title: Quantitative high-throughput screen identifies inhibitors of the Schistosoma mansoni redox cascade.
abstract: Schistosomiasis is a tropical disease associated with high morbidity and mortality, currently affecting over 200 million people worldwide. Praziquantel is the only drug used to treat the disease, and with its increased use the probability of developing drug resistance has grown significantly. The Schistosoma parasites can survive for up to decades in the human host due in part to a unique set of antioxidant enzymes that continuously degrade the reactive oxygen species produced by the host's innate immune response. Two principal components of this defense system have been recently identified in S. mansoni as thioredoxin/glutathione reductase (TGR) and peroxiredoxin (Prx) and as such these enzymes present attractive new targets for anti-schistosomiasis drug development. Inhibition of TGR/Prx activity was screened in a dual-enzyme format with reducing equivalents being transferred from NADPH to glutathione via a TGR-catalyzed reaction and then to hydrogen peroxide via a Prx-catalyzed step. A fully automated quantitative high-throughput (qHTS) experiment was performed against a collection of 71,028 compounds tested as 7- to 15-point concentration series at 5 microL reaction volume in 1536-well plate format. In order to generate a robust data set and to minimize the effect of compound autofluorescence, apparent reaction rates derived from a kinetic read were utilized instead of end-point measurements. Actives identified from the screen, along with previously untested analogues, were subjected to confirmatory experiments using the screening assay and subsequently against the individual targets in secondary assays. Several novel active series were identified which inhibited TGR at a range of potencies, with IC(50)s ranging from micromolar to the assay response limit ( approximately 25 nM). This is, to our knowledge, the first report of a large-scale HTS to identify lead compounds for a helminthic disease, and provides a paradigm that can be used to jump-start development of novel therapeutics for other neglected tropical diseases.
authors.affiliation: NIH Chemical Genomics Center, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Anton
authors.initials: A
authors.lastname: Simeonov
authors.forename: Ajit
authors.initials: A
authors.lastname: Jadhav
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Sayed
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Wang
authors.forename: Michael E
authors.initials: ME
authors.lastname: Nelson
authors.forename: Craig J
authors.initials: CJ
authors.lastname: Thomas
authors.forename: James
authors.initials: J
authors.lastname: Inglese
authors.forename: David L
authors.initials: DL
authors.lastname: Williams
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Austin
mesh_terms: D000818:Animals; D004353:Drug Evaluation, Preclinical; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009602:Nitrosamines / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D054464:Peroxiredoxins / Q000037:antagonists & inhibitors / Q000378:metabolism; D012550:Schistosoma mansoni / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D012555:Schistosomiasis mansoni / Q000188:drug therapy / Q000503:physiopathology
chemical_list: D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D009602:Nitrosamines; C041199:N-nitrosoallyl-2,3-dihydroxypropylamine; D006861:Hydrogen Peroxide; D054464:Peroxiredoxins; D009247:NADH, NADPH Oxidoreductases; C466433:thioredoxin glutathione reductase