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.

Schistosomiasis, caused by infection with blood fluke schistosomes, is a neglected tropical disease that negatively impacts the lives of approximately 300 million people worldwide. In the absence of a vaccine, it is currently controlled by a single drug, Praziquantel (PZQ). Although incredibly valuable in controlling disease burden, PZQ-mediated chemotherapy is ineffective against juvenile worms and may not be sustainable should resistance develop. The need to identify an alternative or combinatorial drug is, therefore, a priority in contributing to the control of this parasitic disease into the 21^st century. In this study, we have identified a new class of anthelmintic, N-acyl homoserine lactones, which are normally used by bacteria for quorum sensing and population density control. The tested N-acyl homoserine lactones were active against all intra-human schistosome lifecycle stages, in particular, when a thiolactone modification to the core N-acyl homoserine ring was made. Interestingly, these N-acyl homoserine lactones also displayed antimicrobial activities against Gram⁺Staphylococcus aureus. By demonstrating broad activities against schistosomes and bacteria exemplars, this study identified a potential route for the further development of a new anti-infective class.

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.

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 β-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.

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.

Sex role attributes, symptom distress, and defensive style among college men and women

Eighty-four male and 90 female college students completed the PRF-Andro masculinity and femininity scales, a symptom checklist, and a defense mechanism inventory. Results indicated that interrelations among sex role attributes, defense preferences, and symptom distress differed for men and women. Cross-sex-typed persons mostly accounted for differences in symptom distress within each sex: Masculine women reported relatively low and feminine men reported relatively high degrees of symptom distress. In addition, sex roles interacted with sex in determining defense preferences. We also explored the possibility that defensive styles mediated between sex role attributes and symptom distress. Among women, an association between masculine attributes and a rejection of self-blaming defenses accounted for the negative relation between masculinity and symptom distress. Among men, sex role attributes and defensive styles, for the most part, contributed independently to symptom distress.