Optimizing Oncolytic Viral Design to Enhance Antitumor Efficacy: Progress and Challenges

A review exploring the fusion of oncolytic viruses and cancer immunotherapy: An innovative strategy in the realm of cancer treatment

Oncolytic viruses (OVs) are increasingly recognized as potent tools in cancer therapy, effectively targeting and eradicating oncogenic conditions while sparing healthy cells. They enhance antitumor immunity by triggering various immune responses throughout the cancer cycle. Genetically engineered OVs swiftly destroy cancerous tissues and activate the immune system by releasing soluble antigens like danger signals and interferons. Their ability to stimulate both innate and adaptive immunity makes them particularly attractive in cancer immunotherapy. Recent advancements involve combining OVs with other immune therapies, yielding promising results. Transgenic OVs, designed to enhance immunostimulation and specifically target cancer cells, further improve immune responses. This review highlights the intrinsic mechanisms of OVs and underscores their synergistic potential with other immunotherapies. It also proposes strategies for optimizing armed OVs to bolster immunity against tumors.

Therapeutic bacteria and viruses to combat cancer: double-edged sword in cancer therapy: new insights for future

Cancer, ranked as the second leading cause of mortality worldwide, leads to the death of approximately seven million people annually, establishing itself as one of the most significant health challenges globally. The discovery and identification of new anti-cancer drugs that kill or inactivate cancer cells without harming normal and healthy cells and reduce adverse effects on the immune system is a potential challenge in medicine and a fundamental goal in Many studies. Therapeutic bacteria and viruses have become a dual-faceted instrument in cancer therapy. They provide a promising avenue for cancer treatment, but at the same time, they also create significant obstacles and complications that contribute to cancer growth and development. This review article explores the role of bacteria and viruses in cancer treatment, examining their potential benefits and drawbacks. By amalgamating established knowledge and perspectives, this review offers an in-depth examination of the present research landscape within this domain and identifies avenues for future investigation.

Systemic delivery of glycosylated-PEG-masked oncolytic virus enhances targeting of antitumor immuno-virotherapy and modulates T and NK cell infiltration

Rationale: Immuno-virotherapy has emerged as a promising approach for cancer treatment, as it directly and cytotoxically eliminates tumors with systemic immune stimulation. However, the clinical efficacy of this approach remains limited by inappropriate delivery routes, robust antiviral responses, and the tumor immunosuppressive microenvironment. Methods: To address these challenges, we propose a surface engineering strategy that masks oncolytic herpes simplex virus (oHSV) with a galactose-polyethylene-glycol (PEG) polymer chain to minimize host antiviral responses and selectively targets tumors by limiting exposure to circulation upon systemic administration. We evaluated the antitumor efficacy of glycosylated-PEG-oHSV by examining tumor growth in animal models and analyzing tumor-infiltrating CD8+T cells and NK cells in the tumor microenvironment (TME). To assess the neutralizing antibody levels after systemic administration of glycosylated-PEG-oHSV, we utilized a mouse model and measured oHSV-specific IgG. Results: We demonstrate that the glycosylated-PEG modified oHSV does not affect the replication of oHSV yet exhibits high specificity to the asialoglycoprotein receptor (ASGPR) overexpressed in hepatocellular carcinoma cells. This results in selectively targeting cancer cells and deep penetration into tumors while avoiding spreading into the brain. Our approach also effectively reduces oHSV-specific neutralizing antibody levels to mitigate host antiviral immune response. Notably, our glycosylated-PEG-oHSV alleviates the immunosuppressive microenvironment within tumors by reducing regulatory T cells, augmenting the infiltration of activated CD8+T cells and NK cells with increasing release of anti-tumor cytokines, to impede tumor progression. Conclusion: Our findings offer a widely applicable and universal strategy to enhance cancer immuno-virotherapy through systemic administration of non-genetically engineered oncolytic viruses. This approach has the potential to overcome the limitations of current immune-virotherapy strategies and may improve clinical outcomes for cancer patients.

A new strategy for treating colorectal cancer: Regulating the influence of intestinal flora and oncolytic virus on interferon

Colorectal cancer (CRC) has the third highest incidence and the second highest mortality in the world, which seriously affects human health, while current treatments methods for CRC, including systemic therapy, preoperative radiotherapy, and surgical local excision, still have poor survival rates for patients with metastatic disease, making it critical to develop new strategies for treating CRC. In this article, we found that the gut microbiota can modulate the signaling pathways of cancer cells through direct contact with tumor cells, generate inflammatory responses and oxidative stress through interactions between the innate and adaptive immune systems, and produce diverse metabolic combinations to trigger specific immune responses and promote the initiation of systemic type I interferon (IFN-I) and anti-viral immunity. In addition, oncolytic virus-mediated immunotherapy for regulating oncolytic virus can directly lyse tumor cells, induce the immune activity of the body, interact with interferon, inhibit the anti-viral effect of IFN-I, and enhance the anti-tumor effect of IFN-II. Interferon plays an important role in the anti-tumor process. We put forward that exploring the effects of intestinal flora and oncolytic virus on interferon to treat CRC is a promising therapeutic option.

Oncolytic Virus Engineering and Utilizations: Cancer Immunotherapy Perspective

Oncolytic viruses have positively impacted cancer immunotherapy over the past 20 years. Both natural and genetically modified viruses have shown promising results in treating various cancers. Various regulatory authorities worldwide have approved four commercial oncolytic viruses, and more are being developed to overcome this limitation and obtain better anti-tumor responses in clinical trials at various stages. Faster advancements in translating research into the commercialization of cancer immunotherapy and a comprehensive understanding of the modification strategies will widen the current knowledge of future technologies related to the development of oncolytic viruses. In this review, we discuss the strategies of virus engineering and the progress of clinical trials to achieve virotherapeutics.

Oncolytic virotherapy evolved into the fourth generation as tumor immunotherapy

BACKGROUND

Oncolytic virotherapy (OVT) is a promising anti-tumor modality that utilizes oncolytic viruses (OVs) to preferentially attack cancers rather than normal tissues. With the understanding particularly in the characteristics of viruses and tumor cells, numerous innovative OVs have been engineered to conquer cancers, such as Talimogene Laherparepvec (T-VEC) and tasadenoturev (DNX-2401). However, the therapeutic safety and efficacy must be further optimized and balanced to ensure the superior safe and efficient OVT in clinics, and reasonable combination therapy strategies are also important challenges worthy to be explored.

MAIN BODY

Here we provided a critical review of the development history and status of OVT, emphasizing the mechanisms of enhancing both safety and efficacy. We propose that oncolytic virotherapy has evolved into the fourth generation as tumor immunotherapy. Particularly, to arouse T cells by designing OVs expressing bi-specific T cell activator (BiTA) is a promising strategy of killing two birds with one stone. Amazing combination of therapeutic strategies of OVs and immune cells confers immense potential for managing cancers. Moreover, the attractive preclinical OVT addressed recently, and the OVT in clinical trials were systematically reviewed.

CONCLUSION

OVs, which are advancing into clinical trials, are being envisioned as the frontier clinical anti-tumor agents coming soon.

Attenuated Dengue virus PV001-DV induces oncolytic tumor cell death and potent immune responses

BACKGROUND

Viral therapies developed for cancer treatment have classically prioritized direct oncolytic effects over their immune activating properties. However, recent clinical insights have challenged this longstanding prioritization and have shifted the focus to more immune-based mechanisms. Through the potential utilization of novel, inherently immune-stimulating, oncotropic viruses there is a therapeutic opportunity to improve anti-tumor outcomes through virus-mediated immune activation. PV001-DV is an attenuated strain of Dengue virus (DEN-1 #45AZ5) with a favorable clinical safety profile that also maintains the potent immune stimulatory properties characterstic of Dengue virus infection.

METHODS

In this study, we utilized in vitro tumor killing and immune multiplex assays to examine the anti-tumor effects of PV001-DV as a potential novel cancer immunotherapy.

RESULTS

In vitro assays demonstrated that PV001-DV possesses the ability to directly kill human melanoma cells lines as well as patient melanoma tissue ex vivo. Importantly, further work demonstrated that, when patient peripheral blood mononuclear cells (PBMCs) were exposed to PV001-DV, a substantial induction in the production of apoptotic factors and immunostimulatory cytokines was detected. When tumor cells were cultured with the resulting soluble mediators from these PBMCs, rapid cell death of melanoma and breast cancer cell lines was observed. These soluble mediators also increased dengue virus binding ligands and immune checkpoint receptor, PD-L1 expression.

CONCLUSIONS

The direct in vitro tumor-killing and immune-mediated tumor cytotoxicity facilitated by PV001-DV contributes support of its upcoming clinical evaluation in patients with advanced melanoma who have failed prior therapy.

The Clinical Advances of Oncolytic Viruses in Cancer Immunotherapy

A promising future for oncology treatment has been brought about by the emergence of a novel approach utilizing oncolytic viruses in cancer immunotherapy. Oncolytic viruses are viruses that have been exploited genetically to assault malignant cells and activate a robust immune response. Several techniques have been developed to endow viruses with an oncolytic activity through genetic engineering. For instance, redirection capsid modification, stimulation of anti-neoplastic immune response, and genetically arming viruses with cytokines such as IL-12. Oncolytic viral clinical outcomes are sought after, particularly in more advanced cancers. The effectiveness and safety profile of the oncolytic virus in clinical studies with or without the combination of standard treatment (chemotherapy, radiotherapy, or primary excision) has been assessed using response evaluation criteria in solid tumors (RECIST). This review will comprehensively outline the most recent clinical applications and provide the results from various phases of clinical trials in a variety of cancers in the latest published literature.

An oncolytic poxvirus encoding hNIS, shows anti-tumor efficacy and allows tumor imaging in a liver cancer model

Oncolytic viruses (OVs) are live viruses that can selectively replicate in cancer cells. We have engineered an OV (CF33) to make it cancer-selective through the deletion of its J2R (thymidine kinase) gene. Additionally, this virus has been armed with a reporter gene, human sodium iodide symporter (hNIS), to facilitate non-invasive imaging of tumors using positron emission tomography (PET). In this study we evaluated the oncolytic properties of the virus (CF33-hNIS) in liver cancer model, and its usefulness in tumor imaging. The virus was found to efficiently kill liver cancer cells and the virus-mediated cell death exhibited characteristics of immunogenic death based on the analysis of 3 damage associate molecular patterns (DAMPs): calreticulin, ATP and HMGB1. Furthermore, local or systemic administration of a single dose of the virus showed anti-tumor efficacy against a liver cancer xenograft model in mice and significantly increased survival of treated mice. Lastly, PET scanning was performed following injection of the radioisotope I-124, for imaging of tumors, and a single dose of virus as low as 1E03 pfu, administered intratumorally (I.T.) or intravenously (I.V.), allowed for PET imaging of tumors. In conclusion, CF33-hNIS is safe and effective in controlling human tumor xenografts in nude mice, and it also facilitates non-invasive imaging of tumors.

Engineering Rapalog-Inducible Genetic Switches Based on Split-T7 Polymerase to Regulate Oncolytic Virus-Driven Production of Tumour-Localized IL-12 for Anti-Cancer Immunotherapy

The approval of different cytokines as anti-neoplastic agents has been challenged by dose-limiting toxicities. Although reducing dose levels affords improved tolerability, efficacy is precluded at these suboptimal doses. Strategies combining cytokines with oncolytic viruses have proven to elicit potent survival benefits in vivo, despite promoting rapid clearance of the oncolytic virus itself. Herein, we developed an inducible expression system based on a Split-T7 RNA polymerase for oncolytic poxviruses to regulate the spatial and temporal expression of a beneficial transgene. This expression system utilizes approved anti-neoplastic rapamycin analogues for transgene induction. This treatment regimen thus offers a triple anti-tumour effect through the oncolytic virus, the induced transgene, and the pharmacologic inducer itself. More specifically, we designed our therapeutic transgene by fusing a tumour-targeting chlorotoxin (CLTX) peptide to interleukin-12 (IL-12), and demonstrated that the constructs were functional and cancer-selective. We next encoded this construct into the oncolytic vaccinia virus strain Copenhagen (VV-iIL-12mCLTX), and were able to demonstrate significantly improved survival in multiple syngeneic murine tumour models through both localized and systemic virus administration, in combination with rapalogs. In summary, our findings demonstrate that rapalog-inducible genetic switches based on Split-T7 polymerase allow for regulation of the oncolytic virus-driven production of tumour-localized IL-12 for improved anti-cancer immunotherapy.

Development of Adenovirus Containing Liposomes Produced by Extrusion vs. Homogenization: A Comparison for Scale-Up Purposes

Adenovirus (Ad) is a widely studied viral vector for cancer therapy as it can be engineered to cause selective lysis of cancer cells. However, Ad delivery is limited in treating cancers that do not have coxsackievirus and adenovirus receptors (CAR). To overcome this challenge, Ad-encapsulated liposomes were developed that enhance the delivery of Ads and increase therapeutic efficacy. Cationic empty liposomes were manufactured first, to which an anionic Ad were added, which resulted in encapsulated Ad liposomes through charge interaction. Optimization of the liposome formula was carried out with series of formulation variables experiments using an extrusion process, which is ideal for laboratory-scale small batches. Later, the optimized formulation was manufactured with a homogenization technique-A high shear rotor-stator blending, that is ideal for large-scale manufacturing and is in compliance with Good Manufacturing Practices (GMP). Comparative in vitro transduction, physicochemical characterization, long-term storage stability at different temperature conditions, and in vivo animal studies were performed. Ad encapsulated liposomes transduced CAR deficient cells 100-fold more efficiently than the unencapsulated Ad (p ≤ 0.0001) in vitro, and 4-fold higher in tumors injected in nude mice in vivo. Both extrusion and homogenization performed similarly-with equivalent in vitro and in vivo transduction efficiencies, physicochemical characterization, and long-term storage stability. Thus, two Ad encapsulated liposomes preparation methods used herein, i.e., extrusion vs. homogenization were equivalent in terms of enhanced Ad performance and long-term storage stability; this will, hopefully, facilitate translation to the clinic.

Intratumoral delivery of a novel oncolytic adenovirus encoding human antibody against PD-1 elicits enhanced antitumor efficacy

To date, diverse combination therapies with immune checkpoint inhibitors (ICIs), particularly oncolytic virotherapy, have demonstrated enhanced therapeutic outcomes in cancer treatment. However, high pre-existing immunity against the widely used adenovirus human serotype 5 (AdHu5) limits its extensive clinical application. In this study, we constructed an innovative oncolytic virus (OV) based on a chimpanzee adenoviral vector with low seropositivity in the human population, named AdC68-spE1A-αPD-1, which endows the parental OV (AdC68-spE1A-ΔE3) with the ability to express full-length anti-human programmed cell death-1 monoclonal antibody (αPD-1). In vitro studies indicated that the AdC68-spE1A-αPD-1 retained parental oncolytic capacity, and αPD-1 was efficiently secreted from the infected tumor cells and bound exclusively to human PD-1 (hPD-1) protein. In vivo, intratumoral treatment with AdC68-spE1A-αPD-1 resulted in significant tumor suppression, prolonged overall survival, and enhanced systemic antitumor memory response in an hPD-1 knockin mouse tumor model. This strategy outperformed the unarmed OV and was comparable with combination therapy with intratumoral injection of AdC68-spE1A-ΔE3 and systemic administration of commercial αPD-1. In summary, AdC68-spE1A-αPD-1 is a cost-effective approach with potential clinical applications. ‬‬‬‬

Oncolytic Activity of Wild-type Newcastle Disease Virus HK84 Against Hepatocellular Carcinoma Associated with Activation of Type I Interferon Signaling

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is listed as one of the most common causes of cancer-related death. Oncolytic therapy has become a promising treatment because of novel immunotherapies and gene editing technology, but biosafety concerns remain the biggest limitation for clinical application. We studied the the antitumor activity and biosafety of the wild-type Newcastle disease virus HK84 strain (NDV/HK84) and 10 other NDV strains.

METHODS

Cell proliferation and apoptosis were determined by cell counting Kit-8 and fluorescein isothiocyanate Annexin V apoptosis assays. Colony formation, wound healing, and a xenograft mouse model were used to evaluate in vivo and in vitro oncolytic effectiveness. The safety of NDV/HK84 was tested in nude mice by an in vivo luciferase imaging system. The replication kinetics of NDV/HK84 in normal tissues and tumors were evaluated by infectious-dose assays in eggs. RNA sequencing analysis was performed to explore NDV/HK84 activity and was validated by quantitative real-time PCR.

RESULTS

The cell counting Kit-8 assays of viability found that the oncolytic activity of the NDV strains differed with the multiplicity of infection (MOI). At an MOI of 20, the oncolytic activity of all NDV strains except the DK/JX/21358/08 strain was >80%. The oncolytic activities of the NDV/HK84 and DK/JX/8224/04 strains were >80% at both MOI=20 and MOI=2. Only NDV/HK84 had >80% oncolytic activities at both MOI=20 and MOI=2. We chose NDV/HK84 as the candidate virus to test the oncolytic effect of NDV in HCC in the in vitro and in vivo experiments. NDV/HK84 killed human SK-HEP-1 HCC cells without affecting healthy cells.

CONCLUSIONS

Intratumor infection with NDV/HK84 strains compared with vehicle controls or positive controls indicated that NDV/HK84 strain specifically inhibited HCC without affecting healthy mice. High-throughput RNA sequencing showed that the oncolytic activity of NDV/HK84 was dependent on the activation of type I interferon signaling.

Engineering strategies to enhance oncolytic viruses in cancer immunotherapy

Oncolytic viruses (OVs) are emerging as potentially useful platforms in treatment methods for patients with tumors. They preferentially target and kill tumor cells, leaving healthy cells unharmed. In addition to direct oncolysis, the essential and attractive aspect of oncolytic virotherapy is based on the intrinsic induction of both innate and adaptive immune responses. To further augment this efficacious response, OVs have been genetically engineered to express immune regulators that enhance or restore antitumor immunity. Recently, combinations of OVs with other immunotherapies, such as immune checkpoint inhibitors (ICIs), chimeric antigen receptors (CARs), antigen-specific T-cell receptors (TCRs) and autologous tumor-infiltrating lymphocytes (TILs), have led to promising progress in cancer treatment. This review summarizes the intrinsic mechanisms of OVs, describes the optimization strategies for using armed OVs to enhance the effects of antitumor immunity and highlights rational combinations of OVs with other immunotherapies in recent preclinical and clinical studies.

Systemic Delivery of mLIGHT-Armed Myxoma Virus Is Therapeutic for Later-Stage Syngeneic Murine Lung Metastatic Osteosarcoma

Cancers that metastasize to the lungs represent a major challenge in both basic and clinical cancer research. Oncolytic viruses are newly emerging options but successful delivery and choice of appropriate therapeutic armings are two critical issues. Using an immunocompetent murine K7M2-luc lung metastases model, the efficacy of MYXV armed with murine LIGHT (TNFSF14/CD258) expressed under virus-specific early/late promoter was tested in an advanced later-stage disease K7M2-luc model. Results in this model show that mLIGHT-armed MYXV, delivered systemically using ex vivo pre-loaded PBMCs as carrier cells, reduced tumor burden and increased median survival time. In vitro, when comparing direct infection of K7M2-luc cancer cells with free MYXV vs. PBMC-loaded virus, vMyx-mLIGHT/PBMCs also demonstrated greater cytotoxic capacity against the K7M2 cancer cell targets. In vivo, systemically delivered vMyx-mLIGHT/PBMCs increased viral reporter transgene expression levels both in the periphery and in lung tumors compared to unarmed MYXV, in a tumor- and transgene-dependent fashion. We conclude that vMyx-mLIGHT, especially when delivered using PBMC carrier cells, represents a new potential therapeutic strategy for solid cancers that metastasize to the lung.

The oncolytic virus VT09X optimizes immune checkpoint therapy in low immunogenic melanoma

Tumors with a low level of pre-existing immune cell infiltration respond poorly to immune checkpoint therapies. Oncolytic viruses optimize immunotherapies by modulating the tumor microenvironment and affecting multiple steps in the cancer-immunity cycle, making them an attractive agent for combination strategies. We engineered an HSV-1-based oncolytic virus and investigated its antitumor effects in combination with the marketed PD-1 antibody Keytruda (pembrolizumab) in hPD-1 knock-in mice bearing non-immunogenic B16-F10 melanoma. Our results showed enhanced CD8⁺ and CD4⁺ T cell infiltration, IFN-γ secretion and PD-L1 expression in tumors, subsequently leading to the prolonged overall survival of mice. Systemic changes in lymphocyte cell proportions were also observed in the peripheral blood. In summary, these findings provide evidence that oncolytic viruses can be engineered as a potential platform for combination therapies, especially to treat tumors that are poorly responsive to immune checkpoint therapy.

Development of oncolytic viruses for cancer therapy

Oncolytic virotherapy is a therapeutic approach that uses replication-competent viruses to kill cancers. The ability of oncolytic viruses to selectively replicate in cancer cells leads to direct cell lysis and induction of anticancer immune response. Like other anticancer therapies, oncolytic virotherapy has several limitations such as viral delivery to the target, penetration into the tumor mass, and antiviral immune responses. This review provides an insight into the different characteristics of oncolytic viruses (natural and genetically modified) that contribute to effective applications of oncolytic virotherapy in preclinical and clinical trials, and strategies to overcome the limitations. The potential of oncolytic virotherapy combining with other conventional treatments or cancer immunotherapies involving immune checkpoint inhibitors and CAR-T therapy could form part of future multimodality treatment strategies.

Oncolytic Viruses: Newest Frontier for Cancer Immunotherapy

Cancer remains a leading cause of death worldwide. Despite many signs of progress, currently available cancer treatments often do not provide desired outcomes for too many cancers. Therefore, newer and more effective therapeutic approaches are needed. Oncolytic viruses (OVs) have emerged as a novel cancer treatment modality, which selectively targets and kills cancer cells while sparing normal ones. In the past several decades, many different OV candidates have been developed and tested in both laboratory settings as well as in cancer patient clinical trials. Many approaches have been taken to overcome the limitations of OVs, including engineering OVs to selectively activate anti-tumor immune responses. However, newer approaches like the combination of OVs with current immunotherapies to convert "immune-cold" tumors to "immune-hot" will almost certainly improve the potency of OVs. Here, we discuss strategies that are explored to further improve oncolytic virotherapy.

The application of oncolytic viruses in cancer therapy

Oncolytic therapy is a treatment method used to directly combat tumor cells by modifying the genes of naturally occurring low pathogenic viruses to form "rhizobia" virus. By taking the advantage of abnormal signal pathways in cancer cells, it selectively replicates in tumor cells leading to tumor cell lysis and death. At present, clinical studies widely employ biomolecular technology to transform oncolytic viruses to exert stronger oncolytic effects and reduce their adverse reactions. This review summarizes the current progresses and the molecular mechanism of oncolytic viruses towards tumor treatment and management.

Enhanced anti-tumor response elicited by a novel oncolytic HSV-1 engineered with an anti-PD-1 antibody

Oncolytic viruses as cancer vaccines modulate the tumor microenvironment and act synergistically with immune checkpoint inhibitors to overcome resistance. Taking advantage of the loading capacity for exogenous genes, we generated a recombinant herpes simplex virus type 1 (HSV-1), HSV-aPD-1, carrying a full-length humanized anti-PD-1 monoclonal antibody (anti-PD-1 mAb) that replicates and expresses anti-PD-1 mAbs in tumor cells in vitro and in vivo. Its anti-tumor effect was assessed in human PD-1 knock-in mice by analyzing tumor inhibition, cell populations and RNA expression in tumors, and serum cytokine levels. Enhanced anti-tumor immune responses and T-cell infiltration were induced by HSV-aPD-1 compared with unloaded virus or anti-PD-1 therapy in both MC38 and B16-F10 models, resulting in improved treatment efficacy in the latter. Moreover, compared with unloaded HSV-1 or HSV-1 loaded with GM-CSF/IL-2 combined with anti-PD-1 mAbs, HSV-aPD-1 displayed similar therapeutic control of tumor growth. Finally, tumor RNAseq analysis in the B16-F10 model showed upregulated IFN pathway and antigen processing and presentation genes, and downregulated angiogenesis and cell adhesion genes, which all contribute to tumor inhibition. These findings indicate the clinical potential of HSV-aPD-1 as monotherapy or combination therapy, especially in tumors resistant to immune checkpoint inhibitors.

Oncolytic viruses as a promising therapeutic strategy for hematological malignancies

The incidence of hematological malignancies such as multiple myeloma, leukemia, and lymphoma has increased over time. Although bone marrow transplantation, immunotherapy and chemotherapy have led to significant improvements in efficacy, poor prognosis in elderly patients, recurrence and high mortality among hematological malignancies remain major challenges, and innovative therapeutic strategies should be explored. Besides directly lyse tumor cells, oncolytic viruses can activate immune responses or be engineered to express therapeutic factors to increase antitumor efficacy, and have gradually been recognized as an appealing approach for fighting cancers. An increasing number of studies have applied oncolytic viruses in hematological malignancies and made progress. In particular, strategies combining immunotherapy and oncolytic virotherapy are emerging. Various phase I clinical trials of oncolytic reovirus with lenalidomide or programmed death 1(PD-1) immune checkpoint inhibitors in multiple myeloma are ongoing. Moreover, preclinical studies of combinations with chimeric antigen receptor T (CAR-T) cells are underway. Thus, oncolytic virotherapy is expected to be a promising approach to cure hematological malignancies. This review summarizes progress in oncolytic virus research in hematological malignancies. After briefly reviewing the development and oncolytic mechanism of oncolytic viruses, we focus on delivery methods of oncolytic viruses, especially systemic delivery that is suitable for hematological tumors. We then discuss the main types of oncolytic viruses applied for hematological malignancies and related clinical trials. In addition, we present several ways to improve the antitumor efficacy of oncolytic viruses. Finally, we discuss current challenges and provide suggestions for future studies.

Combination Therapy of Novel Oncolytic Adenovirus with Anti-PD1 Resulted in Enhanced Anti-Cancer Effect in Syngeneic Immunocompetent Melanoma Mouse Model

Malignant melanoma, an aggressive form of skin cancer, has a low five-year survival rate in patients with advanced disease. Immunotherapy represents a promising approach to improve survival rates among patients at advanced stage. Herein, the aim of the study was to design and produce, by using engineering tools, a novel oncolytic adenovirus AdV-D24- inducible co-stimulator ligand (ICOSL)-CD40L expressing potent co-stimulatory molecules enhancing clinical efficacy through the modulation of anti-cancer immune responses. Firstly, we demonstrated the vector's identity and genetic stability by restriction enzyme assay and sequencing, then, by performing in vitro and in vivo pre-clinical studies we explored the anti-cancer efficacy of the virus alone or in combination with anti PD-1 inhibitor in human melanoma cell lines, i.e., MUG Mel-1 and MUG Mel-2, and in immunocompetent C57BL/6 melanoma B16V mouse model. We showed that both monotherapy and combination approaches exhibit enhanced anti-cancer ability and immunogenic cell death in in vitro settings. Furthermore, AdV-D24-ICOSL-CD40L combined with anti PD-1 revealed a fall in tumor volume and 100% survival in in vivo context, thus suggesting enhanced efficacy and survival via complementary anti-cancer properties of those agents in melanoma therapy. Collectively, the novel oncolytic vector AdV-D24-ICOSL-CD40L alone or in combination with anticancer drugs, such as check point inhibitors, may open novel therapeutic perspectives for the treatment of melanoma.

Talimogene Laherparepvec (T-VEC): An Intralesional Cancer Immunotherapy for Advanced Melanoma

Simple Summary

Talimogene laherparepvec (T-VEC; IMLYGIC®, Amgen Inc.) is the first oncolytic viral immunotherapy to be approved for the local treatment of unresectable metastatic stage IIIB/C–IVM1a melanoma. Its direct intratumoral injection aim to trigger local and systemic immunologic responses leading to tumor cell lysis, followed by release of tumor-derived antigens and subsequent activation of tumor-specific effector T-cells. Its approval has fueled the interest to study its possible sinergy with other immunotherapeutics in preclinical models as well as in clinical contextes. In fact, it has been shown that intratumoral administration of this immunostimulatory agent successfully synergizes with immune checkpoint inhibitors. The objectives of this review are to resume the current state of the art of T-VEC treatment when used in monotherapy or in combination with immune checkpoint inhibitors, describing the strong rationale of its development, the adverse events of interest and the clinical outcome in selected patient’s populations.

Abstract

Direct intralesional injection of specific or even generic agents, has been proposed over the years as cancer immunotherapy, in order to treat cutaneous or subcutaneous metastasis. Such treatments usually induce an effective control of disease in injected lesions, but only occasionally were able to demonstrate a systemic abscopal effect on distant metastases. The usual availability of tissue for basic and translational research is a plus in utilizing this approach, which has been used in primis for the treatment of locally advanced melanoma. Melanoma is an immunogenic tumor that could often spread superficially causing in-transit metastasis and involving draining lymph nodes, being an interesting model to study new drugs with different modality of administration from normal available routes. Talimogene laherperepvec (T-VEC) is an injectable modified oncolytic herpes virus being developed for intratumoral injection, that produces granulocyte-macrophage colony-stimulating factor (GM-CSF) and enhances local and systemic antitumor immune responses. After infection, selected viral replication happens in tumor cells leading to tumor cell lysis and activating a specific T-cell driven immune response. For this reason, a probable synergistic effect with immune checkpoints inhibition have been described. Pre-clinical studies in melanoma confirmed that T-VEC preferentially infects melanoma cells and exerts its antitumor activity through directly mediating cell death and by augmenting local and even distant immune responses. T-VEC has been assessed in monotherapy in Phase II and III clinical trials demonstrating a tolerable side-effect profile, a promising efficacy in both injected and uninjected lesions, but a mild effect at a systemic level. In fact, despite improved local disease control and a trend toward superior overall survival in respect to the comparator GM-CSF (which was injected subcutaneously daily for two weeks), responses as a single agent therapy have been uncommon in patients with visceral metastases. For this reason, T-VEC is currently being evaluated in combinations with other immune checkpoint inhibitors such as ipilimumab and pembrolizumab, with interesting confirmation of activity even systemically.

Oncolytic Adenoviruses for Cancer Therapy

Many immuno-therapeutic strategies are currently being developed to fight cancer. In this scenario, oncolytic adenoviruses (Onc.Ads) have an interesting role for their peculiar tumor selectivity, safety, and transgene-delivery capability. The major strength of the Onc.Ads is the extraordinary immunogenicity that leads to a strong T-cell response, which, together with the possibility of the delivery of a therapeutic transgene, could be more effective than current strategies. In this review, we travel in the adenovirus (Ads) and Onc.Ads world, focusing on a variety of strategies that can enhance Onc.Ads antitumoral efficacy, passing through tumor microenvironment modulation. Onc.Ads-based therapeutic strategies constitute additional weapons in the fight against cancer and appear to potentiate conventional and immune checkpoint inhibitors (ICIs)-based therapies leading to a promising scenario.

The Strategy of Conditionally Replicating Adenovirus-Mediated PreS2 Mini-Antibody Expression Has Dual Effects of Inhibiting HBV Infection and Preventing Hepatocellular Carcinoma

Aim

To investigate the inhibitory effect of hepatitis B virus (HBV) preS2 mini-antibody (mPreS2) against HBV infection, HBV-associated liver injury and HBV-associated hepatic carcinogenesis.

Methods

A recombinant adenovirus vector with the human survivin promoter and mPreS2 gene, Ad5SVP-mPreS2, was constructed. Fluorescence microscopy examination and TCID 50 analysis were utilized to determine the specific proliferation of recombinant adenovirus in liver cancer cells. Western blot analysis was used to determine the mPreS2 expression levels. Enzyme-linked immunosorbent assay (ELISA) was used to examine HBsAg levels to evaluate the inhibitory effect of mPreS2 against HBV infection. The protective effects on hepatic function and preventive effects against hepatic carcinogenesis of Ad5SVP-mPreS2 were studied in diethylnitrosamine (DEN)-treated HBV transgenic Imprinting Control Region mice.

Results

The recombinant adenovirus regulated by the human survivin promoter proliferated exclusively in liver cancer cells rather than normal liver cells. The expression levels of mPreS2 were increased in liver cancer cells compared with normal liver cells, and mPreS2 could be used to recognize liver cells from HBV transgenic mice. ELISA showed that HBsAg levels were decreased in the group treated with Ad5SVP-mPreS2. Ad5SVP-mPreS2 had a protective effect on hepatic function in a DEN-induced liver injury model because of lower serum levels of alanine transaminase and aspartate transaminase. Additionally, HBV transgenic mice treated with Ad5SVP-mPreS2 had fewer and smaller cancerous nodes after induction with DEN than untreated mice.

Conclusion

Conditionally replicating adenovirus-mediated mPreS2 expression inhibited HBV infection and had an inhibitory effect on liver injury and hepatocellular carcinogenesis in HBV transgenic mice.

Mesenchymal stem cells and oncolytic viruses: joining forces against cancer

The development of oncolytic viruses (OVs) has increased significantly in the past 20 years, with many candidates entering clinical trials and three of them receiving approval for some indications. Recently, OVs have also gathered interest as candidates to use in combination with immunotherapies for cancer due to their immunogenic properties, which include immunogenic cell death and the possibility to carry therapeutic transgenes in their genomes. OVs transform non-immunogenic 'cold' tumors into inflamed immunogenic 'hot' tumors, where immunotherapies show the highest efficacy. However, in monotherapy or in combination with immunotherapy, OVs face numerous challenges that limit their successful application, in particular upon systemic administration, such as liver sequestration, neutralizing interactions in blood, physical barriers to infection, and fast clearance by the immune system. In this regard, the use of mesenchymal stem cells (MSCs) as cells carrier for OV delivery addresses many of these obstacles acting as virus carriers and factories, expressing additional transgenes, and modulating the immune system. Here, I review the current progress of OVs-loaded MSCs in cancer, focusing on their interaction with the immune system, and discuss new strategies to improve their therapeutic efficacy.

[Antitumoral microorganisms: The Swiss army knife of immunotherapy]

Research on viruses, bacteria and protozoa-based immunotherapy has been on the rise for several years. The antitumoral efficacy of these microorganisms relies on three main mechanisms: Destruction of tumor cells, stimulation of the immune response and reprogramming of the tumor microenvironment. In order to optimize their immunotherapeutic action, these microorganisms can be genetically engineered to enhance their tumor-targeting efficacy or to vectorize immunostimulating molecules and/or antibodies. To this aim, molecular engineering allows the design of new antibody formats optimizing their functions. From whole antibodies to tandem single-chain variable fragments, various antibody formats can be vectorized by microorganisms to target receptors such as immune checkpoints or recruit immune effector cells within the tumor. Such possibilities broaden the arsenal of immunotherapeutic cancer treatment. This review focuses on these innovations and their advantages for immunotherapy.

The discovery and development of oncolytic viruses: are they the future of cancer immunotherapy?

Introduction: Despite diverse treatment modalities and novel therapies, many cancers and patients are not effectively treated. Cancer immunotherapy has recently achieved breakthrough status yet is not effective in all cancer types or patients and can generate serious adverse effects. Oncolytic viruses (OVs) are a promising new therapeutic modality that harnesses virus biology and host interactions to treat cancer. OVs, genetically engineered or natural, preferentially replicate in and kill cancer cells, sparing normal cells/tissues, and mediating anti-tumor immunity.Areas covered: This review focuses on OVs as cancer therapeutic agents from a historical perspective, especially strategies to boost their immunotherapeutic activities. OVs offer a multifaceted platform, whose activities are modulated based on the parental virus and genetic alterations. In addition to direct viral effects, many OVs can be armed with therapeutic transgenes to also act as gene therapy vectors, and/or combined with other drugs or therapies.Expert opinion: OVs are an amazingly versatile and malleable class of cancer therapies. They tend to target cellular and host physiology as opposed to specific genetic alterations, which potentially enables broad responsiveness. The biological complexity of OVs have hindered their translation; however, the recent approval of talimogene laherparepvec (T-Vec) has invigorated the field.

Viroimmunotherapy for breast cancer: promises, problems and future directions

Virotherapy, a strategy to use live viruses as therapeutics, is a relatively novel field in the treatment of cancer. With the advancements in molecular biology and virology, there has been a huge increase in research on cancer virotherapy. For the treatment of cancer, viruses could be used either as vectors in gene therapy or as oncolytic agents. A variety of viruses have been studied for their potential usage in gene therapy or oncolytic therapy. In this review, we discuss virotherapy with a special focus on breast cancer. Breast cancer is the most common cancer and the leading cause of cancer-related deaths in women worldwide. Current treatments are insufficient to cure metastatic breast cancer and are often associated with severe side effects that further deteriorates patients' quality of life. Therefore, novel therapeutic approaches such as virotherapy need to be developed for the treatment of breast cancer. Here we summarize the current treatments for breast cancer and the potential use of virotherapy in the treatment of the disease. Furthermore, we discuss the use of oncolytic viruses as immunotherapeutics and the rational combination of oncolytic viruses with other therapeutics for optimal treatment of breast cancer. Finally, we outline the progress made in virotherapy for breast cancer and the shortcomings that need to be addressed for this novel therapy to move to the clinic for better treatment of breast cancer.