Towards a targeted surfactant stabilized ultrasound contrast agent

Gas-filled microbubbles are highly effective when used as ultrasound contrast agents due to the large difference in acoustic impedance between the gas in the bubble and the surrounding blood. The surfactant-based contrast agent ST68 (Span 60, Tween 80) developed in our laboratory (US Patent # 5, 352, 436) and filled with sulfur hexafluoride (SF6), was modified in an attempt to make the agent target specific. Modifications to the agent were done by incorporation an anchor molecule, phosphatidylethanolamine (PE), into the shell of the microbubles. This anchor molecule will serve as a ligand attachment site for a targeting moiety such as a monoclonal antibody. Fluorescent microscopy and phosphate assays were used to evaluate the extent of PE incorporation. NBD (7-Nitro-2-1, 3-benzoxadiazol-4-yl) labeled PE was used to visually confirm that PE was being incorporated into the microbubble shell and a phosphate assay revealed that the optimum PE concentration of 0.21mM in HEPES buffer. The storage stability of the agent at -5oC and -20oC were assessed. SF6-filled ST68 samples prepared in PBS were storage at both temperatures under a SF6 atmosphere. Samples were thaw and both physical and acoustic properties examine over a period of 10 days. Analysis using the coulter multisizer II revealed that the agent stored at -5oC was more stable than the agent stored at -20oC. The acoustic backscatter of the reconstituted samples incubated at -5oC was consistent over the 10 days however, there was variation in the acoustic backscatter of the sample stored at -20oC. An in vivo study was done to evaluate the effectiveness of the agent.M.S., Biochemical Engineering -- Drexel University, 200