In our search for novel inhibitors of herpes simplex virus type 1 (HSV-1), a new class of thiourea inhibitors was discovered. N-{4-[3-(5-Chloro-2,4-dimethoxyphenyl)-thioureido]-phenyl}-acetamide and its 2-fluoro-benzamide derivative inhibited HSV-1 replication. HSV-2, human cytomegalovirus, and varicella-zoster virus were inhibited to a lesser extent. The compounds acted late in the replication cycle by impairing both the cleavage of concatameric viral DNA into progeny genome length and the packaging of the DNA into capsids, indicative of a defect in the encapsidation process. To uncover the molecular target of the inhibition, resistant HSV-1 isolates were generated, and the mutation responsible for the resistance was mapped using marker transfer techniques. Each of three independent isolates had point mutations in the UL6 gene which resulted in independent single-amino-acid changes. One mutation was located in the N terminus of the protein (E121D), while two were located close together in the C terminus (A618V and Q621R). Each of these point mutations was sufficient to confer drug resistance when introduced into wild-type virus. The UL6 gene is one of the seven HSV-1 genes known to play a role in DNA packaging. This novel class of inhibitors has provided a new tool for dissection of HSV-1 encapsidation mechanisms and has uncovered a new viable target for the treatment of herpesviral diseases.The herpesvirus family has many members that are human pathogens and make a significant contribution to morbidity and mortality associated with viral diseases. Based on criteria such as host cell specificity, oncogenicity, length of replication cycle, and genome arrangement, the herpesviruses have been divided into alpha-, beta-, and gammaherpesviruses (31). The alphaherpesviruses herpes simplex virus (HSV) types 1 and 2 latently infect nerve cells. HSV-1 is primarily associated with herpes labialis, and HSV-2 is associated with herpes genitalis, but both types have been associated with both diseases (28,39,47). In immunocompetent adults, these diseases often recur due to reactivation of the virus from the latent state. HSV infections of immunocompromised patients such as transplant and AIDS patients are often chronic and fatal. Current therapy for HSV disease consists of nucleoside analogs such as acyclovir (ACV) and valacyclovir, a prodrug of ACV, and pencyclovir (PCV) and its prodrug, famcyclovir. ACV and PCV are selectively phosphorylated by the viral thymidine kinase in HSVinfected cells, followed by further phosphorylation to the triphosphate by cellular kinases. Triphosphorylated ACV and PCV are both inhibitors of the viral DNA polymerase, and ACV also acts as a chain terminator when incorporated into the nascent viral DNA chain (4, 13). Drug resistance can occur in chronic infections, where replication is ineffectively curtailed by the immune system. Recently increasing numbers of drugresistant HSV strains have been isolated from immunocompromised people. The mechanism of resistance of most ACV-resistant isolates is...

Several compounds that specifically inhibited replication of the H1 and H2 subtypes of influenza virus type A were identified by screening a chemical library for antiviral activity. In single-cycle infections, the compounds inhibited virus-specific protein synthesis when added before or immediately after infection but were ineffective when added 30 min later, suggesting that an uncoating step was blocked. Sequencing of hemagglutinin (HA) genes of several independent mutant viruses resistant to the compounds revealed single amino acid changes that clustered in the stem region of the HA trimer in and near the HA2 fusion peptide. One of the compounds, an N-substituted piperidine, could be docked in a pocket in this region by computer-assisted molecular modeling. This compound blocked the fusogenic activity of HA, as evidenced by its inhibition of low-pH-induced cell-cell fusion in infected cell monolayers. An analog which was more effective than the parent compound in inhibiting virus replication was synthesized. It was also more effective in blocking other manifestations of the low-pH-induced conformational change in HA, including virus inactivation, virus-induced hemolysis of erythrocytes, and susceptibility of the HA to proteolytic degradation. Both compounds inhibited viral protein synthesis and replication more effectively in cells infected with a virus mutated in its M2 protein than with wild-type virus. The possible functional relationship between M2 and HA suggested by these results is discussed.

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