Sonodynamic and chemodynamic therapy based on organic/organometallic sensitizers

Reactive oxygen species (ROS) are a type of active species in body, and can participate in the process of tumor development under the condition of oxidative stress, which can lead to the apoptosis of cancer cells through a variety of different mechanisms. Photodynamic therapy (PDT) is a novel method of treating tumor with photosensitive drugs and laser activation. However, PDT suffers from the poor penetrating depth of tissue of excitation light. By comparison, sonodynamic therapy (SDT) adopts high-penetrating sound waves to trigger the ultrasound-responsive materials called sonosensitizers for the treatment of cancer by different mechanisms such as ROS, ultrasound response cavitation, and thermal effects. The efficiency of SDT is bound up with molecular structures and performances of sonosensitizers, which has promoted the design of sonosensitive agents and their development in various biological fields. In clinical treatment, regulating the tumor microenvironment offers a door and new ideas for effective tumor treatment. For tumor microenvironment (TME) involving pH values, excessive production of hydrogen peroxide, scientists have designed and synthesized many nanomaterials to produce hydroxyl radicals ([rad]OH) for tumor chemodynamic therapy (CDT) through Fenton and Fenton-like reactions. Many studies have indicated that its therapeutic efficiency is associated with the increase of [rad]OH production in situ of the tumor. Many approaches based on Fenton reaction have been used to improve the production of [rad]OH, including the choice of nanomaterials and the adjustment of the microenvironment. In view of the above two new treatment methods, this article summarizes, discusses and enlightens the SDT-related sonosensitizers and CDT-related nanomaterials in recent years, and discusses their applications and potential challenges.