Iguratimod, a promising therapeutic agent for COVID-19 that attenuates excessive inflammation in mouse models.

In severe COVID-19 patients, excessive inflammation can lead to multiorgan dysfunction. Current anti-inflammatory treatments like glucocorticoids partially improve the outcomes, while immune systems are compromised. We have identified that SARS-CoV-2-infected obese mice were a good model of the cytokine storm seen in COVID-19. Here, we revealed that iguratimod (IGU), an approved agent for rheumatoid arthritis, improved survival by attenuating inflammation with minimal immune suppression. In this study, C57BL/6 mice were fed a high-fat diet (HFD) or a normal-fat diet (NFD) for ten weeks before being infected with a mouse-adapted SARS-CoV-2. IGU significantly improved survival rates and reduced lung inflammation in HFD-fed mice, with minimal impact on interferon-induced genes and viral load. Meanwhile, dexamethasone (DEX) did not improve survival, while it suppressed various immune reactions with different mechanisms to IGU. Interestingly, IGU-treated mice had fewer SARS-CoV-2 positive cells in the lung, although viral replication was comparable to the control mice. Neither IGU nor DEX inhibited the SARS-CoV-2 infection in Vero-E6 cells, unlike the antiviral agent, remdesivir. Of note, IGU was effective prophylactically and therapeutically in HFD mice, and showed beneficial effects in NFD-fed mice with a lethal dose exposure of SARS-CoV-2. We demonstrated that IGU could be a promising treatment for severe COVID-19, especially in obese patients, by fine-tuning inflammation without compromising antiviral immunity. This study supports the possibility of drug repositioning for IGU COVID-19 beyond autoimmune diseases.