Targeted functional imaging in breast cancer

Rapid synthesis of [18F]fluoroestradiol: remarkable advantage of microwaving over conventional heating

16α-[(18)F]fluoroestradiol ([(18)F]FES) is known as a clinically important tracer in nuclear medicine as an estrogen receptor ligand for investigating primary and metastatic breast cancers. Synthesizing [(18)F]FES is a two-step process associated with [(18)F]fluoride incorporation to the precursor (3-methoxymethyl 16β,17β-epiestriol-O-cyclic sulfone) and subsequent hydrolysis of the [(18)F]fluorinated intermediate with 2 N HCl. The impact of microwave (MW) heating on both fluorination and hydrolysis reactions was investigated. The duration and temperatures of the fluorination reaction were varied for both MW heating and conventional heating (CH) methods. Chemical and radiochemical purity and radiochemical yields were investigated for CH and compared with MW-assisted radiosyntheses. Quality control tests of MW-assisted [(18)F]FES were performed following US Pharmacopeia procedures for clinical-grade positron emission tomography pharmaceuticals. The results demonstrate that microwaving not only improves the (18)F-fluoride incorporation (~55% improvement at 110°C for 4 min) but also significantly reduces hydrolysis time (approximately sevenfold reduction at 120°C) in comparison with CH under similar conditions. The overall isolated radiochemical yield of purified [(18)F]FES was significantly higher (~90% improvement) with MW, and side products were notably fewer. Quality control test results demonstrated that [(18)F]FES produced by microwaving was suitable for human injection.

Synthesis of Clinical-Grade [(18)F]-Fluoroestradiol as a Surrogate PET Biomarker for the Evaluation of Estrogen Receptor-Targeting Therapeutic Drug

16 α -[(18)F]-fluoroestradiol ([(18)F]FES), a steroid-based positron emission tomography (PET) tracer, has emerged as a dependable tracer for the evaluation and management of estrogen receptor-positive (ER+) breast cancer patients. We have developed a fully automatic, one-pot procedure for the synthesis of [(18)F]FES using the Eckert & Ziegler (E & Z) radiomodular system. After [(18)F]fluorination, the intermediate was hydrolyzed with 2.0 M HCl twice and neutralized with sodium bicarbonate. After high-performance liquid chromatography (HPLC) purification, the decay-corrected radiochemical yield and purity of [(18)F]FES were 40 ± 5.0% (n = 12) and >97%, respectively. The product was stable up to 10 h. Total synthesis time including HPLC purification was 80 min. This new, fully automated rapid synthetic procedure provided high and reproducible yields of [(18)F]FES. Quality control (QC) tests showed that the [(18)F]FES produced by this method met all specifications for human injection.