Apigenin inhibits enterovirus 71 replication through suppressing viral IRES activity and modulating cellular JNK pathway.

Enterovirus 71 (EV71) is a member of genus Enterovirus in Picornaviridae family, which is one of the major causative agents for hand, foot and mouth disease (HFMD), and sometimes associated with severe central nervous system diseases in children. Currently there are no effective therapeutic medicines or vaccines for the disease. In this report, we found that apigenin and luteolin, two flavones that differ only in the number of hydroxyl groups could inhibit EV71-mediated cytopathogenic effect (CPE) and EV71 replication with low cytotoxicity. Both molecules also showed inhibitory effect on the viral polyprotein expression. They prevented EV71-induced cell apoptosis, intracellular reactive oxygen species (ROS) generation and cytokines up-regulation. Time-of-drug addition study demonstrated that apigenin and luteolin acted after viral entry. We examined the effect of apigenin and luteolin on 2A(pro) and 3C(pro) activity, two viral proteases responsible for viral polyprotein processing, and found that they showed less inhibitory activity on 2A(pro) or 3C(pro). Further studies demonstrated that apigenin, but not luteolin could interfere with viral IRES activity. Also, apigenin inhibited EV71-induced c-Jun N-terminal kinase (JNK) activation which is critical for viral replication, in contrast to luteolin that did not. This study demonstrated that apigenin may inhibit EV71 replication through suppressing viral IRES activity and modulating cellular JNK pathway. It also provided evidence that one hydroxyl group difference in the B ring between apigenin and luteolin resulted in the distinct antiviral mechanisms. This study will provide the basis for better drug development and further identification of potential drug targets.