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

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.

Ovarian epithelial carcinoma with estrogen-producing stroma

Malignant ovarian neoplasms derived from ovarian epithelium that produce estrogen are rare among postmenopausal women. Presented herein is a case of stage Ic(a) endometrioid adenocarcinoma in the right ovary of an 81-year-old woman, who complained of mammary tenderness, pain and atypical genital bleeding. Her serum estradiol (E2) concentration was 83 pg/mL before treatment, and the endometrial thickness measured by transvaginal ultrasonography was 5 cm, much thicker than that expected for a woman in her 80s. After surgery, her complaints disappeared and her serum E2 level decreased to normal postmenopausal levels. Immunohistochemical studies demonstrated that the enzymes required to produce estrogen were present in the tumor. Immunohistological data indicated that this epithelial ovarian cancer could produce estradiol by itself, through potential interactions between cancer cells and stromal cells, and that the high level of estradiol in the patient's serum was caused by intratumoral production. This case indicates that in addition to stromal tumors, such as granulosa cell tumors, theca cell tumors, adenofibroma and so on, malignant epithelial tumors with a functioning stroma should also be considered when evaluating ovarian tumors with estrogen production in the elderly.

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.

Estrogens and epithelial ovarian cancer

OBJECTIVE

Molecular mechanisms involved in ovarian carcinogenesis are still unclear, but there is growing evidence that estrogens promote tumor progression in an epithelial ovarian cancer (EOC) subgroup.

METHODS

We reviewed current knowledge on the effects of estrogens in ovarian carcinogenesis and new potential research focuses concerning hormonal therapy of EOC.

RESULTS

Experimentally, estrogen stimulates the growth of ovarian tumor cell lines expressing estrogen receptors (ER). We and other authors have demonstrated differential expression of ERalpha or beta during ovarian carcinogenesis, with overexpression of ERalpha as compared to ERbeta in cancer. This differential expression in ER suggests that estrogen-induced proteins may act as ovarian tumor-promoting agents. Among these proteins, c-myc, fibulin-1, cathepsin-D, or several kallikreins may play a role, since high expression levels have been found in EOC. Consistently, recent prospective epidemiological studies have indicated that estrogen replacement therapy in postmenopausal women may increase ovarian cancer incidence and mortality.

CONCLUSION

Questions on the estrogen-sensitivity and potential benefits of new hormone therapies in an EOC subgroup should be readdressed in the light of recent experimental and clinical data.

Effects of a combination of exemestane and paclitaxel on human tumor cells in vitro

Exemestane, a non-steroidal aromatase inhibitor that shuts down estrogen synthesis, and paclitaxel, an antineoplastic drug, inhibiting microtubule formation and interfering with the cells potential to proliferate, are well established treatments for metastatic breast cancer. Given that exemestane is a treatment for hormone-sensitive tumors in postmenopausal women with more favorable prognosis, while paclitaxel is normally used for women suffering from hormone-insensitive breast cancers with less favorable prognoses, there is currently no experience with the combination of the two drugs. In order to find out to what extent exemestane and paclitaxel add to each other's effects when given concomitantly, the effect of the two drugs alone and in combination on the growth of various gynecological tumor cell lines was assessed. Tumor cell growth was measured according to the cell titer cell proliferation technique, also referred to as the MTS assay, by measurement of relative cell numbers. In gynecological cancer cells expressing aromatase, the effect of a treatment with paclitaxel (10 nM) on cell growth was enhanced by co-treatment with exemestane. This additive effect was independent of ERalpha expression, but dependent on the presence of androstenedione. It was observed in HEC-1A and Ishikawa endometrial adenocarcinoma cells as well as in SK-OV-3 ovarian cancer and in MDA-MB-231 breast cancer cells. Our findings suggest that a combination of paclitaxel with exemestane might be beneficial for the treatment of aromatase-positive gynecological cancer, because it may allow us to reduce the paclitaxel dosage and therefore the toxicity of the treatment.

A phase II trial of D-Trp-6-LHRH (decapeptyl) in pretreated patients with advanced epithelial ovarian cancer

Fourteen patients with advanced ovarian cancer who failed chemotherapy received a long-acting LHRH agonist. All the patients had been previously operated on and all had received at least one regimen of chemotherapy. Duration of decapeptyl administration was between 1 month and 28 weeks. There were no complete or partial responses. Eight patients (57%) had disease stabilization with a median progression-free interval of 14 weeks (range 4-28 weeks). All other patients developed a clear progressive cancer after the first injection of LHRH agonist. Three of these patients are still alive and receiving other forms of chemotherapy (median follow-up after the end of LHRH treatment was 11.5 months). The regimen was well tolerated with only mild toxicity observed (hot flushes in 2 patients). Although D-Trp-6-LHRH (Decapeptyl) was well tolerated, it had insignificant activity in treating patients with epithelial cancer that was resistant or relapsed after first-line platinum-based chemotherapy.

Inhibition of growth of OV-1063 human epithelial ovarian cancer xenografts in nude mice by treatment with luteinizing hormone-releasing hormone antagonist SB-75

Female athymic nude mice bearing xenografts of OV-1063 human epithelial ovarian cancer cell line were treated with potent luteinizing hormone (LH)-releasing hormone (LH-RH) antagonist SB-75 (Cetrorelix; [Ac-D-Nal(2)1, D-Phe(4 CI)2, D-Pal(3)3, D-Cit6, D-Ala10]LH-RH in which Ac-D-Nal(2) = N-acetyl-3-(2-naphthyl)-D-alanine, D-Phe(4CI) = 4-chloro-D-phenylalanine, D-Pal(3) = 3-(3-pyridyl)-D-alanine, and D-Cit = D-Citrulline) or with the agonist [D-Trp6]LH-RH. In the first experiment, SB-75 and [D-Trp6]LH-RH were administered in the form of microcapsules releasing 60 and 25 micrograms/day, respectively. In the second study, the analogs were given by daily s.c. injections in doses of 100 micrograms/day. In both experiments, tumor growth, as measured by reduction in tumor volume, percentage change in tumor volume, tumor burden, and increase in tumor doubling time, was significantly inhibited by treatment with SB-75 but not with [D-Trp6]LH-RH. Uterine and ovarian weights were reduced and serum LH levels decreased by administration of either analog. Chronic treatment with SB-75 greatly reduced the concentration of receptors for epidermal growth factor and insulin-like growth factor I in tumor cell membranes, a phenomenon that might be related to tumor growth inhibition. It is possible that the antitumoral effects of SB-75 on OV-1063 ovarian cancers are exerted not only through the suppression of the pituitary-gonadal axis, but also directly. In view of its strong inhibitory effect on the growth of OV-1063 ovarian cancers in vivo, the potent LH-RH antagonist SB-75 might be considered for possible hormonal therapy of advanced epithelial ovarian carcinoma.

Gonadotropins, estradiol, and growth factors regulate epithelial ovarian cancer cell growth

Indirect evidence suggests that gonadal steroids and gonadotropins may have a role in the genesis of epithelial ovarian cancer. In the studies reported herein, we established 17 beta-estradiol (E2) secreting cell cultures from an omental metastasis of an epithelial ovarian cancer. We demonstrate that human chorionic gonadotropin (hCG), human follicle-stimulating hormone, and epidermal growth factor (EGF) increased cell growth in a dose- and time-dependent manner, whereas E2 inhibited cell growth in the nanomolar range. Epidermal growth factor was able to partially block the negative effect of E2; a similar but quantitatively lesser effect was observed with hCG. These results provide direct evidence to support the view that gonadotropins, EGF, TGF beta (transforming growth factor), and estradiol may modulate growth of metastatic epithelial ovarian cancer cells.

The growth response of BG-1 ovarian carcinoma cells to estradiol, 4OH-tamoxifen, and tamoxifen: evidence for intrinsic antiestrogen activation

The influence of estrogen (E) and antiestrogen (AES) on the in vitro growth of BG-1 ovarian carcinoma cells, which express steroid receptors was examined (K. R. Geisinger, T. E. Kute, M. J. Pettenati, C. E. Welander, Y. Dennard, L. A. Collins, and M. E. Berens, Characterization of a human ovarian carcinoma cell line with estrogen and progesterone receptors, Cancer 63, 280-288, 1989). All determinations were simultaneously referenced under similar conditions to MCF-7 cells, a well-established cell line for modeling hormonal responses in breast cancer. In "complete" media containing fetal calf serum (FCS, 10%), MCF-7 cell numbers increased approximately 7 x in 7 days, remaining at this level Days 8-15. In contrast, BG-1 cells achieved similar numbers by Day 7, but showed apparent exponential growth over Days 8-15 to 15-20 x. Phenol red-free media containing 10% FCS (less than 20 pg estradiol (E2)/ml by RIA) was used to assess responses to E and AES. Growth of both MCF-7 and BG-1 cells slowed in E-free media. E2 (10 nM) stimulated the growth of both cell lines, yet was responsible for exponential increases during Days 8-15 only in BG-1 cell numbers (50-70 x). The metabolically active AES (4OH-tamoxifen, 50 nM) reduced E2-stimulated MCF-7 growth to 3-4 x, while tamoxifen (50 nM) had no effect. Rescue with 10 microM E2 fully overcame the AES inhibition of MCF-7 proliferation. In contrast, BG-1 cells experienced significant E2-stimulated growth reductions in the presence of either 4OH-tamoxifen or tamoxifen. E2 was observed to rescue BG-1 cells from both of these antagonists. We conclude that BG-1 ovarian carcinoma cells respond in vitro to E and AES. Moreover, by virtue of responses to tamoxifen, BG-1 cells may have an intrinsic capacity to hydroxylate tamoxifen to its active metabolite. This property of ovarian carcinoma cells might be worth exploiting in the design of more effective combination chemotherapy regimens.