Near-Infrared Optical Imaging of Epidermal Growth Factor Receptor in Breast Cancer Xenografts

The specificity of a novel epidermal growth factor (EGF)-Cy5.5 fluorescent optical probe in the detection of EGF receptor (EGFr) was assessed using continuous-wave fluorescence imaging accomplished via an intensified charge-coupled device (CCD) camera. Human mammary MDA-MB-468 (EGFr+) and MDA-MB-435 (EGFr-) cancer cells were incubated with Cy5.5, EGF-Cy5.5, or the anti-EGFr monoclonal antibody C225 or EGF followed by EGF-Cy5.5 and examined under a fluorescence microscope. In vivo imaging was performed on mice with s.c. MDA-MB-468 and MDA-MB-435 tumors. Images were obtained every 6 s for 20 min after i.v. injection of each agent and every 24 h after injection for up to 192 h. Additionally, mice with MDA-MB-468 tumors were injected i.v. with C225 24 h before injection of EGF-Cy5.5. EGF-Cy5.5, but not Cy5.5 or indocyanine green dye (ICG), bound to MDA-MB-468 cells. Binding of EGF-Cy5.5 was blocked by C225 and by EGF. In contrast, binding of EGF-Cy5.5 to MDA-MB-435 cells was not observed. Monitoring of the time-fluorescence intensity in mice confirmed that ICG and Cy5.5 had no favorable binding to tumor regardless of EGFr expression level. In contrast, EGF-Cy5.5 accumulated only in MDA-MB-468 tumors. Moreover, tumor uptake of EGF-Cy5.5 was blocked by C225. ICG and Cy5.5 fluorescence was completely absent from the tumor site, regardless of EGFr expression level, 24 h after injection. Little EGF-Cy5.5 fluorescence was detected in MDA-MB-435 tumors 24 h after injection. In MDA-MB-468 tumors, our data suggest that EGF-Cy5.5 may be used as a specific NIR contrast agent for noninvasive imaging of EGFr expression and monitoring of responses to molecularly targeted therapy.