Introduction-Progesterone receptors (PRs) are present in many breast tumors, and their levels are increased by certain endocrine therapies. They can be used as targets for diagnostic imaging and radiotherapy. Results-[ 76 Br]3 was synthesized in 5% overall yield with specific activity being 200~1250 Ci/ mmol. [ 76 Br]3 demonstrated high PR-mediated uptake in the target tissue uterus (8.72 ± 1.84 %ID/ g at 1 h) that was reduced by a blocking dose of unlabeled progestin R5020, but the non-specific uptake in blood and muscle (2.11 ± 0.14 and 0.89 ± 0.16 %ID/g at 1 h, respectively) was relatively high. [ 76 Br]3 was stable in whole rat blood in vitro, but it was not stable in vivo due to the fast metabolism that occurred in the liver, resulting in the formation of a more polar radioactive metabolite and free [ 76 Br]bromide. The level of free [ 76 Br]bromide in blood remained high during the experiment (2.11 ± 0.14 %ID/g at 1 h and 1.52 ± 0.24 %ID/g at 24 h). The tissue distribution of [ 76 Br]3 at 1 and 3 hours was compared with that of the 18 F analogs, [ 18 F]FFNP 1 and ketal 2.
Method-16α,17α-[(R)-1'-α-(5-[
Conclusion-[76 Br]3 may have potential for imaging PR positive breast tumors at early time points, but it is not suitable for imaging at later times or for radiotherapy.