Synthesis and evaluation of ¹⁸F-labeled choline as an oncologic tracer for positron emission tomography: Initial findings in prostate cancer

The up-regulation of rates of choline uptake and phosphorylation in certain malignancies has motivated the development of positron-labeled choline analogues for noninvasive detection of cancer using positron emission tomography (PET). The choline analogue, no-carrier-added [¹⁸F]fluoromethyl-dimethyl-2-hydroxyethyl-ammonium (FCH), was synthesized through the intermediate [¹⁸F]fluorobromomethane. FCH was evaluated in relationship to 2-[¹⁸F]fluoro-2-deoxyglucose (FDG) as an oncological probe in cultured PC-3 human prostate cancer cells, a murine PC-3 human prostate cancer xenograft model, and in PET imaging studies of patients with prostate cancer. FCH was synthesized in 20-40% radiochemical yield and > 98% radiochemical purity. Accumulation of FCH and FDG were comparable in cultured prostate cancer cells, whereas only FCH was inhibited (90%) by hemicholinium-3, a specific inhibitor of choline transport and phosphorylation. FCH showed similar biodistribution to [¹⁴C]choline in the tumor-bearing mouse, with prominent renal and hepatic uptake. Tumor uptake of FCH was similar to choline and FDG in the mouse model, although tumor:blood ratios were moderately higher for FCH. Initial PET imaging studies in prostate cancer patients showed high uptake of FCH in advanced prostate carcinoma and detection of osseous and soft tissue metastases. FCH uptake by tumors was markedly reduced in patients rescanned during androgen deprivation therapy. It is concluded that FCH closely mimics choline uptake by normal tissues and prostate cancer neoplasms. FCH is potentially useful as a PET tracer for detection and localization of prostate cancer and monitoring effects of therapy.