Investigation Of Dual Fluorescence-ultrasound Nanobubbles In A Mouse Tumor Model

Ultrasound contrast agents are gas-filled micro-or nano-bubbles with a stabilizingshell made from a variety of materials such as polymer, protein or lipid. Besidesdiagnostic imaging, ultrasound contrast agents have also been used for targeted gene ordrug delivery in tumors. Clinically, biocompatible microbubbles have now becomeindispensable for vascular imaging. However, due to the large size, microbubbles posesevere limitations in tumor-targeted imaging. Recently, nanobubbles with size below500nm demonstrate great potential to penetrate tumor blood vessel pores through EPR effects.Unfortunately, nanobubbles reported so far have not displayed effective tumor-selectiveimaging over non-targeted organs such as liver.In this study, mouse subcutaneous tumor model was used to investigate a novel dualfluorescence-ultrasound nanobubble synthesized in our laboratory for tumor-selectiveimaging. Major results are summarized as follows:1) Consistent H22subcutaneous tumor model was established in Balb/C mice. Themethod was also reproducible in nude mice.2) Nanobubbles showed good ultrasound enhancement in the tumor model. Our resultsconfirmed nanobubbles selectively accumulate in tumor tissues with a half-life morethan2hours. Modification of nanobubbles with fluorescence dye did not impact theultrasound imaging property.3) In vitro fluorescent analysis and cytotoxicity study showed thatfluorescence-ultrasound nanobubbles had low toxicity on cells at low dose.4) Tumor selective fluorescence imaging was found in subcutaneous tumor model withCy5.5-modified nanobubbles. The fluorescent signal accumulated selectively in tumortissue for more than24h. Further in vivo and collected tissue studies showed thatfluorescent-ultrasound nanobubbles mainly located in tumor and bladder, which fullyconfirmed the tumor-selective accumulation by nanobubbles in vivo.