title: 4-Aminoquinoline resistance of Plasmodium falciparum: insights from the study of amodiaquine uptake.
abstract: The relationship between antimalarial activity and drug accumulation of chloroquine and amodiaquine was evaluated with four chloroquine-resistant and two chloroquine-susceptible isolates of Plasmodium falciparum. Susceptibility of the strains to amodiaquine was correlated with susceptibility to chloroquine (r2 = 0.96). Similarly, accumulation of amodiaquine was correlated with accumulation of chloroquine (r2 = 0.94). Accumulation of both chloroquine and amodiaquine was significantly reduced in chloroquine-resistant isolates (p < 0.005). For the panel of isolates, the accumulation ratio of both drugs was inversely proportional to drug susceptibility (r2 = 0.963 and 0.994 for amodiaquine and chloroquine, respectively). Time course studies highlighted a reduced initial rate of amodiaquine accumulation in chloroquine-resistant isolates compared with chloroquine-susceptible isolates, with no evidence of an enhanced drug efflux rate. Daunomycin, a modulator of parasite chloroquine transport, significantly increased steady state accumulation of both drugs in chloroquine-resistant isolates and, to a lesser extent, in chloroquine-susceptible isolates. Furthermore, daunomycin increased the initial rate of accumulation of amodiaquine in both chloroquine-resistant and chloroquine-susceptible isolates. Resistance to 4-aminoquinoline drugs is associated with reduced drug permeability rather than enhanced cellular exit of preaccumulated drug, and daunomycin seems to increase the permeability of parasites to aminoquinolines. A new model of 4-aminoquinoline resistance is proposed to take account of these and earlier observations.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Liverpool, UK.
authors.forename: P G
authors.initials: PG
authors.lastname: Bray
authors.forename: S R
authors.initials: SR
authors.lastname: Hawley
authors.forename: S A
authors.initials: SA
authors.lastname: Ward
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology*; D000655:Amodiaquine / Q000378:metabolism*; D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D004351:Drug Resistance; D008826:Microbial Sensitivity Tests; D010963:Plasmodium falciparum / Q000187:drug effects*
chemical_list: D000634:Aminoquinolines; D000962:Antimalarials; D000655:Amodiaquine; C001920:4-aminoquinoline