Photodynamic Therapy of Hypoxic Tumors with Ir(III) Complexes

Photodynamic therapy has become a new method to treat cancer because of noninvasive, controllable features and less drug resistance compared with chemotherapy. The photo-sensitization pathway involves the photoactivation of molecular oxygen by photosensitizer. However, due to the hypoxic environment of solid tumors, the photodynamic therapeutic effect of traditional photosensitizers is severely suppressed. Metallic Ir(III) complexes exhibit excellent photo-physical and photo-chemical properties which make them ideal next-generation photosensitizers for photodynamic therapy. It has been reported that some novel Ir(III) complexes show excellent photodynamic therapy effect towards hypoxic tumors. In this review, we focus on the recent studies on the application of Ir(III) complexes to photodynamic therapy under hypoxia. Furthermore, the applications of Ir(III) complexes containing nanocomposite system for hypoxic photodynamic therapy are also summarized, with the hope to provide guidance for the development of novel and efficient photosensitizers for hypoxic tumor.