Comparing the in vivo sonodynamic effects of dual- and single-frequency ultrasound in breast adenocarcinoma

Dual-frequency ultrasound has recently been shown to extensively enhance the acoustic cavitation yield in water. In this study, the in vivo antitumor effect of simultaneous, dual-frequency ultrasound at low-level intensity (I (SATA) = 2 W/cm(2) for 1 MHz and I (SATA) = 0.2 W/cm(2) for 150 kHz) in combination with an intravenous injection of 5 mg/kg hematoporphyrin (Hp) was investigated in a model of breast adenocarcinoma in Balb/c mice. Seventy-one tumor-bearing mice were divided into nine treatment groups: control, sham, Hp injection, and single- and dual-frequency sonication in the presence and absence of Hp. The tumor growth delay was then calculated based on the tumor volume at various times after treatment using the following parameters: relative volume percent, and times (to reach five and two times the initial volume), percent of tumor growth inhibition ratio, and survival period. Our results showed no significant difference between the 150 kHz and 1 MHz single-frequency groups when compared with the sham group after 9 days of treatment (p > 0.05). However, treatment with dual-frequency ultrasound significantly delayed tumor growth when compared with the sham group (p < 0.05) after 9 days of treatment. Furthermore, in vivo experiments showed that combined dual-frequency sonication controlled tumor growth more effectively than single-frequency sonication. Evaluation of the therapeutic effects of single- and dual-frequency ultrasound in sonodynamic therapy revealed that treatment with the combination of dual-frequency ultrasound and Hp resulted in a significant reduction in the relative volume percent of tumors after 3 days of treatment (p < 0.05) compared with the controls. Additionally, the T (5) time and the survival period in the group treated with the combination therapy was significantly longer than those in all the other groups (p < 0.05). These findings were further verified histopathologically. In conclusion, our results reveal that sonodynamic therapy using dual-frequency ultrasound is able to extend the survival time of animals compared with single-frequency sonication.