Characterization of lead compounds targeting the selenoprotein thioredoxin glutathione reductase for treatment of schistosomiasis

Schistosomiasis is a widespread human parasitic disease currently affecting over 200 million people. Chemotherapy for schistosomiasis relies exclusively on praziquantel. Although significant advances have been made in recent years to reduce the incidence and intensity of schistosome infections, these gains will be at risk should drug resistance parasites evolve. Thioredoxin glutathione reductase (TGR) is a selenoprotein of the parasite essential for the survival of schistosomes in the mammalian host. Several high-throughput screening campaigns have identified inhibitors of Schistosoma mansoni TGR. Follow up analyses of select active compounds form the basis of the present study. We identified eight compounds effective against ex vivo worms. Compounds 1 - 5 are active against all major species and development stages. Ability of these compounds to target immature worms is especially critical because praziquantel is poorly active against this stage. Compounds 1 - 5, 7, and 8 displayed schistosomicidal activity even after only one-hour incubation with the worms. Compounds 1 - 4 meet or exceed standards set by the World Health Organization for leads for schistosomiasis therapy activity. The mechanism of TGR inhibition was studied further with wild type and mutant TGR proteins. Compounds 4 - 6 were found to induce an NADPH oxidase activity in TGR, leading to the production of superoxide and hydrogen peroxide. Collectively, this effort has identified several active compound series that may serve as the basis for the development of new schistosomicidal compounds.