IMAGING EGFR WITH MICRO-PET AND I-124

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Non-invasive imaging plays an essential role in diagnosing and managing oncology patients. While current imaging evaluation most commonly uses computed tomography (CT) and positron emission tomography (PET) with fluro-deoxy-glucose (FDG), there is a need for more accurate probes against tumor-specific targets. Monoclonal antibodies (mAbs) have high specificity but are too large to rapidly infiltrate tumors. In order to develop imaging probes for lung cancer, we have isolated novel single chain antibody fragments one-tenth the size of a mAb that bind to an over-expresssed protein on the tumor surface, epidermal growth factor receptor (EGFR). These antibody fragments, called VHH domains, are derived from the variable domain of the heavy-chain-only IgG of camels and llamas. They are extraordinarily stable, display antibody-like specificities and, because of their size (~16 kDa), VHH domains are predicted to infiltrate tumors much faster than mAbs. We chose EGFR as a molecular imaging target because it is well-known to be abundant in many cancers, including lung cancer. The current proposal will continue to develop these probes and then perform micro-PET imaging in an animal model before imaging in human subjects. We will isolated several high affinity binding VHH molecules, and then label them with a radioactive tag. We will then image athymic mice bearing an EGFR over-expressing tumor using the micro-PET system. The amount of uptake will be correlated with tumor cell levels of EGFR. This series of experiments are essential for developing novel imaging probes, which should translate into a more accurate method for diagnosing and following tumors in patients. References: Gottlin EB, Guan XR, Pegram C, Cannedy A,Campa MJ, Patz Jr EF. Isolation of novel EGFR directed VHH domains with diagnostic or therapeutic potential. J Biomolecular Screening 2009;14:77-85. Shankar LK and Sullivan DC. Functional imaging in lung cancer. J Clin Oncol 2005; 23: 3203-3211. Eary JF. Nuclear medicine in cancer diagnosis. Lancet 1999; 354: 853-857.