Stage-specific antileishmanial activity and selectivity of cynarin, apigenin, and luteolin against Leishmania tropica in vitro models.

Leishmaniasis is a parasitic disease caused by Leishmania species and constitutes a significant global public health concern. Pentavalent antimonials, the current first-line therapy for cutaneous leishmaniasis, are limited by toxicity, high cost, and emerging drug resistance. This study aims to evaluate the antipromastigote and intracellular antiamastigote activity of the polyphenolic compounds cynarin (CYN), a hydroxycinnamic acid derivative, and the flavonoids apigenin (API) and luteolin (LUT) against Leishmania tropica. Cytotoxicity was assessed in THP-1-derived macrophages using the CellTiter-Glo® assay. Antileishmanial activity against promastigotes and intracellular amastigotes was assessed using microscopic enumeration and viability assays, with amphotericin B serving as the reference drug. Selectivity index values (SI) were calculated as CC50/IC50, with SI ≥ 10 regarded as therapeutically relevant. CYN, API, and LUT exhibited CC50 values of 561 ± 18.1 μM, 247.3 ± 30.8 μM, and 67.5 ± 7.9 μM, respectively. Among the tested compounds, CYN (IC50: 130.1 ± 9.3 μM) showed the most pronounced antipromastigote activity, whereas API (IC50: 674.6 ± 16.3 μM) and LUT (IC50: 863.8 ± 16 μM) were active only at high concentrations. Both CYN (SI: 21.3) and LUT (SI: 11.6) displayed selective activity against intracellular amastigotes, while API exhibited comparatively modest activity (SI: 8.0), though its effect remained noteworthy. Microscopic analysis confirmed pronounced morphological alterations in both parasite forms at concentrations ≥ IC50. CYN demonstrated the highest selectivity, whereas LUT exhibited enhanced activity against intracellular amastigotes, indicating distinct pharmacological profiles. Nonetheless, comprehensive pharmacokinetic and pharmacodynamic studies in advanced in vivo models are required to validate their translational potential.