The Role of Exosomes as Endogenous Nanocarriers for Targeted Drug Delivery: Isolation, Engineering, and Clinical Progress in Neurological and Other Diseases

Exosomes are extracellular vesicles that carry a variety of biomolecules, including nucleic acids, proteins, and lipids, and they play a vital role in intercellular communication. These endogenous carriers offer several advantages over conventional nanocarriers, such as liposomes. These advantages include high biocompatibility, low immunogenicity, and the ability to cross biological barriers such as the blood-brain barrier, making them a promising platform for targeted drug delivery. In this review, we systematically summarize the biological characteristics of exosomes, methods for their isolation and purification, strategies for drug loading (including endogenous and exogenous approaches), and surface engineering techniques (such as genetic engineering and chemical modification) to enhance targeting and therapeutic efficacy, based on a comprehensive PubMed literature search. We particularly focus on the modification of engineered exosomes as drug delivery systems in various clinical contexts, covering multiple diseases including cancer, diabetes, neurological diseases, cardiovascular diseases, and tissue repair. Administration routes include oral, subcutaneous, intranasal, and intravenous delivery. While exosomes have shown promise in preclinical studies, challenges remain in terms of large-scale production, standardized isolation, drug loading efficiency, and safety evaluation. Herein, we aim to provide a theoretical foundation and suggest future directions for developing exosomes as a next-generation drug delivery platform.