Molecular imaging application of radioiodinated anti-EGFR human Fab to EGFR-overexpressing tumor xenografts.

BACKGROUND Suitable diagnostics could identify patients who might benefit from targeted therapies. Molecular imaging is a promising method estimating the expression of specific molecules in vivo, and the goal of this study was to evaluate a radioiodinated anti-epidermal growth factor receptor (EGFR) human Fab as a molecular imaging agent for diagnosis. MATERIALS AND METHODS Three human tumor cell lines representing tumors with different levels of EGFR expression were selected and their corresponding xenografts produced. (125)I was conjugated to a human anti-EGFR Fab that recognizes the native extracellular domain of EGFR evidenced by immunoprecipitation (IP) and fluorescence-activated cell sorting (FACS) assays. Single-photon-emission computed tomography (SPECT) imaging of (125)I-Fab being administered to nude mice bearing xenografts were obtained, and further analyzed by region of interest (ROI) assay. RESULTS The (125)I-Fab was achieved successfully without losing its immunoreactivity. The scintigrams as well as ROI assay showed that (125)I-Fab was able to clearly quantitatively distinguish the different expression levels of EGFR in vivo. CONCLUSION (125)I-Fab is a potential molecular imaging agent for clinical diagnosis of EGFR-overexpressing tumors.