plomestane and formestane

Aromatase, a cytochrome P450 enzyme, catalyses the rate-limiting step in the biosynthesis of estrogens. Many processes in male and female development and reproduction and especially in the growth of hormone-dependent cancers, are dependent on estrogens. Therefore, controlling estrogen production by inhibition of aromatase is a logical treatment strategy. Two classes of aromatase inhibitors, steroidal and non-steroidal compounds, are now coming into use. Among the steroid substrate analogs, 4-hydroxyandrostenedione has been shown to be effective in breast cancer patients with advanced disease and was recently approved for treatment in the United Kingdom. Several highly potent and selective non-steroidal inhibitors are now in clinical trials. The variety of compounds that act as aromatase inhibitors should provide breast cancer patients with a number of new treatment options.

Topics: Aminoglutethimide; Androstenedione; Antineoplastic Agents; Aromatase; Aromatase Inhibitors; Breast Neoplasms; Estrogens; Half-Life; Humans; Neoplasms, Hormone-Dependent; Pargyline

Topics: Androstenedione; Animals; Aromatase; Aromatase Inhibitors; Breast Neoplasms; Female; Humans; Neoplasms, Hormone-Dependent; Pargyline; Rats

The murine Leydig cell tumor (M5480A) possesses high levels of estrogen receptor and is known to produce estrogens. In these studies we examined the effects of the potent aromatase inhibitor 4-hydroxyandrostenedione (4-OHA) on Leydig tumor cell steroidogenesis both in vitro and in vivo. The addition of 4-OHA to Leydig tumor cells in primary culture resulted in a dose- and a time-dependent decrease in media progesterone levels. The observed decrease was most likely due to impaired synthesis of progesterone, inasmuch as no alteration in progesterone metabolism was seen when progesterone levels were diminishing. However, 4-OHA inhibited progesterone conversion to testosterone following 1 h of incubation, but this effect disappeared coincident with 4-OHA metabolism. Analysis of pregnenolone production revealed a biphasic dose-dependent effect of 4-OHA. At low doses (0.01-0.1 microM), 4-OHA was found to decrease pregnenolone concentrations, while at higher doses (1-10 microM) pregnenolone levels were elevated. Therefore, the actions of 4-OHA on Leydig cell steroidogenesis in vitro appear to be multifocal. Other experiments were performed to evaluate the effects of 4-OHA on tumor-bearing male mice in vivo. In these studies, the predominant effects of 4-OHA were to act as an aromatase inhibitor and to inhibit progesterone production. Thus, while 4-OHA is a potent aromatase inhibitor, we have found that this compound may alter steroidogenesis in Leydig tumor cells at several sites prior to aromatization.

Topics: Androstenedione; Animals; Aromatase Inhibitors; Leydig Cell Tumor; Male; Mice; Pargyline; Pregnenolone; Progesterone; Testosterone

The efficacies of 10-propargylestr-4-ene-3,17-dione (PED), 4-hydroxyandrostenedione (4-OHA) and the imidazole broad spectrum antimycotic drugs, econazole, imazalil, miconazole and ketoconazole, to inhibit the steroid aromatase activities of rat Leydig tumor (R2C) cells and human hepatoma (HEPG2) cells have been determined. The analysis of inhibition of steroid aromatase activity of intact cells provided further insight into the potential use of such drugs to block cellular estrogen synthesis. The IC50 values for the inhibition of aromatase activity of R2C cells by econazole, imazalil, miconazole, ketoconazole, 4-OHA and PED were 4, 9, 40, 1100, 11 and 10 nM, respectively. These drugs also inhibited the steroid aromatase activity of HEPG2 cells with corresponding IC50 values of 13, 27, 20, 15000, 2 and 2 nM, respectively; these findings were suggestive that the steroid aromatase of rat has many similarities to the human enzyme in its interaction with putative inhibitory compounds. Importantly, however, ketoconazole inhibited the rat aromatase more effectively than it did the human enzyme, while PED and 4-OHA were less effective inhibitors of the rat enzyme compared to that of human. These findings indicate differences in the potencies of various drugs to inhibit estrogen biosynthesis in human and rat cells. These may relate to differences in the two aromatase systems and/or differences in the stability of the drugs in the human hepatoma and rat Leydig tumor cells.

Topics: Androstenedione; Animals; Antineoplastic Agents; Aromatase Inhibitors; Carcinoma, Hepatocellular; Cell Line; Drug Screening Assays, Antitumor; Humans; Kinetics; Leydig Cell Tumor; Liver Neoplasms; Male; Pargyline; Rats; Testicular Neoplasms

Topics: Aminoglutethimide; Androstadienes; Androstenedione; Animals; Aromatase Inhibitors; Female; Gonadotropins, Equine; Humans; In Vitro Techniques; Kinetics; Microsomes; Ovary; Pargyline; Placenta; Rats; Rats, Inbred Strains

The presence of aromatase activity, estrogen receptors, and estrogenic responsiveness in MCF-7 human breast cancer cells has allowed this cell line to be used as a unique in vitro system for investigating the biological activities of potentially therapeutic aromatase inhibitors. We now report the results of studies which have examined the cytotoxicity, antiaromatase, and intrinsic estrogenic activities of aminoglutethimide, 1,2-dehydrotestolactone (testolactone), dihydrotestosterone, 4-hydroxy-4-androstene-3,17-dione, and 10-propargylestr-4-ene-3,17-dione within MCF-7 monolayer cultures. Cell viability was determined by trypan blue exclusion, and aromatase activity was assessed by quantifying the amounts of [3H]estradiol formed from [3H]testosterone. Estrogenic activity was assessed by examining the ability of each inhibitor to increase cytoplasmic progesterone receptor and deplete cytoplasmic estrogen receptor concentrations in these cells during a 5-day incubation period. Cytoplasmic progesterone and estrogen receptors were measured by the single-saturating-dose technique using [17 alpha-methyl-3H]-17 alpha, 21-dimethyl-19-norpregna-4,9-diene-3,20-dione and [3H]estradiol as the labeled ligands for each assay, respectively. The results showed that all of these compounds were noncytotoxic aromatase inhibitors in MCF-7 cells but that these agents demonstrated marked differences in inhibitory potency (10-propargylestr-4-ene-3,17-dione greater than 4-hydroxy-4-androstene-3,17-dione much greater than dihydrotestosterone much greater than testolactone = aminoglutethimide). The incubation of cells with 4-hydroxy-4-androstene-3,17-dione resulted in cytoplasmic progesterone and estrogen receptor responses that were similar in magnitude to those observed in other cultures incubated with equimolar concentrations of estradiol. None of the other four agents demonstrated estrogenic activity in this system. However, we have previously observed that dihydrotestosterone has substantial antiestrogenic action in this system. Taken together, these results indicate that some aromatase inhibitors may influence the hormonal regulation of human breast cancer cells by more than one mechanism.

Topics: Aminoglutethimide; Androstenedione; Aromatase Inhibitors; Breast Neoplasms; Cell Line; Dihydrotestosterone; Estradiol; Female; Humans; Oxidoreductases; Pargyline; Receptors, Estrogen; Receptors, Progesterone; Testolactone; Testosterone

The effects of 4-hydroxy-4-androstene-3, 17-dione (4-OH-A) and 10-propargylestr-4-ene-3, 17-dione (PED) on the aromatization of androstenedione (A) and the conversion of A to testosterone (T) were studied in incubations with breast carcinoma and breast adipose tissues. Parallel studies were carried out to determine the effects of 4-OH-A and PED on A metabolism in tissue from 5 patients with breast carcinoma. At 11 micro M, both compounds fully inhibited aromatization, whereas the conversion of A to T was decreased in only 2 incubations. Studies with varying concentrations of 4-OH-A and PED demonstrated that both compounds inhibited estrone (E1) formation by 80% at a concentration of 0.085 micro M, with maximum effect at 0.34 micro M. 90% inhibition of estradiol (E2) formation was observed at inhibitor concentrations of 0.17 micro M or greater. T formation was slightly affected at 0.67 microM, but was progressively inhibited with increasing 4-OH-A or PED concentrations, reaching 70% at 11 micro M. Similar experiments with 4-OH-A in breast adipose tissue homogenates showed that a concentration of 0.1 micro M was sufficient to inhibit aromatization while T inhibition required 11 micro M. 4-OH-A and PED are selective inhibitors of aromatization in human breast tissues and may provide a mechanism for controlling estrogen responsive processes.

Topics: Adipose Tissue; Androstenedione; Breast; Breast Neoplasms; Female; Humans; Kinetics; Pargyline