Abstract
Estrogen receptor (ER) expression level of human breast cancer often reflects the stage of disease and is usually monitored by immunohistochemical staining in vitro. The preferable non-invasive and real-time diagnosis in vivo is more accessible by PET scan using 16α-[18F]FES. The objective of this study was to develop a quick automatic method for synthesis of solvent-free 16α-[18F]FES using a CFN-MPS-200 synthesis system and compare the catalytic efficiency of two phase transfer catalysts, Kryptofix 222/K2CO3 (K222/K2CO3) and tetrabutylammonium hydrogen carbonate (TBA·HCO3). In this method, phase transfer catalysts K222/K2CO3 and TBA·HCO3 were used, respectively. The intermediate products were both hydrolyzed with hydrochloric acid and neutralized with sodium bicarbonate. The crude product was purified with semi-preparative HPLC, and the solvent was removed by rotary evaporation. The effects of radiofluorination temperature and time on the synthesis were also investigated. Radiochemical purity of solvent-free product was above 99% and the decay-corrected radiochemical yield of 16α-[18F]FES was obtained in 48.7 ± 0.95% (catalyzed by K222/K2CO3, n = 4) and 46.7 ± 0.77% (catalyzed by TBA·HCO3, n = 4, respectively). The solvent-free 16α-[18F]FES was studied in clinically diagnosed breast cancer patients, and FES-PET results were compared with pathology diagnosis results to validate the diagnosis value of 16α-[18F]FES. The new method was more reliable, efficient, and time-saving. There was no significant difference in catalytic activity between K222/K2CO3 and TBA·HCO3.
Highlights
Estrogen receptor (ER) expression level in breast cancer is known as a meaningful prognostic indicator
We investigated whether Kryptofix 222 (K222)/K2CO3 or TBA·HCO3 was the appropriate phase transfer catalyst and checked the quality of the radiopharmaceutical catalyzed by K222/K2CO3 or TBA·HCO3 for potential clinical use
We further investigated whether K222/K2CO3 or TBA·HCO3 is the appropriate phase transfer catalyst for the automated synthesis of 16α-[18F]FES
Summary
Estrogen receptor (ER) expression level in breast cancer is known as a meaningful prognostic indicator. An ideal non-invasive method monitoring real-time ER expression in the whole body is preferable in clinical practice. The utility of 16α-[18F]FES, especially in conjunction with [18F]fluorodeoxyglucose, is considered of important diagnostic value. It is a challenge for the routine synthesis of 16α-[18F]FES to meet clinical requirements. The synthesis of 16α-[18F]FES through different methods has been reported by several studies. Most of these studies required more than 60 min with a low yield and mixed radiochemical impurities. Clinical applications of 16α-[18F]FES as an important tool to non-invasively measure ER expression will depend on its ideal radiochemical purity and steady routine production with a high yield
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