Faster replication and higher expression levels of viral glycoproteins give the vesicular stomatitis virus/measles virus hybrid VSV-FH a growth advantage over measles virus

Virus-mediated cell fusion of SARS-CoV-2 variants

SARS-CoV-2 has the ability to form large multi-nucleated cells known as syncytia. Little is known about how syncytia affect the dynamics of the infection or severity of the disease. In this manuscript, we extend a mathematical model of cell-cell fusion assays to estimate both the syncytia formation rate and the average duration of the fusion phase for five strains of SARS-CoV-2. We find that the original Wuhan strain has the slowest rate of syncytia formation (6.4×10-4/h), but takes only 4.0 h to complete the fusion process, while the Alpha strain has the fastest rate of syncytia formation (0.36 /h), but takes 7.6 h to complete the fusion process. The Beta strain also has a fairly fast syncytia formation rate (9.7×10-2/h), and takes the longest to complete fusion (8.4 h). The D614G strain has a fairly slow syncytia formation rate (2.8×10-3/h), but completes fusion in 4.0 h. Finally, the Delta strain is in the middle with a syncytia formation rate of 3.2×10-2/h and a fusing time of 6.1 h. We note that for these SARS-CoV-2 strains, there appears to be a tradeoff between the ease of forming syncytia and the speed at which they complete the fusion process.

Mathematical Modeling of Virus-Mediated Syncytia Formation: Past Successes and Future Directions

Many viruses have the ability to cause cells to fuse into large multi-nucleated cells, known as syncytia. While the existence of syncytia has long been known and its importance in helping spread viral infection within a host has been understood, few mathematical models have incorporated syncytia formation or examined its role in viral dynamics. This review examines mathematical models that have incorporated virus-mediated cell fusion and the insights they have provided on how syncytia can change the time course of an infection. While the modeling efforts are limited, they show promise in helping us understand the consequences of syncytia formation if future modeling efforts can be coupled with appropriate experimental efforts to help validate the models.

The role of syncytia during viral infections

Respiratory syncytial virus (RSV) is a common, contagious infection of the lungs and the respiratory tract. RSV is characterized by syncytia, which are multinuclear cells created by cells that have fused together. We use a mathematical model to study how different assumptions about the viral production and lifespan of syncytia change the resulting infection time course. We find that the effect of syncytia on viral titer is only apparent when the basic reproduction number for infection via syncytia formation is similar to the reproduction number for cell free viral transmission. When syncytia fusion rate is high, we find the presence of syncytia can lead to slowly growing infections if viral production is suppressed in syncytia. Our model provides insight into how the presence of syncytia can affect the time course of a viral infection.

MeV-Stealth: A CD46-specific oncolytic measles virus resistant to neutralization by measles-immune human serum

The frequent overexpression of CD46 in malignant tumors has provided a basis to use vaccine-lineage measles virus (MeV) as an oncolytic virotherapy platform. However, widespread measles seropositivity limits the systemic deployment of oncolytic MeV for the treatment of metastatic neoplasia. Here, we report the development of MeV-Stealth, a modified vaccine MeV strain that exhibits oncolytic properties and escapes antimeasles antibodies in vivo. We engineered this virus using homologous envelope glycoproteins from the closely-related but serologically non-cross reactive canine distemper virus (CDV). By fusing a high-affinity CD46 specific single-chain antibody fragment (scFv) to the CDV-Hemagglutinin (H), ablating its tropism for human nectin-4 and modifying the CDV-Fusion (F) signal peptide we achieved efficient retargeting to CD46. A receptor binding affinity of ~20 nM was required to trigger CD46-dependent intercellular fusion at levels comparable to the original MeV H/F complex and to achieve similar antitumor efficacy in myeloma and ovarian tumor-bearing mice models. In mice passively immunized with measles-immune serum, treatment of ovarian tumors with MeV-Stealth significantly increased overall survival compared with treatment with vaccine-lineage MeV. Our results show that MeV-Stealth effectively targets and lyses CD46-expressing cancer cells in mouse models of ovarian cancer and myeloma, and evades inhibition by human measles-immune serum. MeV-Stealth could therefore represent a strong alternative to current oncolytic MeV strains for treatment of measles-immune cancer patients.

Vaccine strains of the measles virus (MeV) have been shown to be promising anti-cancer agents because of the frequent overexpression of the host-cell receptor CD46 in human malignancies. However, anti-MeV antibodies in the human population severely restrict the use of MeV as an oncolytic agent. Here, we engineered a neutralization-resistant MeV vaccine, MeV-Stealth, by replacing its envelope glycoproteins with receptor-targeted glycoproteins from wild-type canine distemper virus. By fully-retargeting the new envelope to the receptor CD46, we found that in mouse models of ovarian cancer and myeloma MeV-Stealth displayed oncolytic properties similar to the parental MeV vaccine. Furthermore, we found that passive immunization with measles-immune human serum did not eliminate the oncolytic potency of the MeV-Stealth, whereas it did destroy the potency of the parental MeV strain. The virus we here report may be considered a suitable oncolytic agent for the treatment of MeV-immune patients.

Fusogenic oncolytic vaccinia virus enhances systemic antitumor immune response by modulating the tumor microenvironment

Oncolytic viruses induce antitumor immunity following direct viral oncolysis. However, their therapeutic effects are limited in distant untreated tumors because their antitumor function depends on indirect antitumor immunity. Here, we generated a novel fusogenic oncolytic vaccinia virus (FUVAC) and compared its antitumor activity with that of its parental non-fusogenic virus. Compared with the parent, FUVAC exerted the cytopathic effect and induced immunogenic cell death in human and murine cancer cells more efficiently. In a bilateral tumor-bearing syngeneic mouse model, FUVAC administration significantly inhibited tumor growth in both treated and untreated tumors. However, its antitumor effects were completely suppressed by CD8⁺ T cell depletion. Notably, FUVAC reduced the number of tumor-associated immune-suppressive cells in treated tumors, but not in untreated tumors. Mice treated with FUVAC before an immune checkpoint inhibitor (ICI) treatment achieved complete response (CR) in both treated and untreated tumors, whereas ICI alone did not show antitumor activity. Mice achieving CR rejected rechallenge with the same tumor cells, suggesting establishment of a long-term tumor-specific immune memory. Thus, FUVAC improves the tumor immune microenvironment and enhances systemic antitumor immunity, suggesting that, alone and in combination with ICI, it is a novel immune modulator for overcoming oncolytic virus-resistant tumors.

Oncolytic Virus with Attributes of Vesicular Stomatitis Virus and Measles Virus in Hepatobiliary and Pancreatic Cancers

Recombinant vesicular stomatitis virus (VSV)-fusion and hemagglutinin (FH) was developed by substituting the promiscuous VSV-G glycoprotein (G) gene in the backbone of VSV with genes encoding for the measles virus envelope proteins F and H. Hybrid VSV-FH exhibited a multifaceted mechanism of cancer-cell killing and improved neurotolerability over parental VSV in preclinical studies. In this study, we evaluated VSV-FH in vitro and in vivo in models of hepatobiliary and pancreatic cancers. Our results indicate that high intrahepatic doses of VSV-FH did not result in any significant toxicity and were well tolerated by transgenic mice expressing the measles virus receptor CD46. Furthermore, a single intratumoral treatment with VSV-FH yielded improved survival and complete tumor regressions in a proportion of mice in the Hep3B hepatocellular carcinoma model but not in mice xenografted with BxPC-3 pancreatic cancer cells. Our preliminary findings indicate that VSV-FH can induce potent oncolysis in hepatocellular and pancreatic cancer cell lines with concordant results in vivo in hepatocellular cancer and discordant in pancreatic cancer without the VSV-mediated toxic effects previously observed in laboratory animals. Further study of VSV-FH as an oncolytic virotherapy is warranted in hepatocellular carcinoma and pancreatic cancer to understand broader applicability and mechanisms of sensitivity and resistance.

Advancing Aptamers as Molecular Probes for Cancer Theranostic Applications-The Role of Molecular Dynamics Simulation

Theranostics cover emerging technologies for cell biomarking for disease diagnosis and targeted introduction of drug ingredients to specific malignant sites. Theranostics development has become a significant biomedical research endeavor for effective diagnosis and treatment of diseases, especially cancer. An efficient biomarking and targeted delivery strategy for theranostic applications requires effective molecular coupling of binding ligands with high affinities to specific receptors on the cancer cell surface. Bioaffinity offers a unique mechanism to bind specific target and receptor molecules from a range of non-targets. The binding efficacy depends on the specificity of the affinity ligand toward the target molecule even at low concentrations. Aptamers are fragments of genetic materials, peptides, or oligonucleotides which possess enhanced specificity in targeting desired cell surface receptor molecules. Aptamer-target binding results from several inter-molecular interactions including hydrogen bond formation, aromatic stacking of flat moieties, hydrophobic interaction, electrostatic, and van der Waals interactions. Advancements in Systematic Evolution of Ligands by Exponential Enrichment (SELEX) assay has created the opportunity to artificially generate aptamers that specifically bind to desired cancer and tumor surface receptors with high affinities. This article discusses the potential application of molecular dynamics (MD) simulation to advance aptamer-mediated receptor targeting in targeted cancer therapy. MD simulation offers real-time analysis of the molecular drivers of the aptamer-receptor binding and generate optimal receptor binding conditions for theranostic applications. The article also provides an overview of different cancer types with focus on receptor biomarking and targeted treatment approaches, conventional molecular probes, and aptamers that have been explored for cancer cells targeting.

Syncytia Formation in Oncolytic Virotherapy

Oncolytic virotherapy uses replication-competent virus as a means of treating cancer. Whereas this field has shown great promise as a viable treatment method, the limited spread of these viruses throughout the tumor microenvironment remains a major challenge. To overcome this issue, researchers have begun looking at syncytia formation as a novel method of increasing viral spread. Several naturally occurring fusogenic viruses have been shown to possess strong oncolytic potential and have since been studied to gain insight into how this process benefits oncolytic virotherapy. Whereas these naturally fusogenic viruses have been beneficial, there are still challenges associated with their regular use. Because of this, engineered/recombinant fusogenic viruses have also been created that enhance nonfusogenic oncolytic viruses with the beneficial property of syncytia formation. The purpose of this review is to examine the existing body of literature on syncytia formation in oncolytics and offer direction for potential future studies.

In Vivo Imaging of Oncolytic Measles Virus Propagation with Single-Cell Resolution

Recombinant measles viruses (MVs) have oncolytic activity against a variety of human cancers. However, their kinetics of spread within tumors has been unexplored. We established an intravital imaging system using the dorsal skin fold chamber, which allows for serial, non-invasive imaging of tumor cells and replication of a fusogenic and a hypofusogenic MV. Hypofusogenic virus-infected cells were detected at the earliest 3 days post-infection (dpi), with peak infection around 6 dpi. In contrast, the fusogenic virus replicated faster: infected cells were detectable 1 dpi and cells were killed quickly. Infection foci were significantly larger with the fusogenic virus. Both viruses formed syncytia. The spatial relationships between cells have a major influence on the outcome of therapy with oncolytic viruses.

PTEN expression by an oncolytic herpesvirus directs T-cell mediated tumor clearance

Engineered oncolytic viruses are used clinically to destroy cancer cells and have the ability to boost anticancer immunity. Phosphatase and tensin homolog deleted on chromosome 10 loss is common across a broad range of malignancies, and is implicated in immune escape. The N-terminally extended isoform, phosphatase and tensin homolog deleted on chromosome 10 alpha (PTENα), regulates cellular functions including protein kinase B signaling and mitochondrial adenosine triphosphate production. Here we constructed HSV-P10, a replicating, PTENα expressing oncolytic herpesvirus, and demonstrate that it inhibits PI3K/AKT signaling, increases cellular adenosine triphosphate secretion, and reduces programmed death-ligand 1 expression in infected tumor cells, thus priming an adaptive immune response and overcoming tumor immune escape. A single dose of HSV-P10 resulted in long term survivors in mice bearing intracranial tumors, priming anticancer T-cell immunity leading to tumor rejection. This implicates HSV-P10 as an oncolytic and immune stimulating therapeutic for anticancer therapy.

Oncolytic viruses are a promising therapeutic approach for cancer treatment. The authors demonstrate the efficacy of an engineered HSV-1 expressing PTENα as an oncolytic and immune stimulating therapy against brain cancer metastases.

The emerging role of oncolytic virus therapy against cancer

This review discusses current clinical advancements in oncolytic viral therapy, with a focus on the viral platforms approved for clinical use and highlights the benefits each platform provides. Three oncolytic viruses (OVs), an echovirus, an adenovirus, and a herpes simplex-1 virus, have passed governmental regulatory approval in Latvia, China, and the USA and EU. Numerous other recombinant viruses from diverse families are in clinical testing in cancer patients and we highlight the design features of selected examples, including adenovirus, herpes simplex virus, measles virus, retrovirus, reovirus, vaccinia virus, vesicular stomatitis virus. Lastly, we provide thoughts on the path forward for this rapidly expanding field especially in combination with immune modulating drugs.

Fusogenic Viruses in Oncolytic Immunotherapy

Oncolytic viruses are under intense development and have earned their place among the novel class of cancer immunotherapeutics that are changing the face of cancer therapy. Their ability to specifically infect and efficiently kill tumor cells, while breaking immune tolerance and mediating immune responses directed against the tumor, make oncolytic viruses highly attractive candidates for immunotherapy. Increasing evidence indicates that a subclass of oncolytic viruses, which encodes for fusion proteins, could outperform non-fusogenic viruses, both in their direct oncolytic potential, as well as their immune-stimulatory properties. Tumor cell infection with these viruses leads to characteristic syncytia formation and cell death due to fusion, as infected cells become fused with neighboring cells, which promotes intratumoral spread of the infection and releases additional immunogenic signals. In this review, we discuss the potential of fusogenic oncolytic viruses as optimal candidates to enhance immunotherapy and initiate broad antitumor responses. We provide an overview of the cytopathic mechanism of syncytia formation through viral-mediated expression of fusion proteins, either endogenous or engineered, and their benefits for cancer therapy. Growing evidence indicates that fusogenicity could be an important feature to consider in the design of optimal oncolytic virus platforms for combinatorial oncolytic immunotherapy.

Oncolytic Virus Combination Therapy: Killing One Bird with Two Stones

Over the last 60 years an eclectic collection of microbes has been tested in a variety of pre-clinical models as anti-cancer agents. At the forefront of this research are a number of virus-based platforms that have shown exciting activity in a variety of pre-clinical models and are collectively referred to as oncolytic viruses. Our true understanding of the potential and limitations of this therapeutic modality has been substantially advanced through clinical studies carried out over the last 25 years. Perhaps not surprising, as with all other cancer therapeutics, it has become clear that current oncolytic virus therapeutics on their own are unlikely to be effective in the majority of patients. The greatest therapeutic gains will therefore be made through thoughtful combination strategies built upon an understanding of cancer biology.

CD30-targeted oncolytic viruses as novel therapeutic approach against classical Hodgkin lymphoma

Classical Hodgkin lymphoma (cHL) is a hematopoietic malignancy with a characteristic cellular composition. The tumor mass is made up of infiltrated lymphocytes and other cells of hematologic origin but only very few neoplastic cells that are mainly identified by the diagnostic marker CD30. While most patients with early stage cHL can be cured by standard therapy, treatment options for relapsed or refractory cHL are still not sufficient, although immunotherapy-based approaches for the treatment of cHL patients have gained ground in the last decade. Here, we suggest a novel therapeutic concept based on oncolytic viruses selectively destroying the CD30⁺-positive cHL tumor cells. Relying on a recently described CD30-specific scFv we have generated CD30-targeted measles virus (MV-CD30) and vesicular stomatitis virus (VSV-CD30). For VSV-CD30 the VSV glycoprotein G reading frame was replaced by those of the CD30-targeted MV glycoproteins. Both viruses were found to be highly selective for CD30-positive cells as demonstrated by infection of co-cultures of target and non-target cells as well as through blocking infection by soluble CD30. Notably, VSV-CD30 yielded much higher titers than MV-CD30 and resulted in a more rapid and efficient killing of cultivated cHL-derived cell lines. Mouse tumor models revealed that intratumorally, as well as systemically injected VSV-CD30, infected cHL xenografts and significantly slowed down tumor growth resulting in a substantially prolonged survival of tumor-bearing mice. Taken together, the data support further preclinical testing of VSV-CD30 as novel therapeutic agent for the treatment of cHL and other CD30⁺-positive malignancies.

Recent advances in vesicular stomatitis virus-based oncolytic virotherapy: a 5-year update

Oncolytic virus (OV) therapy is an anti-cancer approach that uses viruses that preferentially infect, replicate in and kill cancer cells. Vesicular stomatitis virus (VSV, a rhabdovirus) is an OV that is currently being tested in the USA in several phase I clinical trials against different malignancies. Several factors make VSV a promising OV: lack of pre-existing human immunity against VSV, a small and easy to manipulate genome, cytoplasmic replication without risk of host cell transformation, independence of cell cycle and rapid growth to high titres in a broad range of cell lines facilitating large-scale virus production. While significant advances have been made in VSV-based OV therapy, room for improvement remains. Here we review recent studies (published in the last 5 years) that address 'old' and 'new' challenges of VSV-based OV therapy. These studies focused on improving VSV safety, oncoselectivity and oncotoxicity; breaking resistance of some cancers to VSV; preventing premature clearance of VSV; and stimulating tumour-specific immunity. Many of these approaches were based on combining VSV with other therapeutics. This review also discusses another rhabdovirus closely related to VSV, Maraba virus, which is currently being tested in Canada in phase I/II clinical trials.

Potential and clinical translation of oncolytic measles viruses

INTRODUCTION

Oncolytic viruses represent a novel treatment modality that is unencumbered by the standard resistance mechanisms limiting the therapeutic efficacy of conventional antineoplastic agents. Attenuated engineered measles virus strains derived from the Edmonston vaccine lineage have undergone extensive preclinical evaluation with significant antitumor activity observed in a broad range of preclinical tumoral models. These have laid the foundation for several clinical trials in both solid and hematologic malignancies, which have demonstrated safety, biologic activity and the ability to elicit antitumor immune responses. Areas covered: This review examines the published preclinical data which supported the clinical translation of this therapeutic platform, reviews the available clinical trial data and expands on ongoing phase II testing. It also looks at approaches to optimize clinical applicability and offers future perspectives. Expert opinion: Reverse genetic engineering has allowed the generation of oncolytic MV strains retargeted to increase viral tumor specificity, or armed with therapeutic and immunomodulatory genes in order to enhance anti-tumor efficacy. Continuous efforts focusing on exploring methods to overcome resistance pathways and determining optimal combinatorial strategies will facilitate further development of this encouraging antitumor strategy.

Enhancing the Oncolytic Activity of CD133-Targeted Measles Virus: Receptor Extension or Chimerism with Vesicular Stomatitis Virus Are Most Effective

Therapy resistance and tumor recurrence are often linked to a small refractory and highly tumorigenic subpopulation of neoplastic cells, known as cancer stem cells (CSCs). A putative marker of CSCs is CD133 (prominin-1). We have previously described a CD133-targeted oncolytic measles virus (MV-CD133) as a promising approach to specifically eliminate CD133-positive tumor cells. Selectivity was introduced at the level of cell entry by an engineered MV hemagglutinin (H). The H protein was blinded for its native receptors and displayed a CD133-specific single-chain antibody fragment (scFv) as targeting domain. Interestingly, MV-CD133 was more active in killing CD133-positive tumors than the unmodified MV-NSe despite being highly selective for its target cells. To further enhance the antitumoral activity of MV-CD133, we here pursued arming technologies, receptor extension, and chimeras between MV-CD133 and vesicular stomatitis virus (VSV). All newly generated viruses including VSV-CD133 were highly selective in eliminating CD133-positive cells. MV-CD46/CD133 killed in addition CD133-negative cells being positive for the MV receptors. In an orthotopic glioma model, MV-CD46/CD133 and MV^SCD-CD133, which encodes the super cytosine deaminase, were most effective. Notably, VSV-CD133 caused fatal neurotoxicity in this tumor model. Use of CD133 as receptor could be excluded as being causative. In a subcutaneous tumor model of hepatocellular cancer, VSV-CD133 revealed the most potent oncolytic activity and also significantly prolonged survival of the mice when injected intravenously. Compared to MV-CD133, VSV-CD133 infected a more than 10⁴-fold larger area of the tumor within the same time period. Our data not only suggest new concepts and approaches toward enhancing the oncolytic activity of CD133-targeted oncolytic viruses but also raise awareness about careful toxicity testing of novel virus types.

Designing and building oncolytic viruses

Oncolytic viruses (OVs) are engineered and/or evolved to propagate selectively in cancerous tissues. They have a dual mechanism of action; direct killing of infected cancer cells cross-primes anticancer immunity to boost the killing of uninfected cancer cells. The goal of the field is to develop OVs that are easily manufactured, efficiently delivered to disseminated sites of cancer growth, undergo rapid intratumoral spread, selectively kill tumor cells, cause no collateral damage and pose no risk of transmission in the population. Here we discuss the many virus engineering strategies that are being pursued to optimize delivery, intratumoral spread and safety of OVs derived from different virus families. With continued progress, OVs have the potential to transform the paradigm of cancer care.

Towards targeted cancer therapy: Aptamer or oncolytic virus?

Cancer is a leading cause of global mortality. Whilst anticancer awareness programs have increased significantly over the years, scientific research into the development of efficient and specific drugs to target cancerous cells for enhanced therapeutic effects has not received much clinical success. Chemotherapeutic agents are incapable of acting specifically on cancerous cells, thus causing low therapeutic effects accompanied by toxicity to surrounding normal tissues. The search for smart, highly specific and efficient cancer treatments and delivery systems continues to be a significant research endeavor. Targeted cancer therapy is an evolving treatment approach with great promise in enhancing the efficacy of cancer therapies via the delivery of therapeutic agents specifically to and into desired tumor cells using viral or non-viral targeting elements. Viral oncotherapy is an advanced cancer therapy based on the use of oncolytic viruses (OV) as elements to specifically target, replicate and kill malignant cancer cells selectively without affecting surrounding healthy cells. Aptamers, on the other hand, are non-viral targeting elements that are single-stranded nucleic acids with high specificity, selectivity and binding affinity towards their cognate targets. Aptamers have emerged as a new class of bioaffinity targeting elements can be generated and molecularly engineered to selectively bind to diverse targets including proteins, cells and tissues. This article discusses, comparatively, the potentials and impacts of both viral and aptamer-mediated targeted cancer therapies in advancing conventional drug delivery systems through enhanced target specificity, therapeutic payload, bioavailability of the therapeutic agents at the target sites whilst minimizing systemic cytotoxicity. This article emphasizes on effective site-directed targeting mechanisms and efficacy issues that impact on clinical applications.

Enhanced lysis by bispecific oncolytic measles viruses simultaneously using HER2/neu or EpCAM as target receptors

To target oncolytic measles viruses (MV) to tumors, we exploit the binding specificity of designed ankyrin repeat proteins (DARPins). These DARPin-MVs have high tumor selectivity while maintaining excellent oncolytic potency. Stability, small size, and efficacy of DARPins allowed the generation of MVs simultaneously targeted to tumor marker HER2/neu and cancer stem cell (CSC) marker EpCAM. For optimization, the linker connecting both DARPins was varied in flexibility and length. Flexibility had no impact on fusion helper activity whereas length had. MVs with bispecific MV-H are genetically stable and revealed the desired double-target specificity. In vitro, the cytolytic activity of bispecific MVs was superior or comparable to mono-targeted viruses depending on the target cells. In vivo, therapeutic efficacy of the bispecific viruses was validated in an orthotopic ovarian carcinoma model revealing an effective reduction of tumor mass. Finally, the power of bispecific targeting was demonstrated on cocultures of different tumor cells thereby mimicking tumor heterogeneity in vitro, more closely reflecting real tumors. Here, bispecific excelled monospecific viruses in efficacy. DARPin-based targeting domains thus allow the generation of efficacious oncolytic viruses with double specificity, with the potential to handle intratumoral variation of antigen expression and to simultaneously target CSCs and the bulk tumor mass.

Oncolytic potency of HER-2 retargeted VSV-FH hybrid viruses: the role of receptor ligand affinity

The hybrid oncolytic vesicular stomatitis virus (VSV-FH) deleted for its G glycoprotein and displaying the measles virus (MV) envelope glycoproteins (hemagglutinin H and fusion F) is fusogenic, infects cells via any of the three MV receptors and has potent oncolytic activity against subcutaneous and disseminated myeloma tumors. To tailor VSV-FH as an oncolytic virus for ovarian cancer, we ablated its natural tropism and retargeted the virus by display of a single-chain antibody (scFv) with specificity to the HER-2/neu receptor. A panel of six VSVFH-αHER2 viruses displaying anti-HER2 scFv that bind to the same HER2 epitope but with different K_d (10⁻⁶ to 10⁻¹¹ M, VSVFH-αHER2#6 to #11, respectively) were rescued and characterized. A K_d of at least 10⁻⁸ M is required for infection of HER-2 positive SKOV3ip.1 cells. The higher affinity viruses (>10⁻⁸ M) were able to infect and fuse SKOV3ip.1 cells more efficiently, inducing more extensive cytopathic effects. We next compared the antitumor potency of the viruses against SKOV3ip.1 tumor xenografts. In contrast to the saline-treated animals, one intratumoral injection of VSVFH-αHER2#9, #10, or #11 resulted in efficient tumor control. There was no significant difference between viruses with an affinity higher than 10⁻⁹ M in terms of oncolytic potency. VSVFH-αHER2 virus may be a promising agent for the treatment of HER-2 positive malignancies.

Oncolytic bovine herpesvirus type 1 as a broad spectrum cancer therapeutic

Oncolytic viruses selectively replicate in tumor cells and elicit antitumor effects in vivo by both direct and indirect methods. They are attractive avenues of cancer therapy due to the absence of toxic side effects often seen in current treatment modalities. Bovine herpesvirus type 1 (BHV-1) holds promise as a broad-spectrum oncolytic vector that is able to infect and kill human tumor cells from a variety of histological origins, including cancer-initiating cells. In the majority of cases, BHV-1 elicits tumor cell death in the absence of a productive infection. In vivo, BHV-1 affects the incidence of secondary lesions in cotton rats bearing subcutaneous breast adenocarcinomas. These recent studies contribute to the characterization of BHV-1 as an oncolytic virus.

Enhanced efficacy with azacytidine and oncolytic BHV-1 in a tolerized cotton rat model of breast adenocarcinoma

Oncolytic viruses selectively replicate in cancer cells by exploiting biochemical differences between normal and tumor cells. Treatment with epigenetic modifiers such as 5-Azacytidine, a DNA methyltransferase inhibitor, increases the replication and cytotoxicity of oncolytic viruses in vivo and in vitro. The cotton rat is an attractive animal to study oncolytic viruses, as syngeneic models of breast adenocarcinoma and osteosarcoma are well established, and many features of primary and secondary tumor growth recapitulate human disease. Treatment of LCRT breast cancer cells with 5-Azacytidine increases bovine herpesvirus type 1 (BHV-1)-mediated cytotoxicity in vitro, with Chou-Talalay analysis indicating a very strong synergy. In vivo, BHV-1 monotherapy delayed tumor growth but did not improve survival of cotton rats with subcutaneous breast adenocarcinomas. However, combination therapy significantly decreased the incidence of secondary lesions, with enhanced tumor cell clearance and evidence of immune cell infiltration compared to BHV-1 monotherapy. Together, these results warrant further investigation of BHV-1 combination therapy with epigenetic modifiers for the treatment of breast cancer, particularly in the context of the prevention and treatment of secondary lesions.