Advances in targeted modification of extracellular vesicles

In recent years, exosomes have become a hotspot in biomedical research. In-depth studies have revealed their advantages as therapeutic drugs or carriers. Exosomes are natural, nanoscale extracellular vesicles that can regulate cell-cell communication. Their cargoes mainly include DNA, RNA, glycoproteins, peptides, and other bioactive substances. Due to their phospholipid bilayer structure, exosomes exhibit good cell compatibility, low immunogenicity, a strong capacity to transfer bioactive substances, high biocompatibility, and specific targeting properties, rendering them favorable for precision medicine applications. Current research is mainly focused on engineering exosomes to achieve drug delivery, immune regulation, and potential biomarkers for disease diagnosis and surveillance. Exosomes have complex extracellular uptake mechanisms. Cells mainly internalize exosomes via endocytosis or membrane fusion, thereby exerting biological effects. However, the mechanism of extracellular exosome uptake is not yet fully understood. Several studies have investigated cholesterol-conjugated aptamers based on the mediating proteins involved in endocytosis and developed exosome-liposome hybrid vesicles loaded with targeting peptides based on applicable modes of membrane fusion. Due to different extents of enrichment, exosomes from different origins have different regulatory effects on different tissues and cells. To enhance the targeting activity of exosomes to specific tissues or organs, multiple researchers have developed a method that modifies the surfaces of natural exosomes, enhancing their desired molecular targeting activity. Although the advantages and disadvantages of several targeting modification methods have been investigated, most methods involve altering the morphology and size of the original exosomes. The engineered targeted exosomes exhibit heterogenous morphology, and the effects of morphological changes on the biological functions of exosomes warrant further investigation. The main exosome modification methods currently being investigated can be classified as either biochemical or physical. Biochemical methods include those involving genetic engineering, metabolic engineering, "click chemistry", aptamer receptors, membrane peptide fusion, and peptide anchoring of CD63. Meanwhile, physical methods involve electrostatic interaction, hydrophobic interaction, magnetic guidance, ultrasonic guidance, and metal nanoparticle modification. The operational procedures used for the physical modification of targeted exosomes are relatively simple; however, the modification efficiency is low and unstable. Conversely, a high efficiency is achieved when exosomes are modified by biochemical methods; however, the operational procedures required for these methods are relatively difficult. These engineering methods are not independent, and the exosome modification process used may involve multiple methods. The modified exosomes are more enriched in target tissues and organs and have significantly better therapeutic effects than natural exosomes. However, when the same modification method is used on exosomes of different origins, the resulting engineered exosomes can exhibit different biological functions. Standardized exosome surface-targeted modification integrated with drug delivery may become a mainstream component of precision medicine research in the future. This article elaborates on the biogenesis process and extracellular uptake of exosomes and reviews exosometargeted modification methods. Furthermore, research progress in the field of exosome-targeted modification methods is summarized, and potential application prospects of exosometargeted modification are discussed.