Efficacy and safety of elinzanetant, a selective neurokinin-1,3 receptor antagonist for vasomotor symptoms: a dose-finding clinical trial (SWITCH-1)

OBJECTIVE

Neurokinin (NK)-3 and NK-1 receptors have been implicated in the etiology of vasomotor symptoms (VMS) and sleep disturbances associated with menopause. This phase 2b, adaptive, dose-range finding study aimed to assess the efficacy and safety of multiple doses of elinzanetant (NT-814), a selective NK-1,3 receptor antagonist, in women experiencing VMS associated with menopause, and investigate the impact of elinzanetant on sleep and quality of life.

METHODS

Postmenopausal women aged 40 to 65 years who experienced seven or more moderate-to-severe VMS per day were randomized to receive elinzanetant 40, 80, 120, or 160 mg or placebo once daily using an adaptive design algorithm. Coprimary endpoints were reduction in mean frequency and severity of moderate-to-severe VMS at weeks 4 and 12. Secondary endpoints included patient-reported assessments of sleep and quality of life.

RESULTS

Elinzanetant 120 mg and 160 mg achieved reductions in VMS frequency versus placebo from week 1 throughout 12 weeks of treatment. Least square mean reductions were statistically significant versus placebo at both primary endpoint time points for elinzanetant 120 mg (week 4: -3.93 [SE, 1.02], P < 0.001; week 12: -2.95 [1.15], P = 0.01) and at week 4 for elinzanetant 160 mg (-2.63 [1.03]; P = 0.01). Both doses also led to clinically meaningful improvements in measures of sleep and quality of life. All doses of elinzanetant were well tolerated.

CONCLUSIONS

Elinzanetant is an effective and well-tolerated nonhormone treatment option for postmenopausal women with VMS and associated sleep disturbance. Elinzanetant also improves quality of life in women with VMS.

Leap of Faith: Does Serum Luteinizing Hormone Always Accurately Reflect Central Reproductive Neuroendocrine Activity?

The function of the central aspects of the hypothalamic-pituitary-gonadal axis has been assessed in a number of ways including direct measurements of the hypothalamic output and indirect measures using gonadotropin release from the pituitary as a bioassay for reproductive neuroendocrine activity. Here, methods for monitoring these various parameters are briefly reviewed and then examples presented of both concordance and discrepancy between central and peripheral measurements, with a focus on situations in which elevated gonadotropin-releasing hormone neurosecretion is not reflected accurately by pituitary luteinizing hormone release. Implications for the interpretation of gonadotropin data are discussed.

Leptin is not the critical signal for kisspeptin or luteinising hormone restoration during exit from negative energy balance

Low levels of the adipocyte hormone leptin are considered to be the key signal contributing to inhibited gonadotrophin-releasing hormone (GnRH) release and reproductive acyclicity during negative energy balance. Hypoleptinaemia-induced inhibition of GnRH may be initiated with upstream inhibition of the secretagogue kisspeptin (Kiss1) because GnRH neurones do not express leptin receptors. The present study aimed to determine whether eliminating the hypoleptinaemia associated with caloric restriction (CR), by restoring leptin to normal basal levels, could reverse the suppression of the reproductive neuroendocrine axis. Fifty percent CR resulted in significant suppression of anteroventral periventricular Kiss1 mRNA, arcuate nucleus (ARH) Kiss1 and neurokinin B (NKB) mRNA levels and serum luteinising hormone (LH). Restoring leptin to normal basal levels did not restore Kiss1 or NKB mRNA or LH levels. Surprisingly, leptin did not activate expression of phosphorylated signal-transducer and activator of transcription-3 in ARC Kiss1 neurones, indicating that these neurones may not relay leptin signalling to GnRH neurones. Previous work in fasting models showing restoration of LH used a pharmacological dose of leptin. Therefore, in a 48-h fast study, replacement of leptin to pharmacological levels was compared with replacement of leptin to normal basal levels. Maintaining leptin at normal basal levels during the fast did not prevent inhibition of LH. By contrast, pharmacological levels of leptin did maintain LH at control values. These results suggest that, although leptin may be a permissive signal for reproductive function, hypoleptinaemia is unlikely to be the critical signal responsible for ARC Kiss1 and LH inhibition during negative energy balance.

Evidence from the agonadal juvenile male rhesus monkey (Macaca mulatta) for the view that the action of neurokinin B to trigger gonadotropin-releasing hormone release is upstream from the kisspeptin receptor

Human genetics have revealed that kisspeptin signaling and neurokinin B (NKB) signaling are both required for robust pulsatile gonadotropin-releasing hormone (GnRH) release, and therefore for puberty and maintenance of adult gonadal function. How these two peptides interact to affect GnRH pulse generation remains a mystery. To address the hierarchy of the NKB and kisspeptin signaling pathways that are essential for GnRH release, two experiments were conducted using agonadal, juvenile male monkeys. Pituitary responsiveness to GnRH was first heightened by a pulsatile GnRH infusion to use the in situ pituitary as a bioassay for GnRH release. In the first experiment (n = 3), the kisspeptin receptor (KISS1R) was desensitized by a continuous 99-hour i.v. infusion of kisspeptin-10 (100 μg/h). During the last 4 h of continuous kisspeptin-10 infusion, desensitization of KISS1R was confirmed by failure of an i.v. bolus of kisspeptin-10 to elicit GnRH release. Desensitization of KISS1R was associated with a markedly blunted GnRH response to senktide. The response to senktide was progressively restored during the 72 h following termination of continuous kisspeptin-10. An analogous design was employed in the second experiment (n = 2) to desensitize the NKB receptor (neurokinin 3 receptor, NK3R) by administration of a continuous 48-hour i.v. infusion of senktide (200 μg/h). While a bolus of senktide during the last 3 h of continuous senktide administration failed to elicit GnRH release, thus confirming desensitization of NK3R, the ability of kisspeptin to stimulate GnRH was unimpaired. The foregoing findings support the view that NKB stimulation of GnRH release is upstream from KISS1R.

Characterisation of arcuate nucleus kisspeptin/neurokinin B neuronal projections and regulation during lactation in the rat

Lactation results in negative energy balance in the rat leading to decreased gonadotrophin-releasing hormone (GnRH) release and anoestrus. Inhibited GnRH release may be a result of decreased stimulatory tone from neuropeptides critical for GnRH neuronal activity, such as kisspeptin (Kiss1) and neurokinin B (NKB). The present study aimed to identify neuronal projections from the colocalised population of Kiss1/NKB cells in the arcuate nucleus (ARH) using double-label immunohistochemistry to determine where this population may directly regulate GnRH neuronal activity. Additionally, the present study further examined lactation-induced changes in the Kiss1 system that could play a role in decreased GnRH release. The colocalised ARH Kiss1/NKB fibres projected primarily to the internal zone of the median eminence (ME) where they were in close proximity to GnRH fibres; however, few Kiss1/NKB fibres from the ARH were seen at the level of GnRH neurones in the preoptic area (POA). Arcuate Kiss1/NKB peptide levels were decreased during lactation consistent with previous mRNA data. Surprisingly, anteroventral periventricular (AVPV) Kiss1 peptide levels were increased, whereas Kiss1 mRNA levels were decreased during lactation, suggesting active inhibition of peptide release. These findings indicate ARH Kiss1/NKB and AVPV Kiss1 appear to be inhibited during lactation, which may contribute to decreased GnRH release and subsequent reproductive dysfunction. Furthermore, the absence of a strong ARH Kiss1/NKB projection to the POA suggests regulation of GnRH by this population occurs primarily at the ME level via local projections.

Sex differences in the regulation of Kiss1/NKB neurons in juvenile mice: implications for the timing of puberty

In mammals, puberty onset typically occurs earlier in females than in males, but the explanation for sexual differentiation in the tempo of pubertal development is unknown. Puberty in both sexes is a brain-dependent phenomenon and involves alterations in the sensitivity of neuronal circuits to gonadal steroid feedback as well as gonadal hormone-independent changes in neuronal circuitry. Kisspeptin, encoded by the Kiss1 gene, plays an essential but ill-defined role in pubertal maturation. Neurokinin B (NKB) is coexpressed with Kiss1 in the arcuate nucleus (ARC) and is also important for puberty. We tested whether sex differences in the timing of pubertal development are attributable to sexual differentiation of gonadal hormone-independent mechanisms regulating hypothalamic Kiss1/NKB gene expression. We found that, in juvenile females, gonadotropin secretion and expression of Kiss1 and NKB in the ARC increased immediately following ovariectomy, suggesting that prepubertal females have negligible gonadal hormone-independent restraint on their reproductive axis. In contrast, in similarly aged juvenile males, no changes occurred in LH levels or Kiss1 or NKB expression following castration, suggesting that gonadal hormone-independent mechanisms restrain kisspeptin/NKB-dependent activation of the male reproductive axis before puberty. Notably, adult mice of both sexes showed comparable rapid increases in Kiss1/NKB expression and LH secretion following gonadectomy, signifying that sex differences in the regulation of ARC Kiss1/NKB neurons are manifest only during peripubertal development. Our findings demonstrate that the mechanisms controlling pubertal activation of reproduction in mice are different between the sexes and suggest that gonadal hormone-independent central restraint on pubertal timing involves Kiss1/NKB neurons in the ARC.

Changes in prodynorphin gene expression and neuronal morphology in the hypothalamus of postmenopausal women

Human menopause is characterised by ovarian failure, gonadotrophin hypersecretion and hypertrophy of neurones expressing neurokinin B (NKB), kisspeptin (KiSS)-1 and oestrogen receptor (ER) alpha gene transcripts within the hypothalamic infundibular (arcuate) nucleus. In the arcuate nucleus of experimental animals, dynorphin, an opioid peptide, is colocalised with NKB, kisspeptin, ER alpha and progesterone receptors. Moreover, ovariectomy decreases the expression of prodynorphin gene transcripts in the arcuate nucleus of the ewe. Therefore, we hypothesised that the hypertrophied neurones in the infundibular nucleus of postmenopausal women would express prodynorphin mRNA and that menopause would be accompanied by changes in prodynorphin gene transcripts. In the present study, in situ hybridisation was performed on hypothalamic sections from premenopausal and postmenopausal women using a radiolabelled cDNA probe targeted to prodynorphin mRNA. Autoradiography and computer-assisted microscopy were used to map and count labelled neurones, measure neurone size and compare prodynorphin gene expression between premenopausal and postmenopausal groups. Neurones expressing dynorphin mRNA in the infundibular nucleus of the postmenopausal women were larger and exhibited hypertrophied morphological features. Moreover, there were fewer neurones labelled with the prodynorphin probe in the infundibular nucleus of the postmenopausal group compared to the premenopausal group. The number of dynorphin mRNA-expressing neurones was also reduced in the medial preoptic/anterior hypothalamic area of postmenopausal women without changes in cell size. No differences in cell number or size of dynorphin mRNA-expressing neurones were observed in any other hypothalamic region. Previous studies using animal models provide strong evidence that the changes in prodynorphin neuronal size and gene expression in postmenopausal women are secondary to the ovarian failure of menopause. Given the inhibitory effect of dynorphin on the reproductive axis, decreased dynorphin gene expression could play a role in the elevation in luteinising hormone secretion that occurs in postmenopausal women.

Tachykinins and tachykinin receptors in human uterus

(1) Studies were undertaken to determine the nature of the receptors mediating contractile effects of tachykinins in the uteri of nonpregnant women, and to analyse the expression of preprotachykinins (PPT), tachykinin receptors and the cell-surface peptidase, neprilysin (NEP), in the myometrium from pregnant and nonpregnant women. (2) The neurokinin B (NKB) precursor PPT-B was expressed in higher levels in the myometrium from nonpregnant than from pregnant women. Faint expression of PPT-A mRNA was detectable in the myometrium from nonpregnant but not pregnant women. PPT-C, the gene encoding the novel tachykinin peptide hemokinin-1 (HK-1), was present in trace amounts in the uteri from both pregnant and nonpregnant women. (3) Tachykinin NK(2) receptors were more strongly expressed in tissues from nonpregnant than from pregnant women. NK(1) receptor mRNA was present in low levels in tissues from both pregnant and nonpregnant women. A low abundance transcript corresponding to the NK(3) receptor was present only in tissues from nonpregnant women. (4) The mRNA expression of the tachykinin-degrading enzyme NEP was lower in tissues from nonpregnant than from pregnant women. (5) Substance P (SP), neurokinin A (NKA) and NKB, in the presence of the peptidase inhibitors thiorphan, captopril and bestatin, produced contractions of myometrium from nonpregnant women. The order of potency was NKA>>SP>/=NKB. The potency of NKA was unchanged in the absence of peptidase inhibitors. (6) The tachykinin NK(2) receptor-selective agonist [Lys(5)MeLeu(9)Nle(10)]NKA(4-l0) was approximately equipotent with NKA, but the tachykinin NK(1) and NK(3) receptor-selective agonists [Sar(9)Met(O(2))(11)]SP and [MePhe(7)]NKB were ineffective in the myometrium from nonpregnant women. (7) The uterotonic effects of [Lys(5)MeLeu(9)Nle(10)]NKA(4-10) were antagonized by the tachykinin NK(2) receptor-selective antagonist SR48968. Neither atropine, nor phentolamine nor tetrodotoxin affected responses to [Lys(5)MeLeu(9)Nle(10)]NKA(4-10). (8) These data are consistent with a role of tachykinins in the regulation of human uterine function, and reinforce the importance of NK(2) receptors in the regulation of myometrial contraction.

Functional characterization of tachykinin NK1 receptors in the mouse uterus

1. Contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of oestrogen-treated mice. 2. In the presence of thiorphan (3 microM), captopril (10 microM), and bestatin (10 microM), substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-related contractions of uterine preparations. The order of potency was SP > or =NKA>NKB. 3. Neither atropine (0.1 microM) nor l-NOLA (100 microM), nor indomethacin (10 microM) alone or in combination with either ranitidine (10 microM) or mepyramine (10 microM), affected responses to SP. These findings indicate that SP actions are not mediated or modulated through the release of acetylcholine, nitric oxide, prostanoids or histamine. 4. In the presence of peptidase inhibitors, the tachykinin NK(1) receptor-selective agonist [Sar(9)Met(O(2))(11)]SP, produced a concentration-dependent contractile effect. The tachykinin NK(2) and NK(3) receptor-selective agonists [Lys(5)MeLeu(9)Nle(10)]NKA(4-10) and [MePhe(7)]NKB were relatively inactive. The potencies of SP analogues in which Glu replaced Gln(5) and/or Gln(6) were similar to that of SP. 5. The tachykinin NK(1) receptor-selective antagonist, SR140333 (10 nM), alone or combined with the tachykinin NK(2) receptor-selective antagonist, SR48968 (10 nM), shifted log concentration curves to SP, NKA and NKB to the right. SR140333 (10 nM) reduced the effect of [Sar(9)Met(O(2))(11)]SP. SR48968 did not affect responses to SP or [Sar(9)Met(O(2))(11)]SP, but reduced the effect of higher concentrations of NKA and shifted the log concentration-response curve to NKB to the right. The tachykinin NK(3) receptor-selective antagonist, SR 142801 (0.3 microM), had little effect on responses to SP and NKB. 6. We conclude that the tachykinin NK(1) receptor mediates contractile effects of SP, NKA and NKB and [Sar(9)Met(O(2))(11)]SP in myometrium from the oestrogen-primed mouse. The tachykinin NK(2) receptor may also participate in the responses to NKA and NKB.

Characterization of NK3 receptors in rabbit isolated iris sphincter muscle

1. Tachykinin NK3 receptors were characterized in the rabbit isolated iris sphincter muscle by use of autoradiography and in vitro functional studies. 2. [125I]-[MePhe7]-neurokinin B (NKB) (1nM), a selective NK3 receptor agonist, specifically labelled a population of NK3 receptors that were uniformly distributed throughout the rabbit iris sphincter muscle. This labelling was inhibited by unlabelled [MePhe7]-NKB (1 microM) but not by the NK1 receptor antagonist CP 99994 (1 microM). 3. In the presence of CP 99994 (1 microM), the selective NK3 receptor agonists senktide (n = 14) and [Pro7]-NKB (n = 4), and the natural preferred ligand for the NK3 receptor, NKB (n = 8), were potent contractile agents in the rabbit iris sphincter muscle. They all produced monophasic concentration-effect curves with pD2 values of 9.53 +/- 0.08, 8.56 +/- 0.09 and 9.75 +/- 0.09, and nH values of 0.93 +/- 0.03, 1.53 +/- 0.17 and 0.76 +/- 0.06, respectively. [MePhe7]-NKB (n = 12) was also a potent agonist, but produced shallow concentration-effect curves which appeared biphasic (nH = 0.45 +/- 0.04). 4. Contractile responses to senktide were surmountably antagonized in a concentration-dependent manner by the selective non-peptide NK3 receptor antagonist, SR 142801 (3-30 nM; pA2 = 8.9; slope = 0.99) and the non-peptide NK2/NK3 receptor antagonist, SR 48968 (3-30 microM; pA2 = 6.1; slope = 1.5). These pA2 values were consistent with functional rabbit NK3 receptors more closely resembling guinea-pig and human NK3 receptors, than rat NK3 receptors. SR 142801 (10-100 nM) and SR 48968 (3 and 30 microM) inhibited responses to low (< or = 1 nM) but not higher (> 1 nM) concentrations of [MePhe7]-NKB, and concentration-effect curves to [MePhe7]-NKb became steeper and monophasic in the presence of either antagonist. 5. SR 142801 (3-30 nM) and SR 48968 (3-30 microM) also surmountably antagonized concentration-effect curves to [Pro7]-NKB and NKB, although results were more difficult to interpret, since the relationship between log concentration-ratios and the concentration of antagonist used did not adhere to the Schild equation. However, analysis of data with the lowest concentration of SR 142801 (3 nM) tested against NKB, and SR 48968 (3 microM) tested against [Pro7]-NKB and NKB, yielded apparent pA2 estimates of 9.3, 6.8 and 6.4, respectively, consistent with blockade of NK3 receptors. 6. SR 142801 (100 nM) had no effect on contractions induced by transmural nerve stimulation (2 Hz, 0.3 ms, 20 V for 30 s), whereas CP 99994 (1 microM) abolished these responses. 7. Phenoxybenzamine pretreatment (20 microM, 10 min) markedly reduced maximum responses to [MePhe7]-NKB (from 101 +/- 6.2% to 38 +/- 9.5% reference contraction, n = 4) and induced a marked (10 fold) rightward shift in the concentration-effect curve. The residual responses to [MePhe7]-NKB after phenoxybenzamine pretreatment were unaffected by 1 microM CP 99994 (maximum response = 41 +/- 9.4%, n = 4). 8. These results demonstrate autoradiographically and functionally, the presence of NK3 receptors in rabbit iris sphincter muscle that mediate contractile responses to NK3 receptor agonists, but not to sensory trigeminal nerve simulation. The present data with senktide and selective NK3 receptor antagonists suggest that functional rabbit NK3 receptors more closely resemble human and guinea-pig NK3 receptors than rat NK3 receptors. However, the pharmacological profiles of [MePhe7]-NKB, SR 142801 and SR 48968 suggest the presence of an 'atypical' NK3 receptor or a heterogeneous population of NK3 receptors in this tissue.