Exemestane is a very potent, orally active, selective and long-lasting steroidal irreversible inhibitor of aromatase. It is 150 times more potent than aminoglutethimide (AG) in inhibiting human placental aromatase (Ki of 4.3 and 671 nM, respectively). The compound is presently under phase III evaluation in Europe and the U.S.A. for the treatment of postmenopausal advanced breast cancer (ABC). Clinical pharmacology studies have been carried out with single doses ranging from 0.5 to 800 mg and repeated doses of up to 600 mg a day, in 132 postmenopausal healthy volunteers and in 185 postmenopausal women with ABC. Results obtained using a very specific and sensitive analytical method (high performance liquid chromatography-radioimmunoassay; HPLC-RIA) indicated that exemestane is extremely effective in inhibiting plasma estrogens levels. Estrogen inhibition is clearly evident at 5 mg a day and maximal suppression for E2, E1 and E1S (>85%, >90% and >90%, respectively) is obtained at 10-25 mg a day. Data from non-controlled phase II studies involving more than 400 patients indicated a clear anti-tumour activity in postmenopausal ABC patients failing multiple hormonal treatments. In 62 patients progressing on AG (> or = 500 mg a day) exemestane treatment resulted in an objective response rate of approximately 24%; disease stabilization > or = 24 weeks was observed in an additional 24% of cases. With regard to safety, although daily doses up to 600 mg were administered, the maximal tolerated dose was not achieved; reported symptoms were mainly related to the pharmacological action of the compound and were usually mild to moderate in severity, resulting in the discontinuation of therapy in less than 3% of cases. In conclusion, the available results suggest that exemestane treatment is associated with minimal toxicity, and may be of significant benefit for ABC women who have exhausted conventional therapy.
The estrogen (ER) and progesterone (PgR) receptor levels in various gynecological tumors were measured. The same tumors were exposed in vitro to toremifene, MPA or their combination and the growth of the tumors was followed by measuring the adenosine triphosphate (ATP) within the cells by a simple bioluminescence assay. Altogether 34 clinical samples were studied. DMBA-induced mammary tumors bearing rats were treated in vivo with toremifene, MPA and their combination. About half of the ovarian cancers and 6 out of the 7 adenocarcinomas of uteri contained ER. The ovarian tumors were PgR rich in 25% and adenocarcinomas of uteri in 6 out of the 7 cases. When compared to control toremifene (concentration 1 mumol/l) was able to decrease the number of living cells to 50% or less in 9/34 samples, MPA (concentration 10 mumol/l) in 17/34 samples, and the combination in 25/34 samples. In five cases the antitumor effect of the combination was synergistic. In two cases signs of weak antagonism were seen. In vivo the antitumor effect of toremifene and MPA was clearly synergistic against DMBA-induced cancers. The effect was dose-dependent and at sufficiently high doses it was possible to eradicate the tumors and cure the animals.
A recent overview of the results of all trials of adjuvant chemotherapy suggests a clinically and statistically significant advantage for premenopausal women with positive axillary nodes. The results of the same approach for all other women with early breast cancer are very disappointing. These data suggest that contrary to the original hypothetical model, adjuvant chemotherapy is exerting its effect indirectly via chemical castration. In contrast, the results of trials of adjuvant tamoxifen have been more promising and, again, in contrast to the original premises, it would appear that a modest improvement in survival and delay in recurrence can be achieved amongst all groups of women independent of age, nodal status and oestrogen receptor content of the primary tumour. In order to explain these counter-intuitive observations, it is necessary to elaborate an alternative biological model. This paper describes the current thinking on the mode of action of the "anti-oestrogens" and the possible role of inhibitory growth factors activated indirectly by anti-oestrogens. Future trials of adjuvant systemic therapy for early breast cancer should include studies on the duration of tamoxifen, comparing 2 yr with longer, and a comparison of tamoxifen alone with polychemotherapy for premenopausal node positive patients.
The 5 alpha-reductase, the enzyme which converts testosterone into dihydrotestosterone (DHT), is present in several CNS structures of the rat. Recent reports from this laboratory indicate that the subcortical white matter and the myelin possess a 5 alpha-reductase activity several times higher than that present in the cerebral cortex. Moreover, previous ontogenetic observations indicate that in all cerebral tissues examined (including the myelin) the 5 alpha-reductase has a higher activity in immature animals. This study was performed in order to verify whether the differences in the 5 alpha-reductase activity on the various brain components might be due to the presence of different concentrations of the same enzyme or to different isoenzymes. To this purpose, the kinetic properties Km and Vmax were measured in the purified myelin as well as in homogenates of the subcortical white matter and of the cerebral cortex, obtained from the brain of adult (60-90-day-old), immature (23-day-old), and aged (greater than 20-month-old) male rats. The results indicate that the enzymes present in the myelin, in the subcortical white matter and in the cerebral cortex of adult male rats possess a very similar apparent Km (1.93 +/- 0.2, 2.72 +/- 0.73 and 3.83 +/- 0.49 microM respectively). On the contrary, the Vmax values obtained in the myelin (34.40 +/- 5.54), in the white matter (19.57 +/- 2.36) and in the cerebral cortex (6.47 +/- 1.03 ng/h/mg protein) of adult animals have been found to be consistently different. Very similar Km values were found in the myelin obtained from the brain of immature and very old rats (2.14 +/- 0.11 and 3.39 +/- 0.75 microM respectively). The Vmax measured in the myelin purified from the immature rat brain (62.25 +/- 4.52) showed a value which was much higher than that found in the myelin of adult animals (34.40 +/- 5.54); a Vmax (34.31 +/- 9.41) almost identical to that of adult animals was found in the myelin prepared from the brain of aged rats.
The pyrethroids are a class of natural and synthetic pesticides which were associated with an epidemic of gynecomastia in Haitian men in 1981. In the present study we tested several pyrethroids for their ability to interact with androgen binding sites in dispersed, intact human genital skin fibroblasts and in human plasma to sex hormone binding globulin (SHBG). All the pyrethroids tested inhibited fibroblast binding of [3H]methyltrienolone (R1881) at 22 degrees C with the following rank order of potency:pyrethrins greater than bioallethrin greater than fenvalerate greater than fenothrin greater than fluvalinate greater than permethrin greater than resmethrin. 50% displacement of [3H]R1881 binding to fibroblast androgen receptors was achieved by 1.5-44 x 10(-5) M concentrations of the competitors, respectively. Previous studies with cimetidine, a known inhibitor of androgen receptor binding, showed 50% competition at a concentration of 1.4 x 10(-4) M in this system. Scatchard analysis of binding experiments performed with increasing concentrations of [3H]R1881 in the presence of the pyrethroids indicated that the binding inhibition was competitive. On the other hand, of the pyrethroids examined only the pyrethrins (50% inhibition) and bioallethrin (43% inhibition) were able to displace [3H]testosterone from SHBG when tested at a concentration of 10(-4) M. These data indicate that a novel class of non-steroidal compounds, the pyrethroids, can interact competitively with human androgen receptors and SHBG. These findings provide a mechanism by which chronic exposure of humans or animals to pesticides containing these compounds may result in disturbances in endocrine effects relating to androgen action.
For many years, hypersecretion of estrogens has been suspected of being one of the major risk factors of breast cancer for premenopausal women. Seventeen premenopausal women, who had undergone lumpectomy because of breast cancer (T1a No Mo) 3 yr before entering the study, were compared to 9 normal women of similar age, parity and body weight. A chemiluminescent method was used for the determination of estrone-3-glucuronide (E1-3G) and pregnanediol-3-glucuronide (Pd-3G) in early morning urine samples collected for an entire menstrual cycle of each of the 26 subjects. During the follicular phase, no significant differences in E1-3G and/or Pd-3G excretion were found between the two groups. During the luteal phase the E1-3G/Pd-3G ratio in the early, middle and late luteal phase had significantly increased in the women with breast cancer, in spite of normal Pd-3G excretion. Therefore, the measurement of glucuronoconjugate metabolites of ovarian hormones in overnight urine might be conveniently applied to the study of ovarian function in subjects with breast cancer. Furthermore, the results of this study may indicate that an estrogen/progesterone imbalance is an additional risk factor for the premenopausal breast cancer patient.
The mechanisms by which ethanol (EtOH) inhibits the human chorionic gonado-tropin (hCG)-stimulated testosterone synthesis was studied in isolated rat Leydig cells in vitro. EtOH inhibited steroidogenesis, but this inhibition was reversed by l-glutamate (Glu) and an uncoupler of the oxidative phosphorylation, 2,4-dinitrophenol (DNP). The mechanism of EtOH-induced inhibition was studied by measuring steroidogenic precursors and comparing them with the cytosolic and mitochondrial NADH redox states during uncoupling or in the presence of Glu. DNP had a dual effect. Low concentrations abolished the EtOH-induced inhibition of progesterone to testosterone formation suggesting that the inhibitory step was at or before progesterone formation. A large concentration led to an overall decrease in steroidogenesis indicating toxic effects on steroidogenesis. The mitochondrial NADH/NAD+ ratio, measured as the 3-hydroxybutyrate/acetoacetate ratio, decreased simultaneously when steroidogenesis was stimulated, either during uncoupling or in the presence of Glu, whereas cytosolic NADH/NAD+ ratio, measured as lactate/pyruvate ratio showed no response. These results demonstrate that the rise in the mitochondrial NADH/NAD+ ratio rather than in the cytosolic one is connected with the inhibition of testosterone synthesis by EtOH in isolated Leydig cells. The EtOH-induced high mitochondrial NADH/NAD+ ratio may deplete mitochondrial oxalacetate concentrations. This can decrease the activity of several transport shuttles and interrupt the flow of mitochondrial citrate into the smooth endoplasmic reticulum, which then reflects to decreased rate of steroidogenesis in the presence of ethanol.
Liver homogenates from female rat strains (Sprague-Dawley, Wistar and Fisher) were incubated in a NADPH regenerating medium in the presence of labelled and unlabelled estrone. Liver microsomes isolated from male rats and female mice were used as positive controls. Using HPLC and paper chromatography, under the experimental conditions used it was found that liver homogenates from female rats were able to convert estrone to various metabolites such as 16 alpha-hydroxyestrone. In a mutagenicity assay (Ames test), with 16 alpha-hydroxyesterone as test substance, two strains (TA98 and TA1538) of the five strains tested showed a 2-3-fold increase in the number of his+ revertants relative to the control values. Estrone did not cause any mutagens in the test used. It is concluded that female rats are able to synthesize 16 alpha-hydroxyestron in vitro. Whether this compound is risk factor for breast cancer remains unclear.
The influence of oral high dose progestin (medroxyprogesterone acetate, MPA and megestrol acetate, MA) treatment on serum hormone levels was studied in ten postmenopausal women with advanced breast cancer. The gonadotropins and ACTH were significantly reduced by greater than 50 and 23%, respectively. Serum cortisol, DHEAS, androstenedione and testosterone were all significantly reduced (mean reduction between 64 and 76%), while serum estrone, estradiol and estrone sulfate were significantly reduced by 20-30%. Sex hormone binding globulin (SHBG) and corticosteroid binding globulin (CGB) were reduced by 68 and 25%, respectively. Although the dose of MA used (160 mg/day) was only 1/6 of the MPA dose (1000 mg/day), the mean serum level of MA was 2-fold higher than the mean serum level of MPA. MPA treatment gave a more pronounced suppression of SHBG than MA treatment, while estrone sulfate levels were more suppressed by MA. These findings suggest a differential effect of MPA and MA on certain plasma hormones, possibly of importance for understanding the mechanism of action of the two drugs. The reduction of estrone sulfate may be beneficial for the action of MA against breast cancer.
Twelve postmenopausal women with inoperable or metastatic breast cancer were given toremifene at a daily dose of 60 mg. The patients had no prior endocrine or cytotoxic therapy and further inclusion criteria were bidimensionally measurable disease, performance status above 50, expected survival of more than 3 months and estrogen receptor status positive or undetermined. Objective response [complete remission (CR) + partial remission (PR)] was achieved in 6 patients (50%) and stable disease was obtained in 5 patients. No side effects of the treatment were noted.
The protein binding of ethinylestradiol (EE2), gestodene (GEST) and 3-keto-desogestrel (KDG) has been determined by ultrafiltration in the serum of women who had either taken a gestodene (n = 37) or desogestrel (n = 28) containing oral contraceptive for a time period of at least 3 months. GEST and KDG were analyzed in individual serum pools whereas EE2 was repeatedly measured in two serum pools, each one representing one treatment group. The respective free fractions of the three steroids were 0.6 ± 0.1% (GEST), 2.5 ± 0.2% (KDG), 1.7 ± 0.6% (EE2, in the gestodene-group) and 1.5 ± 0.2% (EE2, in the desogestrel-group). EE2 was exclusively bound to albumin, whereas GEST and KDG were also bound to sex-hormone-binding globulin (SHBG). The distribution of the two progestins over the serum binding proteins was determined after heat-treatment of serum samples. For GEST, the contribution of albumin and SHBG was 24.1 ± 9.1 and 75.3 ± 9.1%, respectively and for KDG it was 65.9 ± 11.9 and 31.6 ± 12.0%, respectively. SHBG and corticosteroid-binding globulin (CBG) concentrations were measured in the serum samples obtained from both treatment groups. In the gestodene-group 180 ± 61 nmol/1 (SHBG) and 89 ± 13 mg/1 (CBG) were measured, the corresponding values in the desogestrel-group were 226 ± 64 nmol/1 (SHBG) and 93 ± 14 mg/1 (CBG).
The binding of progestin and glucocorticoid hormones was examined in the cytosol of rat adipose precursor cells. Progestin binding sites of high affinity and limited capacity were present in the cytosol of adipose precursor cells from female rats, but not from male rats, by using [3H]R5020 as radioligand. Glucocorticoid binding sites of high affinity and limited capacity were present in the cytosol of these cells from both male and female rats by using [3H]dexamethasone and [3H]triamcinolone acetonide as radioligands. The dissociation constants were in the physiological concentration range. Studies of competitive binding showed that progestin could compete with glucocorticoids at glucocorticoid binding sites. In a serum free medium glucocorticoid effect on cellular differentiation, monitored by glycerophosphate dehydrogenase (GPDH), was effectively counteracted by progesterone which by itself had no effect. These results demonstrate that progestin receptor exists only in rat adipose precursor cells from female rats, while glucocorticoid receptor exists in rat adipose precursor cells of both sexes. Glucocorticoid effects on cellular differentiation in these cells are mediated by the glucocorticoid receptor. Progestin binds to the glucocorticoid receptor and antagonizes glucocorticoid effect on cellular differentiation in these cells.
Two iodinated steroids, E-17 alpha-(2-iodovinyl)-5 alpha-dihydrotestosterone and Z-17 alpha-(2-iodovinyl)-5 alpha-dihydrotestosterone were synthesized in a search for a gamma-emitting androgen that binds with high affinity to the androgen receptor. Such compounds would be extremely useful research tools for studies of androgen responsive tissues and as in vivo probes of androgen responsive tumors such as prostate cancer. These 17 alpha-iodovinyl steroids were synthesized because many 17 alpha-substituents do not interfere markedly with binding to the androgen receptor and because similar analogs of other steroids, estrogens and progestins, have been shown to have the requisite properties for ligands to those receptors. Both of these potential ligands were tested for their ability to compete with [3H]R1881 for binding to the androgen receptor in cytosols from prostate, hypothalamus and pituitary. The relative binding affinities ranged between 5 and 20%, depending upon the tissue and steroid. In order to test the two ligands directly, they were both synthesized labelled with 125I and tested for binding to the androgen receptor in prostatic cytosol and in vivo for specific concentration in androgen responsive tissues. While there was considerable binding in the prostatic cytosol, it was not specific because 5 alpha-dihydrotestosterone did not compete. Likewise in the in vivo experiment there was no evidence for androgen receptor mediated concentration of the tracers. While on the basis of relative binding affinity, these 2 steroids appeared to be good candidates for androgen receptor ligands, neither were useful for this purpose. These results contribute new information which will be valuable in the design of other gamma-emitting androgens and emphasises that, in this process, other factors such as metabolism and nonspecific binding must be considered.
Glucocorticoids kill certain types of lymphoblasts, but the mechanisms are unknown. It is clear that sufficient numbers of functional glucocorticoid receptors are required to mediate lysis, but whether they do so through the classical model of steroid hormone activation and modulation of gene expression has not been established. In this report we have asked which region(s) of the steroid receptor are important for mediating lysis in leukemic T lymphoblasts. CEM-ICR 27 leukemic lymphoblasts, a clone of CEM cells which lack functional glucocorticoid receptors and therefore are neither lysed by dexamethasone nor capable of showing glutamine synthetase induction, were provided with steroid receptors by DNA transfections of various receptor gene constructs. We measured steroid mediated lysis, receptor number and induction of glutamine synthetase in the transfected cells. Our results provide evidence that the lysis mechanism in the ICR27 lymphoblasts is restored when functional receptor number is restored. The DNA binding region specifying high affinity for GRE sites is required. Lysis is mediated by any steroid that allows for activation of the receptor containing such a region. Our data support the view that steroid-mediated cell death occurs by a process requiring direct interaction of steroid-receptor complexes with the genome.
The effect of testosterone on precursor mitochondrial aspartate aminotransferase (pmAAT) mRNA was studied in rat ventral prostate and primary cell cultures of mini-pig prostate. Testosterone induced a 2-3-fold increase in pmAAT mRNA level in both rat ventral prostate and mini-pig prostate cultures. The pmAAT mRNA induction occurred 30 min after testosterone treatment and was maximal by 1.5 h. Prostatic mAAT activity was also induced by testosterone with a 1-2 h lag period. The time-course of induction of pmAAT mRNA, pmAAT activity and mAAT activity was consistent with stimulation of mRNA synthesis followed by increased synthesis and import of pmAAT into mitochondria. The effect of testosterone on pmAAT mRNA was specific because the increase in pmAAT mRNA was at least 2-fold greater than the increase in poly (A+) RNA. These results suggest that testosterone stimulated mAAT activity by induction of pmAAT mRNA. This continues to support our proposal that a major physiological effect of testosterone is increased pmAAT mRNA steady-state levels which result in increased pmAAT synthesis and increased mAAT activity. These changes ultimately result in increased citrate production by prostate epithelial cells.
Thirteen postmenopausal women with advanced local or metastatic breast cancer were treated with the antiestrogen toremifene at a daily dose of 200 mg. All patients had failed previous treatment with different types of endocrine therapy and/or cytotoxic drugs. Objective response was only seen in one patient. Treatment was usually well tolerated but in three cases the drug had to be withdrawn due to side effects.
High concentrations of pregnenolone and its sulfate have been found in several areas of rat and human brain and seem to be controlled by local mechanisms. In the present experiments we have demonstrated pregnenolone binding sites in the cytosolic fraction of the rat olfactory bulb. The pregnenolone binding component showed a Kd = 2.34 ± 0.66 × 10−7 M and Nmax = 7.25 ± 1.20 pmol/mg protein. Pregnenolone, pregnenolone sulfate and 17OH-pregnenolone competed equally for the binding sites while other steroids were less competitive. Protease and trypsin inhibited binding by 48 and 60% respectively. Sucrose density gradient analysis showed a minor peak at 4.6s and a major one at 3.6s. After gel filtration chromatography the pregnenolone binding component appeared as 2 peaks corresponding to molecular weights of approximately 150 and 220 kDa. Heating at 60°C increased binding by 150%. These results indicate that the olfactory bulb pregnenolone binding component is complex in nature. Rat plasma also bound pregnenolone. Plasma binding sites could be partially differentiated from those in the olfactory bulb on the basis of susceptibility to lipoprotein lipase, effect of heating and mobility during polyacrylamide gel electrophoresis.
The kinetics of binding of oestradiol and the steroidal pure antioestrogen ICI 164,384 to the molybdate-stabilized oestrogen receptor, partially purified from pig and human uterine tissue, were determined. ICI 164,384 bound directly to the oestrogen receptor protein and the kinetic parameters of this interaction were, in general, similar to those for the binding of oestradiol, regardless of the source of the receptor protein. However, the rate of association of oestradiol, regardless of the source of the receptor protein. However, the rate of association of the antagonist with the receptor protein was slower when compared to that of oestradiol. Furthermore, the concentration of binding sites for the two ligands was of the same order. The binding of oestradiol resulted in a steroid-receptor complex which could be transformed in vitro, to a form with increased affinity for DNA-cellulose. However, the complex formed between ICI 164,384 and the receptor protein did not show increased affinity for DNA-cellulose when exposed to conditions that transformed agonist-receptor complexes. Therefore, the binding of ICI 164,384 to the oestrogen receptor protein results in a suppression of the transformation process. A similar suppression in vivo may account for the pure antagonist properties of ICI 164,384.
