title: Narasin, a novel antiviral compound that blocks dengue virus protein expression.
abstract: BACKGROUND
  Dengue virus (DENV) is a mosquito-borne virus that causes a spectrum of human diseases ranging from mild dengue fever to dengue haemorrhagic fever and dengue shock syndrome in severe cases. Currently, there is no effective antiviral therapy or vaccine against DENV infection.
  
  
  METHODS
  In order to identify potential antiviral agents against DENV, we performed high-throughput cell-based screening on a highly purified natural products library. Among the screening hits, selected compounds which displayed 50-75% inhibition against DENV2 were validated using secondary assays. Time-of-addition studies, dose-dependent assays, real time quantitative reverse transcriptase (RT)-PCR, Western blot and ultrastructural imaging were conducted in an attempt to elucidate the potential antiviral mechanisms of narasin.
  
  
  RESULTS
  In this study, an ionophore, narasin was selected for detailed analysis due to its strong inhibitory profile against DENV infection with minimal cytotoxicity (50% cytotoxic concentration >1,000 μM). A dose-dependent study revealed narasin to have an 50% inhibitory concentration of less than 1 μM against all four serotypes of DENV. Time-of-addition studies of narasin-treated, DENV2-infected Huh-7 cells suggested narasin to be involved in inhibiting the post-entry stages of viral replication during DENV infection. Proteomic and ultrastructural analyses revealed the antiviral mechanism of narasin as likely to be associated with the disruption of viral protein synthesis. In addition, quantitative RT-PCR studies showed no differences in viral RNA levels between narasin-treated and control DENV2-infected cells.
  
  
  CONCLUSIONS
  Narasin was identified and characterized as a novel agent that inhibits DENV replication in vitro through non-cytotoxic mechanisms, thus indicating its potential to be further developed as a therapeutic anti-DENV agent.
authors.affiliation: Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore.
authors.forename: June Su Yin
authors.initials: JS
authors.lastname: Low
authors.forename: Kan Xing
authors.initials: KX
authors.lastname: Wu
authors.forename: Karen Caiyun
authors.initials: KC
authors.lastname: Chen
authors.forename: Mary Mah-Lee
authors.initials: MM
authors.lastname: Ng
authors.forename: Justin Jang Hann
authors.initials: JJ
authors.lastname: Chu
mesh_terms: D000330:Aedes / Q000166:cytology; D000818:Animals; D000998:Antiviral Agents / Q000737:chemistry / Q000494:pharmacology; D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003716:Dengue Virus / Q000187:drug effects* / Q000254:growth & development; D004305:Dose-Response Relationship, Drug; D057166:High-Throughput Screening Assays; D006801:Humans; D020128:Inhibitory Concentration 50; D007476:Ionophores / Q000737:chemistry / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects*; D011714:Pyrans / Q000737:chemistry / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019595:Severe Dengue / Q000188:drug therapy* / Q000821:virology; D012720:Severity of Illness Index; D054852:Small Molecule Libraries / Q000737:chemistry / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014779:Virus Replication / Q000187:drug effects*
chemical_list: D000998:Antiviral Agents; D007476:Ionophores; D011714:Pyrans; D054852:Small Molecule Libraries; D014764:Viral Proteins; C013612:narasin