Molecular mechanisms of oncolytic properties of Newcastle disease virus (NDV) in human cancer cells
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Date
04/08/2020Author
Jadhav, Archana Chandrabhan
Metadata
Abstract
Newcastle disease virus (NDV) is a single-stranded, non-segmented, negative-sense
enveloped RNA virus, which belongs to the Orthoavulavirus genus of Paramyxoviridae
family. It is a well-known, economically important poultry pathogen worldwide. Over the
last five decades, NDV is known to have oncolytic properties based on its tumourselective replication sparing the healthy cells and immunostimulation affirming potential
candidate for oncovirotherapy.
In this PhD project, the efficacy of naturally occurring and genetically modified GFP
expressing non-pathogenic NDV strains investigated in various human cancer cell lines
as an oncolytic virus. This study has demonstrated that the heterogeneous colorectal
cancer cell line Caco-2 was the most susceptible to the cytotoxicity induced by avirulent
NDV strains amongst the panel of diverse cell lines tested. Despite the high levels of
cell cytotoxicity induced by NDV in Caco-2 cells, a small population of surviving cells
was isolated from NDV superinfected Caco-2 cells 12 days post infection and named
VR Caco-2 cells (virus-resistant Caco-2 cells). The persistent infection with avirulent
strains of NDV was demonstrated in VR Caco-2 cells for the first time.
An integrated approach of cellular, transcriptomic, and proteomic data was used to study
differences between persistently NDV-infected VR Caco-2 cells,and acutely NDVinfected and uninfected Caco-2 cells. This study has shown that persistent NDVinfection resulted in slower cell proliferation of VR Caco-2 cells than parental Caco-2
cells, and production of recoverable and replicating virus at lower titres. VR Caco-2 cells
have demonstrated resistance to NDV re-infection. In contrast, VR Caco-2 cells were
susceptible to other viruses such as avian influenza virus (H9N2) and vesicular
stomatitis virus (VSV). Persistent NDV infection in VR Caco-2 cells resulted in reduced
NDV-induced cytotoxicity, although VR Caco-2 cells were still sensitive to the increased
cell cytotoxicity induced by the VSV infection. This would suggest that a combination of
oncolytic viruses could be used to overcome the effects of NDV persistent infection.
Potential mechanisms of persistence of NDV in Caco-2 cells were explored. Both Caco2 and VR Caco-2 cells demonstrated the lack of efficient induction of IFN-β and ISG15
mRNAs, which could be a potential reason for the establishment of NDV persistent
infection. RNA-seq data analysis demonstrated extensive regulation of thousands of
genes and hundreds of cellular pathways in VR Caco-2 cells while maintaining 50-times
lower viral load compared to acute NDV-infection (in Caco-2 cells). Fluctuation in
SQSTM1/p62, a multifunctional and multidomain signalling adapter protein required in selective autophagy, was also demonstrated suggesting the induction of autophagy in
NDV-infected Caco-2 cells.
The results generated in this PhD project strongly suggest that NDV not only establishes
persistent infection but that too reduces NDV-induced cytotoxicity while regulating
thousands of genes in Caco-2 cells. It also suggests the need for detailed investigation
of persistent NDV-infection in vitro and in vivo models of Caco-2 cells before and after
developing the NDV as an oncolytic therapeutic vaccine for cancer.