMZ and NDV, which could benefit GBM patients.

Two cases of disseminated infection following live organism anti-cancer vaccine administration in cancer patients

Vaccines containing live attenuated bacterial or viral organisms are currently being investigated as potential therapy for locally advanced or metastatic cancers. However, the use of such live organisms in an immunocompromised population, such as patients who recently or are currently receiving chemotherapy, raises the concern that these organisms can themselves disseminate and cause frank infection. We report a hereunto unreported phenomenon of anti-cancer vaccines (containing live attenuated organisms) leading to frank, disseminated infection. We submit that occurrence of this phenomenon must be watched for by all members of the interdisciplinary cancer treatment team.

Pathogens and glioma: a history of unexpected discoveries ushering in novel therapy

In the late 19th century, Dr. William B. Coley introduced the theory that infections may aid in the treatment of malignancy. With the creation of Coley’s toxin, reports of remission during viral illnesses for systemic malignancies soon emerged. A few decades after this initial discovery, Austrian physicians performed intravascular injections of Clostridium to induce oncolysis in patients with glioblastoma. Since then, suggestions between improved survival and infectious processes have been reported in several patients with glioma, which ultimately marshaled the infamous use of intracerebral Enterobacter. These early observations of tumor regression and concomitant infection piloted a burgeoning field focusing on the use of pathogens in molecular oncology.

Mesenchymal stem cells as therapeutic agents and in gene delivery for the treatment of glioma*

Mesenchymal stem cells (MSCs) are plastic-adherent cells with a characteristic surface phenotype and properties of self-renewal, differentiation, and high proliferative potential. The characteristics of MSCs and their tumor-tropic capability make them an ideal tool for use in cell-based therapies for cancer, including glioma. These cells can function either through a bystander effect or as a delivery system for genes and drugs. MSCs have been demonstrated to inhibit the growth of glioma and to improve survival following transplantation into the brain. We briefly review the current data regarding the use of MSCs in the treatment of glioma and discuss the potential strategies for development of a more specific and effective therapy.

Design of a Phase I Clinical Trial to Evaluate M032, a Genetically Engineered HSV-1 Expressing IL-12, in Patients with Recurrent/Progressive Glioblastoma Multiforme, Anaplastic Astrocytoma, or Gliosarcoma

M032 is a second-generation oncolytic herpes simplex virus (oHSV) that selectively replicates in tumor cells. M032 kills tumor cells directly through oncolytic replication and then proceeds to infect tumor cells in proximity, continuing the process of tumor destruction. In addition to this direct oncolytic activity, the virus carries a therapeutic payload-thus acting as a gene therapy vector-and causes the tumor cell to synthesize and secrete the immunity-stimulating protein interleukin-12 (IL-12) before cell death. (1) Human IL-12 is expressed and promotes an immune response against surviving tumor cells, increasing the antitumor effect of the therapy. IL-12 also produces an antiangiogenic effect, by interfering with the production of new tumor blood vessels necessary for tumor growth. Thus, M032 oHSV exerts antitumor effects through three distinct potential mechanisms. The virus has also been genetically engineered to minimize toxic effects for the patient. Preclinical animal models support the safety of intracranial inoculation with M032 in two relevant species (mouse and nonhuman primate). This clinical protocol outlines the dose-escalating phase I study for evaluation of M032 in patients with recurrent or progressive malignant glioma.

Oncolytic Virotherapy for the Treatment of Malignant Glioma

Malignant glioma is the most common primary brain tumor and carries a grim prognosis, with a median survival of just over 14 months. Given the poor outcomes with standard-of-care treatments, novel treatment strategies are needed. The concept of virotherapy for the treatment of malignant tumors dates back more than a century and can be divided into replication-competent oncolytic viruses and replication-deficient viral vectors. Oncolytic viruses are designed to selectively target, infect, and replicate in tumor cells, while sparing surrounding normal brain. A host of oncolytic viruses has been evaluated in early phase human trials with promising safety results, but none has progressed to phase III trials. Despite the 25 years that has passed since the initial publication of genetically engineered oncolytic viruses for the treatment of glioma, much remains to be learned about the use of this therapy, including its mechanism of action, optimal treatment paradigm, appropriate targets, and integration with adjuvant agents. Oncolytic viral therapy for glioma remains promising and will undoubtedly impact the future of patient care.

Adenovirus with DNA Packaging Gene Mutations Increased Virus Release

Adenoviruses (Ads) have been extensively manipulated for the development of cancer selective replication, leading to cancer cell death or oncolysis. Clinical studies using E1-modified oncolytic Ads have shown that this therapeutic platform was safe, but with limited efficacy, indicating the necessity of targeting other viral genes for manipulation. To improve the therapeutic efficacy of oncolytic Ads, we treated the entire Ad genome repeatedly with UV-light and have isolated AdUV which efficiently lyses cancer cells as reported previously (Wechman, S. L. et al. Development of an Oncolytic Adenovirus with Enhanced Spread Ability through Repeated UV Irradiation and Cancer Selection. Viruses2016, 8, 6). In this report, we show that no mutations were observed in the early genes (E1 or E4) of AdUV while several mutations were observed within the Ad late genes which have structural or viral DNA packaging functions. This study also reported the increased release of AdUV from cancer cells. In this study, we found that AdUV inhibits tumor growth following intratumoral injection. These results indicate the potentially significant role of the viral late genes, in particular the DNA packaging genes, to enhance Ad oncolysis.

Mesenchymal stem cells enhance the oncolytic effect of Newcastle disease virus in glioma cells and glioma stem cells via the secretion of TRAIL

BACKGROUND

Newcastle disease virus (NDV) is an avian paramyxovirus, which selectively exerts oncolytic effects in cancer cells. Mesenchymal stem cells (MSCs) have been reported to affect tumor growth and deliver anti-tumor agents to experimental glioblastoma (GBM). Here, we explored the effects of NDV-infected MSCs derived from different sources, on glioma cells and glioma stem cells (GSCs) and the mechanisms involved in their effects.

METHODS

The glioma cell lines (A172 and U87) and primary GSCs that were generated from GBM tumors were used in this study. MSCs derived from bone marrow, adipose tissue or umbilical cord were infected with NDV (MTH-68/H). The ability of these cells to deliver the virus to glioma cell lines and GSCs and the effects of NDV-infected MSCs on cell death and on the stemness and self-renewal of GSCs were examined. The mechanisms involved in the cytotoxic effects of the NDV-infected MSCs and their influence on the radiation sensitivity of GSCs were examined as well.

RESULTS

NDV induced a dose-dependent cell death in glioma cells and a low level of apoptosis and inhibition of self-renewal in GSCs. MSCs derived from bone marrow, adipose and umbilical cord that were infected with NDV delivered the virus to co-cultured glioma cells and GSCs. Conditioned medium of NDV-infected MSCs induced higher level of apoptosis in the tumor cells compared with the apoptosis induced by their direct infection with similar virus titers. These results suggest that factor(s) secreted by the infected MSCs sensitized the glioma cells to the cytotoxic effects of NDV. We identified TRAIL as a mediator of the cytotoxic effects of the infected MSCs and demonstrated that TRAIL synergized with NDV in the induction of cell death in glioma cells and GSCs. Moreover, conditioned medium of infected MSCs enhanced the sensitivity of GSCs to γ-radiation.

CONCLUSIONS

NDV-infected umbilical cord-derived MSCs may provide a novel effective therapeutic approach for targeting GSCs and GBM and for sensitizing these tumors to γ-radiation.

Unlocking the promise of oncolytic virotherapy in glioma: combination with chemotherapy to enhance efficacy

Malignant glioma is a relentless burden to both patients and clinicians, and calls for innovation to overcome the limitations in current management. Glioma therapy using viruses has been investigated to accentuate the nature of a virus, killing a host tumor cell during its replication. As virus mediated approaches progress with promising therapeutic advantages, combination therapy with chemotherapy and oncolytic viruses has emerged as a more synergistic and possibly efficacious therapy. Here, we will review malignant glioma as well as prior experience with oncolytic viruses, chemotherapy and combination of the two, examining how the combination can be optimized in the future.

Development of an Oncolytic Adenovirus with Enhanced Spread Ability through Repeated UV Irradiation and Cancer Selection

Oncolytic adenoviruses (Ads) have been shown to be safe and have great potential for the treatment of solid tumors. However, the therapeutic efficacy of Ads is antagonized by limited spread within solid tumors. To develop Ads with enhanced spread, viral particles of an E1-wildtype Ad5 dl309 was repeatedly treated with UV type C irradiation and selected for the efficient replication and release from cancer cells. After 72 cycles of treatment and cancer selection, AdUV was isolated. This vector has displayed many favorable characteristics for oncolytic therapy. AdUV was shown to lyse cancer cells more effectively than both E1-deleted and E1-wildtype Ads. This enhanced cancer cell lysis appeared to be related to increased AdUV replication in and release from infected cancer cells. AdUV-treated A549 cells displayed greater expression of the autophagy marker LC3-II during oncolysis and formed larger viral plaques upon cancer cell monolayers, indicating increased virus spread among cancer cells. This study indicates the potential of this approach of irradiation of entire viral particles for the development of oncolytic viruses with designated therapeutic properties.

The Long and Winding Road: From the High-Affinity Choline Uptake Site to Clinical Trials for Malignant Brain Tumors

Malignant brain tumors are one of the most lethal cancers. They originate from glial cells which infiltrate throughout the brain. Current standard of care involves surgical resection, radiotherapy, and chemotherapy; median survival is currently ~14-20 months postdiagnosis. Given that the brain immune system is deficient in priming systemic immune responses to glioma antigens, we proposed to reconstitute the brain immune system to achieve immunological priming from within the brain. Two adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1-derived thymidine kinase which converts ganciclovir into a compound only cytotoxic to dividing glioma cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine that attracts dendritic cells to the brain. HSV-1/ganciclovir killing of tumor cells releases tumor antigens that are taken up by dendritic cells within the brain tumor microenvironment. Tumor killing also releases HMGB1, an endogenous TLR2 agonist that activates dendritic cells. HMGB1-activated dendritic cells, loaded with glioma antigens, migrate to cervical lymph nodes to stimulate a systemic CD8+ T cells cytotoxic immune response against glioma. This immune response is specific to glioma tumors, induces immunological memory, and does neither cause brain toxicity nor autoimmune responses. An IND was granted by the FDA on 4/7/2011. A Phase I, first in person trial, to test whether reengineering the brain immune system is potentially therapeutic is ongoing.

Oncolytic viruses for therapy of malignant glioma

Effective treatment of malignant brain tumors is still an open problem. Location of tumor in vital areas of the brain significantly limits capasities of surgical treatment. The presence of tumor stem cells resistant to radiation and anticancer drugs in brain tumor complicates use of chemoradiotherapy and causes a high rate of disease recurrence. A technological improvement in bioselection and production of recombinant resulted in creation of viruses with potent oncolytic properties against glial tumors. Recent studies, including clinical trials, showed, that majority of oncolytic viruses are safe. Despite the impressive results of the viral therapy in some patients, the treatment of other patients is not effective; therefore, further improvement of the methods of oncolytic virotherapy is necessary. High genetic heterogeneity of glial tumor cells even within a single tumor determines differences in individual sensitivity of tumor cells to oncolytic viruses. This review analyses the most successful oncolytic virus strains, including those which had reached clinical trials, and discusses the prospects for new approaches to virotherapy of gliomas.

Oncolytic Replication of E1b-Deleted Adenoviruses

Various viruses have been studied and developed for oncolytic virotherapies. In virotherapy, a relatively small amount of viruses used in an intratumoral injection preferentially replicate in and lyse cancer cells, leading to the release of amplified viral particles that spread the infection to the surrounding tumor cells and reduce the tumor mass. Adenoviruses (Ads) are most commonly used for oncolytic virotherapy due to their infection efficacy, high titer production, safety, easy genetic modification, and well-studied replication characteristics. Ads with deletion of E1b55K preferentially replicate in and destroy cancer cells and have been used in multiple clinical trials. H101, one of the E1b55K-deleted Ads, has been used for the treatment of late-stage cancers as the first approved virotherapy agent. However, the mechanism of selective replication of E1b-deleted Ads in cancer cells is still not well characterized. This review will focus on three potential molecular mechanisms of oncolytic replication of E1b55K-deleted Ads. These mechanisms are based upon the functions of the viral E1B55K protein that are associated with p53 inhibition, late viral mRNA export, and cell cycle disruption.

Microglia and astrocytes attenuate the replication of the oncolytic vaccinia virus LIVP 1.1.1 in murine GL261 gliomas by acting as vaccinia virus traps

Background

Oncolytic virotherapy is a novel approach for the treatment of glioblastoma multiforme (GBM) which is still a fatal disease. Pathologic features of GBM are characterized by the infiltration with microglia/macrophages and a strong interaction between immune- and glioma cells. The aim of this study was to determine the role of microglia and astrocytes for oncolytic vaccinia virus (VACV) therapy of GBM.

Methods

VACV LIVP 1.1.1 replication in C57BL/6 and Foxn1^nu/nu mice with and without GL261 gliomas was analyzed. Furthermore, immunohistochemical analysis of microglia and astrocytes was investigated in non-, mock-, and LIVP 1.1.1-infected orthotopic GL261 gliomas in C57BL/6 mice. In cell culture studies virus replication and virus-mediated cell death of GL261 glioma cells was examined, as well as in BV-2 microglia and IMA2.1 astrocytes with M1 or M2 phenotypes. Co-culture experiments between BV-2 and GL261 cells and apoptosis/necrosis studies were performed. Organotypic slice cultures with implanted GL261 tumor spheres were used as additional cell culture system.

Results

We discovered that orthotopic GL261 gliomas upon intracranial virus delivery did not support replication of LIVP 1.1.1, similar to VACV-infected brains without gliomas. In addition, recruitment of Iba1⁺ microglia and GFAP⁺ astrocytes to orthotopically implanted GL261 glioma sites occurred already without virus injection. GL261 cells in culture showed high virus replication, while replication in BV-2 and IMA2.1 cells was barely detectable. The reduced viral replication in BV-2 cells might be due to rapid VACV-induced apoptotic cell death. In BV-2 and IMA 2.1 cells with M1 phenotype a further reduction of virus progeny and virus-mediated cell death was detected. Application of BV-2 microglial cells with M1 phenotype onto organotypic slice cultures with implanted GL261 gliomas resulted in reduced infection of BV-2 cells, whereas GL261 cells were well infected.

Conclusion

Our results indicate that microglia and astrocytes, dependent on their activation state, may preferentially clear viral particles by immediate uptake after delivery. By acting as VACV traps they further reduce efficient virus infection of the tumor cells. These findings demonstrate that glia cells need to be taken into account for successful GBM therapy development.

Evaluation of the safety and biodistribution of M032, an attenuated herpes simplex virus type 1 expressing hIL-12, after intracerebral administration to aotus nonhuman primates

Herpes simplex virus type 1 (HSV-1) mutants lacking the γ(1)34.5 neurovirulence loci are promising agents for treating malignant glioma. Arming oncolytic HSV-1 to express immunostimulatory genes may potentiate therapeutic efficacy. We have previously demonstrated improved preclinical efficacy, biodistribution, and safety of M002, a γ(1)34.5-deleted HSV-1 engineered to express murine IL-12. Herein, we describe the safety and biodistribution of M032, a γ(1)34.5-deleted HSV-1 virus that expresses human IL-12 after intracerebral administration to nonhuman primates, Aotus nancymae. Cohorts were administered vehicle, 10(6), or 10(8) pfu of M032 on day 1 and subjected to detailed clinical observations performed serially over a 92-day trial. Animals were sacrificed on days 3, 31, and 91 for detailed histopathologic assessments of all organs and to isolate and quantify virus in all organs. With the possible exception of one animal euthanized on day 16, neither adverse clinical signs nor sex- or dose-related differences were attributed to M032. Elevated white blood cell and neutrophil counts were observed in virus-injected groups on day 3, but no other significant changes were noted in clinical chemistry or coagulation parameters. Minimal to mild inflammation and fibrosis detected, primarily in meningeal tissues, in M032-injected animals on days 3 and 31 had mostly resolved by day 91. The highest viral DNA levels were detected at the injection site and motor cortex on day 3 but decreased in central nervous system tissues over time. These data demonstrate the requisite safety of intracerebral M032 administration for consideration as a therapeutic for treating malignant brain tumors.

Virotherapy targeting cyclin E overexpression in tumors with adenovirus-enhanced cancer-selective promoter

Oncolytic virotherapy can selectively destroy cancer cells and is a potential approach in cancer treatment. A strategy to increase tumor-specific selectivity is to control the expression of a key regulatory viral gene with a tumor-specific promoter. We have previously found that cyclin E expression is augmented in cancer cells after adenovirus (Ad) infection. Thus, the cyclin E promoter that is further activated by Ad in cancer cells may have unique properties for enhancing oncolytic viral replication. We have shown that high levels of viral E1a gene expression are achieved in cancer cells infected with Ad-cycE, in which the endogenous Ad E1a promoter was replaced with the cyclin E promoter. Ad-cycE shows markedly selective oncolytic efficacy in vitro and destroys various types of cancer cells, including those resistant to ONYX-015/dl1520. Furthermore, Ad-cycE shows a strong capacity to repress A549 xenograft tumor growth in nude mice and significantly prolongs survival. This study suggests the potential of Ad-cycE in cancer therapy and indicates the advantages of using promoters that can be upregulated by virus infection in cancer cells in development of oncolytic viruses. Key messages: Cyclin E promoter activity is high in cancer cells and enhanced by adenovirus infection. Cyclin E promoter is used to control the E1a gene of a tumor-specific oncolytic adenovirus. Ad-cycE efficiently targets cancer cells and induces oncolysis. Ad-cycE significantly repressed xenograft tumor and prolonged survival.

Encapsulated stem cells loaded with hyaluronidase-expressing oncolytic virus for brain tumor therapy

Despite the proven safety of oncolytic viruses (OV) in clinical trials for glioblastoma (GBM), their efficacy has been hindered by suboptimal spreading within the tumor. We show that hyaluronan or hyaluronic acid (HA), an important component of extracellular matrix (ECM), is highly expressed in a majority of tumor xenografts established from patient-derived GBM lines that present both invasive and nodular phenotypes. Intratumoral injection of a conditionally replicating adenovirus expressing soluble hyaluronidase (ICOVIR17) into nodular GBM, mediated HA degradation and enhanced viral spread, resulting in a significant antitumor effect and mice survival. In an effort to translate OV-based therapeutics into clinical settings, we encapsulated human adipose-derived mesenchymal stem cells (MSC) loaded with ICOVIR17 in biocompatible synthetic extracellular matrix (sECM) and tested their efficacy in a clinically relevant mouse model of GBM resection. Compared with direct injection of ICOVIR17, sECM-MSC loaded with ICOVIR17 resulted in a significant decrease in tumor regrowth and increased mice survival. This is the first report of its kind revealing the expression of HA in GBM and the role of OV-mediated HA targeting in clinically relevant mouse model of GBM resection and thus has clinical implications.

Use of miRNA response sequences to block off-target replication and increase the safety of an unattenuated, glioblastoma-targeted oncolytic HSV

Glioblastoma multiforme (GBM) is an aggressive brain cancer for which there is no effective treatment. Oncolytic HSV vectors (oHSVs) are attenuated lytic viruses that have shown promise in the treatment of human GBM models in animals, but their efficacy in early phase patient trials has been limited. Instead of attenuating the virus with mutations in virulence genes, we engineered four copies of the recognition sequence for miR-124 into the 3'UTR of the essential ICP4 gene to protect healthy tissue against lytic virus replication; miR-124 is expressed in neurons but not in glioblastoma cells. Following intracranial inoculation into nude mice, the miR-124-sensitive vector failed to replicate or show overt signs of pathogenesis. To address the concern that this safety feature may reduce oncolytic activity, we inserted the miR-124 response elements into an unattenuated, human receptor (EGFR/EGFRvIII)-specific HSV vector. We found that miR-124 sensitivity did not cause a loss of treatment efficiency in an orthotopic model of primary human GBM in nude mice. These results demonstrate that engineered miR-124 responsiveness can eliminate off-target replication by unattenuated oHSV without compromising oncolytic activity, thereby providing increased safety.

Choindroitinase ABC I-mediated enhancement of oncolytic virus spread and anti tumor efficacy: a mathematical model

Oncolytic viruses are genetically engineered viruses that are designed to kill cancer cells while doing minimal damage to normal healthy tissue. After being injected into a tumor, they infect cancer cells, multiply inside them, and when a cancer cell is killed they move on to spread and infect other cancer cells. Chondroitinase ABC (Chase-ABC) is a bacterial enzyme that can remove a major glioma ECM component, chondroitin sulfate glycosoamino glycans from proteoglycans without any deleterious effects in vivo. It has been shown that Chase-ABC treatment is able to promote the spread of the viruses, increasing the efficacy of the viral treatment. In this paper we develop a mathematical model to investigate the effect of the Chase-ABC on the treatment of glioma by oncolytic viruses (OV). We show that the model's predictions agree with experimental results for a spherical glioma. We then use the model to test various treatment options in the heterogeneous microenvironment of the brain. The model predicts that separate injections of OV, one into the center of the tumor and another outside the tumor will result in better outcome than if the total injection is outside the tumor. In particular, the injection of the ECM-degrading enzyme (Chase-ABC) on the periphery of the main tumor core need to be administered in an optimal strategy in order to infect and eradicate the infiltrating glioma cells outside the tumor core in addition to proliferative cells in the bulk of tumor core. The model also predicts that the size of tumor satellites and distance between the primary tumor and multifocal/satellite lesions may be an important factor for the efficacy of the viral therapy with Chase treatment.

Gene therapy for malignant glioma

Glioblastoma multiforme (GBM) is the most frequent and devastating primary brain tumor in adults. Despite current treatment modalities, such as surgical resection followed by chemotherapy and radiotherapy, only modest improvements in median survival have been achieved. Frequent recurrence and invasiveness of GBM are likely due to the resistance of glioma stem cells to conventional treatments; therefore, novel alternative treatment strategies are desperately needed. Recent advancements in molecular biology and gene technology have provided attractive novel treatment possibilities for patients with GBM. Gene therapy is defined as a technology that aims to modify the genetic complement of cells to obtain therapeutic benefit. To date, gene therapy for the treatment of GBM has demonstrated anti-tumor efficacy in pre-clinical studies and promising safety profiles in clinical studies. However, while this approach is obviously promising, concerns still exist regarding issues associated with transduction efficiency, viral delivery, the pathologic response of the brain, and treatment efficacy. Tumor development and progression involve alterations in a wide spectrum of genes, therefore a variety of gene therapy approaches for GBM have been proposed. Improved viral vectors are being evaluated, and the potential use of gene therapy alone or in synergy with other treatments against GBM are being studied. In this review, we will discuss the most commonly studied gene therapy approaches for the treatment of GBM in preclinical and clinical studies including: prodrug/suicide gene therapy; oncolytic gene therapy; cytokine mediated gene therapy; and tumor suppressor gene therapy. In addition, we review the principles and mechanisms of current gene therapy strategies as well as advantages and disadvantages of each.

Gene therapy for malignant glioma

Glioblastoma multiforme (GBM) is the most frequent and devastating primary brain tumor in adults. Despite current treatment modalities, such as surgical resection followed by chemotherapy and radiotherapy, only modest improvements in median survival have been achieved. Frequent recurrence and invasiveness of GBM are likely due to the resistance of glioma stem cells to conventional treatments; therefore, novel alternative treatment strategies are desperately needed. Recent advancements in molecular biology and gene technology have provided attractive novel treatment possibilities for patients with GBM. Gene therapy is defined as a technology that aims to modify the genetic complement of cells to obtain therapeutic benefit. To date, gene therapy for the treatment of GBM has demonstrated anti-tumor efficacy in pre-clinical studies and promising safety profiles in clinical studies. However, while this approach is obviously promising, concerns still exist regarding issues associated with transduction efficiency, viral delivery, the pathologic response of the brain, and treatment efficacy. Tumor development and progression involve alterations in a wide spectrum of genes, therefore a variety of gene therapy approaches for GBM have been proposed. Improved viral vectors are being evaluated, and the potential use of gene therapy alone or in synergy with other treatments against GBM are being studied. In this review, we will discuss the most commonly studied gene therapy approaches for the treatment of GBM in preclinical and clinical studies including: prodrug/suicide gene therapy; oncolytic gene therapy; cytokine mediated gene therapy; and tumor suppressor gene therapy. In addition, we review the principles and mechanisms of current gene therapy strategies as well as advantages and disadvantages of each.

Enhanced antitumor efficacy of an oncolytic herpes simplex virus expressing an endostatin-angiostatin fusion gene in human glioblastoma stem cell xenografts

Viruses have demonstrated strong potential for the therapeutic targeting of glioblastoma stem cells (GSCs). In this study, the use of a herpes simplex virus carrying endostatin–angiostatin (VAE) as a novel therapeutic targeting strategy for glioblastoma-derived cancer stem cells was investigated. We isolated six stable GSC-enriched cultures from 36 human glioblastoma specimens and selected one of the stable GSCs lines for establishing GSC-carrying orthotopic nude mouse models. The following results were obtained: (a) VAE rapidly proliferated in GSCs and expressed endo–angio in vitro and in vivo 48 h and 10 d after infection, respectively; (b) compared with the control gliomas treated with rHSV or Endostar, the subcutaneous gliomas derived from the GSCs showed a significant reduction in microvessel density after VAE treatment; (c) compared with the control, a significant improvement was observed in the length of the survival of mice with intracranial and subcutaneous gliomas treated with VAE; (d) MRI analysis showed that the tumor volumes of the intracranial gliomas generated by GSCs remarkably decreased after 10 d of VAE treatment compared with the controls. In conclusion, VAE demonstrated oncolytic therapeutic efficacy in animal models of human GSCs and expressed an endostatin–angiostatin fusion gene, which enhanced antitumor efficacy most likely by restricting tumor microvasculature development.

Oncolytic viral therapy: targeting cancer stem cells

Cancer stem cells (CSCs) are defined as rare populations of tumor-initiating cancer cells that are capable of both self-renewal and differentiation. Extensive research is currently underway to develop therapeutics that target CSCs for cancer therapy, due to their critical role in tumorigenesis, as well as their resistance to chemotherapy and radiotherapy. To this end, oncolytic viruses targeting unique CSC markers, signaling pathways, or the pro-tumor CSC niche offer promising potential as CSCs-destroying agents/therapeutics. We provide a summary of existing knowledge on the biology of CSCs, including their markers and their niche thought to comprise the tumor microenvironment, and then we provide a critical analysis of the potential for targeting CSCs with oncolytic viruses, including herpes simplex virus-1, adenovirus, measles virus, reovirus, and vaccinia virus. Specifically, we review current literature regarding first-generation oncolytic viruses with their innate ability to replicate in CSCs, as well as second-generation viruses engineered to enhance the oncolytic effect and CSC-targeting through transgene expression.

Modern molecular approaches to diagnosis and treatment of high-grade brain gliomas

The review analyzes the current state of the problem of diagnosis and therapy of high-grade gliomas on the basis of the most promising present-day approaches. The diagnostic and treatment perspectives of the molecular genetic analysis of glioblastoma markers located on the tumor cell surface are considered. Gene therapy and the use of dendritic cells and oncolytic viruses are considered as the most interesting approaches to therapy of high-grade gliomas.

Clinical trials of viral therapy for malignant gliomas

Despite recent scientific advances in the understanding of the biology of malignant gliomas, there has been little change in the overall survival for this devastating disease. New and innovative treatments are under constant investigation. Starting in the 1990s, there was an interest in using viral therapeutics for the treatment of malignant gliomas. Multiple strategies were pursued, including oncolytic viral therapy, enzyme/pro-drug combinations and gene transfer with viral vectors. Multiple Phase I and II trials demonstrated the safety of these techniques, but clinically showed limited efficacy. However, this led to a better understanding of the pitfalls of viral therapy and encouraged the development of new approaches and improved delivery methods. Here we review the prior and ongoing clinical trials of viral therapy for gliomas, and discuss how novel strategies are currently being utilized in clinical trials.

Combination of autophagy inducer rapamycin and oncolytic adenovirus improves antitumor effect in cancer cells

Background

Combination of oncolytic adenoviruses (Ads) and chemotherapy drugs has shown promising therapeutic results and is considered as a potential approach for cancer therapy. We previously have shown that autophagy may generate decomposed cellular molecules that can be used as nutrition to support virus replication in cancer cells. In this study, we evaluated a unique combination of the novel oncolytic Ad-cycE with rapamycin, an autophagy inducer and first-line chemotherapeutic drug.

Methods

The combination of oncolytic Ad-cycE and the autophagy inducer rapamycin was assessed for enhanced antitumor effect. We also evaluated the combined effects of rapamycin and Ad-cycE on cancer cell viability. The interaction between Ad-cycE and rapamycin was analyzed with Calcusyn (Biosoft, Ferguson, MO).

Results

We show that rapamycin induces autophagy, enhances Ad E1A expression and increases Ad oncolytic replication. Combination of rapamycin and Ad-cycE elicits stronger cytotoxicity than single treatment alone. The analyzed data indicates that the Ad-cycE and rapamycin combination has a significantly synergistic antitumor effect.

Conclusions

Our study provides a new insight into vector development and demonstrates the novel roles of autophagy in adenovirus replication. The combination of autophagy-induced chemotherapy and oncolytic virotherapy may be a new approach to improve future cancer treatment.

Efficient gene delivery and selective transduction of astrocytes in the mammalian brain using viral vectors

Astrocytes are now considered as key players in brain information processing because of their newly discovered roles in synapse formation and plasticity, energy metabolism and blood flow regulation. However, our understanding of astrocyte function is still fragmented compared to other brain cell types. A better appreciation of the biology of astrocytes requires the development of tools to generate animal models in which astrocyte-specific proteins and pathways can be manipulated. In addition, it is becoming increasingly evident that astrocytes are also important players in many neurological disorders. Targeted modulation of protein expression in astrocytes would be critical for the development of new therapeutic strategies. Gene transfer is valuable to target a subpopulation of cells and explore their function in experimental models. In particular, viral-mediated gene transfer provides a rapid, highly flexible and cost-effective, in vivo paradigm to study the impact of genes of interest during central nervous system development or in adult animals. We will review the different strategies that led to the recent development of efficient viral vectors that can be successfully used to selectively transduce astrocytes in the mammalian brain.

Current status of gene therapy for brain tumors

Glioblastoma (GBM) is the most common and deadliest primary brain tumor in adults, with current treatments having limited impact on disease progression. Therefore the development of alternative treatment options is greatly needed. Gene therapy is a treatment strategy that relies on the delivery of genetic material, usually transgenes or viruses, into cells for therapeutic purposes, and has been applied to GBM with increasing promise. We have included selectively replication-competent oncolytic viruses within this strategy, although the virus acts directly as a complex biologic anti-tumor agent rather than as a classic gene delivery vehicle. GBM is a good candidate for gene therapy because tumors remain locally within the brain and only rarely metastasize to other tissues; the majority of cells in the brain are post-mitotic, which allows for specific targeting of dividing tumor cells; and tumors can often be accessed neurosurgically for administration of therapy. Delivery vehicles used for brain tumors include nonreplicating viral vectors, normal adult stem/progenitor cells, and oncolytic viruses. The therapeutic transgenes or viruses are typically cytotoxic or express prodrug activating suicide genes to kill glioma cells, immunostimulatory to induce or amplify anti-tumor immune responses, and/or modify the tumor microenvironment such as blocking angiogenesis. This review describes current preclinical and clinical gene therapy strategies for the treatment of glioma.

Viability reduction and Rac1 gene downregulation of heterogeneous ex-vivo glioma acute slice infected by the oncolytic Newcastle disease virus strain V4UPM

Oncolytic viruses have been extensively evaluated for anticancer therapy because this virus preferentially infects cancer cells without interfering with normal cells. Newcastle Disease Virus (NDV) is an avian virus and one of the intensively studied oncolytic viruses affecting many types of cancer including glioma. Nevertheless, the capability of NDV infection on heterogeneous glioma tissue in a cerebrospinal fluid atmosphere has never been reported. Recently, Rac1 is reported to be required for efficient NDV replication in human cancer cells and established a link between tumourigenesis and sensitivity to NDV. Rac1 is a member of the Rho GTPases involved in the regulation of the cell migration and cell-cycle progression. Rac1 knockdown leads to significant inhibition of viral replication. In this work, we demonstrated that NDV treatment led to significant reduction of tumour tissue viability of freshly isolated heterogeneous human brain tumour slice, known as an ex vivo glioma acute slice (EGAS). Analysis of gene expression indicated that reduced tissue viability was associated with downregulation of Rac1. However, the viability reduction was not persistent. We conclude that NDV treatment induced EGAS viability suppression, but subsequent downregulation of Rac1 gene may reduce the NDV replication and lead to regrowth of EGAS tissue.

Oncolytic virotherapy for malignant glioma: translating laboratory insights into clinical practice

Glioblastoma multiforme, one of the most common and aggressive brain tumors in adults, is highly resistant to currently available therapies and often recurs. Due to its poor prognosis and difficult management, there is an urgent need for the development and translation of new anti-glioma therapeutic approaches into the clinic. In this context, oncolytic virotherapy arises as an exciting treatment option for glioma patients. These natural or genetically engineered viruses are able to effectively infect cancer cells, inducing a specific anti-tumor cytotoxic effect. In addition, some viruses have been redesigned to modulate glioma microenvironment, to express cytokines to boost a systemic anti-glioma immune response and to incorporate angiostatic genes to decrease glioma vasculature. Although recent clinical trials have confirmed the safety of oncolytic virotherapies in the brain, their moderate clinical efficacy has not yet matched the encouraging preclinical laboratory results. In this review, we will discuss the leading anti-glioma virotherapy approaches that are presently under preclinical and clinical evaluation. We will also review different delivery methods, in vivo virus behavior, fate, replication, intratumoral spread, activation of anti-tumor immune response, and targeting of glioma stem cells. We will focus on the advantages and limitations of each therapeutic approach and how to overcome these hurdles to effectively translate exciting laboratory results into promising clinical trials.

Oncolytic virus therapy for glioblastoma multiforme: concepts and candidates

Twenty years of oncolytic virus development have created a field that is driven by the potential promise of lasting impact on our cancer treatment repertoire. With the field constantly expanding-more than 20 viruses have been recognized as potential oncolytic viruses-new virus candidates continue to emerge even as established viruses reach clinical trials. They all share the defining commonalities of selective replication in tumors, subsequent tumor cell lysis, and dispersion within the tumor. Members from diverse virus classes with distinctly different biologies and host species have been identified. Of these viruses, 15 have been tested on human glioblastoma multiforme. So far, 20 clinical trials have been conducted or initiated using attenuated strains of 7 different oncolytic viruses against glioblastoma multiforme. In this review, we present an overview of viruses that have been developed or considered for glioblastoma multiforme treatment. We outline the principles of tumor targeting and selective viral replication, which include mechanisms of tumor-selective binding, and molecular elements usurping cellular biosynthetic machinery in transformed cells. Results from clinical trials have clearly established the proof of concept and have confirmed the general safety of oncolytic virus application in the brain. The moderate clinical efficacy has not yet matched the promising preclinical lab results; next-generation oncolytic viruses that are either "armed" with therapeutic genes or embedded in a multimodality treatment regimen should enhance the clinical results.

A fiber chimeric CRAd vector Ad5/11-D24 double-armed with TRAIL and arresten for enhanced glioblastoma therapy

Malignant gliomas remain refractory to treatment despite advances in chemotherapy and surgical techniques. Conditionally replicating adenoviral vector (CRAd) could kill the tumor cells by selectively replicating in neoplastic cells, which represents a novel strategy for tumor therapy. Although CRAd with a 24-bp deletion in CR2 of the E1 region (CRAd5-D24) has been shown to have a better therapeutic effect over the other types of CRAd vectors, the current CRAd5-D24 still has some shortcomings for an efficient therapy of gliomas. In this study, we developed for the first time a novel vector CRAd5/11-D24.TRAIL/arresten by the following strategies: (1) modify CRAd5-D24 with Ad5/11 chimeric fiber to improve its infection efficiency for glioblastoma; and (2) insert two transgene expression cassettes into the E3 region and the region between the fiber and E4, respectively, for an enhanced therapeutic effect. The results indicated that the CRAd5/11-D24.TRAIL/arresten achieved nearly complete inhibition of glioma growth in nude mice possibly by increased antiangiogenesis and enhanced tumor apoptosis. The vector is the first reported E1A D24-deleted, Ad5/11 chimeric, and dual-armed oncolytic virus that shows markedly improved antitumor activities compared with the conventional oncolytic viruses. This novel antitumor agent should be evaluated further in future preclinical and clinical studies.

Interferon-β sensitivity of tumor cells correlates with poor response to VA7 virotherapy in mouse glioma models

In our recent study, replicative alphaviral vector VA7 was found to be effective against orthotopic human U87-glioma xenografts in an athymic mouse model eradicating the tumors with single intravenous (i.v.) injection. Here, we tested the efficacy of VA7 in immunocompetent orthotopic GL261 and CT-2A glioma models of C57BL/6 mouse in vivo. The cell lines were susceptible to VA7 infection in vitro, but GL261 infection was highly restricted in confluent cell cultures, and mouse interferon-β (IFNβ) pretreatment prevented the replication of VA7 in both cell lines. When mice bearing orthotopic GL261 or CT-2A tumors were administered neurotropic VA7, either i.v. or intracranially (i.c.), the vector was unable to infect the tumor and no survival benefit was achieved. Pretreatments with immunosuppressive cyclophosphamide (CPA) and rapamycin markedly lowered serum-neutralizing antibodies (NAbs) but had no effect on tumor infection or survival. Intracranial GL261 tumors were refractory also in athymic C57BL/6 mice, which have serious defects in their adaptive immunity. Implanted VA7-infected GL261 cells formed tumors with only slightly delayed kinetics and without improving survival thus excluding the participation of physical barriers and indicating robust host IFN action. Mouse and human IFNβ do not seem be species cross-reactive, which might limit the translational relevance of xenograft models in oncolytic virotherapy.

Preclinical evaluation of a genetically engineered herpes simplex virus expressing interleukin-12

Herpes simplex virus 1 (HSV-1) mutants that lack the γ(1)34.5 gene are unable to replicate in the central nervous system but maintain replication competence in dividing cell populations, such as those found in brain tumors. We have previously demonstrated that a γ(1)34.5-deleted HSV-1 expressing murine interleukin-12 (IL-12; M002) prolonged survival of immunocompetent mice in intracranial models of brain tumors. We hypothesized that M002 would be suitable for use in clinical trials for patients with malignant glioma. To test this hypothesis, we (i) compared the efficacy of M002 to three other HSV-1 mutants, R3659, R8306, and G207, in murine models of brain tumors, (ii) examined the safety and biodistribution of M002 in the HSV-1-sensitive primate Aotus nancymae following intracerebral inoculation, and (iii) determined whether murine IL-12 produced by M002 was capable of activating primate lymphocytes. Results are summarized as follows: (i) M002 demonstrated superior antitumor activity in two different murine brain tumor models compared to three other genetically engineered HSV-1 mutants; (ii) no significant clinical or magnetic resonance imaging evidence of toxicity was observed following direct inoculation of M002 into the right frontal lobes of A. nancymae; (iii) there was no histopathologic evidence of disease in A. nancymae 1 month or 5.5 years following direct inoculation; and (iv) murine IL-12 produced by M002 activates A. nancymae lymphocytes in vitro. We conclude that the safety and preclinical efficacy of M002 warrants the advancement of a Δγ(1)34.5 virus expressing IL-12 to phase I clinical trials for patients with recurrent malignant glioma.