Anti-Parasitic Activity of ssDNA-Aptamers Targeting the Poly(A)-Binding Protein in Leishmania donovani Promastigotes

Abstract

Background: Visceral leishmaniasis caused by Leishmania donovani still depends on a small group of drugs whose value is diminished by toxicity, cost and resistance, so targets specific to the parasite remain attractive. The cytoplasmic poly(A)-binding protein (PABP) of Leishmania governs mRNA stability and translation, processes on which these parasites lean heavily because they lack conventional transcriptional control. Aim: To evaluate the antiparasitic activity against L. ‎donovani promastigotes of two distinct PABP-targeting ssDNA aptamers complexed with Lipofectamine 2000, AP-7/LF and AP-11/LF. Methods: Growth inhibition was measured by the MTT assay at 24 and 48 hours, and PABP protein abundance was quantified by Western blot densitometry against a GAPDH loading control. Results: Both complexes inhibited promastigote growth in a concentration- and time-dependent manner, but AP-11/LF was the stronger agent throughout: its IC50 values were 234 nM after 24 hours and 194 nM after 48 hours against 1810 nM and 1300 nM for AP-7/LF, a difference of roughly 7.7-fold and 6.7-fold, respectively. The Western blot results followed the same ranking, as AP-11/LF lowered PABP to 0.51 of the untreated control (a 48.6% reduction, p = 0.001), whereas AP-7/LF lowered it to 0.67 (a 32.9% reduction, p = 0.018). The lipofectamine alone and the carrier-free aptamers produced only small, non-significant changes. Conclusion: The poly(A)-competitive aptamer (AP-11) outperformed the high-affinity, non-competitive aptamer (AP-7) at both the growth and the protein level, supporting PABP disruption as a workable starting point for antileishmanial drug development.