Abstract 3922: A comparative study of affibody, antibody and EGF for near-infrared fluorescence imaging of EGFR- and EGFRvIII-expressing tumors.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Aberrant overexpression and/or activation of epidermal growth factor receptor (EGFR) is associated with many types of cancers. EGFR variant III (EGFRvIII) is a common in-frame deletion mutant, which lacks a large part of the extracellular portion (exons 2-7), including components of the ligand-binding domain. Although EGFR has been extensively studied as a molecular imaging target, information about EGFRvIII-targeted molecular imaging is lacking. In this study, an EGFR-specific affibody, a therapeutic antibody (panitumumab) and the ligand EGF were labeled with IRDye 800CW (Ex/Em: 774/789 nm), and named as Aff800, Pan800 and EGF800 respectively. The binding affinities of the labeled agents were compared in cell-based assays using a rat glioma cell line F98 parental (F98-p) lacking EGFR, and two F98-derived transgenic cell lines expressing EGFR or EGFRvIII (designated as F98-EGFR and F98-vIII respectively). Results showed that all agents could bind to F98-EGFR, with Pan800 having the highest binding affinity, followed by Aff800 and EGF800. Pan800 and Aff800, but not EGF800, bound to F98-vIII with similar affinities. In vivo animal imaging studies demonstrated that compared to F98-p tumor signals, F98-EGFR tumor generated higher signals for all three agents. However, in the case of F98-vIII, only Pan800 and Aff800 signals were higher. Analysis of tissue lysates showed that a large portion of Pan800 was degraded into small fragments in F98-EGFR and F98-vIII tumors, possibly due to proteolytic digestion after its specific binding and internalization. In conclusion, Pan800 and Aff800 could be used as imaging agents for both wild type EGFR and EGFRvIII, whereas EGF800 only targets wild type EGFR. Citation Format: Haibiao Gong, Joy L. Kovar, Lael Cheung, Eben L. Rosenthal, David M. Olive. A comparative study of affibody, antibody and EGF for near-infrared fluorescence imaging of EGFR- and EGFRvIII-expressing tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3922. doi:10.1158/1538-7445.AM2013-3922