Re-sensitization of antimony-resistant Leishmania by highly potent SbV-porphyrin through the involvement of ERG6-coding gene

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.