Drug Discovery for Schistosomiasis: Hit and Lead Compounds Identified in a Library of Known Drugs by Medium-Throughput Phenotypic Screening

Abstract

BackgroundPraziquantel (PZQ) is the only widely available drug to treat schistosomiasis. Given the potential for drug resistance, it is prudent to search for novel therapeutics. Identification of anti-schistosomal chemicals has traditionally relied on phenotypic (whole organism) screening with adult worms in vitro and/or animal models of disease—tools that limit automation and throughput with modern microtiter plate-formatted compound libraries.MethodsA partially automated, three-component phenotypic screen workflow is presented that utilizes at its apex the schistosomular stage of the parasite adapted to a 96-well plate format with a throughput of 640 compounds per month. Hits that arise are subsequently screened in vitro against adult parasites and finally for efficacy in a murine model of disease. Two GO/NO GO criteria filters in the workflow prioritize hit compounds for tests in the animal disease model in accordance with a target drug profile that demands short-course oral therapy. The screen workflow was inaugurated with 2,160 chemically diverse natural and synthetic compounds, of which 821 are drugs already approved for human use. This affords a unique starting point to ‘reposition’ (re-profile) drugs as anti-schistosomals with potential savings in development timelines and costs.FindingsMultiple and dynamic phenotypes could be categorized for schistosomula and adults in vitro, and a diverse set of ‘hit’ drugs and chemistries were identified, including anti-schistosomals, anthelmintics, antibiotics, and neuromodulators. Of those hits prioritized for tests in the animal disease model, a number of leads were identified, one of which compares reasonably well with PZQ in significantly decreasing worm and egg burdens, and disease-associated pathology. Data arising from the three components of the screen are posted online as a community resource.ConclusionsTo accelerate the identification of novel anti-schistosomals, we have developed a partially automated screen workflow that interfaces schistosomula with microtiter plate-formatted compound libraries. The workflow has identified various compounds and drugs as hits in vitro and leads, with the prescribed oral efficacy, in vivo. Efforts to improve throughput, automation, and rigor of the screening workflow are ongoing.

In vitroandin vivotrematode models for chemotherapeutic studies

“…To my knowledge, the life cycle of S. haematobium is currently maintained only in two laboratories, namely the Theodor Bilharz Research Institute (Giza, Egypt) and the Schistosomiasis Resource Center. ' Sibling ' species of S. haematobium, such as S. bovis, S. matthei or S. margrebowiei, the life cycles of which can be maintained in laboratory rodents, might serve as models for S. haematobium (Agnew et al 1989).…”

“…Schistosomula are incubated in Basch medium (Basch, 1981) supplemented with serum and antibiotics or other culture media (Smyth and Halton, 1983). Our own studies have shown that schistosomula survive for at least 96 h in different media (Basch,MEM,DMEM or TC 199) reported that schistosomula survive in Basch medium for several weeks (Abdulla et al 2009). In Fig.…”

Anti-Schistosomal Activity of Cinnamic Acid Esters: Eugenyl and Thymyl Cinnamate Induce Cytoplasmic Vacuoles and Death in Schistosomula of Schistosoma mansoni

“…Screens were performed at 5 μM and 10 µM against schistosomula and adults, respectively, over the course of 3 days. A previous constrained nomenclature is used to record phenotypes [16] (every 24 h) that describe both motion and morphological changes. For schistosomula, the terms employed are 'dead' (D), 'degenerate' (Deg), 'round' (R), 'overactive' (O) and 'dark' (Dark).…”

“…Maintenance of the S. mansoni life cycle, preparation of schistosomula and adult worms, compound storage and treatment of schistosomula and adult worms were as described [16]. Compounds were dissolved in DMSO.…”

Ortho-nitrobenzyl derivatives as potential anti-schistosomal agents

“…Maintenance of the S. mansoni life cycle, preparation of somules and adult worms, compound storage, and treatment of somules and adult worms were as described (Abdulla et al, 2009;Colley, Wikel, 1974;Duvall, DeWitt, 1967). Somules were cultured for four days in the presence of compounds at three concentrations, 0.1, 1.0 and 10 µM.…”