Exploiting the 2-Amino-1,3,4-thiadiazole Scaffold To Inhibit Trypanosoma brucei Pteridine Reductase in Support of Early-Stage Drug Discovery

Abstract

Pteridine reductase-1 (PTR1) is a promising drug target for the treatment of trypanosomiasis. We investigated the potential of a previously identified class of thiadiazole inhibitors of Leishmania major PTR1 for activity against Trypanosoma brucei (Tb). We solved crystal structures of several TbPTR1-inhibitor complexes to guide the structure-based design of new thiadiazole derivatives. Subsequent synthesis and enzyme- and cell-based assays confirm new, mid-micromolar inhibitors of TbPTR1 with low toxicity. In particular, compound 4m, a biphenyl-thiadiazole-2,5-diamine with IC50 = 16 μM, was able to potentiate the antitrypanosomal activity of the dihydrofolate reductase inhibitor methotrexate (MTX) with a 4.1-fold decrease of the EC50 value. In addition, the antiparasitic activity of the combination of 4m and MTX was reversed by addition of folic acid. By adopting an efficient hit discovery platform, we demonstrate, using the 2-amino-1,3,4-thiadiazole scaffold, how a promising tool for the development of anti-T. brucei agents can be obtained.

High-resolution crystal structure of Trypanosoma brucei pteridine reductase 1 in complex with an innovative tricyclic-based inhibitor

“…3). The crystal asymmetric unit includes a whole functional TbPTR1 tetramer, the structure of which is almost identical to those described previously (Borsari et al, 2016;Linciano et al, 2017;Di Pisa et al, 2017). In subunit C the substrate-binding loop, including residues 207-215, appears to be highly flexible, and residues 208-217 have been excluded from our model.…”

“…The TbPTR1 inhibitors developed to date were conceived as substrate-competitive inhibitors and are based on a wide variety of scaffolds, including 2,4-diaminopteridine (Dawson et al, 2006;Tulloch et al, 2010), quinazoline (Dawson et al, 2010), 2,4-diaminopyrrolopyrimidine (Tulloch et al, 2010), chromone (Borsari et al, 2016;Di Pisa et al, 2017), 2-aminothiadiazole (Linciano et al, 2017), 2-aminobenzimidazole (Mpamhanga et al, 2009), triazine (Tulloch et al, 2010), 1,6-dihydrotriazine (Landi et al, 2019) and 2-aminobenzothiazole (Linciano et al, 2019). More than 60 crystal structures of TbPTR1-inhibitor complexes have now been deposited in the Protein Data Bank (PDB), clarifying the key binding interactions that occur inside the catalytic cavity (Pozzi et al, 2018).…”

Future Prospects in the Treatment of Parasitic Diseases: 2-Amino-1,3,4-Thiadiazoles in Leishmaniasis

“…Kinetoplastea is a class of flagellated parasitic protozoans, which includes clinically important human pathogens that are vectored by insects [49]. The three major human diseases resulting from kinetoplastid infections include human African trypanosomiasis (sleeping sickness) which is caused by Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense , American trypanosomiasis (Chagas disease) caused by Trypanosoma cruzi , and various forms of leishmaniasis caused by different species of Leishmania [50]. These three neglected tropical diseases account for over 60,000 human deaths per year and involve about 4 million disability-adjusted life years (DALYs) [47,48,49,51].…”

Dual and selective inhibitors of pteridine reductase 1 (PTR1) and dihydrofolate reductase-thymidylate synthase (DHFR-TS) from Leishmania chagasi

“…Trypanosomatids dependence on host-synthesized purine and pteridines has long been targeted to fight Chagas disease 13 , human African trypanosomiasis 14 , and leishmaniasis 15 , 16 . Among the enzymes that play a key role in the salvage and folate pathway, dihydrofolate reductase is the macromolecular target of several drugs, including those available to fight malaria 17 .…”