Naturally Occurring Cardenolides Affecting Schistosoma mansoni

[Image: see text] Schistosomiasis is a neglected tropical disease of considerable public health burden. We recently discovered a micromolar activity of several cardenolides against newly transformed schistosomula (NTS) of the parasitic flatworm Schistosoma mansoni in a small compound screen including different substance classes of both natural products as well as synthetic molecules. In further experiments, a focused library of naturally occurring and synthetic steroids was explored against NTS and adult S. mansoni, revealing seven cardenolides with comparable activities as known anthelminthics such as praziquantel. Of these, gomphoside monoacetate and uscharin showed suitable therapeutic indices. In a first in vivo study, at a dose of 10 mg/kg, only minor activity in mice harboring a chronic S. mansoni infection could be shown, which will be further investigated by structure–activity relationship studies as well as pharmacodynamic and pharmacokinetic approaches.