Atovaquone and quinine anti-malarials inhibit ATP binding cassette transporter activity

Abstract

Background: Therapeutic blood plasma concentrations of anti-malarial drugs are essential for successful treatment. Pharmacokinetics of pharmaceutical compounds are dependent of adsorption, distribution, metabolism, and excretion. ATP binding cassette (ABC) transport proteins are particularly involved in drug deposition, as they are located at membranes of many uptake and excretory organs and at protective barriers, where they export endogenous and xenobiotic compounds, including pharmaceuticals. In this study, a panel of well-established anti-malarial drugs which may affect drug plasma concentrations was tested for interactions with human ABC transport proteins.

Methods: The interaction of chloroquine, quinine, artemisinin, mefloquine, lumefantrine, atovaquone, dihydroartemisinin and proguanil, with transport activity of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), bile salt export pump (BSEP) and multidrug resistance-associated proteins (MRP) 1-4 were analysed. The effect of the anti-malarials on the ATP-dependent uptake of radio-labelled substrates was measured in membrane vesicles isolated from HEK293 cells overexpressing the ABC transport proteins.

Results: A strong and previously undescribed inhibition of BCRP-mediated transport by atovaquone with a 50% inhibitory concentration (IC50) of 0.23 μM (95% CI 0.17-0.29 μM) and inhibition of P-gp-mediated transport by quinine with an IC50 of 6.8 μM (95% CI 5.9-7.8 μM) was observed. Furthermore, chloroquine and mefloquine were found to significantly inhibit P-gp-mediated transport. BCRP transport activity was significantly inhibited by all anti-malarials tested, whereas BSEP-mediated transport was not inhibited by any of the compounds. Both MRP1- and MRP3-mediated transport were significantly inhibited by mefloquine.

Conclusions: Atovaquone and quinine significantly inhibit BCRP- and P-gp- mediated transport at concentrations within the clinically relevant prophylactic and therapeutic range. Co-administration of these established anti-malarials with drugs that are BCRP or P-gp substrates may potentially lead to drug-drug interactions.

Figure 1

Inhibitory effect of anti-malarial drugs on ABC transport activity. The inhibitory effect of 100 μM of CQ, Q, ART, MQ, L, ATO, DHA and PG on ABC transporter activity was assessed. Transport was measured in pmol/mg protein/min and expressed as percentage of solvent controls, which represent 100% transport. Bars with * are significantly different from solvent controls, p < 0.05. A P-gp-mediated transport of NMQ was significantly inhibited by CQ, Q, MQ and PG, and increased by ART and DHA. B BCRP-mediated transport of E1S was significantly inhibited by all compounds, most pronounced inhibitors were MQ and ATO. C BSEP-mediated transport of TCA was significantly inhibited by ATO, but not by the other anti-malarials. Induction of transport was observed for CQ, ART and DHA. D-G MRP1-4-mediated E217βG transport. MQ significantly inhibited MRP1 and MRP3 transport activity. Furthermore, induction of MRP1 mediated transport was found for ATO, which, together with ART, also stimulated MRP2 transport activity. MRP3 mediated transport was stimulated by both ART and DHA. Inhibition larger than 66.7% was found for Q and MQ on P-gp transport, as well as MQ, ATO and PG on BCRP transport activity (highlighted bars).

Figure 2

Concentration-dependent inhibition of potent anti-malarial inhibitors of BCRP and P-gp. BCRP activity was inhibited according to the dose–response curves for A ATO B MQ and C PG.The inhibition of NMQ transport by P-gp was determined for D Q and E MQ.