Improved oncolytic activity of a reovirus mutant that displays enhanced virus spread due to reduced cell attachment.

Wild-type reovirus serotype 3 Dearing (T3wt), a non-pathogenic intestinal virus, has shown promise as a cancer therapy in clinical trials, but it would benefit from an increased potency. Given that T3wt is naturally adapted to the intestinal environment (rather than tumors), we genetically modified reovirus to improve its infectivity in cancer cells. Various reovirus mutants were created, and their oncolytic potency was evaluated using plaque size as a measure of virus fitness in cancer cells. Notably, Super Virus 5 (SV5), carrying five oncolytic mutations, displayed the largest plaques in breast cancer cells among the mutants tested, indicating the potential for enhancing oncolytic potency through the combination of mutations. Furthermore, in a HER2+ murine breast cancer model, mice treated with SV5 exhibited superior tumor reduction and increased survival compared with those treated with PBS or T3wt. Intriguingly, SV5 did not replicate faster than T3wt in cultured cells but demonstrated a farther spread relative to T3wt, attributed to its reduced attachment to cancer cells. These findings highlight the significance of increased virus spread as a crucial mechanism for improving oncolytic virus activity. Thus, genetic modifications of reovirus hold the potential for augmenting its efficacy in cancer therapy.