Abstract
Vaccinia virus is one of several live viruses currently being evaluated in clinical trials as cancer therapies. One oncolytic virus, T-VEC, is already in clinical use and is NICE approved for the treatment of melanoma. We have investigated a genetically modified, Copenhagen strain vaccinia virus encoding the fusion suicide gene (FCU1) that is able to convert non-toxic fluorocytosine into the active compound fluorouracil. The mode of cell death attributed to vaccinia virus is variable and multiple modes have been implicated based on tumour type. Through our work with colorectal cancer cell lines we have established that this form of oncolytic vaccinia virus induces cell death through a predominant picture of apoptosis. Furthermore, assessment of its immunogenicity has found there to be an increase in markers of immunogenic cell death following infection with the virus. We have developed an organotypic culture system in our laboratory which enables us to assess oncolytic viruses on ex vivo tissue. Treatment of organotypic cultures from colorectal liver metastases have shown that vaccinia virus successfully infects and replicates in the tumour tissue. A dose-response relationship was observed with the highest doses of virus exerting the most effect on tumour tissue. Assessment of the pro-drug activation system through the conversion of 5-fluorocytosine to 5-fluorouracil in supernatant showed a high percentage conversion, whilst immunohistochemical staining did show evidence of an improved effect with the pro-drug system compared with virus alone. We have evaluated the combination of cavitational ultrasound and sulphur hexafluoride microbubbles to enhance infection with oncolytic virus. Our results have shown that this method enhances infection of organotypic cultures treated with oncolytic vaccinia virus. This has enabled the use of a lower dose of virus whilst maintaining the same effects in tissue as that of virus at higher doses. This finding has translational implications that may enhance the efficacy of systemically administered oncolytic vaccinia virus.