Quorum sensing N-Acyl homoserine lactones are a new class of anti-schistosomal.

BACKGROUND: Schistosomiasis is a prevalent neglected tropical disease that affects approximately 300 million people worldwide. Its treatment is through a single class chemotherapy, praziquantel. Concerns surrounding the emergence of praziquantel insensitivity have led to a need for developing novel anthelmintics. METHODOLOGY/PRINCIPLE FINDINGS: Through evaluating and screening fourteen compounds (initially developed for anti-cancer and anti-viral projects) against Schistosoma mansoni, one of three species responsible for most cases of human schistosomiasis, a racemic N-acyl homoserine (1) demonstrated good efficacy against all intra mammalian lifecycle stages including schistosomula (EC50 = 4.7 µM), juvenile worms (EC50 = 4.3 µM) and adult worms (EC50 = 8.3 µM). To begin exploring structural activity relationships, a further 8 analogues of this compound were generated, including individual (R)- and (S)- enantiomers. Upon anti-schistosomal screening of these analogues, the (R)- enantiomer retained activity, whereas the (S)- lost activity. Furthermore, modification of the lactone ring to a thiolactone ring (3) improved potency against schistosomula (EC50 = 2.1 µM), juvenile worms (EC50 = 0.5 µM) and adult worms (EC50 = 4.8 µM). As the effective racemic parent compound is structurally similar to quorum sensing signaling peptides used by bacteria, further evaluation of its effect (along with its stereoisomers and the thiolactone analogues) against Gram+ (Staphylococcus aureus) and Gram- (Escherichia coli) species was conducted. While some activity was observed against both Gram+ and Gram- bacteria species for the racemic compound 1 (MIC 125 mg/L), the (R) stereoisomer had better activity (125 mg/L) than the (S) (>125mg/L). However, the greatest antimicrobial activity (MIC 31.25 mg/L against S. aureus) was observed for the thiolactone containing analogue (3). CONCLUSION/SIGNIFICANCE: To the best of our knowledge, this is the first demonstration that N-Acyl homoserines exhibit anthelmintic activities. Furthermore, their additional action on Gram+ bacteria opens a new avenue for exploring these molecules more broadly as part of future anti-infective initiatives.

The Anti-mycobacterial Activity of a Diterpenoid-Like Molecule Operates Through Nitrogen and Amino Acid Starvation.

A library of 14 minimally cytotoxic diterpenoid-like compounds (CC50 > 70 µM on HepG2 human liver cells) was screened against Mycobacterium smegmatis, Staphylococcus aureus, and Escherichia coli to determine antimicrobial activity. Some compounds with a phenethyl alcohol (PE) core substituted with a ß-cyclocitral derivative demonstrated anti-mycobacterial activity, with the most active being compound 1 (MIC = 23.4 mg/L, IC50 = 0.6 mg/L). Lower activity was exhibited against S. aureus, while no activity was displayed against E. coli. Low cytotoxicity was re-confirmed on HepG2 cells and additionally on RAW 264.7 murine macrophages (SI for both cell lines > 38). The sub-lethal (IC50 at 6 h) effect of compound 1 on M. smegmatis was examined through untargeted metabolomics and compared to untreated bacteria and bacteria treated with sub-lethal (IC50 at 6 h) concentrations of the antituberculosis drugs ethambutol, isoniazid, kanamycin, and streptomycin. The study revealed that compound 1 acts differently from the reference antibiotics and that it significantly affects amino acid, nitrogen, nucleotides and folate-dependent one-carbon metabolism of M. smegmatis, giving some insights about the mode of action of this molecule. A future medicinal chemistry optimization of this new anti-mycobacterial core could lead to more potent molecules.

Antischistosomal Properties of Sclareol and Its Heck-Coupled Derivatives: Design, Synthesis, Biological Evaluation, and Untargeted Metabolomics.

Sclareol, a plant-derived diterpenoid widely used as a fragrance and flavoring substance, is well-known for its promising antimicrobial and anticancer properties. However, its activity on helminth parasites has not been previously reported. Here, we show that sclareol is active against larval (IC50 ≈ 13 µM), juvenile (IC50 = 5.0 µM), and adult (IC50 = 19.3 µM) stages of Schistosoma mansoni, a parasitic trematode responsible for the neglected tropical disease schistosomiasis. Microwave-assisted synthesis of Heck-coupled derivatives improved activity, with the substituents choice guided by the Matsy decision tree. The most active derivative 12 showed improved potency and selectivity on larval (IC50 ≈ 2.2 µM, selectivity index (SI) ≈ 22 in comparison to HepG2 cells), juvenile (IC50 = 1.7 µM, SI = 28.8), and adult schistosomes (IC50 = 9.4 µM, SI = 5.2). Scanning electron microscopy studies revealed that compound 12 induced blebbing of the adult worm surface at sublethal concentration (12.5 µM); moreover, the compound inhibited egg production at the lowest concentration tested (3.13 µM). The observed phenotype and data obtained by untargeted metabolomics suggested that compound 12 affects membrane lipid homeostasis by interfering with arachidonic acid metabolism. The same methodology applied to praziquantel (PZQ)-treated worms revealed sugar metabolism alterations that could be ascribed to the previously reported action of PZQ on serotonin signaling and/or effects on glycolysis. Importantly, our data suggest that compound 12 and PZQ exert different antischistosomal activities. More studies will be necessary to confirm the generated hypothesis and to progress the development of more potent antischistosomal sclareol derivatives.

An Abies procera-derived tetracyclic triterpene containing a steroid-like nucleus core and a lactone side chain attenuates in vitro survival of both Fasciola hepatica and Schistosoma mansoni.

Two economically and biomedically important platyhelminth species, Fasciola hepatica (liver fluke) and Schistosoma mansoni (blood fluke), are responsible for the neglected tropical diseases (NTDs) fasciolosis and schistosomiasis. Due to the absence of prophylactic vaccines, these NTDs are principally managed by the single class chemotherapies triclabendazole (F. hepatica) and praziquantel (S. mansoni). Unfortunately, liver fluke resistance to triclabendazole has been widely reported and blood fluke insensitivity/resistance to praziquantel has been observed in both laboratory settings as well as in endemic communities. Therefore, the identification of new anthelmintics is necessary for the sustainable control of these NTDs in both animal and human populations. Here, continuing our work with phytochemicals, we isolated ten triterpenoids from the mature bark of Abies species and assessed their anthelmintic activities against F. hepatica and S. mansoni larval and adult lifecycle stages. Full 1H and 13C NMR-mediated structural elucidation of the two most active triterpenoids revealed that a tetracyclic steroid-like nucleus core and a lactone side chain are associated with the observed anthelmintic effects. When compared to representative mammalian cell lines (MDBK and HepG2), the most potent triterpenoid (700015; anthelmintic EC50s range from 0.7 µM-15.6 µM) displayed anthelmintic selectivity (selectivity indices for F. hepatica: 13 for newly excysted juveniles, 46 for immature flukes, 2 for mature flukes; selectivity indices for S. mansoni: 14 for schistosomula, 9 for immature flukes, 4 for adult males and 3 for adult females) and induced severe disruption of surface membranes in both liver and blood flukes. S. mansoni egg production, a process responsible for pathology in schistosomiasis, was also severely inhibited by 700015. Together, our results describe the structural elucidation of a novel broad acting anthelmintic triterpenoid and support further investigations developing this compound into more potent analogues for the control of both fasciolosis and schistosomiasis.

Design, synthesis and anthelmintic activity of 7-keto-sempervirol analogues.

The plant-derived, diterpenoid 7-keto-sempervirol was recently reported to display moderate activity against larval stages of Schistosoma mansoni (IC50 = 19.1 µM) and Fasciola hepatica (IC50 = 17.7 µM), two related parasitic blood and liver flukes responsible for the neglected tropical diseases schistosomiasis and fascioliasis, respectively. Here, we aimed to increase the potency of 7-keto-sempervirol by total synthesis of 30 structural analogues. Subsequent screening of these new diterpenoids against juvenile and adult lifecycle stages of both parasites as well as the human HepG2 liver cell line and the bovine MDBK kidney cell line revealed structure-activity relationship trends. The most active analogue, 7d, displayed improved dual anthelmintic activity over 7-keto-sempervirol (IC50 ≈ 6 µM for larval blood flukes; IC50 ≈ 3 µM for juvenile liver flukes) and moderate selectivity (SI ≈ 4-5 for blood flukes, 8-13 for liver flukes compared to HepG2 and MDBK cells, respectively). Phenotypic studies using scanning electron microscopy revealed substantial tegumental alterations in both helminth species, supporting the hypothesis that the parasite surface is one of the main targets of this family of molecules. Further modifications of 7d could lead to greater potency and selectivity metrics resulting in a new class of broad-spectrum anthelmintic.