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Bovine serum albumin–stabilized gold nanoclusters conjugated with l-methionine and indocyanine green derivative 02.


Leung K.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2012 Oct 01 [updated 2013 Jan 24].


Most amino acids are taken up by tumor cells through an energy-independent l-type amino acid transporter system, a Na-dependent transporter system A, or a Na+-dependent system B0 (1). They are retained in tumor cells due to their metabolic activities, including incorporation into proteins, which are higher than most normal cells (2). Malignant transformation increases the use of amino acids for energy, protein synthesis, and cell division. Tumor cells have been found to have overexpressed transporter systems (3). S-[11C]Methyl-l-methionine ([11C]MET) has been widely used in the detection of brain, head and neck, lung, and breast cancers as well as lymphomas (4) [PubMed]. [11C]MET can cross the blood–brain barrier, and while it is incorporated mainly into proteins, [11C]MET is also incorporated into lipid, RNA, and DNA. Positron emission tomography (PET) imaging with [11C]MET is more sensitive to radiotherapy compared to [18F]FDG and is useful for monitoring treatment of cancer. Among the various optical imaging agents, only indocyanine green (ICG), with NIR fluorescence absorption at 780 nm and emission at 820 nm, is approved by the United States Food and Drug Administration for clinical applications in angiography, blood flow evaluation, and liver function assessment (5-8). It is also under evaluation in several clinical trials for other applications, such as optical imaging and mapping of both the lymphatic vessels and lymph nodes in cancer patients for surgical dissection of tumor cells and endoscopic imaging of the pancreas and colon. Gold (Au) nanoclusters (NCs) are comprised of a few tens of Au atoms that possess the ability to emit strong fluorescence, of which the wavelength is tunable in the range of the visible to near-infrared spectral region (9). Chen et al. (10) prepared bovine serum albumin–stabilized Au NCs (Au-BSA) for conjugation with biomolecules for specific targeting and with near-infrared dye for optical imaging. Met was conjugated to the carboxyl groups of BSA. The ICG derivative 02 (ICG-Der-02, also known as MPA) contains one carboxyl functional group for covalent conjugation to the amino group of BSA on the surface of Au-BSA NCs. MPA is a hydrophilic dye. Chen et al. (10) evaluated Au-BSA-Met-MPA (Au-Met-MPA) for in vivo NIR optical imaging in tumor-bearing mice.

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