Inhibition of Severe Acute Respiratory Syndrome-Associated Coronavirus (SARSCoV) by Calpain Inhibitors and β-D-N 4 -Hydroxycytidine

Abstract

We evaluated two types of compounds for efficacy in inhibiting SARSCoV replication in vitro: calpain inhibitors (a class of cellular cysteine proteinases) and a number of nucleoside analogues. Cytopathic effect reduction assays visually determined with spectrophotometric verification by neutral red (NR) uptake assay were used to evaluate cytotoxicity and antiviral potency of the compounds. Significantly inhibitory compounds were then evaluated in virus yield reduction assays. Two calpain inhibitors, Val-Leu-CHO (calpain inhibitor VI) and Z-Val-Phe-Ala-CHO (calpain inhibitor III), were the most potent inhibitors of SARSCoV. By virus yield reduction assay, calpain inhibitor VI had a 90% effective concentration (EC₉₀) of 3 μM and calpain inhibitor III had an EC₉₀ of 15 μM. β-D-N⁴-hydroxycytidine was the most selective nucleoside analogue inhibitor with an EC90 of 6 μM by virus yield reduction assay. These compounds or analogues warrant further evaluation as potential therapies for treating SARS or could be used as lead compounds for discovery of more potent SARSCoV inhibitors.