Stimuli-sensitive perfluorocarbon emulsions as drug carriers and embolizing agents for tumor therapy

Perfluorocarbon (PFC) microbubbles have been used for several decades as contrast agents in ultrasound imaging; over the last decade, microbubbles have attracted attention as potential drug/gene carriers. The microbubbles would have difficulty in carrying the drug to the tumor due to their sizes in the micron range that preclude effective extravasation. Drug encapsulation in perfluorocarbon nanoemulsions used as microbubble precursors will overcome this problem. Upon nanodroplet accumulation in the tumor tissue, the application of tumor-directed ultrasound triggers the droplet-tobubble transition accompanied by localized drug release from the bubbles formed. We chose perfluoropentane (PFP) and perfluro-15-crown-5-ether (PFCE) emulsions for our drug delivery studies. PFCs were stabilized by polyethylene glycol (PEG) based amphiphilic block copolymers. For the drug delivery studies, doxorubicin (DOX), a widely used drug in chemotherapy, was loaded into the droplets. DOX has intrinsic fluorescence properties, which allowed studying DOX intracellular trafficking as well as cell damage through fluorescence imaging. Cell culture experiments showed that without ultrasound exposure, the intracellular DOX uptake was lower when DOX was delivered in nanodroplets compared to DOX encapsulated in polymeric micelles. This is advantageous for preventing DOX interaction with the healthy tissues. For drug uptake by cells, significant differences (F (2, 42) = 15.7; p << 0.01) were observed between different DOX encapsulated formulations.