Characterization of the In-Vivo Uptake of Novel Contrast Agents Using Photoacoustic Radiofrequency Spectra

In this study, a phase-change contrast agent for photoacoustic (PA) imaging has been developed and tested invivo using a mouse xenograft tumor model. This agent consists of gold nanorods (GNRs) and a perfluorohexane liquid core and a biodegradable polymer PLGA shell. The agent was conjugated to an anti-HER2 antibody (Herceptin) for specific binding to breast cancer cells which overexpress HER2 receptors. The mean size of the nanoparticles (NPs) was about 285 nm. The targeting specificity of PLGA-GNRs was examined using HER2-positive human breast cancer cells (BT474). The targeted and non-targeted PLGA-GNRs were injected intravenously into Balb/c mice bearing subcutaneous BT474 tumors. Tumors were imaged at different time points using the 21 MHz linear array transducer from the VevoLAZR2100 system (Fujifilm VisualSonics, Canada). The PA radiofrequency spectra were studied as a function of time post-injection. Metrics such as integrated spectral power were used to compare the impact of tumor targeting. Our results show that there is a significant (15 dB) increase in contrast attributed to the NP targeting with HER2 receptors, and little enhancement (~1.1x) of non-targeted PLGA-GNRs at 6-hour post-injection.