Remdesivir and Cyclosporine Synergistically Inhibit the Human Coronaviruses OC43 and SARS-CoV-2

Remdesivir, a prodrug targeting RNA-dependent-RNA-polymerase, and cyclosporine, a calcineurin inhibitor, individually exerted inhibitory activity against human coronavirus OC43 (HCoV-OC43) in HCT-8 and MRC-5 cells at EC50 values of 96 +/- 34 similar to 85 +/- 23 nM and 2,920 +/- 364 similar to 4,419 +/- 490 nM, respectively. When combined, these two drugs synergistically inhibited HCoV-OC43 in both HCT-8 and MRC-5 cells assayed by immunofluorescence assay (IFA). Remdesivir and cyclosporine also separately reduced IL-6 production induced by HCoV-OC43 in human lung fibroblasts MRC-5 cells with EC50 values of 224 +/- 53 nM and 1,292 +/- 352 nM, respectively; and synergistically reduced it when combined. Similar trends were observed for SARS-CoV-2, which were 1) separately inhibited by remdesivir and cyclosporine with respective EC50 values of 3,962 +/- 303 nM and 7,213 +/- 143 nM by IFA, and 291 +/- 91 nM and 6,767 +/- 1,827 nM by a plaque-formation assay; and 2) synergistically inhibited by their combination, again by IFA and plaque-formation assay. Collectively, these results suggest that the combination of remdesivir and cyclosporine merits further study as a possible treatment for COVID-19 complexed with a cytokine storm.

Automated summary

Remdesivir and cyclosporine individually and in combination showed inhibitory activity against human coronaviruses OC43 and SARS-CoV-2. These drugs also reduced IL-6 production induced by the viruses. The combination of remdesivir and cyclosporine may be a potential treatment for COVID-19 with cytokine storm.