Lisboaeflavanonol A: a novel Amazonian molecule as a potent antiviral compound with activity against SARS-CoV-2

The COVID-19 pandemic highlighted the urgent need for effective antiviral therapies against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and its emerging variants. Amazonian biodiversity represents an immeasurable source of natural compounds with unexplored potential against viruses. In this context, Lisboaeflavanonol A (LFA) is a novel glycosyl flavonoid isolated from Eugenia lisboae leaves that was shown by our previous in silico analysis to potentially inhibit the SARS-CoV-2 proteins 3-chymotrypsin-like cysteine protease (3CLpro) and RNA-dependent RNA polymerase (RdRp). Here we aimed to validate the anti-SARS-CoV-2 activity of LFA. This was first assessed using a VSV/SARS-CoV-2 pseudotyped virus system in Vero E6 cells. LFA exhibited a CC₅₀ of 209.7 µg/ml (≈ 370.0 µM), EC₅₀ of 11.6 µg/ml (≈ 20.5 µM), and a selective index (SI) of 18.1. Furthermore, using a SARS-CoV-2_WT infectious clone expressing Neongreen in A549-ACE2-TMPRSS2 cells, LFA had a CC₅₀ and EC₅₀ of 185.7 µg/ml (≈ 327.8 µM) and of 4.6 µg/ml (≈ 8.1 µM), respectively; and SI of 40.4. In time of addition assays, LFA strongly inhibited SARS-CoV-2 at post-entry stages and further characterize the post-entry activity we used a SARS-CoV-2 subgenomic replicon and demonstrated that RNA synthesis was also strongly inhibited by LFA. Finally, LFA showed cross-variant antiviral potential against SARS-CoV-2 Delta and Omicron variants. Our findings suggest that LFA possesses great potential as an antiviral compound and can serve as a scaffold for the development of novel antiviral drugs against SARS-CoV-2.