Ultrasound Nano-Scale Phase Change Contrast Agent for Hepatocellular Carcinoma Radiosensitization
Authors:   , Falatah Hebah A. , Eisenbrey John Robert , Wheatley Margaret A. 
Published: November 2023

The purpose of this study was to develop and characterize nano-scale phase change droplets less than 200 nm from commercially available ultrasound contrast agents and demonstrate their ability to enhance hepatocellular carcinoma (HCC) radiosensitization, which is critically needed to enhance the poor outcomes (two years survival < 50%) of current HCC radiotherapy treatments. Primary liver cancer is the third cause of cancer death worldwide with 906,000 new cases and 830,000 deaths annually. Of these, 75-85% of patients present with hepatocellular carcinoma (HCC), while the remaining 15-25% are intrahepatic cholangiocarcinoma and other types. Due to the late clinical presentation of the disease and treatment limitations of chemotherapy and immunotherapies, HCC has a poor prognosis. Localized radiotherapy in the early and mid-stages of HCC has shown some success in treatment response 25-50%. In such therapy, the hepatic artery supplying blood to the cancer is injected with radioisotope yttrium-90 (Y90), a beta particle emitter that provides localized radiation therapy. Another therapeutic option is external beam radiation (XRT) with MRI or CT guidance. XRT has been used cautiously in HCC treatment due to the radiosensitivity of liver tissue and technological limitations. Fractionated approaches are used to overcome the toxicity to the liver or radiation-induced liver diseases caused by high doses of radiation. The result of these limitations is that the overall five years survival for HCC patients in the United States is 20%, and the two years survival is less than 50%. Therefore, developing more effective HCC treatments is essential to improve patient outcomes. In recent years, researchers have been exploring a variety of radiosensitizers as a means of overcoming radiotherapy resistance. One promising radiotherapy enhancement mechanism is ultrasound-mediated microbubble destruction, which has been shown to sensitize solid tumors to radiotherapy through endothelial cell disruption in tumors. Ultrasound microbubbles have a diameter between 1 to 8 (micrometers) [mu]m and consist of a high molecular weight gas encapsulated by a lipid, protein, or polymer shell. However, the relatively large size of the bubbles prevents them from passing into extravascular spaces, and as a result researchers have developed phase-change contrast agents (PCCAs). PCCAs contain a low boiling point such as -37oC liquid in place of the usual gas and can transition from the liquid to the gaseous state under external stimuli. This technology has been widely used in ultrasound medical imaging, vascular occlusion, and cavitation activity enhancement. The small diameters < 400 nm of these PCCAs allow them to diffuse and accumulate in solid tumors via the enhanced permeability and retention effect before the phase transition. Using ultrasound as an acoustic stimulus can provide local vaporization as well as cavitation of the resultant microbubble, thereby generating local force in tumor tissues. The development and characterization of sub-micrometer (< 200 nm diameter) phase change droplets from commercial ultrasound contrast agents, including their ability to decrease tumor vascularity and enhance cell apoptosis are described in addition to their ability to enhance HCC tumor radiosensitization.