Preclinical characterization of the antiglioma activity of a tropism-enhanced adenovirus targeted to the retinoblastoma pathway

The oncolytic adenovirus Delta-24-RGD in combination with ONC201 induces a potent antitumor response in pediatric high-grade and diffuse midline glioma models

BACKGROUND

Pediatric high-grade gliomas (pHGGs), including diffuse midline gliomas (DMGs), are aggressive pediatric tumors with one of the poorest prognoses. Delta-24-RGD and ONC201 have shown promising efficacy as single agents for these tumors. However, the combination of both agents has not been evaluated.

METHODS

The production of functional viruses was assessed by immunoblotting and replication assays. The antitumor effect was evaluated in a panel of human and murine pHGG and DMG cell lines. RNAseq, the seahorse stress test, mitochondrial DNA content, and γH2A.X immunofluorescence were used to perform mechanistic studies. Mouse models of both diseases were used to assess the efficacy of the combination in vivo. The tumor immune microenvironment was evaluated using flow cytometry, RNAseq and multiplexed immunofluorescence staining.

RESULTS

The Delta-24-RGD/ONC201 combination did not affect the virus replication capability in human pHGG and DMG models in vitro. Cytotoxicity analysis showed that the combination treatment was either synergistic or additive. Mechanistically, the combination treatment increased nuclear DNA damage and maintained the metabolic perturbation and mitochondrial damage caused by each agent alone. Delta-24-RGD/ONC201 cotreatment extended the overall survival of mice implanted with human and murine pHGG and DMG cells, independent of H3 mutation status and location. Finally, combination treatment in murine DMG models revealed a reshaping of the tumor microenvironment to a proinflammatory phenotype.

CONCLUSIONS

The Delta-24-RGD/ONC201 combination improved the efficacy compared to each agent alone in in vitro and in vivo models by potentiating nuclear DNA damage and in turn improving the antitumor (immune) response to each agent alone.

An autologous ex vivo model for exploring patient-specific responses to viro-immunotherapy in glioblastoma

Oncolytic virus (OV) clinical trials have demonstrated remarkable efficacy in subsets of patients with glioblastoma (GBM). However, the lack of tools to predict this response hinders the advancement of a more personalized application of OV therapy. In this study, we characterize an ex vivo co-culture system designed to examine the immune response to OV infection of patient-derived GBM neurospheres in the presence of autologous peripheral blood mononuclear cells (PBMCs). Co-culture conditions were optimized to retain viability and functionality of both tumor cells and PBMCs, effectively recapitulating the well-recognized immunosuppressive effects of GBM. Following OV infection, we observed elevated secretion of pro-inflammatory cytokines and chemokines, including interferon γ, tumor necrosis factor α, CXCL9, and CXCL10, and marked changes in immune cell activation markers. Importantly, OV treatment induced unique patient-specific immune responses. In summary, our co-culture platform presents an avenue for personalized screening of viro-immunotherapies in GBM, offering promise as a potential tool for future patient stratification in OV therapy.

Gut microbiota composition is associated with the efficacy of Delta-24-RGDOX in malignant gliomas

Glioblastoma, the most common primary brain tumor, has a 6.8% survival rate 5 years post diagnosis. Our team developed an oncolytic adenovirus with an OX-40L expression cassette named Delta-24-RGDOX. While studies have revealed the interaction between the gut microbiota and immunotherapy agents, there are no studies linking the gut microbiota with viroimmunotherapy efficacy. We hypothesize that gut bacterial signatures will be associated with oncolytic viral therapy efficacy. To test this hypothesis, we evaluated the changes in gut microbiota in two mouse cohorts: (1) GSC-005 glioblastoma-bearing mice treated orally with indoximod, an immunotherapeutic agent, or with Delta-24-RGDOX by intratumoral injection and (2) a mouse cohort harboring GL261-5 tumors used to mechanistically evaluate the importance of CD4+ T cells in relation to viroimmunotherapy efficacy. Microbiota assessment indicated significant differences in the structure of the gut bacterial communities in viroimmunotherapy-treated animals with higher survival compared with control or indoximod-treated animals. Moreover, viroimmunotherapy-treated mice with prolonged survival had a higher abundance of Bifidobacterium. The CD4+ T cell depletion was associated with gut dysbiosis, lower mouse survival, and lower antitumor efficacy of the therapy. These findings suggest that microbiota modulation along the gut-glioma axis contributes to the clinical efficacy and patient survival of viroimmunotherapy treated animals.

New hopes for the breast cancer treatment: perspectives on the oncolytic virus therapy

Oncolytic virus (OV) therapy has emerged as a promising frontier in cancer treatment, especially for solid tumours. While immunotherapies like immune checkpoint inhibitors and CAR-T cells have demonstrated impressive results, their limitations in inducing complete tumour regression have spurred researchers to explore new approaches targeting tumours resistant to current immunotherapies. OVs, both natural and genetically engineered, selectively replicate within cancer cells, inducing their lysis while sparing normal tissues. Recent advancements in clinical research and genetic engineering have enabled the development of targeted viruses that modify the tumour microenvironment, triggering anti-tumour immune responses and exhibiting synergistic effects with other cancer therapies. Several OVs have been studied for breast cancer treatment, including adenovirus, protoparvovirus, vaccinia virus, reovirus, and herpes simplex virus type I (HSV-1). These viruses have been modified or engineered to enhance their tumour-selective replication, reduce toxicity, and improve oncolytic properties.Newer generations of OVs, such as Oncoviron and Delta-24-RGD adenovirus, exhibit heightened replication selectivity and enhanced anticancer effects, particularly in breast cancer models. Clinical trials have explored the efficacy and safety of various OVs in treating different cancers, including melanoma, nasopharyngeal carcinoma, head and neck cancer, and gynecologic malignancies. Notably, Talimogene laherparepvec (T-VEC) and Oncorine have. been approved for advanced melanoma and nasopharyngeal carcinoma, respectively. However, adverse effects have been reported in some cases, including flu-like symptoms and rare instances of severe complications such as fistula formation. Although no OV has been approved specifically for breast cancer treatment, ongoing preclinical clinical trials focus on four groups of viruses. While mild adverse effects like low-grade fever and nausea have been observed, the effectiveness of OV monotherapy in breast cancer remains insufficient. Combination strategies integrating OVs with chemotherapy, radiotherapy, or immunotherapy, show promise in improving therapeutic outcomes. Oncolytic virus therapy holds substantial potential in breast cancer treatment, demonstrating safety in trials. Multi-approach strategies combining OVs with conventional therapies exhibit more promising therapeutic effects than monotherapy, signalling a hopeful future for OV-based breast cancer treatments.

Gene therapy in glioblastoma multiforme: Can it be a role changer?

Glioblastoma multiforme (GBM) is one of the most lethal cancers with a poor prognosis. Over the past century since its initial discovery and medical description, the development of effective treatments for this condition has seen limited progress. Despite numerous efforts, only a handful of drugs have gained approval for its treatment. However, these treatments have not yielded substantial improvements in both overall survival and progression-free survival rates. One reason for this is its unique features such as heterogeneity and difficulty of drug delivery because of two formidable barriers, namely the blood-brain barrier and the tumor-blood barrier. Over the past few years, significant developments in therapeutic approaches have given rise to promising novel and advanced therapies. Target-specific therapies, such as monoclonal antibodies (mAbs) and small molecules, stand as two important examples; however, they have not yielded a significant improvement in survival among GBM patients. Gene therapy, a relatively nascent advanced approach, holds promise as a potential treatment for cancer, particularly GBM. It possesses the potential to address the limitations of previous treatments and even newer advanced therapies like mAbs, owing to its distinct properties. This review aims to elucidate the current status and advancements in gene therapy for GBM treatment, while also presenting its future prospects.

Chimeric oncolytic adenovirus evades neutralizing antibodies from human patients and exhibits enhanced anti-glioma efficacy in immunized mice

Oncolytic viruses are a promising treatment for patients with high-grade gliomas, but neutralizing antibodies can limit their efficacy in patients with prior virus exposure or upon repeated virus injections. Data from a previous clinical trial using the oncolytic adenovirus Delta-24-RGD showed that generation of anti-viral neutralizing antibodies may affect the long-term survival of glioma patients. Past studies have examined the effects of neutralizing antibodies during systemic virus injections, but largely overlooked their impact during local virus injections into the brain. We found that immunoglobulins colocalized with viral proteins upon local oncolytic virotherapy of brain tumors, warranting a strategy to prevent virus neutralization and maximize oncolysis. Thus, we generated a chimeric virus, Delta-24-RGD-H43m, by replacing the capsid protein HVRs from the serotype 5-based Delta-24-RGD with those from the rare serotype 43. Delta-24-RGD-H43m evaded neutralizing anti-Ad5 antibodies and conferred a higher rate of long-term survival than Delta-24-RGD in glioma-bearing mice. Importantly, Delta-24-RGD-H43m activity was significantly more resistant to neutralizing antibodies present in sera of glioma patients treated with Delta-24-RGD during a phase 1 clinical trial. These findings provide a framework for a novel treatment of glioma patients that have developed immunity against Delta-24-RGD.

Magnetic Resonance Imaging-Aided SmartFlow Convection Delivery of DNX-2401: A Pilot, Prospective Case Series

BACKGROUND

The Combination Adenovirus + Pembrolizumab to Trigger Immune Virus Effects (CAPTIVE) study is a phase II clinical trial testing the efficacy of a recombinant adenovirus DNX-2401 combined with the immune checkpoint inhibitor pembrolizumab. Here, we report the first patients in this study who underwent viral delivery through real-time magnetic resonance imaging (MRI) stereotaxis-guided SmartFlow convection delivery of DNX-2401.

METHODS

Patients who underwent real-time MRI-guided DNX-2401 delivery through the SmartFlow convection catheter were prospectively followed.

RESULTS

Precise catheter placement was achieved in all patients treated, and no adverse events were noted. Average radial error from target was 0.9 mm. Average procedural time was 3 hours 16 minutes and was comparable to other convection-enhanced delivery techniques. In 2 patients, delivery of DNX-2401 was visualized as >1 cm maximal diameter of T1 hypointensity infusate on MRI obtained immediately after completion of viral infusion. These patients exhibited partial response based on Response Assessment in Neuro-Oncology assessment. The remaining patient showed <1 cm maximal diameter of infusate on immediate postinfusion MRI and showed disease progression on subsequent MRI.

CONCLUSIONS

Our pilot case series supports compatibility of the SmartFlow system with oncolytic adenovirus delivery and provides the basis for future validation studies.

Advances in oncolytic herpes simplex virus and adenovirus therapy for recurrent glioma

Recurrent glioma treatment is challenging due to molecular heterogeneity and treatment resistance commonly observed in these tumors. Researchers are actively pursuing new therapeutic strategies. Oncolytic viruses have emerged as a promising option. Oncolytic viruses selectively replicate within tumor cells, destroying them and stimulating the immune system for an enhanced anticancer response. Among Oncolytic viruses investigated for recurrent gliomas, oncolytic herpes simplex virus and oncolytic adenovirus show notable potential. Genetic modifications play a crucial role in optimizing their therapeutic efficacy. Different generations of replicative conditioned oncolytic human adenovirus and oncolytic HSV have been developed, incorporating specific modifications to enhance tumor selectivity, replication efficiency, and immune activation. This review article summarizes these genetic modifications, offering insights into the underlying mechanisms of Oncolytic viruses' therapy. It also aims to identify strategies for further enhancing the therapeutic benefits of Oncolytic viruses. However, it is important to acknowledge that additional research and clinical trials are necessary to establish the safety, efficacy, and optimal utilization of Oncolytic viruses in treating recurrent glioblastoma.

Oncolytic viruses against cancer, promising or delusion?

Cancer treatment is one of the most challenging topics in medical sciences. Different methods such as chemotherapy, tumor surgery, and immune checkpoint inhibitors therapy (ICIs) are potential approaches to treating cancer and killing tumor cells, but clinical studies have shown that they have been successful for a limited group of patients. Using viruses as a treatment can be considered as an effective treatment in the field of medicine. This is considered as a potential treatment, especially in comparison to chemotherapy, which has severe side effects related to the immune system. Most oncolytic viruses (OVs) have the potential to multiply in cancer cells, which are more than normal cells in malignant tissue and can induce immune responses. Therefore, tons of efforts and research have been started on the utilization of OVs as a treatment for cancer and have shown promising in treating cancers with less side effects. In this article, we have gathered studies about oncolytic viruses and their effectiveness in cancer treatment.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 1 Given name: [Omid Salahi] Last name [Ardekani], Author 2 Given name: [Mohammad Mehdi] Last name [Fazeli], Author 3 Given name: [Nillofar Asadi] Last name [Jemezghani]. Also, kindly confirm the details in the metadata are correct.Confirmed.

Oncolytic virotherapies for pediatric tumors

INTRODUCTION

Many pediatric patients with malignant tumors continue to suffer poor outcomes. The current standard of care includes maximum safe surgical resection followed by chemotherapy and radiation which may be associated with considerable long-term morbidity. The emergence of oncolytic virotherapy (OVT) may provide an alternative or adjuvant treatment for pediatric oncology patients.

AREAS COVERED

We reviewed seven virus types that have been investigated in past or ongoing pediatric tumor clinical trials: adenovirus (AdV-tk, Celyvir, DNX-2401, VCN-01, Ad-TD-nsIL-12), herpes simplex virus (G207, HSV-1716), vaccinia (JX-594), reovirus (pelareorep), poliovirus (PVSRIPO), measles virus (MV-NIS), and Senecavirus A (SVV-001). For each virus, we discuss the mechanism of tumor-specific replication and cytotoxicity as well as key findings of preclinical and clinical studies.

EXPERT OPINION

Substantial progress has been made in the past 10 years regarding the clinical use of OVT. From our review, OVT has favorable safety profiles compared to chemotherapy and radiation treatment. However, the antitumor effects of OVT remain variable depending on tumor type and viral agent used. Although the widespread adoption of OVT faces many challenges, we are optimistic that OVT will play an important role alongside standard chemotherapy and radiotherapy for the treatment of malignant pediatric solid tumors in the future.

Oncolytic DNX-2401 virotherapy plus pembrolizumab in recurrent glioblastoma: a phase 1/2 trial

Immune-mediated anti-tumoral responses, elicited by oncolytic viruses and augmented with checkpoint inhibition, may be an effective treatment approach for glioblastoma. Here in this multicenter phase 1/2 study we evaluated the combination of intratumoral delivery of oncolytic virus DNX-2401 followed by intravenous anti-PD-1 antibody pembrolizumab in recurrent glioblastoma, first in a dose-escalation and then in a dose-expansion phase, in 49 patients. The primary endpoints were overall safety and objective response rate. The primary safety endpoint was met, whereas the primary efficacy endpoint was not met. There were no dose-limiting toxicities, and full dose combined treatment was well tolerated. The objective response rate was 10.4% (90% confidence interval (CI) 4.2-20.7%), which was not statistically greater than the prespecified control rate of 5%. The secondary endpoint of overall survival at 12 months was 52.7% (95% CI 40.1-69.2%), which was statistically greater than the prespecified control rate of 20%. Median overall survival was 12.5 months (10.7-13.5 months). Objective responses led to longer survival (hazard ratio 0.20, 95% CI 0.05-0.87). A total of 56.2% (95% CI 41.1-70.5%) of patients had a clinical benefit defined as stable disease or better. Three patients completed treatment with durable responses and remain alive at 45, 48 and 60 months. Exploratory mutational, gene-expression and immunophenotypic analyses revealed that the balance between immune cell infiltration and expression of checkpoint inhibitors may potentially inform on response to treatment and mechanisms of resistance. Overall, the combination of intratumoral DNX-2401 followed by pembrolizumab was safe with notable survival benefit in select patients (ClinicalTrials.gov registration: NCT02798406).

Adjuvant Therapy with Oncolytic Adenovirus Delta-24-RGDOX After Intratumoral Adoptive T-cell Therapy Promotes Antigen Spread to Sustain Systemic Antitumor Immunity

Cancer cell heterogeneity and immunosuppressive tumor microenvironment (TME) pose a challenge in treating solid tumors with adoptive cell therapies targeting limited tumor-associated antigens (TAA), such as chimeric antigen receptor T-cell therapy. We hypothesize that oncolytic adenovirus Delta-24-RGDOX activates the TME and promote antigen spread to potentiate the abscopal effect of adoptive TAA-targeting T cells in localized intratumoral treatment. Herein, we used C57BL/6 mouse models with disseminated tumors derived from B16 melanoma cell lines to assess therapeutic effects and antitumor immunity. gp100-specific pmel-1 or ovalbumin (OVA)-specific OT-I T cells were injected into the first subcutaneous tumor, followed by three injections of Delta-24-RGDOX. We found TAA-targeting T cells injected into one subcutaneous tumor showed tumor tropism. Delta-24-RGDOX sustained the systemic tumor regression mediated by the T cells, leading to improved survival rate. Further analysis revealed that, in mice with disseminated B16-OVA tumors, Delta-24-RGDOX increased CD8⁺ leukocyte density within treated and untreated tumors. Importantly, Delta-24-RGDOX significantly reduced the immunosuppression of endogenous OVA-specific CTLs while increasing that of CD8⁺ leukocytes and, to a lesser extent, adoptive pmel-1 T cells. Consequently, Delta-24-RGDOX drastically increased the density of the OVA-specific CTLs in both tumors, and the combination synergistically enhanced the effect. Consistently, the splenocytes from the combination group showed a significantly stronger response against other TAAs (OVA and TRP2) than gp100, resulted in higher activity against tumor cells. Therefore, our data demonstrate that, as an adjuvant therapy followed TAA-targeting T cells in localized treatment, Delta-24-RGDOX activates TME and promotes antigen spread, leading to efficacious systemic antitumor immunity to overcome tumor relapse.

Significance

Adjuvant therapy with oncolytic viruses promotes antigen spread to potentiate localized intratumoral adoptive T-cell therapy with limited TAA targets, leading to sustainable systemic antitumor immunity to overcome tumor relapse.

Current Status and Challenges of Oncolytic Virotherapy for the Treatment of Glioblastoma

Despite decades of research and numerous clinical trials, the prognosis of patients diagnosed with glioblastoma (GBM) remains dire with median observed survival at 8 months. There is a critical need for novel treatments for GBM, which is the most common malignant primary brain tumor. Major advances in cancer therapeutics such as immune checkpoint inhibitors and chimeric antigen receptor (CAR) T-cell therapy have not yet led to improved outcomes for GBM. Conventional therapy of surgery followed by chemoradiation with or without tumor treating fields remains the standard of care. One of the many approaches to GBM therapy currently being explored is viral therapies. These typically work by selectively lysing target neoplastic cells, called oncolysis, or by the targeted delivery of a therapeutic transgene via a viral vector. In this review, we discuss the underlying mechanisms of action and describe both recent and current human clinical trials using these viruses with an emphasis on promising viral therapeutics that may ultimately break the field's current stagnant paradigm.

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.

Oncolytic virotherapy for the treatment of pediatric brainstem gliomas

Diffuse intrinsic pontine glioma (DIPG) is the most frequent brainstem glioma and the most lethal brain tumor in childhood. Despite transient benefit with radiotherapy, the prognosis of children with this disease remains dismal with severe neurological morbidity and median survival less than 12months. Oncolytic immunovirotherapy is emerging as a potential therapeutic approach in neuro-oncology. The oncolytic adenovirus Delta-24-RGD has shown efficacy in adult patients with recurrent GBM. Our group has demonstrated that Delta-24-RGD has oncolytic activity and triggers immune response in preclinical models of DIPG, and has a synergistic effect with radiotherapy in animal models of this disease. In this scenario, we conducted a first-in-human phase 1 clinical trial to evaluate the safety and efficacy of intratumoral injection of Delta-24-RGD in pediatric patients with newly diagnosed DIPG prior to standard radiotherapy. The study confirmed the feasibility of this treatment with an acceptable safety profile and encouraging efficacy results. Correlative analyses showed a biological activity from Delta-24-RGD in DIPG. Further advanced trials are needed to validate these results. Meanwhile, plenty of opportunities to increase the potential contribution of oncolytic viruses in the management of devastating tumors with no current effective treatment such as DIPG need to be explored and exploited.

Oncolytic virus-based suicide gene therapy for cancer treatment: a perspective of the clinical trials conducted at Henry Ford Health

Gene therapy manipulates or modifies a gene that provides a new cellular function to treat or correct a pathological condition, such as cancer. The approach of using gene manipulation to modify patient's cells to improve cancer therapy and potentially find a cure is gaining popularity. Currently, there are 12 gene therapy products approved by US-FDA, EMA and CFDA for cancer management, these include Rexin-G, Gendicine, Oncorine, Provange among other. The Radiation Biology Research group at Henry Ford Health has been actively developing gene therapy approaches for improving clinical outcome in cancer patients. The team was the first to test a replication-competent oncolytic virus armed with a therapeutic gene in humans, to combine this approach with radiation in humans, and to image replication-competent adenoviral gene expression/activity in humans. The adenoviral gene therapy products developed at Henry Ford Health have been evaluated in more than 6 preclinical studies and evaluated in 9 investigator initiated clinical trials treating more than100 patients. Two phase I clinical trials are currently following patients long term and a phase I trial for recurrent glioma was initiated in November 2022. This systematic review provides an overview of gene therapy approaches and products employed for treating cancer patients including the products developed at Henry Ford Health.

Effects of pre-existing anti-adenovirus antibodies on transgene expression levels and therapeutic efficacies of arming oncolytic adenovirus

Oncolytic adenoviruses (OAds), most of which are based on species C human adenovirus serotype 5 (Ad5) (OAd5), have recently received much attention as potential anticancer agents. High seroprevalence of anti-Ad5 neutralizing antibodies is a major hurdle for Ad5-based gene therapy. However, the impacts of anti-Ad5 neutralizing antibodies on OAd5-mediated transgene expression in the tumor and antitumor effects remain to be fully elucidated. In this study, we examined the impact of anti-Ad5 neutralizing antibodies on the OAd5-mediated antitumor effects and OAd5-mediated transgene expression. The luciferase expression of OAd-tAIB-Luc, which contains the cytomegalovirus promoter-driven luciferase gene, was inhibited in human cultured cells in the presence of human serum. Although the inhibitory effects of human serum possessing the low anti-Ad5 neutralizing antibody titers were overcome by long-term infection, the in vitro tumor cell lysis activities of OAd-tAIB-Luc were entirely attenuated by human serum containing the high titers of anti-Ad5 neutralizing antibodies. OAd-tAIB-Luc-mediated luciferase expression in the subcutaneous tumors 3 days after administration and tumor growth suppression levels following intratumoral administration were significantly lower in mice possessing the high titers of anti-Ad5 neutralizing antibodies, compared to those in control mice. These results suggested that pre-existing anti-Ad5 antibodies attenuated both transgene expression and potential antitumor effects of OAd5 following intratumoral administration.

Immunovirotherapy: The role of antibody based therapeutics combination with oncolytic viruses

Despite the fact that the new drugs and targeted therapies have been approved for cancer therapy during the past 30 years, the majority of cancer types are still remain challenging to be treated. Due to the tumor heterogeneity, immune system evasion and the complex interaction between the tumor microenvironment and immune cells, the great majority of malignancies need multimodal therapy. Unfortunately, tumors frequently develop treatment resistance, so it is important to have a variety of therapeutic choices available for the treatment of neoplastic diseases. Immunotherapy has lately shown clinical responses in malignancies with unfavorable outcomes. Oncolytic virus (OV) immunotherapy is a cancer treatment strategy that employs naturally occurring or genetically-modified viruses that multiply preferentially within cancer cells. OVs have the ability to not only induce oncolysis but also activate cells of the immune system, which in turn activates innate and adaptive anticancer responses. Despite the fact that OVs were translated into clinical trials, with T-VECs receiving FDA approval for melanoma, their use in fighting cancer faced some challenges, including off-target side effects, immune system clearance, non-specific uptake, and intratumoral spread of OVs in solid tumors. Although various strategies have been used to overcome the challenges, these strategies have not provided promising outcomes in monotherapy with OVs. In this situation, it is increasingly common to use rational combinations of immunotherapies to improve patient benefit. With the development of other aspects of cancer immunotherapy strategies, combinational therapy has been proposed to improve the anti-tumor activities of OVs. In this regard, OVs were combined with other biotherapeutic platforms, including various forms of antibodies, nanobodies, chimeric antigen receptor (CAR) T cells, and dendritic cells, to reduce the side effects of OVs and enhance their efficacy. This article reviews the promising outcomes of OVs in cancer therapy, the challenges OVs face and solutions, and their combination with other biotherapeutic agents.

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.

Targeting the Retinoblastoma/E2F repressive complex by CDK4/6 inhibitors amplifies oncolytic potency of an oncolytic adenovirus

CDK4/6 inhibitors (CDK4/6i) and oncolytic viruses are promising therapeutic agents for the treatment of various cancers. As single agents, CDK4/6 inhibitors that are approved for the treatment of breast cancer in combination with endocrine therapy cause G1 cell cycle arrest, whereas adenoviruses induce progression into S-phase in infected cells as an integral part of the their life cycle. Both CDK4/6 inhibitors and adenovirus replication target the Retinoblastoma protein albeit for different purposes. Here we show that in combination CDK4/6 inhibitors potentiate the anti-tumor effect of the oncolytic adenovirus XVir-N-31 in bladder cancer and murine Ewing sarcoma xenograft models. This increase in oncolytic potency correlates with an increase in virus-producing cancer cells, enhanced viral genome replication, particle formation and consequently cancer cell killing. The molecular mechanism that regulates this response is fundamentally based on the reduction of Retinoblastoma protein expression levels by CDK4/6 inhibitors.

Neither CDK4/6 inhibitors nor oncolytic adenoviruses show high efficiency as monotherapy in the treatment of cancer. Authors show here that when combined, CDK4/6 inhibitors deplete Retinoblastoma protein levels, which leads to more efficient virus replication and an increase in oncolytic virus-producing cancer cells and thus to efficient anti-tumor response in mouse xenograft sarcoma models.

Emerging immune-based technologies for high-grade gliomas

INTRODUCTION

The selection of a tailored and successful strategy for high-grade gliomas (HGGs) treatment is still a concern. The abundance of aberrant mutations within the heterogenic genetic landscape of glioblastoma strongly influences cell expansion, proliferation, and therapeutic resistance. Identification of immune evasion pathways opens the way to novel immune-based strategies. This review intends to explore the emerging immunotherapies for HGGs. The immunosuppressive mechanisms related to the tumor microenvironment and future perspectives to overcome glioma immunity barriers are also debated.

AREAS COVERED

An extensive literature review was performed on the PubMed/Medline and ClinicalTrials.gov databases. Only highly relevant articles in English and published in the last 20 years were selected. Data about immunotherapies coming from preclinical and clinical trials were summarized.

EXPERT OPINION

The overall level of evidence about the efficacy and safety of immunotherapies for HGGs is noteworthy. Monoclonal antibodies have been approved as second-line treatment, while peptide vaccines, viral gene strategies, and adoptive technologies proved to boost a vivid antitumor immunization. Malignant brain tumor-treating fields are ever-changing in the upcoming years. Constant refinements and development of new routes of drug administration will permit to design of novel immune-based treatment algorithms thus improving the overall survival.

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.

Gospel of malignant Glioma: Oncolytic virus therapy

Glioma accounts for nearly 80% of all intracranial malignant tumors. It is a major challenge to society as it is causes to impaired brain function in many patients. Currently, gliomas are mainly treated with surgery, postoperative radiotherapy, and chemotherapy. However, the curative effects of these treatments are not satisfactory. Oncolytic virus (OV) is a novel treatment which works by activating the immune functions and inducing apoptosis of tumor cells. The OV propagates indefinitely in the host cell, eventually leading to the death of host cell. Subsequently, a large number of antigens and signal molecules are released which exert antitumor immunity. Several preclinical and clinical studies have shown that G207, DNX2401, Zika and other viruses have important roles in malignant tumors. For example, these viruses can reduce the growth of tumor cells without causing severe complications. However, the known OVs have not been clearly classified. Herein, we divided OVs into neurotropic and non-neurophilic OVs based on whether the OVs are naturally neurotropic or not. The therapeutic effects of each group were compared. Finally, challenges encountered in the clinical application of OVs in the treatment of malignant gliomas were summarized.

Immunovirotherapy for Pediatric Solid Tumors: A Promising Treatment That is Becoming a Reality

Immunotherapy has seen tremendous strides in the last decade, acquiring a prominent position at the forefront of cancer treatment since it has been proven to be efficacious for a wide variety of tumors. Nevertheless, while immunotherapy has changed the paradigm of adult tumor treatment, this progress has not yet been translated to the pediatric solid tumor population. For this reason, alternative curative therapies are urgently needed for the most aggressive pediatric tumors. In recent years, oncolytic virotherapy has consolidated as a feasible strategy for cancer treatment, not only for its tumor-specific effects and safety profile but also for its capacity to trigger an antitumor immune response. This review will summarize the current status of immunovirotherapy to treat cancer, focusing on pediatric solid malignancies. We will revisit previous basic, translational, and clinical research and discuss advances in overcoming the existing barriers and limitations to translate this promising therapeutic as an every-day cancer treatment for the pediatric and young adult populations.

Exploiting 4-1BB immune checkpoint to enhance the efficacy of oncolytic virotherapy for diffuse intrinsic pontine gliomas

Diffuse intrinsic pontine gliomas (DIPGs) are aggressive pediatric brain tumors, and patient survival has not changed despite many therapeutic efforts, emphasizing the urgent need for effective treatments. Here, we evaluated the anti-DIPG effect of the oncolytic adenovirus Delta-24-ACT, which was engineered to express the costimulatory ligand 4-1BBL to potentiate the antitumor immune response of the virus. Delta-24-ACT induced the expression of functional 4-1BBL on the membranes of infected DIPG cells, which enhanced the costimulation of CD8⁺ T lymphocytes. In vivo, Delta-24-ACT treatment of murine DIPG orthotopic tumors significantly improved the survival of treated mice, leading to long-term survivors that developed immunological memory against these tumors. In addition, Delta-24-ACT was safe and caused no local or systemic toxicity. Mechanistic studies showed that Delta-24-ACT modulated the tumor-immune content, not only increasing the number, but also improving the functionality of immune cells. All of these data highlight the safety and potential therapeutic benefit of Delta-24-ACT the treatment of patients with DIPG.

Advances in local therapy for glioblastoma - taking the fight to the tumour

Despite advances in neurosurgery, chemotherapy and radiotherapy, glioblastoma remains one of the most treatment-resistant CNS malignancies, and the tumour inevitably recurs. The majority of recurrences appear in or near the resection cavity, usually within the area that received the highest dose of radiation. Many new therapies focus on combatting these local recurrences by implementing treatments directly in or near the tumour bed. In this Review, we discuss the latest developments in local therapy for glioblastoma, focusing on recent preclinical and clinical trials. The approaches that we discuss include novel intraoperative techniques, various treatments of the surgical cavity, stereotactic injections directly into the tumour, and new developments in convection-enhanced delivery and intra-arterial treatments.

Immunotherapy of glioblastoma: recent advances and future prospects

Glioblastoma (GBM) stands out as the most common, aggressive form of primary malignant brain tumor conferring a devastatingly poor prognosis. Despite aggressive standard-of-care in surgical resection and chemoradiation with temozolomide, the median overall survival of patients still remains no longer than 15 months, due to significant tumor heterogeneity, immunosuppression induced by the tumor immune microenvironment and low mutational burden. Advances in immunotherapeutic approaches have revolutionized the treatment of various cancer types and become conceptually attractive for glioblastoma. In this review, we provide an overview of the basic knowledge underlying immune targeting and promising immunotherapeutic strategies including CAR T cells, oncolytic viruses, cancer vaccines, and checkpoint blockade inhibitors that have been recently investigated in glioblastoma. Current clinical trials and previous clinical trial findings are discussed, shedding light on novel strategies to overcome various limitations and challenges.

Superior infectivity of the fiber chimeric oncolytic adenoviruses Ad5/35 and Ad5/3 over Ad5-delta-24-RGD in primary glioma cultures

Ad5-delta-24-RGD is currently the most clinically advanced recombinant adenovirus (rAd) for glioma therapy. We constructed a panel of fiber-modified rAds (Ad5RGD, Ad5/3, Ad5/35, Ad5/3RGD, and Ad5/35RGD, all harboring the delta-24 modification) and compared their infectivity, replication, reproduction, and cytolytic efficacy in human and rodent glioma cell lines and short-term cultures from primary gliomas. In human cells, both Ad5/35-delta-24 and Ad5/3-delta-24 displayed superior infectivity and cytolytic efficacy over Ad5-delta-24-RGD, while Ad5/3-delta-24-RGD and Ad5/35-delta-24-RGD did not show further improvements in efficacy. The expression of the adenoviral receptors/coreceptors CAR, DSG2, and CD46 and the integrins αVβ3/αVβ5 did not predict the relative cytolytic efficacy of the fiber-modified rAds. The cytotoxicity of the fiber-modified rAds in human primary normal cultures of different origins and in primary glioma cultures was comparable, indicating that the delta-24 modification did not confer tumor cell selectivity. We also revealed that CT-2A and GL261 glioma cells might be used as murine cell models for the fiber chimeric rAds in vitro and in vivo. In GL261 tumor-bearing mice, Ad5/35-delta-24, armed with the immune costimulator OX40L as the E2A/DBP-p2A-mOX40L fusion, produced long-term survivors, which were able to reject tumor cells upon rechallenge. Our data underscore the potential of local Ad5/35-delta-24-based immunovirotherapy for glioblastoma treatment.

Advances in immunotherapy for glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive malignant brain tumor of the central nervous system and has a very poor prognosis. The current standard of care for patients with GBM involves surgical resection, radiotherapy, and chemotherapy. Unfortunately, conventional therapies have not resulted in significant improvements in the survival outcomes of patients with GBM; therefore, the overall mortality rate remains high. Immunotherapy is a type of cancer treatment that helps the immune system to fight cancer and has shown success in different types of aggressive cancers. Recently, healthcare providers have been actively investigating various immunotherapeutic approaches to treat GBM. We reviewed the most promising immunotherapy candidates for glioblastoma that have achieved encouraging results in clinical trials, focusing on immune checkpoint inhibitors, oncolytic viruses, nonreplicating viral vectors, and chimeric antigen receptor (CAR) immunotherapies.

Engineering surface patterns on nanoparticles: New insights on nano-bio interactions

The surface properties of nanoparticles affect their fates in biological systems. Based on nanotechnology and methodology, pioneering works have explored the effects of chemical surface patterns on the behavior of...

Local treatment of a pediatric osteosarcoma model with a 4-1BBL armed oncolytic adenovirus results in an antitumor effect and leads to immune memory

Osteosarcoma is an aggressive bone tumor occurring primarily in pediatric patients. Despite years of intensive research, the outcomes of patients with metastatic disease or who do not respond to therapy have remained poor and have not changed in the last 30 years. Oncolytic virotherapy is becoming a reality to treat local and metastatic tumors while maintaining a favorable safety profile. Delta-24-ACT is a replicative oncolytic adenovirus engineered to selectively target cancer cells and to potentiate immune responses through expression of the immune costimulatory ligand 4-1BB. This work aimed to assess the antisarcoma effect of Delta-24-ACT. MTS and replication assays were used to quantify the antitumor effects of Delta-24-ACT in vitro in osteosarcoma human and murine cell lines. Evaluation of the in vivo antitumor effect and immune response to Delta-24-ACT was performed in immunocompetent mice bearing orthotopic K7M2 cell line. Immunophenotyping of the tumor microenvironment was characterized by immunohistochemistry and flow cytometry. In vitro, Delta-24-ACT killed osteosarcoma cells and triggered the production of danger signals. In vivo, local treatment with Delta-24-ACT led to antitumor effects against both the primary tumor and spontaneous metastases in a murine osteosarcoma model. Viral treatment was safe, with no noted toxicity. Delta-24-ACT significantly increased the median survival time of treated mice. Collectively, our data identify Delta-24-ACT administration as an effective and safe therapeutic strategy for local and metastatic osteosarcoma. These results support clinical translation of this viral immunotherapy approach.

Current development in adenoviral vectors for cancer immunotherapy

Adenoviruses are well characterized and thus easily modified to generate oncolytic vectors that directly lyse tumor cells and can be "armed" with transgenes to promote lysis, antigen presentation, and immunostimulation. Oncolytic adenoviruses (OAds) are safe, versatile, and potent immunostimulants in patients. Since transgene expression is restricted to the tumor, adenoviral transgenes overcome the toxicities and short half-life of systemically administered cytokines, immune checkpoint blockade molecules, and bispecific T cell engagers. While OAds expressing immunostimulatory molecules ("armed" OAds) have demonstrated anti-tumor potential in preclinical solid tumor models, the efficacy has not translated into significant clinical outcomes as a monotherapy. However, OAds synergize with established standards of care and novel immunotherapeutic agents, providing a multifaceted means to address complexities associated with solid tumors. Critically, armed OAds revitalize endogenous and adoptively transferred immune cells while simultaneously enhancing their anti-tumor function. To properly evaluate these novel vectors and reduce the gap in the cycle between bench-to-bedside and back, improving model systems must be a priority. The future of OAds will involve a multidimensional approach that provides immunostimulatory molecules, immune checkpoint blockade, and/or immune engagers in concert with endogenous and exogenous immune cells to initiate durable and comprehensive anti-tumor responses.

Viral targeting of glioblastoma stem cells with patient-specific genetic and post-translational p53 deregulations

Cancer therapy urges targeting of malignant subsets within self-renewing heterogeneous stem cell populations. We dissect the genetic and functional heterogeneity of human glioblastoma stem cells (GSCs) within patients by their innate responses to non-pathogenic mouse parvoviruses that are tightly restrained by cellular physiology. GSC neurospheres accumulate assembled capsids but restrict viral NS1 cytotoxic protein expression by an innate PKR/eIF2α-P response counteractable by electric pulses. NS1 triggers a comprehensive DNA damage response involving cell-cycle arrest, neurosphere disorganization, and bystander disruption of GSC-derived brain tumor architecture in rodent models. GSCs and cancer cell lines permissive to parvovirus genome replication require p53-Ser15 phosphorylation (Pp53S15). NS1 expression is enhanced by exogeneous Pp53S15 induction but repressed by wtp53. Consistently, patient-specific GSC subpopulations harboring p53 gain-of-function mutants and/or Pp53S15 are selective viral targets. This study provides a molecular foundation for personalized biosafe viral therapies against devastating glioblastoma and other cancers with deregulated p53 signaling.

A new insight into aggregation of oncolytic adenovirus Ad5-delta-24-RGD during CsCl gradient ultracentrifugation

Two-cycle cesium chloride (2 × CsCl) gradient ultracentrifugation is a conventional approach for purifying recombinant adenoviruses (rAds) for research purposes (gene therapy, vaccines, and oncolytic vectors). However, rAds containing the RGD-4C peptide in the HI loop of the fiber knob domain tend to aggregate during 2 × CsCl gradient ultracentrifugation resulting in a low infectious titer yield or even purification failure. An iodixanol-based purification method preventing aggregation of the RGD4C-modified rAds has been proposed. However, the reason explaining aggregation of the RGD4C-modified rAds during 2 × CsCl but not iodixanol gradient ultracentrifugation has not been revealed. In the present study, we showed that rAds with the RGD-4C peptide in the HI loop but not at the C-terminus of the fiber knob domain were prone to aggregate during 2 × CsCl but not iodixanol gradient ultracentrifugation. The cysteine residues with free thiol groups after the RGD motif within the inserted RGD-4C peptide were responsible for formation of the interparticle disulfide bonds under atmospheric oxygen and aggregation of Ad5-delta-24-RGD4C-based rAds during 2 × CsCl gradient ultracentrifugation, which could be prevented using iodixanol gradient ultracentrifugation, most likely due to antioxidant properties of iodixanol. A cysteine-to-glycine substitution of the cysteine residues with free thiol groups (RGD-2C2G) prevented aggregation during 2 × CsCl gradient purification but in coxsackie and adenovirus receptor (CAR)-low/negative cancer cell lines of human and rodent origin, this reduced cytolytic efficacy to the levels observed for a fiber non-modified control vector. However, both Ad5-delta-24-RGD4C and Ad5-delta-24-RGD2C2G were equally effective in the murine immunocompetent CT-2A glioma model due to a primary role of antitumor immune responses in the therapeutic efficacy of oncolytic virotherapy.

Immunotherapy in Glioblastoma: A Clinical Perspective

Glioblastoma is the most frequent and the most aggressive brain tumor. It is notoriously resistant to current treatments, and the prognosis remains dismal. Immunotherapies have revolutionized the treatment of numerous cancer types and generate great hope for glioblastoma, alas without success until now. In this review, the rationale underlying immune targeting of glioblastoma, as well as the challenges faced when targeting these highly immunosuppressive tumors, are discussed. Innovative immune-targeting strategies including cancer vaccines, oncolytic viruses, checkpoint blockade inhibitors, adoptive cell transfer, and CAR T cells that have been investigated in glioblastoma are reviewed. From a clinical perspective, key clinical trial findings and ongoing trials are discussed for each approach. Finally, limitations, either biological or arising from trial designs are analyzed, and strategies to overcome them are presented. Proof of efficacy for immunotherapy approaches remains to be demonstrated in glioblastoma, but our rapidly expanding understanding of its biology, its immune microenvironment, and the emergence of novel promising combinatorial approaches might allow researchers to finally fulfill the medical need for GBM patients.

Oncolytic Adenovirus: Prospects for Cancer Immunotherapy

Immunotherapy has moved to the forefront of modern oncologic treatment in the past few decades. Various forms of immunotherapy currently are emerging, including oncolytic viruses. In this therapy, viruses are engineered to selectively propagate in tumor cells and reduce toxicity for non-neoplastic tissues. Adenovirus is one of the most frequently employed oncolytic viruses because of its capacity in tumor cell lysis and immune response stimulation. Upregulation of immunostimulatory signals induced by oncolytic adenoviruses (OAds) might significantly remove local immune suppression and amplify antitumor immune responses. Existing genetic engineering technology allows us to design OAds with increasingly better tumor tropism, selectivity, and antitumor efficacy. Several promising strategies to modify the genome of OAds have been applied: capsid modifications, small deletions in the pivotal viral genes, insertion of tumor-specific promoters, and addition of immunostimulatory transgenes. OAds armed with tumor-associated antigen (TAA) transgenes as cancer vaccines provide additional therapeutic strategies to trigger tumor-specific immunity. Furthermore, the combination of OAds and immune checkpoint inhibitors (ICIs) increases clinical benefit as evidence shown in completed and ongoing clinical trials, especially in the combination of OAds with antiprogrammed death 1/programed death ligand 1 (PD-1/PD-L1) therapy. Despite remarkable antitumor potency, oncolytic adenovirus immunotherapy is confronted with tough challenges such as antiviral immune response and obstruction of tumor microenvironment (TME). In this review, we focus on genomic modification strategies of oncolytic adenoviruses and applications of OAds in cancer immunotherapy.

CD137 and PD-L1 targeting with immunovirotherapy induces a potent and durable antitumor immune response in glioblastoma models

Background

Glioblastoma (GBM) is a devastating primary brain tumor with a highly immunosuppressive tumor microenvironment, and treatment with oncolytic viruses (OVs) has emerged as a promising strategy for these tumors. Our group constructed a new OV named Delta-24-ACT, which was based on the Delta-24-RGD platform armed with 4-1BB ligand (4-1BBL). In this study, we evaluated the antitumor effect of Delta-24-ACT alone or in combination with an immune checkpoint inhibitor (ICI) in preclinical models of glioma.

Methods

The in vitro effect of Delta-24-ACT was characterized through analyses of its infectivity, replication and cytotoxicity by flow cytometry, immunofluorescence (IF) and MTS assays, respectively. The antitumor effect and therapeutic mechanism were evaluated in vivo using several immunocompetent murine glioma models. The tumor microenvironment was studied by flow cytometry, immunohistochemistry and IF.

Results

Delta-24-ACT was able to infect and exert a cytotoxic effect on murine and human glioma cell lines. Moreover, Delta-24-ACT expressed functional 4-1BBL that was able to costimulate T lymphocytes in vitro and in vivo. Delta-24-ACT elicited a more potent antitumor effect in GBM murine models than Delta-24-RGD, as demonstrated by significant increases in median survival and the percentage of long-term survivors. Furthermore, Delta-24-ACT modulated the tumor microenvironment, which led to lymphocyte infiltration and alteration of their immune phenotype, as characterized by increases in the expression of Programmed Death 1 (PD-1) on T cells and Programmed Death-ligand 1 (PD-L1) on different myeloid cell populations. Because Delta-24-ACT did not induce an immune memory response in long-term survivors, as indicated by rechallenge experiments, we combined Delta-24-ACT with an anti-PD-L1 antibody. In GL261 tumor-bearing mice, this combination showed superior efficacy compared with either monotherapy. Specifically, this combination not only increased the median survival but also generated immune memory, which allowed long-term survival and thus tumor rejection on rechallenge.

Conclusions

In summary, our data demonstrated the efficacy of Delta-24-ACT combined with a PD-L1 inhibitor in murine glioma models. Moreover, the data underscore the potential to combine local immunovirotherapy with ICIs as an effective therapy for poorly infiltrated tumors.

Oncolytic Viruses for Malignant Glioma: On the Verge of Success?

Glioblastoma is one of the most difficult tumor types to treat with conventional therapy options like tumor debulking and chemo- and radiotherapy. Immunotherapeutic agents like oncolytic viruses, immune checkpoint inhibitors, and chimeric antigen receptor T cells have revolutionized cancer therapy, but their success in glioblastoma remains limited and further optimization of immunotherapies is needed. Several oncolytic viruses have demonstrated the ability to infect tumors and trigger anti-tumor immune responses in malignant glioma patients. Leading the pack, oncolytic herpesvirus, first in its class, awaits an approval for treating malignant glioma from MHLW, the federal authority of Japan. Nevertheless, some major hurdles like the blood–brain barrier, the immunosuppressive tumor microenvironment, and tumor heterogeneity can engender suboptimal efficacy in malignant glioma. In this review, we discuss the current status of malignant glioma therapies with a focus on oncolytic viruses in clinical trials. Furthermore, we discuss the obstacles faced by oncolytic viruses in malignant glioma patients and strategies that are being used to overcome these limitations to (1) optimize delivery of oncolytic viruses beyond the blood–brain barrier; (2) trigger inflammatory immune responses in and around tumors; and (3) use multimodal therapies in combination to tackle tumor heterogeneity, with an end goal of optimizing the therapeutic outcome of oncolytic virotherapy.

An immune-competent, replication-permissive Syrian Hamster glioma model for evaluating Delta-24-RGD oncolytic adenovirus

BACKGROUND

Oncolytic adenoviruses are promising new treatments against solid tumors, particularly for glioblastoma (GBM), and preclinical models are required to evaluate the mechanisms of efficacy. However, due to the species selectivity of adenovirus, there is currently no single animal model that supports viral replication, tumor oncolysis, and a virus-mediated immune response. To address this gap, we took advantage of the Syrian hamster to develop the first intracranial glioma model that is both adenovirus replication-permissive and immunocompetent.

METHODS

We generated hamster glioma stem-like cells (hamGSCs) by transforming hamster neural stem cells with hTERT, simian virus 40 large T antigen, and h-RasV12. Using a guide-screw system, we generated an intracranial tumor model in the hamster. The efficacy of the oncolytic adenovirus Delta-24-RGD was assessed by survival studies, and tumor-infiltrating lymphocytes were evaluated by flow cytometry.

RESULTS

In vitro, hamster GSCs supported viral replication and were susceptible to Delta-24-RGD mediated cell death. In vivo, hamster GSCs consistently developed into highly proliferative tumors resembling high-grade glioma. Flow cytometric analysis of hamster gliomas revealed significantly increased T cell infiltration in Delta-24-RGD infected tumors, indicative of immune activation. Treating tumor-bearing hamsters with Delta-24-RGD led to significantly increased survival compared to hamsters treated with PBS.

CONCLUSIONS

This adenovirus-permissive, immunocompetent hamster glioma model overcomes the limitations of previous model systems and provides a novel platform in which to study the interactions between tumor cells, the host immune system, and oncolytic adenoviral therapy; understanding of which will be critical to implementing oncolytic adenovirus in the clinic.

Current strategies of virotherapy in clinical trials for cancer treatment

As a novel immune-active agent for cancer treatment, viruses have the ability of infecting and replicating in tumor cells. The safety and efficacy of viruses has been tested and confirmed in preclinical and clinical trials. In the last decade, virotherapy has been adopted as a monotherapy or combined therapy with immunotherapy, chemotherapy, or radiotherapy, showing promising outcomes against cancer. In this review, the current strategies of viruses used in clinical trials are classified and described. Besides this, the challenge and future prospects of virotherapy in the management for cancer patients are discussed in this review.

Oncolytic Virotherapy for Cancer: Clinical Experience

Oncolytic viruses are a new class of therapeutics which are largely in the experimental stage, with just one virus approved by the FDA thus far. While the concept of oncolytic virotherapy is not new, advancements in the fields of molecular biology and virology have renewed the interest in using viruses as oncolytic agents. Backed by robust preclinical data, many oncolytic viruses have entered clinical trials. Oncolytic viruses that have completed some levels of clinical trials or are currently undergoing clinical trials are mostly genetically engineered viruses, with the exception of some RNA viruses. Reolysin, an unmodified RNA virus is clinically the most advanced oncolytic RNA virus that has completed different phases of clinical trials. Other oncolytic viruses that have been studied in clinical trials are mostly DNA viruses that belong to one of the three families: herpesviridae, poxviridae or adenoviridae. In this review work we discuss recent clinical studies with oncolytic viruses, especially herpesvirus, poxvirus, adenovirus and reovirus. In summary, the oncolytic viruses tested so far are well tolerated, even in immune-suppressed patients. For most oncolytic viruses, mild and acceptable toxicities are seen at the currently defined highest feasible doses. However, anti-tumor efficacies of oncolytic viruses have been modest, especially when used as monotherapy. Therefore, the potency of oncolytic viruses needs to be enhanced for more oncolytic viruses to hit the clinic. Aiming to achieve higher therapeutic benefits, oncolytic viruses are currently being studied in combination with other therapies. Here we discuss the currently available clinical data on oncolytic viruses, either as monotherapy or in combination with other treatments.

Endovascular Selective Intra-Arterial Infusion of Mesenchymal Stem Cells Loaded With Delta-24 in a Canine Model

BACKGROUND

Delta-24-RGD, an oncolytic adenovirus, shows promise against glioblastoma. To enhance virus delivery, we recently demonstrated that human bone marrow-derived mesenchymal stem cells loaded with Delta-24-RGD (hMSC-D24) can eradicate glioblastomas in mouse models. There are no studies examining the safety of endovascular selective intra-arterial (ESIA) infusions of MSC-D24 in large animals simulating human clinical situations.

OBJECTIVE

To perform canine preclinical studies testing the feasibility and safety of delivering increasing doses of hMSCs-D24 via ESIA infusions.

METHODS

ESIA infusions of hMSC-D24 were performed in the cerebral circulation of 10 normal canines in the target vessels (internal carotid artery [ICA]/P1) via transfemoral approach using commercially available microcatheters. Increasing concentrations of hMSC-D24 or particles (as a positive control) were injected into 1 hemisphere; saline (negative control) was infused contralaterally. Toxicity (particularly embolic stroke) was assessed on postinfusion angiography, diffusion-weighted magnetic resonance imaging, clinical exam, and necropsy.

RESULTS

ESIA injections were performed in the ICA (n = 7) or P1 (n = 3). In 2 animals injected with particles (positive control), strokes were detected by all assays. Of 6 canines injected with hMSC-D24 through the anterior circulation, escalating dose from 2 × 106 cells/20 mL to 1 × 108 cells/10 mL resulted in no strokes. Two animals had ischemic and hemorrhagic strokes after posterior cerebral artery catheterization. A survival experiment of 2 subjects resulted in no complications detected for 24-h before euthanization.

CONCLUSION

This novel study simulating ESIA infusion demonstrates that MSCs-D24 can be infused safely at least up to doses of 1 × 108 cells/10 mL (107 cells/ml) in the canine anterior circulation using commercially available microcatheters. These findings support a clinical trial of ESIA infusion of hMSCs-D24.

Current Approaches for Glioma Gene Therapy and Virotherapy

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in the adult population and it carries a dismal prognosis. Inefficient drug delivery across the blood brain barrier (BBB), an immunosuppressive tumor microenvironment (TME) and development of drug resistance are key barriers to successful glioma treatment. Since gliomas occur through sequential acquisition of genetic alterations, gene therapy, which enables to modification of the genetic make-up of target cells, appears to be a promising approach to overcome the obstacles encountered by current therapeutic strategies. Gene therapy is a rapidly evolving field with the ultimate goal of achieving specific delivery of therapeutic molecules using either viral or non-viral delivery vehicles. Gene therapy can also be used to enhance immune responses to tumor antigens, reprogram the TME aiming at blocking glioma-mediated immunosuppression and normalize angiogenesis. Nano-particles-mediated gene therapy is currently being developed to overcome the BBB for glioma treatment. Another approach to enhance the anti-glioma efficacy is the implementation of viro-immunotherapy using oncolytic viruses, which are immunogenic. Oncolytic viruses kill tumor cells due to cancer cell-specific viral replication, and can also initiate an anti-tumor immunity. However, concerns still remain related to off target effects, and therapeutic and transduction efficiency. In this review, we describe the rationale and strategies as well as advantages and disadvantages of current gene therapy approaches against gliomas in clinical and preclinical studies. This includes different delivery systems comprising of viral, and non-viral delivery platforms along with suicide/prodrug, oncolytic, cytokine, and tumor suppressor-mediated gene therapy approaches. In addition, advances in glioma treatment through BBB-disruptive gene therapy and anti-EGFRvIII/VEGFR gene therapy are also discussed. Finally, we discuss the results of gene therapy-mediated human clinical trials for gliomas. In summary, we highlight the progress, prospects and remaining challenges of gene therapies aiming at broadening our understanding and highlighting the therapeutic arsenal for GBM.

Current Immunotherapies for Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive malignant tumor found in the central nervous system. Currently, standard treatments in the clinic include maximal safe surgical resection, radiation, and chemotherapy and are mostly limited by low therapeutic efficiency correlated with poor prognosis. Immunotherapy, which predominantly focuses on peptide vaccines, dendritic cell vaccines, chimeric antigen receptor T cells, checkpoint inhibitor therapy, and oncolytic virotherapy, have achieved some promising results in both preclinical and clinical trials. The future of immune therapy for GBM requires an integrated effort with rational combinations of vaccine therapy, cell therapy, and radio- and chemotherapy as well as molecule therapy targeting the tumor microenvironment.

Overcoming the barriers to optimization of adenovirus delivery using biomaterials: Current status and future perspective

Adenovirus (Ad) is emerging as a promising modality for cancer gene therapy due to its ability to induce high level of therapeutic transgene expression with no risk of insertional mutagenesis, ability to be facilely produced at a high titer, and capacity to induce robust antitumor immune response. Despite these excellent attributes of human serotype 5 Ad, poor systemic administration capability, coxsackie and adenovirus receptor (CAR)-dependent endocytic mechanism limiting potentially targetable cell types, nonspecific shedding to normal organs, and poor viral persistence in tumor tissues are major hindrances toward maximizing the therapeutic benefit of Ad in clinical setting. To address the abovementioned shortcomings, various non-immunogenic nanomaterials have been explored to modify Ad surface via physical or chemical interactions. In this review, we summarize the recent developments of different types of nanomaterials that had been utilized for modification of Ad and how tumor-targeted local and system delivery can be achieved with these nanocomplexes. Finally, we conclude by highlighting the key features of various nanomaterials-coated Ads and their prospects to optimize the delivery of virus.

Self-assembled Viral Nanoparticles as Targeted Anticancer Vehicles

Viral nanoparticles (VNPs) comprise a variety of mammalian viruses, plant viruses, and bacteriophages, that have been adopted as building blocks and supra-molecular templates in nanotechnology. VNPs demonstrate the dynamic, monodisperse, polyvalent, and symmetrical architectures which represent examples of such biological templates. These programmable scaffolds have been exploited for genetic and chemical manipulation for displaying of targeted moieties together with encapsulation of various payloads for diagnosis or therapeutic intervention. The drug delivery system based on VNPs offer diverse advantages over synthetic nanoparticles, including biocompatibility, biodegradability, water solubility, and high uptake capability. Here we summarize the recent progress of VNPs especially as targeted anticancer vehicles from the encapsulation and surface modification mechanisms, involved viruses and VNPs, to their application potentials.

Clinically Explored Virus-Based Therapies for the Treatment of Recurrent High-Grade Glioma in Adults

As new treatment modalities are being explored in neuro-oncology, viruses are emerging as a promising class of therapeutics. Virotherapy consists of the introduction of either wild-type or engineered viruses to the site of disease, where they exert an antitumor effect. These viruses can either be non-lytic, in which case they are used to deliver gene therapy, or lytic, which induces tumor cell lysis and subsequent host immunologic response. Replication-competent viruses can then go on to further infect and lyse neighboring glioma cells. This treatment paradigm is being explored extensively in both preclinical and clinical studies for a variety of indications. Virus-based therapies are advantageous due to the natural susceptibility of glioma cells to viral infection, which improves therapeutic selectivity. Furthermore, lytic viruses expose glioma antigens to the host immune system and subsequently stimulate an immune response that specifically targets tumor cells. This review surveys the current landscape of oncolytic virotherapy clinical trials in high-grade glioma, summarizes preclinical experiences, identifies challenges associated with this modality across multiple trials, and highlights the potential to integrate this therapeutic strategy into promising combinatory approaches.

Synthetic and systems biology principles in the design of programmable oncolytic virus immunotherapies for glioblastoma

Oncolytic viruses (OVs) are a class of immunotherapeutic agents with promising preclinical results for the treatment of glioblastoma (GBM) but have shown limited success in recent clinical trials. Advanced bioengineering principles from disciplines such as synthetic and systems biology are needed to overcome the current challenges faced in developing effective OV-based immunotherapies for GBMs, including off-target effects and poor clinical responses. Synthetic biology is an emerging field that focuses on the development of synthetic DNA constructs that encode networks of genes and proteins (synthetic genetic circuits) to perform novel functions, whereas systems biology is an analytical framework that enables the study of complex interactions between host pathways and these synthetic genetic circuits. In this review, the authors summarize synthetic and systems biology concepts for developing programmable, logic-based OVs to treat GBMs. Programmable OVs can increase selectivity for tumor cells and enhance the local immunological response using synthetic genetic circuits. The authors discuss key principles for developing programmable OV-based immunotherapies, including how to 1) select an appropriate chassis, a vector that carries a synthetic genetic circuit, and 2) design a synthetic genetic circuit that can be programmed to sense key signals in the GBM microenvironment and trigger release of a therapeutic payload. To illustrate these principles, some original laboratory data are included, highlighting the need for systems biology studies, as well as some preliminary network analyses in preparation for synthetic biology applications. Examples from the literature of state-of-the-art synthetic genetic circuits that can be packaged into leading candidate OV chassis are also surveyed and discussed.

Delta-24 adenoviral therapy for glioblastoma: evolution from the bench to bedside and future considerations

Delta-24-based oncolytic viruses are conditional replication adenoviruses developed to selectively infect and replicate in retinoblastoma 1 (Rb)-deficient cancer cells but not normal cell with intact Rb1 pathways. Over the years, there has been a significant evolution in the design of Delta-24 based on a better understanding of the underlying basis for infection, replication, and spread within cancer. One example is the development of Delta-24-RGD (DNX-2401), where the arginine-glycine-aspartate (RGD) domain enhances the infectivity of Delta-24 for cancer cells. DNX-2401 demonstrated objective biological and clinical responses during a phase I window of opportunity clinical trial for recurrent human glioblastoma. In long-term responders (> 3 years), there was evidence of immune infiltration (T cells and macrophages) into the tumor microenvironment with minimal toxicity. Although more in-depth analysis and phase III studies are pending, these results indicate that Delta-24-based adenovirus therapy may induce an antitumor response in glioblastoma, resulting in long-term antitumor immune response. In this review, the authors discuss the preclinical and clinical development of Delta-24 oncolytic adenoviral therapy for glioblastoma and describe structural improvements to Delta-24 that have enhanced its efficacy in vivo. They also highlight ongoing research that attempts to address the remaining obstacles limiting efficacy of Delta-24 adenovirus therapy for glioblastoma.

Oncolytic Viruses and Immune Checkpoint Inhibitors: Preclinical Developments to Clinical Trials

Immuno-oncology (IO) has been an active area of oncology research. Following US FDA approval of the first immune checkpoint inhibitor (ICI), ipilimumab (human IgG1 k anti-CTLA-4 monoclonal antibody), in 2011, and of the first oncolytic virus, Imlygic (talimogene laherparepvec), in 2015, there has been renewed interest in IO. In the past decade, ICIs have changed the treatment paradigm for many cancers by enabling better therapeutic control, resuming immune surveillance, suppressing tumor immunosuppression, and restoring antitumor immune function. However, ICI therapies are effective only in a small subset of patients and show limited therapeutic potential due to their inability to demonstrate efficacy in 'cold' or unresponsive tumor microenvironments (TMEs). Relatedly, oncolytic viruses (OVs) have been shown to induce antitumor immune responses, augment the efficacy of existing cancer treatments, and reform unresponsive TME to turn 'cold' tumors 'hot,' increasing their susceptibility to checkpoint blockade immunotherapies. For this reason, OVs serve as ideal complements to ICIs, and multiple preclinical studies and clinical trials are demonstrating their combined therapeutic efficacy. This review will discuss the merits and limitations of OVs and ICIs as monotherapy then progress onto the preclinical rationale and the results of clinical trials of key combination therapies.