To investigate the effect of treatment with ultrasound-stimulated microbubbles (USMB) for different durations in enhancing blood perfusion in MC38 tumors in mice, and to analyze the underlying mechanism preliminarily.

A total of 54 tumor-bearing mice with MC38 tumor cells implanted subcutaneously on the inner thigh were selected and treated by microbubble cavitation stimulated using the VINNO US system in Vflash mode (mechanical index=0.3). The mice were randomly divided into 6 groups according to the treatment duration, with 9 mice in each group: Group A, t=1 min; Group B, t=3 min; Group C, t=5 min; Group D, t=7 min; Group E, t=10 min; Group F (control group), no ultrasound therapy. Contrast-enhanced ultrasound examinations were performed before and after treatment for each group, and tumor perfusion was evaluated comprehensively by peak intensity (PI) ratio, area under curve (AUC) ratio, and tumor perfusion area ratio before and after treatment.Two mice in each group were randomly selected to take tumor tissues for HE staining to observe the pathological changes after treatment. The remaining 7 mice in each group were collected for the determination of nitric oxide (NO) content.

After ultrasonic stimulation, the PI ratio, AUC ratio, and perfusion area ratio in Groups C, D, and E were significantly higher than those of the control group (P<0.05). Group D had the highest PI ratio and AUC ratio, which were significantly higher than those of Groups C (P<0.05), B (P<0.05), and A (P<0.01), and the perfusion area ratio in Group D was higher than those of Groups A (P<0.01) and B (P<0.05). The pathological results showed that the tumor microvessels in Groups C, D, and E were dilated and congested, with the number of dilated microvessels being most and congestion being most obvious in group D. The content of NO in tumor tissues of each group undergoing ultrasound therapy was higher than that of the control group. The content of NO in group D was the highest, but there was no significant difference among the groups (P>0.05).

Ultrasound-stimulated microbubbles can enhance blood perfusion of MC38 tumors in mice, and the enhancement effect is more obvious when the ultrasound treatment time is extended to more than 5 minutes. The best enhancement effect of tumor blood flow can be achieved when the ultrasound treatment time is 7 minutes. The therapeutic mechanism may be related to microvascular dilatation caused by ultrasound-stimulated microbubbles.