Zinc(II)-Sterol Hydrazone Complex as a Potent Anti-Leishmania Agent: Synthesis, Characterization, and Insight into Its Mechanism of Antiparasitic Action

Searching for new alternatives for treating leishmaniasis, we present the synthesis, characterization, and biological evaluation against Leishmania amazonensis of the new ZnCl(2)(H3)(2) complex. H3 is 22-hydrazone-imidazoline-2-yl-chol-5-ene-3β-ol, a well-known bioactive molecule functioning as a sterol Δ(24)-sterol methyl transferase (24-SMT) inhibitor. The ZnCl(2)(H3)(2) complex was characterized by infrared, UV-vis, molar conductance measurements, elemental analysis, mass spectrometry, and NMR experiments. The biological results showed that the free ligand H3 and ZnCl(2)(H3)(2) significantly inhibited the growth of promastigotes and intracellular amastigotes. The IC(50) values found for H3 and ZnCl(2)(H3)(2) were 5.2 µM and 2.5 µM for promastigotes, and 543 nM and 32 nM for intracellular amastigotes, respectively. Thus, the ZnCl(2)(H3)(2) complex proved to be seventeen times more potent than the free ligand H3 against the intracellular amastigote, the clinically relevant stage. Furthermore, cytotoxicity assays and determination of selectivity index (SI) revealed that ZnCl(2)(H3)(2) (CC(50) = 5 μΜ, SI = 156) is more selective than H3 (CC(50) = 10 μΜ, SI = 20). Furthermore, as H3 is a specific inhibitor of the 24-SMT, free sterol analysis was performed. The results showed that H3 was not only able to induce depletion of endogenous parasite sterols (episterol and 5-dehydroepisterol) and their replacement by 24-desalkyl sterols (cholesta-5,7,24-trien-3β-ol and cholesta-7,24-dien-3β-ol) but also its zinc derivative resulting in a loss of cell viability. Using electron microscopy, studies on the fine ultrastructure of the parasites showed significant differences between the control cells and parasites treated with H3 and ZnCl(2)(H3)(2). The inhibitors induced membrane wrinkle, mitochondrial injury, and abnormal chromatin condensation changes that are more intense in the cells treated with ZnCl(2)(H3)(2).