Trypanosoma cruzi: Activities of lapachol and α- and β-lapachone derivatives against epimastigote and trypomastigote forms
Graphical abstract
Derivatives obtained by chemical modifications of lapachol, α- and β-lapachones, have been synthesized and their trypanocidal activity evaluated in vitro in Trypanosoma cruzi epimastigote and trypomastigote forms.
Introduction
Chagas disease is one of the most important endemic diseases caused by Trypanosoma cruzi, which affects 16–18 million people in large areas of Latin America.1, 2 The drugs used for the treatment of this disease are nifurtimox, a nitrofuran derivative, and benznidazole, a nitroimidazole derivate. Both drugs present severe side effects. Furthermore, nifurtimox is no longer used in several countries because of its toxicity.3, 4, 5 The need of effective drugs, without adverse effects, has stimulated the search for new compounds with potential clinical utility.
Many natural and synthetic naphthoquinones have been tested against T. cruzi parasites as possible anti-chagasic agents. Among natural naphthoquinones, lapachol (1), β-lapachone (2), and its α-isomer (3) have demonstrated trypanocidal activities.6, 7, 8, 9 Compound 2 inhibited parasite motility progressively and also the growth of epimastigote cultures at a concentration of 0.8 μg/mL. This was one of the first natural product-derived molecules that showed evidence of oxidative stress generated in parasites.10, 11, 12, 13 Interestingly, compounds derived from β-lapachone and with an imidazole ring linked to the naphthopyrane moiety showed enhanced activity compared with 2.14 On the other hand, an oxyran derivative of α-lapachone has been described as potent trypanocidal agent.15
In the search for new trypanocidal agents, in this work, we evaluate the trypanocidal activity of lapachol, α- and β-lapachone derivatives through inhibition of T. cruzi epimastigote growth and trypomastigote viability. We also investigate biological activity, including parasite free radical production and respiration inhibition of the parasite.
Trypanocidal activity of all compounds was tested against T. cruzi epimastigote growth. The quinones were incorporated into the medium at different concentrations. Growth inhibition until day 10 was evaluated in comparison to control at day 5. Nifurtimox and benznidazol were used as the reference trypanocidal drugs. To establish the relative efficacy of the quinones in vitro compared with the standard drugs, the ICk50 was determined. ICk50 is defined as the drug concentration needed to decrease the growth constant (k) by 50%.
The anti-trypanosomal activity of quinones has been attributed to oxygen radical formation and consequently strong oxidative stress.16, 17, 18, 19 To evaluate this possibility, oxygen uptake experiments with and without cyanide were undertaken. Respiration is a composite value where oxygen uptake depends upon mitochondrial reactions as well as extra-mitochondrial reactions such as redox cycling.20 Thus, cyanide addition inhibits oxygen consumption in the respiratory chain and allows possible redox cycling induced by the drug to be observed more clearly. The effect of quinones on T. cruzi respiration was studied measuring oxygen consumption by epimastigotes at different concentrations of these compounds. The results are presented in Table 1.
Section snippets
Chemistry
Lapachones 2 and 3 and its hydroxylic derivative 4 were obtained from the commercially available lapachol (1) by treatment with different acid conditions21 and meta-chloroperbenzoic acid (MCPBA),22 respectively (Scheme 1). Pyranonaphthoquinones 7–8 were prepared from the easily available Michael adduct 623 by reduction with sodium borohydride followed by cyclization in acid conditions, without isolation of the respective alcohol intermediate, in 64–75% yields (Scheme 2). In the present study,
Conclusion
The most active compound against epimastigote and trypomastigote forms of T. cruzi was the aza-α-lapachone derivative 18. The results presented herein indicate that compound 18 is a potential lead compound for the design of new drugs for Chagas disease. This result may also be important for the design of new β-lapachone derivatives with a nitrogen isosteric modification on the aromatic ring in order to improve the anti-T. cruzi activity.
General remarks
Melting points were determined with a Meltemp apparatus and are not corrected. IR spectra were recorded on a Bruker Model Vector 22 spectrophotometer using KBr discs. 1H and 13C NMR spectra were obtained on Bruker ACP-200 and AM-400 instruments, using tetramethylsilane as internal reference. Column chromatography was performed on silica gel Merck 60 (70–230 mesh). High-resolution mass spectrum was obtained using a Thermo Finnigan Model MAT95XP instrument.
Synthetic procedures
Compounds 11–1325, 26 and 18–2125, 26, 27
Acknowledgments
This research was supported by FONDECYT (Research Grants 1020874 and 1061072), Proyecto Anillo ACT 29 CONICYT/PBCT, and DIPUC (Proyecto de Inicio 22 PI/2005).
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2021, Bioorganic and Medicinal ChemistryCitation Excerpt :Nonetheless, these have not become drugs, but they have been extensively explored in medicinal chemistry to seek new trypanocidal compounds yet since these are considered privileged scaffolds.43–45 Then, Salas et al.41 determined the activity of lapachol, α-lapachone, and β-lapachone (Figure 2) toward amastigotes and trypomastigotes of T. cruzi Tulahuén strain. Still, Bourguignon et al. verified that β-lapachone reduced the activity (>65%) of T. cruzi proteic whole extract of cysteine proteinase at 4.9 ± 1.0 µmol min−1 mg of protein-1 concentration.