Development of probes to study epigenetic processes in parasites

Schistosoma mansoni is a water-born parasite and one of the main causes of schistosomiasis - a disease endemic in tropical regions. The disease affects an estimated 230 million people with symptoms ranging from abdominal pain and diarrhoea to liver damage. S. mansoni has a varied and diverse life cycle, with phenotypic changes hypothesised to be directed by epigenetic processes. Currently, the only treatment for schistosomiasis is the drug praziquantel, however, this compound is only effective against a juvenile form of the parasite, and resistance has been reported. Thus, there is a need for alternative drugs to combat this disease. Given the predicted role of epigenetic processes in the phenotypic changes throughout the parasite's life cycle, our hypothesis is that inhibitors for epigenetic proteins, specifically the bromodomains, would provide insight into the importance of these proteins in this species, and potentially be a target for future anti-infective drugs. We aim to develop potent and selective ligands for a bromodomain-containing protein of S. mansoni, SmBRD3. In collaboration with the Hoffmann group at the University of Aberystwyth, these ligands will be used in phenotypic screening to probe the role of this bromodomain containing protein in S. mansoni, providing information for future drug discovery efforts for targeting this class of proteins. We have identified a protein containing two tandem bromodomains, which we have called SmBRD3. Known human bromodomain ligands have been previously tested with this protein, with some compounds showing Kd values in the sub micro-molar range. However, to provide the basis for an anti-infective drug, a probe is needed with high affinity for the parasite protein and low affinity for the human protein. A previously obtained co-crystal structure of the second domain, SmBRD3(2), with a human bromodomain ligand provides important structural information to help achieve this. Using the co-crystal structure, we aim to develop a high-affinity ligand for this domain via synthetic structure-activity relationship studies (SAR) and in silico docking. Once this is achieved, a similar approach of protein crystallisation and SAR can be directed to the first domain, SmBRD3(1), to develop another high-affinity ligand for the first domain. These ligands can be bound via an appropriate chemical linker to form a bivalent ligand, which we propose should improve affinity and selectivity for the tandem SmBRD3 bromodomains. Each ligand developed will be phenotypically screened to assess their effect at different stages in the S. mansoni life cycle, which partnered with in vitro studies will guide the direction of the project. This work falls into the BBRSC area of 'systems approaches to the biosciences'.