The Parasite Reduction Ratio (PRR) assay version 2: standardized assessment of Plasmodium falciparum viability after antimalarial treatment in vitro

With artemisinin-resistant Plasmodium falciparum parasites emerging in Africa, the need for new antimalarial chemotypes is persistently high. The ideal pharmacodynamic parameters of a candidate drug are a rapid onset of action and a fast rate of parasite killing or clearance. To determine these parameters, it is essential to discriminate viable from nonviable parasites, which is complicated by the fact that viable parasites can be metabolically inactive, whilst dying parasites can still be metabolically active and morphologically unaffected. Standard growth inhibition assays, read out via microscopy or [3H] hypoxanthine incorporation, cannot reliably discriminate between viable and nonviable parasites. Conversely, the in vitro parasite reduction ratio (PRR) assay is able to measure viable parasites with high sensitivity. It provides valuable pharmacodynamic parameters, such as PRR, 99.9% parasite clearance time (PCT99.9%) and lag phase. Here we report the development of the PRR assay version 2 (V2), which comes with a shorter assay duration, optimized quality controls and an objective, automated analysis pipeline that systematically estimates PRR, PCT99.9% and lag time and returns meaningful secondary parameters such as the maximal killing rate of a drug (Emax) at the assayed concentration. These parameters can be fed directly into pharmacokinetic/pharmacodynamic models, hence aiding and standardizing lead selection, optimization, and dose prediction. © 2023 by the authors

First-in-man safety and pharmacokinetics of synthetic ozonide OZ439 demonstrates an improved exposure profile relative to other peroxide antimalarials

AIMS: To asses the safety and pharmacokinetics of a new synthetic ozonide antimalarial, OZ439, in a first-in-man, double-blind study in healthy volunteers. METHODS: OZ439 was administered as single oral daily doses of a capsule formulation (50-1200 mg) or an oral dispersion (400-1600 mg, fed and fasted states) for up to 3 days as an oral dispersion (200-800 mg/day). Plasma concentrations of OZ439 and its metabolites were measured by LC-MS. RESULTS: The pharmacokinetic (PK) profile of OZ439 was characterised by a t(max) of around 3 hours, followed by multiphasic profile with a terminal half-life of 25-30 hours. The PK parameters were approximately dose proportional for each group, and profiles of the metabolites followed a similar pattern to that of the parent compound. Following dosing for 3 days, accumulation was less than 2-fold but steady state was not achieved. In the presence of food, no effect was observed on the t(1/2) of OZ439 while the exposure was increased by 3 to 4.5-fold. Exposure was higher and inter-subject variability was reduced when OZ439 was administered as an oral dispersion compared to a capsule. The urinary clearance of OZ439 and its metabolites was found to be negligible, and OZ439 did not induce CYP3A4. The antimalarial activity profiles of a subset of serum samples suggested that the major antimalarial activity originated from OZ439 rather than from any of the metabolites. CONCLUSION: The safety and pharmacokinetic profile of OZ439 merits progression to Phase 2a proof-of concept studies in the target population of acute uncomplicated malari

In-depth study of homogeneity in DBS using two different techniques: Results from the EBF DBS-microsampling consortium

Background: At the start of their work, the European Bioanalysis Forum dried blood spots microsampling consortium did not form a dedicated team to investigate the spot homogeneity. However, two teams performed experiments that produced results relating to sample homogeneity. Results: The data, which were produced via two different approaches (a radiolabeled and a nonradiolabeled approach), are highly complementary and demonstrate clear effects on sample inhomogeneity due to the substrate type, compound and hematocrit levels. Conclusion: The results demonstrate that sample inhomogeneity is a significant hurdle to the use of dried blood spots for regulated bioanalysis that should be investigated further in the method establishment phase if the whole spot is not sampled. © 2013 Future Science Ltd