In Vitro Activity of Cysteamine Against SARS-CoV-2 Variants Alpha, Beta,Gamma and Delta

Global COVID-19 pandemic is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Continuous emergence of new variants and their rapid spread are jeopardizing vaccine countermeasures to a significant extent. While currently available vaccines are effective at preventing illness associated with SARS-CoV-2 infection, these have been shown to be less effective at preventing breakthrough infection and transmission from a vaccinated individual to others. Here we demonstrate broad antiviral activity of cysteamine HCl in vitro against variants of SARS-CoV-2 assayed in a highly permissible Vero cell line. Cysteamine HCl inhibited infection of alpha, beta, gamma and delta variants effectively and the inhibitory activity was shown to manifest during the early stages of viral infection. Cysteamine is a very well-tolerated US FDA-approved drug used chronically as a topical ophthalmic solution to treat ocular cystinosis in patients who receive it hourly or QID lifelong at concentrations 3 to 4 times higher than that required to inhibit SARS CoV-2 in tissue culture. Application of cysteamine as a topical nasal treatment can potentially : 1) mitigate existing infection 2) prevent infection in exposed individuals, and 3) limit the contagion in vulnerable populations.. ### Competing Interest Statement Jess Thoene and Robert Gavin are inventors on a patent application related to the use of cysteamine for the prevention and treatment of COVID 19 infections. It is assigned to the University of Michigan, licensed by ACIC Pharmaceuticals, Inc who funded this study. Jess Thoene is a consultant to ACIC