Metabolism of Piperaquine to Its Antiplasmodial Metabolites and Their Pharmacokinetic Profiles in Healthy Volunteers

The effect of malaria-induced alteration of metabolism on piperaquine disposition in Plasmodium yoelii infected mice and predicted in malaria patients

OBJECTIVES

Malaria-induced alteration of physiological parameters and pharmacokinetic properties of antimalarial drugs may be clinically relevant. Whether and how malaria alters the disposition of piperaquine (PQ) was investigated in this study.

METHODS

The effect of malaria on drug metabolism-related enzymes and PQ pharmacokinetic profiles was studied in Plasmodium yoelii-infected mice in vitro/in vivo. Whether the malaria effect was clinically relevant for PQ was evaluated using a validated physiologically-based pharmacokinetic model with malaria-specific scalars obtained in mice.

RESULTS

The infection led to a higher blood-to-plasma partitioning (Rbp) for PQ, which was concentration-dependent and correlated to parasitemia. No significant change in plasma protein binding was found for PQ. Drug metabolism-related genes (CYPs/UDP-glucuronosyltransferase/nuclear receptor, except for CYP2a5) were downregulated in infected mice, especially at the acute phase. The plasma oral clearances (CL/F) of three probe substrates for CYP enzymes were significantly decreased (by ≥35.9%) in mice even with moderate infection. The validated physiologically-based pharmacokinetic model indicated that the hepatic clearance (CLH) of PQ was the determinant of its simulated CL/F, which was predicted to slightly decrease (by ≤23.6%) in severely infected mice but not in malaria patients. The result fitted well with the plasma pharmacokinetics of PQ in infected mice and literature data on malaria patients. The blood clearance of PQ was much lower than its plasma clearance due to its high Rbp.

CONCLUSIONS

The malaria-induced alteration of drug metabolism was substrate-dependent, and its impact on the disposition of PQ and maybe other long-acting aminoquinoline antimalarials was not expected to be clinically relevant.

Extended blood stage sensitivity profiles of Plasmodium cynomolgi to doxycycline and tafenoquine, as a model for Plasmodium vivax

Testing Plasmodium vivax antimicrobial sensitivity is limited to ex vivo schizont maturation assays, which preclude determining the IC50s of delayed action antimalarials such as doxycycline. Using Plasmodium cynomolgi as a model for P. vivax, we determined the physiologically significant delayed death effect induced by doxycycline [IC50(96 h), 1,401 ± 607 nM]. As expected, IC50(96 h) to chloroquine (20.4 nM), piperaquine (12.6 µM), and tafenoquine (1,424 nM) were not affected by extended exposure.

The antiplasmodial activity of the carboxylic acid metabolite of piperaquine and its pharmacokinetic profiles in healthy volunteers

BACKGROUND

The long-acting antimalarial drug piperaquine can be metabolized into the carboxylic acid metabolite (PQM). However, the clinical relevance of PQM remains unclear.

OBJECTIVES

The pharmacodynamics/pharmacokinetics of PQM were studied.

METHODS

The antimalarial activity of PQM was studied in vitro (Plasmodium strains Pf3D7 and PfDd2) and in vivo (murine Plasmodium yoelii). The toxicity of PQM was evaluated in mice, in terms of the general measures of animal well-being, serum biochemical examination and ECG monitoring. The pharmacokinetic profiles of piperaquine and its metabolite PQM were investigated in healthy subjects after recommended oral doses of piperaquine.

RESULTS

PQM showed no relevant in vitro antimalarial activity (IC50 > 1.0 μM) with no significant toxicity. After recommended oral administration of piperaquine to healthy subjects, the maximum concentration of PQM was less than 30.0 nM, and it did not accumulate after repeated dosing.

CONCLUSIONS

With a low antimalarial potency, PQM should not contribute to the efficacy of piperaquine with clinically acceptable doses.

-Pharmacokinetics of antimalarial drugs used to treat uncomplicated malaria in breastfeeding mother-infant pairs: An observational pharmacokinetic study

Background: Data surrounding the exposure of the breastfed infant to drugs and any associated risks are sparse. Drugs usually are transferred to milk in small quantities, and many have been used without obviously noticeable infant toxicity for many years - this lack of a 'safety signal' has further reduced the interest in studying mother-to-infant transfer of the drugs. In sub-Saharan Africa, pregnant women are at risk of  Plasmodium falciparum infection, and one in four women have evidence of placental infection at the time of delivery. Artemisinin-based combination therapies (ACTs), primarily artemether-lumefantrine (AL), are the current first-line treatment for uncomplicated Plasmodium falciparum malaria, with the same dosing recommendations in breastfeeding women as those in the adult population. Dihydroartemisinin-piperaquine (DP) is routinely used as an alternative to AL in Uganda. However, lactation pharmacokinetics (PK) of ACTs are unknown. Pharmacokinetic characterization of anti-malarial transfer to breast milk and breastfed infants is crucial in understanding the potential consequences to the infant, in terms of therapeutic- and prophylactic effects as well as potential toxicity.   Methods: This observational study will enroll 30 mother-infant pairs, and aims to characterize the breastmilk transfer of antimalarial medications (AL and DP) to infants when these ACTs are administered to mothers as part of treatment for uncomplicated malaria. In addition, we will assess the mental health of the breastfeeding mothers enrolled as well as the well-being of their children. PK samples of maternal blood, breastmilk and breastfeeding infant's blood will be obtained at specific times points. Pharmacokinetic data will be analyzed using a population pharmacokinetic approach. Conclusions: We anticipate that findings from this research will guide to develop a PK model describing lumefantrine and piperaquine disposition and will provide a framework to foster other lactation pharmacokinetic studies in different disease areas.

Semimechanistic Pharmacokinetic and Pharmacodynamic Modeling of Piperaquine in a Volunteer Infection Study with Plasmodium falciparum Blood-Stage Malaria

Dihydroartemisinin-piperaquine is a recommended first-line artemisinin combination therapy for Plasmodium falciparum malaria. Piperaquine is also under consideration for other antimalarial combination therapies. The aim of this study was to develop a pharmacokinetic-pharmacodynamic model that might be useful when optimizing the use of piperaquine in new antimalarial combination therapies. The pharmacokinetic-pharmacodynamic model was developed using data from a previously reported dose-ranging study where 24 healthy volunteers were inoculated with 1,800 blood-stage Plasmodium falciparum parasites. All volunteers received a single oral dose of piperaquine (960 mg, 640 mg, or 480 mg) on day 7 or day 8 after parasite inoculation in separate cohorts. Parasite densities were measured by quantitative PCR (qPCR), and piperaquine levels were measured in plasma samples. We used nonlinear mixed-effect modeling to characterize the pharmacokinetic properties of piperaquine and the parasite dynamics associated with piperaquine exposure. The pharmacokinetics of piperaquine was described by a three-compartment disposition model. A semimechanistic parasite dynamics model was developed to explain the maturation of parasites, sequestration of mature parasites, synchronicity of infections, and multiplication of parasites, as seen in natural clinical infections with P. falciparum malaria. Piperaquine-associated parasite killing was estimated using a maximum effect (E _max) function. Treatment simulations (i.e., 3-day oral dosing of dihydroartemisinin-piperaquine) indicated that to be able to combat multidrug-resistant infections, an ideal additional drug in a new antimalarial triple-combination therapy should have a parasite reduction ratio of ≥10² per life cycle (38.8 h) with a duration of action of ≥2 weeks. The semimechanistic pharmacokinetic-pharmacodynamic model described here offers the potential to be a valuable tool for assessing and optimizing current and new antimalarial drug combination therapies containing piperaquine and the impact of these therapies on killing multidrug-resistant infections. (This study has been registered in the Australian and New Zealand Clinical Trials Registry under no. ANZCTRN12613000565741.).

Metabolic Retroversion of Piperaquine (PQ) via Hepatic Cytochrome P450-Mediated N-Oxidation and Reduction: Not an Important Contributor to the Prolonged Elimination of PQ

As a partner antimalarial with an extremely long elimination half-life (∼30 days), piperaquine (PQ) is mainly metabolized into a pharmacologically active N-oxide metabolite [piperaquine N-oxide (PN1)] in humans. In the present work, the metabolic retroversion of PQ and PN1, potentially associated with decreased clearance of PQ, was studied. The results showed that interconversion existed for PQ and its metabolite PN1. The N-oxidation of PQ to PN1 was mainly mediated by CYP3A4, and PN1 can rapidly reduce back to PQ via cytochrome P450 (P450)/flavin-containing monooxygenase enzymes. In accordance with these findings, the P450 nonselective inhibitor (1-ABT) or CYP3A4 inhibitor (ketoconazole) inhibited the N-oxidation pathway in liver microsomes (>90%), and the reduction metabolism was inhibited by 1-ABT (>90%) or methimazole (∼50%). Based on in vitro physiologic and enzyme kinetic studies, quantitative prediction of hepatic clearance (CL_H) of PQ was performed, which indicated its negligible decreased elimination in humans in the presence of futile cycling, with the unbound CL_H decreasing by 2.5% (0.069 l/h per kilogram); however, a minor decrease in unbound CL_H (by 12.8%) was found in mice (0.024 l/h per kilogram). After an oral dose of PQ (or PN1) to mice, the parent form predominated in the blood circulation, and PN1 (or PQ) was detected as a major metabolite. Other factors probably associated with delayed elimination of PQ (intestinal metabolism and enterohepatic circulation) did not play a key role in PQ elimination. These data suggested that the metabolic interconversion of PQ and its N-oxide metabolite contributes to but may not significantly prolong its duration in humans. SIGNIFICANCE STATEMENT: This paper investigated the interconversion metabolism of piperaquine (PQ) and its N-oxide metabolite in vitro as well as in mice. The metabolic profiles of PQ were reestablished by this futile cycling, which contributes to but may not significantly prolong its elimination in humans. Enzyme phenotyping indicated a low possibility of interaction of PQ during artemisinin drug-based combination therapy treatment.

In Vivo Efficacy and Metabolism of the Antimalarial Cycleanine and Improved In Vitro Antiplasmodial Activity of Semisynthetic Analogues

Bisbenzylisoquinoline (BBIQ) alkaloids are a diverse group of natural products that demonstrate a range of biological activities. In this study, the in vitro antiplasmodial activity of three BBIQ alkaloids (cycleanine [compound 1], isochondodendrine [compound 2], and 2′-norcocsuline [compound 3]) isolated from the Triclisia subcordata Oliv. medicinal plant traditionally used for the treatment of malaria in Nigeria are studied alongside two semisynthetic analogues (compounds 4 and 5) of cycleanine.

Bisbenzylisoquinoline (BBIQ) alkaloids are a diverse group of natural products that demonstrate a range of biological activities. In this study, the in vitro antiplasmodial activity of three BBIQ alkaloids (cycleanine [compound 1], isochondodendrine [compound 2], and 2′-norcocsuline [compound 3]) isolated from the Triclisia subcordata Oliv. medicinal plant traditionally used for the treatment of malaria in Nigeria are studied alongside two semisynthetic analogues (compounds 4 and 5) of cycleanine. The antiproliferative effects against a chloroquine-resistant Plasmodium falciparum strain were determined using a SYBR green 1 fluorescence assay. The in vivo antimalarial activity of cycleanine is then investigated in suppressive, prophylactic, and curative murine malaria models after infection with a chloroquine-sensitive Plasmodium berghei strain. BBIQ alkaloids (compounds 1 to 5) exerted in vitro antiplasmodial activities with 50% inhibitory concentration (IC₅₀) at low micromolar concentrations and the two semisynthetic cycleanine analogues showed an improved potency and selectivity compared to those of cycleanine. At oral doses of 25 and 50 mg/kg body weight of infected mice, cycleanine suppressed the levels of parasitemia and increased mean survival times significantly compared to those of the control groups. The metabolites and metabolic pathways of cycleanine were also studied using high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry. Twelve novel metabolites were detected in rats after intragastric administration of cycleanine. The metabolic pathways of cycleanine were demonstrated to involve hydroxylation, dehydrogenation, and demethylation. Overall, these in vitro and in vivo results provide a basis for the future evaluation of cycleanine and its analogues as leads for further development.