Assessing the Mechanism of Reovirus Oncolysis

Abstract

Cancer remains to be one of the leading causes of death worldwide. Current treatment methods are not effective, and so newer therapies are needed, particularly in applied virology, where aspects of viral growth and replication are targeted to tumour lysis (termed viral oncolysis). Reoviruses are naturally occurring oncolytic viruses. Since most cancers are epithelial in origin, but also include fibroblastic properties due to the epithelial-mesenchymal transitions within tumours, my investigations mainly focused on the biology of Reoviruses in both fibroblast and epithelial cells. We studied the genetic basis for Protein Kinase R sensitivity and its role in lung tropism, as well as the study of tumour oncolysis by Reoviruses and their reassortants. We also investigated the growth and protein production of Reovirus and four oncolytic reassortants and their interferon susceptibilities in L929 fibroblast cells, CT26 mouse colon tumour cells, interferon-deficient Vero cells and interferon producing CV-1 cells. We found that PKR protected the bronchiolar epithelium from infection from Reovirus. In PKR knockout mice lungs, the ability to infect the bronchial epithelium was attributed to the T3D σ1s non-structural protein, encoded by the S1 gene segment. T1L infection of PKR+/+ Balb-c mice enhanced disease, whereas T3D growth and replication was limited by PKR. Studies in viral oncolysis showed that treatments of CT26 tumour-bearing mice with high viral doses of Reovirus or oncolytic reassortants resulted in death from enhanced virus toxicity. However, treatments at lower and multiple doses significantly increased survival rates of mice. Growth of parental Reoviruses in mouse colon tumour CT26 cells showed that there is an enhanced effect of the virus infection leading to the 18 hour time point, where the virus induced the breakdown of host factors. There was also a major increase in T3D viral proteins at this time point, where we also observed the decrease in host proteins such as actin, eIF2α, interferon regulatory factors and PKR. We proposed that the Reovirus μ2 protein may be involved in this process, which induces the degradation of host inhibitors to result in enhanced viral gene and protein expression. Our results also showed that parental and oncolytic reassortant viruses behaved differently with respect to growth and IFN response in different cell lines. We demonstrated a complicated interplay between Reovirus gene products, resulting in a unique interaction involving other viral and cell proteins to achieve a certain trait, in the context of the cell type.