RNA viruses as virotherapy agents.

RNA viruses are rapidly emerging as extraordinarily promising agents for oncolytic virotherapy. Integral to the lifecycles of all RNA viruses is the formation of double-stranded RNA, which activates a spectrum of cellular defense mechanisms including the activation of PKR and the release of interferon. Tumors are frequently defective in their PKR signaling and interferon response pathways, and therefore provide a relatively permissive substrate for the propagation of RNA viruses. For most of the oncolytic RNA viruses currently under study, tumor specificity is either a natural characteristic of the virus, or a serendipitous consequence of adapting the virus to propagate in human tumor cell lines. Further refinement and optimization of these oncolytic agents can be achieved through virus engineering. This article provides a summary of the current status of oncolytic virotherapy efforts for seven different RNA viruses, namely, mumps, Newcastle disease virus, measles virus, vesicular stomatitis virus, influenza, reovirus, and poliovirus.