ABSTRACT
The emergence of the highly-pathogenic severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19 (coronavirus disease-2019), has caused an unprecedented global health crisis, as well as societal and economic disruption. The SARS-CoV-2 spike (S), a surface-anchored trimeric class-I fusion glycoprotein essential for entry into host cells, represents a key target for developing vaccines and therapeutics capable of blocking virus invasion. The emergence of several SARS-CoV-2 spike variants that facilitate virus spread and may affect the efficacy of recently developed vaccines, creates great concern and highlights the importance of identifying antiviral drugs to reduce SARS-CoV-2-related morbidity and mortality. Nitazoxanide, a thiazolide originally developed as an antiprotozoal agent with recognized broad-spectrum antiviral activity in-vitro and in clinical studies, was recently shown to be effective against several coronaviruses, including SARS-CoV-2. Using biochemical and pseudovirus entry assays, we now demonstrate that nitazoxanide interferes with the SARS-CoV-2 spike biogenesis, hampering its maturation at an endoglycosidase H-sensitive stage, and hindering its fusion activity in human cells. Besides membrane fusion during virus entry, SARS-CoV-2 S-proteins in infected cells can also trigger receptor-dependent formation of syncytia, observed in-vitro and in COVID-19 patients tissues, facilitating viral dissemination between cells and possibly promoting immune evasion. Utilizing two different quantitative cell-cell fusion assays, we show that nitazoxanide is effective in inhibiting syncytia formation mediated by different SARS-CoV-2 spike variants in human lung, liver and intestinal cells. The results suggest that nitazoxanide may represent a useful tool in the fight against COVID-19 infections, inhibiting SARS-CoV-2 replication and preventing spike-mediated syncytia formation.
Competing Interest Statement
Financial support for this study was in part provided by Romark Laboratories LC, the company that owns the intellectual property rights related to nitazoxanide. JF Rossignol is an employee and stockholder of Romark Laboratories, LC.