Anti-schistosomal action of the calcium channel agonist FPL-64176

Subversion of parasite neuromuscular function is a key strategy for anthelmintic drug development. Schistosome Ca(2+) signaling has been an area of particular interest for decades, with a specific focus on L-type voltage-gated Ca(2+) channels (Ca(v)s). However, the study of these channels has been technically challenging. One barrier is the lack of pharmacological probes that are active on flatworms, since the dihydropyridine (DHP) based ligands typically used to study Ca(v)s are relatively ineffective on schistosomes. Here, we have characterized the effect of a structurally distinct putative L-type Ca(v) agonist, FPL-64176, on schistosomes cultured ex vivo and in an in vivo murine model of infection. Unlike DHPs, FPL-64176 evokes rapid and sustained contractile paralysis of adult Schistosoma mansoni reminiscent of the anthelmintic praziquantel. This is accompanied by tegument disruption and an arrest of mitotic activity in somatic stem cells and germ line tissues. Interestingly, this strong ex vivo phenotype was temperature dependent, with FPL-64176 treatment being less potent at 37 °C than 23 °C. However, FPL-64176 caused intra-tegument lesions at the basement membrane of worms cultured ex vivo under both conditions, as well as an in vivo hepatic shift of parasites from the mesenteric vasculature of infected mice to the liver. Gene expression profiling of worms harvested following in vivo FPL-64176 exposure reveals differences in transcripts associated with muscle and extracellular matrix function, as well as female reproduction, which is consistent with the worm phenotypes observed following ex vivo drug treatment. These data advance FPL-64176 as a useful tool to study schistosome Ca(2+) signaling, and the benzoyl pyrrole core as a hit compound that may be optimized to develop new parasite-selective leads.