Carsten Gründker

Antiproliferative Signaling of Luteinizing Hormone-Releasing Hormone in Human Endometrial and Ovarian Cancer Cells through G Proteinα I-Mediated Activation of Phosphotyrosine Phosphatase1

The signaling pathway through which LHRH acts in endometrial and ovarian cancers is distinct from that in the anterior pituitary. The LHRH receptor interacts with the mitogenic signal transduction of growth factor receptors, resulting in down-regulation of expression of c-fos and proliferation. Only limited data are available on the cross-talk between LHRH receptor signaling and inhibition of mitogenic signal transduction. The present experiments were performed to analyze in endometrial and ovarian cancer cells: 1) whether mutations or splice variants of the LHRH receptor are responsible for differences in LHRH signaling, 2) the coupling of G protein subtypes to LHRH receptor, 3) the phosphotyrosine phosphatase (PTP) activation counteracting growth factor receptor tyrosine kinase activity. For these studies, the well characterized human Ishikawa and Hec-1A endometrial cancer cell lines and human EFO-21 and EFO-27 ovarian cancer cell lines were used, which express LHRH and its receptor. 1) Sequencing of the complementary DNA of the LHRH receptor from position 31 to position 1204, covering the complete coding region (position 56 to position 1042) showed that there are neither mutations nor splice variants of the LHRH receptor transcript in Ishikawa and Hec-1A endometrial cancer cells or in EFO-21 and EFO-27 ovarian cancer cells. 2) All analyzed cell lines except for the ovarian cancer cell line EFO-27 expressed both G proteins, alpha(i) and alpha(q), as shown by RT-PCR and Western blotting. In the EFO-27 cell line only G protein alpha(i), not G protein alpha(q), expression was found. Cross-linking experiments using disuccinimidyl suberate revealed that in the cell lines expressing G protein alpha(i) and G protein alpha(q), both G proteins coupled to the LHRH receptor. Inhibition of epidermal growth factor (EGF)-induced c-fos expression by LHRH, however, was mediated through pertussis toxin (PTX)-sensitive G protein alpha(i). Moreover, LHRH substantially antagonized the PTX-catalyzed ADP-ribosylation of G protein alpha(i). 3) Using a phosphotyrosine phosphatase assay based on molybdate-malachite green, treatment of quiescent EFO-21 and EFO-27 ovarian cancer cells and quiescent Ishikawa and Hec-1A endometrial cancer cells with 100 nM of the LHRH agonist triptorelin resulted in a 4-fold increase in PTP activity (P < 0.001). This effect was completely blocked by simultaneous treatment with PTX, supporting the concept of mediation through G protein alpha(i). As shown by quantitative Western blotting, EGF-induced tyrosine autophosphorylation of EGF receptors was reduced 45-63% after LHRH (100 nM) treatment (P < 0.001). This effect was completely blocked using the PTP inhibitor vanadate (P < 0.001). These results demonstrate that mutations or splice variants of the LHRH receptor in human endometrial and ovarian cancer cells are not responsible for the different signal transduction compared with that in pituitary gonadotrophs. We provide evidence that the tumor LHRH receptor couples to multiple G proteins, but the antiproliferative signal transduction is mediated through the PTX-sensitive G protein alpha(i). The tumor LHRH receptor activates a PTP counteracting EGF-induced tyrosine autophosphorylation of EGF receptor, resulting in down-regulation of mitogenic signal transduction and cell proliferation.

Phytoestrogen genistein stimulates the production of osteoprotegerin by human trabecular osteoblasts.

The anti‐resorptive effects of estrogen on bone metabolism are thought to be mediated through modulation of paracrine factors produced by osteoblastic lineage cells that act on osteoclastic lineage cells. Receptor activator of nuclear factor‐κB ligand (RANKL) is the essential factor for osteoclast formation and activation and enhances bone resorption. By contrast, osteoprotegerin (OPG), which is produced by osteoblastic lineage cells acts as a decoy receptor that neutralizes RANKL and prevents bone loss. Recently, 17β‐estradiol was found to stimulate OPG mRNA levels and protein secretion in a human osteoblastic cell line through activation of the estrogen receptor (ER)‐α. In this study, we assessed the effects of the phytoestrogen genistein on OPG mRNA steady state levels (by semiquantitative RT‐PCR and Northern analysis) and protein production (by ELISA) in primary human trabecular osteoblasts (hOB) obtained from healthy donors. Genistein increased OPG mRNA levels and protein secretion by hOB cells by up to two‐ to six‐fold in a dose‐ (P < 0.0001) and time‐dependent (P < 0.0001) fashion with a maximum effect at 10−7 M. Co‐treatment with the pure ER antagonist ICI 182,780 completely abrogated the stimulatory effects of genistein on OPG protein secretion, indicating that these effects were specific and directly mediated through the ER. Pre‐treatment with genistein partially prevented the inhibitory effects of the glucocorticoid dexamethasone on OPG mRNA and protein production. The stimulation of OPG mRNA levels by genistein was not affected by the protein synthesis inhibitor, cycloheximide and was shown to be due to enhancement of OPG gene transcription. In conclusion, our data suggest that the phytoestrogen genistein is capable of upregulating the production of OPG by human osteoblasts. Thus, dietary sources of phytoestrogens may help to prevent bone resorption and bone loss by enhanced osteoblastic production of OPG. J. Cell. Biochem. 84: 725–735, 2002.

Role of gonadotropin-releasing hormone (GnRH) in ovarian cancer

The expression of GnRH (GnRH-I, LHRH) and its receptor as a part of an autocrine regulatory system of cell proliferation has been demonstrated in a number of human malignant tumors, including cancers of the ovary. The proliferation of human ovarian cancer cell lines is time- and dose-dependently reduced by GnRH and its superagonistic analogs. The classical GnRH receptor signal-transduction mechanisms, known to operate in the pituitary, are not involved in the mediation of antiproliferative effects of GnRH analogs in these cancer cells. The GnRH receptor rather interacts with the mitogenic signal transduction of growth-factor receptors and related oncogene products associated with tyrosine kinase activity via activation of a phosphotyrosine phosphatase resulting in downregulation of cancer cell proliferation. In addition GnRH activates nucleus factor κB (NFκB) and protects the cancer cells from apoptosis. Furthermore GnRH induces activation of the c-Jun N-terminal kinase/activator protein-1 (JNK/AP-1) pathway independent of the known AP-1 activators, protein kinase (PKC) or mitogen activated protein kinase (MAPK/ERK).Recently it was shown that human ovarian cancer cells express a putative second GnRH receptor specific for GnRH type II (GnRH-II). The proliferation of these cells is dose- and time-dependently reduced by GnRH-II in a greater extent than by GnRH-I (GnRH, LHRH) superagonists. In previous studies we have demonstrated that in ovarian cancer cell lines except for the EFO-27 cell line GnRH-I antagonist Cetrorelix has comparable antiproliferative effects as GnRH-I agonists indicating that the dichotomy of GnRH-I agonists and antagonists might not apply to the GnRH-I system in cancer cells. After GnRH-I receptor knock down the antiproliferative effects of GnRH-I agonist Triptorelin were abrogated while the effects of GnRH-I antagonist Cetrorelix and GnRH-II were still existing. In addition, in the ovarian cancer cell line EFO-27 GnRH-I receptor but not putative GnRH-II receptor expression was found. These data suggest that in ovarian cancer cells the antiproliferative effects of GnRH-I antagonist Cetrorelix and GnRH-II are not mediated through the GnRH-I receptor.

Luteinizing Hormone-Releasing Hormone Induces Nuclear Factorκ B-Activation and Inhibits Apoptosis in Ovarian Cancer Cells

More than 80% of human ovarian cancers express LHRH and its receptor as part of a negative autocrine mechanism of growth control. This study was conducted to investigate whether LHRH affects apoptosis in ovarian cancer. EFO-21 and EFO-27 ovarian cancer cells were treated with LHRH agonist Triptorelin or with cytotoxic agent Doxorubicin in the absence or presence of Triptorelin. Apoptotic cells were quantified by flow cytometry. Expression of nuclear factor kappa B (NFkappaB) was assessed by RT-PCR and immunoblotting. For determination of Triptorelin-induced NFkappaB activation, cells were transfected with a NFkappaB-secreted alkaline phosphatase reporter gene plasmid (pNFkappaB-SEAP) and cultured for 96 h with or without Triptorelin. The causal relation between Triptorelin-induced NFkappaB activation and Triptorelin-induced protection against apoptosis was investigated using SN50, an inhibitor for nuclear translocation of activated NFkappaB. Apoptosis induction by Triptorelin was never observed. Treatment with Doxorubicin (1 nmol/L) for 72 h increased the percentage of apoptotic cells in EFO-21 and EFO-27 ovarian cancer cell lines to 31% or 34%, respectively. In cultures treated simultaneously with Triptorelin (100 nmol/L), the percentage of apoptotic cells was reduced significantly, to 17% or 18%, respectively (P < 0.001). RT-PCR and immunoblotting experiments showed that NFkappaB subunits p50 and p65 were expressed by ovarian cancer cell lines EFO-21 and EFO-27. When EFO-21 or EFO-27 cells were transfected with pNFkappaB-SEAP and subsequently treated with Triptorelin (100 nmol/L), NFkappaB-induced SEAP expression increased 5.3-fold or 4.7-fold, respectively (P < 0.001). Triptorelin-induced reduction of Doxorubicin-induced apoptosis was blocked by SN50-mediated inhibition of NFkappaB translocation into the nucleus. We conclude that LHRH induces activation of NFkappaB and thus reduces Doxorubicin-induced apoptosis in human ovarian cancer cells. This possibility to protect ovarian cancer cells from programmed cell death is an important feature in LHRH signaling in ovarian tumors, apart from the inhibitory interference with the mitogenic pathway.

Atorvastatin stimulates the production of osteoprotegerin by human osteoblasts

Recently, HMG‐CoA reductase inhibitors (statins), potent inhibitors of cholesterol biosynthesis, have been linked to protective effects on bone metabolism. Because of their widespread use, prevention of bone loss and fractures would be a desirable side effect. However, the mechanisms how statins may affect bone metabolism are poorly defined. Here, we evaluated the effect of atorvastatin on osteoblastic production of receptor activator of nuclear factor‐κB ligand (RANKL) and osteoprotegerin (OPG), cytokines that are essential for osteoclast cell biology. While RANKL enhances osteoclast formation and activation, thereby, promoting bone loss, OPG acts as a soluble decoy receptor and antagonizes the effects of RANKL. In primary human osteoblasts (hOB), atorvastatin increased OPG mRNA levels and protein secretion by hOB by up to three fold in a dose‐dependent manner with a maximum effect at 10−6 M (P < 0.001). Time course experiments indicated a time‐dependent stimulatory effect of atorvastatin on OPG mRNA levels after 24 h and on OPG protein secretion after 48–72 h (P < 0.001). Treatment of hOB with substrates of cholesterol biosynthesis that are downstream of the HMG‐CoA reductase reaction (mevalonate, geranylgeranyl pyrophosphate) reversed atorvastatin‐induced enhancement of OPG production. Of note, atorvastatin abrogated the inhibitory effect of glucocorticoids on OPG production. Treatment of hOB with atorvastatin enhanced the expression of osteoblastic differentiation markers, alkaline phosphatase and osteocalcin. In summary, our data suggest that atorvastatin enhances osteoblastic differentiation and production of OPG. This may contribute to the bone‐sparing effects of statins.

Membrane-bound melatonin receptor MT1 down-regulates estrogen responsive genes in breast cancer cells.

Abstract:  Melatonin possesses anti‐estrogenic effects on estrogen receptor expressing (ER+) breast cancer cells in culture by reducing cell cycle progression and cell proliferation. There is increasing agreement that on a cellular level the effects of melatonin are primarily induced by the membrane‐bound receptor MT1. The participation of a second, nuclear receptor of the group of ligand‐dependent transcription factors, called RZRα, is under debate. In this study we used a number of breast cancer cell lines differing in their expression of the estrogen receptor and the two known melatonin receptors. In MCF‐7 breast cancer cells transfected with a vector carrying the MT1 gene (MCF‐7Mel1a) binding of CREB‐protein to the cAMP‐responsive element of the breast cancer suppressing gene BRCA‐1 was more strongly reduced by treatment with melatonin than in the parental cells. Expression of estrogen responsive genes was determined in serum‐starved cells, cells stimulated for 16 hr with estradiol and cells subsequently treated with melatonin. Expression of BRCA‐1, p53, p21WAF and c‐myc were up‐regulated by estradiol. Treatment of the stimulated cells with melatonin counteracted the increase induced by estradiol almost completely. The more MT1 a cell line expressed, the stronger was the reduction of the expression of the estradiol‐induced genes. There was no correlation between the expression of the nuclear receptor RZRα and the effects of melatonin on these genes.

Gonadotropin-Releasing Hormone Type II Antagonists Induce Apoptotic Cell Death in Human Endometrial and Ovarian Cancer Cells In vitro and In vivo

In human endometrial and ovarian cancers, gonadotropin-releasing hormone type I (GnRH-I), GnRH-II, and their receptors are parts of a negative autocrine regulatory system of cell proliferation. Based on a tumor-specific signal transduction, GnRH-I and GnRH-II agonists inhibit the mitogenic signal transduction of growth factor receptors and related oncogene products associated with tyrosine kinase activity via activation of a phosphotyrosine phosphatase resulting in down-regulation of cancer cell proliferation. Induction of apoptosis is not involved. In this study, we show that treatment of human endometrial and ovarian cancer cells with GnRH-II antagonists results in apoptotic cell death via dose-dependent activation of caspase-3. The antitumor effects of the GnRH-II antagonists could be confirmed in nude mice. GnRH-II antagonists inhibited the growth of xenotransplants of human endometrial and ovarian cancers in nude mice significantly, without any apparent side effects. Thus, GnRH-II antagonists seem to be suitable drugs for an efficacious and less toxic endocrine therapy for endometrial and ovarian cancers.

Luteinizing hormone-releasing hormone induces JunD–DNA binding and extends cell cycle in human ovarian cancer cells

Expression of luteinizing hormone-releasing hormone (LHRH) and its receptor as part of an autocrine regulatory system of cell proliferation has been demonstrated in a number of human malignant tumors, including cancers of the ovary. This study was conducted to investigate whether LHRH induces activation of JunD and affects cell cycle regulation and DNA synthesis. Treatment of primary human ovarian cancer cells and human ovarian cancer cell lines EFO-21 and EFO-27 with LHRH agonist triptorelin (100 nM) resulted in an increase in G(0/1) phase and a decrease in G(2/S) phase of cell cycle. Treatment of quiescent EFO-21 or EFO-27 cells with triptorelin (100 nM) resulted in a 46.7 or 44.2-fold increase of AP-1 activation, respectively (p<0.001). Maximal binding of JunD on DNA consensus sequence was found after 4 h of treatment of quiescent EFO-21 or EFO-27 cells with triptorelin (100 nM). DNA synthesis was significantly decreased to 45.5+/-11.4% (day 0=control=100%; p<0.001) after 3 days of triptorelin (1 nM) treatment. These results suggest that LHRH agonist triptorelin induces JunD-DNA binding, resulting in reduced proliferation as indicated by increased G(0/1) phase of cell cycle and decreased DNA synthesis. Since LHRH activates nucleus factor kappa B (NF kappa B) and protects ovarian cancer cells from doxorubicin-induced apoptosis and JunD is shown to decrease cell cycle and cell proliferation, we propose that JunD activated by LHRH acts as a modulator of cell proliferation and cooperates with the anti-apoptotic and anti-mitogenic functions of LHRH.

CD36-mediated activation of endothelial cell apoptosis by an N-terminal recombinant fragment of thrombospondin-2 inhibits breast cancer growth and metastasis in vivo

Thus far the clinical benefits seen in breast cancer patients treated with drugs targeting the vascular endothelial growth factor (VEGF) pathway are only modest. Consequently, additional antiangiogenic approaches for treatment of breast cancer need to be investigated. Thrombospondin-2 (TSP-2) has been shown to inhibit tumor growth and angiogenesis with a greater potency than the related molecule TSP-1. The systemic effects of TSP-2 on tumor metastasis and the underlying molecular mechanisms of the antiangiogenic activity of TSP-2 have remained poorly understood. We generated a recombinant fusion protein consisting of the N-terminal region of TSP-2 and the IgG-Fc1 fragment (N-TSP2-Fc) and could demonstrate that the antiangiogenic activity of N-TSP2-Fc is dependent on the CD36 receptor. We found that N-TSP2-Fc inhibited VEGF-induced tube formation of human dermal microvascular endothelial cells (HDMEC) on matrigel in vitro and that concurrent incubation of anti-CD36 antibody with N-TSP2-Fc resulted in tube formation that was comparable to untreated control. N-TSP2-Fc potently induced apoptosis of HDMEC in vitro in a CD36-dependent manner. Moreover, we could demonstrate a CD36 receptor-mediated loss of mitochondrial membrane potential and activation of caspase-3 in HDMEC in vitro. Daily intraperitoneal injections of N-TSP2-Fc resulted in a significant inhibition of the growth of human MDA-MB-435 and MDA-MB-231 tumor cells grown in the mammary gland of immunodeficient nude mice and in reduced tumor vascularization. Finally, increased serum concentrations of N-TSP2-Fc significantly inhibited regional metastasis to lymph nodes and distant metastasis to lung as shown by quantitative real-time alu PCR. These results identify N-TSP2-Fc as a potent systemic inhibitor of tumor metastasis and provide strong evidence for an important role of the CD36 receptor in mediating the antiangiogenic activity of TSP-2.

Dose escalation and pharmacokinetic study of AEZS-108 (AN-152), an LHRH agonist linked to doxorubicin, in women with LHRH receptor-positive tumors

OBJECTIVES Receptors for luteinizing hormone-releasing hormone (LHRH) can be utilized for targeted chemotherapy of cytotoxic LHRH analogs. The compound AEZS-108 (previously AN-152) consists of [D-Lys⁶]LHRH linked to doxorubicin. The objectives of this first study in humans with AESZ-108 were to determine the maximum tolerated dose and to characterize the dose-limiting toxicity, pharmacokinetics, preliminary efficacy, and hormonal effects. METHODS The study included 17 women with histologically confirmed epithelial cancer of the ovary, endometrium, or breast that was metastatic or unresectable and for which standard curative or palliative measures could not be used or were no longer effective or tolerated. In each patient, immunohistochemistry of primary tumor or metastatic lesion confirmed that the tumors expressed LHRH receptors. RESULTS One patient each received intravenous doses of 10, 20, 40, or 80 mg/m² of AEZS-108, six received 160 mg/m² and seven 267 mg/m² at 3 week intervals. Dose-limiting leukopenia and neutropenia were observed at the highest dose. A total of 6 patients, 3 patients each in both upper dose groups, showed responses to AEZS-108. The half-life of AESZ-108 was estimated to be about 2h. CONCLUSIONS The maximum tolerated dose of AESZ-108 in the absence of supportive medication is 267 mg/m² and this dose is recommended as starting dose for therapeutic Phase II studies.