16-ALPHA-[BR-77]BROMO-11 BETA-METHOXYESTRADIOL-17-BETA - A GAMMA-EMITTING ESTROGEN IMAGING AGENT WITH HIGH UPTAKE AND RETENTION BY TARGET ORGANS

Abstract

16.alpha.-[77Br]Bromo-11.beta.-methoxyestradiol-17.beta. [MBE(Br-77)], a compound with high affinity for the estrogen receptor and with low nonspecific binding, was prepared with an effective specific activity of 770-1450 Ci/mmol at the time of synthesis. In immature female rats, this compound is taken up selectively by the uterus and retained for prolonged periods. This is presumably due to the binding of this compound to the estrogen receptor, as uterine uptake is blocked selectively by coadministration of an excess of unlabeled estradiol, and administration of a chase dose of unlabeled estradiol results in a rapid decrease in activity in the uterus. In double-label experiments with 16.alpha.-[125I]estradiol and MBE(Br-77), the 2 compounds showed equally selective uterine uptake at 1 h, but the Br-labeled compound became increasingly more selective at 3 and 6 h. MBE(Br-77) may be a more favorable agent for imaging human breast tumors than the previously described compound, 16.alpha.-[77Br]bromoestradiol-17.beta.