title: Tafenoquine and NPC-1161B require CYP 2D metabolism for anti-malarial activity: implications for the 8-aminoquinoline class of anti-malarial compounds.
abstract: BACKGROUND
  Tafenoquine (TQ) is an 8-aminoquinoline (8AQ) that has been tested in several Phase II and Phase III clinical studies and is currently in late stage development as an anti-malarial prophylactic agent. NPC-1161B is a promising 8AQ in late preclinical development. It has recently been reported that the 8AQ drug primaquine requires metabolic activation by CYP 2D6 for efficacy in humans and in mice, highlighting the importance of pharmacogenomics in the target population when administering primaquine. A logical follow-up study was to determine whether CYP 2D activation is required for other compounds in the 8AQ structural class.
  
  
  METHODS
  In the present study, the anti-malarial activities of NPC-1161B and TQ were assessed against luciferase expressing Plasmodium berghei in CYP 2D knock-out mice in comparison with normal C57BL/6 mice (WT) and with humanized/CYP 2D6 knock-in mice by monitoring luminescence with an in vivo imaging system. These experiments were designed to determine the direct effects of CYP 2D metabolic activation on the anti-malarial efficacy of NPC-1161B and TQ.
  
  
  RESULTS
  NPC-1161B and TQ exhibited no anti-malarial activity in CYP 2D knock-out mice when dosed at their ED100 values (1 mg/kg and 3 mg/kg, respectively) established in WT mice. TQ anti-malarial activity was partially restored in humanized/CYP 2D6 knock-in mice when tested at two times its ED100.
  
  
  CONCLUSIONS
  The results reported here strongly suggest that metabolism of NPC-1161B and TQ by the CYP 2D enzyme class is essential for their anti-malarial activity. Furthermore, these results may provide a possible explanation for therapeutic failures for patients who do not respond to 8AQ treatment for relapsing malaria. Because CYP 2D6 is highly polymorphic, variable expression of this enzyme in humans represents a significant pharmacogenomic liability for 8AQs which require CYP 2D metabolic activation for efficacy, particularly for large-scale prophylaxis and eradication campaigns.
authors.affiliation: Division of Experimental Therapeutics, Military Malaria Research Program, Walter Reed Army Institute of Research, 503 Robert Grant Ave, Silver Spring, MD 20910, USA. sean.r.marcsisin.mil@mail.mil.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Marcsisin
authors.forename: Jason C
authors.initials: JC
authors.lastname: Sousa
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Reichard
authors.forename: Diana
authors.initials: D
authors.lastname: Caridha
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zeng
authors.forename: Norma
authors.initials: N
authors.lastname: Roncal
authors.forename: Ronan
authors.initials: R
authors.lastname: McNulty
authors.forename: Julio
authors.initials: J
authors.lastname: Careagabarja
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Sciotti
authors.forename: Jason W
authors.initials: JW
authors.lastname: Bennett
authors.forename: Victor E
authors.initials: VE
authors.lastname: Zottig
authors.forename: Gregory
authors.initials: G
authors.lastname: Deye
authors.forename: Qigui
authors.initials: Q
authors.lastname: Li
authors.forename: Lisa
authors.initials: L
authors.lastname: Read
authors.forename: Mark
authors.initials: M
authors.lastname: Hickman
authors.forename: N P
authors.initials: NP
authors.lastname: Dhammika Nanayakkara
authors.forename: Larry A
authors.initials: LA
authors.lastname: Walker
authors.forename: Bryan
authors.initials: B
authors.lastname: Smith
authors.forename: Victor
authors.initials: V
authors.lastname: Melendez
authors.forename: Brandon S
authors.initials: BS
authors.lastname: Pybus
mesh_terms: D000634:Aminoquinolines / Q000378:metabolism*; D000818:Animals; D000962:Antimalarials / Q000378:metabolism*; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D008288:Malaria / Q000188:drug therapy* / Q000469:parasitology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010962:Plasmodium berghei / Q000187:drug effects*; D013386:Succinates / Q000378:metabolism*
chemical_list: C511302:8-((4-amino-1-methylbutyl)amino)-5-(3,4-dichlorophenoxy)-6-methoxy-4-methylquinoline; D000634:Aminoquinolines; D000962:Antimalarials; D013386:Succinates; C055852:tafenoquine; D019389:Cytochrome P-450 CYP2D6