Ebselen and Diphenyl Diselenide Inhibit SARS-CoV-2 Replication at Non-Toxic Concentrations to Human Cell Lines

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was the causative agent of the COVID-19 pandemic, a global public health problem. Despite the numerous studies for drug repurposing, there are only two FDA-approved antiviral agents (Remdesivir and Nirmatrelvir) for non-hospitalized patients with mild-to-moderate COVID-19 symptoms. Consequently, it is pivotal to search for new molecules with anti-SARS-CoV-2 activity and to study their effects in the human immune system. Ebselen (Eb) is an organoselenium compound that is safe for humans and has antioxidant, anti-inflammatory, and antimicrobial properties. Diphenyl diselenide ((PhSe)₂) shares several pharmacological properties with Eb and is of low toxicity to mammals. Herein, we investigated Eb and (PhSe)₂ anti-SARS-CoV-2 activity in a human pneumocytes cell model (Calu-3) and analyzed their toxic effects on human peripheral blood mononuclear cells (PBMCs). Both compounds significantly inhibited the SARS-CoV-2 replication in Calu-3 cells. The EC₅₀ values for Eb and (PhSe)₂ after 24 h post-infection (hpi) were 3.8 µM and 3.9 µM, respectively, and after 48 hpi were 2.6 µM and 3.4 µM. These concentrations are safe for non-infected cells, since the CC₅₀ values found for Eb and (PhSe)₂ on Calu-3 were greater than 200 µM. Importantly, the concentration rates tested on viral replication were not toxic to human PBMCs. Therefore, our findings reinforce the efficacy of Eb and demonstrate (PhSe)₂ as a new candidate to be tested in future trials against SARS-CoV-2 infection/inflammation conditions.