Growth Inhibition Of Subcutaneous VX₂ Tumor By Using Microbubble Enhanced Ultrasound Cavitation

Background:Tumor angiogenesis is critical and essential in tumor growth and metastasis. Once the neovasculature is builded up to provide enough nutrition, tumor growth would become inevitable. Anti-angiogenesis therapy has been accepted as an new anti-tumor strategy. Nowadays, almost all of the anti-angiogenesis approaches take advantage of using chemical or biological drugs to attack specific receptor targets on angiogenesis. It is featured with insufficient therapeutic effect and some side-effects.This study is based on our previous findings that MBs enhanced ultrasound cavitation could selectively disrupt the microvasculature of rabbit VX2 tumor resulting in tumor circulation blockage.Objective:The purpose of this study is to investigate effects of MBs enhanced ultrasound cavitation on tumor growth and metastasis inhibition in a VX2 tumor model of rabbit.Materials and Methods:(1) Materials:Therapeutic ultrasound instrument: specific designed pulsed focused ultrasound (PFUS) devices, with the transducers frequency of 1.2 MHz, adjustable duty cycle and peak acoustic pressure.Diagnostic ultrasound imaging system: GE Logiq 9 ultrasound system, 9L probe, eligible to perform contrast enhanced ultrasonography (CEUS) with low MI. Microbubbles: Zhifuxian, a perfluoropropane filled lipid MB, with bubbles concentration of 4~9×109/ml, average 2μm in diameter, and 98% of the MBs less than 8μm in diameter.(2) Methods: Thirty New Zealand white rabbits bearing subcutaneous VX2 tumor were randomly divided into 3 groups for the impact factors including microbubbles (MB) and ultrasound (US). Pulsed focused ultrasound was delivered directly to the tumor surface for 10 minutes during intravenous infusion of microbubbles in the experimental (US+MB) group. The two control groups were applied with either ultrasound exposure (US) or saline injection (SHAM). The procedure was repeated every 72 hours until the 30th day. Contrast enhanced US and grey scale ultrasonography were acquired after every treatment to get the tumor perfusion images, size and volume measurements.At the end of the experiment, gross inspection and counting of tumor metastatic lesions at lung, liver, kidney and pelvic lymph nodes were performed following the animal sacrifice. The VX2 tumor metastasis was classified into 0-3 grade according to the counting number of meatastic lesions.Results:The average tumor volume of the US+MB, US, and the SHAM groups at the baseline were 0.4±0.2cm3,0.6±0.3cm3,0.5±0.2cm3 respectively. It grew to 4.5±3.1cm3,35.1±46.7cm3,48.2±44.3cm3 within a 30d experimental period, respectively. The average tumor volume of the US+MB group was significantly smaller than that of the two control groups at the end of experiment(P﹤0.05). The VX2 tumor metastatic counting also showed significant declines at lung and kidney in the experimental group(P﹤0.05). Conclusions:Multiple MBs enhanced ultrasound cavitation therapy can induce growth inhibition of VX2 tumor. It is also able to reduce VX2 tumor metastasis in lung and kidney.