Sonodynamic therapy using protoporphyrin IX encapsulated microbubbles inhibits tumor growth

Sonodynamic therapy is a cancer treatment using drugs called “sonosensitizers” which, upon exposure to ultrasound (US), generate reactive oxygen species (ROS), thereby causing cell death. Despite the potential of sonodynamic therapy, many ideal sonosensitizers, such as protoporphyrin IX (PpIX), are hydrophobic compounds; poor water solubility limits systemic delivery and constrains clinical translation. We hypothesized that a PpIX-loaded lipid microbubble (MB) would have advantages over PpIX alone by ultimately allowing systemic delivery and also by locally concentrating US energy for greater PpIX activation. Accordingly, we developed an efficiently PpIX-loaded MB formulation and characterized its US-induced cytotoxicity in vitro and in an in vivo tumor model.