Lipidic Microbubble Targeting of Surface Proteins Using an in Vitro System

Abstract

Lipidic microbubble contrast media containing targeting molecules, e.g. antibodies specific for some tumor-related protein, in their outer shell, are a promising strategy to improve the contrast of tumor lesions in ultrasound imaging. The preparation and characterization of such targeted lipidic microbubbles is a difficult task mainly because of their short lifespan and fragile structure as well as their continuous “floating to the surface” due to buoyancy. Moreover, few cancerrelated surface proteins are available in pure form. Classical immunochemical tests, like ELISA, cannot be employed for the analysis of targeted lipidic microbubbles. Instead, cancer cell lines can be used for in vitro experiments. Two different types of in vitro experiments are presented, both addressing the tissue factor (TF) as the tumor-related protein and using lipidic soft-shell microbubbles with attached monoclonal anti-TF antibody as the contrast media. Flow cytometry was used to analyze the interaction between targeting microbubbles and U-937 cancer cells growing in suspension. Perfusion in a microfluidic channel was used to study the interaction between microbubbles and the surface adherent cell line U87-MG.