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3-{4-[2-[Benzoxazol-2-yl-methylamino]ethoxy]phenyl}-2-(2-[18F]fluoroethoxy)propionic acid.


The MICAD Research Team.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2007 Apr 02 [updated 2007 May 15].


Peroxisome proliferator–activated receptors (PPARs), once considered orphan receptors, are now believed to be the primary modulators of glucose and lipid metabolism in animals. PPARs are also believed to regulate the storage and catabolism of dietary fat (1). There are three subtypes of the receptors, designated as PPAR-α, PPAR-β/δ, and PPAR-γ (2). Among these, PPAR-γ is the most extensively investigated and has been cloned from a variety of species including fish, amphibians, rodents, and mammals (2). PPAR-γ has been shown to be an important transcription factor receptor that regulates adipocyte differentiation (3), represses the ob gene that regulates leptin expression (4), and modulates obesity and inflammation in mice (5). There is evidence that activation of PPAR-γ can have an anti-carcinogenic effect on colon cancer (6), and that PPAR-γ can alter the malignant phenotype of some human colon carcinoma cell lines (7, 8). PPAR-γ levels were shown to be elevated in breast cancer cell lines and during metastases in animal tumor models for breast cancer (9). Although PPAR-γ ligands induced tumor differentiation in animal models, not all cell lines that were positive for PPAR-γ respond to the ligands. With these observations the investigators suggest receptor phosphorylation may be necessary for responsiveness because the phosphorylated receptor had a low ligand affinity (10), which led to a reduced responsiveness of S112 cells that probably had a previously phosphorylated receptor (11). Kim et al (12). suggest that the nonphosphorylated form of PPAR-γ may be a novel target for tumor therapy and that radiotracers could be used to identify tumors retaining the ability to bind the ligands. They suggest that functional imaging of the tumors may help identify, and allow direction of therapy for, patients who are most likely to benefit. This would reduce time lost in providing therapies to individuals who are unlikely to respond to treatment, as such patients could be provided alternative therapies. In an effort to develop a radiotracer compound that could be used to study tissue distribution of PPAR-γ and provide a high contrast between target and non-target tissue, Kim et al. selected a very potent synthetic ligand belonging to the 3-phenylpropionic acid (SB 213 068) class of compounds, a [18F]fluorine-substituted analog, 3-{4-[2-[-(benzoxazol-2-yl-methylamino])ethoxy]phenyl}-2-(2-[18F]fluoroethoxy)propionic acid (12), also designated as compound [18F]22. The tissue distribution of compound [18F]22 was studied in two animal models (rats and SCID mice) by the investigators.

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