Improved Inhibitors of Trypanothione Reductase by Combination of Motifs: Synthesis, Inhibitory Potency, Binding Mode, and Antiprotozoal Activities

Abstract

Trypanothione reductase (TR) is an essential enzyme in the trypanothione-based redox metabolism of trypanosomatid parasites. This system is absent in humans and, therefore, offers a promising target for the development of selective new drugs against African sleeping sickness and Chagas' disease. Over the past two decades, a variety of nonpeptidic small-molecule ligands of the parasitic enzyme were discovered. A current goal is to decipher the binding mode of these known inhibitors in order to optimize their structures. We analyzed the binding mode of recently reported 1-(1-(benzo[b]thiophen-2-yl)cyclohexyl)piperidine (BTCP) analogues using computer modeling methods. This led us to conclude that the analogues occupy a different region of the active site than the diaryl sulfide-based class of inhibitors. A combination of the two motifs significantly increased affinity for the enzyme compared to the respective parent compounds. The newly synthesized conjugates exhibit K(ic) values for TR as low as 0.51±0.1 μM and high selectivity for the parasitic enzyme over the related human glutathione reductase (hGR), as was predicted by our molecular modeling studies. In vitro studies showed IC(50) values in the low micromolar to submicromolar range against Trypanosoma brucei rhodesiense, often in combination with low cytotoxicity against mammalian cells. Interestingly, even stronger activities were found against Plasmodium falciparum.

Structure- and ligand-based drug design approaches for neglected tropical diseases

“…As expected, the most promising inhibitor (1) (K i = 0.51 μM, Fig. 1D) showed a competitive type of inhibition with respect to the substrate trypanothione disulfide (TS 2 ), and at the concentration of 20 μM, did not affect the activity of the human homolog glutathione reductase (GR, 40 % sequence identity to TR) [19]. Additionally, compound 1 exhibited in vitro activity in the sub-to low micromolar range against a panel of protozoan parasites, including Trypanosoma cruzi, Trypanosoma brucei rhodesiense, Leishmania donovani, and Plasmodium falciparum, with selectivity index (SI) between 4 and 165 (SI = IC 50 L6 cells/IC 50 parasite).…”

“…Nonetheless, molecular modeling strategies have been employed to provide useful structural information for inhibitor drug design [16][17][18]. An important example is the design of a series of diaryl sulfidebased derivatives as new TR inhibitors [19]. In this work, molecular docking strategies were employed for the previously reported lead compound BTCP (K i = 1 μM) [18], suggesting the binding of the ligand to the hydrophobic Z-site of the TR enzyme (Fig.…”

Current Advances in Computational Strategies for Drug Discovery in Leishmaniasis

“…This enzyme participates in the reduction of oxidative agents by using trypanothione and this molecule is only present in kinetoplastids. This enzyme has been studied extensively as drug target, confirming the predictions of the mathematical model (Eberle., et al 2011). LmjF31.2940 and LmjF21.0845, encoding for squalene synthase and hypoxanthine-guanine phosphoribosyltransferase respectively, were also predicted as lethal in the network.…”

High Throughput Screening against the Peroxidase Cascade of African Trypanosomes Identifies Antiparasitic Compounds That Inactivate Tryparedoxin

“…The dithiol is kept reduced by NADPH and the flavoenzyme trypanothione reductase (TR), the system replacing the glutathione/glutathione reductase couple of the mammalian host (4). TR is the most thoroughly studied enzyme of the trypanothione metabolism, and a large number of inhibitors has been identified (5)(6)(7)(8)(9). Tpx is a distant member of the thioredoxin (Trx) protein family.…”