Inhibition of growth of human ovarian cancer in nude mice by luteinizing hormone-releasing hormone antagonist Cetrorelix (SB-75*)†‡*Cetrorelix (SB-75), Asta Medica, Frankfurt-Main, Germany.†Presented at the annual meeting of the Pacific Coast Fertility Society, Indian Wells, California, April 20 to 24, 1994.‡Supported by grants from the Long Beach Memorial Health Services University of California, Irvine, Cancer Research Coordinating Committee

Effect of gonadotropin-releasing hormone agonist on ES-2 ovarian cancer cells

OBJECTIVE

Gonadotropin-releasing hormone (GnRH) receptor is found in the ovarian tissue, including epithelial ovarian cancer (EOC), suggesting that GnRH agonists may have direct action on EOC.

MATERIALS AND METHODS

Ovarian clear cell cancer (ES-2) cells were treated with low-dose GnRH agonist with/without low-dose paclitaxel (1 μM D-Lys(6) with/without 0.5 μM or 1.0 μM paclitaxel). Growth and behavior of ES-2 cells were evaluated.

RESULTS

Use of either D-Lys(6) or paclitaxel or a combination of the two did not affect the morphology and growth pattern of ES-2 cells. However, ability of migration and invasion of ES-2 cells was significantly decreased in either use of D-Lys(6) or paclitaxel and more apparent with the combination. Type I GnRH receptor expression of ES-2 was not altered significantly by the combination.

CONCLUSION

GnRH agonist might modify the ES-2 ovarian cancer cells, and its role might be independent, additional or synergistic, suggesting the potential role of the use of GnRH agonist in the management of clear cell type of the ovarian cancer. However, the results of this study were derived using ES-2 ovarian cancer cells, and might not be valid in other cell types of ovarian cancers.

Is lGnRH-III the most potent GnRH analog containing only natural amino acids that specifically inhibits the growth of human breast cancer cells?

Analogs of the decapeptide, gonadotropin-releasing hormone (GnRH), used in the treatment of hormone-dependent tumors, contain numerous unnatural amino acids, giving rise to many adverse effects. lGnRH-III, a natural isoform of GnRH isolated from the sea lamprey, is a weak agonist of GnRH in the pituitary, but inhibits the growth of human cancer cells in micromolar concentrations. As lGnRH-III is not a natural ligand in humans, it is possible that a more potent peptide, also containing only natural amino acids, can be synthesized. A positional scanning peptide library, focused on the variable region of the GnRH family of peptides, residues 5-8, was synthesized. The synthesized peptides were analyzed in competitive binding experiments and six new analogs were designed on the basis of the results. Their biological activities were evaluated in cell growth experiments. The only natural sequence selected was chicken GnRH-II. The synthetic library did not yield a more potent peptide than lGnRH-III.

Multi-factorial role of GnRH-I and GnRH-II in the human ovary

Normal ovarian functions are regulated by a wide variety of endocrine hormones, local paracrine and autocrine factors, which functionally interact with each other in a highly coordinated fashion. Recent findings have demonstrated that both forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed in various compartments of the human ovary including the granulosa-luteal cells, ovarian surface epithelial cells and ovarian tumors, and their expressions have been shown to be tightly regulated by gonadal steroids and gonadotropins. Functionally, these neuropeptides exert diverse biological effects in the ovary via binding to their cognate receptors, supporting the notion that these peptides act as paracrine and autocrine factors in modulating local ovarian functions. In this review, we will summarize recent literatures regarding the regulation of GnRH-I and GnRH-II gene expressions in the human ovary, and discuss the possible signal transduction mechanisms by which these hormones exert their actions in the gonad. Recent cloning of the second form of the GnRH receptor (GnRH-II receptor) in primates and other vertebrates demonstrated that it was structurally, and thus, functionally distinct from the GnRH-I receptor. Cell proliferation studies showed that GnRH-II inhibited the growth of human ovarian cancer cells that express GnRH-II but not GnRH-I receptor, indicating that the GnRH-II binding sites are functional in these cells. However, it remains unknown if GnRH-II receptor is expressed as a full-length, properly processed and functional gene transcript in humans, and its potential physiological roles such as differential regulation of gonadotropin secretion, neuroendocrine modulation and female sexual behavior await further investigation.

Expression of receptors for luteinizing hormone-releasing hormone in human ovarian and endometrial cancers: frequency, autoregulation, and correlation with direct antiproliferative activity of luteinizing hormone-releasing hormone analogues

OBJECTIVE

Several recent reports have demonstrated the expression of luteinizing hormone-releasing hormone receptors by human ovarian and endometrial cancers. Controversy persists on the relevance of this finding, in particular whether these receptors mediate direct antiproliferative effects of luteinizing hormone-releasing hormone analogues. We correlated the expression of luteinizing hormone-releasing hormone receptors by well-characterized ovarian and endometrial cancer cell lines with the ability of luteinizing hormone-releasing hormone analogues to reduce their proliferation and studied the autoregulation of luteinizing hormone-releasing hormone receptor expression by luteinizing hormone-releasing hormone agonist triptorelin and antagonist cetrorelix. The expression of luteinizing hormone-releasing hormone receptors was assessed in a series of specimens from primary ovarian and endometrial cancers.

STUDY DESIGN

Luteinizing hormone-releasing hormone receptor expression was assessed by semiquantitative reverse transcriptase-polymerase chain reaction and radioligand binding assay. Antiproliferative effects were ascertained by proliferation assays in the absence or presence of luteinizing hormone-releasing hormone analogues.

RESULTS

Ovarian (4/6 cell lines) and endometrial (5/6 cell lines) cancer cell lines expressed luteinizing hormone-releasing hormone receptors. The proliferation of these luteinizing hormone-releasing hormone receptor-positive cell lines was dose- and time-dependently reduced by agonistic and antagonistic luteinizing hormone-releasing hormone analogues. Luteinizing hormone-releasing hormone receptor density was reduced to 80% of controls (control, 100 %; P <.001) by luteinizing hormone-releasing hormone analogues. Seventy percent of primary ovarian cancers and 83% of primary endometrial cancers expressed luteinizing hormone-releasing hormone receptors.

CONCLUSION

These findings suggest that luteinizing hormone-releasing hormone receptors that are expressed by human ovarian and endometrial cancer cell lines mediate direct antiproliferative effects of luteinizing hormone-releasing hormone analogues. Because most respective primary cancers expressed luteinizing hormone-releasing hormone receptors, these receptors might be used for novel antiproliferative therapeutic approaches and should be further evaluated.

Gonadotropin-releasing hormone antagonist: how good is the new hope?

Gonadotropin-releasing hormone agonists have been widely used to prevent luteinizing hormone surges during controlled ovarian stimulation in assisted reproductive technologies. Treatment with gonadotropin-releasing hormone agonists of uterine myoma, endometriosis and some hormone-dependent cancers, such as breast, ovarian, endometrial and prostate cancer, also seems to have a beneficial effect. Gonadotropin-releasing hormone agonists have the disadvantage of inducing an initial stimulatory effect on gonadotropin secretion, necessitating 2-3 weeks before pituitary desensitization is achieved. Gonadotropin-releasing hormone antagonists, on the contrary, cause an immediate inhibition of gonadotropin secretion by competitive blocking of pituitary gonadotropin-releasing hormone receptors. Some advantages of their clinical use in controlled ovarian stimulation have already been demonstrated. Randomized comparative studies are needed to investigate their benefit over gonadotropin-releasing hormone antagonists for myoma and hormone-related disorders.

In vitro targeting of a cytotoxic analog of luteinizing hormone-releasing hormone AN-207 to ES-2 human ovarian cancer cells as demonstrated by microsatellite analyses

Targeting of cytotoxic agents represents a modern approach to the treatment of various cancers, that improves the efficacy and reduces peripheral toxicity. Recently we developed a powerful cytotoxic analog of luteinizing hormone-releasing hormone (LHRH), AN-207, designed to be targeted to tumors that express LHRH receptors. This analog consists of the superactive derivative of doxorubicin (DOX), 2-pyrrolino-DOX (AN-201), linked to [D-Lys6]LHRH carrier. In the present study we investigated the cytocidal effects of AN-207 and AN-201 on the LHRH receptor-positive ES-2 ovarian cancer cells. The targeting of AN-207 to ES-2 cells in the presence of LHRH receptor-negative UCI-107 ovarian cancer cells was also evaluated by semi-quantitative polymerase chain reaction (PCR) amplification of microsatellite markers. Ligand competition assays showed a single class of high-affinity and low-capacity binding sites in ES-2 cells with a mean dissociation constant (KD) of 3.93 +/- 0.1 nM and a mean maximal binding capacity (Bmax) of 271 +/- 26.1 fmol/mg membrane protein. Kinetic assays indicated that AN-207 caused cell death in a concentration- and time-dependent manner in ES-2 cells, but not in UCI-107 cells, while the kinetics of cytotoxic effects of AN-201 were similar in both cell lines. To investigate targeting, ES-2 cells were co-cultured with UCI-107 cells, treated with 10 nM AN-207 or AN-201 for different times and then cultured for 48 h in the absence of cytotoxic agents. Genomic DNA was extracted for microsatellite analyses using different markers. Semi-quantitative analyses of the intensity of the alleles that correspond to each cell line indicated that AN-207 was selectively targeted to ES-2 cells, while AN-201 showed no selectivity for either cell line. These results extend our previous findings that AN-207 can be targeted to ovarian cancers and other tumors that express receptors for LHRH. Cytotoxic analogs of LHRH, such as AN-207, should be considered for treatment of LHRH receptor-positive tumors.

Antitumor effect of GnRH agonist in epithelial ovarian cancer

OBJECTIVE

The effects of the gonadotropin releasing hormone (GnRH) agonist (D-Trp(6)) were examined in two human ovarian cancer cell lines and in severe combined immune deficiency (SCID) mice to evaluate its potential as a cytocidal, cytostatic, or differentiating antitumor agent.

METHODS

We treated the human ovarian cancer cell lines OVCAR-3 and SKOV-3 for 5 or 7 days and sex-matched SCID mice with GnRH agonist for 29 days. The antitumor effect of GnRH agonist were studied in various aspects. To confirm the antiproliferative effect, we used 3-(4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide colorimetric assay, in vitro, and a serial measurement of tumor growth in vivo. The disturbances of progression in the cell cycle and the changes of cyclin-dependent kinase 1 following treatment with GnRH agonist were evaluated with flow cytometric analysis in vitro. The induction of apoptosis following treatment with GnRH agonist was studied using in situ terminal deoxyribonucleotidyl transferase (Tdt) and further quantitated with ELISA in vitro. The presence of telomerase activity following treatment with GnRH agonist was measured by PCR-based telomeric repeat amplification protocol and ELISA detection in cell lines and xenografts in vitro and in vivo.

RESULTS

Continuous exposure of cell lines and xenografts to GnRH agonist resulted in growth inhibition of cancer cells in a dose- and time-dependent manner. In cultured cells, the GnRH agonist blocked cell cycle progression in G0/G1 phase and thus reduced the number of cells in S and G2/M phases. The phenomenon of apoptosis was documented in cultured cells treated with GnRH agonist by in situ Tdt assay. The frequency of apoptotic cells in the in situ Tdt assay was 5-6% compared with control, 4-5%. Apoptosis quantified by ELISA revealed a high incidence in cultured cells treated with GnRH agonist. The activities of telomerase in cell lines and xenografts were not decreased by GnRH agonist. There were not any significant changes of expression of CA-125 by flow cytometry and of the cellular morphology observed with light microscopy.

CONCLUSIONS

Our results indicate that the antiproliferative effect of GnRH agonist in epithelial ovarian cancer cells may be mainly attributed to cytostatic activities resulting in blocking of cell cycle progression in the G0/G1 phase and minimally related to the induction of apoptosis.

Targeted cytotoxic analog of luteinizing hormone-releasing hormone AN-207 inhibits growth of OV-1063 human epithelial ovarian cancers in nude mice

OBJECTIVE

The aim of the study was to investigate the effects of the cytotoxic analog of luteinizing hormone-releasing hormone AN-207 on the growth of the OV-1063 human epithelial ovarian cancers, which express luteinizing hormone-releasing hormone receptor. AN-207 consists of doxorubicin derivative 2-pyrrolinodoxorubicin (AN-201) linked with the carrier [D-lysine6 ]luteinizing hormone-releasing hormone.

STUDY DESIGN

Female nude mice bearing xenografts of OV-1063 ovarian cancers were treated with analog AN-207, cytotoxic radical AN-201, or agonist [D-lysine6 ]luteinizing hormone-releasing hormone. The levels and expression of messenger ribonucleic acid of receptors for luteinizing hormone-releasing hormone and epidermal growth factor were evaluated.

RESULTS

The growth of OV-1063 tumor was significantly inhibited by 3 to 5 nmol AN- 207 but not by [D-lysine6 ]luteinizing hormone-releasing hormone. Cytotoxic radical AN-201 was toxic at these doses. After treatment with AN-207 receptors for luteinizing hormone-releasing hormone were not detectable, epidermal growth factor receptor levels declined, and expressions of their respective messenger ribonucleic acids were decreased.

CONCLUSIONS

Targeted cytotoxic luteinizing hormone-releasing hormone analog AN-207 is less toxic than equimolar doses of its radical 2-pyrrolinodoxorubicin and effectively inhibits ovarian tumor growth. Targeted chemotherapy may improve management of ovarian cancer.

Expression of gonadotropin-releasing hormone receptor mRNA in the rat ventral prostate and dunning R3327 PAP adenocarcinoma before and after castration

BACKGROUND

Continuous administration of gonadotropin-releasing hormone (GnRH) agonists in prostate cancer patients results in involution of the tumors due to suppression of androgen production. In addition to the effect of GnRH at the hypothalamic-pituitary level, experiments in vitro on breast, ovary, and prostatic cells have shown an inhibition of cell proliferation, indicating the presence of local GnRH receptors (GnRH-R). The aim of the present study was to investigate the expression of GnRH-R mRNA in the normal rat ventral prostate (VP) and Dunning R3327 PAP adenocarcinoma and to evaluate the effects of castration on receptor mRNA expression.

METHODS

RNA was prepared from ovaries, pituitaries, VP, and Dunning tumors from both intact and castrated animals. GnRH-R mRNA levels were quantified by a competitive reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS

GnRH-R mRNA was detected in normal VP and Dunning tumors. Normal VP showed lower amounts of GnRH-R mRNA compared to Dunning tumors. An elevation of mRNA expression was observed 7 days after castration in Dunning tumors.

CONCLUSIONS

GnRH-R mRNA was found in both VP and Dunning tumors, indicating the presence of a local GnRH system. Normal VP showed lower amounts of GnRH-R mRNA when compared to malignant tissues. GnRH-R mRNA levels were elevated in Dunning tumors following castration.

Hormonal interactions in ovarian cancer

According to the epidemiologic literature and the laboratory characterization of receptor content and molecular interactions, there is a relationship between the microenvironment of ovarian cancer and steroid hormones. Advances in our knowledge of the molecular-hormonal nature of ovarian cancer will help in designing a rationale for clinical trials in appropriate subsets of patients. However, currently, development of successful therapies and prevention strategies for women at risk remains a true challenge.

Growth inhibition of human ovarian cancers by cytotoxic analogues of luteinizing hormone-releasing hormone

BACKGROUND

Receptors for luteinizing hormone-releasing hormone (LH-RH) are found in nearly 80% of human ovarian cancers. The chemotherapeutic agent doxorubicin can be linked to [D-lysine6]LH-RH to form a cytotoxic analogue (AN-152) that may have greater specificity for tumor cells. This study was conducted to investigate the effects of AN-152 on the growth of LH-RH receptor-positive OV-1063 human epithelial ovarian cancers.

METHODS

Nude mice bearing human ovarian tumors, OV-1063 or UCI-107 (LH-RH receptor negative), were injected intraperitoneally with saline (control) or with equimolar doses of AN-152 or doxorubicin; experiments involving mice with OV-1063 tumors also included groups that were administered [D-lysine6]LH-RH either alone or in combination with doxorubicin. Tumor volume, weight, doubling time, and burden (i.e., tumor weight/body weight) as well as tumor apoptotic and mitotic indices were determined. The levels of receptors for LH-RH and epidermal growth factor (EGF) and their messenger RNAs were measured by use of radioreceptor and reverse transcription-polymerase chain reaction assays, respectively.

RESULTS

The growth of OV-1063 ovarian tumors in nude mice, as based on reduction in tumor volume, was inhibited significantly (all P<.05, two-sided) 4 weeks after treatment with AN-152, even at the lowest dose tested (413 nmol/20 g weight); the toxic effects of an equivalent dose of doxorubicin caused substantial mortality. High-affinity receptors for LH-RH and EGF were found on cell membranes of OV-1063 cancers; however, after in vivo treatment with AN-152, LH-RH receptor-binding sites were not detectable and EGF receptors were reduced in number. The growth of UCI-107 ovarian cancers was not inhibited by AN-152.

CONCLUSIONS

In nude mice bearing LH-RH receptor positive OV-1063 epithelial ovarian cancers, systemic administration of AN-152 is less toxic and inhibits tumor growth better than equimolar doses of doxorubicin.

Insulin-like growth factor-II participates in the biphasic effect of a gonadotropin-releasing hormone agonist on ovarian cancer cell growth

OBJECTIVE

To examine the involvement of insulin-like growth factors (IGFs) in growth regulation of an ovarian cancer cell line and to investigate whether the GnRH agonist tryptorelin might influence a potential autocrine or paracrine loop involving IGFs.

DESIGN

In vitro, prospective, randomized controlled study.

SETTING

In vitro experiments at the Section of Gynecologic Oncology, Surgery Branch, National Cancer Institute.

PATIENT(S)

None. Human ovarian adenocarcinoma cell line IGROV-1.

INTERVENTION(S)

The proliferative effect of tryptorelin on IGROV-1 cells was analyzed by using the MTT (93-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide) colorimetric assay. The ribonuclease protection assay was used to investigate whether an autocrine pathway involving IGF-I or IGF-II might participate in the growth of these cells. The expression of GnRH receptor was assessed by the 125I-GnRH binding assay.

MAIN OUTCOME MEASURE(S)

Changes in cell growth and expression of IGF-I and IGF-II messenger RNA (mRNA).

RESULT(S)

Tryptorelin exhibited a bimodal, dose- and time-dependent effect on IGROV-1 cells when compared with untreated control cells: Cellular proliferation was enhanced during the first 24 hours of exposure, but longer incubations resulted in growth inhibition. The mitogenic effect of tryptorelin was inhibited when cells were co-incubated with either IGF binding protein-5 (IGFBP-5) or anti-IGF-II antibody, which can both bind to IGF-II and neutralize it. Insulin-like growth factor-I mRNA was not detected in IGROV-1 cells. However, IGF-II transcripts were detected after incubation with tryptorelin for 12 hours, but thereafter, no mRNA was observed, even after prolonged exposure. Binding analysis revealed a specific, high-affinity GnRH binding site.

CONCLUSION(S)

These data suggest that tryptorelin exerts a bimodal growth effect on ovarian cancer cells by a mechanism involving the autocrine production of IGF-II. The effect of tryptorelin on IGF-II gene transcription in these ovarian cancer cells appears to mirror the desensitizing effects of prolonged GnRH exposure on pituitary gonadotropin production.

Fertility drugs and ovarian cancer

Recent case reports of ovarian cancer associated with infertility treatment raise the question of a possible etiopathogenetic role of fertility drugs in ovarian cancer. In this paper, the possible relationship between infertility treatment and ovarian cancer is reviewed with respect to the epidemiological and pathogenetic profiles of ovarian cancer and the potential risk factors associated with fertility drugs; a case report review and a critical reappraisal are also provided within this article. Currently available data in the literature, from epidemiological studies and case reports, suggest that a direct causal effect of infertility treatment on ovarian cancer seems unlikely. Since infertile women are likely to have a higher risk for the development of ovarian cancer, and the role of fertility drugs in the etiopathogenesis of ovarian carcinoma is not established, a close clinical examination of infertile patients before, during and after infertility treatment is recommended. Moreover, further investigation is required to resolve the question of the possible association between fertility drugs and ovarian cancer through large prospective epidemiological or retrospective case-control studies.

Ovarian surface epithelium, ovulation and carcinogenesis

It appears that ovarian surface epithelial cells activated by contact with gonadotropin-stimulated preovulatory follicles can release bioactive substances that weaken the tunica albuginea and apical follicular wall (e.g. collagenolytic enzymes) and induce cell death (e.g. apoptotic agents). However, a definitive obligatory role of the ovarian surface epithelium in ovulation remains equivocal. Epithelium exfoliated from the dome of ovulatory follicles is replenished by generative stem cell replication and migration from the wound edges. Mutagenesis has been related to successive bouts of ovulation and mitosis. Common epithelial ovarian cancer is a deadly insidious disease, mainly because it is asymptomatic until the malignancy has reached beyond the ovaries. The most important susceptibility factors are nulliparity and association to an affected first-degree relative. It will be critical to resolve whether parity and oral contraceptive use confer significant protection to women with a family history of ovarian carcinoma. Clearly, innovative approaches to non-invasive screening and treatment are needed. Early detection is the key to saving lives (90% cure by salpingo-ovariectomy alone if diagnosis is at Stage I). Active immunization with defined tumor epitopes or (passive) intraperitoneal administration of effector-functional humanized antibodies may be of special value in the regional management of common epithelial ovarian cancer.