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

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

DYNAMICAL RECOVERY AND DIFFUSION

Il est possible d'appliquer les techniques de la déformation plastique pour étudier l'autodiffusion dans le silicium et le germanium. On a pu déduire de cette façon des énergies d'activation de 2,8 eV et de 3,6 eV pour le Ge et le Si respectivement. Pour le Si, le facteur préexponentiel Do a été estimé à 0,5 cm2/s. On discute ces résultats en terme de diffusion par monolacunes.Plastic deformation techniques can be applied to investigate self-diffusion in Si and Ge. By this way, activation energies of 2.8 eV and 3.6 eV for Ge and Si, respectively, were deduced. For Si, the pre-exponential factor Do was estimated to be 0.5 cm2/s. These results are discussed in terms of diffusion by a monovacancy mechanism

RECOVERY PROCESSES IN THE HIGH-TEMPERATURE DEFORMATION OF GERMANIUM, SILICON AND INDIUM ANTIMONIDE

Les courbes contrainte-déformation de Ge, Si et InSb montrent, indépendamment du stade III restauration bien connu, et aux temperatures élévées, un autre stade de restauration (stade V). Tandis qu'un processus de diffusion permet de rendre compte de l'existence du stade III, un mécanisme de "glissement dévié" a été proposé pour rendre compte de l'existence du stade V. Ces interprétations sont déduites de l'analyse de la dérivée première des courbes contrainte-déformation, c'est-à-dire du coefficient d'écrouissage et conduisent finalement à la conclusion que le regime où la loi-puissance n'est plus suivie et qui est obtenue dans le stade III pour les fortes contraintes, pourrait également être gouverné par un phénomène de "glissement dévié". Le modèle de trainage des crans de Barrett et Nix appliqué à la restauration au stade III conduit à des coefficients d'autodiffusion des monolacunes D = 41 exp (-3,0 eV/kT) cm2s-1 pour Ge et D = 0,63 exp (3,7 eV/kT) cm2s-1 pour Si. Ces valeurs confortent celles obtenues à partir d'expériences de diffusion de traceurs.The stress-strain curves of Ge, Si and InSb show, besides the well known recovery stage III, at high temperatures a second recovery stage (stage V). While stage III has been explained in terms of a diffusion-controlled recovery process, for stage V a cross-slip mechanism has been proposed. These ideas are corroborated by an analysis of the first derivative of the stress-strain curves, i.e. the workhardening coefficient, which finally leads to the conclusion, that the regime of power-law breakdown, which is observed in stage III at high stresses, may also be governed by cross-slip. The jog-dragging model of Barrett and Nix, when applied to stage III recovery, yields coefficients of monovacancy self-diffusion of D=41 exp (-0.3 eV/kT) cm2 s-1 for Ge and D=0.63 exp(3.7 eV/kT) cm2s-1 for Si. These parameters favorably compare to those evaluated from tracer diffusion experiments