An integrated approach towards the discovery of novel non-nucleoside Leishmania major pteridine reductase 1 inhibitors.

Despite the fact that Leishmania ssp are pteridine auxotrophs, Dihydrofolate Reductase-Thymidylate Synthase (DHFR-TS) inhibitors are ineffective against Leishmania major. On the other hand Pteridine Reductase 1 (PTR1) inhibitors proved to be lethal to the parasite. Aiming at identifying hits that lie outside the chemical space of known PTR1 inhibitors, pharmacophore models that differentiate true-binders from decoys and explain the structure-activity relationships of known inhibitors were employed to virtually screen the lead-like subset of ZINC database. This approach leads to the identification of Z80393 (IC50 = 32.31 ± 1.18 µM), whose inhibition mechanism was investigated by Thermal Shift Assays. This experimental result supports a competitive mechanism and was crucial to establish the docking search space as well as select the best pose, which was then investigated by molecular dynamics studies that corroborate the hit putative binding profile towards LmPTR1. The information gathered from such studies shall be useful to design more potent non-nucleoside LmPTR1 inhibitors.

Structure-guided discovery of thiazolidine-2,4-dione derivatives as a novel class of Leishmania major pteridine reductase 1 inhibitors.

Leishmania major, as other protozoan parasites, plague human kind since pre-historic times but it remains a worldwide ailment for which the therapeutic arsenal remains scarce. Although L. major is pteridine- and purine-auxotroph, well-established folate biosynthesis inhibitors, such as methotrexate, have poor effect over the parasite survival. The lack of efficiency is related to an alternative biochemical pathway in which pteridine reductase 1 (PTR1) plays a major role. For this reason, this enzyme has been considered a promising target for anti-leishmanial drug development and several inhibitors that share the substrate scaffold have been reported. In order to design a novel class of PTR1 inhibitors, we employed the thiazolidinone ring as a bioisosteric replacement for pteridine/purine ring. Among seven novel thiazolidine-2,4-dione derivatives reported herein, 2d was identified as the most promising lead by thermal shift assays (ΔTm = 11 °C, p = 0,01). Kinetic assays reveal that 2d has IC50 = 44.67 ± 1.74 µM and shows a noncompetitive behavior. This information guided docking studies and molecular dynamics simulations (50 000 ps) that supports 2d putative binding profile (H-bonding to Ser-111 and Leu-66) and shall be useful to design more potent inhibitors.