Elisabeth Davioud-Charvet

Three sub-series of 3-benzylmenadiones were discovered as new antischistosomal agents. The most potent representatives, called schistodiones, exhibited IC50 values <5 μM against larvae and ex vivoSchistosoma mansoni adult worms and moderate activity per os in the S. mansoni-infected mouse model in vivo. We synthesized the putative 3-benzoylmenadione metabolites of the most active compounds and explored the possible mode(s) of action using the yeast model and the recombinant drug target S. mansoni thioredoxin-glutathione reductase. Two drug targets were identified in yeast: the yeast NADH dehydrogenase and Cox15, involved in events responsible for respiratory growth defect in yeast, respectively: (i) the bioreductive activation step producing reactive oxygen species and (ii) the heme a synthase inhibition. These two drug targets are discussed in the context of S.mansoni biology, with S. mansoni thioredoxin–glutathione reductase redox-cycling and a potential source of oxidative stress in the parasite.

In the search for new antischistosomal 3-benzylmenadiones (benzylMDs), the screening of a library developed in our laboratory led to the identification of two regioisomeric analogues, the 2′,5′- and 3′,5′-dimethoxy-benzylMD—designated schistodiones A_2′,5′ and A_3′,5′—which were investigated for their activity against the platyhelminth Schistosoma mansoni and various protozoan parasites, bacteria, and fungi. Reported work has shown that benzylMDs act as prodrugs: their bioactivation undergoes a cascade of redox reactions within the parasite, generating multiple drug metabolites, e.g., the main benzoylmenadione (benzoylMD) intermediates, and reactive oxygen species that interfere with key metabolic pathways. Among the secondary metabolites, benzoxanthones have been identified as potential products generated along this oxidative pathway. The aim of the study was to synthetize methoxylated benzoxanthones, as putative metabolites generated from these antischistosomal benzylMDs. During the synthetic work, several difficulties arose, including the absence of starting reagents, the incompatibility of certain reactions with methoxy groups, the possible formation of several isomers, and the easy re-oxidation of sensitive intermediates. To overcome these obstacles, we developed a new retrosynthetic strategy using modified precursors: replacing methoxy groups with O-methylenemethoxy (OMOM) groups that are more stable in basic media, using aldehydes or aromatic esters as precursors, and replacing certain substituents with groups that are easier and less costly to introduce (chlorine or nitro). Selected metabolites (benzoylMDs, benzoxanthones) were then tested in parasite and cellular assays. Furthermore, benzoylMDs were tested as subversive substrates of S. mansoni thioredoxin-glutathione reductase (SmTGR) and selected drug metabolites were investigated in SmTGR modeling experiments. From a One Health perspective, these benzylMD derivatives pose limited environmental risk because their metabolites lack toxicity when encountered externally, as toxicity requires intracellular metabolic activation and localized formation of reactive intermediates in close proximity to their cellular targets inside parasites.

Chagas disease, caused by Trypanosoma cruzi , is a neglected parasitic infection. The very limited arsenal of anti- T . cruzi treatments calls for the development of new drugs. Recently, a library of 3-benzylmenadione derivatives was synthesized, with cruzidione being the most efficient and specific compound against the parasite. To decipher its mode of action, we used the yeast Saccharomyces cerevisiae as a model. Evidence pinpointed at the heme A synthase Cox15 as a primary target of cruzidione: (i) a mutation in Cox15 (i.e., S429F) renders the yeast cells highly sensitive to the drug, (ii) treatment with cruzidione led to the loss of cytochrome c oxidase, an enzyme that relies on heme A as an essential cofactor, and (iii) replacement of the yeast Cox15 by T. cruzi enzyme resulted in a high sensitivity to cruzidione. We then investigated the effect of cruzidione in T. cruzi and observed a significant reduction in the heme contents, most likely involving the inhibition of the heme A synthase. This, in turn, led to a decrease in O ₂ consumption by the parasite. Finally, using the yeast model, we showed that, similar to what we previously found for the antimalarial benzylmenadione plasmodione, NADH-dehydrogenase plays a key role in cruzidione bioactivation. We proposed that the reduced benzoylmenadione metabolites, produced by the reaction with NADH-dehydrogenase, act as Cox15 inhibitors. This study, through the identification of the mode of action of cruzidione, highlighted Cox15 as a novel target for antiparasitic drugs.

Plasmodione is a potent early antiplasmodial compound. A metabolic study on mice treated with plasmodione revealed that 6-hydroxy–plasmodione was the main metabolite eliminated in the urine of treated mice. To block the metabolic pathway in the host, the introduction of fluorine at C-6 of the 3-benzylmenadione core was applied and showed potent antiplasmodial activity similar to that of the plasmodione analogue in vitro. In this work, a library of 38 6-fluoro-3-benzylmenadione analogues (a series) was constructed by incorporating structurally diverse groups in place of the 4-(trifluoromethyl) substituent present in the antiplasmodial plasmodione, via three synthetic routes. All new compounds were tested against the P. falciparum NF54 strain and for cytotoxicity with the rat L6 line. With a fluorine atom at C-6, A-a-21 was revealed to be the only compound from the a series, superior to the 6-H- analogue from the b series, with an IC₅₀ value of 70 nM versus 200 nM. Then, five other fluorine-based 3-benzylmenadiones, in which the fluorine was introduced in various positions of the 3-benzylmenadione core, were synthetized to assist our understanding of the impact of fluorine on antiplasmodial potencies in vitro; in particular, the aim here was to compare the effects of human serum and P. berghei species in these drug screens. This was also conducted in vivo with the P. berghei-infected mouse model. In the P. berghei species assay, PD and the 4′-fluoro-3′-trifluoromethyl-benzylmenadione A-b-9 exhibited a similar antiplasmodial behavior toward P. falciparum versus P. berghei. In the human serum versus Albumax assays, only the 6-fluoro–plasmodione showed a lower shift factor between Albumax assays and human serum conditions, suggesting a lower protein binding for the 6-F-PD compared to plasmodione or A-b-9. In vivo, 6-fluoro–plasmodione proved to be the most potent 3-benzylmenadione, reducing parasitemia by 50% after oral administration at 50 mg/kg.

This study explores the synthesis and evaluation of novel 1,2,3‐triazole‐methyl‐1,4‐naphthoquinone hybrids, focusing on their electrochemical properties and antiparasitic efficacies against two human blood‐dwelling parasites Plasmodium falciparum and Schistosoma mansoni. Using copper‐catalyzed azide‐alkyne cycloaddition (CuAAC), a well‐established tool in click chemistry, two synthetic routes were assessed to develop α‐ and β‐[triazole‐methyl]‐menadione derivatives. By optimizing the CuAAC reaction conditions, yields were significantly improved, reaching up to 94 % for key intermediates and resulting in the formation of a library of approximately 30 compounds. Biological evaluation of the compounds in antiparasitic drug assays demonstrated notable antischistosomal potencies, while no significant activity was observed for the same series against P. falciparum parasites. Electrochemical and ‘benzylic’ oxidation studies confirmed that the active ‘benzoyl’ metabolite responsible for the antiplasmodial activity of plasmodione cannot be generated. These findings highlight the potential of triazole‐linked menadione hybrids as promising early candidates for antischistosomal drug development, and provides insights into structure‐activity relationships crucial for future therapeutic strategies.

The development of redox‐sensitive molecular fluorescent probes for the detection of redox changes in Plasmodium falciparum ‐parasitized red blood cells remains of interest due to the limitations of current genetically encoded biosensors. This study describes the design, screening and synthesis of new pro‐fluorophores based on flavylium azido dyes coupled by CuAAC click chemistry to alkynyl analogues of plasmodione oxide, the key metabolite of the potent redox‐active antimalarial plasmodione. The photophysical and electrochemical properties of these probes were evaluated, focusing on their fluorogenic responses. The influence of both the redox status of the quinone and the length of the PEG chain separating the fluorophore from the electrophore on the photophysical properties was investigated. The fluorescence quenching by photoinduced electron transfer is reversible and of high amplitude for probes in oxidized quinone forms and fluorescence is reinstated for reduced hydroquinone forms. Our results demonstrate that shortening the PEG chain has the effect of enhancing the fluorogenic response, likely due to non‐covalent interactions between the two chromophores. All these systems were evaluated for their antiparasitic activities and fluorescence imaging suggests the efficacy of the fluorescent flavylium dyes in P. falciparum ‐parasitized red blood cells, paving the way for future parasite imaging studies to monitor cellular redox processes.

Ψ-1,4-naphthoquinones (Ψ-NQ) are non-quinoid compounds in which aromaticity—found in 1,4-naphthoquinones—is broken by the introduction of an angular methyl at C-4a or -8a. This series was designed to act as prodrugs of 1,4-naphthoquinones in an oxidative environment. Furthermore, from a medicinal chemistry point of view, the loss of planarity of the scaffold might lead to an improved solubility and circumvent the bad reputation of quinones in the pharmaceutical industry. In this work, we illustrated the concept by the synthesis of Ψ -plasmodione regioisomers as prodrugs of the antimalarial plasmodione. The presence of a chiral center introduces a new degree of freedom to be controlled by enantioselectivity and regioselectivity of the cycloaddition in the Diels–Alder reaction. The first strategy that was followed was based on the use of a chiral enantiopure sulfoxide to govern the stereoselective formation of (+)Ψ-NQ or (−)Ψ-NQ, depending on the chirality of the sulfoxide (R or S). New sulfinylquinones were synthesized but were found to be ineffective in undergoing cycloaddition with different dienes under a wide range of conditions (thermal, Lewis acid). The second strategy was based on the use of boronic acid-substituted benzoquinones as auxiliaries to control the regioselectivity. Using this methodology to prepare the (±)Ψ-NQ racemates, promising results (very fast cycloaddition time: ~2 h) were obtained with boronic acid-based quinones 25 and 27 in the presence of 1-methoxy-1,3-butadiene, to generate the 4a- and the 8a-Ψ-plasmodione regioisomers 1 and 2 (synthesized in six steps with a total yield of 10.5% and 4.1%, respectively. As the expected prodrug effect can only be revealed if the molecule undergoes an oxidation of the angular methyl, e.g., in blood-feeding parasites that digest hemoglobin from the host, the antimalarial and the antischistosomal properties of both (±)Ψ-NQ regioisomers were determined in drug assays with Plasmodium falciparum and Schistosoma mansoni. Metabolic studies under quasi-physiological conditions and LC-MS analyses were undertaken to reveal the generation of plasmodione from both the 4a- and the 8a-Ψ-plasmodione regioisomers.

The apicoplast is an essential organelle for the viability of apicomplexan parasites Plasmodium falciparum or Toxoplasma gondii, which has been proposed as a suitable drug target for the development of new antiplasmodial drug-candidates. Plasmodione, an antimalarial redox-active lead drug is active at low nM concentrations on several blood stages of Plasmodiumsuch as early rings and gametocytes. Nevertheless, its precise biological targets remain unknown. Here, we described the synthesis and the evaluation of new heteroaromatic analogues of plasmodione, active on asexual blood P. falciparum stages and T. gondii tachyzoites. Using a bioimaging-based analysis, we followed the morphological alterations of T. gondii tachyzoites and revealed a specific loss of the apicoplast upon drug treatment. Lipidomic and fluxomic analyses determined that drug treatment severely impacts apicoplast-hosted FASII activity in T. gondii tachyzoites, further supporting that the apicoplast is a primary target of plasmodione analogues. To follow the drug localization, "clickable" analogues of plasmodione were designed as tools for fluorescence imaging through a Cu(I)-catalyzed azide-alkyne cycloaddition reaction. Short-time incubation of two probes with P. falciparum trophozoites and T. gondii tachyzoites showed that the clicked products localize within, or in the vicinity of, the apicoplast of both Apicomplexa parasites. In P. falciparum, the fluorescence signal was also associated with the mitochondrion, suggesting that bioactivation and activity of plasmodione and related analogues are potentially associated with these two organelles in malaria parasites.

Understanding the mechanisms of drug action in malarial parasites is crucial for the development of new drugs to combat infection and to counteract drug resistance. Proteomics is a widely used approach to study host‐pathogen systems and to identify drug protein targets. Plasmodione is an antiplasmodial early‐lead drug exerting potent activities against young asexual and sexual blood stages in vitro with low toxicity to host cells. To elucidate its molecular mechanisms, an affinity‐based protein profiling (AfBPP) approach was applied to yeast and P. falciparum proteomes. New (pro‐) AfBPP probes based on the 3‐benz(o)yl‐6‐fluoro‐menadione scaffold were synthesized. With optimized conditions of both photoaffinity labeling and click reaction steps, the AfBPP protocol was then applied to a yeast proteome, yielding 11 putative drug‐protein targets. Among these, we found four proteins associated with oxidoreductase activities, the hypothesized type of targets for plasmodione and its metabolites, and other proteins associated with the mitochondria. In Plasmodium parasites, the MS analysis revealed 44 potential plasmodione targets that need to be validated in further studies. Finally, the localization of a 3‐benzyl‐6‐fluoromenadione AfBPP probe was studied in the subcellular structures of the parasite at the trophozoite stage.