title: Ivermectin is a potent inhibitor of flavivirus replication specifically targeting NS3 helicase activity: new prospects for an old drug.
abstract: OBJECTIVE
  Infection with yellow fever virus (YFV), the prototypic mosquito-borne flavivirus, causes severe febrile disease with haemorrhage, multi-organ failure and a high mortality. Moreover, in recent years the Flavivirus genus has gained further attention due to re-emergence and increasing incidence of West Nile, dengue and Japanese encephalitis viruses. Potent and safe antivirals are urgently needed.
  
  
  METHODS
  Starting from the crystal structure of the NS3 helicase from Kunjin virus (an Australian variant of West Nile virus), we identified a novel, unexploited protein site that might be involved in the helicase catalytic cycle and could thus in principle be targeted for enzyme inhibition. In silico docking of a library of small molecules allowed us to identify a few selected compounds with high predicted affinity for the new site. Their activity against helicases from several flaviviruses was confirmed in in vitro helicase/enzymatic assays. The effect on the in vitro replication of flaviviruses was then evaluated.
  
  
  RESULTS
  Ivermectin, a broadly used anti-helminthic drug, proved to be a highly potent inhibitor of YFV replication (EC₅₀ values in the sub-nanomolar range). Moreover, ivermectin inhibited, although less efficiently, the replication of several other flaviviruses, i.e. dengue fever, Japanese encephalitis and tick-borne encephalitis viruses. Ivermectin exerts its effect at a timepoint that coincides with the onset of intracellular viral RNA synthesis, as expected for a molecule that specifically targets the viral helicase.
  
  
  CONCLUSIONS
  The well-tolerated drug ivermectin may hold great potential for treatment of YFV infections. Furthermore, structure-based optimization may result in analogues exerting potent activity against flaviviruses other than YFV.
authors.affiliation: Dipartimento di Scienze Biomolecolari e Biotecnologie,  Università degli Studi di Milano, via Celoria 26, 20133 Milano,  Italy.
authors.forename: Eloise
authors.initials: E
authors.lastname: Mastrangelo
authors.forename: Margherita
authors.initials: M
authors.lastname: Pezzullo
authors.forename: Tine
authors.initials: T
authors.lastname: De Burghgraeve
authors.forename: Suzanne
authors.initials: S
authors.lastname: Kaptein
authors.forename: Boris
authors.initials: B
authors.lastname: Pastorino
authors.forename: Kai
authors.initials: K
authors.lastname: Dallmeier
authors.forename: Xavier
authors.initials: X
authors.lastname: de Lamballerie
authors.forename: Johan
authors.initials: J
authors.lastname: Neyts
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Hanson
authors.forename: David N
authors.initials: DN
authors.lastname: Frick
authors.forename: Martino
authors.initials: M
authors.lastname: Bolognesi
authors.forename: Mario
authors.initials: M
authors.lastname: Milani
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology*; D002522:Chlorocebus aethiops; D003716:Dengue Virus / Q000187:drug effects; D018349:Encephalitis Viruses, Japanese / Q000187:drug effects; D004669:Encephalitis Viruses, Tick-Borne / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007559:Ivermectin / Q000494:pharmacology*; D056004:Molecular Dynamics Simulation; D020365:RNA Helicases / Q000037:antagonists & inhibitors / Q000737:chemistry; D012697:Serine Endopeptidases / Q000737:chemistry; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D014779:Virus Replication / Q000187:drug effects; D015005:Yellow fever virus / Q000187:drug effects*; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
chemical_list: D000998:Antiviral Agents; D004791:Enzyme Inhibitors; D007559:Ivermectin; D020365:RNA Helicases; D012697:Serine Endopeptidases; D017361:Viral Nonstructural Proteins; C060028:NS3 protein, flavivirus; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases