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Alexa Fluor 680-glycylglycylglycine-bombesin[7-14]NH2 peptide.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2007 Jul 20 [updated 2007 Aug 25].


Alexa Fluor 680-glycylglycylglycine-bombesin[7-14]NH2 peptide (Alexa Fluor 680-G-G-G-BN[7-14]NH2), a peptide analog of human gastrin-releasing peptide (GRP) conjugated with Alexa Fluor 680, was developed for optical imaging of tumors with overexpressed GRP receptors (1). Alexa Fluor 680 is a fluorescence dye with an absorption maximum of 679 nm, an emission maximum of 720 nm, and an extinction coefficient of 180,000 cm−1M−1 (2). The amphibian bombesin (BBN or BN), a peptide of 14 amino acids, is an analog of human GRP (a peptide of 27 amino acids) that binds to GRP receptors (GRP-R) with high affinity and specificity (1, 3). Both GRP and BN share an amidated C-terminus sequence homology of 7 amino acids, -Trp-Ala-Val-Gly-His-Leu-Met-NH2. BN-Like peptides have been shown to induce various biological responses in diverse tissues, including the central nervous system (CNS) and the gastrointestinal (GI) system (4, 5). They also act as potential growth factors for both normal and neoplastic tissues. Specific BN receptors (BN-R) have been identified on CNS and GI tissues and a number of tumor cell lines. The BN-R superfamily includes at least 4 different subtypes, namely the GRP-R subtype (BB2), the neuromedin B (NMB) receptor subtype (BB1), the BB3 subtype, and the BB4 subtype (6). The findings of GRP-R overexpression in various human tumors, such as breast, prostate, lung, colon, ovarian, and pancreatic cancers, provide opportunities for tumor imaging by designing specific molecular imaging agents to target the GRP-R (1, 7-10). A review by Smith et al. (10) indicated varying degrees of success in the current development of GRP-R–targeted radiopharmaceuticals for diagnostic or therapeutic applications. Various BN analogs have been labeled with 99mTc and 111In for single-photon emission computed tomography imaging. BN analogs labeled with 68Ga-, 18F-, or 64Cu have been studied for positron emission tomography imaging (8, 11, 12). Optical imaging is a method that utilizes light photons emitted from bioluminescence and fluorescence probes (13). Depth penetration is a major limiting factor for in vivo optical imaging. Currently, in vivo optical imaging has wide applications in small animal imaging but only limited applications in large animal and human studies (14). Near-infrared (NIR) fluorescence imaging (light range, 650−900 nm) has the advantages of relatively higher tissue penetration and lower autofluorescence from nontarget tissue. Alexa fluorochromes are spectrally unique fluorescent probes with relatively high quantum yields in their excitation and emission wavelength ranges (2, 15). These fluorochromes can be used in succinimidyl ester form for conjugation with the primary amines of biomolecules. Ma et al. (1) prepared and evaluated the fluorescence probe Alexa Fluor 680-G-G-G-BN[7-14]NH2 for optical imaging of breast cancer in mice.

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