Abstract
Acoustic cavitation is a typical non-thermal phenomenon induced in liquids and biotissues exposed to ultrasound. Its effects may be useful for therapeutic purposes if properly controlled. Techniques for promotion and suppression of acoustic cavitation will provide such controlling methods. We have been pursuing acoustical and chemical approaches. As chemicals for reducing cavitation threshold, we found that certain photosensitizers, such as rose bengal, in xanthene family are effective both in water and murine liver. They also act as sensitizers of cavitational effects. One of our research targets is applying these chemicals to cancer treatment. However, such xanthenes have poor affinities with tumor tissues. As an approach to obtain xanthenes with improved affinities with tumor tissues, we synthesized amphiphilic rose bengal derivatives. We previously reported that a derivative with incorporated alkyl groups as the lipophilic group and carboxilic group as the hydrophilic group showed significantly increased affinities with subcutaneously-implanted murine tumor tissues while maintaining its ability to reduce cavitation threshold in water. We this time investigated the anti-tumor effect on subcutaneously-implanted murine tumor induced by ultrasound exposure (0.5 MHz and 1.0 MHz, 15 W/cm^2 each) with and without the new derivative. Significant synergistic effects of ultrasound and the derivative were observed. To ensure the effects are sonochemical ones, we measured the temperature rise in tumor tissues during the ultrasound exposure. We also measured the sub-harmonic emissions from tumor tissues. Results suggested that the synergistic effects are due to sonochemical mechanism rather than thermal one.
