Influence of Phase Change Droplet Activation and Microbubble Cavitation on the Microenvironment of Hepatocellular Carcinoma.

OBJECTIVE: Both microbubble ultrasound contrast agents and acoustic phase change droplets (APCD) have been explored in hepatocellular carcinoma (HCC). This work aimed to evaluate changes to the HCC microenvironment following either microbubble or APCD destruction in a syngeneic pre-clinical model. METHODS: Mouse RIL-175 HCC tumors were grown in the right flank of 64 immunocompetent mice. Pre-treatment, photoacoustic volumetric tumor oxygenation, and power Doppler measurements were obtained using a Vevo 3100 system (VisualSonics, Toronto, Canada). The experimental groups received a 0.1 mL bolus injection of either Definity ultrasound contrast agent (Lantheus Medical Imaging) or APCD fabricated by condensing Definity. Following injection, ultrasound destruction was performed using flash-replenishment sequences on a Sequoia with a 10L4 probe (Siemens) for the duration of enhancement. Tumor oxygenation and power Doppler measurements were then repeated immediately post-ultrasound treatment. Twenty-four hours post-treatment, animals were euthanized, and tumors were harvested and stained for CD31, Cleaved Caspase 3 and CD45. RESULTS: Imaging biomarkers demonstrated a significant reduction in percent vascularity following either microbubble or APCD destruction in the tumor microenvironment ( p < 0.022) but no significant changes in tumor oxygenation (p = 0.12). Similarly, immunohistochemistry data demonstrated a significant decrease in CD31 expression (p < 0.042) and an increase in apoptosis (p < 0.014) in tumors treated with destroyed microbubbles or APCD relative to controls. Finally, a significant increase in CD45 expression was observed in tumors treated with APCD (p = 0.046), indicating an increase in tumor immune response. CONCLUSION: Ultrasound-triggered destruction of both microbubbles and APCD reduces vascularity, increases apoptosis, and may also increase immune response in this HCC model.

Activation of Phase Change Contrast Agents Using Ionizing Radiation.

The feasibility of activating phase change contrast agents (PCCA) made from Definity (Lantheus Medical Imaging) using X-rays was investigated. A 10 mL of Definity PCCA (0.1 mL PCCA/mL) were injected into gelatin phantoms and irradiated using doses of 0, 30, 50, and 100 Gy. Size distribution and PCCA activation were measured after irradiation. Definity PCCAs were activated at a threshold of 50 Gy. Changes were visible with microscopy, visual inspection of T-flasks, and ultrasound imaging of gelatin phantoms. Moreover, increasing the radiation dose above 50 Gy appeared to further activate PCCA. These results indicate Definity PCCAs may be useful for ultrasound-based radiation dosimetry.