Novel coumarins active against Trypanosoma cruzi and toxicity assessment using the animal model Caenorhabditis elegans

Abstract

Background: Chagas disease (CD) is a tropical parasitic disease. Although the number of people infected is very high, the only drugs available to treat CD, nifurtimox (Nfx) and benznidazole, are highly toxic, particularly in the chronic stage of the disease. Coumarins are a large class of compounds that display a wide range of interesting biological properties, such as antiparasitic. Hence, the aim of this work is to find a good antitrypanosomal drug with less toxicity. The use of simple organism models has become increasingly attractive for planning and simplifying efficient drug discovery. Within these models, Caenorhabditis elegans has emerged as a convenient and versatile tool with significant advantages for the toxicological potential identification for new compounds.

Methods: Trypanocidal activity: Forty-two 4-methylamino-coumarins were assayed against the epimastigote form of Trypanosoma cruzi (Tulahuen 2 strain) by inhibitory concentration 50% (IC₅₀). Toxicity assays: Lethal dose 50% (LD₅₀) and Body Area were determined by Caenorhabditis elegans N2 strain (wild type) after acute exposure. Structure-activity relationship: A classificatory model was built using 3D descriptors.

Results: Two of these coumarins demonstrated near equipotency to Nifurtimox (IC₅₀ = 5.0 ± 1 μM), with values of: 11 h (LaSOM 266), (IC₅₀ = 6.4 ± 1 μM) and 11 g (LaSOM 231), (IC₅₀ = 8.2 ± 2.3 μM). In C. elegans it was possible to observe that Nfx showed greater toxicity in both the LD₅₀ assay and the evaluation of the development of worms. It is possible to observe that the efficacy between Nfx and the synthesized compounds (11 h and 11 g) are similar. On the other hand, the toxicity of Nfx is approximately three times higher than that of the compounds. Results from the QSAR-3D study indicate that the volume and hydrophobicity of the substituents have a significant impact on the trypanocidal activities for derivatives that cause more than 50% of inhibition. These results show that the C. elegans model is efficient for screening potentially toxic compounds.

Conclusion: Two coumarins (11 h and 11 g) showed activity against T. cruzi epimastigote similar to Nifurtimox, however with lower toxicity in both LD₅₀ and development of C. elegans assays. These two compounds may be a feasible starting point for the development of new trypanocidal drugs.

Keywords: Caenorhabditis elegans; Chagas disease; Coumarins; Structure-activity relationship; Trypanosoma cruzi.

Fig. 1

Workflow of new compounds development with anti-trypanosome activity

Fig. 2

Reagents and conditions: (a) H2SO4, rt., overnight; (b) KI, THF-Water, 50 °C, 1.5 h

Fig. 3

Effect of 4-methylamino-coumarins (9 h series) on the growth of Tripanosoma cruzi epimastigotes

Fig. 4

Effect of 4-methylamino-coumarins (10 h series) on the growth of Tripanosoma cruzi epimastigotes

Fig. 5

Effect of 4-methylamino-coumarins (11 h series) on the growth of Tripanosoma cruzi epimastigotes

Fig. 6

Lethality of 10 g (a), 11 g (b), 11 h (c) and Nifurtimox (d) after acute exposure of C. elegans. Data were obtained from at least 3 independent experiments performed in duplicate

Fig. 7

Body areas of C. elegans after acute treatment (30 min) with 10 g, (a) 11 g (b), 11 h (c) and Nifurtimox (d). Results are expressed as mean ± SEM (n = 3 independent experiments performed in duplicate). *p < 0.05, **p < 0.01, ***p < 0.001 compared to the control group. Statistical comparisons were made using one way ANOVA/Bonferroni post-hoc test

Fig. 8

GRIND selected descriptors of Model 1 associated with active compounds

Fig. 9

Plot of the loading and score vectors