Eeyarestatin I, an inhibitor of the valosin-containing protein, exhibits potent virucidal activity against the flaviviruses

Cellular responses to stress generally lead to the activation of the endoplasmic reticulum-associated protein degradation (ERAD) pathway. Several lines of study support that ERAD may be playing a proviral role during flaviviral infection. A key host factor in ERAD is the valosin-containing protein (VCP), an ATPase which ushers ubiquitin-tagged proteins to degradation by the proteasome. VCP exhibits different proviral activities, such as engaging in the biogenesis of viral replication organelles and facilitating flavivirus genome uncoating after the viral particle entry. To investigate the possible antiviral value of drugs targeting VCP, we tested two inhibitors: eeyarestatin I (EEY) and xanthohumol (XAN). Both compounds were highly effective in suppressing Zika virus (ZIKV) and Usutu virus (USUV) replication during infection in cell culture. Further analysis revealed an unexpected virucidal activity for EEY, but not for XAN. Preincubation of ZIKV or USUV with EEY before inoculation to cells resulted in significant decreases in infectivity in a dose- and time-dependent manner. Viral genomes in samples previously treated with EEY were more sensitive to propidium monoazide, an intercalating agent, with 10- to 100-fold decreases observed in viral RNA levels, supporting that EEY affects viral particle integrity. Altogether, these results support that EEY is a strong virucide against two unrelated flaviviruses, encouraging further studies to investigate its potential use as a broad-acting drug or the development of improved derivatives in the treatment of flaviviral infection.