Identification of new compounds targeting the Schistosoma mansoni protein methylation machinery

Abstract

Schistosomiasis represents the second most deadly human parasitic disease behind malaria. Through its digenetic life cycle, the helminth Schistosoma mansoni shows a phenotypic plasticity heavily influenced by both biotic and abiotic stresses. Hence, the analysis of schistosome adaptation in response to different environmental stimuli may highlight key targets for anti-schistosomal drug development. Epigenetic pathways (mainly DNA methylation and histone acetylation) have been recently identified as crucial components in parasite developmental progression. Due to the limited knowledge about the specific contribution of the histone methylation, the characterisation and validation of histone methyltransferases/demethylases as suitable drug targets was undertaken. Interrogation of the parasite genome led to the identification of 27 histone methyltransferases (SmHMTs) and 14 histone demethylases (SmHDMs), including six novel members previously unknown in the literature. The presence of these epigenetic enzymes within the two other humaninfective schistosome species (Schistosoma haematobium and Schistosoma japonicum) suggests that a pan-Schistosoma anthelmintic could be developed. The application of homology modelling first and in silico virtual screening second led to the identification of new compounds targeting distinct SmHMT (Smp_138030, Smp_307060 and Smp_016750) and SmHDM members (Smp_150560 and Smp_160810). Exploration of the chemical space of the most promising compound family (GPV3, targeting Smp_138030) and subsequent medicinal chemistry optimisation of the lead compound (GPV56; selectivity index = 23) led to the creation and testing of 21 analogues, some with more potent and selective anti-schistosomal activities (e.g. compound 6.8, selectivity index = 29K). Selective RNAi-based experiments broadly replicated the compound-mediated anti-schistosomal phenotypes. While recombinant expression of many of these epigenetic enzymes was attempted in three different systems, variable levels of expression in both soluble and insoluble fractions prohibited the further progression of target-based validation experiments. Collectively, this multidisciplinary project demonstrated that the schistosome histone methylation machinery represents a viable target for schistosome drug discovery

Date of Award	2019
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Karl Hoffmann (Supervisor), Andrea Brancale (Supervisor) & Iain Chalmers (Supervisor)