title: Comparison of two site-specifically (18)F-labeled affibodies for PET imaging of EGFR positive tumors.
abstract: The epidermal growth factor receptor (EGFR) serves as an attractive target for cancer molecular imaging and therapy. Our previous positron emission tomography (PET) studies showed that the EGFR-targeting affibody molecules (64)Cu-DOTA-ZEGFR:1907 and (18)F-FBEM-ZEGFR:1907 can discriminate between high and low EGFR-expression tumors and have the potential for patient selection for EGFR-targeted therapy. Compared with (64)Cu, (18)F may improve imaging of EGFR-expression and is more suitable for clinical application, but the labeling reaction of (18)F-FBEM-ZEGFR:1907 requires a long synthesis time. The aim of the present study is to develop a new generation of (18)F labeled affibody probes (Al(18)F-NOTA-ZEGFR:1907 and (18)F-CBT-ZEGFR:1907) and to determine whether they are suitable agents for imaging of EGFR expression. The first approach consisted of conjugating ZEGFR:1907 with NOTA and radiolabeling with Al(18)F to produce Al(18)F-NOTA-ZEGFR:1907. In a second approach the prosthetic group (18)F-labeled-2-cyanobenzothiazole ((18)F-CBT) was conjugated to Cys-ZEGFR:1907 to produce (18)F-CBT-ZEGFR:1907. Binding affinity and specificity of Al(18)F-NOTA-ZEGFR:1907 and (18)F-CBT-ZEGFR:1907 to EGFR were evaluated using A431 cells. Biodistribution and PET studies were conducted on mice bearing A431 xenografts after injection of Al(18)F-NOTA-ZEGFR:1907 or (18)F-CBT-ZEGFR:1907 with or without coinjection of unlabeled affibody proteins. The radiosyntheses of Al(18)F-NOTA-ZEGFR:1907 and (18)F-CBT-ZEGFR:1907 were completed successfully within 40 and 120 min with a decay-corrected yield of 15% and 41% using a 2-step, 1-pot reaction and 2-step, 2-pot reaction, respectively. Both probes bound to EGFR with low nanomolar affinity in A431 cells. Although (18)F-CBT-ZEGFR:1907 showed instability in vivo, biodistribution studies revealed rapid and high tumor accumulation and quick clearance from normal tissues except the bones. In contrast, Al(18)F-NOTA-ZEGFR:1907 demonstrated high in vitro and in vivo stability, high tumor uptake, and relative low uptake in most of the normal organs except the liver and kidneys at 3 h after injection. The specificity of both probes for A431 tumors was confirmed by their lower uptake on coinjection of unlabeled affibody. PET studies showed that Al(18)F-NOTA-ZEGFR:1907 and (18)F-CBT-ZEGFR:1907 could clearly identify EGFR positive tumors with good contrast. Two strategies for (18)F-labeling of affibody molecules were successfully developed as two model platforms using NOTA or CBT coupling to affibody molecules that contain an N-terminal cysteine. Al(18)F-NOTA-ZEGFR:1907 and (18)F-CBT-ZEGFR:1907 can be reliably obtained in a relatively short time. Biodistribution and PET studies demonstrated that Al(18)F-NOTA-ZEGFR:1907 is a promising PET probe for imaging EGFR expression in living mice.
authors: Department of Nuclear Medicine, Zhongshan Hospital Xiamen University , Xiamen 361004, China.
authors: Xinhui
authors: X
authors: Su
authors: Kai
authors: K
authors: Cheng
authors: Jongho
authors: J
authors: Jeon
authors: Bin
authors: B
authors: Shen
authors: Gianina Teribele
authors: GT
authors: Venturin
authors: Xiang
authors: X
authors: Hu
authors: Jianghong
authors: J
authors: Rao
authors: Frederick T
authors: FT
authors: Chin
authors: Hua
authors: H
authors: Wu
authors: Zhen
authors: Z
authors: Cheng
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D052160:Benzothiazoles / Q000737:chemistry; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes / Q000737:chemistry; D066246:ErbB Receptors / Q000737:chemistry*; D005260:Female; D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18 / Q000737:chemistry*; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D051379:Mice; D008819:Mice, Nude; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D009570:Nitriles / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D049268:Positron-Emission Tomography; D017434:Protein Structure, Tertiary
chemical_list: C578355:2-cyanobenzothiazole; D052160:Benzothiazoles; D003301:Copper Radioisotopes; D005462:Fluorine Radioisotopes; D009570:Nitriles; D010455:Peptides; D019788:Fluorodeoxyglucose F18; D066246:ErbB Receptors
keywords: 18F; CBT; EGFR; NOTA; PET; affibody