Investigation into the binding domains of platelet factor 4 unlocks new avenues for the design and synthesis of selective sulfated pseudo-tetrasaccharide aminoglycoside ligands.

Platelet factor 4 (PF4) is a natural chemokine that binds to negatively charged glycosaminoglycans (GAGs), including the anticoagulant heparin. The formation of the PF4-heparin complex elicits an immune response that results in platelet activation, leading to serious thrombotic complications. This study explores the structure-activity relationships (SAR) of sulfated pseudo-tetrasaccharide aminoglycoside ligands. The binding interactions of these synthetically designed compounds with heparanase (HPSE) and PF4 were systematically elucidated. Through computational design, a library of sulfated aminoglycoside ligands was synthesized in 10-13 steps from readily available paromomycin and neomycin. The SAR studies revealed that hydroxyl-capped ligands interacted with the fondaparinux-binding domain of PF4, while hydrophobic-capped ligands bound to the heparin-binding domain. Notably, steric hindrance imposed by hydrophobic groups impedes the binding of the ligands to PF4's shallow binding site. In contrast, these hydrophobic-capped ligands demonstrated a strong binding affinity for HPSE. The most selective ligands reduced the viability of HPSE-overexpressing cancer cells, highlighting their potential efficacy in modulating the enzymatic activity of HPSE. This SAR study provides a foundational framework for the design of sulfated aminoglycoside-based therapeutics with minimized adverse effects associated with PF4.