Synthesis and preliminary evaluation of a 18 F‐labeled ethisterone derivative [ 18 F]EAEF for progesterone receptor targeting

To develop a novel progesterone receptor‐targeting probe for positron emission tomography imaging, an ethisterone derivative [ 18 F]EAEF was designed and prepared in high decay‐corrected radiochemical yield (30–35%) with good radiochemical purity (>98%). [ 18 F]EAEF is a lipophilic tracer (log P  = 0.53 ± 0.06) with very good stability in saline and serum. In the biodistribution study, high radioactivity accumulation of [ 18 F]EAEF were found in uterus (5.73 ± 1.83% ID/g) and ovary (4.05 ± 0.73% ID/g) at 2 hr postinjection (p.i.), which have high progesterone receptor expression after treated with estradiol, while the muscle background has very low uptake (0.50 ± 0.17% ID/g). For positron emission tomography imaging, [ 18 F]EAEF showed high uptake in progesterone receptor‐positive MCF‐7 tumor (3.15 ± 0.07% ID/g at 2 hr p.i.) with good tumor to muscle ratio (2.90), and obvious lower tumor uptakes were observed in MCF‐7 with EAEF blocking (1.84 ± 0.05% ID/g at 2 hr p.i.) or in progesterone receptor‐negative MDA‐MB‐231 tumor (1.80 ± 0.03% ID/g at 2 hr p.i.). Based on the good stability and specificity of [ 18 F]EAEF, it may be a good candidate for imaging progesterone receptor and worth further investigation.