Enhanced cytotoxicity of reovirus and radiotherapy in melanoma cells is mediated through increased viral replication and mitochondrial apoptotic signalling

Oncolytic viruses selectively target and replicate in cancer cells, providing us with a unique tool with which to target and kill tumour cells. These viruses come from a diverse range of viral families including reovirus type 3 Dearing (RT3D), a non-pathogenic human double-stranded RNA oncolytic virus, which has been shown to be an effective therapeutic agent, both as a mono-therapy and in combination with traditional chemotherapeutic drugs. This study investigated the interaction between RT3D and radiotherapy in melanoma cell lines with a BRAF mutant, Ras mutant or BRAF/Ras wild type genotype. The data indicates that RT3D combined with radiotherapy significantly increased cytotoxicity relative to either single agent, independent of genotype, both in vitro and in vivo. The mechanism of enhanced cytotoxicity was dependent on an increase in viral replication, mediated by CUG2 up-regulation and subsequent down-regulation of pPKR and p-eIF2α, leading to the activation of mitochondrial apoptotic signalling resulting in increased cell death.