Oncolytic vaccinia virus for the treatment of cancer

Cancer therapy with the viral and bacterial pathogens: The past enemies can be considered the present allies

Cancer continues to be one of the leading causes of mortality worldwide despite significant advancements in cancer treatment. Many difficulties have arisen as a result of the detrimental consequences of chemotherapy and radiotherapy as a common cancer therapy, such as drug inability to penetrate deep tumor tissue, and also the drug resistance in tumor cells continues to be a major concern. These obstacles have increased the need for the development of new techniques that are more selective and effective against cancer cells. Bacterial-based therapies and the use of oncolytic viruses can suppress cancer in comparison to other cancer medications. The tumor microenvironment is susceptible to bacterial accumulation and proliferation, which can trigger immune responses against the tumor. Oncolytic viruses (OVs) have also gained considerable attention in recent years because of their potential capability to selectively target and induce apoptosis in cancer cells. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria and viruses in cancer treatment, discusses the limitations and challenges, outlines various strategies, summarizes recent preclinical and clinical trials, and emphasizes the importance of optimizing current strategies for better clinical outcomes.

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Vaccines and Dementia: Part I. Non-Specific Immune Boosting with BCG: History, Ligands, and Receptors

Vaccines such as Bacille Calmette-Guérin (BCG) can apparently defer dementia onset with an efficacy better than all drugs known to date, as initially reported by Gofrit et al. (PLoS One14, e0224433), now confirmed by other studies. Understanding how and why is of immense importance because it could represent a sea-change in how we manage patients with mild cognitive impairment through to dementia. Given that infection and/or inflammation are likely to contribute to the development of dementias such as Alzheimer's disease (Part II of this work), we provide a historical and molecular background to how vaccines, adjuvants, and their component molecules can elicit broad-spectrum protective effects against diverse agents. We review early studies in which poxvirus, herpes virus, and tuberculosis (TB) infections afford cross-protection against unrelated pathogens, a concept known as 'trained immunity'. We then focus on the attenuated TB vaccine, BCG, that was introduced to protect against the causative agent of TB, Mycobacterium tuberculosis. We trace the development of BCG in the 1920 s through to the discovery, by Freund and McDermott in the 1940 s, that extracts of mycobacteria can themselves exert potent immunostimulating (adjuvant) activity; Freund's complete adjuvant based on mycobacteria remains the most potent immunopotentiator reported to date. We then discuss whether the beneficial effects of BCG require long-term persistence of live bacteria, before focusing on the specific mycobacterial molecules, notably muramyl dipeptides, that mediate immunopotentiation, as well as the receptors involved. Part II addresses evidence that immunopotentiation by BCG and other vaccines can protect against dementia development.

Mathematical modeling predicts pathways to successful implementation of combination TRAIL-producing oncolytic virus and PAC-1 to treat granulosa cell tumors of the ovary

The development of new cancer therapies requires multiple rounds of validation from in vitro and in vivo experiments before they can be considered for clinical trials. Mathematical models assist in this preclinical phase by combining experimental data with human parameters to provide guidance about potential therapeutic regimens to bring forward into trials. However, granulosa cell tumors of the ovary lack a relevant mouse model, complexifying preclinical drug development for this rare tumor. To bridge this gap, we established a mathematical model as a framework to explore the potential of using a tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-producing oncolytic vaccinia virus in combination with the chemotherapeutic agent first procaspase activating compound (PAC-1). We have previously shown that TRAIL and PAC-1 act synergistically on granulosa tumor cells. In line with our previous results, our current model predicts that, although it is unable to stop the tumor from growing in its current form, combination oral PAC-1 with oncolytic virus (OV) provides the best result compared to monotherapies. Encouragingly, our results suggest that increases to the OV infection rate can lead to the success of this combination therapy within a year. The model developed here can continue to be improved as more data become available, allowing for regimen-tailoring via virtual clinical trials, ultimately shepherding effective regimens into trials.

Modeling of oncolytic viruses in a heterogeneous cell population to predict spread into non-cancerous cells

New cancer treatment modalities that limit patient discomfort need to be developed. One possible new therapy is the use of oncolytic (cancer-killing) viruses. It is only recently that our ability to manipulate viral genomes has allowed us to consider deliberately infecting cancer patients with viruses. One key consideration is to ensure that the virus exclusively targets cancer cells and does not harm nearby non-cancerous cells. Here, we use a mathematical model of viral infection to determine the characteristics a virus would need to have in order to eradicate a tumor, but leave non-cancerous cells untouched. We conclude that the virus must differ in its ability to infect the two different cell types, with the infection rate of non-cancerous cells needing to be less than one hundredth of the infection rate of cancer cells. Differences in viral production rate or infectious cell death rate alone are not sufficient to protect non-cancerous cells.

Vaccinia virus and peptide-receptor radiotherapy synergize to improve treatment of peritoneal carcinomatosis

Tumor-specific overexpression of receptors enables a variety of targeted cancer therapies, exemplified by peptide-receptor radiotherapy (PRRT) for somatostatin receptor (SSTR)-positive neuroendocrine tumors. While effective, PRRT is restricted to tumors with SSTR overexpression. To overcome this limitation, we propose using oncolytic vaccinia virus (vvDD)-mediated receptor gene transfer to permit molecular imaging and PRRT in tumors without endogenous SSTR overexpression, a strategy termed radiovirotherapy. We hypothesized that vvDD-SSTR combined with a radiolabeled somatostatin analog could be deployed as radiovirotherapy in a colorectal cancer peritoneal carcinomatosis model, producing tumor-specific radiopeptide accumulation. Following vvDD-SSTR and ¹⁷⁷Lu-DOTATOC treatment, viral replication and cytotoxicity, as well as biodistribution, tumor uptake, and survival, were evaluated. Radiovirotherapy did not alter virus replication or biodistribution, but synergistically improved vvDD-SSTR-induced cell killing in a receptor-dependent manner and significantly increased the tumor-specific accumulation and tumor-to-blood ratio of ¹⁷⁷Lu-DOTATOC, making tumors imageable by microSPECT/CT and causing no significant toxicity. ¹⁷⁷Lu-DOTATOC significantly improved survival over virus alone when combined with vvDD-SSTR but not control virus. We have therefore demonstrated that vvDD-SSTR can convert receptor-negative tumors into receptor-positive tumors and facilitate molecular imaging and PRRT using radiolabeled somatostatin analogs. Radiovirotherapy represents a promising treatment strategy with potential applications in a wide range of cancers.

Oncolytic therapy with recombinant vaccinia viruses targeting the interleukin-15 pathway elicits a synergistic response

We developed recombinant variants of oncolytic vaccinia virus LIVP strain expressing interleukin-15 (IL-15) or its receptor subunit alpha (IL-15Rα) to stimulate IL-15-dependent immune cells. We evaluated their oncolytic activity either alone or in combination with each other in vitro and in vivo using the murine CT26 colon carcinoma and 4T1 breast carcinoma models. We demonstrated that the admixture of these recombinant variants could promote the generation of the IL-15/IL-15Rα complex. In vitro studies indicated that 4T1 breast cancer cells were more susceptible to the developed recombinant viruses. In vivo studies showed significant survival benefits and tumor regression in 4T1 breast cancer syngeneic mice that received a combination of LIVP-IL15-RFP with LIVP-IL15Ra-RFP. Histological analysis showed recruited lymphocytes at the tumor region, while no harmful effects to the liver or spleen of the animals were detected. Evaluating tumor-infiltrated lymphocytes represented profound activation of cytotoxic T cells and macrophages in mice receiving combination therapy. Thus, our experiments showed superior oncolytic effectiveness of simultaneous injection of LIVP-IL15-RFP and LIVP-IL15Ra-RFP in breast cancer-bearing mice. The combined therapy by these recombinant variants represents a potent and versatile approach for developing new immunotherapies for breast cancer.

Adenovirus as a Vector and Oncolytic Virus

Adenoviral vectors, both oncolytic viruses and gene delivery vectors, are among the earliest approved and commercialised vectors for gene therapy. Adenoviruses have high cytotoxicity and immunogenicity. Therefore, lentiviruses or adeno-associated viruses as viral vectors and herpes simplex virus as an oncolytic virus have recently drawn attention. Thus, adenoviral vectors are often considered relatively obsolete. However, their high cargo limit and transduction efficiency are significant advantages over newer viral vectors. This review provides an overview of the new-generation adenoviral vectors. In addition, we describe the modification of the fiber knob region that enhances affinity of adenoviral vectors for cancer cells and the utilisation of cancer-cell-specific promoters to suppress expression of unwanted transgenes in non-malignant tissues.

Multi-targeted immunotherapeutics to treat B cell malignancies

The concept of multi-targeted immunotherapeutic systems has propelled the field of cancer immunotherapy into an exciting new era. Multi-effector molecules can be designed to engage with, and alter, the patient's immune system in a plethora of ways. The outcomes can vary from effector cell recruitment and activation upon recognition of a cancer cell, to a multipronged immune checkpoint blockade strategy disallowing evasion of the cancer cells by immune cells, or to direct cancer cell death upon engaging multiple cell surface receptors simultaneously. Here, we review the field of multi-specific immunotherapeutics implemented to treat B cell malignancies. The mechanistically diverse strategies are outlined and discussed; common B cell receptor antigen targeting strategies are outlined and summarized; and the challenges of the field are presented along with optimistic insights for the future.

Recombinant Strains of Oncolytic Vaccinia Virus for Cancer Immunotherapy

Cancer virotherapy is an alternative therapeutic approach based on the viruses that selectively infect and kill tumor cells. Vaccinia virus (VV) is a member of the Poxviridae, a family of enveloped viruses with a large linear double-stranded DNA genome. The proven safety of the VV strains as well as considerable transgene capacity of the viral genome, make VV an excellent platform for creating recombinant oncolytic viruses for cancer therapy. Furthermore, various genetic modifications can increase tumor selectivity and therapeutic efficacy of VV by arming it with the immune-modulatory genes or proapoptotic molecules, boosting the host immune system, and increasing cross-priming recognition of the tumor cells by T-cells or NK cells. In this review, we summarized the data on bioengineering approaches to develop recombinant VV strains for enhanced cancer immunotherapy.

Cross-talk between cancer stem cells and immune cells: potential therapeutic targets in the tumor immune microenvironment

Ongoing research has revealed that the existence of cancer stem cells (CSCs) is one of the biggest obstacles in the current cancer therapy. CSCs make an influential function in tumor progression, recurrence and chemoresistance due to their typical stemness characteristics. CSCs are preferentially distributed in niches, and those niche sites exhibit characteristics typical of the tumor microenvironment (TME). The complex interactions between CSCs and TME illustrate these synergistic effects. The phenotypic heterogeneity within CSCs and the spatial interactions with the surrounding tumor microenvironment led to increased therapeutic challenges. CSCs interact with immune cells to protect themselves against immune clearance by exploiting the immunosuppressive function of multiple immune checkpoint molecules. CSCs also can protect themselves against immune surveillance by excreting extracellular vesicles (EVs), growth factors, metabolites and cytokines into the TME, thereby modulating the composition of the TME. Therefore, these interactions are also being considered for the therapeutic development of anti-tumor agents. We discuss here the immune molecular mechanisms of CSCs and comprehensively review the interplay between CSCs and the immune system. Thus, studies on this topic seem to provide novel ideas for reinvigorating therapeutic approaches to cancer.

A Comparative Study of Oncolytic Vaccinia Viruses Harboring Different Marine Lectins in Breast Cancer Cells

Our previous studies demonstrated that arming vaccinia viruses with marine lectins enhanced the antitumor efficacy in several cancer cells. This study aims to compare the efficacy of oncolytic vaccinia viruses harboring Tachypleus tridentatus lectin (oncoVV-TTL), Aphrocallistes vastus lectin (oncoVV-AVL), white-spotted charr lectin (oncoVV-WCL), and Asterina pectinifera lectin (oncoVV-APL) in breast cancer cells (BC). These results indicated that oncoVV-AVL elicited the highest anti-tumor effect, followed by oncoVV-APL, while oncoVV-TTL and oncoVV-WCL had lower effects in BC. Further studies showed that apoptosis and replication may work together to enhance the cytotoxicity of oncoVV-lectins in a cell-type dependent manner. TTL/AVL/APL/WCL may mediate multiple pathways, including ERK, JNK, Hippo, and PI3K pathways, to promote oncoVV replication in MDA-MB-231 cells. In contrast, these pathways did not affect oncoVV-TTL/AVL/APL/WCL replication in MCF-7 cells, suggesting that the mechanisms of recombinant viruses in MCF-7 (ER⁺, PR⁺) and MDA-MB-231 (TNBC) cells were significantly different. Based on this study, we hypothesized that ER or PR may be responsible for the differences in promoting viral replication and inducing apoptosis between MCF-7 and MDA-MB-231 cells, but the specific mechanism needs to be further explored. In addition, small-molecule drugs targeting key cellular signaling pathways, including MAPK, PI3K/Akt, and Hippo, could be conjunction with oncoVV-AVL to promote breast cancer therapy, and key pathway factors in the JNK and PI3K pathways may be related to the efficacy of oncoVV-APL/TTL/WCL. This study provides a basis for applying oncolytic vaccinia virus in breast carcinoma.

Global trends of Vaccinia oncolytic virus therapy over the past two decades: Bibliometric and visual analysis

Background

In recent years, the vaccinia oncolytic virus has entered the clinical trial stage of examination and shown good progress. It has many advantages, such as good safety, high oncolytic efficiency, and the regulation ability of the tumor microenvironment, and is expected to be successfully used in the clinical treatment of tumors in the future. However, no bibliometric analysis has so far been performed that generalizes horizontally across this field. Therefore, this study aims to assess the research status and trends in this field from a global perspective to help guide future research priorities.

Methods

In this study, the literature related to vaccinia oncolytic virus published in English on Web of Science from 2002 to 2022 was retrieved, and the bibliometric indicators were analyzed using the Histcite. Pro 2.0 tool, while VOSviewer was used to visualize the research trends and hotspots in this field.

Results

In total, 408 related studies were included. In the past 20 years, the number of related publications in this field has increased year by year, and breakthroughs were made in this field in 2008 and 2013. The research has grown rapidly since 2008, and will likely continue to expand in the years to come. The United States plays a leading role in this area. "MOLECULAR THERAPY-ONCOLYTICS", "MOLECULAR THERAPY" and "JOURNAL OF TRANSLATIONAL MEDICINE" are core journals that publish high-quality literature on the latest advances in the field. Some authors with numerous high-quality publications include Bell JC and Szalay AA. At present, the research hotspot in this field focus on the clinical application of vaccinia oncolytic virus.

Conclusion

Overall, the number of vaccinia oncolytic virus-related studies is growing rapidly, in relation to which the United States is the most influential country. The clinical application of vaccinia oncolytic virus will affect the crucial development of future research.

The employment of vaccinia virus for colorectal cancer treatment: A review of preclinical and clinical studies

Colorectal cancer (CRC) is one of the leading malignancies that causes death worldwide. Cancer vaccines and oncolytic immunotherapy bring new hope for patients with advanced CRC. The capability of vaccinia virus (VV) in carrying foreign genes as antigens or immunostimulatory factors has been demonstrated in animal models. VV of Wyeth, Western Reserve, Lister, Tian Tan, and Copenhagen strains have been engineered for the induction of antitumor response in multiple cancers. This paper summarized the preclinical and clinical application and development of VV serving as cancer vaccines and oncolytic vectors in CRC treatment. Additionally, the remaining challenges and future direction are also discussed.

Therapeutic Efficacy of Oncolytic Viruses in Fighting Cancer: Recent Advances and Perspective

Immunotherapy is at the cutting edge of modern cancer treatment. Innovative medicines have been developed with varying degrees of success that target all aspects of tumor biology: tumors, niches, and the immune system. Oncolytic viruses (OVs) are a novel and potentially immunotherapeutic approach for cancer treatment. OVs reproduce exclusively in cancer cells, causing the tumor mass to lyse. OVs can also activate the immune system in addition to their primary activity. Tumors create an immunosuppressive environment by suppressing the immune system’s ability to respond to tumor cells. By injecting OVs into the tumor, the immune system is stimulated, allowing it to generate a robust and long-lasting response against the tumor. The essential biological properties of oncolytic viruses, as well as the underlying mechanisms that enable their usage as prospective anticancer medicines, are outlined in this review. We also discuss the increased efficacy of virotherapy when combined with other cancer medications.

Immunotherapy as a Therapeutic Strategy for Gastrointestinal Cancer-Current Treatment Options and Future Perspectives

Gastrointestinal (GI) cancer constitutes a highly lethal entity among malignancies in the last decades and is still a major challenge for cancer therapeutic options. Despite the current combinational treatment strategies, including chemotherapy, surgery, radiotherapy, and targeted therapies, the survival rates remain notably low for patients with advanced disease. A better knowledge of the molecular mechanisms that influence tumor progression and the development of optimal therapeutic strategies for GI malignancies are urgently needed. Currently, the development and the assessment of the efficacy of immunotherapeutic agents in GI cancer are in the spotlight of several clinical trials. Thus, several new modalities and combinational treatments with other anti-neoplastic agents have been identified and evaluated for their efficiency in cancer management, including immune checkpoint inhibitors, adoptive cell transfer, chimeric antigen receptor (CAR)-T cell therapy, cancer vaccines, and/or combinations thereof. Understanding the interrelation among the tumor microenvironment, cancer progression, and immune resistance is pivotal for the optimal therapeutic management of all gastrointestinal solid tumors. This review will shed light on the recent advances and future directions of immunotherapy for malignant tumors of the GI system.

Structure-Function Analysis of Two Interacting Vaccinia Proteins That Are Critical for Viral Morphogenesis: L2 and A30.5

An enduring mystery in poxvirology is the mechanism by which virion morphogenesis is accomplished. A30.5 and L2 are two small regulatory proteins that are essential for this process. Previous studies have shown that vaccinia A30.5 and L2 localize to the ER and interact during infection, but how they facilitate morphogenesis is unknown. To interrogate the relationship between A30.5 and L2, we generated inducible complementing cell lines (CV1-HA-L2; CV1-3xFLAG-A30.5) and deletion viruses (vΔL2; vΔA30.5). Loss of either protein resulted in a block in morphogenesis and a significant (>100-fold) decrease in infectious viral yield. Structure-function analysis of L2 and A30.5, using transient complementation assays, identified key functional regions in both proteins. A clustered charge-to-alanine L2 mutant (L2-RRD) failed to rescue a vΔL2 infection and exhibits a significantly retarded apparent molecular weight in vivo (but not in vitro), suggestive of an aberrant posttranslational modification. Furthermore, an A30.5 mutant with a disrupted putative N-terminal α-helix failed to rescue a vΔA30.5 infection. Using our complementing cell lines, we determined that the stability of A30.5 is dependent on L2 and that wild-type L2 and A30.5 coimmunoprecipitate in the absence of other viral proteins. Further examination of this interaction, using wild-type and mutant forms of L2 or A30.5, revealed that the inability of mutant alleles to rescue the respective deletion viruses is tightly correlated with a failure of L2 to stabilize and interact with A30.5. L2 appears to function as a chaperone-like protein for A30.5, ensuring that they work together as a complex during viral membrane biogenesis. IMPORTANCE Vaccinia virus is a large, enveloped DNA virus that was successfully used as the vaccine against smallpox. Vaccinia continues to be an invaluable biomedical research tool in basic research and in gene therapy vector and vaccine development. Although this virus has been studied extensively, the complex process of virion assembly, termed morphogenesis, still puzzles the field. Our work aims to better understand how two small viral proteins that are essential for viral assembly, L2 and A30.5, function during early morphogenesis. We show that A30.5 requires L2 for stability and that these proteins interact in the absence of other viral proteins. We identify regions in each protein required for their function and show that mutations in these regions disrupt the interaction between L2 and A30.5 and fail to restore virus viability.

Stereotactic body radiation combined with oncolytic vaccinia virus induces potent anti-tumor effect by triggering tumor cell necroptosis and DAMPs

Radiation is an integral part of cancer therapy. With the emergence of oncolytic vaccinia virus immunotherapy, it is important to study the combination of radiation and vaccinia virus in cancer therapy. In this study, we investigated the anti-tumor effect of and immune mechanisms underlying the combination of high-dose hypofractionated stereotactic body radiotherapy (SBRT) and oncolytic vaccinia virus in preclinical murine models. The combination enhanced the in vivo anti-tumor effect and increased the numbers of splenic CD4⁺Ki-67⁺ helper T lymphocytes and CD8⁺Ki-67⁺ cytotoxic T lymphocytes. Combinational therapy also increased tumor-infiltrating CD3⁺CD4⁺ helper T lymphocytes and CD3⁺CD8⁺ cytotoxic T lymphocytes, but decreased tumor-infiltrating regulatory T cells. In addition, SBRT combined with oncolytic vaccinia virus enhanced in vitro cell death, partly through necroptosis, and subsequent release of damage-associated molecular patterns (DAMPs), and shifted the macrophage M1/M2 ratio. We concluded that SBRT combined with oncolytic vaccinia virus can trigger tumor cell necroptosis and modify macrophages through the release of DAMPs, and then generate potent anti-tumor immunity and effects. Thus, combined therapy is potentially an important strategy for clinical cancer therapy.

In silico trials predict that combination strategies for enhancing vesicular stomatitis oncolytic virus are determined by tumor aggressivity

Background

Immunotherapies, driven by immune-mediated antitumorigenicity, offer the potential for significant improvements to the treatment of multiple cancer types. Identifying therapeutic strategies that bolster antitumor immunity while limiting immune suppression is critical to selecting treatment combinations and schedules that offer durable therapeutic benefits. Combination oncolytic virus (OV) therapy, wherein complementary OVs are administered in succession, offer such promise, yet their translation from preclinical studies to clinical implementation is a major challenge. Overcoming this obstacle requires answering fundamental questions about how to effectively design and tailor schedules to provide the most benefit to patients.

Methods

We developed a computational biology model of combined oncolytic vaccinia (an enhancer virus) and vesicular stomatitis virus (VSV) calibrated to and validated against multiple data sources. We then optimized protocols in a cohort of heterogeneous virtual individuals by leveraging this model and our previously established in silico clinical trial platform.

Results

Enhancer multiplicity was shown to have little to no impact on the average response to therapy. However, the duration of the VSV injection lag was found to be determinant for survival outcomes. Importantly, through treatment individualization, we found that optimal combination schedules are closely linked to tumor aggressivity. We predicted that patients with aggressively growing tumors required a single enhancer followed by a VSV injection 1 day later, whereas a small subset of patients with the slowest growing tumors needed multiple enhancers followed by a longer VSV delay of 15 days, suggesting that intrinsic tumor growth rates could inform the segregation of patients into clinical trials and ultimately determine patient survival. These results were validated in entirely new cohorts of virtual individuals with aggressive or non-aggressive subtypes.

Conclusions

Based on our results, improved therapeutic schedules for combinations with enhancer OVs can be studied and implemented. Our results further underline the impact of interdisciplinary approaches to preclinical planning and the importance of computational approaches to drug discovery and development.

Virotherapy, gene transfer and immunostimulatory monoclonal antibodies

Malignant cells are susceptible to viral infection and consequent cell death. Virus-induced cell death is endowed with features that are known to stimulate innate and adaptive immune responses. Thus danger signals emitted by cells succumbing to viral infection as well as viral nucleic acids are detected by specific receptors, and tumor cell antigens can be routed to professional antigen-presenting cells. The anticancer immune response triggered by viral infection is frequently insufficient to eradicate malignancy but may be further amplified. For this purpose, transgenes encoding cytokines as co-stimulatory molecules can be genetically engineered into viral vectors. Alternatively, or in addition, it is possible to use monoclonal antibodies that either block inhibitory receptors of immune effector cells, or act as agonists for co-stimulatory receptors. Combined strategies are based on the ignition of a local immune response at the malignant site plus systemic immune boosting. We have recently reported examples of this approach involving the Vaccinia virus or Semliki Forest virus, interleukin-12 and anti-CD137 monoclonal antibodies.

Hitting the Target but Missing the Point: Recent Progress towards Adenovirus-Based Precision Virotherapies

More people are surviving longer with cancer. Whilst this can be partially attributed to advances in early detection of cancers, there is little doubt that the improvement in survival statistics is also due to the expansion in the spectrum of treatments available for efficacious treatment. Transformative amongst those are immunotherapies, which have proven effective agents for treating immunogenic forms of cancer, although immunologically "cold" tumour types remain refractive. Oncolytic viruses, such as those based on adenovirus, have great potential as anti-cancer agents and have seen a resurgence of interest in recent years. Amongst their many advantages is their ability to induce immunogenic cell death (ICD) of infected tumour cells, thus providing the alluring potential to synergise with immunotherapies by turning immunologically "cold" tumours "hot". Additionally, enhanced immune mediated cell killing can be promoted through the local overexpression of immunological transgenes, encoded from within the engineered viral genome. To achieve this full potential requires the development of refined, tumour selective "precision virotherapies" that are extensively engineered to prevent off-target up take via native routes of infection and targeted to infect and replicate uniquely within malignantly transformed cells. Here, we review the latest advances towards this holy grail within the adenoviral field.

The Oncolytic Virus in Cancer Diagnosis and Treatment

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

Novel Oncolytic Virus Armed with Cancer Suicide Gene and Normal Vasculogenic Gene for Improved Anti-Tumor Activity

Here, we developed a novel oncolytic vaccinia virus (NOV) with the dual advantages of cancer selectivity and normal vessel reconstructive activity by replacing the viral thymidine kinase (vTk) and vaccinia growth factor (VGF) genes with genes encoding TNF-related apoptosis-inducing ligand (TRAIL) and angiopoietin 1 (Ang1), respectively. The pan-cancer-specific oncolytic potency of NOV was confirmed in various human and mouse cancer cell lines (colon, liver, pancreas, cholangiocarcinoma, cervical cancer, osteosarcoma, and melanoma). Vaccinia virus (VV) treatment directly induced early apoptosis in tumors within 24 h, and this effect was enhanced with further engineering; VGF and Tk deletion with Ang1 and TRAIL insertion. Meanwhile, treatment with the conventional anti-cancer drug cisplatin did not induce apoptosis. A virus-treated CT26 mouse colon cancer syngeneic model showed attenuated tumor growth, which was in accordance with the results of percent survival measurement, CD8 expression analysis, and TUNEL staining with advanced genetic engineering (vAng1 < vTRAIL < NOV). Taken together, our results indicate that NOV induces cancer tissue apoptosis and anti-tumor immunity and may constitute a highly advantageous therapeutic agent for next-generation solid tumor virotherapy with pan-cancer-specific oncolytic activity and high biosafety.

Oncolytic poxvirus CF33-hNIS-ΔF14.5 favorably modulates tumor immune microenvironment and works synergistically with anti-PD-L1 antibody in a triple-negative breast cancer model

Triple-negative breast cancer is the most aggressive subtype of breast cancer and is difficult to treat. Breast cancer is considered to be poorly immunogenic and hence is less responsive to immunotherapies. We tested whether the oncolytic poxvirus CF33-hNIS-ΔF14.5 could modulate tumor immune microenvironment and make the tumors responsive to the immune checkpoint inhibitor anti-PD-L1. We found that virus infection causes the upregulation of PD-L1 levels on triple-negative breast cancer cells in vitro as well as in vivo in mice. In a mouse model of orthotopic triple-negative breast cancer, the virus was found to increase tumor infiltration by CD8+ T cells. Likewise, in mice treated with CF33-hNIS-ΔF14.5 high levels of proinflammatory cytokines IFNγ and IL-6 were found in the tumors but not in the serum. The levels of immune modulation were even higher in mice that were treated with a combination of the virus and anti-PD-L1 antibody. While CF33-hNIS-ΔF14.5 and anti-PD-L1 antibody failed to exert significant anti-tumor effect as a single agent, a combination of the two agents resulted in significant anti-tumor effect with 50% mice experiencing complete tumor regression when both agents were injected intra-tumorally. Furthermore, the ‘cured’ mice did not develop tumor after re-challenge with the same cancer cells suggesting that they developed immunity against those cancer cells. Taken together, our study shows that CF33-hNIS-ΔF14.5 favorably modulates tumor immune microenvironment in triple-negative breast cancer model making them responsive to the immune checkpoint inhibitor anti-PD-L1, and hence warrants further studies to determine the clinical applicability of this combination therapy.

Synergistic Combination of Oncolytic Virotherapy and Immunotherapy for Glioma

PURPOSE

We hypothesized that the combination of a local stimulus for activating tumor-specific T cells and an anti-immunosuppressant would improve treatment of gliomas. Virally encoded IL15Rα-IL15 as the T-cell activating stimulus and a prostaglandin synthesis inhibitor as the anti-immunosuppressant were combined with adoptive transfer of tumor-specific T cells.

EXPERIMENTAL DESIGN

Two oncolytic poxviruses, vvDD vaccinia virus and myxoma virus, were each engineered to express the fusion protein IL15Rα-IL15 and a fluorescent protein. Viral gene expression (YFP or tdTomato Red) was confirmed in the murine glioma GL261 in vitro and in vivo. GL261 tumors in immunocompetent C57BL/6J mice were treated with vvDD-IL15Rα-YFP vaccinia virus or vMyx-IL15Rα-tdTr combined with other treatments, including vaccination with GARC-1 peptide (a neoantigen for GL261), rapamycin, celecoxib, and adoptive T-cell therapy.

RESULTS

vvDD-IL15Rα-YFP and vMyx-IL15Rα-tdTr each infected and killed GL261 cells in vitro. In vivo, NK cells and CD8⁺ T cells were increased in the tumor due to the expression of IL15Rα-IL15. Each component of a combination treatment contributed to prolonging survival: an oncolytic virus, the IL15Rα-IL15 expressed by the virus, a source of T cells (whether by prevaccination or adoptive transfer), and prostaglandin inhibition all synergized to produce elimination of gliomas in a majority of mice. vvDD-IL15Rα-YFP occasionally caused ventriculitis-meningitis, but vMyx-IL15Rα-tdTr was safe and effective, causing a strong infiltration of tumor-specific T cells and eliminating gliomas in 83% of treated mice.

CONCLUSIONS

IL15Rα-IL15-armed oncolytic poxviruses provide potent antitumor effects against brain tumors when combined with adoptive T-cell therapy, rapamycin, and celecoxib.

Target Therapy With Vaccinia Virus Harboring IL-24 For Human Breast Cancer

Background: Breast cancer is a heterogeneous disease with high aggression and novel targeted therapeutic strategies are required. Oncolytic vaccinia virus is an attractive candidate for cancer treatment due to its tumor cell-specific replication causing lysis of tumor cells as well as a delivery vector to overexpress therapeutic transgenes. Interleukin-24 (IL-24) is a novel tumor suppressor cytokine that selectively induces apoptosis in a wide variety of tumor types, including breast cancer. In this study, we used vaccinia virus as a delivery vector to express IL-24 gene and antitumor effects were evaluated both in vitro and in vivo. Methods: The vaccinia virus strain Guang9 armed with IL-24 gene (VG9-IL-24) was constructed via disruption of the viral thymidine kinase (TK) gene region. The cytotoxicity of VG9-IL-24 in various breast cancer cell lines was assessed by MTT and cell cycle progression and apoptosis were examined by flow cytometry. In vivo antitumor effects were further observed in MDA-MB-231 xenograft mouse model. Results: In vitro, VG9-IL-24 efficiently infected and selectively killed breast cancer cells with no strong cytotoxicity to normal cells. VG9-IL-24 induced increased number of apoptotic cells and blocked breast cancer cells in the G2/M phase of the cell cycle. Western blotting results indicated that VG9-IL-24-mediated apoptosis was related to PI3K/β-catenin signaling pathway. In vivo, VG9-IL-24 delayed tumor growth and improved survival. Conclusions: Our findings provided documentation that VG9-IL-24 was targeted in vitro and exhibited enhanced antitumor effects, and it may be an innovative therapy for breast cancer.

A Cancer-Favoring, Engineered Vaccinia Virus for Cholangiocarcinoma

While oncolytic vaccinia virus-based therapy has shown promising results for uncured patients with cancer, its effects on cholangiocarcinoma (CCA) remain unclear. Here, we evaluated the anti-cancer activity of the cancer-favoring oncolytic vaccinia virus (CVV), which was recognized as a promising therapy for stem cell-like colon cancer cells (SCCs) and metastatic hepatocellular carcinoma (HCC) in previous studies. CCA presents major challenges, such as clinical complexity, stem cell cancer characteristics, a high refractory rate, resistance to conventional therapy, and a dismal prognosis. In the present study, we confirmed the oncolytic activity of the CVV in CCA with a slightly alkaline microenvironment (pH 7-8), in which the CVV was stable and highly effective at infecting CCA. Taken together, our findings suggest that CVV-based therapy is highly suitable for the treatment of CCA.

Oncolytic Vaccinia Virus Expressing Aphrocallistes vastus Lectin as a Cancer Therapeutic Agent

Lectins display a variety of biological functions including insecticidal, antimicrobial, as well as antitumor activities. In this report, a gene encoding Aphrocallistes vastus lectin (AVL), a C-type lectin, was inserted into an oncolytic vaccinia virus vector (oncoVV) to form a recombinant virus oncoVV-AVL, which showed significant in vitro antiproliferative activity in a variety of cancer cell lines. Further investigations revealed that oncoVV-AVL replicated faster than oncoVV significantly in cancer cells. Intracellular signaling elements including NF-κB2, NIK, as well as ERK were determined to be altered by oncoVV-AVL. Virus replication upregulated by AVL was completely dependent on ERK activity. Furthermore, in vivo studies showed that oncoVV-AVL elicited significant antitumor effect in colorectal cancer and liver cancer mouse models. Our study might provide insights into a novel way of the utilization of marine lectin AVL in oncolytic viral therapies.

Recombinant Oncolytic Vaccinia Viruses Expressing Human β-Defensin 2 Enhance Anti-tumor Immunity

Cancer is still a leading of cause of death worldwide. Among the bio-therapy strategies for cancer, vaccinia virus (VV) has been widely used as an expression vector because of its potent oncolytic activities in addition to its large capacity for insertion of foreign genes and excellent safety records. In the present study, a novel recombinant VV, VV-HBD2-lacZ, expressing human β-defensin 2 (HBD2), an anti-microbial peptide of the innate immune system, was constructed. First, the chemotaxis characteristics of HBD2 expressed on VV-HBD2-lacZ-infected cells toward dendritic cells (DCs) in vitro and in vivo were demonstrated. The anti-tumor effects of VV-HBD2-lacZ in vitro and in vivo in a mouse melanoma cancer model were then investigated. It was found that VV-HBD2-lacZ was able to inhibit tumor growth and metastasis significantly. It was further demonstrated that VV-HBD2-lacZ induced potent cytotoxic activity by increasing the tumor-infiltrating CD4⁺ and CD8⁺ T cells. These results indicate that HBD2-expressing VV recruited plasmacytoid DCs (pDCs) to the tumor location, leading to cytotoxic T cell response against the tumor, and thus inhibited tumor growth in vitro and in vivo. In conclusion, oncolytic HBD2-expressing VV provides an effective treatment for tumors by triggering innate and adaptive immunity.

Oncolytic virotherapy for anaplastic and poorly differentiated thyroid cancer: a promise or a clinical reality?

Oncolytic viruses (OVs) selectively infect and lyse cancer cells. A direct lytic effect of OVs has been theorized in the initial studies; however, the antineoplastic effect of OVs is also due to the induction of an immune response against cancer cells. Anaplastic thyroid cancer is one of the most aggressive human malignancies with a short survival time of about 6–12 months from the diagnosis. The lack of effective therapies has prompted to investigate the efficacy of OVs in anaplastic thyroid carcinoma. Different OVs have been tested in preclinical studies, either as single agents or in combinatorial treatments. In this review, the results of these studies are summarized and future perspective discussed.

Tachypleus tridentatus Lectin Enhances Oncolytic Vaccinia Virus Replication to Suppress In Vivo Hepatocellular Carcinoma Growth

Lectins play diverse roles in physiological processes as biological recognition molecules. In this report, a gene encoding Tachypleus tridentatus Lectin (TTL) was inserted into an oncolytic vaccinia virus (oncoVV) vector to form oncoVV-TTL, which showed significant antitumor activity in a hepatocellular carcinoma mouse model. Furthermore, TTL enhanced oncoVV replication through suppressing antiviral factors expression such as interferon-inducible protein 16 (IFI16), mitochondrial antiviral signaling protein (MAVS) and interferon-beta (IFN-β). Further investigations revealed that oncoVV-TTL replication was highly dependent on ERK activity. This study might provide insights into a novel way of the utilization of TTL in oncolytic viral therapies.

Rapid Generation of Multiple Loci-Engineered Marker-free Poxvirus and Characterization of a Clinical-Grade Oncolytic Vaccinia Virus

Recombinant poxviruses, utilized as vaccine vectors and oncolytic viruses, often require manipulation at multiple genetic loci in the viral genome. It is essential for viral vectors to possess no adventitious mutations and no (antibiotic) selection marker in the final product for human patients in order to comply with the guidance from the regulatory agencies. Rintoul et al. have previously developed a selectable and excisable marker (SEM) system for the rapid generation of recombinant vaccinia virus. In the current study, we describe an improved methodology for rapid creation and selection of recombinant poxviruses with multiple genetic manipulations solely based on expression of a fluorescent protein and with no requirement for drug selection that can lead to cellular stress and the risk of adventitious mutations throughout the viral genome. Using this improved procedure combined with the SEM system, we have constructed multiple marker-free oncolytic poxviruses expressing different cytokines and other therapeutic genes. The high fidelity of inserted DNA sequences validates the utility of this improved procedure for generation of therapeutic viruses for human patients. We have created an oncolytic poxvirus expressing human chemokine CCL5, designated as vvDD-A34R-hCCL5, with manipulations at two genetic loci in a single virus. Finally, we have produced and purified this virus in clinical grade for its use in a phase I clinical trial and presented data on initial in vitro characterization of the virus.

Efficacy and Safety of Doubly-Regulated Vaccinia Virus in a Mouse Xenograft Model of Multiple Myeloma

Multiple myeloma is a malignancy of plasma cells of the bone marrow. Although the prognosis is variable, no curative therapy has been defined. Vaccinia virus infects cancer cells and kills such cells in a variety of ways. These include direct infection, triggering of immunomediated cell death, and vascular collapse. The potential of the vaccinia virus as an anti-tumor therapy has attracted the attention of oncologists. Interestingly, our preliminary experiments revealed that myeloma cells were particularly susceptible to vaccinia virus. To exploit this susceptibility and to render vaccinia more myeloma specific, we generated thymidine-kinase-deleted microRNA (miRNA)-regulated vaccinia viruses in which the essential viral gene B5R was regulated by miRNAs of normal human cells. Of the miRNAs examined, let-7a was found to be the most reliable in terms of regulating viral transmission. Exposure to unregulated vaccinia virus killed myeloma-transplanted severe combined immunodeficiency (SCID) mice; the animals succumbed to viral toxicity. In contrast, the thymidine-kinase-deleted let-7a-regulated virus remained localized within myeloma cells, triggering tumor regression and improving overall survival. In conclusion, a thymidine-kinase-deleted let-7a-regulated vaccinia virus was safe and effective for mice, warranting clinical trials in humans.

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

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

Evolutionary cancer-favoring engineered vaccinia virus for metastatic hepatocellular carcinoma

Engineered vaccinia virus-based therapy shows promising results in patients with advanced hepatocellular carcinoma, although a strategic virus design for the metastatic liver and the study of its efficacy in treating the cancer has not been well assessed. In this paper, we proposed a simple and strategic virus design for targeting metastatic hepatocellular carcinoma. We developed an evolutionary cancer-favoring engineered vaccinia virus (CVV, which is produced by repeated selective replication in cancerous tissues and then deleting viral thymidine kinase genes) and investigated its therapeutic effects on metastatic liver cancer. The expression of the cell surface marker, CD44, which is associated with cancer stem cells, seems to be correlated with the cells’ metastatic characteristics; cellular migration, epithelial-mesenchymal transition (EMT) expression and liver tumorigenicity. The highly metastatic and tumorigenic Sk-Hep-1 cell line was selected and injected directly onto the liver tissue to develop a liver-to-colon metastasis model. In an animal study, the subjects were treated with sorafenib, CVV, or sorafenib with CVV. Metastatic regions were interestingly rare in the CVV-treated groups (i.e., CVV or sorafenib with CVV) whereas metastatic regions existed in the sorafenib-treated group. From results, we concluded that our simple strategy of developing a cancer-favoring virus can successfully eradicate metastatic liver cancer cells, provided that our CVV can be a promising therapeutic virus that targets metastatic liver cancer.

Establishing elements of a synthetic biology platform for Vaccinia virus production: BioBrick™ design, serum-free virus production and microcarrier-based cultivation of CV-1 cells

Vaccinia virus (VACV) is an established vector for vaccination and is beginning to prove effective as an oncolytic agent. Industrial production of VACV stands to benefit in future from advances made by synthetic biology in genome engineering and standardisation. The CV-1 cell line can be used for VACV propagation and has been used extensively with the CRISPR/Cas9 system for making precise edits of the VACV genome. Here we take first steps toward establishing a scalable synthetic biology platform for VACV production with CV-1 cells featuring standardised biological tools and serum free cell cultivation. We propose a new BioBrick™ plasmid backbone format for inserting transgenes into VACV. We then test the performance of CV-1 cells in propagation of a conventional recombinant Lister strain VACV, VACVL-15 RFP, in a serum-free process. CV-1 cells grown in 5% foetal bovine serum (FBS) Dulbecco’s Modified Eagle Medium (DMEM) were adapted to growth in OptiPRO and VP-SFM brands of serum-free media. Specific growth rates of 0.047 h⁻¹ and 0.044 h⁻¹ were observed for cells adapted to OptiPRO and VP-SFM respectively, compared to 0.035 h⁻¹ in 5% FBS DMEM. Cells adapted to OptiPRO and to 5% FBS DMEM achieved recovery ratios of over 96%, an indication of their robustness to cryopreservation. Cells adapted to VP-SFM showed a recovery ratio of 82%. Virus productivity in static culture, measured as plaque forming units (PFU) per propagator cell, was 75 PFU/cell for cells in 5% FBS DMEM. VP-SFM and OptiPRO adaptation increased VACV production to 150 PFU/cell and 350 PFU/cell respectively. Boosted PFU/cell from OptiPRO-adapted cells persisted when 5% FBS DMEM or OptiPRO medium was observed during the infection step and when titre was measured using cells adapted to 5% FBS DMEM or OptiPRO medium. Finally, OptiPRO-adapted CV-1 cells were successfully cultivated using Cytodex-1 microcarriers to inform future scale up studies.

Viruses as nanomedicine for cancer

Oncolytic virotherapy, a type of nanomedicine in which oncolytic viruses (OVs) are used to selectively infect and lyse cancer cells, is an emerging field in cancer therapy. Some OVs exhibit a specific tropism for cancer cells, whereas others require genetic modification to enhance their binding with and entry into cancer cells. OVs both kill tumor cells and induce the host’s immune response against tumor cells. Armed with antitumor cellular molecules, antibodies, and/or in combination with anticancer drugs, OVs can accelerate the lysis of cancer cells. Among the OVs, vaccinia virus has been the focus of preclinical and clinical research because of its many favorable properties. In this review, the basic mechanisms of action of OVs are presented, including their entry, survival, tumor lysis, and immune activation, and the latest research in vaccinia virus-based virotherapy and its status as an anticancer nanomedicine in prospective clinical trials are discussed.

Oncolytic virus efficiency inhibited growth of tumour cells with multiple drug resistant phenotype in vivo and in vitro

Background

Tumour resistance to a wide range of drugs (multiple drug resistant, MDR) acquired after intensive chemotherapy is considered to be the main obstacle of the curative treatment of cancer patients. Recent work has shown that oncolytic viruses demonstrated prominent potential for effective treatment of diverse cancers. Here, we evaluated whether genetically modified vaccinia virus (LIVP-GFP) may be effective in treatment of cancers displaying MDR phenotype.

Methods

LIVP-GFP replication, transgene expression and cytopathic effects were analysed in human cervical carcinomas KB-3-1 (MDR−), KB-8-5 (MDR+) and in murine melanoma B-16 (MDR−), murine lymphosarcomas RLS and RLS-40 (MDR+). To investigate the efficacy of this therapy in vivo, we treated immunocompetent mice bearing murine lymphosarcoma RLS-40 (MDR+) (6- to 8-week-old female CBA mice; n = 10/group) or melanoma B-16 (MDR−) (6- to 8-week-old female C57Bl mice; n = 6/group) with LIVP-GFP (5 × 10⁷ PFU of virus in 0.1 mL of IMDM immediately and 4 days after tumour implantation).

Results

We demonstrated that LIVP-GFP replication was effective in human cervical carcinomas KB-3-1 (MDR−) and KB-8-5 (MDR+) and in murine melanoma B-16 (MDR−), whereas active viral production was not detected in murine lymphosarcomas RLS and RLS-40 (MDR+). Additionally, it was found that in tumour models in immunocompetent mice under the optimized regimen intratumoural injections of LIVP-GFP significantly inhibited melanoma B16 (33 % of mice were with complete response after 90 days) and RLS-40 tumour growth (fourfold increase in tumour doubling time) as well as metastasis.

Conclusion

The anti-tumour activity of LIVP-GFP is a result of direct oncolysis of tumour cells in case of melanoma B-16 because the virus effectively replicates and destroys these cells, and virus-mediated activation of the host immune system followed by immunologically mediated destruction of of tumour cells in case of lymphosarcoma RLS-40. Thus, the recombinant vaccinia virus LIVP-GFP is able to inhibit the growth of malignant cells with the MDR phenotype and tumour metastasis when administered in the early stages of tumour development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1002-x) contains supplementary material, which is available to authorized users.

Expression of DAI by an oncolytic vaccinia virus boosts the immunogenicity of the virus and enhances antitumor immunity

In oncolytic virotherapy, the ability of the virus to activate the immune system is a key attribute with regard to long-term antitumor effects. Vaccinia viruses bear one of the strongest oncolytic activities among all oncolytic viruses. However, its capacity for stimulation of antitumor immunity is not optimal, mainly due to its immunosuppressive nature. To overcome this problem, we developed an oncolytic VV that expresses intracellular pattern recognition receptor DNA-dependent activator of IFN-regulatory factors (DAI) to boost the innate immune system and to activate adaptive immune cells in the tumor. We showed that infection with DAI-expressing VV increases expression of several genes related to important immunological pathways. Treatment with DAI-armed VV resulted in significant reduction in the size of syngeneic melanoma tumors in mice. When the mice were rechallenged with the same tumor, DAI-VV-treated mice completely rejected growth of the new tumor, which indicates immunity established against the tumor. We also showed enhanced control of growth of human melanoma tumors and elevated levels of human T-cells in DAI-VV-treated mice humanized with human peripheral blood mononuclear cells. We conclude that expression of DAI by an oncolytic VV is a promising way to amplify the vaccine potency of an oncolytic vaccinia virus to trigger the innate-and eventually the long-lasting adaptive immunity against cancer.

Oncolytic viruses for therapy of malignant glioma

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

Targeting tumor vasculature through oncolytic virotherapy: recent advances

The oncolytic virotherapy field has made significant advances in the last decade, with a rapidly increasing number of early- and late-stage clinical trials, some of them showing safety and promising therapeutic efficacy. Targeting tumor vasculature by oncolytic viruses (OVs) is an attractive strategy that offers several advantages over nontargeted viruses, including improved tumor viral entry, direct antivascular effects, and enhanced antitumor efficacy. Current understanding of the biological mechanisms of tumor neovascularization, novel vascular targets, and mechanisms of resistance has allowed the development of oncolytic viral vectors designed to target tumor neovessels. While some OVs (such as vaccinia and vesicular stomatitis virus) can intrinsically target tumor vasculature and induce vascular disruption, the majority of reported vascular-targeted viruses are the result of genetic manipulation of their viral genomes. Such strategies include transcriptional or transductional endothelial targeting, "armed" viruses able to downregulate angiogenic factors, or to express antiangiogenic molecules. The above strategies have shown preclinical safety and improved antitumor efficacy, either alone, or in combination with standard or targeted agents. This review focuses on the recent efforts toward the development of vascular-targeted OVs for cancer treatment and provides a translational/clinical perspective into the future development of new generation biological agents for human cancers.

Oncolytic gene therapy with recombinant vaccinia strain GLV-2b372 efficiently kills hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) commonly presents at a late stage when surgery is no longer a curative option. As such, novel therapies for advanced HCC are needed. Oncolytic viruses are a viable option for cancer therapy owing to their ability to specifically infect, replicate within, and kill cancer cells. In this study, we have investigated the ability of GLV-2b372, a novel light-emitting recombinant vaccinia virus derived from a wild-type Lister strain, to kill HCC.

METHODS

Four human HCC cell lines were assayed in vitro for infectivity and cytotoxicity. Viral replication was quantified via standard viral plaque assays. Flank HCC xenografts generated in athymic nude mice were treated with intratumoral GLV-2b372 to assess for tumor growth inhibition and viral biodistribution.

RESULTS

Infectivity occurred in a time- and concentration-dependent manner with 70% cell death in all cell lines by day 5. All cell lines supported efficient viral replication. At 25 days after infection, flank tumor volumes decreased by 50% whereas controls increased by 400%. Tumor tissue demonstrated substantial GLV-2b372 infection at 24 hours, 48 hours, and 2 weeks.

CONCLUSION

We demonstrate that GLV-2b372 efficiently kills human HCC in vitro and in vivo and is a viable treatment option for patients with HCC.

Chemovirotherapy: combining chemotherapeutic treatment with oncolytic virotherapy

Oncolytic virotherapy has made significant progress in recent years, however, widespread approval of virotherapeutics is still limited. Primarily, this is due to the fact that currently available virotherapeutics are mostly tested in monotherapeutic clinical trials exclusively (ie, not in combination with other therapies) and so far have achieved only small and often clinically insignificant responses. Given that the predominantly immunotherapeutic mechanism of virotherapeutics is somewhat time-dependent and rapidly growing tumors therefore exhibit only minor chances of being captured in time, scenarios with combination partners are postulated to be more effective. Combinatory settings would help to achieve a rapid stabilization or even reduction of onset tumor masses while providing enough time (numerous months) for achieving immuno(viro)therapeutic success. For this reason, combination strategies of virotherapy with highly genotoxic regimens, such as chemotherapy, are of major interest. A number of clinical trials bringing the concepts of chemotherapy and virotherapy together have previously been undertaken, but optimal scheduling of chemovirotherapy (maximizing the anti-tumor effect while minimizing the risk of overlapping toxicity) still constitutes a major challenge. Therefore, an overview of published as well as ongoing Phase I–III trials should improve our understanding of current challenges and future developments in this field.

Anti-tumour activity of oncolytic Western Reserve vaccinia viruses in canine tumour cell lines, xenografts, and fresh tumour biopsies

Cancer is one of the most common reasons for death in dogs. One promising approach is oncolytic virotherapy. We assessed the oncolytic effect of genetically modified vaccinia viruses in canine cancer cells, in freshly excised tumour biopsies, and in mice harbouring canine tumour xenografts. Tumour transduction efficacy was assessed using virus expressing luciferase or fluorescent marker genes and oncolysis was quantified by a colorimetric cell viability assay. Oncolytic efficacy in vivo was evaluated in a nude mouse xenograft model. Vaccinia virus was shown to infect most tested canine cancer cell lines and primary surgical tumour tissues. Virus infection significantly reduced tumour growth in the xenograft model. Oncolytic vaccinia virus has antitumour effects against canine cancer cells and experimental tumours and is able to replicate in freshly excised patient tumour tissue. Our results suggest that oncolytic vaccinia virus may offer an effective treatment option for otherwise incurable canine tumours.

Oncolytic Poxviruses

Current standard treatments of cancer can prolong survival of many cancer patients but usually do not effectively cure the disease. Oncolytic virotherapy is an emerging therapeutic for the treatment of cancer that exploits replication-competent viruses to selectively infect and destroy cancerous cells while sparing normal cells and tissues. Clinical and/or preclinical studies on oncolytic viruses have revealed that the candidate viruses being tested in trials are remarkably safe and offer potential for treating many classes of currently incurable cancers. Among these candidates are vaccinia and myxoma viruses, which belong to the family Poxviridae and possess promising oncolytic features. This article describes poxviruses that are being developed for oncolytic virotherapy and summarizes the outcomes of both clinical and preclinical studies. Additionally, studies demonstrating superior efficacy when poxvirus oncolytic virotherapy is combined with conventional therapies are described.

GMCSF-armed vaccinia virus induces an antitumor immune response

Oncolytic Western Reserve strain vaccinia virus selective for epidermal growth factor receptor pathway mutations and tumor-associated hypermetabolism was armed with human granulocyte-macrophage colony-stimulating factor (GMCSF) and a tdTomato fluorophore. As the assessment of immunological responses to human transgenes is challenging in the most commonly used animal models, we used immunocompetent Syrian golden hamsters, known to be sensitive to human GMCSF and semipermissive to vaccinia virus. Efficacy was initially tested in vitro on various human and hamster cell lines and oncolytic potency of transgene-carrying viruses was similar to unarmed virus. The hGMCSF-encoding virus was able to completely eradicate subcutaneous pancreatic tumors in hamsters, and to fully protect the animals from subsequent rechallenge with the same tumor. Induction of specific antitumor immunity was also shown by ex vivo co-culture experiments with hamster splenocytes. In addition, histological examination revealed increased infiltration of neutrophils and macrophages in GMCSF-virus-treated tumors. These findings help clarify the mechanism of action of GMCSF-armed vaccinia viruses undergoing clinical trials.

Oncolytic viral therapy: targeting cancer stem cells

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