Extracellular vesicles: An advanced delivery platform for photosensitizers in tumor photodynamic therapy

Photodynamic therapy (PDT) has demonstrated great advantages in increasing the significant advantages in enhancing the efficacy of solid tumor treatment and minimizing side effects. In PDT, Photosensitizers (PSs), which selectively accumulate at tumor sites under specific light conditions, interact with oxygen to generate reactive oxygen species (ROS), inducing apoptosis, DNA damage and immune response. However, drawbacks of PSs such as poor solubility, aggregation and off-target effects have necessitated the development of safe and efficient delivery platforms. Over the past decade, biomimetic drug delivery systems (BDDSs) have gained widespread use for delivering therapeutic drugs including PSs. Extracellular vesicles (EVs), naturally occurring liposome-like bilayer structured nanoparticles released by cells with prolonged circulation time, immune evasion capability and tumor homing ability offer promising potential as natural delivery systems for PSs due to their role in intercellular communication and biomolecule transport. Here, we provide an elaborate discussion on the concept and characteristics of EVs along with methods for their isolation and purification. Additionally, we summarize the advantages of EVs as nanocarriers for tumor treatment while exploring strategies to enhance targeting efficiency. Furthermore, we focus on efficient delivery approaches utilizing different sources of EVderived PSs. Lastly, this review also presents future perspectives on utilizing EVs as a platform for PSs delivery in oncology treatment. We anticipate that this comprehensive review will serve as a catalyst towards further utilization of PDT in oncology.