Recent advances in organelle-targeted organic photosensitizers for efficient photodynamic therapy

Photodynamic therapy (PDT) is a long known, FDA approved, and highly promising therapeutic modality, which is still developing. Photosensitizers (PSs) are at the core of PDT action and a worldwide effort has been put to develop PSs having multiple functionalities. In the design of new generation PSs, an attractive approach is to target organelles to get an exceptional therapeutic outcome as damaging these vital subcellular compartments improve the photocytotoxic effect of the PSs. To this end, small molecule organic PSs are suitable candidates due to ease of chemical modification, which allows simple implementation of the organelle targeting units on the PS structure. Furthermore, they hold unique characteristics such as low dark toxicity, high reactive oxygen species (ROS) generation capacity, biocompatibility, and tunable photophysical and photochemical properties. Accordingly, a wide variety of organelle-targeted organic PSs have been developed and proved to be highly successful both in therapeutic action and bioimaging applications. In this review article, we have summarized the recent advances in organelle localizing organic-based PSs by discussing the design principles, organelle targeting strategies and related bio-applications in detail. PSs targeting seven different organelles have been included. We have also highlighted the current challenges and gave a comprehensive outlook for the future of organelle-targeted PSs.