title: Influence of the Plasmodium falciparum P-glycoprotein homologue 1 (pfmdr1 gene product) on the antimalarial action of cyclosporin.
abstract: OBJECTIVE
  The immunosuppressant cyclosporin A and a number of other cyclosporins have potent and selective antimalarial activity. Their exact mechanism of antimalarial action is unknown but the structure-activity relationships for malarial parasite inhibition and immunosuppression differ markedly. The 3'-keto derivative of cyclosporin D (valspodar) is particularly potent against the human malarial parasite Plasmodium falciparum in culture but causes negligible immunosuppression. Multidrug resistance in mammalian cancer cells, the result of overproduction of the P-glycoprotein, can be reversed by certain cyclosporins, particularly valspodar. We therefore investigated the possibility that the antimalarial target of cyclosporin might be a P-glycoprotein homologue. P. falciparum P-glycoprotein homologue 1 (Pgh1; the pfmdr1 gene product) is located in the digestive vacuole (DV) membrane of the parasite. Its function is unknown but it modulates the susceptibility of parasites to quinolines and related antimalarial drugs, including quinine, mefloquine, halofantrine and chloroquine, and to artemisinin.
  
  
  RESULTS
  Here we demonstrate that (i) sequence polymorphisms in pfmdr1 altered the susceptibility of parasites to cyclosporin A and (ii) pfmdr1-overexpressing strains were slightly less susceptible to the drug. Furthermore, we found synergistic antimalarial interactions between cyclosporin A and quinine, mefloquine or halofantrine and antagonism between cyclosporin A and chloroquine. However, we were unable to detect a direct interaction between cyclosporin and Pgh1.
  
  
  CONCLUSIONS
  The amino acid sequence and copy number of Pgh1 may influence cyclosporin susceptibility as a result of a direct interaction between the drug and the protein, or via indirect effects on the physiology of the DV.
authors.affiliation: Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin, Trinity College Dublin 2, Ireland.
authors.forename: C S
authors.initials: CS
authors.lastname: Gavigan
authors.forename: M
authors.initials: M
authors.lastname: Shen
authors.forename: S G
authors.initials: SG
authors.lastname: Machado
authors.forename: A
authors.initials: A
authors.lastname: Bell
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D016572:Cyclosporine / Q000494:pharmacology*; D004351:Drug Resistance / Q000235:genetics*; D004357:Drug Synergism; D005786:Gene Expression Regulation / Q000187:drug effects; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics*; D021261:Parasitic Sensitivity Tests; D010963:Plasmodium falciparum / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011110:Polymorphism, Genetic
chemical_list: D000962:Antimalarials; D016572:Cyclosporine; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C513498:Mdr1 protein, Plasmodium falciparum