Several aspects of steroid biochemistry as they are related to hormonally dependent tumors, especially breast cancer, are to be studied. Our recent identification of a new class of steroids, non-polar lipoidal derivatives in steroidogenic tissue has been extended and we have isolated a lipoidal derivative of estradiol that is biosynthesized in mammary tumors and the uterus. Experiments are being conducted to determine the chemical structure of the non-polar group covalently linked to estradiol. These studies will be performed by radiochemical techniques in conjunction with purification by high pressure liquid chromatography and identification by gas chromatography/mass spectroscopy, as well as other classical methods. Further experiments will also be carried out to determine the biochemical events involved in the synthesis of this substance as well as its physiological role. The relationship of the lipoidal estrogen to estrogen responsive tissue and the estrogen receptor as well as the endogenous concentration of this substance will be explored. Our success in synthesizing 16 alpha-125I-estradiol, a gamma-emitting derivative of estradiol, which binds with high affinity and specificity to the estrogen receptor will be fully expanded. While the apparent specific activity, greater than 100 Ci/mM, of the iodinated estrogen is now more than adequate for usual receptor studies, attempts are being made to synthesize carrier free trace greater than 2000 Ci/mM) for increased sensitivity and for use with small clinical samples. The material now available is being used to develop an assay for the detection of estrogen receptor in breast tumors. 131I labelled estradiol is being prepared for in vivo imaging and as a possible palliative agent. In addition, doubly labelled estradiol (125I and 131I) is to be utilized in vitro for experiments on receptor turnover and subcellular localization. Furthermore, 16 alpha-125I-estradiol has been found to bind to antibodies formed against estradiol haptens conjugated at position c-3, c-6 and c-17 of the steroid nucleus to bovine serum albumin. Sensitive redioimmunoassays for estradiol are being developed. The exchange technique used for the synthesis of the iodinated estrogen is to be used for the synthesis of other radioiodine labelled steroids that bind to progesterone, androgen, and corticoid receptors.