Synthesis and Evaluation of Cu-64 Labeled Repebody for EGFR-mediated Cancer Imaging in Small Animals

172 Objectives The epidermal growth factor receptor (EGFR) is known as a member of the HER family and expressed in many kinds of tumors. Anti-EGFR repebody using this study is a newly designed protein scaffold for tumor targeting that has leucine rich repeat modules. In this study, we performed microPET studies with two kinds of 64Cu labeled complexes (repebody with DOTA and DTPA) and evaluated characteristics in H1650 (human non-small cell lung cancer cell line) bearing nude mice. Methods DOTA-NHS ester and ρ-SCN-Bn-DTPA were dissolved in water and pH was adjusted to 9.0 by adding 1M of NaOH. This solutions were added to the repebody in a 1:5 mole ratio (repebody : DOTA-NHS ester, ρ-SCN-Bn-DTPA)1. Purified compounds were radiolabeled with 64Cu by addition of 64CuCl2 in 0.1 N NaOAc (pH5.5) buffer followed by incubation for 1 h at 40°C. The radiolabeled complexes were purified by a PD-10 column. The mircoPET images were obtained at 1, 6, and 24 h after i.v.injection of 64Cu labeled repebody (7.4MBq)in H1650 (EGFR positive) bearing nude mice. The static images at 1, 6, and 24 h were acquired for 10 min. The ROIs were drawn in the tumor and liver. The tumor-to-liver ratio (T/L) were obtained from max SUV of ROI. Results Radiochemical yields of 64Cu-DOTA-repebody and 64Cu-DTPA-repebody were approximately 60~70%. H1650 tumor was clearly visible after injection of each repebody, with high tumor-to-background ratio for whole time points.64Cu labeled repebody was accumulated specifically at 1 h after i.v. injection and retained in H1650. Uptake of64Cu-DOTA-repebody (1, 6 h SUVmax: 1.80, 2.20) and 64Cu-DTPA-repebody (1, 6 h SUVmax: 1.81, 2.19) were increased from 1 h to 6 h. Both 64Cu-DOTA- and 64Cu-DTPA-repebody showed slow clearance from liver as T/Ls were 0.49, 0.59, 0.43 and 0.47, 0.50, 0.41 respectively at 1, 6 and 24 h. Conclusions 64Cu-DOTA-repebody and 64Cu-DTPA-repebody demonstrated specific uptake in H1650 tumor bearing model and might have a potential to be utilized as a novel EGFR targeting agent for PET.