A fission yeast-based platform for nematode PDE inhibitor discovery

Class I cyclic nucleotide phosphodiesterases (PDEs) form a family of enzymes that hydrolyze the signaling molecules cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Highly potent and selective inhibitors of mammalian PDEs have been developed, demonstrating that this enzyme family is eminently druggable. The genomes of the free-living nematode and model organism Caenorhabditis elegans and those of related parasitic nematodes possess six PDE genes representing six of the eleven PDE families found in mammals. Here, we expressed the C. elegans PDEs or their catalytic domains in the fission yeast Schizosaccharomyces pombe and screened a collection of small molecule inhibitors of mammalian PDEs obtained from our previous high throughput screens for ones with activity against one or more C. elegans PDEs. Consistent with an earlier study, the C. elegans PDE-4 enzyme is relatively insensitive to mammalian PDE4 inhibitors such as Rolipram, as are PDE-4 enzymes from three parasitic nematodes. Much of this is due to a single amino acid difference between mammalian PDE4s and nematode PDE4, as replacing arginine 580 with threonine in C. elegans PDE-4 restores substantial sensitivity to Rolipram. Finally, several of the most effective C. elegans PDE inhibitors were tested for their impact on C. elegans growth and fertility, two of which displayed toxic effects on C. elegans viability and fecundity using two different assessment methods, while a third showed a significant effect on fecundity. The strategy described herein offers an approach for discovery of novel anthelmintic and nematicidal compounds targeting parasitic nematode PDEs.