Dengue virus (DENV) infection causes one of the most widespread mosquito-borne diseases in the world. Despite the great need, effective vaccines and practical antiviral therapies are still under development. Intracellular lipid levels are regulated by sterol regulatory elements-binding proteins (SREBPs), which are activated by serine protease, site 1 protease (S1P). Small compound PF-429242 is known as a S1P inhibitor and the antivirus effects have been reported in some viruses. In this study, we examined the anti-DENV effects of PF-429242 using all four serotypes of DENV by several primate-derived cell lines. Moreover, emergence of drug-resistant DENV mutants was assessed by sequential passages with the drug. DENV dependency on intracellular lipids during their infection was also evaluated by adding extracellular lipids. The addition of PF-429242 showed suppression of viral propagation in all DENV serotypes. We showed that drug-resistant DENV mutants are unlikely to emerge after five times sequential passages through treatment with PF-429242. Although the levels of intracellular cholesterol and lipid droplets were reduced by PF-429242, viral propagations were not recovered by addition of exogenous cholesterol or fatty acids, indicating that the reduction of LD and cholesterol caused by PF-429242 treatment is not related to its mechanism of action against DENV propagation. Our results suggest that PF-429242 is a promising candidate for an anti-DENV agent.

For the development of effective treatment strategies for Japanese encephalitis (JE), it is important to identify the viral factors causing severe disease during JE virus (JEV) infection. In this study, we assessed whether amino acid substitutions are critical factors for higher mortality of JaTH160 compared with JaOArS982 in mice using the technique of infectious cDNA clones. We raised the possibility that two amino acids of C₁₂₄ and NS3₄₈₂ of JaTH160 may contribute to increased mortality in mice. However, simultaneous substitutions of these amino acids did not significantly increase the virulence of JaOArS982, suggesting that high mortality due to JaTH160 viral infection cannot be simply attributed to the specific amino acids. Multiple and complex, but not simple, mechanisms may induce the high mortality of JaTH160 infection in mice.