Visceral leishmaniasis caused by Leishmania donovani is still a life-threatening disease with limited therapeutic options. The poly(A)-binding protein (PABP) is essential for post-transcriptional gene regulation in trypanosomatids and represents a parasite-privileged drug target. To comparatively evaluate two mechanistically distinct PABP-targeting ssDNA aptamers, AP-11 (poly(A)-competitive) and AP-7 (non-competitive), complexed with Lipofectamine 2000 against L. donovani amastigotes. Growth inhibition was assessed by MTT assay in amastigotes at 24 and 48 hours. Cytotoxicity was determined for selectivity index calculation in the RAW 264.7 cell line (Macrophage). PABP expression was demonstrated by western blot in both axenic culture and intracellular amastigote models. AP-11/LF demonstrated 4-6-times greater potency than AP-7/LF (IC₅₀: 130/80 nM versus 550/460 nM at 24/48 h). Both complexes exhibited favorable selectivity indices (47-84). AP-11/LF depleted PABP by >93% in axenic culture and about 80% in intracellular amastigotes (p < 0.01), whereas AP-7/LF produced moderate, inconsistently significant reductions (45-50%). Functional disruption of the PABP–poly(A) interaction, rather than binding affinity alone, determines antiparasitic potency, validating PABP as a pharmacologically tractable antileishmanial target. Remarkably, this is the first in vitro experimental study to demonstrate that aptamers targeting the PABP complexed with lipofectamine 2000 exert direct anti-leishmanial activity at both the axenic culture and intracellular levels.
