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3rd International Congress 3rd International of Nuclear Congress Medicine of Nuclear & 15th Medicine Iranian Annual & 15th Iranian Congress Annual of Nuclear Congress Medicine of Nuclear Medicine Shahid Beheshti Shahid Beheshti University University of Medical Sciences of Medical 19-21 Sciences May 201119-21 May 2011 Radiolabeled Affibody molecules as novel class of tumor targeted peptides for imaging and therapy Seyed Jalal Hosseinimehr 1 , Anna Orlova 2 , Vladimir Tolmachev 2 , 1 Department of Radiopharmacy 2 Division of Biomedical Radiation Sciences, Uppsala, Sweden Affibody molecules are small, very stable, 58-amino acid residue proteins derived from one of the IgG-binding domains of staphylococcal protein A with the three-helix bundle structure. Affibody molecules with small size (7 kDa) have rapid tumor localization with fast clearance from nonspecific tissues. Affibody molecules can bind to HER2, IGF-1R and EGFR with high affinity. With these advantages, Affibody molecules are interesting as tumor targeted peptide for nuclear medicine. Another advantage of Affibody molecules is that they can be labeled with different radionuclides such as gamma- and beta- emitters for imaging and therapy. Recently, our research team prepared radiolabeled Affibody molecule for tumor imaging with 99mTc and 111In. These radiolabeled peptides showed excellent specific binding in vitro. Tumor bearing mice imaging showed a high contrast imaging with tumor localization. Affibody molecules can be labeled with beta emitters, such as 177Lu or 186Re, and used a therapeutic agents. Recently, we have evaluate a series of peptide-based chelators for 99mTc (and potentially for 186/188 Re), which can be incorporated a C-orN-terminus of Affibody molecules. We have shown that modification of amino acids in such chelators enables modification of biodistribution of Affibody molecules. Keywords: Affibody, molecules imaging, 99mTc 80
3rd International Congress of of Nuclear Medicine & & 15th 15th Iranian Annual Annual Congress of Congress of Nuclear Medicine Shahid Beheshti Shahid Beheshti University University of Medical of Medical Sciences Sciences 19-21 19-21 May May 2011 Synthesis and labeling of a new bombesin analogue with 67Ga for imaging of BBN receptors Seyed Pezhman Shirmardi, Mostafa Erfani (Gandomkar), Mohammad Ghannadi Maragheh Nuclear Science & Technology Research Institute (NSTRI), Atomic Energy Organization of Iran Introduction: Bombesin (BBN) is a peptide showing high affinity for the gastrin releasing peptide receptor (GRPr). Tumors such as prostate, small cell lung cancer, breast, gastric and colon cancer are known to over express receptors to bombesin (BBN) and gastrin releasing peptide (GRP). Methods: The goal of this study was to evaluate a new 67Ga radiolabeled BBN analogue based upon the bifunctional chelating ligand DOTA which could be used as a tool for diagnosis of GRP receptor-positive tumors. DOTA-GABA-Bombesin (7-14) NH2 was synthesized using a standard Fmoc strategy. Labeling with 67Ga was performed at 95°C for 30 min in ammonium acetate buffer (pH = 4.8). The stability of radiopeptide was examined in the presence of human serum at 37 °C up to 24 h. The receptor bound internalization and externalization rates were studied in GRP receptor expressing PC-3 cells. Biodistribution of radiopeptide was studied in mice. Results: labeling yield of >90% was obtained corresponding to a specific activity of 2.6 MBq/nmol. The radioligand showed a good and specific internalization into PC-3 cells (16.13 ± 0.71% at 4 h). After 4 h a considerable amount of activity (52.42 ± 1.86%) was externalized. In animal biodistribution studies, a receptor-specific uptake of radioactivity was observed in GRP-receptor-positive organs. After 4 h, the uptake in mouse tumor and pancreas was 1.30 ± 0.18% ID/g and 1.21 ± 0.13% ID/g respectively. Conclusion: These data show that [67Ga]-DOTA-GABA-Bombesin (7-14) NH2 is a specific radioligand for gastrin-releasing peptide receptor positive tumors and is a suitable candidate for clinical studies. Keywords: 67Ga Bombesin, synthesis, labeling 81
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