Non-Peptide Gonadotropin-Releasing Hormone Receptor Antagonists

Safety, Pharmacokinetics, and Pharmacodynamics of SHR7280, a Non-peptide GnRH Antagonist in Premenopausal Women with Endometriosis: A Randomized, Double-Blind, Placebo-Controlled Phase 1 Study

BACKGROUND

Oral gonadotropin-releasing hormone (GnRH) antagonists are promising agents in the treatment of endometriosis-related pain. Here we assessed the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of SHR7280, an oral non-peptide GnRH antagonist in premenopausal women with endometriosis.

METHODS

In the Phase 1 part of the randomized, double-blinded, placebo-controlled, dose-ascending, Phase 1/2 trial, premenopausal women with endometriosis were randomized (4:1) to receive SHR7280 or placebo treatment for 21 consecutive days. The treatment dose started from 200 mg QD, and then increased to 300 mg QD and 200 mg BID. Safety, PK, and PD parameters were assessed.

RESULTS

In total, 30 patients received assigned treatment, 24 with SHR7280 and 6 with placebo. SHR7280 was well tolerated. Adverse events (AEs) were reported in 19 (79.2%, 19/24) patients in the SHR7280 group and 5 (83.3%, 5/6) patients in the placebo group. Most AEs were mild and no severe AEs occurred. SHR7280 showed a rapid absorption, with a time to maximum plasma concentration (Tmax) of 1.0 h, 1.0 h, and 0.8 h for the 200 mg QD, 300 mg QD, and 200 mg BID regimens, respectively. Plasma concentration of SHR7280 was dose dependent. The mean half-life (t1/2) at steady state was 6.9 h, 7.4 h, and 2.8 h, respectively, and little or no accumulation was observed. Pharmacodynamic analysis showed that SHR7280 could effectively suppress estradiol and luteinizing hormone concentrations and prevent progesterone increase in a dose-dependent manner. SHR7280 at doses of 300 mg QD and 200 mg BID could suppress estradiol levels within the desired therapeutic window of 20-50 pg/mL throughout the treatment period.

CONCLUSIONS

SHR7280 showed favorable safety, PK, and PD profiles in the doses of 200 mg QD, 300 mg QD, and 200 mg BID. The results of this study provide evidence to support the further development of SHR7280 as a GnRH antagonist for the treatment of endometriosis-related pain in the subsequent Phase 2 trial.

TRIAL REGISTRY

Trial registration number: Clinicaltrials.gov, identifier: NCT04417972. Trial registration date: 5 June 2020.

Research advances in drug therapy of endometriosis

Endometriosis is one of the most common benign gynecological disorders in reproductive-aged women. The major symptoms are chronic pelvic pain and infertility. Despite its profound impact on women's health and quality of life, its pathogenesis has not been fully elucidated, it cannot be cured and the long-term use of drugs yields severe side effects and hinders fertility. This review aims to present the advances in pathogenesis and the newly reported lead compounds and drugs managing endometriosis. This paper investigated Genetic changes, estrogen-dependent inflammation induction, progesterone resistance, imbalance in proliferation and apoptosis, angiogenesis, lymphangiogenesis and neurogenesis, and tissue remodeling in its pathogenesis; and explored the pharmacological mechanisms, constitutive relationships, and application prospects of each compound in the text. To date, Resveratrol, Bay1316957, and bardoxifene were effective against lesions and pain in controlled animal studies. In clinical trials, Quinagolide showed no statistical difference with the placebo group; the results of phase II clinical trial of the IL-33 antibody have not been announced yet; clinical trial stage III of vilaprisan was suspended due to drug toxicity. Elagolix was approved for the treatment of endometriosis-related pain, but clinical studies of Elagolix for the pretreatment of patients with endometriosis to before In vitro fertilization treatment have not been fulfilled. The results of a clinical study of Linzagolix in patients with moderate to severe endometriosis-related pain have not been disclosed yet. Letrozole improved the fertility of patients with mild endometriosis. For endometriosis patients with infertility, oral GnRH antagonists and aromatase inhibitors are promising drugs, especially Elagolix and Letrozole.

Elagolix Sodium Salt and Its Synthetic Intermediates: A Spectroscopic, Crystallographic, and Conformational Study

Elagolix sodium salt is the first marketed orally active non-peptide gonadotropin-releasing hormone receptor antagonist (GnRHR-ant) for the management of hormone dependent diseases, such as endometriosis and uterine fibroids. Despite its presence on the market since 2018, a thorough NMR analysis of this drug, together with its synthetic intermediates, is still lacking. Hence, with the aim of filling this literature gap, we here performed a detailed NMR investigation, which allowed the complete assignment of the ¹H, ¹³C, and ¹⁵N NMR signals. These data allowed, with the support of the conformational analysis, the determination of the stereochemical profile of the two atropisomers, detectable in solution. Moreover, these latter were also detected by means of cellulose-based chiral HPLC, starting from a sample prepared through an implemented synthetic procedure with respect to the reported ones. Overall, these results contribute to further understanding of the topic of atropisomerism in drug discovery and could be applied in the design of safe and stable analogs, endowed with improved target selectivity.

Physiological and Pharmacological overview of the Gonadotropin Releasing Hormone

Gonadotropin-releasing Hormone (GnRH) is a decapeptide responsible for the control of the reproductive functions. It shows C- and N-terminal aminoacid modifications and two other distinct isoforms have been so far identified. The biological effects of GnRH are mediated by binding to high-affinity G-protein couple receptors (GnRHR), showing characteristic very short C tail. In mammals, including humans, GnRH-producing neurons originate in the embryonic nasal compartment and during early embryogenesis they undergo rapid migration towards the hypothalamus; the increasing knowledge of such mechanisms improved diagnostic and therapeutic approaches to infertility. The pharmacological use of GnRH, or its synthetic peptide and non-peptide agonists or antagonists, provides a valid tool for reproductive disorders and assisted reproduction technology (ART). The presence of GnRHR in several organs and tissues indicates additional functions of the peptide. The identification of a GnRH/GnRHR system in the human endometrium, ovary, and prostate has extended the functions of the peptide to the physiology and tumor transformation of such tissues. Likely, the activity of a GnRH/GnRHR system at the level of the hippocampus, as well as its decreased expression in mice brain aging, raised interest in its possible involvement in neurogenesis and neuronal functions. In conclusion, GnRH/GnRHR appears to be a fascinating biological system that exerts several possibly integrated pleiotropic actions in the complex control of reproductive functions, tumor growth, neurogenesis, and neuroprotection. This review aims to provide an overview of the physiology of GnRH and the pharmacological applications of its synthetic analogs in the management of reproductive and non-reproductive diseases.

Preclinical models of prostate cancer - modelling androgen dependency and castration resistance in vitro, ex vivo and in vivo

Prostate cancer is well known to be dependent on the androgen receptor (AR) for growth and survival. Thus, AR is the main pharmacological target to treat this disease. However, after an initially positive response to AR-targeting therapies, prostate cancer will eventually evolve to castration-resistant prostate cancer, which is often lethal. Tumour growth was initially thought to become androgen-independent following treatments; however, results from molecular studies have shown that most resistance mechanisms involve the reactivation of AR. Consequently, tumour cells become resistant to castration - the blockade of testicular androgens - and not independent of AR per se. However, confusion still remains on how to properly define preclinical models of prostate cancer, including cell lines. Most cell lines were isolated from patients for cell culture after evolution of the tumour to castration-resistant prostate cancer, but not all of these cell lines are described as castration resistant. Moreover, castration refers to the blockade of testosterone production by the testes; thus, even the concept of "castration" in vitro is questionable. To ensure maximal transfer of knowledge from scientific research to the clinic, understanding the limitations and advantages of preclinical models, as well as how these models recapitulate cancer cell androgen dependency and can be used to study castration resistance mechanisms, is essential.

Safety, pharmacokinetics, and pharmacodynamics of SHR7280, an oral gonadotropin-releasing hormone antagonist in healthy premenopausal women

Background: Treatment with gonadotropin-releasing hormone (GnRH) antagonists is a powerful strategy to suppress gonadotropin activity in women with sex hormone-dependent disorders. Herein, we provide the safety, pharmacokinetics (PK), and pharmacodynamics (PD) profiles of SHR7280, an oral non-peptide GnRH antagonist in healthy premenopausal women. Methods: In this randomized, double-blinded, placebo-controlled, dose-ascending, phase 1 trial, healthy premenopausal women were randomized to receive SHR7280 or placebo orally. Four doses of SHR7280 (200, 300, 400, and 500 mg BID) were planned. Safety, PK, and PD parameters were evaluated. Results: SHR7280 presented tolerable toxicity and most adverse events were mild in severity. SHR7280 showed rapid onset of action (median T_max ranged from 1.0 to 1.2 h for each dose), and plasma exposure was dose-dependent. PD results showed that SHR7280 300 mg BID and above suppressed estrogen concentration within the estradiol (E₂) treatment window for endometriosis (20-50 pg/ml), inhibited the emergence of the peak of luteinizing hormone (LH) and the concentration of follicle stimulating hormone (FSH), and maintained the concentration of progesterone (P) in an anovulatory state (2 nmol/L). Conclusion: SHR7280 showed favorable safety, PK, and PD profiles in the dose range of 200-500 mg BID in healthy premenopausal women. This study supports the continued clinical development of SHR7280 as a GnRH antagonist for sex hormone-dependent disorders in women. Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT04554043, Identifier NCT04554043.

Discovery of the thieno[2,3-d]pyrimidine-2,4-dione derivative 21a: A potent and orally bioavailable gonadotropin-releasing hormone receptor antagonist

The gonadotropin releasing hormone receptor (GnRH-R) is a G protein-coupled receptor (GPCR) belonging to the rhodopsin family. GnRH-R antagonists suppress testosterone to castrate level more rapidly than gonadotropin releasing hormone agonists but lack the flare phenomenon often seen during the early period of GnRH-R agonist treatment. Recently orgovyx (relugolix) was approved as the first oral GnRH-R antagonist for the treatment of advanced prostate cancer. However, orgovyx has demonstrated poor pharmacokinetic profile with low oral bioavailability and high efflux. Here, we rationally designed and synthesized a series of derivatives (13a-m, 21a-i) through the modification and structure-activity relationship study of relugolix, which led to the discovery of 21a as a highly potent GnRH-R antagonist (IC₅₀ = 2.18 nM) with improved membrane permeability (Papp, A-B = 0.98 × 10^-6 cm/s) and oral bioavailability (F % = 44.7). Compound 21a showed high binding affinity (IC₅₀ = 0.57 nM) and potent in vitro antagonistic activity (IC₅₀ = 2.18 nM) at GnRH-R. 21a was well tolerated and efficacious in preclinical studies to suppress blood testosterone levels, which merits further investigation as a candidate novel GnRH-R antagonist for clinical studies.

Clinical evaluation of the oral gonadotropin-releasing hormone-antagonist elagolix for the management of endometriosis-associated pain

Endometriosis is an estrogen-dependent chronic inflammatory disease associated with pelvic pain symptoms that are often severe, mainly dysmenorrhea, nonmenstrual pelvic pain and dyspareunia. This condition is also associated with peripheral and central sensitization. The current medical treatment options for endometriosis-associated pain are limited. Recently, the US FDA approved the novel, oral, nonpeptide gonadotropin-releasing hormone antagonist elagolix for the management of moderate to severe endometriosis-associated pain. Elagolix produces dose-dependent estrogen suppression, from partial suppression at lower doses to nearly full suppression at higher doses. This review article summarizes the current understanding of the pathophysiology of endometriosis, with a focus on the role of estrogen and the mechanisms of pain symptoms, and reviews the clinical development of elagolix in women with endometriosis-associated pain.

Uterine fibroids: an update on current and emerging medical treatment options

Uterine fibroids are the most common gynecological disorder, classically requiring surgery when symptomatic. Although attempts at finding a nonsurgical cure date back to centuries, it is only around the middle of the last century that serious attempts at a medical treatment were carried out. Initially, both progestins and estrogen–progestin combinations have been utilized, although proof of their usefulness is lacking. A major step forward was achieved when peptide analogs of the GnRH were introduced, first those with superagonist properties and subsequently those acting as antagonists. Initially, the latter produced side effects preventing their routine utilization; eventually, this problem was overcome following the synthesis of cetrorelix. Because both types of analogs produce hypoestrogenism, their use is limited to a maximum of 6 months and, for this reason, today they are utilized as an adjuvant treatment before surgery with overall good results. Over the last decade, new, nonpeptidic, orally active GnRH-receptor blockers have also been synthesized. One of them, Elagolix, is in the early stages of testing in women with fibroids. Another fundamental development has been the utilization of the so-called selective progesterone receptor modulators, sometimes referred to as “antiprogestins”. The first such compound to be applied to the long-term treatment of fibroids was Mifepristone; today, this compound is mostly used outside of Western Countries, where the substance of choice is Ulipristal acetate. Large clinical trials have proven the effectiveness of Ulipristal in the long-term medical therapy of fibroids, although some caution must be exercised because of the rare occurrence of liver complications. All selective progesterone receptor modulators produce unique endometrial changes that are today considered benign, reversible, and without negative consequences. In conclusion, long-term medical treatment of fibroids seems possible today, especially in premenopausal women.

Synthesis and biological evaluation of 3-(2-aminoethyl) uracil derivatives as gonadotropin-releasing hormone (GnRH) receptor antagonists

We investigated a series of uracil analogues by introducing various substituents on the phenyl ring of the N-3 aminoethyl side chain and evaluated their antagonistic activity against human gonadotropin-releasing hormone (GnRH) receptors. Analogues with substituents at the ortho or meta position demonstrated potent in vitro antagonistic activity. Specifically, the introduction of a 2-OMe group enhanced nuclear factor of activated T-cells (NFAT) inhibition up to 6-fold compared to the unsubstituted analogue. We identified compound 12c as a highly potent GnRH antagonist with moderate CYP inhibition. Compound 12c showed potent and prolonged LH suppression after a single dose was orally administered in castrated monkeys compared to a known antagonist, Elagolix. We believe that our SAR study offers useful insights to design GnRH antagonists as a potential treatment option for endometriosis.

Recent Development of Non-Peptide GnRH Antagonists

The decapeptide gonadotropin-releasing hormone, also referred to as luteinizing hormone-releasing hormone with the sequence (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH₂) plays an important role in regulating the reproductive system. It stimulates differential release of the gonadotropins FSH and LH from pituitary tissue. To date, treatment of hormone-dependent diseases targeting the GnRH receptor, including peptide GnRH agonist and antagonists are now available on the market. The inherited issues associate with peptide agonists and antagonists have however, led to significant interest in developing orally active, small molecule, non-peptide antagonists. In this review, we will summarize all developed small molecule GnRH antagonists along with the most recent clinical data and therapeutic applications.

An efficient synthesis of deuterium-labeled degarelix acetate, a third-generation gonadotropin-releasing hormone receptor antagonist

Degarelix acetate, a third-generation gonadotropin-releasing hormone receptor antagonist, shows great potential in the treatment of many androgen-related diseases. To support clinical studies of degarelix acetate, deuterium-labeled degarelix is highly desired for use as an internal standard. Using D₂ O/D₃ PO₄ as a deuterium source, 2-amino-3-(naphthalen-2-yl)propanoic acid was converted to deuterated degarelix acetate in 13 steps and in 14% overall yield.

Discovery of an Orally Bioavailable Gonadotropin-Releasing Hormone Receptor Antagonist

We developed a compound library for orally available gonadotropin-releasing hormone (GnRH) receptor antagonists that were based on a uracil scaffold. On the basis of in vitro activity and CYP inhibition profile, we selected 18a (SKI2496) for further in vivo studies. Compound 18a exhibited more selective antagonistic activity toward the human GnRH receptors over the GnRHRs in monkeys and rats, and this compound also showed inhibitory effects on GnRH-mediated signaling pathways. Pharmacokinetic and pharmacodynamic evaluations of 18a revealed improved bioavailability and superior gonadotropic suppression activity compared with Elagolix, the most clinically advanced compound. Considering that 18a exhibited highly potent and selective antagonistic activity toward the hGnRHRs along with favorable pharmacokinetic profiles, we believe that 18a may represent a promising candidate for an orally available hormonal therapy.

GnRH and GnRH receptors in the pathophysiology of the human female reproductive system

BACKGROUND

Human reproduction depends on an intact hypothalamic-pituitary-gonadal (HPG) axis. Hypothalamic gonadotrophin-releasing hormone (GnRH) has been recognized, since its identification in 1971, as the central regulator of the production and release of the pituitary gonadotrophins that, in turn, regulate the gonadal functions and the production of sex steroids. The characteristic peculiar development, distribution and episodic activity of GnRH-producing neurons have solicited an interdisciplinary interest on the etiopathogenesis of several reproductive diseases. The more recent identification of a GnRH/GnRH receptor (GnRHR) system in both the human endometrium and ovary has widened the spectrum of action of the peptide and of its analogues beyond its hypothalamic function.

METHODS

An analysis of research and review articles published in international journals until June 2015 has been carried out to comprehensively summarize both the well established and the most recent knowledge on the physiopathology of the GnRH system in the central and peripheral control of female reproductive functions and diseases.

RESULTS

This review focuses on the role of GnRH neurons in the control of the reproductive axis. New knowledge is accumulating on the genetic programme that drives GnRH neuron development to ameliorate the diagnosis and treatment of GnRH deficiency and consequent delayed or absent puberty. Moreover, a better understanding of the mechanisms controlling the episodic release of GnRH during the onset of puberty and the ovulatory cycle has enabled the pharmacological use of GnRH itself or its synthetic analogues (agonists and antagonists) to either stimulate or to block the gonadotrophin secretion and modulate the functions of the reproductive axis in several reproductive diseases and in assisted reproduction technology. Several inputs from other neuronal populations, as well as metabolic, somatic and age-related signals, may greatly affect the functions of the GnRH pulse generator during the female lifespan; their modulation may offer new possible strategies for diagnostic and therapeutic interventions. A GnRH/GnRHR system is also expressed in female reproductive tissues (e.g. endometrium and ovary), both in normal and pathological conditions. The expression of this system in the human endometrium and ovary supports its physiological regulatory role in the processes of trophoblast invasion of the maternal endometrium and embryo implantation as well as of follicular development and corpus luteum functions. The GnRH/GnRHR system that is expressed in diseased tissues of the female reproductive tract (both benign and malignant) is at present considered an effective molecular target for the development of novel therapeutic approaches for these pathologies. GnRH agonists are also considered as a promising therapeutic approach to counteract ovarian failure in young female patients undergoing chemotherapy.

CONCLUSIONS

Increasing knowledge about the regulation of GnRH pulsatile release, as well as the therapeutic use of its analogues, offers interesting new perspectives in the diagnosis, treatment and outcome of female reproductive disorders, including tumoral and iatrogenic diseases.

Discovery and optimization of novel antagonists to the human neurokinin-3 receptor for the treatment of sex-hormone disorders (Part I)

Neurokinin-3 receptor (NK3R) has recently emerged as important in modulating the tonic pulsatile gonadotropin-releasing hormone (GnRH) release. We therefore decided to explore NK3R antagonists as therapeutics for sex-hormone disorders that can potentially benefit from lowering GnRH pulsatility with consequent diminished levels of plasma luteinizing hormone (LH) and correspondingly attenuated levels of circulating androgens and estrogens. The discovery and lead optimization of a novel N-acyl-triazolopiperazine NK3R antagonist chemotype achieved through bioisosteric lead change from the high-throughput screening (HTS) hit is described. A concomitant improvement in the antagonist bioactivity and ligand lipophilic efficiency (LLE) parameter were the principal guidelines in the lead optimization efforts. Examples of advanced lead analogues to demonstrate the amenability of this chemotype to achieving a suitable pharmacokinetic (PK) profile are provided as well as pharmacokinetic-pharmacodynamic (PKPD) correlations to analyze the trends observed for LH inhibition in castrated rats and monkeys that served as preliminary in vivo efficacy models.

Histidine(7.36(305)) in the conserved peptide receptor activation domain of the gonadotropin releasing hormone receptor couples peptide binding and receptor activation

Transmembrane helix seven residues of G protein-coupled receptors (GPCRs) couple agonist binding to a conserved receptor activation mechanism. Amino-terminal residues of the GnRH peptide determine agonist activity. We investigated GnRH interactions with the His(7.36(305)) residue of the GnRH receptor, using functional and computational analysis of modified GnRH receptors and peptides. Non-polar His(7.36(305)) substitutions decreased receptor affinity for GnRH four- to forty-fold, whereas GnRH signaling potency was more decreased (~150-fold). Uncharged polar His(7.36(305)) substitutions decreased GnRH potency, but not affinity. [2-Nal(3)]-GnRH retained high affinity at receptors with non-polar His(7.36(305)) substitutions, supporting a role for His(7.36(305)) in recognizing Trp(3) of GnRH. Compared with GnRH, [2-Nal(3)]-GnRH potency was lower at the wild type GnRH receptor, but unchanged or higher at mutant receptors. Results suggest that His(7.36(305)) of the GnRH receptor forms two distinct interactions that determine binding to Trp(3) and couple agonist binding to the conserved transmembrane domain network that activates GPCRs.

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

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

Discovery of 1-{4-[1-(2,6-difluorobenzyl)-5-[(dimethylamino)methyl]-3-(6-methoxypyridazin-3-yl)-2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidin-6-yl]phenyl}-3-methoxyurea (TAK-385) as a potent, orally active, non-peptide antagonist of the human gonadotropin-releasing hormone receptor

We previously discovered an orally active human gonadotropin-releasing hormone (GnRH) receptor antagonist, thieno[2,3-d]pyrimidine-2,4-dione derivative 1 (sufugolix). To reduce the cytochrome P450 (CYP) inhibitory activity and improve in vivo GnRH antagonistic activity, further optimization of this scaffold was carried out. We focused our synthetic efforts on chemical modification at the 5 and 3 positions of the thieno[2,3-d]pyrimidine-2,4-dione ring based on computational modeling, which resulted in the discovery of 1-{4-[1-(2,6-difluorobenzyl)-5-[(dimethylamino)methyl]-3-(6-methoxypyridazin-3-yl)-2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidin-6-yl]phenyl}-3-methoxyurea (16b) as a highly potent and orally active GnRH antagonist. Compound 16b showed potent in vitro GnRH antagonistic activity in the presence of fetal bovine serum (FBS) without CYP inhibition. Oral administration of 16b maintained the suppressive effect of the plasma luteinizing hormone levels in castrated cynomolgus monkeys at a 3 mg/kg dose for more than 24 h. Compound 16b is currently under clinical development with the code name of TAK-385.

Luteinizing hormone-releasing hormone antagonists

BACKGROUND

Luteinizing hormone-releasing hormone (LH-RH) plays a central role in the vertebrate reproduction by regulating gonadal activity. Based on its binding to pituitary LH-RH receptors, as well as to LH-RH receptors expressed on cancer cells, LH-RH agonists and antagonists have been developed for different therapeutic applications.

OBJECTIVE/METHOD

Here we give an overview of the most relevant LH-RH antagonists and their therapeutic applications. Recently patented compounds as well as drug formulations and dosage are presented.

CONCLUSION

LH-RH antagonists have found clinical applications in in vitro fertilization, benign prostatic hyperplasia, endometriosis and in the treatment of hormone-dependent tumors. Work in progress is focused on further development of both peptidic and orally active non-peptidic LH-RH antagonists.

Plasma membrane expression of gonadotropin-releasing hormone receptors: regulation by peptide and nonpeptide antagonists

Gonadotropin-releasing hormone acts via cell surface receptors but most human (h) GnRH receptors (GnRHRs) are intracellular. A membrane-permeant nonpeptide antagonist [(2S)-2-[5-[2-(2-axabicyclo[2.2.2]oct-2-yl)-1,1-dimethy-2-oxoethyl]-2-(3,5-dimethylphenyl)-1H-indol-3-yl]-N-(2-pyridin-4-ylethyl)propan-1-amine (IN3)] increases hGnRHR expression at the surface, apparently by facilitating its exit from the endoplasmic reticulum. Here we have quantified GnRHR by automated imaging in HeLa cells transduced with adenovirus expressing hemagglutinin-tagged GnRHR. Consistent with an intracellular site of action, IN3 increases cell surface hGnRHR, and this effect is not blocked or mimicked by membrane-impermeant peptide antagonists [Ac-D2Nal-D4Cpa-D3Pal-Ser-Tyr-d-Cit-Leu-Arg-Pro-d-Ala-NH(2) (cetrorelix) and antide]. However, when the C-terminal tail of a Xenopus (X) GnRHR was added (h.XGnRHR) to increase expression, both peptides further increased cell surface GnRHR. Cetrorelix also synergized with IN3 to increase expression of hGnRHR and a G-protein coupling-deficient mutant (A261K-hGnRHR). Cetrorelix also increased cell surface expression of hGnRHR, h.XGnRHR, and mouse GnRHR in gonadotrope-lineage LbetaT2 cells, and in HeLa cells it slowed h.XGnRHR internalization (measured by receptor-mediated antihemagglutinin uptake). Thus cetrorelix has effects other than GnRHR blockade; it acts as an inverse agonist in internalization assays, supporting the potential importance of ligand-biased efficacy at GnRHR. We also developed an imaging assay for GnRH function based on Ca(2+)-dependent nuclear translocation of a nuclear factor of activated T cells reporter. Using this in HeLa and LbetaT2 cells, IN3 and cetrorelix behaved as competitive antagonists when coincubated with GnRH, and long-term pretreatment (16 h) with IN3 reduced its effectiveness as an inhibitor whereas pretreatment with cetrorelix increased its inhibitory effect. This distinction between peptide and nonpeptide antagonists may prove important for therapeutic applications of GnRH antagonists.

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.

Will GnRH antagonists improve prostate cancer treatment?

Androgen ablation forms a basis for treating prostate cancer and is achieved either by surgical castration, or pharmacologically using oestrogens, anti-androgens and/or gonadotropin-releasing hormone (GnRH) analogues. GnRH antagonists (or blockers) offer a new means of treatment by directly blocking GnRH receptors. Advantages of GnRH antagonists include lack of the initial stimulation of gonadotropin and testosterone production, lack of gonadotropin microsurges and sustained follicle-stimulating hormone suppression; disadvantages include increased histamine release. This review discusses advantages and disadvantages of the GnRH antagonists currently in development, in light of receptor physiology and pre-clinical and clinical data. Comparative clinical trials will ultimately establish their efficacy in comparison to other pharmacotherapies. Therefore, continuing development and refinement is needed to improve prostate cancer treatment.