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68Ga-1,4,7-Triazacyclononane-1,4,7-triacetic acid-polyethylene glycol-single-chain Cys-tagged vascular endothelial growth factor-121.


Leung K1.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2010 Nov 17 [updated 2011 Feb 17].

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National Center for Biotechnology Information, NLM, NIH, Bethesda, MD


Vascular endothelial growth factor (VEGF) consists of at least six isoforms with various numbers of amino acids (121, 145, 165, 183, 189, and 206 amino acids) produced through alternative splicing (1). VEGF121, VEGF165, and VEGF189 are the forms secreted by most cell types and are active as homodimers linked by disulfide bonds. VEGF121 does not bind to heparin like the other VEGF species do (2). VEGF is a potent angiogenic factor that induces proliferation, sprouting, migration, and tube formation of endothelial cells. There are three high-affinity tyrosine kinase VEGF receptors (VEGFRs) on endothelial cells (VEGFR-1, Flt-1; VEGFR-2, KDR/Flt-1; and VEGFR-3, Flt-4). Several types of non-endothelial cells, such as hematopoietic stem cells, melanoma cells, monocytes, osteoblasts, and pancreatic β cells, also express VEGFRs (1). VEGFRs have been found to be overexpressed in various tumor cells and tumor-associated endothelial cells but are not detectable in quiescent endothelial cells (3). Inhibition of VEGFR function has been shown to inhibit pathological angiogenesis as well as tumor growth and metastasis (4, 5). Radiolabeled VEGF has been developed as a tracer for imaging solid tumors and angiogenesis in humans (6-8). A 15-amino-acid fusion tag (Cys-tag) was developed for site-specific conjugation via the free sulfhydryl group of Cys. Backer et al. (9) prepared a Cys-tagged vector of VEGF121 by cloning two single-chain 3–112 amino acid fragments of VEGF121 joining head-to-tail to express as scVEGF, which was labeled as 64Cu-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-polyethylene glycol (PEG)-scVEGF (64Cu-DOTA-PEG-scVEGF), 99mTc-hydrazinonicotinic acid (HYNIC)-scVEGF (99mTc-HYNIC-scVEGF), and Cy5.5-scVEGF for imaging VEGFR expression to study tumor angiogenesis. In this chapter, 68Ga-1,4,7-Triazacyclononane-1,4,7-triacetic acid-PEG-scVEGF (68Ga-NOTA-PEG-scVEGF) is being developed for positron emission tomography (PET) imaging of VEGFR-2 in tumor vasculature (10).

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