title: Different pH requirements are associated with divergent inhibitory effects of chloroquine on human and avian influenza A viruses.
abstract: Chloroquine is a 4-aminoquinoline previously used in malaria therapy and now becoming an emerging investigational antiviral drug due to its broad spectrum of antiviral activities. To explore whether the low pH-dependency of influenza A viruses might affect the antiviral effects of chloroquine at clinically achievable concentrations, we tested the antiviral effects of this drug on selected human and avian viruses belonging to different subtypes and displaying different pH requirements. Results showed a correlation between the responses to chloroquine and NH4Cl, a lysosomotropic agent known to increase the pH of intracellular vesicles. Time-of-addition experiments showed that the inhibitory effect of chloroquine was maximal when the drug had been added at the time of infection and was lost after 2 h post-infection. This timing approximately corresponds to that of virus/cell fusion. Moreover, there was a clear correlation between the EC50 of chloroquine in vitro and the electrostatic potential of the HA subunit (HA2) mediating the virus/cell fusion process. Overall, the present study highlights the critical importance of a host cell factor such as intravesicular pH in determining the anti-influenza activity of chloroquine and other lysosomotropic agents.
authors.affiliation: Dept. of Food and Animal Health, Istituto Superiore di Sanità, Rome, Italy. livia.ditrani@iss.it
authors.forename: Livia
authors.initials: L
authors.lastname: Di Trani
authors.forename: Andrea
authors.initials: A
authors.lastname: Savarino
authors.forename: Laura
authors.initials: L
authors.lastname: Campitelli
authors.forename: Sandro
authors.initials: S
authors.lastname: Norelli
authors.forename: Simona
authors.initials: S
authors.lastname: Puzelli
authors.forename: Daniela
authors.initials: D
authors.lastname: D'Ostilio
authors.forename: Edoardo
authors.initials: E
authors.lastname: Vignolo
authors.forename: Isabella
authors.initials: I
authors.lastname: Donatelli
authors.forename: Antonio
authors.initials: A
authors.lastname: Cassone
mesh_terms: D000643:Ammonium Chloride / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival; D002738:Chloroquine / Q000494:pharmacology*; D003588:Cytopathogenic Effect, Viral / Q000187:drug effects; D004285:Dogs; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects / Q000502:physiology; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects / Q000502:physiology; D053124:Influenza A Virus, H5N1 Subtype / Q000187:drug effects / Q000502:physiology; D009980:Influenza A virus / Q000187:drug effects* / Q000502:physiology; D008247:Lysosomes / Q000378:metabolism; D011200:Poultry; D012367:RNA, Viral / Q000096:biosynthesis; D013997:Time Factors; D014779:Virus Replication / Q000187:drug effects
chemical_list: D000998:Antiviral Agents; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D012367:RNA, Viral; D000643:Ammonium Chloride; D002738:Chloroquine