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 ⁶⁴Cu-DOTA-Z_EGFR:1907 and ¹⁸F-FBEM-Z_EGFR:1907 can discriminate between high and low EGFR-expression tumors and have the potential for patient selection for EGFR-targeted therapy. Compared with ⁶⁴Cu, ¹⁸F may improve imaging of EGFR-expression and is more suitable for clinical application, but the labeling reaction of ¹⁸F-FBEM-Z_EGFR:1907 requires a long synthesis time. The aim of the present study is to develop a new generation of ¹⁸F labeled affibody probes (Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907) and to determine whether they are suitable agents for imaging of EGFR expression. The first approach consisted of conjugating Z_EGFR:1907 with NOTA and radiolabeling with Al¹⁸F to produce Al¹⁸F-NOTA-Z_EGFR:1907. In a second approach the prosthetic group ¹⁸F-labeled-2-cyanobenzothiazole (¹⁸F-CBT) was conjugated to Cys-Z_EGFR:1907 to produce ¹⁸F-CBT-Z_EGFR:1907. Binding affinity and specificity of Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 to EGFR were evaluated using A431 cells. Biodistribution and PET studies were conducted on mice bearing A431 xenografts after injection of Al¹⁸F-NOTA-Z_EGFR:1907 or ¹⁸F-CBT-Z_EGFR:1907 with or without coinjection of unlabeled affibody proteins. The radiosyntheses of Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 were completed successfully within 40 and 120 min with a decay-correctedmore » 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 ¹⁸F-CBT-Z_EGFR:1907 showed instability in vivo, biodistribution studies revealed rapid and high tumor accumulation and quick clearance from normal tissues except the bones. In contrast, Al¹⁸F-NOTA-Z_EGFR: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 Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 could clearly identify EGFR positive tumors with good contrast. Two strategies for ¹⁸F-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. Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 can be reliably obtained in a relatively short time. Biodistribution and PET studies demonstrated that Al¹⁸F-NOTA-Z_EGFR:1907 is a promising PET probe for imaging EGFR expression in living mice.« less

Authors:

Su, Xinhui ^[1]; Cheng, Kai ^[2]; Jeon, Jongho ^[3]; Shen, Bin ^[2]; Venturin, Gianina Teribele ^[4]; Hu, Xiang ^[2]; Rao, Jianghong ^[2]; Chin, Frederick T. ^[2]; Wu, Hua ^[5]; Cheng, Zhen ^[2]

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+ Show Author Affiliations

1. Department of Nuclear Medicine, Zhongshan Hospital Xiamen University, Xiamen 361004, China, Molecular Imaging Program at Stanford (MIPS), Department of Radiology, Bio-X Program, and Stanford Cancer Center, Stanford University School of Medicine, Stanford, California 94305, United States
2. Molecular Imaging Program at Stanford (MIPS), Department of Radiology, Bio-X Program, and Stanford Cancer Center, Stanford University School of Medicine, Stanford, California 94305, United States
3. Molecular Imaging Program at Stanford (MIPS), Department of Radiology, Bio-X Program, and Stanford Cancer Center, Stanford University School of Medicine, Stanford, California 94305, United States, Research Division for Biotechnology, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 29 Geumgu-gil, Jeongeup-si, Jeonbuk 580-185, Republic of Korea
4. Molecular Imaging Program at Stanford (MIPS), Department of Radiology, Bio-X Program, and Stanford Cancer Center, Stanford University School of Medicine, Stanford, California 94305, United States, Instituto do Cérebro do Rio Grande do Sul (InsCer), Universidade Católica do Rio Grande do Sul (PUCRS), Porto Alegre, Brazil
5. Department of Nuclear Medicine, The First Affiliated Hospital of Xiamen University, Xiamen 361003, China

Publication Date:

2014-07-14

Research Org.:

Stanford Univ., CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1188056

Alternate Identifier(s):

OSTI ID: 1440565

Grant/Contract Number:  

SC0008397

Resource Type:

Published Article

Journal Name:

Molecular Pharmaceutics

Additional Journal Information:

Journal Name: Molecular Pharmaceutics Journal Volume: 11 Journal Issue: 11; Journal ID: ISSN 1543-8384

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

62 RADIOLOGY AND NUCLEAR MEDICINE; 18F; affibody; CBT; EGFR; NOTA; PET