Efficacy enhancement of folate-receptor targeted phasetransition contrast agent for HIFU ablation of tumor in vivo

Abstract

Objective To explore the value of Folate-receptor targeted phaseransition nanoparticle contrast agent (FR-PNPCA) in increasing efficacy of high intensity focused ultrasound (HIFU) ablation of xerograft tumor in vivo. Methods Firstly, the FR-PNPCA and non-targeted phasetransition nanoparticle contrast agent (PNPCA) were prepared by a two-step emulsification method respectively. Then 36 nude mice bearing xerograft ovary tumor were randomly divided into 3 groups and underwent HIFU ablation respectively. Group A was the control group, which was irradiated at 2 h after the injection of saline by the tail vein. Group B was the untargeted group, which was irradiated at 2 h after the injection of PNPCA. Group C was the targeted group, which was irradiated at 2 h after the injection of FR-PNPCA.The gray-scale changes of irradiating areas in tumors were observed during ablation. Some mice were sacrificed at 1 h after ablation and the tumors were resected to observe the coagulative necrosis by TTC staining and HE staining. Lastly, The remain mice were sacrificed at 24 h after ablation, and the tumor sections were analyzed with immunohistochemical method including PCNA and TUNEL to explore the effect of HIFU ablation on tumor cell proliferating and necrosis. Results Obvious gray-scale changes could be seen in all tumors in group B and C immediately after HIFU irradiation, but almost no changes were founded in group A. The differences of gray-scale change values and squares between group B and C were statistically significant (P<0.05). Coagulative necrosis with irregular shape and clear boundary was observed in group B and C after irradiation, and the range of necrosis in group C was much larger than that in group B (P<0.01), but little necrosis was founded in group A. In addition, the differences of proliferating rate and necrosis rate between group B and C were statistically significant (P<0.05). Conclusions FR-PNPCA can not only significantly enhance the efficacy, but also can help monitoring the process during HIFU ablation of tumor ablation. Therefore, it is a promising synergistic agent for HIFU ablation. Key words: High-intensity focused ultrasound; Microbubbles; Nanoechnology; Folate-receptor