Passive and Active Tumor Targeting in Photodynamic Therapy of Cancer: Mini-Review

Photodynamic therapy (PDT) is a minimally invasive treatment procedure that utilizes a light of specific wavelength and a chemically nontoxic drug photosensitizer (PS) to generate reactive oxygen species (ROS) that can selectively destroy cancer cells or other targeted tissues. However, to increase the efficiency and application of PDT, several issues still need to be resolved. One of the main challenges in PDT is ensuring that the photosensitizing agent accumulates specifically in cancer cells and not in healthy tissues. This is particularly challenging for solid tumors, which have a complex microenvironment and poor vascularization. Passive and active targeting are two strategies in PDT that aim to improve treatment outcomes by enhancing the selective accumulation of PS in tumors thereby improving the cancer therapeutic outcome. These strategies play a critical role in optimizing the efficacy and safety of PDT for cancer treatment. Passive and active targeting strategies have their advantages and limitations. In this mini-review, we focus on the advantages and disadvantages of each method and discuss the role of stimuli-responsive changes in PS delivery.