Development and Validation of a Quantitative, High-Throughput, Fluorescent-Based Bioassay to Detect Schistosoma Viability

BackgroundSchistosomiasis, caused by infection with the blood fluke Schistosoma, is responsible for greater than 200,000 human deaths per annum. Objective high-throughput screens for detecting novel anti-schistosomal targets will drive ‘genome to drug’ lead translational science at an unprecedented rate. Current methods for detecting schistosome viability rely on qualitative microscopic criteria, which require an understanding of parasite morphology, and most importantly, must be subjectively interpreted. These limitations, in the current state of the art, have significantly impeded progress into whole schistosome screening for next generation chemotherapies.Methodology/Principal FindingsWe present here a microtiter plate-based method for reproducibly detecting schistosomula viability that takes advantage of the differential uptake of fluorophores (propidium iodide and fluorescein diacetate) by living organisms. We validate this high-throughput system in detecting schistosomula viability using auranofin (a known inhibitor of thioredoxin glutathione reductase), praziquantel and a range of small compounds with previously-described (gambogic acid, sodium salinomycin, ethinyl estradiol, fluoxetidine hydrochloride, miconazole nitrate, chlorpromazine hydrochloride, amphotericin b, niclosamide) or suggested (bepridil, ciclopirox, rescinnamine, flucytosine, vinblastine and carbidopa) anti-schistosomal activities. This developed method is sensitive (200 schistosomula/well can be assayed), relevant to industrial (384-well microtiter plate compatibility) and academic (96-well microtiter plate compatibility) settings, translatable to functional genomics screens and drug assays, does not require a priori knowledge of schistosome biology and is quantitative.Conclusions/SignificanceThe wide-scale application of this fluorescence-based bioassay will greatly accelerate the objective identification of novel therapeutic lead targets/compounds to combat schistosomiasis. Adapting this bioassay for use with other parasitic worm species further offers an opportunity for great strides to be made against additional neglected tropical diseases of biomedical and veterinary importance.Author SummaryWith only one effective drug, praziquantel, currently used to treat most worldwide cases of schistosomiasis, there exists a pressing need to identify alternative anthelmintics before the development of praziquantel-resistant schistosomes removes our ability to combat this neglected tropical disease. At present, the most widely adopted methodology used to identify promising new anti-schistosome compounds relies on time consuming and subjective microscopic examination of parasite viability in response to in vitro schistosome/compound co-culturing. In our continued effort to identify novel drug and vaccine targets, we detail a dual-fluorescence bioassay that can objectively be used for assessing Schistosoma mansoni schistosomula viability in a medium or high- throughput manner to suit either academic or industrial settings. The described methodology replaces subjectivity with sensitivity and provides an enabling technology useful for rapid in vitro screens of both natural and synthetic compound libraries. It is expected that results obtained from these quantifiable in vitro screens would prioritize the most effective anti-schistosomal compounds for follow-up in vivo experimentation. This highly-adaptable dual-fluorescence bioassay could be integrated with other methods for measuring schistosome phenotype and, together, be used to greatly accelerate our search for novel anthelmintics