Agonists and antagonists of GnRH-I and -II reduce metastasis formation by triple-negative human breast cancer cells in vivo

Therapeutic dosing and targeting efficacy of Pt-Mal-LHRH towards triple negative breast cancer

OBJECTIVE

Pt-Mal-LHRH is a newly synthesized chemotherapeutic agent that was designed to selectively target the luteinizing hormone-releasing hormone (LHRH) receptor expressed by triple negative breast cancer (TNBC). The aim of this study was to evaluate the therapeutic dosing, tumor reduction efficacy, and selective distribution of Pt-Mal-LHRH in-vivo.

METHODS AND RESULTS

LHRH tissue expression levels in-vivo were investigated using western blotting and LHRH was found to be increased in reproductive tissues (mammary, ovary, uterus). Further, Pt-Mal-LHRH was found to have increased TNBC tumor tissue platinum accumulation compared to carboplatin by inductively coupled plasma mass spectrometry analysis. The platinum family, compound carboplatin, was selected for comparison due to its similar chemical structure and molar equivalent doses were evaluated. Moreover, in-vivo distribution data indicated selective targeting of Pt-Mal-LHRH by enhanced reproductive tissue accumulation compared to carboplatin. Further, TNBC tumor growth was found to be significantly attenuated by Pt-Mal-LHRH compared to carboplatin in both the 4T1 and MDA-MB-231 tumor models. There was a significant reduction in tumor volume in the 4T1 tumor across Pt-Mal-LHRH doses (2.5-20 mg/kg/wk) and in the MDA-MB-231 tumor at the dose of 10 mg/kg/wk in models conducted by an independent contract testing laboratory.

CONCLUSION

Our data indicates Pt-Mal-LHRH is a targeting chemotherapeutic agent towards the LHRH receptor and reduces TNBC tumor growth in-vivo. This study supports drug conjugation design models using the LHRH hormone for chemotherapeutic delivery as Pt-Mal-LHRH was found to be a more selective and efficacious than carboplatin. Further examination of Pt-Mal-LHRH is warranted for its clinical use in TNBCs, along with, other reproductive cancers overexpressing the LHRH receptor.

Rewiring of the Endocrine Network in Triple-Negative Breast Cancer

The immunohistochemical definition of estrogen/progesterone receptors dictates endocrine feasibility in the treatment course of breast cancer. Characterized by the deficiency of estrogen receptor α, ERα-negative breast cancers are dissociated from any endocrine regimens in the routine clinical setting, triple-negative breast cancer in particular. However, the stereotype was challenged by triple-negative breast cancers’ retained sensitivity and vulnerability to endocrine agents. The interplay of hormone action and the carcinogenic signaling program previously underscored was gradually recognized along with the increasing investigation. In parallel, the overlooked endocrine-responsiveness in ERα-negative breast cancers attracted attention and supplied fresh insight into the therapeutic strategy in an ERα-independent manner. This review elaborates on the genomic and non-genomic steroid hormone actions and endocrine-related signals in triple-negative breast cancers attached to the hormone insensitivity label. We also shed light on the non-canonical mechanism detected in common hormone agents to showcase their pleiotropic effects.

Biodistribution studies for cell therapy products: Current status and issues

Information on the biodistribution (BD) of cell therapy products (CTPs) is essential for prediction and assessment of their efficacy and toxicity profiles in non-clinical and clinical studies. To conduct BD studies, it is necessary to understand regulatory requirements, implementation status, and analytical methods. This review aimed at surveying international and Japanese trends concerning the BD study for CTPs and the following subjects were investigated, which were considered particularly important: 1) comparison of guidelines to understand the regulatory status of BD studies in a global setting; 2) case studies of the BD study using databases to understand its current status in cell therapy; 3) case studies on quantitative polymerase chain reaction (qPCR) used primarily in non-clinical BD studies for CTPs; and 4) survey of imaging methods used for non-clinical and clinical BD studies. The results in this review will be a useful resource for implementing BD studies.

Estrogens and Progestogens in Triple Negative Breast Cancer: Do They Harm?

Triple-negative breast cancers (TNBC) occur more frequently in younger women and do not express estrogen receptor (ER) nor progesterone receptor (PR), and are therefore often considered hormone-insensitive. Treatment of premenopausal TNBC patients almost always includes chemotherapy, which may lead to premature ovarian insufficiency (POI) and can severely impact quality of life. Hormone replacement therapy (HRT) is contraindicated for patients with a history of hormone-sensitive breast cancer, but the data on safety for TNBC patients is inconclusive, with a few randomized trials showing increased risk-ratios with wide confidence intervals for recurrence after HRT. Here, we review the literature on alternative pathways from the classical ER/PR. We find that for both estrogens and progestogens, potential alternatives exist for exerting their effects on TNBC, ranging from receptor conversion, to alternative receptors capable of binding estrogens, as well as paracrine pathways, such as RANK/RANKL, which can cause progestogens to indirectly stimulate growth and metastasis of TNBC. Finally, HRT may also influence other hormones, such as androgens, and their effects on TNBCs expressing androgen receptors (AR). Concluding, the assumption that TNBC is completely hormone-insensitive is incorrect. However, the direction of the effects of the alternative pathways is not always clear, and will need to be investigated further.

Synthesis of Radiolabeled Technetium- and Rhenium-Luteinizing Hormone-Releasing Hormone (99mTc/Re-Acdien-LHRH) Conjugates for Targeted Detection of Breast Cancer Cells Overexpressing the LHRH Receptor

Currently, ^186/188Re and ^99mTc are widely used radionuclides for cancer detection and diagnosis. New advancements in modalities and targeting strategies of radiopharmaceuticals will provide an opportunity to enhance imagery and detection of smaller colonies of cancer cells while lowering false-positive diagnoses. To understand the chemistry of agents derived from fac-[^99mTc(CO)₃(H₂O)₃]⁺ species, the nonradioactive [Re(CO)₃(H₂O)₃]⁺ analogue was used. We have designed and synthesized Re-Acdien-LHRH, Re-Acdien-peg-LHRH, and a radiolabeled ^99mTc-Acdien-LHRH (rhenium- and technetium-luteinizing hormone-releasing hormone) conjugates using a tridentate linker to detect cancers overexpressing the LHRH receptor. Re-Acdien-LHRH and Re-Acdien-peg-LHRH were synthesized from non-PEGylated and PEGylated LHRH-Acdien, respectively. Cellular uptake of the compounds ^99mTc-Acdien-LHRH, Re-Acdien-LHRH, and Re-Acdien-peg-LHRH was found to be significantly enhanced compared to that of untargeted ^99mTc alone and unlabeled [Re(CO)₃(H₂O)₃]⁺. In addition, the conjugate compounds showed no difference in cellular toxicity compared to untargeted ^99mTc alone or unlabeled [Re(CO)₃(H₂O)₃]⁺. Further, a competition assay using LHRH indicated selective targeting of Re-Acdien-peg-LHRH toward the LHRH receptor (p < 0.05) compared to that of [Re(CO)₃(H₂O)₃]⁺ alone. Together, our data show the design paradigm and synthesis of targeting radionuclides using the LHRH peptide. Our data suggests that utilizing the LHRH peptide can lead to selective targeting and diagnosis of breast cancers expressing the LHRH receptor.

Identification of drivers of breast cancer invasion by secretome analysis: insight into CTGF signaling

An altered consistency of tumor microenvironment facilitates the progression of the tumor towards metastasis. Here we combine data from secretome and proteome analysis using mass spectrometry with microarray data from mesenchymal transformed breast cancer cells (MCF-7-EMT) to elucidate the drivers of epithelial-mesenchymal transition (EMT) and cell invasion. Suppression of connective tissue growth factor (CTGF) reduced invasion in 2D and 3D invasion assays and expression of transforming growth factor-beta-induced protein ig-h3 (TGFBI), Zinc finger E-box-binding homeobox 1 (ZEB1) and lysyl oxidase (LOX), while the adhesion of cell-extracellular matrix (ECM) in mesenchymal transformed breast cancer cells is increased. In contrast, an enhanced expression of CTGF leads to an increased 3D invasion, expression of fibronectin 1 (FN1), secreted protein acidic and cysteine rich (SPARC) and CD44 and a reduced cell ECM adhesion. Gonadotropin-releasing hormone (GnRH) agonist Triptorelin reduces CTGF expression in a Ras homolog family member A (RhoA)-dependent manner. Our results suggest that CTGF drives breast cancer cell invasion in vitro and therefore could be an attractive therapeutic target for drug development to prevent the spread of breast cancer.

Neoadjuvant chemotherapy modifies serum pyrrolidone carboxypeptidase specific activity in women with breast cancer and influences circulating levels of GnRH and gonadotropins

PURPOSE

Functional studies have demonstrated that gonadotropin-releasing hormone (GnRH) regulates cell proliferation, apoptosis, and tissue remodeling. GnRH is metabolized by the proteolytic regulatory enzyme pyrrolidone carboxypeptidase (Pcp) (E.C. 3.4.19.3), which is an omega peptidase widely distributed in fluids and tissues. We previously reported a decrease in both rat and human Pcp activity in breast cancer, suggesting that GnRH may be an important local hormonal factor in the pathogenesis of breast cancer. Recently, we have described that postmenopausal women with breast cancer show lower levels of serum Pcp activity than control postmenopausal women. To determine the effect of neoadjuvant chemotherapy (NACT) on serum Pcp specific activity and circulating levels of GnRH, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and steroid hormones 17-ß-estradiol and progesterone in pre- and postmenopausal women diagnosed with infiltrating ductal carcinoma.

METHODS

Serum Pcp activity was measured fluorometrically using pyroglutamyl-ß-naphthylamide. Circulating GnRH levels were dosed using a commercial RIA kit. Circulating LH and FSH levels were measured by enzyme immunoassays. Levels of steroid hormones were measured in serum samples by dissociation-enhanced lanthanide fluorescence immunoassay.

RESULTS AND CONCLUSION

Our results show the effect of NACT on the hypothalamic-pituitary axis, with the consequent alteration of circulating gonadotropins in premenopausal women with breast cancer. However, the results obtained in postmenopausal women with breast cancer treated with NACT, that is, the significant decrease in the concentration of GnRH and FSH compared to control postmenopausal women, differ from those obtained for premenopausal women. The only difference between pre- and postmenopausal women is their hormonal profile at the beginning of the study, that is, the presence of menopause and the consequent alteration of the hypothalamic-pituitary-gonadal axis.

Treatment of Breast Cancer With Gonadotropin-Releasing Hormone Analogs

Although significant progress has been made in the implementation of new breast cancer treatments over the last three decades, this neoplasm annually continues to show high worldwide rates of morbidity and mortality. In consequence, the search for novel therapies with greater effectiveness and specificity has not come to a stop. Among the alternative therapeutic targets, the human gonadotropin-releasing hormone type I and type II (hGnRH-I and hGnRH–II, respectively) and its receptor, the human gonadotropin-releasing hormone receptor type I (hGnRHR-I), have shown to be powerful therapeutic targets to decrease the adverse effects of this disease. In the present review, we describe how the administration of GnRH analogs is able to reduce circulating concentrations of estrogen in premenopausal women through their action on the hypothalamus–pituitary–ovarian axis, consequently reducing the growth of breast tumors and disease recurrence. Also, it has been mentioned that, regardless of the suppression of synthesis and secretion of ovarian steroids, GnRH agonists exert direct anticancer action, such as the reduction of tumor growth and cell invasion. In addition, we discuss the effects on breast cancer of the hGnRH-I and hGnRH-II agonist and antagonist, non-peptide GnRH antagonists, and cytotoxic analogs of GnRH and their implication as novel adjuvant therapies as antitumor agents for reducing the adverse effects of breast cancer. In conclusion, we suggest that the hGnRH/hGnRHR system is a promising target for pharmaceutical development in the treatment of breast cancer, especially for the treatment of advanced states of this disease.

Spotlight on triptorelin in the treatment of premenopausal women with early-stage breast cancer

Endocrine treatment represents the cornerstone of endocrine-sensitive premenopausal early breast cancer. The estrogen blockade plays a leading role in the therapeutic management of hormone receptor-positive breast cancer together with surgery, radiotherapy, and selective antiestrogen treatments. For several years, selective estrogen receptor modulators, such as tamoxifen, have represented the mainstay of therapy. The role of amenorrhea has been extensively elucidated in the past year: the benefit observed with chemotherapy-induced amenorrhea has strengthened its therapeutic role. Luteinizing hormone-releasing hormone (LHRH) has been introduced in oncology practice to induce amenorrhea in order to increase the advantage obtained from endocrine treatment. Triptorelin is one of the most widely used LHRH analogs currently available in clinical practice. It was recently investigated in two major clinical trials that studied the role of complete estrogen blockade in the premenopausal setting. Both showed the clinical benefit due to ovarian suppression treatment, primarily in high-risk patients. Furthermore, triptorelin and other LHRH analogs have recently been investigated in the attempt to preserve the ovarian function in young patients. The medical treatment of early breast cancer is always evolving in the effort to search for safe and efficacious treatments. The role of LHRH analogs is actually well recognized as contributing to the improvement of the medical treatment of premenopausal women with early breast cancer.

Could gonadotropin-releasing hormone analogs be helpful in the treatment of triple-negative breast cancer?

AIM

Treatment of triple-negative breast cancer (TNBC) imposes great challenges, due to a lack of molecular targets. While use of gonadotropin-releasing hormone (GnRH) analogs has been validated in ER-positive breast cancer, this option has not been investigated in TNBC, even though a significant portion of these tumors upregulate GnRH receptors. We performed a meta-analysis of the literature to evaluate the effect of GnRH analogs in TNBC.

METHODS

Four studies were included in this study.

RESULTS

We detected a non-significant improvement in overall survival with GnRH analogs, while progression-free survival was unchanged.

DISCUSSION

The majority of the trials evaluated in this analysis were designed to test efficacy of GnRH analogs in preventing premature ovarian failure. This may represent a limitation of our study as these trials were not specifically designed to detect differences in survival outcome measures.

CONCLUSION

Our results suggest that GnRH analogs may be useful as a targeted therapy in TNBC. Randomized prospective clinical trials are needed to investigate this hypothesis in the clinic.

The Role of Gonadotropin-Releasing Hormone in Cancer Cell Proliferation and Metastasis

In several human malignant tumors of the urogenital tract, including cancers of the endometrium, ovary, urinary bladder, and prostate, it has been possible to identify expression of gonadotropin-releasing hormone (GnRH) and its receptor as part of an autocrine system, which regulates cell proliferation. The expression of GnRH receptor has also been identified in breast cancers and non-reproductive cancers such as pancreatic cancers and glioblastoma. Various investigators have observed dose- and time-dependent growth inhibitory effects of GnRH agonists in cell lines derived from these cancers. GnRH antagonists have also shown marked growth inhibitory effects on most cancer cell lines. This indicates that in the GnRH system in cancer cells, there may not be a dichotomy between GnRH agonists and antagonists. The well-known signaling mechanisms of the GnRH receptor, which are present in pituitary gonadotrophs, are not involved in forwarding the antiproliferative effects of GnRH analogs in cancer cells. Instead, the GnRH receptor activates a phosphotyrosine phosphatase (PTP) and counteracts with the mitogenic signal transduction of growth factor receptors, which results in a reduction of cancer cell proliferation. The PTP activation, which is induced by GnRH, also inhibits G-protein-coupled estrogen receptor 1 (GPER), which is a membrane-bound receptor for estrogens. GPER plays an important role in breast cancers, which do not express the estrogen receptor α (ERα). In metastatic breast, ovarian, and endometrial cancer cells, GnRH reduces cell invasion in vitro, metastasis in vivo, and the increased expression of S100A4 and CYR61. All of these factors play important roles in epithelial-mesenchymal transition. This review will summarize the present state of knowledge about the GnRH receptor and its signaling in human cancers.

Establishment of an mKate2-Expressing Cell Line for Non-Invasive Real-Time Breast Cancer In Vivo Imaging

PURPOSE

Non-invasive real-time in vivo imaging experiments using mice as animal models have become crucial for understanding cancer development and treatment. In this study, we have developed and validated a new breast cancer cell line MDA-MB-435s that stably express a far-red fluorescence protein (mKate2) and that could serve as a highly valuable cell model for studying breast cancer detection and therapy using in vivo fluorescence imaging in nude mice.

PROCEDURES

The new cell line (MDA-MB-435s-mKate2) was constructed by plasmid transfection. The stability and sensitivity of mKate2, and the cell biological activities, were tested in vitro using different experimental approaches. For its potential use in tumor growth research and drug therapy in vivo, MDA-MB-435s-mKate2 was validated using the immunocompromised Balb/c nude mice tumor model. In addition, the new cell line has been characterized as a luteinizing hormone-releasing hormone receptor (LHRHR) positive cell line.

RESULTS

Firstly, MDA-MB-435s-mKate2 has shown a stable chromosomal integration of the amplified mKate2 gene and good fluorescence sensitivity for detection using a fluorescence reflectance imaging (FRI) device. Compared to its parental cell line, no significant difference in cell migration, proliferation, and clone formation was observed in vitro. Secondly, using the quantification of tumor-fluorescence surface area in live animals, we were able to monitor and detect the tumor progress or tumor inhibition rate (by Paclitaxel treatment) non-invasively and in real-time. Furthermore, MDA-MB-435s-mKate2 has been positively tested for LHRHR; these findings open the possibility to use this cell line for future studies of breast cancer therapy based on LHRH analogs in vivo.

CONCLUSION

In the present research, we have successfully built the MDA-MB-435s-mKate2 cell line that can be used as a suitable cell model for breast cancer therapy and anti-cancer drug evaluation by non-invasive fluorescence imaging in mice.

Invasion and increased expression of S100A4 and CYR61 in mesenchymal transformed breast cancer cells is downregulated by GnRH

S100 calcium binding protein A4 (S100A4) and cysteine-rich angiogenic inducer 61 (CYR61) play important roles in epithelial-mesenchymal-transition (EMT), invasion and metastasis by promoting cancer cell motility. Recently we were able to show that invasion of GnRH receptor-positive breast cancer cells is time- and dose-dependently reduced by GnRH analogs. We have now analyzed whether GnRH treatment affects S100A4 and CYR61 in mesenchymal transformed breast cancer cells. S100A4 and CYR61 expression was analyzed using RT-PCR. Invasion was quantified by assessment of breast cancer cell migration rate through an artificial basement membrane. The role of S100A4 and CYR61 in invasion of breast cancer cells was analyzed by neutralizing their biological activity. Expression of S100A4, CYR61 and GnRH receptor in human breast cancers, normal and other non-malignant breast tissues was analyzed by immuno-histochemistry. Invasion and expression of S100A4 and CYR61 in MDA-MB-231 breast cancer cells were significant higher as compared with MCF-7 breast cancer cells. Invasion and expression of S100A4 and CYR61 were significantly increased in mesenchymal transformed MCF-7 cells (MCF-7-EMT). The increased invasion of MCF-7-EMT cells could be reduced by anti-S100A4 and anti-CYR61 antibodies. In addition, invasion of MDA-MB-231 cells was decreased by anti-S100A4 and anti-CYR61 antibodies. Treatment of MCF-7-EMT and MDA-MB-231 cells with GnRH agonist Triptorelin resulted in a significant decrease of invasion and expression of S100A4 and CYR61. Both, S100A4 and CYR61 were found highly expressed in biopsy specimens of breast hyperplasia and malignant breast cancers. GnRH receptor expression was detectable in approximately 71% of malignant breast cancers. Our findings suggest that S100A4 and CYR61 play major roles in breast cancer invasion. Both, invasion and expression of S100A4 and CYR61 can be inhibited by GnRH treatment.

Concurrent Gonadotropin-Releasing Hormone Agonist Administration with Chemotherapy Improves Neoadjuvant Chemotherapy Responses in Young Premenopausal Breast Cancer Patients

Purpose

This study aimed to determine the oncologic efficacy of gonadotropin-releasing hormone (GnRH) agonist treatment concurrent with chemotherapy in a neoadjuvant setting.

Methods

A retrospective analysis was performed on 332 cases of invasive breast cancer in patients who were <40 years old at diagnosis and received GnRH agonists concurrent with neoadjuvant chemotherapy (GnRH agonist group) or neoadjuvant chemotherapy alone (neochemotherapy-alone group) from December 2010 to September 2014. Pathologic complete response rates (pCR) and Ki-67 changes were evaluated between the two groups.

Results

Median age was 32±3.9 and 36±3.0 years in the GnRH agonist group and neochemotherapy-alone group, respectively (p<0.001). After adjustment for tumor size, grade, lymph node metastasis, hormone receptor (HR) status, and chemotherapy regimen, the GnRH agonist group exhibited a higher pCR rate with an odds ratio (OR) of 2.98 (95% confidence interval [CI], 1.37-6.34) and a greater decrease in Ki-67 expression after treatment (p=0.05) than the neochemotherapy-alone group. For HR-negative tumors, the GnRH agonist group showed a higher pCR rate (multivariate OR, 3.50; 95% CI, 1.37-8.95) and a greater decrease in Ki-67 expression (p=0.047). For HR-positive breast cancer, the pCR rate, change in Ki-67 index, and clinical response were higher, and preoperative endocrine prognostic index scores were lower, in the GnRH agonist group, but these did not reach statistical significance.

Conclusion

Concurrent administration of GnRH agonists during neoadjuvant chemotherapy improved pCR rates and suppressed Ki-67 expression, especially in HR-negative tumors.

Beyond the C18 frontier: Androgen and glucocorticoid metabolism in breast cancer tissues: The role of non-typical steroid hormones in breast cancer development and progression

Breast cancer's hormonal dependence is well known and has been so for a long time. However in the last two decades great advances have been made in understanding the local metabolism of steroids within tissue. In the form of aromatase inhibition this is already one of the mainstays of breast cancer therapy. This review aims to summarise briefly what is known in terms of the metabolism of C18 steroids but perhaps more importantly to touch on the new developments regarding the importance of the metabolism of androgens and glucocorticoids in breast tissue. It is our hope that this review should provide the reader with a "birds eye view" of the current state of knowledge regarding localised steroid metabolism in the breast.

Goserelin for ovarian protection during breast-cancer adjuvant chemotherapy

BACKGROUND

Ovarian failure is a common toxic effect of chemotherapy. Studies of the use of gonadotropin-releasing hormone (GnRH) agonists to protect ovarian function have shown mixed results and lack data on pregnancy outcomes.

METHODS

We randomly assigned 257 premenopausal women with operable hormone-receptor-negative breast cancer to receive standard chemotherapy with the GnRH agonist goserelin (goserelin group) or standard chemotherapy without goserelin (chemotherapy-alone group). The primary study end point was the rate of ovarian failure at 2 years, with ovarian failure defined as the absence of menses in the preceding 6 months and levels of follicle-stimulating hormone (FSH) in the postmenopausal range. Rates were compared with the use of conditional logistic regression. Secondary end points included pregnancy outcomes and disease-free and overall survival.

RESULTS

At baseline, 218 patients were eligible and could be evaluated. Among 135 with complete primary end-point data, the ovarian failure rate was 8% in the goserelin group and 22% in the chemotherapy-alone group (odds ratio, 0.30; 95% confidence interval [CI], 0.09 to 0.97; two-sided P=0.04). Owing to missing primary end-point data, sensitivity analyses were performed, and the results were consistent with the main findings. Missing data did not differ according to treatment group or according to the stratification factors of age and planned chemotherapy regimen. Among the 218 patients who could be evaluated, pregnancy occurred in more women in the goserelin group than in the chemotherapy-alone group (21% vs. 11%, P=0.03); women in the goserelin group also had improved disease-free survival (P=0.04) and overall survival (P=0.05).

CONCLUSIONS

Although missing data weaken interpretation of the findings, administration of goserelin with chemotherapy appeared to protect against ovarian failure, reducing the risk of early menopause and improving prospects for fertility. (Funded by the National Cancer Institute and others; POEMS/S0230 ClinicalTrials.gov number, NCT00068601.).

Animal cancer models of skeletal metastasis

The bony skeleton is one of the most common sites of metastatic spread of cancer and is a significant source of morbidity in cancer patients, causing pain and pathologic fracture, impaired ambulatory ability, and poorer quality of life. Animal cancer models of skeletal metastases are essential for better understanding of the molecular pathways behind metastatic spread and local growth and invasion of bone, to enable analysis of host-tumor cell interactions, identify barriers to the metastatic process, and to provide platforms to develop and test novel therapies prior to clinical application in human patients. Thus, the ideal model should be clinically relevant, reproducible and representative of the human condition. This review summarizes the current in vivo animal models used in the study of cancer metastases of the skeleton.

Reproductive physiology of a humanized GnRH receptor mouse model: application in evaluation of human-specific analogs

The human GnRH receptor (GNRHR1) has a specific set of properties with physiological and pharmacological influences not appropriately modeled in laboratory animals or cell-based systems. To address this deficiency, we have generated human GNRHR1 knock-in mice and described their reproductive phenotype. Measurement of pituitary GNRHR1 transcripts from homozygous human GNRHR1 knock-in (ki/ki) mice revealed a severe reduction (7- to 8-fold) compared with the mouse Gnrhr1 in wild-type mice. ¹²⁵I-GnRH binding assays on pituitary membrane fractions corroborated reduced human GNRHR1 protein expression in ki/ki mice, as occurs with transfection of human GNRHR1 in cell lines. Female homozygous knock-in mice displayed normal pubertal onset, indicating that a large reduction in GNRHR1 expression is sufficient for this process. However, ki/ki females exhibited periods of prolonged estrous and/or metestrous and reduced fertility. No impairment was found in reproductive maturity or adult fertility in male ki/ki mice. Interestingly, the serum LH response to GnRH challenge was reduced in both knock-in males and females, indicating a reduced GNRHR1 signaling capacity. Small molecules targeting human GPCRs usually have poor activities at homologous rodent receptors, thus limiting their use in preclinical development. Therefore, we tested a human-specific GnRH1 antagonist, NBI-42902, in our mouse model and demonstrated abrogation of a GnRH1-induced serum LH rise in ki/ki mice and an absence of effect in littermates expressing the wild-type murine receptor. This novel model provides the opportunity to study the human receptor in vivo and for screening the activity of human-specific GnRH analogs.

KISS1R induces invasiveness of estrogen receptor-negative human mammary epithelial and breast cancer cells

Kisspeptins (KPs), peptide products of the KISS1 metastasis-suppressor gene, are endogenous ligands for a G protein-coupled receptor (KISS1R). KISS1 acts as a metastasis suppressor in numerous human cancers. However, recent studies have demonstrated that an increase in KISS1 and KISS1R expression in patient breast tumors correlates with higher tumor grade and metastatic potential. We have shown that KP-10 stimulates invasion of estrogen receptor α (ERα)-negative MDA-MB-231 breast cancer cells via transactivation of the epidermal growth factor receptor (EGFR). Here, we report that either KP-10 treatment of ERα-negative nonmalignant mammary epithelial MCF10A cells or expression of KISS1R in MCF10A cells induced a mesenchymal phenotype and stimulated invasiveness. Similarly, exogenous expression of KISS1R in ERα-negative SKBR3 breast cancer cells was sufficient to trigger invasion and induced extravasation in vivo. In contrast, KP-10 failed to transactivate EGFR or stimulate invasiveness in the ERα-positive MCF7 and T47D breast cancer cells. This suggested that ERα negatively regulates KISS1R-dependent breast cancer cell migration, invasion, and EGFR transactivation. In support of this, we found that these KP-10-induced effects were ablated upon exogenous expression of ERα in the MDA-MB-231 cells, by down-regulating KISS1R expression. Lastly, we have identified IQGAP1, an actin cytoskeletal binding protein as a novel binding partner of KISS1R, and have shown that KISS1R regulates EGFR transactivation in breast cancer cells in an IQGAP1-dependent manner. Overall, our data strongly suggest that the ERα status of mammary cells dictates whether KISS1R may be a novel clinical target for treating breast cancer metastasis.

Gonadotropin-releasing hormone receptor activates GTPase RhoA and inhibits cell invasion in the breast cancer cell line MDA-MB-231

Background

Gonadotropin-releasing hormone (GnRH) and its receptor (GnRHR) are both expressed by a number of malignant tumors, including those of the breast. In the latter, both behave as potent inhibitors of invasion. Nevertheless, the signaling pathways whereby the activated GnRH/GnRHR system exerts this effect have not been clearly established. In this study, we provide experimental evidence that describes components of the mechanism(s) whereby GnRH inhibits breast cancer cell invasion.

Methods

Actin polymerization and substrate adhesion was measured in the highly invasive cell line, MDA-MB-231 transiently expressing the wild-type or mutant DesK191 GnRHR by fluorometry, flow cytometric analysis, and confocal microscopy, in the absence or presence of GnRH agonist. The effect of RhoA-GTP on stress fiber formation and focal adhesion assembly was measured in MDA-MB-231 cells co-expressing the GnRHRs and the GAP domain of human p190Rho GAP-A or the dominant negative mutant GAP-Y1284D. Cell invasion was determined by the transwell migration assay.

Results

Agonist-stimulated activation of the wild-type GnRHR and the highly plasma membrane expressed mutant GnRHR-DesK191 transiently transfected to MDA-MB-231 cells, favored F-actin polymerization and substrate adhesion. Confocal imaging allowed detection of an association between F-actin levels and the increase in stress fibers promoted by exposure to GnRH. Pull-down assays showed that the effects observed on actin cytoskeleton resulted from GnRH-stimulated activation of RhoA GTPase. Activation of this small G protein favored the marked increase in both cell adhesion to Collagen-I and number of focal adhesion complexes leading to inhibition of the invasion capacity of MDA-MB-231 cells as disclosed by assays in Transwell Chambers.

Conclusions

We here show that GnRH inhibits invasion of highly invasive breast cancer-derived MDA-MB-231 cells. This effect is mediated through an increase in substrate adhesion promoted by activation of RhoA GTPase and formation of stress fibers and focal adhesions. These observations offer new insights into the molecular mechanisms whereby activation of overexpressed GnRHRs affects cell invasion potential of this malignant cell line, and provide opportunities for designing mechanism-based adjuvant therapies for breast cancer.

GnRH receptors in cancer: from cell biology to novel targeted therapeutic strategies

The crucial role of pituitary GnRH receptors (GnRH-R) in the control of reproductive functions is well established. These receptors are the target of GnRH agonists (through receptor desensitization) and antagonists (through receptor blockade) for the treatment of steroid-dependent pathologies, including hormone-dependent tumors. It has also become increasingly clear that GnRH-R are expressed in cancer tissues, either related (i.e. prostate, breast, endometrial, and ovarian cancers) or unrelated (i.e. melanoma, glioblastoma, lung, and pancreatic cancers) to the reproductive system. In hormone-related tumors, GnRH-R appear to be expressed even when the tumor has escaped steroid dependence (such as castration-resistant prostate cancer). These receptors are coupled to a G(αi)-mediated intracellular signaling pathway. Activation of tumor GnRH-R by means of GnRH agonists elicits a strong antiproliferative, antimetastatic, and antiangiogenic (more recently demonstrated) activity. Interestingly, GnRH antagonists have also been shown to elicit a direct antitumor effect; thus, these compounds behave as antagonists of GnRH-R at the pituitary level and as agonists of the same receptors expressed in tumors. According to the ligand-induced selective-signaling theory, GnRH-R might assume various conformations, endowed with different activities for GnRH analogs and with different intracellular signaling pathways, according to the cell context. Based on these consistent experimental observations, tumor GnRH-R are now considered a very interesting candidate for novel molecular, GnRH analog-based, targeted strategies for the treatment of tumors expressing these receptors. These agents include GnRH agonists and antagonists, GnRH analog-based cytotoxic (i.e. doxorubicin) or nutraceutic (i.e. curcumin) hybrids, and GnRH-R-targeted nanoparticles delivering anticancer compounds.

GPCRs and cancer

G-protein-coupled receptors (GPCRs), which represent the largest gene family in the human genome, play a crucial role in multiple physiological functions as well as in tumor growth and metastasis. For instance, various molecules like hormones, lipids, peptides and neurotransmitters exert their biological effects by binding to these seven-transmembrane receptors coupled to heterotrimeric G-proteins, which are highly specialized transducers able to modulate diverse signaling pathways. Furthermore, numerous responses mediated by GPCRs are not dependent on a single biochemical route, but result from the integration of an intricate network of transduction cascades involved in many physiological activities and tumor development. This review highlights the emerging information on the various responses mediated by a selected choice of GPCRs and the molecular mechanisms by which these receptors exert a primary action in cancer progression. These findings provide a broad overview on the biological activity elicited by GPCRs in tumor cells and contribute to the identification of novel pharmacological approaches for cancer patients.

GnRH receptor activation competes at a low level with growth signaling in stably transfected human breast cell lines

Background

Gonadotrophin releasing hormone (GnRH) analogs lower estrogen levels in pre-menopausal breast cancer patients. GnRH receptor (GnRH-R) activation also directly inhibits the growth of certain cells. The applicability of GnRH anti-proliferation to breast cancer was therefore analyzed.

Methods

GnRH-R expression in 298 primary breast cancer samples was measured by quantitative immunofluorescence. Levels of functional GnRH-R in breast-derived cell lines were assessed using ¹²⁵I-ligand binding and stimulation of ³H-inositol phosphate production. Elevated levels of GnRH-R were stably expressed in cells by transfection. Effects of receptor activation on in vitro cell growth were investigated in comparison with IGF-I and EGF receptor inhibition, and correlated with intracellular signaling using western blotting.

Results

GnRH-R immunoscoring was highest in hormone receptor (triple) negative and grade 3 breast tumors. However prior to transfection, functional endogenous GnRH-R were undetectable in four commonly studied breast cancer cell lines (MCF-7, ZR-75-1, T47D and MDA-MB-231). After transfection with GnRH-R, high levels of cell surface GnRH-R were detected in SVCT and MDA-MB-231 clones while low-moderate levels of GnRH-R occurred in MCF-7 clones and ZR-75-1 clones. MCF-7 sub-clones with high levels of GnRH-R were isolated following hygromycin phosphotransferase transfection. High level cell surface GnRH-R enabled induction of high levels of ³H-inositol phosphate and modest growth-inhibition in SVCT cells. In contrast, growth of MCF-7, ZR-75-1 or MDA-MB-231 clones was unaffected by GnRH-R activation. Cell growth was inhibited by IGF-I or EGF receptor inhibitors. IGF-I receptor inhibitor lowered levels of p-ERK1/2 in MCF-7 clones. Washout of IGF-I receptor inhibitor resulted in transient hyper-elevation of p-ERK1/2, but co-addition of GnRH-R agonist did not alter the dynamics of ERK1/2 re-phosphorylation.

Conclusions

Breast cancers exhibit a range of GnRH-R immunostaining, with higher levels of expression found in triple-negative and grade 3 cancers. However, functional cell surface receptors are rare in cultured cells. Intense GnRH-R signaling in transfected breast cancer cells did not markedly inhibit growth, in contrast to transfected HEK 293 cells indicating the importance of intracellular context. GnRH-R signaling could not counteract IGF-I receptor-tyrosine kinase addiction in MCF-7 cells. These results suggest that combinatorial strategies with growth factor inhibitors will be needed to enhance GnRH anti-proliferative effects in breast cancer