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2013 20: 16 originally published online 25 September 2012Reproductive SciencesOrkun Tan, Bruce R. Carr, Victor E. Beshay and Orhan Bukulmez

ReviewThe Extrapituitary Effects of GnRH Antagonists and Their Potential Clinical Implications: A Narrated

  

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The Extrapituitary Effects of GnRHAntagonists and Their Potential ClinicalImplications: A Narrated Review

Orkun Tan, MD1, Bruce R. Carr, MD1,Victor E. Beshay, MD1, and Orhan Bukulmez, MD1

AbstractPotential roles of gonadotropin-releasing hormone (GnRH) antagonists on GnRH/GnRH receptor systems and their effects onthe extrapituitary tissues are largely elusive. In this narrated review, we summarized the systemic effects of GnRH antagonists onovary, endometrium, embryo implantation, placental development, fetal teratogenicity, reproductive tissue cancer cells, and heartwhile briefly reviewing the GnRH and GnRH receptor system. GnRH antagonists may have direct effects on ovarian granulosacells. Data are conflicting regarding their effects on endometrial receptivity. The GnRH antagonists may potentially have detri-mental effect on early placentation by decreasing the invasive ability of cytotrophoblasts if the exposure to them occurs duringearly pregnancy. The GnRH antagonists were not found to increase the rates of congenital malformations. Comparative clinicaldata are required to explore their systemic effects on various extrapituitary tissues such as on cardiac function in the long term aswell as their potential use in other human cancers that express GnRH receptors.

KeywordsGnRH types, GnRH receptors, GnRH antagonist, implantation, endometrium, ovary, heart, controlled ovarian stimulation

Introduction

Gonadotropin-releasing hormone type I (GnRH-I) is the classic

hypothalamic hormone that controls the synthesis and secretion

of gonadotropins in the pituitary.1 The GnRH-I is also present

in extrapituitary tissues such as endometrium,2 myometrium,3

fallopian tube epithelium,4 ovarian surface epithelial (OSE)

cells,5 ovarian granulosa lutein (GL) cells,6 preimplantation

embryo,7 and placenta8 (Table 1).

A gene-encoding GnRH-II was also cloned from human

brain tissue.9 The human GnRH-I gene is longer than the

GnRH-II gene because introns 2 and 3 of the GnRH-I gene are

larger9 (see Figure 1 for comparison of GnRH-I and GnRH-II

genes in humans). In humans, GnRH-II is expressed in extrahy-

pothalamic tissues such as human endometrium,10 breast

tissue,11 ovarian GL,12,13 and ovarian surface epithelial (OSE)

cells12 (Table 1). Although GnRH-IIR is present in the human

tissues, to date, a fully functional GnRH-II and GnRH-IIR com-

plex has not been shown due to a frameshift mutation in GnRH-

IIR leading to the gene disruption.14 In human midbrain and

hypothalamus, GnRH-III containing neurons were also identi-

fied by immunohistochemistry15 (Table 1). Similar to GnRH-I

and -II, GnRH-IR (Figure 2) and GnRH-IIR (Figure 3) were

detected in pituitary16,17 and extrapituitary human tissues.18–20

To date, many GnRH analogues with different biological

potencies have been developed for the treatment of various

reproductive disorders.21-23 The GnRH antagonists (GnRH-

ants) are commonly used in in vitro fertilization cycles for

pituitary suppression, however, they are also being used to treat

various systematic disorders such as prostate cancer. Since the

systemic effects of many available GnRH-ants on various

extrapituitary tissues and the receptors (GnRH-IR or GnRH-

IIR) with which they exert their effects are largely unknown,

we found it timely to summarize the direct systemic effects

of GnRH-ants on endometrium, implantation, ovary, breast

tissue, prostate, and heart while briefly reviewing the GnRH

and GnRH receptor system.

Search Methods

All peer-reviewed journal articles published before June 2012

for each area discussed (role of GnRH-ants in ovary,

1 Department of Obstetrics and Gynecology, Division of Reproductive

Endocrinology and Infertility, University of Texas Southwestern Medical

Center, Dallas, TX, USA

Corresponding Author:

Orkun Tan, Department of Obstetrics and Gynecology, University of Texas

Southwestern Medical Center, Division of Reproductive Endocrinology and

Infertility, 5323 Harry Hines Blvd. J6, Dallas, TX 75390, USA

Email: orkun.tan@utsouthwestern.edu

Reproductive Sciences20(1) 16-25ª The Author(s) 2013Reprints and permission:sagepub.com/journalsPermissions.navDOI: 10.1177/1933719112459244http://rs.sagepub.com

at Cairo University on May 10, 2014rsx.sagepub.comDownloaded from

endometrium, embryo implantation, pregnancy rates, placental

development, fetal teratogenicity, cancer cells, and heart) were

searched by PubMed, Medline, Cochrane database, and Scopus

for a narrated literature review and the relevant findings were

summarized. The search was limited to both prospective and

retrospective studies that were published as full text in English

only. The search was without temporal limits but mainly

yielded publications between 1995 and 2012. Ninety-six per-

cent of the studies described were performed during the past

12 years (2000-2012); more specifically, 4% of the studies

were performed during the period from 1995 to 1999, 33% of

the studies were performed during the period from 2000 to

2005, and 53% in the period from 2006 to June 2012.

Gonadotropin-Releasing HormoneAntagonists

There are 4 GnRH-ants currently approved by the Food and

Drug Administration (FDA).24 Ganirelix (Antagon, Ganirelix

acetate; Merck, New Jersey) and Cetrorelix (Cetrotide; EMD Ser-

ono International S.A., Geneve, Switzerland) are commercially

available for the prevention of premature LH surge during in vitro

fertilization (IVF) cycles. Both Degarelix acetate (Firmagon;

Ferring Pharmauceticals, Saint-Prex, Switzerland) and Abarelix

(Plenaxis; Praecis Pharmaceuticals Inc, Waltham, Massachu-

setts) are the third-generation GnRH-ants, and they have been

approved for the treatment of advanced stage prostatic cancer.

Abarelix has been discontinued in the market.24,25

Ozarelix and F-75998 are the fourth-generation GnRH-ants,

and they are currently being utilized in experimental studies.26,27

An orally active nonpeptide GnRH-ant, Elagolix, has been stud-

ied for the treatment of uterine fibroids, endometriosis, and

benign prostatic hyperplasia.24,28,29 Elagolix is not yet FDA

approved.24

The Role of GnRH Antagonists in Ovary

Both GnRH-IR and GnRH-IIR have been identified in the

ovary.30 Choi et al31 investigated the GnRH/GnRH-IR expres-

sion during the development of human ovarian follicle. They

showed that GnRH-I, -II, and GnRH-IR immunoreactivity

were not present in the primordial and early antral stage folli-

cles. However, GnRH-I, -II, and GnRH-IR were expressed in

the granulosa cell layer; whereas the theca internal layer was

weakly positive. Significant GnRH-I, -II, and GnRH-IR immu-

noreactivity were also observed in granulose lutein cells in the

corpus luteum.31

The common use of GnRH antagonists raised many ques-

tions regarding their potential role in ovarian function through

GnRH receptors.30 Weiss et al demonstrated in vitro that ganir-

elix and cetrorelix do not affect the steroidogenesis in the

ovary.32 Another in vitro study in human granulosa luteinized

cell cultures showed similar results that is both leuprolide and

cetrorelix did not affect ovarian steroidogenesis.33

However, in some studies, GnRH-ant has been shown to be

associated with lower levels of estradiol on the day of human

chorionic gonadotropin (hCG) administration.34,35 If GnRH-

ant has a suppressive effect on the ovary, it is unclear whether

this effect is via suppression of aromatase and/or the central

inhibitory effects of the GnRH-ants. Winkler et al showed that

mRNA expressions of anti-Mullerian hormone (AMH),

CYP19IIa (gonadal aromatase promoter), and steroidogenic

factor 1 (SF-1) were decreased by GnRH-ant (cetrorelix) in

human granulosa cells.36 Similarly Garcia-Velasco et al35

demonstrated decreased follicular fluid estradiol concentra-

tions in patients treated with GnRH-ants than in those treated

with GnRH agonist (GnRH-ag). Therefore, GnRH-ants could

play a direct role in ovarian granulosa cells’ function besides

their suppressive effects on pituitary gonadotropin release.24,36

However, further studies are required to validate these results

and explore other potential pathways.

Gonadotropin-Releasing HormoneAntagonists and Their Role inEndometrium and Embryo Implantation

Gonadotropin-releasing hormone receptor is present during all

the developmental stages of the embryo, suggesting that the

embryo interacts with the maternal tubal epithelium and endo-

metrium to stimulate endometrial receptivity and embryonic

development.4,7 It was debated whether the ovarian stimulation

during an IVF cycle may negatively affect embryo implanta-

tion37,38 since GnRH-I, GnRH-II, and the GnRH-IR are

expressed in normal endometrium.39 The GnRH has been

shown to modulate matrix metalloproteinases (MMPs) that

play a role in endometrial remodeling and preparation of endo-

metrium for implantation. Therefore, many questions were

raised about the possible negative impacts of GnRH-ant on

endometrial receptivity.40-43

Bukulmez et al have previously shown that the sandwich

GnRH-ant protocol resulted in lower clinical pregnancy rates

Table 1. Localization of Different GnRH Types in Humans

GnRH Type I GnRH Type II GnRH Type III

Hypothalamus Hypothalamus HypothalamusEndometrium Endometrium MidbrainFallopian tube epithelium KidneyOvarian GL cells Ovarian GL cellsOvarian surface

epitheliumOvarian surface

epitheliumOvarian carcinoma Ovarian carcinomaPlacenta PlacentaBreast tissue ProstateBreast cancer Breast tissuePreimplantation embryoa Breast cancer

Bone marrow

Expression of GnRH-I has been demonstrated in hypothalamic and extrahy-pothalamic human tissues. The GnRH-II is expressed at significantly higherlevels outside the brain. The GnRH-III containing neurons are demonstratedin the hypothalamus and midbrain of humans.aPresent in blastomeres as well as in the trophoectoderm and inner cell mass ofthe blastocyst.Abbreviations: GL, granulosa lutein; GnRH, gonadotropin-releasing hormone.

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compared with the GnRH-ag long protocol while the blastocyst

progression and quality were comparable in the same study.44

The same authors then tried to determine whether higher

cetrorelix levels in the GnRH-ant group, might be the cause

of the difference in clinical pregnancy rates compared to the

GnRH-ag long protocol group, however, they did not find any

significant differences in serum cetrorelix concentrations

between these 2 groups.45

Haouzi et al investigated the effects of GnRH-ag long pro-

tocols and GnRH-ant protocols on endometrial receptivity

compared with natural cycles by analyzing the global gene

expression profile during receptive stages of stimulated

Figure 1. The structure of GnRH-I and GnRH-II genes in humans.Human GnRH-I gene is composed of 4 exons separated by 3 introns. The first exon consists of 61 base pairs. The second exon encodes the signal sequence, theGnRH decapeptide, and the first 11 GAP residues. The third exon encodes the next 32 GAP residues. The fourth exon contains the translation termination codon.The GnRH-II gene comprises 4 exons interrupted by 3 introns. The human GnRH-II gene (2.1 kb) is shorter than the GnRH-I gene (5 kb) because introns 2 and 3of the latter are much larger. GnRH indicates gonadotropin-releasing hormone; GAP, GnRH-associated peptide.

Figure 2. Expression of GnRH-I receptor in humans.The GnRH-I receptor (-IR) is present in many human tissues. *Epithelial ovarian carcinoma and multiple ovarian cancer cell lines express GnRH-IR mRNA.**Human endometrial cancer and Ishikawa endometrial cancer cell lines express GnRH-IR mRNA. ***Breast carcinoma and MCF-7 breast cancer cells expressGnRH-IR mRNA. GnRH indicates gonadotropin-releasing hormone; mRNA, messenger RNA.

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cycles.46 The number of downregulated genes common

between stimulated and natural cycles was found to be similar

when comparing GnRH-ag long protocol with the GnRH-ant

protocol (10% in common with their natural cycle under the

GnRH-ag protocol versus 7% under the GnRH-ant protocol).

In the same study, of those genes upregulated during the recep-

tive stage of the natural cycle, 5% matched those upregulated

under GnRH-ag long protocol; whereas 36% were common

to the profile resulting from the GnRH-ant protocol. In compar-

ison to the endometrial receptivity under the GnRH-ag proto-

col, endometrial receptivity under the GnRH-ant protocol

was more similar to that of the natural cycle.46

In addition, a prospective randomized study was performed

to assist in clarifying the direct action of GnRH-ants on endo-

metrial receptivity and pregnancy rates in oocyte donation

cycles.47 Patients were randomly stratified either to receive a

GnRH-ant concomitant to donor during their endometrial pre-

paration with estradiol (group 1, n ¼ 49) or to receive only

estradiol for their endometrial preparation (group 2, n ¼ 49).

Pregnancy rate was 55.1% in group 1 and 59.1% in group 2.

Pregnancy rates were similar between the 2 groups, indicating

that GnRH-ant administration during the proliferative phase

does not have any adverse effect on implantation and pregnancy

rates in oocyte recipients.47 Although the study had limited

power due to the small number of patients, these results appear

to be reassuring regarding the direct effects of GnRH-ant on

endometrial development and implantation. Similarly Martinez

et al48 compared the pregnancy and implantation rates among

premenopausal oocyte recipients synchronized by pituitary sup-

pression with GnRH-ag or GnRH-ant and standard endometrium

preparation with estrogen and progestin. They did not observe

any difference in pregnancy rates comparing GnRH-ant group

(52.4%) with the GnRH-ag group (56.1%).

Homeobox A10 (HOXA10) is one of the mediators of endo-

metrial receptivity. Rackow et al assessed endometrial HOXA10

expression in GnRH-ant, GnRH-ag, and natural cycles in order

to determine the effect of GnRH-ants on endometrial receptiv-

ity.49 Expression of HOXA10 was significantly decreased in

endometrial stromal cells in GnRH-ant-treated cycles com-

pared with GnRH-ag-treated cycles or natural cycle control

participants. There was no significant difference in glandular

cell HOXA10 expression among the 3 groups. It was concluded

that the use of GnRH-ant may be associated with impaired

HOXA10 expression in endometrial stromal cells and thus may

affect endometrial receptivity.49

In conclusion, the data are conflicting regarding the impact of

GnRH-ag long protocol and GnRH-ant protocols on endometrial

receptivity, regardless of the approaches to assess endometrial

receptivity itself.47,49-51 The differences between the results of the

studies investigating the effects of GnRH analogues on endome-

trial receptivity could be due to (a) discrepancies in the timing of

the endometrial biopsies, (b) differences in the controlled ovarian

hyperstimulation (COH) protocols used, (c) differences in patient

profiles, (d) inappropriate comparisons between samples, and (e)

limited numbers of endometrial samples studied46 as well as the

intracellular molecular interactions mediating the effects of

GnRH-ags and GnRH-ants in human tissues.

Gonadotropin-Releasing HormoneAntagonists and Pregnancy Rates

The results of studies published 10 years ago were inconsistent

as to whether GnRH-ag long protocol is associated with higher

clinical pregnancy rates compared to that of the GnRH-ant pro-

tocols during IVF cycles.52-55 However, in a 2006 meta-

analysis, there was no statistically significant difference in live

birth rates comparing GnRH-ag with GnRH-ant protocols.56 In

line with the 2006 meta-analysis,56 a 2011 meta-analysis also

did not find any significant difference in ongoing pregnancy

rates between the GnRH-ag and GnRH-ant protocols in oocyte

donation cycles.57 A recently published update of 2011

Cochrane review included 45 trials addressing live birth or

ongoing pregnancy rate in GnRH-ant and GnRH-ag protocols

among women undergoing assisted reproduction.58 In 9 trials

involving 1515 women, the average live birth rates with

GnRH-ag and GnRH-ant treatment were 31.5% and 30%,

respectively. However, live birth rates with GnRH-ag treatment

were not statistically significant compared to those with GnRH-

ant treatment. The relative risk of ovarian hyperstimulation syn-

drome (OHSS) with GnRH-ant treatment was 50% of that with

GnRH-ag treatment (P¼ .003).58 Therefore, these findings may

now justify a move away from the standard GnRH-ag long pro-

tocol to a GnRH-ant protocol for pituitary suppression.

Gonadotropin-Releasing HormoneAntagonists: Placental Developmentand Fetal Teratogenicity

The GnRH-IR has also been identified in the cytotrophoblasts

and syncytiotrophoblasts of the human placenta by in situ

hybridization.59,60 Both GnRH-I and GnRH-II bind to the

GnRH-I receptor to stimulate the production and secretion of

Figure 3. Expression of GnRH-II receptor in humans.The GnRH-II receptor (GnRH-IIR) distribution is not concentrated in anyorgan system such as endocrine glands or reproductive tissues. The GnRH-IIR is detectable in ovary, breast, endometrium, gastrointestinal organs, andin mature human sperm. *Although present in certain tissues, functionalGnRH-IIR transcript in human tissues is lacking. GnRH indicates gonadotropinreleasing hormone.

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Beta-human chorionic gonadotropin (b-hcg). Placental GnRH-

IR expression peaks at around 9 weeks of gestation, which is

parallel to the peak of hcg.59 The MMPs are present in human

placental trophoblasts and they are one of the key mediators of

trophoblast cell invasion and extracellular matrix degradation.

Recently, GnRH-I and GnRH-II have been found to regulate

the expression of MMP-2 and -9 in human placental tropho-

blasts, and they also may play a role in trophoblast invasion

through the activation of MMPs, plasminogen activators, and

angiogenic factors.61 Therefore, GnRH-I and GnRH-II may

work together in mediating the effects of different protease sys-

tems in placenta.62,63 Liu et al studied how MMP-26 is regu-

lated by GnRH-I and GnRH-II in human immortalized

cytotrophoblast-like cell line (B6Tert-1).64 It was shown that

GnRH-I and GnRH-II stimulated MMP-26 production by the

primary cytotrophoblasts, and they stimulated the invasive

ability of B6Tert-1 cells.64 Both GnRH-I and GnRH-II have

been shown to affect the expression of matrix metalloproteases

and plasminogen activators at the maternal–fetal interface and

promote trophoblast invasion.61,62 These findings could raise

the issue whether GnRH-ants may have any detrimental effect

on early placentation by decreasing the invasive ability of cyto-

trophoblasts if the exposure to GnRH-ants occurs during the

early pregnancy.

It has been debated whether GnRH-ants have any teratogenic

potential on the early embryo24 since GnRH-I has been shown to

be present in trophoectoderm and inner cell mass of the

blastocyst.65 In a rat study, the effects of cetrorelix on early

implantation were investigated.66 This study showed that the

administration of the cetrorelix at various doses (15, 75, and

150 mg/kg cetrorelix vs saline) in the early postimplantation

period suppressed fetoplacental development, decreased embryo

weight, delayed delivery, and caused serious fetal malformations.

However, the applicability of these results to humans is question-

able since cetrorelix was used at very high doses in that study. In

clinical studies, GnRH-ants were not found to increase the rates of

congenital malformations when used in IVF protocols.67-69

In line with these previous human studies, obstetrical and

neonatal data from 969 live born infants after GnRH-ant (ganir-

elix) treatment were compared with 963 live born infants after

long GnRH-ag (buserelin) treatment.70 Incidence of major con-

genital malformations in fetuses with gestational age �26

weeks was 5.0% in the ganirelix group versus 5.4% in the

GnRH-ag group. These findings suggest that GnRH-ant (ganir-

elix) use during controlled ovarian stimulation is as safe as tra-

ditional GnRH-ag protocol (buserelin).70 Kyrou et al

investigated whether there is any relationship between the pro-

portion of chromosomally abnormal blastomeres and the type

of pituitary suppression used in controlled ovarian stimulation

cycles.71 They did not find any statistical difference in the pro-

portion of abnormal blastomeres in the chromosomes when

comparing GnRH-ag with the GnRH-ant protocol.71

In view of the current evidence, treatment with the GnRH-

ants during controlled ovarian stimulation cycles is considered

as safe as traditional GnRH-ags regarding the risk of congenital

malformations.

The Effects of GnRH Antagonists onReproductive Tissue Cancer Cells

The antiproliferative and apoptotic effects of GnRH-ants on

reproductive tissue cancer cells have been a recent area of

interest.26,72-76 The majority of human cancer cells such as

endometrium, ovary, breast, and prostate cancer express

receptors for GnRH.73-75 The role of GnRH-ants in preventing

proliferative and invasive capabilities of these cancer cells has

been extensively studied in vitro.

For example, GnRH-ant (MI-1544) showed an antiprolifera-

tive effect in human breast cancer cell lines (MCF-7 and MDA-

MB-231).77 In androgen-independent prostate cancer cell lines,

GnRH-ant (cetrorelix) has also been shown to inhibit prolifera-

tion and invasive capabilities of these cell lines.72 Similarly, a

fourth-generation GnRH-ant (ozarelix) showed antiprolifera-

tive effects in androgen receptor negative prostate cancer cell

lines and produced an accumulation of cells in G2/M cell cycle

phase.26 Maudsley et al showed that selective GnRH-ants

(135-18 and 135-25) exert potent antiproliferative effects on

JEG-3 choriocarcinoma and benign prostate hyperplasia cells

that express type I GnRH receptor. In that study, it was con-

cluded that the ability of GnRH receptor antagonists to exert

an antiproliferative effect on reproductive tumors may be

dependent on ligand-selective activation of the G-alpha(i)-

coupled form of the type I GnRH receptor.73 However, another

study showed that although GnRH-ant cetrorelix similarly

showed antiproliferative effects on endometrial and ovarian

cancer cells, these effects were not mediated through type I

GnRH receptor.74

The effects of GnRH-ants on antiproliferation and apoptosis

in some cancer cell lines (ovary, endometrium, prostate) are

very different from their effects on gonadotropin secretion.

Ligand-induced selective signaling theory was in fact sug-

gested from experiments in cancer cell lines. There are over

20 Ga proteins classified in 4 families: Gaq/11 phospholipase

C, Gas, Gai, and Ga12/13 small GTPases.78 The GnRH-ants

may antagonize Gaq but may act as full agonists in inhibiting

cell growth through Gai. The GnRH-ants may induce different

G proteins or may influence various intracellular pathways

including small molecule GTPases or RhoA, disrupting mem-

brane assembly, spindle function, and cytoskeleton by affecting

receptor configuration in GnRHR-I, since GnRHR-II may not

be functional in humans (Figure 4).79

Although GnRH-ants may have antiproliferative and

antimetastatic effects on certain cancer cells, well-designed

randomized controlled clinical trials are needed to determine

the efficacy and safety of GnRH-ants in the treatment of

GnRH-receptor-positive human cancers.

Gonadotropin-Releasing HormoneAntagonists and Heart

Both the GnRH receptor mRNA80 and immunoreactive

receptor81 have been demonstrated in human heart, providing

evidence for an evolutionarily conserved role for GnRH in

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the heart. Since heart has GnRH receptors, GnRH-ants may

potentially affect heart in many different ways. First, we would

like to briefly mention about the effects of GnRH-ag on heart

with long-term use. The GnRH-ags are used therapeutically

to chemically castrate men with prostate cancer. This treatment

is accompanied by various side effects (hot flashes, weight

gain, and decreased libido), and has recently been associated

with an overtly increased cardiovascular risk, although this

effect was ascribed to the loss of circulating testosterone.82

However, some epidemiological studies have provided evi-

dence of a significant increase in the prevalence of coronary

heart disease, myocardial infarction, and sudden cardiac death

in patients receiving GnRH-ag treatment compared to

untreated and castrated men,83,84 resulting in an FDA warning.

In addition, oral antiandrogen monotherapy is not associated

with negative cardiac outcomes,85 favoring the hypothesis that

the GnRH-ags per se, rather than the loss of androgenic effects,

are directly responsible for the negative health outcome.86

Because GnRH-ag treatment is associated with increased

coronary heart disease and myocardial infarction, a recent

study investigated the impact of GnRH on cardiomyocyte

contractility.86 The GnRH had positive cardiomyocyte

contractile effects via a GnRH receptor/phosphokinase

A-dependent (PKA) mechanism in mice. The GnRH-induced

cardiomyocyte mechanical responses were abolished or

significantly attenuated by cetrorelix and PKA inhibitor

(H89), suggesting an involvement of GnRH receptor and

PKA in the GnRH-elicited cardiomyocyte contractile

responses in mice. If present in the human heart,

GnRH-ants may theoretically compromise cardiac contractile

properties via inhibition of GnRH receptor/PKA-dependent

pathway, leading to serious cardiac side effects.

In line with the above-mentioned hypothesis, a study in

2011 investigated the association of baseline cardiovascular

disease risk profile, dosing regimen, and treatment duration

with the incidence of cardiovascular disease events during

androgen-deprivation therapy with degarelix in patients with

prostate cancer.87 Cardiovascular event rates were similar

before and after degarelix treatment in the total population

(5.5 vs 6.1 of 100 person-years, P ¼ .45) and in men without

cardiovascular disease (5.6 vs 4.3 of 100 person-years,

P ¼ .11). In contrast, event rates appeared to be higher after

degarelix treatment in men with cardiovascular disease at base-

line (5.3-10.5 events per 100 person-years, P ¼ .0013).87 The

mechanisms by which degarelix could increase the risk of car-

diovascular events in this population is currently unknown,87

and the safety of degarelix and other GnRH-ants in other organ

systems such as cardiovascular system needs to be determined

by placebo-controlled randomized trials in order to fully

determine the comparative safety of GnRH-ants.

Figure 4. Intracellular signaling mechanisms of GnRH-l/GnRH-IR system. The GnRH-I acts primarily via Gq/11 protein to stimulatephospholipase C, with consequent mobilization of Ca2þ. The GnRH-I also activates phospholipase A2, thus releasing arachidonic acid as wellas phospholipase D. It also activates protein kinase C isozymes, extracellular signal-regulated kinase (ERK), Jun N-terminal kinase (JNK), andmitogen-activated protein kinase (MAPK) cascades which, together with Ca2þ/calmodulin and its effectors, control gonadotropin synthesis.*Gq/11 protein belongs to G-protein subfamily. GnRH-IR indicates gonadotropin releasing hormone I receptor; IP3, inositol 1, 4, 5-triphosphate; DAG, diacylglycerol; Ca2þ, calcium; F-GnRH-II, functional GnRH-II. **Functional GnRH-II receptor in humans is lacking.

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Conclusion and Future Perspective

Both peptide (ganirelix, cetrorelix, antarelix, abarelix, iturelix,

degarelix) and nonpeptide (elagolix, WAY-207024, TAK-013)

GnRH-ants were developed, and they are currently utilized in

gynecology, urology, oncology, and reproductive medicine for

therapeutic or research purposes.24 Pregnancy and live birth

rates are not statistically significant comparing GnRH-ant pro-

tocols with GnRH-ag long protocols, while the risk of ovarian

hyperstimulation syndrome is lower with GnRH-ant protocols.

The GnRH-ants are not associated with increased rate of con-

genital malformations. In addition to their use in the treatment

of prostate cancer, GnRH-ants may also be used in the future

for the treatment of other human cancers (such as ovary, endo-

metrium, and breast) that express GnRH receptors.

The GnRH-ants have complex effects and they seem to be

dependent on the cell type (Table 2). The long-term effects

of GnRH-ants on various organ systems are largely elusive.

The current limited evidence suggests that GnRH-ants may

impose differential effects on heart, which may have implica-

tions for their long-term use.87 The different effects of

GnRH-ants in extrapituitary tissues may be due to the complex

intracellular signaling pathways and receptor cross talks.88

Since many other peptide and nonpeptide GnRH-ants are cur-

rently being tested for their efficacy and safety, they will even-

tually find their way into clinical practice for long-term use. It

may not be appropriate to predict GnRH-ants’ systemic side

effects by extrapolating the data from the long-term GnRH-

ag use or short-term use of peptide GnRH-ants in assisted

reproduction technologies. Due to the various, tissue-specific

receptor interactions, more detailed and comparative clinical

data are needed to explore especially the long-term effects of

GnRH-ants on various extrapituitary tissues when they are

administered in a systemic fashion.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to

the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, author-

ship, and/or publication of this article.

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Table 2. Summary of the Effects of GnRH Antagonists on Various Extrapituitary Tissues

Tissue Presence of GnRH Type Effect of GnRH Antagonist

Ovary GnRH-l and -II Debatable; no effect on ovarian steroidogenesis 32,33; possible suppression of ovariansteroidogenesis 35,36

Endometrium/embryoimplantation

GnRH-l and -II Debatable; no effect on implantation47,48; possible interference with implantation dueto decreased HOXA10 by Gn-antagonist treatment49

Placenta GnRH-l and -II Both GnRH-l and -II affect the expression of MMPs, and plasminogen activators andpromote trophoblast invasion in placenta,61,62 but the direct effects of GnRHantagonists on placenta are unknown.

Fetus GnRH-la No increased rate of fetal malformations when used in in vitro fertilization protocols67-69

Reproductive cancercellsb

GnRH-l and GnRH-ll Antiproliferative in human breast cancer cell lines (such as MCF-7)77 and androgen-independent prostate cancer cell lines (DU145 and PC3).72; antiproliferative in benignprostate hyperplasia and JEG-3 choriocarcinoma cells.73; antiproliferative in ovarianand endometrial cancer cells.74

Heart GnRH-l and -II No increased risk of cardiovascular events after GnRH-antagonist (degarelix) treat-ment in prostate cancer patients without cardiovascular disease, however, ques-tionable increased risk of cardiovascular event rates in prostate cancer patients withcardiovascular disease at baseline.87

Abbreviation: GnRH, gonadotropin-releasing hormone.aDifferent GnRH types are present in various extrapituitary tissues. GnRH-I is present in preimplantation embryos as well as in the trophectoderm and inner cellmass of the blastocyst.bSuch as endometrium, ovary, breast, and prostate cancer.

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