Schistosoma Epigenetics - Targets, Regulation, New Drugs
Keywords: Schistosoma, histone modifying enzyme, epigenetics, molecular modelling, high-throughput screen, inhibitor, RNAi, gene expression signature, drug
We propose to develop novel drug leads for the therapy of the major human parasitic disease, schistosomiasis, using a holistic approach that will enable us to progress from cloned target proteins to lead compounds and from epigenetic inhibitors to the validation of crucial targets. For this, we have chosen to target the histone modifying enzymes (HME) : histone deacetylases (HDAC), histone acetyltransferases (HAT), histone methyltransferases (HMT) and histone demethylases (HDM) of Schistosoma mansoni. In the course of the project, the members of the HDAC, HAT, HMT and HDM families encoded in the genome will be identified. In parallel, a reverse chemical genetics approach using generic inhibitors of HME subclasses available within the consortium in cultures of schistosome larvae will identify those classes that are bona fide drug targets. These enzymes will be validated as therapeutic targets individually or collectively using RNAi to invalidate the corresponding genes. Potential inhibitors (HDACi, HATi, HMTi, HDMi) will be screened by in silico docking to the modelled catalytic domains of the enzymes and collections of analogues will be tested for their ability to inhibit the activity of the corresponding recombinant proteins in high-throughput assays. We will also establish gene expression profiles corresponding to HME invalidation (by RNAi) and inhibition (using drug candidates in cultured larval stages (schistosomula)) that will enable the determination of the specificity of action of the compounds. Finally, in vivo testing of the best candidates will be done in infected mice. In this way, during the study period we aim to develop a series of candidate molecules that can progress to clinical
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Schistosomes are flatworm parasites that infect about 200 million individuals in over 75 countries in tropical or sub-tropical regions and cause more than 280,000 deaths annually. The burden of disease, measured in DALYS (disability adjusted life years), has recently been shown to be much more severe than previously thought. Schistosomiasis is consequently the second most important parasitic disease of man after malaria. However, schistosomiasis is also a neglected disease and only one effective drug is currently available. Moreover, reduced efficacy of this drug and resistant parasite strains are increasingly reported.
We aim to characterize novel therapeutic targets, concentrating in particular on enzymes involved in the modification of chromatin and therefore in controlling gene transcription, and to develop inhibitors of these enzymes that will be lead compounds for drug development.
We intend to characterize and clone most of the enzymes involved in histone acetylation/deacetylation and methylation/demethylation. Promising candidates will be expressed as recombinant proteins and the structures of their catalytic domains will be determined by crystallography or in silico modelling. Phenotypic profiling using RNAi and generic inhibitors of histone modifying enzymes will validate potential targets and generate gene expression profiles that will define specific inhibition. Inhibitors will be validated both in silico and in vitro and optimised drug candidates will be tested in vivo. Overall we expect to generate several candidate schistosomicidal drugs that will go forward for further testing.
The principal applications will be the improvement of the chemotherapy of schistosomiasis. However, in addition to improving knowledge of histone modifying enzymes and their evolution, the development of inhibitors may well also provide leads to improving their application to the therapy of other diseases, including both parasitic infections and cancer.