Newcastle Disease Virus Establishes Persistent Infection in Tumor Cells In Vitro: Contribution of the Cleavage Site of Fusion Protein and Second Sialic Acid Binding Site of Hemagglutinin-Neuraminidase

The multifaceted interactions between Newcastle disease virus proteins and host proteins: a systematic review

Newcastle disease virus (NDV) typically induces severe illness in poultry and results in significant economic losses for the worldwide poultry sector. NDV, an RNA virus with a single-stranded negative-sense genome, is susceptible to mutation and immune evasion during viral transmission, thus imposing enormous challenges to avian health and poultry production. NDV is composed of six structural proteins and two nonstructural proteins that exert pivotal roles in viral infection and antiviral responses by interacting with host proteins. Nowadays, there is a particular focus on the mechanisms of virus-host protein interactions in NDV research, yet a comprehensive overview of such research is still lacking. Herein, we briefly summarize the mechanisms regarding the effects of virus-host protein interaction on viral infection, pathogenesis, and host immune responses. This review can not only enhance the present comprehension of the mechanism underlying NDV and host interplay, but also furnish a point of reference for the advancement of antiviral measures.

Exploiting RIG-I-like receptor pathway for cancer immunotherapy

RIG-I-like receptors (RLRs) are intracellular pattern recognition receptors that detect viral or bacterial infection and induce host innate immune responses. The RLRs family comprises retinoic acid-inducible gene 1 (RIG-I), melanoma differentiation-associated gene 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2) that have distinctive features. These receptors not only recognize RNA intermediates from viruses and bacteria, but also interact with endogenous RNA such as the mislocalized mitochondrial RNA, the aberrantly reactivated repetitive or transposable elements in the human genome. Evasion of RLRs-mediated immune response may lead to sustained infection, defective host immunity and carcinogenesis. Therapeutic targeting RLRs may not only provoke anti-infection effects, but also induce anticancer immunity or sensitize "immune-cold" tumors to immune checkpoint blockade. In this review, we summarize the current knowledge of RLRs signaling and discuss the rationale for therapeutic targeting RLRs in cancer. We describe how RLRs can be activated by synthetic RNA, oncolytic viruses, viral mimicry and radio-chemotherapy, and how the RNA agonists of RLRs can be systemically delivered in vivo. The integration of RLRs agonism with RNA interference or CAR-T cells provides new dimensions that complement cancer immunotherapy. Moreover, we update the progress of recent clinical trials for cancer therapy involving RLRs activation and immune modulation. Further studies of the mechanisms underlying RLRs signaling will shed new light on the development of cancer therapeutics. Manipulation of RLRs signaling represents an opportunity for clinically relevant cancer therapy. Addressing the challenges in this field will help develop future generations of cancer immunotherapy.

Metabolic Reprogramming in Colon Cancer Cells Persistently Infected with Newcastle Disease Virus

Newcastle disease virus (NDV) is an oncolytic agent against various types of mammalian cancers. As with all cancer therapies, the development of cancer resistance, both innate and acquired, is becoming a challenge. In this study, we investigated persistently NDV-infected Caco-2 colon cancer cells, designated as virus-resistant (VR) Caco-2 cells, which were then able to resist NDV-mediated oncolysis. We applied single-cell Raman spectroscopy, combined with deuterium isotope probing (Raman-DIP) techniques, to investigate the metabolic adaptations and dynamics in VR Caco-2 cells. A linear discriminant analysis (LDA) model demonstrated excellent performance in differentiating VR Caco-2 from Caco-2 cells at single-cell level. By comparing the metabolic profiles in a time-resolved manner, the de novo synthesis of proteins and lipids was found upregulated, along with decreased DNA synthesis in VR Caco-2. The results suggest that VR Caco-2 cells might reprogram their metabolism and divert energy from proliferation to protein synthesis and lipidic modulation. The ability to identify and characterise single resistant cells among a population of cancer cells would help develop a deeper understanding of the resistance mechanisms and better tactics for developing effective cancer treatment.

Delivery of a novel membrane-anchored Fc chimera enhances NK cell-mediated killing of tumor cells and persistently virus-infected cells

Antibody-dependent cellular cytotoxicity (ADCC) is one of the most powerful mechanisms for Natural Killer (NK) cells to kill cancer cells or virus-infected cells. A novel chimeric protein (NA-Fc) was created, which when expressed in cells, positions an IgG Fc domain on the plasma membrane, mimicking the orientation of IgG bound to the cell surface. This NA-Fc chimera was tested with PM21-NK cells, produced through a previously developed particle-based method which yields superior NK cells for immunotherapeutic applications. Real time viability assays revealed higher PM21-NK killing of both ovarian and lung cancer cells expressing NA-Fc, which correlated with increased release of TNF-α and IFN-γ cytokines from NK cells and was dependent on CD16-Fc interactions. Lentivirus delivery of NA-Fc to target cells increased the rate of PM21-NK cell killing of A549 and H1299 lung, SKOV3 ovarian and A375 melanoma cancer cells. This NA-Fc-directed killing was extended to virus infected cells, where delivery of NA-Fc to lung cells that were persistently infected with Parainfluenza virus resulted in increased killing by PM21-NK cells. In contrast to its effect on PM21-NK cells, the NA-Fc molecule did not enhance complement mediated lysis of lung cancer cells. Our study lays the foundation for application of the novel NA-Fc chimera that could be delivered specifically to tumors during oncolytic virotherapy to mark target cells for ADCC by co-treatment with adoptive NK cells. This strategy would potentially eliminate the need to search for unique cancer specific antigens for development of new antibody therapeutics.

Biological Significance of Dual Mutations A494D and E495K of the Genotype III Newcastle Disease Virus Hemagglutinin-Neuraminidase In Vitro and In Vivo

As a multifunctional protein, the hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) is involved in various biological functions. A velogenic genotype III NDV JS/7/05/Ch evolving from the mesogenic vaccine strain Mukteswar showed major amino acid (aa) mutations in the HN protein. However, the precise biological significance of the mutant HN protein remains unclear. This study sought to investigate the effects of the mutant HN protein on biological activities in vitro and in vivo. The mutant HN protein (JS/7/05/Ch-type HN) significantly enhanced the hemadsorption (HAd) and fusion promotion activities but impaired the neuraminidase (NA) activity compared with the original HN protein (Mukteswar-type HN). Notably, A494D and E495K in HN exhibited a synergistic role in regulating biological activities. Moreover, the mutant HN protein, especially A494D and E495K in HN, enhanced the F protein cleavage level, which can contribute to the activation of the F protein. In vitro infection assays further showed that NDVs bearing A494D and E495K in HN markedly impaired the cell viability. Simultaneously, A494D and E495K in HN enhanced virus replication levels at the early stage of infection but weakened later in infection, which might be associated with the attenuated NA activity and cell viability. Furthermore, the animal experiments showed that A494D and E495K in HN enhanced case fatality rates, virus shedding, virus circulation, and histopathological damages in NDV-infected chickens. Overall, these findings highlight the importance of crucial aa mutations in HN in regulating biological activities of NDV and expand the understanding of the enhanced pathogenicity of the genotype III NDV.

Oncolytic viral vectors in the era of diversified cancer therapy: from preclinical to clinical

With the in-depth research and wide application of immunotherapy recently, new therapies based on oncolytic viruses are expected to create new prospects for cancer treatment via eliminating the suppression of the immune system by tumors. Currently, an increasing number of viruses are developed and engineered, and various virus vectors based on effectively stimulating human immune system to kill tumor cells have been approved for clinical treatment. Although the virus can retard the proliferation of tumor cells, the choice of oncolytic viruses in biological cancer therapy is equally critical given their therapeutic efficacy, safety and adverse effects. Moreover, previously known oncolytic viruses have not been systematically classified. Therefore, in this review, we summarized and distinguished the characteristics of several common types of oncolytic viruses: herpes simplex virus, adenovirus, measles virus, Newcastle disease virus, reovirus and respiratory syncytial virus. Subsequently, we outlined that these oncolytic viral vectors have been transformed from preclinical studies in combination with immunotherapy, radiotherapy, chemotherapy, and nanoparticles into clinical therapeutic strategies for various advanced solid malignancies or circulatory system cancers.

Optimizing environmental safety and cell-killing potential of oncolytic Newcastle Disease virus with modifications of the V, F and HN genes

Newcastle Disease Virus (NDV) is an avian RNA virus, which was shown to be effective and safe for use in oncolytic viral therapy for several tumour malignancies. The presence of a multi basic cleavage site (MBCS) in the fusion protein improved its oncolytic efficacy in vitro and in vivo. However, NDV with a MBCS can be virulent in poultry. We aimed to develop an NDV with a MBCS but with reduced virulence for poultry while remaining effective in killing human tumour cells. To this end, the open reading frame of the V protein, an avian specific type I interferon antagonist, was disrupted by introducing multiple mutations. NDV with a mutated V gene was attenuated in avian cells and chicken and duck eggs. Although this virus still killed tumour cells, the efficacy was reduced compared to the virulent NDV. Introduction of various mutations in the fusion (F) and hemagglutinin-neuraminidase (HN) genes slightly improved this efficacy. Taken together, these data demonstrated that NDV with a MBCS but with abrogation of the V protein ORF and mutations in the F and HN genes can be safe for evaluation in oncolytic viral therapy.

Identification of a new amino acid mutation in the HN protein of NDV involved in pathogenicity

The fusion (F) and haemagglutinin-neuraminidase (HN) proteins of Newcastle disease virus (NDV) are viral entry proteins and are recognized as the major virulence determinants. Previously, a lentogenic NDV virus (CE16) was derived from a mesogenic strain (CI10) through sequential passages in chick embryos. Whole-genome sequence analysis revealed that the two homologous strains shared the same F protein but differed in HN with two amino acid (aa) substitutions (A215G and T430A). To elucidate the molecular reasons for virulence attenuation, two original plasmids (HN-CI10 and HN-CE16) and two single-point mutants (G215A and A430T) reverse-mutated from HN-CE16 were constructed to analyse the known biological functions of HN. The results showed that the A430T substitution significantly weakened the haemadsorption (HAd) activity, increased the neuraminidase (NA) activity, improved the fusion-promoting activity, and enhanced the cleavage-promoting activity of HN-CE16. However, G215A failed to induce obvious functional changes. Therefore, the aa residue HN430 may play a key role in determining virulence. To test this hypothesis, further studies on A430T were conducted through reverse genetics using an infectious cDNA clone. At the viral level, the A430T-mutated virus showed dramatic promotion of viral plaque formation, propagation, and pathogenicity in vitro and in vivo. This study demonstrates a new virulence site associated with HN protein functions, viral propagation, and pathogenicity. All these findings could lay a foundation for illuminating the molecular mechanism of NDV virulence.

Lentogenic NDV V protein inhibits IFN responses and represses cell apoptosis

The V protein of Newcastle disease virus (NDV) has been shown to inhibit the secretion of interferon (IFN) during infection, which is responsible for the promotion of NDV pathogenicity. However, the ability of the V protein to suppress host innate immunity is not well understood. In this study, we explored the function of V protein and its relationship with virulence by generating V protein-inserted recombinant (r) NDVs. Using rNDVs as a model, we examined the efficiency of infection, IFN responses, and apoptosis of host cells during infection. We found that viral propagation occurred smoothly when V protein from lentogenic NDV is inserted instead of the V protein from the velogenic strain. The infection of lentogenic V protein-inserted rNDV induced less expression of IFNs and downstream antiviral proteins via efficient degradation of p-STAT1 and MDA5. Moreover, velogenic V protein triggered a higher apoptosis rate during infection thereby restricting the replication of NDV. Conversely, lentogenic V protein inhibits IFN responses efficiently and induces less apoptosis compared to the velogenic strain. Our findings provide a novel understanding of the role of V protein in NDV pathogenicity.

Persistent Newcastle disease virus infection in bladder cancer cells is associated with putative pro-survival and anti-viral transcriptomic changes

Background

Newcastle disease virus (NDV) is an oncolytic virus with excellent selectivity against cancer cells, both in vitro and in vivo. Unfortunately, prolonged in vitro NDV infection results in the development of persistent infection in the cancer cells which are then able to resist NDV-mediated oncolysis. However, the mechanism of persistency of infection remains poorly understood.

Methods

In this study, we established persistently NDV-infected EJ28 bladder cancer cells, designated as EJ28P. Global transcriptomic analysis was subsequently carried out by microarray analysis. Differentially expressed genes (DEGs) between EJ28 and EJ28P cells identified by the edgeR program were further analysed by Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA) analyses. In addition, the microarray data were validated by RT-qPCR.

Results

Persistently NDV-infected EJ28 bladder cancer cells were successfully established and confirmed by flow cytometry. Microarray analysis identified a total of 368 genes as differentially expressed in EJ28P cells when compared to the non-infected EJ28 cells. GSEA revealed that the Wnt/β-catenin and KRAS signalling pathways were upregulated while the TGF-β signalling pathway was downregulated. Findings from this study suggest that the upregulation of genes that are associated with cell growth, pro-survival, and anti-apoptosis may explain the survivability of EJ28P cells and the development of persistent infection of NDV.

Conclusions

This study provides insights into the transcriptomic changes that occur and the specific signalling pathways that are potentially involved in the development and maintenance of NDV persistency of infection in bladder cancer cells. These findings warrant further investigation and is crucial towards the development of effective NDV oncolytic therapy against cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08345-y.

Residues 315 and 369 in HN Protein Contribute to the Thermostability of Newcastle Disease Virus

Thermostable Newcastle disease virus (NDV) vaccines have been widely used in areas where a “cold-chain” is not reliable. However, the molecular mechanism of NDV thermostability remains poorly understood. In this work, we constructed chimeric viruses by exchanging viral fusion (F) and/or hemagglutinin-neuraminidase (HN) genes between the heat-resistant strain HR09 and thermolabile strain La Sota utilizing a reverse genetic system. The results showed that only chimeras with HN derived from the thermostable virus exhibited a thermostable phenotype at 56°C. The hemagglutinin (HA) and neuraminidase (NA) activities of chimeras with HN derived from the HR09 strain were more thermostable than those containing HN from the La Sota strain. Then, we used molecular dynamics simulation at different temperatures (310 K and 330 K) to measure the HN protein of the La Sota strain. The conformation of an amino acid region (residues 315–375) was observed to fluctuate. Sequence alignment of the HN protein revealed that residues 315, 329, and 369 in the La Sota strain and thermostable strains differed. Whether the three amino acid substitutions affected viral thermostability was investigated. Three mutant viruses based on the thermolabile strain were generated by substituting one, two or three amino acids at positions 315, 369, and 329 in the HN protein. In comparison with the parental virus, the mutant viruses containing mutations S315P and I369V possessed higher thermostablity and HA titers, NA and fusion activities. Taken together, these data indicate that the HN gene of NDV is a major determinant of thermostability, and residues 315 and 369 have important effects on viral thermostability.

Optimization of oncolytic effect of Newcastle disease virus Clone30 by selecting sensitive tumor host and constructing more oncolytic viruses

The direct oncolytic effect of Newcastle disease virus (NDV) depends on the following two aspects: the susceptibility of cancer cells to virus infection and the ability of virus itself to lyse cancer cells. First, we investigate the susceptibility of cancer cells to NDV infection, HepG2, MDA-MB-231, and SH-SY5Y cells were susceptible, A549, MCF7, and LoVo cells were less susceptible. To investigate the molecular mechanism responsible for cancer cell susceptibility, transcriptome sequencing was carried out. We found that the levels of alpha-sialic acid acyltransferase were upregulated in MDA-MB-231 cells compared with MCF7 cells, and the interferon was downregulated. Second, to optimize the oncolytic capacity of the wild-type rClone30, a series of chimeric viruses rClone30-Anh(HN), rClone30-Anh(F), and rClone30-Anh(HN-F) were constructed by exchanging the HN gene, F gene or both of non-lytic rClone30 strain with lytic strain Anhinga. rClone30-Anh(F) and rClone30-Anh(HN-F) enhanced the oncolytic effect of the rClone30, and this enhancement is more obvious in the susceptible cells. The oncolytic mechanism of rClone30-Anh(F) was analyzed by transcriptome analyses, in comparison with rClone30, rClone30-Anh(F) upregulated the expression of ATG5, Beclin 1, and MAP1LC3B, thus activating autophagy and promoting the production of syncytia. In conclusion, our study provides a strategy to enhance the oncolytic effect of rClone30.

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.

Evaluation of a Recombinant Newcastle Disease Virus Expressing Human IL12 against Human Breast Cancer

The Newcastle disease virus (NDV) strain AF2240 is an avian avulavirus that has been demonstrated to possess oncolytic activity against cancer cells. However, to illicit a greater anti-cancer immune response, it is believed that the incorporation of immunostimulatory genes such as IL12 into a recombinant NDV backbone will enhance its oncolytic effect. In this study, a newly developed recombinant NDV that expresses IL12 (rAF-IL12) was tested for its safety, stability and cytotoxicity. The stability of rAF-IL12 was maintained when passaged in specific pathogen free (SPF) chicken eggs from passage 1 to passage 10; with an HA titer of 2⁹. Based on the results obtained from the MTT cytotoxic assay, rAF-IL12 was determined to be safe as it only induced cytotoxic effects against normal chicken cell lines and human breast cancer cells while sparing normal cells. Significant tumor growth inhibition (52%) was observed in the rAF-IL12-treated mice. The in vivo safety profile of rAF-IL12 was confirmed through histological observation and viral load titer assay. The concentration and presence of the expressed IL12 was quantified and verified via ELISA assay. In summary, rAF-IL12 was proven to be safe, selectively replicating in chicken and cancer cells and was able to maintain its stability throughout several passages; thus enhancing its potential as an anti-breast cancer vaccine.

Breaking Therapy Resistance: An Update on Oncolytic Newcastle Disease Virus for Improvements of Cancer Therapy

Resistance to therapy is a major obstacle to cancer treatment. It may exist from the beginning, or it may develop during therapy. The review focusses on oncolytic Newcastle disease virus (NDV) as a biological agent with potential to break therapy resistance. This avian virus combines, upon inoculation into non-permissive hosts such as human, 12 described anti-neoplastic effects with 11 described immune stimulatory properties. Fifty years of clinical application of NDV give witness to the high safety profile of this biological agent. In 2015, an important milestone was achieved, namely the successful production of NDV according to Good Manufacturing Practice (GMP). Based on this, IOZK in Cologne, Germany, obtained a GMP certificate for the production of a dendritic cell vaccine loaded with tumor antigens from a lysate of patient-derived tumor cells together with immunological danger signals from NDV for intracutaneous application. This update includes single case reports and retrospective analyses from patients treated at IOZK. The review also presents future perspectives, including the concept of in situ vaccination and the combination of NDV or other oncolytic viruses with checkpoint inhibitors.

Potential of genotype VII Newcastle disease viruses to cause differential infections in chickens and ducks

Newcastle disease (ND), caused by ND virus (NDV), is one of the most infectious and economically important diseases of the poultry industry worldwide. While infections are reported in a wide range of avian species, the pathogenicity of chicken-origin virulent NDV isolates in ducks remains elusive. In this study, two NDV strains were isolated and biologically and genetically characterized from an outbreak in chickens and apparently healthy ducks. Pathogenicity assessment indices, including the mean death time (MDT), intracerebral pathogenicity index (ICPI) and cleavage motifs in the fusion (F) protein, indicated that both isolates were velogenic in nature. While these isolates carried pathogenic characteristics, interestingly they showed differential pathogenicity in ducks. The chicken-origin isolate caused high (70%) mortality, whereas the duck-origin virus resulted in low (20%) mortality in 4-week-old ducks. Intriguingly, both isolates showed comparable disease pathologies in chickens. Full-genome sequence analysis showed that the virus genome contains 15 192 nucleotides and carried features that are characteristic of velogenic strains of NDV. A phylogenetic analysis revealed that both isolates clustered in class II and genotype VII. However, there were several mutations in the functionally important regions of the fusion (F) and haemagglutinin-neuraminidase (HN) proteins, which may be responsible for the differential pathogenicity of these viruses in ducks. In summary, these results suggest that NDV strains with the same genotype show differential pathogenicity in chickens and ducks. Furthermore, chicken-origin virulent NDVs are more pathogenic for ducks than duck-origin viruses. These findings propose a role for chickens in the evolution of viral pathogenicity and the potential genetic resistance of ducks to poultry viruses.

Newcastle disease virus strain AF2240 as an oncolytic virus: A review

The discovery of tumour selective virus-mediated apoptosis marked the birth of an alternative cancer treatment in the form of oncolytic viruses. Even though, its oncolytic efficiency was demonstrated more than 50 years ago, safety concerns which resulted from mild to lethal side effects hampered the progress of oncolytic virus research. Since the classical oncolytic virus studies rely heavily on its natural oncolytic ability, virus manipulation was limited, thereby, restricted efforts to improve its safety. In order to circumvent such restriction, experiments involving non-human viruses such as the avian Newcastle disease virus (NDV) was conducted using cultured cells, animal models and human subjects. The corresponding reports on its significant tumour cytotoxicity along with impressive safety profile initiated immense research interest in the field of oncolytic NDV. The varying degree of oncolytic efficiency and virulency among NDV strains encouraged researchers from all around the world to experiment with their respective local NDV isolates in order to develop an oncolytic virus with desirable characteristics. Such desirable features include high tumour-killing ability, selectivity and low systemic cytotoxicity. The Malaysian field outbreak isolate, NDV strain AF2240, also currently, receives significant research attention. Apart from its high cytotoxicity against tumour cells, this strain also provided fundamental insight into NDV-mediated apoptosis mechanism which involves Bax protein recruitment as well as death receptor engagement. Studies on its ability to selectively induce apoptosis in tumour cells also resulted in a proposed p38 MAPK/NF-κB/IκBα pathway. The immunogenicity of AF2240 was also investigated through PBMC stimulation and macrophage infection. In addition, the enhanced oncolytic ability of this strain under hypoxic condition signifies its dynamic tumour tropism. This review is aimed to introduce and discuss the aforementioned details of the oncolytic AF2240 strain along with its current challenges which outlines the future research direction of this virus.

Parainfluenza Virus Infection Sensitizes Cancer Cells to DNA-Damaging Agents: Implications for Oncolytic Virus Therapy

A parainfluenza virus 5 (PIV5) with mutations in the P/V gene (P/V-CPI^-) is restricted for spread in normal cells but not in cancer cells in vitro and is effective at reducing tumor burdens in mouse model systems. Here we show that P/V-CPI^- infection of HEp-2 human laryngeal cancer cells results in the majority of the cells dying, but unexpectedly, over time, there is an emergence of a population of cells that survive as P/V-CPI^- persistently infected (PI) cells. P/V-CPI^- PI cells had elevated levels of basal caspase activation, and viability was highly dependent on the activity of cellular inhibitor-of-apoptosis proteins (IAPs) such as Survivin and XIAP. In challenge experiments with external inducers of apoptosis, PI cells were more sensitive to cisplatin-induced DNA damage and cell death. This increased cisplatin sensitivity correlated with defects in DNA damage signaling pathways such as phosphorylation of Chk1 and translocation of damage-specific DNA binding protein 1 (DDB1) to the nucleus. Cisplatin-induced killing of PI cells was sensitive to the inhibition of wild-type (WT) p53-inducible protein 1 (WIP1), a phosphatase which acts to terminate DNA damage signaling pathways. A similar sensitivity to cisplatin was seen with cells during acute infection with P/V-CPI^- as well as during acute infections with WT PIV5 and the related virus human parainfluenza virus type 2 (hPIV2). Our results have general implications for the design of safer paramyxovirus-based vectors that cannot establish PI as well as the potential for combining chemotherapy with oncolytic RNA virus vectors.IMPORTANCE There is intense interest in developing oncolytic viral vectors with increased potency against cancer cells, particularly those cancer cells that have gained resistance to chemotherapies. We have found that infection with cytoplasmically replicating parainfluenza virus can result in increases in the killing of cancer cells by agents that induce DNA damage, and this is linked to alterations to DNA damage signaling pathways that balance cell survival versus death. Our results have general implications for the design of safer paramyxovirus-based vectors that cannot establish persistent infection, the repurposing of drugs that target cellular IAPs as antivirals, and the combined use of DNA-damaging chemotherapy agents in conjunction with oncolytic RNA virus vectors.

Cleavage site of Newcastle disease virus determines viral fitness in persistent infection cells

Newcastle disease, caused by infection with virulent strains of Newcastle disease virus (NDV), poses a risk for the poultry industry. The virulence of NDV is mainly determined by the cleavage site of F protein. Lentogenic NDV can become velogenic after passages in SPF chicken brain and air sac based on some strains isolated from water birds, because the proportion of virulent-related strains gradually increases. In contrast, this proportion remains unchanged if NDV is passaged via 10-day-old SPF chicken embryos. This information suggests that environmental conditions rather than mutation affect NDV fitness in quasispecies. However, it is unknown how the environment selects virulent-related strains from a viral population. In this study, velogenic and lentogenic NDV marked by green or red fluorescence were used to establish persistent infection (PI) in BHK-21 cells. Monitoring viruses by different methods, we found that, without competition, persistently infected cells harbored lentogenic and velogenic NDV strains similarly in terms of viral release, viral spread and the period of persistent viral infection. In contrast, under competitive co-infection, velogenic NDV became dominant in quasispecies from the fifth passage of PI cells, which resulted in the progressive disappearance of the lentogenic NDV strain. This domination was concomitant with a short-term reduction in the superinfection exclusion and supernatant interference in PI cells resulting in a velogenic virus rebound. We concluded that virulent-related F protein cleavage site facilitates the spread and replication of NDV in conditions under which cells do not secret trypsin-like proteases and do not inhibit free virus infection, resulting in a gradual increase in virulent strains in quasispecies with the number of passages.