Antiviral activity of Inonotusin A an active compound isolated from Boletus bellinii and Boletus subtomentosus

Mushrooms produce various classes of secondary metabolites that could be used as antivirals in the future. The aim of this study was to determine the antiviral activity of methanolic extracts obtained from two edible mushrooms, Boletus bellinii (B. bellinii) and Boletus subtomentosus (B. subtomentosus), collected from the north forests of Tunisia, against Herpes Simplex Virus type 2 and Coxsackie Virus B type 3. In vitro micro-inhibition assays and cytotoxicity screening were performed on Vero cells. The tested Boletus methanolic extracts were found to be non-cytotoxic at high doses (50% cytotoxic concentration - CC₅₀ > 1 mg/mL) and exhibited relevant viral inhibition with 50% inhibitory concentration, i.e., IC₅₀ of 3.60 ± 0.66 µg/mL and 35.70 ± 7.42 µg/mL for B. bellinii, and 5.67 ± 1.02 µg/mL and 56.88 ± 9.56 µg/mL for B. subtomentosus, against HSV-2 and CVB-3, respectively. Interestingly, Boletus methanolic extracts showed high selectivity index (SI) values against both viruses, with the highest values against HSV-2 (SI > 800). Both viral strains were inhibited when treated with extracts during the early stages of virus replication. Inonotusin A was isolated and identified as the compound responsible for these activities. The latter is a novel antiviral agent that may have clinical utility or serve as a lead compound for further development. This study is the first attempt to investigate the antiviral activity of inonotusin A, isolated from the genus Boletus. The information from the present work should be a valuable reference for future studies on the antiviral activity of inonotusin A.