Inhibition of RNase L and RNA-dependent Protein Kinase (PKR) by Sunitinib Impairs Antiviral Innate Immunity

RNase L and RNA-dependent protein kinase (PKR) are effectors of the interferon antiviral response that share homology in their pseudokinase and protein kinase domains, respectively. Sunitinib is an orally available, ATP-competitive inhibitor of VEGF andPDGFreceptors used clinically to suppress angiogenesis and tumor growth. Sunitinib also impacts IRE1, an endoplasmic reticulum protein involved in the unfolded protein response that is closely related to RNase L. Here, we report that sunitinib is a potent inhibitor of both RNase L and PKR with IC50 values of 1.4 and 0.3 mu M, respectively. In addition, flavonol activators of IRE1 inhibited RNase L. Sunitinib treatment of wild type (WT) mouse embryonic fibroblasts resulted in about a 12-fold increase in encephalomyocarditis virus titers. However, sunitinib had no effect on encephalomyocarditis virus growth in cells lacking both PKR and RNase L. Furthermore, oral delivery of sunitinib inWTmice resulted in 10-fold higher viral titers in heart tissues while suppressing by about 2-fold the IFN-beta levels. In contrast, sunitinib had no effect on viral titers in mice deficient in both RNase L and PKR. Also, sunitinib reduced mean survival times from 12 to 6 days in virus-infectedWTmice while having no effect on survival of mice lacking both RNase L and PKR. Results indicate that sunitinib treatments prevent antiviral innate immune responses mediated by RNase L and PKR.