A rationally designed A34R mutant oncolytic poxvirus: improved efficacy in peritoneal carcinomatosis.

Oncolytic poxviruses have demonstrated initial promising results in patients with cancer in clinical trials, yet further improvements are needed. It has been shown that a single point mutation in the A34R gene resulted in the production of more total progeny virus and more extracellular enveloped virus (EEV), a form that can be immune-evasive and with enhanced spread. We have genetically engineered a new oncolytic poxvirus (designated vA34R) by incorporating this mutated A34R gene into a viral backbone (vvDD) which was designed for tumor-selective replication. This rationally designed virus can evade neutralization from antipoxvirus antibodies and is highly cytotoxic to cancer cells. It demonstrates improved spread and increased replication within the peritoneal cavity resulting in improved antitumor effects in a peritoneal carcinomatosis (PC) model of MC38 colon cancer. Impressively, after carrier cell-mediated delivery in the preimmunized host, vA34R displayed high replication in tumor nodules yet low accumulation in normal tissues thus enhancing the therapeutic index leading to 70% long-term cures. These results demonstrate that vA34R gains an enhanced therapeutic index for PC via immune evasion, increased spread, and production of more progeny virus. Thus, vA34R may be a potent oncolytic virus (OV) for patients with PC, even after prior exposure to vaccinia virus (VV).