Genomic and biological features of Plasmodium falciparum resistance against antimalarial endoperoxide N-89.

Drug resistance of malaria parasites remains a problem affecting antimalarial treatment and control of the disease. We previously synthesized an antimalarial endoperoxide, N-89, having high antimalarial effects in vitro and in vivo. In this study we seek to understand the resistant mechanism against N-89 by establishing a highly N-89-resistant clone, named NRC10H, of the Plasmodium falciparum FCR-3 strain. We describe gene mutations in the parent FCR-3 strain and the NRC10H clone using whole-genome sequencing and subsequently by expression profiling using quantitative real-time PCR. Seven genes related to drug resistance, proteolysis, glycophosphatidylinositol anchor biosynthesis, and phosphatidylethanolamine biosynthesis exhibited a single amino acid substitution in the NRC10H clone. Among these seven genes, the multidrug resistance protein 2 (mdr2) variant A532S was found only in NRC10H. The genetic status of the P. falciparum endoplasmic reticulum-resident calcium binding protein (PfERC), a potential target of N-89, was similar between the NRC10H clone and the parent FCR-3 strain. These findings suggest that the genetic alterations of the identified seven genes, in particular mdr2, in NRC10H could give rise to resistance of the antimalarial endoperoxide N-89.

Pharmacokinetic analysis of new synthetic antimalarial N-251.

BACKGROUND: With the emergence and growing number of drug-resistant Plasmodium falciparum, a new drug for malaria control must be urgently developed. The new antimalarial synthetic compound N-251 was recently discovered. As an endoperoxide structure in the body, the compound shows high antimalarial activity and curative effects. We performed a pharmacokinetic (PK) analysis of N-251 under various conditions using mice to understand the inhibitory effect of N-251 in parasite-infected mice. RESULTS: PK study of N-251 after intravenous and oral administration in mice showed plasma concentration of N-251 was decreased drastically by intravenous route. C max was reached in 2 h after oral administration of N-251, and the level decreased to a level similar to that obtained after intravenous administration. The area under the curves (AUCs) of the plasma concentration of N-251 increased dose-proportionally in both administrations, and bioavailability (F) was approximately 23%. Additionally, T max, C max, AUC, and F increased in fasted mice compared to normal-fed mice after the administration of N-251, indicating the influence of diet on the absorption kinetics of N-251. Furthermore, in parasite-infected fasted mice, the plasma concentration-time profile of N-251 was similar to that in normal-fasted mice. Based on the PK parameters of single oral administration of N-251, we investigated the effect of multiple oral doses of N-251 (68 mg/kg three times per day for 2 days) in normal-fed mice. The plasma concentration of N-251 was between 10 and 1000 ng/mL. The simulation curve calculated based on the PK parameters obtained from the single-dose study well described the plasma concentrations after multiple oral dosing, indicating that N-251 did not accumulate in the mice. Multiple oral administrations of N-251 in mice were required to completely eliminate parasites without accumulation of N-251. CONCLUSIONS: N-251 has been selected as a potent antimalarial candidate. We found that N-251 showed short half-life in plasma, and AUCs increased proportionally to dose. With multiple doses of N-251, the plasma level of N-251 was greater than 10 ng/mL in normal-fed mice, and accumulation of N-251 was not observed; however, multiple treatments with N-251 are required for the complete cure of parasite-infected mice. Determining the appropriate dosage was an important step in the clinical applications of N-251.