CYP3A4-mediated metabolism of artemisinin to 10β-hydroxyartemisinin with comparable anti-malarial potency

The most widely used anti-malarial drug artemisinin (ART) is metabolized extensively, but the therapeutic capacity of its major metabolite remains unknown. Whether the major metabolite of ART (ART-M) contributes to its antiplasmodial potency was investigated in this study.

The metabolite identification and enzyme phenotyping of ART were performed using human liver microsomes (HLMs). The stereostructure of the major metabolite ART-M was elucidated by spectroscopic and X-ray crystallographic analysis. The anti-malarial activity of ART-M against two reference Plasmodium strains (Pf3D7 and PfDd2) was evaluated. The pharmacokinetic profiles of ART and its metabolite ART-M were investigated in healthy Chinese subjects after a recommended two-day oral dose of ART plus piperaquine. Pharmacodynamic parameters based on minimum inhibitory concentration (MIC₅₀) and free plasma concentration were employed to evaluate the therapeutic potency of ART-M, including fAUC_0-t/MIC₅₀, fC_max/MIC₅₀ and T > MIC₅₀.

A major metabolite 10β-hydroxyartemisinin (ART-M) was found for ART in human, and CYP3A4/3A5 was the major enzymes responsible for ART 10β-hydroxylation. Compared with ART (MIC₅₀, 10.1 nM against Pf3D7), weaker antiplasmodial activity was found for ART-M (MIC₅₀, 61.4 nM against Pf3D7). However, a 3.5-fold higher maximal free plasma concentration was achieved for ART-M (fC_max, 180.0 nM vs. 51.8 nM for ART). ART-M displayed comparable antiplasmodial potency to ART, in terms of fAUC_0-t/MIC₅₀ (12.5 h), fC_max/MIC₅₀ (2.8) and T > MIC₅₀ (5 h).

The major metabolite 10β-hydroxyartemisinin contributes to the antiplasmodial efficacy of ART, which should be considered when evaluation of ART dosing regimens and/or clinical outcomes.