Malaria; N-acylhydrazones; Marine Sponges; Plasmodium falciparum purine nucleoside phosphorylase; Plasmodium falciparum orotidine 5'-monophosphate decarboxylase.

Malaria continues to be a serious public health issue, demanding the urgent development of new drugs due to the increasing resistance of parasites to available antimalarial treatments. In this study, initially, 26 extracts from nine marine sponges collected in Salvador, Bahia, Brazil, were evaluated in vitro for their antiplasmodial and cytotoxic activity. All extracts demonstrated activity against Plasmodium falciparum, a chloroquine-resistant strain (W2), with IC50 values ranging from 0.28 to 22.34 μg/mL and low cytotoxicity against the human lung fibroblast-derived adherent lineage (ATCC® CCL-95.1™) (IC50 > 89 μg/mL). Subsequently, synthetic compounds of the N-acylhydrazone class (AH1 – AH7) were analyzed. According to the ideal parameters for the development of new antimalarials, compounds AH1, AH2, AH4, and AH5 demonstrated activity against Plasmodium falciparum, a chloroquine-resistant strain, with IC50 values ranging from 0.07 to 2.15 µM and no cytotoxicity against the fibroblast lineage (ATCC® CCL-95.1™) (IC50 > 100 µM). Compounds AH5, AH4, and AH1 presented the best IC50 values, namely, (0.07 ± 0.07 µM), (0.09 ± 0.05 µM), (0.19 ± 0.10 µM), respectively, and a high selectivity index (SI > 100). In order to understand the possible mechanism of action, the selected N-acylhydrazone compounds were subjected to a reverse virtual screening process using the Brazilian Malaria Molecular Targets (BraMMT) database. Based on the energy values generated, it was observed that compound AH5 exhibited lower energy than the crystallographic ligand for 12 targets, indicating low selectivity. In contrast, compound AH4 showed lower binding energy only in relation to the crystallographic ligand of the Plasmodium falciparum purine nucleoside phosphorylase (PfPNP) target (PDB:3PHC). On the other hand, compound AH1 did not show lower binding energy compared to the crystallographic ligands. Additionally, compounds AH4 and AH5 met the in silico criteria for physicochemical properties compatible with good oral bioavailability. Continuing the research in the quest for new antimalarials, the third stage explored the biosynthesis of pyrimidines in Plasmodium falciparum. The target Plasmodium falciparum orotidine 5'-monophosphate decarboxylase (PfOMPDC) (PDB: 3N3M) was selected through the BraMMT platform. The OMP substrate of the 3N3M enzyme was used as a reference in the search for compounds in previously known databases. This in silico screening process employed the Pharmit platform, in conjunction with the ZINC database, resulting in the selection of seven compounds with significant potential for future investigations. These compounds exhibited satisfactory pharmacokinetic properties with the potential for oral bioavailability.