Yohann Le Govic

Malaria remains the leading parasitic infection worldwide, and the effectiveness of antimalarial drugs is increasingly threatened by the emergence of multidrug-resistant Plasmodium falciparum (P. falciparum) strains. In this context, our team previously developed a series of novel aminopyridinemethanol derivatives, among which GBPS336 showed potent nanomolar activity against P. falciparum strains with reduced susceptibility to reference antimalarials. Here, we investigated the effects of GBPS336 on the intraerythrocytic developmental cycle and transcriptional response of the parasite by combining microscopic phenotyping with whole-transcriptome RNA sequencing (Illumina) of synchronized P. falciparum 3D7 cultures exposed or not to the compound. In GBPS336-treated cultures, microscopic analysis revealed reduced parasitaemia, a marked delay and disruption of intraerythrocytic development and morphological alterations indicative of a parasite stress response. Transcriptomic profiling identified 356 differentially expressed genes at H24 post-exposition in ring-stage cultures with enrichment in functional categories associated with erythrocyte invasion and the parasite–host interface. Altogether, these findings demonstrate the antimalarial activity of GBPS336 and highlight invasion-related pathways as a potentially important component of its mechanism of action. Further studies will be required to determine whether these pathways are directly affected and to identify the molecular target(s) underlying the activity of the compound.

La physiopathologie des infections déterminées par les Scedosporium est encore mal connue. Cependant, l’aptitude de ces champignons à accéder aux ressources en fer constitue vraisemblablement un facteur clé de leur virulence, le fer étant impliqué dans de nombreux processus biologiques essentiels. Le premier objectif de cette thèse était donc d’identifier, par une analyse in silico, les gènes potentiellement impliqués dans le métabolisme du fer chez S. apiospermum, en particulier dans l’acquisition du fer médiée par les sidérophores. La biosynthèse de ces petites molécules chélatrices du fer fait intervenir des mégaenzymes appelées NRPSs (non-ribosomal peptide synthetases). Etant donné l’importance des NRPSs dans le métabolisme secondaire fongique, nous avons ensuite étendu l’analyse bio-informatique à l’ensemble des clusters de gènes comportant une NRPS, révélant ainsi le potentiel de synthèse des peptides nonribosomiques chez S. apiospermum. Par ailleurs, des mutants défectifs pour le gène codant la NRPS chargée d’orchestrer la production d’un sidérophore extracellulaire ont été générés. L’étude de ces mutants a permis d’identifier la structure exacte du sidérophore produit, et de démontrer son importance pour la croissance et la virulence du champignon. Nos expériences ont également dévoilé la capacité de ce sidérophore à pirater le fer lié à d’autres sidérophores comme la pyoverdine, ce qui pourrait expliquer l’antagonisme rapporté entre les Scedosporium et le bacille pyocyanique dans le contexte de mucoviscidose. Au total, ces résultats indiquent un rôle majeur du système sidérophore chez Scedosporium, qui pourrait donc constituer une nouvelle cible thérapeutique pour ces champignons très peu sensibles aux antifongiques actuels.

Currently, artemisinin-based combination therapy is recommended as first-line treatment of uncomplicated falciparum malaria. Arylamino alcohols (AAAs) such as mefloquine (MQ) are the preferred partner drugs due to their longer half-life, reliable absorption and strong antimalarial activity. However, the mode of action of MQ remains poorly understood and its neurotoxicity limits its use. Furthermore, the emergence of drug-resistant parasites requires development of new antimalarial drugs. The aim of this study was to evaluate the β-hematin inhibition capacity of three pairs of enantiopure AAAs 1–3 (a/S and b/R) derived from MQ or enpiroline (ENP), a pyridine-based MQ analog with strong antimalarial activity. Inhibition of β-hematin—the synthetic counterpart of hemozoin formation—was determined for each compound. Antimalarial activity against W2 and 3D7 Plasmodium falciparum strains as well as percentages of inhibition of β-hematin formation were compared to those of reference molecules, i.e., chloroquine (CQ), MQ and ENP. Furthermore, a cytotoxicity study on the human-derived hepatocarcinoma cell line HepG2 was performed. With high antimalarial activity, stronger ability to inhibit β-hematin formation and low cytotoxicity, AAAs 1a-b and 2a are the most promising. These findings provide a better understanding of their potential mechanisms of action and may pave the way toward developing new lead compounds.

Despite considerable efforts, malaria remains one of the most devastating infectious disease worldwide. In the absence of an effective vaccine, the prophylaxis and management of Plasmodium infections still rely on the therapeutic use of antimalarial agents. However, the emergence of resistant parasites has jeopardized the efficiency of virtually all antimalarial drugs, including artemisinin combination therapies (ACTs). Thus, there is an urgent need for innovative treatments with novel targets to avoid or overcome drug resistance. In this context, Huang & colleagues prioritized compounds that can block the activity of epigenetic enzymes, and described the discovery of a selective P. falciparum histone deacetylase (HDAC) inhibitor with high activity against various stages of the parasite. These findings may pave the way toward developing new lead compounds with broad‐spectrum activity, thus facilitating malaria treatment and elimination.

Scedosporium species rank second among the filamentous fungi capable to colonize chronically the respiratory tract of patients with cystic fibrosis (CF). Nevertheless, there is little information on the mechanisms underpinning their virulence. Iron acquisition is critical for the growth and pathogenesis of many bacterial and fungal genera that chronically inhabit the CF lungs. In a previous study, we showed the presence in the genome of Scedosporium apiospermum of several genes relevant for iron uptake, notably SAPIO_CDS2806, an ortholog of sidD, which drives the synthesis of the extracellular hydroxamate-type siderophore fusarinine C (FsC) and its derivative triacetylfusarinine C (TAFC) in Aspergillus fumigatus. Here, we demonstrate that Scedosporium apiospermum sidD gene is required for production of an excreted siderophore, namely, N^α-methylcoprogen B, which also belongs to the hydroxamate family. Blockage of the synthesis of N^α-methylcoprogen B by disruption of the sidD gene resulted in the lack of fungal growth under iron limiting conditions. Still, growth of ΔsidD mutants could be restored by supplementation of the culture medium with a culture filtrate from the parent strain, but not from the mutants. Furthermore, the use of xenosiderophores as the sole source of iron revealed that S. apiospermum can acquire the iron using the hydroxamate siderophores ferrichrome or ferrioxamine, i.e., independently of N^α-methylcoprogen B production. Conversely, N^α-methylcoprogen B is mandatory for iron acquisition from pyoverdine, a mixed catecholate-hydroxamate siderophore. Finally, the deletion of sidD resulted in the loss of virulence in a murine model of scedosporiosis. Our findings demonstrate that S. apiospermum sidD gene drives the synthesis of a unique extracellular, hydroxamate-type iron chelator, which is essential for fungal growth and virulence. This compound scavenges iron from pyoverdine, which might explain why S. apiospermum and Pseudomonas aeruginosa are rarely found simultaneously in the CF lungs.

Schistosoma Hybrid Parasite Infecting Migrant