Nitro radical anion formation from nifurtimox. Part 1: Biological evidences in Trypanosoma cruzi

Indazoles: a new top seed structure in the search of efficient drugs against Trypanosoma cruzi

For years, Chagas disease treatment has been limited to only two drugs of highly questionable and controversial use (Nifurtimox® and Benznidazole®). In the search of effective drugs, many efforts have been made, but only a few structures have emerged as actual candidates. Heading into this, the multitarget-directed approach appears as the best choice. In this framework, indazoles were shown to be potent Trypanosoma cruzi growth inhibitors, being able to lead both the formation of reactive oxygen species and the inhibition of trypanothione reductase. Herein, we discuss the main structural factors that rule the anti-T. cruzi properties of indazoles, and how they would be involved in the biological properties as well as in the action mechanisms, attempting to make parallels between the old paradigms and current evidences in order to outline what could be the next steps to follow in regard to the future drug design for Chagas disease treatment.

Mode of action of nifurtimox and N-oxide-containing heterocycles against Trypanosoma cruzi: is oxidative stress involved?

Chagas disease is caused by the trypanosomatid parasite Trypanosoma cruzi and threatens millions of lives in South America. As other neglected diseases there is almost no research and development effort by the pharmaceutical industry and the treatment relies on two drugs, Nifurtimox and Benznidazole, discovered empirically more than three decades ago. Nifurtimox, a nitrofurane derivative, is believed to exert its biological activity through the bioreduction of the nitro-group to a nitro-anion radical which undergoes redox-cycling with molecular oxygen. This hypothesis is generally accepted, although arguments against it have been presented. In the present work we studied the ability of Nifurtimox and five N-oxide-containing heterocycles to induce oxidative stress in T. cruzi. N-Oxide-containing heterocycles represent a promising group of new trypanosomicidal agents and their mode of action is not completely elucidated. The results here obtained argue against the oxidative stress hypothesis almost for all the studied compounds, including Nifurtimox. A significant reduction in the level of parasitic low-molecular-weight thiols was observed after Nifurtimox treatment; however, it was not linked to the production of reactive oxidant species. Besides, redox-cycling is only observed at high Nifurtimox concentrations (>400microM), two orders of magnitude higher than the concentration required for anti-proliferative activity (5microM). Our results indicate that an increase in oxidative stress is not the main mechanism of action of Nifurtimox. Among the studied N-oxide-containing heterocycles, benzofuroxan derivatives strongly inhibited parasite dehydrogenase activity and affected mitochondrial membrane potential. The indazole derivative raised intracellular oxidants production, but it was the least effective as anti-T. cruzi.

Design, synthesis and biological evaluation of new potent 5-nitrofuryl derivatives as anti-Trypanosoma cruzi agents. Studies of trypanothione binding site of trypanothione reductase as target for rational design

Design, using force-field calculations on the catalytic site of trypanothione reductase from Trypanosoma cruzi, has led to the development of new 5-nitrofuryl derivatives as potential anti-trypanosomal agents. The synthesized compounds were tested in vitro against T. cruzi and more than 75% of the prepared derivatives showed higher activity than nifurtimox. Compounds 5 and 11, hexyl 4-(5-nitrofurfurylidene)carbazate and N-hexyl 3-(5-nitrofuryl)propenamide, showed the highest in vitro trypanocidal effect reported to date for members of the nitrofuran family. Partition coefficients and energies for the single-electron reduction of compounds were theoretically determined. These properties could be not the major cause of the activities' differences. The physicochemical environment around E19, W22, C53 and Y111 residues within the trypanothione binding site of trypanothione reductase resulted a valuable target for the rational design of anti-trypanosomal drugs.