title: Fitness of artemisinin-resistant Plasmodium falciparum in vitro.
abstract: OBJECTIVE
  Drug resistance confers a fitness advantage to parasites exposed to frequent drug pressure, yet these mutations also may incur a fitness cost. We assessed fitness advantages and costs of artemisinin resistance in Plasmodium falciparum in vitro to understand how drug resistance will spread and evolve in a competitive environment.
  
  
  METHODS
  Genotyping of SNPs, drug susceptibility assays and copy number determination were used to assess the impact of artemisinin resistance on parasite fitness. An artemisinin-resistant clone (C9) selected in vitro from an isogenic parental clone (D6) was used to conduct competitive growth studies to assess fitness of artemisinin resistance. The resistant and susceptible clones were mixed or grown alone in the presence and absence of drug pressure (dihydroartemisinin or pyrimethamine) to quantify the rate at which artemisinin resistance was gained or lost.
  
  
  RESULTS
  We experimentally demonstrate for the first time that artemisinin resistance provides a fitness advantage that is selected for with infrequent exposure to drug, but is lost in the absence of exposure to artemisinin drugs. The best correlations with artemisinin resistance were decreased in vitro drug susceptibility to artemisinin derivatives, increased copy number of Pf3D7_1030100 and an SNP in Pf3D7_0307600. An SNP conferring an E208K mutation in the kelch gene (Pf3D7_1343700) was not associated with resistance. Furthermore, we observed second-cycle ring-stage dormancy induced by pyrimethamine, suggesting that dormancy is a fitness trait that provides an advantage for survival from antimalarial drug stress.
  
  
  CONCLUSIONS
  Artemisinin-resistant P. falciparum have a fitness advantage to survive and predominate in the population even in the face of infrequent exposure to artemisinin drugs.
authors.affiliation: Morsani College of Medicine, University of South Florida, Tampa, FL, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Hott
authors.affiliation: Global Health Infectious Disease Research Program, College of Public Health, University of South Florida, Tampa, FL, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Tucker
authors.affiliation: Global Health Infectious Disease Research Program, College of Public Health, University of South Florida, Tampa, FL, USA.
authors.forename: Debora
authors.initials: D
authors.lastname: Casandra
authors.affiliation: Global Health Infectious Disease Research Program, College of Public Health, University of South Florida, Tampa, FL, USA.
authors.forename: Kansas
authors.initials: K
authors.lastname: Sparks
authors.affiliation: Global Health Infectious Disease Research Program, College of Public Health, University of South Florida, Tampa, FL, USA dkyle@health.usf.edu.
authors.forename: Dennis E
authors.initials: DE
authors.lastname: Kyle
mesh_terms: D000962:Antimalarials / Q000494:pharmacology*; D037621:Artemisinins / Q000494:pharmacology*; D004351:Drug Resistance; D018628:Gene Dosage; D017125:Genes, Protozoan; D056084:Genetic Fitness; D005838:Genotype; D006801:Humans; D008018:Life Cycle Stages; D021261:Parasitic Sensitivity Tests; D010641:Phenotype; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D020641:Polymorphism, Single Nucleotide
chemical_list: D000962:Antimalarials; D037621:Artemisinins; C031327:artemisinin