1B-3 Ultrasound Radiation Force Enables Targeted Deposition of Molecularly Targeted Nanoparticles Loaded on Microbubbles Under Flow Conditions

Novel drug delivery vehicles that specifically target using ultrasound radiation force (USRF) and molecular interactions are presented. The first model vehicle consists of commercially available Neutravidin fluorescent nanobeads bound directly to the biotinylated lipid shells of preformed microbubbles. USRF was used to deflect the vehicle from the center of flow to a tube surface in order to facilitate molecular interactions and induce adhesion. In order to reduce acoustic reflections, a cellulose tube was used as the substrate. At wall shear stress levels commensurate with venous and arterial flow, USRF (1.3 sec pulse at 3 MHz and 150 kPa peak negative pressure (PNP)) was used to direct these model vehicles to the biotinylated cellulose tube surface. Subsequent high-pressure pulses (three 5-cycle pulses at 1.5 MHz and 1.1 MPa PNP) fragmented the carrier, and biotin-Neutravidin interactions induced deposition of the nanobeads on the wall. Targeting of nanobeads to the cellulose tube was molecularly specific and dependent on, in order of importance, vehicle concentration, wall shear stress, nanobead size, and insonation time. The second vehicle takes the next steps to molecularly target the nanoparticles to biologically-relevant receptors/ligands and change the fluorescence emission to the near infrared to allow for in vivo imaging. This is accomplished by attaching Peptide LLP2A, which specifically targets integrin alpha₄beta₁ expressed on angiogenic vessels, to commercially available quantum dots which emit at 800 nm. These new vehicles specifically adhere to the MOLT-4 cell line which highly expresses integrin alpha₄beta₁, while vehicles without the specific peptide had minimal binding. This versatile method of delivery is shown to enable targeted deposition of nanoparticles in shear flow and could be used as a diagnostic tool to optically observe diseased areas as well as modified to carry therapeutic agents for control- led release in targeted delivery applications