Leishmaniasis is the generic denomination to the neglected diseases caused by more than 20 species of protozoa belonging to the genus Leishmania. The toxic and parenteral-delivered pentavalent antimonials remain to be the first-line treatment. However, all the current used drugs have restrictions. The species Aureliana fasciculata (Vell.) Sendtner var. fasciculata is a native Brazilian species parsimoniously studied on a chemical point of view. In this study, the antileishmanial activity of A. fasciculata was evaluated. Among the evaluated samples of the leaves, the dichloromethane partition (AFfDi) showed the more pronounced activity, with IC₅₀ 1.85 µg/ml against promastigotes of L. amazonensis. From AFfDi, two active withanolides were isolated, the Aurelianolides A and B, with IC₅₀ 7.61 μM and 7.94 μM, respectively. The withanolides also proved to be active against the clinically important form, the intracellular amastigote, with IC₅₀ 2.25 μM and 6.43 μM for Aurelianolides A and B, respectively. Furthermore, withanolides showed results for in silico parameters of absorption, distribution, metabolism, excretion, and toxicity (ADMET) similar to miltefosine, the reference drug, and were predicted as good oral drugs, with the advantage of not being hepatotoxic. These results suggest that these compounds can be useful as scaffolds for planning drug design.

Leishmaniasis chemotherapy faces significant challenges, including high costs, severe side effects, and the emergence of drug-resistant parasites, demanding global efforts to identify novel antileishmanial agents. Pentavalent antimony (Sb^V), the primary treatment for over 78 years, suffers from reduced efficacy and high toxicity, underscoring the urgent need for alternatives. We have synthesized metalloporphyrins with potent antileishmanial properties, including the Sb^V-porphyrin complex (Sb^VT4MPP). Sb^VT4MPP exhibited high potency against both Sb-sensitive and Sb-resistant Leishmania spp. with IC₅₀ as low as 0.05 and 0.12 µM, respectively, for amastigotes and promastigotes; 170-fold more effective than Sb^V and with a 28-37-fold selectivity index, highlighting the importance of host cells on drug activity. Sterol profiling of L. infantum revealed that Sb^VT4MPP ablated ergosterol production while accumulating cholestane-based sterols (e.g., cholesta-5,7,22-trien-3β-ol). Additional sterols appeared exclusively under Sb^VT4MPP treatment, accompanied by upregulated erg6, encoding sterol-C-24 methyltransferase (SMT), a key enzyme in sterol biosynthesis. Overexpression of ERG6 reduced Sb^VT4MPP potency, increasing the IC₅₀ by 2.5-fold, confirming ERG6's role in its mode of action. Disruption of ergosterol biosynthesis was indirectly confirmed through hypoosmotic shock assays, which indicated increased membrane fluidity in Sb^VT4MPP-treated Leishmania. In vivo studies revealed a 96 % reduction in parasite load, highlighting Sb^VT4MPP's efficacy in visceral leishmaniasis model. Since ERG6 is absent in mammals, it represents a selective and promising pharmacological target. Our findings position Sb^VT4MPP as a novel chemical entity with potent in vitro and in vivo antileishmanial efficacy, providing mechanistic insights and warranting further preclinical investigation as a promising drug candidate for leishmaniasis treatment.