Inhibition effects of high mechanical index ultrasound contrast on hepatic metastasis of cancer in a rat model.

Rational And Objectives: The liver is the most common organ for tumor metastasis. The development of new methods to depress hepatic metastasis is of great importance in improving survival. The aim of this study was to observe the effects of high-mechanical index ultrasound contrast on hepatic metastasis of colorectal cancer.

Materials And Methods: Hepatic metastasis models were established by injecting human colon carcinoma LoVo cells into the spleens of Sprague-Dawley rats. The rats were divided into a control group, a microbubble plus ultrasound group, a simple ultrasound group, and a simple microbubble group. The ultrasound contrast agent SonoVue (1 mL/kg) was injected via the tail vein, and high-mechanical index ultrasound contrast (frequency, 1.5 MHz; mechanical index, 1.7) was performed on the spleen intermittently for 2 minutes. The animals were sacrificed after 10 days, and the sizes and number of hepatic metastases were measured and compared. Histologic pathology and splenic ultrastructure were observed.

Results: The number and sizes of hepatic metastases patently decreased in rats in the microbubble plus ultrasound group (P < .01). There were no obvious differences among the control group, simple ultrasound group, and simple microbubble group in hepatic metastases (P > .05). Histologic pathology showed that the number of tumor cells in the spleens decreased considerably, and massive necroses, hemorrhages, and thrombi were observed in the tumor and spleen tissues of rats in the microbubble plus ultrasound group. Transmission electron microscopy showed that the mitochondria of tumor cells and endothelial cells were clearly swelled, and there were gaps among endothelial cells and platelets aggregated in capillary vessels.

Conclusion: This research shows that intermittent high-mechanical index ultrasound contrast may inhibit the hepatic metastasis of cancer in a rat model.