The use of lytic viruses to preferentially infect and eliminate
cancer cells while sparing normal cells is a promising experimental therapeutic approach for treating
cancer. However, the efficacy of
oncolytic virotherapy is often limited by two innate immunity pathways, the
protein kinase PKR and the 2'-5'-oligoadenylate (OAS)/
RNase L systems, which are widely present in many but not all
tumor cell types. Previously, we reported that the anticancer drug,
sunitinib, an inhibitor of
VEGF-R and PDGF-R, has off-target effects against both PKR and
RNase L. Here we show that combining
sunitinib treatments with
infection by an oncolytic virus,
vesicular stomatitis virus (VSV), led to the elimination of prostate, breast, and kidney malignant
tumors in mice. In contrast, either virus or
sunitinib alone slowed
tumor progression but did not eliminate
tumors. In prostate
tumors excised from treated mice,
sunitinib decreased levels of the phosphorylated form of translation
initiation factor, eIF2-α, a substrate of PKR, by 10-fold while increasing median viral titers by 23-fold. The
sunitinib/VSV regimen caused complete and sustained
tumor regression in both immunodeficient and immunocompetent animals. Results indicate that transient inhibition of innate immunity with
sunitinib enhances
oncolytic virotherapy allowing the recovery of
tumor-bearing animals.