Polycytidine Tract Deletion from Microrna-Detargeted Oncolytic Mengovirus Optimizes the Therapeutic Index in a Murine Multiple Myeloma Model

Mengovirus is an oncolytic picornavirus whose broad host range allows for testing in immunocompetent cancer models. Two pathogenicity-ablating approaches, polycytidine (polyC) tract truncation and microRNA (miRNA) targets insertion, eliminated the risk of encephalomyocarditis. To investigate whether a polyC truncated, miRNA-detargeted oncolytic Mengovirus might be boosted, we partially or fully rebuilt the polyC tract into the 50 noncoding region (NCR) of polyC-deleted (MC0) oncolytic constructs (NC) carrying miRNA target (miRT) insertions to eliminate cardiac/ muscular (miR-133b and miR-208a) and neuronal (miR-124) tropisms. PolyC-reconstituted viruses (MC24-NC and MC37-NC) replicated in vitro and showed the expected tropism restrictions, but reduced cytotoxicity and miRT dele-tions were frequently observed. In the MPC-11 immune competent mouse plasmacytoma model, both intratumoral and systemic administration of MC0-NC led to faster tumor responses than MC24-NC or MC37-NC, with combined dura-ble complete response rates of 75%, 0.5%, and 30%, respec-tively. Secondary viremia was higher following MC0-NC versus MC24-NC or MC37-NC therapy. Sequence analysis of virus progeny from treated mice revealed a high prevalence of miRT sequences loss among MC24- and MC37- viral ge-nomes, but not in MC0-NC. Overall, MC0-NC was capable of stably retaining miRT sites and provided a more effective treatment and is therefore our lead Mengovirus candidate for clinical translation.