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

Genetically engineered Newcastle disease virus expressing interleukin 2 is a potential drug candidate for cancer immunotherapy

Newcastle disease virus (NDV) is an intrinsically tumor-specific virus, several clinical trials have reported that mesogenic NDV is a safe and effective agent for human cancer therapy. Interleukin 2 (IL2) is a cytokine that stimulates T cell propagation to trigger innate and adaptive immunity. IL2 has been used for cancer therapy and has achieved curative effects. In this study, a recombinant NDV LaSota strain expressing human interleukin 2 (rLaSota/IL2) was generated. The ability of rLaSota/IL2 to express human IL2 was detected in the infected tumor cells. In addition, the activity of IL2 was analyzed. The antitumor potential of rLaSota/IL2 was studied by xenograph mice carrying H22 and B16-F10 cells. Tumor-specific CD4(+) and CD8(+) T cells and MHC II were also analyzed in the two tumor-bearing models. Our study showed that rLaSota/IL2 significantly stimulated tumor-specific cytotoxic T-lymphocyte (CTL) responses and increased regulatory CD4(+) and cytotoxic CD8(+) T cells proliferation. The treatment with rLaSota/IL2 led to tumor regression in tumor-bearing mice and prolonged the survival of tumor-bearing mice. Furthermore, tumor challenging experiments demonstrated that rLaSota/IL2 invoked mice a unique capacity to remember a pathogen through the generation of memory T cells, which protect the host in the event of reinfection and form adaptive immune system. The result indicates that tumor-infiltrating CD4(+) T regulatory cells may denote the effective regression of tumors. Taken together, rLaSota/IL2 has potential for immunotherapy and oncolytic therapy of cancers and may be an ideal candidate for clinical application in future cancer therapy.

Newcastle disease virus: current status and our understanding

Newcastle disease (ND) is one of the highly pathogenic viral diseases of avian species. ND is economically significant because of the huge mortality and morbidity associated with it. The disease is endemic in many third world countries where agriculture serves as the primary source of national income. Newcastle disease virus (NDV) belongs to the family Paramyxoviridae and is well characterized member among the avian paramyxovirus serotypes. In recent years, NDV has lured the virologists not only because of its pathogenic potential, but also for its oncolytic activity and its use as a vaccine vector for both humans and animals. The NDV based recombinant vaccine offers a pertinent choice for the construction of live attenuated vaccine due to its modular nature of transcription, minimum recombination frequency, and lack of DNA phase during replication. Our current understanding about the NDV biology is expanding rapidly because of the availability of modern molecular biology tools and high-throughput complete genome sequencing.

Different responses of human pancreatic adenocarcinoma cell lines to oncolytic Newcastle disease virus infection

Newcastle disease virus (NDV) is a naturally occurring oncolytic virus with clinically proven efficacy against several human tumor types. Selective replication in and killing of tumor cells by NDV is thought to occur because of differences in innate immune responses between normal and tumor cells. In our effort to develop oncolytic virotherapy with NDV for patients with pancreatic cancer, we evaluated the responses to NDV infection and interferon (IFN) treatment of 11 different established human pancreatic adenocarcinoma cell lines (HPACs). Here we show that all HPACs were susceptible to NDV. However, this NDV infection resulted in different replication kinetics and cytotoxic effects. Better replication resulted in more cytotoxicity. No correlation was observed between defects in the IFN pathways and NDV replication or NDV-induced cytotoxicity. IFN production by HPACs after NDV infection differed substantially. Pretreatment of HPACs with IFN resulted in diminished NDV replication and decreased the cytotoxic effects in most HPACs. These findings suggest that not all HPACs have functional defects in the innate immune pathways, possibly resulting in resistance to oncolytic virus treatment. These data support the rationale for designing recombinant oncolytic NDVs with optimized virulence that should likely contain an antagonist of the IFN pathways.

Rescue of recombinant Newcastle disease virus from cDNA

Newcastle disease virus (NDV), the prototype member of the Avulavirus genus of the family Paramyxoviridae(1), is a non-segmented, negative-sense, single-stranded, enveloped RNA virus (Figure 1) with potential applications as a vector for vaccination and treatment of human diseases. In-depth exploration of these applications has only become possible after the establishment of reverse genetics techniques to rescue recombinant viruses from plasmids encoding their complete genomes as cDNA(2-5). Viral cDNA can be conveniently modified in vitro by using standard cloning procedures to alter the genotype of the virus and/or to include new transcriptional units. Rescue of such genetically modified viruses provides a valuable tool to understand factors affecting multiple stages of infection, as well as allows for the development and improvement of vectors for the expression and delivery of antigens for vaccination and therapy. Here we describe a protocol for the rescue of recombinant NDVs.

[Genetic, immunological, and pharmacological strategies to generate improved oncolytic viruses]

Since over a century, medical literature has reported cases of viral infections leading to tumour regression. This phenomenon, now understood, can be exploited for cancer therapy. It involves viruses defined as "oncolytic". These viruses, either wild-type or genetically engineered, replicate preferentially in malignant cells. They induce tumour regression through various mechanisms including direct cell lysis and stimulation of an anti-tumour immune response. Several oncolytic viruses have reached late-stage clinical investigation and could be approved soon for treating certain neoplasms. While already promising, there is still room for improvement and various genetic, immunological, and pharmacological strategies are currently under development to increase their therapeutic efficacy.

Cell-type-specific innate immune response to oncolytic Newcastle disease virus

Virotherapy of cancer exploits the potential of naturally occurring and engineered oncolytic viruses to selectively replicate in and cause cytotoxicity to tumor cells without affecting healthy normal cells. The tumor selectivity of Newcastle disease virus (NDV), a member of the family Paramyxoviridae, depends on the differential type I interferon (IFN) response. Further understanding of the key mechanisms and immune effector molecules involved will aid in augmenting the oncolytic properties of NDV. Here we report on the infection kinetics and innate immune responses to a recombinant LaSota strain of NDV (rLaSota eGFP) in human tumor and normal cells. We observed varying replicative fit and cytotoxicity of rLaSota eGFP depending on the tumor cell type, with severely restricted replication in normal cells. The absence of retinoic acid-inducible gene I (RIG-I), a cytosolic RNA sensor, determined sensitivity to NDV. Productive NDV infection with a moderate IFN-α induction in human multiple myeloma cells suggested a role for IFN-independent mechanisms or lack of type I IFN reinforcement by RIG-I. Proinflammatory cytokines and chemokines were altered differentially in infected normal and tumor cells. Our results suggest that tumor selectivity is dependent on variations in the cellular antiviral response to infection with NDV and RIG-I expression.

Oncolytic Newcastle disease virus for cancer therapy: old challenges and new directions

Newcastle disease virus (NDV) is an avian paramyxovirus, which has been demonstrated to possess significant oncolytic activity against mammalian cancers. This review summarizes the research leading to the elucidation of the mechanisms of NDV-mediated oncolysis, as well as the development of novel oncolytic agents through the use of genetic engineering. Clinical trials utilizing NDV strains and NDV-based autologous tumor cell vaccines will expand our knowledge of these novel anticancer strategies and will ultimately result in the successful use of the virus in the clinical setting.

Epigenetic silencing of IRF7 and/or IRF5 in lung cancer cells leads to increased sensitivity to oncolytic viruses

Defective IFN signaling results in loss of innate immunity and sensitizes cells to enhanced cytolytic killing after Vesticular Stomatitis Virus (VSV) infection. Examination of the innate immunity status of normal human bronchial epithelial cells Beas2B and 7 lung cancer cells revealed that the abrogation of IFN signaling in cancer cells is associated with greater sensitivity to VSV infection. The disruption of the IFN pathway in lung cancer cell lines and primary tumor tissues is caused by epigenetic silencing of critical interferon responsive transcription factors IRF7 and/or IRF5. Although 5-aza-2′-deoxycytidine treatment fails to reactivate IRF7 and IRF5 expression or protect cells from VSV infection, manipulating IFN signaling by altering IRF expression changes the viral susceptibility of these cells. Lung cancer cells can be partially protected from viral killing using IRF5+IRF7 overexpression, whereas IFN pathway disruption by transfection of siRNAs to IRF5+IRF7 increases cells' vulnerability to viral infection. Therefore, IRF5 and IRF7 are key transcription factors in IFN pathway that determine viral sensitivity of lung cancer cells; the epigenetically impaired IFN pathway in lung cancer tissues provides potential biomarkers for successful selective killing of cancer cells by oncolytic viral therapy.

Oncolytic Sindbis virus targets tumors defective in the interferon response and induces significant bystander antitumor immunity in vivo

Sindbis virus (SBV) has been shown to possess oncolytic potential in many human xenograft tumor models in immunocompromised mice. However, the mechanism underlying the tumor selectivity of SBV remains undetermined. In this study, we provide evidence that the tumor tropism of SBV infection is not determined by the levels of SBV receptor but by the status of the type I interferon (IFN) response in the tumors. Our results demonstrate that cells with defects in the IFN response (in either IFN-β production or IFN signaling) were highly susceptible to SBV infection in vitro. The results of oncolysis experiments conducted in immunocompetent animals further confirmed that the success of SBV-mediated oncolysis is greatly dependent on the presence of defects in IFN signaling in tumors. In all cases, viral titers rapidly declined in tumors due to host immune responses in immunocompetent animals. Interestingly, however, tumor-specific immune responses were concomitantly elicited, which might contribute to the sustained antitumor effect observed after the clearance of SBV. These findings indicate that SBV-mediated virotherapy is a promising therapeutic strategy for cancers defective in the IFN response and underscore the importance of bystander antitumor immunity in the efficacy of this virotherapy.

Safety and clinical usage of newcastle disease virus in cancer therapy

Newcastle disease virus (NDV) is an avian virus that causes deadly infection to over 250 species of birds, including domestic and wild-type, thus resulting in substantial losses to the poultry industry worldwide. Many reports have demonstrated the oncolytic effect of NDV towards human tumor cells. The interesting aspect of NDV is its ability to selectively replicate in cancer cells. Some of the studies have undergone human clinical trials, and favorable results were obtained. Therefore, NDV strains can be the potential therapeutic agent in cancer therapy. However, investigation on the therapeutic perspectives of NDV, especially human immunological effects, is still ongoing. This paper provides an overview of the current studies on the cytotoxic and anticancer effect of NDV via direct oncolysis effects or immune stimulation. Safety of NDV strains applied for cancer immunotherapy is also discussed in this paper.

Replicating viral vectors for cancer therapy: strategies to synergize with host immune responses

Tumour‐specific replicating (oncolytic) viruses are novel anticancer agents, currently under intense investigation in preclinical studies and phase I–III clinical trials. Until recently, most studies have focused on the direct antitumour properties of these viruses. There is now an increasing body of evidence indicating that host immune responses may be critical to the efficacy of oncolytic virotherapy. Although the immune response to oncolytic viruses can rapidly restrict viral replication, thereby limiting the efficacy of therapy, oncolytic virotherapy also has the potential to induce potent antitumoural immune effectors that destroy those cancer cells, which are not directly lysed by virus. In this review, we discuss the role of the immune system in terms of antiviral and antitumoural responses, as well as strategies to evade or promote these responses in favour of improved therapeutic potentials.

Bevacizumab with angiostatin-armed oHSV increases antiangiogenesis and decreases bevacizumab-induced invasion in U87 glioma

Bevacizumab (BEV) is an antiangiogenic drug approved for glioblastoma (GBM) treatment. However, it does not increase survival and is associated with glioma invasion. Angiostatin is an antiangiogenic polypeptide that also inhibits migration of cancer cells, but is difficult to deliver. Oncolytic viruses (OV) can potentially spread throughout the tumor, reach isolated infiltrating cells, kill them and deliver anticancer agents to uninfected cells. We have tested a combination treatment of BEV plus an OV expressing angiostatin (G47Δ-mAngio) in mice-bearing human GBM. Using a vascular intracranial human glioma model (U87) in athymic mice, we performed histopathological analysis of tumors treated with G47Δ-mAngio or BEV alone or in combination, followed tumor response by magnetic resonance imaging (MRI), and assessed animal survival. Our results indicate that injection of G47Δ-mAngio during BEV treatment allows increased virus spread, tumor lysis, and angiostatin-mediated inhibition of vascular endothelial growth factor (VEGF) expression and of BEV-induced invasion markers (matrix metalloproteinases-2 (MMP2), MMP9, and collagen). This leads to increased survival and antiangiogenesis and decreased invasive phenotypes. We show for the first time the possibility of improving the antiangiogenic effect of BEV while decreasing the tumor invasive-like phenotype induced by this drug, and demonstrate the therapeutic advantage of combining systemic and local antiangiogenic treatments with viral oncolytic therapy.

Recent advances in oncolytic virus design

The cytolytic properties of viruses can be used to treat cancer. Replication of certain viruses is favoured in cancer cells, whereas others can be modified to obtain tumour specificity. This approach has evolved to become a new discipline called virotherapy. In addition, these replication-competent (oncolytic) viruses can be adapted as vectors for cancer gene therapy. The "armed" viruses show a double mechanism of action: direct destruction of cancer cells as a consequence of the lytic viral cycle, in combination with the effect of the therapeutic gene incorporated in the viral genome. Current trends in the field include strategies to increase the oncolytic potency of existing viruses; the evaluation of new candidates; the search for synergistic effects between different viruses and conventional therapies; and a rational approach to take advantage of the interplay between the viruses and the host immune system. This review summarises the most relevant achievements in recent years.

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.

Use of attenuated paramyxoviruses for cancer therapy

Paramyxoviruses, measles virus (MV), mumps virus (MuV) and Newcastle disease virus (NDV), are well known for causing measles and mumps in humans and Newcastle disease in birds. These viruses have been tamed (attenuated) and successfully used as vaccines to immunize their hosts. Remarkably, pathogenic MuV and vaccine strains of MuV, MV and NDV efficiently infect and kill cancer cells and are consequently being investigated as novel cancer therapies (oncolytic virotherapy). Phase I/II clinical trials have shown promise but treatment efficacy needs to be enhanced. Technologies being developed to increase treatment efficacy include: virotherapy in combination with immunosuppressive drugs (cyclophosphamide); retargeting of viruses to specific tumor types or tumor vasculature; using infected cell carriers to protect and deliver the virus to tumors; and genetic manipulation of the virus to increase viral spread and/or express transgenes during viral replication. Transgenes have enabled noninvasive imaging or tracking of viral gene expression and enhancement of tumor destruction.

Construction of a minigenome rescue system for Newcastle disease virus strain Italien

Newcastle disease virus (NDV) Italien, a velogenic strain, is an oncolytic virus that is considered to be a potential agent for antitumor viral therapy. We constructed three helper plasmids expressing the NP, P and L genes of NDV Italien based on the eukaryotic expression plasmid pcDNA3.1(+). The minigenome consisting of the 3' leader and 5' trailer regions of NDV Italien flanking a reporter gene encoding firefly luciferase was constructed to examine the efficacy of the three helper plasmids in viral genome replication and transcription. After co-transfection of BSR-T7/5 cells with the three helper plasmids and the minigenome plasmid, replication of minigenome RNA was evaluated by determining luciferase activity. In the minigenome rescue system, expression of the reporter gene was detected. Our results indicate that the three proteins NP, P, and L are correctly expressed and can assemble into a functional ribonucleoprotein complex that effectively directs the transcription of minigenome RNA.

Therapeutic effects of a fusogenic newcastle disease virus in treating head and neck cancer

BACKGROUND

Newcastle disease virus (NDV) is a paramyxovirus that is pathogenic in birds but causes only mild flulike symptoms in human beings. NDV(F3aa)-GFP is a genetically modified, fusogenic NDV. We assessed the utility of NDV(F3aa)-GFP in treating head and neck squamous cell carcinoma.

METHODS AND RESULTS

At a multiplicity of infection (MOI) of 1, NDV(F3aa)-GFP infection of 3 cell lines supported strong GFP expression by 36 hours. Four cell lines were highly sensitivite to viral cytotoxicity, with >75% of cells lysed by day 6 at MOI 0.1, and 2 other cell lines were partially susceptible. Murine SCC25 flank tumors exhibited robust GFP expression after a single intratumoral viral injection and showed near-complete tumor regression over 34 days. There were no adverse effects attributable to therapy.

CONCLUSIONS

We demonstrate that a fusogenic NDV exerts potent oncolytic effects against human head and neck cancer and support its continued investigation for clinical application.

Genetically engineered oncolytic Newcastle disease virus effectively induces sustained remission of malignant pleural mesothelioma

Malignant pleural mesothelioma is a highly aggressive tumor. Alternative treatment strategies such as oncolytic viral therapy may offer promising treatment options in the future. In this study, the oncolytic efficacy and induction of tumor remission by a genetically engineered Newcastle disease virus [NDV; NDV(F3aa)-GFP; GFP, green fluorescent protein] in malignant pleural mesothelioma is tested and monitored by bioluminescent tumor imaging. The efficacy of NDV(F3aa)-GFP was tested against several mesothelioma cell lines in vitro. Firefly luciferase-transduced MSTO-211H* orthotopic pleural mesothelioma tumor-bearing animals were treated with either single or multiple doses of NDV(F3aa)-GFP at different time points (days 1 and 10) after tumor implantation. Tumor burden was assessed by bioluminescence imaging. Mesothelioma cell lines exhibited dose-dependent susceptibility to NDV lysis in the following order of sensitivity: MSTO-211H > MSTO-211H* > H-2452 > VAMT > JMN. In vivo studies with MSTO-211H* cells showed complete response to viral therapy in 65% of the animals within 14 days after treatment initiation. Long-term survival in all of these animals was >50 days after tumor installation (control animals, <23 d). Multiple treatment compared with single treatment showed a significantly better response (P = 0.005). NDV seems to be an efficient viral oncolytic agent in the therapy of malignant pleural mesothelioma in an orthotopic pleural mesothelioma tumor model.

The anti-tumor effect of Newcastle disease virus HN protein is influenced by differential subcellular targeting

BACKGROUND

Immunotherapy is emerging as a major player in the current standard of care for aggressive cancers such as non-small cell lung cancer (NSCLC). The Newcastle disease virus with its tumor-specific replicative and oncolytic abilities is a promising immunotherapeutic candidate. A DNA vaccine expressing the major immunogenic hemagglutinin-neuraminidase (HN) protein of this virus has shown promising results as an immunotherapeutic agent.

METHODS

In the present study, three different DNA vaccine constructs encoding differentially targeted HN proteins (cytoplasmic or Cy-HN, secreted or Sc-HN and membrane-anchored or M-HN) were generated to evaluate their anti-tumor effect in vitro and in vivo.

RESULTS

Although all three DNA constructs elicited an immune response, tumor-bearing mice intratumorally injected with M-HN demonstrated a significantly better anti-tumor effect than those injected with Cy-HN or Sc-HN. We also showed that this anti-tumor effect was mediated by higher lymphocyte proliferative response and CTL activity in mice intratumorally injected with M-HN.

CONCLUSION

The membrane-anchored form of the HN protein appears to be an ideal candidate to develop as an immunotherapeutic agent for NSCLC.

Oncolytic Viruses for Cancer Therapy: Overcoming the Obstacles

Targeted therapy of cancer using oncolytic viruses has generated much interest over the past few years in the light of the limited efficacy and side effects of standard cancer therapeutics for advanced disease. In 2006, the world witnessed the first government-approved oncolytic virus for the treatment of head and neck cancer. It has been known for many years that viruses have the ability to replicate in and lyse cancer cells. Although encouraging results have been demonstrated in vitro and in animal models, most oncolytic viruses have failed to impress in the clinical setting. The explanation is multifactorial, determined by the complex interactions between the tumor and its microenvironment, the virus, and the host immune response. This review focuses on discussion of the obstacles that oncolytic virotherapy faces and recent advances made to overcome them, with particular reference to adenoviruses.

Engineering oncolytic viruses to exploit tumor specific defects in innate immune signaling pathways

BACKGROUND

The use of oncolytic viruses for treatment of cancer marks a significant alteration in the battle between host and virus. Viruses are confronted by cellular innate immune responses and contain an armamentarium of immunomodulatory proteins that suppress innate immunity. Tumorigenesis can result in impairment of innate immune responses. Viruses engineered to be vulnerable to normal responses may mediate tumor-specific killing with minimal off-target toxicity.

OBJECTIVE

To examine the mechanisms by which mammalian cells respond to viral infections in normal versus cancer cells and how viruses overcome these responses and to illustrate how this knowledge is used to develop physiologically targeted oncolytic viruses.

METHODS

Literature describing studies investigating innate responses to virus infections, cancer-specific molecular defects, immunosuppressive viral products and design of oncolytic viruses is extensively reviewed, and pertinent concepts are distilled and developed.

RESULTS/CONCLUSION

Innate responses to viral infections are complex involving i) viral detection; ii) induction of interferon and other cytokines; and iii) establishment of an antiviral state. Oncolytic viruses are engineered to be susceptible to antiviral responses in normal cells. Cancers can be partially vulnerable to these viruses because they have defective antiviral responses but the antitumor potency of physiologically targeted viruses may be significantly diminished.

Oncolytic viruses from the perspective of the immune system

Cancer treatment with oncolytic viruses is at a crucial intersection from where two very different routes can be taken. The key role of the immune system needs to be addressed proactively to succeed. An immunocentric point of view posits that the intense immunosuppression induced by tumors can be outbalanced by the natural immunogenicity of viruses. To their advantage, viruses can be safely armed to be even more immunostimulatory. The microbe-associated inflammatory response is optimal for antigen presentation and helps to reveal the hidden tumor antigens. The induced immune effector cells patrol the organs to destroy disseminated tumor cells out of the reach of the oncolytic virus. However, as tumor immunosuppression is localized, this concept needs to be revisited because every tumor focus will have to be reached by the oncolytic virus. By contrast, virocentrics see the immune system as an obstacle to virotherapy. A virus is so immunogenic that it dominates all the elicited immunity to the detriment of a response towards tumor antigens. For them immunosuppression is the way to go, and the intense immunosuppression in and around the tumor is now an advantage, offering a privileged site for virus replication. A better oncolytic virus evades the immune system, but such a virus should be very tumor-selective to be safe. Although the trend favors immunocentrics, clinical results have been more often documented in immunocompromised patients. Trials of comparative interventions on the immune system will validate immunocentrism or virocentrism. What seems clear is that at this intersection one should take one route or the other to overcome the current limitations of virotherapy.