Evidence for linkage of pfmdr1, pfcrt, and pfk13 polymorphisms to lumefantrine and mefloquine susceptibilities in a Plasmodium falciparum cross

BACKGROUND

Lumefantrine and mefloquine are used worldwide in artemisinin-based combination therapy (ACT) of malaria. Better understanding of drug susceptibility and resistance is needed and can be obtained from studies of genetic crosses.

METHODS

Drug response phenotypes of a cross between Plasmodium falciparum lines 803 (Cambodia) and GB4 (Ghana) were obtained as half-maximal effective concentrations (EC50s) and days to recovery (DTR) after 24 h exposure to 500 nM lumefantrine. EC50s of mefloquine, halofantrine, chloroquine, and dihydroartemisinin were also determined. Quantitative trait loci (QTL) analysis and statistical tests with candidate genes were used to identify polymorphisms associated with response phenotypes.

RESULTS

Lumefantrine EC50s averaged 5.8-fold higher for the 803 than GB4 parent, and DTR results were 3-5 and 16-18 days, respectively. In 803 × GB4 progeny, outcomes of these two lumefantrine assays showed strong inverse correlation; these phenotypes also correlated strongly with mefloquine and halofantrine EC50s. By QTL analysis, lumefantrine and mefloquine phenotypes mapped to a chromosome 5 region containing codon polymorphisms N86Y and Y184F in the P. falciparum multidrug resistance 1 protein (PfMDR1). Statistical tests of candidate genes identified correlations between inheritance of PfK13 Kelch protein polymorphism C580Y (and possibly K189T) and lumefantrine and mefloquine susceptibilities. Correlations were detected between lumefantrine and chloroquine EC50s and polymorphisms N326S and I356T in the CVIET-type P. falciparum chloroquine resistance transporter (PfCRT) common to 803 and GB4.

CONCLUSIONS

Correlations in this study suggest common mechanisms of action in lumefantrine, mefloquine, and halofantrine responses. PfK13 as well as PfMDR1 and PfCRT polymorphisms may affect access and/or action of these arylaminoalcohol drugs at locations of hemoglobin digestion and heme metabolism. In endemic regions, pressure from use of lumefantrine or mefloquine in ACTs may drive selection of PfK13 polymorphisms along with versions of PfMDR1 and PfCRT associated with lower susceptibility to these drugs.

The impact of digestion is essential to the understanding of milk as a drug delivery system for poorly water soluble drugs

Milk has previously been considered as a potential lipid-based drug delivery system for poorly water soluble drugs but it has never gained significant attention. This is in part because relying on solubility in lipid-based formulations (in this case milk) does not provide a complete picture of the behavior of such systems upon digestion. Herein, we demonstrate using time resolved X-ray scattering that the digestion of milk is actually crucial to the solubilisation of a poorly water-soluble drug, halofantrine. Halofantrine was chosen because its behaviour in lipid-based formulations has been widely investigated and because of its close structural relationship to lumefantrine, an antimalarial drug of current interest for the treatment of paediatric malaria. The transformation of the drug from a crystalline solid form in suspension in milk, to a solubilised form as a direct consequence of lipolysis highlights that consideration of digestion of the milk lipids as a critical process that influences drug solubilisation and availability for absorption is vital.

Chemotherapeutic interaction between Khaya grandifoliola (WELW) CDC stem bark extract and two anti-malarial drugs in mice

In malarial endemic countries especially in the tropics, conventional antimalarial drugs are used with herbal remedies either concurrently or successively. Khaya grandifoliola is one of such popular herbs used in the treatment of malaria.Various doses of ethanol extract of K. grandifoliola stem bark (50-400 mg/kg/day) were administered orally to Swiss albino mice infected with Plasmodium yoelii nigerense. A dose of 100 mg/kg/day of the extract was also combined with 2.5 mg/kg/day of chloroquine or 6.25 mg/kg/day of halofantrine in both early and established malaria infection test models. The results showed that in the early malaria infection test, K. grandifoliola in combination with chloroquine or halofantrine elicited enhanced antiplasmodial effect in the established infection, there was significantly greater parasite clearance following administration of the combination when compared to the effects of K. grandifoliola or the conventional drugs alone. The mean survival period of parasitized animals was also enhanced by the extract/halofantrine combination. Lower therapeutic doses of halofantrine may be required to potentiate parasite clearance when used in combination with K. grandifoliola. This may constitute great advantage to halofantrine which is associated with cardiotoxicity at high doses.