In Vivo Monitoring of a Fluorescently Labeled Antibody in Mice With Breast Cancer Xenografts

Following the uptake kinetics of a monoclonal antibody cancer therapy in vivo is addressed in this study via the use of a surface probe to assay a fluorescent label attached to the antibody. Female NCr-nu athymic mice were implanted with cells from a human breast cancer MCF7HER2 line that over expresses clinically relevant levels of the HER2/neu protein. Herceptin (trastuzumab) and a negative control antibody for mouse IgG Ab-1 were labeled with Alexa Fluor 647 fluorescent dye and the mice received a single bolus injection (tail vein) of one of the two antibodies. The relative signal in the tumor region was compared with that from normal tissue and a ratio of the signal levels was recorded as a function of time. As expected, Herceptin was found to concentrate in the HER2+ tumors (high tumor-to-normal ratio), whereas the tumor-to-normal ratio for the negative control antibody was flat in time and close to unity. It is suggested that fluorescence assays of this type might be possible in vivo in humans using a telemetric, implantable version of the probe used in this study.