Identification of Novel Natural Products as Effective and Broad-Spectrum Anti-Zika Virus Inhibitors

Abstract

Zika virus (ZIKV) infection during pregnancy leads to severe congenital Zika syndrome, which includes microcephaly and other neurological malformations. No therapeutic agents have, so far, been approved for the treatment of ZIKV infection in humans; as such, there is a need for a continuous effort to develop effective and safe antiviral drugs to treat ZIKV-caused diseases. After screening a natural product library, we have herein identified four natural products with anti-ZIKV activity in Vero E6 cells, including gossypol, curcumin, digitonin, and conessine. Except for curcumin, the other three natural products have not been reported before to have anti-ZIKV activity. Among them, gossypol exhibited the strongest inhibitory activity against almost all 10 ZIKV strains tested, including six recent epidemic human strains. The mechanistic study indicated that gossypol could neutralize ZIKV infection by targeting the envelope protein domain III (EDIII) of ZIKV. In contrast, the other natural products inhibited ZIKV infection by targeting the host cell or cell-associated entry and replication stages of ZIKV. A combination of gossypol with any of the three natural products identified in this study, as well as with bortezomib, a previously reported anti-ZIKV compound, exhibited significant combinatorial inhibitory effects against three ZIKV human strains tested. Importantly, gossypol also demonstrated marked potency against all four serotypes of dengue virus (DENV) human strains in vitro. Taken together, this study indicates the potential for further development of these natural products, particularly gossypol, as the lead compound or broad-spectrum inhibitors against ZIKV and other flaviviruses, such as DENV.

Curcumin as an Antiviral Agent

“…In their initial screen in Vero E6 cells, curcumin (amongst other compounds) had a lower IC 50 (~5-14 µM) relative to CC 50 (~53 µM) against several strains of ZIKV as determined by plaque assay. Time-of-addition assays again suggested that curcumin exerts anti-ZIKV activity through an ability to interfere with cell attachment [15]. Taken together, these studies demonstrate curcumin's potential against ZIKV.…”

“…Protein expression Enterovirus 71 [13] Conformation of viral/cellular surface proteins Viral attachment Zika virus Chikungunya virus Vesicular stomatitis virus [14][15][16] Human respiratory syncytial virus [17,18]…”

“…Viral attachment Chikungunya virus Vesicular stomatitis virus [14][15][16] Human respiratory syncytial virus [17,18] HSC71 expression Viral entry Viral hemorrhagic septicemia virus [9] NF-κB signalling Replication Influenza A virus [19]…”

“…Gao et al [15] evaluated a natural product library for phytochemicals, including curcumin, for compounds with anti-ZIKV activity. In their initial screen in Vero E6 cells, curcumin (amongst other compounds) had a lower IC 50 (~5-14 µM) relative to CC 50 (~53 µM) against several strains of ZIKV as determined by plaque assay.…”

“…In addition to evaluating curcumin against ZIKV, Gao et al [15] also investigated the same selection of compounds against dengue virus (DENV). Curcumin reduced plaque formation of all four strains (DENV-1-4, IC 50 of 9.37, 3.07, 2.09, and 4.83 µM, respectively) examined in LLC-MK2 cells while showing limited toxicity (CC 50 of 59.42 µM) [15].…”