Comparison of the Distribution of Bromine-77-Bromovinyl Steroidal and Triphenylethylene Estrogens in the Immature Rat

The specific uptake and distribution of steroidal and non-steroidal [77Br]bromovinylestrogens were studied in immature female rats to assess the potential of these radioligands for imaging or therapy of estrogen receptor (ER) positive cancers. E-17 alpha [77Br]bromovinylestradiol, its 3 methyl ether and 11 beta-methoxy derivative, as well as the triphenylethylene estrogen, 1,1-bis[4-hydroxy-phenyl]-2-[77Br]bromo-2- phenylethylene all showed diethylstilbestrol inhibitable, specific uptake of radiobromine between 2 and 16 hr after i.p. administration. The highest concentrations in the estrogen target tissues and the highest target tissue-to-blood ratios were found with E-17 alpha-[Br]bromovinyl-11 beta-methoxyestradiol, but it also had rather high nonspecific uptake in all tissues. The triphenylethylene estrogen showed comparable specific uptake in estrogen target tissues to 17 alpha [77Br]bromovinylestradiol at 2 hr but better apparent retention, indicated by higher specific target tissue levels at the later time points. Thus, [77Br]bromovinyl-11 beta- methoxyestradiol and 1,1-bis[4-hydroxyphenyl]-2-[77Br]bromo-2-phenylethylene appear most favorable for these applications.