Histotripsy-mediated reactive oxygen species generation in vitro

Forms of sonodynamic therapy rely on close interactions between microbubbles and agents to generate cytotoxic reactive oxygen species. Microbubbles are inherently intravascular agents, which limits the therapeutic range for effective distribution of reactive oxygen species. Histotripsy is a focused ultrasound therapy that ablates tissue via the generation of a dense cloud of bubbles spontaneously without the need for microbubbles. This study investigated the capacity of histotripsy to generate the hydroxyl radical with and without sonodynamic agents. In the absence of sonodynamic agents, histotripsy produced the hydroxyl radical at rate that was increased by a factor of three relative to other forms of therapeutic ultrasound. These sonochemical reactions were found to correlate strongly with acoustic emissions tracked with passive cavitation imaging. Histotripsy bubble activity was found to increase the rate of hydroxyl radical production for multiple sonosensitizers relative to controls, particularly for ultrasound pulses longer than 20 cycles (i.e., 20 μs) in duration. Overall, these data indicate histotripsy may be a viable approach for activating sonosensitve agents, and this activation may be tracked based on acoustic emission.