7α- and 17α-Substituted estrogens containing tridentate tricarbonyl rhenium/Technetium complexes: synthesis of estrogen receptor imaging agents and evaluation using microPET with technetium-94m Original Research Article

To develop technetium and rhenium-labeled imaging agents for estrogen receptor (ER) positive breast tumors, we have prepared tridentate metal tricarbonyl chelates substituted at the 7α- and 17α-positions of estradiol. Some of the Re(CO)3 conjugates have high binding for the ER in vitro. The in vivo biodistribution of the highest affinity of these novel metal tricarbonyl conjugates, prepared as the 94mTc labeled analogue, was evaluated by tissue dissection and microPET imaging. Although target tissue-selective uptake was not apparent, it is notable that microPET imaging identified the stomach as a major site of activity deposition, a site that might have been missed by standard tissue distribution studies.