Acidic pH-Activated Gas-Generating Nanoparticles with Pullulan Decorating for Hepatoma-Targeted Ultrasound Imaging

Contrast-enhanced ultrasound (US) is a widely used imaging modality for hepatocellular carcinoma diagnosis. Mostly, US imaging is confined to the intravascular process because of the limitation of the microbubble contrast agent currently utilized. Targeted contrast agents that incline to accumulate in tumor tissue or tumor cells and enhance the US signal may advance the sensitivity of ultrasonography and exploit the dimension of US imaging of tumor at the molecular level. In this study, we developed CaCO3/pul-PCB (CPP) hybrid nanoparticles with hepatoma-targeting pullulan decorating on the surface through a mineralization route using the pullulan-graft-poly(carboxybetaine methacrylate) (pul-PCB) copolymer as a modifier. This particle was stable in blood physiological pH and generated echogenic CO2 bubbles under tumoral acidic conditions, which enabled the US signal enhancement. Upon intravenous injection, CPP hybrid nanoparticles accumulated efficiently in tumor tissue and exhibited sixfold contrast enhancement in 35 min at the tumor site in the hepatoma-bearing mice model. By contrast, there was barely any signal change in normal liver tissue. Therefore, the presented CPP hybrid nanoparticle is a promising contrast agent for effective US imaging of hepatoma.