Gonadotropin-releasing-hormone-receptor antagonists

Gi protein-mediated translocation of serine/threonine phosphatase to the plasma membrane and apoptosis of ovarian cancer cell in response to gonadotropin-releasing hormone antagonist cetrorelix

Serine/threonine protein phosphatase 2A (PP2A), a crucial enzyme in apoptosis control, has been demonstrated within the plasma membrane as well as in the soluble fraction. This study aimed to examine hormonal translocation of PP2A to the plasma membrane in gonadotropin-releasing hormone (GnRH)-responsive ovarian cancer cells. Apoptosis of ovarian cancer cell lines Caov-3 and SK-Ov-3 was quantified by nuclear morphology after staining with Hoechst 33342 dye. PP2A protein and activity in plasma membrane were assessed by immunohistochemical staining with PP2A-specific antibodies and by the measurement of the dephosphorylation of phosphopeptide highly selective for the PP2A, respectively. Incubation for 48 h with a GnRH antagonist cetrorelix caused parallel increases in the percentage of cells undergoing apoptosis and the membrane-associated PP2A activity; half-maximal effects occurred with 5 nmol/l cetrorelix. PP2A protein was also localised to the plasma membrane when the cell lines were exposed to cetrorelix. Pretreatment of the cells with pertussis toxin, but not cholera toxin, completely inhibited cetrorelix-stimulated apoptotic cell death and PP2A redistribution. These findings demonstrate that translocation of PP2A to plasma membrane is closely coupled to the onset of apoptosis in ovarian cancer cells exposed to GnRH antagonist. These GnRH-induced cellular events may be mediated through pertussis toxin-sensitive Gi protein-linked GnRH receptor.

Chemotherapy-induced female infertility and protective action of gonadotropin-releasing hormone analogues

This review aimed to critically discuss the current protocols using gonadotropin-releasing hormone analogue (GnRHa) for the management of chemotherapy-induced premature ovarian failure. In in-vitro experiments, GnRHa retards doxorubicin-induced granulosa cell damage, suggesting an additional GnRH's activity to protect the gonads during chemotherapy through GnRH receptor-mediated mechanism(s). GnRHa acts to protect the gonads during radiation and/or chemotherapy by preferentially steering cells into cell cycle arrest with a decline in response to the chemotherapeutic agents. The ovarian protection by GnRHa co-treatment against chemotherapy can enable the preservation of future fertility in survivors and prevent the bone demineralisation and osteoporosis associated with hypooestrogenism and ovarian failure.

Management of uterine fibroids in the patient pursuing assisted reproductive technologies

Uterine leiomyomas are present in 30-70% of women of reproductive age. In addition to causing menstrual disorders and pain, uterine fibroids negatively affect fertility and pregnancy outcome for patients pursuing assisted reproduction. The two questions that have to be addressed are: which fibroids should be treated and how should they be treated? Submucosal fibroids are associated with a 70% reduction in delivery rate. Intramural fibroids had a lesser effect and reduced the delivery rate by approximately 30%. By contrast, studies have demonstrated that subserosal fibroids did not negatively impact fertility. Furthermore, both submucosal and intramural fibroids were associated with an increased risk of spontaneous miscarriage. Myomectomy is considered the treatment of choice to alleviate these detrimental effects. Further research is needed before alternative treatments can be recommended.

Degarelix and its therapeutic potential in the treatment of prostate cancer

Degarelix is a gonadotropin-releasing hormone (GnRH) antagonist for the treatment of patients with prostate cancer in whom hormonal therapy is indicated. Two phase II trials and one phase III have been published as full papers in the literature. In the dose-finding phase II studies an initial dose of 240 mg degarelix sc followed by a monthly injection of 80 mg or 160 mg degarelix sc was sufficient to keep testosterone levels < or = 0.5 ng/ml. In a phase III trial it was demonstrated that degarelix was not inferior (in terms of testosterone suppression and prostate-specific antigen [PSA] decline) compared to standard hormonal therapy, ie, a GnRH agonist such as leuprolide. In fact, degarelix was associated with a faster testosterone suppression and PSA decline than leuprolide. Adverse events such as injection site reactions (40% vs <1%) and chills (4% vs 0%) were more commonly associated with degarelix. Also, degarelix is currently only available as one-month depot whereas in daily practice three-month depots (of GnRH agonists) are the preferred regimen. However, degarelix was recently approved by the US Food and Drug Administration for the treatment of advanced prostate cancer.

Mild ovarian stimulation for IVF

BACKGROUND

Mild ovarian stimulation for in vitro fertilization (IVF) aims to achieve cost-effective, patient-friendly regimens which optimize the balance between outcomes and risks of treatment.

METHODS

Pubmed and Medline were searched up to end of January 2008 for papers on ovarian stimulation protocols for IVF. Additionally, references to related studies were selected wherever possible.

RESULTS

Studies show that mild interference with the decrease in follicle-stimulating hormone levels in the mid-follicular phase was sufficient to override the selection of a single dominant follicle. Gonadotrophin-releasing hormone antagonists compared with agonists reduce length and dosage of gonadotrophin treatment without a significant reduction in the probability of live birth (OR 0.86, 95% CI 0.72-1.02). Mild ovarian stimulation may be achieved with limited gonadotrophins or with alternatives such as anti-estrogens or aromatase inhibitors. Another option is luteinizing hormone or human chorionic gonadotrophin administration during the late follicular phase. Studies regarding these approaches are discussed individually; small sample size of single studies along with heterogeneity in patient inclusion criteria as well as outcomes analysed does not allow a meta-analysis to be performed. Additionally, the implications of mild ovarian stimulation for embryo quality, endometrial receptivity, cost and the psychological impact of IVF treatment are discussed.

CONCLUSIONS

Evidence in favour of mild ovarian stimulation for IVF is accumulating in recent literature. However, further, sufficiently powered prospective studies applying novel mild treatment regimens are required and structured reporting of the incidence and severity of complications, the number of treatment days, medication used, cost, patient discomfort and number of patient drop-outs in studies on IVF is encouraged.

The mechanism responsible for the supraphysiologic gonadotropin surge in females treated with gonadotropin-releasing hormone (GnRH) agonist and primed with GnRH antagonist

OBJECTIVE

To elucidate the physiologic mechanism responsible for the supraphysiologic gonadotropin release from the pituitary induced by gonadotropin-releasing hormone (GnRH) agonist in female rats primed with GnRH antagonist.

DESIGN

Controlled experimental intervention.

SETTING

Government research facility.

ANIMAL(S)

Forty 8-week-old Sprague-Dawley rats.

INTERVENTION(S)

Forty oophorectomized rats were randomized into four treatment groups of 10: group A, control vehicles; group B, GnRH agonist (leuprolide acetate; 1.7 microg/kg twice a day) on day 4; group C, GnRH antagonist (Nal-Lys; 3 mg/kg each day) days 1 to 4; or group D, GnRH antagonist (Nal-Lys; 3 mg/kg each day) days 1 to 4 plus GnRH agonist (1.7 microg/kg twice a day) on day 4.

MAIN OUTCOME MEASURE(S)

Immunohistochemical methods, Northern and in situ hybridization to quantitate pituitary follicle-stimulating hormone beta (FSH-beta), luteinizing hormone beta (LH-beta), and GnRH receptor (GnRH-R) messenger RNA (mRNA), and receptor protein levels in all treatment groups.

RESULT(S)

Treatment with GnRH antagonist was associated with increased storage of gonadotropin in the pituitary for FSH-beta and LH-beta, but mRNA levels were unchanged. The GnRH-R mRNA decreased after GnRH-agonist treatment but remained stable in the GnRH-antagonist treatment groups. Levels of GnRH-R were decreased after GnRH-antagonist treatment.

CONCLUSION(S)

These data indicate that the in vivo mechanism responsible for the exaggerated release of gonadotropins in rats primed with GnRH antagonist and treated with GnRH agonist was an increase in releasable gonadotropin pools coupled with a reduction in GnRH-R, but receptor function was preserved.

Suppression of gonadotropins and estradiol in premenopausal women by oral administration of the nonpeptide gonadotropin-releasing hormone antagonist elagolix

CONTEXT

Parenteral administration of peptide GnRH analogs is widely employed for treatment of endometriosis and fibroids and in assisted-reproductive therapy protocols. Elagolix is a novel, orally available nonpeptide GnRH antagonist.

OBJECTIVE

Our objective was to evaluate the safety, pharmacokinetics, and inhibitory effects on gonadotropins and estradiol of single-dose and 7-d elagolix administration to healthy premenopausal women.

DESIGN

This was a first-in-human, double-blind, placebo-controlled, single- and multiple-dose study with sequential dose escalation.

PARTICIPANTS

Fifty-five healthy, regularly cycling premenopausal women participated.

INTERVENTIONS

Subjects were administered a single oral dose of 25-400 mg or placebo. In a second arm of the study, subjects received placebo or 50, 100, or 200 mg once daily or 100 mg twice daily for 7 d. Treatment was initiated on d 7 (+/-1) after onset of menses.

MAIN OUTCOME MEASURES

Safety, tolerability, pharmacokinetics, and serum LH, FSH, and estradiol concentrations were assessed.

RESULTS

Elagolix was well tolerated and rapidly bioavailable after oral administration. Serum gonadotropins declined rapidly. Estradiol was suppressed by 24 h in subjects receiving at least 50 mg/d. Daily (50-200 mg) or twice-daily (100 mg) administration for 7 d maintained low estradiol levels (17 +/- 3 to 68 +/- 46 pg/ml) in most subjects during late follicular phase. Effects of the compound were rapidly reversed after discontinuation.

CONCLUSIONS

Oral administration of a nonpeptide GnRH antagonist, elagolix, suppressed the reproductive endocrine axis in healthy premenopausal women. These results suggest that elagolix may enable dose-related pituitary and gonadal suppression in premenopausal women as part of treatment strategies for reproductive hormone-dependent disease states.

The efficacy and safety of degarelix: a 12-month, comparative, randomized, open-label, parallel-group phase III study in patients with prostate cancer

OBJECTIVE

To evaluate the efficacy and safety of degarelix, a new gonadotrophin-releasing hormone (GnRH) antagonist (blocker), vs leuprolide for achieving and maintaining testosterone suppression in a 1-year phase III trial involving patients with prostate cancer.

PATIENTS AND METHODS

In all, 610 patients with adenocarcinoma of the prostate (any stage; median age 72 years; median testosterone 3.93 ng/mL, median prostate-specific antigen, PSA, level 19.0 ng/mL) were randomized and received study treatment. Androgen-deprivation therapy was indicated (neoadjuvant hormonal treatment was excluded) according to the investigator's assessment. Three dosing regimens were evaluated: a starting dose of 240 mg of degarelix subcutaneous (s.c.) for 1 month, followed by s.c. maintenance doses of 80 mg or 160 mg monthly, or intramuscular (i.m.) leuprolide doses of 7.5 mg monthly. Therapy was maintained for the 12-month study. Both the intent-to-treat (ITT) and per protocol populations were analysed.

RESULTS

The primary endpoint of the trial was suppression of testosterone to <or=0.5 ng/mL at all monthly measurements from day 28 to day 364, thus defining the treatment response. This was achieved by 97.2%, 98.3% and 96.4% of patients in the degarelix 240/80 mg, degarelix 240/160 mg and leuprolide groups, respectively (ITT population). At 3 days after starting treatment, testosterone levels were <or=0.5 ng/mL in 96.1% and 95.5% of patients in the degarelix 240/80 mg and 240/160 mg groups, respectively, and in none in the leuprolide group. The median PSA levels at 14 and 28 days were significantly lower in the degarelix groups than in the leuprolide group (P < 0.001). The hormonal side-effect profiles of the three treatment groups were similar to previously reported effects for androgen-deprivation therapy. The s.c. degarelix injection was associated with a higher rate of injection-site reactions than with the i.m. leuprolide injection (40% vs <1%; P < 0.001, respectively). There were additional differences between the degarelix and leuprolide groups for urinary tract infections (3% vs 9%. P < 0.01, respectively), arthralgia (4% vs 9%, P < 0.05, respectively) and chills (4% vs 0%, P < 0.01, respectively). There were no systemic allergic reactions.

CONCLUSIONS

Degarelix was not inferior to leuprolide at maintaining low testosterone levels over a 1-year treatment period. Degarelix induced testosterone and PSA suppression significantly faster than leuprolide; PSA suppression was also maintained throughout the study. Degarelix represents an effective therapy for inducing and maintaining androgen deprivation for up to 1 year in patients with prostate cancer, and has a different mechanism of action from traditional GnRH agonists. Its immediate onset of action achieves a more rapid suppression of testosterone and PSA than leuprolide. Furthermore, there is no need for antiandrogen supplements to prevent the possibility of clinical 'flare'.

Leuprolide acetate reduces both in vivo and in vitro ovarian steroidogenesis in infertile women undergoing assisted reproduction

Despite the probable inhibitory effects of GnRH analogues on ovarian steroidogenesis in vitro, their association with assisted reproduction protocols shows favorable results. This suggests that there are important differences in the behaviors of these drugs when administered in vivo versus in vitro. To clarify these differences, this study was designed to analyze the effect of leuprolide acetate (LA) on ovarian steroidogenesis in women undergoing In Vitro Fertilization (IVF). A prospective, randomized open label study was conducted on 14 women (26-35 years): seven receiving only gonadotrophins (Group 1) and seven receiving gonadotrophin plus LA at 1mg/day (Group 2). The LA in vivo effect was determined with serum and follicular fluid (FF) samples and via luteinized granulosa cell cultivation (GCC), where cells were obtained during oocyte retrieval after ovarian hyperstimulation. In vitro analysis was performed via addition of LA to GCC only for Group 1 (without LA) at progressively higher concentrations (0, 10(-12), 10(-9) and 10(-6)M). In vivo, the main observation was a reduction in androgen production in Group 2, represented by lower androstenedione production in FF (G1=6479+/-3458; G2=3021+/-1119 ng/ml; p=0.04) and a lower testosterone peak in GC at 96h (G1=0.64+/-0.12 ng/ml; G2=0.50+/-0.19 ng/ml; P=0.02), but a higher fertilization rate (G1=67%; G2=83%; p=0.009). In vitro, testosterone, estradiol and progesterone were also reduced by LA, even though this reduction occurred for progesterone only at the highest LA dosage (10(-6)M; 606.0+/-114.3 ng/ml versus 1524.0+/-246.5 ng/ml; p=0.02). Results show that LA reduces ovarian steroidogenesis in vivo by essentially inhibiting androgen synthesis; whereas, in vitro, ovarian steroidogenesis is reduced overall.

G protein-coupled receptors of the hypothalamic-pituitary-gonadal axis: a case for Gnrh, LH, FSH, and GPR54 receptor ligands

The hypothalamic-pituitary-gonadal (HPG) axis, important in reproduction and sex hormone-dependent diseases, is regulated by a number of G protein-coupled receptors. The recently "deorphanized" GPR54 receptor activated by the peptide metastin is thought to be the key regulator of the axis, mainly by releasing gonadotropin-releasing hormone (GnRH) from the hypothalamus. The latter decapeptide, through the activation of the GnRH receptor in the anterior pituitary, causes the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which subsequently activate their respective receptors on the gonadotrope cells. In this review we will discuss the small molecule agonists and antagonists that are currently being developed to intervene with the action of these four receptors. For GnRH receptors, 14 different chemical classes of non-peptidic antagonists have been reported, while for the LH receptor three classes of agonists have been described. Both agonists and antagonists have been introduced for the FSH receptor. Recently, the first non-peptidic agonist for GPR54 was reported.

New drugs in development for the treatment of endometriosis

Endometriosis is a common and enigmatic disease causing pelvic pain and infertility. Current treatment is mainly based on the use of surgery and ovarian suppressive agents. There is in particular the need for new therapeutic options able to allow a normal menstrual cycle to occur and also consent pregnancy. In the present review, we aimed to give a concise and practical overview in order to allow the clinician to clearly understand the level of development of these drugs. We have presented only treatments supported by in vivo researches with a special attention to studies in humans. Results show appealing new possibilities are emerging from agents counteracting the endometriosis-associated inflammation. Recent data also suggests that there is still the opportunity to refine the use of already available agents.

Testosterone surge: rationale for gonadotropin-releasing hormone blockers?

Gonadotropin-releasing hormone (GnRH) agonists currently form the mainstay of management of advanced prostate cancer. They effectively suppress serum testosterone levels, which in turn inhibits tumor growth. However, the initial response to GnRH agonists is a transient increase in the serum testosterone levels. Known as a testosterone surge, this can lead to a worsening of symptoms and can adversely affect survival. Therefore, much interest exists in the development of a new class of drugs-GnRH antagonists-which produce immediate suppression of luteinizing hormone and testosterone without a testosterone surge. The most promising GnRH antagonist to date is degarelix.

Luteinizing hormone-dependent Cushing's syndrome in a pet ferret (Mustela putorius furo)

Hyperadrenocorticism in ferrets is associated with increased circulating concentrations of adrenal androgens, whereas plasma concentrations of cortisol and ACTH are usually not affected. Here, we report on a 5-year-old castrated male pet ferret (Mustela putorius furo) in which the major presenting signs were polyuria and polyphagia. Routine biochemistry values were within their reference ranges. The urinary corticoid:creatinine ratio (UCCR) was increased and the plasma ACTH concentration was suppressed. Abdominal ultrasonography revealed an enlarged right adrenal gland and atrophy of the left adrenal gland. Administration of hCG resulted in an increase of plasma cortisol and androstenedione concentrations. Based on these findings LH/hCG-dependent hypercortisolism and hyperandrogenism were suspected and treatment was started with a depot GnRH-agonist implant containing 9.4mg deslorelin. Within 3 weeks after placement of the implant all clinical signs had disappeared. Three months later the endocrine parameters had normalized, while abdominal ultrasonography revealed that the right adrenal gland had diminished in size and the left adrenal gland was considered of normal size. No recurrences of clinical signs were seen within 2 years after placement of the deslorelin implant. At that time urinary corticoid and plasma hormone concentrations were within their reference ranges, and no further change in the size of the adrenal glands was seen. In conclusion, this is the first confirmed case of LH-dependent hypercortisolism in a ferret that was treated successfully with a depot GnRH-agonist.

Management of advanced prostate cancer: can we improve on androgen deprivation therapy?

Gonadotrophin-releasing hormone (GnRH) agonists are currently the mainstay in the management of advanced prostate cancer. Used either as monotherapy or combined with antiandrogens, GnRH agonists suppress serum testosterone levels and thus slow the growth of the tumour cells that depend on testosterone for growth. GnRH agonists have largely replaced orchidectomy in the management of advanced prostate cancer, because patients are reluctant to undergo surgical castration. However, can we do better in androgen-deprivation therapy? There is some evidence to suggest that GnRH agonists do not achieve the level of testosterone suppression attained with orchidectomy, or as rapidly, factors which could be expected to affect overall survival. Together, these observations highlight the need to develop newer agents that can achieve rapid, profound and sustained testosterone suppression, equivalent to that with orchidectomy. Preliminary data for the GnRH blocker, degarelix, suggest that this new agent might overcome the shortcomings associated with GnRH agonists. Further clinical data are therefore awaited with much interest.

The role of sex steroids and gonadectomy in the control of thymic involution

A major underlying cause for aging of the immune system is the structural and functional atrophy of the thymus, and associated decline in T cell genesis. This loss of naïve T cells reduces adaptive immunity to new stimuli and precipitates a peripheral bias to memory cells against prior antigens. Whilst multiple mechanisms may contribute to this process, the temporal alliance of thymic decline with puberty has implicated a causative role for sex steroids. Accordingly ablation of sex steroids induces profound thymic rejuvenation. Although the thymus retains some, albeit highly limited, function in healthy adults, this is insufficient for resurrecting the T cell pool following cytoablative treatments such as chemo- and radiation-therapy and AIDS. Increased risk of opportunistic infections and cancer relapse or appearance, are a direct consequence. Temporary sex steroid ablation may thus provide a clinically effective means to regenerate the thymus and immune system in immunodeficiency states.

Preservation of female fertility during cancer treatment

Improvements in the success of cancer treatments have resulted in increased awareness of the long-term effects of treatment, of which gonadal failure is the most significant. Thus, preservation of fertility potential has become a major goal and could be realized by preventing ovarian toxicity or by cryopreservation of reproductive cells/tissues. This review aimed to critically discuss the current protocols for the management of chemotherapy-inducced/radiotherapy-induced premature ovarian failure (POF). A medical approach using the gonadotropin-releasing hormone analog (GnRHa) may act to protect the gonads during radiation and/or chemotherapy by preferentially steering cells into cell cycle arrest with a decline in responsibility to the chemotherapeutic agents. Ovarian protection by GnRHa cotreatment against chemotherapy can enable the preservation of future fertility in survivors and prevent the bone demineralization and osteoporosis associated with hypestrogenism and POF. In vitro fertilization of retrieved oocytes could enable embryo freezing in some patients. Embryo cryopreservation is considered standard practice and widely available, but may seldom be used because of a lack of a male partner, the need to postpone cancer therapy for a few weeks and the possibility that an estrogen rise may be undesirable in sensitive cancer patients. Improvement in oocyte cryopreservation may offer additional possibilities; the prolonged culture of primordial and primary follicles in vitro is still unfeasible. Currently, the cryopreservation of ovarian cortex, which hosts thousands of immature follicles, is an investigational method, but has the advantage of requiring neither a sperm donor nor ovarian stimulation. Fertility preservation is often possible in women undergoing cancer treatment. To preserve the full range of options, fertility preservation procedures should be considered as early as possible during therapy planning. (Reprod Med Biol 2008; 7: 17-27).

Chronobiology in the endocrine system

Biological signaling occurs in a complex web with participation and interaction of the central nervous system, the autonomous nervous system, the endocrine glands, peripheral endocrine tissues including the intestinal tract and adipose tissue, and the immune system. All of these show an intricate time structure with rhythms and pulsatile variations in multiple frequencies. Circadian (about 24-hour) and circannual (about 1-year) rhythms are kept in step with the cyclic environmental surrounding by the timing and length of the daily light span. Rhythmicity of many endocrine variables is essential for their efficacy and, even in some instances, for the qualitative nature of their effects. Indeed, the continuous administration of certain hormones and their synthetic analogues may show substantially different effects than expected. In the design of drug-delivery systems and treatment schedules involving directly or indirectly the endocrine system, consideration of the human time organization is essential. A large amount of information on the endocrine time structure has accumulated, some of which is discussed in this review.

Chronobiology, drug delivery, and chronotherapeutics

Biological processes and functions are organized in space, as a physical anatomy, and time, as a biological time structure. The latter is expressed by short-, intermediate-, and long-period oscillations, i.e., biological rhythms. The circadian (24-h) time structure has been most studied and shows great importance to the practice of medicine and pharmacotherapy of patients. The phase and amplitude of key physiological and biochemical circadian rhythms contribute to the known predictable-in-time patterns in the occurrence of serious and life-threatening medical events, like myocardial infraction and stroke, and the manifestation and severity of symptoms of chronic diseases, like allergic rhinitis, asthma, and arthritis. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and, most important to the theme of this special issue, medications. Rhythmicity in the pathophysiology of disease is one basis for chronotherapeutics--purposeful variation in time of the concentration of medicines in synchrony with biological rhythm determinants of disease activity--to optimize treatment outcomes. A second basis is the control of undesired effects of medications, especially when the therapeutic range is narrow and the potential for adverse effects high, which is the case for cancer drugs. A third basis is to meet the biological requirements for frequency-modulated drug delivery, which is the case for certain neuroendocrine peptide analogues. Great progress has been realized with hydrogels, and they offer many advantages and opportunities in the design of chronotherapeutic systems for drug delivery via the oral, buccal, nasal, subcutaneous, transdermal, rectal, and vaginal routes. Nonetheless, innovative delivery systems will be necessary to ensure optimal application of chronotherapeutic interventions. Next generation drug-delivery systems must be configurable so they (i) require minimal volitional adherence, (ii) respond to sensitive biomarkers of disease activity that often vary in time as periodic (circadian rhythmic) and non-periodic (random) patterns to release medication to targeted tissue(s) on a real time as needed basis, and (iii) are cost-effective.

Advances in the development of hormonal modulators for the treatment of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a leading disorder of the ageing male population and is characterized by a progressive enlargement of the prostate, resulting in the obstruction of the proximal urethra and hence the disturbance in normal urinary flow and further quality of life of the patients. Therefore, there is an imperative need to develop a therapeutic modality to combat the overgrowth of the prostate with improvements in both the urinary flow rate and the quality of life of the patients. At present, alpha-blockers, which act on the dynamic component of the disease to regulate the increased adrenergic tone of the lower urinary tract smooth muscles, and 5-alpha-reductase inhibitors, which control the overgrowth of the prostate and hence static component by regulating the levels of androgens, are the mainstay of therapies for the treatment of BPH and associated lower urinary tract symptoms. However, each target class has its own limitations in terms of compromised efficacy or tolerability. Therefore, it is pertinent to have an effective and safe therapeutic modality for the further improvement of life of the geriatric male population. Hormone modulators, which regulate the overgrowth of the prostate, represent one of the important categories that have been explored and that is still undergoing certain investigations towards the development of a therapeutic entity for the treatment of BPH. The key lies in achieving the differentiation in terms of improved tolerability with comparable or better efficacy over the existing class of drugs. Gonadotropin receptor modulators and vitamin D receptor agonists may represent promising druggable targets in this therapeutic area, due to the availability of proof of principles and concepts in preclinical animal models and human subjects.

Selection, synthesis, and structure–activity relationship of tetrahydropyrido[4,3-d]pyrimidine-2,4-diones as human GnRH receptor antagonists

The present article describes a selection of a new class of small molecule antagonists for the h-GnRH receptor, their preparation, and evaluation in vitro. Three computational methods were combined into a consensus score, to rank order virtual templates. The top 5% of templates were further evaluated in silico and assessed for novelty and synthetic accessibility. The tetrahydropyrido[4,3-d]pyrimidine-2,4-dione core was selected for synthesis and evaluated in vitro. Using an array approach for analog design and synthesis, we were able to drive the binding below 10nM for the h-GnRH receptor after two rounds of optimization.

The role of gonadotropin releasing hormone in normal and pathologic endocrine processes

PURPOSE OF REVIEW

Gonadotropin releasing hormone is the hypothalamic hormone that activates pituitary gonadotropin production and, ultimately, determines reproductive competence. This review will highlight advances in the basic biology of the gonadotropin releasing hormone neuron that give insight into disorders of pubertal development, and clinical studies with gonadotropin releasing hormone analogs in infertility and prostate cancer treatment.

RECENT FINDINGS

Factors that control gonadotropin releasing hormone neuronal migration such as fibroblast growth factor receptor-1 and others that modulate secretion at puberty including kisspeptin/G-protein-coupled receptor 54 have been identified. Mutations in these pathways cause disorders during puberty. Clinical trials have defined the utility of gonadotropin releasing hormone agonists and antagonists for ovulation induction, and the effects of long-term administration for prostate cancer.

SUMMARY

Research into the role of the fibroblast growth factor receptor-1 and kisspeptin/G-protein-coupled receptor 54 pathways in gonadotropin releasing hormone neuronal development may identify the molecular defects in idiopathic hypogonadotropic hypogonadism and refine our understanding of normal negative and positive feedback by sex steroids. Clarification of the advantages and disadvantages of gonadotropin releasing hormone analog use in ovulation induction may improve the cost and success of infertility treatment. Insight into long-term effects of gonadotropin releasing hormone analogs in prostate cancer may lead to directed therapies to combat these consequences. Together these studies outline effects of modulation of gonadotropin releasing hormone in normal and pathophysiologic states.

Hormonal therapy in ovarian cancer

Ovarian carcinoma continues to be the leading cause of death due to gynecological malignancy. Epidemiologic studies indicate that steroid hormones play roles in ovarian carcinogenesis. Gonadotropins, estrogen, and androgen may be causative factors, while gonadotropin-releasing hormone and progesterone may be protective factors in ovarian cancer pathogenesis. Experimental studies have shown that hormonal receptors are expressed in ovarian cancer cells and mediate the growth-stimulatory or growth-inhibitory effects of the hormones on these cells. Hormonal therapeutic agents have been evaluated in several clinical trials. Most of these trials were conducted in patients with recurrent or refractory ovarian cancer, with modest efficacy and few side effects. Better understanding of the mechanisms through which hormones affect cell growth may improve the efficacy of hormonal therapy. Molecular markers that can reliably predict major clinical outcomes should be investigated further in well-designed trials.

[Some neurological and psychiatric complications of the disorders of the hypothalamo-hypophyseal system]

Connection between the central nervous system and the endocrine system is extremely complex. The hypothalamus serves as a crucial centre for the integration and coordination of autonomic functions by neuronal and hormonal pathways. It plays a central role in the homeostatic regulation of internal physiological conditions. It controls growth and reproduction, stress reactions, and determines rhythmicity, periodicity and timing of physiological processes. Beside its well-known functions, antidiuretic hormone has a role in social behavior as it enhances aggression via vasopressin receptor 1A. Oxitocin is affected in the formation of maternal behavior, and in other social interactions, like the pair bounding, as well as in analgesia and pain modulation. The corticotrop-releasing hormone acts as a neurotransmitter, it has a special role in stress-behavior, anxiety, and depression, and it blocks deep sleeping. Among the neurotransmitters and neuropeptids of the hypothalamus, serotonin, norepinephrine, GABA, cholecystokinin, neuropeptide-Y, Agouti-related protein, alpha-MSH and ghrelin have essential importance in the eating disorders. The levels of leptin and galanin determine whether formation of anabolic or catabolic neurotransmitters should take place. In the thermoregulation the central thermoreceptors play role, and suprachiasmatic nucleus is responsible for circadian rhythm, through "timing genes". The diseases of the hypothalamus cause most frequently bulimia or anorexia, hypersomnia, impotency, and attacks of anxiety. The most common expansive process of the hypothalamus is craniopharyngioma. The lack or diminution of vasopressin causes diabetes insipidus, while inappropriate antidiuretic hormone secretion induces Schwartz-Barter syndrome. Fröhlich-, Kleine-Levin- or Prader-Willi syndromes have characteristic neuropsychiatric features. The main psychiatric symptom of hypopituitarism is a combination of dementia and delirium. The most characteristic neurological sign of pituitary adenoma is the visual field defect. Carpal tunnel syndrome, obstructive sleeping apnoe and headache are typical neurological features in somatotrop adenomas.

Trapping of a Nonpeptide Ligand by the Extracellular Domains of the Gonadotropin-Releasing Hormone Receptor Results in Insurmountable Antagonism

Drugs that exhibit insurmountable antagonism are proposed to provide improved clinical efficacy through extended receptor blockade. Long-term suppression of the gonadotropin-releasing hormone receptor (GnRHR) is an important therapeutic approach for a number of sex hormone-dependent diseases. In this study, we describe the mechanism and structural components required for insurmountable activity of a GnRHR antagonist. TAK-013 behaves as an insurmountable antagonist at the human receptor (hGnRHR) but as a surmountable antagonist at the macaque receptor (mGnRHR). Mutation of the eight residues that differ between hGnRHR and mGnRHR identified Ser-203 and Leu-300 in extracellular loops (ECL) 2 and 3 of hGnRHR as essential for the insurmountability of TAK-013. Substitution of the corresponding residues in mGnRHR with Ser and Leu (mGnRHR-P203S/V300L) converts TAK-013 to an insurmountable antagonist. In addition, mutation of Met-24 to Leu in the amino terminus of hGnRHR also ablates the insurmountable antagonism of TAK-013. The mechanism of insurmountability of TAK-013 was determined to be governed by its rate of dissociation from the receptor. Although the association rates of TAK-013 to hGnRHR, mGnRHR, and mGnRHR-P203S/V300L do not differ, the dissociation rate half-life correlates closely with the degree of insurmountability observed (169, 9, and 55 min, respectively). Taken together, these data suggest a model of the GnRHR in which ECL2, ECL3, and the amino terminus engage with TAK-013 upon its binding to the transmembrane region of the receptor. These additional interactions form a "trap door" above TAK-013, restricting its dissociation and thus resulting in its insurmountability.

Pharmacological characterization of a novel nonpeptide antagonist of the human gonadotropin-releasing hormone receptor, NBI-42902

Suppression of the hypothalamic-pituitary-gonadal axis by peptides that act at the GnRH receptor has found widespread use in clinical practice for the management of sex-steroid-dependent diseases (such as prostate cancer and endometriosis) and reproductive disorders. Efforts to develop orally available GnRH receptor antagonists have led to the discovery of a novel, potent nonpeptide antagonist, NBI-42902, that suppresses serum LH concentrations in postmenopausal women after oral administration. Here we report the in vitro and in vivo pharmacological characterization of this compound. NBI-42902 is a potent inhibitor of peptide radioligand binding to the human GnRH receptor (K(i) = 0.56 nm). Tritiated NBI-42902 binds with high affinity (K(d) = 0.19 nm) to a single class of binding sites and can be displaced by a range of peptide and nonpeptide GnRH receptor ligands. In vitro experiments demonstrate that NBI-42902 is a potent functional, competitive antagonist of GnRH stimulated IP accumulation, Ca(2+) flux, and ERK1/2 activation. It did not stimulate histamine release from rat peritoneal mast cells. Finally, it is effective in lowering serum LH in castrated male macaques after oral administration. Overall, these data provide a benchmark of pharmacological characteristics required for a nonpeptide GnRH antagonist to effectively suppress gonadotropins in humans and suggest that NBI-42902 may have clinical utility as an oral agent for suppression of the hypothalamic-pituitary-gonadal axis.

QSAR models for predicting the activity of non-peptide luteinizing hormone-releasing hormone (LHRH) antagonists derived from erythromycin A using quantum chemical properties

Multiple linear regression (MLR) combined with genetic algorithm (GA) and Bayesian-regularized Genetic Neural Networks (BRGNNs) were used to model the binding affinity (pK(I)) of 38 11,12-cyclic carbamate derivatives of 6-O-methylerythromycin A for the Human Luteinizing Hormone-Releasing Hormone (LHRH) receptor using quantum chemical descriptors. A multiparametric MLR equation with good statistical quality was obtained that describes the features relevant for antagonistic activity when the substituent at the position 3 of the erythronolide core was varied. In addition, four-descriptor linear and nonlinear models were established for the whole dataset. Such models showed high statistical quality. However, the BRGNN model was better than the linear model according to the external validation process. In general, our linear and nonlinear models reveal that the binding affinity of the compounds studied for the LHRH receptor is modulated by electron-related terms.

Abarelix for injectable suspension: first-in-class gonadotropin-releasing hormone antagonist for prostate cancer

Abarelix, a gonadotropin-releasing hormone antagonist, with its indication for advanced symptomatic prostate cancer, represents the newest category of hormonal therapy introduced in the past 15 years. Results from Phase II and III clinical trials demonstrate the advantages of abarelix over commonly used luteinizing hormone-releasing hormone (LHRH) agonist therapy: abarelix does not cause a surge in serum testosterone that can precipitate a flare phenomenon or worsening of disease, particularly dangerous for patients with metastatic, symptomatic disease, and produces medical castration more quickly. Abarelix was also demonstrated to promptly and substantially reduce follicle-stimulating hormone levels to lower than LHRH agonist. Study results demonstrate effective anticancer responses during extended exposure to abarelix: improvements in pain score and/or analgesic use, improvements in urinary symptoms (including urinary catheter removal) and complete avoidance of bilateral orchiectomy for patients undergoing at least 12 weeks of treatment. In Phase III clinical trials, abarelix demonstrated a similar overall safety profile when compared with LHRH agonist monotherapy, and a superior safety profile when compared with LHRH agonist plus antiandrogen combination therapy. Abarelix patients experienced a greater incidence of immediate-onset systemic allergic reactions as compared with control arms.

Cetrorelix in the treatment of female infertility and endometriosis

The use of cetrorelix within ovarian-stimulation protocols demonstrates several advantages compared with gonadotropin-releasing hormone (GnRH) agonist-containing protocols, which include, for example, significantly less time for analogue treatment and a reduction in the amount of gonadotropins needed. Furthermore, fewer side effects can be expected. There is no difference regarding endometrium quality and hormone profiles, and the results of assisted reproduction cycles are comparable. Cetrorelix also seems to be useful in the treatment of endometriosis which, in most cases, is an estrogen-dependent disease. Furthermore, fewer side effects occur with this agent (e.g., postmenopausal symptoms) and no estradiol add-back is needed. In the future, new nonpeptic GnRH antagonists are expected to be available for oral administration. Although they are still under investigation, these agents have the potential to improve patients' comfort and compliance.

Direct Protection by a Gonadotropin-Releasing Hormone Analog from Doxorubicin-Induced Granulosa Cell Damage

BACKGROUND/AIMS

Recent clinical applications suggest a beneficial effect of gonadotropin-releasing hormone analog (GnRHa) as a gonadal protector from chemotherapy-induced premature ovarian failure. This study aimed to determine cellular mechanisms involved in the protective action of GnRHa against granulosa cell damage caused by doxorubicin.

METHODS

Granulosa cells were obtained by ultrasound-guided follicular aspiration from patients undergoing in vitro fertilization, and screened for GnRH receptor expression prior to analyses. The cellular function was assessed by measuring the conversion of exogenously supplied androstenedione to estradiol-beta (E2) in response to follicle-stimulating hormone (FSH) (1 microM).

RESULTS

Exposing to doxorubicin for 12 h before FSH stimulation caused a concentration-dependent inhibition of the E2 secretion to a minimum level of 20% of control. When the cells were incubated with a GnRHa for 12 h before and during exposure to doxorubicin, granulosa cells produced an equal level of E2 to that of control cells. The protective action of GnRHa was dose-dependent; a half-maximal effect occurred at 10 nM. Preincubation with GnRHa alone had no effect on FSH-induced E2 production.

CONCLUSION

These findings demonstrate that a GnRHa may retard doxorubicin-induced granulosa cell damage, suggesting an additional GnRH activity to protect the gonads during chemotherapy through GnRH receptor-mediated mechanism(s).

Suppression of serum luteinizing hormone in postmenopausal women by an orally administered nonpeptide antagonist of the gonadotropin-releasing hormone receptor (NBI-42902)

CONTEXT

Parenteral administration of peptide GnRH analogs is widely used in clinical practice for the suppression of pituitary gonadotropins. NBI-42902 is an orally available, high-affinity nonpeptide antagonist of the human GnRH receptor.

OBJECTIVE

The objective was to evaluate the safety, pharmacokinetics, and inhibitory effects on gonadotropin secretion of NBI-42902 in postmenopausal women.

DESIGN

This was a phase I, double-blind, placebo-controlled, single-dose study with sequential dose escalation.

PARTICIPANTS

Fifty-six healthy, postmenopausal women were included. FSH levels were greater than 40 IU/liter, and body mass index was within 20% of ideal values for all subjects.

INTERVENTIONS

Subjects were administered 5, 10, 25, 50, 75, 100, 150, or 200 mg NBI-42902 as an oral solution.

MAIN OUTCOME MEASURES

Safety, tolerability, and serum LH and FSH concentrations were evaluated.

RESULTS

NBI-42902 was well tolerated. Serum LH concentrations rapidly declined, and dose-dependent suppression was observed. Maximal change from baseline LH concentrations ranged from -19 +/- 5% in the 5-mg group to -55 +/- 2% in the 150-mg group. Suppression of FSH was less pronounced (-15 to -22% of baseline). NBI-42902 was rapidly absorbed after oral administration with a terminal elimination half-life ranging from 2.7 +/- 0.3 to 4.8 +/- 0.8 h. A clear relationship between plasma NBI-42902 concentrations and LH suppression was evident.

CONCLUSIONS

Dose-dependent LH suppression was achieved by oral administration of a nonpeptide GnRH antagonist suggesting that compounds such as NBI-42902 may enable adjustable gonadotropin suppression as part of novel treatment strategies for benign gynecological conditions.

Long-term suppression of reproductive function by a single dose of gonadotropin-releasing hormone antagonists in a sheep model

OBJECTIVE

To determine the effect of single long-acting doses of GnRH antagonists on reproductive function in a sheep model.

DESIGN

Observational, model study.

SETTING

University-affiliated research unit.

ANIMAL(S)

Nine intact mature Merino sheep in experiment 1 and 12 mature Merino-crossed ewes with the ovary autotransplanted to the neck in experiment 2.

INTERVENTION(S)

Synchronization of estrous cycle either with intravaginal progestins or prostaglandin F2alpha analogues and treatment with a single dose of GnRH antagonist; evaluation of reproductive activity, plasma sampling, and ovarian ultrasonography.

MAIN OUTCOME MEASURE(S)

Determination of estrus behavior; plasma concentrations of P, FSH, LH, and inhibin A; and number and size of ovarian follicles.

RESULT(S)

In both experiments, the concentrations of FSH and LH were suppressed when compared with those in control ewes. In experiment 1, the ovulatory cycles were suppressed for > or = 55 days in treated sheep. In experiment 2, there were no follicles sized > or = 5 mm in treated ewes for 50 days.

CONCLUSION(S)

The suppression of the development of large follicles for > or = 30 days after a single injection of a long-acting GnRH antagonist provides a novel convenient method of pretreatment before COS.

Cetrorelix suppression test to assess the source of androgen overproduction in postmenopausal hirsutism

A 75-year-old woman presenting with recent onset hirsutism and severely elevated serum androgen levels was evaluated to assess the source of excessive androgen production. Commonly recommended hormonal stimulation and suppression tests, and the usually employed imaging techniques were non-diagnostic. In this report, we describe a new suppression test based on the use of the GnRH receptor antagonist, cetrorelix, to determine whether androgen production was LH-dependent. Cetrorelix, administered in a daily dose of 250 microg subcutaneously, suppressed serum LH within 24 h and reduced serum androgen levels to normal within 48-72 h, indicating that androgen overproduction was of ovarian origin. This diagnosis was confirmed by laparoscopic ovariectomy.

CONCLUSION

The cetrorelix suppression test is a simple procedure that provides valuable information regarding the source of androgen excess in postmenopausal hirsutism.

Kinetics of nonpeptide antagonist binding to the human gonadotropin-releasing hormone receptor: Implications for structure–activity relationships and insurmountable antagonism

Numerous nonpeptide ligands have been developed for the human gonadotropin-releasing hormone (GnRH) receptor as potential agents for treatment of disorders of the reproductive-endocrine axis. While the equilibrium binding of these ligands has been studied in detail, little is known of the kinetics of their receptor interaction. In this study we evaluated the kinetic structure-activity relationships (SAR) of uracil-series antagonists by measuring their association and dissociation rate constants. These constants were measured directly using a novel radioligand, [3H] NBI 42902, and indirectly for unlabeled ligands. Receptor association and dissociation of [3H] NBI 42902 was monophasic, with an association rate constant of 93+/-10 microM(-1) min(-1) and a dissociation rate constant of 0.16+/-0.02 h(-1) (t(1/2) of 4.3 h). Four unlabeled compounds were tested with varying substituents at the 2-position of the benzyl group at position 1 of the uracil (-F, -SO(CH3), -SO2(CH3) and -CF3). The nature of the substituent did not appreciably affect the association rate constant but varied the dissociation rate constant >50-fold (t(1/2) ranging from 52 min for -SO(CH3) to >43 h for -CF3). This SAR was poorly resolved in standard competition assays due to lack of equilibration. The functional consequences of the varying dissociation rate were investigated by measuring antagonism of GnRH-stimulated [3H] inositol phosphates accumulation. Slowly dissociating ligands displayed insurmountable antagonism (decrease of the GnRH E(max)) while antagonism by more rapidly dissociating ligands was surmountable (without effect on the GnRH E(max)). Therefore, evaluating the receptor binding kinetics of nonpeptide antagonists revealed SAR, not evident in standard competition assays, that defined at least in part the mode of functional antagonism by the ligands. These findings are of importance for the future definition of nonpeptide ligand SAR and for the identification of potentially useful slowly dissociating antagonists for the GnRH receptor.

Semi-mechanistic pharmacodynamic modeling for degarelix, a novel gonadotropin releasing hormone (GnRH) blocker

An integrated semi-mechanistic pharmacodynamic (PD) model describing the relationship between luteinizing hormone (LH) and testosterone (T) after short-term administration of degarelix was developed. Data from three clinical studies involving, intravenous (IV) and subcutaneous (SC) dosing, in healthy male subjects were available. Degarelix pharmacokinetic (PK) data from all studies were modeled simultaneously. One intravenous study was used to develop the PD model and the two other studies (IV and SC dosing) were used to qualify the model. Degarelix PK follows a two-compartment model and exhibits flip-flop kinetics after subcutaneous dosing. Based on physiological mechanism, the gonadotropin releasing hormone (GnRH) time course was described using a pulsatile release model. A precursor-dependent pool model was used to describe the kinetics of LH in the pituitary and plasma compartment. In males, LH regulates T production in leydig cells. Degarelix inhibits the release of LH from the pool compartment to the plasma compartment leading to decreased T production. The plasma half-life of LH (2.6-3.3 hr) and T (2.7 hr) match well with the literature reports. The proposed PD model reasonably described the time course of LH and T including the LH rebound for short-term studies. The model predicted the time course of LH and T for the second IV and SC dosing studies very well. However, the long term simulations from the final model did not match with literature reports. A modification is suggested based on the physiological understanding of the system. The proposed novel modification to precursor models can be of general use for predicting long term responses.

LH in the follicular phase: neither too high nor too low

The role of LH in the natural menstrual cycle is not disputed. However, there are a variety of opinions regarding the potential role of exogenous LH in ovulation induction and whether it is actually needed. Recent years have seen renewed interest in this issue for several reasons. First, ovulation-inducing drugs are increasingly being administered to normally ovulating women. Second, recombinant human FSH products completely devoid of LH activity are now available. Third, gonadotrophin-releasing hormone (GnRH) analogues (agonists and antagonists) prevent the untimely LH surge but also suppress endogenous LH activity during the follicular phase. This review analyses whether or not all patients need LH for follicular growth stimulation and new opportunities for improved treatment as a result of the availability of recombinant human LH both in patients with ovulatory disorders (World Health Organization (WHO) groups I and II anovulatory patients) and those undergoing multiple follicular development for assisted reproduction.