Discovery of NovelSchistosoma MansoniPDE4A Inhibitors as Potential Agents against Schistosomiasis

Abstract

Aim: Due to the urgent need for effective drugs to treat schistosomiasis that act through a known molecular mechanism of action, we focused on a target-based approach with the aim to discover inhibitors of a cyclic nucleotide phosphodiesterase from Schistosoma mansoni (SmPDE4A). Materials & methods: To discover new inhibitors of SmPDE4A homology models of the enzyme structure were constructed based on known human and protozoan homologs. The best two models were selected for subsequent virtual screening of our in-house chemical library. Results & conclusion: A total of 25 library compounds were selected for experimental confirmation as SmPDE4A inhibitors and after dose-response experiments, three top hits were identified. The results presented validate the virtual screening approach to identify new inhibitors for clinically relevant phosphodiesterases.

Cloning and functional complementation of ten Schistosoma mansoni phosphodiesterases expressed in the mammalian host stages

“…As is clear from the data in Fig 7A , besides TbrPDEB1 (positive control), SmPDE1, SmPDE4A, SmPDE8, SmPDE9A and SmPDE11 were able to complement the temperature sensitivity of the pde1/2 deletion strain, indicative of cAMP degrading PDE activity. Complementation by SmPDE4A was anticipated as the purified protein was shown to possess cAMP degrading activity in an earlier study [ 45 ] and we show in this study also complementation in T . b .…”

“…SmPDE4A, SmPDE8, SmPDE9A and SmPDE11 were able to complement the temperature sensitivity of the pde1/2 deletion strain, indicative of cAMP degrading PDE activity. Complementation by SmPDE4A was anticipated as the purified protein was shown to possess cAMP degrading activity in an earlier study [45] and we show in this study also complementation in T. b. brucei. For the other complementing SmPDE genes, this is the first report highlighting them as potential cAMP degrading enzymes.…”

“…The EC 50 s for each complementation line (TbrPDEB1, TbrPDEB2, SmPDE4A) all exhibited excellent correlation with the EC 50 s for the wild-type control ( Fig 5B ), and the same inhibitor rankings, showing that, as expected, all three enzymes display very similar pharmacology. Indeed, both TbrPDEB1 and SmPDE4A have a high similarity with human PDE4 [ 33 , 44 , 45 ] ( S3 Fig ) and as such each of these inhibitors also inhibits hPDE4B1 (pEC 50 range 8.4–10.3); it is likely that the successsful complementation by SmPDE4A in T . b .…”

“…They went on to identify by BLAST-P searches four S. mansoni PDE sequences: SmPDE4A-C (confirmed in the current manuscript) and SmPDE4D, which we here propose to rename SmPDE8 based on its phylogenetic alignment with hPDE8B, and concluded that SmPDE4A is likely to mediate the effects of the benzoxaboroles under study, in part via expression of SmPDE4A in pde4-deficient C. elegans. Further inhibitors of SmPDE4A were recently identified by in silico screening of PDE inhibitors against a homology model of SmPDE4A [45] and the PDE4 inhibitor roflumilast was investigated for activity against S. mansoni in vitro and in a mouse model [71].…”

“…The EC 50 s for each complementation line (TbrPDEB1, TbrPDEB2, SmPDE4A) all exhibited excellent correlation with the EC 50 s for the wild-type control (Fig 5B), and the same inhibitor rankings, showing that, as expected, all three enzymes display very similar pharmacology. Indeed, both TbrPDEB1 and SmPDE4A have a high similarity with human PDE4 [33, 44,45] (S3 Fig) and as such each of these inhibitors also inhibits hPDE4B1 (pEC 50 range 8.4-10.3); it is likely that the successsful complementation by SmPDE4A in T. b. brucei is at least in part due to its similarity to TbrPDEB1. The PDE3-selective compound Trequinsin, which has a low activity against TbrPDEB1 [46], was used as a negative control (EC 50 > 25 μM for 2T1-WT and all complementation strains), whereas the EC 50 values of all strains for the positive control, pentamidine, were not significantly different from each other ( Table 3).…”