Quantitative structure-activity relationship of various endogenous estrogen metabolites for human estrogen receptor alpha and beta subtypes: Insights into the structural determinants favoring a differential subtype binding.

To search for endogenous estrogens that may have preferential binding affinity for human estrogen receptor (ER) alpha or beta subtype and also to gain insights into the structural determinants favoring differential subtype binding, we studied the binding affinities of 74 natural or synthetic estrogens, including more than 50 steroidal analogs of estradiol-17beta (E2) and estrone (E1) for human ER alpha and ER beta. Many of the endogenous estrogen metabolites retained varying degrees of similar binding affinity for ER alpha and ER beta, but some of them retained differential binding affinity for the two subtypes. For instance, several of the D-ring metabolites, such as 16 alpha-hydroxyestradiol (estriol), 16 beta-hydroxyestradiol-17 alpha, and 16-ketoestrone, had distinct preferential binding affinity for human ER beta over ER alpha (difference up to 18-fold). Notably, although E2 has nearly the highest and equal binding affinity for ER alpha and ER beta, E1 and 2-hydroxyestrone (two quantitatively predominant endogenous estrogens in nonpregnant woman) have preferential binding affinity for ER alpha over ER beta, whereas 16 alpha-hydroxyestradiol (estriol) and other D-ring metabolites (quantitatively predominant endogenous estrogens formed during pregnancy) have preferential binding affinity for ER beta over ER alpha. Hence, facile metabolic conversion of parent hormone E2 to various metabolites under different physiological conditions may serve unique functions by providing differential activation of the ER alpha or ER beta signaling system. Lastly, our computational three-dimensional quantitative structure-activity relationship/comparative molecular field analysis of 47 steroidal estrogen analogs for human ER alpha and ER beta yielded useful information on the structural features that determine the preferential activation of the ER alpha and ER beta subtypes, which may aid in the rational design of selective ligands for each human ER subtype.

Enzymes involved in the formation and transformation of steroid hormones in the fetal and placental compartments.

Human fetal and placental compartments have all the enzymatic systems necessary to produce steroid hormones. However, their activities are different and complementary: the fetus is very active in converting acetate into cholesterol, in transforming pregnanes to androstanes, various hydroxylases, sulfotransferases, whilst all these transformations are absent or very limited in the placenta. This compartment can transform cholesterol to C21-steroids, convert 5-ene to 4-ene steroids, and has a high capacity to aromatize C19 precursors and to hydrolyse sulfates. Steroid hormone receptors are present at an early stage of gestation and are functional for important physiological activities. The production rate of some steroids increases drastically with fetal evolution (e.g. estriol increases 500-1000 times in relation to non-pregnant women). We can hypothesize that the control of active steroid hormones could be carried out by fetal and placental factors, which act by stimulating or inhibiting the enzymes involved in their formation and transformation during pregnancy evolution and, consequently, limiting the high levels of the biologically active hormone.

Vaginal absorption of two estriol preparations. A comparative study in postmenopausal women.

In a comparative randomized cross-over study the absorption of a single dose of 0.5 mg estriol from a vaginal cream or a vaginal suppository (OvestinR, Organon, The Netherlands) was studied. Eight healthy postmenopausal women participated and the preparations were given with an interval of 14 days. Blood sampling was performed twice before application and then after 1/4, 1/2, 1, 2, 4, 6, 8, 24 and 48 hours. Serum was analysed for unconjugated and conjugated estriol (E3), FSH and LH by radio-immunoassay. Considerable interindividual variations in serum levels of unconjugated E3 were found but mean values were about equal throughout the study for the two preparations. Peak levels of 0.5-0.6 nmol/l were achieved 1-2 hours after application of the preparations and after 24 hours no unconjugated E3 was measurable. Conjugated E3 rose rapidly but within 48 hours serum concentrations reached baseline levels. A maximum decrease in serum LH levels of about 40% was obtained with both preparations after 6 hours and the return to baseline within 24 hours indicates a relationship to unconjugated E3. FSH in serum was maximally suppressed 6-12%. Estriol is thus readily absorbed by the vaginal route and peak levels of unconjugated E3 after insertion of 0.5 mg estriol seem to be comparable to those obtained after 8-12 mg estriol given orally.

Effect of diet on plasma and urinary hormones in South African black men with prostatic cancer.

Epidemiological evidence suggests that the incidence and death rate from prostatic cancer, an endocrine-associated disease, are related to environmental factors including diet. In this study, a comparison of serum and urinary levels of steroid hormones was carried out in healthy elderly rural vegetarian South African black men, a low-risk population, and a comparable group of men with prostatic cancer. In these prostatic cancer patients, plasma androgen levels decreased, while estrogen levels increased. Concomitantly, the androsterone:etiocholanolone ratio increased, and a greater proportion of estrogens was excreted as estriol. When transferred to a Western diet, plasma androgens showed a further decrease and a greater increase in estrone in prostatic cancer patients. In prostatic cancer patients, the total urinary androgen and estrogen levels were unaltered. However, in elderly healthy men, the Western diet decreased the excretion of estrogens and androgens. Thus, a Western diet supplemented the decrease in plasma androgens initially present in these patients. Evidence suggests that the decrease in plasma androgens increases the estrogen: androgen ratio, which may lead to hyperplasia of the prostatic ductal epithelia, a change enhanced by a Western diet. Changes in urinary steroid hormone levels in South African black patients comparable to those reported in white prostatic cancer patients indicate that hormonal changes must be related to several environmental factors, apart from diet. A simultaneous study of the steroid hormone composition of blood and prostatic fluid in this low-risk population is suggested.

Comparative properties of the catechol estrogens, I: methylation by catechol-O-methyltransferase and binding to cytosol estrogen receptors.

Five catechol estrogens and two 2-methoxyestrogens were compared for their relative affinity of binding to hypothalamic, pituitary, and uterine cytosol estrogen receptors; and for the kinetics of the catechols' methylation by hepatic catechol-0-methyltransferase. All of the catechol estrogens tested have similar Km's for 0-methylation (9-14 muM). Estrogen receptor affinities, however, differ widely. In hypothalamus, for example, where estradiol-17 beta has a Kd of 0.039 +/- 0.008 nanomolar, 4-hydroxyestradiol also binds tightly (0.12 +/- 0.02 nM), 2-hydroxyestradiol and 4-hydroxyestrone with intermediate affinity (0.26 +/- 0.06 and 0.28 +/- 0.07 nM, respectively), and 2-hydroxyestrone and 2-hydroxyestriol much less well (1.68 +/- 0.79 and 1.27 +/- 0.26 nM, respectively). The binding of the 2-methoxyestrogens is extremely weak. These receptor affinities roughly parallel the potencies of these compounds in altering gonadotropin secretion.

Potential test systems for drugs against prostatic cancer.

A number of chemotherapeutic agents have been tested in two systems which could be useful as models in the search for effective drugs for cancer of the prostate. One system involved the effects of the administered drugs on rat prostatic 5 alpha-reductase and arginase activities. Since both enzymic systems are androgen dependent and essential for prostatic function and anatomy, the effectiveness of a drug in these systems could be indicative of its value in the treatment of prostatic cancer. Michaelis constants were obtained with Lineweaver-Burk plots and the conclusions are based on a comparison of these plots with those of the controls. Thus, the following results were obtained: (a) isophosphamide, bleomycin, and procarbazine produced definite inhibition of 5 alpha-reductase in either or both the ventral and dorsolateral glands of the rat; (b) 5-fluorouracil, vincristine, bleomycin, procarbazine, adriamycin, and hexamethyl-melamine inhibited arginase activity significantly in both glands; (c) streptozotocin and 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (NSC-45388) produced inhibition of arginase in the ventral gland only; (d) in contrast to the noncompetitive or uncompetitive inhibition of most of the drugs, particularly in the ventral gland, procarbazine, hexamethylmelamine, bleomycin, adriamycin, and NSC-45388 produced competitive inhibition of arginase in the dorsolateral gland; and (e) seven of the drugs led to an activation of 5 alpha-reductase (5-fluorouracil, vincristine, NSC-45388, hexamethylmelamine, CCNU, streptozotocin, and diglycolaldehyde). The second model system utilized the deposition of labeled estriol and testosterone in the dog prostate and the effects of drug therapy as a possible index of effectiveness in prostatic cancer. Streptozotocin and procarbazine definitely interfered with the deposition of both estriol and testosterone. On the basis of the data obtained, the model systems investigated by us could potentially serve as reliable indicators for the clinical use of drugs against cancer of the prostate.