Systemic reovirus therapy of metastatic cancer in immune-competent mice.

The human reovirus is an oncolytic virus that specifically targets cancer cells with an activated Ras pathway. Because it is replication competent and highly specific for cancer cells, this virus has the potential to be an effective antimetastatic cancer agent through remote site delivery. In this study, we exploited the ability of reovirus to replicate in murine cells to test the efficacy of this virus in eliminating distal and/or metastatic tumors in immune-competent mice. We found that i.v. therapy with reovirus not only inhibited metastatic tumor growth but also led to a significant improvement in animal survival. Combining i.v. reovirus treatment with immune suppression (cyclosporine A or anti-CD4/anti-CD8 antibodies) resulted in further reduction in tumor size and a considerable prolongation in survival, compared with viral therapy alone. Combined therapy was also effective in overcoming a preexisting immunity to reovirus (a common occurrence in humans and thus a potential impediment to oncolytic effectiveness) to induce metastatic tumor regression. This is the first study to use systemic delivery of an oncolytic agent in conjunction with immune-suppressive drugs to effectively prolong animal survival. Altogether, our results suggest that i.v. reovirus therapy may present a feasible, novel alternative in the treatment of metastatic cancer in humans.