A pH-responsive PEG coating strategy for enhancing the enrichment of small extracellular vesicles towards disease regions with acidic microenvironment

The clinical translation of small extracellular vesicles (sEVs) as nanocarriers and therapeutic agents is severely hindered by their rapid clearance, leading to significant off-target effects. Polyethylene glycol (PEG) coating of sEVs provides a straightforward approach to address this challenge, yet it compromises their cellular internalization. To overcome this issue, we developed an acid-responsive PEG coating strategy for sEVs using 2,5-dihydroxy-4-methyl-2,5-dioxo-3-furanpropanoic acid (CDM)-modified methoxy PEG (mPEG-CDM). Western blot analysis and cellular uptake studies demonstrated that mPEG-CDM anchors to sEV membrane proteins through acid-labile cis-aconityl bonds, significantly reducing macrophage-mediated phagocytosis under physiological conditions, while restoring cellular internalization in endothelial cells (bEnd.3) and tumor cells (GL261) under weakly acidic conditions. <i>In vivo</i> imaging revealed that mPEG-CDM-modified sEVs, derived from glioma cells (GsEVs) and induced pluripotent stem cells (IsEVs), selectively accumulated in glioma tumor sites and ischemic brain regions in orthotopic glioma and stroke mouse models, respectively. Furthermore, <i>in vivo</i> studies demonstrated enhanced anti-tumor efficacy of GsEVs as drug carriers for glioma therapy and improved angiogenesis in ischemic stroke using IsEVs. Overall, this pH-responsive PEG coating strategy provides an effective approach for passive enrichment and offers valuable guidance for the design of surface-engineered sEVs in disease therapy.