Arming vaccinia virus for pancreatic cancer oncolytic virotherapy
Vaccinia virus is a 250-300nm enveloped DNA virus from the poxvirus family and is used as a vector for oncolytic viral gene therapy. No unique cell surface receptor has been identified for Vaccinia virus and the reasons for its tropism for cancer cells are unclear. Pancreatic adenocarcinoma (PDAC) is resistant to conventional chemotherapy and typically contains areas that are profoundly hypoxic. We have investigated the utility of Vaccinia virus as a vector for targeting hypoxic regions in pancreatic adenocarcinoma, as other viral vectors have been found to replicate poorly in hypoxia. We found that cytotoxicity was equivalent in normoxia and hypoxia in some PDAC cell lines but in others cytotoxicity was enhanced in hypoxia. This increase in cytotoxicity was only seen in cell lines where there was hypoxic induction of vascular endothelial growth factor (VEGF). Functional studies using over-expression and knockdown of VEGF in pancreatic cancer cell models showed that VEGF can augment viral transgene expression, cytotoxicity and replication in vitro and in vivo. We found that VEGF facilitates the internalisation of Vaccinia virus. These results show that VEGF is an additional factor involved in the tropism and pathogenesis of Vaccinia virus. We then constructed an oncolytic Vaccinia virus to target hypoxic cancer cells using the HIF-1α oxygen degradation domain, encephalomyocarditis virus internal ribosomal entry site and the VEGF 3‟ un-translated region to regulate luciferase expression in hypoxia. We have shown a dose-, time- and oxygen-dependent effect using this construct and propose this may be adapted to regulate therapeutic genes, or produce a conditionally replicating Vaccinia virus, in hypoxic conditions.
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