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Development of ¹⁸F-Fluoroethylcholine for Cancer Imaging with PET: Synthesis, Biochemistry, and Prostate Cancer Imaging

¹ Department of Radiology, International Medical Center of Japan, Tokyo, Japan
² Department of Urology, International Medical Center of Japan, Tokyo, Japan

View larger version (17K): [in a new window]   FIGURE 1. Scheme of synthesis of FECh and 18F-FECh. Fluoroethanol method produces nonradioactive FECh tosylate as final product. TBA method produces radioactive 18F-FECh tosylate as final product.

View larger version (19K): [in a new window]   FIGURE 2. (A) Automated apparatus for 18F-FECh synthesis. Reaction vessel is shown close up. Purification module is out of view. (B) Preparative HPLC of 18F-FECh in automated apparatus for 18F-FECh synthesis. Column used was ODS-silica gel column, 250 x 10 mm; solvent, 50 mmol/L phosphoric acid + 1 mmol/L 2-naphthalenesulfonic acid; flow rate, 5 mL/min. Radioactivity "halfway down the column" is reading of detector (detector 1) placed on side of column to watch approach of 18F-FECh. Radioactivity of effluent from column was monitored by another detector (detector 2).

View larger version (18K): [in a new window]   FIGURE 3. (A) HPLC after incubation of 18F-FECh with choline kinase and with choline oxidase. No-carrier-added 18F-FECh chloride was incubated with yeast choline kinase and 15 µmol ATP or with bacterial choline oxidase. From incubated specimen, methanol-water–soluble component was separated and fractionated on cation- and anion-exchange HPLC. 18F radioactivity was measured in each fraction. (B) HPLC after incubation of 18F-FECh with choline kinase and -32P-ATP. No-carrier-added 18F-FECh chloride (approximately 0.005 µmol) was incubated with yeast choline kinase and 0.01 µmol -32P-ATP. From incubated specimen, methanol-water–soluble component was separated and fractionated on anion-exchange HPLC. 18F and 32P radioactivities were measured in each fraction. kcpm = kilocounts per minute.

View larger version (13K): [in a new window]   FIGURE 4. HPLC of methanol-water layer after incubation of 18F-FECh with Ehrlich ascites tumor cells. No-carrier-added 18F-FECh chloride was incubated with Ehrlich ascites tumor cells (approximately 106 cells/mL) in glucose-fortified Hanks’ solution for 30 min. Methanol-water–soluble component was separated from incubated cells and divided into halves. One half was analyzed on HPLC using cation-exchange resin and other half was analyzed on HPLC using anion-exchange resin. 18F radioactivity was measured in every fraction.

View larger version (88K): [in a new window]   FIGURE 5. TLC of chloroform layer after incubation of 18F-FECh with Ehrlich ascites tumor cells (autoradiography). No-carrier-added 18F-FECh chloride was incubated with Ehrlich ascites tumor cells (approximately 106 cells/mL) in glucose-fortified Hanks’ solution for 30 min. Chloroform-soluble fraction of cell extract was concentrated and developed on TLC silica gel plates. Solvent was as follows: for alkaline system, chloroform, methanol, and 28% ammonia (65:35:5); for acidic system, benzene, pyridine, and formic acid (50:40:10). Autoradiography of TLC plates was performed using imaging plate detector system. Authentic choline-containing phospholipids were developed in same way as above and are indicated by arrows. PCh = phosphatidylcholine; Sph = sphingomyelin; Lyso = lysophosphatidylcholine.

View larger version (14K): [in a new window]   FIGURE 6. Time course of uptake and metabolism of 18F-FECh in Ehrlich ascites tumor cells. No-carrier-added 18F-FECh chloride was incubated with Ehrlich ascites tumor cells (approximately 106 cells/mL) in glucose-fortified Hanks’ solution for various periods up to 60 min. Total 18F uptake was measured after washing cells by centrifugation, and cell-to-medium ratio was calculated after hematocrit determination. After treatment of cells with methanol and chloroform, radioactivities in free 18F-FECh, phosphoryl-18F-FECh, 18F-labeled phospholipids (phosphatidyl-18F-FECh and so forth), and proteins were measured.

View larger version (39K): [in a new window]   FIGURE 7. (A) Time course of radioactivity concentration in blood, prostate cancer, and urine after intravenous injection of 18F-FECh to untreated prostate cancer patient. SUV was calculated from PET data. (B) PET images of prostate cancer with 18F-FECh and 11C-choline and pathologic specimen of resected prostate (patient 5). 18F-FECh and 11C-choline images were taken at 60 and 20 min after injection, respectively. Red represents SUV of 4.0. Under diagnosis of stage B2, total prostatectomy and bilateral pelvic lymph node dissection were performed. Pathologic examination indicated adenocarcinoma of prostate in both lobes (Gleason score, 7) and no metastasis in pelvic lymph nodes (pathologic stage, pT2b, pN0). Largest tumor mass, 1.2 cm in diameter, was located in peripheral zone of left lobe.