Desbutyl-Lumefantrine Is a Metabolite of Lumefantrine with Potent In Vitro Antimalarial Activity That May Influence Artemether-Lumefantrine Treatment Outcome

Abstract

Desbutyl-lumefantrine (DBL) is a metabolite of lumefantrine. Preliminary data from Plasmodium falciparum field isolates show greater antimalarial potency than, and synergy with, the parent compound and synergy with artemisinin. In the present study, the in vitro activity and interactions of DBL were assessed from tritiumlabeled hypoxanthine uptake in cultures of the laboratory-adapted strains 3D7 (chloroquine sensitive) and W2mef (chloroquine resistant). The geometric mean 50% inhibitory concentrations (IC 50 s) for DBL against 3D7 and W2mef were 9.0 nM (95% confidence interval, 5.7 to 14.4 nM) and 9.5 nM (95% confidence interval, 7.5 to 11.9 nM), respectively, and those for lumefantrine were 65.2 nM (95% confidence interval, 42.3 to 100.8 nM) and 55.5 nM (95% confidence interval, 40.6 to 75.7 nM), respectively. An isobolographic analysis of DBL and lumefantrine combinations showed no interaction in either laboratory-adapted strain but mild synergy between DBL and dihydroartemisinin (sums of the fractional inhibitory concentrations of 0.92 [95% confidence interval, 0.87 to 0.98] and 0.94 [95% confidence interval, 0.90 to 0.99] for 3D7 and W2mef, respectively). Using a validated ultra-high-performance liquid chromatography-tandem mass spectrometry assay and 94 day 7 samples from a previously reported intervention trial, the mean plasma DBL was 31.9 nM (range, 1.3 to 123.1 nM). Mean plasma DBL concentrations were lower in children who failed artemether-lumefantrine treatment than in those with an adequate clinical and parasitological response (ACPR) (P ‫؍‬ 0.053 versus P > 0.22 for plasma lumefantrine and the plasma lumefantrine-to-DBL ratio, respectively). DBL is more potent than the parent compound and mildly synergistic with dihydroartemisinin. These properties and the relationship between day 7 plasma concentrations and the ACPR suggest that it could be a useful alternative to lumefantrine as a part of artemisinin combination therapy.Desbutyl-lumefantrine (DBL) or desbutyl-benflumetol is a 2,3-benzindene compound with antimalarial activity. Although previously considered only a putative metabolite of lumefantrine because of a lack of supportive pharmacokinetic data (20,24), recent analytical developments have enabled the reliable detection of relatively low concentrations of DBL in samples of plasma from small numbers of patients treated with conventional doses of artemether-lumefantrine combination therapy (11,15,18). The ratio of the maximum plasma concentration (C max ) of the parent compound to that of the metabolite in this situation has varied substantially, from 6 (18) to Ͼ270 (11).DBL is more potent in vitro against chloroquine (CQ)-resistant Plasmodium falciparum and Plasmodium vivax field isolates than lumefantrine (13, 17, 23). There is evidence of in vitro synergy between lumefantrine and DBL against P. falciparum but at ratios (999:1 and 995:5) that were presumably selected at a time when plasma concentrations of DBL were assumed to be very much lower than those of the parent compound (23,24). Int...

Artemether-Lumefantrine Exposure in HIV-Infected Nigerian Subjects on Nevirapine-Containing Antiretroviral Therapy

“…Finally, we did not measure the metabolite desbutyl-lumefantrine. Some studies have shown that the metabolite has greater in vitro potency against Plasmodium falciparum and may have a role in antimalarial efficacy in humans, despite exposure levels that are substantially lower than those of lumefantrine itself (5,22,26). How coadministered nevirapine influences the balance between lumefantrine and desbutyl-lumefantrine concentrations and thus the overall antimalarial effects of the drug and the metabolite is not known.…”

“…DHA undergoes glucuronidation by uridine diphosphoglucuronosyltransferases. Lumefantrine is metabolized by CYP3A4 into active desbutyl-lumefantrine (2,4,5). Nevirapine is metabolized by CYP3A4 and CYP2B6 while inducing CYP3A4 (6,7).…”

In Vitro Antimalarial Activity and Drug Interactions of Fenofibric Acid

“…For in vitro susceptibility, serial dilutions of each drug were prepared in RPMI 1640 and added in triplicate to 96-well plates at final concentrations of 6.25 to 1,600 nM (CQ), 0.78 to 51.2 nM (DHA), 0.3 M to 200 M (atorvastatin), 6.2 to 800 M (gemfibrozil, fenofibrate, clofibrate), and 39 to 5,000 nM (fenofibric acid). Synchronous parasite suspensions (Ն90% rings) were adjusted to 0.5% parasitemia and a final hematocrit of 1.5% in the drug-parasite mixture and were incubated for 48 h. Parasite growth was measured by a modification of the [ 3 H]hypoxanthine incorporation assay as previously described (15,35). Fifty percent inhibitory concentrations (IC 50 s) were determined by nonlinear regression analysis.…”

“…A modified microdilution isotopic technique (15,34,35) was used to determine the antimalarial activities of pre-and posttreatment plasma using serial dilution in drug-free RPMI. In triplicate experiments, aliquots of 100 l of plasma were added to 90 l of parasite suspension (1% parasitemia, 1.5% hematocrit) and 10 l [ 3 H]hypoxanthine (0.5 Ci) in 96-well plates, and the mixture was incubated, harvested, and counted (22).…”

“…A modified fixed-ratio isobologram method was used to assess drug interactions (20,35). Inhibition assays incorporating 1.5% parasitemia and 1.5% hematocrit were first carried out to determine IC 50 s for individual fibrates, atorvastatin, CQ, and DHA.…”