New Series of 3-Pyridyl-1,3-Thiazoles: In Vitro and In Vivo Anti-Trypanosomatidae Profile, in vitro and in silico Mechanism of Action approach

Trypanosomatidae diseases, such as Chagas disease and leishmaniasis, are caused by protozoan parasites of the Trypanosomatidae family, namely Trypanosoma cruzi and Leishmania species, respectively. There is an urgent need for new therapies. Both pyridine and thiazole rings are recognized as important scaffolds in medicinal chemistry. This study reports the synthesis of 3-pyridyl-1,3-thiazole derivatives (1–18) and their evaluation through in vitro and in vivo assays. In vitro tests were conducted against T. cruzi, L. amazonensis, and L. infantum, with cytotoxicity assessed using L929 fibroblasts and RAW 264.7 macrophages. Mode of action studies included in vitro assays and in silico simulations. Fourteen compounds exhibited trypanocidal activity with IC₅₀ values ranging from 0.2 to 3.9 μM, outperforming benznidazole (4.2 μM). Compound 7 displayed an IC₅₀ of 0.4 μM and a selectivity index of 530.8. However, the compounds were inactive in in vivo assays at a dose of 100 mg/kg/day. Compounds 1, 7, 8, and 10 demonstrated trypanostatic effects, mitochondrial disruption, apoptosis induction, and parasite membrane damage. These compounds also modulated nitric oxide, IL-6, IL-10 and TNF production. In silico analysis indicated strong interactions with cruzain and favorable bioavailability, drug-likeness, and stability profiles. The leishmanicidal activity was negligible or absent. Despite promising in vitro trypanocidal activity, further structural optimization or formulation strategies are required to enhance oral stability and bioavailability, providing a foundation for the development of new therapeutic agents.