Preclinical evaluation of the efficacy of α−Difluoromethylornithine and Sulindac against SARS-CoV-2 infection

Despite numerous research efforts and several effective vaccines and therapies developed against COronaVIrus Disease 2019 (COVID-19), drug repurposing remains an attractive alternative to identify new treatments for SARS-CoV-2 virus variants and other viral infections that may emerge in the future. Cellular polyamines support viral propagation and tumor growth. Here we tested the antiviral activity of an irreversible inhibitor of polyamine biosynthesis, α-difluoromethylornithine (DFMO) and a non-steroidal anti-inflammatory drug (NSAID) Sulindac, which have been previously evaluated for colon cancer chemoprevention. The drugs were tested as single agents and in combination in human Calu-3 lung adenocarcinoma and Caco-2 colon adenocarcinoma cell lines and the K18-hACE2 transgenic mouse model of severe COVID-19. DFMO/Sulindac combination significantly suppressed SARS-CoV-2 N1 Nucleocapsid mRNA and ACE2 mRNA levels in the infected human cell lines by interacting synergistically when cells were pretreated with drugs and additively when treatment was applied to the infected cells. The antiviral activity of DFMO and Sulindac was tested in vivo as prophylaxis (drug supplementation at the doses equivalent to the human chemoprevention trial started 7 days before infection) or as treatment (drug supplementation started 24 hours post-infection). Prophylaxis with DFMO and Sulindac as single agents significantly increased survival rates in the young male mice (p=0.01, and p=0.027, respectively), and the combination was effective in the aged male mice (p=0.042). Young female mice benefited the most from the prophylaxis with Sulindac alone (p=0.001) and DFMO/Sulindac combination (p=0.018), while aged female mice did not benefit significantly from any interventions. The treatment regime was ineffective in suppressing SARS-CoV-2 infection in K18-hACE2 mice. Overall, animal studies demonstrated the protective age- and sex-dependent antiviral efficacy of DFMO and Sulindac against SARS-CoV-2.