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

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Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

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Alexa Fluor 680-Bevacizumab

, PhD
National Center for Biotechnology Information, NLM, NIH, vog.hin.mln.ibcn@dacim

Created: ; Last Update: December 16, 2008.

Chemical name:Alexa Fluor 680-Bevacizumab
Abbreviated name:Alexa680-Bevacizumab
Agent category:Antibody
Target:Vascular endothelial growth factor (VEGF)
Target category:Antigen
Method of detection:Optical, near-infrared fluorescence
Source of signal/contrast:Alexa Fluor 680 (Alexa680)
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Click on protein, nucleotide (RefSeq), and gene for more information about VEGF.



Optical fluorescence imaging is increasingly used to obtain biological functions of specific targets (1, 2). However, the intrinsic fluorescence of biomolecules poses a problem when visible light (350–700 nm) absorbing fluorophores are used. Near-infrared (NIR) fluorescence (700–1,000 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorophores have wider dynamic range and minimal background as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity, resulting from low infrared background, and high extinction coefficients, which provide high quantum yields. The NIR region is also compatible with solid-state optical components, such as diode lasers and silicon detectors. NIR fluorescence imaging is becoming a non-invasive alternative to radionuclide imaging.

Vascular endothelial growth factor (VEGF) consists of at least six isoforms of various numbers of amino acids (121, 145, 165, 183, 189, and 206 amino acids) produced through alternative splicing (3). 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 (4). 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 (VEGFR-1, Flt-1; VEGFR-2, KDR/Flt-1; and VEGFR-3, Flt-4) on endothelial cells. Several types of non-endothelial cells such as hematopoietic stem cells, melanoma cells, monocytes, osteoblasts, and pancreatic β cells also express VEGF receptors (3).

VEGF is overexpressed in various tumor cells and tumor-associated endothelial cells (5). Inhibition of VEGF receptor function has been shown to inhibit pathological angiogenesis as well as tumor growth and metastasis (6, 7). Radiolabeled VEGF has been developed as a single-photon emission computed tomography tracer for imaging solid tumors and angiogenesis in humans (8-10). However, several studies have shown that cancer treatments (photodynamic therapy, radiotherapy, and chemotherapy) can lead to increased tumor VEGF expression and subsequently to more aggressive disease (11, 12). Therefore, it is important to measure VEGF levels in the tumors to design better anti-cancer treatment protocols. Bevacizumab is a humanized antibody against VEGF-A. It binds to all VEGF isoforms. Bevacizumab is approved for clinical use in metastatic colon carcinoma and non-small cell lung cancer. Chang et al. (13) prepared Alexa Fluor 680-bevacizumab (Alexa680-bevacizumab) for imaging VEGF expression in tumors. Alexa680 is a NIR fluorescent dye with absorbance maximum at 684 nm and emission maximum at 707 nm with a high extinction coefficient of 183,000 (mol/L)-1cm-1.



Alexa Fluor 680 N-succinimidyl ester and bevacizumab were incubated in sodium bicarbonate buffer (pH 9) for 60 min at room temperature (13). Alexa680-bevacizumab was isolated from the incubation mixture with column chromatography. There were six dye molecules per antibody molecule.

In Vitro Studies: Testing in Cells and Tissues


No publication is currently available.

Animal Studies



Chang et al. (13) performed biodistribution studies of Alexa680-bevacizumab in mice bearing PC-3 prostate, AsPC-1 pancreatic, or Capan-1 pancreatic tumors. Images were obtained after injection of 100 μg Alexa680-bevacizumab at 1, 3, 6, and 24 h. Substantial contrasts were observed between the tumors and normal tissue as early as 1 h. Fluorescent intensity increased during the first 6 h and leveled by 24 h. Negligible fluorescence uptake into the tumors was observed with injection of Alexa680 or Alexa680-IgG. There was a linear correlation between the level of Alexa680-bevacizumab accumulation and the level of VEGF expression in the tumor homogenates as determined with ELISA. There was also a good correlation between the level of Alexa680-bevacizumab accumulation and the tumor microvessel density, as measured with histoimmunochemistry (r = 0.64, P < 0.05). Pretreatment with bevacizumab (1 mg/mouse) in mice bearing PC-3 tumors (3.4 contrast units) reduced fluorescent uptake into the tumor (2.0 contrast units), whereas BSA (1 mg/mouse) and MLN591 antibody (1 mg/mouse) showed no reduction. Photodynamic therapy delivered to the tumor-bearing mice showed a two-fold increase in both tumor Alexa680-bevacizumab accumulation and VEGF concentration as shown previously (11, 12).

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.

NIH Support

P01 CA84203


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