Plasmodium falciparum Ferredoxin-NADP+ Reductase-Catalyzed Redox Cycling of Plasmodione Generates
Both Predicted Key Drug Metabolites: Implication for Antimalarial
Drug Development
posted on 2021-04-15, 12:33authored byBogdan
Adam Cichocki, Maxime Donzel, Kim C. Heimsch, Mindaugas Lesanavičius, Liwen Feng, Enrique Jose Montagut, Katja Becker, Alessandro Aliverti, Mourad Elhabiri, Narimantas Čėnas, Elisabeth Davioud-Charvet
Plasmodione (PD) is a potent antimalarial
redox-active 3-benzyl-menadione
acting at low nanomolar range concentrations on different malaria
parasite stages. The specific bioactivation of PD was proposed to
occur via a cascade of redox reactions starting from one-electron
reduction and then benzylic oxidation, leading to the generation of
several key metabolites including corresponding benzylic alcohol (PD-bzol,
for PD benzhydrol) and 3-benzoylmenadione (PDO, for PD oxide). In
this study, we showed that the benzylic oxidation of PD is closely
related to the formation of a benzylic semiquinone radical, which
can be produced under two conditions: UV photoirradiation or catalysis
by Plasmodium falciparum apicoplast ferredoxin–NADP+ reductase (PfFNR) redox cycling in the presence
of oxygen and the parent PD. Electrochemical properties of both PD
metabolites were investigated in DMSO and in water. The single-electron
reduction potential values of PD, PD-bzol, PDO, and a series of 3-benzoylmenadiones
were determined according to ascorbate oxidation kinetics. These compounds
possess enhanced reactivity toward PfFNR as compared
with model quinones. Optimal conditions were set up to obtain the
best conversion of the starting PD to the corresponding metabolites.
UV irradiation of PD in isopropanol under positive oxygen pressure
led to an isolated yield of 31% PDO through the transient semiquinone
species formed in a cascade of reactions. In the presence of PfFNR, PDO and PD-bzol could be observed during long lasting
redox cycling of PD continuously fueled by NADPH regenerated by an
enzymatic system. Finally, we observed and quantified the effect of
PD on the production of oxidative stress in the apicoplast of transgenic
3D7[Api‑roGFP2‑hGrx1]P. falciparum parasites by using the described genetically encoded glutathione
redox sensor hGrx1-roGFP2 methodology. The observed fast reactive
oxygen species (ROS) pulse released in the apicoplast is proposed
to be mediated by PD redox cycling catalyzed by PfFNR.