In Vitro Replication Inhibitory Activity of Xanthorrhizol against Severe Acute Respiratory Syndrome Coronavirus 2.

In spite of the large number of repositioned drugs and direct-acting antivirals in clinical trials for the management of the ongoing COVID-19 pandemic, there are few cost-effective therapeutic options for severe acute respiratory syndrome (SARS) coronavirus 2 (SCoV2) infection. In this paper, we show that xanthorrhizol (XNT), a bisabolane-type sesquiterpenoid compound isolated from the Curcuma xanthorrhizza Roxb., a ginger-line plant of the family Zingiberaceae, displays a potent antiviral efficacy in vitro against SCoV2 and other related coronaviruses, including SARS-CoV-1 (SCoV1) and a common cold-causing human coronavirus. XNT reduced infectious SCoV2 titer by ~3-log10 at 20 µM and interfered with the replication of the SCoV1 subgenomic replicon, while it had no significant antiviral effects against hepatitis C virus and noroviruses. Further, XNT exerted similar antiviral functions against SCoV2 variants, such as a GH clade strain and a delta strain currently predominant worldwide. Neither SCoV2 entry into cells nor the enzymatic activity of viral RNA polymerase (Nsp12), RNA helicase (Nsp13), or the 3CL main protease (Nsp5) was inhibited by XNT. While its CoV replication inhibitory mechanism remains elusive, our results demonstrate that the traditional folk medicine XNT could be a promising antiviral candidate that inhibits a broad range of SCoV2 variants of concern and other related CoVs.

Inhibition of hepatitis C virus replication by Monascus pigment derivatives that interfere with viral RNA polymerase activity and the mevalonate biosynthesis pathway.

OBJECTIVES: Hepatitis C virus (HCV) infection causes chronic liver disease and is a major public health problem worldwide. The aim of this study was to evaluate the potential of Monascus pigment derivatives, which were derived from a microbial secondary metabolite synthesized from polyketides by Monascus spp., as HCV antiviral agents. METHODS: We performed an in vitro RNA-dependent RNA polymerase (RdRp) assay to screen for HCV RdRp inhibitors. The anti-HCV activity of RdRp inhibitors in HCV-replicating cells was evaluated by quantification of the RNA viral genome. Molecular docking analysis was performed to predict the binding sites of the selected RdRp inhibitors. RESULTS: We have identified a Monascus pigment and its derivatives as inhibitors of the HCV NS5B RdRp. A group of Monascus orange pigment (MOP) amino acid derivatives, in which the reactive oxygen moiety was changed to amino acids, significantly inhibited HCV replication. Further, combination of the MOP derivatives (Phe, Val or Leu conjugates) with interferon (IFN)-α inhibited HCV replication more than IFN-α treatment alone. Lastly, molecular docking studies indicate the inhibitors may bind to a thumb subdomain allosteric site of NS5B. The antiviral activity of the MOP derivatives was related to a modulation of the mevalonate pathway, since the mevalonate-induced increase in HCV replication was suppressed by the MOP compounds. CONCLUSIONS: Our results identify amino acid derivatives of MOP as potential anti-HCV agents and suggest that their combination with IFN-α might offer an alternative strategy for the control of HCV replication.