In Vitro Antileishmanial Activity and Cytotoxicity Evaluation of 2-(Thiophen-2-ylmethyl)quinazolin-4(3H)-one Derivatives Against Leishmania tropica and Leishmania infantum

Background/Objectives: Leishmaniasis is a neglected tropical disease and the toxicity, limited efficacy and emerging drug resistance of current therapies underscore the urgent need for new antileishmanial agents. This study aimed to experimentally assess the in vitro antileishmanial activity, cytotoxicity and selectivity of quinazolin-4(3H)-one derivatives against Leishmania tropica and Leishmania infantum and to computationally investigate the potential interaction of compound E9 with trypanothione reductase. Methods: The in vitro antileishmanial activities of sixteen quinazolin-4(3H)-one derivatives (E1-E16) against the promastigote forms of L. tropica and L. infantum were evaluated. Additionally, the most active compounds were subjected to an evaluation of their cytotoxicity in human umbilical vein endothelial cells (HUVECs) and their selectivity indices (SIs) were subsequently calculated. Molecular docking and molecular mechanics/generalized Born surface area (MM/GBSA) analyses were performed for compound E9 against L. infantum trypanothione reductase. Results: Compounds E2, E9 and E11 showed activity against L. tropica, with half-maximal inhibitory concentration (IC50) values of 23.2, 22.4 and 76.0 μM, respectively. In contrast, compounds E2, E3, E9 and E11 were active against L. infantum, with IC50 values of 38.1, 69.7, 28.2 and 86.7 μM, respectively, suggesting species-dependent activity. Furthermore, among the tested compounds, E2 showed the most favorable selectivity profile against L. tropica and L. infantum, with SI values of 8.8 and 5.4, respectively. Moreover, molecular docking of E9 produced a docking score of −8.070 kcal/mol, with MM/GBSA analysis indicating a binding free energy of −82.44 kcal/mol. Conclusions: These findings support further investigation of quinazolin-4(3H)-one derivatives as potential antileishmanial agents, with E2 emerging as the most selective compound. Furthermore, they suggest that the biological activity of this compound series may differ among Leishmania species. The molecular modeling findings suggest a potential interaction between E9 and trypanothione reductase, supporting the need for further evaluation of these compounds in intracellular amastigote models and subsequent in vivo studies.