Washington: Scientists have identified several existing compounds that block the replication of the COVID-19-causing SARS-CoV-2 virus within human cells grown in the laboratory, by targeting a key viral enzyme.The inhibitors all demonstrated potent chemical and structural interactions with viral proteins critical to the virus's ability to proliferate, according to the study published in the journal Cell Research.The most promising drug candidates -- including the USFDA-approved hepatitis C medication boceprevir and an investigational veterinary antiviral drug known as GC-376 -- target the SARS-CoV-2 main protease (Mpro) enzyme, the researchers from the University of South Florida (USF) in the US said.The enzyme cuts out proteins from a long.