Inhibitors of Serine Acetyltransferase Induce Lethality in <i>Entamoeba histolytica</i> and <i>Leishmania donovani</i>

The limited efficacy and emerging resistance to current antiamoebic agents highlight the urgent need for new therapies. Serine acetyltransferase isoform 3, essential for cysteine biosynthesis in <i>Entamoeba histolytica</i>, plays a crucial role in cellular survival and pathogenicity, making it a promising drug target. We performed structure-guided virtual screening of 1.35 million compounds using ligand-based pharmacophore modeling and molecular docking, identifying ten top inhibitors with distinct binding poses in the enzyme's elongated active site. Group I and II compounds occupied both the serine- and CoA-binding pockets and showed potent inhibition (IC₅₀: 9-18 μM). Group III compounds, binding only the serine site, showed modest activity, while Group IV compounds exhibited strong enzymatic and cellular inhibition despite similar binding, indicating effective single-site targeting. Molecular dynamics confirmed binding stability. Eight compounds inhibited <i>E. histolytica</i> growth, with four fully suppressing parasite growth. Notably, Group IV compound F0473-0289 also targeted <i>Leishmania donovani</i> with minimal mammalian THP-1 cell toxicity, highlighting its potential as a selective and safe antiparasitic lead.