Differential effects of clinically used derivatives and metabolites of artemisinin in the activation of constitutive androstane receptor isoforms

Abstract

BACKGROUND AND PURPOSEWidespread resistance to antimalarial drugs requires combination therapies with increasing risk of pharmacokinetic drug-drug interactions. Here, we explore the capacity of antimalarial drugs to induce drug metabolism via activation of constitutive androstane receptors (CAR) by ligand binding. EXPERIMENTAL APPROACHA total of 21 selected antimalarials and 11 major metabolites were screened for binding to CAR isoforms using cellular and in vitro CAR-coactivator interaction assays, combined with in silico molecular docking. Identified ligands were further characterized by cell-based assays and primary human hepatocytes were used to elucidate induction of gene expression. KEY RESULTSOnly two artemisinin derivatives arteether and artemether, the metabolite deoxyartemisinin and artemisinin itself demonstrated agonist binding to the major isoforms CAR1 and CAR3, while arteether and artemether were also inverse agonists of CAR2. Dihydroartemisinin and artesunate acted as weak inverse agonists of CAR1. While arteether showed the highest activities in vitro, it was less active than artemisinin in inducing hepatic CYP3A4 gene expression in hepatocytes. CONCLUSIONS AND IMPLICATIONSArtemisinin derivatives and metabolites differentially affect the activities of CAR isoforms and of the pregnane X receptor (PXR). This negates a common effect of these drugs on CAR/PXR-dependent induction of drug metabolism and further provides an explanation for artemisinin consistently inducing cytochrome P450 genes in vivo, whereas arteether and artemether do not. All these drugs are metabolized very rapidly, but only artemisinin is converted to an enzyme-inducing metabolite. For better understanding of pharmacokinetic drug-drug interaction possibilities, the inducing properties of artemisinin metabolites should be considered.

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

“…Even if pharmacokinetic data from a few clinical studies seem to support this hypothesis, final proof of carboxymefloquine-mediated induction of ADME genes by mefloquine in vivo still requires a controlled clinical study. The increasing necessity of the coadministration of antimalarial drugs with antiretroviral and/or antituberculosis medications in treating malaria patients coinfected with HIV and/or tuberculosis strongly indicates the need to evaluate the pharmacokinetic interaction potentials of antimalarials, including their major metabolites; this is the case even if this and our previous study (13) indicate that the induction of drug metabolism and transport by activating the human xenosensors PXR and CAR is not a concern for most nonartemisinin antimalarials.…”

“…Rifampin and dimethyl sulfoxide (DMSO) were purchased from Sigma-Aldrich (Taufkirchen, Germany). The supply sources of the antimalarial drugs and drug metabolites have been noted previously (13).…”

“…Other artemisinin-type drugs, such as artesunate and dihydroartemisinin, showed weak human CAR inverse agonism, with differential effects on CAR isoforms (13). When screening 21 antimalarial drugs and 11 major drug metabolites, we did not identify any drug outside the artemisinin class as binding to and thereby activating CAR (13). However, the potential of nonartemisinin antimalarials in activating PXR has not yet been analyzed.…”

“…Upon activation, both receptors induce the expression of a battery of genes involved in absorption, distribution, metabolism, and excretion (ADME), comprising phase I cytochrome P450 and phase II conjugating drug-metabolizing enzymes, as well as phase 0/III drug transporters in the intestines and liver (9,10). In previous studies, we and others showed that the artemisinin-type antimalarial drugs artemisinin, artemether, and arteether, as well as the pharmacologically inactive artemisinin metabolite deoxyartemisinin, are ligands of human PXR and human and mouse CAR, and by that, induce ADME gene expression (11)(12)(13). Other artemisinin-type drugs, such as artesunate and dihydroartemisinin, showed weak human CAR inverse agonism, with differential effects on CAR isoforms (13).…”

“…In previous studies, we and others showed that the artemisinin-type antimalarial drugs artemisinin, artemether, and arteether, as well as the pharmacologically inactive artemisinin metabolite deoxyartemisinin, are ligands of human PXR and human and mouse CAR, and by that, induce ADME gene expression (11)(12)(13). Other artemisinin-type drugs, such as artesunate and dihydroartemisinin, showed weak human CAR inverse agonism, with differential effects on CAR isoforms (13). When screening 21 antimalarial drugs and 11 major drug metabolites, we did not identify any drug outside the artemisinin class as binding to and thereby activating CAR (13).…”