Identification of reovirus reassortants with enhanced oncolytic activity in human fibrosarcoma cells.

Fibrosarcoma is a rare, clinically aggressive soft-tissue sarcoma that can be difficult to treat once advanced, highlighting the need for new therapeutic strategies. Oncolytic virotherapy is an emerging approach that uses replication-competent viruses to selectively infect and lyse tumor cells while stimulating antitumor immune responses. Mammalian orthoreovirus (reovirus) is an attractive candidate due to its generally benign clinical profile and capacity to replicate in many cancer cells. Reoviruses exhibit substantial genetic diversity arising from mutations and reassortment of their segmented genomes during co-infection, enabling the emergence of variants with distinct phenotypes. However, most preclinical and clinical studies have relied on a single prototype strain (T3D; clinically formulated as pelareorep), leaving open the possibility that other variants may exhibit superior activity in rare cancers. Using an in vitro screen, HT-1080 human fibrosarcoma cells were infected with a diverse panel of parental and reassortant reoviruses and assessed for cytopathicity and infectivity. One reassortant emerged as a top-performing candidate, combining robust infectivity with pronounced cytotoxicity and increased viral protein accumulation over time compared with a prototype strain. Pharmacologic pathway interrogation indicated that virus-induced cytopathicity in this model was predominantly caspase-dependent, supporting apoptosis as the primary mode of cell death rather than necroptosis. Collectively, these findings demonstrate that reassortant reoviruses can markedly enhance oncolytic activity in fibrosarcoma cells relative to commonly used strains, motivating broader evaluation of genetically diverse reoviruses across additional sarcoma models and in combination regimens to optimize therapeutic potential.