Amodiaquine, its desethylated metabolite, or both, inhibit the metabolism of debrisoquine (CYP2D6) and losartan (CYP2C9) in vivo

An update on pharmacogenetic factors influencing the metabolism and toxicity of artemisinin-based combination therapy in the treatment of malaria

INTRODUCTION

Artemisinin-based combination therapies (ACTs) are recommended first-line antimalarials for uncomplicated Plasmodium falciparum malaria. Pharmacokinetic/pharmacodynamic variation associated with ACT drugs and their effect is documented. It is accepted to an extent that inter-individual variation is genetically driven, and should be explored for optimized antimalarial use.

AREAS COVERED

We provide an update on the pharmacogenetics of ACT antimalarial disposition. Beyond presently used antimalarials, we also refer to information available for the most notable next-generation drugs under development. The bibliographic approach was based on multiple Boolean searches on PubMed covering all recent publications since our previous review.

EXPERT OPINION

The last 10 years have witnessed an increase in our knowledge of ACT pharmacogenetics, including the first clear examples of its contribution as an exacerbating factor for drug-drug interactions. This knowledge gap is still large and is likely to widen as a new wave of antimalarial drug is looming, with few studies addressing their pharmacogenetics. Clinically useful pharmacogenetic markers are still not available, in particular, from an individual precision medicine perspective. A better understanding of the genetic makeup of target populations can be valuable for aiding decisions on mass drug administration implementation concerning region-specific antimalarial drug and dosage options.

Effect of CYP2C9 genetic polymorphism and breviscapine on losartan pharmacokinetics in healthy subjects

1. Breviscapine was an active ingredient of flavonoid glycosides. Our present study was conducted to evaluate the impact of breviscapine on the pharmacokinetics of losartan and its active metabolite E-3174, and that relationship with the gene polymorphism of CYP2C9 in healthy Chinese volunteers, to provide a basis for clinical rational drug use.2. The genotypes of 217 healthy Chinese subjects were determined using PCR-RFLP. Twelve healthy subjects were selected and were known CYP2C9 genotypes (six CYP2C9*1/*3 and six CYP2C9*1/*1) in a two-phase randomised crossover design study. These subjects were given daily doses of 120 mg (40 mg, three times a day) of breviscapine or a placebo for 14 days, followed by 50 mg losartan on day 15.3. Compared with individuals carrying the CYP2C9*1/*1 genotype, the CYP2C9*1/*3 genotype showed an increase in the AUC_(0-36) (833.6 ± 379.8 ng h ml^-1 vs. 526.1 ± 140.1 ng h ml^-1, p < 0.05) and a decrease in the MR (the metabolic ratio of losartan, AUC_E-3174/AUC_losartan) (2.67 ± 1.40 vs. 4.56 ± 0.83, p < 0.05) of losartan during the placebo treatment phase. Individuals with genotype CYP2C9*1/*3 showed a significant increase in AUC_(0-36) (2335 ± 851.8 ng h ml^-1 vs. 1927 ± 949.5 ng h ml^-1, p < 0.05) and AUC_(0-∞) (2363 ± 875.6 ng h ml^-1 vs. 1966 ± 966.1 ng h ml^-1, p < 0.05) of E-3174 after breviscapine treatment compared to the placebo group.4. In healthy subjects, breviscapine had no significant effect on the pharmacokinetics of losartan. The activity of CYP2C9 enzyme to losartan metabolism was more significant in subjects with CYP2C9*1/*3 than those with CYP2C9*1/*1 genotype.

Assessment of NR4A Ligands That Directly Bind and Modulate the Orphan Nuclear Receptor Nurr1

Nurr1/NR4A2 is an orphan nuclear receptor transcription factor implicated as a drug target for neurological disorders including Alzheimer's and Parkinson's diseases. Previous studies identified small-molecule NR4A nuclear receptor modulators, but it remains unclear if these ligands affect transcription via direct binding to Nurr1. We assessed 12 ligands reported to affect NR4A activity for Nurr1-dependent and Nurr1-independent transcriptional effects and the ability to bind the Nurr1 ligand-binding domain (LBD). Protein NMR structural footprinting data show that amodiaquine, chloroquine, and cytosporone B bind the Nurr1 LBD; ligands that do not bind include C-DIM12, celastrol, camptothecin, IP7e, isoalantolactone, ethyl 2-[2,3,4-trimethoxy-6-(1-octanoyl)phenyl]acetate (TMPA), and three high-throughput screening hit derivatives. Importantly, ligands that modulate Nurr1 transcription also show Nurr1-independent effects on transcription in a cell type-specific manner, indicating that care should be taken when interpreting the functional response of these ligands in transcriptional assays. These findings should help focus medicinal chemistry efforts that desire to optimize Nurr1-binding ligands.

Prediction of inter-individual variability on the pharmacokinetics of CYP2C8 substrates in human

Inter-individual variability in pharmacokinetics can lead to unexpected side effects and treatment failure, and is therefore an important factor in drug development. CYP2C8 is a major drug-metabolizing enzyme known to be involved in the metabolism of over 100 drugs. In this study, we predicted the inter-individual variability in AUC/Dose of CYP2C8 substrates in healthy volunteers using the Monte Carlo simulation. Inter-individual variability in the hepatic intrinsic clearance of CYP2C8 substrates (CL_int,h,2C8) was estimated from the inter-individual variability in pharmacokinetics of pioglitazone, which is a major CYP2C8 substrate. The coefficient of variation (CV) of CL_int,h,2C8 was estimated to be 40%. Using this value, the CVs of AUC/Dose of other major CYP2C8 substrates, rosiglitazone and amodiaquine, were predicted to validate the estimated CV of CL_int,h,2C8. As a result, the reported CVs of both substrates were within the 2.5-97.5 percentile range of the predicted CVs. Furthermore, the CVs of AUC/Dose of the CYP2C8 substrates loperamide and chloroquine, which are affected by renal clearance, were also successfully predicted. Combining this value with previously reported CVs of other CYPs, we were able to successfully predict the inter-individual variability in pharmacokinetics of various drugs in clinical.

Multiplex Phenotyping for Systems Medicine: A One-Point Optimized Practical Sampling Strategy for Simultaneous Estimation of CYP1A2, CYP2C9, CYP2C19, and CYP2D6 Activities Using a Cocktail Approach

Phenotyping of the CYP450 enzyme activities contributes to personalized medicine, but the past phenotyping approaches have followed a piecemeal strategy measuring single enzyme activities in vivo. A barrier to phenotyping of populations in rural and remote areas is the limited time and resources for sample collection. The CEIBA cocktail approach allows metabolic capacity estimation of multiple CYP450 enzymes in a single sample analysis, but the attendant sample collection schemes for applications in diverse global settings are yet to be optimized. The present study aimed to select an optimal matrix to simultaneously analyze CYP450 enzyme activities so as to simplify the sampling schemes in the phenotyping protocol to enhance its throughput and feasibility in native populations or in remote and underserviced geographies and social contexts. We evaluated 13 Ecuadorian healthy volunteers for CYP1A2, CYP2C9, CYP2C19, and CYP2D6 genotypes and their metabolic phenotypes, including CYP3A4, in plasma and urine after administering one reduced dose of caffeine, losartan, omeprazole, and dextromethorphan. Pharmacokinetic analyses were performed, and the correlation between AUC parent/AUC metabolite and the ratio between concentrations of probe drugs and their corresponding metabolites at timepoints ranging from 0 to 12 hours post-dose were analyzed. A single sampling timepoint, 4 hours post-dose in plasma, was identified as optimal to reflect the metabolic activity of the attendant CYP450 enzymes. This study optimizes the CEIBA multiplexed phenotyping approach and offers new ways forward for integrated drug metabolism analyses, in the pursuit of global personalized medicine applications in resource-limited regions, be they in developed or developing countries.

Tetrazole-based deoxyamodiaquines: synthesis, ADME/PK profiling and pharmacological evaluation as potential antimalarial agents

A series of new deoxyamodiaquine-based compounds was synthesized via the modified TMSN3-Ugi multi-component reaction and evaluated in vitro for antiplasmodial activity. The most potent compounds, 6b, 6c and 6j, showed IC50 values in the range of 6-77nM against chloroquine-resistant K1- and W2-strains of Plasmodium falciparum. In vitro ADME characterization of frontrunner compounds 6b and 6c indicates that these two compounds are rapidly metabolized and have a high clearance rate in human and rat liver microsomes. This result correlated well with an in vivo pharmacokinetics study, which showed low bioavailability of 6c in rats. Tentative metabolite identification was determined by LC-MS and suggested metabolic lability of groups attached to the tertiary nitrogen. Preliminary studies on 6b and 6c suggested strong inhibitory activity against the major CYP450 enzymes. In silico docking studies were used to rationalize strong inhibition of CYP3A4 by 6c. Full characterization and biological evaluation of the metabolites is currently underway in our laboratories.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Effect of soy extract administration on losartan pharmacokinetics in healthy female volunteers

BACKGROUND

osartan is metabolized by CYP2C9 and CYP3A4 to an active metabolite, E-3174, which has greater antihypertensive activity than the parent compound. Soy extract has been shown to be an activator of CYP2C9 and CYP3A4 in vitro. Coadministration of soy extract and losartan may therefore alter the pharmacokinetics of losartan and E-3174.

OBJECTIVE

To determine whether, when losartan was used in combination with soy extract, a significant pharmacokinetic interaction would be observed in healthy female volunteers.

METHODS

Eighteen healthy Chinese female volunteers were recruited. In an open-label, 2-phase study, losartan 50 mg was given to each subject, with and without soy extract. Plasma concentrations of losartan and E-3174 were determined by liquid chromatography-tandem mass spectrometry for 12 and 24 hours, respectively. On day 8 through day 21 of the study, following a 7-day washout period, each subject consumed two 1000-mg Genistein Soy Complex tablets orally after meals, twice daily, for 14 days. On day 22, all volunteers received losartan 50 mg and blood samples were collected again.

RESULTS

All subjects completed the study, without adverse drug effects. Over the 14-day pretreatment period, soy extract did not significantly influence the pharmacokinetics of losartan or E-3174. The ratio of the area under the curve of the drug and metabolite after losartan administration, with and without soy extract ingestion, was 0.21 +/- 0.05 and 0.23 +/- 0.05 (mean +/- SD), respectively. The difference was not statistically significant (p = 0.22).

CONCLUSIONS

Our data indicate that a significant interaction between soy extract and losartan is unlikely to occur in females.

Clinical pharmacology of artemisinin-based combination therapies

Malaria, a disease transmitted by the female Anopheles mosquito, has had devastating effects on human populations for more than 4000 years. Treatment of the disease with single drugs, such as chloroquine, sulfadoxine/pyrimethamine or mefloquine, has led to the emergence of resistant Plasmodium falciparum parasites that lead to the most severe form of the illness. Artemisinin-based combination therapies are currently recommended by WHO for the treatment of uncomplicated P. falciparum malaria. Artemisinin and semisynthetic derivatives, including artesunate, artemether and dihydroartemisinin, are short-acting antimalarial agents that kill parasites more rapidly than conventional antimalarials, and are active against both the sexual and asexual stages of the parasite cycle. Artemisinin fever clearance time is shortened to 32 hours as compared with 2-3 days with older agents. To delay or prevent emergence of resistance, artemisinins are combined with one of several longer-acting drugs--amodiaquine, mefloquine, sulfadoxine/pyrimethamine or lumefantrine--which permit elimination of the residual malarial parasites. The clinical pharmacology of artemisinin-based combination therapies is highly complex. The short-acting artemisinins and their long-acting counterparts are metabolized and/or inhibit/induce cytochrome P450 enzymes, and may thus participate in drug-drug interactions with multiple drugs on the market. Alterations in antimalarial drug plasma concentrations may lead to either suboptimal efficacy or drug toxicity and may compromise treatment.

A field-adapted HPLC method for determination of amodiaquine and its metabolite in whole blood dried on filter paper

A reversed-phase high performance liquid chromatographic method was developed and validated for the quantitative determination of amodiaquine (AQ) and its metabolite desethylamodiaquine (DAQ) in whole blood collected on filter paper. The structure analogue 4-(4-dimethylamino-1-methylbutylamino)-7-chloroquinoline was used as internal standard. Upon collection, blood was added to 10% phosphoric acid in a 1:1 ratio and then spotted onto filter paper. The samples were alkalinized (pH approximately 9.2) with potassium hydroxide at the time of assay and the compounds were extracted together with internal standard into di-isopropyl ether and then re-extracted into an aqueous phase with 0.1M phosphate buffer at pH 4. The chromatographic analysis was performed using an Agilent Technologies ChemStation LC System. The absorbance of the compounds was monitored at 333 nm. Mean extraction recoveries of AQ and DAQ were 49 and 48%, respectively. Intra-day and inter-day coefficients of variation were <10.5%. The limit of quantification was 50 nM for both compounds (sample size 100 microl). Both AQ and DAQ that were previously reported to be unstable have been stored on filter paper for at least 19 weeks. The method was applied on samples from healthy volunteers.

Population pharmacokinetics of amodiaquine and desethylamodiaquine in pediatric patients with uncomplicated falciparum malaria

The study aimed to characterize the population pharmacokinetics of amodiaquine (AQ) and its major metabolite N-desethylamodiaquine (N-DEAQ), and to assess the correlation between exposure to N-DEAQ and treatment outcome. Blood samples from children in two studies in Zanzibar and one in Papua New Guinea were included in the pharmacokinetic analysis (n = 86). The children had been treated with AQ in combination with artesunate or sulphadoxine-pyrimethamine. The population pharmacokinetics of AQ and N-DEAQ were modeled using the non-linear mixed effects approach as implemented in NONMEM. Bayesian post-hoc estimates of individual pharmacokinetic parameters were used to generate individual profiles of N-DEAQ exposure. The correlation between N-DEAQ exposure and effect was studied in 212 patients and modeled with logistic regression in NONMEM. The pharmacokinetics of AQ and N-DEAQ were best described by two parallel two-compartment models with a central and a peripheral compartment for each compound. The systemic exposure to AQ was low in comparison to N-DEAQ. The t(1/2 lambda) of N-DEAQ ranged from 3 days to 12 days. There was a statistically significant, yet weak, association between N-DEAQ concentration on day 7 and treatment outcome. The age-based dosing schedule currently recommended in Zanzibar appeared to result in inadequate exposure to N-DEAQ in many patients.