Off-TargetInteractions of Vancomycin with VascularWall Involving Elastin-Induced Self-Assembly

Off-target effects, which arise from drug interactions in nontarget tissues, can lead to unfavored side effects. The treatment efficacy of vancomycin (Vanco) in Gram-positive bacterial infections is often compromised by the frequent occurrence of Vanco-induced vascular injury. However, the potential targets and underlying molecular mechanisms of this phenomenon remain unclear. Here, we developed multidimensional two-photon imaging for dynamic tracking of fluorescently labeled Vanco in vivo, characterizing the molecular behavior of Vanco in situ after administration and providing the first direct evidence of its interactions with vascular wall. Morphological analysis combined with colocalization imaging identified elastin within the vascular wall as the molecular target. After binding, Vanco underwent self-assembly into forming irregular nanoaggregates, primarily driven by electrostatic and hydrophobic forces. This persistent binding and self-assembly on the elastic lamina resulted in significant endothelial cytotoxicity and subsequent apoptosis, suggesting a mechanistic link to the vascular injury observed in clinical settings. Taken together, our findings revealed off-target molecular interactions between Vanco and vascular elastin in situ, highlighting the importance of considering unintended drug–vascular interactions.