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-patho-genic intestinal virus, has shown promise as a cancer therapy in clinical trials, but it would benefit from an increased po-tency. 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 in vitro 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 reduc-tion 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 rela-tive to T3wt, attributed to its reduced attachment to cancer cells. These findings highlight the significance of increased vi-rus spread as a crucial mechanism for improving oncolytic vi-rus activity. Thus, genetic modifications of reovirus hold the potential for augmenting its efficacy in cancer therapy.