Design, Synthesis and Biological Properties of Estrogen Receptor Binding Breast Tumor Localizing Agents

Abstract

316 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.Several steroidal estrogens halogenated on the D-ring were synthesized and subjected to preliminary in vitro evaluation for usefulness as estrogen receptor binding radiopharmaceuticals. Two of these compounds, 16(alpha)-bromoestradiol-17(beta) and 11(beta)-methoxy-16(alpha)-bromoestradiol-17(beta) exhibited high binding affinity for the estrogen receptor, and were predicted to exhibit high binding selectivity as well. They were chosen for development into radiopharmaceuticals with the potential to act as breast tumor localizing agents. A mild, regioselective method for high yield radiobromination of enol acetate derivatives of D-ring steroidal ketones involving in situ oxidation of no-carrier-added radiobromide was developed for the synthesis of {('77)Br}-16(alpha)-bromoestrone-3-acetate and the corresponding 11(beta)-methoxy derivative from estrone-3,17-enol diacetate or 11(beta)-methoxy-estrone-3,17-enol diacetate and no-carrier-added {('77)Br}-sodium bromide. Limited kinetic and mechanistic studies indicated that the oxidizing agent was peroxyacetic acid, and the radiobrominating agent was {('77)Br}-hypobromous acid. The gamma-emitting radiobromoketone acetates were reduced to the desired {('77)Br}-16(alpha)-bromoestradiol-17(beta) or the corresponding 11(beta)-methoxy derivative (and their 17(alpha) epimers) with lithium aluminum hydride. Conditions were optimized (-78(DEGREES)C, 10 min) to minimize debromination on the no-carrier-added scale. High pressure liquid chromtography allowed both radiobrominated estradiol derivatives to be isolated at 1000 Ci/mMol specific activity on a routine basis. Subsequent biological experiments showed that they were concentrated selectively in estrogen target tissues of the immature female rat and estrogen receptor containing DMBA induced mammary tumors in mature female rats by a mechanism presumably involving the estrogen receptor. The radiobrominated 11(beta)-methoxy estradiol was more effective in this respect than the corresponding des-methoxy compound, for the immature uterus-to-blood uptake ratio for {('77)Br}-11(beta)-methoxy-16(alpha)-bromoestradiol-17(beta) was 25.7 (+OR-) 5.9 to 1, while the corresponding ratio for {('77)Br}-16(alpha)-bromoestradiol-17(beta) was 13.0 (+OR-) 3.4 to 1 at one hour post-injection. Other biological experiments concerning the time course of tracer uptake and clearance form the target tissues, subcellular distribution of tracer in target tissues, metabolic fate, and comparison to analogous radioiodinated compounds in vivo as well as experiments concerning the receptor and non-receptor binding properties of the compounds in vitro are described. Both radiobromosteroids were shown to meet all the necessary criteria for use as estrogen receptor binding radiopharmaceuticals. They were used to image DMBA induced mammary adenocarcinoma in mature female rats with the use of the Anger scintillation camera. {('77)Br}-16(alpha)-Bromoestradiol-17(beta) was further evaluated (dosimetry, pharmacology) for use as a scintigraphic agent in humans. This compound was used to obtain an image of a primary human breast tumor that was shown to contain high levels of estrogen receptor upon removal. These results are the first example of scintigraphic imaging of estrogen receptor containing mammary tumors in animals or humans utilizing a receptor binding radiopharmaceutical.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD