Tumour heterogeneity is a key hurdle for the effective treatment of cancer using oncolytic viruses (OVs). A better understanding of the pathways involved in delineating tumour cell resistance and hypersensitivity to OVs is critical in order to guide the development of new therapeutic strategies to enhance OVs. In this thesis, I performed a comparative genetic and epigenetic study of the murine OV-resistant colon cancer cell line CT26.WT and its hypersensitive subclone CT26.lacZ. This study led to the identification of retroviral insertion sites in AKAP7 and TP53RK genes, that are potentially involved in conveying sensitivity to infection by OVs and the dysregulation of the interferon antiviral response in the CT26.lacZ cell line. Gene overexpression and gene silencing experiments suggest a functional role of these proteins in controlling viral growth. Further investigation of these genes and their relationship to antiviral response pathways is warranted and may lead to novel strategies for improving the therapeutic activity of OVs.

Oncolytic viruses promise to significantly improve current cancer treatments through their tumour-selective replication and multimodal attack against cancer cells. However, one of the biggest setbacks for oncolytic virus therapies is the intravenous delivery of the virus, as it can be cleared by neutralizing antibodies (nAbs) from the bloodstream before it reaches the tumour cells. In our group, we have succeeded in developing aptamers to vesicular stomatitis virus (VSV), as well as to rabbit anti-VSV polyclonal neutralizing antibodies (nAbs). We tested these aptamers’ biological activity with a cell-based plaque forming assay and found that the aptamers prevented in vitro neutralization of VSV by nAbs and increased the virus infection rate of transformed cells up to 77%. In line with this approach, we enhanced the delivery of oncolytic viruses by selecting aptamers to the CT26 colon carcinoma cell line. The binding of aptamer pools has been tested on flow cytometry and the best pools were subjected to high throughput sequencing. Selected aptamers were linked to anti-VSV aptamers and applied for target delivery of the virus to cancer cells. Development of this aptamer-based technology aims to improve viral anti-cancer therapies, with a potential to be applied as treatment for patients affected with cancer. Finally, in collaboration with a group from Erlangen University, we performed an aptamer selection using capillary electrophoresis and cell-SELEX. The target, the extracellular domain of human CD83, is a maturation marker for dendritic cells and is involved in the regulation of the immune system. Selected aptamer sequences bound selectively to mature dendritic cells, in comparison to immature dendritic cells, and thus hold promise to be applied for further studies leading to a better understanding of CD83’s mechanism of action.