PET imaging of EGFR expression using an 18F-labeled RNA aptamer

Siyuan Cheng; Orit Jacobson; Guizhi Zhu; Zhen Chen; Steve H Liang; Rui Tian; Zhen Yang; Gang Niu; Xiaohua Zhu; Xiaoyuan Chen

doi:10.1007/s00259-018-4105-1

PET imaging of EGFR expression using an ¹⁸F-labeled RNA aptamer

Eur J Nucl Med Mol Imaging. 2019 Apr;46(4):948-956. doi: 10.1007/s00259-018-4105-1. Epub 2018 Aug 1.

Authors

Siyuan Cheng^{1

2}, Orit Jacobson², Guizhi Zhu³, Zhen Chen⁴, Steve H Liang⁴, Rui Tian², Zhen Yang², Gang Niu⁵, Xiaohua Zhu⁶, Xiaoyuan Chen⁷

Affiliations

¹ Department of Nuclear Medicine and PET, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1095 Jiefang Ave, Wuhan, 430000, Hubei, People's Republic of China.
² Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health (NIH), 35A Convent Drive Rm GD959, Bethesda, MD, 20892, USA.
³ Department of Pharmaceutics, School of Pharmacy, Virginia Commonwealth University, 410 North 12th Street Rm 454D, Richmond, VA, 23298, USA. gzhu2@vcu.edu.
⁴ Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, USA.
⁵ Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health (NIH), 35A Convent Drive Rm GD959, Bethesda, MD, 20892, USA. gang.niu@nih.gov.
⁶ Department of Nuclear Medicine and PET, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1095 Jiefang Ave, Wuhan, 430000, Hubei, People's Republic of China. evazhu@vip.sina.com.
⁷ Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health (NIH), 35A Convent Drive Rm GD959, Bethesda, MD, 20892, USA. shawn.chen@nih.gov.

Abstract

Objective: Epidermal growth factor receptor (EGFR) is a theranostic biomarker for a variety of cancer types. The aim of the present study was to develop an ¹⁸F radiolabeled EGFR targeting RNA aptamer, and to investigate its ability to visualize and quantify EGFR in xenograft models.

Methods: Biolayer interferometry binding assay was used to detect the binding affinity of the alkyne-modified EGFR aptamer MinE07 (denoted as ME07) with recombinant human wild-type EGFR protein and the mutant EGFRvIII protein. Cy5-conjugated ME07 was used for flow cytometry and immunofluorescence staining, and an Alexa Fluor 488-labeled EGFR antibody (ab193244) was used as a control. ¹⁸F-Fluorobenzoyl (FB) azide was employed as a synthon to produce ¹⁸F-FB-ME07 via click chemistry, and the cellular uptake and internalization characteristics of ¹⁸F-FB-ME07 were investigated. Static PET scans, 60-min dynamic scans, and biodistribution study of ¹⁸F-FB-ME07 were performed in three types of tumor models.

Results: The K_d values of ME07 to wtEGFR and EGFRvIII proteins were 0.3 nM and 271 nM respectively. The A431, U87MG, and HCT-116 cells showed strong, weak, and negative binding with Cy5-ME07, which is consistent with EGFR expression level in these cells. Peak cell uptake values of ¹⁸F-FB-ME07 in A431, U87MG and HCT-116 cells were 2.86%, 2.19% and 0.88% of the added dose respectively. The mean internalization of ¹⁸F-FB-ME07 in these cells were 60.02%, 53.1%, and 52.8% of the total accumulated radioactivity. In static PET imaging, despite high uptake in the liver and kidneys, ¹⁸F-FB-ME07 showed reasonable accumulation in A431 tumors (1.02 ± 0.13 %ID/g at 30 min after injection). Of note, the uptake of ¹⁸F-FB-ME07 in A431 xenografts was significantly higher than that in U87MG and HCT-116 xenografts. In A431 xenografted mice, the tumor/blood ratio was 3.89 and the tumor/muscle ratio reached 8.65.

Conclusions: We for the first time generated an aptamer-derived EGFR targeting PET tracer ¹⁸F-FB-ME07, which showed highly selective targeting ability in mouse tumor models expressing different levels of EGFR. Our results suggest that ¹⁸F-FB-ME07 is a potential EGFR targeting molecular imaging probe for future clinical translation.

Keywords: 18F-FB-ME07; EGFR; PET; RNA aptamer.

MeSH terms

Animals
Aptamers, Nucleotide / chemistry*
Aptamers, Nucleotide / pharmacokinetics
Cell Line, Tumor
ErbB Receptors / metabolism*
Female
Fluorine Radioisotopes*
Gene Expression Regulation, Neoplastic*
Humans
Isotope Labeling
Mice
Positron-Emission Tomography*
Tissue Distribution

Substances

Aptamers, Nucleotide
Fluorine Radioisotopes
ErbB Receptors
Fluorine-18

Abstract

MeSH terms

Substances

Grants and funding