title: Towards an in vitro model of Plasmodium hypnozoites suitable for drug discovery.
abstract: BACKGROUND
  Amongst the Plasmodium species in humans, only P. vivax and P. ovale produce latent hepatic stages called hypnozoites, which are responsible for malaria episodes long after a mosquito bite. Relapses contribute to increased morbidity, and complicate malaria elimination programs. A single drug effective against hypnozoites, primaquine, is available, but its deployment is curtailed by its haemolytic potential in glucose-6-phosphate dehydrogenase deficient persons. Novel compounds are thus urgently needed to replace primaquine. Discovery of compounds active against hypnozoites is restricted to the in vivo P. cynomolgi-rhesus monkey model. Slow growing hepatic parasites reminiscent of hypnozoites had been noted in cultured P. vivax-infected hepatoma cells, but similar forms are also observed in vitro by other species including P. falciparum that do not produce hypnozoites.
  
  
  METHODS
  P. falciparum or P. cynomolgi sporozoites were used to infect human or Macaca fascicularis primary hepatocytes, respectively. The susceptibility of the slow and normally growing hepatic forms obtained in vitro to three antimalarial drugs, one active against hepatic forms including hypnozoites and two only against the growing forms, was measured.
  
  
  RESULTS
  The non-dividing slow growing P. cynomolgi hepatic forms, observed in vitro in primary hepatocytes from the natural host Macaca fascicularis, can be distinguished from similar forms seen in P. falciparum-infected human primary hepatocytes by the differential action of selected anti-malarial drugs. Whereas atovaquone and pyrimethamine are active on all the dividing hepatic forms observed, the P. cynomolgi slow growing forms are highly resistant to treatment by these drugs, but remain susceptible to primaquine.
  
  
  CONCLUSIONS
  Resistance of the non-dividing P. cynomolgi forms to atovaquone and pyrimethamine, which do not prevent relapses, strongly suggests that these slow growing forms are hypnozoites. This represents a first step towards the development of a practical medium-throughput in vitro screening assay for novel hypnozoiticidal drugs.
authors.affiliation: Université Pierre et Marie Curie-Paris 6, UMR S945, Paris, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Dembele
authors.forename: Audrey
authors.initials: A
authors.lastname: Gego
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Zeeman
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Franetich
authors.forename: Olivier
authors.initials: O
authors.lastname: Silvie
authors.forename: Armelle
authors.initials: A
authors.lastname: Rametti
authors.forename: Roger
authors.initials: R
authors.lastname: Le Grand
authors.forename: Nathalie
authors.initials: N
authors.lastname: Dereuddre-Bosquet
authors.forename: Robert
authors.initials: R
authors.lastname: Sauerwein
authors.forename: Geert-Jan
authors.initials: GJ
authors.lastname: van Gemert
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Vaillant
authors.forename: Alan W
authors.initials: AW
authors.lastname: Thomas
authors.forename: Georges
authors.initials: G
authors.lastname: Snounou
authors.forename: Clemens H M
authors.initials: CH
authors.lastname: Kocken
authors.forename: Dominique
authors.initials: D
authors.lastname: Mazier
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology; D002478:Cells, Cultured; D022781:Hepatocytes / Q000469:parasitology*; D006801:Humans; D008252:Macaca fascicularis; D010961:Plasmodium / Q000187:drug effects / Q000502:physiology*; D034101:Sporozoites / Q000187:drug effects / Q000502:physiology*
chemical_list: D000962:Antimalarials