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Biological activity of esters of quinoxaline-7-carboxylate 1,4-di-N-oxide against E. histolytica and their analysis as potential thioredoxin reductase inhibitors

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Abstract

Amoebiasis is caused by the protozoan Entamoeba histolytica that affects millions of people throughout the world. The standard treatment is metronidazole, however, this drug causes several side effects, and is also mutagenic and carcinogenic. Therefore, the search for therapeutic alternatives is necessary. Quinoxaline 1,4-di-N-oxides (QdNOs) derivatives have been shown to exhibit activity against different protozoan. In the present study, the effects of esters of quinoxaline-7-carboxylate 1,4-di-N-oxide (7-carboxylate QdNOs) derivatives on E. histolytica proliferation, morphology, ultrastructure, and oxidative stress were evaluated, also their potential as E. histolytica thioredoxin reductase (EhTrxR) inhibitors was analyzed. In vitro tests showed that 12 compounds from n-propyl and isopropyl series, were more active (IC50 = 0.331 to 3.56 μM) than metronidazole (IC50 = 4.5 μM). The compounds with better biological activity have a bulky, trifluoromethyl and isopropyl group at R1-, R2-, and R3-position, respectively. The main alterations found in trophozoites treated with some of these compounds included changes in chromatin, cell granularity, redistribution of vacuoles with cellular debris, and an increase in reactive oxygen species. Interestingly, docking studies suggested that 7-carboxylate QdNOs derivatives could interact with amino acid residues of the NADPH-binding domain and/or the redox-active site of EhTrxR. Enzymatic assays demonstrated that selected 7-carboxylate QdNOs inhibits EhTrxR disulfide reductase activity, and diaphorase activity shows that these compounds could act as electron acceptor substrates for the enzyme. Taken together, these data indicate that among the mechanisms involved in the antiamoebic effect of the 7-carboxylate QdNOs derivatives studied, is the induction of oxidative stress and the inhibition of EhTrxR activity.

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Acknowledgments

We thank Oliver Ornelas-Lopez and Maria del Rosario Espinoza Mellado, from the Microscopy Unit of ENCB, Mexico for their technical help in TEM assays.

Funding

This work was supported by the Instituto Politécnico Nacional, Mexico (SIP-20180520 and SIP-20190295); Consejo Nacional de Ciencia y Tecnología (CONACYT), Mexico; and ANPCyT (PICT2016-1778), Argentina.

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Correspondence to Esther Ramírez-Moreno.

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On behalf of all authors, the corresponding author states that there is no conflict of interest.

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Section Editor: Yaoyu Feng

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Appendix

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Fig. 8
figure 8

Predicted model showing the interaction of E. histolytica thioredoxin reductase (EhTrxR) with a Auranofin and b Metronidazole. 3D representation (left) and 2D Ligplot (right) showing protein-ligand interactions during docking. Hydrogen bonds are highlighted in green with the respective distances between the atoms involved, whereas hydrophobic contacts are represented by an arc with spokes radiating towards the ligand atom

Fig. 9
figure 9

EhTrxR disulfide reductase activity inhibition profiles. The assays were performed at 30 °C and pH 7.0 in the presence of 5 mM DTNB, 200 μM NADPH, 0.1 μM EhTrxR, and different concentrations of T-001, T-067, or T-116. The activities were normalized to measurements performed in the absence of the compounds

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Soto-Sánchez, J., Caro-Gómez, L.A., Paz-González, A.D. et al. Biological activity of esters of quinoxaline-7-carboxylate 1,4-di-N-oxide against E. histolytica and their analysis as potential thioredoxin reductase inhibitors. Parasitol Res 119, 695–711 (2020). https://doi.org/10.1007/s00436-019-06580-8

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  • DOI: https://doi.org/10.1007/s00436-019-06580-8

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