Evaluation of metal-conjugated compounds as inhibitors of 3CL protease of SARS-CoV

3C-like (3CL) protease is essential for the life cycle of severe acute respiratory syndrome-coronavirus (SARS-CoV) and therefore represents a key anti-viral target. A compound library consisting of 960 commercially available drugs and biologically active substances was screened for inhibition of SARS-CoV 3CL protease. Potent inhibition was achieved using the mercury-containing compounds thimerosal and phenylmercuric acetate, as well as hexachlorophene. As well, 1-10 μM of each compound inhibited viral replication in Vero E6 cell culture. Detailed mechanism studies using a fluorescence-based protease assay demonstrated that the three compounds acted as competitive inhibitors (K _i=0.7, 2.4, and 13.7 μM for phenylmercuric acetate, thimerosal, and hexachlorophene, respectively). A panel of metal ions including Zn ²⁺ and its conjugates were then evaluated for their anti-3CL protease activities. Inhibition was more pronounced using a zinc-conjugated compound (1-hydroxypyridine-2-thione zinc; K_i=0.17μM) than using the ion alone (K_i=1.1μM).