Role of P Glycoprotein in Absorption of Novel Antimalarial Drugs

Abstract

Bidirectional transport of four novel antimalarial compounds was determined using Caco-2 cell monolayers. P glycoprotein-mediated efflux was greatest for pyronaridine (5 to 20 M) and low for naphthoquine (5 M). With 20 M naphthoquine, net efflux was blocked, suggesting saturation of the transporter. Piperaquine and dihydroartemisinin were not transported by the system. Permeability glycoprotein (P-gp) ATP-dependent transporters influence the passage of many drugs across epithelial barriers in the intestine, brain, liver, and kidney (1) and may alter their pharmacokinetic and/or pharmacodynamic properties. Several antimalarial drugs are substrates and/or inhibitors of P-gp (9, 10, 15). In the intestine, P-gp has a secretory function which can contribute to low bioavailability and substrate-inhibitor interactions (14). The antimalarials dihydroartemisinin, naphthoquine, piperaquine, and pyronaridine are highly lipid soluble, with logP (log octanol-water partition coefficient) values of 2.6, 6.16, 6.16, and 4.98, respectively (ACD I Lab Software version 8.14 for Solaris; ACD Labs, Toronto, Canada). Evidence suggests that dihydroartemisinin and piperaquine have oral bioavailabilities of Ͻ50% (6, 7), while pyronaridine may interfere with P-gp-mediated transport (10, 11). We therefore investigated whether these four drugs are P-gp substrates and whether P-gp-mediated efflux explains the apparently low bioavailabilities of dihydroartemisinin and piperaquine.Drug transport was studied with an in vitro gastrointestinal model by using a monolayer of a CLEFF9 subclone of human Caco-2 cells with high P-gp-mediated efflux (4) and previously reported experimental protocols (3-5). Briefly, cells were seeded onto 0.6-cm 2 polycarbonate filters in 24-well plates and grown in high-glucose Dulbecco's modified Eagle's medium for 3 weeks. Following incubation in buffered Hanks balanced salt solution (HBSS) with or without specific efflux inhibitors for 30 min at 37°C, transepithelial electrical resistance was measured and assay medium/inhibitors were placed in the receiver chambers. Antimalarial drugs were added to the donor chamber of each well. The apical and basolateral chambers received 0.3 and 0.6 ml medium, respectively. Transepithelial electrical resistance measurements were repeated at the conclusion of the studies to ensure continued monolayer integrity.Naphthoquine was assayed using high-performance liquid chromatography (HPLC) with UV detection at 260 nm after separation through an Eclipse XDB-C 8 column (Agilent Technologies, Forest Hill, Australia) with a mobile phase of 22% acetonitrile, 10% methanol, and 68% 20 mM KH 2 PO 4 , with 11 mM triethylamine and 0.1% trifluoroacetic acid pumped at 1.2 ml/min. The limit of detection (LOD) was 30 nM. Pyronaridine was assayed by HPLC with detection at 277 nm after separation through a 100-by 4.6-mm (inside diameter), 3.5-m XTerra C 18 column (Waters Associates, Milford, MA), with acetonitrile buffer (80 mM KH 2 PO 4 , 22 mM triethylamine HCl, and 0.1% trifluoroacetic acid, pH 2....

Pharmacokinetics and Metabolism of the Antimalarial Piperaquine After Intravenous and Oral Single Doses to the Rat

“…This is also seen in clinical use with substantial inter‐individual variability in the pharmacokinetics of piperaquine after oral administration 7, 8. Previously published in vitro findings suggest piperaquine not to be a substrate for P‐glycoprotein and no major efflux by this transporter is therefore to be expected during absorption 15…”

Artemisinin-Naphthoquine Combination Therapy for Uncomplicated Pediatric Malaria: a Pharmacokinetic Study

“…Group 1 patients had additional venous blood samples drawn through the cannula at 1,2,4,8,12,18,24,48, and 72 h and by venesection at 4, 7, 14, 28, 42, and 56 days. Blood was collected into lithium heparin tubes and was centrifuged at 1,800 ϫ g for 5 min, and the separated plasma was stored at Ϫ80°C until analysis for the NQ concentration within 8 months of collection.…”

“…These children were reassessed clinically at 4 and 24 h and on days 2, 3, 7, 14, 28, and 56 (7). Group 2 and 3 patients had further 2.5-ml blood samples for drug assay taken at 1,2,4,8,12,18,24,48, and 72 h through the sampling cannula and by venesection at 4, 7, 14, 28, and 42 days. Group 3 patients received a second ART-NQ dose with water at 24 h. Posttreatment clinical and other monitoring for groups 2 and 3 was similar to that performed for group 1 (7).…”

“…It has been shown that NQ is a P-glycoprotein substrate and that NQ efflux is saturable (12), suggesting that absorption could be nonlinear at high doses. However, the Chinese volunteer study of ART-NQ found dose-proportional increases in the maximum concentration in plasma (C max ) and AUC for NQ at doses between 200 and 600 mg (41).…”

Investigation of the Functional Role of P-Glycoprotein in Limiting the Oral Bioavailability of Lumefantrine

“…The extensive overlap in the substrate specificities, tissue localization, and coinducibility of P-gp and CYP3A4, in which P-gp controls the access of the drug to the metabolizing enzyme and results in increased metabolism from prolonged exposure to the enzyme through repeated cycles of absorption and efflux, has led to the hypothesis that these two proteins work together to protect the body from absorption of harmful xenobiotics, including drugs (1,5,6). It has been reported that some of the antimalarial drugs, like pyronaridine and naphthoquine, are P-gp substrates, which explains their low oral bioavailability (7).…”