Combining bioinformatics, cheminformatics, functional genomics and whole organism approaches for identifying epigenetic drug targets in Schistosoma mansoni

Gilda Padalino,Salvatore Ferla,Andrea Brancale,Iain W Chalmers,Karl F Hoffmann

doi:10.1016/j.ijpddr.2018.10.005

Abstract

Schistosomiasis endangers the lives of greater than 200 million people every year and is predominantly controlled by a single class chemotherapy, praziquantel (PZQ). Development of PZQ replacement (to combat the threat of PZQ insensitivity/resistance arising) or combinatorial (to facilitate the killing of PZQ-insensitive juvenile schistosomes) chemotherapies would help sustain this control strategy into the future. Here, we re-categorise two families of druggable epigenetic targets in Schistosoma mansoni, the histone methyltransferases (HMTs) and the histone demethylases (HDMs). Amongst these, a S. mansoni Lysine Specific Demethylase 1 (SmLSD1, Smp_150560) homolog was selected for further analyses. Homology modelling of SmLSD1 and in silico docking of greater than four thousand putative inhibitors identified seven (L1 – L7) showing more favourable binding to the target pocket of SmLSD1 vs Homo sapiens HsLSD1; six of these seven (L1 – L6) plus three structural analogues of L7 (L8 – L10) were subsequently screened against schistosomula using the Roboworm anthelmintic discovery platform. The most active compounds (L10 - pirarubicin > L8 – danunorubicin hydrochloride) were subsequently tested against juvenile (3 wk old) and mature (7 wk old) schistosome stages and found to impede motility, suppress egg production and affect tegumental surfaces. When compared to a surrogate human cell line (HepG2), a moderate window of selectivity was observed for the most active compound L10 (selectivity indices - 11 for schistosomula, 9 for juveniles, 1.5 for adults). Finally, RNA interference of SmLSD1 recapitulated the egg-laying defect of schistosomes co-cultivated in the presence of L10 and L8. These preliminary results suggest that SmLSD1 represents an attractive new target for schistosomiasis; identification of more potent and selective SmLSD1 compounds, however, is essential. Nevertheless, the approaches described herein highlight an interdisciplinary strategy for selecting and screening novel/repositioned anti-schistosomals, which can be applied to any druggable (epigenetic) target encoded by the parasite's genome.

Highlights

Until a safe, reliable and efficacious prophylactic vaccine is developed, human schistosomiasis will continue to be primarily treated by anthelmintic chemotherapy
By re-classifying two opposing enzymatic families responsible for histone methylation and demethylation, we have identified SmLSD1 as a druggable candidate
With the further repositioning of antineoplastic compounds (L8 - daunorubicin and L10 - pirarubicin) as putative SmLSD1 inhibitors, medicinal chemistry optimisation could lead to the generation of more potent and selective anti-schistosomals that negatively affect epigenetic processes underlying schistosome development and pathogenesis

Summary

Introduction

Reliable and efficacious prophylactic vaccine is developed, human schistosomiasis will continue to be primarily treated by anthelmintic chemotherapy. Protein coupled receptor antagonist (Chan et al, 2017)) raises concerns over its sustainability in helping to meet the World Health Organisation's objective of regional schistosomiasis elimination by 2020 and beyond (WHO, 2012). Added to these concerns is the spectre of praziquantel-insensitive or resistant parasites developing (Cupit and Cunningham, 2015). As HMEs are critical regulators of developmental fate and disease pathogenesis in other metazoans (Butler et al, 2012), their selection as druggable epigenetic targets in early-stage schistosome drug discovery projects is well justified

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Results

Conclusion