3-Alkoxy-1-Benzyl-5-Nitroindazole Derivatives Are Potent Antileishmanial Compounds

Abstract

Indazoles have previously been identified as molecules with antiprotozoal activity. In this study, we evaluate the in vitro activity of thirteen 3-alkoxy-1-benzyl-5-nitroindazole derivatives (series D) against L. amazonensis, L. infantum, and L. mexicana. In vitro, cytotoxicity against mouse peritoneal macrophages and growth inhibitory activity in promastigotes were evaluated for all compounds, and those showing adequate activity and selectivity were tested against intracellular amastigotes. Transmission and scanning electron microscopy were employed to study the effects of 3-alkoxy-1-benzyl-5-nitroindazole and 2-benzyl-5-nitroindazolin-3-one derivatives on promastigotes of L. amazonensis. Compounds NV6 and NV8 were active in the two life stages of the three species, with the latter showing the best indicators of activity and selectivity. 3-alkoxy-1-benzyl-5-nitroindazole derivatives (series D) showed in vitro activity comparable to that of amphotericin B against the promastigote stage of Leishmania spp. Two compounds were also found to be active the amastigote stage. Electron microscopy studies confirmed the antileishmanial activity of the indazole derivatives studied and support future research on this family of compounds as antileishmanial agents.

Keywords: 2-benzyl-5-nitroindazolin-3-one; 3-alkoxy-1-benzyl-5-nitroindazole; amastigote; antileishmanial activity; leishmaniasis; promastigote.

Figure 1

Series of 5-nitroindazolin-3-one structures evaluated against T. cruzi.

Figure 2

New series of compounds designed for inhibition studies of T. cruzi.

Figure 3

Growth curves of the promastigotes of the three species of Leishmania.

Figure 4

Scanning electron microscopy of NV8 (IC₅₀ = 0.007 μM, ½ IC₅₀ = 0.0035 μM, ¼ IC₅₀ = 0.0017 μM) and VATR 131 (IC₅₀ = 2.13 μM, ½ IC₅₀ = 1.065 μM, ¼ IC₅₀ = 0.53 μM) against promastigotes of L. amazonensis. Scale bar = 0.5 µm.

Figure 5

Transmission electron microscopy of L. amazonensis promastigotes after 72 h of incubation: Control Group (A), DMSO 0.1% (B), IC₅₀ = 0.007 μM (C–E), ½ IC₅₀ = 0.0035 μM (F–H), and ¼ IC₅₀ = 0.0017 μM (I–K) of NV8 compound. Scale bar = 0.5 µm. Flagellum (F), Flagellar Pocket (FP), Kinetoplast (K), Nucleus (N), Mitochondria (M), Cytoplasmic Vacuoles (V), Dead Parasites (black star), Deformed Flagellar Pocket (*), Dead Parasites with extruded cytoplasm (+) and Cytosolic Granules (CG).

Figure 6

Transmission electron microscopy of L. amazonensis promastigotes after 72 h of incubation with ¼ IC₅₀ = 0.53 μM (A,B), ½ IC₅₀ = 1.065 μM (C,D) and IC₅₀ = 2.13 μM (E,F) of compound VATR 131. Scale bar = 1 µm.