Computer-aided search of novel inhibitors of n-myristoyl transferase with trypanocidal effects

Background: Computer-guided drug repurposing is regarded as an interesting strategy for the search of new treatments for neglected tropical diseases. It consists in the search of new therapeutic indications for already known drugs. N-myristoyl transferase (NMT) has been identified as a druggable drug target in trypanosomatids. We report the experimental assay against Trypanosoma cruzi and Trypanosoma brucei of potential NMT inhibitors emerging from a virtual screening campaign. Methods & Materials: An ensemble of ligand-based linear classifiers capable of discriminating within NMT inhibitors and non-inhibitors was inferred from a 224 training set. After internal and external validation, the model ensemble was applied to screen the DrugBank 4.0 database, using positive predictive value (PPV) surfaces to optimize the score threshold and applicability domain estimations. Three hits were acquired and experimentally tested: dicyclomine (previously used for the treatment of irritable bowel syndrome), quinestrol (used in hormone replacement therapy) and danazol (for the treatment of endometriosis and fibrocystic breast disease). The effect of different concentrations of the candidates on T. cruzi epimastigotes was assayed and the correspondent EC50 calculated. Also, the viability of T. cruzi trypomastigotes at 20 μM of the candidates were tested. Finally, the effects of the compounds on T. brucei trypomastigotes was measured. Results: The three tested drugs showed a strong trypanocidal activity on T. cruzi epimastigotes. Dicyclomine, quinestrol and danazol showed an EC50 of 4.2 μM, 4.8 μM and 1.8 μM respectively. Conversely, the inhibition of T. cruzi trypomastigotes was moderate: only quinestrol reduced the viability more than 50% at 20 μM. The calculated EC50 for quinestrol on these forms of the parasites was 8 μM. Finally, these drugs showed EC50s against T. brucei procyclic and bloodstream trypomastigotes between 10-20 μM. Conclusion: With the help of computational tools we have found three new trypanocidal compounds with potential against American and African trypanosomiasis, with a minimal investment of time and money.