Evaluation of P450 Inhibition and Induction by Artemisinin Antimalarials in Human Liver Microsomes and Primary Human Hepatocytes

Abstract

ABSTRACT:Artemisinin drugs have become the first-line antimalarials in areas of multidrug resistance. However, monotherapy with artemisinin drugs results in comparatively high recrudescence rates. Autoinduction of cytochrome P450 (P450)-mediated metabolism, resulting in reduced exposure, has been supposed to be the underlying mechanism. To better understand the autoinduction and metabolic drug-drug interactions (DDIs), we evaluated the P450s (particularly CYP2B6 and CYP3A4) inhibited or induced by two artemisinin drugs, Qing-hao-su (QHS) and dihydroartemisinin (DHA) using human liver microsome, recombinant P450 enzymes, and primary human hepatocytes. The results suggested that QHS was a weak reversible inhibitor of CYP2B6 (K i 4.6 M), but not CYP3A4 (IC 50 ϳ 50 M) and did not show measurable time-dependent inhibition of either CYP2B6 or CYP3A4. DHA inhibited neither CYP2B6 nor CYP3A4 (IC 50 > 125 M). In addition, it was found that QHS induced the activity of CYP3A4 (E max 3.5-fold and EC 50 5.9 M) and CYP2B6 (E max 1.9-fold and EC 50 0.6 M). Of the other P450s, UDP glucuronosyltransferases, and transporters studied, QHS and DHA had no significant effect except for minor induction of mRNA expression of CYP1A2 (E max 7.9-fold and EC 50 5.2 M) and CYP2A6 (E max 11.7-fold and EC 50 4.0 M) by QHS. Quantitative prediction of P450-mediated DDIs indicate autoinduction of QHS clearance with the AUC i /AUC ratio decreasing to 59%, as a result of a 1.9-fold increase in CYP3A4 and a 1.6-fold increase in CYP2B6 activity. These data suggest that QHS drugs are potential inducers of P450 enzymes, and the possible drug interactions (or lack thereof) with artemisinin drugs may be clinically relevant.

Effect of CAR polymorphism on the pharmacokinetics of artemisinin in healthy Chinese subjects

“…4,5) CYP2B6 is most sensitive to regulation by CAR, and QHS was an agonist of CAR1/3. 8,9) No polymorphic influence of CYP2B6*6 was detected for QHS derivatives (dihydroartemisinin, artemether and artesunate) in Cambodia and Tanzania patients.…”

“…[1][2][3] The auto-induction metabolism has been suggested for this time-dependency. 4,5) The elimination of QHS is mediated primarily by CYP2B6, with a probably secondary contribution of CYP3A and CYP2A6. 6,7) QHS appears to induce several enzymes including CYP2B6.…”

“…6,7) QHS appears to induce several enzymes including CYP2B6. 3,5) CYP2B6 is most sensitive to the inductive effect of constitutive androstane receptor (CAR), which can be activated by QHS. 8,9) The human genes coding for CYP2B6 and CAR are highly polymorphic, 10,11) which could probably lead to interindividual variability in QHS pharmacokinetics, auto-induction metabolism and response to treatment.…”

“…15) CYP3A played a minor role in the auto-induction metabolism of QHS. 5) The between-subject variability in CYP3A4 activity may be the result of transcriptional regulation. Considering that mutations of CYP3A4*1B, *2, *4, *5 and *6 are rare in Chinese populations, the polymorphism of these SNPs may not influence QHS clearance in this study.…”

Carboxymefloquine, the Major Metabolite of the Antimalarial Drug Mefloquine, Induces Drug-Metabolizing Enzyme and Transporter Expression by Activation of Pregnane X Receptor

“…With respect to clinically relevant induction, it is known only that artemisinin-type antimalarial drugs, especially artemisinin itself, autoinduce their elimination (5) by increasing cytochrome P450-dependent metabolism (6), thereby suggesting a significant drugdrug interaction potential of the compounds. Drug-drug interactions by artemisinin-induced CYP2B6 and CYP3A4 expression and activities have been further predicted by quantitative modeling (7).…”