Filip Zmuda, Sharon M. Shepherd, Michael A. J. Ferguson, David. W. Gray, Leah S. Torrie, Manu De Rycker
Antimicrob Agents Chemother [Internet]. 2019 Aug 12;AAC.01082-19. DOI: 10.1128/AAC.01082-19
Chagas’ disease, which is caused by the Trypanosoma cruzi parasite, has become a global health problem that is currently treated with poorly tolerated drugs that require prolonged dosing. Therefore, there is a clinical need for new therapeutic agents that can mitigate these issues. The phosphomannomutase (PMM) and guanosine diphosphate-mannose pyrophosphorylase (GDP-MP) enzymes form part of the de novo biosynthetic pathway to the nucleotide sugar guanosine diphosphate-mannose. This nucleotide sugar is used either directly, or indirectly via the formation of dolichol-phosphomannose, for the assembly of all mannose-containing glycoconjugates. In T. cruzi, mannose-containing glycoconjugates include the cell-surface glycoinositol-phospholipids and the glycosylphosphatidylinositol-anchored mucin-like glycoproteins that dominate the cell surface architectures of all life-cycle stages. This makes PMM and GDP-MP potentially attractive targets for a drug discovery programme against Chagas’ disease. To assess the ligandability of these enzymes in T. cruzi, we have screened 18,117 structurally diverse compounds exploring drug-like chemical space and 16,845 small polar fragment compounds using an assay interrogating activities of both PMM and GDP-MP enzymes simultaneously. This resulted in 48 small fragment hits, and on re-testing 20 were found to be active against the enzymes. Deconvolution revealed that these were all inhibitors of T. cruzi GDP-MP, with compounds 2 and 3 acting as uncompetitive and competitive inhibitors, respectively. Based on these findings, the T. cruzi PMM and GDP-MP enzymes were deemed not ligandable and poorly ligandable, respectively, using small-molecules from conventional drug discovery chemical space. This presents a significant hurdle to exploiting these enzymes as therapeutic targets for Chagas’ disease.