Sonodynamic therapy

Sonodynamic therapy involves the use of drugs that only become cytotoxic upon exposure to ultrasound. Since ultrasound can be focused into small tissue volumes within the body, it provides a means of localizing treatment and reducing the risk of toxic side-effects elsewhere in the body. In this respect it is similar to photodynamic therapy, which uses light for drug activation, and there are several drugs that have been shown to be sensitive to both light and sound. The main advantage of sonodynamic over photodynamic therapy is the much greater tissue depth that can be reached non-invasively by ultrasound compared to light. Sonodynamic therapy involves the use of drugs that only become cytotoxic upon exposure to ultrasound. Since ultrasound can be focused into small tissue volumes within the body, it provides a means of localizing treatment and reducing the risk of toxic side-effects elsewhere in the body. In this respect it is similar to photodynamic therapy, which uses light for drug activation, and there are several drugs that have been shown to be sensitive to both light and sound. The main advantage of sonodynamic over photodynamic therapy is the much greater tissue depth that can be reached non-invasively by ultrasound compared to light. Upon activation, sonodynamic therapy drugs or “sonosensitisers” produce reactive oxygen species (ROS) that generate the cytotoxic effect. The detailed mechanisms of ROS production are not fully understood but several studies have indicated that acoustic cavitation and the associated thermal, chemical or luminescence phenomena may be involved. Cytotoxicity has been shown to be significantly increased in the presence of cavitation nuclei such as microbubbble ultrasound contrast agents, particularly when these are loaded with oxygen. Sonodynamic therapy has been shown to be effective in the treatment of tumours in a range of in vitro and in vivo studies and is also being explored for other applications including as an antimicrobial treatment. There have been a limited number of clinical trials to date.