Targeted microbubble-mediated ultrasound therapy: A feasibility study

In this study, microbubble (MB) mediated ultrasound (US) therapy was used in conjunction with antibody-labeled MBs to determine if localization of MBs would improve drug uptake. The custom experimental US setup involved a single element immersion transducer in series with a signal generator and power amplifier. 2LMP breast cancer cells were infected with a replication incompetent adenovirus vector to induce expression of human somatostatin receptors with an HA tag for targeting. Cells were plated on acoustically transparent plates. Streptavidin coated MBs were labeled with either biotinylated anti-HA antibody or biotinylated anti-mouse IgG antibodies. Cell plates were injected with calcein dye and MBs (anti-HA antibody or IgG isotype control antibody). Cells underwent combination therapy using the following US parameters: transmit frequency of 1.0 MHz, 5.0 min duration, pulse repetition period (PRP) of 0.01 sec, duty cycle of 20% and a mechanical index (MI) of 0.1, 1.0 or 2.0. Fluorescent signals from internalized calcein molecules were quantified for each cell population using flow cytometer. Light microscopy images were acquired and registered to fluorescence images to visibly validate tracer uptake. Comparing anti-HA antibody-labeled MB data to that obtained using control MBs, MB-mediated US therapy at an MI of 0.1 produced a significant increase in internalized tracer concentrations (p < 0.001). At an MI of 1.0 or 2.0, increases in the amount of internalized fluorescent tracers were also observed when comparing targeted and control MB group data (p > 0.44 and p < 0.001, respectively) but considerable lower than that found MB-mediated US therapy at an MI of 0.1. These results suggest targeted MB-mediated US exposure using low MI exposure is effective at modulating cell permeability and improving drug uptake.