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99mTc-ethylenediamine N,N’-diacetic acid/hydrazinonicotinamide-Tyr3-octreotide.

Authors

Chopra A1.

Source

Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2007 Oct 12 [updated 2007 Nov 07].

Author information

1
National Center for Biotechnology Information, NLM, NIH, Bethesda, MD 20894, Email: micad@ncbi.nlm.nih.gov

Excerpt

Somatostatin (SS) is a cyclic peptide that is primarily expressed in the central nervous system and some peripheral tissues (1). Receptors for SS have been identified in the central nervous system, cells of neuroendocrine origin, the gastrointestinal tract, and even in lymphocytes (2). The SS receptor has a seven-transmembrane domain structure and belongs to the G-protein–coupled receptor family. Five subtypes of the SS receptor have been identified, and each subtype is produced from a single gene located on a different chromosome. This indicates tissue-specific regulation of SS receptor expression and suggests that each subtype has a distinct function in the various organs (2). Because of its several physiological functions, SS is considered to be a neurotransmitter or a hormone that acts through the autocrine and paracrine processes (3). In general, SS inhibits the production of hormones from various glands. SS has been evaluated for the treatment of various diseases, including cancers of endocrine origin as a result of hyperactive glands. However, SS has a short plasma half-life because of rapid enzymatic degradation and has been observed to be ineffective for such therapy (2). The development of SS analogs resistant to enzymatic degradation, but with a biological activity similar to SS, led to the application of these analogs for the treatment of cancerous tumors (4, 5). The mechanism by which SS and its analogs inhibit tumor growth was detailed by Moody et al. (6). A cyclic octapeptide SS analog, octreotide, was synthesized and conjugated with diethylenetriamine pentaacetic acid (DTPA) for chelating radioactive indium (111In) to obtain 111In-DPTA-octreotide (111In-DPTA-OCT). On binding to the SS receptor, 111In-DPTA-OCT is rapidly internalized and results in accumulation of the radiochemical in the tumor cells. Subsequently, the tumors can be detected by scintigraphy and treated with radiolabeled peptides (6). Although 111In-DPTA-OCT is considered suitable for the detection and diagnosis of tumors bearing SS receptors, the use of 111In as a radionuclide has some limitations. This radioelement has limited availability, a long physical half-life (67 h), high gamma energy that results in increased radiation exposure of the patient, and suboptimal image characteristics (7, 8). Therefore, Decristoforo et al. used radioactive technetium (99mTc) with a half-life of 6 h to generate 99mTc-labeled hydrazinonicotinamide-Tyr3-octreotide (99mTc-HYNIC-TOC), a radiochemical with superior imaging properties compared to 111In-DPTA-octreotide (9). This chapter describes the synthesis, in vitro and in vivo, and clinical studies performed with 99mTc-HYNIC-TOC.

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