Progress in the development of nanosensitizers for X-ray-induced photodynamic therapy

[Display omitted] •X-ray-induced photodynamic (X-PDT) is a new approach to tackle deep tumors.•X-ray-induced sensitizers (XSs) are the key to X-PDT.•The development of XSs is discussed in four types based on different compositions.•X-ray dosages and therapeutic effects of different XSs are summarized.•Suggestions of improving XSs’ sensitizing efficiency are given. In recent years, photodynamic therapy has been applied in cancer treatment because of its high selectivity and marginal invasion properties. However, the excitation light used has limited ability to penetrate tissue, which creates a stumbling block for its future development. To overcome this, X-rays have been introduced to transmit energy to deeper tissues. Given that a large number of X-ray-induced sensitizers have been designed to facilitate X-ray excitation and generate reactive oxygen species (ROS), this has led to the concept of X-ray-induced photodynamic therapy (X-PDT). After 10 years of development, this treatment now shows good therapeutic effects as well as shortcomings. Going forward, it will be important to improve tumor targeting and a standard deep-seated tumor model should be established.