Engineered Exosome for Drug Delivery: Recent Development and Clinical Applications

Abstract

Exosomes are nano-sized membrane vesicles that transfer bioactive molecules between cells and modulate various biological processes under physiological and pathological conditions. By applying bioengineering technologies, exosomes can be modified to express specific markers or carry therapeutic cargo and emerge as novel platforms for the treatment of cancer, neurological, cardiovascular, immune, and infectious diseases. However, there are many challenges and uncertainties in the clinical translation of exosomes. This review aims to provide an overview of the recent advances and challenges in the translation of engineered exosomes, with a special focus on the methods and strategies for loading drugs into exosomes, the pros and cons of different loading methods, and the optimization of exosome production based on the drugs to be encapsulated. Moreover, we also summarize the current clinical applications and prospects of engineered exosomes, as well as the potential risks and limitations that need to be addressed in exosome engineering, including the standardization of exosome preparation and engineering protocols, the quality and quantity of exosomes, the control of drug release, and the immunogenicity and cytotoxicity of exosomes. Overall, engineered exosomes represent an exciting frontier in nanomedicine, but they still face challenges in large-scale production, the maintenance of storage stability, and clinical translation. With continuous advances in this field, exosome-based drug formulation could offer great promise for the targeted treatment of human diseases.

Keywords: clinical application; drug delivery; engineered exosomes; preparation strategy.

Figure 1

Image taken by transmission electron microscope showing exosomes isolated through ultracentrifugation. Those exosomes were obtained from the culture supernatant of J774A.1 cell, a mouse macrophage cell line, grown in Dulbecco’s Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum. The supernatant was collected and centrifuged at 300 g for 10 minutes to remove cell debris, followed by filtration through a 0.22 μm filter. The filtered supernatant was then centrifuged at 120,000 g for 70 minutes to pellet the exosomes. The exosome pellet was resuspended in phosphate-buffered saline (PBS) and loaded onto a copper grid coated with carbon film. The grid was stained with 2% uranyl acetate and examined under a transmission electron microscope. The image shows the morphology and size distribution of the exosomes, which appear as round or oval vesicles with a diameter for most of the exosomes ranging from 30 to 150 nm.

Figure 2

The biogenesis of exosomes. Cells generate small vesicular carriers through endocytosis, whereby the internalized vesicles coalesce to form early endosomes that progressively mature into late endosomes. As the late endosomal compartments produce abundant intraluminal vesicles (ILVs) through inward budding of the endosomal membrane, they transform into multivesicular bodies (MVBs) hosting ILVs within their lumen. Finally, these ILVs encapsulated in MVBs are secreted extracellularly as exosomes when the outer MVB membrane fuses with the cellular plasma membrane. Created with BioRender.com.

Figure 3

Schematic diagram showing the exogenous loading methods for preparing drug-loaded exosomes. The exogenous loading methods include drug co-incubation, ultrasonic incubation, electroporation incubation, saponin treatment, freeze-thaw cycles, extrusion, and transfection. Created with BioRender.com.

Figure 4

Clinical applications of drug-loaded exosomes. Engineered exosomes can deliver drugs or nucleic acids to target cells or tissues, modulating their biological functions and achieving therapeutic effects. Drug-loaded exosomes have been tested in preclinical or clinical trials for various diseases, such as liver diseases, cardiovascular diseases, cancer, immune system diseases, neurodegenerative diseases, and AIDS. Therefore, drug-loaded exosomes offer a novel and promising drug delivery system for a wide range of diseases.