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

Abstract

BackgroundSchistosomiasis 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 findingsThrough 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 active 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/SignificanceTo 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.Author SummarySchistosomiasis, 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 21st 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.

Anti-schistosomal activities of quinoxaline-containing compounds: From hit identification to lead optimisation

“…Compound-induced phenotype and motility effects were quantified using an adapted version of the WHO-TDR scoring system (in summary: 0 = dead, 1 = movement of the suckers only and slight contraction of the body, 2 = movement at the anterior and posterior regions only, 3 = full body movement but sluggish and 4 = normal movement) [ 58 ]. Additionally, differential uptake of propidium iodide (PI, P1304MP, Sigma-Aldrich, UK) was used to quantify worm viability as previously described [ 11 , 59 ]. In brief, after 15 min incubation with 2 μg/ml PI, the parasite cultures were imaged under both bright-field and fluorescent settings (PI detection, 562 and 624 excitation and emission wavelengths, respectively) using an ImageXpressXL high content imager (Molecular Devices, UK).…”

“…Initially the cells were handled under sterile conditions and grown at 37 °C in a humidified atmosphere containing 5% CO 2 . Cytotoxicity was evaluated by way of a 3-(4, 5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay as previously described [ 8 , 11 , 74 ]. The cells were counted in a dual chamber counting slide using the BIORAD TC-10 Automated cell counter, seeded in a 96- well plate (Fisher Scientific, Loughborough, UK) at a density of 2 × 10 4 cells/well and incubated in an atmosphere of 5% CO 2 at 37 °C.…”

“…Towards this goal, several drug discovery strategies have been applied in the pursuit of identifying novel chemotherapeutic agents and include (e.g.) drug repositioning [ [8] , [9] , [10] ], ‘piggybacking’ approaches [ [11] , [12] , [13] ], machine learning [ 14 ] and the de novo design of compounds using either ligand- or target-based molecular modelling approaches [ [15] , [16] , [17] , [18] , [19] ].…”