In vitro metabolism of chloroquine: identification of CYP2C8, CYP3A4, and CYP2D6 as the main isoforms catalyzing N-desethylchloroquine formation

Drug Metab Dispos. 2003 Jun;31(6):748-54. doi: 10.1124/dmd.31.6.748.


In humans, the antimalarial drug chloroquine (CQ) is metabolized into one major metabolite, N-desethylchloroquine (DCQ). Using human liver microsomes (HLM) and recombinant human cytochrome P450 (P450), we performed studies to identify the P450 isoform(s) involved in the N-desethylation of CQ. In HLM incubated with CQ, only DCQ could be detected. Apparent Km and Vmax values (mean +/- S.D.) for metabolite formation were 444 +/- 121 microM and 617 +/- 128 pmol/min/mg protein, respectively. In microsomes from a panel of 16 human livers phenotyped for 10 different P450 isoforms, DCQ formation was highly correlated with testosterone 6beta-hydroxylation (r = 0.80; p < 0.001), a CYP3A-mediated reaction, and CYP2C8-mediated paclitaxel alpha-hydroxylation (r = 0.82; p < 0.001). CQ N-desethylation was diminished when coincubated with quercetin (20-40% inhibition), ketoconazole, or troleandomycin (20-30% inhibition) and was strongly inhibited (80% inhibition) by a combination of ketoconazole and quercetin, which further corroborates the contribution of CYP2C8 and CYP3As. Of 10 cDNA-expressed human P450s examined, only CYP1A1, CYP2D6, CYP3A4, and CYP2C8 produced DCQ. CYP2C8 and CYP3A4 constituted low-affinity/high-capacity systems, whereas CYP2D6 was associated with higher affinity but a significantly lower capacity. This property may explain the ability of CQ to inhibit CYP2D6-mediated metabolism in vitro and in vivo. At therapeutically relevant concentrations ( approximately 100 microM CQ in the liver), CYP2C8, CYP3A4, and, to a much lesser extent, CYP2D6 are expected to account for most of the CQ N-desethylation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors
  • Aryl Hydrocarbon Hydroxylases / biosynthesis*
  • Biotransformation
  • Cells, Cultured
  • Chloroquine / analogs & derivatives*
  • Chloroquine / metabolism
  • Chloroquine / pharmacokinetics*
  • Chromatography, High Pressure Liquid
  • Cytochrome P-450 CYP2C8
  • Cytochrome P-450 CYP2D6 / biosynthesis*
  • Cytochrome P-450 CYP2D6 Inhibitors
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / biosynthesis*
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Insecta
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / biosynthesis
  • Kinetics
  • Microsomes, Liver / drug effects
  • Microsomes, Liver / enzymology
  • Recombinant Proteins / antagonists & inhibitors
  • Recombinant Proteins / biosynthesis
  • Spectrometry, Mass, Electrospray Ionization
  • Transfection


  • Cytochrome P-450 CYP2D6 Inhibitors
  • Cytochrome P-450 Enzyme Inhibitors
  • Enzyme Inhibitors
  • Isoenzymes
  • Recombinant Proteins
  • Chloroquine
  • Cytochrome P-450 Enzyme System
  • Aryl Hydrocarbon Hydroxylases
  • CYP2C8 protein, human
  • CYP3A protein, human
  • Cytochrome P-450 CYP2C8
  • Cytochrome P-450 CYP2D6
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • desethylchloroquine