Gonadotropin-releasing-hormone-receptor antagonists

Prolactin secretion before, during, and after chronic gonadotropin-releasing hormone agonist treatments in children

OBJECTIVE

To examine the effect of long-term administration of GnRH agonists (GnRHa) on PRL secretion in children affected by central precocious puberty (CPP) and growth hormone deficiency (GHD).

DESIGN

Prospective analysis of blood sampling before, during, and after GnRHa treatments.

SETTING

Pediatric endocrine center.

PATIENT(S)

One hundred nineteen and 93 children with a diagnosis of CPP and GHD, respectively.

INTERVENTION(S)

Monthly depot injections of GnRHa drugs (leuprorelin acetate 3.75 mg [LA] and triptorelin 3.75 mg [TR]) administered to CPP and GHD patients for 40 and 24 months, respectively.

MAIN OUTCOME MEASURE(S)

Serum PRL levels at baseline and after 6, 12, 18, 24, 30, 36, and 40 months of treatment with GnRHa were compared between CPP and GHD groups. PRL levels at 6 and 12 months after GnRHa withdrawal were also examined.

RESULT(S)

Although serum PRL levels tended to be higher in TR- than in LA-treated patients, no significant difference in circulating PRL in basal condition and during GnRHa treatment was detected between the CPP and GHD groups. However, five children (3.8%) developed hyperprolactinemia during TR treatment.

CONCLUSION(S)

Although there are no general concerns about GnRHa treatment safety, careful PRL monitoring is required in GnRHa-treated children.

Intermedin Functions as a Pituitary Paracrine Factor Regulating Prolactin Release

Calcitonin, α- and β-calcitonin gene-related peptides, amylin, and adrenomedullin belong to a unique group of peptide hormones important for homeostasis maintenance. We recently identified intermedin (IMD) as a novel member of the calcitonin/calcitonin gene-related peptide family expressed in the pituitary, digestive tract, and other organs of vertebrates. Real-time PCR and immunohistochemical analysis of pituitaries from rats at different stages of development showed that IMD is expressed in the intermediate lobe and select adrenocorticotrophs in the anterior lobe, suggesting that IMD could function as a paracrine factor regulating anterior pituitary hormone secretion. In support of a paracrine role for IMD in the pituitary, quantitative and in situ hybridization analyses showed the expression of IMD receptor transcripts including the calcitonin receptor-like receptor and receptor activity-modifying proteins in the pituitary. Treatment with IMD leads to a dose-dependent increase of prolactin release in cultured rat pituitary cells. In contrast, IMD treatment has negligible effects on the release of GH, FSH, or ACTH. Likewise, in vivo treatment with IMD leads to an elevation of plasma prolactin levels in conscious rats. Based on these functional characteristics, we hypothesized that IMD could represent one of the intermediate lobe-derived prolactin-releasing factors important for prolactin regulation during reproduction. In support of this hypothesis, studies of IMD expression in lactating and ovariectomized rats showed that pituitary IMD transcripts in lactating animals increased to more than 2-fold over nonlactating controls whereas ovariectomy leads to a 90% reduction of IMD expression in the pituitary. Of importance, subsequent treatment with 17β-estradiol or diethylstilbestrol increased pituitary IMD expression in ovariectomized rats. In addition, analysis of the proximate region of the IMD gene promoter showed that the IMD gene promoter contains consensus estrogen response element sequences, and estrogen treatments up-regulate the promoter reporter activity in transfected pituitary cells. Collectively, the present study indicates that IMD represents a novel estrogen-dependent intermediate lobe-derived prolactin-releasing factor and could play important roles in the regulation of prolactin release during reproduction in females.

The role of aromatase inhibitors in ameliorating deleterious effects of ovarian stimulation on outcome of infertility treatment

Clinical utilization of ovulation stimulation to facilitate the ability of a couple to conceive has not only provided a valuable therapeutic approach, but has also yielded extensive information on the physiology of ovarian follicular recruitment, endometrial receptivity and early embryo competency. One of the consequences of the use of fertility enhancing agents for ovarian stimulation has been the creation of a hyperestrogenic state, which may influence each of these parameters. Use of aromatase inhibitors reduces hyperestrogenism inevitably attained during ovarian stimulation. In addition, the adjunct use of aromatase inhibitors during ovarian stimulation reduces amount of gonadotropins required for optimum stimulation. The unique approach of reducing hyperestrogenism, as well as lowering amount of gonadotropins without affecting the number of mature ovarian follicles is an exciting strategy that could result in improvement in the treatment outcome by ameliorating the deleterious effects of the ovarian stimulation on follicular development, endometrial receptivity, as well as oocyte and embryo quality.

Antagonist and agonist binding models of the human gonadotropin-releasing hormone receptor

G-protein-coupled receptors (GPCRs) constitute one of the most important classes of drug targets. Since the first high-resolution structure of a GPCR was determined by Palczewski and co-workers [K. Palczewski, T. Kumasaka, T. Hori, C.A. Behnke, H. Motoshima, B.A. Fox, I. Le Trong, D.C. Teller, T. Okada, R.E. Stenkamp, M. Yamamoto, M. Miyano, Crystal structure of rhodopsin: a G-protein-coupled receptor, Science 289 (2000) 739-745], development of in silico models of rhodopsin-like GPCRs could be rationally founded. In this work, we present a model of the human gonadotropin-releasing hormone receptor based on the rhodopsin structure. The transmembrane helices are modeled by homology, while the extra- and intra-cellular loops are modeled in such a way that experimentally determined interactions and microdomains (e.g., hydrophobic cores) are retained. We conclude that specifically tailored models, compared to more automatic approaches, have the benefit that known interactions are easily introduced early in the homology modeling. Furthermore, tailored models, although more tedious to construct, are better suited for drug lead finding and for compound optimization. To test the stability of the receptor, we performed a 1 ns molecular dynamics simulation. Moreover, we docked two agonists (native GnRH and Triptorelin, [dTrp(6)]-GnRH) and two antagonists (Cetrorelix, dNal(1)-dCpa(2)-dPal(3)-Ser(4)-Tyr(5)-dCit(6)-Leu(7)-Arg(8)-Pro(9)-dAla(10)), and the covalently constrained dicyclic decapeptide dicyclo(1,1'-5/4-10)[Ac-Glu(1)(Gly(1)')-dCpa(2)-dTrp(3)-Asp(4)-dbu(5)-dNal(6)-Leu(7)-Arg(8)-Pro(9)-dpr(10)-NH(2)] into the putative receptor binding site. The docked ligand conformations result in ligand-receptor interactions that are generally in good agreement with site-directed mutagenesis and ligand-binding studies presented in the literature. Our results indicate that the binding conformation of the antagonists differs from that of the agonists. This difference can be linked to the activation or inhibition of the receptor.

Structure–activity relationships of 1,3,5-triazine-2,4,6-triones as human gonadotropin-releasing hormone receptor antagonists

SAR studies of 1,3,5-triazine-2,4,6-triones as human gonadotropin-releasing hormone receptor antagonists resulted in potent compounds. The best compound from the series had a binding affinity of 2 nM.

Using gonadotropin-releasing hormone (GnRH) and GnRH analogs to modulate testis function and enhance the productivity of domestic animals

Gonadotropin releasing hormone (GnRH) controls the activity of the gonadotrope cells of the pituitary gland and, as a consequence, is a critical component of the endocrine cascade that determines the growth, development, and functional activity of testicular tissue. The use of GnRH and GnRH analogs is common in domestic animal production systems. Although GnRH and GnRH analogs are most commonly used to control the fertility and reproductive events in female animals, GnRH agonists and antagonists are increasingly used to modulate the fertility, behavior, and productivity of male animals as well. This review will focus on recent advances in this use of GnRH agonists and antagonists.

Ovarian response and follicular development for single-dose and multiple-dose protocols for gonadotropin-releasing hormone antagonist administration

OBJECTIVE

To determine the efficiency of a single-dose and a multiple-dose protocol for GnRH antagonist administration.

DESIGN

Randomized clinical trial.

SETTING

University hospital, tertiary medical center.

PATIENT(S)

Sixty-one patients undergoing controlled ovarian stimulation (COS) and IVF/ICSI.

INTERVENTION(S)

COS with either a multiple-dose (MD) or a single-dose (SD) protocol for GnRH antagonist (cetrorelix) administration, or with a long protocol (LP) for GnRH agonist (buserelin) administration, followed by oocyte retrieval, IVF/ICSI, and embryo transfer.

MAIN OUTCOME MEASURE(S)

Follicular development and serum levels of E2 and LH.

RESULT(S)

The SD protocol for cetrorelix was associated with a more reduced level of follicular development, lower levels of serum estradiol on the day of HCG administration, and a more reduced number of zygotes than the LP for buserelin. The pregnancy and implantation rates did not differ significantly for the three study groups.

CONCLUSION(S)

The MD and SD GnRH antagonist protocols were effective for preventing LH surge and appear to elicit an equivalent pregnancy rate to that corresponding to a LP GnRH agonist. In terms of follicular development, the SD protocol requires further modification, including flexible scheduling or possibly a small reduction of the dosage of the administered cetrorelix.

Emerging drugs in assisted reproduction

Infertility affects approximately 15% of couples of reproductive age. In assisted reproductive technology (ART), medications play a crucial role in stimulating ovaries to produce several oocytes and prepare the endometrium to be receptive after replacing one or more embryos into the uterine cavity. The availability of recombinant human follicle stimulating hormone, luteinising hormone and human chorionic gonadotrophin; of gonadotrophin-releasing hormone (GnRH) agonists and antagonists; and of luteal supplementation with progesterone have allowed the tailoring of several stimulation schemes, which have enhanced the pregnancy outcome after ART treatment. However, the remaining risk of ovarian hyperstimulation syndrome, the still low implantation rates, the unacceptably high rates of multiple pregnancies and the daily parenteral administration of medications do not constitute the features of a patient-friendly procedure. Therefore, a number of molecules with gonadotrophin-like activity, inhibition of GnRH receptor ability, or endometrium receptivity enhancement properties are currently under active investigation. Orally bioactive therapeutic preparations, in particular, may revolutionize in vitro fertilisation (IVF) treatment in the near future. Nevertheless, the implementation of mild ovarian stimulation protocols with single embryo transfer policy and further development of oocyte in vitro maturation techniques may lead to a less drug orientated IVF treatment.

Benzimidazoles as non-peptide luteinizing hormone-releasing hormone (LHRH) antagonists. Part 3: Discovery of 1-(1H-benzimidazol-5-yl)-3-tert-butylurea derivatives

1-(1H-Benzimidazol-5-yl)-3-tert-butylurea derivatives have been identified as a novel class of non-peptide luteinizing hormone-releasing hormone (LHRH) antagonists. Herein, we disclose the synthesis and structure-activity relationships (SAR) of this class resulting in the identification of compound 12c, with dual functional activity on human and rat receptors (rat LHRH: IC50=120 nM; human LHRH: IC50=18 nM). These SAR studies suggest that 1-(1H-benzimidazol-5-yl)-3-tert-butylurea is a new pharmacophore for small molecule LHRH antagonists.

Rapid reduction of leiomyoma volume during treatment with the GnRH antagonist ganirelix

OBJECTIVE

To assess maximal volume reduction of leiomyomas and uterus and the duration of treatment required to reach these reductions with daily GnRH antagonist treatment.

DESIGN

Prospective, open-label study.

SETTING

Large teaching hospital in The Netherlands.

POPULATION

Premenopausal women with symptomatic fibroids, who were scheduled for surgery.

METHODS

Twenty women were treated with daily 2 mg of subcutaneous ganirelix. Prior to the first injection and weekly during treatment, the volume of leiomyomas and the uterus were assessed by ultrasound (USS) and serum hormones were measured. Prior to treatment and when maximal size reduction was observed by USS, the volume of the leiomyomas and the uterus were also assessed by magnetic resonance imaging (MRI).

MAIN OUTCOME MEASURES

Leiomyoma and uterine size reduction, time to maximal reduction.

RESULTS

One woman was excluded from the study due to incorrect administration dose of ganirelix. Data on the remaining 19 women (average age 39 years) with subserosal (n= 9), submucosal (n= 7), intramural (n= 10) and transmural (n= 1) leiomyomas were evaluated. Baseline leiomyoma volumes ranged from small (3-4 mL) to large (>1000 mL). The median duration of treatment up to maximal leiomyoma size reduction was 19 days (range 1-65 days). The maximal size reduction in leiomyomas measured by USS was -42.7% (-77.0% to 14.1%) and -29.2% (-62.2% to 35.6%) by MRI. Comparable uterine size reductions of -46.6% (-78.6% to -6.1%) and -25.2% (-63.6% to 28.9%) were observed by USS and MRI. During the first three weeks of treatment, 8 out of 19 women reported adverse events related to the induced hypoestrogenic state. Most of these events resolved within one week after treatment was discontinued.

CONCLUSION

Daily treatment with 2 mg of ganirelix results in rapid reduction of leiomyoma and uterine volume in premenopausal women with minor side effects. If longer-acting GnRH antagonists become available, pretreatment with GnRH antagonist should be preferred over GnRH agonists prior to surgery.

Uracils as potent antagonists of the human gonadotropin-releasing hormone receptor without atropisomers

Uracil derivatives were designed and synthesized to avoid atropisomers observed in the 6-methyluracils as antagonists of the human GnRH receptor. Optimization at the 1- and 5-positions of the uracil resulted in potent compounds such as 24 (Ki=0.45 nM).

Abarelix: the first gonadotrophin-releasing hormone antagonist for the treatment of prostate cancer

The high incidence of prostate cancer makes it a major healthcare problem and the second leading cancer-related cause of death among men in developed countries. The hormonal treatment of prostate cancer is indicated for the palliation of symptomatic and metastatic disease in older patients, and as neoadjuvant treatment of different modalities of radiotherapy. This hormonal treatment is based on the study conducted by Huggins in 1940 and consists of androgen suppression. Since the clinical availability of the first luteinising hormone-releasing hormone (LHRH) agonist, no significant improvement has been made in the field of medical castration. Taking these data into consideration, the recent approval of abarelix by the FDA, the first gonadotrophin-releasing hormone (GnRH) antagonist, appears to be promising news. The pharmacology of the molecule and the clinical studies that led to FDA approval will be reviewed. The place of GnRH antagonists in the treatment modalities of prostate cancer will then be discussed.

Dose-finding study of daily GnRH antagonist for the prevention of premature LH surges in IVF/ICSI patients: optimal changes in LH and progesterone for clinical pregnancy

BACKGROUND

An optimal range of LH concentrations for achieving pregnancy has not been established. The aim of this study was to investigate the effect of various LH levels induced by different GnRH antagonist doses on IVF outcome.

METHODS

This was a prospective, single centre study including 144 IVF patients, stimulated with recombinant FSH from cycle day 2, and co-treated with daily GnRH antagonist (antide/Iturelix) (2 mg/2 ml, 1 mg/ml, 0.5 mg/ml, 0.5 mg/0.5 ml or 0.25 mg/ml) from cycle day 7 onwards. Serum samples were taken three times daily.

RESULTS

Clinical pregnancies were only observed within a particular range of change in LH levels. The upper and lower thresholds for the mean LH area under the curve (AUC), adjusted for the baseline LH level before the antagonist was started (LH AUC(-S6); S6=stimulation day 6) were -2.2 and 12.4 (IU/l) respectively (a negative value=below baseline levels). There were no clinical pregnancies outside these threshold values. Similar results were found for progesterone, the threshold levels of progesterone AUC(-S6) were 3.98 and -1.21 ng/ml. Moreover, there were no pregnancies with progesterone levels >0.26 ng/ml/follicle on the day of hCG.

CONCLUSIONS

Excessive or insufficient suppression of LH and progesterone levels during GnRH antagonist administration and high progesterone/follicle on hCG day seems to be associated with impaired clinical pregnancy rates.

3-[(2R)-Amino-2-phenylethyl]-1-(2,6-difluorobenzyl)-5-(2-fluoro-3-methoxyphenyl)- 6-methylpyrimidin-2,4-dione (NBI 42902) as a Potent and Orally Active Antagonist of the Human Gonadotropin-Releasing Hormone Receptor. Design, Synthesis, and in Vitro and in Vivo Characterization

Further structure-activity relationship studies of a series of substituted uracils at the 1, 3, and 5 positions resulted in the discovery of several potent antagonists of the human gonadotropin-releasing hormone receptor. Uracils bearing a side chain derived from phenylglycinol at the 3-position were shown to be orally bioavailable in monkeys. 3-[(2R)-Amino-2-phenylethyl]-1-(2,6-difluorobenzyl)-5-(2-fluoro-3-methoxyphenyl)-6-methylpyrimidin-2,4-dione (R-13b, NBI 42902) displayed subnanomolar binding affinity (K(i) = 0.56 nM) and was a potent functional antagonist (IC(50) = 3.0 nM in Ca(2+) flux assay) at the human GnRH receptor. It also bound to the monkey GnRH receptor with high affinity (K(i) = 3.9 nM). In addition, R-13bhad good plasma exposure in cynomolgus monkeys after oral administration, with a C(max) of 737 ng/mL and an AUC of 2392 ng/mL.h at a 10 mg/kg dose. Moreover, oral administration of R-13b to castrated male cynomolgus monkeys resulted in a significant decrease in serum levels of luteinizing hormone. These results demonstrate that compounds from this series of uracils are potent GnRH antagonists with good oral bioavailability and efficacy in nonhuman primates.

Central precocious puberty: current treatment options

Central precocious puberty (CPP) is characterized by early pubertal changes, acceleration of growth velocity, and rapid bone maturation that often result in reduced adult height. An onset of pubertal signs before the age of 8 years in girls and 9 years in boys should always be evaluated. A combination of clinical signs, bone age, pelvic echography in girls, and hormonal data are required to diagnose CPP and make a judgment concerning progression and prognosis. Not all children with apparently true CPP require medical intervention. The main reasons for treatment are to prevent compromised adult height and to avoid psychosocial or behavioral problems. The need for treatment for auxologic reasons is based on estimation of predicted adult height, with the finding of a reduced height potential, which may require a follow-up. Indication for treatment on the basis of psychologic and behavioral anomalies has to be determined on an individual basis. The main short-term aims of therapy are to stop the progression of secondary sex characteristics and menses (in girls) and to treat the underlying cause, when known. Long-term goals are to increase final adult height and to promote psychosocial well-being. Once it has been decided that treatment is appropriate, it should be initiated immediately with depot gonadotropin-releasing hormone (GnRH) agonists. The effective suppression of pituitary gonadal function is achieved with these compounds in practically all CPP patients. Long-term data are now available from 2 decades of GnRH agonist treatment for patients with CPP. Treatment preserves height potential in the majority of patients (especially in younger patients) and improves the final adult height of children with rapidly progressing CPP, with a complete recovery of the hypothalamic-pituitary-gonadal axis after treatment. GnRH agonist treatment using depot preparations is useful and has a good safety profile, with minimal adverse effects and no severe long-term consequences. Although further data are need, there may be a role in the future for combining somatropin (growth hormone) and GnRH agonist treatment for some patients with significantly impaired growth velocity. The introduction of GnRH antagonists is likely to improve the treatment options for CPP.

Sexual precocity: a historical perspective and update

Puberty is the interval in the life cycle during which the child becomes an adult. It is heralded by physical changes such as acceleration of linear growth and appearance of secondary sexual characteristics, capped by attainment of reproductive capability, and orchestrated by increases in the secretion of hypothalamic, pituitary, and gonadal hormones. This article discusses selected historical and contemporary aspects of isosexual precocious puberty, i.e., the development of sexual characteristics prior to the usual age of pubertal onset.

Identification of neutral 4-O-alkyl quinolone nonpeptide GnRH receptor antagonists

A series of neutral, nonbasic quinolone GnRH antagonists were prepared via Mitsunobu alkylation of protected and unprotected 4-hydroxy quinolone intermediates. The synthetic route was improved by utilization of unique reactivity and convergency afforded by the use of mono and bis-trimethylsilylethyl protected quinolones. Potent neutral GnRH antagonists were identified, including ether and lactam derivatives, that show similar in vitro binding affinity and functional activity as compared to the earlier basic 4-aminoalkyl quinolone series of nonpeptide GnRH antagonists.

Suppressing reproductive activity in horses using GnRH vaccines, antagonists or agonists

There are a number of situations in which it is desirable to suppress part or all of the reproductive endocrine system in a horse, notably the competing animal whose tractability during training, or performance during competition, is compromised by the expression of sexual or aggressive behavior. The current therapeutic approaches to reproductive endocrine suppression include gonadectomy and progestagen administration, where the former carries surgical risks and entails irreversible loss of breeding potential, and effective progestagen therapy requires frequent administration for extended periods and is banned in some competing animals as potentially anabolic. In this context, preventing the action of gonadotrophin releasing hormone (GnRH) by blocking its pituitary receptors is an attractive alternative for reversibly rendering mares anestrus or depressing testosterone secretion or spermatogenesis in stallions. This paper reviews the data on effects, efficacy, reversibility, and side effects of GnRH vaccines, antagonists, and agonists for suppressing reproductive activity in horses, within the context of their potential place in the pharmacological armoury of the veterinary clinician.

Backbone metal cyclization: Novel 99mTc labeled GnRH analog as potential SPECT molecular imaging agent in cancer

Gonadotropin-releasing hormone (GnRH) is a decapeptide secreted to the pituitary where it binds to specific receptors on the gonadotropes to regulate gonadotropic hormones (luteinizing hormone (LH) and follicle-stimulating hormone (FSH)) synthesis and secretion. Specific GnRH receptors are overexpressed in breast, prostatic, ovarian, and other tumors. The aim of this study was to synthesize a cyclic GnRH analog with high affinity to GnRH receptors that can be radiolabeled with 99mTc. A precyclic GnRH analog, [Cys-Gly]1[D-Ala]6[N(alpha)(eta-Cys-amino hexyl)]10GnRH (Gn-2), containing two hemi-chelator groups was synthesized. It was cyclized applying the recently reported backbone metal cyclization (BMC) approach, to obtain cyclo(Re(O)1-10)[Cys-Gly]1[D-Ala]6[N(alpha)(eta-Cys-amino hexyl)]10GnRH (cyclo[Re(O)-Gn-2]). For comparative evaluations, Gn-2 was oxidized on-resin to yield cyclo(S-S,1-10)[Cys-Gly]1[D-Ala]6[N(alpha)(eta-Cys-amino hexyl)]10GnRH, (cyclo[S-S-Gn-2]). The binding affinity of cyclo[Re(O)-Gn-2] to rat pituitary membranes showed IC50 of 50 nM, compared to IC50 = 10 nM in the native GnRH. Cyclo(99mTc(O)1-10)[Cys-Gly]1[D-Ala]6[N(alpha)(eta-Cys-amino hexyl)]10GnRH (cyclo[99mTc(O)-Gn-2]) was synthesized from Gn-2 and showed similar chromatographic behavior to its rhenium surrogate.

Synthesis and structure–activity relationships of uracil derived human GnRH receptor antagonists: (R)-3-[2-(2-amino)phenethyl]-1-(2,6-difluorobenzyl)-6-methyluracils containing a substituted thiophene or thiazole at C-5

The synthesis of a series of (R)-3-[2-(2-amino)phenethyl]-1-(2,6-difluorobenzyl)-6-methyluracils containing a substituted thiophene or thiazole at C-5 is described. SAR around C-5 of the uracil led to the discovery that a 2-thienyl or (2-phenyl)thiazol-4-yl group is required for optimal receptor binding. The best compound from the series had a binding affinity of 2 nM (K(i)) for the human GnRH receptor. A novel and convenient preparation of N-1-(2,6-difluorobenzyl)-6-methyluracil is also described.

Dose-finding study of daily gonadotropin-releasing hormone (GnRH) antagonist for the prevention of premature luteinizing hormone surges in IVF/ICSI patients: antide and hormone levels

BACKGROUND

The aim of this study was to define the minimal effective dose of antide (Iturelix) to prevent premature luteinizing hormone (LH) surges in in vitro fertilization (IVF) patients.

METHODS

In a prospective, single centre study, 144 IVF/ICSI patients were stimulated with r-hFSH from cycle day 2 and from cycle day 6 onwards, cotreated with daily 2 mg/2 ml (n=30), 1 mg/ml (n=30), 0.5 mg/ml (n=31), 0.5 mg/0.5 ml (n=23) and 0.25 mg/ml (n=30) GnRH antagonist (antide). Serum samples were taken three times daily during antide administration to assess antide and hormone levels. The minimal effective dose was defined as the lowest dose group with <2 LH surges (LH >12.4 IU/l and progesterone >2 ng/ml).

RESULTS

Serum antide levels, mean LH and E2 levels per day and their area under the curves were dose-related to antide. The bioavailability of antide almost doubled after dilution in larger volumes. Pre-injection LH levels gradually increased during GnRH antagonist treatment. LH surges occurred in the lowest dose groups 0.5 mg/ml (3.2%), 0.5 mg/0.5 ml (6.7%) and 0.25 mg/ml (13.3%). Hence, 0.5 mg/ml is considered to be the minimal effective dose. Antide was overall well tolerated and safe.

CONCLUSIONS

0.5 mg/ml antide is the minimal effective dose to prevent an untimely LH surge in IVF patients stimulated with r-hFSH.

Serum oxytocinase activity is related to tumor growth parameters in N-methyl nitrosourea induced rat breast cancer

Oxytocinase has been reported to hydrolyse the peptide hormone oxytocin (OT). We have previously described changes in oxytocinase activity in human breast cancer, where a highly significant increase occurred in tumoral tissue. In the present work, we analysed oxytocinase activity in serum of rats with breast cancer induced by N-methyl-nitrosourea (NMU). We also correlated these data with the number and size of tumors and the body weight of the animals to evaluate the putative value of this activity as a biological marker of the disease. Our results confirm the involvement of OT in carcinogenesis and suggest a mayor role for oxytocinase activity in the development of breast cancer.

Synthesis and structure–activity relationships of ( R )-1-alkyl-3-[2-(2-amino)phenethyl]-5-(2-fluorophenyl)-6-methyluracils as human GnRH receptor antagonists

The synthesis of a series of (R)-1-alkyl-3-[2-(2-amino)phenethyl]-5-(2-fluorophenyl)-6-methyluracils is discussed. SAR around N-1 of the uracil was explored, which led to the discovery that an electron-deficient 2,6-disubstituted benzyl group is required for optimal receptor binding. The best compound from the series had binding affinity of 0.7 nM (K(i) for the human GnRH receptor, which was 8-fold better than the 2,6-difluorobenzyl analog.

Safety of GnRH agonists and antagonists

The widespread application of protocols using gonadotropin-releasing hormone (GnRH) agonists or antagonists in assisted reproduction treatment has led to an increasing number of pregnancies exposed to these drugs. This issue has raised scepticism as to the safety of these medications, concerning both pregnant women and their offspring. The main parameters that can be studied to ensure the safety of GnRH analogues include: a) systemic and local reactions to the medication; b) incidence of ovarian hyperstimulation syndrome (OHSS); c) direct effect on oocytes and embryos; and d) the health of those children exposed. So far, no systemic side effects and no major local reactions have been reported following the use of GnRH agonists or third-generation antagonists. On the other hand, the incidence of OHSS seems to be higher with GnRH agonist protocols compared to conventional or GnRH antagonist protocols. The recent cloning of the GnRH receptor has led to the demonstration of GnRH receptor gene expression in the human ovary, although the existence of GnRH receptors per se remains controversial. Similarly, the potential direct effect of GnRH analogues on the follicles and oocytes remains a matter of debate. The incidence of miscarriage and the health of children born as a result of in vitro fertilisation (IVF) treatment do not appear to be influenced by the GnRH agonist treatment. This also seems to be the case for the GnRH antagonists, although the available information on this issue is still limited. Therefore, most of the accumulated data concerning the safety of the GnRH analogues are encouraging, and no serious side effects have been reported. On the other hand, as no definite conclusions about the safety of these drugs can be drawn until now, continued assessment of the aforementioned parameters in long-term follow-up studies is recommended.

A Vaccination Strategy for the Long-Term Suppression of Androgens in Advanced Prostate Cancer

OBJECTIVES

We have previously reported the ability of D17DT (formerly GnRH-DT) vaccination to produce castrate levels of androgens in men with advanced prostate cancer. This study examines the efficacy and tolerability of 3 and 15 micrograms of D17DT in 12 patients with advanced prostate cancer to establish a dose-response relationship.

METHODS

12 patients received either 3 or 15 micrograms of D17DT as 3 deep intramuscular injections over 6 weeks. Outcome was assessed in terms of physical and biochemical evaluations of clinical progression and antibody titres.

RESULTS

Significant titres of anti-GnRH antibodies were detected in 2 out of 6 subjects who received 15 micrograms of D17DT; suppression of testosterone to castrate levels accompanied by a significant and prolonged reduction in PSA was also demonstrated. No responses were seen following treatment with 3 micrograms of D17DT.

CONCLUSION

The induction of anti-GnRH antibodies through vaccination with 15 micrograms D17DT can produce and sustain castrate levels of testosterone in men with advanced prostate cancer.

Novel roles of neuropeptide processing enzymes: EC3.4.24.15 in the neurome

Neuropeptide processing metalloenzymes, such as angiotensin converting enzyme, neprilysin, endothelin converting enzyme, neurolysin, and EC3.4.24.15 (EP24.15), are central to the formation and degradation of bioactive peptides. We present EP24.15 as a paradigm for novel functions ascribed to these enzymes in the neurome. Although the neurome typically encompasses proteomes of the brain and central nervous system, exciting new roles of these neuropeptidases have been demonstrated in other organ systems. We discuss the involvement of EP24.15 with clinical sequelae involving the use of gonadotropin-releasing hormone (GnRH; LHRH) analogs that act as enzyme inhibitors, in vascular physiology (blood pressure regulation), and in the hematologic system (immune surveillance). Hemodynamic forces, such as cyclic strain and shear stress, on vascular cells, induce an increase in EP24.15 transcription, suggesting that neuropeptidase-mediated hydrolysis of pressor/depressor peptides is likely regulated by changes in hemodynamic force and blood pressure. Lastly, EP24.15 regulates surface expression of major histocompatibility complex Class I proteins in vivo, suggesting that EP24.15 may play an important role in maintenance of immune privilege in sites of increased endogenous expression. In these extraneural systems, regulation of both neuropeptide and other peptide substrates by neuropeptidases indicates that the influence of these enzymes may be more global than was anticipated previously, and suggests that their attributed role as neuropeptidases underestimates their physiologic actions in the neural system.

The biology of gonadotropin hormone-releasing hormone: role in the control of tumor growth and progression in humans

It is now well known that different forms of GnRH coexist in the same vertebrate species. In humans, two forms of GnRH have been identified so far. The first form corresponds to the hypophysiotropic decapeptide, and is now called GnRH-I. The second form has been initially identified in the chicken brain, and it is referred to as GnRH-II. GnRH-I binds to and activates specific receptors, belonging to the 7 transmembrane (7TM) domain superfamily, present on pituitary gonadotropes. These receptors (type I GnRH receptors) are coupled to the Gq/11/PLC intracellular signalling pathway. A receptor specific for GnRH-II (type II GnRH receptor) has been identified in non-mammalian vertebrates as well as in primates, but not yet in humans. In the last 10-15 years experimental evidence has been accumulated indicating that GnRH-I is expressed, together with its receptors, in tumors of the reproductive tract (prostate, breast, ovary, and endometrium). In these hormone-related tumors, activation of type I GnRH receptors consistently decreases cell proliferation, mainly by interfering with the mitogenic activity of stimulatory growth factors (e.g., EGF, IGF). Recent data seem to suggest that GnRH-I might also reduce the migratory and invasive capacity of cancer cells, possibly by affecting the expression and/or activity of cell adhesion molecules and of enzymes involved in the remodelling of the extracellular matrix. These observations point to GnRH-I as an autocrine negative regulatory factor on tumor growth progression and metastatization. Extensive research has been performed to clarify the molecular mechanisms underlying the peculiar antitumor activity of GnRH-I. Type I GnRH receptors in hormone-related tumors correspond to those present at the pituitary level in terms of cDNA nucleotide sequence and protein molecular weight, but do not share the same pharmacological profile in terms of binding affinity for the different synthetic GnRH-I analogs. Moreover, the classical intracellular signalling pathway mediating the stimulatory activity of the decapeptide on gonadotropin synthesis and secretion is not involved in its inhibitory activity on hormone-related tumor growth. In these tumors, type I GnRH receptors are coupled to the Gi-cAMP, rather than the Gq/11-PLC, signal transduction pathway. Recently, we have reported that GnRH-I and type I GnRH receptors are expressed also in tumors not related to the reproductive system, such as melanoma. Also in melanoma cells, GnRH-I behaves as a negative regulator of tumor growth and progression. Interestingly, the biochemical and pharmacological profiles of type I GnRH receptors in melanoma seem to correspond to those of the receptors at pituitary level. The data so far reported on the expression and on the possible functions of GnRH-II in humans are still scanty. The decapeptide has been identified, together with a 'putative' type II GnRH receptor, both in the central nervous system and in peripheral structures, such as tissues of the reproductive tract (both normal and tumoral). The specific biological functions of GnRH-II in humans are presently under investigation.

Synthesis and structure-activity relationships of 1-arylmethyl-3-(2-aminopropyl)-5-aryl-6-methyluracils as potent GnRH receptor antagonists

The novel synthesis and SAR studies of 6-methyluracils as human GnRH receptor antagonists are discussed. Introduction of a small methyl substituent at the beta-position from N3 of the uracil improved the GnRH binding potency by 5- to 10-fold. The best compound from the series had binding affinity of 5 nM (K(i)) to the human GnRH receptor.

Synthesis and structure–Activity relationships of thieno[2,3- d ]pyrimidine-2,4-dione derivatives as potent GnRH receptor antagonists

The synthesis and SAR studies of thieno[2,3-d]pyrimidine-2,4-diones as human GnRH receptor antagonists to treat reproductive diseases are discussed. It was found that the 2-(2-pyridyl)ethyl group on the 5-aminomethyl functionality of the core structure was a key feature for good receptor binding activity. SAR study of the 6-(4-aminophenyl) group suggests that hydrophobic substituents were preferred. The best compound from this series had binding affinity (K(i)) of 0.4 nM to the human GnRH receptor.

Suppression and recovery of LH secretion by a potent and selective GnRH-receptor antagonist peptide in healthy early follicular-phase women are mediated via selective control of LH secretory burst mass

AIM

GnRH antagonists are competitive inhibitors of GnRH receptors. Their administration induces prompt suppression of the gonadal axis. In animals, GnRH antagonists upregulate the activity of GnRH-secreting neurones, which could cause gonadotrophin rebound following inhibition. The aim of this study was to evaluate the effects of a potent GnRH antagonist, Teverelix (TEV), on the gonadal axis in healthy young women.

SUBJECTS AND MEASUREMENTS

In nine women [20-35 years old, body mass index (BMI) 19-25 kg/m2] in the early follicular phase, serum LH and FSH levels were evaluated every 10 min from 08.00 to 12.00 h before, and 24 h and 96 h after TEV injection (2.5 mg in 1 ml subcutaneously on day 0). Serum gonadotrophin and oestradiol levels were also evaluated at baseline and at 6, 8, 12, 48, 72 h after TEV.

RESULTS

The antagonist reduced both serum LH and FSH concentrations; LH levels were significantly and promptly reduced at +6 h (nadir at +8 h) until +48 h and recovered at +72 h, while FSH levels were reduced (P<0.05) 24 h after the antagonist and normalized at +48 h. LH (but not FSH) concentrations at +96 h exceeded baseline (P<0.05). TEV suppressed oestradiol concentrations (P<0.05) with a nadir at +24 h, comparable reduction at +48 h and recovery to baseline at +72 h. Deconvolution analysis showed that the antagonist peptide suppressed (P<0.02) the pulsatile production rate, burst mass and amplitude of LH on day 1. Pulsatile FSH secretion also fell at this time (P<0.05). LH and FSH pulse frequency were not modified by TEV. At +96 h, LH pulsatility did not significantly differ from that at baseline. Suppression of mean LH or FSH concentrations did not affect the relative pattern regularity (approximate entropy) of LH and FSH secretion.

CONCLUSIONS

This study demonstrates that the acute administration of a potent GnRH antagonist induces prompt inhibition of the gonadal axis lasting for 2 days in women due to mechanistically specific suppression of LH secretory burst mass and the mean FSH secretion rate. The trend toward rebound release of LH following the end of the pharmacological effect of the antagonist could reflect a rise in endogenous GnRH activity.

Treatment of perimenopausal women with uterine myoma: successful use of a depot GnRH agonist leading to a natural menopause

Gonadotrophin-releasing hormone agonists (GnRHa) reduce the size of uterine fibroids and relieve patients of myoma-related symptoms. However, rapid regrowth frequently occurs after the therapy is stopped. We attempted to determine whether GnRHa therapy could lead perimenopausal women carrying symptomatic myomas to the natural onset of the menopause. A retrospective analysis of 145 patients who received GnRHa for 24 weeks demonstrated that after cessation of therapy no menstruation occurred over 25 weeks in women aged over 45 years, with elevated levels of follicle-stimulating hormone (FSH) and luteinising hormone (LH) > 25 mIU/ml. To extend this study, we studied prospectively 21 women, aged 45 years and older who had regular menstruation with symptoms attributed to myomas and elevated days 3 - 5 FSH and days 3 - 5 LH levels ( > 25 mIU/ml). After discontinuation of GnRHa (leuprorelin acetate, 1.88 mg) therapy for 6 months, menstruation occurred in only two of 21 individuals but the remaining 19 cases had no menstrual bleeding. It is suggested from this study that the rise in early follicular phase serum gonadotrophins, in particular FSH > 25 mIU/ml, may precede the natural menopause following (or during) GnRHa therapy in older women. Measuring days 3 - 5 serum FSH concentrations may make it easier to decide on the optimal duration of therapy for symptomatic uterine fibroids in perimenopausal women aged > 45 years.

Peptides with anticancer use or potential

This review is an attempt to illustrate the diversity of peptides reported for a potential or an established use in cancer therapy. With 612 references, this work aims at covering the patents and publications up to year 2000 with many inroads in years 2001-2002. The peptides are classed according to four categories of effective (or plausible) biological mechanisms of action: receptor-interacting compounds; inhibitors of protein-protein interaction; enzymes inhibitors; nucleic acid-interacting compounds. The fifth group is made of the peptides for which no mechanism of action has been found yet. Incidentally this work provides an overview of many of the modern targets of anticancer research.

Safety and efficacy of a 3 mg dose of the GnRH antagonist cetrorelix in preventing premature LH surges: report of two large multicentre, multinational, phase IIIb clinical experiences

Gonadotrophin-releasing hormone antagonists are effective and safe in preventing premature LH surges, a leading cause of cycle cancellation or failure during assisted conception. Two studies assessed two administration regimens for cetrorelix (as Cetrotide): the multiple-dose (MD, 0.25 mg/day, n = 1066) and single-dose (SD, 3 mg, n = 541) protocols. Patient outcomes were very similar: >90% reached criteria for human chorionic gonadotrophin (HCG) administration and underwent oocyte retrieval; embryo transfer was performed in 83-84%; failure to retrieve oocytes was rare (0.8%); on average, 11 follicles > or =10 mm in diameter were seen on the day of HCG administration. The SD protocol was associated with higher numbers of oocytes retrieved and available for insemination, although the numbers of embryos obtained or transferred were comparable. A total of 251 and 121 pregnancies were reported in the MD and SD groups respectively. Pregnancy rates per embryo transfer were 27 and 28% respectively. Severe ovarian hyperstimulation syndrome (OHSS) occurred in <1% of cycles. Twelve per cent of patients reported local reactions to injections in the MD group, compared with 8% in the SD group; none was serious or led to discontinuation. Seventy-three per cent of patients in the SD group received only one injection. These two studies therefore show that the single-dose cetrorelix protocol offers equal efficacy and safety to the MD regimen, while having the advantage of requiring only one injection in most patients.

Biological characterization of a novel, orally active small molecule gonadotropin-releasing hormone (GnRH) antagonist using castrated and intact rats

Gonadotropin-releasing hormone (GnRH) receptor antagonists have potential in treating numerous hormone-dependent pathologies including cancers of the prostate, breast, and ovary, endometriosis, and fertility disorders. An unmet clinical need exists for an orally available GnRH receptor antagonist. Guided by structure-activity relationships, ligand-based targeted library designs, and biomarker measurements, our discovery efforts have yielded a novel, small molecule GnRH receptor antagonist, 5-[(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthalenyl)methyl]-N-(2,4,6-trimethoxyphenyl)-2-furamide (CMPD1). CMPD1 bound with low nanomolar affinities to human, rat, and mouse GnRH receptors (6.0, 3.8, and 2.2 nM, respectively). CMPD1 was more than 100-fold selective for GnRH receptors versus various G-protein-coupled receptors and other enzymes and ion channels. In cells expressing recombinant rat GnRH receptors, CMPD1 was a competitive antagonist of GnRH-stimulated increases in extracellular acidification rates in Cytosensor microphysiometer assays. In cells expressing recombinant human GnRH receptors, CMPD1 was a potent inhibitor of GnRH-stimulated total inositol phosphate accumulation. The effects of CMPD1 on circulating levels of luteinizing hormone (LH) and testosterone were studied in castrated and intact male rats, respectively. Intravenous and oral administration of CMPD1 dose dependently suppressed GnRH-mediated elevations of LH in castrated male rats and testosterone in gonad-intact male rats. Moreover, CMPD1, when given at 20 mg/kg i.v. to intact male rats, inhibited the elevations of LH and testosterone stimulated by the superagonist of GnRH, [d-Ala(6), des-Gly(10)]GnRH (GnRH-A). These data suggest that CMPD1 is a potent, selective, orally active GnRH receptor antagonist that may have potential application as a therapeutic agent for treating hormone-dependent cancers and diseases.

Phase II study of abarelix depot for androgen independent prostate cancer progression during gonadotropin-releasing hormone agonist therapy

PURPOSE

We determine the clinical efficacy of the gonadotropin-releasing hormone (Gn-RH) antagonist abarelix in patients with androgen independent prostate cancer, and measure its effect on serum follicle-stimulating hormone (FSH) and testosterone.

MATERIALS AND METHODS

A total of 20 patients with prostate cancer progression during Gn-RH agonist therapy received 100 mg. abarelix depot by intramuscular injection on days 1, 15 and 29, and then every 28 days for up to 24 weeks. Gn-RH agonist therapy was not continued. Patients who met criteria for prostate specific antigen (PSA) response after 24 weeks of therapy could receive treatment for up to 52 weeks. PSA response was the primary end point and was defined as a 50% decrease confirmed 4 weeks later. Secondary end points of this study were the effect of therapy on serum FSH and testosterone.

RESULTS

No patient met the criteria for PSA response. At the end of the 6 cycles of therapy 2 patients remained stable without PSA progression or other signs of disease progression. Median time to progression was 8 weeks (95% CI 5.7-10.3). Mean serum FSH decreased by more than 50% from a baseline of 5.7 IU/l. (95% CI 4.2-7.1) and remained suppressed throughout the observation period. Mean serum testosterone did not change after 4 and 8 weeks of therapy and remained in the anorchid range. Treatment was well tolerated with no grade 3 or higher toxicity.

CONCLUSIONS

Treatment of androgen independent prostate cancer with abarelix decreases circulating FSH and maintains anorchid testosterone but does not result in clinical responses.

Design and structure-activity relationships of 2-alkyl-3-aminomethyl-6-(3-methoxyphenyl)-7-methyl-8-(2-fluorobenzyl)imidazolo[1,2-a]pyrimid-5-ones as potent GnRH receptor antagonists

SAR studies of 7-phenylpyrrolo[1,2-a]pyrimid-4-ones 1 and 2, and 2-phenylimidazolo[1,2-a]pyrimidines 3 and 4, as nonpeptide human GnRH receptor antagonists, lead us to believe that the aromatic ring at position-2 of 4 is no longer crucial for the binding once an aryl group is incorporated at postion-6. We report here the use of a 2-alkyl group on the imidazolo[1,2-a]pyrimidone core to generate potent GnRH receptor antagonists. This discovery enabled us to obtain smaller but equally potent GnRH receptor antagonists.

A transcriptionally active human type II gonadotropin-releasing hormone receptor gene homolog overlaps two genes in the antisense orientation on chromosome 1q.12

GnRH-II peptide hormone exhibits complete sequence conservation across vertebrate species, including man. Type-II GnRH receptor genes have been characterized recently in nonhuman primates, but the human receptor gene homolog contains a frameshift, a premature stop codon (UGA), and a 3' overlap of the RBM8A gene on chromosome 1q.12. A retrotransposed pseudogene, RBM8B, retains partial receptor sequence. In this study, bioinformatics show that the human receptor gene promoter overlaps the peroxisomal protein 11-beta gene promoter and the premature UGA is positionally conserved in chimpanzee. A CGA [arginine (Arg)] occurs in porcine DNA, but UGA is shifted one codon to the 5' direction in bovine DNA, suggesting independent evolution of premature stop codons. In contrast to marmoset tissue RNA, exon- and strand-specific probes are required to distinguish differently spliced human receptor gene transcripts in cell lines (HP75, IMR-32). RBM8B is not transcribed. Sequencing of cDNAs for spliced receptor mRNAs showed no evidence for alteration of the premature UGA by RNA editing, but alternative splicing circumvents the frameshift to encode a two-membrane-domain protein before this UGA. A stem-loop motif resembling a selenocysteine insertion sequence and a potential alternative translation initiation site might enable expression of further proteins involved in interactions within the GnRH system.

Gonadotropin-releasing hormone and reproductive medicine

The hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator of the reproductive system, mainly through its effects on pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release. Gonadotropin-releasing hormone analogues are modifications of the natural decapeptide, being either agonists (GnRHa) or antagonists. GnRHa may imitate the native hormone and induce an endogenous LH surge; however, sustained treatment with GnRHa results in complete refractoriness of LH and FSH production. This aspect of GnRHa action is the main application of the GnRHa in reproduction today. The hypogonadotropic hypogonadal state that results from the sustained treatment is the basis for additional applications of the GnRHa. The agonists appear to be effective, to some extent, for the treatment of endometriosis and were proved to be beneficial prior to surgery for fibroma uteri. GnRHa is used in assisted reproduction for both induction of an endogenous LH surge and for induction of ovulation, and its capacity to cause refractoriness of the pituitary may be used to avoid a premature LH surge. It is suggested that the GnRHa have a direct effect on ovarian steroidogenesis, which is independent of its action on the pituitary. This unwanted effect and other possible drawbacks of the agonists are thought to be eliminated with the use of the antagonists. The mechanism of action of these antagonists is through competitive blocking of the GnRH receptor, which results in a rapid but reversible suppression of gonadotropin secretion. As for GnRHa, GnRH antagonists have been proven effective to prevent the LH surge and to reduce the incidence of severe ovarian hyperstimulation syndrome in controlled ovarian stimulation cycles.

The place of gonadotrophin-releasing hormone antagonists in reproductive medicine

Gonadotrophin-releasing hormone (GnRH) antagonists have recently been introduced into clinical practice. They appear to offer a promising alternative to the long-established GnRH agonist regimens for prevention of a premature LH surge during ovarian stimulation for assisted reproductive techniques. Clinical outcomes achieved with antagonists are comparable with those of a long GnRH agonist protocol, while treatment times and gonadotrophin requirements are reduced and safety is improved. In particular, the antagonists appear to be associated with a lower risk of ovarian hyperstimulation syndrome (OHSS) than do agonists. Patient surveys suggest a preference for antagonist over agonist treatment cycles. These benefits suggest that GnRH antagonists have the potential to replace agonists as the treatment of choice in ovarian stimulation for assisted reproductive techniques. Two agents, cetrorelix and ganirelix, are currently in clinical use. Cetrorelix is available in single- and multiple-dose formulations, offering increased flexibility compared with ganirelix.

Depot GnRH agonist versus the single dose GnRH antagonist regimen (cetrorelix, 3 mg) in patients undergoing assisted reproduction treatment

The objective of this study was to compare, in a centre with previous experience of gonadotrophin-releasing hormone (GnRH) antagonist use, single administration of a GnRH antagonist [cetrorelix (Cetrotide) 3 mg] with a single administration of a GnRH agonist [Decapeptyl Retard 3.75 mg] in patients undergoing assisted reproduction treatment (n = 307 and 364 respectively). GnRH agonist was administered on the first day of menses, while cetrorelix was administered when the largest follicle reached 14 mm. Ovarian stimulation was performed with recombinant human FSH (r-hFSH; 150-225 IU/day). Human chorionic gonadotrophin (HCG, 10,000 IU) was administered when at least two follicles reached a mean diameter > or =18 mm. Over 90% of patients in both groups reached the criteria for HCG administration and underwent oocyte retrieval and embryo transfer. Duration of FSH therapy (9.95 versus 11.25 days) and cumulative dose of r-hFSH (1604 versus 1980 IU) were significantly reduced (P < 0.01) in the cetrorelix 3 mg group. The number of oocytes retrieved was lower (8.5 versus 11.2; P < 0.01) with cetrorelix, but the number of embryos replaced was similar (2.2 versus 2.3; NS). The pregnancy rates per oocyte retrieval were the same, 24.5%, in the antagonist and agonist groups. This study indicates that although fewer oocytes are recovered, similar pregnancy rates can be achieved with a GnRH antagonist compared with a GnRH agonist. Additionally, a single dose of 3 mg cetrorelix was administered in 84% of patients, thus being simpler and more convenient for patients. Cetrorelix 3 mg may thus be proposed as a first choice for preventing both a premature LH surge and detrimental rises in LH during ovarian stimulation prior to assisted reproduction treatment.

Comparable effectiveness using flexible single-dose GnRH antagonist (cetrorelix) and single-dose long GnRH agonist (goserelin) protocol for IVF cycles – a prospective, randomized study

This prospective randomized study compared the effectiveness of a flexible single-dose gonadotrophin-releasing hormone (GnRH) antagonist (cetrorelix) and a single-dose long GnRH agonist (goserelin) protocol for ovarian stimulation in IVF/intracytoplasmic sperm injection (ICSI) cycles. All patients from the waiting list were successively included in the study, pre-programmed with an oral contraceptive, and randomized into goserelin and cetrorelix groups. Depending on the date on which their menstrual period started, patients took oral contraceptives for one or two cycles. Ultimately, 236 patients in the first group received a single dose of depot preparation of goserelin and 224 patients received a single 3 mg dose of cetrorelix in the late follicular phase, when the mean follicle diameter exceeded 12 mm. The mean number of ampoules of FSH and the duration of stimulation was statistically significantly lower in the cetrorelix group than in the goserelin group (25.9 versus 34.5, and 9.6 versus 12.2 days, P < 0.01). The mean number of oocytes retrieved was similar (6.7 +/- 4.5 versus 7.2 +/- 4.6, NS). Similar results were observed in fertilization rates, blastulation rates and blastocyst transfer rates in both groups. Clinical pregnancy and delivery rates per cycle were higher in the goserelin group (34.3 and 30.1%) than in the cetrorelix group (31.9 and 28.3%), but the differences were not statistically significant. The flexible single-dose GnRH antagonist protocol is an advantageous alternative to the long GnRH agonist protocol, with similar efficacy, shorter duration, a significant reduction in the number of FSH ampoules used and without the menopause-like effects of the GnRH antagonist.

GnRH antagonists in the treatment of infertility

GnRH analogues were introduced into clinical practice more than 20 years ago. The recent development of new GnRH antagonists (GnRHant) has revolutionized the treatment protocols of infertility. Ovarian stimulation has become easier, safer and more convenient for patients. This review presents data on the physiological background of GnRH and its analogues--agonists as well as antagonists--and highlights the different aspects of the clinical use of these substances. Two protocols, the single dose and multiple dose protocol are available and lead to comparable results. Data from prospective, randomized trials as well as meta-analyses suggest, that a more tailored, individualized approach concerning the day of administration of GnRHant may lead to more favorable results with regard to ovarian response, implantation and pregnancy rates. Possible negative effects of GnRHant, mainly based on in vitro models are discussed. The outcome of children born after GnRHant use has shown, that this medication is safe. On the whole, the use of GnRHant is advantageous as compared to the traditional way of ovarian stimulation, i.e., the GnRH agonist long protocol. However, especially the effectiveness of these compounds will have to be clarified in the near future by carefully designed prospective, randomized studies.

A novel synthesis of 7-aryl-8-fluoro-pyrrolo[1,2-a]pyrimid-4-ones as potent, stable GnRH receptor antagonists

A new class of small molecule GnRH antagonists, the 7-aryl-8-fluoro-pyrrolo[1,2-a]pyrimid-4-ones, was designed and a novel synthesis for these compounds was developed. The synthesis utilizes a base-catalyzed intramolecular cyclization of fluoromethyl pyrimidone 5 to generate the bicyclic core. Amongst the compounds synthesized, we discovered some highly potent GnRH receptor antagonists (e.g., 12, K(i)=9 nM), which showed enhanced stability towards acidic physiological conditions compared to the des-fluoro analogues.

The discovery of novel small molecule non-peptide gonadotropin releasing hormone (GnRH) receptor antagonists

A novel series of non-peptide derivatives 1, 14, and 15 that bind with high affinity to the human GnRH receptors is discussed. The discovery was made from screening our in-house libraries that contained the active structure 2 along with a trace amount of a second active structure 1 that was derived from an acid-induced rearrangement. From this structure type 1, a series of guanidine and non-guanidine containing analogues were prepared and tested as GnRH receptor antagonists. Compounds derived from this series bind to both human and rat GnRH receptors and antagonize GnRH-mediated increases in inositol phosphate production in cells containing recombinant human receptors. These compounds or their analogues may be useful as therapeutic agents for the treatment of hormone-dependent pathologies including prostate, breast and ovarian cancers.