Authors

Discussion

Schistosomiasis is a neglected tropical disease caused by the parasitic flatworm genus Schistosoma. The disease has the highest infection rates in the developing world. Currently, there is only one drug treatment available, an anthelmintic called Praziquantel. This reliance on one single medication has raised significant concerns over drug resistance in the worms and the continued effectiveness of the treatment. However, regulatory systems including cyclic nucleotide metabolism are emerging as primary candidates for drug discovery. Here, we report the cloning, and the complementation of S. mansoni cyclic nucleotide phosphodiesterases (SmPDEs), specifically SmPDE7var, SmPDE1, SmPDE8, and SmPDE9C in a specialised Trypanosoma brucei cell line constructed as a model for heterologous expression of PDEs, created for this purpose by the deletion both alleles of the essential locus TbrPDEB1/B2. The growth of the final transfection was dependent on tetracycline-induced expression of the Schistosoma PDE gene (functional complementation); removal of tetracycline from the medium, as a control, was designed to result in cell death. In addition to this, a construct of TbrPDEB1 with the catalytic domain of SmPDEs 4A or SmPDE7var, successfully complemented the PDEB1/B2 null strain of T. brucei. SmPDE11 failed to complement the T. brucei cell line and was assessed in a Schizosaccharomyces pombe system. It was found to hydrolyse cGMP over cAMP. This explains its failure to complement in T. brucei system, as there is no known role for cGMP in these cells, but hydrolysis of cAMP is essential.

This project has established that S. mansoni PDEs 1, 7var, 8 and 9C are functional cAMP phosphodiesterases and that SmPDE 11 is a cGMP phosphodiesterase. The resulting cell lines are now employed to screen several classes of PDE inhibitors to establish the pharmacological profile of each PDE separately, in a cellular system.