Enterovirus 71 is one of the most important pathogens in the family of Picornaviridae that can cause severe complications in the postpoliovirus era, such as encephalitis, pulmonary edema, and even death. Pyridyl imidazolidinone is a novel class of potent and selective human enterovirus 71 inhibitor. Pyridyl imidazolidinone was identified by using computer-assisted drug design. This virologic investigation demonstrates that BPR0Z-194, one of the pyridyl imidazolidinones, targets enterovirus 71 capsid protein VP1. Time course experiments revealed that BPR0Z-194 effectively inhibited virus replication in the early stages, implying that the compound can inhibit viral adsorption and/or viral RNA uncoating. BPR0Z-194 was used to select and characterize the drug-resistant viruses. Sequence analysis of the VP1 region showed that the resistant variants differed consistently by seven amino acids in VP1 region from their parental drug-sensitive strains. Sitedirected mutagenesis of enterovirus 71 infectious cDNA revealed that a single amino acid alteration at the position 192 of VP1 can confer resistance to the inhibitory effects of BPR0Z-194.Enterovirus 71 (EV71) was first isolated in 1969 in California (J. Blomberg, E. Lycke, K. Ahlfors, T. Johnsson, S. Wolontis, and G. von Zeipel, Letter, Lancet i:112). Two adults and 18 children were infected in that outbreak and one 5-year-old child died. Thereafter, mortalities caused by EV71 were reported in Bulgaria (6), Hungary (23), and Malaysia. In 1998, an EV71 epidemic occurred in Taiwan, with the virus infecting over 120,000 people and killing 78 children (1,5,13,14). The central nervous system is the most vulnerable target of EV71 infection. After the central nervous system is virus infected, a patient can die very quickly from severe complications, such as encephalitis (19) and pulmonary edema (2, 16).EV71, like other viruses in the family of Picornaviridae, is a small, nonenveloped, spherical particle with a diameter of ϳ30 nm. The virus has a single-stranded positive-sense RNA enclosed by the capsid proteins VP1, VP2, VP3, and VP4. The capsid contains 60 structural proteins symmetrically arranged into an icosahedral lattice (15,31,32). In addition to protecting the viral RNA from nuclease cleavage, the capsid recognizes the receptors on the surface of the specific host cells (3, 9, 18) and displays antigenicity (20,38). The surface of the virion has a prominent star-shaped plateau at the fivefold axis of symmetry, surrounded by a deep depression ("canyon"). The canyon has been shown to serve as a receptor-binding site in poliovirus and rhinovirus (29,30).Pleconaril, one of the WIN compounds with capsid-binding capability targeting VP1, is a novel agent for treating picornavirus infections. Pleconaril has passed the last stage of clinical trials (4, 26) and has shown excellent antiviral effects for most of the enteroviruses and rhinoviruses (27,28,33,34). However, pleconaril did not neutralize the cytopathic effect (CPE) induced by EV71 (37). Therefore, a series of imidazol...