Aromatase activity in human ovarian cancer

Steroid metabolism and hormonal dynamics in normal and malignant ovaries

The ovaries are key steroid hormone production sites in post-pubertal females. However, current research on steroidogenic enzymes, endogenous hormone concentrations and their effects on healthy ovarian function and malignant development is limited. Here, we discuss the importance of steroid enzymes in normal and malignant ovaries, alongside hormone concentrations, receptor expression and action. Key enzymes include STS, 3β-HSD2, HSD17B1, ARK1C3, and aromatase, which influence ovarian steroidal action. Both androgen and oestrogen action, via their facilitating enzyme, drives ovarian follicle activation, development and maturation in healthy ovarian tissue. In ovarian cancer, some data suggest STS and oestrogen receptor α may be linked to aggressive forms, while various oestrogen-responsive factors may be involved in ovarian cancer metastasis. In contrast, androgen receptor expression and action vary across ovarian cancer subtypes. For future studies investigating steroidogenesis and steroidal activity in ovarian cancer, it is necessary to differentiate between disease subtypes for a comprehensive understanding.

Ovarian estradiol production and lipid metabolism in postmenopausal women

OBJECTIVE

Menopause is defined as the permanent cessation of menses. Although previous studies demonstrated a slight production of androgens and estrogens by postmenopausal ovaries, the impact of hormone production on lipid metabolism is still uncertain. The aim of this study was to evaluate whether the postmenopausal ovary is hormonally active and whether hormone status contributes to lipid metabolism.

METHODS

This was a prospective study of 87 women who were treated for gynecological diseases (29% had cervical cancer, 49% had endometrial cancer, 7% had fibroid tumors, and 15% had cervical intraepithelial neoplasia). They were categorized as early postmenopausal (n = 40; mean [SD], 56.8 [3.8] y) or late postmenopausal (n = 47; mean [SD], 66.6 [5.7] y) women. Serum specimens were collected from the peripheral and ovarian veins of participants undergoing bilateral oophorectomy. Sex steroid hormone levels and lipid profiles were determined.

RESULTS

Statistically significant differences in estradiol (E2) and testosterone were seen between the ovarian samples and the peripheral samples in all groups. E2 and estrone obtained from ovarian venous samples gradually decreased with age in postmenopausal women. There was a significant correlation between ovarian E2 and high-density lipoprotein cholesterol levels and the low-density lipoprotein-to-high-density lipoprotein ratio. However, there was no correlation between peripheral E2 levels and any of the lipid parameters examined.

CONCLUSIONS

Although this study investigates women with gynecological diseases, the postmenopausal ovary is hormonally active, and the E2 produced by postmenopausal ovaries may therefore contribute to the maintenance of lipid metabolism.

Dysregulated estrogen receptor signaling in the hypothalamic-pituitary-ovarian axis leads to ovarian epithelial tumorigenesis in mice

The etiology of ovarian epithelial cancer is poorly understood, mainly due to the lack of an appropriate experimental model for studying the onset and progression of this disease. We have created a mutant mouse model in which aberrant estrogen receptor alpha (ERα) signaling in the hypothalamic-pituitary-ovarian axis leads to ovarian epithelial tumorigenesis. In these mice, termed ERα^d/d, the ERα gene was conditionally deleted in the anterior pituitary, but remained intact in the hypothalamus and the ovary. The loss of negative-feedback regulation by estrogen (E) at the level of the pituitary led to increased production of luteinizing hormone (LH) by this tissue. Hyperstimulation of the ovarian cells by LH resulted in elevated steroidogenesis, producing high circulating levels of steroid hormones, including E. The ERα^d/d mice exhibited formation of palpable ovarian epithelial tumors starting at 5 months of age with 100% penetrance. By 15 months of age, 80% of ERα^d/d mice die. Besides proliferating epithelial cells, these tumors also contained an expanded population of luteinized stromal cells, which acquire the ability to express P450 aromatase and synthesize E locally. In response to the elevated levels of E, the ERα signaling was accentuated in the ovarian epithelial cells of ERα^d/d mice, triggering increased ERα-dependent gene expression, abnormal cell proliferation, and tumorigenesis. Consistent with these findings, treatment of ERα^d/d mice with letrozole, an aromatase inhibitor, markedly reduced circulating E and ovarian tumor volume. We have, therefore, developed a unique animal model, which serves as a useful tool for exploring the involvement of E-dependent signaling pathways in ovarian epithelial tumorigenesis.

Ovarian cancer is currently the most lethal gynecological cancer in the United States. Multiple epidemiological studies indicate that women who take hormone replacement therapy, estrogen or estrogen with progesterone, peri- or postmenopause will have an increased chance of developing ovarian cancer. Unfortunately, the five-year survival rate after diagnosis is very low indicating that better tools are needed to diagnose and treat ovarian cancer. The models that would allow investigation of this disease are severely limited. In this article we introduce a mouse model that develops epithelial ovarian tumors, and by employing inhibitors of estrogen synthesis, we show that ovarian tumorigenesis in this model is dependent on estrogen production within the ovarian tumor. These studies suggest that estrogen may play a role in promoting ovarian tumor growth.

Hormonal therapies and gynaecological cancers

Hormonal therapy has an established place in the management of women with gynaecological malignancies, including first-line therapy for recurrent receptor-positive endometrial cancer and low-grade stromal sarcoma. There is no place for adjuvant hormonal treatment of these cancers after primary surgery. Primary treatment with either oral or intra-uterine progestagens to preserve fertility in younger women with endometrial carcinoma is effective in about 70% of cases. Response rates to tamoxifen in advanced/recurrent ovarian cancers approximates 10%. To the authors' knowledge, no studies that reasonably compare different progestagens, different routes of therapy, different doses and different hormonal preparations have been published.

Estradiol-induced ezrin overexpression in ovarian cancer: a new signaling domain for estrogen

We have for the first time exposed estrogen's role in the epithelial ovarian cancer (OVCA) metastatic cascade and discovered that it is related to the induction of ezrin over-expression. 17beta Estradiol (E2) was administered to SKOV3 (ERalpha>beta) and DOV13 (ERalpha<ERbeta) OVCA cells in serum-and phenol red-free medium fortified with transferrin and insulin. Incubated cells that penetrated Matrigel membranes were counted, immunostained and analyzed for immunoreactive ezrin. E2 induced an invasive phenotype with translocation of ezrin to cell edges, including pseudopodia and ruffles. A strong correlation was found between ezrin expression and Matrigel penetration induced by E2. Increases in cell number and ezrin expression were confirmed by flask incubations. E2 stimulation of OVCA cell proliferation, motility and Matrigel penetration was dose-related and raloxifene or tamoxifen blocked E2's effect, supporting an ER action. This previously unreported effect of estrogen on ezrin expression may play a role in the clinical course of estrogen-sensitive cancers and other normal or diseased cell actions.

Aromatase expression in ovarian epithelial cancers

Our study focused on aromatase cytochrome P450 (CYP19) expression in ovarian epithelial normal and cancer cells and tissues. Aromatase mRNA expression was analyzed by real-time PCR in ovarian epithelial cancer cell lines, in human ovarian surface epithelial (HOSE) cell primary cultures, and in ovarian tissue specimens (n=94), including normal ovaries, ovarian cysts and cancers. Aromatase mRNA was found to be expressed in HOSE cells, in BG1, PEO4 and PEO14, but not in SKOV3 and NIH:OVCAR-3 ovarian cancer cell lines. Correlation analysis of aromatase expression was performed according to clinical, histological and biological parameters. Aromatase expression in ovarian tissue specimens was higher in normal ovaries and cysts than in cancers (P<0.0001). Using laser capture microdissection in normal postmenopausal ovaries, aromatase was found to be predominantly expressed in epithelial cells as compared to stromal component. Using immunohistochemistry (IHC), aromatase was also detected in the epithelium component. There was an inverse correlation between aromatase and ERalpha expression in ovarian tissues (P<0.001, r=-0.34). In the cancer group, no significant differences in aromatase expression were observed according to tumor histotype, grade, stage and survival. Aromatase activity was evaluated in ovarian epithelial cancer (OEC) cell lines by the tritiated water assay and the effects of third-generation aromatase inhibitors (AIs) on aromatase activity and growth were studied. Letrozole and exemestane were able to completely inhibit aromatase activity in BG1 and PEO14 cell lines. Interestingly, both AI showed an antiproliferative effect on the estrogen responsive BG1 cell line co-expressing aromatase and ERalpha. Aromatase expression was found in ovarian epithelial normal tissues and in some ovarian epithelial cancer cells and tissues. This finding raises the possibility that some tumors may respond to estrogen and provides a basis for ascertaining an antimitogenic effect of AI in a subgroup of ovarian epithelial cancers.

Intratumoral aromatase in human breast, endometrial, and ovarian malignancies

In human estrogen-dependent neoplasms such as breast, endometrioid endometrial, and surface epithelial-stromal ovarian carcinomas, intratumoral aromatase is considered to play important roles in converting circulating androgens derived from adrenal cortex and/or ovary to estrogens, possibly in association with 17 beta-HSD type 1 and estrogen sulfatase. Analysis of intratumoral aromatase in these estrogen-dependent neoplasms is important not only in understanding the development and biological behavior of these tumors, but also in the clinical management of these patients, because suppression of intratumoral aromatase by newly developed aromatase inhibitors may provide new potentials in endocrine therapy of these patients.

From Endocrinology to Intracrinology

Recently, in situ formation of active sex steroids at the sites of their actions from biologically inactive precursors in the circulation have been demonstrated to play very important roles in sex steroid-dependent neoplasms. These tissues in which the conversion occurs are designated as intracrine tissues and their mechanisms of actions can be designated as intracrinology in contrast to endocrinology. Aromatase, which converts serum androgens to estrone, and 17B-hydroxysteroid dehydrogenase I, which is involved primarily in the conversion of estrone to estradiol, are two major enzymes which function in the in situ formation of biologically active estrogens from circulatory androgens. In human estrogen-dependent neoplasms, including breast, endometrioid endometrial, and common epithelial ovarian carcinoma, we recently demonstrated overexpression of aromatase, especially in stromal cells at sites of frank invasion possibly under a new promoter usage and that of 17B-hydroxysteroid dehydrogenase I in these carcinoma cells. These estrogen-dependent carcinomas are considered to have a common characteristic in estrogen metabolism (i.e., the expression of aromatase in the stromal cells and of 17B-hydroxysteroid dehydrogenase I in the epithelial cells). With these in situ mechanisms of generating biologically active estrogens from circulating androgens, that is, "intracrine manner," these estrogen-dependent neoplasms can exert estrogenic actions on carcinoma cells despite low circulating serum estrogen levels, as observed in postmenopausal women. Evaluation of intracrine mechanisms can provide new insights into various estrogen-related biological phenomena in humans.

Adrenal 4-binding protein in common epithelial and metastatic tumors of the ovary

Adrenal 4-binding protein (Ad4BP) is a transcription factor that regulates the expression of steroidogenic enzymes. Ovarian tumors other than sex cord stromal tumors are occasionally associated with functioning stroma or hormonal abnormalities. To determine the steroidogenic potential of these tumors, the authors determined the immunohistochemical distribution of Ad4BP in 75 patients with primary common epithelial tumors (20 cystadenomas, 15 carcinomas of low malignant potential, and 40 carcinomas), and seven patients with metastatic carcinoma of the ovary. Ad4BP immunoreactivity was observed in intratumoral stromal cells in 3 of 15 (20%) carcinomas of low malignant potential, 26 of 40 (65%) carcinomas, and three of seven (43%) metastatic carcinomas. Ad4BP immunoreactivity was not observed in the stroma of cystadenomas. Among the positive cases, Ad4BP-positive stromal cells were particularly distributed adjacent to invasive carcinomatous glands. Among ovarian carcinomas, mucinous carcinoma showed a significantly higher number of Ad4BP-positive intratumoral stromal cells than did other histological types. Results suggest that invasion of primary or metastatic carcinoma into the ovarian stroma, especially in the case of mucinous carcinoma, may render the stromal cells to acquire the potential of metabolizing and synthesizing steroid hormones.

Experience with hormonal therapy in advanced epithelial ovarian cancer

The experience from using different hormonal trials in 33 ovarian cancer patients, who were beyond the stage of standard therapies and experimental cytotoxic therapies in a single institution, are reported. Agents used were progestins, an antiestrogen (tamoxifen), an antiandrogen (flutamide) and a GnRH-agonist (decapeptyl). Twenty-one patients completed at least 8 weeks of treatment. Two patients obtained an objective response (10%): one partial response on tamoxifen for 6 months and one complete response on decapeptyl for 38 + months. Two further patients achieved disease stabilizations on tamoxifen and flutamide for 6 and 8 months respectively. Although the objective response rate with hormonal therapies is limited in these circumstances the absence of important toxicities favor their use. It is suggested to further study this in patients who do not reach a complete response after standard induction chemotherapy, particularly in those with well-differentiated tumors.

Relationship between aromatase activity and steroid receptor levels in ovarian tumors from postmenopausal women

Aromatase activity, as well as steroid receptors, exists in nonfunctional ovarian tumors. Steroid receptor status has been reported to be related to prognosis in ovarian cancer patients. We determined aromatase activity and progesterone receptor (PR) and estrogen receptor (ER) levels in 43 ovarian tumors obtained from postmenopausal women. Aromatase activity was detected in 35 tumors (81%), PR in 21 tumors (49%) and ER in 13 tumors (30%). Eighty-three percent (10/12) of mucinous cystadenoma tissues showed positive PR with high aromatase activity, while 93% (13/14) of malignant tumors showed negative PR and low aromatase activity. Aromatase activity was detected in 95% (20/21) of PR-positive tumors, being greater than in PR-negative tumors (P < 0.002). There was a positive correlation between aromatase activity and PR (rs = 0.49, P < 0.001). However, there was no correlation between aromatase activity and ER. In 17 patients (43%), the serum estradiol level was higher than 30 pg/ml and there was a positive correlation among estradiol, estrone, androstenedione and testosterone. However, serum steroid levels were not correlated with aromatase activity, PR or ER. Aminoglutethimide inhibited aromatase activity of benign and malignant ovarian tumors, uterine myoma, choriocarcinoma cells and purified human placental P-450arom in a similar manner. These results suggest that aromatase activity is correlated with PR in ovarian tumors of postmenopausal women. In addition to steroid receptor status, aromatase activity may be a useful prognostic factor in ovarian cancers.

What's new in the localization of sex steroids in the human ovary and its tumors?

It is important to understand the distribution of steroidogenesis in steroid producing tissues in order to obtain a better understanding of steroid metabolism. Recent advances in purification and subsequent generation of antibodies against cytochromes P-450 specific for steroid hormone biosynthesis have made it possible to localize the sites of steroidogenesis immunohistochemically. This review provides the localization of sex-steroid hormone biosynthesis in normal and pathological human ovaries including sex-cord stromal tumors, hyperthecosis and Brenner tumor, as determined by the tissue distribution of immunoreactivity of individual enzymes specific for different stages of the biosynthetic process.

Endocrine characterization of a human ovarian carcinoma (BG-1) established in nude mice

The steroid receptor-positive human ovarian cancer (BG-1) was evaluated to determine its usefulness as a tumor model. This tumor grows in intact male and female nude mice without hormone supplements. Moreover, its growth was significantly accelerated in ovariectomized mice, and the increased growth rate could be reversed by estradiol administration. Evaluation of tumor growth following endocrine therapy revealed that, while antiandrogens did not affect the tumor growth, both an aromatase inhibitor and a luteinizing hormone-releasing hormone agonist significantly impaired growth of this human ovarian tumor. Estradiol was also shown to up-regulate both estrogen and progesterone receptors in tumors grown in ovariectomized mice. Therefore, the BG-1 human ovarian carcinoma grows without hormonal supplements and yet responds to specific forms of endocrine therapy. Moreover, the steroid receptors present in this tumor respond to exogenous steroids. In conclusion, this tumor may serve as an ideal model for the study of hormonal regulation of ovarian tumor growth.