Abstract 2859: Sensitive, specific detection of Her-2 positive tumors in mice using superparamagnetic relaxometry (SPMR)

Superparamagnetic Relaxometry (SPMR) is a non-invasive technique that utilizes superconducting quantum interference device (SQUID) detectors to localize and quantify the magnetization of superparamagnetic iron oxide (Fe3O4) nanoparticles (NPs) specifically bound to cancerous tumors. In an SPMR measurement, polyethylene glycol (PEG) coated NPs are functionalized with a tumor-targeting monoclonal antibody and injected intravenously. NPs that reach and bind to the target tissue are measured by the MRX™ instrument, while unbound nanoparticles, such as those freely circulating in the bloodstream, are not detected. Here, we demonstrate the use of SPMR for specific cancer detection using long-circulating anti-Her2 antibody conjugated PrecisionMRX® NPs in vitro and in vivo. The stability and biofunctionality of conjugated nanoparticles were measured by dynamic light scattering, gel electrophoresis, and ELISA. A cell competition assay was developed to measure specific binding of NPs to Her2 positive (BT474) and Her2 negative (MCF7) cells in vitro. Specificity was defined by the ability of the native antibody to competitively block the binding of the anti-Her2 conjugated NPs to the Her-2 antigen expressed on the cell surface. For in vivo studies, nude mice with xenograft BT474 tumors were intravenously injected with anti-Her2 NPs at a dose of 20 mg/kg of body mass, while control mice were injected with PEG only NPs. Mice were measured individually on the MRX™ instrument at successive time points over the course of 24 hours. At selected intervals during the 24-hour period, blood, tumor, and organs were harvested and analyzed for SPMR signals and anti-Her2 content. In vitro, the anti-Her2 NPs exhibited specific binding to BT474 cells, with little to no binding in MCF7 cells. In vivo, MRX measurements of mice injected with anti-Her2 NPs showed a measurable magnetic signal in the tumor that reached a near maximum approximately four hours after injection. Conversely, mice injected with unconjugated nanoparticles had no measurable tumor uptake. Finally, 24 hours post-injection, 4 – 8% of NPs and anti-Her2 were measurable in the blood, indicating long-term stability of the NP construct in circulation. Together, these results suggest targeted delivery of conjugated NPs to cancerous tissue in vivo and the utility of SPMR for the sensitive and specific detection of cancer in vivo. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Sc