Active targeting of nano-photosensitizer delivery systems for photodynamic therapy of cancer stem cells

Cancer stem cells are believed to be the basis for tumor initiation, development, metastasis and recurrence; are resistant to most traditional therapies (e.g., chemotherapy and radiotherapy); and have the ability to self-renew, proliferate and differentiate. Photodynamic therapy may be a promising novel treatment for drug-resistant cancer stem cells because of the selectivity of the photosensitizer. One of the most important issues to overcome in photodynamic therapy is the photosensitizer-targeted delivery to tumor cells, especially cancer stem cells. Nano-photosensitizers comprising molecular photosensitizers and water-dispersible nanocarriers with or without moieties possessing the ability for specific binding to cancer cells or cancer stem cells are a promising strategy for active targeted photosensitizer delivery and photodynamic therapy-targeted therapy of tumors. In this review, we highlight current and future prospects for potential strategies based on nanoscience and nanotechnology for nano-photosensitizer-targeted delivery in the photodynamic therapy treatment of cancer cells, especially cancer stem cells.