Aureonitol, a Fungi-Derived Tetrahydrofuran, Inhibits Influenza Replication by Targeting Its Surface Glycoprotein Hemagglutinin

<div><p>The influenza virus causes acute respiratory infections, leading to high morbidity and mortality in groups of patients at higher risk. Antiviral drugs represent the first line of defense against influenza, both for seasonal infections and pandemic outbreaks. Two main classes of drugs against influenza are in clinical use: M2-channel blockers and neuraminidase inhibitors. Nevertheless, because influenza strains that are resistant to these antivirals have been described, the search for novel compounds with different mechanisms of action is necessary. Here, we investigated the anti-influenza activity of a fungi-derived natural product, aureonitol. This compound inhibited influenza A and B virus replication. This compound was more effective against influenza A(H3N2), with an EC₅₀ of 100 nM. Aureonitol cytoxicity was also very low, with a CC₅₀ value of 1426 μM. Aureonitol inhibited influenza hemagglutination and, consequently, significantly impaired virus adsorption. Molecular modeling studies revealed that aureonitol docked in the sialic acid binding site of hemagglutinin, forming hydrogen bonds with highly conserved residues. Altogether, our results indicate that the chemical structure of aureonitol is promising for future anti-influenza drug design.</p></div

Effects of aureonitol on influenza attachment/entry.

<p>(A) Virus particles were pre-treated for 1 h at room temperature. This mixture was diluted and incubated with MDCK cells for 1 h at 37°C (black bar). MDCK cells were pre-treated for 1 h at 37°C and washed. The cells were then exposed to pseudotyped influenza for 1 h at 4°C, washed again, and the temperature was shifted to 37°C (white bar). MDCK cells were exposed to the indicated influenza pseudotyped virus and treated for 1 h at 4°C. The cells were then washed with PBS and the temperature was raised to 37°C (gray bars). (B) Using the last treatment approach, pseudotyped influenza viruses representative of the indicated strains were used, and different concentrations of aureonitol were evaluated. (C) MDCKs (2 x 10⁶ cells) were infected with influenza at a MOI of 1.0 for 1 h at 4°C in the presence of the indicated treatments. After that, the cells were washed, lysed with buffer A and centrifuged (10 min. at 1000 x <i>g</i>). RNA was extract from the supernatant fraction, and quantitative RT-PCR to detect influenza A genome was performed. In panels A and B, luciferase activity was measured with a commercial kit (Promega). In panel C, the standard curve method was employed using a plasmid containing the influenza M1 gene as a reference. The experiments were performed 4 times. *<i>P <</i> 0.01.</p

Chemical structure of aureonitol.

<p>Chemical structure of aureonitol.</p

Antiviral activity of Aureonitol against influenza A and B viruses.

<p>*Laboratory-adapted influenza A(H3N2).</p><p>Antiviral activity of Aureonitol against influenza A and B viruses.</p

Cytotoxicity of aureonitol.

<p>MDCKs were seeded at full confluence (2 x 10⁴ cells) (A) or semi-confluence (2 x 10³ cells) (B) in 96-well plates. The cells were then incubated with the indicated concentrations of the compound for 72 h, after which XTT (5 mg/ml) and PMS (0.01%) were added. After 4 h of incubation, the plates were read at 492 nm and 620 nm. Experiments from both panels were performed 5 times in triplicate.</p

Aureonitol does not inhibit influenza NA activity.

<p>The NA activity of the influenza A H3N2 virus was measured in the presence of the indicated concentrations of aureonitol or the reference compound OST-c using a chemiluminescent substrate, NA-star kit (Applied Biosystems, CA). The results were obtained in relative luminescence units (RLU) but were converted to a percentage of the control for normalization of the data displayed. This experiment was performed 4 times.</p