[Oncolytic vesicular stomatitis viruses as intravesical agents against non-muscle-invasive bladder cancer]

Patients with high-risk bladder cancer who do not respond to bacillus Calmette-Guerin (BCG) immunotherapy represent a significant therapeutic challenge. The addition of interferon to BCG has recently evolved as a second-line treatment option; however, many high-grade tumors are nonresponsive to interferon. Thus, replication-competent oncolytic vesicular stomatitis viruses (VSV) that selectively target interferon-refractory tumors are promising intravesical agents. In vitro, wild-type VSV as well as a mutant variant (AV3) that has an impaired ability to shut down innate immunity preferentially killed undifferentiated, interferon-nonresponsive bladder cancer cells. Testing of these viruses in an orthotopic murine model of high-grade bladder cancer, which we have recently validated, revealed that both AV3 and wild-type VSV significantly inhibited orthotopic tumor growth. Despite the use of immunocompromised nude mice, there was no evidence of toxicity. In conclusion, VSV instillation therapy demonstrated strong antitumor activity and safety in an orthotopic model of high-risk disease. These findings provide preclinical proof-of-principle for the intravesical use of VSV, especially in interferon-refractory patients.