Abstract
Leishmaniasis remains a global health challenge, and the search for effective and selective therapeutic agents is crucial. This study evaluated the in vitro antileishmanial and cytotoxic activities of thiosemicarbazone compounds (LT-70, LT-73, LT-75, and LT-89) against Leishmania infantum promastigote and axenic amastigote forms. The compounds demonstrated strong leishmanicidal activity, with IC50 values ranging from 10.5 to 14 µM. At the lowest tested concentration (20 µM) the compounds produced percent inhibitions of 100% (LT-70), 100% (LT-73), 100% (LT-75) and 100% (LT-89). Cytotoxicity assays on J774.A1 macrophages revealed CC50 values from 60 µM to >75 µM, with LT-73 and LT-75 showing low toxicity (CC50 > 75µM). Selectivity index (SI) ranged from 7.1 for LT-75 and 5.8 for LT-73, indicating potential for further development. Ultrastructural analysis by SEM and TEM revealed cellular and organelle damage, including membrane rupture and mitochondrial swelling, especially after LT-73 and LT-75 treatment. Immunomodulatory assays indicated induction of TNF-α and IFN-γ production, with significant IL-6 reduction. Flow cytometry data suggest mitochondrial dysfunction and apoptosis-like features, particularly for LT-73. Membrane potential assays suggested mitochondrial depolarization by LT-73. LT thiosemicarbazone derivatives present specific structural modifications that enhance antileishmanial selectivity and reveal a dual mechanism of action combining mitochondrial dysfunction and immunomodulatory effects. These findings support the potential of thiosemicarbazone derivatives as promising antileishmanial agents with selective cytotoxicity and immunomodulatory effects.