Fusogenic vesicular stomatitis virus for the treatment of head and neck squamous carcinomas

Construction of VSVΔ51M oncolytic virus expressing human interleukin-12

The use of oncolytic viruses (OVs) in combination with cytokines, such as IL-12, is a promising approach for cancer treatment that addresses the limitations of current standard treatments and traditional cancer immunotherapies. IL-12, a proinflammatory cytokine, triggers intracellular signaling pathways that lead to increased apoptosis of tumor cells and enhanced antitumor activity of immune cells via IFN-γ induction, making this cytokine a promising candidate for cancer therapy. Targeted expression of IL-12 within tumors has been shown to play a crucial role in tumor eradication. The recent development of oncolytic viruses enables targeted delivery and expression of IL-12 at the tumor site, thereby addressing the systemic toxicities associated with traditional cancer therapy. In this study, we constructed an oncolytic virus, VSVΔ51M, based on the commercially available VSV wild-type backbone and further modified it to express human IL-12. Our preclinical data confirmed the safety and limited toxicity of the modified virus, VSV-Δ51M-hIL-12, supporting its potential use for clinical development.

A Novel Chimeric Oncolytic Virus Vector for Improved Safety and Efficacy as a Platform for the Treatment of Hepatocellular Carcinoma

Oncolytic viruses represent an exciting new aspect of the evolving field of cancer immunotherapy. We have engineered a novel hybrid vector comprising vesicular stomatitis virus (VSV) and Newcastle disease virus (NDV), named recombinant VSV-NDV (rVSV-NDV), wherein the VSV backbone is conserved but its glycoprotein has been replaced by the hemagglutinin-neuraminidase (HN) and the modified, hyperfusogenic fusion (F) envelope proteins of recombinant NDV. In comparison to wild-type VSV, which kills cells through a classical cytopathic effect, the recombinant virus is able to induce tumor-specific syncytium formation, allowing efficient cell-to-cell spread of the virus and a rapid onset of immunogenic cell death. Furthermore, the glycoprotein exchange substantially abrogates the off-target effects in brain and liver tissue associated with wild-type VSV, resulting in a markedly enhanced safety profile, even in immune-deficient NOD.CB17-prkdc^scid/NCrCrl (NOD-SCID) mice, which are highly susceptible to wild-type VSV. Although NDV causes severe pathogenicity in its natural avian hosts, the incorporation of the envelope proteins in the chimeric rVSV-NDV vector is avirulent in embryonated chicken eggs. Finally, systemic administration of rVSV-NDV in orthotopic hepatocellular carcinoma (HCC)-bearing immune-competent mice resulted in significant survival prolongation. This strategy, therefore, combines the beneficial properties of the rapidly replicating VSV platform with the highly efficient spread and immunogenic cell death of a fusogenic virus without risking the safety and environmental threats associated with either parental vector. Taking the data together, rVSV-NDV represents an attractive vector platform for clinical translation as a safe and effective oncolytic virus.IMPORTANCE The therapeutic efficacy of oncolytic viral therapy often comes as a tradeoff with safety, such that potent vectors are often associated with toxicity, while safer viruses tend to have attenuated therapeutic effects. Despite promising preclinical data, the development of VSV as a clinical agent has been substantially hampered by the fact that severe neurotoxicity and hepatotoxicity have been observed in rodents and nonhuman primates in response to treatment with wild-type VSV. Although NDV has been shown to have an attractive safety profile in humans and to have promising oncolytic effects, its further development has been severely restricted due to the environmental risks that it poses. The hybrid rVSV-NDV vector, therefore, represents an extremely promising vector platform in that it has been rationally designed to be safe, with respect to both the recipient and the environment, while being simultaneously effective, both through its direct oncolytic actions and through induction of immunogenic cell death.

Reovirus FAST Protein Enhances Vesicular Stomatitis Virus Oncolytic Virotherapy in Primary and Metastatic Tumor Models

The reovirus fusion-associated small transmembrane (FAST) proteins are the smallest known viral fusogens (∼100–150 amino acids) and efficiently induce cell-cell fusion and syncytium formation in multiple cell types. Syncytium formation enhances cell-cell virus transmission and may also induce immunogenic cell death, a form of apoptosis that stimulates immune recognition of tumor cells. These properties suggest that FAST proteins might serve to enhance oncolytic virotherapy. The oncolytic activity of recombinant VSVΔM51 (an interferon-sensitive vesicular stomatitis virus [VSV] mutant) encoding the p14 FAST protein (VSV-p14) was compared with a similar construct encoding GFP (VSV-GFP) in cell culture and syngeneic BALB/c tumor models. Compared with VSV-GFP, VSV-p14 exhibited increased oncolytic activity against MCF-7 and 4T1 breast cancer spheroids in culture and reduced primary 4T1 breast tumor growth in vivo. VSV-p14 prolonged survival in both primary and metastatic 4T1 breast cancer models, and in a CT26 metastatic colon cancer model. As with VSV-GFP, VSV-p14 preferentially replicated in vivo in tumors and was cleared rapidly from other sites. Furthermore, VSV-p14 increased the numbers of activated splenic CD4, CD8, natural killer (NK), and natural killer T (NKT) cells, and increased the number of activated CD4 and CD8 cells in tumors. FAST proteins may therefore provide a multi-pronged approach to improving oncolytic virotherapy via syncytium formation and enhanced immune stimulation.

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.

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

VSV-FH is a hybrid vesicular stomatitis virus (VSV) with a deletion of its G glycoprotein and encoding the measles virus (MV) fusion (F) and hemagglutinin (H) envelope glycoproteins. VSV-FH infects cells expressing MV receptors and is fusogenic and effective against myeloma xenografts in mice. We evaluated the fusogenic activities of MV and VSV-FH in relationship to the density of receptor on the target cell surface and the kinetics of F and H expression in infected cells. Using a panel of cells expressing increasing numbers of the MV receptor CD46, we evaluated syncytium size in MV- or VSV-FH-infected cells. VSV-FH is not fusogenic at low CD46 density but requires less CD46 for syncytium formation than MV. The size of each syncytium is larger in VSV-FH-infected cells at a specific CD46 density. While syncytium size reached a plateau and did not increase further in MV-infected CHO cells expressing ≥4,620 CD46 copies/cell, there was a corresponding increase in syncytium size with increases in CD46 levels in VSV-FH-infected CD46-expressing CHO (CHO-CD46) cells. Further analysis in VSV-FH-infected cell lines shows earlier and higher expression of F and H mRNAs and protein. However, VSV-FH cytotoxic activity was reduced by pretreatment of the cells with type I interferon. In contrast, the cytopathic effects are not affected in MV-infected cells. In summary, VSV-FH has significant advantages over MV as an oncolytic virus due to its higher viral yield, faster replication kinetics, and larger fusogenic capabilities but should be used in cancer types with defective interferon signaling pathways.

IMPORTANCE

We studied the cytotoxic activity of a vesicular stomatitis/measles hybrid virus (VSV-FH), which is superior to that of measles virus (MV), in different cancer cell lines. We determined that viral RNA and protein were produced faster and in higher quantities in VSV-FH-infected cells. This resulted in the formation of larger syncytia, higher production of infectious particles, and a more potent cytopathic effect in permissive cells. Importantly, VSV-FH, similar to MV, can discriminate between low- and high-expressing CD46 cells, a phenotype important for cancer therapy as the virus will be able to preferentially infect cancer cells that overexpress CD46 over low-CD46-expressing normal cells.

Preclinical safety and activity of recombinant VSV-IFN-β in an immunocompetent model of squamous cell carcinoma of the head and neck

BACKGROUND

Recombinant vesicular stomatitis virus expressing interferon-β (VSV-IFN-β) has demonstrated antitumor activity in vitro and in vivo. In preparation for clinical testing in human squamous cell carcinoma (SCC) of the head and neck, we conducted preclinical studies of VSV-IFN-β in syngeneic SCC models.

METHODS

In vitro, VSV-IFN-β (expressing rat or mouse interferon [IFN]-β)-induced cytotoxicity and propagated in rat (FAT-7) or mouse (SCC-VII) SCC cells during normoxia and hypoxia. In vivo, intratumoral administration of VSV-rat-IFN-β or VSV-human-IFN-β in FAT-7 bearing or non-tumor bearing immunocompetent rats did not result in acute organ toxicity or death.

RESULTS

VSV-r-IFN-β replicated predominantly in tumors and a dose dependent anti-VSV antibody response was observed. Intratumoral or intravenous administration of VSV-IFN-β resulted in growth delay and improved survival compared with controls.

CONCLUSION

The above data confirm safety and feasibility of VSV-IFN-β administration in immunocompetent animals and support its clinical evaluation in advanced human head and neck cancer.

Oncolytic vesicular stomatitis virus in an immunocompetent model of MUC1-positive or MUC1-null pancreatic ductal adenocarcinoma

Vesicular stomatitis virus (VSV) is a promising oncolytic agent against various malignancies. Here, for the first time, we tested VSV in vitro and in vivo in a clinically relevant, immunocompetent mouse model of pancreatic ductal adenocarcinoma (PDA). Our system allows the study of virotherapy against PDA in the context of overexpression (80% of PDA patients) or no expression of human mucin 1 (MUC1), a major marker for poor prognosis in patients. In vitro, we tested three VSV recombinants, wild-type VSV, VSV-green fluorescent protein (VSV-GFP), and a safe oncolytic VSV-ΔM51-GFP, against five mouse PDA cell lines that either expressed human MUC1 or were MUC1 null. All viruses demonstrated significant oncolytic abilities independent of MUC1 expression, although VSV-ΔM51-GFP was somewhat less effective in two PDA cell lines. In vivo administration of VSV-ΔM51-GFP resulted in significant reduction of tumor growth for tested mouse PDA xenografts (+MUC1 or MUC1 null), and antitumor efficacy was further improved when the virus was combined with the chemotherapeutic drug gemcitabine. The antitumor effect was transient in all tested groups. The developed system can be used to study therapies involving various oncolytic viruses and chemotherapeutics, with the goal of inducing tumor-specific immunity while preventing premature virus clearance.

Vesicular stomatitis virus as a flexible platform for oncolytic virotherapy against cancer

Oncolytic virus (OV) therapy is an emerging anti-cancer approach that utilizes viruses to preferentially infect and kill cancer cells, while not harming healthy cells. Vesicular stomatitis virus (VSV) is a prototypic non-segmented, negative-strand RNA virus with inherent OV qualities. Antiviral responses induced by type I interferon pathways are believed to be impaired in most cancer cells, making them more susceptible to VSV than normal cells. Several other factors make VSV a promising OV candidate for clinical use, including its well-studied biology, a small, easily manipulated genome, relative independence of a receptor or cell cycle, cytoplasmic replication without risk of host-cell transformation, and lack of pre-existing immunity in humans. Moreover, various VSV-based recombinant viruses have been engineered via reverse genetics to improve oncoselectivity, safety, oncotoxicity and stimulation of tumour-specific immunity. Alternative delivery methods are also being studied to minimize premature immune clearance of VSV. OV treatment as a monotherapy is being explored, although many studies have employed VSV in combination with radiotherapy, chemotherapy or other OVs. Preclinical studies with various cancers have demonstrated that VSV is a promising OV; as a result, a human clinical trial using VSV is currently in progress.

Oncolytic specificity of Newcastle disease virus is mediated by selectivity for apoptosis-resistant cells

Newcastle disease virus (NDV) is a negative-sense RNA virus that has been shown to possess oncolytic activity. NDV's selective replication in tumor cells has been previously suggested to be due to the lack of a proper antiviral response in these cells. Here we demonstrate that NDV possesses oncolytic activity in tumor cells capable of a robust type I interferon (IFN) response, suggesting that another mechanism underlies NDV's tumor specificity. We show that the oncolytic selectivity of NDV for tumor cells is dependent upon tumor cell resistance to apoptosis. Utilizing the human non-small-cell lung cancer cell line A549 overexpressing the antiapoptotic protein Bcl-xL, we show significant enhancement of oncolytic activity and NDV replication. Interestingly, while the Bcl-xL-overexpressing cells were resistant to apoptotic stimuli induced by chemotherapeutic agents and early viral replication, during the subsequent viral cycles, we observed a paradoxical increase in apoptosis in response to NDV. The increased oncolytic activity seen was secondary to enhanced viral replication and syncytium formation. The induction of a type I IFN response was enhanced in Bcl-xL cells. Overall, these findings propose a new mechanism for cancer cell specificity for NDV, making it an attractive anticancer agent for chemoresistant tumors with enhanced antiapoptotic activity.

Enhanced oncolytic activity of vesicular stomatitis virus encoding SV5-F protein against prostate cancer

PURPOSE

Vesicular stomatitis virus has been investigated as an oncolytic agent for cancer therapy because it preferentially replicates in tumor but not in normal cells due to the lack of a robust interferon antiviral system in transformed cells. However, wild-type vesicular stomatitis virus can induce a strong systemic immunological response and replicate in the central nervous system, potentially limiting its clinical usefulness. We report the construction of the recombinant, replication restricted vesicular stomatitis virus encoding SV5-F, which can induce syncytial formation with enhanced oncolytic properties against TRAMP-C2 tumors in an immunocompetent mouse model of prostate cancer.

MATERIALS AND METHODS

We constructed the SV5-F recombinant restricted virus vector by replacing the vesicular stomatitis virus G gene with that of the SV5-F transgene to generate rVSV-DeltaG-SV5-F. Morphological changes and DNA fragmentation induced by rVSV-DeltaG-GFP or rVSV-DeltaG-SV5-F were determined by phase contrast microscopy and gel electrophoresis. In vitro cytotoxicity by recombinant vesicular stomatitis virus was done by MTT assay. In vivo study of rVSV treatment was done in immunocompetent mice by subcutaneous administration of TRAMP-C2 cells.

RESULTS

In vitro characterization of the recombinant fusogenic VSV-DeltaG vector on TRAMP-C2 cells showed significantly enhanced apoptotic and cytotoxic effects relative to a similar virus encoding green fluorescent protein, that is rVSV-DeltaG-GFP. Regardless of initial tumor size intratumor rVSV-DeltaG-SV5-F administration in mice bearing subcutaneous TRAMP-C2 tumors resulted in a significantly reduced tumor load over that of the nonfusogenic green fluorescent control virus and of heat inactivated recombinant vesicular stomatitis virus in treated animals (p <0.01).

CONCLUSIONS

Results show that G complemented recombinant VSV-DeltaG vectors, especially rVSV-DeltaG-SV5-F, are an effective oncolytic agent against mouse prostate cancer cells in vitro and in an in vivo immunocompetent mouse model system.

Engineered newcastle disease virus as an improved oncolytic agent against hepatocellular carcinoma

Newcastle disease virus (NDV) is an intrinsically tumor-specific virus, which is currently under investigation as a clinical oncolytic agent. Several clinical trials have reported NDV to be a safe and effective agent for cancer therapy; however, there remains a clear need for improvement in therapeutic outcome. The endogenous NDV fusion (F) protein directs membrane fusion, which is required for virus entry and cell-cell fusion. Here, we report a novel NDV vector harboring an L289A mutation within the F gene, which resulted in enhanced fusion and cytotoxicity of hepatocellular carcinoma (HCC) cells in vitro, as compared with the rNDV/F3aa control virus. In vivo administration of the recombinant vector, termed rNDV/F3aa(L289A), via hepatic arterial infusion in immune-competent Buffalo rats bearing multifocal, orthotopic liver tumors resulted in tumor-specific syncytia formation and necrosis, with no evidence of toxicity to the neighboring hepatic parenchyma. Furthermore, the improved oncolysis conferred by the L289A mutation translated to significantly prolonged survival compared with control NDV. Taken together, rNDV/F(L289A) represents a safe, yet more effective vector than wild-type NDV for the treatment of HCC, making it an ideal candidate for clinical application in HCC patients.

Genetically engineered Newcastle disease virus for malignant melanoma therapy

Despite the advances in cancer therapies in the past century, malignant melanoma continues to present a significant clinical challenge due to lack of chemotherapeutic response. Systemic therapy with immunostimulatory agents such as interferon and interleukin-2 (IL-2) has shown some promise, though each is associated with significant side effects. Over the past 50 years, oncolytic Newcastle disease virus (NDV) has emerged as an alternative candidate for cancer therapy. The establishment of reverse-genetics systems for the virus has allowed us to further manipulate the virus to enhance its oncolytic activity. Introduction of immunomodulatory molecules, especially IL-2, into the NDV genome was shown to enhance the oncolytic potential of the virus in a murine syngeneic colon carcinoma model. We hypothesize that a recombinant NDV expressing IL-2 would be an effective agent for therapy of malignant melanoma. We show that recombinant NDV possesses a strong cytolytic activity against multiple melanoma cell lines, and is effective in clearing established syngeneic melanoma tumors in mice. Moreover, introduction of murine IL-2 into NDV significantly enhanced its activity against syngeneic melanomas, resulting in increased overall animal survival and generation of antitumor immunity. These findings warrant further investigations of IL-2-expressing NDV as an antimelanoma agent in humans.

Enhancement of oncolytic properties of recombinant newcastle disease virus through antagonism of cellular innate immune responses

Newcastle disease virus (NDV) has been previously shown to possess oncolytic activity, causing specific lysis of cancerous but not normal cells. Here we show that despite these findings, the oncolytic efficiency of naturally occurring NDV strains can still be relatively low, as many tumors exhibit strong innate immune responses that suppress viral replication and spread. To overcome this problem, we generated a recombinant fusogenic NDV expressing influenza NS1 protein, a protein exhibiting interferon (IFN)-antagonist and antiapoptotic functions in human and mouse cells. Interestingly, the resultant virus was dramatically enhanced in its ability to form syncytia, lyse a variety of human and mouse tumor cell lines, and suppressed the induction of the cellular IFN responses. Using the aggressive syngeneic murine melanoma model, we show that the NDV-NS1 virus is more effective than virus not expressing NS1 in clearing the established footpad tumors and results in higher overall long-term animal survival. In addition, mice treated with NDV-NS1 exhibited no signs of toxicity to the virus and developed tumor-specific cytotoxic T lymphocyte (CTL) responses. These findings demonstrate that modulation of innate immune responses by NDV results in enhancement of its oncolytic properties and warrant further investigation of this strategy in design of oncolytic NDV vectors against human tumors.

A hyperfusogenic F protein enhances the oncolytic potency of a paramyxovirus simian virus 5 P/V mutant without compromising sensitivity to type I interferon

Viral fusogenic membrane proteins have been proposed as tools to increase the potency of oncolytic viruses, but there is a need for mechanisms to control the spread of fusogenic viruses in normal versus tumor cells. We have previously shown that a mutant of the paramyxovirus simian virus 5 (SV5) that harbors mutations in the P/V gene from the canine parainfluenza virus (P/V-CPI(-)) is a potent inducer of type I interferon (IFN) and apoptosis and is restricted for spread through normal but not tumor cells in vitro. Here, we have used the cytopathic P/V-CPI(-) as a backbone vector to test the hypothesis that a virus expressing a hyperfusogenic glycoprotein will be a more effective oncolytic vector but will retain sensitivity to IFN. A P/V mutant virus expressing an F protein with a glycine-to-alanine substitution in the fusion peptide (P/V-CPI(-)-G3A) was more fusogenic than the parental P/V-CPI(-) mutant. In two model prostate tumor cell lines which are defective in IFN production (LNCaP and DU145), the hyperfusogenic P/V-CPI(-)-G3A mutant had normal growth properties at low multiplicities of infection and was more effective than the parental P/V-CPI(-) mutant at cell killing in vitro. However, in PC3 cells which produce and respond to IFN, the hyperfusogenic P/V-CPI(-)-G3A mutant was attenuated for growth and spread. Killing of PC3 cells was equivalent between the parental P/V-CPI(-) mutant and the hyperfusogenic P/V-CPI(-)-G3A mutant. In a nude mouse model using LNCaP cells, the hyperfusogenic P/V-CPI(-)-G3A mutant was more effective than P/V-CPI(-) at reducing tumor burden. In the case of DU145 tumors, the two vectors based on P/V-CPI(-) were equally effective at limiting tumor growth. Together, our results provide proof of principle that a cytopathic SV5 P/V mutant can serve as an oncolytic virus and that the oncolytic effectiveness of P/V mutants can be enhanced by a fusogenic membrane protein without compromising sensitivity to IFN. The potential advantages of SV5-based oncolytic vectors are discussed.

Combined VSV oncolytic virus and chemotherapy for squamous cell carcinoma

OBJECTIVES

Vesicular stomatitis virus (VSV) is a negative-strand ribonucleic acid (RNA) virus that replicates specifically in tumor cells and has oncolytic effects in a variety of malignant tumors. We previously demonstrated recombinant VSV vectors incorporating viral fusion protein (rVSV-F) and interleukin 12 (rVSV-IL12) to have significant antitumor effects against squamous cell carcinoma (SCC) in a murine model. Here we evaluate the potential to combine a potent chemotherapeutic agent for SCC (cisplatin) with rVSV-F and rVSV-IL12 to improve efficacy.

STUDY DESIGN

In vitro, three SCC cell lines were tested using rVSV-F and rVSV-IL12 with cisplatin, monitoring viral replication and cell survival. In an orthotopic floor of mouth murine SCC model, intratumoral injections of virus combined with systemic cisplatin were tested for tumor control and animal survival.

RESULTS

In vitro, virus and cisplatin combination demonstrated rapid replication and enhanced tumor cell kill. Human keratinocytes were unaffected by virus and cisplatin. In vivo, combined rVSV-F with cisplatin reduced tumor burden and improved survival (P = .2 for both), while rVSV-IL12 monotherapy had better tumor control (P = .06) and survival (P = .024) than combination therapy.

CONCLUSIONS

Addition of cisplatin did not affect the ability of either virus to replicate in or kill murine SCC cells in vitro. In vivo, combination therapy enhancedrVSV-F antitumor activity, but diminished rVSV-IL12 antitumor activity. Combination therapy may provide useful treatment for SCC with the development of more efficient viral vectors in combination with different chemotherapy agents or immunostimulatory agents.