Bioselection Reveals miR-99b and miR-485 as Enhancers of Adenoviral Oncolysis in Pancreatic Cancer

Oncolytic viruses are designed for cancer treatment. Cell-virus interactions are key determinants for successful viral replication. Therefore, the extensive reprogramming of gene expression that occurs in tumor cells might create a hurdle for viral propagation. We used a replication-based approach of a microRNA (miRNA) adenoviral library encoding up to 243 human miRNAs as a bioselection strategy to identify miRNAs that facilitate adenoviral oncolytic activity in pancreatic ductal adenocarcinoma. We identify two miRNAs, miR-99b and miR-485, that function as enhancers of adenoviral oncolysis by improving the intra- and extracellular yield of mature virions. An increased adenoviral activity is the consequence of enhanced E1A and late viral protein expression, which is probably mediated by the downregulation of the transcriptional repressors ELF4, MDM2, and KLF8, which we identify as miR-99b or miR-485 target genes. Arming the oncolytic adenovirus ICOVIR15 with miR-99b or miR-485 enhances its fitness and its antitumoral activity. Our results demonstrate the potential of this strategy to improve oncolytic adenovirus potency, and they highlight miR-99b and miR-485 as sensitizers of adenoviral replication. Oncolytic adenoviruses are a promising alternative therapy for refractory cancers, including pancreatic cancer; however, more potent viruses are needed. This paper describes an approach to identify oncolytic adenoviruses with enhanced features. It is based on the construction of a library encoding up to 243 miRNAs, followed by a bioselection strategy to determine miRNAs that enhance adenoviral replication. We identified miR-99b and miR-485 as oncolytic adenoviral sensitizers, and we show the mechanism of enhanced activity. The new viruses display improved anticancer efficacy in xenograft models. This approach could be applied to other oncolytic viruses, expanding the interest in the oncolytic virus community.