Chemotherapy Augmentation Using Low-Intensity Ultrasound Combined with Microbubbles with Different Mechanical Indexes in a Pancreatic Cancer Model

Abstract

The aim of the study was to explore the optimal mechanical indexes (MIs) for low-intensity ultrasound (LIUS) combined with microbubbles to enhance tumor blood perfusion and improve drug concentration in pancreatic cancer-bearing nude mice. Fifty-four nude mice bearing bilateral pancreatic tumors on the hind legs were randomly divided into three groups (the MI was set at 0.3, 0.7 and 1.1 in groups A, B and C, respectively). Five nude mice in each group were intravenously injected with the fluorescent dye DiR iodide (DiIC18(7),1,1′-dioctadecyl-3,3,3′,3′-tetramethylindotricarbocyanine iodide); for each mouse, one tumor was treated with LIUS combined with microbubbles, and the contralateral tumor was exposed to sham ultrasound. In vivo fluorescence imaging was performed to detect the enrichment of intratumoral DiR iodide. Twelve mice in each group were intravenously injected with doxorubicin (DOX) and underwent ultrasound therapy as described above. Tumor blood perfusion changes were quantitatively evaluated with pre- and post-treatment contrast-enhanced ultrasound (CEUS, MI = 0.08). One hour after the post-treatment CEUS, nude mice were sacrificed to determine the DOX concentration in tumor tissue; one mouse in each group was sacrificed after ultrasound treatment for tumor hematoxylin–eosin staining examination. CEUS quantitative analysis and in vivo fluorescence images confirmed that LIUS at MI = 0.3 combined with microbubbles was able to enhance tumor blood flow and increase regional fluorescence dye DiR iodide concentration. The DOX concentration on the therapeutic side was significantly higher than that on the control side after ultrasound-stimulated (MI = 0.3) microbubble cavitation (USMC) treatment (1.45 ± 0.53 μg/g vs. 1.07 ± 0.46 μg/g, t = –5.163, p = 0.001). However, in groups B and C, there were no significant differences in DOX concentration between the therapeutic and control sides (Z = –0.297, –0.357, p = 0.766, 0.721). No hemorrhage or other tissue damage was observed in hematoxylin–eosin-stained tumor specimens of both sides in all groups. LIUS at MI = 0.3 combined with microbubbles was able to enhance tumor blood perfusion and improve local drug concentration in nude mice bearing pancreatic cancer.